Apparatus and Method for Aligning a Substrate

Abstract

The present invention relates to an apparatus and method for aligning a substrate.

Description

Field of the Invention

[0001] The present invention relates to an apparatus and a method for aligning substrates. Background Art

[0002] Many apparatuses and methods for wedge error compensation are known in the prior art. Wedge error compensation is of decisive importance, for example, in lithography, especially in photolithography, because it is necessary to ensure that the photomask is positioned parallel to the surface of the substrate to be exposed. Any inclined position between the photomask and the substrate results in exposure distortion of the photosensitive layer on the substrate. Wedge error compensation has also been disclosed for imprint lithography equipment. Thus, WO2012028166A1 shows an apparatus and a method in which an interferometer measures the distance between two substrate surfaces. The measurement is carried out through one of two transparent substrates here. The substrate is a nanoprint stamp (Nanoprägestempel). The core idea of WO2012028166A1 is to compensate for the wedge error between the substrate surfaces on which the embossed structures are located. In contrast, WO0210721A2 discloses wedge error compensation through a surface that is not part of the functional surface. This approach is not optimal because it cannot be assumed that the surface on which the measurement is carried out is parallel to the functional surface, which is, in this example, the surface with the embossed structure. Document US20090101037A1 discloses an apparatus and a method for measuring the distance between two surfaces. However, the wedge error cannot be compensated by measurements at a single location.

[0003] In recent years, wedge error compensation between substrates to be joined has become increasingly important, and thus attempts have been made to adopt concepts from lithography into the joining technology.

[0004] A major problem in the prior art is that no such device or method has been shown by means of which wedge error compensation can be carried out at the necessary speed. Yield is of decisive importance for economic success, especially during joining. Another disadvantage is that most substrates used for joining are opaque to the electromagnetic radiation used, especially to visible light and infrared light. Although silicon wafers are infrared transparent, the infrared transmissivity is destroyed by the metal coatings regularly applied to the silicon wafers. Summary of the Invention

[0005] The object of the present invention is therefore to present a device and a method for aligning substrates which at least partially eliminate, in particular completely eliminate, the disadvantages listed in the prior art. Additionally, an improved device and an improved method for aligning substrates, in particular for compensating for wedge errors between substrates, should be presented. In particular, a device and a method should be presented by means of which wedge compensation can be carried out quickly and efficiently during the processing of substrates, in particular during bonding. Furthermore, a device and a method should be presented by means of which opaque substrates, in particular substrates for electromagnetic radiation, in particular for visible light and for infrared light, can be aligned.

[0006] The current object is solved by the features of the dependent claims. Advantageous developments of the invention are given in the dependent claims. All combinations of at least two features given in the description, the claims and / or the drawings also fall within the scope of the invention. In the given value ranges, the values within the mentioned limits should also be regarded as being disclosed as boundary values and can be claimed in any combination.

[0007] The invention thus relates to a device for aligning substrates, in particular wafers, having:

[0008] - a first substrate holder for receiving a first substrate on a first substrate holder surface,

[0009] - a second substrate holder for receiving a second substrate on a second substrate holder surface,

[0010] - wherein the first substrate holder surface faces the second substrate holder surface, and

[0011] - wherein the first substrate holder has at least three internal distance sensors for measuring a first distance to the first substrate, in particular to the substrate surface of the first substrate, characterized in that

[0012] - the first substrate holder has at least three external distance sensors for measuring a second distance to the second substrate holder surface of the second substrate holder.

[0013] Furthermore, the invention relates to a method for aligning substrates, in particular wafers, in particular by means of a device for aligning substrates, having the following steps, in particular having the following sequence:

[0014] i) receiving a first substrate on the first substrate holder surface of the first substrate holder,

[0015] ii) receiving a second substrate on the second substrate holder surface of the second substrate holder, wherein the first substrate holder surface faces the second substrate holder surface,

[0016] iii) Measuring a first distance between at least three internal distance sensors of the first substrate holder and the first substrate, in particular between the substrate surface of the first substrate.

[0017] iv) Measuring a second distance between at least three external distance sensors of the first substrate holder and the surface of the second substrate holder of the second substrate holder.

[0018] In one embodiment of the invention, it is provided that a respective one of at least three internal distance sensors and a respective one of at least three external distance sensors together form a distance sensor pair, wherein preferably, the internal distance sensor and the external distance sensor of the distance sensor pair are aligned in the radial direction starting from a reference point on the surface of the first substrate holder, in particular from the center.

[0019] Here, the internal distance sensor in the distance sensor pair is arranged in such a way that it can measure the first distance to the first substrate arranged on the surface of the first substrate holder. The associated external distance sensor in the distance sensor pair is not covered by the first substrate and can measure the second distance to the opposite substrate holder surface of the second substrate holder, wherein preferably, the external distance sensor is aligned with the internal distance sensor in the distance sensor pair in the radial direction. The external distance sensor thus measures the substrate holder surface at a point which is preferably aligned in the radial direction with the point measured by the internal distance sensor. Thereby, in addition to the structural advantages, in particular, the measurement accuracy can be improved or the wedge error can be compensated particularly well when aligning another substrate.

[0020] In a very particular embodiment of the invention, the internal distance sensors are designed such that they can directly measure the wedge error between the substrates by measuring the distance between two facing substrate surfaces. The measurement principle is preferably based on interferometry. In this case, the substrate fixed on one side of the distance sensor must be transparent to the corresponding electromagnetic radiation.

[0021] In another embodiment of the invention, it is provided that the first substrate holder has at least three distance sensor pairs, wherein the respective internal distance sensors and the respective external distance sensors of at least three distance sensor pairs are preferably aligned with each other in the radial direction. At least three, in particular all, distance sensor pairs thus preferably have distance sensors aligned in the radial direction. In this way, the measurement accuracy can be advantageously improved or the wedge error can be compensated particularly well when aligning another substrate.

