WO2013014503A1

WO2013014503A1 - Reduction of mechanical interference in a low-pressure substrate bonding system

Info

Publication number: WO2013014503A1
Application number: PCT/IB2012/001264
Authority: WO
Inventors: Arnaud Castex
Original assignee: Soitec
Priority date: 2011-07-23
Filing date: 2012-06-22
Publication date: 2013-01-31
Also published as: FR2978297A1; TW201305042A

Abstract

A substrate bonding system (200) is provided in which a mechanical interference reduction system (260) reduces the influence of mechanical forces acting on substrates to be bonded in a process chamber (250) of the bonding system (200). In this manner, reliability and robustness of a low pressure bonding process may be enhanced.

Description

Reduction of mechanical interference in a low-pressure substrate bonding system

The present invention generally relates to techniques and systems for mechanically connecting substrates usable for fabricating microstructural features, such as micromechanical components, microelectronic devices and the like, wherein the process of mechanically connecting substrates, also referred to as bonding of substrates, results in a tight connection so as to form a composite substrate, which may comprise a plurality of individual devices. The mechanical coupling of substrates, such as wafers as used for fabricating microelectronic devices, micromechanical devices, optoelectronic devices and the like has developed into a widely used process technique in order to provide appropriate composite carrier materials, such as SOI (silicon on insulator) substrates and/or enabling the fabrication of complex semiconductor-based devices on two individual substrates, which may later be connected so as to obtain a complete micromechanical or microelectronic device. When connecting substrates by direct mechanical contact without providing any intermediate material systems typically substantially plane surface portions of the substrates facing each other are mechanically coupled in order to finally establish a desired robust chemical connection between the plane substrate surface areas.. Usually plane surface areas to be connected are appropriately conditioned, for instance subjected to cleaning processes on the basis of wet chemical etch procedures, plasma assisted processes and the like in order to prepare the exposed surface areas for the subsequent direct contact with a corresponding surface area of the complementary substrate. Furthermore, frequently upon mechanically connecting the oppositely positioned surface areas mechanical pressure and elevated temperatures are applied in order to initiate the formation of chemical bonds between the contacting surface areas. For example, frequently moderately high mechanical pressure values and elevated temperatures up to 1000 °C are applied in order to obtain a robust and reliable connection between the individual substrate surfaces. Although any such bonding techniques may be well applicable to substrates prior to processing one or both of these substrates according to process techniques which may result in the fabrication of temperature sensitive devices, in other cases the moderately high temperatures during the bonding process are not compatible with any microstructural features that may have been formed in one or both of the substrates prior to the bonding process. For these reasons, efficient low temperature bonding techniques have been developed in which typically the substrates are treated in a process chamber in which a moderately low process pressure is established. After preliminarily mechanically contacting the substrates the pressure in the process chamber may further be reduced until a spontaneous bonding may be initiated, ie. a so-called bonding wave is generated, thereby forming a chemical connection between the contacting surface areas. This spontaneous bonding process may take place at relatively low temperatures, such as room temperature, thereby enabling the processing of substrates having formed thereon highly temperature-sensitive microstructural features, such as semiconductor devices in the form of sensors, micromechanical devices and the like. Furthermore, this type of bonding process is also compatible with the requirements of complex metallization systems, which may typically comprise sophisticated metals and dielectric material that may not allow process temperatures above, for instance 400 °C.

Furthermore, a low pressure bonding process regime as described above is also highly advantageous in view of reducing the overall overlay errors upon connecting the two substrates, since after precisely aligning the substrates to each other any pronounced mechanical forces as well as any pronounced gas currents in the process chamber are not required, since generally the bonding process may take place at moderately low process pressures of approximately 100 mbar and significantly less, while the initiation of the spontaneous bonding wave may be induced without any external mechanical forces, for instance simply by gravity forced by the weight of the overlying substrate.

- With reference to Figs 1 a and 1 b a low pressure substrate bonding system and the operation thereof will now be described in more detail.

