Method and device for influencing a bonding wave during bonding
Patent Information
- Application Number
- EP2022770019
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2022-09-02
- Publication Date
- 2025-07-09
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Method and device for influencing a bond wave during bonding
[0003] The invention relates to a method and a device for influencing a bonding wave during substrate bonding. Furthermore, the invention relates to a method and a device for bonding with a substrate holder having at least one zone. Such zones are essential in some devices and methods for individually processing, fixing, and bonding the substrate to other substrates or substrate stacks.
[0004] The prior art contains numerous publications describing substrate holders for securing substrates. Some of these substrate holders are used for joining two substrates, a process known as bonding. Among the bonding processes, fusion or direct bonding is of particular importance. In fusion bonding, two substrates are joined together based solely on their hydrophobic or hydrophilic substrate surface properties. In a first process step, known as pre-bonding, contact is made between the two substrates at one point, particularly at a central point. After contact has been made, the fixing of at least one substrate, particularly the upper one, is released, so that the two substrates bond together along their facing substrate surfaces.The bonding process takes place via a progressive bond wave that spreads from the contact point to the periphery of the two substrates. After this bonding process, a separation of the two substrates using appropriate methods and devices is conceivable. Separation is necessary if it is determined that the substrates have not been optimally bonded. Very few substrates have an untreated substrate surface. In most cases, the substrates have already been processed and have different structures. Possible examples include integrated circuits, microprocessors, LEDs, MEMS, etc. These structures are then to be aligned with the structures on a second substrate and connected to them.What is particularly important is that each individual structure on the first substrate must be correctly aligned and connected to the structure on the opposite, second substrate.
[0005] After creating a pre-bond, the resulting substrate stack is typically subjected to thermal treatment to increase the bond strength between the two substrate surfaces. Once this thermal treatment is complete, the bond is referred to as a fusion or permanent bond. From this point onward, the two substrates can no longer be separated non-destructively.
[0006] As the bond wave advances, individual substrate regions near the bond wave can become distorted to such an extent that the alignment accuracy between the opposing structures is no longer maintained. In particular, multiple such distortions can even lead to a global distortion that increases toward the periphery, particularly starting from the center. In extreme cases, the distortions can even be anisotropic, i.e., direction-dependent.
[0007] The industry has therefore developed several substrate holders whose goal is to influence the bonding wave. Control or regulation is preferably achieved by the fixing elements, with the help of which the substrate can be fixed to the substrate holder. For example, the documents WO2017162272A1, W02018028801A1 and WO2019057286A1 describe ways of influencing the bonding wave using the zones of the zone substrate holder. A zone is understood to be an area that has at least one, possibly several, fixing elements. The zones are usually physically separated from one another, but can also simply be regions in which the fixing elements are switched according to a predetermined plan.
[0008] In particular, a substrate holder can also have only a single zone, in which, generally, several fixing elements are present. However, substrate holders with several zones separated from one another by partition walls are particularly preferred. In the case of a substrate holder with only one zone, the outer periphery can be considered the partition wall within the meaning of the invention, which separates the single zone from the surroundings.
[0009] One type of substrate holder is the vacuum substrate holder. The space between the substrate and the substrate holder is evacuated via the fixing elements, which usually consist of small holes, and atmospheric pressure presses the substrate down and fixes it to the substrate holder. Initially, only individual holes were drilled into the substrate holder, forming very simple fixing elements. The entire area between the substrate and the substrate holder surface was evacuated. All existing fixing elements were connected to the same vacuum line. This created a full-surface, locally non-controllable, non-adjustable fixation of the substrate when a vacuum was applied.
[0010] Through the further development of these substrate holders and the possibility of controlling individual fixation elements, it became possible to control or regulate the fixation with spatial resolution.
[0011] A further development of the substrate holders consisted in combining the fixing elements and zones with a pins chuck. A pins chuck is a substrate holder that has been milled out at several, particularly symmetrically distributed, positions. The milling is not carried out over the entire surface, but preferably symmetrically along radial, azimuthal, or rectangular lines. This leaves raised areas between these lines in relation to the milled-back area, which are referred to in the prior art as nubs. By resting a substrate on these nubs, on the one hand, more or less full-surface support is still achieved, albeit with a very significant reduction in the contact area. Furthermore, it is possible to evacuate the spaces between the nubs, which leads to a more even contact pressure due to the surrounding atmosphere.In particular, the nub density can be varied as a function of location, particularly as a function of radius, in order to achieve a more homogeneous force application to the substrate when using multiple fixing elements per zone. The milled nubs result in a recessed structure that is generally identical to a zone. Adjacent zones are separated from each other by a partition. The partition is either made of non-milled material or by an intentionally introduced seal, particularly a polymer seal. The partition completely encloses a zone and, in a vacuum substrate holder, can also be considered a vacuum seal.
[0012] The problem with the prior art is that neighboring zones or separated regions are generally evacuated to different degrees as the bonding wave moves across the dividing wall of one zone. This creates a strong pressure gradient on the bonding wave as it moves across the dividing walls of two zones. This pressure gradient leads to significant distortion between the substrates.
