Method of making a multi-layer silicon structure
First Claim
1. A method for making a multi-layer silicon structure comprising the steps ofpolishing and cleaning surfaces of silicon wafers, one of said wafers having aluminum electric conductor tracks on a surface thereof,dipping said wafers in a solution consisting essentially of fuming nitric acid having a temperature of from about 15°
- C. to 30°
C., said dipping not destroying the aluminum conductor tracks, then rinsing said wafers with de-ionized water and drying the wafers;
assembling the thus polished surfaces of the wafers together in a substantially particle-free atmosphere, andsubjecting the assembled wafers to a heating treatment to form a secure silicon-to-silicon bond, said heating treatment being carried out at a temperature between about 100°
C. and about 400°
C.
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Accused Products
Abstract
Multi-layer silicon structures particularly micromechanical sensors, can be made by cleaning and polishing respective surfaces of two silicon wafers, assembling the wafers together under clean room conditions and adhering them together by temperature treatment. This method is improved by the pretreatment of the wafer surfaces using fuming nitric acid (e.g., 100% HNO3), rinsing with de-ionized water, drying, and temperature treatment at a lower temperature than was previously thought necessary, namely between 100° and 400° C. This has the advantage that such gentler treatment preserves previously-applied integrated circuit structures, which can therefore be applied before the wafer assembly steps. The method is particularly suitable for producing pressure sensors having a pressure-responsive silicon membrane, and an evaluation circuit integrated on the silicon wafer. Such sensors are suitable for use in motor vehicles for measuring engine pressures and for measuring brake fluid pressures in anti-lock braking systems (ABS).
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Citations
13 Claims
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1. A method for making a multi-layer silicon structure comprising the steps of
polishing and cleaning surfaces of silicon wafers, one of said wafers having aluminum electric conductor tracks on a surface thereof, dipping said wafers in a solution consisting essentially of fuming nitric acid having a temperature of from about 15° - C. to 30°
C., said dipping not destroying the aluminum conductor tracks, then rinsing said wafers with de-ionized water and drying the wafers;assembling the thus polished surfaces of the wafers together in a substantially particle-free atmosphere, and subjecting the assembled wafers to a heating treatment to form a secure silicon-to-silicon bond, said heating treatment being carried out at a temperature between about 100°
C. and about 400°
C. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
- C. to 30°
Specification