Method and apparatus for influencing bond waves during bonding - Patents.com

Abstract

1. A method and apparatus for influencing a bonding wave (6) when bonding a first substrate (4) to a second substrate (4'), comprising: securing at least the first substrate (4) to a first substrate holder (1) having at least one zone (7', 7''), each having at least one separation element (10) at least partially forming the substrate holder surface, the at least one separation element (10) separating the at least one zone (7', 7'') from another zone (7, 7') of the first substrate holder (1) or from the surrounding environment, and each at least one zone (7', 7'') having at least one fixation element (12), each providing a holding force for fixing the first substrate (4) to the first substrate holder (1).

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for influencing a bonding wave when bonding substrates together. Furthermore, the present invention relates to a method and apparatus for bonding comprising a substrate holder having at least one zone. Such a zone is essential in some apparatus and methods for individually processing, fixing and bonding a substrate to another substrate or to a stack of substrates.

[0002] The prior art contains numerous publications describing substrate holders for fixing substrates. Some of these substrate holders are used for the bonding process of two substrates, known as bonding. Among bonding methods, so-called fusion bonding or direct bonding is particularly important. In fusion bonding, two substrates are bonded to each other solely based on their hydrophobic or hydrophilic substrate surface properties. In the first method step, so-called pre-bonding, the two substrates are brought into contact, particularly at a central point. After contact, at least one of the upper substrates is released, thereby bonding the two substrates to each other along their facing substrate surfaces. In this case, the bonding process is carried out by a traveling bonding wave that starts at the contact point and propagates toward the periphery of both substrates. After this bonding process, the two substrates can also be separated using appropriate methods and devices. Separation is necessary if it is determined that the substrates have not been optimally bonded to each other. At least the substrates have an untreated substrate surface. In most cases, the substrates have already been processed and have different structures. These structures may be, for example, integrated circuits, microprocessors, LEDs, MEMS, etc. These structures must be aligned with and bonded to structures on a second substrate. It is particularly important that each individual structure on a first substrate must be properly aligned with and bonded to the structures present on the opposing second substrate.

[0003] After the temporary bond is formed, the resulting substrate stack is usually subjected to a heat treatment to increase the adhesion strength between the two substrate surfaces. After this heat treatment, a fusion bond or permanent bond is formed. From this point on, the two substrates can no longer be separated from each other without breaking.

[0004] As the bonding wave advances, individual substrate regions in the vicinity of the bonding wave are distorted to such an extent that alignment precision between opposing structures no longer exists. In particular, multiple such distortions can even result in full-surface distortions that begin in the center and increase toward the periphery. In extreme cases, the distortions can even be anisotropic, i.e., directionally dependent.

[0005] Therefore, various types of substrate holders have been developed in the industry for the purpose of influencing the bonding wave. Preferably, open-loop or closed-loop control is performed by means of fastening elements that can fasten the substrate to the substrate holder. For example, WO 2017162272, WO 2018028801, or WO 2019057286 describe the possibility of influencing the bonding wave by means of zones in zonal substrate holders. A zone refers to an area that has at least one, and possibly even several, fastening elements. While zones are often physically separated from one another, they may simply be areas in which fastening elements are switched according to a predefined scheme.

[0006] In particular, the substrate holder may generally have only one zone in which multiple fixing elements are present. However, substrate holders with multiple zones separated from one another by separation walls are particularly preferred. In the case of a substrate holder with only one zone, the outer periphery can be considered as a separation wall in the sense of the present invention, which separates the single zone from the surrounding environment.

[0007] One type of substrate holder is the vacuum substrate holder. The space between the substrate and the substrate holder is evacuated through a clamping element, often just a small hole, and atmospheric pressure presses against the substrate, clamping it to the substrate holder. Initially, only individual holes were drilled in the substrate holder, forming a very simple clamping element. The entire area between the substrate and the substrate holder surface was evacuated. All clamping elements present were connected to the same vacuum line. This resulted in a full-surface clamping of the substrate when the vacuum was applied, which could not be locally controlled in an open or closed loop.

[0008] Further developments of these substrate holders and the possibility to control individual clamping elements have made it possible to achieve spatially resolved open-loop or closed-loop control of clamping.

[0009] A further development of the substrate holder was the combination of the fastening elements and zones with pin-shaped substrate holders (English: pin chucks). Pin-shaped substrate holders are substrate holders that are milled at multiple, particularly symmetrically distributed positions. The milling is not performed over the entire surface, but preferably symmetrically along radial, azimuthal, or rectangular lines. This leaves multiple protrusions, known as pins in the prior art, between these lines in the areas recessed by the milling. By placing the substrate on these pins, a more or less complete support is still achieved, albeit with a significantly reduced contact area. Furthermore, the intermediate spaces between the pins can be evacuated, which allows for a uniform pressure from the surrounding atmosphere. To achieve a uniform force on the substrate, especially when using multiple fastening elements per zone, the pin density can be varied as a function of position, particularly as a function of radius. The milled pins result in a recessed structure that generally corresponds to a zone. Adjacent zones are separated from each other by a separating wall, which may be a non-milled or purposely machined seal, especially made of polymer, that surrounds a zone all the way around and can also be considered a vacuum seal in a vacuum substrate holder.

[0010] In light of the above, a problem with the prior art is that while the bonding wave is moving across the separating wall of one zone, adjacent zones or separated areas are typically evacuated with different strengths, which causes a strong pressure gradient to act on the bonding wave while it is moving across the separating wall of the two zones, which causes a strong strain between the substrates.

