Reaction chemistry and resulting surface structure of HgCdTe etched in CH4/H2 and H2 ECR plasmas

We report on several new aspects of etching of Hg1−xCdxTe (x = 0.22), HgTe, and CdTe in CH4/H2/Ar plasmas generated by an electron cyclotron resonance plasma source. Using a residual gas analyzer, we have identified elemental Hg, TeH2, Te(CH3)2, and Cd(CH3)2 as the primary reaction products escaping from a HgCdTe surface during the plasma exposure. We have also demonstrated that a bias is not needed to etch HgCdTe at moderate temperatures (30-40°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 etching. Moreover, we have examined by x-ray photoelectron spectroscopy analysis and ellipsometry the surface condition of HgCdTe resulting from etching with this technique at zero bias. After exposure to the CH4/H2Ar plasma (or to a H2/Ar plasma only), the HgCdTe samples exhibited a depletion of the HgTe component in the near surface region (increase of the x-value). The depletion covered a range from virtually x = 1 after H2/Ar (10:2 in sccm) etching to values 0.4 < x < 0.5 after CH4/H2Ar (7:7:2 in seem) etching. Exposures to the plasmas were found to result in surface roughening of HgCdTe, however, plasmas rich in H2 were observed to cause significantly rougher surfaces than plasmas with small H2/CH4 ratios. This difference in the resulting surface condition is attributed solely to chemical effects since the respective ion energies are considered to be below the damage threshold for HgCdTe in both cases. We also investigated the etching of HgTe and CdTe single crystals. The etch rate of HgTe was found to be over one order of magnitude 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 depletion of the HgCdTe surface region.

[1]  A. McDaniel,et al.  Coupled gas and surface reactions in the organometallic vapor-phase epitaxy of cadmium telluride , 1992 .

[2]  J. Piotrowski,et al.  Modification of Mercury Cadmium Telluride, Mercury Manganese Tellurium, and Mercury Zinc Telluride by Ion Etching , 1989 .

[3]  W. C. Dautremont-Smith,et al.  Reactive ion etching of InP using CH4/H2 mixtures: Mechanisms of etching and anisotropy , 1989 .

[4]  J. Asmussen.  Electron cyclotron resonance microwave discharges for etching and thin‐film deposition , 1989 .

[5]  E. Finkman,et al.  Ion beam milling effect on electrical properties of Hg1−xCdxTe , 1989 .

[6]  D. Aspnes.  Optical properties of thin films , 1982 .

[7]  H. Wilson,et al.  Stoichiometric dry etching of mercury cadmium telluride using a secondary afterglow reactor , 1989 .

[8]  E. Dobisz,et al.  Electron cyclotron resonance reactive ion etching of fine features in HgxCd1−xTe using CH4/H2 plasmas , 1993 .

[9]  S. P. Beamont,et al.  Reactive ion etching of GaAs using a mixture of methane and hydrogen , 1987 .

[10]  S. J. Pearton,et al.  Plasma etching of III–V semiconductors in CH4/H2/Ar electron cyclotron resonance discharges , 1990 .

[11]  E. Dobisz,et al.  Nanometer scale fabrication in mercury cadmium telluride using methane/hydrogen electron cyclotron resonance microwave plasmas , 1993 .

[12]  K. Lübke,et al.  Dry etching of CdTe/GaAs epilayers using CH4/H2 gas mixtures , 1993 .

[13]  E. Dobisz,et al.  Nanometer fabrication in mercury cadmium telluride by electron cyclotron resonance microwave plasma reactive ion etching , 1993 .

[14]  U. Solzbach,et al.  Sputter cleaning and dry oxidation of CdTe, HgTe, and Hg0.8Cd0.2Te surfaces , 1980 .

[15]  P. Leech,et al.  Novel CH4/H2 metalorganic reactive ion etching of Hg1−xCdxTe , 1991 .

[16]  C. T. Elliott,et al.  Type conversion in CdxHg1-xTe by ion beam treatment , 1987 .

[17]  David R. Rhiger,et al.  Use of ellipsometry to characterize the surface of HgCdTe , 1993 .

[18]  J. Elkind,et al.  Reactive ion etching of HgCdTe with methane and hydrogen , 1992 .

[19]  T. Schimert,et al.  Methyl radical etching of compound semiconductors with a secondary afterglow reactor , 1990 .