Correlation between morphological defects, electron beam-induced current imaging, and the electrical properties of 4H–SiC Schottky diodes

Abstract

Defects in SiC degrade the electrical properties and yield of devices made from this material. This article examines morphological defects in 4H–SiC and defects visible in electron beam-induced current (EBIC) images and their effects on the electrical characteristics of Schottky diodes. Optical Nomarski microscopy and atomic force microscopy were used to observe the morphological defects, which are classified into 26 types based on appearance alone. Forward and reverse current–voltage characteristics were used to extract barrier heights, ideality factors, and breakdown voltages. Barrier heights decrease about linearly with increasing ideality factor, which is explained by discrete patches of low barrier height within the main contact. Barrier height, ideality, and breakdown voltage all degrade with increasing device diameter, suggesting that discrete defects are responsible. Electroluminescence was observed under reverse bias from microplasmas associated with defects containing micropipes. EBIC measurements reveal several types of features corresponding to recombination centers. The density of dark spots observed by EBIC correlates strongly with ideality factor and barrier height. Most morphological defects do not affect the reverse characteristics when no micropipes are present, but lower the barrier height and worsen the ideality factor. However, certain multiple-tailed defects, irregularly shaped defects and triangular defects with 3C inclusions substantially degrade both breakdown voltage and barrier height, and account for most of the bad devices that do not contain micropipes. Micropipes in these wafers are also frequently found to be of Type II, which do not run parallel to the c axis.

Characterization of Defects Evolution in Bulk SiC by Synchrotron X-Ray Imaging

“…MPs appear as line segments, of which lengths are dependent on the wafer thickness, the miscut angle, and the sample tilting relative to the beam. The MPs run in different directions instead of lying parallel to the growth direction, similar to the observation described in an earlier paper [32]. In fact, the majority of MPs deviated from the growth direction and inclined toward one another or other defects in all six wafers studied.…”

Carbon Nanotube Array Thermal Interfaces for High-Temperature Silicon Carbide Devices

“…When defects are present, breakdown of a device is often accelerated. Recent published results examining how SiC Schottky Barrier diodes (SBD) are influenced by defects have demonstrated that forward and reverse characteristics are sensitive to essentially any defect within the active region of the device [1][2][3][4]. Defects that are known to degrade diode characteristics include micropipes, comets, carrots, inclusions, small-angle boundaries, and screw dislocations.…”

Development of Process Technologies for High-Performance MOS-Based SiC Power Switching Devices

“…EBIC has been used to measure minority carrier diffusion length in both 4H-and 6H-SiC [91,92]. It also has been used to characterize electrical active surface defect in 4H-SiC diodes [93,94].…”