Remotely induced high-density hollow-anode plasma and its application to fast deposition of photosensitive microcrystalline silicon thin film with preferential <110> orientation

Abstract

We investigated the application of a less hydrogen-dilute and low gas pressure hollow-anode plasma to fast chemical-vapor deposition of photosensitive hydrogenated microcrystalline silicon (μc-Si:H). The hollow-anode plasma was remotely induced at a processing space by transferring a hollow-cathode plasma through a nozzle attached to a partition plate, which operated as an anode and separated the processing space from a hollow-cathode discharge space in an ultrahigh-vacuum hollow-electrode-enhanced glow-plasma transportation (HEEPT) system. The hollow-cathode plasma was excited by applying a very-high-frequency (VHF, 105 MHz) power to a cathode in the hollow-cathode discharge space. Through the use of this hollow-anode plasma under a gas flow rate ratio ([H2]/[SiH4]) of 1.25 (30 sccm/24 sccm), pressure of 80 Pa, and VHF power of 150 W (the highest power tested in this work), we fabricated a well-crystallized and photosensitive μc-Si:H thin film with a highly preferred crystal orientation along the direction at a growth rate of 13 nm/s. Electrical analysis on the self-bias voltage of the cathode (Vdc) revealed that hollow-cathode discharges in the HEEPT system were approximately equivalent to symmetric discharge, i.e., Vdc ≒ 0 V. Optical analysis indicated that the hollow-anode plasma produced an enough amount of atomic hydrogen to grow well-crystallized μc-Si:H thin films, even at the lowest [H2]/[SiH4] ratio (1.25). Optical and electrical analyses and computational plasma simulation demonstrated that the hollow-anode plasma had a lower electron temperature and higher plasma space potential compared with those features of a glow discharge plasma enhanced by a conventional parallel-electrodes system.