Oxygen diffusion and precipitation in Czochralski silicon

The objective of this article is to review our understanding of the properties of oxygen impurities in Czochralski silicon that is used to manufacture integrated circuits (ICs). These atoms, present at a concentration of similar to 10(18) cm(-3), occupy bond-centred sites (O(i)) in as-grown Si and the jump rate between adjacent sites defines 'normal' diffusion for the temperature range 1325-330 degrees C. Anneals at high temperatures lead to the formation of amorphous SiO(2) precipitates that act as traps for fast diffusing metallic contaminants, such as Fe and Cu, that may be inadvertently introduced at levels as low as 10(11) cm(-3). Without this 'gettering', there may be severe degradation of fabricated ICs. To accommodate the local volume increase during oxygen precipitation, there is parallel generation of self-interstitials that diffuse away and form lattice defects. High temperature (T > 700 degrees C) anneals are now well understood. Details of lower temperature processes are still a matter of debate: measurements of oxygen diffusion into or out of the Si surface and O(i) atom aggregation have implied enhanced diffusion that has variously been attributed to interactions of O(i) atoms with lattice vacancies, self-interstitials, metallic elements, carbon, hydrogen impurities etc. There is strong evidence for oxygen-hydrogen interactions at T < 500 degrees C and the formation of fast diffusing O(2) dimers. These observations have led to significant advances in understanding the growth and structures of small oxygen clusters, identified with the so-called thermal donor and shallow thermal donor defects. There is a need to improve this understanding because the temperatures of device processing will continue to decrease as the size of future device features decreases below the lower end of the sub-micron range, currently close to 0.18 mu m.