Modeling vapor deposition of low-K polymers: Parylene and polynaphthalene

By using different mechanisms of deposition and growth, new models of Paryl ene deposition rates have been developed and compared with experimental dat a over a wide range of conditions. It is shown that the surface adsorption (boundary) condition is a crucial factor in determining how the results of these models behave. Minimal differences in the behavior of the overall rat es of deposition are obtained among the Parylene models using the same adso rption condition with either surface or bulk film reactions. However, their basic structures are considerably different. Although both diffusion/react ion and surface reaction models with either Langmuir-type or Flory-type mon omer adsorption have attractive features, they fail to represent the data o n rates of deposition over the wide range of conditions reported in the lit erature. In contrast, the models based on Brunauer, Emmett, and Teller mult ilayer adsorption seem to include the benefits of both Langmuir and Flory a dsorption and simulate the data well over a much broader range of temperatu re. This suggests that multilayer adsorption is an important phenomenon in the low temperature vapor deposition of these polymers. Here we try to clar ify the important physical/chemical mechanisms involved as well as the simi larities and differences among various approaches to formulation of deposit ion models. A polynaphthalene deposition model is developed on the basis of both gas phase reactions followed by adsorption on the surface with subseq uent reaction to form the film. The model is capable of simulating the data very accurately. However, the data available are limited in range and more experimental data are required to establish the uniqueness of the rate equ ations proposed. (C) 1999 American Vacuum Society. [S0734-2101(99)01901-6].