METHOD AND DEVICE FOR ALIGNING A SUBSTRATE

Description

[0001] The present invention relates to a method and a device for aligning a substrate.

[0002] In the semiconductor industry, alignment systems (aligners) are used to align substrates, especially wafers, with each other or with other components. Substrates can have any shape and are preferably circular. The diameter of the substrates is standardized, particularly in industry. For wafers, the industry-standard diameters are 1 inch, 2 inches, 3 inches, 4 inches, 5 inches, 6 inches, 8 inches, 12 inches, and 18 inches. In special embodiments of the alignment systems, even rectangular substrates or panels can be aligned and bonded with the highest precision.

[0003] The joining of semiconductor substrates, especially those that are aligned, is called bonding.

[0004] In the so-called bonding process, the substrates to be bonded are aligned with each other and then joined together in a further process step. Particularly precise alignment of the substrates relative to each other is necessary for this.

[0005] Alignment processes in which the alignment marks are located on the substrate surfaces to be bonded are referred to as face-to-face alignments.

[0006] Insofar as at least one of the substrates is not transparent to the electromagnetic radiation used for measuring the substrates, in order to enable the detection and / or determination of the position and location of the alignment marks from the outer substrate surfaces facing away from the substrate surfaces to be bonded, alignment marks are detected in the prior art using image acquisition means between the substrates before the substrates are brought close together.

[0007] This had several disadvantages. In particular, particles could be deposited from the camera onto the substrate surfaces. Furthermore, a large distance had to be maintained between the substrates to position the camera for scanning. This more complex alignment process and the correspondingly longer travel distances resulted in greater alignment errors.

[0008] Especially when bringing the substrates to be bonded closer together and setting a specific distance between the bonding surfaces, optimal alignment is essential to obtain the best possible bonding result.

[0009] Another problem with the current state of the art is that increasing alignment accuracy requirements can no longer be met using simple methods. Methods in which substrates are measured relative to reference points and, for example, blindly aligned after an initial approach to contact, fail to meet these new alignment accuracy requirements.

[0010] For example, patent US6214692B1 is based on the comparison and position correction of two images of alignment markers. The position of the alignment markers on the two face-to-face substrates is individually captured using a camera system. From a calculated relative position of the alignment markers, a positioning stage (substrate holder and stage) is controlled to correct the misalignment. Patent US10692747B2 is based on the comparison and position correction of a total of three images of flat alignment markers. The position of the alignment markers on the two face-to-face substrates is individually captured using a camera system.A third detection unit detects a third alignment mark, which establishes a correlation between an alignment mark of the substrate and the back of the substrate holder or the back of the substrate, thus enabling a more precise alignment of two substrates.

[0011] Further devices and methods are known from publications EP3734650A1 and CN111354714A.

[0012] Therefore, visual inspection of two substrates when aligned face-to-face is not possible, or only possible if at least one of the substrates is at least partially transparent. Precise alignment of the surfaces when aligned face-to-face is thus only possible with difficulty and to a limited extent.

[0013] It has proven particularly disadvantageous that refocusing is necessary when capturing alignment marks. Refocusing is inherently necessary during adjustment movements, especially of the optics used to capture the alignment marks. These adjustment movements involve superimposed, parasitic movements in addition to the required movement, causing deviations from the ideal movement of the respective optics. Therefore, any movement results in a shift of the focal point. For example, the focal point is shifted in the xy plane, which is perpendicular to the optics or an optical axis of the optics. This shift of the focal point reduces the accuracy of the alignment mark measurement, thus decreasing the alignment accuracy.

[0014] It is therefore an object of the present invention to disclose a method and a device for aligning a substrate which eliminate at least some, and in particular completely eliminate, the disadvantages listed in the prior art. It is a particular object of the invention to disclose an improved method and an improved device for aligning a substrate. It is a particular object of the present invention to disclose a method and a device for aligning a substrate which do not require refocusing of a detection unit during alignment. It is further an object of the present invention to disclose a method and a device for aligning a substrate which can be carried out with particular reliability, accuracy, and freedom from contamination, or which aligns with particular reliability, accuracy, and freedom from contamination.

[0015] The present problem is solved by the features of the dependent claims. Advantageous embodiments of the invention are specified in the sub-claims. The scope of the invention also includes all combinations of at least two features specified in the description, the claims, and / or the drawings. Where specified value ranges are given, values ​​lying within the stated limits are also considered disclosed limits and may be claimed in any combination.

[0016] Accordingly, the invention relates to a method for aligning a substrate comprising at least the following steps: i) Provision of a substrate holder with a substrate holder surface designed to receive the substrate and an alignment marking field fixed to the substrate holder, ii) alignment of the substrate, characterized in that the substrate is aligned using alignment marks arranged one above the other in the alignment marking field, wherein the alignment of the substrate in step ii) comprises the following steps, in particular with the following sequence: a) detection of a first alignment mark of a first level of the alignment marking field by a detection unit, b) fixing a focus position of the detection unit after detection in step a), c) movement of the substrate holder perpendicular to the first level of the alignment marking field, d) detection of a second alignment mark of a second level of the alignment marking field by the detection unit,wherein the first plane and the second plane are arranged parallel to each other, and wherein the first plane and the second plane are spaced apart from each other.

[0017] The substrate, or a substrate stack, is aligned using the alignment marks arranged one above the other. The alignment mark field is fixed in position relative to the substrate holder or the substrate holder surface. In particular, the exact position of the alignment mark field and the respective positions of the alignment marks within the alignment mark field relative to the substrate holder are known. The alignment marks, or at least two alignment marks within the alignment mark field, are arranged one above the other.

[0018] The arrangement of at least two alignment marks in the alignment mark field, one above the other, means that they are arranged in different planes. The alignment mark field thus has a specific height (z-direction) relative to the substrate holder surface. The at least two alignment marks are therefore arranged in different z-planes.

[0019] The alignment markers preferably do not obscure each other in the z-direction, so that the at least two alignment markers of the alignment marker field can be viewed unobstructed from any viewing direction. In other words, the alignment markers of an alignment marker field are preferably offset from each other and arranged one above the other in parallel planes, so that any alignment marker is perceptible in any plane of the alignment marker field.

[0020] Furthermore, it is conceivable that the at least two alignment marks arranged one above the other in the alignment marking field are partially or completely overlapping in the z-direction. In other words, the at least two alignment marks arranged one above the other can be at least partially aligned with each other in the z-direction. In this case, the different z-planes or layers of the alignment marking field are transparent, particularly for different wavelengths, so that any further alignment mark in any other plane of the alignment marking field can be detected. In this process, the planes / layers upstream in the viewing direction and / or the upstream alignment marks are penetrated for viewing, so that the at least partially aligned alignment mark of a subsequent plane can be detected.

[0021] By detecting one alignment mark and subsequently detecting another alignment mark positioned above it, the known positions of the respective alignment marks can be compared. Since the properties, structures, and positions of the alignment mark field are preferably known, the distance between the alignment marks can be determined. Based on this distance, for example, alignment can be achieved by relative movement of the substrate holder using the superimposed alignment marks, without requiring refocusing of the detection means. In this way, a substrate can be aligned with particular precision in at least one direction, as the known distance between the superimposed alignment marks can be detected and thus adjusted.

[0022] Furthermore, precise alignment in at least one direction allows for easy and accurate positioning of the bond gap. The substrate holder can be aligned directly by visual inspection, depending on the alignment marker field. Additionally, only one sensing device is required for alignment, thus reducing the potential for errors. This is particularly advantageous when bonding opaque substrates in a face-to-face process, enabling precise positioning of the substrate holder and, consequently, the substrate itself. The superimposed alignment markers and the resulting height information allow for alignment without refocusing the sensing device. Therefore, the substrate to be aligned can be moved with exceptional precision and visual control over a specific distance.

[0023] The method for aligning a substrate provides that the alignment of the substrate in step ii) comprises at least the following steps, in particular with the following sequence: a) Detection of a first alignment mark of a first level of the alignment marking field by a detection unit, b) Fixing a focus position of the detection unit after detection in step a), c) Movement of the substrate holder perpendicular to the first level of the alignment marking field, d) Detection of a second alignment mark of a second level of the alignment marking field by the detection unit, wherein the first plane and the second plane are arranged parallel to each other, and wherein the first plane and the second plane are spaced apart from each other.

[0024] The alignment marker field preferably contains several alignment markers arranged side-by-side in the respective layer. This ensures that at least one first alignment marker or at least one second alignment marker of the corresponding layer is detected. Furthermore, the alignment marker field between the layers is preferably transparent to the detection unit, allowing the superimposed alignment markers to be detected. It is also conceivable that the alignment markers of the first layer are offset from the alignment markers of the second layer, and that the alignment marker field has different levels of detail. In addition, the detection unit can detect further alignment markers of the first layer besides the respective first alignment marker, as long as these are located within the focus area. The same applies to the second layer.The detection unit is designed in such a way that several alignment marks, in particular alignment marks arranged next to each other of the respective level, can be detected.