Fig 1 a schematically illustrates a top view of a substrate bonding system 100 in which substrates or wafers may be received on the basis of corresponding wafer container handling stations 1 10g, 1 10f, which may for instance receive boxes of substrates including the "bottom substrate" and the "top substrate" in order to form a composite substrate. The system 100 may typically further comprise components 1 10a, 1 10b that represent appropriate cleaning stations for preparing the surface areas to be bonded within a process chamber 150. Furthermore, if required, an inspection station 1 10d, such as an infrared inspection stage, may be provided so as to inspect one or more of the substrates to be processed in the system 100 prior to or after performing the bonding process. Furthermore, the system 100 comprises a plurality of components 1 10e, 1 10c that are appropriately configured to supply and remove the substrates to the various stations within the system 100. For example, a pre-aligner station 1 10c may be provided and which is configured to coarsely align substrates which are subsequently to be positioned within the process chamber 150 so as to perform therein the actual bonding process. To this end, an appropriate robot system 1 10e is typically provided and has any appropriate configuration, as is well known in the art.

Fig 1 b schematically illustrates a cross-sectional view of the system 100 in a highly simplified manner. As shown, the process chamber 150 comprises an appropriate substrate holder 151 configured to receive and hold in place a substrate, on top of which subsequently a further substrate is positioned in an accurately aligned state prior to actually mechanically connecting the substrates within the process chamber 150. The process chamber 150 including the substrate holder 151 is connected to a frame 101 of the system 100 on the basis of any appropriate mechanical system 152, which may also include appropriate drive assemblies and the like, as is required for instance for loading and removing substrates from the chamber 150 and the like. It should further be appreciated that any other components, for instance as required for establishing an appropriate temperature for the substrates, and in particular for establishing a desired process pressure within the chamber 150 are not shown in Fig 1 b. Furthermore, the various components of the system 100 are represented by the components 1 10c, 1 10e, which are components comprising moveable parts such as robot arms, spinning substrate holders and the like. Upon loading substrates into the system 100 and performing any pre-processing such as cleaning processes, inspections processes, if required, and the like in the stations 1 10a, 1 10b, 1 10d the pre-alignment and the transport into the process chamber 150 are accomplished on the basis of well known process strategies. In the process chamber 150 the low pressure bonding process is carried out by, for instance, applying a first phase in which the two substrates are facing each other and are aligned with high precision, for instance with reference to the periphery or the centre of the corresponding substrates. In this phase, the substrates are still separated by a short distance in the range of 10 - 1 000 μιη. Moreover, in this phase of the bonding process the pressure in the process chamber is adjusted to approximately 100 mbar and significantly less, such as 20 - 40 mbar. In a second phase of the process the two substrates are preliminarily mechanically contacted, which in some cases is achieved by simply releasing the upper substrate from any appropriate substrate transport system and letting this substrate drop under gravitational force while the remaining environmental pressure within the chamber 150 is still in the above- identified range. After the two substrates have been brought into contact, which may thus be accomplished without significant alignment errors due to the absence of additional mechanical forces except for gravity, the process pressure in the chamber 150 is steadily reduced from the above-specified range down to approximately 1 mbar - 0.1 mbar, at a specific trigger pressure a bonding wave spontaneously builds up and spreads across the entire surface of the substrate, thereby forming a robust connection between the two substrates. That is, the actual bonding phase, ie. the generation and spreading out of the bonding wave, is essentially initiated without any external applied forces and is thus triggered by gravity, ie. by the top substrate's weight. The specific pressure, upon which a spontaneous bonding process is initiated, depends on the characteristics of the substrate, ie. the shape and bow and the weight thereof, and typically the corresponding trigger pressure is in the range of 5 mbar - 0.1 mbar.

Although the above-described low pressure bonding system enables the formation of composite substrates with significantly reduced alignment errors it turns out, however, that overall uniformity and precision are still deteriorated when operating the system 100 in a continuous high throughput environment since, for instance, any additional external mechanical forces may result in an interaction with the substrates to be bonded. As a result of any such controlled mechanical interaction the generation of the bonding wave may be initiated in an arbitrary manner, thereby negatively affecting the overall reliability and uniformity of the bonding process.

