Growth of Mixed-Phase Amorphous and Ultra Nanocrystalline Silicon Thin Films in the Low Pressure Regime by a VHF PECVD Process

A mixed-phase of amorphous (a-Si:H) and ultra nanocrystalline silicon thin films (ultra nc-Si:H) were grown in a low deposition pressure regime (0.10–0.62 Torr) using a very high frequency (60 MHz) plasma enhanced chemical vapor deposition (VHF PECVD) technique. The deposition rate, stress, hydrogen configuration and morphology varying with the deposition pressure were systematically studied. The maximum deposition rate was found to be 8.3 Å/s at a pressure of 0.47 Torr. The stress of these films decreases from 669.7 MPa to 285 MPa with the increase of deposition pressure from 0.10 to 0.62 Torr. The change in deposition pressure showed the variation of the microstructure and hydrogen bonding configuration of the nc-Si:H films. The ultra small crystallites (size ~ 2 nm) were formed in the films which were confirmed by the X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) measurements. An attempt was made to understand their growth by analysis of the bonding environment.