Wenting Yin

Fabrication and evaulation of the CdZnTe microlens arrays

This paper presents a modified thermal reflow process to fabricate CdZnTe (CZT) microlens arrays and a new convenient method to evaluate the quality of the microlens. In the fabrication experiment, square photoresist (PR) isolated-islands with almost zero gap each other were formed on a CdZnTe substrate by the underexposure photolithographic process firstly. Then, high fill-factor (almost 100 %) PR microlens arrays were generated via thermal reflow the islands at 110 °C for 30 minutes. Finally, through etching the substrate using the PR microlens arrays as the mask by an inductively coupled plasma (ICP) dry etching process with Ar/N2/CH4 gas, the high fill-factor CdZnTe microlens arrays were achieved. Besides, a new convenient method to evaluate the quality of the microlens was also established in this paper. At the first step of the evaluation, the data of surface topography of the microlens fabricated was recorded by the confocal scanning laser microscope (CSLM). Then, the characteristic of the microlens such as the surface topography, focusing properties, the light intensity distribution of the microlens, etc. was simulated and displayed by the procedure base on the CZT optical parameters and the data of the actual surface topography of the microlens. The results show that the microlens fabricated by the modified thermal reflow process can focus 80 % incident light of the pixel on the 30 % central region, with only 1.6 % optical crosstalk.

Studies on a novel mask technique with high selectivity and aspect-ratio patterns for HgCdTe trenches ICP etching

A novel mask technique, combining high selectivity silicon dioxide patterns over high aspect-ratio photoresist (PR) patterns has been exploited to perform mesa etching for device delineation and electrical isolation of HgCdTe third-generation infrared focal plane arrays (IRFPAs). High-density silicon dioxide film covering high aspect-ratio PR patterns was deposited at the temperature of 80°C and silicon dioxide film patterns over high aspect-ratio PR patterns of HgCdTe etching samples was developed by standard photolithography and wet chemical etch. Scanning electron microscopy (SEM) shows that the surfaces of inductively coupled plasma (ICP) etched samples are quite clean and smooth. The etching selectivity between the novel mask and HgCdTe of the samples is increased to above 32: 1 while the side-wall impact of etching plasma is suppressed by the high aspect ratio patterns. These results show that the combined patterning of silicon dioxide film and thick PR film is a readily available and promising masking technique for HgCdTe mesa etching.

N2 atmosphere annealing effect on HgCdTe electrical damage induced by ICP etching process

N2 atmosphere annealing process to recover ICP etching induced damage on p type mercury vacancy HgCdTe film has been exploited in this paper. ICP etching and N2 atmosphere annealing processes were carried out on a series of Hgvacancy-doping p-type HgCdTe samples. The carrier transport and lifetime properties of these samples were characterized by Hall measurement and microwave reflectance method respectively. P-to-n electrical damage of the surface HgCdTe film induced by the ICP etching process was deduced from the polarity inversion of Hall coefficient. The carrier transport and lifetime properties were similar to those of the non-etched samples, indicating that the surface HgCdTe electrical damage was recovered partially by annealing at 210°C for 2 hours. I-V and R-V characteristics curves of photodiodes fabricated on the etched and N2 atmosphere annealing processed MCT samples were also comparable to those of photodiodes on the non-etched MCT samples in the following experiments. These results show that N2 atmosphere annealing process is a readily available and promising recovering technique for HgCdTe ICP etching induced damage.

Spray coater technology in HgCdTe third-generation infrared focal plane arrays

HgCdTe third-generation infrared focal plane arrays such as avalanche photodiodes, two-color detectors and multi-color detectors usually have mesa microstructures, which bring on huge challenge in device technology, especially coating resist process and exposing process. Using conventional spinning coater technology, the thickness of different position in the structure usually is incoordinate, the resist in the bottom of trench is often very thick, but the resist on the top corner of trench is often very thin, sometimes may be nothing. Spray coater technology is a new resist coating technology, which can make the resist equably distribute. The equipment we used is spin module Delta Alta Spray coater (AK 995023) produced by Suss Micro Tec. Through adjusting the parameters of the equipment, such as flux of resist, flux of nitrogen, chuck temperature, arm speed, scan times and so on, we have obtained multifarious resist figure with diverse thickness in order to satisfy different requirements. Now, we have already experimented three different mesa microstructures, the resist thickness we have obtained can change from zero point five micrometer to five micrometers. The pictures gained by scanning electronic microscope show that the resist have good uniformity, which increase the maneuverability of exposure process which we will do next.