[0013] In this respect, the prior art also presents the problem that, even in the case of a substrate holder with only one zone, a pressure gradient exists between the individual zone and the environment. In this case, the dividing wall of the substrate holder is simultaneously the periphery that separates the zone from the environment. If a bonding wave runs to the edge on such a substrate holder, the same problem arises as when crossing a dividing wall that separates several zones from one another: the substrate regions close to the bonding wave can be distorted. It is therefore the object of the invention to at least partially eliminate, and in particular to completely eliminate, the disadvantages cited in the prior art. In particular, it is an object of the invention to demonstrate an improved method and device for bonding.Furthermore, it is an object of the present invention to provide a method and a device with which the bonding result, in particular the distortion between two substrates, can be reduced.
[0014] The present object is achieved by the features of the independent claims. Advantageous developments 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. For specified value ranges, values within the specified limits are also considered to be disclosed as limit values and can be claimed in any combination.
[0015] Accordingly, the invention relates to a method for influencing a bonding wave during the bonding of a first substrate to a second substrate, wherein at least the first substrate is fixed on a first substrate holder with at least one zone and the at least one zone each has at least one separating element that at least partially forms the substrate holder surface, and wherein the at least one separating element separates the at least one zone from a further zone or an environment of the first substrate holder, and wherein the at least one zone each has at least one fixing element and the at least one fixing element each provides a holding force for fixing the first substrate to the first substrate holder,wherein the method comprises at least the following steps: i) initiating a bonding wave by contacting the second substrate with the first substrate and then ii) adapting the holding force of the at least one fixing element of the at least one zone to a holding force of a fixing element of a further zone located immediately upstream in a propagation direction of the bonding wave or to an ambient pressure of the environment.
[0016] In other words, the at least one zone is controlled by adjusting the holding forces of the fixing elements of the zone substrate holder such that the pressure gradient of the at least one zone in the direction of propagation of the bonding wave, particularly in the region of the separating element, is as low as possible. By adjusting the holding force of the at least one fixing element to the ambient pressure, particularly to the pressure of the last zone in the propagation direction, it is ensured that the atmospheric pressure during bonding matches the holding force of the zone at the outer edge at the moment the bonding wave crosses the separating wall at the edge of the substrate holder.
[0017] The pressure within at least one zone, especially the last one, can be adjusted to the ambient pressure. Since adjusting the pressure within the zone can be accomplished more quickly and efficiently than changing the pressure in a large chamber or the surrounding area, this advantageously influences the bonding wave. In this process, the holding force on the lower substrate is reduced, or even completely eliminated, allowing it to expand unhindered at the edge.
[0018] Preferably, the at least one zone has a plurality of controllable fixing elements, whereby the holding forces can be specifically varied. This enables the generation of a holding force gradient within a zone in order to better control the advancing bonding wave within the at least one zone. The bonding wave is preferably initiated by centrally contacting the second substrate with the first substrate, so that the bonding wave propagates radially symmetrically.
[0019] Substrate holders with multiple zones are particularly preferred, i.e. at least one zone and at least one further zone. Therefore, in the further course of the text, the embodiment of a substrate holder with multiple zones is often described, in which at least one dividing wall exists that separates two zones from one another. For the alternative embodiment of the method with a substrate holder with only one zone, in which the outermost dividing wall simultaneously represents the periphery of the substrate holder and in which there is no second zone but instead the adjacent surroundings, the holding force is preferably adapted to the last zone or the outermost zone, so that a particularly uniform transition over the last or outermost dividing wall is enabled. The dividing wall can also be inserted elements, in particular a sealing lip.The partition wall therefore does not necessarily have to be formed from a milled-back section of the substrate holder, but can be an attached component. In this case, the pressure in the outermost zone is adjusted to the ambient pressure.
[0020] The zones can be divided into several segments perpendicular to the propagation direction of the bonding wave. Thus, several isosceles trapezoidal segments can form a zone, wherein the segments preferably each have at least one fixing element. Thus, along the preferably circular substrate holder, the bonding wave can advantageously be adjusted simultaneously at several points, regardless of the radial position. The adjustment takes place after the initiation of the bonding wave and preferably in the region where the bonding wave travels (the first and second substrates are contacted or connected). This enables particularly distortion-free bonding.
[0021] In a preferred embodiment of the alignment method, it is provided that, during the adjustment in step ii), the ambient pressure is additionally adjusted to the holding force of the fixing element of the at least one zone. In this respect, the prevailing atmospheric pressure or the ambient pressure in the bonding chamber is adjusted. In this way, the holding force in the at least one zone can advantageously be adjusted indirectly, since the ambient pressure acts on the first substrate.
[0022] In a preferred embodiment of the alignment method, the adjustment in step ii) is carried out such that the holding force is the same immediately before and after the at least one separating element in the direction of propagation of the bonding wave. In other words, adjusting the holding force in the region of the separating elements during the period in which the bonding wave is exceeded ensures that a low-distortion connection can be made, even in the region of the zone transition. The holding force can also be adjusted continuously. It is crucial that the large difference in holding force between the zones immediately before and after the bonding wave of the separating turn is minimal, which is desired for regulating the bonding wave. In this way, distortion in the region of the zone transitions can advantageously be ensured.
