Accurate screening of defective oxide on SiC using consecutive multiple threshold-voltage measurements

A high rate of early failures in gate oxide is one of the most serious concerns regarding the reliability of silicon carbide metal-oxide-semiconductor field-effect transistors. An intensive screening test using high-voltage gate stress is key to reducing this rate. However, a threshold-voltage (V-TH) shift is a frequent side effect, and the degraded chips need to be eliminated. We propose a screening procedure to detect adverse degradation with improved accuracy. We first analyzed the V-TH hysteresis, which deteriorates the measurement accuracy of V-TH shifts and found that its wide variation is due to several causes. We thus investigated multiple consecutive V-TH measurements to isolate the hysteretic component from data and confirmed that our procedure is highly useful in detecting the adverse V-TH shift. In particular, it can identify a negative V-TH shift hidden by the hysteresis. This procedure is advantageous for negative-voltage screening in which small gate leakage can alter its V-TH.