An Analysis of Low Frequency Discharge in a CH3SiCl3-Ar-H2 Mixture by Optical Emission Spectroscopy and Actinometry

Abstract

Low frequency (100 kHz) discharge in Ar-H2 and CH3SiCl3-Ar-H2 mixtures was studied to obtain information on the processes involved in plasma deposition of SixCy:H films from CH3SiCl3-Ar-H2 plasma once the properties of Ar-H2 plasma are known. The plasmas were studied using optical emission spectroscopy. The addition of small amounts of nitrogen to the plasma mixtures also permitted the use of an actinometry technique. First, plasma parameters (electron density and temperature) and actinometric concentrations of atomic hydrogen in an argon–hydrogen plasma were investigated as a function of the hydrogen content in the feed. Second, the emission intensities of Si, Si+, CH, H, Ar and Ar+ species produced in the CH3SiCl3-Ar-H2 discharge were analysed as a function of time following the introduction of CH3SiCl3 (methyltrichlorosilane, MTCS) to the argon–hydrogen plasmas with various proportions of the feed gasses. The results reveal a rapid decay of the Si-excited state number density versus time, while those of Si+ and CH fell off more slowly. The emission of atomic silicon was believed to be a result of electron impact dissociative and excitation processes occurring in the bulk of the discharge, whereas the Si+ and CH seemed to originate mainly from products of sputtering of the growing film surface. The fragmentation of the MTCS associated with HCl formation and enhanced atomic hydrogen production as a result of HCl dissociation are proposed. Variations in the radical densities of H and CH3 were determined using an actinometry technique. The results indicate a significant role for H2 in gas-phase reactions occurring in the CH3SiCl3-Ar-H2 plasma, as well as in gas-surface interactions, leading to competition between deposition and chemical sputtering of already deposited material.