Full-wafer spatial mapping of macrodefects on HgCdTe epitaxial wafers grown by MBE

Abstract

We have constructed an optical microscopy system to automatically locate, count, and determine the size of polycrystalline ''void'' defects on epitaxial layers of HgCdTe grown on CdZnTe or Si substrates. Void macrodefects are readily imaged because their polycrystalline surface is rough, and consequently they scatter light out of the image under specular reflection imaging conditions. Using a computer-controlled stage to move the wafer, a succession of individual, contiguous bright-field images is recorded over the entire wafer. Each image is analyzed by software to locate and characterize all the lightscattering objects present in the frame. Several different representations of the spatial distribution and size of defects are generated, and these can be presented either as false-color density maps or dot-location maps. In addition, various types of statistics on the defect population and size distributions are also available. These data not only convey overall information on the quality of a given wafer, and as such are quite useful for screening to determine which wafers are suitable for array fabrication, but they also allow inferences to be made concerning the origin or root cause of different classes of defects. Several examples are presented to illustrate the use of full-wafer defect mapping to identify macrodefect problems in HgCdTe growth on CdZnTe that can arise from substrate temperature lateral nonuniformity, nonmatched source flux angular distributions, substrate contamination, and intrinsic substrate imperfections.

MBE Growth and Transfer of HgCdTe Epitaxial Films from InSb Substrates

“…Full-wafer void defect mapping was performed using an automated optical microscope and custom image analysis software. 8,9 HgCdTe/InSb wafers were annealed in closed ampoules under Hg-saturated conditions, and secondary-ion mass spectrometry (SIMS) depth profiling was performed to assess In diffusion. A commercial wafer bonder was employed to bond HgCdTe/InSb heteroepitaxial device wafers to Si substrates using an adhesive bonding approach.…”

“…The defects observed appear to be randomly distributed across the substrate in all cases, with no aggregation of defects into lines or large clusters, which commonly occur with HgCdTe growth on CdZnTe substrates and are thought to be associated with aligned Te precipitates, deep damage from substrate polishing or extremely large Te precipitates in the substrate. 8,9 This extremely low residual density of void defects and complete absence of large void clusters for HgCdTe growth on InSb is anticipated to significantly improve FPA operability due to the elimination of pixel outages associated with void defect clusters.…”

Improved Defect and Fourier Transform Infrared Spectroscopy Analysis for Prediction of Yield for HgCdTe Multilayer Heterostructures

“…This work follows directly that of Roth et al, where all MCT macrodefects on the wafer were mapped and characterized. 15 These two techniques, FTIR and defect inspection, form a composite yield for any given wafer. The FTIR analysis tells us what percentage of the wafer will pass the detector response cutoff and thickness specifications, while the defect inspection provides defect yield information.…”