Method for bonding a first substrate to a second substrate, device for bonding and assembly of a first and second substrate

Abstract

Method for bonding a first substrate (2u) to a second substrate (2o), wherein the first substrate (2u) has a primary section and the second substrate (2o) has a secondary section, wherein when bonding the first substrate (2u) to the second substrate (2o), a bonding wave (3) advancing along a bonding direction is formed between - a first subsection in which the first substrate (2u) and the second substrate (2o) are bonded, and - a second subsection in which the first substrate (2u) and the second substrate (2o) are still to be bonded, wherein preferably a subregion of the second substrate (2o) in the second subsection is offset in height relative to a subregion of the second substrate (2o) in the first subsection in a direction perpendicular to a main extension plane, and wherein a first curvature of the first substrate (2u) and / or a second curvature of the second substrate (2o) is modified by means of a deformation system in a region adjacent to the bonding wave (3) and / or in a region surrounding the bonding wave (3) for the relative alignment of the primary section and the secondary section with respect to one another, in particular with respect to a direction running substantially parallel to the bonding direction.

Description

[0001] Method for bonding a first substrate to a second substrate, device for bonding and arrangement of first and second substrate

[0002] The present invention relates to a method for bonding a first substrate to a second substrate, a device for bonding and an arrangement of first and second substrate.

[0003] In the semiconductor industry, several different processes exist for joining substrates, especially wafers, together. This joining process is called bonding. The bonding process can be either temporary or permanent. A temporary bond usually only serves to bond a product substrate to a carrier substrate for processing. A permanent bond is used to permanently connect two substrates. The substrates to be bonded are preferably product substrates. Each of the product substrates generally already has structures, in particular entire functional units such as microchips, memory chips, LEDs, MEMS, etc. Permanent bonding allows product substrates with different functional units to be combined into a substrate stack.

[0004] It is conceivable, for example, that several microchips are located on a first product substrate and several memory chips on a second product substrate. By appropriately designing the functional units on both product substrates, it is possible to assign a memory chip to each microchip. The connection of the functional units beyond the bond interface preferably occurs via the contact interface of two vias. Since the substrate surfaces are directly connected to one another, this is also referred to as a direct bond. A special type of direct bond is a fusion bond. A fusion bond is a direct bond between dielectric substrate surfaces, in particular substrate surfaces made of oxide. A particularly important fusion bond is a hybrid bond. A hybrid bond is a bond between two substrate surfaces that consist of electrical and dielectric regions.The dielectric regions are usually an oxide, particularly silicon oxide. The silicon oxide is opened at several locations through various process steps. The openings are usually radially symmetrical. These openings are then filled with a metal. The metal extends as far as the functional units buried beneath the dielectric layer and represents the outward-reaching contacts. After the manufacturing process, a substrate surface remains consisting of a primarily dielectric region and several small, distributed electrical regions. Several such substrates can then be aligned and contacted with one another using a hybrid bond. It is of fundamental importance that the metallic regions contact one another correctly, otherwise no electrical contact can be established between the functional elements.The metallic areas are called vias. If the via also passes through silicon, they are usually called through-silicon vias (TSVs). The surfaces of vias are the most important type of structures that must be aligned during a fusion bonding process, as they provide the electrical contact between the various functional units.

[0005] With the increasing use of fusion bonds, especially hybrid bonds, for the production of next-generation semiconductor chips, there is a need to continuously improve the quality of bonding results. A key quality criterion for bonded substrates is the precision of the structure location, especially the vias. This is referred to as an "overlay." This essentially refers to the actual position of the structures compared to the expected position.

[0006] Throughout the semiconductor industry, structures are manufactured with feature sizes in the micrometer and now even in the nanometer range. Transistors, for example, have feature sizes in the nanometer range. TSVs can have feature sizes in the micrometer range. Entire microchips have feature sizes in the millimeter or micrometer range. All structures are developed using software and stored digitally. This means that every structure created on the substrate in a subsequent manufacturing process first has a well-defined, precise position and size in the computer. This idealized state is referred to below as the target state.

[0007] To create the structures on a substrate, several dozen, sometimes even several hundred, process steps are necessary. Each process step can generally only be performed with a certain degree of accuracy or is subject to errors. For example, the diffraction limit is a classic example of the maximum achievable accuracy in photolithography when it comes to transferring the structure of a mask into a photoresist. This physical limit can be pushed to the limit, but not circumvented. A typical example of an error-prone process would be play in mechanical elements that must perform a movement. The mechanical components cannot be built without play and therefore always produce some kind of error, which ultimately affects the accuracy of the manufactured structures.

[0008] Although enormous progress has been made in recent decades in producing structures on a substrate with increasing precision, while simultaneously continuously increasing their areal density, it is still the case that every fabricated structure on a substrate generally deviates, albeit only very slightly, from the desired state. This actual state of the structures on a substrate is referred to below as the actual state.

[0009] However, the term "overlay" is used much more generally in the semiconductor industry. An overlay is generally understood to be the set of displacement vectors of individual points on a substrate, representing the displacement of the point from a position before a process step to a position after the process step. Each individual process step can therefore lead to a displacement of the structures and thus to an overlay. In this context, the state before the process step is referred to as the desired state, and the state after the process step is referred to as the actual state.

[0010] The structures of two substrates to be bonded are therefore generally not ideal even before the bonding process, but distorted in relation to the desired state. Another, even more serious problem arises during the bonding process. In fusion bonding, the bonding process occurs through the propagation of a bonding wave. The substrates are initially contacted at a point, particularly centrally. Afterwards, at least one of the two substrates is moved in such a way that the bonding surface between the two substrates can expand and expand. It is conceivable that the upper substrate is dropped, particularly in a controlled manner, or that fixing elements of the upper substrate holder are continuously switched, particularly from the inside out, so that the upper substrate lowers from the contact point towards the periphery. It would also be conceivable for the two substrate holders, and thus the substrates, to move closer to one another.A combination of the above possibilities is also conceivable. In each case, a bond wave propagates outward from the contact point. During this bonding process, several competing forces develop, particularly along the bond wave. These forces lead to distortion of the lower and / or upper substrate as the bond wave propagates, and thus to undesirable deviations between the upper and lower structures, particularly functional units. Even if the structures had been manufactured in the desired state, which is technically impossible or very difficult, the bonding process would lead to the creation of new distortions.

