Bipolar Degradation of 6.5 kV SiC pn-Diodes: Result Prediction by Photoluminescence

Abstract

The stability of 6.5 kV pn-diodes is dependent on the absence of critical crystal defects, such as basal plane dislocations. In this paper, we present a method to detect these defects on wafer level by utilizing photoluminescence (PL). The PL scan is performed immediately after epitaxy and also after the implantation process steps with subsequent high temperature annealing. The analysis of both scans enables the prediction of devices that will drift due to bipolar degradation, and devices that will exhibit non-drifting behaviour. To validate this PL scanning technique, forward bias electrical stress tests have been performed on the fabricated 6.5 kV pn-diodes.

Erlangen—An Important Center of Crystal Growth and Epitaxy: Major Scientific Results and Technological Solutions of the Last Four Decades

“…By scanning the substrate directly after the epi‐process with the UVPL scanner it was possible to predict which devices would later drift due to bipolar degradation, and which devices would exhibit reliable behavior. This procedure was validated by forward bias electrical stress tests performed on the fabricated 6.5 kV pn diodes . Nowadays, UVPL augmented by surface imaging has become an indispensable tool for SiC R&D and industrial production.…”

Optical Stressing of 4H-SiC Material and Devices

“…Hence, a non-electric wafer level in-line quality control is required for identifying critical structural defects in wafers, epilayers, and partially processed devices. Photoluminescence (PL) imaging is able to reveal these structural defects in SiC material [3] and devices and to predict the bipolar degradation of pn diodes in an early stage of device production [4]. In this paper we report on an optical stress test which can significantly enhance the BPD and SF identification by UVPL technique on wafer level.…”