Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-06-18
2004-01-06
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C438S456000, C438S458000, C438S459000
Reexamination Certificate
active
06673189
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for producing a re-releasable bond between two wafers which is stable at high temperatures and is mechanically stable.
Modern semiconductor devices are increasingly produced on very thin semiconductor bodies, including ones that are thinner than 100 &mgr;m. Typically used for this purpose are conventional wafers that have a thickness of 500-700 &mgr;m and are ground until thin before the production of the semiconductor devices.
However, on account of their mechanical properties, such ultrathin wafers are very difficult to handle and therefore cannot be handled by the same production machines and transporting and securing devices as wafers of a standard thickness. It is therefore necessary to provide production machines and transporting devices which are modified specifically for ultrathin wafers, are configured for special wafer cassettes and have gripping devices for feeding the production machines that are configured specifically for ultrathin wafers and usually have to be operated manually. Furthermore, here the devices for fixing the ultrathin wafers during the actual production process, such as for example chucks, are converted for the requirements of the ultrathin wafers, which is laborious to various extents. There are, however, narrow limits to the modification of production machines for the purposes of handling ultrathin wafers, on account of their increasing complexity.
For all these reasons mentioned, the provision of new or modified production machines for the handling of ultrathin wafers is extremely complex and cost-intensive.
A significantly more simple method for producing and handling ultrathin wafers is described below.
A first wafer, known as the product wafer, on which the semiconductor devices are later to be applied and which therefore is to be ground until ultrathin, is placed and fastened in an interlocking manner onto a second wafer, known as the support wafer. The product wafer can then be ground until thin and the semiconductor devices can be introduced into the thin-ground product wafer using the corresponding production technology. Finally, the product wafer can be re-detached from the support wafer.
The interlocking and frictionally engaging bond is created here for example by a wax or adhesive bond or by a two-sided adhesive film disposed between the support wafer and the product wafer. The disadvantage of this method is that the interlocking and frictionally engaging bond is configured only for very low temperatures. At high temperatures, typical for the semiconductor process technology, the bond of wax, adhesive or film would however come apart again, that is to say a temperature-stable bond between the two wafers is no longer ensured here. In addition, if the materials mentioned above are used, foreign atoms could diffuse into the semiconductor body and contaminate it undesirably.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for producing a stable bond between two wafers which overcomes the above-mentioned disadvantages of the prior art methods of this general type, which is stable at high temperatures and is mechanically stable.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing a re-releasable bond being stable at high temperatures and being mechanically stable. The method includes the step of placing two wafers to be bonded one on top of another such that a surface of a first wafer is disposed on a surface of a second wafer, resulting in a creation of interspaces between the two wafers. The interspaces at least partially connecting the surface of the first wafer to the surface of the second wafer. A liquid glass compound is introduced into the interspaces forming a liquid glass film wetting inner surfaces of the interspaces. In the process, voids connected to an atmosphere surrounding the two wafers remain inside the interspaces wetted with the liquid glass compound. The two wafers lying one on top of the other are subjected to a temperature treatment to transform the liquid glass film into a solid silicon dioxide film.
The present method makes it possible for the two wafers to be bonded to each other according to the invention with a bond which is mechanically stable and is stable at high temperatures in a very simple but nevertheless effective way such that a product wafer as is known can subsequently be ground until thin and further processed. For the further processing of the product wafer, all the equipment of conventional silicon technology can be advantageously used, that is to say no additionally modified production machines or transporting devices for handling the thin-ground wafers are required here. The special advantage of the present invention is that the wafers bonded to each other by a thin silicon dioxide film can be detached from each other again very simply—for example by a hydrofluoric acid compound.
In accordance with an added mode of the invention, there is the step of carrying out the temperature treatment step for turning the liquid glass film into the solid silicon dioxide film at a temperature of between 120° C. and 450° C.
In accordance with an additional mode of the invention, there is the step of subjecting the two wafers lying one on top of the other to a uniform pressure over a large surface area during the temperature treatment step.
In accordance with another mode of the invention, there is the step of using the first wafer as a support for the second wafer. The second wafer, on which semiconductor devices to be created are provided, is ground until thin or etched until thin after the production of the bond.
In accordance with a further mode of the invention, there is the step of forming trenches running in a plane of one of the surface of the first wafer and the surface of the second wafer. The trenches can be formed such that they run at least one of parallel and perpendicular to one another. The trenches have a depth of from 2 &mgr;m to 10 &mgr;m and are disposed at a distance of from 1 &mgr;m to 10 &mgr;m from one another.
In accordance with another added mode of the invention, there is the step forming the trenches to have a cross section being a rectangular cross section or a trapezoidal cross section.
In accordance with another additional mode of the invention, there is the step of disposing a multiplicity of fibers between the two wafers, and regions between neighboring fibers forming the interspaces.
In accordance with a further added mode of the invention, there are the steps of applying a layer of the liquid glass compound to one of the two wafers; subsequently placing the two wafers one on top of the other in an interlocking and frictionally engaging manner to create the liquid glass film; and spinning off excess liquid glass compound located in the interspaces by high-speed rotation of the two wafers, utilizing a centrifugal force.
In accordance with an added mode of the invention, there are the steps of placing the two wafers one on top of the other in an interlocking and frictionally engaging manner; disposing the two wafers in a liquid glass reservoir such that the liquid glass compound can penetrate into the interspaces, utilizing capillary suction; and spinning off excess liquid glass compound located in the interspaces by high-speed rotation of the two wafers, utilizing centrifugal force to create the liquid glass film.
In accordance with another mode of the invention, there are the steps of forming a through hole in at least one of the two wafers; placing the two wafers one on top of the other in an interlocking and frictionally engaging manner; spinning off the liquid glass compound through the through hole into the interspaces between the two wafers; and spinning off excess liquid glass compound located in the interspaces by high-speed rotation of the two wafers, utilizing centrifugal force, to create the liquid glass film.
In accordance with another mode of the invention, there is the s
Gerss Matthias
Kröner Friedrich
Ball Michael W.
Greenberg Laurence A.
Haran John T.
Infineon - Technologies AG
Maybeck Gregory L.
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