SXRT Investigations on Electrically Stressed 4H-SiC PiN Diodes for 6.5 kV

Abstract

4H-SiC PiN diodes for 6.5 kV were manufactured on both 4° and 8° off-cut substrates and subjected to an electrical stress test on wafer level and subsequent analysis of structural defects present in the active area of the diodes. For 8° off-cut diodes, the electrical characteristics with respect to leakage current and forward voltage drift are worse than the electrical characteristics of 4° off-cut diodes. Furthermore, a large number of stacking faults was found in 8° off-cut diodes, but little evidence for bipolar degradation was found in 4° off-cut diodes. Therefore, bipolar degradation was significantly reduced by avoiding BPDs in the active area of PiN diodes, i.e. by the use of 4° off-cut substrates. Furthermore, a strong correlation was found between the electrical screening test on wafer level and critical defects.

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

“…Based on experimental and theoretical results from different groups worldwide the off‐cut angle of the vicinal substrates was changed during that time in the whole SiC industry from 8° to 4° because of the related increase of the conversion probability for BPDs into TEDs during the epitaxial growth. As a result, a much higher yield of bipolar devices on a SiC wafer, which do not show degradation of the forward voltage, was achieved …”

Modelling of Effective Minority Carrier Lifetime in 4H-SiC n-Type Epilayers

“…For holes a capture cross section of 2•10 -14 cm -2 is used [8]. The initial excitation profile inside the SiC material is calculated based on Lambert-Beer's law with the absorption coefficient [1,4] and the power density for the UV light source used in the experiment.…”

“…The microwave photoconductivity decay measurement technique by optical UV excitation (µ-PCD) is commonly used to determine the effective minority carrier lifetime (τ eff ) of 4H-SiC epiwafers [1]. This method is applied to evaluate the influence of several epigrowth parameters during process development (e.g.…”

Optical Stressing of 4H-SiC Material and Devices

“…Although great progress has been made in the last decade with regard to the quality, wafer size, availability and price of SiC material, it is still more expensive and more defective than silicon material. Some defects, such as basal plane dislocations (BPDs) and stacking faults (SFs), are known to limit the performance and lifetime of bipolar power devices [1,2]. Apart from immediate failures of the device, these defects can cause a slow degradation of device performance during operation.…”