Optimization of dry etch process conditions for HgCdTe detector arrays

Abstract

A key technology required for fabricating single and multi-band mesa photodiodes with pixel sizes less than or equal to 25 µm is the development of an anisotropic etch process for HgCdTe. The primary approach investigated for this purpose has been electron cyclotron resonance (ECR) dry etching. This paper reviews an experiment used to optimize the ECR etch process at Lockheed Martin IR Imaging Systems, Inc. and then the use of the process to produce state-of-the-art LW photodiodes. In this work, a Ar:H plasma was used in a Plasma Therm series 700 ECR plasma etcher. Reactor variables were optimized by a designed experiment against the following response parameters: anisotropy, etch uniformity and “damage,” as measured by the photodiode zero bias and reverses bias impedance characteristics. The critical process variables of Ar:H gas pressure, lower magnet current, and electrode height were all optimized. The optimized process parameters were then utilized to fabricate arrays with 80K cut-off wavelengths in excess of 11 µm, R₀As of 29 Ω-cm², Rd_20mV/Rd_0mV>13 and quantum efficiency>71%.