APPLICATION AND PROPERTIES OF SUB-MONOMOLECULAR LAYERS OF SILICON DIOXIDE DEPOSITED UNDER MILD CONDITIONS

Ultra-thin Layers of silicon dioxide (< 1 nm) can be applied via the U VO3CVD method whereby a gas mixture of O-3/O-2 and TMOS/N-2, (TMOS = t etramethyl orthosilicate) is decomposed with UV light (254 nm) to form silicon dioxide at room temperature and atmospheric pressure. A react ion chamber is designed and the parameters that influence the depositi on rate are optimized. The deposition rate is independent of the TMOS concentration, but depends on the ozone concentration. Probably, the r eaction kinetics is pseudo-first-order in the ozone concentration. Wit h increased distance between the UV lamp and the substrate the deposit ed silicon dioxide contains more organic groups. Silicon dioxide layer s deposited on metal substrates are analyzed with static-SIMS, XPS, RE S, SEM, and glancing incidence asymmetric Bragg diffraction (GIABD). B oth with XPS and with RES the maximum deposition rate of the present e quipment is determined to be 1 Angstrom/min. According to the XPS meas urements the O/Si ratio in the deposit is 2.2 and the carbon content i s near zero. With static-SIMS characteristic fragment ions of silicon dioxide and the metal substrate are detected. The relative peak intens ities of these fragments linearly relate with the silicon dioxide laye r thickness when the layer thickness is smaller than 2 nm, With SEM ul tra-thin silicon-dioxide layers can be visualized, because the seconda ry electron emission of a coated and an uncoated metal surface is diff erent. This is probably attributable to a difference in surface potent ial. With GIABD a 29 nm thick layer was found to be crystalline, but n o known diffraction pattern. of SiOx fitted the measured pattern. Meta ls can be coated with ultra-thin silicon dioxide. It was found that th ese ultra-thin layers inhibit metal corrosion. A metal surface coated with ultra-thin silicon dioxide can be further modified with known cou pling agents, such as silanes, as if the metal was silicon dioxide.