[0011] In this regard, the prior art also suffers from the problem that a pressure gradient exists between a single zone and the surrounding environment, even in the case of substrate holders with only one zone. In this case, the peripheral edge separating the zone from the surrounding environment simultaneously constitutes the separation wall of the substrate holder. When the bond wave reaches the edge of such a substrate holder, the same problem occurs as when it overcomes the separation wall separating multiple zones from each other, which results in distortion of the substrate area close to the bond wave.

[0012] It is therefore an object of the present invention to at least partially eliminate, in particular completely eliminate, the drawbacks described in the prior art. In particular, it is an object of the present invention to provide an improved method and apparatus for bonding. Furthermore, it is an object of the present invention to provide a method and apparatus that can reduce distortion in the bonding result, in particular between the two substrates.

[0013] This problem is solved by the features of the independent claims. Advantageous refinements of the invention are set forth in the dependent claims. All combinations of at least two features set forth in the description, claims and / or drawings are also within the scope of the invention. In the stated ranges, values ​​lying within the stated limits are also considered as disclosed limits and can be claimed in any combination.

[0014] The present invention therefore relates to a method for influencing a bonding wave when bonding a first substrate to a second substrate, wherein at least the first substrate is fixed to a first substrate holder having at least one zone, each of the at least one zone having at least one separating element at least partially forming the substrate holder surface, which at least one separating element separates the at least one zone from another zone of the first substrate holder or from the surrounding environment, each of the at least one zone having at least one fixing element, which respectively provides a holding force for fixing the first substrate to the first substrate holder, the method comprising at least the steps of: i) initiating a bonding wave by bringing the second substrate into contact with the first substrate; and thereafter ii) adapting the holding force of the at least one fixing element of the at least one zone to the holding force of a fixing element of another zone located immediately upstream in the direction of propagation of the bonding wave or to the ambient environmental pressure of the surrounding environment.

[0015] In other words, at least one zone is controlled by adapting the holding forces of the fastening elements of the zonal substrate holder, so that the pressure gradient in the at least one zone in the direction of propagation of the bonding wave, in particular in the region of the separating elements, is as small as possible. In the case of adapting the holding force of the at least one fastening element to the ambient pressure, in particular the pressure of the last zone in the direction of propagation, it is ensured that during bonding, when the bonding wave crosses the separating wall at the edge of the substrate holder, the atmospheric pressure adapts to the holding force of the zone at the outer edge.

[0016] In this case, the pressure in at least one, especially the last, zone can be adjusted to the ambient pressure. The pressure adjustment in the zone can be achieved more quickly and efficiently than a pressure change in a large chamber or in the ambient environment, which has a beneficial effect on the bonding wave. In this case, the holding force on the underlying substrate is particularly reduced or even completely eliminated, so that it can spread unhindered at the edges.

[0017] Preferably, at least one zone has a plurality of controllable fixing elements, in which case the holding force may be tailored. This allows a holding force gradient to be generated within a zone, thereby allowing for better control of the advancing bond wave within the at least one zone. Initiation of the bond wave preferably occurs by centrally contacting the first substrate with the second substrate, which results in radially symmetric propagation of the bond wave.

[0018] Substrate holders with multiple zones, i.e., at least one zone and at least one further zone, are particularly preferred. Therefore, the remainder of this specification will generally describe embodiments of substrate holders with multiple zones, in which at least one separation wall is present, separating the two zones from one another. In alternative embodiments of the method with a substrate holder with only one zone, in which the outermost separation wall simultaneously forms the periphery of the substrate holder but, due to the absence of a second zone, an adjacent ambient environment, the holding force of the last or outermost zone is preferably adapted, thereby enabling a particularly uniform transition over the last or outermost separation wall. The separation wall may also be an inserted element, in particular a sealing lip. Therefore, the separation wall does not necessarily have to originate from a milled recessed area of ​​the substrate holder, but may also be a mounted component. In this case, the pressure in the outermost zone is preferably adapted to the ambient pressure.

[0019] In this case, the zone may be divided into several segments perpendicular to the propagation direction of the bonding wave. Thus, several segments of an isosceles trapezoid can form a zone, each preferably having at least one fixing element. Thus, the bonding wave can be adapted to several locations simultaneously along the preferably circular substrate holder, advantageously independent of the radial position. In this case, the adaptation takes place after the bonding wave is initiated, preferably in the area where the bonding wave is advanced (where the first and second substrates are brought into contact or joined). This allows for particularly distortion-free bonding.

[0020] A preferred embodiment of the alignment method specifies that during the adaptation in step ii), the ambient pressure is additionally adapted to the holding force of the fixing element in at least one zone. In this regard, the atmospheric pressure or the ambient pressure existing in the bonding chamber is adapted. In this way, the holding force of at least one zone can be advantageously adapted indirectly, since the ambient pressure acts on the first substrate.

[0021] In a preferred embodiment of the alignment method, it is specified that the adaptation in step ii) is performed so that the holding forces are equal in magnitude immediately before and immediately after at least one separation element, respectively, in the direction of propagation of the bonding wave. In other words, by adapting the holding forces in the region of the separation element during the bonding wave overrun period, it is ensured that a low-distortion bond can also be achieved in the region of the zone transition. In this case, the holding forces can also be adapted continuously. It is important that the large zonal holding force differences desired for the bonding wave adjustment are minimized immediately before and immediately after the bonding wave overrun of the separation transition. In this way, it is possible to advantageously ensure distortion in the region of the zone transition.

