PRECIPITATE STRAIN RELIEF VIA POINT-DEFECT INTERACTION - MODELS FOR SIO2 IN SILICON

Precipitation in the solid state is often accompanied by a volume mism atch, creating strain which inhibits precipitation. For the SiO2/Si sy stem, this strain, if unrelieved, is large enough to prevent precipita tion altogether. The strain is usually assumed to be relieved via emis sion or absorption of point defects. Here, we suggest a model in which only one species of point defect is involved, and the emission/absorp tion relieves the strain only partially. We generate a Gibbs free ener gy equation in two variables, and by monitoring the atom movements dur ing precipitation, are able to derive two relationships: an expression for the critical radius and, more importantly, a direct correlation b etween strain and point defect supersaturations. We use this approach to study three systems: SiO2 strain relief via interstitial emission, vacancy absorption and carbon absorption. Finally, the importance of t he strain/supersaturation relationship is emphasized by noting its imp act upon nucleation rates. Even small point defect supersaturations ca n eliminate nucleation, and must therefore be considered carefully in studies of precipitation.