Glass manufacturing – Processes – Reshaping or surface deformation of glass preform
Patent
1997-10-06
1998-10-27
Chin, Peter
Glass manufacturing
Processes
Reshaping or surface deformation of glass preform
65 36, 65 40, 65 41, 65 54, 65 591, 65 594, 65104, 65154, C03B 2300
Patent
active
058273433
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND
1. Field of the Invention
The invention relates to a process for changing the flexion of anodically bonded two-dimensional composites of glass and metal or semiconductor material.
2. Description of the Prior Art
Anodic bonding is a technique for bonding metals or semiconductor materials to glass. It is characterized by applying an electric field at a process temperature below the transformation temperature Tg of the glass and is described, for example, in U.S. Pat. Nos. 3,397,278 and 3,417,459.
In anodic bonding, a polished glass plate is. brought into intimate contact with a polished plate of metal or semiconductor material. The application of a direct voltage between the bonding partners so that the glass is given a cathode potential while the semiconductor/metal is given an anode potential causes the alkali metal ions of the glass to migrate in the direction of the cathode at elevated temperatures. The negatively charged oxygen ions generated on the interface towards the bonding partner are firmly bound in the glass network, producing a strong electrostatic attraction between the glass and the semiconductor/metal. This attraction causes the bonding partners to approach each other down to the atomic range. The irreversible chemical bonding between glass and the metal or semiconductor material results from the formation of oxygen bridges between the bonding partners.
EP 0 139 334 A2 teaches a three-ply composite which consists of a GaAs layer, a support glass (verre de soutien) and a buffer glass (verre de tampon) located between the semiconductor layer and the support glass. The softening temperature of the buffer glass lies below that of the support glass, being softened, or stress-relieved, at the desorption temperature. During desorption, the entire composite is stress-relieved, as the support glass and semiconductor layer "float" on the soft buffer glass layer, freely expanding or contracting. During subsequent cooling, strains corresponding to the differences in the coefficients of expansion re-occur which are compensated by a third glass.
Typical bonding voltages lie in the range of 50 to 1000 volts. The possible bonding temperature range is limited at the lower end by alkali mobility (about 250.degree. in the case of borosilicate glass) and, at the upper end, by the transformation point of the glass (about 520.degree. for borosilicate glass). Anodic bonding above the transformation point is possible, but can cause plastic deformation of the glass which should contain a minimum quantity of alkali metal ions. In the case of the commonly employed glasses, the proportion is in the range of (1 to 5) atomic percent (Schott 8330.apprxeq.3%, Hoya SD2.apprxeq.2%). At the present time, Schott 8330 and Corning 7740 glasses are very frequently used for anodic bonding.
One general purpose of the bonding is to obtain a base and/or cover of glass for thin layers of metal or semiconductor and/or to assemble a component. Known applications of bonding are the stabilization and encapsulation of sensors of microstructured silicon (e.g. pressure and acceleration sensors), the covering of fluidic structures of microstructured silicon (i.e., channels, valves and the like) and the generation of micromechanical actors based, for example, on piezo-electrically-deflected glass membranes over pumping chambers structured in silicon.
After bonding, the composites obtained are cooled to room temperature. Such cooling process takes several minutes depending on the thickness of the composites.
Undesired strains between the mutually-bonded materials, leading to undesired flexions of the components, arise during the cooling that follows anodic bonding. Such strains are due, inter alia, to non-optimally matched coefficients of expansion of the metal or semiconductor material and the glass concerned as well as inhomogeneous temperatures in the bond structure. It is sometimes possible to reduce such strains by employing a more homogeneous temperature distribution during bonding or by using a glass having a more closely-mat
REFERENCES:
Michael Harz and Winfried Brueckner, "Thermally Induced Bend Change of Anodically Bonded Silicon and PYREX Wafers" Chemical Abstracts, vol. 123, No. 26 (abstract No. 355935, Dec. 25, 1995 (Same in Semiconductor Wafe Bonding:Physics and Applications III, Proceedings, Electrochemical Society, (Jul. 1995), pp. 315-325.
S.M. Rekhson, "Annealing of Glass-to-Metal and Glass-to-Ceramic Seals, Part 1. Theory," Glass Technology, vol. 20, No. 1 (Feb. 1979), pp. 29, 30.
K. Sooriakumar et al., "Thermal Mismatch Strain in Anodically Bonded Silicon and Glass," Extended Abstracts, No. 1 (1993), pp. 1210, 1211.
George Wallis and Daniel I. Pomerantz, "Field Assisted Glass-Metal Sealing", Journal of Applied Physics, vol. 40, No. 10 (Sep. 1969) pp. 3946-3949.
Engelke Heinrich
Harz Michael
Chin Peter
Colaianni Michael P.
Kramsky Elliott N.
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