[0011] Another problem is that the distortions induced by the bonding process may not necessarily have a local, but rather global, impact. Any distortion at an inner radial position of the substrate generally also affects the bonding result at more outer radial positions.

[0012] Another problem is so-called edge voids. These micrometer- to millimeter-sized defects, which are likely gas inclusions, have been a known and troublesome problem in the semiconductor industry for years. The formation of edge defects is still a highly researched phenomenon in technology, and their prevention is a desirable goal.

[0013] Another problem is increased distortion at the edge of the substrate. While distortion generally occurs along the entire substrate surface during the bonding process, distortions are particularly severe at the edge. Based on this, the present invention aims to avoid the disadvantages known from the prior art or to reduce their impact on the bonding process and the bonded product.

[0014] The present invention solves this problem with a method for bonding a first substrate to a second substrate according to claim 1 and with a bonding device according to claim 7 and an arrangement according to claim 15. Advantageous developments of the invention are specified in the subclaims. The scope of the invention also includes all combinations of at least two features specified in the description, the claims and / or the drawings. For specified value ranges, values ​​lying within the stated limits should also be considered disclosed as limit values ​​and can be claimed in any combination. If properties are described in the description and the claims for the first substrate and the first substrate holder, these apply analogously to the second substrate and the second substrate holder.

[0015] According to a first aspect of the present invention, a method for bonding a first substrate to a second substrate is provided, wherein the first substrate has a primary section and the second substrate has a secondary section, wherein during bonding of the first substrate to the second substrate, a bonding wave advancing along a bonding direction is formed between

[0016] -- a first section in which the first substrate and the second substrate are connected, and

[0017] -- a second subsection, in which the first substrate and the second substrate are still to be connected, is formed, wherein preferably a subregion of the second substrate in the second subsection is offset in height relative to a subregion of the second substrate in the first subsection in a direction running perpendicular to a main extension plane, and wherein for the relative alignment of the primary section and the secondary section to one another, in particular with respect to a direction running substantially parallel to the bonding direction, a first curvature of the first substrate and / or a second curvature of the second substrate is modified by means of a deformation system in a region adjacent to the bonding wave and / or in a region comprising the bonding wave.In contrast to the methods known from the prior art, the invention provides for the first curvature and / or the second curvature to be specifically modified locally in the region adjacent to the bonding wave or in the region encompassing the bonding wave, in particular immediately before the region adjacent to the bonding wave is bonded. In particular, it is provided that the modification of the first curvature and / or the second curvature results in a corresponding adjustment that ensures that, after the bonding process, the primary section and the secondary section are arranged one above the other, preferably congruent with one another, in a direction perpendicular to the main extension plane. In other words: the overlay is optimized.In this way, it is advantageously possible to increase positioning accuracy, ensuring that the primary section and secondary section of the first and second substrates are not offset from one another in a direction parallel to the bonding direction. This proves particularly advantageous if structures and / or functional units are formed in the primary section and secondary section, which are intended to connect to one another, in particular electrically, in the bonded state. These structures and / or functional units include, for example, vias and / or connections of electrical or electronic components, such as MEMS or LEDs.

[0018] It has been found that by specifically adjusting the first curvature and / or the second curvature, in particular in the area adjacent to the bonding wave or in the area comprising the bonding wave, it is possible to control the positional accuracy, in particular the relative alignment of the primary section and the secondary section, in such a way that the probability of exclusion is significantly reduced. Such exclusion of the bonded arrangement comprising the first and second substrates occurs when the primary section and the secondary section are offset from one another in such a way that, for example, no sufficient connection can be established between the primary section and the secondary section or between the corresponding functional units in the primary section and the secondary section. In particular, it is provided that specifically in an area that borders the bonding wave and / or comprises the bonding wave, ieThe first or second curvature is influenced in a targeted, locally limited area. In particular, it is thus provided that a targeted, local influence is exerted on the first or second curvature. A global or globally acting deformation can additionally be provided. Preferably, only the first substrate or the second substrate, i.e., only one of the substrates to be bonded, is influenced by means of a deformation system. This advantageously reduces the number of parameters to be controlled and monitored, and limits the handling to a single substrate.

[0019] In particular, it is provided that the modification of the first and / or second curvature serves to adapt the first curvature and the second curvature to one another in the region adjacent to the bond wave. For example, it is conceivable that a difference between the first curvature and the second curvature should not exceed a specified threshold value or should be kept essentially constant. A curvature is understood, in particular, to be the reciprocal value of a radius of the circle whose section-wise course describes the curved partial region of the first substrate or the second substrate.

[0020] The bonding between the first substrate and the second substrate takes place via the substrate surfaces of the first substrate and the second substrate, which are brought into contact with each other during bonding, ie during the bonding operation or process.

[0021] The main extension plane is preferably defined by a support surface of a substrate holder, i.e., a first substrate holder and / or a second substrate holder. The support surface extends, with its general profile, preferably along the main extension plane. In particular, the main extension plane is defined by the general profile of the first subsection, in particular by the general profile of the region of the first subsection that is not curved or is free of curvature and essentially flat.

[0022] The bonding process is characterized in particular in that during bonding the first subsection, in which bonding has already taken place, is arranged substantially in the main extension plane, while the first substrate and / or the second substrate in the second subsection is at least partially offset in height from the first subsection in a direction running perpendicular to the main extension plane. In particular, it is provided that during bonding the first substrate is raised in sections in the area adjacent to the bonding wave. By spacing the second substrate holder from the second substrate holder, the second substrate also has a second curvature in the area adjacent to the bonding wave. As a result, a first curvature and a second curvature are already produced in the area of ​​the bonding wave by the bonding process, without the deformation system influencing the first curvature or the second curvature. The modification orThe extent of the modification emanating from the deformation system is thus determined in relation to the first curvature and / or second curvature, which would have to be determined during the bonding process without a deformation system.

[0023] In particular, the region adjacent to or encompassing the bonding wave extends over at least 5 mm, preferably at least 2.5 mm, and particularly preferably at least 1 mm. It is preferably provided that outside of such a dimensioned region, the deformation or the modification and effect on the first curvature by the deformation sections or the deformation system or fixing elements is negligibly small. The region adjacent to or encompassing the bonding wave can extend over the first partial region and the second partial region.

