NUCLEAR REACTION MEASUREMENT OF IMPLANTED OXYGEN-18 TRANSPORT DURING WATER DIFFUSION IN THIN SILICON-DIOXIDE FILMS

In an investigation of the mechanism responsible for the transport of water through SiO(,2) thin films, we have performed tracer diffusion measurements involving network ('18)O demonstrating the importance of oxygen exchange between the SiO(,2) network and molecularly dissolved water. We have found that in the presence of water, bound network oxygen diffuses through SiO(,2) as a constituent of molecularly dissolved water.;The observed thermal broadening of ion-implant distributions permitted bulk diffusivity to be measured conveniently at temperatures or gas-phase concentrations much lower than previously possible. Diffusions conducted in steam at 1 atm (at temperatures as low as 250C) showed an activation energy of about 17 kcal/mol, which is close to that originally measured for water permeation in SiO(,2). Diffusions in both air and dry nitrogen showed a similar activation energy, with respective pre-exponential factors two and three orders of magnitude below the steam value. Diffusions in low pressure water vapor showed a clearly linear dependence on gas phase water concentration down to 80 ppm, in contrast to thermal oxidation results reported by others.;The results of this study are consistent with a recently proposed model of water diffusion in SiO(,2) in which the diffusion mechanism is the interstitial transport of dissolved molecular water accompanied by a reversible reaction with silicon-oxygen bonds in the network.;Employing methods common to state-of-the-art semiconductor technology, the central region within a thermal oxide layer grown on silicon was enriched with immobile ('18)O by ion implantation. After heating in atmospheres with different water contents, the extent of ('18)O diffusion was determined by observing changes in the concentration profile (i.e. the chemical concentration as a function of depth) of implanted ('18)O by means of nuclear resonance profiling. In this technique, high-energy protons from a Van de Graaff accelerator lose energy in their passage through the oxide until their energy falls to a resonant energy of the ('18)O(p,(alpha))('15)N reaction. High-energy alpha particles, emitted in this inelastic reaction from the ('18)O which is located at that depth, are detected after escaping from the surface.