Thermal processing of strained silicon-on-insulator for atomically precise silicon device fabrication

▸ Strained silicon-on-insulator (sSOI) samples were flash-annealed at high temperature under ultra-high vacuum conditions. ▸ The extend of surface strain relaxation depends on the annealing temperature with no strain relaxation observed below 1020°C. ▸ A 2×1 reconstructed surface with low defect density can be achieved. ▸ The annealed sSOI surface shows enhanced step undulations due to the unique energetics caused by surface strain. We investigate the ability to reconstruct strained silicon-on-insulator (sSOI) substrates in ultra-high vacuum for use in atomic scale device fabrication. Characterisation of the starting sSOI substrate using μRaman shows an average tensile strain of 0.8%, with clear strain modulation in a crosshatch pattern across the surface. The surfaces were heated in ultra-high vacuum from temperatures of 900°C to 1100°C and subsequently imaged using scanning tunnelling microscopy (STM). The initial strain modulation on the surface is observed to promote silicon migration and the formation of crosshatched surface features whose height and pitch increases with increasing annealing temperature. STM images reveal alternating narrow straight SA steps and triangular wavy SB steps attributed to the spontaneous faceting of SB and preferential adatom attachment on SB under biaxial tensile strain. Raman spectroscopy shows that despite these high temperature anneals no strain relaxation of the substrate is observed up to temperatures of 1020°C. Above 1100°C, strain relaxation is evident but is confined to the surface.