[0023] In a preferred embodiment of the alignment method, after initiating the bonding wave in step i), the position of the bonding wave is continuously determined, and the holding force of the at least one zone is adjusted such that, when the bonding wave transitions over the at least one separating element, the holding force in front of and behind the at least one separating element is the same. By determining the position of the bonding wave, the adjustment in step ii) can advantageously take place in exactly the time period in which the bonding wave moves over the separating elements. In this way, the desired holding force differences in regions outside the separating elements or between them can be implemented to regulate the bonding wave without creating distortion in the region of the zone transitions.In a preferred embodiment of the alignment method, it is provided that the at least one fixing element of the at least one zone is in each case designed as a vacuum fixing element, and the at least one separating element fluidically separates the at least one zone from the further zone or the surroundings. The substrate holder is particularly preferably a vacuum zone substrate holder which is divided into a plurality of controllable vacuum zones arranged symmetrically in the radial direction and in the direction of propagation. The substrate arranged on the separating elements is thus sucked in and fixed. The holding force of the vacuum fixing elements is advantageously set individually in each zone (or segment), since these are fluidically tight and thus suitable for vacuum. In this way, the fixing element can advantageously act over the entire area, and the bonding wave can be regulated as fully as possible.The substrate holder can be flushed with an inert gas, preferably helium. It is also conceivable that the vacuum lines could be flushed with the inert gas.
[0024] In a preferred embodiment of the alignment method, the adjustment in step ii) is performed by flooding or evacuating the at least one zone or by flooding or evacuating the surrounding area. In this way, the holding force can be provided advantageously simply, quickly, and over a large area. Furthermore, the holding force can be adjusted particularly quickly at the transition in the region of the zone transitions or in the region of the separating elements, and can then advantageously be quickly adjusted to the desired holding forces for regulating the bond wave in the regions between the separating elements.
[0025] In a preferred embodiment of the alignment method, the adjustment in step ii) comprises determining a pressure difference between the at least one zone and the further zone or the surrounding area, wherein the pressure difference is compensated by the adjustment. This ensures that a particularly low pressure gradient prevails in front of and behind the separating element, minimizing distortion during bonding. Furthermore, the area in front of the separating element can advantageously be flooded instead of evacuated.
[0026] In a preferred embodiment of the alignment method, the pressure of at least one zone is adjusted to the pressure of the other zone. This advantageously provides sufficient time to precisely determine the position of the bonding wave and to adjust the pressure only in the zone downstream of the propagation direction.
[0027] In one embodiment of the alignment method, the holding force of the at least one zone and the additional zone are adjusted to compensate for the pressure gradient. In this case, the additional zone also has corresponding fixing elements with variable holding force. Furthermore, if the ambient pressure is adjusted to the last zone in the propagation direction, the adjustment can also occur simultaneously with the adjustment of the holding force of the at least one zone.
[0028] Furthermore, the invention relates to a device for influencing a bonding wave during the bonding of a first substrate to a second substrate, at least comprising a first substrate holder for fixing the first substrate with at least one zone, wherein the at least one zone has at least one separating element that at least partially forms a substrate holder surface of the first substrate holder, and at least one fixing element arranged in the at least one zone with a holding force for fixing the first substrate to the first substrate holder, a control unit for adjusting the holding force of the at least one fixing element of the at least one zone,wherein the control unit is configured to adapt the holding force of the at least one fixing element of the at least one zone to a holding force of a fixing element of a further zone located immediately upstream in a propagation direction of the bonding wave or to an ambient pressure during an advance of the bonding wave.
[0029] The control unit is thus configured to adjust the holding force of the at least one fixing element to the holding force of the upstream zone. With respect to the alternative, in which the holding force is adjusted to the ambient pressure, in particular the holding force of the last zone on the periphery of the substrate holder is adjusted depending on the ambient pressure. In other words, a zone substrate holder is provided with several controllable fixing elements, wherein the fixing elements are controlled such that optimal holding forces are provided before and after a separating wall separating the zone during bonding, so that distortion during the transition is reduced. The side of the first substrate facing away from the second substrate rests on the separating element which at least partially forms the substrate holder surface.By controlling the holding forces before and after the transition over the partition, a bond wave can move particularly evenly and undisturbed in the area of the partition. This reduces the undesired influence of different holding forces before and after the partition, on the bond wave, which propagates particularly from the inside to the outside. Different holding forces acting between the zones can be desired to regulate the bond wave. If a bonding process is not initiated from the center, the outer zone with the fixing element with adjustable holding force can also be arranged closer to the center of the substrate holder. It is crucial that the holding force of the following zone, particularly in the area of the partition, can be adjusted in the direction of the expected bond wave in order to compensate for the influence of the different holding forces acting (before and after the partition).This ensures advantageously low distortion in the area of the separating element. The dependency can also be determined based on empirical or initial tests and adjusted accordingly. The control unit is not limited to pure control, but can also regulate the holding forces depending on additional parameters (e.g., bond wave position). The holding forces of the fixing elements are preferably adjustable by the control unit. Furthermore, the substrate holder preferably has several separating elements, which in turn can be divided into several segments along the preferably circular substrate holder.
[0030] These segments of a zone, distributed around the circumference, are aligned, particularly along the direction of propagation, so that the trapezoidal segments, for example, become larger toward the periphery. Overall, the device advantageously minimizes stress and distortion, particularly in the area of zone transitions or from the inner to the outer zone. The control unit can also regulate the respective holding forces depending on additional parameters.