In view of the situation described above, it is an object of the present invention to provide techniques and systems for performing a bonding process while avoiding or at least reducing the effects of one or more of the problems identified above. According to one aspect of the present invention the object is addressed by a substrate bonding system that comprises a process chamber that is configured to establish a bond process ambient for bonding a first substrate to a second substrate. The first substrate and/or the second substrate are usable to form microstructural features thereon and the process chamber is configured to hold in place the first and second substrates, at least during a bonding phase. The substrate bonding system further comprises a mechanical interference reduction system configured to reduce mechanical forces acting on the first and second substrates during the bonding phase. The inventive substrate bonding system is thus appropriately configured to take into account the occurrence of any external mechanical forces, which may otherwise non-controllably interact with the substrates and thus disturb the actual bonding phase, ie. a phase in which the actual bonding may be initiated upon achieving a specific trigger pressure level. For example, it has been recognized that even minute displacements of the composite substrate stack prior to intentionally applying the trigger pressure level may result in a non-controllable initiation of a bonding wave, which may thus result in a high degree of non-uniformity of the process result. By reducing the mechanical forces acting on the first and second substrates during the actual bonding phase the inventive system is thus appropriately configured so as to maintain the external mechanical forces below a corresponding trigger level in order to avoid any uncontrolled mechanical connection of the first and second substrate.

In one illustrative embodiment the mechanical interference reduction system comprises at least one mechanical damping mechanism that is directly connected to a substrate holder positioned in the process chamber and/or to at least one other component of the substrate bonding system.

In this manner, any mechanical forces which may finally act on the first and second substrates may significantly be reduced by appropriately positioning the at least one damping mechanism. That is, in some alternatives the at least one damping mechanism is mechanically directly connected to the substrate holder, thereby forming a mechanical interface between the substrate holder and any rigid frame of the substrate bonding system. In this manner, even any mechanical forces originating from outside the substrate bonding system may efficiently be reduced. In other cases, in addition to or alternatively to, providing a damping mechanism in direct connection to the substrate holder one or more components of the substrate bonding system are provided with a damping mechanism, preferably components including moveable parts, thereby appropriately damping any mechanical "noise" at the point of generating the mechanical forces.

In one illustrative embodiment, the at least one mechanical damping mechanism comprises a passive absorber component.

By using any passive damping mechanism in order to absorb at least a portion of the resulting mechanical forces, a plurality of damping mechanisms are available without requiring sophisticated electronics and/or mechanical systems the characteristics of the passive mechanical absorbers may efficiently be adapted to the specific type of mechanical interference to be expected during the bonding process, such as any type of vibrations, which may in a non-damped manner, result in a significant disturbance of the actual bonding phase. For example, appropriate time constants and intensity with respect to the damping effect may appropriately be selected for mechanical forces having a specified damporal and intensity characteristic.

In a further illustrative embodiment, the passive absorber component comprises a resilient material provided as an interface between the substrate holder and/or the at least one further component and a rigid part of the substrate bonding system.

In this case, any appropriate resilient materials may be provided within the bonding system, thereby enabling an efficient reduction of the overall mechanical interference without requiring sophisticated damping mechanisms. In this manner, even existing substrate bonding systems may readily be reconfigured in order to enable superior results in a low pressure bonding process. Preferably, the passive absorber component comprises a constraint layer viscoelastic component and/or a viscous fluid device and/or a magneto Theological fluid device and/or a passive piezoelectric damper unit and/or a tuned mass damper unit acting as a vibration absorber.

Consequently, a plurality of well-established damping mechanisms are available, as are for instance used in sensitive telescopes for mirror motion control or generally in other sophisticated systems in which a precise mechanical control of motion is required. In a further illustrative embodiment, the at least one damping mechanism comprises an active motion compensation mechanism.

This embodiment ensures superior flexibility in responding to a plurality of different mechanical interferences since the damping mechanism itself may appropriately adapt to a wide variety of mechanical forces. In some cases, even a self-adapting algorithm may be implemented in which the damping mechanism automatically increases its efficiency in responding to a repeatedly occurring mechanical interference.

In one embodiment, the active motion compensation mechanism is configured to reduce an externally induced displacement of 10 m or less by at least 50 percent. In this manner the efficiency of the compensation is selected such that typical mechanical displacements, as may conventionally occur during the actual bonding phase of the first and second substrates, may sufficiently be reduced in order to avoid a non-controlled bonding process. In further variants, the efficiency of the active motion compensation mechanism may be still further increased by, for instance, restricting the range of mechanical displacements to be responded to by approximately 5 m or even less, wherein the degree of reduction may be significantly higher than 50 percent of the undisturbed magnitude of the displacement.

