Device and method for preventing edge defects by means of an edge coating

Abstract

The invention relates to a method and a device for fusion bonding and to substrate stacks. According to the invention, edge defects can be prevented by means of an edge coating, and fusion bonding includes a heat treatment.

Description

[0001] Description

[0002] Device and method for preventing edge defects by means of an edge coating

[0003] The present invention relates to a method and a device for preventing edge defects during fusion bonding by means of an edge coating. The substrates or substrate stacks are subjected to a heat treatment.

[0004] For several years, substrates have been joined together using so-called bonding processes. In particular, the direct bonding of two surfaces at room temperature, which initially forms a so-called pre-bond followed by a subsequent heat treatment step, is of immense interest to the semiconductor industry.

[0005] This bonding method is known as direct or fusion bonding. With fusion bonding, it is possible to immediately bond the substrate surfaces together after an alignment process that aligns both substrates. The adhesion properties of the surfaces, particularly their hydrophilicity, are specifically utilized. The substrates are first brought together at a very close distance. This is followed by a bend in the substrate, particularly the upper one, so that the two substrates come into contact, ideally at a point. Shortly thereafter, the bonding of the substrate, particularly the upper one, is released. Due to gravity and / or targeted control, a bonding wave propagates from the contact point, creating a full-surface contact and thus a full-surface pre-bond between the two substrates. The resulting substrate stack is often then heat-treated.

[0006] During the propagation process of the bond wave, gases in front of the bond wave are compressed and pushed forward. The bond interface remains, at least for the most part, free of gas inclusions.

[0007] A very common phenomenon during the creation of pre-bonds are so-called edge defects, in particular edge voids. These edge voids are gas inclusions that form when the gas condenses due to a change in its physical state. The bonding wave then spreads across the condensed gas and locally encloses it. After the pre-bond has been created, the physical state changes again, resulting in the evaporation of the previously condensed gas. This evaporation then leads to local destruction of the pre-bond, which can be detected by ultrasonic or infrared measurements. Castex et al., Mechanism of Edge Bonding Void Formation in Hydrophilic Direct Wafer Bonding, 2013 ECS Solid State Lett. 2 P47 describe in great detail how the condensation of the gas occurs before the bonding wave.The substrate surfaces of the substrates or substrate stacks to be bonded are not entirely pure. Different atoms and molecules are adsorbed onto substrate surfaces, even if only in a single layer or monolayer. Due to the fact that every atmosphere contains a significant amount of water vapor, water is one of the dominant components detectable on the substrate surface. Furthermore, organic substances, even particles or atomic or molecular gases such as oxygen, nitrogen, or helium, can adhere to the substrate surface. It is assumed that the substrate surface is free of organic components, especially particles. The typical size of edge defects, especially voids, is between 1 micrometer and 500 micrometers.

[0008] Gases, and especially gas mixtures, have a Joule-Thompson coefficient (JTC) that depends on pressure and temperature. The JTC determines whether a gas or gas mixture cools or heats up during isenthalpic expansion. Isenthalpic expansion is the transition of a gas or gas mixture from a first, compressed state to a second, less compressed state in which the enthalpy of the gas is conserved. Gases or gas mixtures with a positive JTC cool down during isenthalpic expansion. Gases or gas mixtures with a negative JTC heat up during isenthalpic expansion.

[0009] The underlying physical effect is the ability of the molecules to attract or repel each other. If the molecules attract each other at a given temperature, work must be done, i.e. energy must be used to separate them. This work is removed from the system, thereby reducing the speed of the molecules and thus the temperature. If the molecules repel each other at a given temperature, work is done by the system, i.e. energy is released. This released energy increases the speed of the molecules and thus the temperature. The paper Castex et al., Mechanism of Edge Bonding Void Formation in Hydrophilic Direct Wafer Bonding, 2013 ECS Solid State Lett. 2 P47 describes in great detail which physical processes take place near the substrate edge.

[0010] To simplify matters, the gas or gas mixture experiences a very strong pressure drop upon exiting the substrate space. Due to the fact that the process takes place in a fraction of a second, the energy cannot be dissipated quickly enough, and the process can be considered isenthalpic. Consequently, the JTC of the gas or gas mixture determines whether the gas or gas mixture cools or heats up during isenthalpic expansion. The cooling of the gas or gas mixture can be so strong that the temperature falls below the dew point of the gas or gas mixture, and the gas or gas mixture, or individual components of the gas mixture, condense. The substrate surface serves as a crystallization nucleus. This is therefore a heterogeneous nucleation process, which requires an even lower

[0011] Nucleation energy is higher than homogeneous nucleation in the gas phase. This physical process of condensation must be avoided.

[0012] US 10964562B2 describes an approach to avoid the aforementioned effects. Here, the substrate bonding plane was enlarged using auxiliary means to move the condensation site away from the actual substrate surface.

[0013] Furthermore, the local atmosphere and / or pressure between the substrates to be bonded was influenced, as disclosed in US20220139735A1 or US 11 101 132B2. The described technical teachings attempt to shift the location of the condensation or to change the condensation by means of complex devices and influencing the atmosphere and / or pressure.

[0014] It is therefore the object of the invention to at least partially eliminate, and in particular to completely eliminate, the disadvantages listed in the prior art. In particular, it is an object of the invention to provide improved methods and devices for preventing edge defects during fusion bonding. It is also an object of the present invention to remove fluids or gas mixtures between the bonding substrates or substrate stacks and to prevent them from condensing.

[0015] The present object is achieved by the features of the independent claims. 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 ​​within the specified limits are also considered to be disclosed as limit values ​​and can be claimed in any combination.

