WO2025026563A1 - Method for bonding a first substrate to a second substrate, device for bonding, substrate holder for such a device, and sensor element - Google Patents

Abstract

Method for bonding a first substrate (10) to a second substrate, wherein the first substrate has a primary section and the second substrate (10) has a secondary section, wherein, during bonding of the first substrate to the second substrate (10), a bonding wave advancing along a bonding direction is formed between -- a first subsection in which the first substrate and the second substrate (10) are bonded and -- a second subsection in which the first substrate and the second substrate (10) are yet to be bonded, wherein a subregion of the second substrate (10) in the second subsection is offset in height relative to a subregion of the second substrate (10) in the first subsection in a direction perpendicular to a main extension plane, and wherein, prior to and/or during bonding, in order to determine the state of an object, light is directed onto a surface of the object and reflected and the light reflected by the surface is measured by means of a sensor element (15) for determining the distance of the sensor element (15) to the surface and a distance (a) of the sensor element (15) to the surface is determined.

Description

Method for bonding a first substrate to a second substrate, device for bonding, substrate holder for such a device and sensor element

The present invention relates to a method for bonding a first substrate to a second substrate, a device for bonding, a substrate holder for such a device and a sensor element.

In the semiconductor industry, substrates of different sizes, shapes and materials are regularly connected to one another. The connection process is called bonding. Bonding is roughly divided into permanent and temporary bonding. With permanent bonding, a connection is created between the two substrates that cannot be separated. This permanent connection is made by interdiffusion of metals, by cation-anion transport in anodic bonding or by the formation of covalent bonds between oxides and/or semiconductor materials in fusion bonding. In temporary bonding, so-called bonding adhesives are mainly used. These are adhesives that are applied to the surface of one or both substrates using a coating process in order to act as an adhesion promoter between the substrates.

In fusion bonding, two substrates are joined together in a connection that can initially be separated, a prebond. This prebond is mainly created due to van der Waals bridge bonds between the two highly pure, flat, defect- and particle-free substrate surfaces, which are brought into close contact with each other. Hybrid bonding is a subtype of fusion bonding. Hybrid bonding represents the connection of two substrate surfaces, each of which consists of an electrical and a dielectric substrate region. The corresponding correlating (dielectric) substrate regions are connected to each other using a fusion bond (prebond). When the prebond is converted into a permanent bond, permanent electrical contact is created between the electrical substrate regions of the substrates. All bonding methods use bonders to join the substrates to be bonded together. The two substrates to be joined can be subjected to pre-treatments such as surface activation, a cleaning step, an alignment step, until the actual pre-bonding step takes place.

During the prebond step, the substrate surfaces are brought into contact with each other over a very small area. In other words, the joining reaction is initiated, after which the joining reaction, i.e. the formation of the bridge bonds, can take place without external energy supply. The joining process takes place continuously through the propagation of a bonding wave. The theoretical background is described in US 7,479,441 B2, US 8,475,612 B2, US 6,881,596 B2, and WO 2014/191 033.

If the bond wave was initiated centrally on two identical, non-structured substrates, it ideally runs as a concentrically growing circular front along the substrate radius. Structured substrates, defects, etc. change the path of the bond wave. Under non-optimal conditions, non-bonded areas (voids) can arise between the two substrates, e.g. due to gas inclusions, particle inclusions, etc.

Under non-optimal conditions, structures on the substrates or the anisotropy of the substrate material can change the course of the bonding wave. Any change in the course of the bonding wave can be measured by a specialist as an alignment error on the joined substrate stack. Furthermore, joining errors can arise as a result of alignment errors (in particular from the following error components: scaling errors, run-out errors), rotation errors, translation errors, residual errors, temperature compensation errors. Undetected or non-critical errors in the individual substrates or in particular in functional units manufactured using thin-film technology can add up in an error propagation and can only be detected and quantified after the pre-bonding process.

Although the substrates can be aligned very precisely with each other using alignment equipment, distortions of the substrates can occur during the bonding process itself. Due to the resulting distortions, the functional units will not necessarily be correctly aligned with each other at all positions. The alignment inaccuracy at a certain point on the substrate can be a result of distortion, a scaling error, a lens error (magnification or reduction error), etc. In the semiconductor industry, all topics that deal with such problems are subsumed under the term "overlay". An introduction to this topic can be found, for example, in: Mack, Chris. Fundamental Principles of Optical Lithography - The Science of Microfabrication. WILEY, 2007, Reprint 2012.

Every functional unit is designed on the computer before the actual manufacturing process. For example, circuit paths, microchips, MEMS, or any other structure that can be manufactured using microsystem technology are designed in a CAD (computer-aided design) program. During the manufacture of the functional units, however, it becomes apparent that there is always a deviation between the ideal functional units designed on the computer and the real functional units produced in the clean room. The differences are mainly due to limitations of the hardware, i.e. engineering problems, but very often to physical limits.

The resolution accuracy of a structure produced by a photolithographic process is limited by the size of the apertures of the photomask and the wavelength of the light used (electromagnetic radiation). Mask distortions are transferred directly into the photoresist and thus into the structures produced. Movement devices such as guides with the drive systems coupled to them can move to reproducible positions within a specified tolerance, etc. It is therefore not surprising that the functional units of a substrate cannot exactly match the structures designed on the computer.

All substrates therefore have a non-negligible deviation from the ideal state even before the bonding process.

If one now compares the positions and/or shapes of two opposing functional units of two substrates, i.e. a first substrate and a second substrate, assuming that neither of the two substrates is distorted by a bonding process, one finds that in general there is already an imperfect coverage of the functional units, since these deviate from the ideal computer model due to the errors described above. The most common errors are shown in https://commons.wikimedia.org/wiki/File%3AOverlay - typical model terms DE.svg , 24.05.2013 and Mack, Chris. Fundamental Principles of Optical Lithography - The Science of Microfabrication. Chichester: WJLEY, p. 312, 2007, Reprint 2012. According to the figures, one can roughly distinguish between global and local or symmetrical and asymmetrical overlay errors. A global overlay error is homogeneous, therefore regardless of location. It produces the same deviation between two opposing functional units regardless of position. The classic global overlay errors are errors I and II, which arise from a translation or rotation of the two substrates relative to each other. The translation or rotation of the two substrates produces a corresponding translational or rotational error for all opposing functional units on the substrates. A local overlay error arises depending on location, predominantly due to elasticity and/or plasticity problems, in this case mainly caused by the continuously propagating bond wave. Of the overlay errors shown, errors III are particularly common. and IV. are referred to as "run-out" errors. This error is primarily caused by a distortion of at least one substrate during a bonding process. The distortion of at least one substrate also distorts the functional units of the first substrate in relation to the functional units of the second substrate. Errors I. and II. can also be caused by a bonding process, but are usually so heavily overlaid by errors III and IV. that they are difficult to detect or measure.

In the state of the art, there is already a system that can be used to at least partially reduce local distortions. This involves local equalization through the use of active control elements. Such a system is described, for example, in EP 2 656 378 B1.

