Silane versus silicon tetrafluoride in the growth of microcrystalline silicon films by standard radio frequency glow discharge

Properties of microcrystalline silicon (μc-Si) films produced by standard radio frequency glow discharge from SiH₄ or SiF₄ precursors were studied. Spectroscopic ellipsometry (SE), Raman spectroscopy and time resolved microwave conductivity (TRMC) were used for their characterisation. Although modelling of SE spectra shows that μc-Si films with crystalline fractions up to 100% can be deposited from both types of precursors, we have found that SiF₄ allows obtaining films with improved electronic properties. A detailed analysis of the SE data reveals that such improvement relates to the larger grain size for films deposited from SiF₄ in comparison with the ones deposited from SiH₄. Interestingly, the deposition rate, the fraction of large grains, and the mobility of carriers for the films grown from SiF₄ display close dependencies on the product of pressure and inter-electrode distance. These results are discussed with respect to the contribution of the plasma-synthesised nanocrystals to deposition.