ARSENIC REDISTRIBUTION AT THE SIO2 SI INTERFACE DURING OXIDATION OF IMPLANTED SILICON/

The behavior of ion-implanted As in (100) silicon wafers, following th ermal oxidation, has been investigated by Rutherford backscattering sp ectroscopy, 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 deg rees C, dry 1100 degrees C) span quite a broad range of phenomena, giv ing rise to As diffusion in the bulk, and/or segregation and precipita tion at the SiO2/Si interface. The surface roughness is correlated to that measured at the interface, although the oxide presence strongly r educes the value with respect to that present at the interface. Rough interfaces and surfaces are formed when the arsenic concentration exce eds the solid solubility and precipitation occurs. The SiAs precipitat es are characterized by a monoclinic structure with low surface energy for the (100) facet, as determined by the Wulff plot. Residual roughn ess 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 di ffusion equation, taking into account the interface movement, the As r edistribution at the interface between oxide and bulk silicon, the for mation, growth, and dissolution of precipitates, and, of course, the d rive-in process. The dependence of the diffusion coefficient on the do pant concentration has been also considered and determined as a conver ging parameter, considering iteratively the differential equation solu tion. In all the investigated cases the agreement between experimental data and calculations has been found to be good. [S0163-1829(98)08539 -7].