Thickness uniformity of gas-phase coatings in narrow channels: II. One-side confined channels

The process of the coating profile formation in one-side confined narrow channels in the course of the gas-phase deposition was theoretically investigated for the aspect ratio exceeding 20. The coating thickness distribution along a channel was shown to be described analytically only for the first-order deposition process. The correlation in an analytic form was established between the conformity parameters for the deposition processes of any order neglecting the sink of the film-forming substance to the end wall of the channel. In double relative coordinates (x/l, δ/δ₀), where the distance is expressed in fractions of the channel length, the coating thickness distribution was shown to be described by a single universal curve for any fixed deposition order, operation conditions, channel shapes and sizes. The combined invariant parameter of the process was found, which is the only value defining the coating thickness distribution. The coating thickness distributions were also obtained by numerical methods for some non-first-order deposition processes using the fourth-order Runge–Kutta method. The effect of the main process parameter as well as temperature and pressure on the ratio of the minimum and maximum film thicknesses (step coverage quality) and the parameter of the film thickness nonuniformity was analysed. Comparison of the theoretical conclusions with the experimental results on the poly-p-xylylene (PPX-N) deposition demonstrated a good agreement. All qualitative conclusions made for infinitely long channels were shown to be valid for one-side confined channels.