In the state of the art, there are already other approaches to correcting run-out errors. US 2012 0 077 329 A1 describes a method for achieving a desired alignment accuracy between the functional units of two substrates during and after bonding. In most cases, the resulting run-out errors become stronger radially symmetrically around the contact point, and therefore increase from the contact point to the circumference. In most cases, the run-out errors increase linearly. Under special conditions, the run-out errors can also increase non-linearly.

Under particularly good conditions, the run-out errors can not only be determined by appropriate measuring instruments (EP 2 463 892 B1), but can also be described, or at least approximated, by mathematical functions. Since the overlay errors represent translations and/or rotations and/or scalings between well-defined points, they are preferably described by vector functions. In general, This vector function is a function f:R2-> R2, and therefore a mapping rule that maps the two-dimensional definition range of the position coordinates onto the two-dimensional value range of "run-out" vectors. Although an exact mathematical analysis of the corresponding vector fields has not yet been carried out, assumptions are made regarding the function properties. The vector functions are most likely at least C ^A n n>= 1 , functions, and therefore continuously differentiable at least once. Since the "run-out" errors increase from the contact point to the edge, the divergence of the vector function will probably be different from zero. The vector field is therefore most likely a source field.

Many errors such as gas inclusions or scaling errors are primarily due to the prebond step, in particular to the course of the bonding wave or the nature and/or design and/or functionality of the respective substrate holder (chuck). In the state of the art, methods are known which provide a quantitative statement about the course of the bonding wave.

The most commonly used method for monitoring the bonding process is to observe the path of the bonding wave using optical means, particularly camera systems, especially using a transmitted light method, particularly in the infrared spectrum, whereby the substrates must have sufficient transparency to observe the bonding wave. Although this method is common practice, it has disadvantages. Not all substrates are suitable for transmitted light methods; in particular, metallizations prevent the observability of the bonding interface that is created when the two substrate surfaces to be joined are connected. Furthermore, doping in semiconductor substrates can influence the transmittance of electromagnetic radiation. In addition, a transmitted light method places special demands on all substrate holders, as they must also be permeable to the radiation, which can also cause problems with the reproducibility of the results.

All previously known techniques that measure the course of the bonding wave observe the prebonding process directly through the substrates or measure the effect of the attractive force at which the substrates are joined. There is currently no precise, commercially available measuring method or measuring device that can observe the course of the bonding wave with high spatial resolution for all substrates, regardless of their material properties, and/or can be used to calibrate the bonding device. It is therefore an object of the invention to disclose an improved device and a method for measuring and influencing the bonding wave during fusion bonding of two substrates.

The present invention solves the problem with a method for bonding a first substrate to a second substrate according to claim 1 and with a device for bonding according to claim 11 as well as a substrate holder according to claim 14 and a sensor element according to claim 15. Advantageous developments of the invention are specified in the subclaims. The scope of the invention also includes all combinations of at least two features specified in the description, in the claims and/or in the drawings. In the case of specified value ranges, values lying within the stated limits should also be considered as disclosed limit values and can be claimed in any combination.

According to a first aspect, a method is provided for bonding a first substrate to a second substrate, wherein the first substrate has a primary section and the second substrate has a secondary section, wherein during bonding of the first substrate to the second substrate a bonding wave advancing along a bonding direction between

-- a first section in which the first substrate and the second substrate are connected, and

-- a second subsection is formed in which the first substrate and the second substrate are still to be connected, wherein a subregion of the second substrate in the second subsection is offset in height relative to a subregion of the second substrate in the first subsection in a direction running perpendicular to a main extension plane, wherein before and/or during bonding to determine the state of an object, light is directed onto a surface of the object and reflected and the light reflected from the surface is measured by means of a sensor element to determine the distance between the sensor element and the surface and a distance between the sensor element and the surface is determined.

In contrast to the methods known from the prior art, reflected light from the surface of an object, for example from a back side of the second substrate, is used to determine the state of the object, for example the second substrate. In particular, the method proves to be particularly advantageous because different objects or object types with different optical properties can be measured, especially if they have a certain reflectivity for the light used. In this case, it is advantageous to limit the design to a method with which several objects can be measured with the same sensor element. For example, in addition to determining the state of the second substrate during bonding, it is also possible to determine an alignment of the substrate holder for the first substrate before bonding with the same sensor element. All of this can be ensured with a single design measure on the bonding device, in particular with the sensor element for detecting the reflected light. This is not possible, for example, if an X-ray method is provided for the second substrate, since a substrate holder for the first substrate or a first substrate cannot usually be X-rayed. An alternative measurement method would be required here. Preferably, the method is provided for determining the state of two different objects.

Furthermore, determining the distance using reflected light has also proven to be particularly advantageous because it makes it possible to determine the distance between the sensor element and the surface as accurately and reliably as possible. State determination is understood to mean, in particular, a current position or orientation of at least a partial section of the object, for example the second substrate or a substrate holder of the first or second substrate, before or during bonding, particularly preferably in the area of the bonding wave or in an area adjacent to the bonding wave. The procedure of using reflected light to determine the state has proven to be particularly advantageous because this is also possible when the object, for example the second substrate, is not transparent to a wavelength with which the second substrate is examined. The method according to the invention therefore proves to be particularly advantageous compared to methods in which, for example, the second substrate is illuminated. Such a procedure known from the prior art is ultimately limited to second substrates with a certain transparency for the wavelength used. In the following, the second substrate and the upper substrate on the one hand and the first substrate and the lower substrate on the other hand are preferably used synonymously. The state determination also includes, for example, an at least locally detected distance between the primary section of the first substrate and the secondary section of the second substrate. It is also conceivable that the object, for example the second substrate, is modified on its surface in such a way that its reflectivity is increased, in particular in comparison to an unmodified surface. For example, a coating that increases the reflectivity is conceivable.

Preferably, at least one optical fiber element is used as a component of the sensor element, and a fiber optic distance sensor is preferably used as the sensor element. The use of a fiber element allows the light to be guided to an area that is arranged relatively close to the second substrate or the object, while, for example, a light source that develops heat can be as far away from the second substrate or the object as possible. This advantageously prevents the light source and its heat development from affecting the second substrate or the object to be measured. It is also conceivable that an interferometric sensor system is used to determine the distance, or a system in which the travel times of light pulses are determined by superimposing them and then used to determine the distance. This also makes it possible to register particularly slight shifts or changes in distance. The light used is preferably laser light. A preferred wavelength can advantageously be used here, which is advantageous for the maximum possible reflection on the object or several different objects and/or for coupling into the fiber element.

A particular advantage of fiber optics is that the number of sensor elements per unit area, i.e. the sensor element surface density, can be greatly increased, which enables an extreme increase in resolution accuracy. Sensor elements used in the prior art are very large and bulky, as they are usually installed on the substrate holder together with the electronics. For this purpose, it is preferably provided that fiber elements are provided in which fiber ends are provided for signal reception. The fiber elements also comprise signal transmission sections, which are provided for signal guidance, for example. The signal transmission sections are preferably provided for light guidance and/or for transmitting electrical signals. This advantageously makes it possible to arrange the fiber ends on a substrate holder or in its vicinity. This allows the density of fiber ends in the area of the substrate holder to be increased. This has a positive effect on the spatial resolution. An evaluation device can be placed at a sufficiently large distance from the fiber end in signal transmission sections. In other words: The placement of signal converters or evaluation devices on the substrate holder can advantageously be avoided.