[0022] In another embodiment of the present invention, it is arranged that the at least three external distance sensors are arranged offset symmetrically, especially on a first circle around a reference point on the surface of the first substrate holder, especially around the center point. The external distance sensors are preferably arranged equidistantly from each other in the circumferential direction of the first circle. Due to the especially symmetrically offset arrangement of the external distance sensors on the first circle, it is possible to advantageously detect wedge errors at different points at the same distance from the reference point on the oppositely arranged substrate holder surfaces, and especially improve the measurement accuracy.

[0023] In another embodiment of the present invention, it is arranged that at least three internal distance sensors are arranged offset symmetrically, especially on a second circle around a reference point on the surface of the first substrate holder, especially the center point, wherein preferably the first circle and the second circle are preferably concentric with each other. The internal distance sensors are preferably arranged equidistantly from each other in the circumferential direction of the second circle. Due to the especially symmetrically offset arrangement of the internal distance sensors on the second circle, it is possible to advantageously detect wedge errors at different points at the same distance from the reference point on the first substrate, and especially improve the measurement accuracy. Due to the concentric arrangement, the first circle and the second circle have a common center point, namely the reference point. This arrangement is especially advantageous for the measurement accuracy of the wedge error between the substrates. In addition, especially when calculating the wedge error compensation, the same position reference system can be advantageously used.

[0024] In another embodiment of the present invention, it is arranged that at least three internal distance sensors and / or at least three external distance sensors are arranged below the surface of the first substrate holder. Thereby, especially the construction cost can be reduced and the device can be advantageously made smaller. In addition to saving space, the sensor cables and other leads of the distance sensors can be arranged within the substrate holder. Furthermore, the internal distance sensors can measure the distance from the first substrate with as close and as small an interference factor as possible. In addition, when the distance sensors are placed into the first substrate holder, the substrate can advantageously move parallel to the surface of the first substrate holder without hitting the distance sensors.

[0025] In another embodiment of the present invention, it is arranged that the surface of the first substrate holder and the surface of the second substrate holder can be arranged at least partially, preferably completely, overlapping each other, such that the first substrate can fall onto the second substrate. Therefore, the first substrate holder is preferably and for example the upper substrate holder and the second substrate holder is the lower substrate holder. Thereby, when the first substrate is transferred to the second substrate holder, especially during calibration, the first substrate can advantageously fall onto the second substrate by gravity. For this purpose, especially only the release by the fixing element is required. Therefore, especially no other devices for transfer are needed.

[0026] In another embodiment of the present invention, it is arranged that at least three internal distance sensors and / or at least three external distance sensors can move in the radial direction relative to a reference point, in particular the center point, of the surface of the first substrate holder. The distance sensor pair can thus advantageously be adapted to substrates of different sizes, in particular wafers having different diameters. The corresponding device can thus advantageously be aligned with substrates of variable size.

[0027] In another embodiment of the present invention, it is arranged that at least three internal distance sensors can move along a second circle and / or at least three external distance sensors can move along a first circle. The distance sensors can thus advantageously be positioned for the respective process. For example, in additional method steps, other components may prevent or deteriorate the measurement. Due to the movability along the first and second circles, the position can be adjusted accordingly. In addition, comparisons can be made at different measurement points along the first and second circles, so that the measurement accuracy can be improved.

[0028] In another embodiment of the present invention, it is arranged that at least three internal distance sensors and / or at least three external distance sensors can move perpendicular to the surface of the first substrate holder. In this way, the vertical position of the distance sensors can be advantageously adjusted. For example, the distance sensors can be completely embedded in the substrate holder and the first substrate can be directly abutted against the surface of the first substrate holder. In addition, the distance sensors can be advantageously adjusted for maintenance. In particular, it is also advantageous that the focus of the distance sensors can be advantageously adjusted and the measurement range can thus be optimally adapted to the respective process and the substrate used.

[0029] In another embodiment of the present invention, it is arranged that the first substrate holder and / or the second substrate holder can be aligned with each other, in particular according to the first distance and / or the second distance, so that the wedge error between the first substrate and the second substrate can be compensated. The substrate holder can be arbitrarily moved, in particular by an actuator. Thereby, the wedge error between the first substrate and the second substrate measured by the distance sensors and calculated by the electronic data processing device can be compensated. In particular, it is not necessary here to align both substrate holders. Thus, it is also possible to align only one of the substrate holders. In particular, the first substrate holder and / or the second substrate holder can also be aligned in the horizontal and / or vertical direction relative to the respective substrate holder surface. In this way, the substrates to be aligned can be advantageously brought closer to each other, and in particular the measurement accuracy can be improved.

[0030] In another embodiment of the present invention, it is arranged that the first substrate holder and / or the second substrate holder have adjustable fixing elements, so that the first substrate and / or the second substrate can be fixed and / or released. Therefore, especially during calibration, when the first substrate holder is arranged above the second substrate holder, the first substrate can be dropped onto the second substrate by releasing the substrate through the fixing element. In addition, the sliding of the substrate can be prevented by fixing the substrate. Furthermore, it can be ensured by the fixing element that when measured by the distance sensor, each substrate abuts against the corresponding substrate holder surface at a predetermined position. Thereby, the measurement accuracy can be especially improved.

