A microwave-induced plasma source: Characterization and application for the fast deposition of crystalline silicon films

Abstract

A microwave-induced plasma source is developed and is applied for the fast deposition of crystalline silicon films. In this paper, the plasma source is diagnosed first. Electron density, electron temperature, and discharge gas temperature of the plasmas generated in ambient air are studied using the optical emission spectroscopy method. The electron density is estimated by analyzing the Stark broadening of the hydrogen Hβ emission profile and is found to be as high as >1015 cm−3 over wide conditions. The Boltzmann plot method is used to calculate the electron temperature, which shows a value smaller than 1 eV. Analysis of the rotational structure of OH molecular emission reveals a discharge gas temperature in a range of ∼400–800 °C. Preliminary efforts of using the plasma source for Si film fast deposition are performed at a reduced pressure by using SiCl4 as the source gas. A fast deposition rate of 150 nm/s has been achieved for Si film with a high Raman crystallinity of Ic/Ia>10 even without using substrate heating and under a low H2 dilution condition. Mechanisms for these results are discussed in detail.