Arsenic redistribution at the SiO2/Si interface during oxidation of implanted silicon

The behavior of ion-implanted As in (100) silicon wafers, following thermal oxidation, has been investigated by Rutherford backscattering spectroscopy, atomic force microscopy, transmission electron microscopy, and extended x-ray-absorption fine structure. The adopted fluences (3 x 10(15) and 3 x 10(16) cm(-2)) and oxidation conditions (wet 920 degrees C, dry 1100 degrees C) span quite a broad range of phenomena, giving rise to As diffusion in the bulk, and/or segregation and precipitation at the SiO2/Si interface. The surface roughness is correlated to that measured at the interface, although the oxide presence strongly reduces the value with respect to that present at the interface. Rough interfaces and surfaces are formed when the arsenic concentration exceeds the solid solubility and precipitation occurs. The SiAs precipitates are characterized by a monoclinic structure with low surface energy for the (100) facet, as determined by the Wulff plot. Residual roughness is left at the oxide surface even if precipitates initially formed dissolve during subsequent oxidation. The depth profile of the dopant has been quantitatively computed by the analytical solution of the diffusion equation, taking into account the interface movement, the As redistribution at the interface between oxide and bulk silicon, the formation, growth, and dissolution of precipitates, and, of course, the drive-in process. The dependence of the diffusion coefficient on the dopant concentration has been also considered and determined as a converging parameter, considering iteratively the differential equation solution. In all the investigated cases the agreement between experimental data and calculations has been found to be good. [S0163-1829(98)08539-7]. RI Raineri, Vito/C-5307-2009; La Via, Francesco/E-8035-2011