Wide Bandgap Fluorinated Silicon-Carbide-Nitride Films Using NF₃

Abstract

Amorphous hydrogenated silicon carbide has been studied extensively because of its properties as a wide bandgap material. However, a large amount of methane is needed to deposit the material. Also, the high carbon content of these films poses some problems. The addition of NF₃ to the gas stream results in wide bandgap films with a substantial reduction in the required CH₄ flow for deposition. Amorphous SiC_xN_y:H:F films were prepared using rf glow discharge decomposition of silane, methane, and nitrogen trifluoride in a parallel-plate stainless steel reactor. Gas flow rate and power density were varied. For a gas mixture containing 6% NF₃ and 78% CH₄, FTIR measurements reveal a reduction in C-H peak heights at 2960 cm⁻¹ and 2880 cm⁻¹ with respect to the Si-H peak at 2080 cm⁻¹ indicating a smaller carbon content in the film. The C-H peaks shift to higher wavenumbers with increasing NF₃. The use of NF₃ increases the bandgap from 2.6 to 3.14 eV while reducing the refractive index from 2.12. to 1.87. A maximum deposition rate of 625 Å/min was achieved. This should be compared to the very low deposition rate of 18 Å/min for comparable bandgap Si-C films deposited using 97% methane in silane. Increasing the deposition power density resulted in a larger bandgap and a smaller refractive index.