[0022] A preferred embodiment of the alignment method specifies that after initiation of the bond wave in step i), the position of this bond wave is continuously checked and the holding force of at least one zone is adapted so that the holding forces before and after the transition of the bond wave over the at least one separating element are equal to each other. By determining the position of the bond wave, the adaptation in step ii) can advantageously be performed precisely during the period in which the bond wave is moved over the separating element. In this way, desired holding force differences can be achieved in areas other than or between the separating elements for adjusting the bond wave, without further distortion in the zone transition area.

[0023] In a preferred embodiment of the alignment method, at least one clamping element in at least one zone is formed as a vacuum clamping means, and at least one separation element fluidically separates at least one zone from another zone or the surrounding environment. Particularly preferred is a vacuum-zone substrate holder divided into a plurality of closed-loop controllable vacuum zones arranged symmetrically in the radial direction and in the propagation direction. Thus, the substrate placed on the separation element is attracted and clamped. In this case, the holding force of the vacuum clamping means is advantageously adjusted individually in each zone (or segment), since these zones are fluid-tight and thus suitable for vacuum. This advantageously allows the clamping element to act on all areas, enabling as complete a control of the bonding wave as possible. The substrate holder can be purged, in particular with an inert gas, preferably helium. It is also possible to purge the vacuum line with an inert gas.

[0024] In a preferred embodiment of the alignment method, it is specified that the adaptation in step ii) is carried out by venting or evacuating at least one zone or the surrounding environment. In this way, the holding force can be advantageously provided easily and quickly over a large area. Furthermore, the holding force can be adapted particularly quickly during transitions in the area of ​​zone transitions or separation elements, and then advantageously quickly compensated for by a desired holding force for adjusting the bonding wave in the area between the separation elements.

[0025] In a preferred embodiment of the alignment method, the adaptation in step ii) is specified to involve determining a pressure difference between at least one zone and another zone or the surrounding environment, and to compensate for this pressure difference by the adaptation. This ensures that the pressure gradient across the separation element is particularly small, minimizing distortion during bonding. Furthermore, advantageously, the region located upstream of the separation element can be vented rather than evacuated.

[0026] A preferred embodiment of the alignment method specifies compensating the pressure of at least one zone to the pressure of another zone, thus advantageously allowing sufficient time to accurately determine the position of the bonding wave and to first adapt the pressure in the zone located downstream in the propagation direction.

[0027] In one embodiment of the alignment method, the holding force of at least one zone is adapted to the holding force of another zone in order to compensate for the pressure gradient. In this case, the other zone also has a corresponding fixing element with a variable holding force. Furthermore, in the case where the adjustment of the ambient pressure of the last zone in the propagation direction is performed, this can also be performed simultaneously with the holding force of at least one zone.

[0028] The present invention further relates to an apparatus for influencing a bonding wave when bonding a first substrate to a second substrate, the apparatus comprising at least a first substrate holder for clamping the first substrate, the first substrate holder comprising at least one zone, the at least one zone having at least one separating element at least partially forming a substrate holder surface of the first substrate holder, at least one clamping element arranged in the at least one zone and having a holding force for clamping the first substrate to the first substrate holder, and a control unit for adapting the holding force of the at least one clamping element of the at least one zone, the control unit being configured to adapt the holding force of the at least one clamping element of the at least one zone during the advance of the bonding wave to the holding force of a clamping element of another zone located immediately upstream in the direction of propagation of the bonding wave or to the ambient environmental pressure.

[0029] The control unit is therefore configured to compensate for the holding force of at least one clamping element relative to the holding force of the upstream zone. Regarding the alternative in which the holding force is adapted to the ambient pressure, the holding force of the last zone, particularly at the periphery of the substrate holder, is adapted in response to the ambient pressure. In other words, a zonal substrate holder is provided with controllable clamping elements, which are controlled to provide optimal holding forces before and after a separation wall separating the zones during bonding, thereby reducing distortion during transition. In this case, the first substrate rests with its face opposite the second substrate on a separation element that at least partially forms the substrate holder surface. By controlling the holding force before and after the transition over the separation wall, the bonding wave can proceed particularly uniformly and without any hindrance in the region of the separation wall. Therefore, undesirable effects of different holding forces before and after the separation wall, especially on a bonding wave propagating from the inside to the outside, are reduced. In this case, different holding forces acting between the zones may be desired for adjustment of the bonding wave. If the bonding process does not start from the center, outer zones with variable-holding-force fastening elements can be arranged near the middle of the substrate holder. It is important to adapt the holding forces of the following zones, especially in the region of the separating elements, in the direction of the expected bonding wave, so as to compensate for the effects of holding forces that act to different degrees (before and after the separating wall). This advantageously ensures a reduction in distortion in the region of the separating elements.

[0030] In this case, the relationship can be determined empirically or based on initial experiments and adapted accordingly. In this case, the control unit is not limited to pure control but can also perform closed-loop control of the holding force as a function of another parameter (e.g., the bond wave position). In this case, the holding force of the fixing element can preferably be adjusted by the control unit. Furthermore, the substrate holder preferably has a plurality of separation elements, which can also be divided into a plurality of segments along the preferably circular substrate holder. These segments, distributed over the entire circumference of a zone, are aligned in particular along the propagation direction, so that, for example, trapezoidal segments become larger in the direction of the periphery. Overall, the device advantageously minimizes stresses and strains, especially in the region of zone transitions or in the region of zone transitions from an inner zone to an outer zone. In this case, the control unit can also adjust the respective holding forces as a function of another parameter.

