Patent ID: 8546170

Claim:
A method of fabricating a micro-electrical-mechanical system (MEMS) transducer, the method comprising: forming a membrane on a first side of a substrate; and forming a back-volume through the substrate from a second side; wherein the step of forming a back-volume in the substrate comprises the steps of forming a first back-volume portion and a second back-volume portion, the back-volume having a step in a sidewall of the back-volume, said step defining a separation between the first back-volume portion from the second back-volume portion; and wherein the step of forming the first back-volume portion further comprises the steps of: applying a first mask layer to the second side of the substrate, the first mask layer having an opening corresponding substantially to the cross-sectional area of the first back-volume portion; etching the substrate to a first depth; enlarging the opening of the first mask layer, such that said opening corresponds substantially to the cross-sectional area of the second back-volume portion; and etching the substrate to a second depth.