The preferred sensor element is a fiber optic distance sensor. The fiber optic distance sensor contains at least one radiation source, an optical fiber and an evaluation unit. The optical fiber contains at least two fibers or two fiber bundles. One fiber is used as a line for coupling the radiation from the radiation source onto the substrate and one fiber is used to decouple the changed measurement signal and feed the signal into the evaluation unit. The evaluation unit calculates the course of the bond wave in particular from the change in the measured value of the particularly calibrated fiber optic distance sensor.

The measured signal of the fiber optic distance sensor is preferably an intensity change that is correlated with a distance or distance change. The distance between the fiber and the reflective surface is measured using the characteristic function of the reflected intensity. In other words, the fiber optic distance sensor is used for the contactless measurement of a distance or a fine displacement between the sensor and a surface to be probed, in particular the back of a substrate or the surface of the substrate holder. Distance differences or distances of less than 5 nanometers and/or frequencies of over 100 MHz can be detected contactlessly using fiber optic distance sensors. The fiber optic measuring system allows working distances in the micrometer to centimeter range with high distance and temporal resolution. The radiation beam emitted from an optical fiber is picked up by a second optical fiber after reflection on the measurement object, in particular the back of the substrate, and converted into an electrical voltage by optoelectronic converters. Due to the distance-dependent imaging of the radiation beam onto the receiver-side optical fiber, different radiation currents are directed to the receiver, i.e. to the evaluation unit. The course of the voltage-distance characteristic curve is determined by the optical imaging behavior and the photometric distance law. The optical imaging behavior can be approximately described using the mean light beam. This beam emerges in the middle of the transmitting optical fiber, hits the measuring object, in particular the back of the substrate, at a certain angle between the optical fibers and reaches the receiving optical fiber at the same angle through reflection. The intensity course can be described in Depending on the angle of incidence, the intensity can be described with a sine function. The path length of the light also influences the intensity. The intensity I decreases quadratically with the distance a, whereby the distance between the fiber element and the measurement object, in particular the first and/or second substrate, is to be measured. If the model is to be described more precisely, all beam paths must be included integrally in addition to the middle beam. The light intensity on the measurement object can be described in a simplified manner with the following equation: l(measurement object)=K' * sin(angle of incidence a) * 1 / a ^A 2

The angle a is the angle between the incident or reflected beam and the surface of the measurement object, in particular the back of the substrate. The constant K' or K represents a system constant that essentially depends on the properties of the optical fibers and the reflection properties of the measurement object.

Since the light now continues from the measuring object or the surface of the object to the receiver, the equation must be applied once more. The intensity that is present at the receiver and evaluated in the evaluation unit corresponds qualitatively to the following curve: l(receiver)=K * sin(angle of incidence a) * (1 / a ^A 2) * sin(angle of incidence a) * (1 / a ^A 2)

The distance sensor can be operated in two working ranges. In the rising range, the sensor has a higher sensitivity (slope) than in the falling range. A disadvantage of fiber optic distance measurement is the need for relatively large measuring areas. The areas can be reduced by making the optical fibers or fiber elements smaller. However, making them smaller would mean a reduction in the luminous flux in the optical fiber. As a result, not enough light energy can be coupled into the receiver to generate a sufficiently high signal. This problem is reduced by using a whole fiber bundle instead of two optical fibers. Half of the optical fibers are used to output the light, while the other half of the bundle is used to couple the radiation to the receiver. The distribution of the individual fibers can be stochastic.

At the beginning of the signal path is the light source. The wavelength of the light must match the optical fibers, the surfaces to be scanned, especially substrates and/or Substrate holders and the optoelectronic converter, which is used as an evaluation unit. The radiation source can preferably be an LED. The LED can be operated with direct current. In alternative embodiments of the device, radiation feeds with oscillating radiation or light can also be used. The radiation constantly changes its intensity. This type of modulation or lock-in has the advantage that the interference and possible sources of error from temperature drift and/or ambient brightness are eliminated. The radiation source is coupled into the optical fibers in a suitable form. Integrated arrangements (LED - optical fiber) are common. The radiation can be transmitted over greater distances to the surface to be scanned. This is preferred in the bonding device according to the invention, because it allows the heat sources to be kept away from the substrates to be bonded.

The receiving optical fiber is arranged directly on the transmitting optical fiber. The entry and exit surfaces of the optical fibers are ground flat to prevent direct light transmission across the fiber. Preferably, at least two fiber elements are provided.

In particular, an adjustable, in particular angle-dependent, fastening of a sensor head of the sensor element with the optical fibers in the substrate holder is provided. The transmission via the optical fiber, i.e. the fiber element, can also be implemented in the receiver part over greater distances, so that a functionally integrated unit consisting of radiation source and evaluation unit can advantageously be formed.

The signal path for measuring the bond wave during fusion bonding begins with a radiation source, preferably an LED. In this disclosure, light is referred to in particular as visible light and electromagnetic radiation that is not visible to the human eye is referred to as radiation, but the person skilled in the art understands that light and radiation are largely interchangeable terms in the disclosure. If LEDs are referred to as a radiation source below, it is clear to the person skilled in the art that other radiation sources can also be involved. The light or radiation from the LED is coupled into the fiber bundle, passed on and reaches in particular the surface of the back of the substrate to be measured. From there, the emitted light is reflected in particular on the back of the substrate and coupled into the receiving fiber. The optical fibers end at the optoelectronic Evaluation unit and couple the light there. The optoelectronic converter can in particular be a phototransistor or a photodiode or a secondary electron multiplexer (SEv), which converts the optical signal into an electronic signal. The electrical signal currents or signal voltages generated are preferably then amplified by operational amplifiers. The signals obtained in this way, in particular analogue ones, can be connected to a data line after an analogue-digital conversion and can be further processed and/or stored and/or displayed, in particular with computer support.

Preferably, a set distance between the sensor element and the surface of the object assumes a value between 10 pm and 1000 pm, preferably between 10 pm and 500 pm and particularly preferably between 10 pm and 200 pm. For example, the sensor element can be moved to a (rough) distance that lies in the corresponding value range in order to be able to determine distance values with the highest possible resolution. The set distance is understood to be the distance that is assumed when aligning the sensor element with respect to the surface to be measured.

A target value of the position to be approached, in particular an alignment mark, is an ideal value. A movement device with which a substrate holder is moved approaches the ideal value. Reaching a defined area around the ideal value can be understood as reaching the target value. A positioning device is understood to be a coarse positioning device if the approach and/or repeat accuracy deviates from the target value by more than 0.1%, preferably more than 0.05%, particularly preferably more than 0.01%, based on the entire travel path or rotation range, a full rotation of 360 degrees in the case of rotary drives that can rotate.

For example, a coarse positioning device with a travel of more than 600 mm (twice the substrate diameter) results in an approach accuracy of 600 mm * 0.01%, i.e. more than 60 micrometers as residual uncertainty.

In other embodiments of the coarse positioning, the residual uncertainty of the approach or repeat accuracy is less than 100 micrometers, preferably less than 50 micrometers, particularly preferably less than 10 micrometers. The thermal disturbances should also be taken into account. However, this is known to the person skilled in the art. A coarse positioning device only fulfils the positioning task with sufficient accuracy if the deviation between the actual position reached and the target value of the position lies within the travel range of an associated fine positioning device.

