CN120858315A - Multi-layer measurement system and method - Google Patents

Abstract

Multilayer metrology systems and methods are described. The prior art is configured to measure the bottom grating of a metrology target (e.g., a single layer grating of an overlay target) to determine the reference position of layer (n) with respect to only another layer in the semiconductor layer stack. Depending on the product or layer, the present system and method is configured to facilitate alignment of layer n on layer n-1 or layer n-2 (or an average of both), and/or to extract overlay information from these previous layers to improve alignment and/or other metrology determinations. The present systems and methods are configured to align multiple subsequent layers to the same metrology mark, even though the mark includes two or more gratings directly overlying one another, and to use the same physical mark for alignment, overlay, and/or other metrology operations.

Description

Multi-layer metrology system and method

Cross Reference to Related Applications

The present application claims priority from U.S. application 63/450,243 filed on 3/6 of 2023, the entire contents of which are incorporated herein by reference.

Technical Field

The present specification relates generally to multi-layer metrology systems and methods.

Background

Lithographic projection apparatus can be used, for example, in the manufacture of Integrated Circuits (ICs). The patterning device (e.g., mask) may comprise or provide a pattern corresponding to an individual layer of the IC (the "design layout"), and this pattern may be transferred onto a target portion (e.g., comprising one or more dies) on a substrate (e.g., a silicon wafer) that is coated with a layer of radiation-sensitive material (the "resist"), by a method such as irradiating the target portion through the pattern on the patterning device. Typically, a single substrate includes a plurality of adjacent target portions to which the pattern is successively transferred one target portion at a time by a lithographic projection apparatus. In one type of lithographic projection apparatus, the pattern on the entire patterning device is transferred to a target portion in one operation. Such devices are commonly referred to as steppers. In an alternative device, commonly referred to as a step-and-scan device, the projection beam scans the patterning device in a given reference direction (the "scanning" direction), while simultaneously moving the substrate parallel or anti-parallel to the reference direction. Different portions of the pattern on the patterning device are progressively transferred to a target portion.

The substrate may undergo various processes such as priming, resist coating, and soft baking before transferring the pattern from the patterning device to the substrate. After exposure, the substrate may undergo other processes ("post-exposure processes") such as post-exposure bake (PEB), development, hard bake, and measurement/inspection of the transferred pattern. This series of processes is used as a basis for fabricating individual layers of a device (e.g., an IC). The substrate may then undergo various processes such as etching, ion implantation (doping), metallization, oxidation, deposition, chemical mechanical polishing, etc., all in order to complete the individual layers of the device. If several layers are required in the device, the entire process or variants thereof are repeated for each layer. Eventually, one device will appear in each target portion on the substrate. These devices are then separated from each other by techniques such as dicing or sawing to mount individual devices on a carrier, connect to pins, etc.

Thus, the fabrication of devices such as semiconductor devices generally involves processing a substrate (e.g., a semiconductor wafer) using a variety of fabrication processes to form various features and layers of the device. Such layers and features are typically fabricated and processed using, for example, deposition, photolithography, etching, deposition, chemical mechanical polishing, and ion implantation. Multiple devices may be fabricated on multiple dies on a substrate and then separated into individual devices. The device manufacturing process may be considered a patterning process. Patterning processes involve patterning steps, such as optical and/or nanoimprint lithography using patterning devices in a lithographic apparatus, to transfer a pattern on the patterning device onto a substrate, and often, but optionally, involve one or more associated pattern processing steps, such as resist development by a developing apparatus, baking the substrate using a baking tool, etching the pattern using an etching apparatus, deposition, and so forth.

Photolithography is a core step in the fabrication of devices such as ICs, where patterns formed on a substrate define the functional elements of the device, such as microprocessors, memory chips, and the like. Similar photolithographic techniques are also used in the formation of flat panel displays, microelectromechanical systems (MEMS) and other devices.

With the continued advancement of semiconductor manufacturing processes, the size of functional elements has been decreasing and the number of functional elements (such as transistors) per device has steadily increased over several decades, a trend commonly referred to as "moore's law. In the state of the art, device layers are manufactured using a lithographic projection apparatus that projects a design layout onto a substrate using radiation from a deep ultraviolet or extreme ultraviolet radiation source, thereby creating individual functional elements that are well below 100nm in size, i.e. less than half the wavelength of the radiation source (e.g. 193nm radiation source).

The process of printing features with dimensions smaller than the classical resolution limit of a lithographic projection apparatus is commonly referred to as low-k ₁ lithography according to the resolution formula cd=k ₁ ×λ/NA, where λ is the wavelength of radiation used, NA is the numerical aperture of the projection optics in the lithographic projection apparatus, CD is the "critical dimension", typically the minimum feature size of the printing, and k ₁ is the empirical resolution factor. In general, the smaller the k ₁, the more difficult it is to reproduce on a substrate a pattern that is similar in shape and size to what is planned by a designer to achieve a particular electrical function and performance. To overcome these difficulties, complex fine tuning steps are applied to lithographic projection apparatus, design layouts, or patterning devices. For example, these include, but are not limited to, optimizing NA and optical coherence settings, tailoring the irradiance scheme, using phase-shift patterning devices, optical proximity correction in the design layout (OPC, sometimes also referred to as "optical and process correction"), or other methods commonly defined as "resolution enhancement techniques" (RET).

Disclosure of Invention

Multilayer metrology systems and methods are described. The prior art is configured to measure a single layer grating, which may be the bottom grating of a metrology target (e.g., an overlay target), to determine the exposure reference position of layer (n) with respect to only another layer in the semiconductor layer stack. Depending on the product or layer, the present system and method is configured to facilitate alignment of layer n on layer n-1 and/or layer n-2 (or some set, such as an average of both), and/or to extract overlay information from these previous layers to improve alignment and/or other metrology determinations. The present systems and methods are configured to align multiple subsequent layers to the same metrology mark, even though the mark includes two or more gratings directly overlying one another, and to use the same physical mark for alignment, overlay, and/or other metrology operations.

According to one embodiment, a metrology system is provided. The metrology system includes a radiation source configured to irradiate a first metrology mark in a first layer of a patterned substrate and a second metrology mark in a second layer of the patterned substrate with radiation. The metrology system includes a radiation sensor configured to generate a metrology signal based on reflected radiation received from a first metrology mark and a second metrology mark. The metrology signal includes alignment position information and/or overlay information for the first layer and the second layer.

In some embodiments, the metrology signal is an alignment signal or an overlay signal.

In some embodiments, the radiation source is configured to irradiate at least three metrology marks in at least three layers of the patterned substrate with radiation. The radiation sensor is configured to generate a metrology signal based on reflected radiation received from the at least three metrology marks. In some embodiments, the metrology signal includes alignment position information and/or overlay information for some or all of the at least three layers.

In some embodiments, the second metrology mark is located directly above the first metrology mark in the patterned substrate. In some embodiments, the first metrology mark and the second metrology mark comprise diffraction-based overlay metrology marks. In some embodiments, the first metrology mark and the second metrology mark comprise gratings. The gratings may have different pitches. In some embodiments, the first and second metrology marks form an overlay (Continuous Bias Diffraction Based Overlay, cDBO) target based on continuous offset diffraction, wherein the first and second metrology marks comprise gratings in the first and second layers of the patterned substrate. In some embodiments, the cDBO targets include eight pads, each having dimensions of about 10 μm by 5 μm.

In some embodiments, the first metrology mark and the second metrology mark each include a first grating having a larger first pitch (pl) and a second grating having a smaller second pitch (pl). The difference in pitch between the larger pitch (pl) and the smaller pitch (ps) follows the relationship ps/pl= (i-1)/i. In some embodiments, i is an integer greater than 4 and less than 8.

In some embodiments, the system includes one or more processors configured to determine an alignment position of the first layer and/or the second layer based on the metrology signals. In some embodiments, the one or more processors are configured to determine the alignment position by determining a phase difference between positive and negative diffraction orders of the reflected radiation of the first metrology mark and/or the second metrology mark. In some implementations, determining the phase difference includes determining a phase shift.

In some embodiments, the metrology signal includes and/or is used to generate a two-dimensional (2D) interference pattern. The one or more processors are configured to detect a shift of the first metrology mark or the second metrology mark based on the interference pattern, as the shift of either metrology mark causes a different effect on the interference pattern than the shift of the other metrology mark. In some embodiments, the one or more processors are configured to detect a shift in the first direction of a first fringe associated with the first metrology mark in the two-dimensional interference pattern, the shift being indicative of a relative shift of the first metrology mark compared to a second fringe associated with the second metrology mark that is indicative of a position of the second metrology mark. In some embodiments, the one or more processors are configured to detect a shift in the second direction of a second fringe in the two-dimensional interference pattern associated with the second metrology mark, the shift being indicative of a relative shift of the second metrology mark compared to the first fringe associated with the first metrology mark, indicative of a position of the first metrology mark.

In some embodiments, the one or more processors are configured to determine the alignment positions of the first layer and the second layer simultaneously based on the metrology signals.

In some embodiments, the metrology signal includes overlay information for the first layer and the second layer, and the one or more processors are configured to determine the overlay of the first layer and the second layer based on the metrology signal.