In one illustrative embodiment, the active motion compensation mechanism comprises an active piezoelectric damper unit and/or an active resonance damper unit.

Consequently, well-established and highly efficient active damping mechanisms are used in this embodiment without requiring a significant modification of the overall configuration of the bonding system.

In a further illustrative embodiment, the mechanical interference reduction system comprises a control unit operatively connected to at least some system components of the substrate bonding system, which component includes moveable parts wherein the control unit is configured to control the at least some system components so as to discontinue movement of the moveable parts, at least during the bonding phase.

According to this configuration of the bonding system in addition to or alternatively to other embodiments as described above the origin of many mechanical interferences may be "neutralized" during the bonding phase by appropriately coordinating the operation of components in the bonding system, which have moveable parts and which may thus significantly contribute to the overall mechanical "noise" within the bonding system. Preferably in combination with other damping mechanisms of the mechanical interference reduction system, superior mechanical noise reduction may thus be achieved, since the number of any system internal mechanical noise sources is reduced, while the additional damping mechanisms may efficiently reduce mechanical interferences that originate from outside of the bonding system.

According to a further aspect of the present invention the above-described object is addressed by a method for bonding a first substrate to a second substrate. The method comprises mechanically contacting a first surface of the first substrate with a second surface of the second substrate in a substrate bonding system at a process pressure that is above a trigger pressure. The method further comprises reducing the process pressure to or below the trigger pressure so as to initiate a bonding phase for mechanically bonding the first surface to the second surface. Moreover, the method comprises controlling a mechanical status of the first and second substrates during the bonding phase so as maintain displacement of the first and second substrates below a displacement trigger level for initiating a non-pressure inducing bonding wave.

The inventive method is also based on the concept that during the sensitive bonding phase the first and second substrates have to be mechanically isolated from the environment in order to maintain any externally induced displacement of these substrates below a specified displacement trigger level, thereby efficiently suppressing the occurrence of a non-controlled initiation of a bonding wave.

Preferably, the trigger pressure is selected to 5 mbar or less and the displacement trigger level is 5 m or higher. In this case the process conditions and the mechanical noise situation of a wide variety of sensitive low pressure bonding regimes is covered, thereby enabling superior uniformity and reliability of the overall bonding process.

In one illustrative embodiment controlling a mechanical status of the first and second substrates comprises: discontinuing movement of at least some moveable parts of the substrate bonding system at least during the bonding phase.

Hence, as already discussed above, the discontinuation of the movement of at least some moveable parts of the bonding system eliminates the generation of mechanical noise during the critical phase of the bonding process. To this end, the corresponding system components are appropriately controlled, for instance a process component for establishing a desired process pressure and the system components including the moveable parts are supplied with appropriate control signals in order to coordinate the operation of these components so as to establish the required process pressure and avoiding the generation of mechanical interferences. For example, in this strategy a predictive algorithm may be implemented in order to coordinate the substrate handling processes and any other activities within the system in order to enable a discontinuation of the activities of the moveable parts without unduly interfering with the overall functioning of the bonding system. In a further illustrative embodiment, controlling a mechanical status of the first and second substrates comprises: damping mechanical vibrations acting on the first and second substrates during the bonding phase.

The advantageous effect of introducing a damping mechanism is already described above and ensures superior process results without requiring undue modifications of the bonding system.

In a further illustrative embodiment, damping mechanical vibrations acting on the first and second substrates comprises, damping the first and second substrates and/or components of the substrate bonding system that comprise moveable parts. Again, as already discussed above, the damping mechanism may be implemented so as to directly act on a substrate holder in the presence of the first and second substrates while in other cases, in addition to or alternatively, the damping of moveable parts may be implemented thereby also reducing the noise at the point of generation of the noise within the bonding system. In a further illustrative embodiment, controlling the mechanical status of the first and second substrates comprises: increasing a weight of the first substrate and/or the second substrate prior to reducing the process pressure. In this manner the mechanical characteristics of the composite stack of substrates is significantly influenced so as to respond to any mechanical forces with reduced displacement, thereby also providing for a more robust and reliable bonding process.