An alternative coarse positioning device only fulfils the positioning task with sufficient accuracy if the deviation between the actual position actually reached and the target value of the position is within half the travel range of an associated fine positioning device.

A positioning device is understood to be a fine positioning device if the residual uncertainty of the approach and/or repeat accuracy of the target value does not exceed less than 500 ppb, preferably less than 100 ppb, ideally 1 ppb based on the entire travel path or rotation range.

Preferably, a fine positioning device will have an absolute positioning error of less than 5 micrometers, preferably less than 1 micrometer, particularly preferably less than 100 nm, most preferably less than 10 nm, optimally less than 5 nm, ideally less than 1 nm.

Preferably, at least one positioning device with high accuracy and reproducibility is provided. A concept of mutual error corrections can be used for the quality of the alignment of the substrate to the other substrate. For example, a known offset (twisting and/or shifting) of a substrate and the corresponding positioning device can be increased by adjusting and correcting the position of the other substrate with correction values or correction vectors. It is a question of the size and type of twisting and/or shifting how the control or regulation uses coarse and fine positioning or only coarse or only fine positioning to correct the error.

In a preferred embodiment of the device, the substrates can be deformed and/or tempered using mechanical adjusting elements and/or piezo elements, ie deformation elements, in order to minimize the offset during bonding. The targeted change in temperature changes the shape and size of at least one of the substrates. The targeted change in the shape of the substrate holder changes the shape of the substrate attached to it. In the following, positioning devices (coarse or fine or composite positioning devices) and alignment means are considered synonyms. The alignment of the first substrate to the second substrate can preferably take place in all six degrees of freedom of movement: three translations according to the coordinate directions x, y and z and three rotations around the coordinate directions. According to the invention, the movements can be carried out in any direction and orientation. Robots for substrate handling and for substrate stack handling are subsumed as movement devices. The holding devices can be component-integrated or functionally integrated in the movement devices.

Furthermore, the device for the ground preferably contains control systems and/or evaluation systems, in particular computers, in order to carry out the described steps, in particular movement sequences, embossing and separation, to carry out corrections, to analyze and store operating states of the device according to the invention.

In particular, it is provided that an arrangement of a plurality of sensor elements is used for spatial resolution, preferably more than 10 sensor elements, particularly preferably more than 30 sensor elements and particularly preferably more than 50 sensor elements. This makes it possible to determine a corresponding, in particular locally resolved, orientation of at least a partial area of the object or of the entire object based on the distances recorded between the sensor element and the object. The sensor elements are preferably distributed in a predetermined pattern, for example a checkerboard pattern or on circular paths.

It is particularly preferred that a higher spatial resolution can be achieved by the increased number of sensor elements. The sensor elements are preferably arranged in a two-dimensional arrangement. The sensor elements are preferably arranged along imaginary circular paths, in particular when bonding starts from a center of the substrates. It is particularly preferred that a sensor surface element is constant, preferably in the radial direction. This ensures a homogeneous spatial resolution. It is particularly preferred that the adjacent sensor elements are arranged equidistant from one another at least along one direction. An average distance between adjacent sensor elements is preferably less than 5 cm, preferably less than 2.5 cm and particularly preferably less than 1.5 cm. In this case, an average is taken over all distances between adjacent sensor elements. In particular, it is provided that the sensor element is designed to receive signals. and sends the recorded signal to an evaluation device. In the case of a fiber optic, several fiber ends can be arranged next to each other and the fiber elements run individually or in a bundle to a common evaluation device that is spaced from the fiber ends that are aligned for signal recording.

It is particularly preferred if the object is the first substrate or the second substrate. The determination of the state of the second substrate during bonding is particularly advantageous because the measurement allows the progression of the bonding wave and the deformation of the second substrate during bonding to be recorded. This allows, for example, the bonding to be adjusted in real time. The first substrate is preferably examined before bonding in order to check its correct alignment before bonding.

It is preferably provided that, for the temporal resolution, several state determinations are measured to determine a state change recorded over time, in particular to record a bond wave development of the second substrate, during bonding. This makes it possible, for example, to record a bond wave, in particular with regard to its temporal development, for example to determine a bond speed. For this purpose, in particular a displacement of the rear side of the second substrate during bonding is measured and determined. For this purpose, preferably more than ten sensors, particularly preferably more than 30 sensors, very particularly preferably more than 50 sensors are used, which are in particular integrated equidistantly on the substrate holder. In particular, it is therefore provided that an arrangement of a plurality of sensor elements is used for spatial resolution, preferably more than 10 sensor elements, particularly preferably more than 30 sensor elements and particularly preferably more than 50 sensor elements. This arrangement preferably covers a two-dimensional section. Preferably, at least one fiber optic distance sensor is used for measuring the bond wave, wherein the fiber optic distance sensor is fixed in a statically determined manner and wherein the adjustment of the fiber optic distance sensor takes place without twisting the fiber and/or the fiber optic distance sensor.

In particular, the spatial and local course of a bond wave can be recorded or calculated from a large number of measured values from sensors distributed over the substrate surface. be determined so that the course of the bonding wave can be influenced in a closed-loop control system. For this purpose, the recorded position data of the bonding wave as well as the anisotropies and/or anomalies, in particular distortions or deformations, are compared in particular with a computer-aided model of the ideal bonding wave course and the observed error during bonding, in particular during fusion bonding, is corrected promptly, in particular in real time, by controlling the individual vacuum zones (time and extent of the pressure change, in particular the release of an individual zone).

The radiation coupling and evaluation take place outside the substrate holder in a preferably separate evaluation unit. The end of the light guide is mounted in the substrate holder, preferably in the upper substrate holder itself, so that the back of the substrate is in the working area of the sensors during the bonding process.

In an exemplary method, the temporal and spatial progression of a bonding wave during fusion bonding can be determined. The distance between the back of the upper substrate and the upper substrate holder is determined over time, stored, visualized and/or taken into account in the form of correction factors to correct the alignment errors. The distances and/or distance changes are measured as a function of time, in particular synchronized with over 50 sensors. In a particularly preferred embodiment of the device, 52 fiber optic distance sensors can be distributed over the substrate holder to enable close monitoring of the bonding wave.

Preferably, it is provided that an alignment, for example a position and/or an orientation, of the second substrate is determined during and/or after insertion into a substrate holder for determining the state. For example, it is provided that the state determination is used to minimize the distance to be set between the first substrate and the second substrate before bonding. An exemplary method provides for the measurement of the local deviations and scattering of the vertical distance when aligning a lower substrate and an upper substrate to one another before bonding, in particular fusion bonding. The vertical distance during alignment is also referred to as the bond gap and serves to ensure that the substrates can be aligned with one another with as little distance as possible, without touching one another. The local variations in the vertical distance can arise due to the manufacturing tolerances of the substrate holder, especially the upper substrate holder. From series of measurements of different substrates on the same substrate holders with the fiber optic distance sensors, conclusions can be drawn about local unevenness and/or shape deviations of the substrate holder, so that a correction of the respective substrate holder is possible.