[0024] The bonding is preferably a direct bonding process, preferably a fusion bonding process, and particularly preferably a hybrid bonding process. The substrates are preferably wafers, for example silicon wafers, which are particularly preferably bonded to a product substrate or a temporary substrate by bonding.

[0025] The first curvature and / or the second curvature is preferably adjusted by means of a deformation system comprising coatings, fixing elements and / or deformation means. Those skilled in the art understand fixing elements to be, in particular, devices designed to hold partial sections of the first and / or second substrate. Preferably, the individual fixing elements can be transferred individually or in groups between a fixed state and a release state. In the bonding process, the fixing elements serve to bring specific portions of the first substrate and the second substrate into contact. For example, individual fixing elements in a second substrate holder are transferred to the release state in order to allow a portion of the second substrate to fall, thereby coming into contact with a corresponding portion of the first substrate. The first curvature can also be influenced by the specific adjustment of the fixing force.In a preferred embodiment, the deformation system is formed at least partially or completely by fixing elements. It is also conceivable that the deformation means is preferably designed exclusively for adjusting the first curvature and / or the second curvature and, for example, cannot fix or hold the first substrate and / or the second substrate in order to control the bonding process. A person skilled in the art preferably understands a structure to be an object of any kind that is manufactured on a substrate using a wide variety of processes. Examples of a structure would be the smallest units of a transistor, TSVs, but also the functional units defined below. The word structure is therefore used as a generic term. A person skilled in the art understands a functional unit to be a structure that has a functional character, i.e., one that can be regarded as an active part.Examples of this would be microchips, memory chips, LEDs, MEMS, etc. The person skilled in the art understands a displacement in particular to mean the change in position of a point from a first position to a second position. From a physical point of view, the person skilled in the art understands a distortion or stretching to mean the change in length relative to the initial length. Mathematically, it is the partial derivative of the displacement. The person skilled in the art understands a stretching to mean the lengthening of a body due to a distortion or stretching. The person skilled in the art understands a target state to be the idealized set of all structures with their ideal positions, in particular a set generated, calculated, and stored on a computer, or the set of all structures before a process step.A person skilled in the art preferably understands an actual state to be the real set of all structures, in particular those already created on the substrate, with their real positions, or the set of all structures after a process step. A person skilled in the art understands an overlay, in particular, to be a measure of the vector displacement of structures from a first process step to a second process step. An overlay is generally represented as a displacement vector field. Each structure on a substrate can be assigned a position for a first process step and a second process step. The displacement is the difference vector between these two positions, and the displacement vector field, or overlay, is the set of all these difference vectors between all structures.

[0026] A person skilled in the art preferably understands a substrate holder to be any component, in particular any group of components, with the aid of which a substrate is fixed and with the aid of which the advancing bond wave can be manipulated. A bond wave is understood to be the set of all interface points between two substrates that are being connected to one another, which delimit the outer regions that have not yet been bonded from the inner regions that have already been bonded. A synonym for bond wave would be bond interface or bond front. The modification of the first curvature and / or the second curvature is preferably carried out via fixing elements. The majority of all substrate holders already have corresponding fixing elements. There are also already substrate holders that have a plurality of fixing elements, in particular symmetrically distributed ones, so that position-controlled fixing of the substrate, i.e. the first substrate and / or the second substrate, is possible.By specifically controlling a fixation element, especially before and / or during and / or after the bonding wave passes over it, the applied force, and thus the resulting stretching or curvature, can be precisely adjusted. If the substrate holder has several fixation elements distributed across the substrate surface, the bonding wave can be controlled spatially.

[0027] Preferably, the deformation system comprises a plurality of deformation means arranged along the bonding direction. A plurality of deformation means, which are particularly homogeneously distributed along the bonding direction, advantageously makes it possible to locally influence the first curvature and / or second curvature throughout the entire bonding process, particularly in a targeted manner in the respective region to be bonded. Preferably, the deformation means and / or measures are arranged substantially equidistant from one another along the bonding direction. In the case of a radially propagating bonding wave, for example, the radial distance between two adjacent deformation means is substantially constant.

[0028] In particular, it is provided that during bonding by means of the deformation system, a difference between the first and second curvature is kept essentially constant, at least in sections, along the bonding direction. Preferably, the difference between the first and second curvature is deliberately kept constant over a distance which makes up more than 50%, preferably more than 75% and particularly preferably more than 80% of a bonding distance, wherein the bonding distance refers to the entire length over which the bonding process takes place. It has been found that by appropriately adapting the first and second curvatures to one another, the distortion or extent of the distortion between the first and second substrates can be kept as low as possible, which has a positive effect on any tension between the first substrate and the second substrate, as well as on positional accuracy when aligning the first substrate and the second substrate to one another."Substantially constant" means that the first curvature and / or second curvature deviate by no more than 15%, preferably no more than 10%, and particularly preferably no more than 5% from twice the arithmetic mean of the first curvature and the second curvature. Furthermore, it is preferably provided that the various deformation means in the individual deformation sections along the bonding path specifically ensure that the first curvature and the second curvature are essentially constant in their sum. The influence of the individual deformation means can differ from one another. In particular, the deformation means are individualized with regard to their influence or effect for the respective area to be bonded, which is assigned to the individual deformation means.

[0029] In particular, it is provided that the deformation system is changed during bonding, for example by means of a control device. For example, it is conceivable that the influence exerted by an individual deformation means in a deformation section is specifically controlled in order to influence the first curvature and / or the second curvature, in particular during the bonding process. This can advantageously take place during the bonding process. This makes it possible, for example, to even react to changes occurring during the bonding process and to adapt the influence accordingly to modify the first and / or second curvature. This can preferably be achieved, for example, by displaceable components that can be moved, for example, along a height direction running perpendicular to the main extension plane.In this case, the control device can be used to arrange the corresponding components at different heights using appropriate controls. It is also conceivable that a coating on the substrate holder could be controlled accordingly, for example, via an electrical voltage.

