Plasma characterization and modelling for c-Si solar cells thin film deposition
In this work, plasmas produced during thin film deposition are characterized. The proposed investigations focused on plasmas constituted by silane (SiH4) and ammonia (NH3) gas mixtures due to their extensive use for the deposition of dielectric layers in particular silicon nitride (SiNx). Moreover, plasma characterization using optical emission spectroscopy (OES) is the focus of this work, due to its fast and non-intrusive nature making it ideal for industrial applications. The novelty of this research lies in the quantitative use of plasma emission to extract important plasma parameters, followed by the utilization of the results for modelling purposes. The investigated plasma parameters are the electron density and the shape of the electron energy distribution. OES-based plasma parameters are used to calculate electron impact dissociation rates for silane and ammonia. Aminosilane species were found to be the most important precursors for silicon nitride growth. The calculated radical densities were used to interpret the experimental SiNx layer compositions. When varying the ammonia-to-silane gas flow, three different plasma regimes were found depending on the main precursor for the layer growth. Moreover, SiNx layer characteristics highly depend on the regime in which it was deposited.