COMPARISON OF CH4/H2/AR REACTIVE ION ETCHING AND ELECTRON-CYCLOTRON RESONANCE PLASMA-ETCHING OF IN-BASED III-V ALLOYS

An electron cyclotron resonance plasma etching system with the capability of additionally radio-frequency biasing the substrate has been used to study the etching characteristics of InP, InAs, InSb, InGaAs, and AlInAs in CH4/H-2-based discharges. The etch rates of these materials increase linearly with rf power and retain smooth surface morphologies for microwave powers below 150 W. At higher microwave powers the surface becomes rough due to preferential removal of the group V species. The quality of Au Schottky diode contacts on InP degrades for high-bias etching, but the addition of PCl3 to the discharge retards this degradation by providing an overpressure of P. The room temperature photoluminescence intensity of InP is also preserved by this PCl3 addition. We obtained highly anisotropic etching of all five semiconductors over the whole pressure range investigated (1-20 mTorr). Low-bias (25-100 V) etching occurs with rates in the range 10-140 angstrom min-1, dependent on the particular semiconductor (InP is the fastest and AlInAs the slowest). Etch rates up to 500 angstrom min-1 are obtained for high-bias (less-than-or-equal-to 1000 V) conditions. The use of CH3Cl in preference to CH4 in order to increase the etch rate of InGaAs and AlInAs was investigated; this appears to have few advantages since the etch rates are comparable to those with CH4/H-2. The degree of polymer deposition during CH4/H-2/Ar etching on the type of mask used (photoresist, W, or SiO2) was also studied-for short duration or low-bias etches any of these masks perform adequately, but SiO2 is a superior choice under all other conditions. Finally, the uniformity of etch depth for ECR plasma etching of 2 in. diam InP substrates was found to +/- 3.0% over the whole wafer and +/- 2.4% over a randomly chosen 1600 x 1600-mu-m2 area.