It is preferably provided that the bonding is influenced depending on the state determination, in particular a bond wave speed is controlled or regulated. In a preferred method, the control or preferably the regulation of the bond wave shape can be made possible. The distance measurement values of the fiber optic distance sensors when bonding the upper substrate to the lower substrate are correlated with the control of individually switchable vacuum zones on the upper substrate holder in particular in such a way that the bond wave can pass through in one plane as distortion-free as possible and the substrate-related asymmetries and/or anisotropy can be compensated in order to achieve an optimal bonding result that is as distortion-free as possible. The measurement of the bond as an overlay measurement on the finished substrate stack can be taken into account as a further correction in the bonding process. Another advantage of using fiber optic distance sensors is that the precise setting of the working distance with the adjustment according to the invention using fine adjustment elements such as play-free micrometer screws, which can position the optical fiber in particular without constraint, means that sensors with higher accuracy can be used, but with a smaller measuring range. This reduces errors during bonding, because smaller device paths cause smaller errors in alignment.

According to a preferred embodiment, it is provided that the object is a component of a device for carrying out the method, for example a holding element and/or a deformation element of the device and/or a loading pin.

In an exemplary method, a position, in particular a parallelism, of the upper substrate holder to the lower substrate holder is determined. It has surprisingly been found that instead of adjusting the flatness based on the measurement results from three dynamic pressure sensors or optical sensors, in particular offset by 120 degrees, worse local distortions can be achieved during bonding than adjusting the parallelism of the entire substrate holder surfaces to one another in an independent optimization process with the aim of using the local distance values to create the most global possible to achieve a uniformly parallel alignment of the upper substrate holder to the lower substrate holder. For the actual adjustment, fine adjustment elements such as micrometer screws, in particular fine-thread screws, can locally change the substrate holder surfaces to one another. In other words, a global optimum of parallelism over the entire surface of the substrate holder is calculated and set using the large number of locally measured distances between the substrate holders. By improving the parallelism of the substrate holder surfaces to one another, the bonding results between individual bonding modules improve, so that the reproducibility and repeatability of bonding processes between devices with fiber optic distance sensors is increased.

Preferably, it is provided that the state determination of the second substrate is used to determine a fixing and/or actuating means with which the first substrate and/or the second substrate is held and/or fed to the bonding.

Another method provides for the setting of the loading pins of the lower substrate holder to be observed or determined. Finally, in a modification of the third application, the fiber optic distance sensors can be used to measure the parallelism of the loaded lower substrate to the upper substrate holder and adjust it accordingly.

Another exemplary method provides that the shape of the upper or second substrate is observed or determined during loading of the upper substrate holder. From the shape of the upper substrate during loading, conclusions can be drawn about the bonding behavior, such as an expected deflection or sagging of the upper substrate, and taken into account during bonding, in particular how far a distance must be set for the upper substrate before bonding so that the upper substrate and the lower substrate do not touch each other undesirably during alignment but a small working distance can be achieved.

Another exemplary method provides that the lower and/or the upper substrate, ie the first and/or the second substrate, is observed and recorded during attachment to the respective substrate holder, in particular such that deformations of the respective substrate can be recorded in a temporally and spatially correlated manner when the vacuum is applied. In particular, the controls for the vacuum zones can be the circuit sequence as well as the vacuum level used in order to be able to bond the substrates with as little distortion as possible. A particularly important aspect is that the substrates can be deformed in a targeted manner for bonding before bonding with the attachment to the substrate holder in order to compensate for and/or reduce known distortions of the respective substrate. In other words, the plane parallelism of the upper substrate to the lower substrate is not necessarily considered to be the best starting point for a successful and optimally aligned fusion bond, but measured and appropriately deformed substrates are bonded to one another using fusion bonding in such a way that the resulting substrate stack has as few alignment errors as possible.

Another exemplary method provides that adaptive loading of the substrates is enabled by using the measured values of the fiber optic distance sensors in the upper substrate holder to actively control individually switchable, in particular isolated vacuum segments of the upper and/or lower substrate holder, so that the sequence and force of the suction result in substrates that are as distortion-free as possible. In another embodiment, the substrates can be deformed in a targeted manner. The person skilled in the art can deduce this independently from the application described here. In this way, the natural scattering of the substrate properties is immediately compensated for by measuring the substrate during loading and fastening to the substrate holder.

Furthermore, all applications can be automatically visualized, especially with computer support, so that process engineers or technicians can more quickly discover and eliminate possible sources of error.

A further aspect of the present invention is a device for bonding a first substrate to a second substrate, in particular by means of a method according to one of the preceding claims, wherein the first substrate has a primary section and the second substrate has a secondary section, wherein the device is configured such that when bonding the first substrate to the second substrate, a bonding wave advancing along a bonding direction between

-- a first section in which the first substrate and the second substrate are connected, and

-- a second section in which the first substrate and the second substrate are still to be connected, is formed, wherein a partial region of the second substrate in the second partial section is offset in height relative to a partial region of the second substrate in the first partial section in a direction running perpendicular to a main extension plane, wherein the device comprises a sensor element, wherein the device comprises a sensor element, wherein the device for determining the state of an object is designed such that before and/or during bonding to determine the state of an object, light is directed onto a surface of the object and reflected, and the light reflected from the surface is measured by means of a sensor element to determine the distance between the sensor element and the surface, and a distance between the sensor element and the surface is determined. All of the advantages and properties described for the method can be transferred analogously to the device.

In a first embodiment of the measuring device, the optical fibers of the sensor head are installed. The sensor head contains both the optical fiber that guides the radiation from the radiation source to the substrate and the optical fiber for coupling out the measurement signal. The optical fibers are installed in the sensor head so that they can be adjusted independently of one another, whereby the optical fibers are not twisted, so that the respective working distance and the measuring range can be set precisely. In particular, spring-loaded or spring-loaded backlash-free adjustment elements such as pre-tensioned micrometer screws, in particular backlash-free pre-tensioned differential screw gears, can be used for this purpose.

Since fiber optic distance sensors have ground fiber ends and the manufacturing accuracy of the optical fiber and thus of the sensors is finite, the measurement uncertainty resulting from the undefined angular position of an optical fiber is at least reduced, preferably eliminated, with the present invention. This is because the optical fiber is installed in the sensor head at a specific angular position, at least without twisting it. This means that distances and distance changes can be recorded with less uncertainty, so that the course of the bond wave can be precisely recorded and controlled accordingly. For this purpose, the sensors can be integrated in the substrate holder in particular with play-free click or play-free bayonet connections.

In particular, it is provided that the sensor element has a fiber end and a signal transmission section, wherein the sensor element is designed such that the Fiber end for signal reception and the signal transmission section for signal transmission to a spaced-apart evaluation device.

It is particularly advantageous for the device with the structural separation of the radiation source and the evaluation unit from the sensor head to be able to accommodate a large number of sensors in the substrate holder. By miniaturizing the adjustment and the entire sensor head in particular, the number of sensor heads used in the device can be advantageously increased in order to be able to closely monitor the bond wave both temporally and spatially. The radiation sources and evaluation units are preferably placed far away from the substrate holder.