[0025] When the first alignment mark on the first level of the alignment marking field is detected, the detection unit identifies the respective alignment mark. The detection unit preferably has focusing means, preferably a lens, which focuses or sharpens the first alignment mark during detection. The detection unit or lens assumes a focus position in which it can detect a specific focus area. The focus area of ​​a specific focus position of the detection unit or lens is thus focused, and alignment marks arranged within this focus area can be detected. Preferably, only alignment marks of the respective level can be detected or identified during detection, since a focus area for the detection unit comprises exactly one level.The distance between the first plane and the second plane is therefore preferably greater than the depth of the focus area.

[0026] Following the detection of the first alignment mark on the first level, the focus position of the detection unit is fixed. This defines the focus area, ensuring that the detection unit can subsequently only detect alignment marks within this defined area. The substrate is then moved perpendicular to the first level of the alignment mark field, thus aligning it. The substrate holder is moved at least until the detection unit can detect the second alignment mark on the second level of the alignment mark field. In this way, the substrate is advantageously moved by the distance required for focusing. For example, a bonding distance between the substrate and another substrate to be bonded can be set in this manner.Alignment errors due to refocusing of the detection unit can thus be advantageously prevented.

[0027] In a preferred embodiment of the method for aligning a substrate, it is provided that in step a) additional alignment marks on the substrate holder or on the substrate are detected by at least one additional detection unit.

[0028] The additional alignment markers can advantageously be correlated to a position of the first alignment marker or placed in spatial relation to it. These additional alignment markers are, in particular, a planar alignment marker field without overlapping alignment markers. In other words, these additional alignment markers are not arranged in planes one above the other.

[0029] The additional alignment markings also allow for the advantageous alignment of the substrate holder relative to the alignment marks of the alignment marking field. Furthermore, the sensing unit can also align the substrate holder, or the substrate arranged on the substrate holder, relative to the additional alignment markings. The at least one additional sensing unit allows, in particular, the determination of the position of an additional substrate to be bonded to the substrate relative to the alignment marking field. The additional alignment marks and the additional sensing unit enable even more precise alignment.

[0030] In a preferred embodiment of the method for aligning a substrate, it is provided that during the movement of the substrate holder in step iv) the detection unit continuously measures the alignment marking field in the focus position.

[0031] If further alignment marks are arranged in additional levels between the first and second levels, these can be measured by the detection unit as the substrate holder is moved, thus enabling particularly precise and controlled movement of the substrate holder. Furthermore, the alignment can be made even more accurate by detecting multiple alignment marks whose positions within the alignment marking field are known.

[0032] In a preferred embodiment of the method for aligning a substrate, it is provided that after fixing the focus position in step b), the detection unit is held in a fixed position.

[0033] The scanning unit is not only fixed at a specific distance from the alignment marker, but also in a horizontal position. This fixed position relative to the alignment marker also ensures a fixed position relative to the substrate holder and, consequently, to the substrate mounted on the holder. This advantageously ensures that, in addition to fixing the focus position of the scanning unit or lens, the position of the scanning unit itself is also fixed. This allows for even more precise substrate alignment and prevents alignment errors caused by inaccurate movement of the scanning unit.

[0034] In a preferred embodiment of the method for aligning a substrate, it is provided that when the first alignment mark is detected in step a) and / or when the second alignment mark is detected in step d), the detection unit additionally provides information about the position of the respective alignment mark within the alignment mark field.

[0035] The alignment markers preferably contain information regarding their respective position within the alignment marker field. In addition to their position along the alignment marker field (xy-position), the respective height or distance between the levels is also known. Thus, when the first alignment marker is detected, it can advantageously be determined in which level it is located. Particularly when an alignment marker field has more than two levels with different distances between them, the alignment can be controlled or regulated more easily, since the respective height information regarding the alignment marker is recorded. For example, with continuous detection during movement or when the first alignment marker is detected, it is advantageous to determine which level or stage is being detected in the focus area.Furthermore, if a position between two levels or steps is detected, it is advantageous to approach a level or step located above or below it. Additionally, the position in the xy-axis can be advantageously detected and monitored.

[0036] The aforementioned advantages and features relating to the alignment method shall also be disclosed in connection with the following device.

[0037] Furthermore, the invention relates to a device for aligning a substrate, at least comprising: A) a substrate holder with a substrate holder surface designed to receive the substrate, and B) an alignment marking field with alignment marks, fixed to the substrate holder and / or the substrate, characterized in that the substrate can be aligned using alignment marks arranged one above the other, the device further comprising: C) a detection unit for detecting the alignment marks of the alignment marking field and D) a movement device for moving the substrate holder, wherein the alignment marks of the alignment marking field are arranged in a first plane and a second plane, and wherein the first plane and the second plane are arranged parallel to each other, and wherein the first plane and the second plane are spaced apart from each other, and wherein a first alignment mark of the alignment marks of the first plane can be detected in a focus position of the detection unit, and wherein the focus position of the detection unit can be fixed, and wherein a second alignment mark of the alignment marks of the second plane can be detected by the detection unit in the focus position.and wherein the substrate holder is movable perpendicular to the first level by the movement device.

[0038] The alignment marks arranged one above the other in the alignment marking field have a known distance between them in one direction of the alignment marking field. In this way, the alignment of the substrate holder or the substrate arranged on the substrate holder surface can advantageously be carried out solely on the basis of the alignment marks by one, and in particular exactly one, detection means.

[0039] The device for aligning a substrate is provided to further include: C) a detection unit for detecting the alignment marks of the alignment marking field and D) a movement device for moving the substrate holder, wherein the alignment marks of the alignment marking field are arranged in a first plane and a second plane, and wherein the first plane and the second plane are arranged parallel to each other, and wherein the first plane and the second plane are spaced apart from each other, and wherein a first alignment mark of the alignment marks of the first plane can be detected in a focus position of the detection unit, and wherein the focus position of the detection unit can be fixed, and wherein a second alignment mark of the alignment marks of the second plane can be detected in the focus position by the detection unit, and wherein the substrate holder can be moved perpendicular to the first plane by the movement device.

[0040] The device is designed such that the focus position of the detection unit can be fixed immediately after the first alignment mark of the first level of the alignment marking field has been detected. The fixed focus position of the detection unit defines the sharply imaged focus area. In this way, the distance between the first level and the second level can advantageously be adjusted by the movement device, so that the substrate holder or the substrate can be moved precisely in one direction by the specified distance using the alignment marking field. The detection unit is also preferably held in a fixed position, so that the distance between the levels can be adjusted simply by detecting the alignment marks and moving the substrate holder.When the alignment device is used to set a bond gap between two substrates to be bonded, the distance between the first and second planes is preferably the desired distance before initiating a bonding process. In other words, the bond gap corresponds to a bond gap. The alignment with the device is advantageously directly controllable by detecting the second alignment mark of the second plane. Direct visual inspection by a single detection unit can thus advantageously verify correct alignment.

[0041] In a preferred embodiment of the device for aligning a substrate, it is provided that the alignment marks of the first level and the alignment marks of the second level are arranged in the alignment marking field in a line one above the other, in particular congruently.

[0042] Between the planes, the alignment marker field is preferably transparent to the detection unit. The aligned arrangement of the alignment markers one above the other advantageously allows the detection of the second alignment mark to verify whether the movement of the substrate holder by the motion device was performed exactly perpendicular to the first plane. In this case, the detection unit has a focal point in its focus position, to which the respective position of the second alignment mark is comparable with respect to the first alignment mark. Furthermore, it is conceivable that the alignment mark of the first plane is rotated or mirrored relative to the corresponding aligned alignment mark of the second plane. The alignment mark preferably has a non-point-symmetrical shape or outer contour, so that at least parts of this alignment mark can be detected by rotation or mirroring.

[0043] In a preferred embodiment of the device for aligning a substrate, the alignment marks of the first level are arranged in a step-like offset to the alignment marks of the second level.

[0044] In this embodiment, the alignment marking field itself can be stepped, with the respective levels containing the alignment markings forming a surface of the alignment marking field. In this case, the detection unit is preferably designed such that several steps of the alignment marking field can be detected without relative movement. For example, the focus area of ​​the detection means is wide enough to detect multiple steps. It is also conceivable that the detection unit has several adjacent means, each for detecting a step. For example, the detection unit can have several adjacent optics with corresponding lenses. In this case, the focus position of all detection means of the detection unit is fixed after the first alignment mark has been detected.The alignment marking field is preferably circular, and the transitions between the planes are circular. In other words, the planes containing the alignment markings are arranged in a ring, with the plane located at the center being circular.

[0045] In this way, the detection unit can advantageously detect the surface or an alignment mark of the alignment mark field located near the surface.

[0046] In a preferred embodiment of the device for aligning a substrate, the alignment marking field is arranged on the back side of the substrate holder facing away from the substrate holder surface.

[0047] The alignment marker field can be located on the back or embedded in the substrate holder, for example. Alternatively, the alignment marker field can also be formed by the substrate holder itself. Advantageously, the detection unit can be positioned on the back side, facing away from the substrate holder surface.

[0048] In a preferred embodiment of the device for aligning a substrate, it is provided that a center point of the alignment marking field on the back of the substrate holder is at least partially aligned with a center point of the substrate holder surface.

[0049] The central placement of the alignment marker field allows for advantageously precise alignment of the substrate holder. In this embodiment, linear error components or rotations of the substrate holder, and thus of the substrate holder surface, relative to the detection unit can also be advantageously detected. In particular, wedge errors with respect to the lens of the optics can also be detected and corrected. The alignment errors can be broken down into their component parts. This allows for the characterization of linear, rotational, magnification, and higher-order errors.

