Methane-hydrogen low energy electron enhanced etching (LE4) of mercury cadmium telluride.

摘要

Low energy electron enhanced etching (LE4) is applied to HgCdTe with methane (CH4) and hydrogen (H2) process gas to eliminate ion-induced surface damage. The LE4 results from photoresist (PR) mesa patterned HgCdTe samples illustrate that LE4 successfully etches patterns into HgCdTe with good anisotropy and smooth surface. The competition between pure LE4 and polymer deposition under LE4 process of HgCdTe is studied in terms of three etch variables: electron energy (sample bias), CH4 concentration (gas composition), and sample temperature.;In order to understand polymer deposition separately from the overall LE4 process, plasma polymerization experiments are performed on a tantalum (Ta) substrate with Ar (90%) and CH4 (10%) dc plasma. The results show reduction in polymer as the electron or ion energy and the substrate temperature increase.;From the study in terms of the three etch variables, reduction in Cd accumulation, smooth surface and minimal polymer are obtained at high electron energy: 30 V dc bias relative to earth (dc bias range: -29--30 V relative to earth) with 0.05% CH4 and sample temperature of room temperature for unpattemed HgCdTe sample. By calculation using Langmuir probe measurement and plasma sheath analysis, the electron energy values are 9-21 eV at bias values of 0, 10, 20, and 30 V relative to earth. The etch yields are 0.01-0.05 atom/electron for those electron energy values.;Smooth surface and minimal polymer are obtained at low CH4 concentration: 0.05%-2% CH4 with various do bias and sample temperature conditions for unpatterned and PR mesa patterned HgCdTe samples. High etch rate and smooth surface are obtained at the sample temperature of 60°C. Thermal desorption of Hg occurs above 60°C in these etching experiments.