[0031] In a preferred embodiment of the device for influencing a bonding wave during bonding, the device additionally comprises means for adapting the ambient pressure to the holding force of the at least one zone. In this way, the bonding wave can be advantageously indirectly influenced or the holding force can be adjusted, since the ambient pressure acts on the first substrate. If the fixing elements are vacuum fixing elements that operate with pressure, the pressures can advantageously be adjusted, so that the bonding wave runs out particularly gently.
[0032] In a preferred embodiment of the device for influencing a bonding wave during bonding, the control unit is configured to adjust the holding force of the at least one fixing element or the ambient pressure after contacting during bonding of the second substrate to the first substrate. The control unit is thus configured such that the adjustment of the holding forces or the ambient pressure only occurs after initiation of a bonding wave during bonding. In this way, the device or the control unit can perform the adjustment 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 a bonding wave during bonding, the control unit is configured to determine the holding force of the at least one fixing element of the at least one zone using a sensor. The sensor is preferably arranged in the region of the separating element in the at least one outer and / or inner zone. In addition, a sensor is preferably provided that determines the ambient pressure. In this way, the control unit can advantageously regulate the adjustment of the holding forces based on real values, so that distortion can be further reduced.
[0034] In a preferred embodiment of the device for influencing a bonding wave during bonding, it is provided that the control unit is configured to keep the holding force of the at least one fixing element of the at least one zone and the holding force of at least one further fixing element of a further zone the same during bonding of the first substrate to the second substrate. In this way, the bonding wave is able to make the transition from the inner to the outer zone particularly gently and without distortion. In addition, uniform holding forces can be efficiently and uniformly set in several, in particular consecutive, zones. This further improves the bonding result and ensures low distortion during the transition over the partition.In a preferred embodiment of the device for influencing a bonding wave during bonding, it is provided that the control unit is configured to keep the holding force of the at least one fixing element of the at least one zone and the holding force of the at least one fixing element of the further zone equal directly in the region of the at least one separating element and during the period in which a bonding wave passes over the at least one separating element. In this case, the position of the bonding wave is preferably also determined by a measuring device, particularly preferably optically designed, and the period of adjustment is optimally adapted to the position of the bonding wave. In this way, the regulation of the holding forces between the separating elements for influencing the bonding wave can advantageously be continued quickly after the separating elements have been passed. In addition, further improved bonding results can be achieved, particularly in the region of the separating elements.
[0035] In a preferred embodiment of the device for influencing a bonding wave during bonding, it is provided that the at least one fixing element of the further zone and the at least one fixing element of the at least one zone are designed as vacuum fixings and the separating element fluidically separates the inner zone and the outer zone from one another. With a substrate placed on the first substrate holder, a fixing of the substrate to the first substrate holder can thus advantageously be created over a large area in the entire zone region by means of negative pressure (with respect to the atmosphere or the environment). This holding force can advantageously be changed quickly, precisely and in each zone. In addition, contamination of the first substrate can be kept to a minimum since no contact with the substrate is necessary to apply the force.The zones, which are fluidically separated from one another and controlled by vacuum fixing elements, are thus predestined for use in the device for influencing the bonding wave. In a preferred embodiment of the device for influencing a bonding wave during bonding, the control unit is configured to keep a pressure difference between a pressure of the further zone and a pressure of the at least one zone during bonding as low as possible, preferably to keep them the same. The pressure is preferably regulated by means of pressure sensors arranged in the respective zones. When bonding the first substrate to the second substrate, a uniform and distortion-free connection can thus advantageously be created, particularly in the region of the separating elements.
[0036] In a preferred embodiment of the device for influencing a bonding wave during bonding, the control unit is configured to allow the means for varying the ambient pressure to adjust the ambient pressure to the pressure of the at least one zone immediately before and after the bonding wave passes over the at least one separating element. The above effects and advantages of the outer zone apply analogously to the further outer zone. By arranging multiple zones in the direction of propagation of the bonding wave, bonding can be performed particularly precisely, uniformly, and without distortion.
[0037] In the following, an outer zone is understood to mean at least one zone or a zone downstream in the propagation direction of a bond wave. An inner zone is a further zone or the last zone if the ambient pressure is adjusted. The inner zone is a zone upstream in the propagation direction. The holding force of the downstream or at least one zone is preferably adjusted to the holding force of the upstream zone.
[0038] A particularly advantageous effect of the device and method for influencing the bond wave during bonding is that no or only negligible distortions occur between the two substrates near the partition walls that separate the zones. This enables a seamless, smooth, and non-distorting transition of the bond wavefront across the partition wall. This reduces distortion, particularly in the area of the partition walls, and reduces stresses in the bonded substrate stack.
[0039] Another aspect is to continuously control or regulate the pressure in the zones shortly before and / or during and / or after the transition of the bond wave front across the partition. Preferably, the pressure of a zone behind the bond wave or of a zone in which the bond wave is currently located is continuously changed to match the pressure of the zone into which the bond wave is moving.