[0050] In a preferred embodiment of the device for aligning a substrate, the alignment marking field is arranged on a side of the substrate facing the substrate holder surface.

[0051] In this embodiment, the substrate holder has a through-opening in the area of ​​the alignment marking field. Furthermore, it is conceivable that the substrate holder is transparent to the detection unit, so that the alignment marking field arranged on the substrate can be detected, particularly from the back of the substrate holder. In this way, visual inspection can advantageously be carried out directly on the substrate to be aligned. The substrate, and thus the alignment marking field, is held stationary relative to the substrate holder. For example, alignment errors due to an uneven substrate holder surface are avoided. Furthermore, the alignment marking field can advantageously be individually adapted to the substrate. In addition, the alignment marking field can be formed or mapped by the substrate itself.

[0052] In a preferred embodiment of the device for aligning a substrate, it is provided that the alignment marking field has at least one further plane with the alignment marks, wherein the at least one further plane is arranged parallel to the first plane and the second plane.

[0053] Preferably, the alignment marker field has at least three levels with alignment markers. The alignment markers provide information about the level on which they are located. Furthermore, this allows the device to move to several specific distances. The distances between the levels can be equal. Preferably, however, the levels are arranged at different distances from each other. This allows for flexible positioning to multiple distances. Particularly when using the device for bonding substrates, this advantageously allows for setting different bonding distances or aligning the substrate with particular precision relative to another substrate.

[0054] In a preferred embodiment of the device for aligning a substrate, it is provided that the device has at least one further alignment marking field and at least one further detection unit for detecting the at least one further alignment marking field, wherein the at least one further alignment marking field is arranged in a fixed position relative to the substrate holder.

[0055] The additional alignment marker field allows for even more precise alignment, as detection occurs at multiple points. For example, this makes it particularly easy to detect and correct displacements and / or rotational errors. The alignment marker field and the at least one additional alignment marker field are preferably arranged offset along the substrate holder. The device preferably comprises a total of three alignment marker fields and three detection units, each distributed around a center point on the substrate holder surface, and in particular arranged with uniform radial offsets from one another.

[0056] Preferably, the respective planes of the alignment marker field and of at least one further alignment marker field have the same distances to each other. In this way, alignment is particularly precise, since the distance can be verified at at least two points, preferably spatially offset points.

[0057] A key aspect of the invention is that, prior to substrate alignment, at least two alignment marks are detected on at least two different planes or heights of the alignment marking field. The alignment marking field is preferably attached to one of the substrates to be aligned or to the substrate holder. The alignment marks each provide 3D position information for aligning the substrates. Preferably, the alignment marking field is not located on the contact surfaces of the substrates. Preferably, the alignment marking field is located on a side of the substrate or substrate holder facing away from or parallel to the contact surface.

[0058] The alignment of the substrates relative to each other is achieved indirectly, in particular, by means of alignment marks located on the contact surfaces of the substrates. The alignment marks on opposite sides of the opposing substrates are, in particular, complementary to each other. Alignment marks can be any mutually alignable objects such as crosses, circles, squares, propeller-like shapes, or grid structures, especially phase gratings for the spatial frequency domain.

[0059] In a particularly advantageous embodiment of the device, alignment markings can at least partially include QR codes, which in particular describe an absolute, machine-readable position encoding (x, y, z position) of the respective alignment mark.

[0060] In a further particularly advantageous embodiment, alignment markings can include at least partially alphanumeric characters, which in particular describe an absolute, machine-readable position encoding (x, y, z position) of the respective alignment mark.

[0061] The alignment marks and / or alignment marking fields are preferably detected using electromagnetic radiation of specific wavelengths and / or wavelength ranges. These include, for example, infrared radiation, visible light, or ultraviolet radiation. The use of shorter wavelength radiation, such as EUV (extreme ultraviolet radiation) or X-rays, is also possible.

[0062] A particularly important aspect of the present invention is that the alignment and adjustment of the bond distance is achieved, in particular exclusively, by detecting the superimposed alignment marks of the alignment marking field. "Exclusively" means that the additional alignment marks are not detected or detectable during the alignment process. Therefore, the bond distance can be precisely adjusted using the superimposed alignment marks, under visual control.

[0063] The alignment marker field preferably contains uniquely assigned and / or assignable alignment markers or alignment marks in at least two different planes. The alignment marker field has steps or at least partially transparent layers, so that the alignment marks are arranged one above the other. Thus, in addition to the usual xy position, height information is also indirectly provided. The alignment marks can also directly provide 3D position information. The height information is provided by the arrangement in different planes. Since the distances between the planes are known, it is sufficient to provide information on which plane the detected alignment mark is located within the alignment marker field.

[0064] The alignment marker field consists of, or rather comprises, position-coded and height-coded alignment markers, which provide unambiguous position and height information for the substrates and / or the substrate holder for alignment without refocusing the third detection unit. The alignment markers of the alignment marker field will be understood as height-coded alignment markers in the following, even without explicitly mentioning the height coding and / or 3D position information.

[0065] Preferably, the size or dimensions of the alignment marker field are adapted to the respective field of view of the optical detection means, so that at least two steps or alignment marker planes can be viewed. The number of steps and the overall height of the alignment marker field are also matched to the distance to be set. For example, if a bonding distance of 500 micrometers is to be set, preferably 550 micrometers of height-coded position information are displayed in the alignment marker field to allow the distance to be reached without refocusing.

[0066] The acquisition is preferably carried out using suitable imaging optical systems, so that the imaging depth can be selected to be less than the step height or layer thickness of the alignment marker field. The imaging depth (depth of focus, DOF) is the area in the image space of an imaging optical system in which a sufficiently sharp image of a focused object, in particular an alignment marker, is produced. Conversely, this means that the image plane (an image acquisition device, sensor) can be moved within the imaging depth range without the image of an object becoming noticeably blurred.

[0067] If the detection of an alignment mark of the alignment marking field is carried out with a small imaging depth, which is smaller than the step height, preferably smaller than half the step height, particularly preferably smaller than 0.1 step height, the position of the alignment marking field can be clearly determined, especially in the z-direction.

[0068] The imaging depth of the detection means is less than 50 micrometers, preferably less than 20 micrometers, particularly preferably less than 10 micrometers, most preferably less than 5 micrometers, and in the optimal case less than 4 micrometers.

[0069] However, if the image depth is sufficient to sharply image at least two step heights, the positioning uncertainty of the device is increased, because then a clear assignment of a z-height to a step cannot be made.

[0070] In a preferred embodiment of the device, an image capture means or a capture means of the capture unit can be reproducibly shifted by 0.2 step heights without refocusing the image. This can be used to determine which alignment mark of the alignment mark field should be used for positioning when the image-side focus plane lies directly at the height of two adjacent steps and both steps appear equally sharp. A decision regarding the alignment marks to be used can be made with this small shift of the image capture means (also as a computer-implemented, independent, inventive method).

[0071] Due to physical limitations, only one level or step is sharply imaged at a time when the alignment marker field is captured. Therefore, preferably only one level or step is within the focus area of ​​the capture unit. Since the alignment markers of the alignment marker field are position- and location-coded, position information, particularly of the substrate holder, can be determined from a sharply captured alignment marker of a level within a spatial coordinate system.

[0072] According to an advantageous embodiment of the invention, the first substrate and the second substrate are arranged between the first substrate holder and the second substrate holder with a distance A between the first contact surface and the second contact surface in a Z-direction. The distance A is particularly less than 500 micrometers, more preferably less than 100 micrometers, more preferably less than 50 micrometers, and most preferably less than 10 micrometers.

[0073] The method for aligning a substrate is suitable for aligning at least two substrates relative to each other using any electromagnetic radiation, in particular UV light, preferably infrared light, and most preferably visible light. The substrate to be aligned, or the substrate arranged on the substrate holder surface, can also be moved relative to other components by the distance between the planes and thus aligned.

[0074] The method enables the observation and / or acquisition of the first and second alignment marks, supplemented by at least one additional optical path for the precise reconstruction of the substrate and substrate holder position. This path is not located between the substrates during alignment, but rather allows for external acquisition, particularly by observing and / or acquiring at least one alignment mark field. The alignment mark field preferably provides the height information for setting a desired bond distance between the first and second levels.

[0075] In a particularly preferred method, a substrate can be opaque to the electromagnetic radiation used for detecting the alignment marks of a first and second substrate. The alignment marks are detected through the back of the substrate, which is transparent to the electromagnetic radiation used for this purpose.

[0076] The alignment procedure increases the alignment accuracy, in particular by means of additional XYZ position and / or orientation information, which is captured with additional alignment marker fields and corresponding additional detection units and used to control and / or regulate the alignment.

[0077] For this purpose, the alignment device preferably includes a control unit, in particular a software-based one, by means of which the steps described here are carried out and components are controlled. Closed control loops and control systems are to be understood as subsumed under the control unit.