In some embodiments, the system includes one or more lenses configured to receive reflected radiation from the first metrology mark and the second metrology mark and direct the received reflected radiation toward the radiation sensor.

In some embodiments, the metrology signals are configured to be used by one or more processors to regulate a semiconductor device manufacturing process.

In some embodiments, the radiation source is configured to generate two pairs of off-axis illuminations.

In some embodiments, a given metrology mark includes a one-dimensional (1D) pattern, and the radiation sensor includes a photodiode or an image-based sensor.

According to another embodiment, a method of measuring is provided, the method comprising one or more of the above operations.

Drawings

The above aspects and other aspects and features will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments in conjunction with the accompanying drawings.

FIG. 1 schematically depicts a lithographic apparatus according to an embodiment.

FIG. 2 schematically depicts an embodiment of a lithography unit or cluster according to an embodiment.

FIG. 3 schematically depicts an example metrology system according to an embodiment.

FIG. 4 schematically depicts an example metrology technique in accordance with an embodiment.

FIG. 5 illustrates a relationship between a radiation exposure point and a metrology target of an inspection system in accordance with an embodiment.

FIG. 6 illustrates a measurement method according to an embodiment.

FIG. 7 schematically depicts another example metrology system according to an embodiment.

Fig. 8 illustrates an alignment strategy used in existing systems according to embodiments.

Fig. 9 illustrates an alignment strategy used in the present system (e.g., the system shown in fig. 3 and the system shown in fig. 7) and method (e.g., the method shown in fig. 6) according to an embodiment.

Fig. 10 illustrates an example of the grating shown in fig. 9 according to an embodiment.

FIG. 11 illustrates an example two-dimensional (2D) interference pattern, according to an embodiment.

FIG. 12 is a block diagram of an example computer system, according to an embodiment.

Detailed Description

In semiconductor device fabrication, determining alignment generally includes determining the location of a metrology target, such as an alignment mark in a layer of a semiconductor device structure. Alignment is typically determined by irradiating the alignment mark with radiation and comparing the characteristics of the radiation of the different diffraction orders reflected from the alignment mark. Similar techniques are used to measure overlay and/or other parameters. To meet the ever smaller node sizes and/or to more efficiently utilize limited substrate surfaces, ever smaller metrology (e.g., alignment, overlay, etc.) targets, multi-purpose targets (e.g., one metrology target that may be used for both overlay and alignment), and/or other space-saving techniques are needed. Smaller targets and/or targets that may be used for a variety of purposes facilitate the need for fewer targets, placing targets in a field of limited area, placing targets closer to the edge of the substrate, and/or other advantages.

As one example, existing metrology systems are configured to measure a single layer grating, which may be a bottom grating of a metrology target (e.g., a single bottom grating of an overlay target), so that a reference position of exposure of layer (n) may be determined with respect to only another layer in a semiconductor layer stack. Determining the second reference position of the second layer would require another target spaced apart from the bottom grating, which requires additional space on the substrate. In addition, existing metrology systems utilize separate sensors and metrology targets for the overlay and alignment operations. This may result in a difference between the alignment position and the overlay, even when the same mark is measured, which may degrade the overlay (On Product Overlay, OPO) on the product and/or have other negative effects.

The present systems and methods are configured to facilitate alignment of a substrate layer n on one or more existing layers (e.g., layer n-1, layer n-2, layer n-3, etc.) and/or extract overlay information from these previous layers to improve alignment and/or other metrology determinations using a single multi-layer metrology target. The present systems and methods are configured to align multiple subsequent layers to the same metrology target, even though the target includes two or more marks (e.g., gratings) directly overlying one another, and to use the same physical target for alignment, overlay, and/or other metrology operations.

As a brief introduction, the following description relates generally to semiconductor device fabrication and patterning processes. More specifically, the following paragraphs describe several components of the system and/or related systems. As described above, these systems and methods may be used to measure alignment in a semiconductor device manufacturing process, for example, or for other operations.

Although specific reference may be made in this text to the manufacture of Integrated Circuits (ICs) and alignment measurements of semiconductor devices, it should be appreciated that this description has many other possible applications. For example, it may be used to measure overlay and/or other parameters. It can be used to manufacture integrated optical systems, guidance and detection patterns for magnetic domain memories, liquid crystal display panels, thin film magnetic heads, etc. Those skilled in the art will appreciate that any use of the terms "reticle," "wafer," or "die" herein, in the context of such alternative applications, should be considered interchangeable with the more general terms "mask," "substrate," and "target portion," respectively.

The term "projection optics" should be construed broadly to include various types of optical systems, including refractive optics, reflective optics, aperture, and catadioptric optics, for example. The term "projection optics" may also include components that operate to collectively or individually direct, shape, or control the projection beam of radiation according to any of these design types. The term "projection optics" may include any optical component in a lithographic projection apparatus, wherever the optical component is located on the optical path of the lithographic projection apparatus. The projection optics may include optical components for shaping, conditioning and/or projecting the radiation from the source before it passes through the patterning device, and/or optical components for shaping and/or projecting the radiation after it passes through the patterning device. Projection optics typically do not include a light source and patterning device.

FIG. 1 schematically depicts an embodiment of a lithographic apparatus LA. The apparatus includes an irradiance system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation, DUV radiation, or EUV radiation), a support structure (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and connected to a first positioner PM configured to accurately position the patterning device in accordance with certain parameters, a substrate table (e.g. a wafer table) WT (e.g. WTA, WTB, or both) WT configured to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate in accordance with certain parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies, and commonly referred to as a field) of the substrate W. The projection system is supported on a reference frame RF. As shown, the apparatus is transmissive (e.g., employing a transmissive mask). Alternatively, the apparatus may be reflective (e.g., employing a programmable mirror array, or employing a reflective mask).

The illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to form part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

The illuminator IL may change the intensity distribution of the beam. The illuminator may be arranged to limit the radial extent of the radiation beam such that the intensity distribution in the annular region in the pupil plane of the illuminator IL is non-zero. Additionally or alternatively, the illuminator IL may be used to limit the beam distribution in the pupil plane such that the intensity distribution of the plurality of equidistant sectors in the pupil plane is non-zero. The intensity distribution of the radiation beam in the pupil plane of the illuminator IL may be referred to as an illumination mode.

The illuminator IL may comprise an adjuster AD configured to adjust the (angular/spatial) intensity distribution of the beam. Generally, at least the outer and/or inner radial extent (commonly referred to as outer σ and inner σ, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. The illuminator IL may be used to change the angular distribution of the beam. For example, the illuminator may be used to change the number and angular extent of sectors in the pupil plane in which the intensity distribution is non-zero. By adjusting the intensity distribution of the beam in the pupil plane of the illuminator, different illumination modes can be achieved. For example, by limiting the radial and angular extent of the intensity distribution in the pupil plane of the illuminator IL, the intensity distribution may have a multipole distribution, such as a dipole, quadrupole or hexapole distribution. For example, the desired illumination pattern may be obtained by inserting optics providing the desired illumination pattern into the illuminator IL or using a spatial light modulator.

The illuminator IL may be used to change the polarization of the beam, and may be used to adjust the polarization using an adjuster AD. The polarization state of the radiation beam in the pupil plane of the illuminator IL may be referred to as a polarization mode. The use of different polarization modes may enable greater contrast in the image formed on the substrate W. The radiation beam may be unpolarized. Alternatively, the illuminator may be arranged to linearly polarize the radiation beam. The polarization direction of the radiation beam may vary in a pupil plane of the illuminator IL. The polarization direction of the radiation may be different in different regions in the pupil plane of the illuminator IL. The polarization state of the radiation may be selected according to the illumination mode. For a multi-pole illumination mode, the polarization of each pole of the radiation beam is generally perpendicular to the position vector of that pole in the pupil plane of the illuminator IL. For example, for a dipole illumination mode, the rays may be linearly polarized in a direction substantially perpendicular to a line bisecting two opposing sectors of the dipole. The radiation beam may be polarized in one of two different orthogonal directions, which may be referred to as an X-polarization state and a Y-polarization state. For a quadrupole illumination mode, the radiation in a sector of each pole can be linearly polarized in a direction substantially perpendicular to a line bisecting the sector. This polarization mode may be referred to as XY polarization. Similarly, for a hexapole illumination mode, radiation in a sector of each pole may be linearly polarized in a direction substantially perpendicular to a line bisecting the sector. This polarization mode may be referred to as TE polarization.

In addition, the illuminator IL generally comprises various other components, such as an integrator In and a condenser CO. The illumination system may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.

The illuminator thus provides a conditioned beam of radiation B, having a desired uniformity and intensity distribution in its cross-section.

The support structure MT supports the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions (e.g., whether or not the patterning device is held in a vacuum environment). The support structure may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be, for example, a frame or a table, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the term "reticle" or "mask" may be considered synonymous with the more general term "patterning device".