The adjustment of the fiber optic distance sensors installed in the substrate holder, in particular the upper substrate holder, is carried out using a calibration and adjustment procedure. The following steps are carried out for calibration, in particular the following procedure.

Preferably, the optical fiber element is aligned for calibration. In a first process step, for example, an upper substrate is loaded and secured on the upper substrate holder. In a second process step, the fiber optic distance sensors are adjusted, in particular iteratively, so that the respective sensor has at least a minimal distance to the back of the second substrate. In a third process step, the individual sensors are read out and the intensity signals and/or the distances are stored. In a fourth process step, the stored intensity signals are set as a zero distance. In a fifth process step, the upper substrate is released from the upper substrate holder and unloaded from the bonding space of the bonder. In a sixth process step, a lower substrate is loaded and secured on the lower substrate holder. In a seventh process step, the distances from the fiber optic distance sensors in the upper substrate holder - and thus from the upper substrate holder - to the bonding interface of the lower substrate on the lower substrate holder are measured. In an eighth process step, the upper substrate holder and/or the lower substrate holder are moved to a different working distance. In a ninth process step, the change in the distance between the upper substrate holder and the lower substrate holder is recorded, as well as the distance between the upper substrate holder and the lower substrate holder, at the same time as the eighth process step. In a tenth process step, the actual actual distances are compared with the target value of the distance change of the upper and lower substrate holders and the differences are recorded for each sensor in order to record the specific correction values of the fiber optic distance sensors as well as the intensity curves. In the eleventh process step, the calibration with exchanged substrates is iteratively recorded as a series of measurements in order to create the correction values of the fiber optic distance sensors as a knowledge store and/or database. The curves approximated to the family of points of the intensity values at given distances are called intensity curves. In particular, the intensity curves can be approximated using empirical mathematical formulas so that the expected intensities can be interpolated for a given distance between the substrate holders in the bonding device. Conversely, the distances are determined for each sensor from the measured intensities.

Exchanging the substrates for calibration means that a statistically relevant number of measurements are carried out with different substrates: In particular, the variations in the thickness of the substrates, the variations in the reflectance of a material as well as the variations in the material differences or the variations due to the different positioning on the substrate holders can be recorded and used as correction values for measuring the bond wave and thus for influencing the bond wave. In this way, system- and substrate-specific correction values are determined.

This means that during fusion bonding in the working range of the fiber optic distance sensors, all possible distances between the upper substrate holder and the lower substrate holder can be better detected spatially and temporally.

In particular, the bonding process is influenced depending on the state determination, in particular a bonding wave speed is controlled. For this purpose, deformation and/or fixing elements are specifically controlled and part of the second substrate is dropped or held.

Preferably, it is provided that in order to influence the bonding process depending on the state determination, the findings of a machine learning algorithm and/or empirical values stored in a database are used. In order to utilize the measured state determination, which is obtained over a large number of bonding processes, The recorded state determinations can be made available together with a result of the bonding process as a test set to a neural network, which uses the test sets to develop new strategies for controlling the bonding process for certain state determinations and preferably applies them in the next bonding process for comparable state determinations. This allows the method to be used to further optimize the bonding process.

It is preferably provided that the sensor element has at least one optical fiber element and preferably comprises a fiber optic distance sensor. It is particularly preferably provided that the at least one optical fiber element is integrated into the device in a displaceable, in particular pivotable, manner.

The device for bonding substrates comprises in particular the following functional components and/or modules:

-Substrate holder: Substrate holders are used for the substrate holder. For this purpose, at least one substrate holder provided with sensors and actuators is used. Further, in particular independent inventions are understood to be an improved device with a substrate holder with at least one, preferably with over 30 sensors and 30 actuators for influencing the bonding wave. In particularly preferred embodiments of the device, substrate holders have over 50 sensors and 50 actuators.

Preferably, the device for bonding comprises at least one fiber optic distance sensor as sensors, preferably the same number of fiber optic distance sensors as there are vacuum zones that can be switched independently. In particular, the fiber optic distance sensors can be integrated in the substrate holder, in particular in the upper substrate holder, in an adjustable manner.

In particular, the substrate holders have individually switchable zones that are fluidically isolated from one another, in particular vacuum zones, which are each assigned to a fiber-optic distance sensor. In particular, the fiber-optic distance sensor is integrated in the respective vacuum zone, so that the measurement of the fastening of a substrate and the vacuum control are connected to one another in the shortest possible control loop, and the measurement of the deformation of the substrate takes place where the effect of the vacuum zone deforms the substrate. The substrate holders have fixings. The fixings serve to hold the substrates. The fixings can be

1. Mechanical fixations, especially

1.1. Terminals

2. Vacuum fixations, especially with

2.1 . individually controllable vacuum tracks

2.2. interconnected vacuum tracks

3. Electrical fixations, especially

3.1. Electrostatic fixations

4. Magnetic fixations

5. Adhesive fixations, especially

6. Gel-Pak fixations

7. Fixations with adhesive, particularly controllable, surfaces.

The fixations can be controlled electronically in particular. Vacuum fixation is the preferred type of fixation. Vacuum fixation preferably comprises several vacuum tracks that emerge on the surface of the substrate holder. The vacuum tracks can preferably be controlled individually. In an application that is more technically feasible, some vacuum tracks can be combined to form vacuum track segments that can be controlled individually and can therefore be evacuated or flooded. However, each vacuum segment is independent of the other vacuum segments. This makes it possible to set up individually controllable vacuum segments. The vacuum segments are preferably designed in a ring shape. However, any shape can be conceivable as a vacuum zone. This enables a substrate to be fixed and/or released from the substrate holder in a targeted manner.

The device according to the invention with fiber optic distance sensors can be used, among others, for the following possible applications, which are particularly considered as independent inventions: -Movement and/or alignment means for the substrates with the adjusting elements, actuators for generating force for changing the substrate curvature.

In one embodiment of the device, the movement means for receiving the substrates can reproducibly deform the substrates.

-Movement and/or alignment means for the substrate, such as coarse and/or fine drives,

-Bond initiation agents for fusion bonding, in particular pins, fluidic pressure media, in particular nozzles with gas overpressure, and/or their combination,

-Movement and/or alignment means are understood in the device according to the invention preferably as movement devices with drive systems, guide systems, holding devices and measuring systems in order to move, position and align the optical systems and/or substrates with each other.

The motion devices can generate each movement as a result of individual movements, so that the motion devices can preferably contain fast coarse positioning devices that do not meet the accuracy requirements as well as precisely operating fine positioning devices.

Fiber optic distance sensors offer particular advantages for use as measuring devices in bonding devices: the optical fiber enables a compact design, which means that a high density of measuring devices can be integrated into substrate holders. Retrofitting bonding devices is also possible, since the evaluation and the radiation source do not have to be placed directly on the substrates and/or substrate holders. Another advantage is the high achievable data density compared to conventional measuring methods such as laser or confocal sensors.

Furthermore, according to an advantageous embodiment, a device can comprise supply and auxiliary and/or supplementary systems (compressed air, vacuum, electrical energy, liquids such as hydraulics, coolants, heating means, means and/or devices for temperature stabilization, electromagnetic shielding, ionizers and/or deionizers, electrostatic dust traps).

