Plasma characterization of oxygen-tetramethylsilane mixtures for the plasma-enhanced CVD of SiOxCyHz thin films

The plasma-enhanced (PE)CVD of SiOxCyHz thin films from O-2/Ar/tetramethylsilane (TMS) mixtures, in a low-pressure microwave electron cyclotron resonant (ECR) plasma reactor, has been studied. The discharge has been analyzed by mass spectrometry (MS) and optical emission spectroscopy (OES) for varying amounts of oxygen in the gas mixture both in the presence and in the absence of argon. The films obtained have been characterized by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). It is found that the electron impact of the TMS molecules and their dissociative ionization play an important role in the deposition process. Si(OH)(x)(CH3)(3-x), species, produced by reactions between the Si(CH3)(4) molecule and Si(CH3)(3)(+) ion fragments with O and O-2, have been identified as important reaction intermediates. Such species form in different proportions depending on the O-2/TMS ratio in the gas mixture. It is proposed that their incorporation onto the surface of the growing films accounts for the wide range of compositions achieved (ranging from SiO2 to almost Si:C:H) and the high concentration of Si-C bonds experimentally detected in the SiOxCyHz thin films.