The term "patterning device" should be broadly interpreted as referring to any device that can be used to impart a pattern in a target portion of a substrate. In one embodiment, the patterning device is any device that can be used to impart the radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that, for example, if the pattern comprises phase shifting features or so-called assist features, the pattern applied to the radiation beam may not correspond exactly to the desired pattern in the target portion of the substrate. Typically, the pattern applied to the radiation beam will correspond to a particular functional layer in a device created in a target portion of the device, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. One example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.

The term "projection system" should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" may be considered as synonymous with the more general term "projection system".

The projection system PS may include a plurality of optical (e.g., lens) elements, and may further include an adjustment mechanism configured to adjust one or more of the optical elements to correct for aberrations (phase changes across a pupil plane in the field of view). To achieve this, the adjustment mechanism may manipulate one or more optical (e.g., lens) elements within the projection system PS in one or more different ways. The projection system may have a coordinate system in which its optical axis extends in the z-direction. The adjustment mechanism may be used to perform any combination of displacing one or more optical elements, tilting one or more optical elements, and/or deforming one or more optical elements. The displacement of the optical element may be in any direction (x, y, z or a combination thereof). The tilt of the optical element is typically deviated from a plane perpendicular to the optical axis by rotation about an axis in the x and/or y direction, although rotation about the z axis may be used for non-rotationally symmetric aspheric optical elements. The deformation of the optical element may include a low frequency shape (e.g., astigmatism) and/or a high frequency shape (e.g., free form asphere). The deformation of the optical element may be performed, for example, using one or more actuators to apply force on one or more sides of the optical element and/or using one or more heating elements to heat one or more selected regions of the optical element. In general, the projection system PS may not be adjustable to correct for apodization (transmission changes across the pupil plane). In designing a patterning device (e.g., mask) MA for lithographic apparatus LA, a transmission map of projection system PS may be used. Using computational lithography techniques, patterning device MA may be designed to at least partially correct for apodization.

The lithographic apparatus may be of a type having two (dual stage) or more tables (e.g., two or more substrate tables WTa, WTb, two or more patterning device tables, substrate tables WTa and WTb under the projection system, without a substrate dedicated to facilitating, for example, measurement and/or cleaning, etc.). In such "multiple stage" machines the additional tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. For example, alignment measurements made using the alignment sensor AS and/or level (height, tilt, etc.) measurements made using the level sensor LS may be made.

In operation of the lithographic apparatus, the radiation beam is conditioned and provided by the illumination system IL. The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device. After passing through the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g., an interferometer, linear encoder, 2-D encoder or capacitive sensor), the substrate table WT can be moved accurately, e.g., so as to position different target portions C in the path of the radiation beam B. Likewise, the first positioner PM and another position sensor (which is not explicitly depicted in fig. 1) can be used to accurately position the patterning device MA with respect to the path of the radiation beam B, e.g. after mechanical retrieval from a mask library, or during a scan. In general, movement of the support structure MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Likewise, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks are shown to occupy dedicated target portions, they may be located in spaces between target portions (these are referred to as scribe-lane (scribe-lane) alignment marks). Similarly, where multiple dies are provided on patterning device MA, patterning device alignment marks may be located between the dies.

The depicted device may be used in at least one of the following modes. In step mode, the support structure MT and the substrate table WT are kept essentially stationary, while a pattern imparted to the radiation beam is projected onto a target portion C at one time (i.e. a single static exposure). The substrate table WT is then shifted in the X and/or Y direction so that different target portions C can be exposed. In step mode, the maximum size of the exposure field is limited to the size of the target portion C imaged in a single static exposure. In scan mode, the support structure MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure MT may be determined by the magnification (or demagnification) and image reversal characteristics of the projection system PS. In the scanning mode, the maximum size of the exposure field limits the width of the target portion (in the non-scanning direction) in a single dynamic exposure, while the length of the scanning motion determines the height of the target portion (in the scanning direction. In another mode, the support structure MT is kept essentially stationary to hold the programmable patterning device and the substrate table WT is moved or scanned while a pattern applied to the radiation beam is projected onto the target portion C.

Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

The substrate may be processed before or after exposure, for example in a track (track), a tool that typically applies a layer of resist to the substrate and develops the exposed resist, or a metrology or inspection tool. Where applicable, the present disclosure may be applied to such and other substrate processing tools. Further, the substrate may be processed multiple times, for example, in order to create a multi-layer IC, so the term substrate may also refer to a substrate that already includes multiple processed layers.

The terms "radiation" and "beam" used in the context of lithography encompass all types of electromagnetic radiation, including Ultraviolet (UV) or Deep Ultraviolet (DUV) radiation (e.g. having a wavelength of 365, 248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g. having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

The various patterns on or provided by the patterning device may have different process windows, i.e., process variable spaces under which the patterns are generated within the specification. Examples of pattern specifications associated with potential systematic defects include inspection for necking, line rollback, line thinning, CD, edge location, overlay, photoresist top loss, photoresist undercut, and/or bridging. The process window of the pattern on the patterning device or region thereof may be obtained by merging (e.g., overlay) the process window of each individual pattern. The boundaries of the process windows of a set of patterns comprise the boundaries of the process windows of some individual patterns. In other words, the individual patterns limit the process window of the set of patterns.

As shown in fig. 2, the lithographic apparatus LA may form part of a lithographic cell LC, sometimes also referred to as a lithographic cell or cluster, which further comprises an apparatus for performing pre-exposure and post-exposure processes on a substrate. Conventionally, these apparatuses include one or more spin coaters SC for depositing one or more resist layers, one or more developers for developing the exposed resist, one or more chill plates CH, and/or one or more bake plates BK. The substrate handler or robot RO picks up one or more substrates from the input/output ports I/O1, I/O2, moves the substrates between different processing apparatuses, and transfers the substrates to a Loading Bay (LB) of the lithographic apparatus. These devices (often collectively referred to as tracks) are controlled by a track control unit TCU, which itself is controlled by a monitoring system SCS, which also controls the lithographic apparatus via a lithographic control unit LACU. Thus, different equipment can be operated to maximize yield and process efficiency.

In order to properly and consistently expose a substrate exposed by a lithographic apparatus and/or to monitor a portion of a patterning process (e.g., a device manufacturing process) that includes at least one pattern transfer step (e.g., a photolithography step), the substrate or other object needs to be inspected to measure or determine one or more properties, such as alignment, overlay (e.g., which may be between structures in an overlayer, or between structures in the same layer that are separately provided to the layer by a double patterning process), line thickness, critical Dimension (CD), focus offset, material properties, and the like. Thus, the manufacturing facility in which the lithography unit LC is located typically also includes a metrology system for measuring some or all of the substrate W (fig. 1) or other objects in the lithography unit that have been processed in the lithography unit. The metrology system may be part of the lithographic cell LC, for example it may be part of the lithographic apparatus LA, such AS an alignment sensor AS (fig. 1).

The one or more measured parameters may include, for example, alignment between successive layers formed in or on the patterned substrate, critical Dimensions (CD) (e.g., critical line width) of features formed on or in the patterned substrate, focus or focus error of the photolithography step, dose or dose error of the photolithography step, optical aberration of the photolithography step, etc. Such measurements are typically performed on dedicated metrology targets disposed on a substrate. Such measurements may be performed after resist development but before etching, after deposition, and/or at other times.

There are various techniques that can be used to measure structures formed in the patterning process, including the use of scanning electron microscopes, image-based measurement tools, and/or various specialized tools. In a fast and non-invasive dedicated metrology tool, radiation is directed onto a target on the substrate surface and the characteristics of the scattered (diffracted/reflected) beam are measured. By evaluating one or more characteristics of the radiation scattered by the substrate, one or more characteristics of the substrate may be determined. Traditionally, this may be referred to as diffraction-based metrology. One application of such diffraction-based metrology is alignment measurement. For example, alignment may be measured by comparing portions of the diffraction spectra (e.g., comparing different diffraction orders in the diffraction spectra of the periodic grating).

Thus, in a device manufacturing process (e.g., a patterning process or a photolithography process), a substrate or other object may receive various types of measurements during or after the process. The measurements may determine whether a particular substrate is defective, adjustments may be made to the process and equipment used in the process (e.g., aligning two or more layers on the substrate, or aligning a patterning device with the substrate), the performance of the process and equipment may be measured, or may be used for other purposes. Examples of measurements include optical imaging (e.g., optical microscopy), non-imaging optical measurements (e.g., diffraction-based measurements such as ASML YIELDSTAR metrology tools, ASML SMASH metrology systems), mechanical measurements (e.g., profile analysis using a stylus, atomic Force Microscopy (AFM)), and/or non-optical imaging (e.g., scanning Electron Microscopy (SEM)).

The measurement results may be directly or indirectly provided to the monitoring system SCS. If an error is detected, the exposure of the subsequent substrate may be adjusted (particularly if the inspection may be done fast enough and fast enough that one or more other substrates of the lot still need to be exposed) and/or the subsequent exposure of the exposed substrate. In addition, the already exposed substrate may be stripped and reworked to increase throughput, or discarded, thereby avoiding further processing of the known defective substrate. In case that only some target portions of the substrate are defective, only the target portions that meet the specifications may be further exposed. Other manufacturing process adjustments are also contemplated.

