Paper péÉÅá~ä fëëìÉ Äó dìÉëí bÇáíçêëW lêÖ~åáÅ-íç-fåçêÖ~åáÅ`çåîÉêëáçå mêçÅÉëë Ñçê mçäóãÉê-aÉêáîÉÇ`Éê~ãáÅë çåîÉêëáçå çÑ mÉêÜóÇêçéçäóëáä~ò~åÉíçpáäáÅ~qÜáå cáäãë Äó bñéçëìêÉ íç s~éçê Ñêçã^èìÉçìë^ããçåá~~í oççã qÉãéÉê~íìêÉ Perhydropolysilazane PHPS films ca. 0.2 mm in thickness were deposited by spin-coating on Si100 and silica glass substrates. The PHPS films obtained were suspended over aqueous ammonia of various concentrations for various periods of time at room temperature. The Si-H and N-H infrared absorption peaks decreased, while the Si-O-Si peaks increased, and the nitrogen content decreased from 33.6 to 0.5 atomicಚ, suggesting that PHPS-to-silica conversion occurs on the exposure treatment. The refractive index decreased from 1.56 to 1.48, and the contact angle decreased from 94 to 67c on the exposure treatment. The changes in infrared absorption spectra and in refractive index were more significant when the as-deposited PHPS film was suspended over aqueous ammonia of higher concentrations, indicating that the use of aqueous ammonia of higher concentrations for exposure treatment is more effective in PHPS-to-silica conversion. As the PHPS-to-silica conversion proceeded, the durability of the films in hot water increased, evidenced in both series of films subjected to the exposure for various periods of time and those suspended over aqueous ammonia of various concentrations. When the exposed film was fired at 900c C, the nitrogen content further decreased from 0.5 to 0.01 atomicಚ, the refractive index decreased from 1.48 to 1.45, and the contact angle decreased from 67 to 29c , all of which approached those of pure and dense silica glass. These changes observed on firing suggest that the silica thin films obtained by the exposure treatment at room temperature are not identical to pure and dense silica glass.
Spin-coating was conducted on single-crystal silicon substrates using a xylene solution of perhydropolysilazane (PHPS) to obtain 0.14-μm-thick PHPS films. The PHPS films obtained were suspended over various acidic and basic solutions at room temperature so that they were exposed to the vapors from the solutions. PHPS-to-silica film conversion was studied by infrared absorption spectroscopy, and the stability of the exposed films in hot water was examined by soaking the films in 80 °C water. The as-deposited PHPS films were found to be dissolved in water. When the PHPS films were suspended over water, the films were partially converted into silica, but the resultant film had low stability in hot water. Higher degrees of PHPS-to-silica conversion and higher stabilities in hot water were found on exposing the PHPS films to basic or acidic vapors. Exposure to highly basic vapors from aqueous solutions of ammonia and ethylamine was significantly effective in PHPS-to-silica film conversion, which provided silica thin films with high stability in hot water.
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