Integrated thin-film diaphragm

Claim 1

A process for fabricating a thin film microsensor for air flow, characterized by the steps of: a) providing a single crystal (100) silicon wafer (11) having a front planar surface, a backside surface and having a <110> direction; b) depositing and delineating a rectangular area (13) of a thin film layer of sacrificial selectively etchable material on the silicon front surface (12); c) depositing a thin film (14) of silicon nitride on the selectively etchable material (13) and the rest of the silicon front surface (12), the film being thicker than the thickness of the sacrificial material; d) depositing and delineating a thin film (15) of electrically resistive material on the silicon nitride (14) to form desired circuit elements such as detector resistors, circuit resistors and a heater resistor, said heater resistor and detector resistors being located over said sacrificial material area (13); e) depositing an additional thin film (16) of silicon nitride over the resistive material (15) and the previous silicon nitride (14); f) depositing a thin film (18) of silicon nitride over the backside surface; g) opening a cut (19) through the silicon nitride (18) on the backside to expose an area of the backside silicon surface, the cut being rectangular and orthogonal to the <110> direction; h) introducing an anisotropic etch to the backside silicon surface at said nitride cut to anisotropically etch a first anisotropic pit (19′) through the silicon wafer (11) until the layer (13) of sacrificial selectively etchable material is reached; i) introducing selective etch through the first anisotropic pit to etch out all of the sacrificial selectively etchable material (13) leaving a thin cavity (27) in its place; and, j) introducing the anisotropic etch through the first pit and the thin cavity to anisotropically etch the silicon (28) exposed by the removal of the sacrificial material (13) and form a second anisotropic etch pit (29).