The metrology system may be used to determine one or more characteristics of a substrate structure, in particular how one or more properties of different substrate structures change, or how different layers of the same substrate structure change layer by layer. The metrology system may be integrated into the lithographic apparatus LA or the lithographic cell LC or may be a stand-alone apparatus.

To achieve metrology, one or more targets are typically provided exclusively on the substrate. The targets may include alignment marks, such as overlay targets and/or other targets. In general, the targets are specifically designed and may include one or more periodic structures. For example, the target on the substrate may include one or more 1-D periodic structures (e.g., geometric features such as gratings) in one or more layers of the substrate, which are printed such that after development, the periodic structure features are formed from solid resist lines. As another example, the target may include one or more 2-D periodic structures (e.g., gratings) in one or more layers that are printed such that, after development, the one or more periodic structures are formed from solid resist pillars or vias in the resist. The bars, pillars, or vias may alternatively be etched into the substrate (e.g., into one or more layers on the substrate).

FIG. 3 depicts an example inspection (metrology) system 10 that may be used to detect alignment, overlay, and/or perform other metrology operations. It comprises a radiation source 2 for projecting or otherwise irradiating radiation onto a substrate W. The substrate W may generally include metrology targets 30, such as overlay targets, alignment marks, and/or other structures. The redirected radiation is passed to a radiation sensor, such as a spectrometer detector 4 and/or other sensor, which measures the spectrum of the specularly reflected and/or diffracted radiation (intensity as a function of wavelength), as shown in the left-hand graph of fig. 4. The sensor may generate metrology signals conveying alignment data, overlay data, and/or other data indicative of the reflected radiation characteristics. From these data, the structure or profile that produced the detection spectrum can be reconstructed by one or more processors PRO, a general example of which is shown in fig. 4, but also by other operations. Note that these are general examples. Typically, illumination of an object, such as an overlay object and/or alignment mark, is performed orthogonal to the object and/or mark, rather than at an angle as shown in fig. 3.

As in the lithographic apparatus LA of fig. 1, one or more substrate tables (not shown in fig. 4) may be provided to hold the substrate W during a metrology operation. One or more of the substrate tables may be similar or identical in form to the substrate table WT of fig. 1 (WTa or WTb or both). In examples where the inspection system 10 is integrated with a lithographic apparatus, they may even be the same substrate table. The coarse positioner and the fine positioner may be provided and configured to accurately position the substrate with respect to the measurement optical system. Various sensors and actuators are provided, for example, to acquire the position of a target portion of interest (e.g., an overlay target and/or alignment mark) of a structure and to position it under an objective lens. Typically, many measurements will be made of the target portion of the structure at different locations on the substrate W. The substrate support may be moved in the X and Y directions to acquire different targets, and also in the Z direction to acquire a desired position of the target portion relative to the focal point of the optical system. When, for example, in practice the optical system may remain substantially stationary (typically in the X and Y directions, but also in the Z direction) and the substrate is moving, it is convenient to take the objective lens to different positions relative to the substrate to think and describe the operation. It is not important as long as the relative positions of the substrate and the optical system are correct, in principle which is moving, or both, or a part of the optical system is moving (e.g. in the Z and/or tilt direction) while the rest of the optical system is stationary and the substrate is moving (e.g. in the X and Y directions, but optionally also in the Z and/or tilt direction).

For a typical metrology measurement, the target (portion) 30 on the substrate W may be a 1-D grating, which is printed such that after development, strips are formed from solid resist lines (which may be covered by a deposited layer, for example) and/or other materials. Or the target 30 may be a 2-D grating that is printed such that after development, the grating is formed from solid resist pillars and/or other features in the resist. The bars, pillars, vias, and/or other features may be etched into or onto the substrate (e.g., into one or more layers on the substrate), deposited onto the substrate, covered by a deposited layer, and/or have other characteristics. The target (portion) 30 (e.g., a bar, a post, a via, etc.) is sensitive to process variations in the patterning process (e.g., optical aberrations in the lithographic projection apparatus, such as optical distortions in the projection system, focal spot variations, dose variations, etc.), such that the process variations appear as variations of the target 30. Thus, measurement data from the target 30 may be used to determine adjustments to one or more manufacturing processes, and/or as a basis for making actual adjustments. Note that in this example, the targets 30 may represent one or more layers that include one or more metrology targets.

For example, measurement data from the target 30 may indicate alignment of layers of the semiconductor device, and/or other information. The measurement data from the target 30 may be used (e.g., by one or more processors) to determine one or more semiconductor device manufacturing process parameters based on the alignment, overlay, and/or other information, and to determine adjustments to the semiconductor device manufacturing apparatus based on the determined one or more semiconductor device manufacturing process parameters. In some embodiments, this may include, for example, stage position adjustment, or this may include adjustment of a determination mask design, metrology target (e.g., overlay target and/or alignment mark) design, semiconductor device design, radiation intensity, radiation incidence angle, radiation wavelength, pupil size and/or shape, resist material, and/or other process parameters.

Fig. 5 illustrates a plan view of a typical target (e.g., an overlay target, an alignment mark, etc.) 30, and the extent of the radiation exposure spot S in the system of fig. 4. Generally, to obtain a diffraction spectrum that is not disturbed by surrounding structures, in one embodiment, the target 30 includes one or more periodic structures (e.g., gratings) that are greater than the width (e.g., diameter) of the illumination point S. The width of the spot S may be smaller than the width and length of the target. In other words, the target is illuminated "underfilled" and the diffraction signal is substantially unaffected by any signal other than the target itself, product features, etc. For example, the illumination arrangement may be configured to provide illumination of uniform intensity at the back focal plane of the objective lens. Alternatively, the illumination may be limited to on-axis or off-axis directions, for example, by including an aperture in the illumination path.

Fig. 6 illustrates a metrology method 600. In some embodiments, the method 600 is performed as part of a semiconductor device manufacturing process. In some embodiments, one or more operations of method 600 may be implemented in system 10 shown in fig. 3 and 4 (and fig. 7 described below), in a computer system (e.g., as shown in fig. 12 and described below), and/or in or by other systems. In some embodiments, the method 600 includes irradiating (operation 602) a metrology target in a patterned substrate with radiation, and generating (operation 604) a metrology signal based on the radiation received from the metrology mark, and/or other operations. The method 600 is described below in the context of alignment, but this is not meant to be limiting. The method 600 may be generally applied to many different processes.

The operations of method 600 presented below are intended to be illustrative. In some embodiments, method 600 may be implemented by one or more additional operations not described, and/or without one or more operations already discussed. For example, in some embodiments, the method 600 may include additional operations including determining adjustments to the semiconductor device manufacturing process. Furthermore, the order in which the operations of method 600 are illustrated in FIG. 6 and described below is not meant to be limiting.

In some embodiments, one or more portions of method 600 may be implemented in and/or controlled by one or more processing devices (e.g., a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information—see description of processor PRO). The one or more processing devices may include one or more devices that perform some or all of the operations of method 600 in response to instructions stored electronically on an electronic storage medium. The one or more processing devices may include one or more devices configured by hardware, firmware, and/or software that are specifically designed to perform one or more operations of method 600 (e.g., see discussion below in connection with fig. 12).

Operation 602 comprises irradiating a metrology target in a patterned substrate with radiation. In some embodiments, the metrology targets include one or more metrology marks, and/or other features, in different layers of the patterned substrate. In some embodiments, the metrology targets are associated with alignment and/or overlay measurements of the patterned substrate. For example, the metrology targets may be or include dedicated overlay targets and/or alignment marks that include one or more diffraction gratings. The radiation may be diffracted by the diffraction grating(s). In some embodiments, the metrology targets include one or more structures (e.g., metrology targets or some other structure (s)) in the patterned substrate capable of providing diffraction signals. In some embodiments, the metrology target may be any structure in the pattern design layout capable of generating a wide angle diffraction signal.

In some embodiments, for example, the metrology targets may be included in one or more layers of a substrate in a semiconductor device structure. In some embodiments, the metrology targets include one or more geometric features, such as 1D or 2D features and/or other geometric features. By way of several non-limiting examples, the metrology targets may include a line, an edge, a series of fine-pitch lines and/or edges, a set of a plurality of fine-pitch series of lines and/or edges, and/or other features.

In some embodiments, a radiation source (e.g., source 2 shown in fig. 3) is configured to irradiate a metrology target with radiation, the metrology target including a first metrology mark in a first layer of a patterned substrate and a second metrology mark in a second layer of the patterned substrate. Note that "first" and "second" need not refer to a first handle layer and a second handle layer, nor even to a continuous layer in a patterned substrate. The "first" and "second" layers may be any two layers of the stack structure. In some embodiments, the radiation source is configured to irradiate at least three metrology marks in at least three layers (which may or may not be continuous layers) of the patterned substrate with radiation. In some embodiments, the second (and/or third, fourth, fifth, etc.) metrology marks are located directly above the first metrology marks in the patterned substrate in the second layer of the semiconductor structure.

In some embodiments, the first and second metrology marks (and/or third, fourth, fifth, etc.) include diffraction-based overlay metrology marks, such as gratings and/or other metrology marks. For example, the gratings may have different pitches and/or other features. In some embodiments, the first metrology mark and the second metrology mark (or any two metrology marks in different layers) form an overlay (cDBO) target based on continuous offset diffraction, wherein the first metrology mark and the second metrology mark comprise a grating in a first layer and a grating in a second layer of the patterned substrate.