[0030] The movable components are controlled or regulated before and / or during and / or after the passage of the bonding wave in such a way that raising or lowering the components creates a new, in particular geometrically modified, state for the bonding wave or the area adjacent to the bonding wave. In particular, convex and / or concave regions can be created as a function of location. This controls the distortions locally in the substrates so that an optimal bonding result is achieved. Preferably, the deformation system is adjusted before bonding. In particular, the extent to which the first and / or second curvature is influenced in the individual deformation sections is determined depending on the type of the first and / or second substrate and particularly preferably based on corresponding empirical values.For example, one can draw on previous bonding processes which, for example, based on stress conditions within the arrangement of the first and second substrate, make it possible to determine in which areas a corresponding adjustment of the first and second curvature is advantageous during the bonding process. In order to gain knowledge of this behavior, the bonded substrates are preferably analyzed after the bonding process in order to determine the displacements between the structures on the lower and upper substrate as a function of position. This information makes it possible to modify the substrate surface of the, in particular the first, substrate holder such that the behavior of the bonding wave delivers a desired, optimal result at every point. The deformation system is then preferably used for a batch of first and second substrates to be bonded.For example, the roughness and / or waviness and / or adhesion ability of the substrate holder can already be considered and implemented during the production of the substrate holder.

[0031] For example, the procedure includes the following steps:

[0032] In a first method step, a first substrate is loaded onto a first substrate holder and fixed in place. In a second method step, a second substrate is loaded onto a second substrate holder and fixed in place. In a third method step, the first substrate is preferably aligned with the second substrate, preferably with the aid of appropriate optical devices. In a fourth method step, the substrate surface of the first substrate is bonded to the substrate surface of the second substrate on a substrate holder. In a fifth method step, the bonded substrate stack is removed from the device. In an optional sixth method step, the substrate stack is heat-treated. The modification of the first curvature and / or the second curvature preferably takes place in the fourth step.For the process in which the extent of the deformation influence is determined prior to bonding, substrate holders with fixture features such as a microstructure and / or a coating are particularly suitable. For the process in which the first curvature is influenced during the bonding process, a first substrate holder with a movable component proves advantageous. The individual fixtures are presented in detail below.

[0033] It is preferably provided that, to adjust the first curvature, a coating is arranged between the first substrate and a first substrate holder, which supports the first substrate during the bonding process. Preferably, a layer is deposited as the coating on at least one of the two substrates to be bonded together. The layer is applied to the substrate side opposite the substrate side to be bonded. This substrate side is referred to as the substrate back. The thickness of the layer is in particular inhomogeneous, i.e. it changes as a function of the location. Preferably, the layer is not applied over the entire surface of the substrate back, but only at specially provided locations, but generally at each location with a thickness intended for this purpose. The use of masks makes it particularly easy to coat those areas of the substrate back that are to be coated.In a preferred embodiment, the layer is an inorganic layer. The layer is preferably applied using a PVD, CVD, or PE-CVD process. Particular preference, especially using PE-CVD, is given to depositing a layer exclusively on the periphery of the substrate, preferably in a circular segment with a circular segment thickness between 1 mm and 10 mm. The exact circular segment thickness depends on the desired result. The layer should preferably consist of one of the following material classes, particularly the materials mentioned: metal, oxide, preferably SiO2, carbide, preferably SiCN, SiC, and / or nitride, preferably SiCN and / or SiN.

[0034] In a particularly preferred embodiment, the inorganic layer is an oxide layer between 10 nm and 5000 nm. The exact thickness of the oxide layer depends on the desired result. In a further development of the embodiment, the layer can be thinned and / or polished after deposition. Preferably, the deposition of the coating creates a targeted curvature of the substrate, particularly as a function of location, particularly in the edge region of the substrate. The layer is preferably deposited at elevated temperatures. Upon cooling, the substrate and the layer will generally expand differently because their thermal expansion coefficients are different. This results in the formation of a bend that compensates for the thermal stresses that occur. This bend then also influences the advancing bond wave during the bonding process.

[0035] A further subject of the present invention is a device for bonding a first substrate to a second substrate, in particular by means of a method according to the invention, wherein the first substrate has a primary section and the second substrate has a secondary section, wherein the device is configured such that during bonding of the first substrate to the second substrate, a bonding wave advancing along a bonding direction between

[0036] -- a first section in which the first substrate and the second substrate are connected, and

[0037] -- a second subsection, in which the first substrate and the second substrate are still to be connected, is formed, wherein preferably a subregion of the second substrate in the second subsection is offset in height relative to a subregion of the second substrate in the first subsection in a direction running perpendicular to a main extension plane, wherein the device for the relative alignment of the primary section and the secondary section to one another, in particular with respect to a direction running substantially parallel to the bonding direction, has a deformation system which is configured such that a first curvature of the first substrate and / or a second curvature of the second substrate can be modified in a region adjacent to the bonding wave or in a region comprising the bonding wave. All advantages and properties described for the method can preferably be applied analogously to the device and vice versa.

[0038] The device preferably comprises a first and / or a second substrate holder. The substrate holders, i.e., the first and / or second substrate holder, have fixing elements. The fixing elements have the primary task of holding and, in particular, fixing the first substrate and / or the second substrate during the bonding process. By selectively releasing fixing elements or by changing a state in which the fixing element holds or does not hold the substrate, the bonding process can be selectively adjusted in subregions of the first substrate and the second substrate, in particular such that a bonding process occurs along the bonding direction.The fixation elements can be mechanical fixations, in particular clamps; vacuum fixations, in particular with individually controllable vacuum tracks and / or interconnected vacuum tracks; electrical fixations, in particular electrostatic fixations; magnetic fixations; adhesive fixations, in particular Gel-Pak fixations; fixations with an adhesive, in particular controllable, surface. The fixation elements are in particular electronically controllable.

[0039] Vacuum fixation is the preferred fixation type. The vacuum fixation preferably comprises several vacuum tracks that emerge at the surface of the substrate holder. The vacuum tracks are preferably individually controllable. In a preferred embodiment, some vacuum tracks are combined to form vacuum track segments that can be individually controlled and thus evacuated or flooded. However, each vacuum segment is independent of the other vacuum segments. This makes it possible to construct individually controllable vacuum segments. The vacuum segments are preferably designed in a ring shape. This enables targeted, radially symmetrical fixation and / or detachment of a substrate from the substrate holder, particularly from the inside out.

