Patent ID: 7205665

Claim:
A silicon structure useful for making porous silicon in selected areas of a silicon substrate via anodic etching, the silicon substrate having a frontside and a backside, the silicon structure comprising: a barrier layer adjacent to the frontside of the silicon substrate, the barrier layer including a plurality of discrete barrier openings positioned within and bounded by a contiguous frontside portion of the barrier layer, the contiguous frontside portion of the barrier layer defining a first aperture having a first shape and a first center point; and an opaque ohmic contact layer adjacent to the backside of the silicon substrate, the ohmic contact layer including a second aperture bounded by a contiguous backside portion of the ohmic contact layer, the second aperture having a second shape and a second center point; wherein the first and second center points share an axis substantially perpendicular to the frontside and the backside of the silicon substrate, and wherein the first shape is substantially the same as the second shape but larger, and wherein the first shape is trans-concentrically positioned relative to the second shape about the axis.