[0031] In a preferred embodiment of the device for influencing the bonding wave during bonding, it is specified that the device additionally has means for adapting the ambient pressure to the holding force of at least one zone. In this way, the bonding wave can be advantageously influenced or the holding force can be adapted indirectly, since the ambient pressure acts on the first substrate. If the fixing element is a vacuum fixing element that operates by pressure, a pressure compensation adjustment can advantageously be performed, which results in a particularly gentle progression of the bonding wave.

[0032] In a preferred embodiment of the device for influencing the bonding wave during bonding, it is specified that the control unit is configured to adapt the holding force or the ambient pressure of the at least one fastening element after the second substrate is brought into contact with the first substrate. That is, the control unit is configured so that the adaptation of the holding force or the ambient pressure during bonding only occurs after the initiation of the bonding wave. In this way, the device or the control unit can perform the adaptation taking into account the position of the bonding wave, in particular based on empirical data in the control unit.

[0033] In a preferred embodiment of the device for influencing the bonding wave during bonding, it is specified that the control unit is configured to determine the holding force of at least one fastening element in at least one zone by means of a sensor, which is preferably arranged in at least one outer and / or inner zone in the region of the separating element, respectively. Furthermore, a sensor for determining the ambient pressure may preferably be provided. In this way, the control unit can advantageously perform closed-loop control of the adaptation of the holding force based on the actual value, which can further reduce distortion.

[0034] In a preferred embodiment of the device for influencing the bonding wave during bonding, the control unit is configured to maintain the holding force of at least one fastening element in at least one zone and the holding force of at least one other fastening element in another zone equal to each other during bonding of the first substrate to the second substrate. This allows the transition of the bonding wave from the inner zone to the outer zone to be carried out particularly gently and without distortion. Furthermore, a uniform holding force can be efficiently and uniformly generated in multiple, particularly adjacent, zones. This further improves the bonding result and ensures reduced distortion during the transition over the separation wall.

[0035] In a preferred embodiment of the device for influencing the bonding wave during bonding, the control unit is configured to maintain the holding force of the at least one fastening element and the holding force of the at least one fastening element of the other zone equal to each other directly in the region of the at least one separating element and during the period when the bonding wave passes over the at least one separating element. In this case, the position of the bonding wave is preferably also determined, particularly preferably by an optically configured measuring device, and the period of adaptation is optimally adapted to the position of the bonding wave. In this way, advantageously, after passing over the separating element, the adjustment of the holding force between the separating elements can be continued quickly in order to influence the bonding wave. Furthermore, further improved bonding results can be obtained, especially in the region of the separating element.

[0036] In a preferred embodiment of the apparatus for influencing a bonding wave during bonding, at least one clamping element in at least one zone and at least one clamping element in another zone are configured as vacuum clamping means, with a separating element fluidically separating the inner and outer zones from each other. Thus, when a substrate is placed on the first substrate holder, a negative pressure (relative to the atmosphere or surrounding environment) can advantageously be used to clamp the substrate to the first substrate holder over a large area across the entire zone region. This holding force can advantageously be varied quickly and precisely in each zone. Furthermore, contamination of the first substrate can be kept low because contact with the substrate is not required to apply the force. Thus, fluidically separated zones controlled via vacuum clamping elements are predetermined for use in the apparatus for influencing a bonding wave.

[0037] In a preferred embodiment of the device for influencing the bonding wave during bonding, the control unit is configured to keep the pressure difference between the pressure in the other zone and the pressure in at least one zone during bonding as small as possible, preferably equal. The pressure is preferably regulated by a pressure sensor arranged in each zone. Thus, when bonding the first substrate to the second substrate, a uniform and distortion-free bond can be advantageously provided, especially in the area of ​​the separation element.

[0038] In a preferred embodiment of the device for influencing the bonding wave during bonding, the control unit specifies that the means for changing the ambient pressure is configured to compensate for and adjust the ambient pressure to the pressure of at least one zone immediately before and after the bonding wave overcomes at least one separating element. The effects and advantages of the earlier outer zones apply analogously to the subsequent outer zones. Multiple zones in the direction of the propagation direction of the bonding wave allow bonding to be performed particularly accurately, uniformly, and without distortion.

[0039] In the following, outer zone means at least one zone or zones located downstream in the propagation direction of the bonding wave. In the case where the ambient pressure is adapted, the inner zone is the next or last zone. The inner zone is the zone located upstream in the propagation direction. Preferably, the holding force of the downstream zone or at least one zone is adapted to the holding force of the upstream zone.

[0040] A particularly advantageous effect of the device and method for influencing the bonding wave during bonding is that no or negligible distortion occurs between both substrates in the vicinity of the separation wall separating the zones from each other, thus allowing a seamless, gentle, distortion-free transition of the bonding wave front over the separation wall, which reduces distortions, especially in the region of the separation wall, and thus reduces stresses in the bonded substrate stack.

[0041] A further aspect consists in continuous open-loop or closed-loop control of the pressure in the zone just before and / or during and / or after the transition of the bonding wave front over the separation wall. Preferably, the pressure in the zone behind the bonding wave or in the zone where the bonding wave is located is continuously varied to be adapted to the pressure in the zone through which the bonding wave is moving.

