Spectroscopic ellipsometric monitoring of electron cyclotron resonance plasma etching of GaAs and AlGaAs

Authors

Paul G. Snyder, University of Nebraska-LincolnFollow
Natale J. Ianno, University of Nebraska-LincolnFollow
B. Wigert, University of Nebraska-Lincoln
S. Pittal, J. A. Woollam Co., Lincoln, Nebraska
B. Johs, J. A. Woollam Co., Lincoln, Nebraska
John A. Woollam, University of Nebraska-LincolnFollow

Date of this Version

11-1-1995

Comments

Published in J. Vac. Sci. Technol. B 13(6), Nov/Dec 1995. ©1995 American Vacuum Society. Used by permission.

Abstract

In situ real time spectroscopic ellipsometry measurements were made during electron cyclotron resonance plasma etching of radio frequency biased GaAs and AlGaAs samples. Gas mixtures used were CH₄/H₂/Ar, pure H₂ , and pure Ar. Ellipsometry provided information about damage to the surface region and AlGaAs epilayer thickness. For the methane mixture GaAs etch, damage appeared in the form of redshifted and broadened E₁ and E₁+ Δ₁ critical point features in a surface layer several tens of nm thick. The damage layer began forming within a few seconds after the start of etching, and stabilized within 1 min. Hydrogen etching caused a thicker damage layer with greater redshifting and broadening, while argon caused relatively little damage. Possible mechanisms for the redshifting are discussed. During etching of an AlGaAs/GaAs heterostructure with the methane mixture, the same redshifting and broadening effects were seen in the AlGaAs critical point structure. The AlGaAs thickness was determined from the real time data, from which an etch rate of about 20 nm/min was derived.