[0040] In particular, it is provided that the first substrate is held in a first substrate holder during bonding, wherein the first substrate holder has fixing sections for fixing the first substrate and deformation sections for adjusting the first curvature. At the same time, it is conceivable that the fixing sections additionally or alternatively influence the first and / or second curvature. This can be achieved, for example, by a correspondingly modulatable fixing force. It is preferably provided that fixing sections and holding sections alternate at least in sections along the bonding direction, preferably over the entire bonding path. In this case, it is preferably provided that the area between two fixing elements that comes into contact with the substrate surface exerts a corresponding influence, so that the first and / or second curvature assumes a desired value.Preferably, the deformation system comprises a coating. In particular, if an adhesive or non-adhesive medium is applied to the contact surface in sections between two fixing elements, it is possible to influence the adhesion with which the first substrate rests against the contact surface in the corresponding area. This, in turn, influences the first curvature. This occurs in particular when, during the bonding process, a second section of the first substrate is raised relative to a first section of the first substrate.

[0041] Preferably, the adhesion capacity of the substrate holder surface can be specifically adjusted as a function of location by means of a coating in order to thereby vary the bond strength between the substrate and the substrate holder as a function of location. In a particularly preferred embodiment, the adhesion capacity could even be switched or regulated in a spatially resolved manner. It is conceivable to use functional polymers that are modified in the micro- and nanometer range so that the lotus blossom effect known from nature can be imitated. Further developments in research have shown that the use of electric and / or magnetic fields can bend these polymer structures, causing them to detach from the object adhering to them. Detaching these functional polymers from a substrate would lead to the van der Waals forces disappearing, thus making the substrate locally detachable.This enables a switchable, adhesive substrate holder surface. The coating is preferably applied to the substrate holder. However, it is also conceivable for the coating to be applied to the substrate and positioned between the substrate and the substrate carrier during operation of the device.

[0042] The deformation system preferably has a microstructure on a contact surface of the first substrate holder. This creates the roughness at the contact surface. It is conceivable to structure the substrate holder surface differently as a function of location in order to vary the adhesion between the substrate and the substrate holder as a function of location. One option would be to produce small holes with different geometries that change in size and / or orientation, particularly depending on the position on the substrate holder. The substrate holder could, for example, be coated with a photopolymer so that the pattern can be imaged into the photopolymer using a photolithographic process. The photopolymer is then developed and stripped. What remains is an etching mask. Using a chemical and / or plasma, the pattern is then etched into the substrate surface.The photopolymer is then removed, leaving a structured substrate surface. The pattern is preferably radially symmetrical.

[0043] Preferably, the deformation system comprises a displaceable contact surface. This can be achieved, for example, via deformation pins that are mounted in corresponding recesses and can be displaced by a corresponding height as required, in order to support the second subsection at least in some areas such that the desired or preferred first curvature and / or second curvature is set. Alternatively, it is conceivable for the displaceable contact surface to be formed by a segment into which several fixing elements are integrated. These displaceable segments can be adjusted in height as a whole in the substrate holder. Corresponding segments are preferably annular and arranged concentrically to one another.During the bonding process, the height of the individual segments is controlled and adjusted, which allows the first curvature in the area adjacent to the bond wave to be influenced accordingly.

[0044] Preferably, the substrate holder has a dynamic, modifiable substrate holder surface. In one embodiment, the substrate holder is constructed from movable segments. The segments can be centrally positioned circular segments. However, it is also conceivable for the centrally positioned circular segments to be further subdivided azimuthally, resulting in several radially and azimuthally divided segments. Each of these segments can be moved along a direction normal to the substrate holder surface, thus influencing the propagation of the bonding wave.

[0045] In one embodiment, the substrate holder has controllable or adjustable deformation elements that can be extended over the substrate holder surface. The substrate holder has a plurality of, in particular symmetrically distributed, recesses, preferably bores, in which movable deformation elements, in particular pins, are located. These deformation elements can be retracted and extended in a controlled or regulated manner and thus cause a local curvature of the substrate fixed to the substrate holder before and / or during and / or after the advancing bonding wave. Since the deformation elements allow for more delicate control than the segments of the previous embodiment, the second embodiment may be more advantageous. Furthermore, such a substrate holder is easier to manufacture and thus more economical.In a very special embodiment, the deformation elements themselves have fixing elements, in particular a bore through which a vacuum can be generated, so that the deformation elements are able to locally fix the substrate resting on the substrate holder and thus subject it not only to pressure but also to tension.

[0046] Preferably, the deformation system has a profiled contact surface. In particular, the individual deformation sections each have a profiled contact surface. The term "profiled" is understood by those skilled in the art to mean, in particular, a concave, convex, and / or stepped profile, which can thus influence the adhesion and support capacity acting from the individual deformation section onto the first subsection and / or second subsection. In a further embodiment, it would be possible to shape the substrate holder surface differently depending on the location, in particular convex or concave. It is also conceivable for the substrate holder surface to have a waviness that varies depending on the location. Due to this shaping, parts of the substrate are already slightly convex or concave, depending on the location.This means that, through purely geometric processing of the substrate holder surface, the bonding wave that later runs over the substrate holder can be influenced even before the bonding process. In a further embodiment, the substrate surface has a deviation from flatness at least at the position at which the substrates make their first contact, because in particular the second substrate is pressed onto the first substrate using a bond pin. This is preferably a dent, in particular a radially symmetrical one. A fixing element that promotes the fixing of the first substrate is preferably also located in the region of this dent. The first substrate is thereby pulled into the dent. Through this local creation of a curvature, the substrate surface of the first substrate to be bonded is compressed at least to its minimum.Preferably, a distortion, in particular a compression, is introduced before the bonding process even begins. Once the bonding process has been fully completed, the fixing elements of the first substrate holder are switched off. The first substrate will stretch the otherwise bonded second substrate slightly. This then leads to the stretching being increased in the area where the bonding wave has only just begun and, ideally, is then the same as the stretching that the second substrate experienced in those areas where the bonding wave was in a stable state. It has been shown that by applying such a distortion before bonding, the bonding result can be optimized and improved. It is preferably provided that the deformation sections have different influences on the first substrate.For example, in the case of movable segments or pin elements, it is conceivable that the set height of the individual deformation sections is different. In particular, it is intended that the deformation sections that are movable only shift during the bonding process, rather than already shifting as soon as the bonding process begins.