[0031] In another embodiment of the present invention, it is arranged that the method additionally has the following steps, especially having the following process:

[0032] a) Store the first distances of at least three internal distance sensors (2i) measured in step iii), especially in an electronic data processing device,

[0033] b) Transfer the first substrate to the second substrate holder (lu) so that the first substrate abuts against the second substrate,

[0034] c) Measure further first distances between at least three internal distance sensors and the first substrate, where the first substrate abuts against the second substrate,

[0035] d) Align the first substrate holder and / or the second substrate holder so that the corresponding differences between the correspondingly further measured first distances of at least three internal distance sensors and the correspondingly stored first distances of at least three internal distance sensors are correspondingly the same, thereby compensating for the wedge error between the first substrate and the first substrate holder,

[0036] e) Store the second distances of at least three external distance sensors from the second substrate holder surface of the second substrate holder measured in step iv), especially in an electronic data processing device,

[0037] where the storage in step e) is carried out after the alignment in step d).

[0038] Store the measurement values of at least three internal distance sensors. Here, the first substrate abuts against the first substrate holder surface. Therefore, especially through this first measurement, not only the distance between the sensor and the substrate surface of the first substrate is determined, but also the distance from the substrate holder surface of the first substrate is determined. In this way, the device is calibrated to the substrate surface of the first substrate or the substrate holder surface of the first substrate holder. Then, the at least three internal distance sensors correspondingly measure the distance from the first substrate again, where the substrate abuts against the second substrate.

[0039] By comparing these two measurements of at least three corresponding internal distance sensors, the wedge error between the substrates can be determined, and the alignment of the first and / or second substrate holders can be carried out such that no wedge error exists between the substrates anymore. In particular, after the wedge error has been compensated, the three external distance sensors immediately measure the distance to the surface of the second substrate holder. In this way, the method for aligning the substrates, in particular for compensating the wedge error, can be advantageously calibrated so that the method does not have to be calibrated again for further substrates to be aligned. The external distance sensors can then be advantageously used for alignment. Thereby, the processing speed is increased and multiple substrates can be effectively aligned with each other.

[0040] In another embodiment of the invention, it is provided that, based on the second distance, in particular based on the second distance stored in step e), the further first substrate and the further second substrate are aligned with each other to compensate for the wedge error between the further first substrate and the further second substrate. In this way, multiple substrates of the same type can be advantageously aligned or processed one after the other, in particular combined. Thereby, the process speed can be significantly increased and the alignment process, in particular the alignment process for compensating the wedge error, can be improved.

[0041] The idea of the invention is based on positioning at least two distance sensors correspondingly in at least three positions of the first substrate holder such that at least one of the two distance sensors measures the base side on the first substrate holder and the corresponding second distance sensor measures the distance to the substrate holder surface of the second substrate holder. By using two distance sensors at each position, the wedge error compensation can be carried out more effectively, in particular more quickly, for further substrate pairs that have to be compensated relative to each other.

[0042] The core of the invention lies in presenting a device and a method by means of which the wedge error can be carried out more effectively between two substrates, in particular two wafers. In particular, the wedge error between opaque substrates can also be effectively carried out by the invention. The invention is in particular based on the use of at least six sensors, where two corresponding ones are integrated into a pair and distributed over at least three positions of the substrate holder.

[0043] The advantage of the invention is that the wedge error between the substrates and simultaneously between the substrate holder surfaces is measured by the calibration process, and the wedge error between the substrates can be compensated in a further process step by readjusting to the distances measured during the calibration process to the substrate holder surfaces.

[0044] Therefore, it is no longer necessary to measure the wedge error between the substrates, especially opaque substrates, and the substrate surfaces, but rather it is replaced by measuring the distance of outward displacement. Thus, the wedge error between opaque substrates can also be compensated. Another important advantage is therefore that the wedge error between opaque substrates can be compensated.

[0045] Preferably, all the substrates to be used have the same thickness variation as a function of position, which should ideally be zero of course. The substrates do not have to have the same thickness, but they should have as planar-parallel surfaces as possible. If the substrates do not have planar-parallel surfaces, then for the device according to the invention, they should at least all have the same shape and the same orientation.

[0046] The present invention describes a device and a method for eliminating the wedge error between two substrates. The substrates can be understood as objects of such a type that they can be fixed on substrate holders. In particular, the substrates are wafers or stamps for imprinting processes.

[0047] In WO2012028166A1, the stamp has already been referred to as a substrate. This general expression is also followed in this document; in the further course of this text, the substrate is mainly understood as a wafer because the corresponding drawings can be designed more simply and clearly.

[0048] In this case, the device and the method are preferably used for wedge error compensation during bonding.

[0049] Substrate holder

[0050] The substrate holder has at least three positions. At each position, there are at least two sensors. The sensors are distance sensors. At least one internal distance sensor and at least one external distance sensor at the same position are also referred to as a pair of distance sensors in this context. The distance sensors are preferably interferometers. The distance sensors are positioned at each position in such a way that one of the two distance sensors can measure the back side of the fixed substrate, while the second distance sensor measures beyond the substrate.

[0051] The distance sensor that measures the back side of the fixed substrate is called the first distance sensor or the internal distance sensor. The distance sensor that measures beyond the substrate is called the second distance sensor or the external distance sensor. The second distance sensor thus measures the substrate surface of the second substrate holder opposite to the first substrate holder.

[0052] It is clear to those skilled in the art that the idea of the present invention can be further improved by using multiple internal distance sensors and / or multiple external distance sensors for each position. However, for the sake of simplicity, only one internal distance sensor and one external distance sensor will be described for each position in the further text.

[0053] The distance sensor pairs are preferably positioned symmetrically at the same angle along a circle. If three distance sensor pairs are used, the angle between the distance sensor pairs is preferably constantly 120°. However, it is also conceivable that they are not positioned at the same angle. This is especially the case when it is not feasible due to structural-technical reasons.