[0040] One aspect of the device and method is that the bond wave's propagation behavior is influenced by controlling or regulating the holding forces of the zones along the propagation direction of the initiated bond wave. The speed or acceleration of the bond wave is specifically adjusted in a zone by controlling or regulating at least one fixing element, in particular by temporally adjusting the pressure state. This enables, in particular, a distortion-free, continuous, and smooth transition of the advancing bond wave across the separating walls of zones.
[0041] In the following process, idealized processes are assumed and described in order to illustrate an example bonding process. In particular, it is assumed that the bond wave propagates radially symmetrically, i.e. as circularly as possible, from the contact point to the periphery. This approach makes it easier to describe the process, as one can always speak of a bond wave in general that needs to be regulated. In general, asymmetric propagation of the bond wave is also conceivable. However, all of the processes, devices and procedures mentioned here are considered with regard to the fact that a bond wave can generally propagate anisotropically and therefore control of the zones in front of and / or behind a bond wave section must be considered, i.e. the control of the zones is generally adapted to the individual bond wave sections that are to cross the partition wall at a certain position.
[0042] The rest of this text refers to closed-loop control. Closed-loop control refers to a process in which a measurement signal for a first physical value is obtained and a second physical value is set based on a desired result. For example, it would be conceivable to measure the position of a bond wave (first physical value) and then adjust the pressure in the zone in front of and / or behind the bond wave (second physical measurement value) to achieve a desired result (minimal distortion of the substrate(s) on the partition).
[0043] In contrast, control is understood as merely specifying a physical value without a corresponding measurement signal. For example, it may be known, based on empirical data, when a physical value must be adjusted to achieve a result. For example, it might be known how a bond wave behaves on identical substrates under identical initial and boundary conditions. In this case, the pressure in the individual zones could be controlled as a function of time, starting from the moment of contact, without having to measure the advancing bond wave.
[0044] The method and device are described using vacuum substrate holders. This means that the fixtures are vacuum fixtures, in particular simple holes drilled into the substrate holder surface that can be evacuated or flooded. It is also conceivable that other fixture elements, such as electrostatic fixtures or magnetic fixtures, could be used. These are then also divided into zones and are suitable for adjusting the respective holding forces. In this case, too, the fixture elements and their holding force are variable / adjustable. The term "fixing element" should therefore be interpreted generally and refers not only, but preferably, to vacuum fixtures.
[0045] 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 are secured using the provided securing elements.
[0046] In a second step of an exemplary method for influencing a bonding wave during bonding, the two substrates are aligned with each other. The alignment is preferably performed using dedicated alignment systems. The alignment between the two substrates is preferably achieved using alignment marks located on the substrates. The methods and devices for alignment will not be discussed in detail.
[0047] In a third method step of an exemplary method for influencing a bonding wave during bonding, the two substrates are brought closer together. The distance between the two substrate surfaces to be bonded is less than 10 mm, preferably less than 5 mm, more preferably less than 1 mm, most preferably less than 0.1 mm, and most preferably less than 0.01 mm.
[0048] It is also conceivable that the third and then the second process step are carried out first.
[0049] In a fourth method step of an exemplary method for influencing a bonding wave during bonding, at least one of the two substrates is deformed such that contact is made between the deformed substrate and the second substrate. Contact is preferably made as point-like as possible. Contact is also preferably made as centrally as possible. The contact point is the beginning of a later advancing bonding wave.
[0050] In a fifth method step of an exemplary method for influencing a bonding wave during bonding, the fixation devices are switched or controlled such that at least one of them can deform the substrate in such a way that a bonding wave begins to propagate. The bonding wave is preferably initiated in the respective center of the substrates and propagates radially symmetrically. As the bonding wave progresses, additional fixation devices are switched or controlled such that the bonding wave continuously moves toward the periphery.
[0051] The sixth method step of an exemplary method for influencing a bonding wave during bonding generally takes place several times and always when a bonding wave section moves towards a separating wall between the zones. In this case, the pressure in at least one zone, in particular in a zone in front of and / or behind the bonding wave section, is regulated. The bonding wave section is thus the region that extends, in particular, radially symmetrically, in which the upper and lower substrates are connected. The regulation is carried out in such a way that the bonding wave section generates minimal, in particular no, distortion between the substrate regions located near the separating wall. For this purpose, the pressure in the zone in front of and / or in the zone behind the bonding wave section must be continuously regulated such that the bonding wave section is exposed to no or a very low pressure gradient.
[0052] In one embodiment of the device for influencing a bonding wave during bonding, the substrate holder has several fixing elements. The fixing elements can be controlled individually. The fixing elements are preferably vacuum fixing elements. With the help of vacuum fixing elements, the contact pressure of the environment on the substrate can be controlled very easily and very precisely. The fixing elements are part of a zone. In general, a zone could have several fixing elements in order to enable finer control of the bonding wave within a zone. In particular in vacuum zones, several fixing elements serve to enable faster evacuation of the zone. By having several fixing elements within a zone, a larger volume flow of gas can then be removed and thus faster control can be carried out. Theoretically, it is also conceivable for the fixing elements within a zone to extract the gas at different speeds.In this case, it would be possible to create a pressure gradient within a zone. However, it is better and more effective to change the pressure within a zone homogeneously and isotropically. Therefore, the pressure within a zone is preferably exclusively a function of time, and several fixation elements are preferably synchronized so that the pressure in a zone is controlled homogeneously and isotropically.
