Surface/Subsurface Damage Of The Machined CZT Crystal

Cadmium Zinc Telluride (Cd_1-xZn_xTe, CZT) which is developed from CdTe in the eighty age of the twentieth century is one of the excellent ternary semiconducting compunds of II-IV type. It has two primary applications: the one is the substrate for HgCdTe; the other is the most promising detector material. Currently, the processing technology of CdZnTe crystals usually is internal cutting-lapping-mechanical polishing/CMP. The damages which are induced by these processes will seriously influence the performance of the detector, e.g., increasing the surface leakage current and being the defect resource for the epitaxial growth of HgCdTe. Therefore, the surface/subsurface damages are detected and analyzed to achieve the low damage, high effieciency and ultra-precision machining for CZT crystal.Based on the existed methods for detecting the damage of hard-brittle crystal material, a set of methods suitable for CZT crystal are proposed to meet the different requirements by doing abundant experiments, and the problems of choosing slurry and corrosive liquid are resloved. The micro-hardness and elastic modulus of different crystal planes or different directions on the same plane are measured by nanoindentation, and then anisotropic mechanical property is analyed; the surface quality is measured by equipments, e.g. OLYMPUS optical microscope, SEM and 3D surface profiler; cross section method is used when subsurface damage depth (SSD) is larger and angle polishing method is used when SSD is lower, and then the damages induced by different machining processes are assessed.We obtain the following results through detection and analysis: the CZT crystal shows the obvious anisotropic characteristic on different planes and directions; great improvement has been made on the surface quality with lower Ra and SSD from internal cutting to lapping/grinding and polishing, the patten of material removal is transformed from brittle fracture to plastic deformation; grinding is adopted to replace lapping and mechanical polishing, resolving the problem of embedded abrasive grain, then it can make good preparation for CMP and finally obtain CZT crystal surface with low damage.