Investigation of thin films made from silicon-containing polyphenylquinoxaline-amides

Thin films in the range of 50 nm to 10 mu m thickness have been prepared from NMP solutions of silicon-containing polyphenylquinoxaline-amides which had been synthesized by the polycondensation reaction of aromatic diaminophenylquinoxalines with bis(p-clorocarbonylphenyl)diphenylsilane A spin-coating technique onto glass plates or onto silicon wafers was used to make the films, followed by gradual heating to remove the solvent. The resulting films were very smooth and free of pinholes when studied by atomic force microscopy (AFM). They showed a strong adhesion to silicon wafers, were thermally stable in air to above 400 degrees C and their dielectric constant was in the range of 3.5-3.7. Thermal treatment of the films was performed in order to induce crosslinking. Such treated films became completely insoluble in organic solvents, maintained their smoothness and strong adhesion to the silicon substrate, and did not show any Tg in DSC experiments. Their FTIR spectra in reflection mode did not show any changes compared with the untreated films, meaning on the one hand that the polymers maintain their structural integrity at high temperature and on the other hand that the number of crosslinks was very low and could not be detected by IR spectroscopy.