The optical beam induced current (OBIC) technique allows a direct imaging of high voltage PN junctions at a microscopic level under reverse operating conditions by measuring the local variation of the photocurrent. In this paper we focus on the application of the UV-OBIC technique for failure analysis of 4H SiC high voltage P+N diodes.
4H SiC P+N diodes with a 2-zone junction termination extension were used. The diodes were characterized in terms of reverse leakage current and breakdown voltage. Various devices were chosen for failure analysis on the base of early breakdown and/or excessive leakage current for OBIC measurements to study extrinsic failures. As a reference we selected diodes that blocked more than 2 kV with a leakage current density of typically less than 0.1 μA/cm2.
OBIC measurements have been used to detect failures in devices that manifest themselves as peaks or “hot spots” in the photocurrent distribution. Early breakdown of diodes could be attributed to formation of hot spots in the periphery of the diodes. The appearance of a hot spot preceded any noticeable increase in reverse leakage current and is thus a very sensitive tool to identify defective diodes already at low voltage levels.
The photocurrent generated by illumination of hot spots has been measured as a function of reverse bias voltage and the current multiplication factor has been determined.