Critical thickness enhancement of epitaxial SiGe films grown on small structures

Abstract

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.

Morphology of Epitaxial Core−Shell Nanowires

“…Ignoring non-linear elastic effects, Hooke's law and equilibrium conditions readily yield the stress distribution. 21,22 Axial symmetry dictates that the variations in stresses and strains are limited to in-plane normal components within the shell. Therefore, the surface stress state is entirely due to the non-zero normal components with similar magnitudes, σ * θθ and σ * zz .…”

Raman spectroscopy and strain mapping in individualGe-SixGe1−xcore-shell nanowires

“…19,32 The strain induced shift of the Raman peak is described by The secular equation can be simplified by considering the form of the core's strain tensor expected when cylindrical symmetry is assumed. [12][13][14] We employ a NW-oriented Cartesian coordinate system with the z-axis along the [111] crystal direction and nanowire main axis, and with the x-and y-axis defined by the [1 1 0] and [11 2 ] crystal directions, respectively. In this coordinate system, the core's strain tensor is expected to take the form: …”

“…The strain distribution of core-shell nanowires, which is markedly different than that of planar heterostructures, has been studied theoretically by several groups. [12][13][14][15] Here we present an experimental study of the strain in individual Ge-Si x Ge 1-x core-shell nanowires, determined using Raman spectroscopy combined with lattice dynamic theory.…”

Design and analysis of nanowire p-type MOSFET coaxially having silicon core and germanium peripheral channel

“…14) Also, the critical thickness of the Ge epitaxy layer on the Si nanowire structure is enhanced and the stress decreases as the Ge layer becomes thicker. 31) Owing to the lack of systematic experiments on critical thickness in the case of condensation processing, it can be safe to reference the results of the epitaxial growth of Ge on Si, and a problematic thickness can be discarded in an actual device realization. Since the nanowire channel surface is basically omnidirectional, the highly angle-dependent strain effects on the on-and off-state current characteristics through the band structure modification become complicated.…”