[0042] One aspect of the device and method is that the forward movement characteristics of the initiated bond wave are influenced by open-loop or closed-loop control of the holding forces of zones along the propagation direction of the initiated bond wave. In this case, the speed or acceleration of the bond wave is precisely adjusted by open-loop / closed-loop control of at least one fastening element in a zone, in particular by adapting the pressure conditions in time. This allows, in particular, a continuous, gentle, distortion-free transition of the advancing bond wave over the separating wall between the zones.

[0043] In the following procedures, an idealized process is assumed to illustrate an exemplary method for bonding. In particular, it is assumed that the bond wave propagates radially symmetrically from the contact point toward the periphery, i.e., as circular as possible. This observation facilitates the description of the method, since it is always possible to generally speak of the bond wave that needs to be adjusted. In general, asymmetric propagation of the bond wave is also possible. However, all methods, devices, and techniques described herein are considered with respect to the fact that the bond wave can generally propagate anisotropically, and therefore, closed-loop control of zones ahead and / or behind the bond wave section must be observed. This means that closed-loop control of zones will be generally adapted to each bond wave section that is to cross the separation wall at a predetermined location.

[0044] In the remainder of this specification, reference will be made to closed-loop control, which refers to a method of obtaining a measurement signal relative to a first physical value and adjusting a second physical value in relation to a desired result. For example, it is possible to measure the position of the bond wave (first physical value) and subsequently adjust the pressure in a zone ahead of the bond wave and / or in a zone behind the bond wave (second physical measurement) so as to achieve the desired result (minimal distortion of the substrates on the separation wall or between the substrates).

[0045] In contrast, open-loop control simply means determining a physical value without a corresponding measurement signal. Therefore, it may be known when a physical value needs to be adjusted to achieve a result based on empirical data sought. For example, it may be known how a bonding wave always behaves on the same type of substrate under the same initial and ambient conditions. In this case, the pressure in the individual zones may be open-loop controlled as a function of time starting from the moment of contact, without the need to measure the advancing bonding wave.

[0046] The method and device are described based on a vacuum substrate holder. That is, the clamping means is a vacuum clamping means, which may be evacuated or vented, in particular a simple hole drilled into the surface of the substrate holder. It is also possible to use other clamping elements, such as electrostatic or magnetic clamping means. In this case, these other clamping elements are also divided into zones and are suitable for adapting their respective holding forces. In this case, too, the clamping elements or their holding forces are variable / adjustable. Therefore, the term clamping element should be interpreted in a general way, but preferably not only applies to vacuum clamping means.

[0047] In a first method step of an exemplary method for influencing a bonding wave during bonding, a lower substrate is loaded onto a lower substrate holder and an upper substrate is loaded onto an upper substrate holder, preferably both substrates being fixed by fixing elements provided for this purpose.

[0048] In a second method step of the exemplary method for influencing a bonding wave during bonding, both substrates are aligned with each other. The alignment is preferably performed by an alignment facility provided for this purpose. The alignment between the two substrates is preferably performed based on alignment marks located on the substrates. A detailed description of the alignment method and device is omitted.

[0049] In a third method step of the exemplary method for influencing a bonding wave during bonding, both substrates are brought close together, with the spacing between the surfaces of both substrates to be bonded together being less than 10 mm, preferably less than 5 mm, even more preferably less than 1 mm, most preferably less than 0.1 mm, and very preferably less than 0.01 mm.

[0050] It is also possible to carry out the third method step first and only afterwards the second method step.

[0051] In a fourth method step of the exemplary method for influencing a bonding wave during bonding, at least one of the substrates is deformed and the deformed substrate is brought into contact with the second substrate. The contact is preferably as point-like as possible. The contact is also preferably as central as possible. The contact point is the starting point of the subsequently advancing bonding wave.

[0052] In a fifth method step of the exemplary method for influencing a bonding wave during bonding, the fastening means are switched or closed-loop controlled to deform at least one of the substrates and initiate a bonding wave that preferably starts at the center of each of the substrates and propagates radially symmetrically. As the bonding wave advances, additional fastening means are switched or closed-loop controlled to move the bonding wave continuously further toward the periphery.

[0053] The sixth method step of the exemplary method for influencing the bonding wave during bonding is typically performed multiple times, whenever the bonding wave section is moved toward the separation wall between the zones. In this case, the pressure in at least one zone, particularly the zone in front of and / or behind the bonding wave section, is closed-loop controlled. The bonding wave section is thus a region that propagates particularly radially symmetrically, in which the upper and lower substrates are bonded to each other. The closed-loop control is performed so that the bonding wave section generates minimal distortion, particularly no distortion, between the substrate regions located near the separation wall. For this purpose, the pressure in the zone in front of the bonding wave section and / or the pressure in the zone behind the bonding wave section must be continuously closed-loop controlled so that the bonding wave section is not exposed to any or only a very slight pressure gradient.

[0054] In one embodiment of the device for influencing the bonding wave during bonding, the substrate holder has multiple clamping elements. These clamping elements are individually controllable. Preferably, the clamping elements are vacuum clamping means. This vacuum clamping means allows for very simple and very precise control of the pressure of the ambient environment applied to the substrate. The clamping elements are part of a zone. In general, a zone may have multiple clamping elements, which allows for more precise control of the bonding wave within the zone. In particular, in the case of a vacuum zone, multiple clamping elements are used to enable faster evacuation of the zone. In this case, multiple clamping elements within a zone allow for a larger volumetric flow rate of gas to be delivered, thus enabling faster closed-loop control. Theoretically, multiple clamping means within a zone could also draw gas at different speeds. In this case, a pressure gradient could be generated within the zone. However, in this case, it would be better and more advantageous to change the pressure within the zone uniformly and isotropically. Therefore, the pressure inside a zone is preferably solely a function of time, and multiple fixing elements are preferably switched simultaneously, thereby providing uniform and isotropic closed-loop control of the pressure inside a zone.

