Curious morphology of silicon-containing polymer films on exposure to oxygen plasma

Thin films of silicon-containing polymers were studied to investigate chang es in surface composition and morphology on exposure to an oxygen plasma. F or low molecular weight poly(pentamethyldisilylstyrene) (P(PMDSS)), a retic ulated structure was observed by atomic force microscopy (AFM) that could l imit future lithographic applications of these materials. The reticulations were of approximately 1 mu m in width and 5 mu m in length, though a highe r molecular weight polymer resulted in smaller feature sizes. In polysilane polymers containing silicon in the backbone and molecular weights signific antly larger than the entanglement molecular weight, the feature dimensions were even smaller. Films etched at lower temperature (0 degrees C) display ed none of the reticulated morphology, retaining instead the smooth appeara nce of pre-etched films. It was found by X-ray photoelectron spectroscopy ( XPS) and Auger electron spectroscopy (AES) that a thin (<100 Angstrom) laye r of SiOx formed on the surface of all of the studied silicon-containing po lymer films. Appearance of the reticulated morphology required the combined presence of heating, oxygen plasma, and silicon in the polymer. The reticu lated structures are believed to result from the destabilization of the thi n films as they undergo the transition from a nonpolar organosilane to a po lar oxide.