Method for bonding a first substrate to a second substrate, substrate holder for such a method, and a device comprising such a substrate holder

Abstract

The invention relates to a method for bonding a first substrate (10') to a second substrate (10), wherein: during the bonding of the first substrate (10') to the second substrate (10), a bonding wave (11) propagating along a bonding direction (BR) is formed between -- a first subsection (T1), in which the first substrate (10') and the second substrate (10) are joined, and -- a second subsection (T2), in which the first substrate (10') and the second substrate (10) are still to be joined; in the second subsection (T2), the first substrate (10') has a primary section (21) and the second substrate (10) has a secondary section (22); a positive pressure is applied to the primary section (21) and / or to the secondary section (22) on a side facing a substrate holder (4, 4') by means of a pressure element (1, 1', 1'', 1''', 1IV, 1V, 1VI, 1VII, 1VIII, 1IX) in order to move the primary section (21) and the secondary section (21) toward one another and to influence a course of the bonding wave (11) during the bonding.

Description

[0001] ■□I

[0002] EV Group E. Thallner GmbH MSP Ref: 45868 PT-WO PM / SK

[0003] Method for bonding a first substrate to a second substrate, substrate holder for such a method and a device with such a substrate holder

[0004] The present invention relates to a method for bonding a first substrate to a second substrate, a substrate holder for such a method and a device with such a substrate holder.

[0005] The ongoing miniaturization in almost all areas of microelectronics and microsystems technology ensures the continuous development of all technologies that enable the increasing density of all types of functional units on substrates. These functional units include, for example, microcontrollers, memory chips, MEMS, all types of sensors, and microfluidic components.

[0006] In recent years, techniques for increasing the lateral density of these functional units have improved significantly. In some subfields of microelectronics and microsystems technology, improvements have progressed to the point where further increases in the lateral density of functional units are no longer possible. In microchip manufacturing, the maximum achievable resolution limit for lithographically produced structures has already been virtually reached. Physical or technological limitations will therefore prevent any further increase in the lateral density of functional units within a few years. Industry has been addressing this problem for several years through the development of 2.5D and 3D technologies. These technologies make it possible to align identical or even differently designed functional units, stack them on top of each other, permanently connect them, and network them using appropriate conductive traces.

[0007] One of the key technologies for realizing such structures is permanent bonding. Permanent bonding encompasses all processes that allow substrates to be joined together in such a way that their separation is only possible with a high energy expenditure and the resulting destruction of the substrates.

[0008] There are different types of permanent bonding, as known to the expert.

[0009] One of the most important permanent bonding methods is fusion bonding, also known as direct bonding or molecular bonding. Fusion bonding is a two-stage process for permanently joining two substrates. In the first stage, also called prebonding, the substrates are held together by relatively weak atomic forces such as van der Waals forces. In the second stage, they are joined together at the molecular and / or atomic level through the formation of covalent bonds. Fusion bonds primarily form on the surfaces of non-metallic, non-organic materials.

[0010] The bond strength induced by the prebond is sufficient to transport the two substrates without causing any displacement between them. Although the bond strength between the two substrates is indeed sufficient to transport the substrate stack without problems, it is so weak that the two substrates can be separated again non-destructively using special devices. This has the crucial advantage that, after prebonding, the structures of the two substrates can be measured and their relative positions, distortions, and orientations determined. If, during the measurement process, a misorientation and / or a local and / or global distortion of the structures is detected, or if particles are present in the interface, the substrate stack can be separated again and reprocessed accordingly.After a successful and, above all, verified pre-bond, the actual permanent bond is created through heat treatment processes. During the heat treatment process, the application of thermal energy chemically and / or physically strengthens the bond between the surfaces of the two substrates. This permanent bond is irreversible in the sense that non-destructive separation of the two substrates is no longer possible. From this point forward, the term "bond" will be used generally, and no explicit distinction will be made between pre-bond and permanent bond.

[0011] The most common fusion bonds are performed on silicon and silicon oxide substrates. Due to its semiconductor properties, silicon often serves as a base material for the production of microelectronic components such as microchips and memory devices. A so-called direct bond can also be formed between highly polished or lapped metal surfaces or on flat glass surfaces. While the underlying bonding properties differ from those of a fusion bond, the mechanism by which the two surfaces are contacted by a propagating bond wave can be described by the same physics. It is also conceivable to join two hybrid surfaces using a so-called hybrid bond. A hybrid surface is defined as a surface consisting of at least two different materials. One of the two materials is usually confined to a small area, while the second material surrounds the first.For example, metal contacts are surrounded by dielectrics. When creating a hybrid bond by bonding two hybrid surfaces, the bond wave is primarily driven by the fusion bond between the dielectrics, while the metal contacts automatically align themselves through the bond wave. Examples of dielectrics and low-k materials are...

[0012] • Non-silicon-based polymers

[0013] ■ Polyimides

[0014] ■ Aromatic polymers

[0015] ■ Parylene

[0016] ■ PTFE oo Amorphous Carbon

[0017] • Silicon-based o Silicate-based

[0018] ■ TEOS (tetraethyl orthosilicate)

[0019] ■ SiOF

[0020] ■ SiOCH

[0021] Glasses (borosilicate glasses, aluminosilicate glasses, lead silicate glasses, alkali silicate glasses, etc.)

