NL2009725A - Cleaning a support that holds a patterning device inside a lithography apparatus. - Google Patents

Description

CLEANING A SUPPORT THAT HOLDS A PATTERNING DEVICE INSIDE

A LITHOGRAPHY APPARATUS

HELD

[0001] The present invention relates to methods and systems for cleaning a support such as a clamp of a chuck, e.g., an electrostatic chuck that is used to hold a patterning device, e.g., a reticle or mask, inside a lithography apparatus.

BACKGROUND

[0002] A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain adjacent target portions that are successively patterned.

[0003] Lithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and/or structures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more critical factor for enabling miniature IC or other devices and/or structures to be manufactured.

[0004] A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in equation (1): CD = kl*— (1)

1 NA

where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, kl is a process dependent adjustment factor, also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. It follows from equation (1) that reduction of the minimum printable size of features can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA or by decreasing the value of kl.

[0005] In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation having a wavelength within the range of 5-20 nm, for example within the range of 13-14 nm. It has further been proposed that EUV radiation with a wavelength of less than 10 nm could be used, for example within the range of 5-10 nm such as 6.7 nm or 6.8 nm. Such radiation is termed extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.

[0006] EUV radiation may be produced using a plasma. A radiation system for producing EUV radiation may include a laser for exciting a fuel to provide the plasma, and a source collector module for containing the plasma. The plasma may be created, for example, by directing a laser beam at a fuel, such as droplets of a suitable fuel material (e.g., tin, which is currently thought to be the most promising and thus likely choice of fuel for EUV radiation sources), or a stream of a suitable gas or vapor, such as Xe gas or Li vapor. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector. The radiation collector may be a mirrored normal incidence radiation collector, which receives the radiation and focuses the radiation into a beam. The source collector module may include an enclosing stmcture or chamber arranged to provide a vacuum environment to support the plasma. Such a radiation system is typically termed a laser produced plasma (LPP) source. In an alternative system, which may also employ the use of a laser, radiation may be generated by a plasma formed by the use of an electrical discharge - a discharge produced plasma (DPP) source.

[0007] An electrostatic chuck (ESC) used in a lithography apparatus to hold a patterning reticle on a scanning stage can become contaminated. This contamination can be transferred from the reticle to the ESC and vice versa. The contamination can also originate in the lithographic chamber itself. The contamination causes overlay error and therefore nonfunctional computer chips.

[0008] Typically, the ESC is manually cleaned. However, the current cleaning leaves a residue of very fine particles. The manual cleaning can only remove particles larger than approximately 3 pm in diameter. Manual cleaning requires the apparatus to be vented to atmospheric pressure and partially disassembled, which in turn causes loss of productivity.

[0009] The state of the art for cleaning an ESC in situ of the lithography tool is a manual solvent wipe with a special reduced particulate wiper. It is not possible to remove the ESC for ex situ traditional wet cleaning since it is electrically and mechanically into a monolithic machine component.

[0010] In semiconductor micro lithography, there are systems where the reticle is reflective and clamped to a surface. This clamp surface must be clean in order to obtain a reasonable yield in chip production. Thus, a user needs to be able to clean the clamp if it becomes contaminated.

SUMMARY

[0011] It is desirable to obviate or mitigate at least one of the problems, whether identified herein or elsewhere, or to provide an alternative to existing apparatus or methods.

[0012] According to a first aspect of the present invention, there is provided a method that includes loading a patterning device into a lithographic apparatus. The patterning device includes a material layer adhered to a backside of the patterning device. The method further includes clamping the patterning device to a support within the lithographic apparatus using an applied voltage. Any particles present on the support are then transferred to the material layer adhered to the backside of the patterning device. Afterwards, the patterning device is removed, along with any particles on the material layer, from the support.

[0013] According to a second aspect of the present invention, there is provided a method for cleaning contaminants off of a surface of a support within a lithographic apparatus. The method includes loading at least a portion of a wafer into the lithographic apparatus. The method further includes clamping the at least a portion of a wafer to the support using an applied voltage. The contaminants are transferred to the at least a portion of a wafer during the clamping. The method then involves removing the at least a portion of a wafer, along with the contaminants, from the support.

