Growth and Nitridation of Silicon-Dioxide Films on Silicon-Carbide
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ABSTRACT Silicon-carbide offers great potential as a wide bandgap semiconductor for electronic applications. A good quality oxide dielectric will allow MOS device fabrication and in particular N-channel mosfets for their higher electron mobility. To date oxides on N-type silicon-carbide (nitrogen doped) have exhibited excellent characteristics while on P-type (aluminium or boron doped) the characteristics are poor. This paper presents results for the oxidation and subsequent nitridation of N and P-type silicon-carbide. It illustrates the role that nitrogen at the interface has in improving the trap densities and that nitric oxide provides the nitrogen well. Nitrous oxide, previously used to nitride silicon dioxide on silicon, is shown to substantially deteriorate the interface density of states for both N and P-type substrates. INTRODUCTION The development of silicon carbide as a semiconductor material may mark the beginning of a new era in high temperature, high power and high frequency electronics. That silicon carbide can be oxidized similarly to silicon is a great advantage over other semiconductor materials with the wide bandgap energy necessary for these applications. Successful growth of high quality silicon dioxide on silicon carbide is crucial for the realization of this new era of SiC metal-oxide-semiconductor (MOS) devices. At present, high quality oxide films can be grown on N-type, but not on P-type SiC[1],[2]. Searching for the solution to this problem, it was initially speculated that the aluminium (used as the P-type dopant in SiC) was adversely affecting the interface. Later, it was shown that boron-doped P-type SiC does not improve the quality of the interface[2], and that aluminium is also present in high-quality oxides grown on N-type SiC[3]. Recently we have presented results which shift the focus from the problem associated with Ptype SiC to the beneficial role of nitrogen which is used as a dopant in N-type SiC and which is known to improve oxide quality in silicon[4],[5]. In this paper we present results for oxidation and subsequent nitridation of SiC using rapid thermal processing. These results show the beneficial effects of NO nitridation of Si0 2 on SiC
as monitored by the high frequency C-V curves of P-type and by the reduction in the density
of fast and slow traps for N-type SiC. Nitridation in N2 0 however was observed to deteriorate the high frequency C-V curves of both P-type and N-type SiC and increase the density of fast and slow traps for N-type SiC. 413
Mat. Res. Soc. Symp. Proc. Vol. 470 01997 Materials Research Society
EXPERIMENTAL DETAILS Si-faced 6H SiC wafers, manufactured by CREE Research, were used in this experiment. The concentration of the nitrogen doped N-type wafer was 4.8x 017cm"3 , while the concentration of the aluminium doped P-type wafer was 2.5x10' 8 cm-3 . The wafers were cut into approximately 1.5xl.5cm pieces and cleaned by both H 2SO 4 :H20 2 solution and RCA cleaning process. Immediately before the oxidation, the samples were dipped in 1% HF for 60sec
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