[0078] The X and Y directions or X and Y positions refer to directions or positions within an XY coordinate system or within any Z-plane of the XY coordinate system, respectively. The Z direction is orthogonal to the XY direction. The X and Y directions correspond, in particular, to lateral directions, preferably along the planes of the alignment marking field. The Z direction is preferably the direction in which the substrate holder is moved when the focus position of the detection unit is fixed in the XY plane.

[0079] Position characteristics are calculated or recorded from the position and / or location values ​​of the alignment markings of the substrates as well as alignment markings on the substrate holder, in particular by recording and evaluating the alignment marking field.

[0080] The alignment marking field is preferably located in close proximity to the alignment markings of the substrates. It is particularly preferred that at least one alignment marking of the substrates and the alignment marking field are arranged on opposite sides of the substrate. Alternatively, the alignment marking field can be located on the back of the substrate holder and opposite the additional alignment markings. If the additional alignment markings and the alignment markings of the alignment marking field are arranged on opposite sides of the substrate holder surface, correlating their positions is particularly easy.

[0081] In a particularly preferred embodiment, at least one alignment marking field is located preferably in the z-direction aligned with the additional alignment markings of the substrates, preferably on a back side of the substrate holder.

[0082] In a further preferred embodiment of the device, at least one alignment marking field is located preferably in the z-direction aligned with the center of the substrate or with the center of the substrate holder surface, in particular on a back side of the substrate holder.

[0083] In a particularly preferred embodiment of the device, two alignment marking fields are preferably aligned in the z-direction with the additional alignment markings of the substrates, in particular on a rear side of the substrate holder.

[0084] In a further preferred embodiment of the device, at least one alignment marking field is located on the substrate side of the substrate holder or on the side of the substrate holder surface, near the substrate, for optical detection of the accessible position.

[0085] A further embodiment of the device includes at least two alignment marking fields on the substrate side of the substrate holder near the substrate edge, for optical detection of the accessible position. This advantageously allows for leveling of the substrate holder.

[0086] The alignment method and the alignment device thus include, in particular, at least one additional detection unit with a corresponding measuring and / or control system and at least one additional alignment marking field, wherein the alignment accuracy is further increased by additional measured values ​​and correlations with at least one of the measured values ​​of the additional detection units, in particular without refocusing, preferably without image-side refocusing.

[0087] By correlating at least one of the measured additional alignment marks, particularly on the contact surfaces of a first substrate and / or second substrate, with at least one alignment mark of the alignment mark field, which is also freely accessible and visible during substrate alignment, the direct observability of an alignment mark and thus real-time measurement and control during alignment are enabled. This increases the alignment accuracy of the substrates.

[0088] Another advantage of the alignment marker field is the acquisition of additional height information, allowing the lower substrate holder with the lower substrate to be positioned more precisely relative to the upper substrate on an upper substrate holder. This eliminates, in particular, the resulting positional inaccuracies caused by the focusing movement of the detection unit.

[0089] The increased accuracy of the vertical positioning of the distance between the upper and lower substrates during bonding allows for a low-tolerance preload on at least one of the substrates, reducing substrate distortion during bonding. This minimizes, and preferably eliminates, run-out of the substrates after bonding. Therefore, the alignment method and the alignment device are ideally suited for alignment during a bonding process.

[0090] In a further embodiment of the device, at least one additional alignment marking field is positioned on the substrate side of a substrate holder near the peripheral edge of the substrate in a position that is permanently accessible to another detection unit. Preferably, one surface of the alignment marking field is located in the same plane as the surface of the substrate attached to the substrate holder that is to be bonded.

[0091] In particular, a unique correlation is established between the additionally added 3D position feature on the substrate holder and the position features on the substrates, which is preferably not changed during alignment and is maintained until the substrates are bonded to each other.

[0092] The addition of 3D position features on the substrate holder, which are clearly correlated with the position features on the substrate, allows direct observation of the alignment marks on the substrate to be replaced by direct observation of the alignment marks on the substrate holder. This has the advantage that the observable part of the substrate holder can practically always be positioned within the field of view or detection range of the detection unit. The 3D position information enables the alignment of the substrates relative to each other to be carried out with increased accuracy.

[0093] Preferably, the detection area of ​​a detection unit is smaller than 3 mm x 3 mm, more preferably smaller than 2 mm x 2 mm, and particularly preferably smaller than 1 mm x 1 mm.

[0094] Active feedback of data for positioning and position correction increases accuracy compared to state-of-the-art controlled positioning, since closed control loops provide a way to monitor the current position.

[0095] One aspect of the alignment method and device is the increased accuracy of aligning two substrates. The alignment method allows for real-time observation of the alignment or movement, particularly from outside the bonding interface. The integrated 3D position information, combined with the provided height information, enables even more precise alignment than with previously known methods. In this process, the substrates are arranged with minimal spacing between them, and preferably no device component, particularly no detection unit, is located between them.

[0096] A correlation is established between the additional alignment markings of a first substrate and / or a second substrate on the respective contact surfaces of the substrates and at least one alignment mark of the alignment marking field. The alignment mark of the alignment marking field can be detected by the detection unit during alignment, particularly directly.

[0097] The direct detectability or observability of at least one alignment mark in the alignment marking field enables real-time measurement of the 3D position of the substrate holder. This increases the alignment accuracy because, with the

[0098] Capturing the first and second alignment marks and the height information they provide eliminates positioning uncertainties, thereby reducing error propagation. This measure improves alignment accuracy by reducing the number of necessary feed movements and ensuring controlled height adjustment during bonding.

[0099] A first embodiment of the alignment device is used in a bonding fixture and includes an upper substrate holder. An upper substrate can be attached to the upper substrate holder. The upper substrate holder is sufficiently transparent, at least locally, so that the alignment markings of the upper substrate are visible with sufficient resolution, contrast, and intensity on the contact surface of the upper substrate, which is the surface facing away from the bearing surface of the upper substrate.

[0100] For this purpose, the upper substrate is sufficiently transparent for the radiation used to detect an initial additional alignment mark of the upper substrate.

[0101] Sufficiently transparent substrate means that the transmittance of the substrate for the electromagnetic radiation used to detect the additional alignment markings is sufficient to detect the additional alignment markings with sufficient resolution, contrast, and intensity.

[0102] A locally sufficiently transparent substrate holder is defined as one whose transmittance is sufficiently high for the electromagnetic radiation used to detect the alignment mark. Alternatively, viewing windows and / or through-holes for observing the substrate and / or substrate pair can be incorporated into the substrate holder.

[0103] During the detection of the additional alignment mark on the substrates, the upper substrate and the upper substrate holder are moved out of focus of the additional detection unit.

[0104] The additional alignment mark on the lower substrate, or on the lower substrate holder, can be detected through the upper substrate holder and through the upper substrate.

[0105] During the acquisition of the additional alignment mark, at least one alignment mark of the alignment mark field is correlated, particularly on the back of the substrate holder, to determine 3D position information of the substrate holder, especially the lower substrate holder.

[0106] The detection unit for detecting the alignment marking field is in particular part of an optical system for detecting the alignment marking field and, according to an advantageous embodiment, includes beam shaping and / or deflection elements such as mirrors, lenses, prisms, radiation sources, in particular for Köhler illumination, as well as image detection means such as cameras (CMOS sensors, or CCD, or area or line or point detection means such as a phototransistor) and movement means for focusing, as well as evaluation means for controlling the optical system.

[0107] In another embodiment of the device, the optical system can be used in combination with a rotation system for substrate positioning according to the principle of inversion adjustment (see Hansen, Friedrich: Adjustment, VEB Verlag Technik, 1964, Section 6.2.4, Inversion Method). Accordingly, in inversion adjustment, at least one measurement is performed in a defined position of the respective substrate and at least one measurement in an inverted position rotated 180 degrees and oriented in the opposite direction. The measurement result obtained in this way is, in particular, corrected for eccentricity errors.

[0108] A further development of the alignment device includes two, in particular identical, structurally identical optical systems with additional detection units aligned to each other and fixable relative to each other for detecting additional alignment marks.

[0109] In a further embodiment of the device for alignment, at least one substrate holder is used which is at least partially, preferably over 95%, transparent at defined points for the simultaneous observation of both substrate sides.

[0110] In a further embodiment of the device, at least one substrate holder is used which has openings and / or penetrations and / or viewing windows at defined locations for the simultaneous observation of both substrate sides.

[0111] Furthermore, a device can include a system for producing pre-bonds. For this purpose, pressure pins and / or adjustable nozzles can be used to initiate the fusion bond for joining substrates. In particular, the adjustable nozzles can be height-adjustable, allowing the relative position to the back of the substrate to be changed and the nozzle flow rate to be controlled. Their alignment can advantageously be achieved using the superimposed alignment marks.

[0112] Furthermore, a device preferably includes motion devices with drive systems, guide systems, holding devices and measuring systems to move, position and precisely align at least the detection unit and the substrate holder and thus the substrate to be aligned.

[0113] The motion devices can generate any movement as a result of individual movements, so the motion devices may preferably include fast, coarse positioning devices that do not meet the accuracy requirements, as well as precise fine positioning devices.

[0114] A positioning device is understood to be a coarse positioning device if the approach and / or repeatability 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 distance or rotation range, or, in the case of recirculating rotary drives, a full rotation of 360 degrees.

[0115] For example, a coarse positioning device with a travel distance of over 600 mm (twice the substrate diameter) results in a approach accuracy of 600 mm * 0.01%, i.e., more than 60 micrometers as residual uncertainty.

