Extremely Enhanced Diffusion of Nitrogen in 4H-SiC Observed in Liquid-Nitrogen Immersion Irradiation of Excimer Laser

Abstract

We report nitrogen (N) doping of 4H-SiC by KrF excimer laser irradiation in liquid N2. In comparison to phosphorus (P) doping performed using phosphoric acid solution, the liquid-N2 immersion-laser doping can introduce N atoms deeper (~ 1 μm depth) into the 4H-SiC, which results in reduction of doped layer resistance by approximately 3 orders of magnitude. Doping is shown to proceed by the thermal diffusion of species, while loss of the host material from the surface by ablation takes place at the same time. Chemical analysis shows that high density carbon (C) vacancies are generated in the N doped region, which suggests enhanced diffusion of N assisted by the presence of C vacancies. pn junction diodes are formed by using the N doping technique. Turn-on voltage is ~ -3V, which is reasonable for a pn junction diode of 4H-SiC.

Al Doping from Laser Irradiated Al Film Deposited on 4H-SiC

“…Laser irradiation to SiC immersed in gas containing dopant species has attracted attention as a candidate of selective doping technique [2,3]. On the other hand, we recently reported that P, N, or Al can be doped into 4H-SiC by KrF excimer laser irradiation in phosphoric acid solution, liquid nitrogen, or aluminum chloride solution, respectively [4][5][6]. However, the doping depth of P or Al is limited to be 30~40 nm even with increasing the laser fluence or the shot number.…”