[0022] General o SisN4 o SiC o SiO2 o SiCN

[0023] • Silsesquioxane o HSSQ o MSSQ

[0024] One of the biggest technical problems in permanently bonding two substrates is the alignment accuracy of the functional units between them. Although the substrates can be precisely aligned using alignment equipment, distortions can occur during the bonding process itself. These distortions mean that the functional units will not necessarily be correctly aligned at all positions. The misalignment at a specific point on the substrate can result from distortion, scaling errors, lens aberrations (magnification or reduction errors), etc. In the semiconductor industry, all topics dealing with such problems are subsumed under the term "overlay." An introduction to this topic can be found, for example, in: Mack, Chris.Fundamental Principles of Optical Lithography - The Science of Microfabrication. WILEY, 2007, Reprint 2012. Each functional unit is typically designed on a computer before the actual manufacturing process. For example, conductive traces, microchips, MEMS, or any other structure that can be manufactured using microsystems technology are designed in a CAD (Computer-Aided Design) program. However, during the manufacturing of the functional units, it becomes apparent that there is always a discrepancy between the ideal, computer-designed units and the actual, cleanroom-produced functional units. These differences are primarily due to natural variations in the materials used, hardware limitations (i.e., engineering problems), but very often also to physical limitations.The resolution accuracy of a structure produced by a photolithographic process is limited by the size of the photomask apertures and the wavelength of the light used. Mask distortions are directly transferred to the photoresist. Drives, (linear) motors, and machine positioning devices made with these components can only reach reproducible positions within a predefined tolerance, etc. Therefore, it is not surprising that the functional units of a substrate cannot exactly match the structures designed on a computer. Consequently, all substrates already exhibit a non-negligible deviation from the ideal state before the bonding process.Comparing the positions and / or shapes of two opposing functional units of two substrates, assuming that neither substrate is distorted by a joining process, one finds that, in general, the functional units already do not perfectly align, as they deviate from the ideal computer model due to the errors described above. The most common errors are described in Mack, Chris. Fundamental Principles of Optical Lithography - The Science of Microfabrication. Chichester: WILEY, p. 312, 2007, Reprint 2012. A broad distinction can be made between global and local, or symmetric and asymmetric, overlay errors. A global overlay error is homogeneous and therefore independent of location. It produces the same deviation between two opposing functional units regardless of their position. The classic global overlay errors are errors I and IL, which are caused by translation and symmetric, respectively.Rotation of the two substrates relative to each other occurs. The translation or rotation of the two substrates generates a corresponding translational or rotational error for all opposing functional units on the substrates. A local overlay error arises location-dependently, primarily due to elasticity and / or plasticity problems, in this case mainly caused by the continuously propagating bond wave. Of the overlay errors shown, errors III and IV are primarily referred to as "run-out" errors. This error arises mainly from distortion of at least one substrate during a bonding process. Due to the distortion of at least one substrate, the functional units of the first substrate are also distorted relative to the functional units of the second substrate. Errors I and II...However, they can also arise from a bonding process, but are usually so heavily masked by errors III and IV that they are difficult to detect or measure.

[0025] A system already exists in the prior art that can at least partially reduce local distortion. This involves local equalization through the use of active control elements (WO 2012 / 083 978 A1).

[0026] The prior art includes initial approaches to correcting run-out errors. US 2012 0 077 329 A1 describes a method for achieving the desired alignment accuracy between the functional units of two substrates during and after bonding by not fixing the lower substrate. This means the lower substrate is not subject to any constraints and can bond freely to the upper substrate during the bonding process. A key feature of this prior art is the flat fixation of a substrate, usually using a vacuum device.

[0027] The resulting run-out defects typically increase radially around the contact point, thus growing from the contact point to the circumference. In most cases, the increase in run-out defects is linear. Under specific conditions, however, the run-out defects can also increase non-linearly.

[0028] Under particularly optimal conditions, run-out errors can be determined not only by appropriate measuring instruments (EP 2 463 892) but also described by mathematical functions. Since run-out errors represent translations and / or rotations and / or scalings between well-defined points, they are preferably described by vector functions. In general, this vector function is a function f: R² R2, therefore, is a mapping rule that maps the two-dimensional domain of the position coordinates to the two-dimensional range of values ​​of "run-out" vectors. Although no exact mathematical analysis of the corresponding vector fields has yet been carried out, assumptions are made regarding the function properties.

[0029] The publication WO 2017 140 347 A1 discloses a device with which the atmosphere between the substrates to be bonded can be precisely controlled. In particular, nozzles that force the gas or gas mixture between the substrates make it possible to create an overpressure between the substrates in order to slow down the propagation of the bond wave.

[0030] Publication WO 2024 046 577 A1 describes a substrate holder consisting of several so-called zone areas. Each zone area has at least one fixing agent with which the substrate is held. By switching off the fixing agents, a bond wave, in particular its shape and propagation speed, can be controlled.

[0031] The publication WO 2023 078 567 A1 discloses a substrate holder with a contact element, in particular a pin, from which a fluid can flow onto the back of a substrate. This fluid acts on the substrate to initiate bonding and create a first section in which the two substrates to be bonded make contact or are connected to each other. This device serves to create initial contact between two substrates to be bonded. The action of the contact element thus creates the first section and a second section in which the substrate and the second substrate are not yet connected, and therefore the bond wave is formed. This publication WO 2023 078 567 A1 is exemplary of countless other similar publications, which, however, focus on deforming a substrate centrally and convexly in order to contact it centrally with a second substrate in order to initiate bonding.to form a first subsection and a second subsection.

[0032] Publication WO 2023 078 528 A1 describes a method for distorting a substrate to adjust, and in particular slow down, the speed of a bond wave. The bond wave speed should generally decrease towards the edge.

[0033] Publication WO 2022 008 047A1 describes a device for influencing a bond wave. The device is designed such that a screw mechanism enables a continuous, mechanically controlled shut-off of fixative from the center to the periphery of the substrate.

[0034] The publications WO 2022 002 345A1, WO 2021 089 173A 1, WO 2020 147 964 A1, WO 2019 057286 A1, WO 2018 157 937 A1, WO 2018 059699 A1, WO 2018 028 801 A1, WO 2017 162 272 A1, WO 2017 140 348A1, WO 2017 140 347A1, WO 2016 162 088 A1 and WO 2014 191 033 A1 disclose further methods and devices for regulating and controlling a bond wave and are hereby disclosed without further description.

[0035] One problem with the prior art is that the bond wave rarely propagates homogeneously and isotropically. Ideally, a bond wave propagates radially symmetrically. The path of the radially outward-propagating bond wave in a top view is ideally circular. This circle describing the bond wave grows larger with increasing bonding time but should remain circular. However, due to the inhomogeneity and / or anisotropy of the substrates, most bond waves also propagate inhomogeneously and / or anisotropically. This leads to some @

[0036] Some sections of the bond wave lag behind others and cannot catch up. They remain behind, leading to a delayed bond completion, particularly at the outermost edge of the substrates.