[0116] In other embodiments of the coarse positioning system, the residual uncertainty of the approach or repeatability accuracy is less than 100 micrometers, preferably less than 50 micrometers, and particularly preferably less than 10 micrometers. Thermal disturbances are also taken into account.

[0117] A coarse positioning device only fulfills the positioning task with sufficient accuracy if the deviation between the actual position achieved and the target position lies within the travel range of an associated fine positioning device.

[0118] An alternative coarse positioning device only fulfills the positioning task with sufficient accuracy if the deviation between the actual achieved position and the target position is within half the travel range of an associated fine positioning device.

[0119] A positioning device is understood to be a fine positioning device if the residual uncertainty of the approach and / or repeatability accuracy from the target value does not exceed 500 ppb, preferably less than 100 ppb, more preferably 1 ppb, with respect to the entire travel distance or rotation range.

[0120] Preferably, a fine positioning device will compensate for an absolute positioning error of less than 5 micrometers, preferably less than 1 micrometer.

[0121] The substrates can be aligned relative to each other in all six degrees of freedom: three translations along the x, y, and z coordinate directions, and three rotations around these coordinate directions. These movements can be performed in any direction and orientation. The alignment of the substrates includes, in particular, passive or active wedge error compensation, preferably as disclosed in EP2612109B1.

[0122] Robots used for substrate handling are classified as motion devices. The restraints can be integrated into the motion devices as components or integrated into their function.

[0123] Furthermore, the device for alignment preferably includes control systems and / or evaluation systems, in particular computers, to carry out the described steps, in particular movement sequences, to make corrections, to analyze and store operating states of the device.

[0124] Processes are preferably created as recipes and executed in machine-readable form. Recipes are optimized sets of parameter values ​​that are functionally or procedurally related. The use of recipes ensures the reproducibility of production processes.

[0125] Furthermore, an alignment device according to an advantageous embodiment includes supply and auxiliary and / or supplementary systems (compressed air, vacuum, electrical energy, fluids such as hydraulics, coolants, heating media, means and / or devices for temperature stabilization, electromagnetic shielding).

[0126] Furthermore, the alignment device may include frames, covers, vibration-suppressing or damping or vibration-absorbing active or passive subsystems.

[0127] Furthermore, an alignment device preferably includes at least one measuring system, preferably with measuring units for each axis of movement, which can be designed in particular as displacement measuring systems and / or as angle measuring systems. The measuring system preferably comprises at least one detection unit or an additional detection unit.

[0128] Both tactile (i.e., probing) and non-tactile measurement methods can be used. The measurement standard, the unit of measurement, can be a physical object, in particular a scale, or it can be implicitly present in the measurement method, such as the wavelength of the radiation used.

[0129] To achieve the required alignment accuracy, at least one of the following measuring systems can be selected and used. Measuring systems implement measurement procedures. In particular, the following can be used: Inductive and / or capacitive and / or resistive methods and / or comparison methods, in particular optical image recognition methods, detection of position markers and / or QR codes and / or incremental or absolute methods (with in particular glass normals as scales, or interferometers, in particular laser interferometers, or with magnetic normals) and / or time-of-flight measurements (Doppler methods, time-of-flight methods) or other time-of-flight methods and / or triangulation methods, in particular laser triangulation, autofocus methods and / or intensity measurement methods such as fiber optic rangefinders, may be used.

[0130] Furthermore, a particularly preferred embodiment of the alignment device includes at least one measuring system which detects the XYZ position and / or orientation and / or angular position of at least one of the substrates and / or one of the substrate holders with respect to a defined reference, in particular the frame. The measuring system comprises at least one detection unit.

[0131] The measuring system, or its acquisition unit, determines 3D positions of the substrate, or preferably the substrate holder, without refocusing, so that height information can be derived from the measurement in addition to the planar position data. For this purpose, at least one alignment marking field consisting of steps and / or layers with unique position markers is recorded.

[0132] A frame can be understood as a part consisting in particular of natural hard rock or mineral casting or spheroidal graphite cast iron or hydraulically bound concrete, which is in particular vibration-damped and / or vibration-isolated and / or mounted with vibration damping.

[0133] By attaching the detection units to the substrate holder and the alignment marker to, for example, the frame, the concept can also be advantageously reversed. In this case, the detection unit moves with the substrate holder, and the alignment marker is fixed to the frame.

[0134] To enable acquisition, evaluation, and control at any given time, particularly continuously, the alignment markers of the alignment marker field are distributed over a larger area of ​​the respective plane than the field of view of an image acquisition system of the acquisition units, according to an advantageous embodiment. This ensures that the control unit (and / or regulating unit) is supplied with measured values, particularly continuously. At each position within the field of view of an image acquisition system, the alignment markers of the alignment marker field are designed such that height information can be acquired from the alignment marker field and / or from the extended planar position information. In other words, at any lateral position of the substrate holder, the spatial position of the substrate holder can be determined by the arrangement of the alignment markers of the alignment marker field, and the correct bond spacing can be set.Since the position of the substrate holder in particular is available as 3D position information, a more precise spatial alignment of the substrates attached to it can be carried out relative to each other.

[0135] In an advantageous embodiment of the alignment device, the additional alignment markings are distributed uniformly on the contact surface of a substrate, except for an edge exclusion zone. In other words, the additional alignment markings of the substrate, which are positioned at a distance of less than 3 mm, preferably less than 2 mm, and particularly preferably less than 500 micrometers from each other, can be used to perform alignment. By correlating the additional alignment markings of the substrate with a spatially defined alignment marking field of a substrate holder, increased local alignment accuracies can be achieved.

[0136] For XYZ position determination, the alignment device can also employ at least one three-beam interferometer with a suitably designed, particularly monolithic, reflector for acquiring the XYZ position and / or orientation of the substrate holder. A further advantageous embodiment of the device can measure a prismatic, monolithic reflector with multiple, particularly three-beam, interferometers. This eliminates error propagation through averaging, differentiation, and measurement series, and further increases alignment accuracy. In other words, sufficiently fast position measurements can be used to control the trajectory of the motion, thus further reducing positional errors of the substrate holder.

[0137] The substrate holder of the alignment device, which is formed in particular from a monolithic block, preferably has at least two of the following functions: Substrate mounting with vacuum (vacuum tracks, connections), and / or with electrostatic means, shape compensation for deformation of the substrate by means of mechanical and / or hydraulic and / or piezoelectronic and / or pyroelectric and / or electrothermal actuating elements, position and / or orientation determination (measuring standards, reflective surfaces and / or prisms, in particular the reflectors for interferometry, reference marks and / or reference mark fields, planar measuring standards for planes, volume standards, in particular steps, layer systems of known layer heights with alignment markings subdivided into planes) movement (guide tracks).

[0138] Motion devices not used for fine adjustment are designed, in particular, as robotic systems, preferably with incremental encoders. The accuracy of these motion devices for auxiliary movements is decoupled from the accuracy for aligning the substrate stack, so that the auxiliary movements are performed with a low repeatability of less than 1 mm, preferably less than 500 micrometers, and particularly preferably less than 150 micrometers.

[0139] The control and / or regulation of the device's movement mechanism for lateral alignment (fine adjustment) is performed primarily based on the detected XYZ positions and / or alignment orientations. For this purpose, the substrate's additional alignment markings are correlated with the alignment markings of the alignment marking field, which are uniquely assigned to them in a viewing area on the back of the substrate holder. The height information is calculated from the alignment marking of the alignment marking field. This results in an XYZ position that can be continuously observed during the alignment movement and when adjusting the distance to the bonding surface, and is particularly useful for real-time error correction of the movement.

[0140] The accuracy of the movement devices for alignment is less than 500 nm, preferably less than 100 nm, particularly preferably less than 50 nm, very particularly preferably less than 10 nm, more preferably 5 nm, most preferably less than 1 nm.

[0141] In particularly preferred embodiments of the device, the error in the alignment accuracy of the device is less than 20% of the permissible maximum alignment error, preferably less than 10%, most preferably less than 1%.

[0142] In other words, if the permissible alignment error of the substrates is, for example, 10 nm, then the positioning error is at most 20% of the value, i.e., 2 nm.

[0143] A first embodiment of an exemplary bonding process that performs the alignment process comprises the following steps, in particular those performed sequentially and / or simultaneously, in particular with the following sequence: First process step: The upper substrate is loaded onto the upper substrate holder with a contact surface, wherein at least one first additional alignment mark is present on the opposite side, the so-called contact side of the upper substrate.

[0144] Second process step: The lower substrate to be aligned is loaded onto the lower substrate holder with a contact surface, whereby at least a second additional alignment mark is present on the opposite side, the so-called contact side of the lower substrate. Third process step: Through the upper substrate, an additional detection unit detects at least the first additional alignment mark and, if applicable, a further additional alignment mark of the upper substrate.

[0145] Fourth process step: The focus position of a lens of the additional detection unit is stored and the lens is fixed.

[0146] Fifth process step: The upper substrate is moved upwards, away from the focal plane, towards the additional detection unit using the upper substrate holder. The travel distance is preferably less than 500 micrometers.

