The large amounts of methane commonly used to prepare wide-gap a-SiC:H films present a lot of problems. This study was aimed at investigating the properties of fluorinated silicon nitride as an alternative to silicon carbide and to study the thermal stability of the films.
The RF glow discharge of NF3 (an etchant gas) and pure SiH4 produced a-Si:H,N,F films. Films were deposited with a gas ratio of NF3 over (NF3 + SiH4) from 0% to 15%. The substrate temperature, chamber pressure, and power were kept constant; only flow rate was varied. Characterizations of the films included AES, FTIR, visible/UV spectroscopy, dark conductivity, and photoconductivity.
Deposition rate increased about eight times with an addition of 6% NF3. The deposition rate increased from 1.22 A/s to 10.5 A/s. The Tauc optical gap increased from 1.72 eV to about 2.06 eV, suggesting excellent N incorporation. The dark conductivity decreased one order of magnitude while the photoconductivity decreased by as much as five orders of magnitude with ELH light. FTIR spectra showed the nitrogen incorporation. The Si-N bonds replaced the Si-Si bonds with increasing NF3 concentration. Also with increasing NF3 content in the gas phase, the hydrogen concentration in the material decreased and the films became more thermally stable.