Optimization of plasma etching of SiO_2 as hard mask for HgCdTe dry etching

摘要

HgCdTe is one of the dominating materials for infrared detection. To pattern this material, our group has proven the feasibility of SiO_2 as a hard mask in dry etching process. In recent years, the SiO_2 mask patterned by plasma with an auto-stopping layer of ZnS sandwiched between HgCdTe and SiO_2 has been developed by our group. In this article, we will report the optimization of SiO_2 etching on HgCdTe. The etching of SiO_2 is very mature nowadays. Multiple etching recipes with deferent gas mixtures can be used. We utilized a recipe containing Ar and CHF_3. With strictly controlled photolithography, the high aspect-ratio profile of SiO_2 was firstly achieved on GaAs substrate. However, the same recipe could not work well on MCT because of the low thermal conductivity of HgCdTe and CdTe, resulting in overheated and deteriorated photoresist. By decreasing the temperature, the photoresist maintained its good profile. A starting table temperature around -5°C worked well enough. And a steep profile was achieved as checked by the SEM. Further decreasing of temperature introduced profile with beveled corner. The process window of the temperature is around 10°C. Reproducibility and uniformity were also confirmed for this recipe.