Thermal Annealing Study of Variable Band-Gap a-SiN:H Alloy Films

ABSTRACTA study of the effects of thermal annealing on the bond structure, optical properties, morphology and stoichiometry of variable band gap a-SixNyHz alloy films deposited by ArF LCVD has been made. These films were generated through two different photochemical pathways resulting from the use of either SiH4/NH3 or Si2H6/NH3 as precursor gases. Thermal annealing study of these films which span a wide compositional (0.22 < x/y < 1.44) and band-gap (Eg) range (1.7–5.2 eV) has led to the analysis of the stability of different bond configurations. We report here hydrogen bond stability and rearrangement of the near-neighbor environment of SiN bonds analyzed through FTIR, refractive index variations measured by ellipsometry and surface morphological changes observed through AFM during to the process of annealing. Results indicate that in the SiH4/NH3 deposited nitrogen-rich SiN:H films, SiHn bonds persist even upto 900°C and SiH bonds are less thermally stable than SiH2. Also, while the total bonded hydrogen decreases, the extent of SiN bond increases through a reaction mechanism involving: SiH + NH → SiN + H2. In the Si2H6/NH3 deposited silicon-rich film, whose initial spectra shows Si-H stretching and Si-H wagging bands, a rapid loss of Si-H bonds occurs at T ≤ 650°C. Based on the bond configurational interpretations of the Random bonding model proposed by Bustarret, we calculate the variations in film stoichiometry and density with the annealing temperature.