Modification by UV-light irradiation of the affinity for copper chemical vapour deposition of self-assembled monolayers of organosilanes on SiO2 substrates

Self-assembled monolayers (SAMs) of (3-mercaptopropyl)trimethoxysilane (MPTMS) [HS-(CH2)3-Si-(OCH3)3] were deposited by vapour phase silylation onto SiO2 substrates. After UV-light irradiation in air, the SAMs exhibit enhanced affinity for copper (Cu) chemical vapour deposition (CVD) (performed by using the precursor (MHY)Cu(hfac) where MHY = 2-methyl-1-hexene-3-yne and hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate) as compared to unirradiated ones, due to oxidation of the thiol head group (–SH) and conversion to sulphonate (–SO3H), thus demonstrating selective Cu CVD. This is confirmed by X-ray Photoelectron Spectroscopy (XPS) measurements performed also on SAMs which were chemically oxidized in hydrogen peroxide (H2O2) or nitric acid (HNO3) solutions. A positive image of the grid mask used for irradiation is formed by the Cu film onto SAMs which were previously irradiated in air. A negative image is formed onto SAMs which were irradiated under controlled atmosphere of nitrogen or argon gas with better selectivity obtained when irradiation was performed through an optical filter which blocks the 184.9 nm line of the light.