Controlling the relaxation mechanism of low strain Si1−xGex/Si(001) layers and reducing the threading dislocation density by providing a preexisting dislocation source

Abstract

Strain relaxed Si 1Àx Ge x buffer layers on Si(001) can be used as virtual substrates for the growth of both strained Si and strained SiGe, which are suitable materials for sub-7 nm CMOS devices due to their enhanced carrier mobility. For industrial applications, the threading dislocation density (TDD) has to be as low as possible. However, a reduction of the TDD is limited by the balance between dislocation glide and nucleation as well as dislocation blocking. The relaxation mechanism of low strain Si 0:98 Ge 0:02 layers on commercial substrates is compared to substrates with a predeposited SiGe backside layer, which provides threading dislocations at the edge of the wafer. It is shown that by the exploitation of this reservoir, the critical thickness for plastic relaxation is reduced and the formation of misfit dislocation bundles can be prevented. Instead, upon reaching the critical thickness, these preexisting dislocations simultaneously glide unhindered from the edge of the wafer toward the center. The resulting dislocation network is free of thick dislocation bundles that cause pileups, and the TDD can be reduced by one order of magnitude.

Nanoscale Mapping of the 3D Strain Tensor in a Germanium Quantum Well Hosting a Functional Spin Qubit Device

“…Alternatively, the MD could be located close to the interface between the top SiGe barrier and the Ge QW or at the interface between the top SiGe barrier and the only 2 nm thin, but highly strained Si cap. Its orientation and slipping plane match that for MDs in the (Si)­Ge/Si(001) system, which typically run parallel to ⟨110⟩ directions within the interface, allowing us to determine the precise orientation of the lattice planes within the SXDM maps.…”

“…We attribute these gradual changes in the Ge QW layer lattice strain, occurring over a length scale of the order of 1 μm, to two interdependent effects. First, the misfit dislocation bunches in the virtual substrate, oriented along the [110] and [ 1 1̅ 0 ] directions, , generate local lattice distortions that propagate upward into the QW layer . Second, these lattice fluctuations are also driving local variations of the Ge content in the SiGe buffer, which, in turn, induce a spatial variation of the in-plane lattice parameter of the coherent QW epilayer .…”