The effects of locally controlled strain on nanostructure formation

Improvements in semiconductor device performance have driven device size down to increase density. Size is approaching functional limits so new technologies are required; Quantum dots (QDs) represent a promising option. However, current methods cannot produce the required distributions of uniform QDs. Surface strain can drive growth kinetics toward self-ordered growth. Therefore, I tested the hypothesis that control of surface strain through varied shapes and patterns of mesotaxially-defined buried stressors would guide surface nanostructure formation during heteroepitaxy.; The strain response of a silicon substrate to buried inclusions was simulated and the results were used to determine the range of inclusion parameters I tested. The simulation results were used to design and fabricate an implant mask to guide mesotaxy. Improvements to the strain patterning process using this mask decreased the minimum inclusion size from 700 to 200 nm. These simulation results correlated well with AFM analysis of the strained surface.; The heteroepitaxial growth of Ge on Si(001) elucidated the influence of surface strain on the growth kinetics. As predicted, the ordering of growth above each inclusion structure depended on strain magnitude and surface uniformity. Strain fields from circular, square and ring-shaped inclusions produced non-uniform deformations, but still directed nucleation and growth. Guided islanding occurred on strain fields from circular inclusions 600nm in diameter, on rings of 800 nm outside diameter & 400 nm inside diameter and atop 800 nm squares. Strain fields generated by line-shaped inclusions nucleated one line (inclusion width ≤ 800 nm) or two lines (width ≥ 1000 nm) of islands with uniform size and spacing. Adjacent to the strain-induced deformation, a denuded region formed, indicating a significant diffusion gradient due to compressive strain. Finally, growth of arrays with single QD elements was observed with excellent correlation to the strain maxima above inclusion arrays. The region between the maxima was completely denuded of growth, again indicating an outward diffusion gradient. The line and array growths resulted in highly ordered structures. These results demonstrate that high resolution strain inclusion patterns can accurately control islanding during heteroepitaxial growth, providing a novel method for nanostructure fabrication.