As a narrow bandgap semiconductor, the preparation of surface passivation layers on HgCdTe film epilayers is essential in the process of device fabrication. Most new infrared detectors use the mesa structure. A stable and reproducible passivation technology which meets the surface uniform cover of the high aspect ratio mesa is particularly important. Atomic layer deposition (ALD) is a new type of accurate surface thin film preparation technique, which has several characteristics such as depositing large-area uniform films, making the film thickness control at nanometer level feasible, and lower deposition temperature. ALD-ZnS film is prepared on the HgCdTe IRFPAs chip at 65°. I-V and R-V curves are similar to that of IRFPAs with CdTe thermal passivation. This shows that ALD ZnS film has a good potential application in the passivation of high aspect ratio mesa-array HgCdTe devices.
HgCdTe is one of the dominating materials for infrared detection. To pattern this material, our group has proven the feasibility of SiO2 as a hard mask in dry etching process. In recent years, the SiO2 mask patterned by plasma with an auto-stopping layer of ZnS sandwiched between HgCdTe and SiO2 has been developed by our group. In this article, we will report the optimization of SiO2 etching on HgCdTe. The etching of SiO2 is very mature nowadays. Multiple etching recipes with deferent gas mixtures can be used. We utilized a recipe containing Ar and CHF3. With strictly controlled photolithography, the high aspect-ratio profile of SiO2 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.
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