[0037] In the prior art, attempts are therefore made to influence the propagation of the bond wave by controlled or regulated switching off of fixative, changing the atmosphere, or creating air cushions between the substrates, in such a way as to achieve a desired, preferably symmetrical, bond wave profile. However, if part of the bond wave lags behind the other parts, it is virtually impossible with the current state of the art to accelerate the lagging part of the bond wave and thus make it catch up.

[0038] Starting from this, the present invention aims to further improve corrective measures that affect the course of the bond wave during bonding, in particular in such a way that the corrective measures do not lead to any time delays in bonding.

[0039] The present invention solves the problem with a method for bonding a first substrate to a second substrate according to claim 1 and with a substrate holder for bonding according to claim 8, as well as a device according to claim 15. Advantageous embodiments of the invention are specified in the dependent claims. The scope of the invention also includes all combinations of at least two features specified in the description, the claims, and / or the drawings. Where specified value ranges are given, values ​​lying within the stated limits are also considered limits and may 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.

[0040] According to a first aspect of the present invention, a method for bonding a first substrate to a second substrate is provided, wherein, during the bonding of the first substrate to the second substrate, a bond wave propagating along a bonding direction is formed between

[0041] -- a first subsection in which the first substrate and the second substrate are connected, and @

[0042] -- a second subsection in which the first substrate and the second substrate are to be joined, wherein in the second subsection the first substrate has a primary section and the second substrate a secondary section, wherein a positive pressure is exerted on the primary section and / or the secondary section on a side facing a substrate holder by means of a pressure element, in particular sectionally, in order to move the primary section and the secondary section towards each other and to influence, in particular to change, the course of the bond wave, in particular along a direction perpendicular to the bonding direction, during bonding. In particular, an actual shape of the course of the bond wave is adapted to a desired shape, preferably an ideal shape for the course of the bond wave.

[0043] Contrary to the prior art, the present invention proposes that at least a section of the first or second substrate, in particular the primary or secondary section, is accelerated by means of positive pressure in order to adapt the bond wave to the desired profile. In particular, the positive pressure serves to influence the bond wave profile locally or in a location-dependent manner. With the invention, it is therefore advantageously possible to influence the profile of a bond wave not only by selectively switching off the fixative, but also by selectively using pressure elements, i.e., by applying positive pressure. While the delayed switching on or off of the fixative primarily slows down the propagation of the bond wave, the pressure elements allow for the selective control and / or manipulation of parts of the bond wave, the bond wave fragments. Furthermore, the entire bonding process can be accelerated.Preferably, the bonding is a permanent bond, in particular a fusion bond, and / or a hybrid bond.

[0044] The pressure element is to be distinguished, in particular, from a contact element with which the bonding process is initiated. The contact element brings the first and second substrates together at a first contact point. Bonding begins from this first contact point. After the start of bonding, a bond wave forms, separating the first sub-area from the second sub-area. Preferably, the first contact point is located centrally in the first or second substrate in a plane parallel to the main extension plane of the first or second substrate. Subsequently, bonding is initiated, for example, such that the bond direction is radially outward and the bond wave propagates radially outward accordingly. The pressure element is, in particular, integrated into the substrate holder and acts on a side facing the substrate holder, i.e., a rear side of the first and / or second substrate.

[0045] The invention is thus based on the idea of ​​applying pressure to the back side of at least one first substrate by means of at least one pressure element, preferably several pressure elements, while the bond wave between the first substrate and a second substrate creates a bond, preferably a fusion bond. Where substrates are generally referred to below, the first substrate and the second substrate are meant in particular.

[0046] The pressure is not applied exclusively through the contact element in a central location, but also at, in particular, several points off-center. By applying pressure to the back side of the first or second substrate, the first or second substrate can be accelerated in a targeted manner, preferably controlled and regulated. The acceleration of at least one section of the first or second substrate causes the bond wave in that section to also accelerate and propagate faster. This makes it possible to selectively accelerate a bond wave that is delayed due to physical and / or chemical properties, particularly in a controlled and / or regulated manner. In general, this enables improved and controllable bond wave control.In contrast to the prior art, in which the bond wave is achieved solely by releasing a fixation of at least one substrate, an improved, extended bond wave control can be achieved in this case by applying pressure.

[0047] In the following text, a bond wave is understood to be the, in particular, complete line connecting two substrates, separating the bonded area from the unbonded area. If two substrates are bonded centrally, the resulting bond wave is completely closed. Special bonding processes initiate the bond at the periphery of the substrates, i.e., at the outer edge of the substrate. In this case, the bond wave travels linearly, in a wave-like or arc-shaped pattern across the substrates, beginning and ending at the periphery. The intended process can, however, control and / or regulate both bond waves. Positive pressure is preferably understood to mean any force, in particular any type of force, acting on the primary or secondary section and directed towards it.This allows the primary and secondary sections to be moved towards each other in specific areas within the second sub-section. This makes it advantageously possible to accelerate bonding in areas where it has been unintentionally slowed down. The positive pressure acts on the primary or secondary section, particularly in specific sections, to selectively press certain sub-sections of the primary or secondary section together, thereby accelerating bonding in a segment of the bonding wave. Preferably, the pressure is applied to the primary or secondary section with spatial resolution. For this purpose, several pressure elements are distributed across the substrate holder, which can preferably be individually controlled.In particular, the positive pressure refers to the pressure that accelerates the primary section towards the secondary section or the secondary section towards the primary section.

[0048] The number of printing elements is greater than 2, preferably greater than 10, even more preferably greater than 50, most preferably greater than 100, and most preferably greater than 500.

[0049] Since the pressure elements are preferably component groups that rely on a fluid dynamic principle to apply the pressure, for example nozzles, the pressure is specified in bar and not in Pascals. The conversion factor is known to those skilled in the art.

[0050] The pressure generated by the pressure elements can be adjusted with a resolution in the millibar range to allow for precise control. Therefore, the pressure can be regulated or controlled with a resolution of less than 1 bar, preferably less than 0.1 bar, more preferably less than 0.01 bar, most preferably less than 0.001 bar, and most preferably less than 0.0001 bar.

[0051] The absolute value of the pressure that can be generated by the pressure elements lies between 0.0001 bar and 10 bar, preferably between 0.001 bar and 5 bar, more preferably between 0.01 bar and 3 bar, most preferably between 0.1 bar and 2 bar, and most preferably between 1 bar and 1.1 bar. In order to utilize a pressure value below 1 bar for a pressure effect on the substrate, the substrate must be stored in a chamber that has been at least partially evacuated.

