Micropatterning of organosilane self-assembled monolayers using vacuum ultraviolet light at 172 nm: resolution evaluation by Kelvin-probe force microscopy

An investigation is carried out to evaluate the resolution of a vacuum ultraviolet (VUV)-exposure system for micropatterning organosilane self-assembled monolayers (SAMs) using Kelvin-probe force microscopy (KFM). An organosilane (CH3(CH2)17Si(OCH3)3) SAM deposited on Si substrates was micropatterned by the use of VUV light of 172 nm in wavelength. From water contact angle measurement results, the exposure time was clearly demonstrated to be shortened down to 300 s with our innovated apparatus from 1200 s attained previously. The optical path of the apparatus, except the space between the photomask and the sample, was designed so as to be purged with nitrogen in order to avoid the attenuation of the VUV light, since oxygen molecules strongly absorb such lights. On the other hand, the photomask-sample space was exposed to ambient air in order to promote oxidation of the SAM with active oxygen species generated by VUV-excitation. KFM images of the VUV-exposed samples showed that various patterns were successfully transferred to the SAM-covered Si substrates. Lines wider than 1 μm and circles larger than 2 μm in diameter were photo-printed.