Method and product for fabricating a resonant-bridge microaccelerometer

• US 4,893,509 A
• Filed: 12/27/1988
• Issued: 01/16/1990
• Est. Priority Date: 12/27/1988
• Status: Expired due to Term

• Current Assignee: General Motors Auto OOO (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: MacIver, Bernard A., Erskine, James C.
• Primary Examiner(s): Powell, William A.
• Application Number:
  US07/291,250
• Time in Patent Office: 385 Days
• Field of Search: 156/628, 156/647, 156/650, 156/657, 156/659.1, 156/662, 73/510, 73/517 R, 73/517 AV, 73/726, 73/754, 357/26, 338/2, 338/4, 338/42, 338/47, 29/621.1
• US Class Current: 73/514.29
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2201/0271 Resonators; ultrasonic resonators
• CPC Class Codes: B81B 2203/0315 Cavities
• CPC Class Codes: B81C 1/00142 Bridges deformable micromirrors G02B26/0841
• CPC Class Codes: B81C 2201/117 Using supercritical fluid, e.g. carbon dioxide, for removing sacrificial layers
• CPC Class Codes: G01P 15/097 by vibratory elements
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
• CPC Class Codes: G01P 2015/0842 the mass being of clover leaf shape
• CPC Class Codes: H01L 21/31111 by chemical means

Abstract

A resonant bridge microaccelerometer is formed using patterned Silicon-on-Insulator (SOI) material. A buried layer is formed in the silicon substrate using preferably oxygen ion implanting techniques. A predetermined proof mass is subsequently formed by selective deposition of an appropriate material on an epitaxially grown layer of silicon generally over the buried layer. The buried layer is subsequently removed by a hydrofluoric acid etch, thereby forming a gap generally everywhere therebetween the proof mass and the supporting silicon substrate, and delineating the resonant microbridges within the microaccelerometer.

Claims

1. A method for forming an accelerometer comprising the following steps:

providing a silicon substrate;

forming a buried layer in said silicon substrate;

forming a predetermined proof mass of appropriate lateral dimensions on said silicon substrate symmetrically disposed generally over said buried layer;

removing silicon from said silicon substrate, so as to delineate a pattern which generally corresponds to said lateral dimensions of said predetermined proof mass and so as to delineate a plurality of microbridges; and

removing said buried layer in said silicon substrate so as to form a cavity generally everywhere therebetween said proof mass and said microbridges, and said silicon substrate.

2. A method for forming an accelerometer as recited in claim 1 wherein an epitaxially grown silicon layer is formed on said silicon substrate after the formation of said buried layer and before the formations of said proof mass.

3. A method for forming an accelerometer as recited in claim 1 wherein a silicon dioxide masking layer is used to delineate the lateral dimensions of said proof mass.

4. A method for forming an accelerometer as recited in claim 1 wherein said predetermined proof mass is formed by the selective deposition of gold.

5. A method for forming an accelerometer as recited in claim 1 wherein said buried layer is removed by a hydrofluoric acid etch.

13. A microaccelerometer formed in accordance with claim 1 comprising:

a mass;

a substrate surrounding said mass with a cavity provided generally everywhere therebetween said substrate and said mass; and

at least two bridges attached at one end to said substrate from which said mass is suspended, said bridges being attached to opposite sides of said mass such that the longitudinal axis through said bridges form a common axis through said mass.

14. A microaccelerometer formed in accordance with claim 13 further comprising drive and sense electrodes corresponding to each of said bridges.

6. A method for forming an accelerometer comprising the following steps:

providing a silicon substrate;

forming a buried layer in said silicon substrate;

epitaxially growing a silicon layer from said silicon substrate generally over said buried layer;

removing silicon from said epitaxially grown silicon layer, so as to delineate a pattern which generally corresponds to said lateral dimensions of said predetermined proof mass and so as to delineate a plurality of microbridges;

forming a layer of silicon dioxide on said epitaxially grown silicon layer and photolithographically delineating said silicon dioxide layer so as to expose at least one region of said epitaxially grown silicon layer;

forming a predetermined proof mass of appropriate lateral dimensions on said exposed region of said epitaxially grown silicon layer by depositing an appropriate material in those delineated regions of said silicon dioxide layer, said predetermined proof mass being symmetrically disposed generally over said buried layer;

removing said silicon dioxide layer; and

removing said buried layer in said silicon substrate so as to form a cavity generally everywhere therebetween said proof mass and said microbridges, and said silicon substrate.

7. A method for forming an accelerometer as recited in claim 6 wherein said epitaxially grown silicon layer comprises n⁺ silicon.

8. A method for forming an accelerometer as recited in claim 6 wherein said predetermined proof mass is formed by the selective deposition of gold.

9. A method for forming an accelerometer as recited in claim 6 wherein said buried layer is removed by a hydrofluoric acid etch.

10. A method for forming an accelerometer as recited in claim 6 wherein appropriate drive and sense electrodes are formed for each of said bridges.

11. A method for forming an accelerometer comprising the following steps:

providing a single crystal silicon substrate;

forming a buried layer in said silicon substrate;

epitaxially growing a n⁺ silicon layer from said silicon substrate generally over said buried layer;

removing silicon from said epitaxially grown silicon layer, so as to delineate a pattern which will generally correspond to the lateral dimensions of a predetermined proof mass and a plurality of microbridges;

thermally growing a layer of silicon dioxide on said epitaxially grown silicon layer and photolithographically delineating said silicon dioxide layer so as to expose at least one region of said epitaxially grown silicon layer;

forming a predetermined proof mass comprising gold of appropriate lateral dimensions on said exposed regions of said epitaxially grown silicon layer by depositing an appropriate material in those delineated regions of said silicon dioxide layer, said predetermined proof mass being symmetrically disposed generally over said buried layer;

removing said silicon dioxide layer; and

removing said buried layer in said silicon substrate using a hydrofluoric acid etch so as to form a cavity generally everywhere therebetween said proof mass and said microbridges, and said silicon substrate.

12. A method for forming an accelerometer as recited in claim 11 wherein appropriate drive and sense electrodes are formed corresponding to each of said bridges.