[0053] A 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 measures a physical parameter, for example, the position of the bonding wave or at least one bonding wave section. The measuring device transmits this data to the control unit. The control unit evaluates the measurement and, depending on the result, determines the necessary physical parameters for controlling or regulating the fixing elements.
[0054] The measuring device preferably consists of an optical system for determining the position of the bond wave. However, sensors that determine the position of a bond wave electromagnetically are also conceivable. Proximity sensors, for example, would be conceivable.
[0055] Of particular interest is also the radius of curvature of a substrate at the point of the bond wave. In this respect, the control of the fixation elements can also be dependent on the radius of curvature of the substrate in the area of the bond wave. The control unit consists of microchips, computers, software, or a combination thereof. In most cases, this will be software within a computer. The measurement signals reach the computer via peripheral devices and are evaluated by the software. The software then controls the fixation elements in the substrate holder via peripheral devices. The use of PID controllers, in which the control is electronically programmed, is also conceivable.
[0056] In the figures, identical components or components with the same function are identified by the same reference numerals. All sketches may be exaggerated for illustrative purposes; therefore, the figures may not necessarily reflect the proportions of the actual embodiments.
[0057] Further advantages, features, and details of the invention will become apparent from the following description of preferred embodiments and from the drawings. These schematically show:
[0058] Figure 1 is a plan view of an embodiment of a substrate holder of a device for influencing a bonding wave during bonding,
[0059] Figure 2a shows a first state of a sixth method step of an exemplary method according to the invention for influencing a bonding wave during bonding,
[0060] Figure 2b shows a second state of a sixth method step of an exemplary method according to the invention for influencing a bonding wave during bonding,
[0061] Figure 2c shows a third state of a sixth method step of an exemplary method according to the invention for influencing a bonding wave during bonding,
[0062] Figure 2d shows a fourth state of a sixth method step of an exemplary method according to the invention for influencing a bonding wave during bonding. In the figures, identical components or components with the same function are identified by the same reference numerals.
[0063] Figure 1 shows the fixing surface of an embodiment of a substrate holder 1 of the bonding device. The base body 2 can be mounted to a device using fastenings 3. The substrate holder 1 has a plurality of zones 7, 7', 7", which are particularly radially and azimuthally defined. In this example, the zones 7, 7', 7" are defined by partition walls 10. The partition walls 10, like the knobs 9, simply remain behind when the base body 2 is milled. The substrate holder 1 could also be designed such that the partition walls 10 are polymer seals or metal seals. The figure shows a central, radially symmetrical zone 7. Furthermore, sixteen zones 7', 7" are arranged radially around the central zone 7 along a first and a second circle.
[0064] The zones 7, 7', 7" are therefore in particular recessed, preferably milled, depressions 11 in which knobs 9 are located at some points. The pin surface of the pins 9 is in particular congruent with the web surface of the partition walls 10. The zones 7, 7', 7" are in particular designed as vacuum zones. The depressions 11 can be evacuated via a fixing means 12, in particular individually and independently of one another due to the separation by the partition walls 10. In this simple case, the fixing element 12 is simply a bore through which the space between the knobs 9 and thus the zone 7, 7', 7" can be evacuated or flooded. If the zones 7, 7', 7" are also used for deformation, a fluid can also flow in via the fixing means 12, which leads to a deformation, in particular local deformation, of a fixed substrate.
[0065] In the center of the substrate holder 1, there is preferably a deformation element 5, which can deform a fixed substrate, in particular centrally. The nubs 9 serve in particular to reduce the contact area of a fixed substrate 4, preferably to prevent contamination. Several sensors 8, in particular pressure sensors, can be located in the zones 7, 7', 7" of the substrate holder 1.
[0066] The figure also shows the area Q, the cross-section of which will be shown in the following figures.
[0067] It is also clear to those skilled in the art that pressure can be defined as a force per unit area. Since the process for influencing a bond wave is described using a vacuum substrate sample holder, and the zones are evacuated to generate a force on the substrate, it is advantageous to speak of pressures. Physical considerations regarding forces and their effects must then be carried out according to the current state of knowledge.
[0068] Figure 2a shows a first state of a sixth method step of a method for influencing a bonding wave during bonding. The cross-section of an area Q (see Fig. 1) through two zones 7', 7", and their separating wall 10 is shown. A lower substrate 4 rests on the knobs 9 and the separating wall 10. An upper substrate 4' is bonded to the lower substrate 4 precisely in this section of the two zones 7', 7". The propagating bonding wave 6 is visible. The bonding wave 6 is shown only as a point in the cross-section. In plan view, the bonding wave 6 would be a completely closed curve, in particular and preferably a circle. Since the advancement of the bonding wave 6 is to be controlled or regulated, the two zones 7', 7" generally have different pressures.In this figure, for example, the pressure p1 in zone 7' is chosen to be lower in order to be able to fix the substrate region 13 of the lower substrate 4 near the bonding wave 6 more strongly and better, so that the substrate region 13' of the upper substrate 4' can bond to it with as little distortion as possible. Zone 7" has a higher pressure p2, in particular close to the ambient pressure, so that the substrate regions 13, 13' which are even further away from the bonding wave 6 can still adapt. A pressure diagram is shown in the lower part of the figure. The abscissa shows the position in any unit, preferably in millimeters, and the ordinate represents the pressure value. Three pressures are shown. Firstly, the external ambient pressure pO. In this case it is approximately 1 bar.