[0055] The bonding device comprises at least one zone substrate holder, preferably at least one measuring device, and at least one control unit. In the case of closed-loop control, the measuring device is responsible for measuring physical parameters, such as determining the position of the bonding wave or at least one bonding wave segment. The measuring device transmits this data to the control unit, which evaluates the measured values ​​and, depending on the results, determines the required physical parameters for open-loop or closed-loop control of the fastening element.

[0056] The measuring device is preferably an optical system for determining the bond wave position, however sensors that determine the bond wave position in an electromagnetic manner are also possible, for example proximity sensors.

[0057] The radius of curvature of the substrate at the point of the bond wave is also of particular importance, in this regard the control of the fastening element may be effected as a function of the radius of curvature of the substrate in the region of the bond wave.

[0058] The control unit can be a microchip, a computer, software, or a combination of these. In most cases, this is software in a computer. Measurement signals reach the computer via peripheral devices and are evaluated by the software. This software then controls the clamping elements on the substrate holder via the peripheral devices in a closed loop. It is also possible to use a PID controller with electronically programmed closed loop control.

[0059] In the drawings, identical components or components having the same function are provided with the same reference numerals. All sketches may be exaggerated for illustrative purposes, so the drawings do not necessarily have to be to the same scale as the actual embodiment.

[0060] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and the drawings. [Brief explanation of the drawings]

[0061] [Figure 1] 1 is a schematic plan view of an embodiment of a substrate holder of an apparatus for influencing a bonding wave during bonding. FIG. [Figure 2a] 3 is a schematic diagram of a first state of the sixth method step of an exemplary method according to the invention for influencing a bonding wave during bonding. [Figure 2b] 10 is a schematic diagram of a second state of the sixth method step of an exemplary method according to the invention for influencing a bonding wave during bonding. [Figure 2c]10 is a schematic diagram of a third state of the sixth method step of an exemplary method according to the invention for influencing a bonding wave during bonding. [Figure 2d] 10 is a schematic diagram of a fourth state of the sixth method step of an exemplary method according to the invention for influencing a bonding wave during bonding.

[0062] In the drawings, identical components or components having the same functions are given the same reference numerals.

[0063] FIG. 1 shows the fixing surface of one embodiment of a substrate holder 1 of a device for bonding. A substrate 2 may be assembled to the device by means of mounting means 3. The substrate holder 1 has a number of zones 7, 7', 7'', which are defined in particular radially and azimuthally. In this example, these zones 7, 7', 7'' are delimited by separation walls 10, which, like the protrusions 9, are simply left behind when milling the substrate 2. In this case, the substrate holder 1 may be configured so that the separation walls 10 are polymer or metal seals. A single radially symmetrical central zone 7 can be seen in the drawing. Furthermore, surrounding this central zone 7, sixteen zones 7', 7'' are arranged radially along first and second circles, respectively.

[0064] The zones 7, 7', 7" are thus in particular recesses 11, preferably formed by milling, in which the projections 9 are located at several points. The pin surfaces of the pins 9 are in particular flush with the web surface of the separating wall 10. The zones 7, 7', 7" are in particular formed as vacuum zones. The recesses 11 may in particular be evacuated via the fastening means 12, individually and independently of one another due to their separation by the separating wall 10. The fastening element 12 is in this simple case simply a single hole, via which the spaces between the projections 9 and thus the zones 7, 7', 7" can be evacuated or vented. If the zones 7, 7', 7" are also to be used for deformation, a fluid may flow via the fastening means 12, which causes a particularly local deformation of the clamped substrate.

[0065] A deformation element 5 is preferably located in the center of the substrate holder 1, which can deform the clamped substrate, in particular centrally. A protrusion 9 serves in particular to reduce the contact area of ​​the clamped substrate 4, thereby preferably avoiding contamination. A number of sensors 8, in particular pressure sensors, may be located in the zones 7, 7', 7'' of the substrate holder 1.

[0066] Also visible in the drawing is region Q, a cross-section of which is shown in the subsequent drawing.

[0067] It is also clear to those skilled in the art that pressure can be defined as force per unit area. Since the method for influencing a bonding wave is described on the basis of a vacuum substrate sample holder and an evacuated zone in order to generate a force applied to the substrate, it is advantageous to refer to pressure. In this case, a physical consideration of the force and its effects must be made in accordance with the state of the art.

[0068] 2a shows a first state of the sixth method step of the method for influencing the bonding wave during bonding. A cross-section of the two zones 7', 7" and the region Q of their separating wall 10 (see FIG. 1) is shown. The lower substrate 4 rests on the projections 9 and the separating wall 10, and the upper substrate 4' is bonded to the lower substrate 4 exactly in this section of both zones 7', 7". The propagating bonding wave 6 can be seen, which is shown only as a point in the cross-section. In plan view, the bonding wave 6 is a closed curve, particularly preferably a circle, over its entire circumference. Since the advance of the bonding wave 6 is to be open-loop or closed-loop controlled, the two zones 7', 7" generally have different pressures. In this figure, for example, the pressure p1 in zone 7' is selected to be relatively low, which allows the substrate region 13 of the lower substrate 4 to be fixed stronger and better in the vicinity of the bonding wave 6, and thus the substrate region 13' of the upper substrate 4' to be bonded to the substrate region 13 with as little distortion as possible. Zone 7'' has a relatively high pressure p2, in particular around the ambient pressure, which allows the substrate regions 13, 13' that are further away from the bonding wave 6 to be better adapted.

