Thermal stability of Si_1-xC_x/Si strained layer superlattices

The thermal stability of epitaxial silicon-carbon alloys grown by molecular beam epitaxy on (001) silicon was investigated using high resolution x-ray diffraction, transmission electron microscopy, and secondary ion mass spectroscopy measurements. Different superlattices, with alloy compositions of Si0.997C0.003, Si0.992C0.008, and Si0.985C0.015, all nominally 6 nm thick, with 24 nm Si spacer layers were employed. Annealing studies determined that there are different pathways to strain relaxation in this material system. At annealing temperatures of 900°C and below, the structures relax only by interdiffusion, indicating that these layers are stable during typical device processing steps. At temperatures of 1000°C and above, SiC precipitation dominates with enhanced precipitation in the Si1-xCx layers with the highest initial carbon content.