[0047] In particular, the first substrate holder has a raised portion in the edge region. This raised portion is designed, for example, as a fully enclosed base. This design feature serves, in particular, to eliminate or at least reduce edge defects (edge ​​voids) and the distortions that occur more frequently at the edge. The raised portion is greater than 10 nm, preferably greater than 500 nm, even more preferably greater than 1000 nm, most preferably greater than 2500 nm, and most preferably greater than 5000 nm. In most cases, the upper substrate of an upper substrate holder is deformed by a bond pin and brought into contact with the lower substrate. During this deformation process, the substrate surface of the second substrate to be bonded is stretched. The second substrate therefore has a convex curvature when viewed from above.To accommodate this stretching, it is advantageous to compress the surface of the first substrate to be bonded. When viewed from above, the first substrate exhibits a concave curvature. The substrate resting on the raised portion is thereby distorted, in particular compressed, in the edge region of its substrate surface to be bonded.

[0048] This is necessary because the deformation of the second substrate at the contact point of the bonding wave towards the edge is smaller, as the mechanical resistance of the wafer is lower (due to shorter remaining unbonded length) and an easier outflow of air from the bonding interface.

[0049] A further subject of the present invention is an arrangement comprising a first substrate and a second substrate, which is produced using a method according to the invention. All advantages and properties described for the device and the method can be applied analogously to the arrangement, and vice versa. Further advantages and features will become apparent from the following description of preferred embodiments of the subject matter according to the invention with reference to the accompanying figures. Individual features of the individual embodiments can be combined with one another within the scope of the invention.

[0050] It shows

[0051] Fig. 1 is a side view of a substrate holder according to a first exemplary embodiment of the present invention,

[0052] Fig. 2 is a side view of a substrate holder according to a second exemplary embodiment of the present invention,

[0053] Fig. 3 is a side view of a substrate holder according to a third exemplary embodiment of the present invention,

[0054] Fig. 4 is a side view of a substrate holder according to a fourth exemplary embodiment of the present invention,

[0055] Fig. 5 is a side view of an area during the bonding process with low fixation and

[0056] Fig. 6 is a side view of an area during the bonding process with strong fixation.

[0057] In the figures, identical components or components with the same function are identified by the same reference numerals. The figures are purely functional and schematic. The features in the figures are not to scale. In particular, some features are exaggerated to improve clarity and understanding. To improve clarity, accurate sectional views have been omitted.

[0058] The fixing elements 5 in the following descriptions of the figures are, for example and preferably, vacuum fixings. The regulation of the holding force of a substrate can be generated and illustrated particularly clearly here by the strength of the suction force. However, all other types of fixing elements are conceivable, in particular electrostatic fixings. Figure 1 shows a schematic side view of a first embodiment of a substrate holder 1 which has a plurality of fixing elements 5, which are arranged in particular in different fixing sections. The substrate holder 1 is used in a device for bonding or connecting a first substrate 2u and a second substrate 2o. In the operating state, the substrate holder 1 receives one of the substrates 2u, 2o to be connected. Preferably, the individual fixing elements 5 can be transferred individually or in groups between a fixing state and a release state.This advantageously also allows a bonding direction to be defined along which the first substrate 2u and the second substrate 2o are connected to each other. A bonding process develops along the bonding direction, with a first section that has already been bonded and a second section that is yet to be bonded being separated from each other by a bonding wave 3. During the bonding process, the bonding wave 3 shifts along the bonding direction.

[0059] In addition to the fixing sections, the substrate holder 1 comprises a deformation system. The deformation system preferably comprises a plurality of deformation sections, in each of which a deformation measure, in particular a deformation means, is provided. The deformation system is preferably designed to specifically adjust a curvature of the substrate 2u, 2o locally in a region adjacent to the bonding wave 3. The adjacent region refers to the region in front of the bonding wave 3, i.e. the region immediately before being bonded. The adjacent region preferably extends over a distance of up to 5 mm, preferably up to 2.5 mm, and particularly preferably up to 1 mm in front of the bonding section. In other words: the deformation system is designed to specifically act locally on the partial region of the substrate 2a, 2u that is arranged immediately in front of the bonding wave 3.In particular, the deformation system provides a deformation section in which the adjacent region is arranged straight and which specifically influences the substrate 2o, 2u in order to adjust its curvature before bonding. It is preferably provided that a plurality of deformation sections are formed along the bonding direction, which can specifically influence the curvature of the substrate 2o, 2u when the region adjacent to the bonding wave 3 enters the respective deformation section during bonding. In this way, the curvature of the substrate can be adjusted location-dependently for each subsection of the substrates to be bonded during bonding. In one embodiment, the deformation sections are formed by the fixing sections, in particular when the curvature of the substrates is influenced by means of the fixing elements. The substrate holder surface 1s of the substrate holder 1 has been modified and thus forms a modified substrate surface ormodified contact surface 6. The contact surface 6 comprises a plurality of deformation sections. In the example shown in Figure 1, the deformation sections and fixing sections alternate. For example, it is provided that the contact surface 6 forms a deformation section between two fixing elements. By modifying the contact surface 6, the curvature of the substrate 2o, 2u during bonding is then influenced. In particular, the contact surfaces 6 in the respective deformation sections are modified such that they increase or reduce the adhesive strength between the contact surface 6 in the deformation section and the substrate 2u, 2o. A modification of the contact surface 6 can also require a raising or lowering of a portion of the substrate.

[0060] Different modifications are shown as enlargements below the substrate holder 1.

[0061] The first type of modification can be achieved by a coating 10, particularly by polymers. The coating influences the bond strength between the substrate holder 1 and a fixed substrate 2 (not shown), particularly during the progression of a bonding wave during a bonding process. The physical properties of the coating 10 can change as a function of location and thus cause a spatially resolved influence on the bonding process, particularly in the area adjacent to the bonding wave.