[0147] Sixth process step: the lower substrate is moved, particularly upwards, into the fixed focus position of the additional detection unit using the lower substrate holder. Wedge error compensation can also take place simultaneously.

[0148] To capture the second additional alignment mark on the lower substrate, the lower substrate is moved in the Z direction using the lower substrate holder until the contact side of the lower substrate is in focus.

[0149] Seventh process step: a second additional alignment mark of the lower substrate is searched for and detected by a second additional detection unit.

[0150] Alternatively, the lower substrate, which is brought into focus by the z-movement of the lower substrate holder, is moved in the XY plane or rotated about the Z-axis so that the desired second additional alignment mark is positioned in the focus area of ​​the first additional detection unit and is detected by it. Preferably, the lower substrate is further aligned so that the desired alignment mark(s) are arranged, in particular centrally, with respect to the optical axes of the attached lenses of the device.

[0151] In an advantageous embodiment, the desired alignment markings can be detected in the vicinity of the optical axis of the respective lens of the detection units at a radius of less than 3 millimeters, preferably less than 2 millimeters, particularly preferably less than 1 millimeter, most preferably less than 500 micrometers, and even more preferably less than 250 micrometers.

[0152] Eighth process step: A measuring system with at least one detection unit for capturing alignment marks of an alignment marking field (in particular a measuring microscope with objective) detects a first alignment mark of a first plane and thus an XYZ position and / or orientation of the lower substrate holder, preferably from the rear side of the substrate holder. The lower substrate holder is held in place, and the position(s) of the additional alignment mark of the lower substrate are correlated with the detected position. The alignment marking field, which is fixed to the substrate holder, is used to detect the position of the lower substrate holder.

[0153] Preferably, a level of the alignment marker field is captured in focus, which is located close to the free surface of the alignment marker field and allows alignment markers to be viewed throughout the entire depth of the alignment marker field.

[0154] In this focused position, the focus position (especially of the lens) of the detection unit is used to capture the

[0155] The alignment marking field is attached. Furthermore, the detection unit is fixed in place or held stationary.

[0156] Ninth process step: the lower substrate is moved downwards a defined distance using the lower substrate holder, while measuring the alignment marks of the steps at different levels within the alignment marking field. This distance is preferably less than 500 micrometers. The distance by which the lower substrate is lowered is the so-called bond gap, i.e., the correct distance to perform a bond, specifically a fusion bond and / or a hybrid bond, with minimal distortion.

[0157] In a particularly preferred embodiment of the exemplary method, the lower substrate with the lower substrate holder is lowered to such an extent that an alignment mark of the nearest stage of another plane is brought into sharp focus in the alignment marking field. In this way, a blind or controlled movement of the substrate holder for alignment is avoided.

[0158] The detection unit records the movement of the lower substrate holder, at least in its initial and target positions, by monitoring the alignment marker field at different levels. In the initial position, at least one alignment mark of the first level is detected, and in the target position, at least one alignment mark of the second level of the alignment marker field is detected.

[0159] Tenth (optional) procedure step: the position of the lower substrate holder is corrected, at least in the lateral plane, using the measured positional errors. The substrate holder is moved so that the corresponding alignment mark of the second plane is in focus, or at least one other alignment mark of the second plane is within the focus range of the detection unit. This allows for visual inspection to ensure that the distance between the first and second planes (i.e., the bond gap) has been set with sufficient accuracy.

[0160] This eliminates the need to refocus the detection unit and avoids alignment errors. The alignment marker provides height information, allowing the desired process-relevant bond distances to be achieved visually, without any blind movement. This eliminates the need to focus and / or refocus the detection unit, thus preventing errors associated with focusing movements.

[0161] Eleventh process step: The upper substrate is lowered again into the focus position of the additional detection unit or its lens using the upper substrate holder.

[0162] Twelfth process step: Using the correlated XYZ position of the lower substrate holder, the upper substrate is aligned to the lower substrate, preferably moving the upper substrate in the XY plane and / or rotating it around the Z-axis.

[0163] In this process step, the first additional alignment marks are aligned with the second additional alignment marks. The actual position of the lower substrate on the lower substrate holder is known because the correlated positions of the lower substrate's alignment marks relative to the alignment mark field have been measured, allowing the upper substrate's alignment marks to be aligned with the known, hidden position of the second alignment marks on the lower substrate.

[0164] Thirteenth process step: The lower substrate is lifted to set the correct bond distance; any deviations can be observed and corrected using the alignment marker field.

[0165] Fourteenth process step: the contact surfaces of the upper and lower substrates are contacted, the substrates are bonded to each other.

[0166] When aligning the substrates to each other, corrections can be made to their relative position if the alignment error exceeds a specified limit.

[0167] The alignment errors for which corrections are applied are for displacements of less than 500 micrometers, preferably less than 100 micrometers, particularly preferably less than 100 nanometers, very particularly preferably less than 10 nanometers, even more preferably less than 5 nanometers, and most preferably less than 1 nanometer.

[0168] The alignment errors for which corrections for twists are applied are less than 50 microradians, preferably less than 10 microradians, particularly preferably less than 5 microradians, very preferably less than 1 microradian, even more preferably less than 0.1 microradians, most preferably less than 0.05 microradians.

[0169] In a further embodiment of the alignment method, acceleration is achieved by parallelizing the process steps; in particular, the loading of the second substrate is already carried out during a pattern recognition step on the first substrate.

[0170] The terms that axes coincide, or coincide, or parallelism, or normality are used in this disclosure as terms of quantities subject to tolerance, so that in particular the tolerances of non-tolerated length or angle dimensions according to ISO 2768 apply, unless the tolerances are explicitly stated.

[0171] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. These show schematically in: Figure 1 is a cross-sectional view of an embodiment of a device according to the invention, Figure 2a is a top view of an exemplary alignment marking field with alignment marks, Figure 2b is a sectional view of an embodiment of an alignment marking field, Figure 3 is a top view of an embodiment of an alignment marking field with alignment marks, Figure 4 is a sectional view of an embodiment of an alignment marking field with a detection unit.

[0172] In the figures, advantages and features of the invention are identified by reference numerals according to embodiments of the invention, wherein components or features with the same or equivalent function are identified by identical reference numerals.

[0173] In Fig. 1Figure 1 is a schematic, not-to-scale functional representation of the main components of an embodiment of an alignment system 1. The alignment system 1 is capable of performing the following functions: Figure 1 To align substrates not shown in the diagram and to bond them together, at least partially and / or provisionally (so-called pre-bond). The terms device and system are used interchangeably.

[0174] The alignment system 1 includes a first substrate holder 9, onto which a first substrate can be loaded and fixed on a substrate holder surface. Furthermore, the alignment system 1 includes a second substrate holder 11, onto which a second substrate can be loaded and fixed.

[0175] The first, lower substrate holder 9, which is to be aligned, is arranged on a first motion device 10 for holding and implementing feeding and adjustment movements (alignment) of the first substrate holder 9. The second, upper, substrate holder 11 is arranged on a second motion device 12 for holding and implementing feeding and adjustment movements (alignment) of the second substrate holder 11. The motion devices 10 and 12 are fixed, in particular, to a common, solid table or frame 8 to reduce / minimize vibrations of all functional components. The frame may, in particular, include active vibration damping.

[0176] For the observation (detection) of additional alignment markings on the substrates, an optical system 2 of the alignment system 1 includes at least one additional detection unit 3, in particular an image detection means, for detecting the additional alignment markings.

[0177] The optical system 2 can be focused onto a focal plane or focus position located between the first and second substrates, preferably between the substrate holders 9 and 11 when these are arranged for alignment. Movements of the optical system 2, particularly in the X, Y, and Z directions, are carried out by means of a positioning device 4. The positioning device 4 can, in particular, be fixed to the solid table or frame.

[0178] At least one additional measuring system 5, in particular an optical system, with at least one detection unit 6 for detecting an alignment marking field 14, is used to increase the alignment accuracy by detecting alignment marks of different levels of the alignment marking field 14. Movement of the additional measuring system is carried out by a positioning device 7.

[0179] Insofar as the optical measuring system 5 is concerned, the positioning device 7 can perform a focus with respect to an alignment mark of a first plane 18 of the alignment marking field 14 by moving the detection unit 6 in the Z direction. Positioning in the XY direction is also conceivable, wherein, in particular, a fixation, preferably on the table / frame, takes place during the alignment.

[0180] In the illustrated embodiment of the alignment system 1, the measuring system 5 or the detection unit 6 is used to detect, in particular, the X-Y position and / or location (especially also the rotational position) and / or the height position of the lower substrate holder 9 with particularly high accuracy.

[0181] To initiate a fusion bond, at least the upper substrate can be prestressed using a substrate prestressing device 13. The prestressing can be achieved by means of mechanical prestressing with a prestressing element, a so-called bond pin. In a further embodiment of the substrate prestressing device, the prestressing of the substrate can be achieved with a fluid, in particular with a gas, from a nozzle, especially from a movable nozzle.

