Low power density multihole cathode very-high-frequency plasma for mixed phase Si:H thin films

Abstract

A low power density very-high-frequency (VHF) (55 MHz) H₂ plasma in a capacitively coupled multihole-cathode (MHC) geometry is studied using Langmuir probe measurements. Radial profiles show a higher ion density (N_i) and lower electron temperature (T_e) compared to a MHC 13.56 MHz H₂ plasma. The N_i dependence on power indicates an Ohmic plasma, while T_e is essentially constant. The MHC-VHF plasma is used to investigate mixed phase microcrystalline+amorphous (μ c+a-) Si:H thin films at a substrate temperature of 60° C. High-resolution photoemission suggests two types of Si, with concentrations in agreement with atomic force microscopy images showing ~ 510± 40 nm crystallites embedded in a-Si:H matrix. The results show that the low power density MHC-VHF plasma is a high-N_i Ohmic collisional plasma, suitable for low temperature deposition of μc+a-Si:H thin films.