[0016] Accordingly, the invention relates to a method for fusion bonding at least two substrates with at least the following steps, in the following order, i) providing a first substrate with an edge coating and providing a second substrate, ii) contacting the first substrate with the second substrate to initiate a bonding wave for fusion bonding to form a substrate stack, wherein in the substrate stack the second substrate rests at least partially on the edge coating of the first substrate in an edge region of the substrate stack, so that in the edge region of the substrate stack the first substrate and the second substrate are spaced apart, iii) heat treatment of the substrate stack, wherein the edge coating is designed to be gas-permeable, so that when the bonding wave propagates during fusion bonding in step ii), fluids are discharged from the substrate stack being formed.

[0017] In other words, a fusion bonding method is presented in which an interruption of the bonding wave is initially caused by the edge coating. This ensures that fluids can escape from the bonding interface throughout the entire fusion bonding process, preventing or reducing entrapment and thus defects in the substrate stack, particularly voids. In a subsequent heat treatment, the edge coating is at least partially, preferably completely, removed from the substrate stack, allowing the two substrates to bond via a further propagating bonding wave, even at the periphery.

[0018] The fluids – gases and / or vapors – expelled from the atmosphere during fusion bonding with the bond wave and condensed at the substrate edge are advantageously stimulated by the external heat input to undergo a phase transition back into the gas phase, so that they are expelled or diverted through the gas-permeable edge coating between the substrates in the bond interface. Gas permeability is achieved by openings in the edge coating, which can be formed, for example, by outlet channels in the edge coating or an open-pore edge coating material.

[0019] In particular, the edge layer is formed in such a way that its viscosity is reduced upon heating, allowing the edge layer to flow out of the substrate stack and be removed. The resulting further approach to the substrate stack edge is understood as a further and slow progression of the bonding wave, which allows the edge layer material to be pushed out of the bonding interface upon heating by this bonding wave.

[0020] Provision is typically made using substrate holders. When the bonding wave is initiated, the second substrate is released, allowing the bonding wave to propagate. After the substrates are connected to the edge, the bonding wave is stopped by the edge coating, leaving a gap between the substrates in the edge region. The gas permeability of the edge coating advantageously allows the fluid in the bonding interface to escape as the bonding wave progresses. Furthermore, the gas permeability allows the fluid to escape when it is forced out during heat treatment. The liquid portion of a fluid can also be drained away through the gas-permeable edge coating.

[0021] The process advantageously leads to a reduction or prevention of edge defects, especially voids. Furthermore, the process can be easily integrated into existing processes to further improve them and increase cycle times. Furthermore, a fusion bond between two substrates is advantageously created in a gentle manner.

[0022] In a preferred embodiment of the fusion bonding method, it is provided that the provision of a first substrate in step i) comprises the application of the edge coating, wherein the application is carried out immediately before fusion bonding. In other words, in addition to any further measures such as surface activation of the surfaces of the substrates to be bonded, the edge coating is advantageously applied before fusion bonding. In this way, the fusion bonding method can be carried out particularly efficiently. In a preferred embodiment of the fusion bonding method, it is provided that the edge coating is at least partially, preferably completely, removed from the substrate stack during the heat treatment. The edge layer material can be heated, in particular in a targeted manner. The edge coating material sublimates and / or liquefies.The substrates that continue to bond together continue to drain fluids from the bond interface.

[0023] In a preferred embodiment of the fusion bonding method, it is provided that during the heat treatment, a counterforce provided by the edge coating is reduced by heating an edge layer material of the edge coating, so that the edge layer material is pressed out of the substrate stack by bonding energy in the edge region. In this way, it can be ensured that as little edge coating material as possible remains in the substrate stack. It has surprisingly been found that, during the heat treatment, the first substrate and the second substrate of the substrate stack, nestling against one another, press the coating material out of the bonding interface and thus divert it in a targeted manner. During this process, fluids can also escape from the bonding interface.In other words, the bond wave stopped by the edge coating continues to propagate because the strength of the edge coating is reduced by the heat treatment, allowing the material to flow out of the substrate stack. Additionally, bonding forces act between the substrates, which can push the edge layer material out of the substrate stack. The edge layer material is specifically directed outwards and towards the periphery of the substrate stack. Residues of the edge coating can remain between the two substrates. The edge coating material can therefore still be present in the edge area of ​​the substrate stack or on the outside of the substrate stack even after the fusion bond. Condensing liquids or other fluids in the bond interface are thus carefully and specifically drained away.In a preferred embodiment of the fusion bonding method, it is provided that during the heat treatment, a counterforce provided by the edge coating is reduced by heating an edge layer material of the edge coating, so that the edge layer material is pressed out of the substrate stack by bonding energy in the edge region. In other words, in particular, the viscosity of the edge coating material or of the edge layer material is reduced, so that the edge coating material flows out of the bonding interface. The bonding energy in the edge region of the substrate stack is greater than the counterforce of the edge coating. In this way, the material can advantageously escape and, at the same time, the remaining fluid can be expelled or removed from the substrate stack particularly effectively. In particular, condensate can be drained away particularly well in this way.In addition, distortion in the edge area is advantageously reduced, thus increasing bonding accuracy.

[0024] In a preferred embodiment of the fusion bonding method, the heat treatment is carried out between 100°C and 1200°C, preferably between 120°C and 600°C, particularly preferably between 140°C and 450°C, and optimally between 150°C and 400°C. In other words, the substrate stack is brought to the aforementioned temperatures during the heat treatment, so that the edge layer is advantageously removed from the substrate stack in a controlled manner. In an alternative embodiment, only the edge region of the substrate stack is gently heated during the heat treatment, so that the remaining inner region can be protected.

