Patent ID: 9580305
Date: 2017-02-28
CPC Classifications: B81B,B81C,G01N

Claim:
1. A method of manufacturing a single silicon wafer micromechanical thermal conduction sensor comprising steps of: providing a silicon substrate having a resistivity ranging from 0.1 to 0.001 ohm-cm and a crystal orientation; depositing a silicon nitride layer on the surface of the silicon substrate by LPCVD (low pressure chemical vapor deposition) which has a thickness in the range of 2000 to 3000 Angstroms; performing first lithographic process including forming a photoresist pattern with a square or a circles shape window in the silicon nitride layer and etching exposed silicon nitride layer in the window; performing anodization in a HF solution to convert the exposed single crystal silicon layer of the silicon substrate into a porous silicon layer; depositing first insulating silicon nitride layer on the surface of the silicon substrate including the surface of the porous silicon layer by LPCVD; depositing a polysilicon layer on the surface of the first insulating silicon nitride layer by LPCVD; performing second photolithography process for creating a polysilicon pattern on the top central region of the porous silicon layer; perform a third fabrication process by depositing second insulating silicon nitride layer coating the surface of the silicon substrate including the surface of the polysilicon pattern by LPCVD; depositing a passivation layer over the surface of the silicon substrate by LPCVD or PECVD (plasma enhanced chemical vapor deposition); performing fourth lithographic process to reveal the bonding pads; performing fifth lithographic process to create at least one opening in the insulating layer so as to reveal its beneath porous silicon layer; etching the porous silicon layer through the openings in a diluted HF solution so as to form a heat transfer cavity having a flat bottom parallel to the surface of substrate, a frame having a side curved wall surrounding the cavity, a thin film bridge suspending over the cavity and having a central section and at least two side sections on the two opposite sides of the central section, which extend to the edge of the frame; and perform a sixth fabrication process creating a heated resistor on the top surface of the polysilicon pattern and a temperature sensor on the periphery top surface of the porous silicon layer by a lift-off process and metal deposition by E-beam evaporation or sputtering.