Thickness distribution of gas phase coatings in confined channels

Conformality of coatings deposited in one-side confined channels from a film-forming gas is scrutinized theoretically for viscous mode of the gas flow. The process was shown to have a universal invariant parameter, which defines conditions of similarity of channels and process regimes with respect to obtaining coatings of equal step coverage quality. Calculation was performed using numerical method to obtain the coating thickness distribution on channel walls for various parameters of deposition reaction. The model reveals increase of step coverage quality with gas pressure increase for the deposition reactions of the order between 1 and 2. Results are specifically applied to deposition of poly-p-xylylene conformal coatings and limits of their validity are shortly discussed.