SPECTROSCOPIC ELLIPSOMETRIC MONITORING OF ELECTRON-CYCLOTRON-RESONANCE PLASMA-ETCHING OF GAAS AND ALGAAS

In situ real time spectroscopic ellipsometry measurements were made du ring electron cyclotron resonance plasma etching of radio frequency bi ased GaAs and AlGaAs samples. Gas mixtures used were CH4/H-2/Ar, pure H-2, and pure Ar. Ellipsometry provided information about damage to th e surface region and AlGaAs epilayer thickness. For the methane mixtur e GaAs etch, damage appeared in the form of redshifted and broadened E (1) and E(1)+Delta(1) critical point features in a surface layer sever al tens of nm thick. The damage layer began forming within a few secon ds after the start of etching, and stabilized within 1 min. Hydrogen e tching caused a thicker damage layer with greater redshifting and broa dening, while argon caused relatively little damage. Possible mechanis ms for the redshifting are discussed. During etching of an AlGaAs/GaAs heterostructure with the methane mixture, the same redshifting and br oadening effects were seen in the AlGaAs critical point structure. The AlGaAs thickness was determined from the real time data, from which a n etch rate of about 20 nm/min was derived. (C) 1995 American Vacuum S ociety.