Whole-wafer mapping of dislocations in 4H-SiC epitaxy

A non-destructive technique to image the dislocations and other extended defects in SiC epitaxial layers has been developed. Basal plane dislocations (BPDs) and threading dislocations (TDs) are imaged. Photo luminescence from the dislocations is excited with the 364 and/or 351 nm lines of an argon ion laser and near-infrared light is collected. A computer controlled probe station takes multiple images and the mm-sized images are stitched together to form whole-wafer maps. The technique is applied to a set of four n(+) wafers from the same boule with 50 um n(-) epitaxial layers. The epitaxy was grown with Cree's low-BPD process. BPDs form as either single, isolated dislocations or as clusters encircling micropipes. The concentration of TDs is on the order 10(4)/cm2 and the local concentration varies more than an order of magnitude. The advantages of mapping dislocations by UV-PL imaging compared to other techniques are discussed.