(A) study on lateral surface treatment of CdTe X-ray image sensor

Abstract

In this study, the effect of lateral surface treatment of Cadmium Telluride (CdTe) X-ray image sensor has been investigated. Because of non-uniform edge pixels in CdTe X-ray sensor, the effective pixels which can be used for final image are reduced, and a line defect is introduced when several sensors are butted together for target resolution. The rough lateral surface after dicing process has many defects and these defects affect the surface leakage and electric field in CdTe sensor. An ATLAS simulation shows the increase of surface leakage and electric field distortion due to high trap density on lateral surface. In order to reduce roughness of lateral surface, polishing process under $40\mu m$ depth is introduced. The polishing process reduces dead pixels by 76% from 304 to 76. Almost dead pixels near device edge, polished lateral surface side, are turn into normal pixels. In order to reduce surface leakage current, 100nm $SiO_2$ is deposited on lateral surface. A passivation layer with $SiO_2$ is deposited by e-beam evaporation method. The output level of edge pixels near the passivation layer are settled down to that of inner pixels. Bad pixels reduce 47% from 287 to 150. The non-uniform edge pixels are improved by lateral surface treatment without affecting inner pixels of CdTe X-ray image sensor. The effective resolution is extended thus the whole area of CdTe X-ray sensor can be used for final image.