Combination of plasma diagnostics and modelling for the investigation of microcrystalline silicon deposition process

In this work is presented a study of the microcrystalline silicon PECVD process using highly diluted silane in hydrogen discharges. The investigation is performed by applying various non-intrusive plasma diagnostics (electrical, optical, mass spectrometric and laser interferometric measurements). Each of these measurements is related to different plasma sub-processes and all of them compose an almost complete set for the investigation of the effect of external discharge parameters on the deposition process. Thus, based on these measurements, a mass transfer model of SiH₄/H₂ discharges that involves gas phase chemistry and plasma surface interaction is used, aiming at the optimization of the deposition rate of μc-Si:H as well as the prediction of the main film precursors at conditions of low and high deposition rates. In this way, the main characteristics of the effect of frequency, discharge geometry, power consumption and total gas pressure on the deposition process are studied. The increase of silane dissociation rate towards neutral radicals (frequency), the contribution of highly sticking radicals (discharge geometry) and the controlled production of higher radicals through secondary gas phase reactions (gas pressure), are presented as prerequisites for the achievement of high deposition rates (> 5Å/sec).