Structure and its thickness dependence of thin films of phenyl and methyl silsesquioxane polymers

Abstract

Silsesquioxane (SSQ) polymers are important thin film materials in lithography, sensing, opto materials, and low k materials in electronics applications. There is a strong fundamental and practical need to understand the network structure in silsesquioxane films. In this study, two types of SSQ polymer (PSSQ), poly(methylsilsesquixoane) (PMSSQ) and poly(phenylsilsesquioxane) (PPhSSQ), were synthesized and their thin films were examined. Grazing angle reflection absorption infrared spectroscopy (GARAIR) was shown to be a good method to characterize the structure of the SSQ films and quantitative analysis can be done on films of a range of thickness between 7 nm and 150 nm. In particular, the orientation of the Si-O-Si network can be probed with GARAIR due to the polarization effect of the measurement. With increasing film thickness, a decrease in the planarity of the chains (orientation) in the Si-O-Si network was observed and possibly an increasing in the degree of condensation happened as indicated by the red shift of one IR absorption peak in PMSSQ. XRD study shows that both PMSSQ and PPhSSQ films have similar network comprising ladder component. Furthermore, GARAIR established that PPhSSQ shows more isolated silanol content while PMSSQ possesses mostly vicinal silanols.