The above-described embodiments and further specific embodiments of the present invention will become more apparent from the following description when referring to the accompanying drawings, in which:

Figs 1 a and 1 b schematically illustrate a top view and a cross-sectional view, respectively, of a conventional substrate bonding system,

Figs 2a - 2c schematically illustrate cross-sectional views of a bonding system including a mechanical interference reduction system according to illustrative embodiments, Figs 2d and 2e schematically illustrate the bonding system according to illustrative embodiments in which active and/or passive damping mechanisms are implemented in at least one component of the bonding system,

Fig 2f schematically illustrates a cross-sectional view of the bonding system according to illustrative embodiments in which an appropriate control unit is implemented in order to discontinue operation of at least some moveable parts in the system, possibly in combination with providing active and/or passive damping mechanisms, and

Fig 2g schematically illustrates a part of the bonding system in which the mechanical response of the composite substrate is modified by increasing a weight according to still further illustrative embodiments.

With reference to Figs 2a - 2g illustrative embodiments of the present invention will now be described in more detail, wherein also reference may be made to Figs 1 a and 1 b, if appropriate.

Fig 2a schematically illustrates a cross-sectional view of a substrate bonding system 200 which may comprise any appropriate frame or housing 201 , which in turn accommodates the various components of the system 200. For example, a plurality of process stations are typically implemented in the system 200, for instance in the form of process stations as are also described above with reference to the system 100. For convenience, in the embodiment shown in Fig 2a, a reduced number of system components is illustrated wherein it should be understood that any number of components may be implemented as required for appropriately operating the system 200. As shown, the system 200 comprises a process chamber 250, which is appropriately equipped in order to enable the establishment of an appropriate process ambient with respect to gas atmosphere, pressure thereof, temperature of substrates and gas atmosphere and the like. For convenience, any such components are not illustrated in Fig 2a, such components however are well known in the art. The process chamber 250 further comprises a substrate holder 251 , such as a wafer chuck and the like, which is appropriately configured to receive and hold in place a substrate, such as a wafer. Moreover, the process chamber 250 comprises any appropriate mechanical attachment system 252 so as to mechanically connect the chamber 250 to the frame 201 . As will be described later on in more detail, the mechanical attachment system 252 may comprise, in some illustrative embodiments, a mechanical damping system. Furthermore, components 210c, 210e are also provided in the system 200 and may represent components, at least one of which includes a moveable part 210m, ie. a part that is moved relatively with respect to the frame 201 . It should be appreciated that any appropriate drive assembly for driving the moveable part 210m is not shown in Fig 2a. Furthermore, the system 200 comprises a mechanical interference reduction system 260 which is to be understood as any appropriate mechanical and/or electronic system for reducing mechanical forces, which may result in undue mechanical displacement of substrates positioned on the substrate holder 251 , at least during a certain phase of the overall bonding process, also indicated as bonding phase. Thus, the system 260 is configured on the concept that a mechanical displacement during a sensitive phase of the bonding process is to be maintained at or below a specific trigger level in order to avoid or at least significantly reduce the occurrence of bonding waves which may be initiated in a non-controlled manner.

Fig 2b schematically illustrates the system 200 in a more detailed representation. As illustrated, a first substrate 21 1 having a first surface 21 1 s to be bonded to a second surface 212s of a second substrate 212 is positioned and held on the substrate holder 251 . On the other hand, the second substrate 212 is positioned above the substrate 21 1 with an appropriate distance on the basis of any appropriate system component, for instance by a robot arm, as illustrated by the component 210c. In this process phase, an appropriate process ambient is established within the process chamber 250, for instance introducing an appropriate gas component and establishing a desired low pressure, for instance in the range of 100 mbar and significantly less, such as 20 - 40 mbar, as is also explained above. The resulting process ambient is indicated as 213a and should be understood as representing the entirety of process parameters and materials required for establishing appropriate process conditions in order to appropriately aligng the second substrate 212 with respect to the first substrate 21 1 and avoiding undue mechanical interaction with the process ambient 213a. In this situation the mechanical interference reduction system 260 may already be functional in some illustrative embodiments when corresponding damping mechanisms and the like are implemented (not shown), while in other cases the system 260 may be substantially inactive in this phase.