[0025] By using special, modified substrates, especially with modified oxide surfaces, the heat treatment temperatures can be reduced to almost room temperature. In this case, the heat treatment is carried out at temperatures below 1200°C, preferably below 800°C, more preferably below 500°C, most preferably below 100°C, and most preferably below 50°C. The publications WO2012100786A1, WO2012136268A1, WO2012136266A1, WO2012136267A1, and WO2014015899A1 disclose such special, modified substrates. In this case, the edge coating material is preferably adapted to the lower temperatures so that removal is still possible.

[0026] In a preferred embodiment of the fusion bonding method, the edge layer material is a thermoplastic. Thermoplastics are polymers that can be reversibly deformed (thermoplastically) within a specific temperature range. Thermoplastics have proven particularly suitable for carrying out the claimed fusion bonding method. Furthermore, thermoplastics can be removed from the substrate stack particularly easily and can be applied particularly easily. Furthermore, thermopastes can stop the bonding wave particularly gently and are also advantageous for the structured coating of the substrate. Furthermore, thermopastes can be easily applied before fusion bonding.

[0027] In a preferred embodiment of the fusion bonding method, the substrates are circular wafers and the edge coating of the first substrate is arranged in a circular ring around an outer circumference of the first substrate. In other words, with circular substrates, the edge coating is arranged regularly over the outer circumference of the substrate. Exit channels can interrupt the edge coating. Furthermore, during fusion bonding, the second substrate can advantageously be stopped or held simultaneously and regularly at the periphery of the forming substrate stack. In a preferred embodiment of the fusion bonding method, a size ratio (D : d) of an outer diameter (D) of the edge coating to an inner diameter (d) of the edge coating is between 1 and 2, preferably between 1.1 and 1.9, more preferably between 1.2 and 1.8, even more preferably between 1.3 and 1.7.

[0028] In a preferred embodiment of the fusion bonding method, the width is less than 10 mm, preferably less than 5.0 mm, even more preferably less than 2.0 mm, most preferably less than 1.0 mm, and most preferably less than 0.5 mm. The width is defined as the difference between the outer radius R of the edge coating and the inner radius r of the edge coating. The aim is to achieve widths that are as small as possible in order to reduce the area of ​​the edge coating, since this can also be regarded as contamination. These widths have surprisingly proven to be particularly suitable for carrying out the fusion bonding method gently and without edge defects. This edge layer width has also proven to be particularly advantageous for gently stopping the bonding wave and providing a support surface for the second substrate.In addition, the edge layer can be easily removed from the substrate stack during heat treatment or pushed outwards from the substrates without leaving any residue.

[0029] In a preferred embodiment of the fusion bonding method, the height h of the edge coating is between 0.01 micrometers and 1000 micrometers, preferably between 0.1 micrometer and 500 micrometers, particularly preferably between 1 micrometer and 250 micrometers, most particularly preferably between 5 micrometers and 200 micrometers, and optimally between 10 micrometers and 150 micrometers. By dimensioning the height of the edge coating, the distance in the edge region of the substrate stack can advantageously be optimally adjusted. The aforementioned dimensions are particularly suitable for stopping the bonding wave and ensuring the escape of fluids.

[0030] In a preferred embodiment of the fusion bonding method, the edge coating is provided with outlet channels. Gases or fluids can escape through these outlet channels during fusion bonding. Furthermore, these outlet channels can advantageously be used to divert gases from the bonding interface during heat treatment.

[0031] In a preferred embodiment of the fusion bonding method, the outlet channels are formed between structures regularly distributed over an outer circumference of the first substrate. In other words, an outlet channel is provided between each structure for the escape and discharge of gases during fusion bonding.

[0032] In a preferred embodiment of the fusion bonding method, the outlet channels are formed between structures arranged so as to be regularly distributed over an outer circumference of the first substrate. The outlet channels are thus indirectly defined by the structures. Such an edge coating can advantageously ensure the escape of fluids and can be applied particularly easily. In addition, the structures can advantageously define a direction for the escape of the fluids. In addition, the removal of the edge layer during heat treatment can advantageously be adjusted by the shape of the structures. In a preferred embodiment of the fusion bonding method, the structures are circular. In this way, the structures can be applied particularly easily and arranged regularly.In addition, a support surface is advantageously provided which only touches or separates the second substrate in certain areas.

[0033] In a preferred embodiment of the fusion bonding method, the structures are circular ring sections. Circular ring sections are particularly suitable for discharging fluids from the substrate stack, as they provide straight outlet channels with increasing cross-sections. It is also possible to first apply a continuous, full-circumference circular ring, followed by the creation of the outlet channels.

[0034] In a preferred embodiment of the fusion bonding method, the edge coating is porous. In other words, the edge coating is provided with a plurality of cavities that allow gases to be dissipated and absorbed.

[0035] In a preferred embodiment of the fusion bonding method, the edge coating is formed from an open-pored and porous material. In other words, the edge coating has a high proportion of interconnected cavities, such that the edge coating is gas-permeable. Gases can then escape through the open pores through the edge coating. In this case, the pores can also particularly advantageously absorb the gases, so that these are removed with the edge layer or with the material during the heat treatment. In this case, the gas can advantageously be absorbed in the porous edge layer material and even condense in it. In this way, the fluid can be drained or removed from the bonding interface particularly effectively. The escape of the fluid takes place particularly evenly, and the escape can advantageously be adjusted by the pore size.Particularly preferably, the pores in the edge coating can be interconnected, making the edge coating open-pored and allowing fluid to escape particularly effectively. During the subsequent heat treatment to close the bond interface and expel the edge coating, the embedded fluids are expelled from the closing bond interface along with the edge coating material, preventing deposits or edge defects from forming in the bond interface.