[0014] According to a third aspect of the present invention, there is provided a lithographic apparatus that includes an illumination system configured to condition a radiation beam, a support constructed to hold a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam, a substrate table constructed to hold a substrate, and a projection system configured to project the patterned radiation beam onto a target portion of the substrate. The lithographic apparatus further includes a cleaning system for cleaning the support and having a material layer on a backside of the patterning device. The first material later attracts any particles present between the support and the patterning device while the support holds the patterning device.

[0015] According to a fourth aspect of the present invention, there is provided a particle cleaning system for use in a lithographic apparatus. The particle cleaning system comprises a first patterning device or a substrate shaped in the shape of the first patterning device. A backside of the first patterning device or the substrate includes a material layer disposed on the backside and designed to clean a surface of a support, such that the support holds a second patterning device. The second patterning device is capable of imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam. The material layer is designed to adhere or absorb any particles present on the surface of the support.

[0016] Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. It is noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

[0017] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the present invention and to enable a person skilled in the relevant art(s) to make and use the present invention.

[0018] Figure 1 shows a lithographic apparatus according to an embodiment of the present invention.

[0019] Figure 2 is a more detailed view of the apparatus of Figure 1, including an LPP source collector module, according to an embodiment.

[0020] Figures 3A and 3B illustrate a top and side view of a first material layer applied to a backside of a patterning device, according to an embodiment.

[0021] Figure 4 illustrates a clamping structure surface, according to an embodiment.

[0022] Figure 5 illustrates a particle removal process, according to an embodiment.

[0023] Figure 6 illustrates a graph of particle transfer rate showing the influence of a polyimide film.

[0024] Figures 7-10 illustrate various configurations for applying a first material layer to the backside of a patterning device, according to embodiments.

[0025] Figures 11 and 12 illustrate different configurations, arrangements, and modes of a patterning device and clamp structure, according to embodiments.

[0026] Figures 13 and 14 illustrate example methods, according to embodiments.

[0027] The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.

DETAILED DESCRIPTION

[0028] This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the present invention. The scope of the present invention is not limited to the disclosed embodiment/s). The present invention is defined by the clauses appended hereto.

[0029] The embodiment(s) described, and references in the specification to "one embodiment", "an embodiment", "an example embodiment", etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicidy described.

[0030] Embodiments of the present invention may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine-readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0031] Before describing such embodiments in more detail, however, it is instructive to present an example environment in which embodiments of the present invention may be implemented.

[0032] Figure 1 schematically shows a lithographic apparatus LAP including a source collector module SO according to an embodiment of the present invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation); a support structure (e.g., a mask table) MT constructed to support a patterning device (e.g., a mask or a reticle) MA and connected to a first positioner PM configured to accurately position the patterning device; a substrate table (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate; and a projection system (e.g., a reflective projection system) PS configured to project a pattern imparted to the radiation beam B by patterning device MA onto a target portion C (e.g., comprising one or more dies) of the substrate W.

[0033] 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.

[0034] The support structure MT holds the patterning device MA in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is held in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, 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.

[0035] The term “patterning device” should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. The pattern imparted to the radiation beam may correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.

[0036] 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. An 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 that is reflected by the mirror matrix.

[0037] The projection system, like 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, as appropriate for the exposure radiation being used, or for other factors such as the use of a vacuum. It may be desired to use a vacuum for EUV radiation since gases may absorb too much radiation. A vacuum environment may therefore be provided to the whole beam path with the aid of a vacuum wall and vacuum pumps.

[0038] As here depicted, the apparatus is of a reflective type (e.g., employing a reflective mask).

[0039] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and/or two or more mask tables). 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.

[0040] Referring to Figure 1, the illuminator IL receives an extreme ultra violet radiation beam from the source collector module SO. Methods to produce EUV light include, but are not necessarily limited to, converting a material into a plasma state that has at least one element, e.g., xenon, lithium or tin, with one or more emission lines in the EUV range. In one such method, often termed laser produced plasma ("LPP") the required plasma can be produced by irradiating a fuel, such as a droplet, stream or cluster of material having the required line-emitting element, with a laser beam. The source collector module SO may be part of an EUV radiation system including a laser, not shown in Figure 1, for providing the laser beam and exciting the fuel. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector, disposed in the source collector module. The laser and the source collector module may be separate entities, for example when a CO2 laser is used to provide the laser beam for fuel excitation.

