Real-Time X-ray Studies of Si Surface Morphology Evolution during Ar+ Ion Bombardment

A systematic study of Si surface evolution during normal- incidence Ar+ ion bombardment is reported. Real-time grazing incidence small- angle x-ray scattering (GISAXS) measurements were performed at the National Synchrotron Light Source of Brookhaven National Laboratory. \textit{Ex- situ} atomic force microscopy was also used to provide real-space information. Si (100) samples were bombarded at ion energies ranging from 300 to 1000 eV. For normal-incidence sputtering at room temperature, the development of correlated structures with two different characteristic length scales was observed. The shorter length scale features (``dot-like structures'') coarsened with time but approached a limiting value of 25-40 nm at all energies examined. These correlations eventually saturate. The surface roughness development then becomes dominated by the growth of the larger length-scale corrugations, causing kinetic roughening. To study the temperature dependence of the surface evolution, Si (100) samples were bombarded with 500 eV ions at temperatures ranging from 25 -- 700 C. There is a transition with increasing temperature from an amorphized surface to a crystalline surface. At high temperatures, the nanoscale correlations coarsen rapidly and are significantly longer in wavelength than the ``dot'' correlations observed at lower sputter erosion temperatures. No saturation is observed during the time of observation. This work is supported by NSF-DMR and DOE-BES. .