EX-SITU VARIABLE-ANGLE SPECTROSCOPIC ELLIPSOMETRY STUDIES OF ELECTRON-CYCLOTRON-RESONANCE ETCHING OF HG1-XCDXTE

The development of low damage anisotropic etching is important for the fabrication of mercury cadmium telluride (Hg1-xCdxTe) based IR device s. Typical methane-hydrogen chemistries have been shown to etch Hg1-xC dxTe causing changes in the surface composition and roughness. To inve stigate these changes, Hg1-xCdxTe samples with (111) A and (111) B ori entations were systematically etched in hydrogen and methane mixtures, with 0%, 5%, 10%, and 20% methane in hydrogen using an electron cyclo tron resonance plasma etching tool. Results were compared with reactiv e ion etched samples. Ellipsometry, atomic force microscopy (AFM) and scatterometry show that as etching proceeds there is considerable surf ace roughening. Quantitative measurements of roughness as measured by the three techniques reveal that etching causes vertical roughening be tween 2 nm and 20 nm. AFM measurements correlated well with scatterome try measurements. Ellipsometry measurements only weakly correlated wit h the other techniques owing to the sensitivity of ellipsometry to rou ghness features less than the wavelength of light as analyzed using ef fective medium theory. Ellipsometry results show that etching changes the surface alloy composition as well as roughness, and in several cas es resulted in apparent vertical grading of composition. The addition of a few per cent methane in hydrogen reduced surface roughness.