# US 5,352,635 A · Silicon accelerometer fabrication method > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,352,635 A - Document ID: US5352635A - Status: Granted - Kind: A - Application number: 08/010,500 - Filed: 1993-01-28 - Granted: 1994-10-04 - Earliest claimed: 1990-07-12 - Inventors: Xiang-Zheng Tu; Yun-Yan Li - Web page: https://patentgrep.com/patent/US5352635A ## CPC - G01P 15/0802: {Details} - G01P 15/123: {by piezo-resistive elements, e.g. semiconductor strain gauges} - 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} - Y10S 438/96: Porous semiconductor - G01P: MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT (measuring or recording blood flow A61B5/02, A61B8/06; monitoring speed or deceleration of electrically-propelled vehicles B60L3/00; vehicle lighting systems adapted to indicate speed B60Q1/54; determining position or course in navigation, measuring ground distance in geodesy or surveying G01C; combined measuring devices for measuring two or more variables of movement G01C23/00; measuring velocity of sound G01H; measuring velocity of light G01J7/00; measuring direction or velocity of solid objects by reception or emission of radiowaves or other waves and based on propagation effects, e.g. Doppler effect, propagation time, direction of propagation, G01S; measuring speed of nuclear radiation G01T; measuring acceleration of gravity G01V; {measuring or recording the speed of trains B61L23/00; speed indicators incorporated in motor vehicles B60K35/00; measuring frequency or phase G01R; traffic control G08G}) - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS ## Abstract A silicon accelerometer comprising a substrate, one or more pairs of beams, a pedestal, a mass on top of the pedestal and a cavity beneath the pedestal all of which is formed by a single-sided processing method. The pedestal is suspended over the cavity by the beams which provides the only support for the pedestal. The beams are supported by the substrate. The main steps of fabricating this structure comprise diffusion or ion implantation and epitaxial growth to form a buried high donor concentration layer on the surface of the substrate, chemical vapor deposition and photoetching to expose a portion of the edge of the buried layer to the ambiente, anodization to convert the high donor concentration layer into porous silicon and selectively etching to remove the porous silicon. ## Claims ### Claim 1 A process for fabricating a silicon accelerometer comprising the steps of: providing a low donor concentration silicon substrate, forming a high donor concentration silicon layer in a predetermined region on the surface of the substrate by diffusion or ion implantation, forming a low donor concentration silicon layer over the surface of said substrate by vapor phase epitaxy, forming at least one opening in said low donor concentration layer thereby exposing edges of said high donor concentration layer, after said forming at least one opening, converting said high donor concentration layer into porous silicon by anodization, said converting of said high donor concentration layer being bounded by said exposed edges of said high donor concentration layer, mounting a mass onto the low donor concentration layer, removing the porous silicon by etching between the substrate and the low donor concentration layer to form a cavity between the substrate and the low donor concentration layer, said etching resulting in a complete removal of the porous silicon. ### Claim 2 (depends on 1) An accelerometer fabrication process according to claim 1 wherein said low donor concentration layer has a concentration between 10.sup.15 and 10.sup.16 cm.sup.-3. ### Claim 3 (depends on 1) An accelerometer fabrication process according to claim 1 wherein said high donor concentration layer has a concentration profile ranging between 10.sup.17 and 10.sup.21 cm.sup.-3. ### Claim 4 (depends on 1) An accelerometer fabrication process according to claim 1 wherein said anodization is carried out in a hydrofluoric acid solution. ### Claim 5 (depends on 4) An accelerometer fabrication process according to claim 4 wherein hydrofluoric acid solution has a concentration between 10 w% and 50 w%. ### Claim 6 (depends on 1) An accelerometer fabrication process according to claim 1 wherein said anodization is carried out at a constant voltage between 3 and 10 volt. ### Claim 7 (depends on 4) An accelerometer fabrication process according to claim 4 wherein said etching of porous silicon is performed in a diluted alkaline solution. ### Claim 8 (depends on 7) An accelerometer fabrication process according to claim 7 wherein said alkaline solution is ammonia hydroxide solution. ### Claim 9 (depends on 8) An accelerometer fabrication process according to claim 8 wherein said ammonia hydroxide solution has a concentration between 1 w% and 10 w%. ### Claim 10 (depends on 9) An accelerometer fabrication process according to claim 9, wherein said alkaline solution is sodium hydroxide solution. ### Claim 11 (depends on 10) An accelerometer fabrication process according to claim 10 wherein said sodium hydroxide solution has a concentration between 1 w% and 10 w%. ### Claim 12 (depends on 7) An accelerometer fabrication process according to claim 7 wherein said alkaline solution is potassium hydroxide solution. ### Claim 13 (depends on 7) An accelerometer fabrication process according to claim 7 wherein said potassium hydroxide solution has a concentration between 1 w% and 10 w%. ### Claim 14 (depends on 7) An accelerometer fabrication process according to claim 7 wherein said alkaline solution is caesium hydroxide solution. ### Claim 15 (depends on 14) An accelerometer fabrication process according to claim 14 wherein said caesium hydroxide solution has a concentration between 1 w% and 10 w%. and more particularly, ### Claim 16 (depends on 4) The accelerometer fabrication process of claim 4 further comprising the step of forming a hydrofluoric-acid resisting and electrically insulating layer on the low donor concentration layer to serve as a mask in the anodization step. ### Claim 17 (depends on 16) The acceleration fabrication process of claim 16 wherein said hydrofluoric-acid resisting and electrically insulating layer comprises a composite layer consisting of silicon dioxide, silicon nitride, and high resistance polysilicon. ### Claim 18 (depends on 17) The accelerator fabrication process of claim 17 wherein said composite layer is formed by low pressure chemical vapor deposition. ### Claim 19 (depends on 1) The accelerometer fabrication process of claim 1 wherein said at least one opening is formed by plasma etching utilizing a patterned metal layer as an etching mask.