Nanostressors and the Nanomechanical Response of a Thin Silicon Film on an Insulator

Abstract

Pseudomorphic three-dimensional Ge nanocrystals (quantum dots) grown on thin silicon-on-insulator substrates can induce significant bending of the silicon template layer that is local on the nanometer scale. We use molecular dynamics simulations and analytical models to confirm the local bending of the Si template and to show that its magnitude approaches the maximum value for a freestanding membrane. The requisite greatly enhanced viscous flow of SiO2 underneath the Si layer is consistent with the dependence of the viscosity of SiO2 on shear stress.

Mechanical stability of ultrathin Ge∕Si film on SiO2: The effect of Si∕SiO2 interface

“…2͑f͔͒. Therefore, it provides an indirect support to the suggestion that the experimentally observed large local bending 6,7 is assisted by the local nonlinear viscous flow of SiO 2 , because no void was observed in the experiment. 6,7 A direct proof, however, requires simulation of the nonlinear viscoelastic property of SiO 2 .…”

“…6 Our theory further showed that the magnitude of the observed local bending approaches the linear elastic limit for a freestanding Si layer, and such bending instability may occur generally for a very thin freestanding Si layer when the Ge island density is low. 7 Because experimentally no vacuum blister ͑void͒ was observed at the Si/ SiO 2 interface, it is suggested that the local bending of Si is achieved by a local nonlinear viscous flow of SiO 2 which makes Si layer behave like a freestanding film. 6,7 In this letter, using finite element analysis ͑FEA͒, we examine the mechanical stability of ultrathin Ge/ Si/ SiO 2 composite film within the linear elastic regime, without viscous flow of SiO 2 .…”

“…7 Because experimentally no vacuum blister ͑void͒ was observed at the Si/ SiO 2 interface, it is suggested that the local bending of Si is achieved by a local nonlinear viscous flow of SiO 2 which makes Si layer behave like a freestanding film. 6,7 In this letter, using finite element analysis ͑FEA͒, we examine the mechanical stability of ultrathin Ge/ Si/ SiO 2 composite film within the linear elastic regime, without viscous flow of SiO 2 . We focus our study on the effect of Si/ SiO 2 interface by employing imperfect interface elements between Si and SiO 2 to simulate different bonding and relaxation mechanisms at the Si/ SiO 2 interface.…”

Germanium hut nanostressors on freestanding thin silicon membranes

“…4, 1 2 h s / R is estimated using Ref. 9 and compared to the strain predicted by elastic strain sharing. 1 For all template layer thicknesses greater than 2.4 nm, the predicted strain at the template layer-hut interface due to curvature exceeds the strain developed by elastic strain sharing, reaching a maximum of 1.6% on 4-nm-thick template layers.…”

“…With appropriate growth conditions, even SOI template layers constrained by the buried oxide layer can be distorted by Ge huts. 8,9 In this letter, we present a conceptually simpler approach: to fabricate Ge huts on freestanding template layers. These layers can be deformed without requiring the unusually high growth temperatures of 700°C that must be used to cause SiO 2 to flow beneath unreleased layers.…”