Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
2001-04-26
2003-01-07
Smith, Matthew (Department: 2325)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S106000, C438S110000, C438S118000, C156S109000, C156S152000, C264S135000
Reexamination Certificate
active
06503847
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of microelectronic circuitry, more specifically to the use of wafer-to-wafer bonding as a technique for circuit fabrication, encapsulation and packaging.
2. Description of the Related Art
Wafer-to-wafer bonding is an important method for wafer level encapsulation as well as for the coupling of device layers in an integrated circuit. For example, Davidson (U.S. Pat. No. 5,880,010) discloses an integrated circuit comprising a plurality of active layers that are electrically and mechanically coupled by means of a wafer bonding method.
The prior art discloses several methods for achieving wafer-to-wafer bonding, each of which involves the imposition of at least one processing step that subjects the wafers to adverse conditions such as application of a high electrical voltage, application of a high temperature or the use of high contact pressures. High temperatures can cause unwanted variations of wafer doping concentrations, internal stresses due to difference in thermal expansion coefficients between layers, wafer warping, crystal dislocations and various other undesirable effects on certain materials, such as bio-materials, already present in the subject devices. In a similar manner, high contact pressures may damage devices formed in the wafers, as can the use of high voltage differences. For example, Ju et al (U.S. Pat. No. 5,273,205) teaches a method of silicon-to-silicon wafer bonding that requires an 1,100° C. heat treatment for 10 minutes in a wet oxygen gas atmosphere. Akaike et al (U.S. Pat. No. 5,820,648) teach an anodic bonding process in which a silicon substrate and a glass substrate are bonded in a process involving the application of both a potential difference between the substrates simultaneously with light irradiation. Bower et al. (U.S. Pat. No. 5,503,704) teach a method for nitrogen based bonding of similar or dissimilar materials at temperatures below 500° C., but still appreciably above room temperature. In addition the method requires plasma activation and a curing time of approximately 4 days. Davidson, (U.S. Pat. No, 5,880,010), already cited above, teaches a method of forming complex integrated circuits by bonding together a plurality of active layers (ie. layers already provided with circuitry). Two bonding methods are taught, thermosonic bonding and nitride laminating. Both methods require the formation of pads to insure the bonding. The prior art also discloses several methods for bonding silicon elastomers to glass, metal and polymeric materials. Plueddemann (U.S. Pat. No. 3,889,023) teaches a method of bonding a silicone rubber of a general organopolysiloxane composition to a solid substrate. Moncur et al. (U.S. Pat. No. 5,378,535) also teaches a method for bonding silicone elastomers to glass or plastic substrates, wherein an organosilane component is formed on silica-based adhesion promoter.
As already noted above, the methods of the prior art either subject the materials to be bonded to adverse conditions such as high temperature, high contact pressure or high voltage or else they require complex process steps and long curing times. It is the purpose of the present invention to provide a bonding method that avoids these shortcomings of the prior art.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a method for wafer-to-wafer bonding that is implemented at room temperature and does not requires the application of electrical potential or high pressures.
It is a second object of the present invention to provide a method for wafer-to-wafer bonding which has a wide application domain in terms of the nature of devices, structures, and materials that may be disposed on said wafers.
It is a third object of the present invention to provide a method for wafer-to-wafer bonding that comprises a simple sequence of process steps.
It is a fourth object of the present invention to provide a method for wafer-to-wafer bonding using materials that are bio-compatible and transparent and which can, thereby, be applied to such uses as the packaging and assembly of bio-MEMS (MicroElectro Mechanical Systems) systems and devices, and other bio-medical devices.
It is a fifth object of the present invention to provide a method for bonding similar or dissimilar materials chosen from, but not limited to, the group consisting of glass, silicon, silicon materials and compounds such as silicon dioxide and silicon nitride, and metals such as Ti, Au, Al and Cr.
The above objects will be realized by the use of polydimethylsiloxane as a bonding agent, which allows the bonding process to be carried out at room temperature (23° C.), in the absence of applied voltages and high pressures and in the following simple sequence of steps: (a) spin coating, (b) alignment and application of light pressure to assure surface-to-surface contact and air bubble removal, (c) curing.
REFERENCES:
patent: 3889023 (1975-06-01), Plueddemann
patent: 4090006 (1978-05-01), Havas et al.
patent: 4721994 (1988-01-01), Mine et al.
patent: 5273205 (1993-12-01), Ju et al.
patent: 5378535 (1995-01-01), Moncur et al.
patent: 5389170 (1995-02-01), Brady et al.
patent: 5503704 (1996-04-01), Bower et al.
patent: 5820648 (1998-10-01), Akaike et al.
patent: 5863988 (1999-01-01), Hashimoto et al.
patent: 5880010 (1999-03-01), Davidson
patent: 5997786 (1999-12-01), Arthur et al.
patent: 6235363 (2001-05-01), Bilodeau
patent: 2002/0031863 (2002-03-01), Nakata et al.
Chen Yu
Foo Pang Dow
Sridhar Uppili
Zou Quanbo
Ackerman Stephen B.
Institute of Microelectronics
Rocchegiani Renzo N.
Saile George O.
Smith Matthew
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