In some embodiments, the cDBO targets include eight pads, each having dimensions of about 10 μm by 5 μm. The first and second metrology marks may each include a first grating having a larger first pitch (pl) and a second grating having a smaller second pitch (pl). The pitch difference between the larger pitch (pl) and the smaller pitch (ps) follows the relationship ps/pl= (i-1)/i. In some embodiments, for example, i is an integer greater than 4 and less than 8.

The radiation may have a target wavelength and/or wavelength range, a target intensity, and/or other characteristics. The target wavelength and/or wavelength range, target intensity, etc. may be entered and/or selected by a user, determined by the system based on previous metrology measurements, and/or otherwise determined. In some embodiments, the radiation includes light and/or other radiation. In some embodiments, the light includes visible light, infrared light, near infrared light, and/or other light. In some embodiments, the radiation may be any radiation suitable for interferometry.

The radiation may be generated by a radiation source (e.g., source 2 shown in fig. 3 and 4 and described above) and/or other components. In some embodiments, radiation may be directed by a radiation source (e.g., through one or more lenses, modulators, and/or other components) onto a metrology target, a sub-portion of a metrology target (e.g., a less-than-whole portion), multiple metrology targets, and/or otherwise onto a substrate.

In some embodiments, the metrology target may be substantially stationary when irradiation occurs, the radiation sensor generates metrology signals, images of the metrology target are generated based on the metrology signals and/or other information, and/or other operations are performed. In some embodiments, for example, the radiation may be scanned over a metrology target. Scanning may include rastering the radiation over the metrology target such that different portions of the metrology target are irradiated at different times. In some embodiments, the characteristics of the radiation (e.g., wavelength, intensity, etc.) may change over time (whether in a stationary mode or a scanning mode). This may generate and/or supplement time-varying radiation for analysis. This may also facilitate analyzing individual portions of the feature, comparing one portion of the feature to another portion and/or other features, and/or performing other analyses.

Operation 604 includes generating a metrology signal based on radiation and/or other information received from a metrology target (e.g., from the first metrology mark, the second metrology mark, and/or other metrology marks described above). The metrology signal may be generated by a radiation sensor (e.g., sensor detector 4 as shown in fig. 3) and/or other components. Operation 604 comprises detecting reflected and/or transmitted radiation from the metrology target. In some embodiments, the radiation sensor is configured to generate the metrology signal based on reflected radiation received from at least three layers (e.g., from at least three gratings in the at least three layers).

In some embodiments, the metrology signal includes alignment position information and/or overlay information for the first layer and the second layer (and/or third layer, fourth layer, fifth layer, etc.). In some embodiments, the metrology signals include, for example, alignment position information and/or overlay information for some or all of the layers.

Detecting such radiation includes detecting an intensity shift of radiation received from one or more geometric features. The one or more phase and/or amplitude offsets correspond to one or more dimensions of the feature. For example, the phase and/or amplitude of the reflected radiation from one side of the feature is different relative to the phase and/or amplitude of the reflected radiation from the other side of the feature. Detecting one or more phase and/or amplitude (intensity) shifts in the radiation from the metrology marks includes measuring local phase shifts (e.g., local phase increments) and/or amplitude changes corresponding to different portions of the metrology marks. For example, the radiation from a particular region of the mark may comprise a sinusoidal waveform having a particular phase and/or amplitude. The radiation from different areas of the mark may also comprise a sinusoidal waveform, but with different phases and/or amplitudes. Detecting the radiation also includes measuring a phase and/or amplitude difference of the radiation of the different diffraction orders. For example, detecting one or more local phase and/or amplitude offsets may be performed using fourier transforms, hilbert transforms, and/or other techniques. Interferometry techniques and/or other operations may be used to measure the phase and/or amplitude differences of reflected radiation of different diffraction orders.

The metrology signal includes metrology information related to the metrology targets. For example, the metrology signal may be an alignment signal including alignment measurement information, an overlay signal including overlay measurement information, and/or other metrology signals. In some embodiments, operation 604 comprises determining an alignment check position for one or more layers of the semiconductor layer structure based on the metrology signals. Measurement information (e.g., alignment inspection position) may be determined using interferometry principles and/or other principles.

The metrology signal includes an electronic signal representing and/or otherwise corresponding to radiation from the metrology target. The metrology signals may be indicative of alignment values, such as overlay values and/or other information, for one or more layers. Generating the metrology signal includes sensing radiation and converting the sensing radiation into an electronic signal. In some embodiments, generating the metrology signal includes sensing different portions of radiation from different portions and/or different geometries of the metrology target (e.g., different gratings in different layers), and combining the different portions of the sensed radiation to form the metrology signal. Such sensing and conversion may be performed by similar and/or identical components and/or by other components as the radiation sensor detector 4 and/or the processor PRO shown in fig. 3, 4 and 12.

Figures 7-10 provide several examples of the various components and/or operations described above.

FIG. 7 illustrates an example metrology system 700. The system 700 is the same or similar to the system 10 described above with respect to fig. 3, wherein one or more components of the system 700 are similar and/or identical to one or more components of the system 10 (and fig. 7 illustrates other possible components of the system). In some embodiments, one or more components of system 700 may replace, be used with, and/or otherwise augment one or more components of system 10. In fig. 7, radiation may be generated by a radiation source (such as source 2 shown in fig. 3) and directed to a metrology target (e.g., target 30) (but not repeated in fig. 7).

In this example, the metrology target 30 on the substrate W includes a 2-D grating (or multiple 1-D gratings) in multiple layers of the substrate W (although only one layer is shown in FIG. 7 for simplicity). For example, the grating may be formed from solid resist pillars, strips, vias, and/or other features. The metrology target 30 may be sensitive to process variations in the patterning process (e.g., optical aberrations, focus variations, dose variations, etc. in a lithographic projection apparatus, such as a projection system), such that the process variations appear as variations of the metrology target 30. Thus, measurement data from the metrology targets 30 may be used to determine adjustments to one or more manufacturing processes and/or as a basis for making actual adjustments. Note again that in this example, the metrology targets 30 may represent one or more layers including one or more metrology marks.

Fig. 7 illustrates one or more lenses 702, 704, the one or more lenses 702, 704 being configured to receive positive primary reflected radiation 706 and negative primary reflected radiation 708, respectively, from the metrology target 30 (e.g., first metrology mark and second metrology mark in different layers described above), and to direct the received reflected radiation 706 and 708 toward the radiation sensor 4. The metrology target 30 has a specific alignment position 716 with respect to the radiation sensor 4. There is a phase difference 714 between the radiation 706 and 708. In this example, the sensor 4 includes a camera, one or more processors, and/or other components. The camera may be configured to generate the metrology signal as described above. The one or more processors may be configured to determine an alignment position of the first layer and/or the second layer based on the metrology signals. In this example, the determination includes performing a phase fit 710, generating and/or analyzing a two-dimensional (2D) interference pattern 712 (e.g., as described below), and/or other operations. For gratings in a single layer, phase fitting is described in PCT patent application publication No. WO2022156978, which is incorporated herein by reference in its entirety. For example, such phase fitting may be extended to 2D patterns.

Fig. 8 illustrates an alignment strategy used in prior art systems. As shown in views 801 and 803 of fig. 8 (described above), existing metrology systems are configured to measure gratings in a single layer of a metrology target so that a reference position of one layer relative to another layer in a semiconductor layer stack may be determined. View 801 illustrates a measurement 800 of a grating 802 in a single layer (layer n-2 in this example) of a metrology target 804, so that a reference position of a layer (layer n-1) in the semiconductor layer stack 806 in this example can be determined relative to another layer (e.g., layer n-2). View 803 illustrates a measurement 808 of different gratings 810 in layer n-2 so that the reference position of layer n in stack 806 relative to only layer n-2 can be determined. In this example, the alignment of layer n and layer n-1 is measured by different gratings in layer n-2, relative to layer n-2, because grating 802 is blocked by grating 812, which may be, for example, another portion of metrology target 804, as shown in view 803. Grating 812 may be the top layer grating of metrology target 804 and grating 802 may be its bottom layer grating. The metrology target 804 may be, for example, an overlay target and/or other targets. In this example, determining the reference position of layer n requires grating 810 to be spaced apart from grating 802, which requires additional space on the substrate, and/or has other drawbacks.

Fig. 9 illustrates an alignment strategy used in the present system (e.g., system 10 shown in fig. 3 and system 700 shown in fig. 7) and method (e.g., method 600). In contrast to that shown in fig. 8, views 901 and 903 of fig. 9 illustrate how the present system and method is configured to facilitate alignment of a substrate layer n on one or more previous layers (e.g., layer n-1, layer n-2, etc.) in a stack 906 and/or extract overlay information from these previous layers to improve alignment and/or other metrology determinations using a single multi-layer metrology target 904. As shown in fig. 9, the present system and method is configured to align multiple subsequent layers (n-1 and layer n in this example) to the same metrology target 904 (which has gratings 902 and 912 in layers n-1 and n-1, respectively), even though the target 904 includes two or more marks (e.g., gratings) directly overlying one another, and to use the same physical target 904 for alignment, overlay, and/or other metrology operations. In this case, the indicia 910 need not be, and thus need not be, printed (e.g., this saves substrate face on the substrate).