[0054] It is also conceivable that the distance sensors are designed to be movable. In one embodiment, they can move along a circle with a constant radius. In a preferred embodiment, it is also conceivable, in particular, a radial movement in addition to the degree of freedom of movement along the circle. Thus, generally, a movement of the distance sensors in at least two directions can be envisaged. The distance sensor pairs can then be adjusted to different substrate diameters, and only the corresponding substrate holders according to the invention can be designed.

[0055] An important aspect is that the precise positioning and fixing of the distance sensors in the z-direction, i.e., in the thickness direction, within the substrate holder is especially irrelevant. This is because during the calibration process, when the substrate is fixed, the internal distance sensors determine the zero point, and in further processing steps, the distances to the same substrate backside are then measured at different positions with reference to this zero point. This feature will be discussed in more detail in the description of the method. However, a movable embodiment of the distance sensors in the z-direction is conceivable and can be implemented. Due to the movability in the z-direction, in particular, the measuring range can be set more optimally. In the most general form, the distance sensors can thus move relative to the substrate holder along three independent spatial directions.

[0056] In another embodiment, additional sensors, in particular infrared sensors, are used for the external and internal distance sensors to obtain an extension of WO2012028166A1 according to the idea of the invention. In addition to the in-situ measurement of the wedge error according to WO2012028166A1, the idea of wedge error compensation according to the invention can also be carried out.

[0057] Technically, it is best to provide 3, preferably more than 3, more preferably more than 5, most preferably more than 10, and all in all most preferably more than 15 distance sensor pairs. However, from an economic point of view, the number of distance sensor pairs is preferably as small as possible because the distance sensors are relatively expensive. Since the tasks to be performed can be solved mathematically precisely with three distance sensor pairs, it is therefore economically preferred and technically sufficient to use exactly three distance sensor pairs.

[0058] The substrate holder has a fixing member. The fixing member is used to fix and hold the substrate. The fixing member can be

[0059] 1. a mechanical fixing member, in particular

[0060] 1.1 Fixture

[0061] 2. Vacuum fixing elements, especially having

[0062] 2.1 Separately controllable vacuum tracks

[0063] 2.2 Interconnected vacuum tracks

[0064] 3 Electrical fixing elements, especially

[0065] 3.1 Electrostatic fixing elements

[0066] 4. Magnetic fixing elements

[0067] 5. Adhesive fixing elements, especially

[0068] 6. Gel - Pak fixing elements

[0069] 7. Fixing elements having an adhesive, especially a manipulable surface.

[0070] The fixing elements are especially electronically manipulable. Vacuum fixing elements are the preferred type of fixing. The vacuum fixing elements preferably comprise a plurality of vacuum tracks which exit at the surface of the substrate holder. The vacuum tracks can preferably be controlled separately. In technically more feasible applications, some of the vacuum tracks are combined into vacuum track segments which can be controlled separately and can thus be evacuated or flooded. However, each vacuum segment is independent of the other vacuum segments. Thus, a feasible solution for constructing separately manipulable vacuum segments can be obtained. The vacuum segments are preferably designed in an annular or circular - segment shape. Thereby, the fixing and / or separation of the substrate from the substrate holder is achieved in a targeted, radially symmetric manner, especially from the inside outwards.

[0071] According to the invention, the surface of the substrate and / or the surface of the substrate holder preferably has as small a roughness as possible. The roughness is given either as mean roughness, root - mean - square roughness or as mean roughness depth. The values determined for mean roughness, root - mean - square roughness and mean roughness depth usually differ for the same measuring path or measuring surface, but are within the same order of magnitude. Therefore, the following numerical ranges for roughness can be understood either as values for mean roughness, root - mean - square roughness or as values for mean roughness depth. The roughness of the substrate surface and / or the substrate holder surface is preferably less than 100 μm, more preferably less than 10 μm, still more preferably less than 1 μm, most preferably less than 100 nm, and most preferably of all less than 10 nm.

[0072] According to the invention, the waviness should likewise be as small as possible. Waviness is understood as the second - order form deviation of the required surface finish.

[0073] In one embodiment according to the present invention, the substrate holders are designed such that they are themselves deformable so as to also deform the substrate by deformation.

[0074] Device

[0075] The device consists of at least one substrate holder. The substrate holder is preferably located at the upper side of the device.

[0076] The device, in particular the lower substrate holder, can have loading pins in order to be able to deposit the lower substrate more optimally.

[0077] Here, the device can have alignment elements in order to be able to align the substrates with respect to one another in the lateral direction, i.e., in the x- and y-directions. In the simplest embodiment, it is a mechanical alignment element, such as a pin, against which the substrates impinge and are thus positioned in their lateral displacement.

[0078] A purely mechanical alignment element such as a pin is used, for example, in a temporary bonding, where it is not necessary to align the substrates with respect to one another with submicron precision.

[0079] In a more preferred embodiment, it is a slider, in particular a movable slider, by means of which the substrate can be laterally displaced and positioned.

[0080] In another embodiment, the device has optical alignment elements by means of which characteristic marks, in particular alignment marks, on the substrate can be detected. The alignment marks are then covered or aligned with respect to one another by relative translation during the alignment process. It may be necessary to combine the wedge error compensation according to the present invention with the relative translational displacement of the substrates in order to correctly obtain the alignment marks within the depth of field of the alignment optics. Another possible option for alignment is to align only the edges of the substrates with respect to one another with the help of the optics.

[0081] Optical alignment is particularly necessary if the substrates are wafers that are to be bonded to one another during a fusion process. In addition, optical alignment is advantageous when at least one of the two substrates is an imprint mold in which an imprint pattern is to be imprinted onto an imprint body on the second substrate. In this case, alignment marks are preferably used to ensure the correct positioning and alignment of the substrates with respect to one another. In a very particular embodiment according to the present invention, an internal distance sensor is part of the first substrate holder and an external distance sensor is part of the second substrate holder.

