Fabrication tool for bonding

A fabrication tool presses a first device surface against a second device surface after the first and the second device surfaces have been plasma activated, to bond the first device surface with the second device surface. The fabrication tool includes a bonding piston to exert force on the first device surface to press the first device surface against the second device surface. The fabrication tool also includes a pressure plate situated between the bonding piston and the first device surface. The fabrication tool further includes a mechanism to ensure that the force exerted by the bonding piston on the first device surface via the pressure plate is initially exerted at one or more first locations on the first device surface and subsequently exerted at one or more second locations on the first device surface.

BACKGROUND

Plasma bonding is a common way to bond together two surfaces of a device. The surfaces are typically polished or otherwise made smooth, and then plasma activated. Plasma activation of the surfaces causes the surfaces to be more receptive to permanent bonding once the surfaces are pressed together. Thus, after smoothing and plasma activation of the surfaces, the surfaces are pressed together to permanently bond them.

Within the prior art, the surfaces of the device being bonded together are presumed to be planar. Therefore, they are pressed together by a force that is substantially uniform across the surfaces. However, when one or more of the surfaces are non-planar, such pressing together with substantially uniform force can be problematic. Air may be trapped in crevices and other non-uniformities within the surfaces. Ultimately, for this and other reasons, a good bond may not result.

DETAILED DESCRIPTION

FIGS. 1A and 1Bcross-sectionally show a fabrication tool100to press a device surface103against a device surface105to form an electronic device101, according to different embodiments of the invention. The electronic device101being formed may be a micro-electromechanical (MEM) device, an optical device, a semiconductor device, and/or another type of electronic device. The device101includes a component112of which the device surface103is a part, and a component114of which the device surface105is a part. Thus, the combination of the components112and114, upon being bonded together, forms at least a portion of the electronic device101.

In one embodiment, the electronic device101is a display MEM device, for use in display devices. The component112may be transparent, such as a glass substrate. The component114may include the micro-electromechanical elements that enable the electronic device101to be a display MEM device.

Prior to utilization of the fabrication tool100to press the device surface103against the device surface105, the surfaces103and105may have been prepared. For instance, they may have first been polished to smooth the surfaces103and105. The surfaces103and105may then have been plasma activated so that upon pressing the device surface103against the device surface105, a strong and permanent bond results.

At least one of the device surfaces103and105is non-planar. InFIGS. 1A and 1B, the device surface103is planar, but the device surface105is non-planar. More particularly, the device surface105includes a surface portion116that is convex. Alternatively, the surface portion116may be concave. The device surface105and/or the device surface103may be non-planar in another way as well.

The fabrication tool100includes a bonding piston102, a pressure plate104, a profiled insert106, and a spring-loaded pushing element110. The bonding piston102is the component of the fabrication tool100that actually exerts force, as can be appreciated by those of ordinary skill within the art. The pressure plate104is situated between the bonding piston102and the component112having the device surface103.

The profiled insert106is situated between the pressure plate104and the component112having the device surface103. The profiled insert106is profiled inFIGS. 1A and 1Bin that it tapers at a angle away from the edges of the device surfaces103and105towards the center of the device surfaces103and105. The profiled insert106may alternatively be profiled in a different way. The profiled insert106may be fabricated from a compliant material, such as Kapton, Viton, Delron, or another compliant material, so that a uniform force is applied to the component112when full force is exerted by the spring-loaded pushing element110. The profiled insert106will thus deform to some extent under a full force load.

The spring-loaded pushing element110is affixed to the pressure plate104and is movable through a hole108within the pressure plate104and the profiled insert106. The pushing element110may also be referred to as a bow pin, and may include a spring ending in a flat or rounded cylinder, as is shown inFIGS. 1A and 1B. The pushing element110, by virtue of its constituent spring, is normally extended beyond the lowest point(s) of the profiled insert106. InFIG. 1A, the pushing element110is located within the center of the fabrication tool100, whereas inFIG. 1B, the pushing element110is located near an edge of the fabrication tool100.

As will be described in more detail later, upon exertion of force by the bonding piston102, the pressure plate104, the profiled insert106, and the pushing element110move downward towards the component112. The pushing element110makes first contact with the component112. As a result, the force exerted by the bonding piston102(via or through the pressure plate104) is first, or initially, exerted at a corresponding location118of the device surface103underneath the pushing element110.

