A new IR transmission topograph apparatus in which video image contrast is enhanced greatly by digital processing is developed for fast and nondestructive evaluation of GaAs wafers. Clear topographs of IR (1 mgr;m) absorption in 2hyphen;in.hyphen;diam GaAs wafers, resulting from the distribution of the native defect EL2, and birefringence, resulting from residual stress, are obtained with good contrast and high signal/noise ratio.
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