Conformability and optical reflectance of Ti∕Au film sputtered on the Si vertical sidewalls

Abstract

A high quality reflective vertical surface is required for various optical micro electro mechanical system (MEMS) devices. In this paper, we discuss an extensive investigation of Ti∕Au sputtering, with respect to temperature, pressure, and electric power input, followed by rapid thermal annealing (RTA) to improve the adhesion and reflection characteristics of a vertical micromirror. The vertical surface was fabricated by means of the deep reactive ion etching (DRIE) process of a silicon-on-insulator (SOI) wafer, with an 80-μm-thick layer of Si. Then, 20-nm-thick Ti and 200-nm-thick Au films were deposited on the vertical surface as adhesion and reflective layers, respectively, using rf/dc magnetron sputtering. The Au films were deposited at room temperature (20°C) and annealed at 380°C for 30s in a RTA chamber. While taking into consideration the conformability and the reflectance of the Au vertical mirror, the process conditions were optimized at an argon pressure of 10mTorr and an electric power input of 300W. The best surface roughness obtained was 7nm (rms) for a useful upper sidewall with a reflectance of 97.5% in the IR (Infrared) range (1500nm–1600nm).