Fig 2c schematically illustrates the process chamber 250 in a situation in which the second substrate 212 is in mechanical contact with the first substrate 21 1 , which may be accomplished by dropping the substrate 212 or by bringing the substrate 212 in contact with the substrate 21 1 by any other appropriate means, wherein however, as discussed above, superior alignment accuracy may be accomplished by performing the contacting step without additional mechanical components. Hence, the surfaces 21 1 s, 212s (cf. Fig 2b) or at least significant portions thereof, are brought into direct mechanical contact which may still be accomplished on the basis of the process ambient 213a.

It should be appreciated that, as discussed above with reference to the bonding system 100, prior to processing the first and second substrates 21 1 , 212 within the process chamber 250, any conditioning processes, inspection processes and the like, may have been performed as required according to the overall process regime to be applied.

Thereafter, a second process ambient 213b may be established by steadily reducing the pressure within the process chamber 250 while during this phase, which is also indicated as a bonding phase, the system 260 is active in order to reduce the influence of mechanical forces 202 acting from outside the composite structure formed by the preliminarily coupled substrates 21 1 , 212. As discussed above, in conventional systems the outside forces 202 may result in a certain displacement 203 of one or both of the substrates 212, 21 1 , which may result in a non-controlled initiation of a bonding wave thereby deteriorating reliability and uniformity of the resulting composite substrate. Thus due to the provision of the system 260, at least in the process ambient 213b, ie. during the actual bonding phase, the system 260 may eliminate or at least reduce the external forces 202 so as to ensure that any mechanical displacement 203 is at or below a pre-selected trigger level, which may for instance by selected to approximately 5 μηη or more. That is, the system 260 counteracts the external mechanical forces 202 so as to avoid a displacement of one or both of the substrates 21 1 , 212 that is greater than 5 μηη and in some illustrative embodiments that is greater than approximately 2 μιτι. In this manner the influence of the external forces 202 is efficiently reduced. To this end, the system 260 is configured to avoid or at least reduce the generation of the mechanical forces 202 and/or reduce the effect of external forces on the substrates 21 1 , 212 or on the substrate holder 251 by appropriately damping the mechanical forces 202, as will be described in more detail later on.

Fig 2d schematically illustrates the system 200 according to illustrative embodiments in which the system 260 comprises a damping mechanism 262 which, in the embodiment shown, is provided so as to act as a mechanical interface between the process chamber 250, or at least between the substrate stage 251 and the rigid frame 201 of the system 200. The damping mechanism 262 comprises one or more damping component, indicated as 262a, 262b, which in some illustrative embodiments represent passive absorber components, for instance provided in the form of a resilient material and the like. In other cases, the passive absorber component, for instance provided in the form of the component 262a and/or 262b is provided as a constraint layer viscoelastic component, a viscous fluid device, a magneto rheological fluid device, a passive piezoelectric damper unit, a tuned mass damper unit acting as vibration absorber and the like. As already explained above, any such passive damping mechanisms are readily available and are frequently used in sensitive mechanical systems. Consequently, any such well known passive damping components can readily be implemented into the bonding system 200, without requiring undue redesign and modification compared to conventional bonding systems. In other illustrative embodiments one or more of the damping components 262a, 262b are provided in the form of an active motion compensation mechanism, for instance in the form of an active piezoelectric damper unit or an active resonant damper unit. Consequently, on the basis of the damping mechanism 262, the process chamber 250 or at least the substrate holder 251 and thus the substrates' position thereon are efficiently mechanically decoupled from the rigid frame 201 , thereby ensuring superior mechanical noise immunity with respect to undue displacement of the substrates positioned in the chamber 250 during the sensitive bonding phase.

