Electron cyclotron resonance reactive ion etching of fine features in HgxCd1−xTe using CH4/H2 plasmas

To date, most dry etching of mercury cadmium telluride (MCT) has involved fabrication of conventional devices, whose minimum feature size is several tens of micrometers. Recent theoretical work has predicted novel effects in nanometer-scale devices making the ability to fabricate nanometer-scale features in narrow band-gap semiconductors such as MCT desirable. As MCT has a very low threshold for damage, realization of either conventional or nanometer size devices requires reduced, controllable ion energies and improved understanding of the etch processes involved. This work presents the results of parametric studies of the etching of MCT using an electron cyclotron resonance (ECR) microwave plasma source and CH4/H2 gas mixtures. The current work is focused on the application of ECR etching for the nanofabrication of MCT. The parameters investigated include % CH4 in H2 (10 to 25); ion energy (0 to 100 eV); pressure (0.10 to 1.0 mTorr), and substrate position with respect to the ECR condition. Optimized process conditions are total gas pressure of 0.50 mTorr, 18% CH4 in H2, ≊−100 V ion energy, and a 32 cm ECR-sample separation. These conditions have produced etch rates of up to 1500 Å/min and etch features with sidewall angles of ≥88°. Feature sizes from 40 nm to 2.0 μm have been investigated.