[0036] In a preferred embodiment of the fusion bonding method, the edge coating is applied over the entire edge region, in particular over its entire circumference. In other words, the edge coating is continuously circular and thus distributed over the entire circumference. In this way, the second substrate can rest particularly well on the edge coating and the bonding wave can be stopped. Furthermore, the edge coating can be applied particularly easily. Furthermore, gas is only discharged through the open pores, so that the gas is additionally retained in the edge coating and removed along with it. Thus, no fluid is deposited on the substrate edge.

[0037] In a further preferred embodiment of the fusion bonding method, the edge coating is applied as a fully circumferential, porous annulus. In a particularly preferred embodiment, the structure is open-pored, so that fluids can escape through the pores of the edge coating. Thus, in particular in a coating process, a porous, in particular open-pored, fully circumferential annulus structure is created, which does not require further processing steps such as exposing the outlet channels. The edge coating can thus guide the fluid flowing out of the bonding interface during fusion bonding and, in particular, absorb it in the pores. Thus, no fluid is deposited on the substrate edge.During the subsequent heat treatment to close the bond interface and to press out the edge coating, the stored fluids are pressed out of the closing bond interface together with the edge coating material, so that no deposits or edge defects can occur in the bond interface.

[0038] All of the aforementioned features of the method and the associated advantages also apply in connection with the substrate stacks and the device.

[0039] Furthermore, the invention relates to a substrate stack comprising a first substrate with an edge coating and a second substrate, wherein the substrate stack is connected by fusion bonding, and wherein in the substrate stack the second substrate rests at least partially on the edge coating of the first substrate in an edge region of the substrate stack, so that in the edge region of the substrate stack the first substrate and the second substrate are spaced apart, and wherein the edge coating is designed to be gas-permeable.

[0040] The provision of such a substrate stack advantageously allows fluids to escape in the bonding interface. Furthermore, heat treatment makes it possible to remove the edge layer from the fusion-bonded substrate stack, preventing gas and liquid inclusions. Gas permeability can be ensured by channels, openings, and / or pores in the wheel coating material. Particularly preferably, fluids can also be trapped or absorbed in the cavities or pores, so that the fluid can be removed from the substrate stack together with the edge coating. The pores advantageously absorb a portion of the fluid. Trapped and thus bound fluid can thus be advantageously removed or expelled from the substrate stack along with the edge coating material.

[0041] The invention further relates to a substrate stack produced by the method for fusion bonding at least two substrates. The substrate stack is particularly free of edge defects and exhibits high bonding accuracy because distortions at the edge are avoided.

[0042] Furthermore, the invention relates to a device for fusion bonding at least two substrates, configured to carry out the method for fusion bonding at least two substrates, at least comprising: a) provision means for providing a first substrate with an edge coating and providing a second substrate, b) contacting means for initiating a bonding wave between the first substrate and the second substrate, for fusion bonding to a substrate stack, wherein in the substrate stack the second substrate can be placed at least partially on the edge coating of the first substrate in an edge region of the substrate stack, so that in the edge region of the substrate stack the first substrate and the second substrate are spaced apart, c) heat treatment means for heat treating the substrate stack, wherein the edge coating is designed to be gas-permeable, so that when the bonding wave propagates during fusion bonding, fluids,can be derived from the forming substrate stack (8). The device advantageously enables gentle and error-free fusion bonds. Edge defects, in particular gas inclusions, can be advantageously avoided. The device preferably comprises an application means for applying the edge coating. In some advantageous embodiments, the device also comprises a heating module.

[0043] In a preferred embodiment of the fusion bonding device, the heat treatment means are configured to specifically heat only the edge region containing the edge coating. This allows the edge coating to be removed from the substrate stack particularly gently.

[0044] A particularly important aspect of the present invention is that, prior to the fusion bonding of substrates or substrate stacks, gas inclusions can be prevented by a particularly annular coating of the substrate edge of at least one substrate or substrate stack. For this purpose, the coating or coating material is automatically compressed in the edge zone, which is particularly relevant for the inclusions, after the aligned fusion bonding during the heat treatment step.

[0045] A modified or alternative fusion bonding process is therefore specified which eliminates edge defects, in particular gas inclusions, by coating the substrate edge. One advantage is the easy integration of the process into existing bonding processes. The process increases bonding accuracy because defects are eliminated. Overall, this increases cycle time and bond quality. An important aspect is that the substrate surface or surfaces are coated in a ring-shaped manner around the entire circumference of the substrate edge in order to keep the coating at a distance from the substrate stack edge during fusion bonding. This prevents the gas, which is displaced from the center outwards by the bonding wave during the bonding process, from condensing between the substrates, particularly near the substrate edges, and forming inclusions. The gases can escape at the open substrate stack edge in the edge region.

[0046] In a heat treatment step, particularly during the conversion of a pre-bond into a permanent bond, the advancing bond wave pushes the softening coating material out of the bond interface along with the remaining gases. This creates a bond free of edge defects. In other words, the gas is forced out of the space between the substrates. Since the condensation site is covered by the coating and thus a distance is maintained between the substrate edges, the condensed gas can escape in a quasi-stationary process during the formation of the permanent bond during annealing of the substrates. During annealing, the coating is compressed by the adhering substrates, so that the edge of the substrate stack is also bonded.

[0047] The goal of obtaining a gas inclusion-free substrate stack edge after fusion bonding is achieved by exploiting the phase transition of the coating of the substrate edge.

[0048] A material, particularly a thermoplastic material, applied to the substrate edge of at least one substrate is used as a thermally deactivated, irreversible spacer during fusion bonding. This locally impedes the bonding wave as it advances toward the substrate stack edge, preventing it from traversing the full diameter of the substrate stack. This prevents the formation of condensed gas inclusions at the substrate stack edge. Heat is used for complete bonding, i.e., for the formation of a covalent bond between the substrate stack. With the controlled energy supply in the form of thermal energy, the coating softens and can be plastically deformed. In other words, the viscosity of the coating material is reduced with heating. This allows the bonding wave to gradually push the heated and thus plastically deformable edge coating out of the bonding interface as it advances again.Thus, the temperature control of the substrate stack influences the progression of the bond wave in the edge zone of the substrate stack. It is advantageous that no constraint or external force acts on the substrate stack, thus also reducing distortion at the substrate stack edge.

