INFLUENCE OF THE GAS-MIXTURE ON THE REACTIVE ION ETCHING OF INP IN CH4-H-2 PLASMAS

The influence of the CH4-H-2 mixture composition on the etching proces s of InP is investigated by means of plasma diagnostics (optical emiss ion spectroscopy and mass spectrometry) and quasi in situ x-ray photoe lectron spectroscopy (XPS) surface analysis. Increasing the mixture co mposition in methane increases the InP etch rate. For example, it rise s from 230 to 380 Angstrom/min when increasing the percentage in CH4 f rom 2.5% to 75%. In pure methane discharge, at a pressure of 50 mTorr, amorphous carbon is deposited on InP. Quasi in situ XPS reveals major changes in the surface chemistry. In particular P depletion decreases and the mean surface stoichiometry improves as the percentage of meth ane increases. The mass spectrometry PH3+ signal (m/e=34 amu) correspo nding to PH3 molecules and the In emission line (lambda=451.1 nm), wh ich are, respectively, characteristic signals of the individual remova l rate of In and P, and the concentration of CH3 radicals in the plasm a as measured by the threshold ionization technique display good agree ment with the etch rate and surface chemical modifications. These resu lts confirm that the etching mechanism of InP is controlled by the etc hing mechanism of In, and that the latter is strongly correlated with the concentration of methane in the mixture. Variable photoelectron em ission angle measurements are performed to determine precisely the loc ation of the species in the damaged layer. A model for the representat ion of the surface in the process of etching is then proposed. (C) 199 7 American Vacuum Society. [S0734-211X(97)02205-1].