[0052] Preferably, a fluid is used by the pressure element to exert pressure on the primary section and / or the secondary section. In one embodiment, the pressure element is thus a fluid element. The fluid element is preferably at least one of the following:

[0053] • Nozzle

[0054] • Hose

[0055] • Cylindrical round bar with bore

[0056] • Easy drilling into the substrate holder surface

[0057] The fluid element conveys the fluid to the back of the substrate and transmits the pressure through the fluid. In specific embodiments, however, the fluid element can also move directly into contact with the substrate and be used as a pressure element without fluid. Preferably, the nozzle tapers and / or has an acceleration zone that is used for the targeted alignment of the fluid. It is also conceivable that the nozzle is pivotable to control the influence of the outflowing fluid. Preferably, the pressure of the fluid at the nozzle exit is regulated, for example, by a controllable pressure source or a throttle valve.

[0058] The fluid element preferably uses at least one of the following gases or gas mixtures.

[0059] • Gas mixture or air, preferably

[0060] ■ Dried air

[0061] ■ Compressed dried air

[0062] • Gas or inert gas, preferably

[0063] Noble gas, preferably • Helium

[0064] ■ Nitrogen

[0065] Preferably, a mechanical force is used by the pressure element to exert pressure on the primary section and / or the secondary section. In a second embodiment, the pressure element is a mechanical pressure element. The mechanical pressure element is preferably at least one of the following elements.

[0066] • Cylindrical round bar

[0067] • Feather

[0068] • Needle

[0069] • studs

[0070] It is conceivable that the efficiency of a pressure element depends on its position. For example, it might be advantageous to install fluid elements predominantly or exclusively at the periphery of the substrate holder, i.e., in an area acting on an outer edge of the first or second substrate, so that the fluid can escape quickly over the edge. A central installation of a fluid element could lead to an undesirable distribution of the fluid and thus to an undesirable and uncontrollable pressure distribution in the center, which might make the use of a mechanical pressure element near the center preferable. Therefore, in general, all the aforementioned pressure elements can be used in combination in a substrate holder at positions considered ideal for this purpose.

[0071] According to an exemplary embodiment of the present invention, an electrical or magnetic force is used by the pressure element to exert pressure on the primary and / or secondary sections. In this embodiment, the pressure element is, for example, an electrostatic pressure element. It is conceivable that the back side of the substrate is, at least partially, electrostatically charged or polarized. In this case, a similarly polarized electrostatic pressure element could cause a repulsion between itself and the substrate section, which also leads to acceleration. Electrostatically charged substrate surfaces are undesirable in the semiconductor industry because a discharge is accompanied by a large discharge current that can destroy functional units, especially ICs and microchips. Polarized substrate surfaces are therefore preferred.

[0072] In another exemplary embodiment, the pressure element is a magnetic pressure element. It is conceivable that the back side of the substrate is magnetized, at least in part. In this case, a magnetic pressure element could generate a repulsion between itself and the substrate section, which also leads to acceleration. It is assumed that two repelling magnetic poles are oriented accordingly. In a particularly preferred embodiment, the magnetic pressure element is an electromagnet and can therefore be switched. In particular, the strength of the magnetic field, and thus the acceleration of the substrate section, can be adjusted by changing the current. A magnetic pressure element can be provided, in particular, if the substrate has a magnetizable layer.The magnetic pole orientation can be determined by means of a pivotable magnetic pressure element, which can be particularly advantageous if the magnetic layer present on the substrate has an unfavorable pole orientation, at least in sections.

[0073] Preferably, in addition to the pressure element for applying positive pressure, a fixing agent is used to influence the bonding wave. The pressure elements can be combined with the fixing agents of the substrate holder to control the bonding wave. Thus, it is conceivable that at least one section of at least one substrate is fixed by means of fixing agents, while at least one other section of at least one substrate is subjected to pressure by at least one pressure element. It is known from the prior art that the fixing agents can be configured to either literally fix the individual sections of the substrate, i.e., prevent displacement or lifting, or to merely delay or slow down the displacement or lifting of the individual sections of the substrate.The fixing elements are therefore generally viewed as decelerating, braking, and retaining elements, while the pressure elements are viewed as accelerating elements. The interplay between the fixing and pressure elements results in particularly efficient control of the bond wave.

[0074] It is also conceivable that the pressure elements could be used for fixation. For example, the pressure element could generate both positive and negative pressure on the primary or secondary section. This would advantageously further increase the flexibility in influencing the course of the bond wave.

[0075] Preferably, the pressure element is controlled and / or regulated in real time. This allows for immediate countermeasures against unwanted behavior of the bond wave, particularly during bonding. For this purpose, the behavior of the bond wave is advantageously monitored, preferably continuously, and compared with an ideal profile. As soon as a deviation from the ideal value exceeds a threshold, the pressure elements can apply positive pressure at the desired location.

[0076] Any type of sensor can be used to observe and / or measure the bond wave. However, distance sensors are preferred. These sensors measure and / or determine the distance between the substrate holder, to which the substrate is fixed, and the substrate side that is fixed to the holder. When a bond wave forms, the substrate, particularly the upper part, detaches from the holder. This creates a gap between the holder and the substrate. The distance between the substrate and the holder is then measured, allowing conclusions to be drawn about the deflection and thus the position of the bond wave. In this method, the bond wave is not directly observed but calculated. To use this method, several sensors must be distributed across the substrate holder. Direct measurement of the bond wave using a camera is also conceivable.This requires a light source that emits photons of a wavelength that experience little, or preferably no, absorption by the materials in the substrate. For example, silicon substrates are transparent to infrared light. If the photons can also be detected by the camera, direct monitoring of the bond wave is possible. In most cases, infrared observation of the interface between two substrates does not work because the substrates contain metallic areas or even entire metallic layers that absorb the infrared radiation. The first method mentioned, involving measuring the distance between the substrate and the substrate holder, always works and is therefore preferred.

[0077] The substrate holder has more than 2, preferably more than 15, even more preferably more than 30, most preferably more than 60, and most preferably more than 100 sensors.