Fig 2e schematically illustrates the system 200 according to further illustrative embodiments in which in addition to or alternatively to the damping mechanism 262 that is directly connected to the process chamber 250 and/or the substrate holder 251 at least one further damping mechanism 263 is provided so as to efficiently decouple one or more components of the system 200 with respect to the rigid frame 201 . For example, the component 21 Oe representing a component having a moveable part, which thus may generate significant mechanical noise during its operation, may efficiently be damped by providing the mechanism 263 acting as an interface between any moveable parts of the component 210e and the rigid frame 201 . The damping mechanism 263 may comprise active or passive absorbers or may simply be implemented in the form of any appropriate resilient material, wherein generally a resilient material is to be understood as a material that responds to externally applied mechanical pressure with a pronounced degree of deformation, a significant part of which is reversible, thereby however converting a significant amount of mechanical energy into heat energy so that at least 50 percent of the amplitude of the incoming mechanical force is "removed" and thus a mechanical force of at least 50 percent reduced strength is at most "output^" at the opposite side of the resilient material. Fig 2f schematically illustrates the system 200 according to further illustrative embodiments in which in addition to or alternatively to providing the one or more damping mechanisms 262, 263 a control unit 265 is implemented in the system 260, which is operatively connected to at least some components of the system 200. In the embodiment shown, the control unit 265 is operatively connected to the component 21 Oe including a moveable part which is thus to be considered as a source of creating mechanical noise during its operation. Consequently, the control unit 265 may provide appropriate control signals 266 in order to activate and deactivate the component 210e, or at least the moveable part thereof. Furthermore, the control unit 265 is operatively connected to the process chamber 250, for instance to pressure valves, vacuum pumps and the like, as indicated by 254, in order to establish a desired process pressure within the process chamber 250, as is also discussed above. During operation of the system 260 the control unit 265 thus provides appropriate control signals 267 to the component 254 in order to establish a desired process pressure, while at the same time operation of at least the moveable part of the component 210e is controlled. Thus, at least during the critical bonding phase, the movement of the moveable part of the component 210e is discontinued upon supplying appropriate control signals 266, thereby significantly reducing the generation of any noise within the system 200. It should be appreciated that the control unit 265 may be connected to a plurality of system components including moveable parts in order to also discontinue the operation thereof during a sensitive bonding phase. In other cases, corresponding system components may be identified in advance, which contribute to the overall mechanical noise in the system 200 in an essential manner, and operation of these components can be controlled by the unit 265. To this end, the control unit 265 has implemented therein any appropriate control algorithm that is configured to not unduly interfere with the overall functioning of the system 200, for instance with respect to throughput and the like, while nevertheless avoiding or reducing the generation of mechanical noise, such as vibrations and the like during a critical phase of the bonding process. For example, a predictive algorithm may be implemented in the unit 265 so as to estimate in advance the requirement for any movements in the component 21 Oe in relation to the establishment of the required process pressure in the chamber 250. For example, it may be assessed whether the component 210e may have to perform an unavoidable activity and in this case the component 254 may appropriately be scheduled in establishing the required, process pressure so as to not interfere with the unavoidable movement of the component 210e. To this end, any appropriate algorithm may be implemented, for instance optimized to reduce the mechanical noise caused by the component 210e, while at the same time substantially not unduly affecting the overall throughput of the system 200.

Fig 2g schematically illustrates the mechanical interference reduction system 260 according to further illustrative embodiments wherein in addition to or alternatively to any of the embodiments described above, the weight of the first substrate 21 1 and/or of the second substrate 212 may temporarily be increased, for instance by attaching thereto an appropriate additional material 264, for instance in the form of a disposable layer material and the like, thereby generally affecting the overall mechanical characteristics of the composite system 21 1 , 212. For example, in any process station within the bonding system or outside of the bonding system, the system 260 may initiate the application of the additional material 264, wherein an appropriate increase of the weight may be determined in advance for otherwise given process conditions during the bonding phase. That is, an appropriate total weight may be determined, which may allow the application of an appropriate process pressure so as to achieve a pressure induced initiation of a bonding wave, as explained above, while on the other hand the additional weight may result in a reduced response of the substrates 21 1 , 212 to external mechanical forces, for instance by maintaining the resulting mechanical displacement, as for instance explained above with reference to the displacement 203 in Fig 2c, below a previously determined trigger level. Hence, the substrates 21 1 , 212 may act as an efficient damping mechanism with respect to a plurality of mechanical influences, which may be determined in advance and in view of appropriate process conditions. Thereafter, the additional weight 264 may be removed, for instance on the basis of any appropriate process technique, such as cleaning processes and the like, while in other cases any additional weight may adhere to the substrates 21 1 , 212 only such that an efficient removal may be initiated upon applying a certain amount of mechanical force and the like.