As the bonding piston102, the pressure plate104, the profiled insert106, and the pushing element110continue to move downward, second contact may be made by the edges of the profiled insert106. This is because these edges of the profiled insert106are lower than other portions of the profiled insert106. In any case, the force exerted by the bonding piston102(via or through the pressure plate104) is second, or subsequently, exerted at corresponding locations120of the device surface103underneath the edges of the profiled insert106.

As the bonding piston102, the pressure plate104, the profiled insert106, and the pushing element110continue to move downward, ultimately contact is made by the entire surface of the profiled insert106. Thus, the force exerted by the bonding piston102(via or through the pressure plate104) is ultimately exerted substantially over the entirety of the device surface103underneath the profiled insert106. Due to the great force exerted by the bonding piston102, the shape of the device surface103may at least substantially correspond to the mirror image of the device surface105. Furthermore, the shape of the top surface of the component112may at least substantially correspond to the shape of the profiled insert106and the spring-loaded pushing element110. This is also described in more detail later.

The profiled insert106and the spring-loaded pushing element110can together be considered a mechanism that ensures that the force exerted by the bonding piston102ultimately on the device surface103is first exerted at the location118, is second exerted at the locations120, and then is finally exerted over the entirety of the device surface103. Thus, the force exerted onto the device surface103is not uniform over time. Rather, the force is selectively exerted onto the device surface103first at the location118, and then also at the locations120, before finally being exerted over the entirety of the device surface103.

In this respect, the fabrication tool100ofFIGS. 1A and 1Bprovides for advantages over the prior art. Unlike in the prior art, where force is exerted onto a device surface uniformly over time, the non-uniform exertion of force over time provided by the fabrication tool100substantially prevents air from being trapped between the device surfaces103and105. Furthermore, because bonding starts at the location118and continues at the locations120before occurring at all the locations of the device surface103, the resultant bond between the device surfaces103and105may be stronger as compared to as if bonding starts over the entirety of the device surface103.

FIG. 2shows a perspective view of the underside of the pressure plate104, according to an embodiment of the invention. The pressure plate104includes a number of instances of profiled inserts, such as the profiled insert106, and a number of instances of spring-loaded pushing elements, such as the spring-loaded pushing element106. The spring-loaded pushing elements are located in the example ofFIG. 2in the centers of their corresponding profiled inserts, as inFIG. 1A, as compared to as inFIG. 1B.

Each instance of a profiled insert and a corresponding spring-loaded pushing element corresponds to a single electronic device. Thus, the pressure plate104inFIG. 2is intended to press together two wafers or other substrates having a large number of such electronic devices. Each profiled insert and corresponding pushing element pushes together a single instance of the electronic device.

FIG. 3shows a method300for fabricating the electronic device101using the fabrication tool100, according to an embodiment of the invention. The device surfaces103and105of the electronic device101are first prepared by polishing and/or smoothing (302). Thereafter, the device surfaces103and105are plasma activated (304). For instance, the device surfaces103and105may be exposed within a plasma chamber to plasma, to ready the device surfaces103and105for ultimate bonding.

FIG. 4Ashows an example of two representative electronic devices101A and101B after performance of the parts302and304of the method300ofFIG. 3, according to an embodiment of the invention. The left portion of the device surfaces103and105corresponds to one electronic device101A, and the right portion of the device surfaces103and105corresponds to another electronic device101B. The device surfaces103and105have been polished and/or smoothed, and plasma activated. The device surface103of the electronic devices101A and101B is planar. The device surface105of the electronic device101A has a surface portion116that is convex, whereas the device surface105of the electronic device101B has a surface portion402that is concave. There is a gap498within the device surface103, which is described in more detail later in the detailed description.

Referring back toFIG. 3, the method300continues by the fabrication tool100exerting force against the device surface103to press the device surface103towards and ultimately against the device surface105(306), to bond the device surfaces103and105of the electronic device101together. As has been described, the force is first exerted at one or more first locations118of the device surface103, and is second exerted at one or more second locations120of the device surface103. Thereafter, ultimately the force is exerted completely over the device surface103.

