Selective and non-selective deposition of thick polysilicon layers for adaptive mirror device

Two IC-process-compatible fabrication schemes, based on the selective and non-selective deposition of a thick polysilicon layer in an epitaxial reactor, are used for adaptive micromirror device fabrication. The micromirror consists of a composite diaphragm (a 0.5 mu m square-shaped silicon nitride membrane on which an additional 5.6 mu m thick polycrystalline silicon layer with a circular aperture is formed) coated with a 0.2 mu m reflective aluminium layer on a bulk micromachined 10.5 mm by 10.5 mm square silicon frame. The additional polycrystalline silicon layer with a circular aperture improves the optical properties of a deflected square-shaped silicon nitride membrane resulting from anisotropic KOH etching.