[0041] In such cases, the laser is not considered to form part of the lithographic apparatus and the radiation beam is passed from the laser to the source collector module with the aid of a beam delivery system comprising, for example, suitable directing mirrors and/or a beam expander. In other cases the source may be an integral part of the source collector module, for example when the source is a discharge produced plasma EUV generator, often termed as a DPP source.

[0042] The illuminator IL may comprise an adjuster for adjusting the angular intensity distribution of the radiation beam. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may comprise various other components, such as facetted field and pupil mirror devices. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.

[0043] 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 being reflected from the patterning device (e.g., mask) 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 PS2 (e.g., an interferometric device, linear 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. Similarly, the first positioner PM and another position sensor PS 1 can be used to accurately position the patterning device (e.g., mask) MA with respect to the path of the radiation beam B. Patterning device (e.g., mask) MA and substrate W may be aligned using mask alignment marks Ml, M2 and substrate alignment marks PI, P2.

[0044] The depicted apparatus could be used in at least one of the following modes: 1. In step mode, the support structure (e.g., mask table) MT and the substrate table WT are kept essentially stationary, while an entire 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 a different target portion C can be exposed.

2. In scan mode, the support structure (e.g., mask table) 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 (e.g., mask table) MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS.

3. In another mode, the support structure (e.g., mask table) MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array of a type as referred to above.

[0045] Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.

[0046] Figure 2 shows the lithographic apparatus LAP in more detail, including the source collector module SO, the illumination system IL, and the projection system PS. The source collector module SO is constructed and arranged such that a vacuum environment can be maintained in an enclosing structure 2 of the source collector module.

[0047] A laser 4 is arranged to deposit laser energy via a laser beam 6 into a fuel, such as xenon (Xe), tin (Sn) or lithium (Li) that is provided from a fuel supply 8 (sometimes referred to as a fuel stream generator). Tin, or another molten metal or intermetallic (most likely in the form of droplets) is currently thought to be the most promising and thus likely choice of fuel for EUV radiation sources. The deposition of laser energy into the fuel creates a highly ionized plasma 10 at a plasma formation location 12 that has electron temperatures of several tens of electron volts (eV). The energetic radiation generated during de-excitation and recombination of these ions is emitted from the plasma 10, collected and focussed by a near normal incidence radiation collector 14. A laser 4 and a fuel supply 8 (and/or a collector 14) may together be considered to comprise a radiation source, specifically an EUV radiation source. The EUV radiation source may be referred to as a laser produced plasma (LPP) radiation source.

[0048] A second laser (not shown) may be provided, the second laser being configured to preheat the fuel before the laser beam 6 is incident upon it. An LPP source that uses this approach may be referred to as a dual laser pulsing (DLP) source.

[0049] Although not shown, the fuel stream generator will comprise, or be in connection with, a nozzle configured to direct a stream of fuel droplets along a trajectory towards the plasma formation location 12.

[0050] Radiation B that is reflected by the radiation collector 14 is focused at a virtual source point 16. The virtual source point 16 is commonly referred to as the intermediate focus, and the source collector module SO is arranged such that the intermediate focus 16 is located at or near to an opening 18 in the enclosing structure 2. The virtual source point 16 is an image of the radiation emitting plasma 10.

[0051] Subsequently, the radiation B traverses the illumination system IL, which may include a facetted field mirror device 20 and a facetted pupil mirror device 22 arranged to provide a desired angular distribution of the radiation beam B at the patterning device MA, as well as a desired uniformity of radiation intensity at the patterning device MA. Upon reflection of the beam of radiation at the patterning device MA, held by the support structure MT, a patterned beam 24 is formed and the patterned beam 24 is imaged by the projection system PS via reflective elements 26, 28 onto a substrate W held by the wafer stage or substrate table WT.

[0052] More elements than shown may generally be present in the illumination system IL and projection system PS. Furthermore, there may be more mirrors present than those shown in the figures, for example there may be 1-6 additional reflective elements present in the projection system PS than shown in Figure 2.

[0053] Figures 3A and 3B show a top view and a side view respectively of a patterning device 302. In one example, the patterning device is a reticle such as a reflective reticle having an array of patterned elements.

