HIGH REFLECTIVITY MICROMIRRORS FABRICATED BY COATING HIGH-ASPECT-RATIO SI SIDEWALLS

Micromachined Si vertical structures were sputter coated with Au onto sidewalls as reflective mirrors. These vertical micromirrors were inte grated with comb drives as optical switching arrays. The micromirrors were first etched in a Cl-2 plasma generated by an electron cyclotron resonance source, followed by a short B diffusion and a wet etch with ethylenediamine pyrocatechol to reduce sidewall roughness and to separ ate the mirrors from the substrate. The sputter-deposited Au films hav e nearly uniform thickness along the sidewalls of the micromirrors. Th ere was only a 6% thickness variation from the top to the bottom of th e mirror sidewalls. Reducing the sputtering pressure from 30 to 4 mTor r improved the coating uniformity for high aspect ratio, closely space d mirrors. For 30-mu m-tall micromirrors with 6 mu m spacing, the Au t hickness close to the bottom of the sidewalls decreased by 52% compare d to the top of the sidewalls when sputtered at 4 mTorr. The roughness along the micromirror sidewalls was found to change from 7.7 to 16.1 nm as the pressure during sputtering was varied from 4 to 30 mTorr. Th e resultant reflectivity for these vertical micromirrors decreased fro m 85% to 70% at a wavelength of 1.55 mu m. For high reflectivity micro mirrors with smooth sidewalls and uniform thickness, sputter depositio n of 400-nm-thick Au at 4 mTorr should be used. (C) 1997 American Vacu um Society.