Design of functional coatings

Based on the principle of macroscopic kinetics, we present the concept of a standard process to compare different rf plasma reactors. Therefore, the mass deposition rate of pure hexamethyldisiloxane (HMDSO) discharges was chosen, since the plasma polymerization of HMDSO is a radical-dominated process and ion-induced effects can be neglected for a wide parameter range. Two experimental series with pure HMDSO discharges were performed within a symmetrical and a strongly asymmetrical rf plasma reactor. The obtained deposition rates were compared to four experimental series taken out of the literature concerning the deposition rates of plasma polymerized HMDSO coatings. While for each reactor design, the "specific energy" W/F was found to describe the deposition rates very well, different apparent activation energies E-a were obtained. To bring the data sets into agreement, a new process constant E-a d(act) is introduced taking the width of the active plasma zone d(act) into account. By this means, functionally gradient SiOC:H films can be designed, e.g., for adhesion, wetting, or barrier improvements. Moreover, processes can be optimized and scaled up. (C) 2005 American Vacuum Society.