Critical thickness enhancement of epitaxial SiGe films grown on small structures

This paper explores stress management in SiGe with two kinds of structures, namely, epitaxial SiGe films on small pillars and fins. In addition to the compliant substrate effect in the film/fin structures, the geometric effect in the film/pillar structures plays another important role in critical thickness enhancement. The stress-strain states of these two systems are calculated and the equilibrium critical thicknesses are predicted, using the work method, for different fin thicknesses, pillar radii, and Ge concentrations. Compared to conventional films grown on planar bulk substrates, the critical thicknesses for fin and pillar structures are increased significantly. SiGe films with various thicknesses and compositions were epitaxially grown around vertical fins and horizontal membranes with thicknesses as thin as 12nm to demonstrate the concepts. Cross-sectional transmission electron microscopy analysis showed that dislocation densities are much smaller than for films grown on bulk Si substrates. The dislocation density versus fin thickness also illustrated the expected trend.