Evolution de la taille des grains du silicium polycristallin pendant des traitements thermiques ou oxydation

We compare the crystallographic morphology of epitaxial polycrystalline silicon layers (9 10-3 03A9.cm resistivity, 450 nm thickness, L.P.C.V.D. at 670 °C by silane decomposition) which undergo for 6 to 180 min a high temperature treatment (900 °C to 1 050 °C) in inert gas ambiance (argon) or oxidizing ambiance (dry oxygen). The crystallite size evolution of the polycrystalline layer has been studied by means of X-Ray diffraction. In both cases, we find a grain size increase (faster in oxygen ambiance) (from 20 to more than 100 nm), corresponding to the crystallization of amorphous zones enhanced by dopant diffusion (phosphorus) at grain boundaries and by mechanical stresses. As compared to single crystal, the oxide formation kinetics is controlled by the random crystallographic orientation of grains and by grain boundaries (intergrain diffusion and dopant segregation). The destructive breakdown of oxide is not direct. We often observe a pre-breakdown followed by self-curing. Dielectric rigidity depends on doping rate and varies from 2 to 5 MV/cm when the oxidation temperature steps from 900 °C to 1000 °C. Revue Phys. Appl. 24 (1989) 133-141 FEVRIER 1989, 1