Site-selective electroless plating on amino-terminated diamond substrate patterned by 126 nm vacuum ultraviolet light lithography

Abstract

A chemically inert diamond surface was modified through photo-oxidation with 126 nm vacuum ultraviolet (VUV) light followed by chemical vapor deposition (CVD) of an amino (NH2)-terminated organosilane. When VUV irradiation was conducted under a residual pressure of 10 or 103Pa, the sample surface became hydrophilic, with its water contact angle dropping from about 92.5° to about 13° or less than 5°, respectively. In contrast, samples treated at 105Pa were less wettable than those prepared at 10 or 103Pa due to insufficient light intensity. The contact angle of the sample treated at 105Pa was about 82°. With all the samples, after 126 nm VUV irradiation, photo-oxidation was found to be greatly enhanced in the topmost region close to the surface (i.e., at a depth of around 3 nm from the surface), while photo-oxidation reactions did not proceed in the deeper regions (i.e., around 10 nm from the surface), as evidenced by angle-resolved x-ray photoelectron spectroscopy (XPS). Following photo-oxidation, the hydrophilized diamond film was exposed to a vapor of N-(6-aminohexyl)-3-aminopropyltrimethoxysilane (AHAPS) diluted with absolute toluene. Due to the chemisorbed AHAPS layer thus formed, the sample surface again became relatively hydrophobic with a water-contact angle of about 64°. We also demonstrated micropatterning of this AHAPS layer based on a simple mesh-mask contact method using the same VUV light source, and applied this micropatterned sample to fabricate copper (Cu) microstructures through site-selective electroless plating. Optical microscopy confirmed that Cu deposition proceeded selectively on regions not irradiated by the VUV light (i.e., NH2-terminated regions), while the irradiated (SiOx layer-covered) areas remained free of Cu deposits. Employing this technique, we succeeded in fabricating 10 μm wide Cu microstructures on the diamond surface. The microstructures obtained showed no sign of peeling even after sonication in acetone or a Scotch® tape peeling test.