[0054] In an embodiment, patterning device 302 includes a first material layer 304 applied to a backside of patterning device 302. The backside of the patterning device may be a side that is clamped to a chuck in order to be held in place within a lithographic apparatus. In one example, the backside of the patterning device is opposite to a patterned side of the patterning device. The patterned side may also include an array of reflective elements.

[0055] First material layer 304 is a softer material than that of patterning device 302, according to an embodiment. For example, first material layer 304 may include a polymer material or a combination of various polymers and/or copolymers. Examples of materials that can be adhered to the backside of patterning device 302 include polyimide, Viton®, PTFE (polytetrafluoroethylene), or any other fluoropolymer materials.

[0056] Alternatively, first material layer 304 may comprise a sticky material such that the sticky material layer is adhered to the backside of patterning device 302. Any commercially available glue may be used as the sticky material as long as the glue does not contaminate the environment and not leave any residue on an object upon adhesion to the object.

[0057] Figure 4 illustrates a support 400 that includes a chuck 402 and a clamping structure 404, according to an embodiment. Support 400 is designed to hold patterning device 302 in place within, for example, a lithographic apparatus. In an embodiment, clamping structure 404 includes a plurality of burls 406. The surface of burls 406 physically contact patterning device 302 or first material layer 304 during the clamping procedure. Although mechanical clamping of patterning device 302 is possible, in an embodiment, clamping structure 404 is an electrostatic clamp (ESC). As such, a voltage may be applied to the electrostatic clamp to hold patterning device 302 in place.

[0058] Also illustrated in Figure 4 are various particles or contaminants on the surface of clamping structure 404. For example, a particle 408 may exist on a surface of clamping structure 404 between burls 406 while another particle 410 may exist on a surface of burl 406. As mentioned previously, any particles present between patterning device 302 and clamping structure 404 can cause misalignment and other patterning defects when performing any type of lithographic process. Particles such as particle 410 can be especially troublesome as they exist on a surface (e.g. burl 406) that is in direct contact with patterning device 302.

[0059] Embodiments as described herein may be used for contamination cleaning in many different lithography tools, including in an extreme ultra-violet (EUV) lithography device. EUV reticles, being reflective by nature, are very vulnerable to contamination, and are difficult to clean using manual procedures.

[0060] Figures 5A-C illustrate a particle removal process, according to an embodiment. A side view of support 400 that includes chuck 402 and its associated clamping device 404 is shown along with the separate patterning device 302 and its associated first material layer 304. Additionally, a particle that is desired to be removed (e.g., particle 410) is illustrated on a burl 406 of clamping device 404. In Figure 5A, patterning device 302 is prepared to be clamped to support 400 via clamping structure 404.

[0061] Turning now to Figure 5B, patterning device 304 is clamped to support 400 via clamping device 404. In an embodiment, patterning device 304 is electrostatically clamped to support 400. Particle 410 is shown as being sandwiched between burl 406 and first material layer 304 on the backside of patterning device 302. In one example, the relative softness and/or textured surface of first material layer 304 causes particle 410 to become trapped or “gripped” by first material layer 304. In another example, an applied voltage used to electrostatically clamp patterning device 302 to support 400 causes an attraction between particle 410 and first material layer 304.

[0062] Turning now to Figure 5C, patterning device 302 is removed from clamping structure 404. In one example, the removing may occur due to turning off the applied voltage to clamping device 404. Particle 410 is illustrated as also being removed from clamping structure 404 due to first material layer 304 on the backside of patterning device 302. In an embodiment, each of the actions illustrated in FIGs. 5A-C can be performed automatically within, for example, a lithographic apparatus. Thus, the cleaning procedure may be performed without the need to manually clean support 400. Manual cleaning of support 400 within, for example, a lithographic apparatus, would require venting and/or disassembling of the apparatus. It should be understood that while only one particle 410 is illustrated as being removed, any number of particles may be removed at one time using the procedure as shown and described above. Additionally, the procedure may be repeated as many times as desired to continue removing any further contaminants from the surface of clamping structure 404. In one example, patterning device 302 is shifted laterally between the various clamping actions so that a “fresh” portion of first material layer 304 is exposed to burls 406 during each clamping step.