[0182] With preferred embodiments of the device (not shown), the following exemplary process steps can be carried out: The first / lower substrate is attached to a first fixing surface, in particular the substrate holder surface, of the first substrate holder 9. A mechanical and / or electrostatic clamping force, also known as vacuum clamping, is used for fastening. This clamping force is generated by a pressure difference between the ambient atmosphere and the vacuum applied to the first substrate holder 9. The fastening is arranged in such a way that the first substrate does not experience any inaccurate or undesired movement relative to the first substrate holder 9 during the entire process.In particular, thermal expansion can be prevented or reduced if the first substrate holder 9 and the first substrate each have a corresponding, preferably linearly corresponding, coefficient of thermal expansion, wherein the difference between the coefficients of thermal expansion and / or the linear progression of the coefficients of thermal expansion is preferably less than 5%, preferably less than 3%, and particularly preferably less than 1%.

[0183] The system is preferably operated in a temperature-stabilized environment, in particular in a cleanroom, in which the temperature fluctuation during an alignment cycle is less than 0.5 Kelvin, preferably less than 0.1 Kelvin, particularly preferably less than 0.05 Kelvin, most preferably less than 0.01 Kelvin.

[0184] The fixed first substrate and the first substrate holder 9 can be understood as a quasi-monolithic body for the execution of the movements of the first substrate, which do not allow any relative movements to each other.

[0185] This substrate fastening can be achieved by positive locking and / or, preferably, by force locking. The quasi-monolithic connection ensures that the influences that can cause displacement, rotation, and / or deformation between the substrate holder and the substrate are at least reduced, preferably reduced by at least one order of magnitude, and most preferably eliminated.

[0186] The substrate can be connected to the substrate holder using positive locking or force locking in such a way that, in particular, the difference in thermal expansion can be suppressed. Furthermore, the substrate holder can reduce, eliminate, and / or correct the substrate's own deformation.

[0187] In one embodiment, both the lower substrate holder 9 and the upper substrate holder 11 can include additional passively and / or actively operated deformation elements and / or intermediate plates to minimize the mechanical and / or thermal properties of the substrates for the reduction of residual alignment error after joining.

[0188] The first substrate holder 9 can be located in an optical path of the additional detection unit 3 during the acquisition of a first additional alignment mark. The first additional alignment mark can be positioned on the contact surface of the first substrate to be bonded within the field of view, particularly in the optical path, preferably in the optical axis of the additional detection unit 3. The additional detection unit 3 generates an image, particularly a digital one, which is then measured. A first alignment mark of a substrate can also consist of several composite alignment marks. A measured value is generated / calculated from the image of the alignment mark, which characterizes, in particular, the XY position and / or orientation (especially in the direction of rotation about a Z-direction), i.e., the alignment state of a first substrate.

[0189] The lower substrate holder 9 and / or the first substrate have the alignment marks of the alignment marking field 14, by means of which the XYZ position and / or orientation, in particular the spatial orientation state of the substrate holder 9 and / or the first substrate, is detected, especially from a different direction, preferably a direction diametrically opposite to the first detection in the Z direction.

[0190] Preferably, a relative movement of the first detection unit 3 to the third detection unit 6 is measurable. Even more preferably, no relative movement occurs between the first additional detection unit 3 and the detection unit 6 from the detection of the first additional alignment mark and an alignment mark of the alignment mark field 14 until contact is made between the first and second substrates.

[0191] The acquisition unit 6 for acquiring the alignment marking field 14 of the additional measuring system 5 provides a measured value of the spatial XYZ position and / or location of the first / lower substrate holder 9 from the measurement of the alignment marks of different levels of the alignment marking field 14.

[0192] The measured values ​​(XY position and / or orientation of the first substrate as well as XYZ position and / or orientation of the first substrate holder 9 or the first substrate 16) are correlated with each other so that the XYZ position of the substrate holder 9 can be reproduced. This allows the substrate attached to the substrate holder 9 to be moved in a controlled manner for alignment and for setting the bond distance, without the additional alignment markings of the substrate being directly observable.

[0193] By assigning the position of the substrate to the spatial position and / or orientation of the substrate holder 9, alignment is possible without directly observing the XY positions and / or orientations of the respective substrate during alignment and / or contacting. Furthermore, the distance between the substrates can be defined and / or minimized during alignment. Preferably, this distance already corresponds to the distance between the substrates during the detection of the first and second additional alignment marks. In other embodiments, the preferred bonding distance can be set.

[0194] In other words, an unobstructed optical path is provided between the substrate holder 9 and the additional measuring system 5, which can be used to control the orientation of the substrates in a closed-loop system. This allows the XYZ position and / or orientation of the first substrate holder 9, and thus of the first substrate fixed to the first substrate holder 9, to be precisely determined and reproducibly restored, which in turn increases the accuracy of bonding, especially fusion bonding.

[0195] Restoring and correctly adjusting the XYZ position and / or alignment, in particular of the substrate holder 9 and especially of the substrate monolithically connected to it, in relation to the other substrate and / or substrate holder, is an important aspect of the alignment device.

[0196] In particular, a repeatability of the positioning (measured as the relative alignment error between the two substrates), also known as backlash, of less than 500 nm, preferably less than 100 nm, particularly preferably less than 30 nm, most preferably less than 10 nm, even more preferably less than 5 nm, and most preferably less than 1 nm is achieved. The backlash can also be the repeated approach to a given position using the motion devices 10, 12 and / or 4, 7. The backlash results from the movements of the motion devices; only the detection location varies, so that the measured quantity exists as a relative alignment error.

[0197] To further increase alignment accuracy, it is preferred to operate the first additional sensing unit 3 and the second additional sensing unit 5 in a time-synchronized manner, particularly with a time difference between the acquisition of the measured values ​​of less than 3 seconds, preferably less than 1 second, particularly preferably less than 500 milliseconds, most preferably less than 100 milliseconds, in a still preferred case less than 10 milliseconds, most preferably less than 1 millisecond, ideally simultaneously. This is particularly advantageous because the effect of disturbances such as mechanical vibrations can be eliminated. Mechanical vibrations propagate through materials at several thousand m / s, including structure-borne sound. If a control system and the sensing means operate faster than the propagation speed of structure-borne sound, disturbances are reduced or eliminated.

[0198] If a disturbance changes the position of the first substrate on the first substrate holder 9 such that the first additional sensing unit 3 has already recorded a measurement and the measuring system 5 with the sensing unit 6 for recording the alignment marking field 14 has not yet recorded a measurement, the disturbance can contribute to a reduction in the alignment accuracy. This is because, in the time between the measurement acquisitions of the additional sensing unit 3 and the sensing unit 6, rapid mechanical position changes, particularly those caused by vibrations, can occur on the order of nanometers or micrometers. If the measurement acquisition is delayed (on the order of seconds or minutes), further disturbances such as thermally induced changes in shape or length can also reduce the alignment accuracy.

[0199] If the first additional detection unit 3 and the detection unit 6 for the detection of the alignment marking field 14 are synchronized with each other (in particular by simultaneous triggering of the detection as well as compensation of the detection time and / or equal integration time for camera systems), some interferences can be reduced, in the best case eliminated, since the detection should take place at a time in which the interferences have the least possible effect on the detection accuracy.

[0200] In a preferred embodiment of the method and the alignment device, known, especially periodic, disturbances, particularly at the peak of the vibration, are detected synchronously. Preferably, vibration sensors (accelerometers, interferometers, vibrometers) can be installed beforehand at accuracy-relevant points on the alignment device. The disturbances are detected by these vibration sensors and, for elimination, are taken into account or corrected by calculation, particularly by processing units. In a further embodiment, the vibration sensors can be permanently installed at characteristic points on the system.

[0201] For the alignment of the substrates, a determined / defined setpoint is used in particular. The setpoint includes, in particular, image data of the alignment marks of the alignment marking field 14 of the first substrate holder 9 and / or the determined XYZ position and / or orientation data for the motion device 10 of the first substrate holder 9 and / or control parameters such as trajectories for optimal approach to the spatial position and / or, in particular, machine-readable values ​​for the drives.

[0202] By means of the first motion device 10, the first substrate holder 9 is moved in a position- and, in particular, orientation-controlled manner until the alignment error, which is calculated from the target value of the detection unit and the current position and / or orientation of the substrate holder, is minimized, ideally eliminated, or until a termination criterion is reached. This movement of the lower substrate holder also includes the correctly set distance for bonding, especially for fusion bonding. In other words, the lower substrate holder 9 is moved in a controlled, regulated manner to the already known, measured XYZ alignment position and is moved in a regulated manner, particularly in the Z direction.

[0203] In further embodiments, residual errors that could not be eliminated during the positioning of the upper and / or lower substrate can also be taken into account here as correction values ​​for the positioning of the other (lower or upper) substrate.

[0204] Figure 2a shows an alignment marking field 14' in a schematic, greatly enlarged top view with exemplary selected alignment marks 15 or alignment markings 15.

[0205] The individual alignment markers 15 symbolically and schematically represent an absolute, unambiguous encoding of the position and location of each individual alignment marker 15. The individual alignment markers 15 can be located on different levels of the alignment marker field 14'. Since the properties (xyz position of each alignment marker 15) of the alignment marker field 14' are known a priori, it is sufficient for the absolute position determination of the substrate holder (not shown) that an absolutely encoded alignment marker 15 is detected.

[0206] Figure 2b shows an alignment marker field 14" with different, exemplary marked layers 16, 16' of the alignment marker field 14" in a schematic sectional view.