[0049] The substrates can be of any shape, but are preferably circular. The diameter of the substrates is, in particular, industrially standardized. For wafers, the standard diameters are 1 inch, 2 inches, 3 inches, 4 inches, 5 inches, 6 inches, 8 inches, 12 inches, and 18 inches. However, in principle, any substrate can be used, regardless of its diameter.

[0050] The method for fusion bonding a first substrate surface of a first substrate to a second substrate surface of a second substrate is characterized in particular in that at least one substrate is coated in a ring-shaped manner, in particular completely - in particular regularly over the entire circumference, at the substrate edge before bonding with a coating material, in particular a thermoplastic coating material, the substrates are joined together in a fusion bonding process, in particular aligned with one another, and that the edge of the substrate stack is kept at a distance by the coating during the prebond, wherein the distance of the edge is eliminated during the production of the permanent bond by the substrates nestling together automatically and the coating is pressed in the process.An exemplary embodiment of the method for fusion bonding comprises the following steps, in particular at least carried out successively and / or simultaneously, in particular with the following sequence:.

[0051] In a first process step, at least one substrate is coated on the peripheral edge, in particular in a ring shape, with an organic or inorganic coating material.

[0052] The coating is preferably applied by one of the following methods:

[0053] • Spin coating,

[0054] • Spray painting,

[0055] • CVD,

[0056] • PECVD or

[0057] • PVD .

[0058] In a second, optional process step, the substrate surfaces to be bonded are activated. Plasma treatment can be used to activate at least one of the substrate surfaces to be bonded.

[0059] In a third process step, the substrate surfaces to be bonded are cleaned or hydrophilized with ultrapure water.

[0060] In a fourth process step, a first substrate is picked up on a first receiving device of the bonder.

[0061] In a fifth process step, a second substrate is picked up on a second receiving device of the bonder.

[0062] In a sixth process step, the substrates are aligned to each other, in particular using alignment marks.

[0063] In a seventh process step, the substrates are brought closer to each other, but not contacted. In an eighth process step, at least one substrate is deformed, for example, by means of a bond pin and / or a fluid flow, to enable point contact, preferably a point contact, less preferably a line contact.

[0064] In a ninth process step, the first and second substrates are brought into contact with each other at a contact point or in a small area section.

[0065] In a tenth process step, at least the first substrate and / or the second substrate are gradually and controlledly released from the respective holding device and thus released. The effect of the release is macroscopically observable as the path of the bonding wave. The bonding wave is prevented from passing completely or stopped by the coating at the substrate edge.

[0066] In an eleventh process step, the substrate stack is removed from the fusion bonding device.

[0067] In a twelfth process step, the substrate stack is placed in a heating device, in particular an oven.

[0068] In a thirteenth process step, heat is added to the substrate stack according to a defined temperature profile. The thermal treatment softens the coating. Since the resistance or counterforce to the bonding energy of the coating is removed, the force ratio shifts towards the elastic forces of attraction, which in turn causes the bonding wave to continue. The slowly advancing substrate surfaces press any gas molecules and coating material out of the bonding surface. This way, the edge of the substrate stack is joined without defects. As the bonding wave progresses slowly, the gases between the substrates have time to resublimate so that they can be completely pushed out of the bonding interface. In a particularly preferred extension, the coating is even completely removed during this process step.In a fourteenth process step, the controlled heat treatment converts the weak holding forces of the substrate stack into strong holding forces, so that hybrid bonds and / or metallic bonds and / or covalent bonds are formed.

[0069] An exemplary embodiment of the device for fusion bonding, in particular a first substrate surface of a first substrate with a second substrate surface of a second substrate, comprises: a first substrate holder for receiving the first substrate, a second substrate holder for receiving the second substrate, wherein at least the first substrate holder has a fixing device for fixing the first substrate and the second substrate holder has a fixing device for fixing the second substrate, at least one substrate holder of the first and / or the second substrate has a controlled deformation device for deforming the first substrate and / or the second substrate,which distorts the substrate and / or the substrates to reduce alignment errors and / or prestresses the first and / or the second substrate to initiate a fusion bond, and wherein the deformation and / or prestressing of the substrate occurs from the side of the substrate opposite the bonding and / or from the substrate edge, and further optionally a coating device with which the edge of the first substrate and / or the second substrate is coated, in particular completely.

[0070] The device can be constructed in a modular design and in particular contain the following modules (at least one module each):

[0071] -Alignment module with an alignment device for aligning the first substrate to be bonded and the second substrate -Fusion bonding module with a fusion bonding device for bonding the first substrate and the second substrate to a fusion-bonded substrate stack,

[0072] -Cleaning module with a cleaning device, in particular with DI water for the removal of particles from the substrate surface and generation of OH bonds for fusion bonding,

[0073] -Edge coating module, with an edge coating device for forming the edge coating on at least one of the substrates to be bonded,

[0074] -Plasma treatment module, with a vacuum plasma chamber,

[0075] -Transport module, with transport device for substrates and / or substrate stacks,

[0076] -Storage and / or transport module, and also

[0077] Supply modules for media, auxiliary modules for particle reduction of the device.

[0078] In a further preferred embodiment of the device, the device may further comprise at least the following modules:

[0079] -Alignment and fusion bonding module with an alignment device in which the fusion bonding device is integrated,

[0080] -at least one cleaning and edge coating module, in which a cleaning device for DI water and an edge coating device are integrated,

[0081] -a plasma treatment module with a vacuum plasma chamber and media supply for the plasma treatment.

