Chemical, optical and tribological characterization of perfluoropolymer films as an anti-stiction layer in micro-mirror arrays

Abstract

Perfluoropolymer (PP) thin films were deposited on aluminum (Al) and tetraethylorthosilicate (TEOS) oxide surfaces by thermal vapor-phase (VP) deposition to prevent the stiction of micro-mirrors during their touchdown operation on TEOS pads. The fluorocarbon (FC) chemicals from the 3M Co. and perfluorodecanoic acid (PFDA) were used as precursors for the film deposition. Static contact angles (SCA) of the PP films on dry-cleaned Al and TEOS were measured and found to be larger than 110 degrees. Dynamic contact angle (DCA) analysis of the films showed the poor surface coverage and poor homogeneity of the films. However, very low surface energies, less than 15 and II dynes/cm, were calculated from the contact angle measurements on Al and TEOS, respectively after film deposition. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) analysis showed the presence of CF, CF2, CF3, and C-C stretching bands on PP films on Al. Optical characterization of the films, using variable angle spectroscopic ellipsometry (VASE), was carried out to determine the thickness of the films. Micro-tribological behavior was investigated by atomic and lateral force microscopy (AFM/LFM) as a function of the applied load. The AFM/LFM analysis showed that there were higher friction forces and a poorer coverage for films deposited on Al than for films deposited on TEOS. The reliability of the films was evaluated by the actual operation of the micro-mirror arrays at 3 KHz in a dry N-2 environment. The micro-mirrors were movable without stiction occurring, even after 2x10(8) touchdown cycles, in the presence of FC surface films. (C) 2000 Elsevier Science B.V. All rights reserved.