Analysis of optical emissions produced by controlled electron impact on Si-organic molecules

Si-organic compounds are used in a variety of plasma-assisted film deposition applications and in plasma polymerization processes. Tetraethoxysilane (TEOS), tetramethyl-silane (TMS), and hexamethyldisiloxane (HMDSO) are common constituents of technological processing plasmas. Mass spectrometry, laser-induced fluorescence techniques and optical emission spectroscopy are the most widely used diagnostics techniques for such plasmas. Optical methods require a detailed knowledge of the interaction of the parent molecule with electrons. While there is a limited data base of ionization and dissociative ionization cross sections for TMS, HMDSO, and TEOS, there have been no studies of the dissociative excitation of these molecules by controlled electron impact under single collision conditions with the exception of some earlier work for TEOS which was limited to the visible region of the optical spectrum. Energetic vacuum ultraviolet (VUV) photons, on the other hand, can cause serious damage of the processed surface. A knowledge of the electron-impact induced production of VUV photons can be an important factor in damage and quality control issues of the deposited materials. This paper reports the results of a detailed analysis of the optical emission spectra from the VUV to the near-infrared (50-800 nm) produced by electron impact on TEOS, HMDSO, and TMS under controlled single collision conditions