In situ spectroscopic ellipsometry studies of electron cyclotron resonance (ECR) plasma etching of oxides of silicon and GaAs

Abstract

In situ spectroscopic ellipsometry (SE) covering the spectral range from 280 to 1000 nm was performed during RF bias assisted electron cyclotron resonance (ECR) etching of SiO 2, GaAs oxide, silicon, and GaAs by a CCl 2F 2/O 2 mixture. The etch rate of SiO 2/Si samples as a function of RF bias power, and total pressure was then measured, in situ, for a constant ECR power of 175 W, and CCl 2F 2/O 2 flow rate ratio of 1 3 by performing SE at selected wavelengths most sensitive to changes in SiO 2 thickness. A wide range of etch parameters can be investigated without changing samples by employing a relatively thick SiO 2 layer. This allows rapid optimization of the etch parameters, and can also provide accurate endpoint detection in the face of a time-dependent etch rate. Ellipsometric monitoring of bulk silicon and GaAs samples cannot provide in situ etch rates, however, insight into the etch mechanism may be gained by observing the effect of the etch process on the native oxide layer, surface roughness, and in the case of GaAs, on the surface stoichiometry.