Patent ID: 8445324

Claim:
A method of fabricating a micromachined device, the method comprising: (a) providing a wafer comprising (i) a substrate having (A) a front side surface and (B) a back side surface opposing the front side surface, (ii) a composite thin film on the front side surface of the substrate, the composite thin film having an internal structure defining one or more etchable portions and one or more etch-resistant portions and including a circuitry layer stack comprising at least one etch resistant metallic layer and insulating material between an uppermost metallic layer and the front side surface of the substrate, and (iii) an etch mask on the back side surface of the substrate, the etch mask defining one or more isolation portions substantially aligned with the etchable portions of the composite thin film; (b) anisotropically etching the back side of the substrate via the isolation portions of the etch mask, thereby forming one or more first isolation trenches, wherein the first isolation trenches (i) are substantially aligned with the etchable portions of the composite thin film and (ii) extend partially into the substrate; (c) removing the etch mask; (d) anisotropically etching the back side of the substrate via the first isolation trenches, thereby extending the first isolation trenches to form one or more second isolation trenches, wherein the second isolation trenches (i) are substantially aligned with the etchable portions of the composite thin film and (ii) extend through the substrate to the composite thin film; and (e) anisotropically etching the etchable portions of the composite thin film, thereby defining one or more final isolation trenches.