Experimental Studies On Lapping And Grinding Of CdZnTe Crystal

CdZnTe crystal is the most promising material for the room temperature radiation detector, and it is widely used as a substrate to grow the epitaxial layers of HgCdTe infrared detector focal plane arrays dominating military systems, due to the advantages of infrared transparency and the best lattice matching to the HgCdTe epilayer in comparison with other alternative materials, so it has attracted much attention. Surface quality plays an important role for the preparation of high-resolution HgCdTe and CdZnTe detectors. Microcracks, plastic deformation, dislocation and subsurface damage induced by the machining increase the surface leakage current, obviously decreasing the resolution of the CdZnTe detector. Moreover, all the defects existing on the CdZnTe substrates will transfer to the HgCdTe films grown from their surfaces, resulting in the failure of HgCdTe detectors. Currently, the Processing Technology of CdZnTe crystals usually is lapping-mechanical polishing-etching, but the conventional method is difficult to decrease the surface roughness and get the perfect surface quality. As the CdZnTe single crystal has soft and brittle nature, it brings forward a challenge to the ultra-precision machining field.The CdZnTe wafers are machined by the lapping process of loose abrasives on the ZYP200 lapping machine, the effects of varieties of abrasives, size of abrasives, rotating speed of spindle, lapping pressure and concentration of slurry on the surface quality and removal rate during lapping experiments are analyzed, respectively, and the optimal process parameters are achieved.A physical model, which is based on the tribology principle and hard-brittle material removal mechanism of two-body abrasive and three-body abrasives, is proposed, the removal mechanism and embedded mechanism of soft-brittle crystals during free abrasives lapping is analyzed, and the experimental results are consistent with those of model prediction. Grinding experiments are carried out on a VG 401 II ultra-precision grinding machine, through the effects of different grits of grinding wheel on the surface roughness and removal mechanism are verified, respectively, and the most optimal parameters are obtained during grinding conducted by the orthogonal experiments. The effects of three kind of processing technology on the surface quality of CdZnTe wafers and machining efficiency are analyzed, and the advantages and disadvantages of the processing technology was compared and analyzed.