[0062] The second type of modification is a structured substrate surface 11. Depending on the design of the structured substrate surface 11, a fixed substrate 2 (not shown) has more or less contact with the substrate holder 1 and is thus more or less firmly fixed. This embodiment is also intended to encompass the principle of roughness, i.e., the unevenness occurring in the nanometer and / or micrometer range.

[0063] The third and fourth types of modification represent a concave curvature 12 and a convex curvature 12'. These curvatures 12, 12' can have different radii of curvature at different positions of the substrate holder 1. If a substrate 2 (not shown) is pulled into a concave curvature 12 by a fixing element 5, for example, the substrate surface to be bonded is compressed. If, on the other hand, a substrate 2 (not shown) rests on a convex curvature 12', its substrate surface to be bonded is stretched. This makes it possible to adjust the distortion state with spatial resolution. The curvatures 12, 12' are shown in the figure as locally limited. However, it is also conceivable for the convex and / or concave curvatures to extend over larger areas of the substrate holder 1, in particular to comprise several fixing elements 5.It is also conceivable that the entire substrate holder surface 1s has only one well-defined concave curvature 12 or convex curvature 12'. In this macroscopic case, one can also speak of waviness.

[0064] Figure 2 shows a schematic side view of a second embodiment of a substrate holder 1. The substrate holder 1 has a raised portion 13 on its periphery. The raised portion 13 can, for example, be designed as a fully enclosed base. It is also conceivable for several such isolated and separate raised portions 13 to be located along a closed curve. The purpose of the raised portion 13 is to slightly raise a substrate 2 (not shown) at the edge. This slight elevation distorts, in particular compresses, the substrate surface to be bonded.

[0065] Figure 3 shows a schematic side view of a third embodiment of a substrate holder 1. The substrate holder 1 has several segments 7 that can be moved independently of one another. The centrally located segment 7 is preferably circular. The other segments 7 can be circular segments. It is also conceivable that the segments 7 are separated from one another in the azimuthal direction.

[0066] Figure 4 shows a schematic side view of a fourth embodiment of a substrate holder 1. The substrate holder 1 has several deformation elements 9 that can move in recesses 8, preferably bores. The deformation elements are controllable. The fixing elements 5, in turn, serve to fix the substrate 2 (not shown), while the deformation elements 9 can introduce distortions into the substrate 2 (not shown). The following two figures illustrate the physical principle of the bonding process as it is possible with the substrate holders 1 described above.All preferred methods can be traced back to the basic idea that the deviation between the structures of a substrate surface of a first substrate to be bonded and the structures of a substrate surface of a second substrate to be bonded is minimal if it is possible to influence the advancing bonding wave 3 during the bonding process such that the occurring distortions 4o, 4u are equal. This goal is achieved in particular by adjusting the distortions 4 in a substrate surface of at least one, preferably the lower, substrate. Influencing a distortion 4, in particular the distortion 4u of the first substrate 2u, is more expedient and easier to control.

[0067] All considerations presented always refer to a point on the interface between the two substrates 2u, 2o and are preferably carried out for all points on the interface. The distortions 4u and 4o shown refer to the substrate surfaces to be bonded on the substrates 2u, 2o, but for clarity, are shown in the center of the substrates 2u, 2o.

[0068] Figure 5a shows the schematic side view of a bonding process between two substrates 2u, 2o along the advancing bonding wave 3.

[0069] The lower substrate 2u was loaded onto a lower substrate holder 1u, and the upper substrate 2o onto an upper substrate holder 1o, and secured. A right-hand section of the bonding process is shown. Bonding wave 3 is represented only as a dot in the side view. Bonding wave 3 advances from left to right in the side view. It can be seen that the upper substrate 2o on the left side has already been bonded to the lower substrate 2u in the first section, while in the second section on the right side it is still held by the upper substrate holder 1o.

[0070] This causes a local lifting of the lower substrate 2u from the lower substrate holder 1u due to the force relationships prevailing around the bonding wave 3. The lower substrate 2u lifts off the lower substrate holder 1u by only a few nanometers or micrometers, in the worst case millimeters. This local lifting also creates local distortions 4u, 4o in the lower substrate 2u and / or in the lower substrate 2o. Figure 5b shows the schematic side view of a bonding process between two substrates 2u, 2o along the advancing bonding wave 3, in which the lifting of the lower substrate 2u from the substrate holder 1 is less pronounced than in Figure 5a. This is due to the influence of a deformation section, which influences the first curvature. It is conceivable and preferred that the lower substrate 2u is prevented from lifting off to a greater extent simply by a stronger fixing effect of the fixing element 5.This would be the simplest method to implement, since almost all substrate holders 1 have fixing elements 5. It is conceivable that the substrate surface has been modified and exerts a stronger adhesive force at this point. It is conceivable that the substrate surface has been coated, thus increasing the adhesive force. In contrast to Figure 5a, the lower substrate 2u does not lift off the lower substrate holder 1u as much because the corresponding fixing force is stronger. As a result, the bonding process also produces smaller distortions 4u in the lower substrate 2u. In general, the distortions 4o in the upper substrate 2o can also change. To better illustrate the bonding process, it is assumed that the distortions 4o in the upper substrate 2o do not change or change only negligibly. This enables a particularly simple comparison of the distortion ratios between Figure 5a and Figure 5b.

[0071] Figure 5c shows a schematic side view of a bonding process between two substrates 2u, 2o along the advancing bonding wave 3, in which the lifting of the lower substrate 2u from the substrate holder 1 is more pronounced than in Figure 5a. This is due to the influence of a deformation agent that influences the first curvature. It is conceivable that the lower substrate 2u experiences greater lifting simply due to a weaker fixing effect of the fixing element 5, because it can be pulled upwards more easily by the upper substrate 2o. This proves to be a comparatively simple way to implement the method, since virtually all substrate holders 1 have fixing elements 5. It is conceivable that the substrate surface has been modified, resulting in a lower adhesive effect at this point. It is conceivable that the substrate surface has been coated, resulting in a lower adhesive effect.In contrast to Figure 5a, the lower substrate 2u is lifted further from the lower substrate holder 1u because the corresponding fixing force is weaker. As a result, the bonding process also generates greater distortions 4u in the lower substrate 2u. In general, the distortions 4o in the upper substrate 2o can also change. To better illustrate the bonding process, it is assumed that the distortions 4o in the upper substrate 2o do not change or change only negligibly. This allows for a particularly simple comparison of the distortion ratios between Figure 5a and Figure 5c.

