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

Abstract

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 microelectromechanical system (MEMS). Liquid sources (3M Co.'s FC722 and FC40) were used to deposit FC films on sputter coated Al surfaces after wet treatment (73% H3PO4, 4% HNO3, 3.5% CH3COOH, 19.5% deionized water) and O2 and O2/CF4 plasma treatments. A vacuum oven, set at 110°C, was used for the experiment. The deposition was carried out at a pressure of 4.5 × 10-2 Torr for 40 min followed by the annealing at 300 Torr for 20 min in N2 to obtain the highest water contact angles on Al. The wet treatments of the surfaces resulted in higher contact angles and thicker FC films than those obtained by the plasma treatments. Attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR) analysis showed the strong CF2 stretching bands in the 1100-1300 cm-1 region. Atomic force microscopy (AFM) analysis revealed the changes of surface morphology before and after FC deposition. Also no stiction of micromirrors was observed when fluorocarbon films were deposited on them even after 2 × 108 touch-down cycles. © 1998 Publication Board, Japanese Journal of Applied Physics.