Plasma Copolymerization of Tetrafluoroethylene/Hexamethyldisiloxane and In Situ Fourier Transform Infrared Spectroscopy of Its Gas Phase

Plasma copolymerization of hexamethyldisiloxane (HMDSO, (CH3)3-Si-O-Si-(CH3)3) and tetrafluoroethylene (CF2=CF2) was performed using an RF plasma enhanced chemical vapor deposition method, for its application to low dielectric constant intermetal dielectrics. Film structure was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. Film composition was controlled gradually from that of fluorinated carbon to organic siloxane by changing the HMDSO mixing ratio. The films possessed a dielectric constant of less than 2.5 for an HMDSO mixing ratio of less than 10%. Thermal treatment of the films revealed that the C-F n , Si-O-Si, Si-(CH3) n and Si-(CH2) n -Si bonds were stable to 400°C, but the C-H2 bonds were not. In situ gas-phase FT-IR spectroscopy was also performed on the plasma, and the reaction mechanisms are discussed.