[0069] In the lower part of the drawing, a pressure diagram is shown. On the horizontal axis, the position is shown in arbitrary units, preferably in mm, and on the vertical axis, the pressure values ​​are plotted. Three pressures are plotted, one of which is the external ambient pressure p0. In this case, this ambient pressure p0 is approximately 1 bar.

[0070] It is also possible that the substrate holder 1 is located in a chamber that increases the outside pressure, in which case the ambient environmental pressure is positive relative to the atmosphere.

[0071] It is also possible for the substrate holder 1 to be located in a chamber that reduces the outside pressure. In this case, the ambient pressure is negative relative to the atmosphere. This embodiment is particularly important when the substrates have to be bonded in an ambient environment with a lower pressure, for example to avoid or reduce contamination.

[0072] In the remainder of this document it is assumed that the device is open to the atmosphere and that the ambient pressure p0 is atmospheric pressure of about 1 bar.

[0073] In general, the ambient pressure p0 may be between 2 bar and 0.1 bar, preferably between 1.5 bar and 0.5 bar, even more preferably between 1.25 bar and 0.75 bar, most preferably between 1.10 bar and 0.90 bar, and most preferably exactly 1.0 bar.

[0074] The pressure in zone 7' is labeled p1. Zone 7' is very strongly evacuated, so pressure p1 is quite low. The pressure in zone 7'' is labeled p2. Zone 7'' is not so strongly evacuated, so pressure p2 is higher than pressure p1.

[0075] Pressures p1, p2 are generally always below the ambient pressure p0. In very special embodiments, it is possible for at least one of the pressures to exceed the ambient pressure p0. In this case, the substrate region 13 of the substrate 4 is raised below the zone where the pressure exceeds the ambient pressure p0.

[0076] The bonding wave 6 is still far enough away from the zone 7" that the pressure difference between the pressure p1 in the zone 7' and the pressure p2 in the zone 7" does not yet cause undesired distortions between the two substrate areas 13, 13'. However, in this method step the bonding wave 6 has already been moved towards the separating wall 10, and therefore it is detected, preferably by an optical system, that a strong pressure change and thus a strong influence on the bonding wave 6 and therefore the bonding behavior between the substrate areas 13, 13' occurs very immediately.

[0077] The values ​​of pressures p1 and p2 are generally process dependent, of course, and must be determined by testing and / or simulation.

[0078] 2b shows a second state of the sixth method step of the method for influencing a bond wave, in which the bond wave 6 has already been sufficiently advanced. In this second state, the pressure p1 in zone 7′ and the pressure p2 in zone 7″ are pre-compensated to ensure that the substrate area 13 of the lower substrate 10 is subjected to as gentle a pressure action as possible during the transition of the bond wave 6 over the separating wall 10.

[0079] The transition from the first state shown in Figure 2a to the second state shown in Figure 2b is of course continuous, i.e. the pressures p1, p2 are continuously adapted to one another while the bonding wave 6 is continuously advanced, with the aim that the substrate areas 13, 13' are bonded to one another without error or with only minimal error.

[0080] The new values ​​of pressures p1 and p2 are generally process dependent, of course, and must be determined by testing and / or simulation.

[0081] 2c shows a third state of the sixth method step of the method for influencing a bonding wave, in which the bonding wave 6 is located on the separating wall 10. In the prior art, different pressure intensities act on the substrate area 13 in zones 7' and 7'', which leads to an inaccurate bonding between the substrate areas 13, 13'. By adapting the holding forces or adjusting the pressures p1, p2 in zones 7', 7'' an optimal bonding process between the substrate areas 13, 13' is possible.

[0082] The values ​​of pressures p1 and p2 are generally, of course, also process-dependent and must be determined by tests and / or simulations. This means that pressures p1 and p2 do not necessarily have to be equal to one another, as illustrated in the drawing, but must be adjusted so that both substrate areas 13 and 13' are bonded to one another as optimally as possible, meaning that possible structures on the substrate surfaces of substrate areas 13 and 13' are bonded in proper alignment with one another.

[0083] FIG. 2d shows a fourth state of the sixth method step of the method, in which the bond wave 6 has been moved beyond the separation wall 10. In this fourth state, the substrate areas 13, 13′ are located in a new zone 7″. The pressure p2 in this zone 7″ may, in this illustration, also be adjusted, for example, to a very low value, in order to fix the underlying substrate 10 while the bond wave 6 advances to the end of zone 7″. The new values ​​of pressures p1, p2 are generally also process-dependent and must be determined by tests and / or simulations.

