Non-Destructive Electro- and Photo-Luminescence Imaging of Dislocations in SiC Epitaxy

Abstract

AbstractElectroluminescence (EL) and photoluminescence (PL) imaging and stressing techniques are presented that are useful characterization tools for SiC epitaxial layers grown for power devices. Both EL and PL techniques are non-destructive, and the PL imaging is non-contact. These features are important for qualifying epitaxial layers before subjecting the layers to the time-consuming and costly process of device fabrication. By imaging at various emission spectral bands, the spectral information are correlated to the geometric features in the images. This correlation enables the differentiation of dissimilar defects having similar geometric shapes. Row average plots of images at various emission spectral bands revealed that threading dislocations (TDs) have strong emission above 900 nm and that basal plane dislocations (BPDs) have a broad spectral emission that are most easily distinguished in the range between 738 nm and 870 nm. The correlation between spectral information and the image features clearly distinguished TDs and BPDs from other defects, such as, organic substance and other surface blemishes. In addition to identifying the defects, understanding their origin can be useful in developing low-defect growth techniques. The defect origination depth is one of the important information for understanding defect origin. Two schemes for determining the defect origination depth are presented. Varying the focus depth by adjusting the objective lens height is a crude but quick scheme. Stressing the epilayer to grow the BPDs till they reach the surface or the epilayer/substrate interface is more time-consuming but more accurate. The scheme of varying the focus was demonstrated using PL imaging on a 50-mm thick n- epilayer with no p+ anode layer. Adjusting the focus on a partial dislocation in the n- epilayer revealed segments of the partial coming more in focus near the epilayer/substrate interface, suggesting the defect origination depth was at or near the interface. The stress and growth scheme was demonstrated on a straight string of half loop defects in a 100-mm thick n- epilayer. During electrical stressing, BPDs emanated from the half loops and eventually propagated to the surface at a lateral distance of 250 mm. With the basal plane at an 8° offcut from the surface, the origin of the BPDs was calculated to be 35 mm below the surface, suggesting the defects to be introduced during the growth process. Either EL or PL technique can be used with any of these two schemes to determine the defect origination depth. However, the PL technique has the benefit that the p+ anode layer and the procedure for forming a metal grid are not required.