Phase diagrams for Si:H film growth by plasma-enhanced chemical vapor deposition

Phase diagrams for plasma-enhanced chemical vapor deposition (PECVD) of thin film silicon (Si:H) describe the thicknesses and deposition-parameter values at which different microstructural and phase transitions are detected during film growth, using real time spectroscopic ellipsometry (RTSE) as a probe. In such diagrams, the positions of the transitions are plotted in the plane defined by the Si:H bulk layer thickness (db) and by the value of a key deposition parameter, usually the hydrogen-to-silane dilution ratio R=[H2]/[SiH4]. In this study, phase diagrams of db vs. R are presented for Si:H films prepared under different rf PECVD conditions on crystalline silicon substrates. The variable parameters explored here include the rf plasma power, substrate temperature, and total gas pressure. The presented diagrams provide insights into the film growth processes that yield optimum electronic quality amorphous and microcrystalline Si:H at elevated deposition rates (>0.3 nm/s).