[0084] 2a-2d specifies that the fastening elements 12 are switched during the transition of the bonding wave 6 over the separating wall 10 of one of the two zones 7', 7" in order to optimize the bonding between the substrate areas 13, 13' and therefore generally between the substrates 4, 4', i.e., to minimize the misalignment between opposing structures on the substrates 4, 4'. In the particular case of the vacuum substrate sample holder 1, this means that the pressure adjustment in the zones 7', 7" is performed in such a way that the substrate areas 13, 13' are subjected to as continuous and gentle a pressure transition as possible during the transition of the bonding wave 6 over the separating wall 10, i.e., so that the pressures p1, p2 are as equal as possible or only slightly different from one another. [Explanation of symbols]

[0085] 1 PCB holder 2 Base 3 Mounting means 4,4' board 5. Transformation Elements 6 Bonding Wave 7,7',7'' zone, inner zone, outer zone, another zone 8 sensors 9 protrusions 10 Separation elements, separation walls 11 Recess 12 Fixed Elements 13,13' board area Q cross-sectional area p0 atmospheric pressure p1, p2 Pressure of the upstream zone / inner zone, pressure of the downstream zone / outer zone

Claims

1. A method for influencing a bonding wave (6) when bonding a first substrate (4) to a second substrate (4'), comprising: at least said first substrate (4) is fixed to a first substrate holder (1) with at least one zone (7', 7''), said at least one zone (7', 7'') each having at least one separating element (10) at least partially forming a substrate holder surface, said at least one separation element (10) separating said at least one zone (7', 7'') from another zone (7, 7') of said first substrate holder (1) or from the surrounding environment, the at least one zone (7', 7'') each has at least one fixing element (12), each of which provides a holding force for fixing the first substrate (4) to the first substrate holder (1); In the method, at least, i) initiating a bonding wave (6) by contacting said second substrate (4') with said first substrate (4), and then ii) the retention force of the at least one fixation element (12) of the at least one zone (7', 7''); a) the holding force of the fastening elements of another zone (7, 7') located immediately upstream in the direction of propagation of said bonding wave (6), or b) the ambient pressure of the ambient environment and the step of adapting 10. A method comprising:

2. 2. The method according to claim 1, wherein during the adaptation in step ii) the ambient pressure is additionally adapted to the holding force of the fixing element (10) in the at least one zone (7'').

3. 2. The method according to claim 1, wherein the adaptation in step ii) is performed in such a way that the holding forces immediately before and immediately after the at least one separating element (10), respectively, are equal in magnitude to one another, viewed in the direction of propagation of the bonding wave (6).

4. 3. The method according to claim 1, further comprising the step of continuously checking the position of the bonding wave (6) after initiation of the bonding wave (6) in step i) and adapting the holding forces of the at least one zone (7', 7'') so that, upon transition of the bonding wave (6) over the at least one separating element (10), the holding forces are equal before and after the at least one separating element (10).

5. 3. The method according to claim 1 or 2, wherein the at least one fixing element (12) of the at least one zone (7', 7'') is formed as a vacuum fixing means, respectively, and the at least one separating element (10) fluidically separates the at least one zone (7', 7'') from the other zone (7, 7') or from the surrounding environment.

6. 3. A method according to claim 1 or 2, wherein the adaptation in step ii) is carried out by venting or evacuation of said at least one zone (7, 7') or said surrounding environment.

7. 3. The method according to claim 1 or 2, wherein the adaptation in step ii) comprises determining a pressure difference between the at least one zone (7', 7'') and the other zone (7, 7') or the surrounding environment, and the pressure difference is compensated for by the adaptation.

8. 3. The method according to claim 1, further comprising compensating the pressure (p2) of the at least one zone (7'') to the pressure (p1) of the other zone (7').

9. 1. A device for influencing a bonding wave (6) when bonding a first substrate (4) to a second substrate (4'), comprising at least: a first substrate holder (1) for fixing said first substrate (4), said first substrate holder (1) comprising at least one zone (7', 7''), said at least one zone (7) being provided via at least one separating element (10) at least partly forming a substrate holder surface of said first substrate holder (1); at least one fixing element (12) arranged in said at least one zone (7) and having a holding force for fixing said first substrate (4) to said first substrate holder (1); a control unit for adapting the holding force of the at least one fixing element (12) of the at least one zone (7); 1. An apparatus having: The control unit controls the holding force of the at least one fastening element (12) of the at least one zone (7', 7'') during the advancement of the bonding wave: a) the holding force of the fastening elements (12) of another zone (7, 7') located immediately upstream in the direction of propagation of said bonding wave (6), or b) Surrounding environmental pressure 10. A device adapted to:

10. 10. The device according to claim 9, additionally comprising means for adapting the ambient pressure to the holding force of the at least one zone (7', 7'').

11. 11. The device according to claim 9 or 10, wherein the control unit is configured to keep the holding force of the at least one fixing element (12) in the at least one zone (7', 7'') and the holding force of at least one other fixing element (12) in another zone equal to each other during bonding of the first substrate (4) to the second substrate (4').

12. 11. The device according to claim 9 or 10, wherein the control unit is configured to keep the holding forces of the at least one fastening element (12) of the at least one zone (7', 7'') and the at least one fastening element (12) of the further zone (7, 7') equal to each other directly in the area of ​​the at least one separating element (10) and during the period when the bonding wave (6) overcomes the at least one separating element (10).

13. 11. The device according to claim 9 or 10, wherein the at least one fixing element (12) of the further zone (7, 7') and the at least one fixing element (12) of the at least one zone (7', 7'') are formed as vacuum fixing means, and the separating element (10) fluidly separates the inner zone (7') and the outer zone (7'') from each other.

14. 11. The device according to claim 9 or 10, wherein the control unit is configured to keep the pressure difference between the pressure (p1) in the further zone (7, 7') and the pressure (p2) in the at least one zone (7', 7'') as small as possible, preferably equal, during the joining.

15. 11. The device according to claim 9 or 10, wherein the control unit is configured such that the means for adapting the ambient pressure compensates for the pressure (p2) in the at least one zone (7'') immediately before and immediately after the bonding wave (6) overcomes the at least one separating element (10).

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