ELECTRON-CYCLOTRON-RESONANCE ETCHING OF SEMICONDUCTOR STRUCTURES STUDIED BY IN-SITU SPECTROSCOPIC ELLIPSOMETRY

The motivation for this work was to develop in-situ monitoring and con trol of electron cyclotron resonance (ECR) as an anisotropic etch doin g minimal surface damage to electronic materials. We have used a modul ar rotating-analyzer spectroscopic ellipsometer in both the in-situ an d ex-situ modes to investigate etching of Si, SiO2, GaAs and InP, as w ell as GaAs/Al1-xGaxAs/GaAs and InP/In1-xGaxAs heterostructures. Etchi ng was done using a 175 W ECR source with mixtures of CCl2F2 and eithe r oxygen or inert gases in various flow ratios in order to prevent pol ymerization. The experimental variables in these experiments were the gas ratios, gas species, r.f. substrate bias voltage (power) and subst rate temperature. Etching was found to create a thin damage region nea r the surface modeled ellipsometrically as crystalline-plus-amorphous semiconductor in a Bruggeman effective-medium mixture.