[0063] Once the particles have been removed from clamping structure 404, patterning device 302 may be removed to have the particles cleaned off it before being clamped back to support 400. In another example, a second patterning device may be loaded and clamped to clamping structure 404, the surface of clamping structure 404 having been previous cleaned by the first patterning device. It should also be understood that patterning device 302 may be an expendable unit that is used only for cleaning particles off of clamping structure 404 before a real patterning device is loaded.

[0(164] In an embodiment, first material layer 304 does not leave behind any residue from, for example, a solvent. The lack of any residue left behind helps to maintain a clean clamp surface on support 400.

[0065] Table 1 provides data relating to particle transfer rate for various materials and for various rounds of electrostatic clamping as illustrated in FIGs. 5A-C. The voltage applied during the clamping procedure was 1600 V.

[0066] In this example, a particle transfer rate of the ESC decreased significantly after using a polyimide layer on the backside of the patterning device. The decrease in particle transfer rate demonstrates that the ESC has been cleaned more effectively by the polyimide layer. This data is also illustrated as a graph in Figure 6.

[0067] Various techniques may be contemplated for ensuring that first material layer 304 makes contact with each burl 406 on clamping structure 404. If contact is not uniformly made, then the particle transfer process will be less efficient.

[0068] In one example, a desired flatness specification, e.g., a desired flatness of the material adhered to the backside of patterning device 302, is chosen based on the cleaning method to be used in the tool (whether electrostatic clamping is used). In most cases, this will require that the top cleaning surface of first material layer 304 be substantially flat when patterning device 302 is sitting on a baseplate. To achieve this Harness, the same methods used in Burl Top IBF may be used. In an embodiment, a height map of the top surface is made with an interferometer, followed by the high spots being etched using an etch media. In another embodiment, since some proposed examples of first cleaning layer 304 are polymers, the etching is performed with Reactive Ions, or a basic sputter etching through a suitable moving aperture. In yet another embodiment, carefully timed exposure to wet etchants may be used to smooth out the surface of first cleaning layer 304.

[0069] Figure 7 illustrates another embodiment of patterning device 302 that includes a second material layer 702 between first material layer 304 and the backside surface of patterning device 302. In one example, second material layer is a thin foam layer. The foam layer may act like a bed of springs under the cleaning layer and push the cleaning layer into contact with burls 406. In an embodiment, an electrode layer (not shown) may be disposed between first material layer 304 and second material layer 702 so that, when a voltage is applied to clamping structure 404, the quasi-free floating first material layer 304 is attracted to the clamp and makes even contact with all of burls 406. The electrode layer may include any number of individual electrodes or be designed as a uniform conductive surface across the boundary between first material layer 304 and second material layer 702.

[0070] Figure 8 illustrates another embodiment of patterning device 302 that includes a flexible layer 802 to make contact with burls 406 of clamping structure 404. In one example, flexible layer 802 includes a material such as Kapton® or Teflon®. Flexible layer 802 may be adhered to a backside surface of patterning device 302 using an adhesive. However, in an embodiment, the adhesive is designed be non-continuous under flexible layer 802, but instead be located at discrete points so that flexible layer 802 has freedom to flex between the discrete points as illustrated in Figure 8. For example, adhesive spots 804a and 804b may be placed on the backside surface of patterning device 302 to anchor flexible layer 802 at those points. Adhesive spots 804a and 804b may be located at positions beyond the extent of clamping structure 404 as shown, or at least be located at positions that do not align with burls 406. In one embodiment, flexible layer 802 includes a conducting layer (not shown) on its bottom side (i.e., facing away from clamping stmcture 406). A

similar procedure to that illustrated in Figures 5A-5C may be performed using patterning device 302 as illustrated in Figure 8 to clean particles off of the surface of clamping structure 404. In an embodiment, the application of voltage to clamping structure 404 draws flexible layer 802 upwards and into contact with burls 406. By managing the conductivity of flexible layer 802 and the electrode layer (if present) behind flexible layer 802, the particle trapping efficiency may be enhanced via electrostatic attraction of the particles towards the surface of flexible film 802 after voltage applied to clamping structure 404 is removed or reversed.

