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

Atomic force microscopy (AFM) measurements have been made on a series of fl uorocarbon films deposited from pulsed plasmas of hexaflouoropropylene oxid e (HFPO), 1,1,2,2-tetrafluoroethane (C2H2F4), and difluoromethane (CH2F2). All of the films give images showing nodular growth (cauliflower-like appea rance), 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 clu sters of smaller nodules around larger nodules, whereas films deposited fro m CH2F2 were characterized by a uniform distribution of smaller nodules, an d films deposited from HFPO had the largest observed nodules. Movchan and D emchishin's structure zone model was applied to the observed films, which w ere all found to be zone 1 structures, indicating that film growth is domin ated by shadowing effects. Increased substrate temperature and incident pow er per nm of film deposited results in decreased rms roughness, consistent with greater atomic mobility during deposition. Larger nodules in the fluor ocarbon films developed on silicon wafer substrates than on rougher Al-coat ed substrates. Advancing contact angles for all of the films were found to be higher than that of PTFE (108 degrees), indicating both hydrophobic and rough surfaces. Specifically, contact angles of films deposited from HFPO w ere found to increase with pulse off-time, the same trend observed for both the CF, fraction of the film and the rms roughness. (C) 1999 John Wiley & Sons, Inc.