Furthermore, a device according to the invention includes frames, claddings, vibration-suppressing or damping or cancelling active or passive subsystems. A frame can be understood as a part, in particular made of natural hard stone or mineral cast or spheroidal graphite cast or hydraulically bound concrete, which is in particular vibration-damped and/or vibration-insulated and/or installed with vibration damping.

Furthermore, a device according to the invention comprises at least one measuring system, preferably with measuring units for each axis of movement, which can be designed in particular as path measuring systems and/or as angle measuring systems. Furthermore, the device contains at least one measuring system, preferably with measuring units for radiation intensity, in particular for the radiation for curing the embossing compound.

Furthermore, the device comprises at least one measuring system for observing and/or checking the adjustment or alignment marks of the first substrate and the second substrate.

Furthermore, the device comprises at least one measuring and control system for pressure, in particular vacuum and/or overpressure, which measures, detects and controls the pressure on/in the substrate during bonding.

Furthermore, a device according to the invention contains at least one measuring system for observing the alignment of the substrates to one another. These are provided, for example, in addition to determining the distance via reflected light.

Both tactile, i.e. probing, and non-tactile measuring methods can be used. The measuring standard, the unit of measurement, can be a physical object, in particular a scale, or it can be implicit in the measuring method, such as the wavelength of the radiation used.

At least one measuring system can be selected and used to achieve alignment accuracy before bonding. Measuring systems implement measuring methods. In particular,

• Inductive methods and/or

Capacitive methods and/or

Resistive methods and/or • Comparison methods, in particular optical image recognition methods, detection of position marks and/or QR codes and/or

• incremental or absolute methods (in particular with glass standards as scale, or interferometers, in particular laser interferometers, or with magnetic standards) and/or

• Runtime measurements (Doppler method, time of flight method) or other time recording methods and/or

• Triangulation methods, especially laser triangulation,

• Autofocus method and/or

• Intensity measurement techniques such as fiber optic rangefinders can be used.

For example, measured values can be combined with one another and/or referenced and/or correlated with one another, so that a measurement of one alignment mark can be used to determine the position of the other alignment mark related to it. In particular, the position of the substrate can be calculated from the position values of the substrate holder and the detected alignment marks and corrected accordingly.

For position determination, in particular 3D position determination at one point or at two points or three points or any number of points, in a first embodiment according to the invention, optical pattern recognition using camera systems can be used to provide a unique reference of the position and height. The patterns are recorded in a real-time system, in particular continuously during the alignment of the substrates. The measurement methods listed can also be used for position determination.

Preferably, movement devices that are not used for fine adjustment are designed in particular as robot systems, preferably with incremental displacement sensors. The accuracy of these movement devices for auxiliary movements is decoupled from the accuracy for aligning the substrates, so that the auxiliary movements are carried out with a low repetition accuracy of less than 1 mm, preferably less than 500 micrometers, particularly preferably less than 150 micrometers. The accuracy of the movement devices for the alignment is preferably less than 200 nm, preferably less than 100 nm, particularly preferably less than 50 nm, most preferably less than 20 nm, optimally less than 10 nm, ideally less than 1 nm.

In particularly preferred embodiments of the device, the error of the alignment accuracy of the device is 20% of the permissible maximum alignment error, particularly preferably 10% of the permissible maximum alignment error, in the optimal case 1%.

Processes are preferably created as recipes and executed in machine-readable form. Recipes are optimized collections of values of parameters that are functionally or procedurally related. The use of recipes makes it possible to ensure the reproducibility of production processes.

In one embodiment of the bonding method, a lower substrate is fusion bonded to an upper substrate, with the following sequence, in particular with the following steps:

In a first process step, the lower substrate is placed on a lower substrate holder and measured with at least one fiber optic distance sensor, which is installed in the upper substrate holder.

In a second method step, the lower substrate is fixed to the lower substrate holder, in particular with vacuum zones, and the fixing is measured with at least one fiber optic distance sensor as an additional control, so that the local deformations of the lower substrate are preferably minimized.

In a third method step, the upper substrate is loaded into the bonding device and measured in free form with the at least one fiber optic distance sensor in order to be able to detect and in particular correct deformations and/or critical distortions of the upper substrate.

In a fourth method step, the upper substrate is attached to the upper substrate holder, in particular by means of vacuum zones, and is measured using at least one fiber-optic distance sensor. The controlled attachment of the upper substrate allows undesirable distortions and/or deformations of the upper substrate to be minimized, preferably eliminated. In a fifth process step, the substrates are aligned to each other, in particular using alignment markings.

In a sixth process step, a fusion bond is initiated by contacting the upper substrate and the upper substrate. The fusion bond can be initiated with a bond pin in particular. The initiation of the path of the bond wave can be observed with at least one fiber optic distance sensor in order to allow the bond wave to pass through in a controlled manner.

In a seventh method step, the course of the bonding wave is observed by means of at least one fiber optic sensor in the upper substrate holder. The distance between the back of the upper substrate and the upper substrate holder is recorded as a function of time and/or stored and/or fed to a control of the bonding wave, in particular the vacuum zone control, and/or visualized and/or processed and/or statistically evaluated.

In an eighth process step, the course of the bonding wave is influenced, in particular in real time to the seventh process step, by influencing the vacuum of at least one vacuum zone of a substrate holder in order to minimize distortions during bonding.

In a ninth process step, the fusion bonding of the substrate stack is completed and the upper substrate holder is separated from the upper substrate. This process step can optionally be carried out with the seventh and/or the eighth process step.

In a tenth process step, the bonded substrate stack in the prebond is removed from the bonding device and, in particular, subjected to a quality control.

To the extent that device features are disclosed here and/or in the following description of the figures, these should also be considered disclosed as process features and vice versa. All numerical values and relational information (parallelism, congruence, normality, flatness, etc.) in this disclosure are used as terms for quantities subject to tolerances, so that in particular the tolerances of non-tolerated length or angle dimensions according to ISO 2768 and the semi-standards relevant to the semiconductor industry (for flatness, waviness, deflection, particle load, etc.) apply, unless the tolerances are explicitly stated. A further subject of the present invention is a substrate holder for a device according to the invention, wherein the sensor element is integrated into the substrate holder. All advantages and properties described for the device can be transferred analogously to the substrate holder and vice versa.

Another subject of the present invention is a sensor element for integration into a device according to the invention or a substrate holder according to the invention. All advantages and properties described for the device can be transferred analogously to the substrate holder and the sensor element and vice versa. In particular, it is intended that the sensor element can be used to upgrade existing devices. For example, the sensor element is dimensioned in such a way that it can be inserted into a recess that was or is originally intended as a vacuum opening or opening for a deformation element. This means that it is only necessary to place the sensor element in the corresponding recess and fix it.

Further advantages, features and details of the invention emerge from the following description of preferred embodiments and from the drawings. These show:

Fig. 1 is a schematic representation of a fusion bonding device with an integrated fiber optic distance sensor.

Fig. 2 is a schematic representation of a section of a substrate holder with an integrated fiber optic sensor.

In the figures, advantages and features of the invention are identified with reference numerals identifying them in accordance with embodiments of the invention, wherein components or features with the same or equivalent function are identified with identical reference numerals.