[0071] Figure 9 illustrates another embodiment of patterning device 302 having a flexible layer 902 in contact with adhesive spots 904a and 904b. In this example, each adhesive spot is aligned with a burl 406 across from it as patterning device 302 is clamped to support 400. Flexible film 902 is stretched to be substantially flat across adhesive spots 904a and 904b in order to make contact with each burl 406.

[0072] Figure 10 illustrates another embodiment of patterning device 302 including a flexible layer 1002 and a plurality of discrete adhesive spots 1004. In this example, each adhesive spot 1004 is located between burls 406. The placement of adhesive spots between burls 406 creates a tiny trampoline-like area in flexible layer 1002 beneath each burl 406. The adhesive may be deposited down in a grid pattern or alternatively as discrete dots so that each area of flexible layer 1002 can flex enough under electrostatic forces to come into contact with its associated burl 406.

[0073] It should be understood that for each of the embodiments illustrated in Figures 8-10, the patterns of the burls and adhesive regions may be altered in a variety of ways without departing from the spirit or scope of the embodiments. For example, the burls may be discrete areas rather than tracks, in which case the adhesive regions may include tracks of glue laid down between the burls. In another example, the adhesive regions may be tracks of glue laid down between burl tracks or criss-crossing over the burl tracks.

[0074] Cleaning particles off of a clamping structure, such as an ESC, may also be achieved via the insertion of an expendable object such as, for example, a silicon wafer or wafer shard, that is repeatedly clamped and unclamped. The conductivity of a silicon wafer allows the wafer to clamp to the ESC via an applied voltage. Furthermore, a silicon wafer may be cut into dimensions (e.g., X and Y dimensions) that are similar to those of patterning devices to be used with the same ESC. Thus, the silicon wafer provides an inexpensive and disposable solution for mechanically removing particles and other contaminants from the ESC surface. Figures 11 and 12 illustrate examples of how the silicon wafer may be loaded in the same or similar fashion as loading a patterning device.

[0075] Figure 11 illustrates an example of how pattering device 302 is introduced to clamping structure 404 within, for example, a lithographic apparatus. Patterning device 302 is placed upon a reticle holder or POD 1102. Typically, patterning device 302 rests upon one or more raised features 1106 to protect a patterned surface 1108 of patterning device 302. A handler arm 1104 is used to transport POD 1102 with patterning device 302 and bring the backside of patterning device 302 into contact with clamping structure 404. In one example, clamping structure 404 is an electrostatic clamp (ESC). Also illustrated is a high voltage power supply 1110 for providing a voltage (typically over 1000 V) to the ESC. In some embodiments, there may exist a second high voltage power supply 1112. Patterning device 302 may include various layers within its structure such as a conductive backside, a nonconducting (dielectric) substrate, an absorber layer, a multilayer reflector, and a circuit layer with a circuit frame.

[0076] Figure 12 illustrates the use of a scratch substrate 1202 in place of patterning device 302 for clamping to clamping structure 404, according to an embodiment. In one example, scratch substrate 1202 is either a silicon wafer or at least a portion of a silicon wafer. Other semi-conductive or conductive materials may be considered as well for scratch substrate 1202. As illustrated in the figure, scratch substrate 1202 may be placed on POD 1102 and brought up to meet clamping structure 404 at substantially the same Z height as patterning device 302.

[0077] In an embodiment, scratch substrate 1202 may be electrostatically clamped to clamping structure 404 (e.g., an ESC) one or more times to aid in the removal of any particles or other contaminants from clamping structure 404. Any particles present will be transferred to scratch substrate 1202 during the clamping process. In one embodiment, scratch substrate 1202 is laterally shifted between each clamping action to ensure that a clean surface of scratch substrate 1202 is in contact with the various burls 406 of clamping structure 404 during each clamping step. Scratch substrate 1202 may be inscribed or printed with bar codes, alignment marks, or any other distinguishing features such that a reticle handling system would perceive scratch substrate 1202 as a reticle to be loaded. Afterwards, scratch substrate 1202 may be removed from die apparatus and patterning device 302 may subsequently be clamped to a clean surface of clamping structure 404.

[0078] In one example, scratch substrate 1202 is coated with a layer to aid in the removal of clamp contaminants. Examples of such layers may include polyimide, Viton®, PTFE (polytetrafluoroethylene), Kapton®, and Teflon®.

