REACTION CHEMISTRY AND RESULTING SURFACE-STRUCTURE OF HGCDTE ETCHED IN CH4 H-2 AND H-2 ECR PLASMAS/

We report on several new aspects of etching of Hg1-xCdxTe (x = 0.22), HgTe, and CdTe in CH4/H-2/Ar plasmas generated by an electron cyclotro n resonance plasma source. Using a residual gas analyzer, we have iden tified elemental Hg, TeH2, Te(CH3)(2), and Cd(CK3)(2) as the primary r eaction products escaping from a HgCdTe surface during the plasma expo sure. We have also demonstrated that a bias is not needed to etch HgCd Te at moderate temperatures (30-40 degrees C), as previously suggested by other researchers. We have also developed a technique that avoids the formation of hydrocarbon polymer films on a HgCdTe sample during e tching. Moreover, we have examined by x-ray photoelectron spectroscopy analysis and ellipsometry the surface condition of HgCdTe resulting f rom etching with this technique at zero bias. After exposure to the CH 4/H-2/Ar plasma (or to a H-2/Ar plasma only), the HgCdTe samples exhib ited a depletion of the HgTe component in the near surface region (inc rease of the x-value). The depletion covered range from virtually x = 1 after H-2/Ar (10:2 in seem) etching to values 0.4 < x < 0.5 after CH 4/H-2/Ar (7:7:2 in seem) etching. Exposures to the plasmas were found to result in surface roughening of HgCdTe, however, plasmas rich in H, were observed to cause significantly rougher surfaces than plasmas wi th small H-2/CH4 ratios. This difference in the resulting surface cond ition is attributed solely to chemical effects since the respective io n energies are considered to be below the damage threshold for HgCdTe in both cases. We also investigated the etching of HgTe and CdTe singl e crystals. The etch rate of HgTe was found to be over one order of ma gnitude higher than that of CdTe under similar conditions. This large difference in etch rates is assumed to be responsible for the observed preferential etching of the HgTe component indicated by the HgTe depl etion of the HgCdTe surface region.