Raman Spectroscopic Study of Vapor Deposited Poly(N,N'-bis(phenoxyphenyl)pyromellitimide) Films.

摘要

The growth of thin polyimide films on solid substrates by means of the controlled deposition of aromatic dianhydride and diamine precursor species from the vapor phase was first demonstrated by Salem et al. This vapor deposition polymerization (VDP) process has a number of potential advantages over the solvent-based methods normally used in commercial applications, such as the fabrication of polyimide interlevel dielectrics for very large scale integration (VLSI) microelectronic devices, and offers the possibility of producing more uniform films with more precisely controllable properties than is possible with conventional spin-coating technology. In this paper we report the results of a Raman spectroscopic study of ca. 200 nm poly N, N'-bis(phenoxphenyl)pyromellitimide (PI) films formed by the imidization of vacuum co-deposited layers of 4,4'-oxydianiline (ODA) and pyromellitic dianhydride (PMDA) of polycrystalline Cu samples. These studied support the finding that the VDP process produces polyamic acid curable to polyimide, but reveal that the precise composition of the films is variable and depends on the ratio of the individual PMDA and ODA flux rates during deposition. A large initial excess of ODA, in particular, leads to the appearance of new and intense Raman bands when the sample is cured. These bands, which also appear weakly in samples prepared using more nearly equal PMDA and ODA flux rates, are attributed to the formation of branches and/or cross-links by the nucleophilic attack of free amine groups on imide carbonyls at temperatures in excess of 250 C. Keywords: Reprints. (aw)