[0078] In particular, it is provided that the pressure element, especially the individual pressure elements of a plurality of pressure elements, is regulated or controlled according to a defined control program, wherein the defined control program is adapted between two bonding processes. A control device is provided for this purpose. The substrate holder is preferably considered part of a system that also enables the measurement and evaluation of bond quality, thereby improving the bonding result. Alternatively or additionally, it is provided that a control program can be used to intervene during a bonding process, i.e., in real time. Such a control program identifies deviations in real time and adjusts instantly to prevent errors during the bonding process.

[0079] In the first process step, two substrates are aligned and bonded to the printing elements using the substrate holder. The bonding process is regulated and / or controlled, particularly in conjunction with the sensors. Therefore, data is available that is acquired directly during the bonding process.

[0080] In a second process step, the bonded substrate stack is measured using a special metrology tool. The purpose of this measurement is to determine the bond quality. Bond quality is represented in particular by displacement and / or distortion maps, whose vectors indicate how much two structures to be bonded deviate from their desired position.

[0081] In a third process step, the measurement data thus obtained, in particular the displacement and / or distortion maps, are loaded into the computer responsible for controlling the bonder. From this data, it can be deduced how the fixing and / or pressure elements need to be switched and / or controlled in a subsequent bond to improve the bond.

[0082] In a fourth process step, a bond is again performed according to the first process step; however, additional data from the third measurement step is now available, which can be used for control and / or regulation. From here, a loop begins that ideally improves all subsequent bonds continuously until an optimum is reached.

[0083] In an optional fifth process step, consideration could be given to skipping process steps two and three if the collection of data from the second process step already leads to further bonds of sufficiently high quality.

[0084] For both real-time control and the adjustment of the control program, a control device is advantageously used, preferably comprising at least one microprocessor to execute the corresponding program. The control device is connected to the pressure elements and, in particular, to sensors. It is also conceivable that the control device, for example, using artificial intelligence, draws on prior knowledge used to regulate and / or control the pressure elements. Corresponding test data sets can, for example, take into account the magnitude of the deviation from the ideal behavior, the position of the deviation, the type of bonding, the material composition of the substrates, and / or environmental factors.

[0085] According to a further aspect, a substrate holder is provided for carrying out a method according to the invention, wherein the substrate holder has a pressure element. All properties and advantages described for the method can be transferred analogously to the substrate holder and vice versa.

[0086] Preferably, the substrate holder includes a contact element for initiating the bond by forming a bond wave that separates a first sub-area from a second sub-area. The substrate holder preferably comprises at least three pressure elements by which pressure can be applied to a section of the back of a substrate to accelerate a progressing bond wave. The substrate holder can be used as an upper and / or lower substrate holder. A system in which two identical substrate holders are used as upper and lower substrate holders is particularly conceivable.

[0087] In particular, the substrate holder is provided to have a zone area in which the substrate holder acts jointly on the first substrate and / or the second substrate, with adjacent zone areas being separated from each other by a zone wall. Preferably, at least one pressure element is assigned to each zone area. In a preferred embodiment, the pressure elements are arranged symmetrically. It is particularly advantageous to specify the positions of the pressure elements with respect to a polar coordinate system. The positions of the pressure elements are then specified with an angle and a radius. In a further embodiment, the pressure elements are positioned along a hexagonal grid. In a further embodiment, the pressure elements are arranged along a rectangular, and in particular square, grid.

[0088] The density of the printing elements determines the resolution of the influence. A higher density of printing elements improves the resolution of the influence.

[0089] It is conceivable that certain printing elements can be grouped together. This grouping can be done for design, process, control, or other reasons.

[0090] If pressure elements are grouped for design reasons, this means that all pressure elements in the group can be controlled and / or regulated simultaneously by a single signal. This type of pressure element grouping is fixed by the design and cannot be changed. This grouping can significantly reduce the complexity of the control system. For example, all pressure elements at the outermost periphery could belong to a single pressure element group. These pressure elements would be designed so that a single signal would cause them all to simultaneously exert positive pressure on the back of the substrate, thus accelerating the substrate symmetrically one last time before the bonding process is complete. The other pressure elements within this outer pressure element group could, for example, be controlled individually.

[0091] In another embodiment, the pressure element grouping is done for control engineering reasons. The assignment of the pressure elements to a pressure element group is carried out in the hardware and / or firmware and / or software, hereinafter referred to simply as the computer. For example, it is conceivable that for a specific first method, it is necessary to group ten pressure elements in the central region into a first pressure element group, five pressure elements in the middle region into a second pressure element group, and twenty pressure elements in the periphery into a third pressure element group. In a completely different, second method, where substrates with different surface properties are used, however, the use of only two pressure element groups could be advantageous and produce an optimal bonding result. In this case, the pressure element groups would have to be regenerated, i.e., reprogrammed in the computer.

[0092] A print element group can also consist of only a single print element; in this case, the print element would be its own print element group. Therefore, every print element belongs to at least one print element group.

[0093] Furthermore, it is preferred that the pressure element is embedded in the zone wall. This allows the pressure element to act particularly effectively on the first substrate and / or second substrate, especially in a transition area between two adjacent zones.

[0094] In particular, the substrate holder is designed to have a fixing agent and / or a studded element, with the fixing agents preferably being embedded in the zone area. Thus, the substrate holder also has fixing agents to fix a substrate, at least partially. Such fixing agents are already known from the prior art and are only described and discussed superficially here. The fixing agents serve to hold the substrate in place. These fixing agents can be...

[0095] - Mechanical fixings, especially clamps

[0096] - Vacuum fixings, in particular with individually controllable vacuum paths and / or interconnected vacuum paths

[0097] - electrical fixings, especially electrostatic fixings

[0098] - magnetic fixings

[0099] - adhesive fixations, in particular

[0100] - Gel-Pak fixations - Fixations with adhesive, especially controllable, surfaces.

[0101] The fixing agents are, in particular, electronically controllable. Vacuum fixing is the preferred fixing method. The vacuum fixing preferably comprises several vacuum channels that emerge from the surface of the substrate holder. The vacuum channels are preferably individually controllable. In one application, several vacuum channels are combined into vacuum channel segments that can be individually controlled and therefore evacuated or flooded. Each vacuum segment, however, is independent of the other vacuum segments. This allows for the construction of individually controllable vacuum segments. The vacuum segments are preferably designed in a ring shape. This enables targeted, radially symmetrical fixing and / or release of a substrate from the sample holder, particularly from the inside out.

