Friction force microscopy study on photodegradation of organosilane self-assembled monolayers irradiated with a vacuum ultraviolet light at 172 nm

Abstract

An alkylsilane self-assembled monolayer (SAM) has been micropatterned by the use of vacuum ultraviolet (VUV) light at 172 nm in wavelength radiated from an excimer lamp. By a chemical vapor deposition method, the SAM was prepared on Si substrates covered with native oxide from a precursor molecule of octadecyltrimethoxysilane. Micropatterning of the SAM was demonstrated based on a simple photomask-contacting method. Due to a distinct difference in friction coefficient between the VUV-irradiated and unirradiated regions, the photoprinted pattern was clearly imaged in friction force microscopy. The VUV-irradiated region showed stronger friction force than the unirradiated SAM surface. As confirmed by friction force microscopy, water contact angle measurements, and x-ray photoelectron spectroscopy, the SAM was found to be decomposed and removed due to the VUV irradiation. This photodegradation mechanism is ascribed to dissociative excitation of C–C and C–H bondings in the organosilane molecules and to subsequently proceeded oxidation with atomic oxygen radicals generated simultaneously through VUV excitation of atmospheric oxygen molecules. Microlines whose width was less than 1 μm could be fabricated based on this VUV lithography.