Performance of the part306of the method300thus first includes pressing the device surface103against the device surface105at one or more first locations118of the device surface103(308). The bonding piston102of the fabrication tool100pushes downward, exerting a force through the pressure plate104, where the spring-loaded pushing elements110make first contact between the fabrication tool100and the electronic device101. As a result, the force exerted by the bonding piston102is first exerted at the locations118of the device surface103correspondingly underneath the spring-loaded pushing elements110.

FIG. 4Bshows example performance of the part308of the method300ofFIG. 3, according to an embodiment of the invention, in relation to the electronic devices101A and101B ofFIG. 4A. Because the spring-loaded pushing elements110normally extend outward from their holes108, they make first contact with the electronic devices101A and101B. As a result, the force exerted by the bonding piston102through the pressure plate104and/or the profiled insert106is first exerted at the locations118of the device surface103. With respect to the first device101A, the device surface103retains its planar shape, since the left location118at which the force is initially exerted is against a highest, convex point of the device surface105. With respect to the second device101B, the device surface103begins to bend to conform to the shape of the device surface105, since the right location118at which the force is initially exerted is against a lowest, concave point of the device surface105.

Referring back toFIG. 3, performance of the part306of the method300next includes pressing the device surface103against the device surface105by exerting force at one or more second locations120of the device surface103(310). The bonding piston102of the fabrication tool100continues to push and move downward, exerting a force through the pressure plate104and to the profiled insert106, such that the profiled insert106makes second contact between the fabrication tool100and the electronic device101. The force exerted by the bonding piston102is exerted at the locations120of the device surface103correspondingly underneath the lowest points of the profiled insert106, as has been described.

FIG. 4Cshows example performance of the part310of the method300ofFIG. 3, according to an embodiment of the invention, in relation to the electronic devices101A and101B ofFIGS. 4A and 4B. The profiled nature of the profiled insert106result in the force exerted by the bonding piston102through the pressure plate104and to the profiled insert106being exerted next at the locations120of the device surface103that are underneath the lowest points of the profiled insert106. In the example ofFIG. 4C, these lowest points of the profiled insert106are the edges of the insert106. The spring-loaded pushing elements110begin to recede into their holes108, as a result of the continuing downward movement of the bonding piston102, the pressure plate104, and the profiled insert106.

Referring back toFIG. 3, performance of the part306of the method300finally includes pressing the device surface103against the device surface105by exerting force over substantially the entirety of the device surface103(312). The bonding piston102of the fabrication tool100continues to push and move downward, exerting a force through the pressure plate104and to the profiled insert106. The surface of the electronic device101incident to the profiled insert106may conform to the profile of the profiled insert106, to provide for the force being exerted over at least substantially all of the device surface103. The device surface103may further conform to the shape of the device surface105, to provide for complete and securing bonding of the surfaces103and105together to result in at least partially the electronic device101.

FIG. 4Dshows example performance of the part312of the method300ofFIG. 3, according to an embodiment of the invention, in relation to the electronic devices101A and101B ofFIGS. 4A,4B, and4C. The force exerting by the bonding piston102through the pressure plate104and to the profiled insert106is exerted over substantially all of the device surface103. The surfaces of the electronic devices101A and101B incident to the profiled insert106have taken on the mirror profile of the profiled insert106. The device surface103, by comparison, has taken on the mirror shape of the device surface105. The spring-loaded pushing elements110have further receded into their holes108, as a result of the continuing downward movement of the bonding piston102, the pressure plate104, and the profiled insert106.

The bonding process described in relation toFIG. 3as exemplarily depicted in relation toFIGS. 4A-4Dis advantageous. The initial exertion of force at the locations118of the device surface103inFIG. 4B, followed by the subsequent exertion of force at the locations120of the surface103inFIG. 4Cand the exertion of force over the entirety of the surface103inFIG. 4Dsubstantially reduces the likelihood that air pockets will become trapped between the surfaces103and105during the bonding process. In one embodiment, the presence of the gap498alleviates the likelihood that air pockets will become trapped between the surfaces103and105during bonding. In particular, such air in this embodiment is pushed into the gap498, such that it is not trapped between the surfaces103and105themselves.

Furthermore, the bonding process is such that the bond between the device surfaces103and105begins at one or more discrete points between the surfaces103and105, at the locations118, and then propagates to the remainder of the surfaces103and105, at the locations120, and then over all the locations. This can cause a stronger resulting plasma bond than if the bond were to start at all the locations between the device surfaces at the same time.