Optimization of GaAs ECR etching in chemically assisted ion beam process using Cl-2/Ar plasma

A study to characterize and optimize the GaAs etching by Cl-2/Ar electron c yclotron resonance (ECR) plasma is reported. Etching characteristics such a s smooth surface morphology and vertical sidewall are the focus of this wor k. In the first group of experiment (group A), the temperature, process pre ssure, microwave power, and RF power were varied to observe the etch rate o f the GaAs substrate. Though the surface was generally rough, starting cond itions for the second group of experiments (group B), were inferred from gr oup A experiments. In group B experiments, the DC self-bias (produced from the RF power) and the Cl-2 as well as Ar flow rates were varied. Crystallog raphic sidewall profile (orientation-dependent etching phenomenon) was obta ined under conditions of < \40\ V DC self-bias (75 W RF power), 120<degrees >C, Cl-2 and Ar total flow rate of 50 sccm, 10 mTorr pressure and 600 W mic rowave power. The crystallographic sidewall has vertical planes and inward- sloped planes in perpendicular directions. The vertical plane was parallel to (0 1 (1) over bar) while the inward-sloped plane was originally parallel to (0 1 1) before plasma etching. Vertical sidewall and smooth surface wer e achieved at a DC bias of \70\ V, 120 degreesC, and Cl-2 and Ar flow rates of 10 and 40 seem, respectively, and these were considered as optimized co nditions under the present circumstances. The root-mean-square (RMS) surfac e roughness associated with the vertical sidewall profile was 3.6 nm, and t he etch rate of GaAs was similar to 40 nm/s. (C) 2000 Elsevier Science Ltd. All rights reserved.