Improvement of nitrogen incorporation into oxynitrides on 4H-SiC(0 0 0 1)

Thin films of oxynitrides are grown on 4H-SiC(0 0 0 1) surfaces to prepare these surfaces for further growth of gate dielectric layers. Our former investigation indicated two major problems by thermal treatment in N2O gas. First: even under optimised preparation conditions the nitrogen incorporation is very low (at the best around 7 at.%). And second: the preparation condition optimised for nitrogen incorporation (high temperature and low N2O pressure) leads to very thin layers (in the order of 1–2 monolayers only) and to graphite formation.Here we report on a surface pre-treatment to overcome these problems. The pre-treatment consists of the evaporation of Si onto the oxidised SiC surface. On the one hand the additional Si prevents the formation of the graphite by compensation of the loss of Si due to SiC decomposition and Si evaporation. On the other hand the excess Si improves the incorporation of N by acting as a sacrificial layer for the growth of oxynitride. Thereby the same high amount of N can be incorporated like observed on Si wafers (see P. Hoffmann et al., J. Non-Cryst. Solids 303 (2002) 6).The as prepared SiC surfaces and oxynitride layers were investigated by photoelectron spectroscopy to examine the chemical composition of both, the SiC surface (graphite formation) and the oxynitride layer (nitrogen incorporation).