ESR Study of Trimethylsilane Plasma Polymer Part II; Effect of Consecutive Treatments and Mixed Gases

An ESR study has indicated that a second plasma treatment on plasma deposited films from trimethylsilane (TMS) monomer gas has the ability to modify the characteristics of the primary plasma polymer significantly in a favorable manner for many applications. The effect of the second plasma polymerization on the primary plasma polymer of TMS depends on the nature of the second monomer. Plasma of F-containing monomer, hexafluoroethane (HFE) and perfluoromethane (CF₄), decreases the ESR signal of TMS and no detectable signal due to F-containing monomer was found. The decay rate of the signal decreased significantly. In contrast to this situation, CH₄ plasma treatment yields an ESR signal that is a composite of that observed from TMS and CH₄ films individually. The overall signal increased in this instance, but didn't show appreciable decay in 24 hr period. A second treatment by nonpolymer forming plasmas also decreased the ESR signal of TMS, and decreased the decay rate, indicating that the second gas plasma treatment yields a somewhat similar effect found with the HFE plasma treatment. Plasma polymerization of mixtures of TMS and nonpolymer-forming gases increased the ESR signal but decreased the decay rate, except in the case of oxygen. A mixture of (TMS + O₂) behaved as a completely different monomer. No ESR signal was found in this system. The ESR analysis was supported by XPS data and an insight into the mechanisms occurring in these thin films are discussed.     

Photoelectron and electron energy loss spectra of epitaxial aluminum nitride

The valence bands of epitaxial layers of A1N were studied by ultraviolet photoelectron spectroscopy and electron energy loss spectroscopy. A self-consistent band structure was calculated and the resultant density of states compared with the UPS spectra. Qualitative agreement was good, with discrepancies arising primarily from the neglect of dipole matrix elements.     

XPS Analysis of the Aging of Thin,Adhesion Promoting,Fluorocarbon Treatments of DC Plasma Polymers

Plasma polymer treatment of aluminum alloys has recently been shown to improve adhesion of primer coatings, thereby reducing the corrosion of thusly protected panels to the levels afforded by conventional chromate conversion coating. One particular plasma polymer system, comprised of a 50 nm trimethylsilane DC plasma polymer capped by an ultrathin layer modified by DC hexafluoroethane plasma treatment, has shown tremendous adhesion increases to a wide variety of primers, yielding a coating that is virtually unremovable with conventional stripping applications. An application window was empirically deduced regarding this improved adhesion, indicating that the primer needed to be applied within 5 days of plasma treatment to display the tenacious adhesion to panels. In an effort to elucidate the differences between fresh and aged panels, an X-ray photoelectron spectroscopy (XPS) time study of this system was undertaken. Some direct correlation to this time frame was observed in the XPS data, indicating that a particular fluorocarbon structure in the films modified upon continued atmospheric exposure, rearranging the local bonding environment by introducing additional C—C bonding with an increase in oxygen incorporation.     

Depth Profiled XPS Analysis of a Polymerized Silicon-Carbon Thin Film

An in situ study of the chemical properties of a polymerized silicon-carbon thin film has been completed. The deposited film was created by plasma enhanced chemical vapor deposition of trimethylsilane onto an aluminum substrate. Depth profiled X-ray photoelectron spectra were obtained. An analysis of the data shows varying chemistry throughout the film as well as an interaction between silicon and aluminum/aluminum oxide at the bi-layer interface.