[0207] It is advantageous if, when aligning the substrate holder, which includes the alignment marker field or is fixedly arranged to it, several alignment marks of different levels are taken into account. In particular, several steps and / or layers 16, 16' of the alignment marker field can be simultaneously or, preferably, sequentially within the field of view or focus area of ​​the detection unit 6 and thus be detected. The known step heights or the known distances between the levels can be used for alignment or for setting the desired distance between the substrates.

[0208] The distance between the planes is between 1 micrometer and 300 micrometers, preferably between 5 micrometers and 200 micrometers, particularly preferably between 10 micrometers and 100 micrometers, in the optimal case between 25 micrometers and 75 micrometers, and in the ideal case between 48 micrometers and 52 micrometers. In special cases, the distance between the planes is 50.00 micrometers.

[0209] It is advantageous if the alignment marks 15, 15' of an alignment marking field 14, 14', 14", 14‴ provide the spatial position and / or orientation of the substrate holder 9 or the substrate arranged on the substrate holder. Furthermore, it is advantageous if the respective alignment marks 15, 15' have detectable positional information that provides the respective position within the alignment marking field 14, 14', 14", 14‴. Thus, the position of each detected alignment mark 15, 15' relative to the alignment marks 15 of the alignment marking field is also known. Preferably, not only is the position of the detected alignment mark 15, 15' relative to the alignment marks 15, 15' of the same plane known, but also the position of the respective plane of the detected alignment mark 15, 15' relative to the other planes of the alignment marking field.This respective position information is made possible, for example, by different angles and different shapes of the alignment markings 15, 15' and is shown schematically as an example.

[0210] For the precise setting of a desired distance or bonding distance between the substrates, the optical system of a detection unit 6 for detecting the alignment marking field 14, 14', 14", 14‴ should preferably have a smaller depth of field or a smaller depth of focus area (especially in the Z direction) than half the distance between the corresponding planes.

[0211] Figure 3Figure 1 shows a possible embodiment of an alignment marker field 14", wherein the individual exemplary alignment marks 15' are supplemented with a machine-readable code. The individual alignment marks 15 can be arranged on different levels (steps and / or layers), and the code can contain an indication of which level each mark belongs to. Furthermore, the code can contain a unique indication of the position and orientation of each alignment mark 15'.

[0212] In Figure 4 Figure 1 shows a cross-sectional view of an embodiment of an alignment marker field 14ʺʺ. The alignment marks 15' of the alignment marker field 14ʺʺ are arranged in three different planes 18, 18', 18" and can be detected by the detection unit 6. The detection unit 6 can only detect the alignment marks 15' within the focus area 19.

[0213] A first level 18 has a known distance 17" to a second level 18'. The second level 18' has a known distance 17' to a third level 18" as well. Furthermore, the distance 17" between the first level 18 and the third level 18" is known. In the illustrated embodiment, the distance 17" and the distance 17' are of different sizes, so that when using the alignment marking field 14ʺʺ to align a substrate, all three distances 17, 17' and 17" can be approached or adjusted.

[0214] Combinations of distances 17, 17', 17'' can also be achieved by repeatedly moving the substrate holder (9), which is stationary relative to the alignment marker field 14ʺʺ. For example, the distance 17'' can first be set, and then the distance 17' can be moved to the same position in the same direction. Alternatively, the substrate holder can be moved by twice the distance 17''. This involves aligning in two steps, with the detection unit being adjusted accordingly between steps, as the focus position and thus the focus area 19 of the detection unit 6 is adjusted. Reference symbol list

[0215] 1 Alignment device, alignment system 2 Optical system 3 Additional detection unit 4 Positioning device 5 Additional measuring system 6 Detection unit (alignment marking field) 7 Positioning device of the additional measuring system 8 Frame 9 Substrate holder, first (to be aligned) substrate holder 10 Movement device of the substrate holder to be aligned, first movement device 11 Second / upper substrate holder 12 Second movement device 13 Substrate deformation device 14, 14', 14", 14‴ Alignment marking field 15, 15' Alignment marks, alignment marking 16, 16' Layers of an alignment mark of an alignment marking field 17, 17', 17" Spacing 18, 18', 18" Planes of the alignment marking field 19 Focus area of ​​the detection unit in a focus position 20 Substrate holder surface of the (to be aligned) substrate holder

Claims

1. A method for aligning a substrate with at least the following steps: i) Provision of a substrate holder (9) with a substrate holder surface (20) designed to mount the substrate and an alignment marking field (14, 14', 14", 14"') fixed with respect to the substrate holder (9), ii) alignment of the substrate, characterised in that the substrate is aligned with the aid of alignment marks (15, 15') of the alignment marking field (14, 14', 14", 14"') arranged one above the other, wherein the alignment of the substrate in step ii) has the following steps, in particular with the following sequence: a) detection of a first alignment mark (15, 15') of a first plane (18, 18', 18") of the alignment marking field (14, 14', 14", 14"') by a detection unit (6), b) fixing of a focus position of the detection unit (6) after the detection in step a), c) movement of the substrate holder (9) perpendicular to the first plane (18, 18', 18") of the alignment marking field (14, 14', 14", 14‴), d) detection of a second alignment mark of a second plane (18, 18', 18") of the alignment marking field (14, 14', 14", 14"') by the detection unit (6), wherein the first plane (18, 18', 18") and the second plane (18, 18', 18") are arranged parallel to one another, and wherein the first plane (18, 18', 18") and the second plane (18, 18', 18") are at a distance (17, 17', 17") from another.

2. The method according to claim 1, wherein in step a) additional alignment marks are detected on the substrate holder (9) or on the substrate by at least one additional detection unit (3).

3. The method according to at least one of the preceding claims, wherein during the movement of the substrate holder (9) in step iv), the detection unit (6) in the focus position continuously measures the alignment marking field (14, 14', 14", 14"').

4. The method according to at least one of the preceding claims, wherein after fixing the focus position in step b), the detection unit (6) is held fixed5. The method according to at least one of the preceding claims, wherein when the first alignment mark (15, 15') is detected in step (a) and / or when the second alignment mark (15, 15') is detected in step d) by the detection unit (6), information on the location of the respective alignment mark (15, 15') within the alignment marking field (14, 14', 14", 14"') is also provided.

6. A device for aligning a substrate, at least comprising A) a substrate holder (9) with a substrate holder surface (20) designed to mount the substrate, and B) an alignment marking field (14, 14', 14", 14"') with alignment marks (15, 15') arranged fixed with respect to the substrate holder (9) and the substrate, characterised in that the substrate can be aligned with the aid of alignment marks (15, 15') arranged upon one another, the device further comprising C) a detection unit (9) for detecting the alignment marks (15, 15') of the alignment marking field (14, 14', 14", 14"') and D) a movement device (10) for moving the substrate holder (9), - wherein the alignment marks (15, 15') of the alignment marking field (14, 14', 14", 14‴) are arranged in a first plane (18, 18', 18") and a second plane (18, 18', 18"), and wherein the first plane (18, 18', 18") and the second plane (18, 18', 18") are arranged parallel to one another, and wherein the first plane (18, 18', 18") and the second plane (18, 18', 18") are at a distance (17, 1 7', 17") from each other, and - wherein a first alignment mark (15, 15') of the alignment marks (15, 15') of the first plane (18, 18', 18") can be detected in a focus position of the detection unit (6), and wherein the focus position of the detection unit (6) can be fixed, and - wherein in the focus position a second alignment mark (15, 15') of the alignment marks (15, 15') of the second plane can be detected by the detection unit (6), and wherein the substrate holder (9) can be moved perpendicular to the first plane (15, 15') by the movement device (10).

7. The device according to at least one of the preceding claims, wherein the alignment marks (15, 15') of the first plane (18, 18', 18") and the alignment marks (15, 15') of the second plane (18, 18', 18") are arranged aligned above one another, in particular congruently, in the alignment marking field (14, 14', 14", 14"').

8. The device according to claim 6, wherein the alignment marks (15, 15') of the first plane (18, 18', 18") are arranged offset step-like with respect to the alignment marks (15, 15') of the second plane (18, 18', 18").

9. The device according to at least one of the preceding claims, wherein the alignment marking field (14, 14', 14", 14"') is arranged on a rear side of the substrate holder (9) facing away from the substrate holder surface (20).

10. The device according to claim 6, wherein a centre-point of the alignment marking field (14, 14', 14", 14‴) on the rear side of the substrate holder (9) is at least partially aligned with a centre-point of the substrate holder surface (20).

11. The device according to at least one of the preceding claims, wherein the alignment marking field (14, 14', 14", 14"') is arranged on the side of the substrate facing towards the substrate holder surface (20).

12. The device according to at least one of the preceding claims, wherein the alignment marking field (14, 14', 14", 14"') comprises at least one further plane (18, 18', 18") with the alignment marks (15, 15'), wherein the at least one further plane (18, 18', 18") is arranged at least parallel to the first plane (18, 18', 18").

13. The device according to at least one of the preceding claims, wherein the device comprises at least one further alignment marking field (14, 14', 14", 14‴) and at least one further detection unit (6) for detecting the at least one further alignment marking field (14, 14', 14", 14"'), wherein the at least one further alignment marking field (14, 14', 14", 14"') is arranged fixed with respect to the substrate holder (9).