[0072] On the right-hand side of Figures 5a to 5c, the resulting distortions 4o of the upper substrate and the resulting distortions of the lower substrate 4u are shown again. The direction of the distortions of the upper substrate 4o was retained. The distortions 4u of the lower substrate were rotated and shifted parallel to the tips of the upper distortions 4o. A distortion 4u of the lower substrate 2u distorts the structures (not shown) on the lower substrate 2u. However, the same thing happens to the structures (not shown) on the upper substrate 4o due to the distortions 4o. Therefore, it is practical to define a resulting distortion 4r, which results from the difference between the two distortions 4u and 4o.This resulting distortion 4r is not necessarily equivalent to a mechanical distortion in the sense of stretching, but is a measure of the deviation of the positions of the structures (not shown) between the lower substrate 2u and the upper substrate 2o.

[0073] Figure 6 shows a schematic side view of a bonding process between two substrates 2u, 2o along the advancing bond wave 3, in which the bond wave 3 is already very close to the edge of the substrates 2u, 2o. Preferably, the distortion 2u of a lower substrate 2u can be adjusted by means of a raised portion 13 such that, together with the distortion 4o of the upper substrate, a resulting distortion 4r is generated, which is the desired result. This embodiment is particularly important for eliminating or at least reducing the edge defects (edge ​​voids).

[0074] In reality, it will not be possible to completely reduce the resulting distortions 4r. Preferably, the resulting distortions 4r should be at least homogeneous, i.e., the same magnitude at every position, at least in terms of magnitude.

[0075] List of reference symbols:

[0076] 1 substrate holder

[0077] 1 u first substrate holder 1o second substrate holder 1s substrate holder surface

[0078] 2u first substrate

[0079] 2o second substrate

[0080] 3 Bond wave 4, 4o, 4u, 4r distortion

[0081] 5 fixing elements

[0082] 6 Contact surface

[0083] 7 movable segment

[0084] 8 Recess 9 Deformation pin

[0085] 10 Coating

[0086] 11 Profiling

[0087] 12 local concave curvature

[0088] 12' local convex curvature 13 elevation

Claims

Claims Method for bonding a first substrate (2u) to a second substrate (2o), wherein the first substrate (2u) has a primary section and the second substrate (2o) has a secondary section, wherein during bonding of the first substrate (2u) to the second substrate (2o) a bonding wave (3) advancing along a bonding direction is formed between -- a first section in which the first substrate (2u) and the second substrate (2o) are connected, and -- a second subsection, in which the first substrate (2u) and the second substrate (2o) are still to be connected, wherein preferably a subregion of the second substrate (2o) in the second subsection is offset in height relative to a subregion of the second substrate (2o) in the first subsection in a direction running perpendicular to a main extension plane, and wherein for the relative alignment of the primary section and the secondary section to one another, in particular with respect to a direction running substantially parallel to the bonding direction, a first curvature of the first substrate (2u) and / or a second curvature of the second substrate (2o) is modified by means of a deformation system in a region adjacent to the bonding wave (3) and / or in a region comprising the bonding wave (3).The method according to claim 1, wherein, during bonding by means of the deformation system, a difference between the first curvature and the second curvature along the bonding direction is kept substantially constant, at least in sections. The method according to one of the preceding claims, wherein the deformation system comprises a plurality of deformation means arranged along the bonding direction. The method according to one of the preceding claims, wherein the deformation system is changed during bonding, for example, by means of a control device. Method according to one of the preceding claims, wherein the deformation system is adjusted prior to bonding. Method according to one of the preceding claims, wherein, for adjusting the first curvature, a coating is arranged between the first substrate (2u) and a first substrate holder (1u), which supports the first substrate (2u) during the bonding process. Device for bonding a first substrate (2u) to a second substrate (2o), in particular by means of a method according to one of the preceding claims, wherein the first substrate (2u) has a primary section and the second substrate (2o) has a secondary section, wherein the device is configured such that, during bonding of the first substrate (2u) to the second substrate (2o), a bonding wave (3) advancing along a bonding direction is formed between -- a first section in which the first substrate (2u) and the second substrate (2o) are connected, and -- a second subsection, in which the first substrate (2u) and the second substrate (2o) are still to be connected, wherein preferably a subregion of the second substrate (2o) in the second subsection is offset in height relative to a subregion of the second substrate (2o) in the first subsection in a direction running perpendicular to a main extension plane, wherein the device for the relative alignment of the primary section and the secondary section to one another, in particular with respect to a direction running substantially parallel to the bonding direction, has a deformation system which is configured such that a first curvature of the first substrate (2u) and / or a second curvature of the second substrate (2o) can be modified in a region adjacent to the bonding wave (3) and / or in a region comprising the bonding wave (3).Device according to claim 7, wherein the first substrate (2u) is held in a first substrate holder (1u) during bonding, wherein the first substrate holder (1u) has fixing sections with fixing element (5) for fixing the first substrate (2u) and / or deformation sections with deformation means for adjusting the first curvature. Device according to claim 8, wherein fixing sections and deformation sections alternate at least in sections along the bonding direction. Device according to one of claims 7 to 9, wherein the deformation system has a coating that is arranged between the first substrate (2u) and the first substrate holder (1u) and / or between the second substrate (2o) and the second substrate holder (1o) during the bonding process. Device according to claims 7 to 10, wherein the deformation system comprises a microstructure on a contact surface (6) of the first substrate holder (1u) and / or second substrate holder (1o). Device according to one of the preceding claims, wherein the deformation system comprises a contact surface (6) that is displaceable at least in sections.Device according to one of the preceding claims, wherein the deformation system has a contact surface (6) that is profiled at least in sections, wherein the profiled contact surface (6) is concave, convex, and / or stepped. Device according to one of claims 6 to 13, wherein the first substrate holder (1u) and / or second substrate holder (1o) has a raised portion in the edge region as part of the deformation system. An arrangement comprising a first substrate (2u) and a second substrate (2o) produced using a method according to one of claims 1 to 6, preferably using a device according to one of claims 7 to 14.

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