Surface morphology of PECVD fluorocarbon thin films from hexafluoropropylene oxide, 1,1,2,2-tetrafluoroethane, and difluoromethane

Abstract

Atomic force microscopy (AFM) measurements have been made on a series of fluorocarbon films deposited from pulsed plasmas of hexafluoropropylene oxide (HFPO), 1,1,2,2-tetrafluoroethane (C2H2F4), and difluoromethane (CH2F2). All of the films give images showing nodular growth (cauliflower-like appearance), with the size and distribution of the nodules dependent on both the precursor, the degree of surface modification to which the growing film is exposed, and the substrate surface. Films deposited from C2H2F4 showed clusters of smaller nodules around larger nodules, whereas films deposited from CH2F2 were characterized by a uniform distribution of smaller nodules, and films deposited from HFPO had the largest observed nodules. Movchan and Demchishin's structure zone model was applied to the observed films, which were all found to be zone 1 structures, indicating that film growth is dominated by shadowing effects. Increased substrate temperature and incident power per nm of film deposited results in decreased rms roughness, consistent with greater atomic mobility during deposition. Larger nodules in the fluorocarbon films developed on silicon wafer substrates than on rougher Al-coated substrates. Advancing contact angles for all of the films were found to be higher than that of PTFE (108°), indicating both hydrophobic and rough surfaces. Specifically, contact angles of films deposited from HFPO were found to increase with pulse off-time, the same trend observed for both the CF2 fraction of the film and the rms roughness. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2439–2447, 1999