[0069] It would also be conceivable for the substrate holder 1 to be located in a chamber in which the external pressure is increased. The ambient pressure would then be an overpressure relative to the atmosphere.
[0070] It would also be conceivable for the substrate holder 1 to be located in a chamber in which the external pressure is reduced. The ambient pressure would then be negative relative to the atmosphere. This embodiment is particularly relevant when the substrates must be bonded in a lower-pressure environment, for example, to avoid or reduce contamination.
[0071] In the rest of the text it is assumed that the device is open to the atmosphere and that the ambient pressure pO is the atmospheric pressure of approximately 1 bar.
[0072] In general, the ambient pressure pO can be between 2 bar and 0.1 bar, preferably between 1.5 bar and 0.5 bar, more preferably between 1.25 bar and 0.75 bar, most preferably between 1.10 bar and 0.90 bar, most preferably exactly 1.0 bar.
[0073] The pressure in zone 7' is designated p1. It is correspondingly low because zone 7' is evacuated very intensively. The pressure in zone 7" is designated p2. It is higher than the pressure p1 because zone 7" is evacuated only slightly.
[0074] The pressures pl, p2 are generally always below the ambient pressure pO. In very special embodiments, it is conceivable that at least one of the pressures is above the ambient pressure pO. In this case, the substrate region 13 of the substrate 4 below the zone in which the pressure is above the ambient pressure pO would be raised. The bonding wave 6 is still far enough away from the zone 7" that the pressure difference between the pressure pl in the zone 7' and the pressure p2 in the zone 7" does not yet lead to any undesired distortion between the two substrate regions 13, 13'. In this method step, however, it is already detected, preferably with an optical system, that the bonding wave 6 is moving towards a partition wall 10 and that a strong pressure change and thus a strong effect on the bonding wave 6 and thus the bonding behavior between the substrate regions 13, 13' will therefore very soon occur.
[0075] The values of the pressures pl, p2 generally depend on the process and must be determined by tests and / or simulations.
[0076] Figure 2b shows a second state of a sixth method step of a method for influencing a bonding wave, in which the bonding wave 6 has already progressed further. To ensure that the substrate regions 13 of the lower substrate 10 experience the gentlest possible pressure during the transition of the bonding wave 6 over the partition 10, the pressures p1 in zone 7' and p2 in zone 7" are already equalized.
[0077] The transition from the first state shown in Figure 2a to the second state shown in Figure 2b is, of course, continuous, i.e., as the bonding wave 6 continuously advances, the pressures p1, p2 are continuously adjusted. The goal is to ensure that the substrate regions 13, 13' are bonded to each other with no or minimal error.
[0078] The new values of the pressures pl , p2 generally depend on the process and must be determined by tests and / or simulations.
[0079] Figure 2c shows a third state of a sixth method step of a method for influencing a bonding wave, in which the bonding wave 6 is located on the partition wall 10. In the prior art, pressures of different strengths would act on the substrate region 13 from zone 7' and zone 7", which would lead to faulty bonding between the substrate regions 13 and 13'. By adjusting the holding forces or by regulating the pressures p1, p2 in the zones 7', 7", an optimal bonding process between the substrate regions 13, 13' is possible.
[0080] The values of the pressures pl, p2 generally depend on the process and must be determined through tests and / or simulations. Therefore, the pressures pl, p2 do not necessarily have to be equal, as shown in this example. Rather, they must be adjusted so that the two substrate areas 13, 13' are bonded to each other as optimally as possible. Optimal bonding means that any structures on the substrate surfaces in the substrate areas 13, 13' are bonded correctly aligned to each other.
[0081] Figure 2d shows a fourth state of a sixth process step of a process in which the bonding wave 6 has moved over the partition 10. The substrate regions 13, 13' are now located in the new zone 7". In this illustration, the pressure p2 in zone 7" could, for example, have been set to a very low value again in order to fix the lower substrate 10 while the bonding wave 6 advances to the end of zone 7". The new values of the pressures p1, p2 generally depend on the process and must be determined through tests and / or simulations.