[0082] It is conceivable that a heating module could be integrated into the bonding device, which would enable full-surface and inclusion-free bonding of the fusion-bonded substrate stack, which is held at a distance at the edges by coating material. In a preferred embodiment, the heating module acts only on the edge region of the substrate stack.

[0083] In another preferred embodiment, the heat treatment is carried out in a furnace. For this purpose, a targeted heat treatment of the substrate stack softens the coating material into a plastically deformable state.

[0084] The first substrate and the second substrate of the substrate stack then press the coating material out of the bonding interface by nestling against each other. During the fusion bonding process, the fluids or gases and / or vapors from the atmosphere, which were pressed out of the bonding interface during the bonding wave and condensed at the substrate edge, undergo a phase transition back into the gas phase with the external heat input, thus forcing them out of the gap between the substrates in the bonding interface.

[0085] Furthermore, in preferred embodiments, the coating material can be designed as a getter which absorbs the gases.

[0086] This is particularly advantageous in the gap, preferably a closed gap between the substrates and the full-circumferential ring, so that the gases are increasingly removed from the gap and the edge zone can be bonded without inclusions.

[0087] In principle, the use of all known types of thermoplastics as coating material for the edge zone of at least one of the substrates to be bonded is conceivable. Preferred, individually or in combination and / or in mixtures, are: Bonding adhesives in general, in particular

[0088] Cycloolefin copolymers

[0089] Polyethylene (PE),

[0090] Polypropylene (PP),

[0091] Polystyrene (PS),

[0092] Polyvinyl chloride (PVC),

[0093] Polyamide (PA),

[0094] Polymethyl methacrylate,

[0095] Acrylonitrile butadiene styrene (AB S) with a melting temperature of 220 - 250°C,

[0096] Polyamides (PA) with a melting temperature of 178 - 260°C,

[0097] Polylactide (PLA) with a melting temperature of 150 - 160°C,

[0098] Polymethyl methacrylate (PMMA) with a melting temperature of 105°C,

[0099] Polycarbonate (PC) with a melting temperature of 280 - 320°C,

[0100] Polyethylene terephthalate (PET) with a melting temperature of 250 - 260°C,

[0101] Polyethylene (PE) with a melting temperature of 80 - 100°C, (PE-LD, 80°C), (PE-HD, 100°C), (PE-LLD, 30-90°C),

[0102] Polypropylene (PP) with a melting temperature of 160 - 165°C, especially with the addition of small amounts of solvents,

[0103] Polystyrene (PS) with a melting point of 240°C for isotactic PS and 270°C for syndiotactic PS,

[0104] Polyetheretherketone (PEEK) with a melting point of 280°C and / or

[0105] Polyvinyl chloride (PVC) with a melting point of 79°C, especially with the addition of a solvent. Metals and / or their alloys, especially CMO S-compatible metal alloys, are also conceivable. Metals and / or alloys with a low melting point are advantageous for use as edge coatings.

[0106] Technical waxes can also be used as edge coatings.

[0107] In a preferred embodiment, the glass transition temperature of the edge coating material is between 40°C and 500°C, preferably between 50°C and 300°C, particularly preferably between 70°C and 250°C.

[0108] The heat treatment temperature at which the edge coating is pressed out of the cavity by the continuing bonding wave, in particular together with the gases adsorbed in the cavity, is between 100°C and 1200°C, preferably between 120°C and 600°C, particularly preferably between 140°C and 450°C, in the optimal case between 150°C and 400°C.

[0109] In preferred embodiments, the layer thickness or height of the edge coating is between 0.01 micrometers and 1000 micrometers, preferably between 0.1 micrometer and 500 micrometers, particularly preferably between 1 micrometer and 250 micrometers, most particularly preferably between 5 micrometers and 200 micrometers, in the optimal case between 10 micrometers and 150 micrometers.

[0110] For all disclosed size specifications, the tolerance specifications customary for the semiconductor industry and / or device technology apply, which are disclosed in the relevant standards such as ISO and / or SEMI.

[0111] The ring width of the edge coating on at least one substrate is between 0.01 micrometers and 5000 micrometers, preferably between 1 micrometer and 3000 micrometers, particularly preferably between 100 micrometers and 2000 micrometers, most particularly preferably between 500 micrometers and 1500 micrometers.

[0112] In a preferred embodiment, the ratio of the height of the edge coating to the width of the edge coating is 1:2, preferably 1:5, particularly preferably 1:10.

[0113] In another preferred embodiment, the ratio of the height of the edge coating to the width of the edge coating is 2:1, preferably 5:3, particularly preferably 3:2.

[0114] In an advantageous embodiment, the edge coating is applied to the unstructured substrate edge of a first and / or second substrate. The unstructured substrate edge in the edge region or periphery is referred to in the literature as the edge exclusion zone.

[0115] In a further advantageous embodiment of the edge coating, the edge coating material is applied to a curve of the substrate edge. This rounded phase creates a specific height difference along the curve in the edge coating, which, as a gradient during the phase transition, exhibits particularly favorable behavior with regard to gas transport and the closure of the cavity between the substrates.

[0116] In a further, particularly advantageous embodiment of the edge coating, the edge coating material is applied both to the unstructured substrate edge and to the curve of the substrate edge (edge ​​beavel). Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. These schematically show:

[0117] Fig. 1a shows an embodiment of a first substrate with an edge coating,

[0118] Fig. 1b the substrate stack before fusion bonding,

[0119] Fig. 1 c the contacted substrate stack during fusion bonding,

[0120] Fig. I d the stopped bond wave during fusion bonding of the first

[0121] Sub strates to a second substrate,

[0122] Fig. le the bonded substrate stack with edge coating material pressed out,

[0123] Fig. 2 shows an embodiment of a substrate with an edge coating,

[0124] Fig. 3 a / b Embodiments of the edge coating in the form of structures,

[0125] Fig. 4 Embodiment of a full-surface and porous edge coating.

