Photoinduced decomposition of alkyl monolayers using 172 nm vacuum ultraviolet light

The photoinduced stability of two alkyl monolayers on Si has been investigated using a Xe2 excimer lamp radiating 172 nm vacuum ultraviolet (VUV) light. The photoinduced stability of 1-octadecene monolayer (ODM) was compared with that of alkylsilane monolayer. 1-octadecene was employed as a starting precursor of alkyl monolayer on Si. The alkylsilane monolayer was formed from otadecyltrimethoxysilane monoalyer (OTSM) onto the SiO2/Si substrate. The decomposition of ODM was investigated under VUV irradiation conducted at 10 and 105 Pa. The VUV light decomposed ODM at both 10 and 105 Pa. The photodecomposition rate at 105 Pa was smaller than that at 10 Pa. The decomposed methyl and ethyl groups from the alkyl chain formed carboxyl groups. The carboxyl coverage on the surface of Si increased with increasing VUV irradiation time ranging from 0 to 60 s at 10 Pa, and decreased after 60 s. In contrast, the Si-O component in x-ray photoelectron Si 2p spectrum drastically increased after the VUV irradiation time of 60 s. The Si-O component indicated complete covering of Si surface. Similar decomposition rates between ODM and OTSM were observed for the VUV irradiation time ranging from 0 to 45 s conducted at 10 Pa. After 45 s, the photodecomposition rate of ODM was smaller than that of OTSM. The effectiveness of VUV light for the micropatterning of ODM was also investigated