Vapor deposition polymerization of 4-fluorostyrene and pentafluorostyrene

Abstract

Solventless deposition of thin, uniform dielectric films is of considerable interest and importance in the microelectronics industry due to environmental concerns and increasing wafer sizes. This work demonstrates a solvent-free method for atmospheric pressure chemical vapor deposition polymerization of thin films on a variety of substrates, including silicon, molybdenum, platinum and copper. Polymerization of 4-fluorostyrene (4FS) and pentafluorostyrene (PFS) is used as a model system. Depth profiling is performed using x-ray photoelectron spectroscopy, ellipsometry, and step profilometry. Film growth is found to be independent of substrate, and proceeds with activation energies of 14±1 and 15±1 kcal/mol, respectively, for 4FS and PFS deposition between 425 and 550 K. Films are shown by gel permeation chromatography to consist of low molecular weight polymer and oligimer species (between 3 and ∼140 repeat units). Atomic force microscopy analysis of films grown by this method indicates that the root mean square thickness variation along the surface is about 2.5%.