Thermal oxidation of As and Ge implanted Si(100)

The thermal oxidation of Ge or As implanted Si single crystals has been investigated for two different oxidation processes (in wet ambient at 920°C and dry ambient at 1100°C). Using the atomic force microscopy the oxide morphology and roughness has been determined as a function of the different oxidation processes. The X-ray absorption spectroscopy has been employed to determine the structural coordination around the dopant atoms. We found that the surface roughness is related to the segregation of Ge or As at the oxide/substrate interface, occurring when the oxidation rate is faster than the dopant diffusion, in particular at the higher implanted dose processed in wet ambient. The segregation of Ge at the interface gives rise to the formation of germanium rich alloy region, whereas the segregation of As induces the precipitation of SiAs monoclinic islands. The formation of islands is directly related to the dopant segregation, but their size is not. In fact, after a critical concentration of dopant at the interface is reached, a dissolution of the precipitates takes place. A memory effect causes the continuous growing of the islands, even once the diffusion of Ge or As takes place.