Characteristics of Polycrystalline beta-SiC Films Deposited by LPCVD with Different Doping Concentration

The physical and electrical properties of polycrystalline beta-SiC were studied according to different nitrogen doping concentration. Nitrogen-doped SiC films were deposited by LPCVD(low pressure chemical vapor deposition) at 900 degrees C and 2 torr using 100 % H2SiCl2 (35 sccm) and 5 % C2H2 in H-2(180 sccm) as the Si and C precursors, and 1 % NH3 in H-2(20 similar to 100 sccm) as the dopant source gas. The resistivity of SiC films decreased from 1.466 Omega.cm with NH3 of 20 sccm to 0.0358 Omega.cm with 100 sccm. The surface roughness and crystalline structure of beta-SiC did not depend upon the dopant concentration. The average surface roughness for each sample 19-21 nm and the average surface grain size is 165 nm. The peaks of SiC(111), SiC(220), SiC(311) and SiC(222) appeared in polycrystalline beta-SiC films deposited on Si/SiO2 substrate in XRD(X-ray diffraction) analysis. Resistance of nitrogen-doped SiC films decreased with increasing temperature. The variation of resistance ratio is much bigger in low doping, but the linearity of temperature dependent resistance variation is better in high doping. In case of SiC films deposited with 20 sccm and 100 sccm of 1 % NH3, the average of TCR(temperature coefficient of resistance) is -3456.1 ppm/degrees C and - 1171.5 ppm/degrees C, respectively.