Studies On Mesa Formation Of HgCdTe IRFPAs Detectors With Suppressed Damages

HgCdTe is one of the most important materials for fabricating Infrared photovoltaic detectors.Among the crucial techniques for third-generation IRFPAs,the mesa formation with suppressed damage is an indispensable one.The mesa formation technique is widely applied in dual-band arrays,avalanche photo-diodes?APDs?and mesa delineation in advanced detectors.This essay focuses on the fabrication of mask for cryogenic etching,HgCdTe etching process optimization at cryogenic temperature,p-to-n conversion mechanism analysis,healing mechanism and detector verification.Finally,this technique was utilized in the fabrication of 30?m-pitch mid/long wavelength dual-band detectors array.All the work are summarized as follow:1.We have fulfilled the cryogenic etching mask with high selectivity,high aspect ratio and the auto-stopping point.The mask techniques for HgCdTe dry etching were summarized.The superiority of SiO₂ mask and the necessity of dry-etching process to pattern the mask were elaborated.Through careful optimization of the SiO₂ etching process,steep sidewall and clean surface were achieved.The SiO₂/ZnS mask was proposed,and the suto-stopping point of ZnS was proved to be feasible.The degeneration of SiO₂ mask was also discussed.It is believed that this phenomenon is inevitable and is caused by the HgCdTe etching process.It also has strong correlation with the sidewall angle of etched HgCdTe.2.We have accomplished the optimization of HgCdTe cryogenic etching process.The technical qualifications for HgCdTe mesa formation were summarized.The necessity of dry etching technique at cryogenic temperature and the influence of temperature on topography of HgCdTe were discussed.After careful modification of ICP etching parameters,optimized results were achieved.The etched surface and sidewalls were smooth and clean as characterized by SEM.The RMS roughness?Rq?was 1.77 nm as measured by the AFM.The non-uniformity of etch rate in 3-inch was about ±4%.The best aspect ratio is about 1.7.And,it was believed that the deflected ion and radicals lead to the poor aspect-ratio.However,the aspect-ratio doesn't influence the photo absorption of HgCdTe mesa.3.The cryogenic etch-induced damage and the healing process were testified and modelled with diffusion mechanism.Different kinds of etch-induced damages were discussed.The relation between some process parameters and the etch-induced damaged was discussed.It was believed that the gas mixture and material component will influence the conversion depth,while the DC-Bias dose not.Anyway,the conversion depth after cryogenic etching was less than 20 nm as measured with step-etching method.The strong correlation between temperature and etch-induced damage clued that the H radical may have little effect on the conversion.The model of etch conversion was set up based on the diffusion mechanism,leading to a migration energy of 63 meV for etch-induced conversion.The healing process had good stability.The n type carrier shown in the QMSA decreased and disappeared after the healing process.The mechanism of healing process was also discussed,including the diffusion of Hg interstitials and the behavior of Hg vacancy.4.It was verified that the cryogenic etching and annealing process will not influence the detector capability.The R0 A reached 5.5×106???cm2?for mid-wavelength detector.And the photo response showed no difference with the wet etched detector.These processes were also testified by the 30?m-pitch mid/long wavelength dual-band detectors array.The resistance showed acceptable results,proving the feasibility of the cryogenic etching and healing process.Howere,the temperature should be high enough to heal the conversion completely.Some advanced and special techniques were also reported to fabricate the detector on both up and down mesas in the dual-band detector.The focus of optimizations is to improve the uniformity and the operability.