A study to characterize and optimize the GaAs
etching by Cl
2/Ar electron cyclotron resonance (ECR) plasma is reported. Etching characteristics such as smooth surface morphology and vertical sidewall are the focus of this work. In the first group of experiment (group A), the temperature, process pressure, microwave power, and RF power were varied to observe the etch rate of the GaAs substrate. Though the surface was generally rough, starting condit
ions for the second group of experiments (group B), were inferred from group 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. Crystallographic sidewall profile (orientat
ion-dependent
etching phenomenon) was obtained under condit
ions of <|40|V DC self-bias (75WRF power), 120°C, Cl
2 and Ar total flow rate of 50sccm, 10mTorr pressure and 600W microwave power. The crystallographic sidewall has vertical planes and inward-sloped planes in perpendicular direct
ions. The vertical plane was parallel to (
011) while the inward-sloped plane was originally parallel to (011) before plasma
etching. Vertical sidewall and smooth surface were achieved at a DC bias of |70| V, 120°C, and Cl
2 and Ar flow rates of 10 and 40sccm, respectively, and these were considered as optimized condit
ions under the present circumstances. The root-mean-square (RMS) surface roughness associated with the vertical sidewall profile was 3.6nm, and the etch rate of GaAs was
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40nm/s.