View 901 illustrates a measurement 900 of grating 902 in layer n-2 of metrology target 904 so that the reference position of layer n-1 in stack 906 relative to layer n-2 may be determined. View 903 illustrates a measurement 908 of grating 902 in layer n-2 so that the reference position of layer n in stack 906 relative to layer n-2 can be determined, and illustrates a measurement 914 of grating 912 in layer n-1 so that the reference position of layer n in stack 906 relative to layer n-1 can also be determined. The two measurements may be performed simultaneously and the two signals may be extracted simultaneously. For example from a single camera image. In this example, the alignment of layers n and n-1 is measured by the same grating in layer n-2, relative to layer n-2, because even grating 902 is located below grating 912, which may be another portion of metrology target 904, as shown in view 903. No additional gratings such as grating 910 are required. Because of the spacing and/or other differences between gratings 902 and 912 in layer n-2 and layer n-1, metrology signals may be acquired from the two gratings and may be resolved to determine the alignment position of the two layers (as described below). Note that alignment is used in fig. 8 and 9 as one possible example metrology measurement, but these principles for measuring two or more gratings on top of each other in two or more layers of a stack structure may be applied to other metrology measurements. It should further be noted that successive layers are shown as examples in fig. 9. However, to apply these principles, the various gratings shown in FIG. 9 need not be formed in successive layers of the stack 906.

Fig. 10 illustrates an example of gratings 902 and 912 shown in fig. 9. As described above, a radiation source (e.g., source 2 shown in fig. 3) is configured to irradiate a metrology target with radiation, the metrology target including a first metrology mark (such as grating 902) in a first layer of a patterned substrate (such as layer n-2) and a second metrology mark (such as grating 912) in a second layer of the patterned substrate (such as layer n-1). In some embodiments, grating(s) 902 and/or 912 include diffraction-based overlay metrology marks and/or other metrology marks. For example, the gratings may have different pitches and/or other features. In some embodiments, gratings 902 and 912 together form cDBO an object (e.g., object 904 shown in FIG. 9), where gratings 902 and 912 are located in layer n-2 and layer n-1 of the patterned substrate.

In some embodiments, cDBO targets include eight pads 1000, 1002, 1004, 1006, 1008, 1010, 1012, and 1014. For example, each pad has a size of about 10 μm×5 μm. Each grating pad may include a first grating having a larger first pitch (pl) and a second grating having a smaller second pitch (ps). Gratings 902 and 912 each include four pads with a larger pitch and four pads with a smaller pitch. In areas where grating 902 has a larger pitch, grating 912 will have a smaller pitch, and vice versa. In some embodiments, the spacing difference between the larger spacing (pl) and the smaller spacing (ps) follows the relationship ps/pl= (i-1)/i. In some implementations, for example, i is an integer greater than 4 and less than 8. In fig. 10, the lighter or smaller rectangles form the top grating and the darker or larger rectangles form the bottom grating. In pads 1000, 1004, 1010, and 1014, the bottom grating has a larger pitch and the top grating has a smaller pitch. In pads 1002, 1006, 1008, and 1012, the bottom grating has a smaller pitch and the top grating has a larger pitch.

Returning to FIG. 6, in some embodiments, the metrology signal (e.g., from the multi-pitch cDBO target described above) includes and/or is used by one or more processors to generate a two-dimensional (2D) interference pattern. The one or more processors may be configured to detect the offset of the first metrology mark or the second metrology mark (e.g., the gratings 902 and/or 912 shown in fig. 9 and described above, and/or another mark in another layer). Such an offset may be detected based on the interference pattern and/or other information. Such a shift can be detected because the shift of one metrology mark has a different effect on the interference pattern than the shift of another metrology mark. For example, the one or more processors may be configured to detect a shift in a first direction of a first stripe (e.g., grating 902 shown in fig. 9) associated with a first metrology mark in the two-dimensional interference pattern, the shift indicating a relative shift of the first metrology mark compared to a second stripe (e.g., grating 912 shown in fig. 9) associated with a second metrology mark that indicates a position of the second metrology mark. Instead, the one or more processors may alternatively or additionally be configured to detect a shift in the second direction of a second fringe in the two-dimensional interference pattern associated with the second metrology mark, the shift being indicative of a relative shift of the second metrology mark compared to the first fringe associated with the first metrology mark, indicative of the position of the first metrology mark. In some embodiments, the metrology signal may be used to determine an absolute positional offset (e.g., not just relative to each other) of the two gratings relative to a reference (e.g., a sensor).

Fig. 11 illustrates an example 2D interference pattern 1100 (e.g., a 2D interference pattern of a single pad of cDBO targets, in actual practice, one cDBO target would have eight such patterns, see fig. 10). Since there are two gratings in the irradiated metrology target described above, a 2D interference pattern 1100 is observed. When one grating position is shifted, the stripes of the pattern 1100 move in one direction. When different grating positions are shifted, different fringes of the pattern 1100 move in the other direction. Thus, two grating alignment positions can be determined. In order to extract the positions of the two gratings, the relation between the signal and the positions of the two gratings must be known. For example, this may be or include a relationship between fringe phase in two different directions and two grating positions (e.g., determined by or based on calibration measurements or analysis of the average of the sensor and signal modeling). The direction of the stripes may be as many as the number of layers. Signal extraction may become more complex but still be possible through modeling or calibration.

With continued reference to the discussion above in connection with fig. 9 and 10, in view of the pattern 1100 shown in fig. 11, the metrology signal (e.g., from the multi-pitch cDBO target) includes one or more processors (PRO, see fig. 3) and/or is used by the processor to generate the 2D interference pattern 1100. The one or more processors may be configured to detect the offset of the first metrology mark or the second metrology mark (e.g., the gratings 902 and/or 912 shown in fig. 9, and/or another mark in another layer). Such an offset may be detected based on the interference pattern 1100 and/or other information. Such a shift can be detected because the effect of the shift of one metrology mark on the interference pattern 1100 is different compared to the shift of another metrology mark. For example, the one or more processors may be configured to detect an offset 1102 of a first stripe (e.g., grating 902 shown in fig. 9) associated with a first metrology mark in the two-dimensional interference pattern 1100 in a first direction, the offset 1102 indicating a relative offset of the first metrology mark compared to a second stripe (e.g., grating 912 shown in fig. 9) associated with a second metrology mark that indicates a position of the second metrology mark. Instead, the one or more processors may alternatively or additionally be configured to detect an offset 1104 in the second direction of a second fringe (e.g., grating 912 shown in fig. 9) associated with the second metrology mark in the two-dimensional interference pattern 1100, the offset 1104 indicating a relative offset of the second metrology mark compared to a first fringe associated with the first metrology mark indicating a position of the first metrology mark.

Thus, in some embodiments, one metrology target (e.g., cDBO alignment targets including gratings 902 and 912 in this example) may be used to align on one and/or two layers (e.g., layers n-2 and n-1) or more, with one alignment using only a first grating (e.g., grating 902) (its fringes) in a first layer (e.g., layer n-2) and another alignment using a second grating (e.g., grating 912) (its fringes) in a second layer (e.g., layer n-1), and/or some combination of the first and second gratings (its fringes) in the first and/or second layers. For example, the set may be or include an average and/or other set. This may save wafer substrate surface to allow a user to pick and choose layers and/or sets of layers to be used for alignment and/or overlay (and/or other metrology operations), and/or other advantages. Furthermore, measurement accuracy may be improved over prior systems because the metrology signals (which may be used for alignment, overlay, and/or other metrology) of these multiple metrology marks (e.g., gratings from cDBO overlay targets) may be acquired in one sensing operation. Furthermore, information from multiple gratings may be used similar to information acquired when using two different wavelengths of radiation, thus improving the available metrology information compared to information acquired from single layer metrology marks.

Returning to fig. 6, in some embodiments, operation 604 includes determining an adjustment of the semiconductor device manufacturing process. In some embodiments, operation 604 comprises determining one or more semiconductor device manufacturing process parameters. One or more semiconductor device manufacturing process parameters may be determined based on one or more detected phase and/or amplitude variations, alignment values indicated by the metrology signals, overlay values indicated by the metrology signals, and/or other information. The one or more parameters may include parameters of the radiation (used to determine the alignment), alignment inspection locations on layers of the semiconductor device structure, overlay values, and/or other parameters. In some embodiments, process parameters may be construed broadly to include stage position, mask design, metrology target design, semiconductor device design, radiation intensity (for exposing resist, etc.), radiation incidence angle (for exposing photoresist, etc.), radiation wavelength (for exposing mask, etc.), pupil size and/or shape, resist material, and/or other parameters.