[0102] It is conceivable that, analogous to pressure element groups, certain fixing elements can be grouped together. This grouping into fixing element groups can be based on design, process, control, or other reasons. All statements regarding pressure element groups apply analogously to fixing element groups and vice versa. The substrate holder preferably has sensors to measure the path of the bond wave. Distance sensors capable of measuring the displacement of the back side of a substrate at multiple positions are conceivable and preferred. However, cameras, particularly infrared cameras, are also conceivable, which can be used to directly measure the interface between the two substrates and thus the bond wave.

[0103] The substrate holder can be designed as a studded substrate holder. Such substrate holders are known in the prior art and are not described in detail here.

[0104] The substrate holder is preferably constructed primarily from one of the following materials

[0105] • Aluminum

[0106] • Silicon nitride (SisN^

[0107] Silicon carbide (SiC) • Silicon-silicon carbide (SiSiC)

[0108] Another aspect concerns a device with the substrate holder according to the invention. All properties and advantages described for the method and the substrate holder can be transferred analogously to the device and vice versa.

[0109] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. These show:

[0110] Figure 1 shows several different printing elements.

[0111] Figure 2 shows a substrate holder with pressure elements,

[0112] Figure 3a shows a first process step in a side view,

[0113] Figure 3b shows a second process step in a side view,

[0114] Figure 3c shows a third process step in a side view,

[0115] Figure 3d shows a fourth process step in a side view,

[0116] Figure 4a shows a first procedural step in a supervisory view,

[0117] Figure 4b shows a second procedural step in a supervisory view, Figure 4c shows a third procedural step in a supervisory view and

[0118] Figure 4d shows a fourth process step in a top view.

[0119] In the figures, identical components or components with the same function are marked with the same reference symbols.

[0120] Figure 1 shows a total of nine possible, different printing elements 1'-1 IX A general printing element is designated by reference numeral 1 in the following figures.

[0121] The first printing element T is a mechanical pin with a flat underside 1f.

[0122] The second pressure element 1" is a pressure element with a non-flat underside 1n. The non-flat underside 1n can be a point, a hemisphere, or another rounded shape. The non-flat underside can be designed, in particular, to apply pressure to the back of the substrate with a minimal contact area. This further minimizes backside contamination.

[0123] The third pressure element T" is a variation of one of the two preceding pressure elements T, 1". This is illustrated by an extension of pressure element T. Pressure element T" has a second material 1m on its underside. This second material 1m could be, for example, a polymer with damping properties. A highly wear-resistant material, particularly one deposited by vapor deposition, would also be conceivable. A carbide or nitride would be a possible candidate.

[0124] At the fourth printing element 1 IV This is a print element that can be considered a variation of one of the three preceding print elements T, 1, T. An example is given using an extension of print element T. Print element 1 IVIt has a bore or thread 1b inside. Throughout the text, reference will always be made to a bore 1b. The bore 1b can direct a fluid to the back of the substrate via a fluid system (not shown). The pressure element 1 lv With its bore 1b, it therefore acts like a nozzle.

[0125] At the fifth printing element 1 v It is a hose. The pressure element 1 v This is illustrated by several hose elements 1c, but not as a limiting factor. The hose elements 1c can be moved relative to each other, in particular rotated, and fixed in place. This makes it possible to manually shape the hose into a desired form in a particularly simple manner. The pressure element 1 vIt could also be a simple plastic hose, braided hose, flexible hose, etc. In particular, when using a plastic hose, there would only be one hose element 1c, the plastic hose itself. Preferably, the pressure element 1 is... v a hose that is flexible, bendable and can be fixed in its shape.

[0126] At the sixth printing element 1 VI This is a nozzle. The nozzle is shown in a simplified form, but its construction can be complex. A nozzle could, for example, mix several gases into a gas mixture inside. Nozzles could also be used to control the pressure, velocity, composition, and other parameters of the exiting gas or gas mixture.

[0127] At the seventh printing element 1 v"This is a magnetic element. The magnetic element is exemplified by a coil 1s with a core magnet 1k. This is therefore a controllable electromagnet. The use of a permanent magnet is also conceivable. The magnetic @ are shown."

[0128] Field lines of 1 mf can act on the back side of a substrate to accelerate it. For this to work, the substrate must possess appropriate magnetic properties. In particular, the pole orientation of the magnetic regions of the substrate must be identical to the pole orientation of the printing element 1. vll This is necessary so that repulsion can occur. A controllable electromagnet ensures that the correct polarity is always adjustable via the current flow direction. This type of pressure element is mentioned only for the sake of completeness and is unlikely to be used in practice.

[0129] At the eighth printing element 1 VI"This is an electrostatic element. The electrostatic element is represented by two electrodes 1e. One of the two electrodes is positively charged, the other negatively charged. The electric field is generated by the atmosphere, represented by the electric field lines 1ef. If there are also positively and negatively charged areas on the substrate, switching the pressure element 1 can generate a positive charge." VI "an acceleration of the substrate takes place. A modification of the pressure element 1" VI "This would be an embodiment with only one electrode 1e, which is either positively or negatively charged. This type of pressure element is also only mentioned for the sake of completeness and is unlikely to find application."

[0130] At the ninth printing element 1 IXThis is a piezoelectric element. The piezoelectric element can be expanded and / or contracted by applying a voltage, particularly via two electrodes attached to its top and bottom surfaces. This allows for a very simple change in length, and thus the application of force to the back of the substrate, by applying a voltage.

[0131] All of the aforementioned pressure elements can be moved translationally and / or rotationally, either to transfer the pressure directly to the substrate and / or to be aligned and / or calibrated.

[0132] In the subsequent figure descriptions, a printing element is represented only by the general reference numeral 1, without referring to a specific embodiment of the printing element according to Figure 1.