[0082] Calibration method

[0083] First, a calibration method is described which must be carried out in particular once in order to subsequently be able to correct the wedge error between substrate pairs.

[0084] In the first calibration process step, the first substrate is loaded and fixed onto the first, in particular upper, substrate holder according to the invention. In this case, the fixing must be carried out in such a way that all the internal distance sensors of the substrate holder according to the invention can measure the distance to the back side of the first substrate. In this calibration process step, the zero point for the distance sensors is determined. Determining the zero point should be understood as meaning that when measurements are carried out in this process step, the internal distance sensors must obtain a zero measurement value. Since it is a distance sensor, the measurement value can be equivalent to a distance value. If the measurement value deviates from zero, the measurement value must be saved accordingly by software and / or hardware and subtracted as an offset in further measurements. A measurement value of zero indicates that the surface of the fixed substrate of the upper fixed substrate is the same as the surface of the substrate holder of the fixed substrate.

[0085] In the second calibration process step, the second lower substrate is loaded onto the second substrate holder. The second substrate holder does not necessarily have to be constructed like the first substrate holder. For the sake of simplicity, a common substrate holder without a pair of distance sensors will be described.

[0086] Of course, it is also conceivable to first load the lower substrate and then load the upper substrate. Thus, the order of the first two calibration process steps can be interchanged.

[0087] In the third calibration process step, an approach of the relative translation of the substrate holders to each other can be carried out. Before this approach step, the substrate holders are far apart from each other and first approach, especially in the third step. In particular, already in the third calibration process step, the substrates can be aligned relative to each other in the x- and y-directions, especially roughly. Since the wedge error has not been corrected at this time, it can only be a rough alignment. Of course, wedge error compensation usually makes fine adjustment fail. The minimum distance between the mutually facing substrate surfaces is less than 5 mm, preferably less than 1 mm, more preferably less than 0.1 mm, most preferably less than 0.01 mm, and most preferably of all less than 0.001 mm.

[0088] In the fourth calibration process step, the upper substrate is dropped or placed onto the lower substrate.

[0089] In the fifth calibration process step, the internal distance sensors measure the distance to the back side of the dropped substrate. Generally speaking, the distances are different.

[0090] In the sixth calibration process step, the wedge error between the substrate surface of the upper substrate and the substrate holder surface of the upper substrate holder can now be compensated. For this purpose, the substrate holders are tilted relative to each other so that the measured distances between the internal distance sensors are the same. Since the zero setting of the internal distance sensors is carried out in the first calibration process step, it is ensured that the measured distances of all the distance sensors are related to the distance between the surface of the upper substrate holder and the back side of the upper substrate.

[0091] In the seventh calibration process step, the distance to the surface of the substrate holder of the lower substrate is then measured using an external distance sensor. These distances are stored and can be used in the case of another loaded pair of substrates to immediately compensate for the wedge error between the two substrates, without the upper substrate having to be lowered again. Of course, the prerequisite for this is that all loaded substrates must have the same thickness distribution, preferably a uniform thickness. Thus, they do not have to have the same thickness, but the thickness must be invariant as a function of position. If the thickness is a function of position, it must also be ensured that the substrates used in the further process have the same substrate holder orientation as the substrates used for the calibration process.

[0092] Due to gravity, of course it is appropriate to use a substrate holder with a pair of distance sensors on the upper side and to lower the upper fixed substrate in the fourth calibration process step. However, it is clear to those skilled in the art that the substrate holder with a pair of distance sensors can also be arranged on the lower side. For example, if the substrates have such good adhesion between their substrate surfaces, as in the case of polished silicon wafers, it is also conceivable to replace the fourth calibration process step of lowering by pulling the lower substrate onto the upper substrate. As long as the two substrates are in contact at least at one point and the bonding wave propagates, the pulling up will occur by spontaneous pre-bonding, which in this case of course cannot be pulled up by the lower substrate that is not fixed by the lower substrate holder.

[0093] Wedge error compensation method

[0094] After calibration, the wedge error between the two substrates can now be corrected.

[0095] In the first process step, the first upper substrate is loaded and fixed to the first upper substrate holder with a pair of distance sensors.

[0096] In the second process step, the second lower substrate is loaded onto the second substrate holder. The second substrate holder does not necessarily have to be a substrate holder with a pair of distance sensors. For simplicity, an ordinary substrate holder will be described.

[0097] Of course, it is also conceivable to first load the lower substrate and then the upper substrate. Thus, the order of the first two process steps can be interchanged.

[0098] In a third process step, an approach of relative translation of the substrate holders with respect to each other can be carried out. In particular, in the third process step, the substrates can already be aligned with each other in the x- and y-directions, preferably roughly and / or finely. However, it must be envisaged that, in the case where a wedge error still exists, the fine alignment can be cancelled again by compensating the wedge error at a later time and must in any case be carried out again in a subsequent process step. However, the fine alignment in this process step can be advantageous for the subsequent result.

[0099] In a fourth process step, the stored distance, i.e., the distance between the two substrate holders multiplied by a real number, i.e., a factor x, is set at the respective positions of the individual external distance sensors. This automatically eliminates the wedge error between the substrates.

[0100] After the fourth process step, the process itself ends. Of course, further process steps will now be followed. However, these further process steps are no longer part of the idea and are therefore only mentioned superficially.

[0101] Some of the mentioned process steps of the calibration and / or wedge error compensation method can be carried out simultaneously.

