US Patent 7091057 Method of making a single-crystal-silicon 3D micromirror

First and second n-doped regions are formed at a surface of a p-doped single crystal silicon substrate. An aluminum layer is patterned overlying some of the second n-doped regions to form thermal actuators. A dielectric layer is deposited overlying the patterned aluminum layer and an underlying thermal oxide layer. A metal layer is deposited thereover and patterned to form bond pads to the thermal actuators and to form reflecting mirror surfaces overlying others of the second n-doped regions to form micromirrors. The substrate is etched away from the backside stopping at the first and second n-doped regions. Then the wafer is diced into mirror array chips. Portions of the first n-doped regions are etched away from the frontside to form flexible springs wherein the second n-doped regions covered by the patterned aluminum layer form thermal actuators and wherein the flexible springs connect the micromirrors to the thermal actuators.