[0126] In the figures, identical components or components with the same function are identified by the same reference numerals. All sketches may be exaggerated for illustrative purposes; therefore, the figures may not necessarily reflect the proportions of the actual embodiments.

[0127] Fig. l a- le show process steps of an exemplary embodiment of the process for fusion bonding substrates.

[0128] Fig. 1a shows a schematic representation of a first substrate 1 with an edge coating 2. Fig. 1b shows a schematic representation of a first substrate 1 with an edge coating 2 and a second substrate 3, which is held on a substrate holder 4 and pre-curved with an exemplary deformation means 5 to initiate a fusion bond. In particular, the first substrate 1 and the second substrate 3 are brought closer to one another. The relative movement and the alignment of the first substrate 1 to the second substrate 3 are not shown.

[0129] Fig. 1 c shows a schematic representation of the fusion bonding process step and the course of the bonding wave. The bonding wave runs from a contact point between the first substrate 1 and the second substrate 3, which has been prestressed with a deformation means 5. The substrate holder 4 and the deformation means 5 coordinate the prestressing of the second substrate 3 and the detachment of the second substrate 3 from the substrate holder 4 with the height adjustment means (not shown), so that the fusion bonding of the first substrate 1 to the second substrate 3 proceeds in a controlled manner. The entire course of the bonding wave is blocked by the edge coating 2, or the progression of the bonding wave is interrupted by the edge coating 2, so that condensed gases in the bonding interface in particular have sufficient time for resublimation and escape from the bonding interface.The gases and condensate can escape from the bonding interface through the edge coating located at the edge of the substrate stack. For this purpose, the edge coating is designed as a ring with regular intervals of interruption, so that the gaps provide outlet channels through which the gas or fluid is forced out by the bonding wave propagating from the center to the edge.

[0130] Fig. 1d shows a schematic representation of the method step in which the bonded substrate stack consisting of the first substrate 1 and the second substrate 3 with the edge coating 2 are at least partially kept at a distance. In this state, the substrate stack can be moved such that the relative position of the first substrate 1 to the second substrate 3 is not changed. In this state, a phase change and / or viscosity change of the edge coating 2 can then be initiated, in particular with controlled thermal energy, so that the gases are forced out of the bond interface together with the softened edge coating 2, thus providing a bond without gas inclusions.

[0131] During heat treatment, substrates 1 and 2 of the substrate stack are brought together, and the heated edge coating is pressed out of the substrate stack. Advantageously, only heat treatment is required at the edge of the substrate stack or the periphery, so that an inner region of the substrate stack does not need to be heated or tempered. This enables a particularly gentle heat treatment.

[0132] Fig. 1e shows the bonded substrate stack as a result of a controlled heat treatment step, consisting of a first substrate 1 and a second substrate 3. The residues of the edge coating 2 pressed out of the bonding interface at the substrate stack edge at the outer edge of the bonding interface are also shown.

[0133] As an effect of the heat treatment, particularly at the edge of the substrate stack, the strength of the edge coating 2 was reduced, so that the attractive forces of the substrates in the bonding interface become greater than the counterforce provided by the edge coating 2 before the heat treatment. Macroscopically observed, heat is added to the incompletely bonded substrate stack, whereupon the bonding wave progresses further and the substrate stack is completely bonded without gas inclusions that cause edge defects. Fig. 2 shows a coated first substrate 1' with an edge coating 2'. The edge coating 2' runs along the peripheral edge of the first substrate 1'. As a coating that runs particularly around the entire circumference, the edge coating 2' can have an outer diameter D and an inner diameter d and a coating height h in the case of circular substrates.

[0134] Fig. 3 a and 3b show embodiments of the edge coating, which were produced in particular with the method for coating substrates.

[0135] Fig. 3a shows that individual discrete dots have been applied as an edge coating 2" on a first substrate 1" at the peripheral edge. In this embodiment, spaced-apart, discrete structures 2" are preferably used as an edge coating on the substrate edge of a first substrate 1" by lithography or by doctor blade coating, screen printing, or spray coating. These discrete structures can also be referred to as edge coating sections.

[0136] Fig. 3b shows an edge coating 2'" discretely applied to a substrate 1'". The preferred method of production here can be spray coating, screen printing, or doctor blade coating. For both embodiments, production by microcontact imprinting is also conceivable.

[0137] The advantage of the embodiments of Figs. 3a and 3b is the gas permeability of the substrate edge of the bonding substrate stack, so that the gases that condense at the substrate edge during bonding can resublimate into the atmosphere between the islands of edge coating 2" and 2'" and escape accordingly. Fig. 4 shows edge coating 2iv applied to a substrate liv in an alternative embodiment, which was applied to the substrate edge as a fully circumferential porous, in particular open-pore, coating.

[0138] Spray coating can be used as the preferred manufacturing method, because by specifically adjusting the spray coating parameters, the desired porosity of the edge coating can be adjusted directly, without an additional manufacturing step. The gas permeability of the edge coating or the substrate edge of the substrate stack to be bonded is ensured, and the fluid enters the pores locally and not onto the substrate, thus preventing edge defects from occurring. The fluid or gases can escape through the pores into the atmosphere. Alternatively, the edge coating 2iv can be applied by spin coating. The porosity is then preferably created by the material properties and / or a heat treatment or another porosity-inducing process and can be advantageously adjusted.

