US 6,465,271 B1 · Method of fabricating silicon capacitive sensor

Abstract

Manufacturing all-silicon force sensors, such as capacitive pressure sensors (100, 200) that have long term stability and good linear sensitivity, and can be built into of a pneumatic tire. The sensors include buried electrical feedthrough (112b) to provide an electrical connection into a sealed silicon cavity (108). The buried feedthrough consists of a conductor (112b) in a shallow groove (106) in a substrate (102), communicating between the sensing cavity (108) and an external contact area (110). The sensor designs also feature a method for forming a silicon-to-silicon fusion bond (SFB) wherein at least one of the two surfaces (152, 252) to be has a tough silicon surface unsuitable for good SFB joints because it was bonded heavily boron-doped by means of diffusion. The method of this invention includes preparing each doped surface (152, 252) for SFB by polishing the surface with a Chemical-Mechanical Polishing (CMP) process. The sensor designs can also include optional reference capacitors (141, 241) on the same chip (100, 200) as the sensing capacitor (140, 240). The reference capacitors (141, 241) are insensitive to pressure (force), but respond to ambient temperature changes in the same way as the sensing capacitor. Suitable external interface circuits can utilize the reference capacitors (141, 241) to pull out the majority of ambient temperature effects.

Claims19

Dependent claims

A method of fabricating silicon capacitive sensors, characterized by the steps of:

providing a first silicon wafer and a second silicon wafer;
for each sensor, etching a groove in the first silicon wafer;
for each sensor, etching a sensing cavity and a contact cavity, each cavity connected to an opposing end of the groove in the first silicon wafer;
for each sensor, after etching the groove and the cavities, forming a continuous and connected conductive area in the bottoms of the groove and the cavities, in the first silicon wafer;
forming a P+ conductive diaphragm layer in the second silicon wafer by means of diffusion doping;
after the step of forming the diaphragm layer in the second silicon wafer, preparing the surface of the diaphragm layer for bonding by polishing with a chemical-mechanical polishing (CMP) process;
bonding the first silicon wafer and the second silicon wafer together using a silicon fusion bonding (SFB) technique;
dissolving the second silicon wafer, except for the diaphragm layer;
after the step of dissolving the second silicon wafer, for each sensor, etching open a fixed electrode contact window through the diaphragm layer to the contact cavity;
and
dicing a plurality of sensors formed from the first and second silicon wafers.

8 more elements

Dependencies are inferred from the claim text.

Method of fabricating silicon capacitive sensor

Life of this patent

Method of fabricating silicon capacitive sensor

Life of this patent

Abstract

Claims19