Claims

A substrate bonding system (200) comprising:

a process chamber (250) configured to establish a bond process ambient (213a, 213b) for bonding a first substrate (21 1 ) to a second substrate (212), at least one of said first and second substrates (21 1 , 212) being usable to form microstructural features thereon, said process chamber (250) being configured to receive and hold in place said first and second substrates (21 1 , 212) at least during a bonding phase and a mechanical interference reduction system (260) configured to reduce mechanical forces acting on said first and second substrates (21 1 , 212) during said bonding phase.

The substrate bonding system according to claim 1 , wherein said mechanical interference reduction system (260) comprises at least one mechanical damping mechanism (262, 263) that is directly connected to a substrate holder (251 ) positioned in said process chamber (250) and/or to at least one other component (210c, 210e) of said substrate bonding system (260).

The substrate bonding system according to claims 1 or 2, wherein said at least one mechanical damping mechanism (262, 263) comprises a passive absorber component.

The substrate bonding system according to claim 3, wherein said passive absorber component comprises a resilient material provided as an interface between said substrate holder (251 ) and/or said at least one further component (210e, 210c) and a rigid part (201 ) of said substrate bonding system (200).

The substrate bonding system according to any of claims 3 or 4, wherein said passive absorber component comprises at least one of a constrained layer viscoelastic component, a viscous fluid device, magnetorheological fluid device, a passive piezoelectric damper unit and a tuned mass damper unit acting as a vibration absorber. The substrate bonding system according to any one of claims 2 to 5, wherein said at least one damping mechanism comprises (262, 263) an active motion compensation mechanism.

The substrate bonding system according to claim 6, wherein said active motion compensation mechanism is configured to reduce an externally induced displacement of 10 m or less by at least 50%.

The substrate bonding system according to claims 6 or 7, wherein said active motion compensation mechanism comprises at least one of an active piezoelectric damper unit and an active resonant damper unit.

The substrate bonding system of any of claims 1 to 8, wherein said mechanical interference reduction system (260) comprises a control unit (265) operatively connected to at least some system components (210e) of said substrate bonding system (200), which include movable parts, wherein said control unit (265) is configured to control said at least some system components (210e) so as to discontinue movement of said movable parts at least during said bonding phase.

A method for bonding a first substrate (21 1 ) to a second substrate (212), the method comprising: mechanically contacting a first surface (21 1 s) of said first substrate (21 1 ) with a second surface (212s) of said second substrate (212) in a substrate bonding system (200) at a process pressure that is above a trigger pressure, reducing said process pressure to or below said trigger pressure so as to initiate a bonding phase for mechanically bonding said first surface (21 1 s) to said second surface (212s), and controlling a mechanical status of said first and second substrates (21 1 , 212) during said bonding phase so as to maintain displacement (203) of said first and second substrates (21 1 , 212) below a displacement trigger level for initiating a non-pressure induced bonding wave.

The method according to claim 10, wherein said trigger pressure is selected to 5 mbar or less and said displacement trigger level is 5pm or greater.

12. The method of claims 10 or 1 1 , wherein controlling a mechanical status of said first and second substrates (21 1 , 212) comprises discontinuing movement of at least some movable parts (210e) of said substrate bonding system (200) at least during said bonding phase.

13. The method of any of claims 10 to 12, wherein controlling a mechanical status of said first and second substrates (21 1 , 212) comprises damping mechanical vibrations acting on said first and second substrates (21 1 , 212) during said bonding phase.

14. The method of any of claims 10 to 13, wherein damping mechanical vibrations acting on said first and second substrates (21 1 , 212) comprises damping said first and second substrates (21 1 , 212) and/or components (21 Oe, 210c) of said substrate bonding system (200) that comprise movable parts (210m).

15. The method of any of claims 10 to 14, wherein controlling said mechanical status of said first and second substrates (21 1 , 212) comprises increasing a weight (264) of at least one of said first and second substrates (21 1 , 212) prior to reducing said process pressure.