[0082] The method illustrated in Figures 2a to 2d provides for switching the fixing element 12 during the transition of a bonding wave 6 over a partition 10 of two zones 7', 7" in such a way that the bonding between the substrate regions 13, 13' and thus generally between the substrates 4, 4' is optimal, i.e., so that the deviations between opposing structures on the substrates 4, 4' are minimal. In the special case of a vacuum substrate sample holder 1, this means that the pressure regulation in the zones 7', 7" is such that during the transition of the bonding wave 6 over the partition 10, the substrate regions 13, 13' experience a pressure transition that is as continuous and smooth as possible, i.e., the pressures p1, p2 are as equal as possible or differ only slightly from one another. List of reference symbols
[0083] 1 substrate holder
[0084] 2 basic bodies
[0085] 3 fastenings
[0086] 4, 4' substrate
[0087] 5 Deformation element
[0088] 6 Bond wave
[0089] 7, 7' ,7“ zone, inner zone, outer zone, further zone
[0090] 8 Sensor
[0091] 9 studs
[0092] 10 Partition element, partition wall
[0093] 11 Deepening
[0094] 12 Fixing element
[0095] 13, 13' substrate area
[0096] Q cross-sectional area p0 atmospheric pressure
[0097] Ph P2 Pressure of the upstream zone / inner zone, the downstream zone / outer zone
Claims
Patent claims 1. Method for influencing a bonding wave (6) when bonding a first substrate (4) to a second substrate (4'), - wherein at least the first substrate (4) is fixed on a first substrate holder (1) with at least one zone (7', 7") and the at least one zone (7', 7") each has at least one separating element (10) at least partially forming the substrate holder surface, and - wherein the at least one separating element (10) separates the at least one zone (7 ', 7") from a further zone (7, 7') or an environment of the first substrate holder (1 ), and - wherein the at least one zone (7', 7") each has at least one fixing element (12) and the at least one fixing element (12) each provides a holding force for fixing the first substrate (4) to the first substrate holder (1), characterized in that the method comprises at least the following steps: i) initiating a bonding wave (6) by contacting the second substrate (4') with the first substrate (4) and then ii) adapting the holding force of the at least one fixing element (12) of the at least one zone (7', 7") a) to a holding force of a fixing element of a further zone (7, 7') located immediately upstream in a propagation direction of the bonding wave (6) or b) to an ambient pressure of the environment.
2. Method according to at least one of the preceding claims, wherein during the adjustment in step ii) the ambient pressure is additionally adjusted to the holding force of the fixing element (10) of the at least one zone (7").
3. The method according to claim 1, wherein the adjustment in step ii) is carried out such that in the propagation direction of the bonding wave (6) the holding force is of equal magnitude immediately in front of and behind the at least one separating element (10).
4. Method according to at least one of the preceding claims, wherein after initiating the bonding wave (6) in step i), the position of the bonding wave (6) is continuously determined and the adjustment of the holding force of the at least one zone (7', 7") is carried out such that when the bonding wave (6) passes over the at least one separating element (10), the holding force in front of and behind the at least one separating element (10) is the same.
5. Method according to at least one of the preceding claims, wherein the at least one fixing element (12) of the at least one zone (7', 7") are each designed as vacuum fixings and the at least one separating element (10) fluidically separates the at least one zone (7', 7") from the further zone (7, 7') or the environment.
6. Method according to at least one of the preceding claims, wherein the adjustment in step ii) is carried out by flooding or evacuating the at least one zone (7, ,7") or the environment.
7. Method according to at least one of the preceding claims, wherein the adjusting in step ii) comprises determining a pressure difference between the at least one zone (7', 7") and the further zone (7, 7') or the environment, wherein the pressure difference is compensated by the adjusting.
8. Method according to at least one of the preceding claims, wherein a pressure (p2) of the at least one zone (7") is adjusted to the pressure (pl) of the further zone (7').
9. Device for influencing a bonding wave (6) when bonding a first substrate (4) to a second substrate (4'), at least comprising: - a first substrate holder (1) for fixing the first substrate (4) with at least one zone (7', 7"), wherein the at least one zone (7) has at least one separating element (10) which at least partially forms a substrate holder surface of the first substrate holder (1), and - at least one fixing element (12) arranged in the at least one zone (7) with a holding force for fixing the first substrate (4) to the first substrate holder (1) - a control unit for adjusting the holding force of the at least one fixing element (12) of the at least one zone (7), characterized in that the control unit is designed to adjust the holding force of the at least one fixing element (12) of the at least one zone (7', 7") a) to a holding force of a fixing element (12) of a further zone (7, 7') located immediately upstream in a propagation direction of the bonding wave (6) or b) to an ambient pressure during an advance of the bonding wave.
10. Device according to claim 1, additionally comprising means for adapting the ambient pressure to the holding force of the at least one zone (7 ', 7").
11. Device according to at least one of the preceding claims, wherein the control unit is configured to keep the holding force of the at least one fixing element (12) of the at least one zone (7', 7") and the holding force of at least one further fixing element (12) of a further zone the same during the bonding of the first substrate (4) to the second substrate (4').
12. Device according to at least one of the preceding claims, wherein the control unit is configured to keep the holding force of the at least one fixing element (12) of the at least one (7', 7") and the holding force of the at least one fixing element (12) of the further zone (7, 7') equal directly in the region of the at least one separating element (10) and during the period in which a bonding wave (6) passes over the at least one separating element (10).
13. Device according to at least one of the preceding claims, 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 designed as vacuum fixings and the separating element (10) fluidically separates the inner zone (7') and the outer zone (7") from one another.
14. Device according to at least one of the preceding claims, wherein the control unit is designed to keep a pressure difference between a pressure (pl) of the further zone (7, 7') and a pressure (p2) of the at least one zone (7', 7") as low as possible during bonding, preferably to keep it the same.
15. Device according to at least one of the preceding claims, wherein the control unit is configured such that the means for adjusting the ambient pressure adjust the ambient pressure to the pressure (p2) of the at least one zone (7") immediately before and after the bonding wave (6) passes over the at least one separating element (10).