For example, the radiation parameters used to determine alignment may include wavelength, intensity, angle of incidence, and/or radiation parameters. These parameters may be adjusted to better measure features having a particular shape, enhance the intensity of reflected radiation, increase and/or otherwise enhance (e.g., maximize) the phase and/or amplitude shift (if any) of reflected radiation from one region of the feature to the next, and/or for other purposes. This may enable and/or enhance detection of more subtle deviations, make phase and/or amplitude shifts easier to detect, and/or have other advantages.

In some embodiments, operation 604 includes determining a process adjustment based on one or more determined semiconductor device manufacturing process parameters, adjusting a semiconductor device manufacturing apparatus based on the determined adjustment, and/or other operations. For example, based on the measured alignment position, wafer deformation may be modeled and used to correct the lithographic exposure. As another example, if the determined alignment is not within process tolerances, the misalignment may be caused by one or more manufacturing processes whose process parameters have drifted and/or otherwise changed such that the process no longer produces an acceptable device (e.g., the alignment measurement may exceed the threshold of acceptability). One or more new or adjusted process parameters may be determined based on the alignment determination. The new or adjusted process parameters may be configured to allow the fabrication process to produce acceptable devices again. For example, new or adjusted process parameters may result in a previously unacceptable alignment (or misalignment) being adjusted back to an acceptable range. The new or adjusted process parameters may be compared to existing parameters for a given process. For example, if there is a discrepancy, the discrepancy may be used to determine an adjustment of the equipment used to produce the device (e.g., the parameter "x" should be increased/decreased/changed to match the new or adjusted version of the parameter "x" determined as part of operation 604). In some embodiments, operation 604 may include electronically adjusting the device (e.g., based on the determined process parameters). Electronically adjusting the device may include sending an electronic signal and/or other communication to the device, which may result in a change in the device, for example. Electronic adjustments may include, for example, changing settings on the device and/or other adjustments.

FIG. 12 is a schematic diagram of an example computer system CS that may be used for one or more of the operations described herein. The computer system CS comprises a bus BS or other communication mechanism for communicating information, and a processor PRO (or processors) coupled with the bus BS for processing information. The computer system CS further comprises a main memory MM, such as a Random Access Memory (RAM) or other dynamic storage device, coupled to the bus BS for storing information and instructions to be executed by the processor PRO. Main memory MM may also be used for storing temporary variables or other intermediate information during execution of instructions by processor PRO. The computer system CS further comprises a Read Only Memory (ROM) ROM or other static storage device coupled to the bus BS for storing static information and instructions for the processor PRO. A storage device SD, such as a magnetic disk or optical disk, is provided and coupled to bus BS for storing information and instructions.

The computer system CS may be coupled via a bus BS to a display DS, such as a Cathode Ray Tube (CRT) or a flat panel or touch panel display, for displaying information to a computer user. An input device ID (including alphanumeric and other keys) is coupled to bus BS for communicating information and command selections to processor PRO. Another type of user input device is a cursor control CC, such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to processor PRO and for controlling cursor movement on display DS. Such input devices typically have two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), which allows the device to specify positions in a plane. A touch panel (screen) display may also be used as an input device.

In some embodiments, portions of one or more methods may be performed by the computer system CS in response to the processor PRO executing one or more sequences of one or more instructions contained in the main memory MM. Such instructions may be read into main memory MM from another computer-readable medium, such as storage device SD. Execution of the sequences of instructions contained in main memory MM causes processor PRO to perform the process steps (operations). One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in main memory MM. In some embodiments, hardwired circuitry may be used in place of or in combination with software instructions. Thus, the present description is not limited to any specific combination of hardware circuitry and software.

The term "computer-readable medium" or "machine-readable medium" refers to any medium that participates in providing instructions to processor PRO for execution. Such a medium may take many forms, including but not limited to, non-volatile media, and transmission media. For example, nonvolatile media includes optical or magnetic disks, such as storage device SD. Volatile media includes dynamic memory, such as main memory MM. Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise bus BS. Transmission media can also take the form of acoustic or light waves, such as those generated during Radio Frequency (RF) and Infrared (IR) data communications. A computer-readable medium may be non-transitory such as a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge. The non-transitory computer readable medium may have instructions recorded thereon. The instructions, when executed by a computer, may implement any of the operations described. For example, a transitory computer readable medium may include a carrier wave or other propagated electromagnetic signal.

Various forms of computer readable media may be involved in carrying one or more sequences of instructions to processor PRO for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to computer system CS can receive the data on the telephone line and use an infra-red transmitter to convert the data to an infra-red signal. An infrared detector coupled to the bus BS can receive the data carried in the infrared signal and place the data on the bus BS. The bus BS carries the data to the main memory MM from which the processor PRO retrieves and executes the instructions. The instructions received by the main memory MM may optionally be stored on storage device SD either before or after execution by processor PRO.

The computer system CS may also comprise a communication interface CI coupled to the bus BS. The communication interface CI provides a bi-directional data communication coupled to a network link NDL which is connected to a local network LAN. For example, the communication interface CI may be an Integrated Services Digital Network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, the communication interface CI may be a Local Area Network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, the communication interface CI sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.

Network link NDL typically provides data communication through one or more networks to other data devices. For example, the network link NDL may provide a connection to the host HC through a local network LAN. This may include data communication services provided over a global packet data communication network, now commonly referred to as the "internet" INT. Local Area Networks (LANs) may use an electrical, electromagnetic or optical signal carrying a digital data stream. The signals through the various networks and the signals on network data link NDL and the signals through communication interface CI, which transmit digital data to and from computer system CS, are exemplary forms of carrier waves transporting the information.

The computer system CS may send messages and receive data, including program code, through the network(s), the network data link NDL and the communication interface CI. In the internet example, the host computer HC may send a request code of an application program through the internet INT, the network data link NDL, the local area network LAN and the communication interface CI. For example, one such downloaded application may provide all or part of the methods described herein. The received code may be executed by processor PRO as it is received, and/or stored in storage device SD or other non-volatile storage for later execution. In this way, the computer system CS may obtain application code in the form of a carrier wave.

Various embodiments of the present system and method are disclosed in the following numbered clause list:

1. A metrology system includes a radiation source configured to irradiate a first metrology mark in a first layer of a patterned substrate and a second metrology mark in a second layer of the patterned substrate with radiation, and a radiation sensor configured to generate a metrology signal based on reflected radiation received from the first metrology mark and the second metrology mark, the metrology signal including alignment position information and/or overlay information of the first layer and the second layer.

2. The system of clause 1, wherein the metrology signal is an alignment signal or an overlay signal.

3. The system of any of the preceding clauses wherein the radiation source is configured to irradiate at least three metrology marks in at least three layers of the patterned substrate with radiation, and the radiation sensor is configured to generate the metrology signals based on reflected radiation received from the at least three metrology marks, the metrology signals including alignment position information and/or overlay information for some or all of the at least three layers.

4. The system of any of the preceding clauses wherein the second metrology mark is located directly above the first metrology mark in the patterned substrate.

5. The system of any one of the preceding clauses wherein the first and second metrology marks comprise diffraction-based overlay metrology marks.

6. The system of any one of the preceding clauses wherein the first and second metrology marks comprise gratings.

7. The system of any one of the preceding clauses wherein the gratings have different pitches.

8. The system of any of the preceding clauses, wherein the first and second metrology marks form an overlay (cDBO) target based on continuously biased diffraction, wherein the first and second metrology marks comprise gratings in the first layer and gratings in the second layer of the patterned substrate.

9. The system of any one of the preceding clauses wherein the cDBO targets comprise eight pads, each pad having dimensions of about 10 μm x 5 μm.

10. The system of any of the preceding clauses, wherein the first metrology mark and the second metrology mark each comprise a first grating having a larger first pitch (pl) and a second grating having a smaller second pitch (pl), and wherein a pitch difference between the larger pitch (pl) and the smaller pitch (ps) follows the relationship ps/pl= (i-1)/i.

11. The system of any one of the preceding clauses wherein i is an integer greater than 4 and less than 8.

12. The system of any one of the preceding clauses, further comprising one or more processors configured to determine an alignment position of the first layer and/or the second layer based on the metrology signal.

13. The system of any one of the preceding clauses, wherein the one or more processors are configured to determine the alignment position by determining a phase difference between positive and negative diffraction orders of the reflected radiation of the first metrology mark and/or the second metrology mark.

14. The system of any one of the preceding clauses, wherein determining the phase difference comprises determining a phase shift.

15. The system of any one of the preceding clauses, wherein the metrology signal comprises and/or is used to generate a two-dimensional (2D) interference pattern.

16. The system of any one of the preceding clauses, wherein the one or more processors are configured to detect the offset of the first metrology mark or the second metrology mark based on the interference pattern, because the offset of any one metrology mark causes a different effect on the interference pattern than the offset of another metrology mark.

17. The system of any of the preceding clauses, wherein the one or more processors are configured to detect a shift in a first direction of a first stripe in the two-dimensional interference pattern associated with the first metrology mark, the shift being indicative of a relative shift of the first metrology mark compared to a second stripe associated with the second metrology mark that is indicative of a position of the second metrology mark.

18. The system of any of the preceding clauses, wherein the one or more processors are configured to detect a shift in a second direction of a second stripe in the two-dimensional interference pattern associated with the second metrology mark, the shift being indicative of a relative shift of the second metrology mark compared to a first stripe associated with the first metrology mark that is indicative of a position of the first metrology mark.