[0079] The technology to produce, clean and measure wafers is appreciated by skilled artisans. Wafers are several orders of magnitude cheaper than reticles. Although there are existing wafer based products designed to clean wafer chucks, these products are adjusted, e.g., cut into shapes appropriate for use as a “pseudo reticle” in appropriately designed pods.

[0080] Figure 13 illustrates a flowchart depicting a method 1300 for adhering a patterning device to a support in a lithographic apparatus, according to an embodiment. The various embodiments of patterning device 302 illustrated in Figures 7-10 may be used in method 1300 to transfer particles to a material placed on the backside of patterning device 302. It is to be appreciated that method 1300 may not include all operations shown, or perform the operations in the order shown.

[0081] Method 1300 begins at step 1302 where a patterning device is loaded into a lithographic apparatus. The patterning device may be loaded using a POD such as POD 1104 illustrated in Figure 11. In an embodiment, the patterning device includes a first material layer adhered to the backside of the patterning device. The first material layer may be a polymer material, for example, polyimide, Viton®, or PTFE (polytetrafluoroethylene).

[0082] At step 1304, the patterning device is clamped to a support using an applied voltage. As such, the support may comprise an electrostatic chuck (ESC).

[0083] At step 1306, any particles present on the support are transferred to the backside of the patterning device. In an embodiment, the particles are transferred to the first material layer on the backside of the patterning device. The applied voltage may be used to aid in driving the particles towards the first material layer due to electrostatic interactions.

[0084] At step 1308, the patterning device is removed, along with any particles thereon, from the support. The patterning device may be further removed from the lithographic apparatus, or in other embodiments, re-clamped to the support to continue transferring particles to the first material layer on the backside of the patterning device.

[0085] Method 1300 may also include other steps beyond those described above. For example, method 1300 may include etching the first material layer to increase a flatness of the first material layer. In another example, method 1300 includes disposing a second material layer between the first material layer and the backside of the patterning device. Additionally, method 1300 may include steps directed to performing lithographical procedures such as imparting a pattern to a beam of radiation via the patterning device on the support and projecting the patterned beam of radiation onto a target portion of a substrate.

[0086] Figure 14 illustrates a flowchart depicting a method 1400 for cleaning contaminants off of a support within a lithographic apparatus, according to an embodiment. The embodiment illustrated in Figure 12 may be used in method 1400 to transfer particles from a support to scratch substrate 1202. It is to be appreciated that method 1400 may not include all operations shown, or perform the operations in the order shown.

[0087] Method 1400 begins with step 1402 where at least a portion of a wafer is introduced into a lithographic apparatus. The at least a portion of a wafer may be loaded using a POD such as POD 1104 illustrated in Figure 12. In an embodiment, the at least a portion of a wafer includes a first material layer adhered to one side. The first material layer may be, for example, polyimide, Viton®, PTFE (polytetrafluoroethylene), Kapton® or Teflon®.

[0088] At step 1404, the at least a portion of a wafer is clamped to a support using an applied voltage. As such, the support may comprise an electrostatic chuck (ESC).

[0089] At step 1406, any particles present on the support are transferred to the at least a portion of a wafer. In an embodiment, the particles are transferred to the first material layer on one side of the at least a portion of a wafer. The applied voltage may be used to aid in driving the particles towards the first material layer due to electrostatic interactions.

[0090] At step 1408, the at least a portion of a wafer is removed, along with any contaminants, from the support. The at least a portion of a wafer may be further removed from the lithographic apparatus, or in other embodiments, re-clamped to the support to continue transferring particles to the at least a portion of a wafer (or a first material layer on one side of the at least a portion of a wafer.

[0091] Method 1400 may also include other steps beyond those described above. For example, method 1400 may include introducing a patterning device to the support after removing the at least a portion of a wafer from the support. The patterning device and the at least a portion of a wafer may each have substantially the same surface area of a surface facing the surface of the support.

[0092] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion", respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0093] The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

[0094] While specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus it will be apparent to one skilled in the art that modifications may be made to the present invention as described without departing from the scope of the clauses that follow.

[0095] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the clauses. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended clauses in any way.

