Study of the pixel-pitch reduction for HgCdTe infrared dual-band detectors

Abstract

The third generation of HgCdTe infrared-detector focal-plane arrays (FPAs) should be able to detect simultaneously in two spectral bands. The feasibility of this type of dual-band detectors has already been shown in our laboratory with a pixel size of 50 µm in the 3-5-µm wavelength range. To improve the detector resolution, it is necessary to decrease the pixel pitch. Dry etching is a key process technology to fulfill this goal because of the high aspect-ratio structures needed (typically 10-15-µm deep and 2-5-µm wide trenches). In this paper, we present results of a parametric study on HgCdTe dry etching, as well as results obtained on detector arrays made with the dry-etching technique. The etching study has been done in a microwave plasma reactor with the aim of controlling the surface roughness, the etch rate, and the slope of the trench side. We show how these parameters are influenced by the reactive gasmixture composition (based on CH 4 , H 2 , and Ar) and the substrate self-bias. We show how polymer film deposition can prevent etching from occurring but can improve anisotropy. We show some examples of results obtained when manufacturing the trenches that separate the pixels, keeping a high fill factor, and anisotropic etching. We also show results of the material surface characterizations done with scanning electron microscopy (SEM) and Hall effect measurements. These studies allow us to evaluate and compare the damages done to the HgCdTe surface with different etching conditions. Our best process allows us to make a light electrical damage, confined to less than a micron deep in the material. Using the dry-etching process, we have developed detector arrays fabricated with a pixel pitch as low as 30 µm. We finally present the results of the first electrical characterizations made on these arrays, showing promising results for the development of high-resolution dual-band detectors.

Status of HgCdTe Bicolor and Dual-Band Infrared Focal Arrays at LETI

“…11). Noise measurements on diode test arrays showed that going from a pure wet etch to a dry etch led to a degradation from BLIP detectors to noisy detectors (see Ref.…”

Plasma Passivation Etching for HgCdTe

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] However, ICP plasma processing, used in HgCdTe, is still maturing and continued research is needed. 4,7,14 ICP plasma processing may also be used to replace conventional wet chemical clean-up, and even be used in the surface preparation for epitaxy of II-VI materials.…”

Morphology of Inductively Coupled Plasma Processed HgCdTe Surfaces

“…[1][2][3][4] Several studies have also reported the effect that high-density ''dry'' electron cyclotron resonance (ECR) plasmas have on HgCdTe epitaxial properties. [5][6][7][8][9][10][11][12][13][14] However, ICP plasma processing, for use in HgCdTe, is still maturing and continued research is needed.…”