The figures are to be understood as sketches from which no size relationships or scales can be derived. They show the relationships of the parts to each other in an exaggerated representation, which is used for illustration purposes.

Fig. 1 shows parts of a device 1 for fusion bonding. The bonding device 1 includes a frame 8 on which the optical detection means 3 for the lower substrate 11 can be fastened to a movable frame 2 with the movement device 4. In particular, in the same optical axis of the optical detection means 3 there is the optical detection means 7 for detecting an alignment mark of an upper substrate, which is not shown. The movable frame 5 and the movement device 6 enable the optical detection means 7 to be focused on the alignment mark.

The lower substrate holder 9 can hold the lower substrate 11. The vacuum segments and the vacuum channels of the substrate holder 9 are not shown. The necessary substrate movements for loading and unloading as well as for adjustment can be carried out by means of the movement device of the lower substrate holder 10.

The upper substrate holder 12 can hold the upper substrate (not shown). The vacuum segments and the vacuum channels of the upper substrate holder 12 are not shown. The necessary substrate movements for loading and unloading as well as for adjustment can be carried out using the movement device of the upper substrate holder 13. The bond pin 14, which starts the bonding wave of the fusion bond after the substrates have approached, is shown schematically. A fiber optic distance sensor 15 is shown with two fictitious, overlapping beams 16, with the aid of which the distance a can be measured, in particular between the upper substrate holder 12 and the substrate 11 or between the upper substrate holder 12 and the lower substrate holder 9 or between the upper substrate holder 12 and the upper substrate. The other fiber optic distance sensors as well as the radiation sources and evaluation units are not shown. In particular, the person skilled in the art understands the sensor element designed as a fiber to be a component whose fiber end is intended for receiving light or signals. These signals are then passed on to a common evaluation device, which is a relatively large component at a distance from the sensor element. Here, the signals from several fibers with fiber ends arranged next to one another preferably converge to be evaluated together in the common evaluation device.

Fig. 2 shows a section of an upper substrate holder 12' in a top view, in which the functional surface is shown schematically. Two fibers of the fiber optic distance sensor are shown with 15'. The vacuum nozzle 17 is in fluidic connection with the vacuum control so that the applied vacuum can be regulated. A schematically shown sealing lip 18 delimits the vacuum zone shown. Another similar vacuum zone with the same elements is shown without markings.

List of reference symbols:

1 device for bonding substrates

2 Movable frame of the upper optical detection means

3 Upper optical detection device

4 Movement device of the upper optical detection means

5 Movable frame of the lower optical detection means

6 Movement device of the lower optical detection means

7 Lower optical detection device

8 frame

9 Lower substrate holder

10 Movement device of the lower substrate holder

11 Lower substrate

12, 12' Upper substrate holder

13 Movement device of the upper substrate holder

14 bond pin

15.15' fibers

16 Symbolic measuring radiation of the fiber optic distance sensor

17 vacuum nozzle

18 Vacuum seal, sealing lip

Claims

claims 1 . Method for bonding a first substrate to a second substrate (10), wherein the first substrate has a primary section and the second substrate (10) has a secondary section, wherein during bonding of the first substrate to the second substrate (10) a bonding wave advancing along a bonding direction between -- a first section in which the first substrate and the second substrate (10) are connected, and -- a second subsection is formed in which the first substrate and the second substrate (10) are still to be connected, wherein a subregion of the second substrate (10) in the second subsection is preferably at least temporarily offset in height during bonding compared to a subregion of the second substrate (10) in the first subsection in a direction running perpendicular to a main extension plane, wherein before and/or during bonding, in order to determine the state of an object, light is directed onto a surface of the object and reflected and the light reflected from the surface is measured by means of a sensor element (15) to determine the distance between the sensor element (15) and the surface and a distance (a) between the sensor element (15) and the surface is determined. 2. Method according to claim 1, wherein at least one optical fiber element is used as a component of the sensor element (15), and wherein a fiber optic distance sensor is preferably used as the sensor element (15). 3. Method according to one of the preceding claims, wherein a set distance between the sensor element (15) and the surface of the object assumes a value between 10 pm and 1000 pm, preferably between 10 pm and 500 pm and particularly preferably between 10 pm and 200 pm. 4. Method according to one of the preceding claims, wherein an arrangement of a plurality of sensor elements (15) is used for spatial resolution, preferably of more than ten sensor elements (15), particularly preferably from more than 30 sensor elements and particularly preferably from more than 50 sensor elements (15) and/or at least one sensor element (15). 5. Method according to one of the preceding claims, wherein the object is the first substrate or the second substrate (10). 6. The method according to claim 5, wherein a plurality of state determinations are recorded during bonding to determine a state change recorded over time, in particular to detect a bond wave development on the second substrate (10). 7. Method according to one of the preceding claims, wherein the bonding is influenced depending on the state determination, in particular a bonding wave speed is controlled. 8. Method according to one of the preceding claims, wherein the state determination is used to minimize a distance to be set between the first substrate and the second substrate (10) before bonding. 9. Method according to one of claims 5 to 8, wherein an orientation of the second substrate (10) and/or the first substrate is determined during and/or after its inclusion in an associated substrate holder (10, 12) for state determination. 10. Method according to one of the preceding claims, wherein the object is a component of a device (1) for carrying out the method, for example a substrate holder (9, 12) and/or a deformation element of the device (1). 11. Device (1) for bonding a first substrate to a second substrate (10), in particular by means of a method according to one of the preceding claims, wherein the first substrate has a primary section and the second substrate (10) has a secondary section, wherein the device is configured such that when bonding the first substrate to the second substrate (10), a bonding wave advancing along a bonding direction between -- a first section in which the first substrate and the second substrate (10) are connected, and -- a second subsection in which the first substrate and the second substrate are still to be connected, in particular for detecting a bond wave development of the second substrate (10), wherein a subregion of the second substrate (10) in the second subsection is offset in height from a subregion of the second substrate (10) in the first subsection in a direction running perpendicular to a main extension plane, wherein the device comprises a sensor element (15), wherein the device for determining the state of an object is designed such that before and/or during bonding to determine the state of an object, light is directed onto a surface of the object and reflected, and the light reflected from the surface is measured by means of a sensor element (15) to determine the distance between the sensor element and the surface, and a distance (a) between the sensor element (15) and the surface is determined. 12. Device (1) according to one of the preceding claims, wherein the sensor element (15) has at least one optical fiber element and preferably comprises a fiber optic distance sensor, wherein an arrangement of a plurality of sensor elements (15) is preferably used for spatial resolution, preferably of more than ten sensor elements (15), particularly preferably of more than 30 sensor elements and particularly preferably of more than 50 sensor elements (15) and/or at least one sensor element (15). 13. Device (1) according to claim 12, wherein the sensor element (15) has a fiber end and a signal transmission section, wherein the sensor element (15) is designed such that the fiber end is provided for signal reception and the signal transmission section is provided for signal transmission to a spaced evaluation device. 14. Substrate holder (12) for a device according to one of claims 10 to 13, wherein the sensor element (15), in particular its fiber end, is integrated into the substrate holder (12). 15. Sensor element (15) for integration into a device (1) according to one of claims 1 to 13 or a substrate holder (12) according to claim 14.