Optimized hydrogen concentration within a remotely induced hollow-anode plasma for fast chemical-vapor-deposition of photosensitive and -preferential microcrystalline silicon thin-films

Abstract

The chemical-vapor-deposition of photosensitive hydrogenated-microcrystalline-silicon (µc-Si:H) thin films with <110>-preferential orientation was optimized by altering the concentration of hydrogen within a high-density hollow-anode plasma. The µc-Si:H thin films were grown using a ratio of hydrogen (H2) to monosilane (SiH4) in the range of 1.25 ≤ [H2]/[SiH4] ≤ 35, with a gas pressure of 80 Pa. The high-density hollow-anode plasma was excited remotely in a processing space by transferring a hollow-cathode plasma via a nozzle on a partition plate, which separated the processing space from a hollow-cathode discharge space and served as an anode in an ultra-high vacuum hollow-electrode-enhanced glow-plasma transportation (HEEPT) system. The hollow-cathode plasma was excited by applying very-high-frequency (VHF, 105 MHz) power to a cathode in the hollow-cathode discharge space. The growth rate, crystalline volume fraction, and <110>-preferential crystal orientation of the films exhibited almost linear correlations with the ratio of the optical emission intensities of hydrogen atoms (Hα: 656 nm) and monosilane radicals (SiH*: 414 nm) (i.e. HαI/SiH*I). Reducing the [H2]/[SiH4] ratio by decreasing [H2] improved the growth rate, crystalline volume fraction, and <110>-preferential crystal orientation of the films. These results indicated that lower concentration of H2 was optimal for the fast deposition of photosensitive µc-Si:H thin-films with <110>-preferential crystal orientation using the HEEPT system. The <110>-preferential crystal orientation was less dependent on the VHF power, whereas the growth rate and crystalline volume fraction increased as the VHF power was increased. This result suggested that there would be a room for faster growth with retaining <110>-preferential crystal orientation.