A study of electrical properties and microstructure of nitrogen-doped poly-SiC films deposited by LPCVD

Abstract

The electrical properties and microstructure of polycrystalline 3C-SiC (poly-SiC) films were studied for different nitrogen doping concentrations. Nitrogen-doped poly-SiC films were deposited by LPCVD (low pressure chemical vapor deposition) at 900 °C and 2 Torr using 100% SiH 2Cl 2 (35 sccm) and 5% C 2H 2 (180 sccm) as the Si and C precursor gases, and 1% NH 3 (20–100 sccm) as the dopant source gas. The resistivity of the poly-SiC films at 30 °C decreased from 1.466 Ω cm to 0.036 Ω cm as the flow of NH 3 dopant source gas increased from 20 sccm to 100 sccm. The surface roughness and crystalline structure of the poly-SiC films did not depend on the dopant concentration. The average surface roughness was 19–21 nm, and the average surface grain size was 165 nm. In XRD spectra, poly-SiC is so highly oriented along the (1 1 1) plane at 2 θ = 35.7° that other peaks corresponding to SiC orientations are not presented. Resistance and temperature coefficient of resistance (TCR) measurements were carried out in the 30–450 °C temperature range. While the resistance decreased with increasing measurement temperature, the magnitude of the resistance change was much larger in the films with lower doping concentration. On the other hand, the linearity of resistance variation was better in the films with higher doping concentration. In case of poly-SiC films deposited with 20 sccm and 100 sccm 1% NH 3, the average TCR is −2050.3 ppm/°C and −1957.0 ppm/°C, respectively.