Etch-induced damage of HgCdTe caused by inductively coupled plasma etching technique

Abstract

HgCdTe third-generation infrared focal plane arrays such as avalanche photodiodes, two-color detectors and multi-color detectors require isolation of high aspect ratio trenches with admissible etch induced damage at the surface and sidewalls. Dry etch has many advantages compare with wet etch such as high anisotropy, good uniformity and good reproducibility. Inductively coupled plasma (ICP) etching is most widely used for its low etch induced damage which is a new high density plasma technique. It's very important to understand etching mechanisms and reduce etch induced damage for the low damage threshold of HgCdTe which is due to weak Hg-Te bond and low volatility of CdTe component. The main work of this paper is researching the influence of etch induced damage caused by different mask technique using inductively coupled plasma etching instrument with a feasible technics. In this experiment we used two different masks, one only has a film of silicon dioxide which we called thin mask, its thickness is less than one micrometer, and the other is composed of resist and silicon dioxide which we called complex thick mask, its thickness is several micrometers. We tested the current-voltage (I-V) characteristics of a chip which has a special structure achieved by dry etch and about one micrometer wet etch to remove the etch induced damage film. Then we found that in a same condition the I-V characteristics of the chip which used complex thick mask is distinctly better than the chip which used thin mask. Resist and silicon dioxide complex thick mask can effectively reduce etch induced damage. The reasons for this result have two aspects, in one hand, the grown process of silicon dioxide can cause damage of HgCdTe surface, make a thick resist between HgCdTe and silicon dioxide can reduce the damage of HgCdTe surface, in the other hand, complex thick mask can hold up the damage of trench sidewall in etch process.