A model for the chemical vapor deposition of poly(para-xylylene) (parylene) thin films

A kinetic model is developed for the chemical vapor deposition of poly(para-xylylene), or parylene, thin polymer films. The growth process is modeled as a multistep process that includes physisorption of monomer on the surface and subsequent chemisorption. The chemisorption step is equivalent to a propagation reaction between the monomer and a radical chain end, and each chemisorption produces a new chemisorption site. The sticking coefficient of the monomer as a function of substrate temperature is extracted from the measured data using the model and is determined to be 2.0 × 10^-5 at 60 °C, increasing to 1.4 × 10^-3 at -60 °C. The heat of physisorption for the monomer is also extracted from the experiment, and the value found (75 kJ/mol) is reasonable when compared to those of other similar molecules. The model fits experimental kinetic data well for a large range of pressures and temperatures, and it should be appropriate for use with all parylene-family polymers.