19. The system of any one of the preceding clauses wherein the one or more processors are configured to determine the alignment positions of the first layer and the second layer simultaneously based on the metrology signals.

20. The system of any of the preceding clauses, wherein the metrology signal includes overlay information of the first layer and the second layer, and the one or more processors are further configured to determine an overlay of the first layer and the second layer based on the metrology signal.

21. The system of any of the preceding clauses, further comprising one or more lenses configured to receive reflected radiation from the first and second metrology marks and direct the received reflected radiation toward the radiation sensor.

22. The system of any one of the preceding clauses wherein the metrology signal is configured to be used by one or more processors to adjust a semiconductor device manufacturing process.

23. The system of any of the preceding clauses wherein the radiation source is configured to generate two pairs of off-axis illuminations.

24. The system of any one of the preceding clauses, wherein a given metrology mark comprises a one-dimensional (1D) pattern, and the radiation sensor comprises a photodiode or an image-based sensor.

25. The system of any of the preceding clauses, wherein the metrology signals are configured to be used by one or more processors to model substrate deformations and to model lithographic exposure based on measured alignment positions.

26. A metrology method includes irradiating a first metrology mark in a first layer of a patterned substrate and a second metrology mark in a second layer of the patterned substrate with radiation from a radiation source, and generating, with a radiation sensor, a metrology signal based on reflected radiation received from the first metrology mark and the second metrology mark, the metrology signal including alignment position information and/or overlay information of the first layer and the second layer.

27. The method of clause 26, wherein the metrology signal is an alignment signal or an overlay signal.

28. The method according to any of the preceding clauses, wherein the radiation source is configured to irradiate at least three metrology marks in at least three layers of the patterned substrate with radiation, and the radiation sensor is configured to generate the metrology signals based on reflected radiation received from the at least three metrology marks, the metrology signals comprising alignment position information and/or overlay information for some or all of the at least three layers.

29. The method of any of the preceding clauses wherein the second metrology mark is located directly above the first metrology mark in the patterned substrate.

30. The method of any of the preceding clauses wherein the first and second metrology marks comprise diffraction-based overlay metrology marks.

31. The method of any one of the preceding clauses wherein the first metrology mark and the second metrology mark comprise gratings.

32. The method of any of the preceding clauses wherein the gratings have different pitches.

33. The method of any of the preceding clauses wherein the first and second metrology marks form an overlay target, cDBO target, based on continuously biased diffraction, wherein the first and second metrology marks comprise gratings in the first and second layers of the patterned substrate.

34. The method of any of the preceding clauses wherein the cDBO targets comprise eight pads, each pad having dimensions of about 10 μm x 5 μm.

35. The method according to any of the preceding clauses, wherein the first metrology mark and the second metrology mark each comprise a first grating having a larger first pitch (pl) and a second grating having a smaller second pitch (pl), and wherein a pitch difference between the larger pitch (pl) and the smaller pitch (ps) follows the relationship ps/pl= (i-1)/i.

36. The method of any one of the preceding clauses wherein i is an integer greater than 4 and less than 8.

37. The method of any of the preceding clauses, further comprising determining, with one or more processors, an alignment position of the first layer and/or the second layer based on the metrology signals.

38. The method of any of the preceding clauses wherein the one or more processors are configured to determine the alignment position by determining a phase difference between positive and negative diffraction orders of the reflected radiation of the first metrology mark and/or the second metrology mark.

39. The method of any of the preceding clauses, wherein determining the phase difference comprises determining a phase shift.

40. The method of any one of the preceding clauses, wherein the metrology signal comprises and/or is used to generate a two-dimensional (2D) interference pattern.

41. The method of any of the preceding clauses wherein the one or more processors are configured to detect the offset of the first metrology mark or the second metrology mark based on the interference pattern, as the offset of any metrology mark causes a different effect on the interference pattern than the offset of another metrology mark.

42. The method of any of the preceding clauses, wherein the one or more processors are configured to detect a shift in a first direction of a first stripe in the two-dimensional interference pattern associated with the first metrology mark, the shift being indicative of a relative shift of the first metrology mark compared to a second stripe associated with the second metrology mark that is indicative of a position of the second metrology mark.

43. The method of any of the preceding clauses, wherein the one or more processors are configured to detect a shift in a second direction of a second stripe in the two-dimensional interference pattern associated with the second metrology mark, the shift being indicative of a relative shift of the second metrology mark compared to a first stripe associated with the first metrology mark that is indicative of a position of the first metrology mark.

44. The method of any of the preceding clauses wherein the one or more processors are configured to determine the alignment positions of the first layer and the second layer simultaneously based on the metrology signals.

45. The method of any of the preceding clauses, wherein the metrology signal includes overlay information of the first layer and the second layer, and the one or more processors are further configured to determine an overlay of the first layer and the second layer based on the metrology signal.

46. The method of any of the preceding clauses, further comprising one or more lenses configured to receive reflected radiation from the first and second metrology marks and direct the received reflected radiation toward the radiation sensor.

47. The method of any preceding clause, wherein the metrology signal is configured to be used by one or more processors to regulate a semiconductor device manufacturing process.

48. The method of any of the preceding clauses wherein the radiation source is configured to generate two pairs of off-axis radiation.

49. The method of any of the preceding clauses, wherein a given metrology mark comprises a one-dimensional (1D) pattern, and the radiation sensor comprises a photodiode or an image-based sensor.

50. The method of any of the preceding clauses, further comprising modeling substrate deformation and modeling lithographic exposure based on the measured alignment position using the metrology signal.

The concepts disclosed herein may be associated with any general-purpose imaging system for imaging sub-wavelength features and are particularly useful for emerging imaging technologies capable of producing ever shorter wavelengths. Emerging technologies that have been in use include EUV (extreme ultraviolet), DUV lithography, which is capable of producing 193nm wavelengths using ArF lasers, even 157nm wavelengths using fluorine lasers. Furthermore, EUV lithography can produce photons in the range of 20-5nm by using synchrotrons or by striking a material (solid or plasma) with high energy electrons to produce the photons in this range.

While the concepts disclosed herein may be used for imaging on a substrate such as a silicon wafer, it should be understood that the disclosed concepts may be used with any type of lithographic imaging system, such as a system for imaging on other substrates than silicon wafers. Furthermore, combinations and subcombinations of the disclosed elements may include separate embodiments.

The above description is intended to be illustrative, and not restrictive. Accordingly, it will be apparent to those skilled in the art that modifications may be made as described above without departing from the scope of the claims set out below.

Claims (15)

1. A measurement system comprising: a radiation source configured to irradiate first metrology marks in a first layer of a patterned substrate and second metrology marks in a second layer of the patterned substrate with radiation; and A radiation sensor is configured to generate a measurement signal based on reflected radiation received from the first measurement mark and the second measurement mark, wherein the measurement signal includes alignment position information and/or overlay information of the first layer and the second layer. 2 . The system of claim 1 , wherein the measurement signal is an alignment signal or an overlay signal. 3. The system of claim 1 or 2, wherein the radiation source is configured to irradiate at least three metrology marks in at least three layers of the patterned substrate with radiation; and The radiation sensor is configured to generate the metrology signal based on reflected radiation received from the at least three metrology marks, the metrology signal comprising alignment position information and/or overlay information of some or all of the at least three layers. 4 . The system according to claim 1 , wherein the second metrology mark is located directly above the first metrology mark in the patterned substrate. 5. The system of any one of claims 1 to 4, wherein the first metrology mark and the second metrology mark comprise diffraction-based overlaid metrology marks. 6. The system according to any one of claims 1 to 5, wherein the first metrology mark and the second metrology mark comprise gratings. The system of claim 6 , wherein the gratings have different pitches. 8. The system of any one of claims 1 to 7, wherein the first metrology mark and the second metrology mark form a continuous bias diffraction based overlay target, i.e., a cDBO target, wherein the first metrology mark and the second metrology mark comprise gratings in the first layer and the second layer of the patterned substrate. 9. The system of claim 8, wherein the cDBO target comprises eight pads, each pad having a size of approximately 10 μm x 5 μm. 10. A system according to claim 8 or 9, wherein the first measurement mark and the second measurement mark each include a first grating having a larger first pitch (pl) and a second grating having a smaller second pitch (pl), and wherein the pitch difference between the larger pitch (pl) and the smaller pitch (ps) follows the relationship: ps/pl = (i-1)/i. The system of claim 10 , wherein i is an integer greater than 4 and less than 8. 12 . The system according to claim 1 , further comprising one or more processors configured to determine an alignment position of the first layer and/or the second layer based on the measurement signal. 13. The system of claim 12, wherein the one or more processors are configured to determine the alignment position by determining a phase difference between positive and negative diffraction orders of the reflected radiation of the first measurement mark and/or the second measurement mark. The system of claim 13 , wherein determining the phase difference comprises determining a phase shift. 15. The system according to any one of claims 12 to 14, wherein the measurement signal comprises a two-dimensional (2D) interference pattern and/or is used to generate a two-dimensional (2D) interference pattern.