[0096] The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0097] The foregoing description of the specific embodiments will so fully reveal the general nature of the present invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

[0098] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following clauses and their equivalents. Other aspects of the invention are set out as in the following numbered clauses: 1. A method of removing particles from a surface of a support within a lithographic apparatus, the method comprising: loading a patterning device into the lithographic apparatus, the patterning device including a material layer adhered to a backside of the patterning device; clamping the patterning device to the support within the lithographic apparatus using an applied voltage; transferring any particles on the support to the material layer adhered to the backside of the patterning device to clean the support; and removing the patterning device along with any particles on the material layer from the support.

2. The method of clause 1, wherein the material layer is a polymeric material.

3. The method of clause 2, wherein the polymeric material is polyimide, or any fluoropolymer.

4. The method of clause 1, wherein the loading, clamping, and removing are each automated.

5. The method of clause 1, wherein the patterning device comprises a reflective reticle.

6. The method of clause 5, wherein the support comprises an electrostatic chuck.

7. The method of clause 1, wherein the material layer comprises an etched surface to increase a flatness of the material layer.

8. The method of clause 7, wherein the surface of the material layer is etched using reactive ion etching or ion beam figuring.

9. The method of clause 7, wherein the surface of the material layer is etched using wet etchant materials.

10. A method for cleaning contaminants off of a surface of a support within a lithographic apparatus, the method comprising: loading at least a portion of a wafer into the lithographic apparatus; clamping the at least a portion of a wafer to the support using an applied voltage; transferring contaminants from the support to the at least a portion of a wafer during the clamping; and removing the at least a portion of a wafer along with the contaminants from the support.

11. The method of clause 10, further comprising loading a patterning device to the support after the removing of the at least a portion of a wafer along with the contaminants from the support.

12. The method of clause 11, wherein the at least a portion of a wafer and the patterning device have substantially the same surface area of a surface facing the surface of the support.

13. The method of clause 10, wherein the at least a portion of a wafer includes a material layer adhered to a surface of the at least a portion of a wafer, and wherein the contaminants are transferred to the material layer during the clamping.

14. The method of clause 10, wherein the clamping and the removing are repeated to further clean contaminants off of the surface of the support.

15. A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to hold a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and a cleaning system configured to clean the support, wherein the cleaning system includes a material layer on a backside of the patterning device, such that the material layer is configured to attract any particles present between the support and the patterning device while the support holds the patterning device.

16. The apparatus of clause 15, wherein the patterning device comprises another material between the material layer and the backside of the patterning device.

17. The apparatus of clause 16, wherein the another material comprises a foam material.

18. The apparatus of clause 17, wherein the patterning device further comprises a layer having one or more electrodes between the material layer and the foam material.

19. The apparatus of clause 16, wherein the another material comprises an adhesive at one or more discrete points between the material layer and the backside of the patterning device.

20. The apparatus of clause 19, wherein the one or more discrete points substantially align with one or more burls on the support while the support holds the patterning device.

21. The apparatus of clause 19, wherein the one or more discrete points are substantially aligned between the burls on the support while the support holds the patterning device.

22. A particle cleaning system for use in a lithographic apparatus, the particle cleaning system comprising: a first patterning device or a substrate shaped in the shape of the first patterning device, wherein a backside of the first patterning device or the substrate includes a material layer disposed on the backside and configured to clean a surface of a support, such that the support is configured to hold a second patterning device, wherein the second patterning device is capable of imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam, wherein the material layer is configured to adhere or absorb any particles present on the surface of the support.

23. The particle cleaning system of clause 22, wherein the material layer is either a sticky or a soft material layer that is deposited or fixedly attached on the backside of the first patterning device or substrate.

24. The particle cleaning system of clause 22, wherein the material layer is a polymeric material.

25. The particle cleaning system of clause 24, wherein the polymeric material is polyimide, or any fluoropolymer.

26. The particle cleaning system of clause 22, wherein the first patterning device comprises a reflective reticle.

27. The particle cleaning system of clause 26, wherein the support comprises a chuck having a clamp to hold the at least first patterning device or substrate.

28. The particle cleaning system of clause 27, wherein the chuck comprises an electrostatic chuck.

29. The particle cleaning system of clause 27, wherein the substrate comprises a wafer.

Claims (1)

A lithography device comprising: an illumination device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.