[0102] A fine alignment between the substrates can be envisaged. Since the wedge error between the substrates has been eliminated, the substrates can now be very precisely aligned with each other in the horizontal plane by fine adjustment. In particular, alignment marks are used to align the substrates with each other.

[0103] It can also be envisaged that the two substrates are further approached in the same way to bring the substrates closer.

[0104] It can also be envisaged that the upper substrate is flexed by a centrally located bending device, in particular a pin. This contact occurs especially during fusion.

[0105] If the upper substrate is a photomask, it can also be envisaged to carry out a photocopying process on the photosensitive layer on the lower substrate.

[0106] If the upper substrate is a stamper, in particular a soft stamper, it can also be envisaged to carry out an imprinting step of the imprinting body on the lower substrate.

[0107] Therefore, the wedge error compensation process is not based on a special technical method but can be used anywhere where two plane surfaces are aligned with each other parallel to each other, i.e., without a wedge error. Description of the Drawings

[0108] Other advantages, features, and details of the present invention result from the following description of the preferred exemplary embodiments and the drawings. Here:

[0109] Figure 1Shows a schematic top view of a first substrate holder according to the present invention,

[0110] Figure 2 Shows a schematic top view of a second substrate holder according to the present invention,

[0111] Figure 3a Shows a first process step of a calibration process,

[0112] Figure 3b Shows a second process step of a calibration process,

[0113] Figure 3c Shows a third process step of a calibration process,

[0114] Figure 3d Shows a fourth process step of a calibration process,

[0115] Figure 3e Shows a fifth process step of a calibration process,

[0116] Figure 3f Shows a sixth process step of a calibration process,

[0117] Figure 3g Shows a seventh process step of a calibration process,

[0118] Figure 4a Shows a first process step of wedge error compensation,

[0119] Figure 4b Shows a second process step of wedge error compensation

[0120] Figure 4c Shows a third process step of wedge error compensation,

[0121] Figure 4d Is a fourth process step of wedge error compensation. Detailed Description of the Invention

[0122] In the drawings, identical components or components with identical functionality are denoted by the same reference numerals.

[0123] Figure 1A schematic top view of the substrate holder 1 is shown, where the surface 1s of the substrate holder can be seen, on which a substrate 3 (not shown) can be fixed. The fixing can be carried out by any fixing element 9. The fixing element 9 can be, for example, a simple vacuum fixing element, especially the holes 6. Three external distance sensors 2a at an angular interval of 120° can be seen along the first circle K1. Three internal distance sensors 2i at an angular interval of 120° can be seen along the second circle K2. A corresponding internal distance sensor 2i and an external distance sensor 2a form a distance sensor pair 5. Further, additional, optional sensors or optics 4 can also be seen, especially along the third circle K3. The sensor or optics 4 can be, for example, an infrared optic, by means of which an image of the surface or interface between two substrates 3o, 3u (not shown) can be made. Thus, the optic 4 is only an additional sensor that has nothing to do with the actual idea of the present invention.

[0124] However, it is also conceivable that if at least the substrate 3 (not shown) fixed to the substrate holder 1 is transparent to the sensor 4, the wedge error between the two substrates can be directly measured by means of the sensor 4. Then the measurement principle is preferably based on interferometry, by means of which the distance between two substrates (not shown) is directly measured. Besides the measurement principle, this measurement principle can also be carried out.

[0125] Figure 2 A schematic top view of the substrate holder 1' is shown. The surface 1s' of the substrate holder can be seen, on which a substrate 3 (not shown) can be fixed. The fixing is carried out by a special fixing element 9. The fixing element 9 consists of a recess 7, which is milled into the substrate holder 1', especially by a milling process. However, the recess is not milled out over the entire surface, but has a protrusion 8 inside it, which serves as a support for the substrate 3 (not shown) fixed to the substrate surface 1s'. Then there is a vacuum opening 6 in the recess 7, through which the recess 7 can be evacuated.

[0126] In particular, each fixing element 9 can be switched individually. This embodiment form of the fixing elements 9 that can be connected and grouped in different regions is known from the document WO2017162272A1. Three external distance sensors 2a at an angular interval of 120° can be seen along the first circle K1. Three internal distance sensors 2i at an angular interval of 120° can be seen along the second circle K2. The internal distance sensor 2i and the external distance sensor 2a correspondingly form a distance sensor pair 5. Further, additional, optional sensors or optics 4 can also be seen, especially along the third circle K3. The sensor or optics 4 can be, for example, an infrared optic, by means of which an image of the surface or interface between two substrates 3o, 3u (not shown) can be made.

[0127] Those skilled in the art understand that the type of the fixing element 9 does not affect the concept, and those skilled in the art can arbitrarily select from a variety of fixing elements.

[0128] The substrate holders 1, 1' especially have a deformation element 10 in the middle. The deformation element 10 is especially a channel, especially a hole, through which a pin (not shown) can bend the fixed wafer. The deformation element 10 can also be designed as a nozzle or a channel, through which fluid reaches the back side of a substrate (not shown) and deforms it by increasing the pressure. However, the curvature of the substrate 3 (not shown) is not an essential part of the present invention and will not be elaborated herein.

[0129] The following figures illustrate the calibration method and the wedge error compensation method by means of schematic cross-sections. Each figure consists of two illustrations.

[0130] The left illustration of each figure shows a reduced, absolutely minimal full side view of the substrate holders 1u, 1o and the substrates 3u, 3o. The substrates 3u, 3o and the substrate holders 1u, 1o are intentionally shown as non-uniform and strongly inclined in order to be able to more easily understand the method. Those skilled in the art understand that, especially, the surfaces of the substrate holders on the front side and the back side are manufactured to be planar parallel to each other with extremely low tolerances. This also applies to the substrate surfaces. Those skilled in the art also understand that the rotational deviation between the substrate holders 1u, 1o or the substrates 3u, 3o is only a few degrees, even if not a few tenths of a degree.