[0133] Figure 2 shows an extremely simplified, not to scale, side view of a substrate holder 4 according to an exemplary embodiment of the present invention. For the representation of this substrate holder 4, substrate holders 4 known from the prior art with their structural features are assumed and simplified to show the @

[0134] Pressure elements 1 are extended. An optimal substrate holder 4, for example, has differently controllable sections, known as zone areas. The zone areas are preferably controllable or adjustable evaluable sections in which a well-defined negative pressure can be generated to fix the substrate in this section. The zones are separated from each other, in particular, by zone walls 3. In the simplest case, the zone walls 3 are raised areas left behind during the milling of the substrate holder 4.

[0135] It is also conceivable that the zone walls 3 are seals, particularly of a different material. The substrate holder 4 preferably has pins or knobs 2 which are intended to largely prevent full-surface contact with the first substrate 10' or the second substrate 10 in order to prevent back-side contamination of a first substrate 10' or a second substrate 10. Such substrate holders 4 are referred to as knobbed substrate holders (English: pin chucks).

[0136] The substrate holder 4 preferably has sensors 5 with which the position and / or shape of a progressing bond wave can be measured. Additional sensors 5 for measuring pressure, temperature, or atmospheric composition are also conceivable. Corresponding sensor systems are used together with the pressure elements 1 to control and / or regulate the bond wave. The data from the sensors 5 are preferably read out via a signal line 9.

[0137] The substrate holder 4 has fixing means 6 with which the first substrate 10' and / or the second substrate 10 can be fixed in a position-dependent manner. The fixing means 6 can be switched individually. Preferably, the fixing means 6 are vacuum fixings controlled by valves 7. The valves 7 can, for example, be connected to each other via a common vacuum line 8. If the fixing means 6 are vacuum fixings, they can be used, in particular, to evacuate the spaces between the pins 2, thus allowing the entire zone to be used as a planar fixing medium 6.

[0138] Preferably, the substrate holder 4 is extended by several pressure elements 1. The pressure elements 1 can be installed in the substrate holder 4 according to any desired pattern, but preferably have a symmetrical distribution. Preferably, the pressure elements are embedded in a zone wall 3.

[0139] Figure 3a shows a first process step to illustrate the application of a pressure element 1 according to an exemplary embodiment of the present invention. A second substrate 10 is loaded onto an upper substrate holder 4 and a first substrate 10' is loaded onto a lower substrate holder 4' and aligned with each other. In this case, the two substrate holders 4, 4' are identical. It is also conceivable that they could be different.

[0140] Figure 3b shows a second process step illustrating the application of a pressure element 1 according to the exemplary embodiment of the present invention. Here, contact is made between the second substrate 10 and the first substrate 10'. This contact is preferably made centrally. Such a preferred central contact serves to initiate a bonding wave between the two substrates 10 and 10' and thus trigger the bonding process. For this purpose, a central contact element 15 is used. The central contact element 15 is usually a mechanical pin that moves translationally from top to bottom, contacts the substrate 10 on its rear side, and presses downwards. If a central zone is present, the fixing means 6 are preferably deactivated in this central zone. The switching of the contact element 15 is represented by a lightning bolt in a shield.For the sake of generality, the mechanical pin is not shown, as the contact element 15 can also be a pressure element 1 as shown in Figure 1. This also applies to all subsequent figures. As soon as initial contact is established between the first substrate 10' and the second substrate 10 by the contact element 15, a bond wave 11 progressing along a bond direction BR is generated between the first substrate and the second substrate 10 to bond them together.

[0141] -- a first subsection T1, in which the first substrate 10' and the second substrate 10 are connected, and

[0142] -- a second subsection T2, in which the first substrate 10' and the second substrate 10 still need to be joined, is formed, i.e., the first subsection T1 and the second subsection T2 are formed only by the action of the contact element 15 on the first substrate 10' and / or second substrate 10. In the bonding shown in Figures 3c and 3d, the bonding takes place along a radially outward-extending bonding direction BR.

[0143] Figure 3c shows a third process step to illustrate the application of a pressure element 1 according to the exemplary embodiment of the present invention. In practice, it regularly occurs that the bond wave 11 does not propagate symmetrically, as in the illustrated case, in particular symmetrically with respect to the central contact point, or, in the case of a radial bond direction, forming a circular bond wave. In the existing sectional drawing, this is illustrated by an exaggerated representation of a first substrate 10' and a second substrate 10', which are already more strongly bonded on the right side. The right bond wave fragment 11r has therefore already crossed a larger area (more precisely, a larger line in the sectional view) than the left bond wave fragment 11. In other words, the first contact point between the first substrate 10' and the second substrate 10 is no longer centrally located in the first sub-area T1.

[0144] Figure 3d shows a fourth process step to illustrate the application of a pressure element 1 according to the exemplary embodiment of the present invention. For this purpose, a pressure element 1 arranged to the left of the first contact point is preferably activated, represented by a lightning bolt in a shield, while the symmetrically opposite pressure element 1 on the right side is not activated, explicitly highlighted by a lightning bolt with a line through it in a shield. The bond wave fragment 111 on the left side is thus accelerated by a pressure force acting on the back of the upper substrate 10, in particular by the secondary section 22 in the second sub-region T2 being accelerated by the pressure caused by the pressure element 1, preferably in the direction of the first substrate 10', in particular towards the first substrate.Through this targeted control and / or regulation, the bond wave 11 can advance as desired, particularly symmetrically, until further correction by additional pressure elements 1 is necessary. The control and / or regulation of the pressure elements 1 is preferably achieved by continuous measurement of the bond wave 11 by the existing sensors 5. Alternatively, a camera can be used to measure the bond wave 11. This camera could, for example, be an infrared camera to see through the substrates 10 and / or 10' at their interface. However, this is usually impossible with metallized substrates 10, 10'. Therefore, in these cases, the sensors 5 are preferably distance sensors that measure the back side of the substrates 10, 10' to obtain a conclusion about the desired, particularly symmetrical, shape of the bond wave.

[0145] To illustrate the activation of the printing elements 1 along a surface, the process steps shown in Figures 3a-d are shown again in a simplified top view.

[0146] Figure 4a shows a simplified top view of a substrate holder 4 for a process step according to Figure 3a. However, only the pressure elements 1 and the contact element, viewed from above, are shown. Also visible is the contour of a substrate 10, or rather the superimposed contours of the first substrate 10' and the second substrate. For the sake of simplicity, any shifts in the contours of the substrates 10 resulting from the bonding process are not shown. In any case, these shifts would be minimal.

