Development of high temperature diffusion technology for edge termination and switching behavior improvement of silicon carbide p-i-n diodes.

摘要

Due to considerable improvement in the quality of SiC material in recent years, the importance of developing efficient and inexpensive SiC device fabrication routine becomes essential. Doping plays a significant role in any semiconductor device fabrication. Historically, selective doping in SiC is realized by ion implantation. However, ion implantation encounters such problems as surface damage, high sheet resistance and low activation efficiency of impurities. All these drawbacks limit the potential possibilities offered by SiC. On the other hand diffusion in SiC requires extremely high temperatures (>1800°C) and a suitable mask material capable of sustaining such high temperatures. This dissertation presents research work focused on the design of a diffusion routine meeting the critical requirements for implementation of diffusion in SiC.;The high diffusion temperature (up to 2200 °C) was provided by using a double wall water-cooled quartz RF heated furnace. Uniform temperature distribution was achieved by optimization of thermal insulation and crucible design with preliminary simulation using Virtual Reactor (SiC) 4.9 software from Semiconductor Technology Research, Inc. The diffusion mechanism of boron and aluminum in SiC was thoroughly investigated in this work. Selective diffusion in SiC was successfully realized by implementing graphite as the mask material. Also, a thin graphite film was used to prevent the SiC surface from degradation at diffusion temperatures. The graphite capping procedure was also successfully implemented in post ion implantation annealing.;Based on the developed diffusion technology, edge termination for Schottky and PIN diodes was developed and test structures were fabricated. For the first time, PIN diodes utilizing diffused junction termination extension exhibited blocking capabilities close to theoretically possible values. I-V characteristics of the 4H-SiC PIN diodes showed excellent rectification properties with a fairly low forward voltage drop (3.3 V at 100 A/cm2) and high blocking voltage (more than 2500 V).;A fabrication technology of p-i-n diodes with reduced switching losses through the incorporation of deep recombination centers via diffusion of boron was developed. The improvement of reverse recovery characteristic is attributed to the effect of localized lifetime control by recombination centers created by diffused boron. It is demonstrated that p-i-n diodes produced by high temperature diffusion exhibit better switching capability compared to epi-grown p-i-n diodes. The improved behavior is attributed to the reduced lifetime region created by the diffused boron layer.;The good performance of SiC devices fabricated with diffusion implementation confirmed the viability of this process.