[0131] The right illustration of each figure shows a reduced cross-sectional side view of the substrate holders 1u, 1o and the substrates 3u, 3o related to a single alignment pair 5. Contrary to the left illustration, the front side and the back side of the substrate holders 1u, 1o are implemented to be planar parallel to each other. This also applies to the substrates 3u, 3o. In addition, the rotational deviation between the substrate holders 1u, 1o and the substrates 3u, 3o is many times smaller than that shown in the illustration.

[0132] The right illustration of the figure is used to make the process steps clearer. The left illustration of each figure allows for a quick detection of the orientation of each surface.

[0133] Figure 3a A section of the device in the first calibration process step is shown, in which the upper substrate 3o is loaded and fixed to the upper substrate holder 1o according to the present invention. In this calibration process step, especially, the zero point is set for the internal distance sensor 2i.

[0134] Figure 3b A section of the device in the second calibration process step is shown, in which the lower substrate 3u is loaded and fixed to the lower substrate holder 1o.

[0135] Figure 3c Shows a section of the device in the third calibration process step, in which the proximity of the two substrates 3u and 3o is effected by moving the substrate holders 1o, 1u relative to one another. In this process step, the two substrates 3u and 3o can already also be aligned approximately in the transverse direction.

[0136] It can be seen in all figures that the distance sensor surfaces 2si, 2sa are not in the same plane. According to the invention, this is also immaterial, since the zero point of the internal distance sensor 2i is determined at the time when the upper substrate 3o is still fixed to the upper substrate holder 1o. In particular, the determination of the zero point is already carried out in the first calibration process step according to the invention, but at the latest at the time point before the upper substrate is released. It is also conceivable that the distance sensor surfaces 2si, 2sa are in the same plane, however the distance sensors 2a, 2i can never be positioned so precisely.

[0137] Figure 3d Shows a section of the device in the fourth calibration process step, in which the upper substrate 3o is placed on or preferably dropped onto the lower substrate 3u.

[0138] Figure 3e Shows a section of the device in the fifth calibration process step, in which the internal distance sensor 2i measures the distance to the substrate surface 3so of the upper substrate 3o. An important aspect is that the distance measured by the internal distance sensor 2i does not represent the distance between the internal distance sensor surface 2si and the substrate surface 3so, but rather the distance between the substrate holder surface 1so and the substrate surface 3so. This step is only part of the calibration and is no longer carried out in the case of wedge error compensation between further substrate pairs.

[0139] Figure 3f Shows a section of the device in the sixth calibration process step, in which the wedge error between the upper substrate holder surface 1so and the substrate surface 3so of the upper substrate 3o is compensated by means of the distance measurement of the internal distance sensor 2i. This step is only part of the calibration and is no longer carried out in the case of wedge error compensation between further substrate pairs.

[0140] Figure 3g Shows a section of the device in the seventh calibration process step, in which the external distance sensor 2a measures the distance to the substrate holder surface 1su of the lower substrate holder 1u. Now these distances are stored.

[0141] Figure 1 The processes shown in a to 1g represent the calibration process. The distances of the external distance sensor 2a obtained by the calibration process can now be used to compensate for the wedge error between further substrate pairs.

[0142] Figure 4a Shows a section of the device in a first process step, in which the upper substrate 3o is loaded and fixed to the upper substrate holder 1o according to the invention.

[0143] Figure 4b Shows a section of the device in a second process step, in which the lower substrate 3u is loaded and fixed to the lower substrate holder 1o.

[0144] Figure 4c Shows a section of the device in a third process step, in which the proximity of the two substrates 3u and 3o takes place in such a way that the substrate holders 1o, 1u move relative to each other. It can also already occur in this process step that the two substrates 3u and 3o are aligned, especially roughly, in the lateral direction.

[0145] Figure 4d Shows a section of the device in a fourth process step, in which the two substrate holders 1u, 1o are adapted to each other until the distance of the external distance sensor stored in calibration process step seven or the distance multiplied by a real number (factor x) is reached. In this state, the wedge error between the substrates 3u, 3o has then been compensated.

[0146] List of reference numerals:

[0147] 1, 1o, 1u, 1' Substrate holders

[0148] 1s, 1so, 1su, 1s' Substrate holder surfaces

[0149] 2i, 2a Distance sensors

[0150] 2si, 2sa Distance sensor surfaces

[0151] 3, 3o, 3u Substrates

[0152] 3so Substrate surface

[0153] 4 Sensors or optical devices

[0154] 5 Distance sensor pairs

[0155] 6 Vacuum openings

[0156] 7 Recesses

[0157] 8 Protrusions

[0158] 9 Fixing elements

[0159] 10 Channels

[0160] K1, K2, K3 Circles

Claims

1. An apparatus for aligning substrates, comprising: - a first substrate holder (1, 1', 1o) for holding a first substrate (3, 3o) on a first substrate holder surface (1s, 1s', 1so), - a second substrate holder (1u) for holding a second substrate (3u) on a second substrate holder surface (1su), - wherein the first substrate holder surface (1s, 1s', 1so) faces the second substrate holder surface (1su), - wherein the first substrate holder (1, 1', 1o) has at least three internal distance sensors (2i) for measuring a first distance of the internal distance sensors from a substrate surface (3so) of the first substrate (3, 3o), and - the first substrate holder (1, 1', 1o) has at least three external distance sensors (2a) for measuring a second distance of the external distance sensors to the second substrate holder surface (1su) of the second substrate holder (1u).