[0147] Figure 4b shows a simplified top view of a substrate holder 4 in a process step according to Figure 3b. The central pressure element 1 is activated, thus initiating contact between the substrates 10, 10' and generating a (still) point-like bond wave 11.

[0148] Figure 4c shows a simplified top view of a substrate holder 4 in a process step according to Figure 3c. It can be seen that the bond wave 11 has propagated asymmetrically. In particular, the right bond wave fragment 11r has propagated faster than the left bond wave fragment 111. The bond wave 11 can generally assume a much more complex and asymmetrical shape. For the sake of simplicity, the simplest possible asymmetrical bond wave is shown.

[0149] Figure 4d shows a simplified top view of a substrate holder 4 in a process step according to Figure 3d. The pressure element 1 is used to accelerate the substrate 10 in front of the bond wave fragment 111 by applying pressure to its back side, such that the bond wave fragment 111 is also accelerated and the symmetry of the bond wave 11 is restored. In general, it is possible to adapt the bond path to the desired shape with the device. It is particularly preferred to achieve a bond path that is as symmetrical as possible. If the contact element contacts the first or second substrate centrally to initiate the bond, and the bond direction is radially outward from the first contact point, the device is preferably controlled such that a substantially circular path is established for the bond wave.However, it is also conceivable that it is advantageous for a bond if the bond wave deliberately deviates from a circular path, for example, an elliptical one. This, too, can be achieved deliberately with the positive pressure of the device.

[0150] Reference symbol list: Pressure element

[0151] 2 pins / studs

[0152] 10' first substrate

[0153] 10 second substrate

[0154] 3-zone wall

[0155] 4, 4' substrate holder

[0156] 5 Sensor

[0157] 6 Fixatives

[0158] 7 valve

[0159] 8 Valve line

[0160] 9 Signal line

[0161] 10, 10' substrate

[0162] 11 Bond wave

[0163] 11, 11' Bond wave fragment

[0164] 15 contact element

[0165] 21 Primary Section

[0166] 22 Secondary section

Claims

1. Claims 1. Method for bonding a first substrate (10') to a second substrate (10), wherein, during the bonding of the first substrate (10') to the second substrate (10), a bond wave (11) propagating along a bond direction (BR) is formed between -- a first subsection (T1) in which the first substrate (10') and the second substrate (10) are connected, and -- a second subsection (T2) in which the first substrate (10') and the second substrate (10) are still to be connected, is formed, wherein in the second subsection (T2) the first substrate (10') forms a primary section (21) and the second substrate (10) has a secondary section (22), wherein a pressure element (1 , T, 1“, T“, 1 IV , 1 v , 1 VI , 1V", 1 Vl ", 1 IX ), in particular section by section, on the primary section (21) and / or the secondary section (22) a positive pressure is applied to move the primary section (21) and the secondary section (22) towards each other and to influence the course of the bond wave (11) during bonding.

2. Method according to claim 1, wherein the pressure element (1 , T, 1“, T“, 1 IV , 1 v , 1 VI , 1 V", 1 Vl ", 1 IX ) a fluid is used to exert positive pressure on the primary section (21) and / or the secondary section (22).

3. Method according to one of the preceding claims, wherein the pressure element (1 , T, 1“, T“, 1 IV , 1 v , 1 VI , 1V", 1 VI ", 1 IX ) an electric or magnetic force is used to exert positive pressure on the primary section (21) and / or the secondary section (22).

4. Method according to one of the preceding claims, wherein the pressure element (1 , T, 1“, T“, 1 IV , 1 v , 1 VI , 1V", 1 VI", 1 IX ) a mechanical force is used to exert positive pressure on the primary section (21) and / or the secondary section (22).

5. Method according to one of the preceding claims, wherein in addition to the printing element (1 , T, 1“, T“, 1 IV , 1 v , 1 VI , 1V", 1 VI ", 1 IX ) a fixing agent (6) is used to influence the bond wave by applying a positive pressure.

6. Method according to one of the preceding claims, wherein the pressure element (1 , T, 1“, T“, 1 IV , 1 v , 1 VI , 1 V", 1 VI ", 1 IX ) is controlled in real time.

7. Method according to one of the preceding claims, wherein the pressure element (1 , T, 1“, T“, 1 IV , 1 v , 1 VI , 1 V", 1 Vl ", 1 IX) is controlled according to a defined control program, whereby the defined control program is adapted between two bonding operations.

8. Substrate holder (4, 4') for carrying out a method according to one of the preceding claims, wherein the substrate holder (4, 4') includes a pressure element (1 IV , 1 v , 1 VI , 1V", 1 VI ", 1 IX ) exhibits.

9. Substrate holder (4, 4') according to claim 8, wherein the substrate holder (4, 4') has a contact element (15) for initiating the bond by forming a bond wave (11) which separates a first sub-area (T1) from a second sub-area (T2).

10. Substrate holder (4, 4') according to one of claims 8 or 9, wherein the substrate holder (4, 4') has a zone area in which the substrate holder (4, 4') preferably acts jointly on the first substrate (10') and / or the second substrate (10'), wherein adjacent zone areas are separated from each other by a zone wall (3).

11. Substrate holder (4, 4') according to one of claims 8 to 10, wherein the pressure element (1 , T, 1“, T“, 1 IV , 1 v , 1 VI , 1V", 1 VI ", 1 IX ) is embedded in the zone wall 12. Substrate holder (4, 4') according to one of claims 8 to 11, wherein the substrate holder has a fixing means (6) and / or a studded element, wherein the fixing means (6) and / or studded element is preferably arranged in the zone area.

13. Substrate holder (4, 4') according to one of claims 8 to 12, wherein the substrate holder (4, 4') has a sensor (5) for detecting the course of the bond wave (11).

14. Substrate holder (4, 4') according to any one of claims 8 to 13, wherein the pressure element (1 , T, 1“, T“, 1 IV , 1 v , 1 VI , 1V", 1 VI ", 1 IX ) is designed to apply a positive pressure and a negative pressure to the first substrate (10') or the second substrate (10).

15. Device with a substrate holder (4, 4') according to any one of claims 8 to 14.

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