Property of plasma-polymerized fluorocarbon film in relation to CH₄/C₄F₈ ratio and substrate temperature

This paper shows the systematic study on the property of plasma-polymerized fluorocarbon (PPFC) film formed by a capacitive coupling-type plasma polymerization equipment using a mixture of CH₄/C₄F₈ gas. The thermal stability of PPFC film was improved with substrate temperature. CH₄ gas was supplied with C₄F₈ gas in order to increase the deposition rate. The deposition rate of a few nanometers per minute was obtained at substrate temperature of 200 °C by the addition of 20% CH₄ gas. The PPFC film showed residual thickness of 80% and water contact angle of 110° even after 20 min annealing at 350 °C in air. The electrical breakdown strength of the film was measured as 0.7-1.3 MV/cm using mercury probe. The PPFC film was effective to prevent `in-use stiction', whose effect was confirmed by a touching test using the electrostatic force for an SOI accelerometer. As another interesting phenomenon, ultra hydrophobic surface (its water contact angle was over 150°) was obtained using the `powder-like' PPFC film, and it was explained by a fractal theory.