2. The apparatus according to claim 1, wherein, the substrate is a wafer.

3. The apparatus according to claim 1, wherein, a respective one of the at least three internal distance sensors (2i) and a respective one of the at least three external distance sensors (2a) together form a distance sensor pair (5).

4. The apparatus according to claim 3, wherein, the respective internal distance sensor (2i) and the respective external distance sensor (2a) of the distance sensor pair (5) are aligned in a radial direction starting from a reference point of the first substrate holder surface (1s, 1s', 1so).

5. The apparatus according to claim 4, wherein, the reference point is a center point.

6. The apparatus according to any one of claims 3 to 5, wherein, the first substrate holder (1, 1', 1o) has at least three distance sensor pairs (5), wherein the respective internal distance sensors (2i) and the respective external distance sensors (2a) of the at least three distance sensor pairs (5) are correspondingly aligned in a radial direction.

7. The apparatus according to claim 1 or 2, wherein, the at least three external distance sensors (2a) are arranged on a first circle (K1) around a reference point of the first substrate holder surface (1s, 1s', 1so).

8. The apparatus according to claim 7, wherein, the reference point is a center point.

9. The apparatus according to claim 7, wherein, the arrangement is symmetrically offset.

10. The apparatus according to claim 7, wherein, the at least three internal distance sensors (2i) are arranged on a second circle (K2) around a reference point of the first substrate holder surface (1s, 1s', 1so).

11. The apparatus according to claim 10, wherein, the reference point is a center point.

12. The apparatus according to claim 10, wherein, the arrangement is symmetrically offset.

13. The apparatus according to claim 10, wherein, the first circle (K1) and the second circle (K2) are concentric with each other.

14. The device according to claim 1 or 2, wherein, the at least three internal distance sensors (2i) and / or the at least three external distance sensors (2a) are arranged below the surface (1s, 1s', 1so) of the first substrate holder.

15. The device according to claim 1 or 2, wherein, the surface (1s, 1s', 1so) of the first substrate holder and the surface (1su) of the second substrate holder can be arranged at least partially overlapping, such that the first substrate (3, 3o) can be placed on the second substrate (3u).

16. The device according to claim 15, wherein, the surface (1s, 1s', 1so) of the first substrate holder and the surface (1su) of the second substrate holder can be arranged completely overlapping, such that the first substrate (3, 3o) can be placed on the second substrate (3u).

17. The device according to claim 1 or 2, wherein, the at least three internal distance sensors (2i) and / or the at least three external distance sensors (2a) are movable in the radial direction relative to a reference point on the surface (1s, 1s', 1so) of the first substrate holder.

18. The device according to claim 17, wherein, the reference point is the center point.

19. The device according to claim 10, wherein, the at least three internal distance sensors (2i) are movable along the second circle (K2) and / or the at least three external distance sensors (2a) are movable along the first circle (K1).

20. The device according to claim 1 or 2, wherein, the at least three internal distance sensors (2i) and / or the at least three external distance sensors (2a) are movable perpendicular to the surface (1s, 1s', 1so) of the first substrate holder.

21. The device according to claim 1 or 2, wherein, the first substrate holder (1, 1', 1o) and / or the second substrate holder (1u) can be aligned with each other depending on the first distance and / or the second distance, so as to compensate for the wedge error between the first substrate (3, 3o) and the second substrate (3u).

22. The device according to claim 1 or 2, wherein, the first substrate holder (1, 1', 1o) and / or the second substrate holder (1u) have adjustable fixing elements (9), such that the first substrate (3, 3o) and / or the second substrate (3u) can be fixed and / or released.

23. A method for aligning substrates using the device according to any one of the preceding claims, having the following steps: i) Receiving a first substrate (3, 3o) on the surface (1s, 1s', 1so) of a first substrate holder (1, 1', 1o), ii) Place the second substrate (3u) on the second substrate holding surface (1su) of the second substrate holder (1u), wherein the first substrate holding surfaces (1s, 1s', 1so) face the second substrate holding surface (1su). iii) Measure a first distance between at least three internal distance sensors (2i) of the first substrate holder (1, 1', 1o) and the substrate surface (3so) of the first substrate (3, 3o). iv) Measure a second distance between at least three external distance sensors (2a) of the first substrate holder (1, 1', 1o) and the second substrate holding surface (1su) of the second substrate holder (1u).

24. The method according to claim 23, wherein, the method further comprises the following steps: a) Store the first distances of the at least three internal distance sensors (2i) measured in step iii) of claim 23 in an electronic data processing device. b) Transfer the first substrate (3, 3o) to the second substrate holder (1u) such that the first substrate (3, 3o) abuts against the second substrate (3u). c) Measure a further first distance between the at least three internal distance sensors (2i) and the first substrate (3, 3o), wherein the first substrate (3, 3o) abuts against the second substrate (3u). d) Align the first substrate holder (1, 1', 1o) and / or the second substrate holder (1u) such that the difference between the respective further measured first distances of the at least three internal distance sensors (2i) and the respective stored first distances of the at least three internal distance sensors (2i) is equal, thereby compensating for the wedge error between the first substrate (3, 3o) and the first substrate holder (1, 1', 1o). e) Store the second distances of the at least three external distance sensors (2a) relative to the second substrate holding surface (1su) of the second substrate holder (1u) measured in step iv) of claim 23 in an electronic data processing device. wherein the storage in step e) is performed after the alignment in step d).

25. The method according to claim 24, wherein, the alignment of the additional first substrate (3, 3o) and the additional second substrate (3u) with respect to each other is performed depending on the second distance, thereby compensating for the wedge error between the additional first substrate (3, 3o) and the additional second substrate (3u).

26. The method according to claim 25, wherein, the second distance is the second distance stored in step e) of claim 24.

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