The vapor phase deposition of fluorocarbon films for the prevention of in-use stiction in micromirrors

The purpose of this study was to explore the vapor-phase (VP) deposition of fluorocarbon (FC) films for the prevention of in-use stiction in a microel ectromechanical system (MEMS). Liquid sources (3M Co.'s FC722 and FC40) wer e used to deposit FC films on sputter coated Al surfaces after wet treatmen t (73% H3PO4, 4% HNO3, 3.5% CH3COOH, 19.5% deionized water) and O-2 and O-2 /CF4 plasma treatments. A vacuum oven, set at 110 degrees C, was used for t he experiment. The deposition was carried out at a pressure of 4.5 x 10(-2) Torr for 40 min followed by the annealing at 300 Torr for 20 min in N-2 to obtain the highest water contact angles on Al. The wet treatments of the s urfaces resulted in higher contact angles and thicker FC films than those o btained by the plasma treatments. Attenuated total reflectance fourier tran sform infrared spectroscopy (ATR-FTIR) analysis showed the strong CF2 stret ching bands in the 1100-1300 cm(-1) region. Atomic force microscopy (AFM) a nalysis revealed the changes of surface morphology before and after FC depo sition. Also no stiction of micromirrors was observed when fluorocarbon fil ms were deposited on them even after 2 x 10(8) touch-down cycles.