[0139] List of reference symbols

[0140] 1, , i", 1"', liv first substrate

[0141] 2, 2', 2", 2"', 2iv coating, edge coating,

[0142] Edge coating section, structures

[0143] 3 second substrate

[0144] 4 Substrate holder of the second substrate

[0145] 5 Forming agents

[0146] 6 Exit channel, exit channels

[0147] 7 Marginal area, periphery

[0148] 8 substrate stacks

[0149] D Outer distance of the edge coating d Inner distance of the edge coating h Height of the edge coating

Claims

P a t e n t a n s p r ü c h e 1. A method for fusion bonding at least two substrates (1, 1', 1", 1"') with at least the following steps, in particular in the following order: i) providing a first substrate (1, 1, 1", 1", liv) with an edge coating (2, 2", 2", 2"', 2iv) and providing a second substrate (3), ii) contacting the first substrate (1, 1, 1", 1"', liv) with the second substrate (3) to initiate a bonding wave for fusion bonding to a substrate stack (8), wherein in the substrate stack (8) the second substrate (3) rests at least partially on the edge coating (2, 2", 2", 2"', 2iv) of the first substrate (1, 1", 1"', 1"', liv) in an edge region (7) of the substrate stack (8), so that in the edge region (7) of the Substrate stack (8) the first substrate (1, 1", 1", 1"', liv) and the second substrate (3) are spaced apart, iii) heat treatment of the substrate stack (8), wherein the edge coating (2, 2", 2", 2"', 2iv) is gas-permeable,so that when the bonding wave propagates during the fusion bonding in step ii), fluids are discharged from the forming substrate stack (8).

2. The method according to claim 1, wherein the provision of a first substrate (1, l', l", 1"', liv) in step i) comprises the application of the edge coating (2, 2', 2", 2"', 2iv), wherein the application is carried out immediately before the fusion bonding, preferably by means of a dosing pump and dosing line.

3. Method according to at least one of the preceding claims, wherein during the heat treatment the edge coating (2, 2', 2", 2"', 2iv) is at least partially, preferably completely, removed from the substrate stack (8).

4. The method according to at least one of the preceding claims, wherein the heat treatment is carried out between 100°C and 1200°C, preferably between 120°C and 600°C, particularly preferably between 140°C and 450°C, optimally between 150°C and 400°C.

5. Method according to at least one of the preceding claims, wherein the edge layer material (2, 2', 2", 2"', 2iv) is a thermoplastic.

6. The method according to at least one of the preceding claims, wherein the substrates (1, l', l", 1"', 3) are circular wafers and the edge coating (2, 2', 2", 2"', 2iv) of the first substrate (1, l', l", 1"', liv) is arranged in a circular ring over an outer circumference of the first substrate (1, l', l", 1"', liv).

7. The method according to at least one of the preceding claims, wherein a height (h) of the edge coating (2, 2', 2", 2"', 2iv) is between 0.01 micrometers and 1000 micrometers, preferably between 0.1 micrometer and 500 micrometers, particularly preferably between 1 micrometer and 250 micrometers, most particularly preferably between 5 micrometers and 200 micrometers, in the optimal case between 10 micrometers and 150 micrometers.

8. The method according to at least one of the preceding claims, wherein the edge layer width is between 0.01 micrometers and 5000 micrometers, preferably between 1 micrometer and 3000 micrometers, particularly preferably between 100 micrometers and 2000 micrometers, most particularly preferably between 500 micrometers and 1500 micrometers.

9. Method according to at least one of the preceding claims, wherein the edge coating (2, 2', 2", 2"') has outlet channels (6).

10. The method according to claim 10, wherein the outlet channels (6) are formed between structures (2, 2', 2", 2"') regularly distributed over an outer circumference of the first substrate (1, l', l", 1', liv). 1 1. Method according to one of claims 1 to 8, wherein the edge coating (2iv) is formed from an open-pored and porous material.

12. The method according to claim 11, wherein the edge coating (2iv) is formed over the entire edge region (7), in particular completely.

13. Substrate stack (8) comprising a first substrate (1, 1, 1", 1", liv) with an edge coating (2, 2", 2", 2"', 2iv) and a second substrate, wherein the substrate stack (8) is connected by fusion bonding, and wherein in the substrate stack (8) the second substrate rests at least partially on the edge coating (2, 2", 2", 2"', 2iv) of the first substrate (1, 1", 1", 1"', liv) in an edge region (7) of the substrate stack (8), so that in the edge region (7) of the substrate stack (8) the first substrate (1, 1, 1", 1"', liv) and the second substrate (3) are spaced apart, and wherein the edge coating (2, 2", 2", 2"', 2iv) is designed to be gas-permeable.

14. Substrate stack (8) produced by the method for fusion bonding at least two substrates (1, 1, 1", 1", 3) according to claims 1 to 12.

15. Device for fusion bonding at least two substrates (1, 1', 1", 1"', 3), in particular designed to carry out the method for fusion bonding at least two substrates according to claims 1 to 12, at least comprising: a) provision means for providing a first substrate (1, 1", 1', liv) with an edge coating (2, 2', 2", 2"', 2iv) and providing a second substrate (3), b) contacting means (5) for initiating a bonding wave between the first substrate (1, 1', 1", 1"', liv) and the second substrate (3), for fusion bonding to a substrate stack (8), wherein in the substrate stack (8) the second substrate (3) is at least partially supported on the edge coating (2, 2', 2", 2"', 2iv) of the first substrate (1, 1', 1", 1"', liv) in an edge region (7) of the substrate stack (8) can be placed so that in the edge region (7) of the substrate stack (8) the first substrate (1, l', l", 1"', liv) and the second substrate (3) are spaced apart,c) heat treatment means for heat treating the substrate stack (8), wherein the edge coating is designed to be gas-permeable, so that when the bonding wave propagates during fusion bonding, fluids can be discharged from the substrate stack (8) being formed.

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