Silicon pressure sensor

• US 3,893,228 A
• Filed: 10/29/1973
• Issued: 07/08/1975
• Est. Priority Date: 10/02/1972
• Status: Expired due to Term

• Current Assignee: Jack L. Saltich, William L. George
• Original Assignee: Jack L. Saltich, William L. George
• Inventors: George, William L., Saltich, Jack L.
• Primary Examiner(s): Tupman, W.
• Application Number:
  US05/410,734
• Time in Patent Office: 617 Days
• Field of Search: 29/580,591,61G,576IW,25.35 317/235M
• US Class Current: 438/53
• CPC Class Codes: G01L 9/0055 bonded on a diaphragm
• CPC Class Codes: H01L 21/30608 Anisotropic liquid etching H01L21/3063 takes precedence
• CPC Class Codes: H01L 29/84 controllable by variation of applied mechanical force, e.g. of pressure
• CPC Class Codes: Y10T 29/49082 Resistor making

Abstract

A method of fabricating a piezoresistive pressure sensor from a monocrystalline silicon wafer depends upon a boron P+ conductivity layer as an etch stop to an anisotropic etch using potassium hydroxide as the etchant. The etching is selectively done so that the inner portion of the wafer is relatively thin and the outer portion is relatively thick. The process permits the fabrication of piezoresistive pressure sensitive elements of a bridge to be formed of monocrystalline silicon in the relatively thin inner portion and also permits the fabrication of pressure insensitive elements, formed of monocrystalline silicon in the outer portion, electrically connected to the pressure sensitive elements. The resultant structure is a monocrystalline silicon wafer cut along the (110) or the (100) crystallographic plane and having at least the pressure sensitive and pressure insensitive elements of the bridge circuit as integral parts.

Claims

1. A METHOD OF MANUFACTURING A SILICON PRESSURE SENSOR FROM A MONOCRYSTALLINE SILICON WAFER CUT ALONG A PRESCRIBED CRYSTALLOGRAPHIC PLANE, COMPRISING THE STEPS OF:

A. FORMING A FIRST LAYER OF A FIRST CONDUCTIVITY TYPE MONCRYSTALLINE SILICON AT ONE SURFACE OF THE WATER, B. FORMING A SECOND LAYER OF A SECOND CONDUCTIVITY TYPE MONOCRYSTALLINE SILICON OVER THE FIRST LAYER, C. FORMING AT LEAST ONE ELONGATED PIEZORESISTIVE PRESSURE SENSITIVE ELEMENT OF THE BRIDGE CIRCUIT BY FORMING A FIRST CONDUCTIVITY TYPE SECTION OF MONOCRYSTALLINE SILICON IN A PRESCRIBED REGION AT THE SURFACE OF THE SECOND LAYER, D. FORMING ELONGATED PRESSURE INSENSITIVE ELEMENTS OF THE BRIDGE CIRCUIT BY FORMING A FIRST CONDUCTIVITY TYPE SECTION OF MONOCRYSTALLINE SILICON AT THE SURFACE OF THE SECOND LAYER AT EACH END OF SAID PRESSURE SENSITIVE ELEMENT AND CONNECTED THERETO, E. SELECTIVELY ETCHING THE WAFER FROM THE OTHER SURFACE TO PROVIDE A RELATIVELY THIN ELONGATED REGION TO SUPPORT THE PIEZORESISTIVE PRESURE SENSITIVE ELEMENT OF THE BRIDGE CIRCUIT WHILE LEAVING UNETCHED SPACED PORTIONS OF THE WAFER UNDERLYING THE PRESSURE INSENSITIVE ELEMENTS TO PROVIDE A RELATIVELY THICK REGION TO SUPPORT THE PRESSURE INSENSITIVE ELEMENTS OF THE BRIDGE CIRCUIT, AND F. INTERCONNECTING THE ELEMENTS OF THE BRIDGE CIRCUIT TO PRODUCE AN OUTPUT WHEN THE PRESSURE SENSITIVE ELEMENTS IS SUBJECTED TO PRESSURE.

2. The method of claim 1 wherein the first layer is of P conductivity type, the second layer is of N conductivity type, and the pressure sensitive and pressure insensitive elements are of P conductivity type.

3. The method of claim 2 wherein the step of forming the first layer further comprises growing an epitaxial layer over the one surface of the wafer.

4. The method of claim 3 wherein the step of forming the second layer further comprises growing an epitaxial layer over the first layer.

5. The method of claim 4 wherein the steps of forming at least one piezoresistive pressure sensitive element and the pressure insensitive elements further compRises diffusing a selected impurity into the second layer at prescribed regions to form the elements of a P type conductivity.

6. The method of claim 5 wherein the wafer is cut along the (110) crystallographic plane.

7. The method of claim 1 wherein two parallel piezoresistive pressure sensitive elements are formed and two parallel pressure insensitive elements are formed.