Photodegradation of Organosilane Self-assembled Monolayers Irradiated with an Excimer Lamp.

Abstract

Photodegradation of organosilane self-assembled monolayers (SAMs), under the presence of atmospheric oxygen molecules, has been studied using an excimer lamp radiating vacuum ultra-violet (VUV) light of 172nm in wavelength. The SAMs were prepared on Si substrates covered with native oxide from a precursor molecule of octadecyltrimethoxysilane [CH3(CH2)17Si(OCH3)3, ODS]. Each of these SAMs was photoirradiated under a controlled pressure from 10 to 105Pa. As confirmed by water contact angle measurements, infrared reflection-absorption spectroscopy and X-ray photoelectron spectroscopy, the SAMs were 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 ODS molecules and to subsequently proceeded oxidation with atomic oxygen radicals generated simultaneously by the VUV-irradiation of O2 molecules. This VUV-degradation of organosilane SAM was, furthermore, applied to to photolithography in which the SAM served as photoresist. A micropattern of 2μm in width was successfully transferred on the Si substrate by a simple photomask-contacting method.