A comparison of free carrier absorption and capacitance voltage methods for interface trap measurements

摘要

This paper aims to establish a new method to characterize the interface between 4H-SiC and passivating dielectric layers. The investigations are made on MOS test structures utilizing AI2O3 and SiCh dielectrics on 4H-SiC. These devices are then exposed to various fluences of Ar~+ implantation and then measured by the new method utilizing optical free carrier absorption (FCA) technique to assess the interface traps. A program has been developed using Matlab to extract surface recombination velocity (SRV) at the oxide/epi-layer interface from the optical data. Capacitance-voltage (CV) is done to extract the density of interface traps (D_(it)) and a comparison was made. It is observed that SiO_2 samples show a large rise of SRVs, from 0.5 ×10~4 cm/s for a reference sample to 8×10~4 cm/s for a fluence of 1×10~(12) cm~(-2), whereas Al_2O_3 samples show more stable SRV, changing from 3×10~4 cm/s for the un-irradiated reference sample to 6×10~4 cm/s for a fluence of 1×10~(12) cm~(-2). A very similar trend is observed for D_(it) values extracted from CV measurements and it can therefore be concluded that the FCA method is a suitable technique for the interface characterization.