2 research outputs found
Imaging Structure and Composition Homogeneity of 300 mm SiGe Virtual Substrates for Advanced CMOS Applications by Scanning X‑ray Diffraction Microscopy
Advanced semiconductor heterostructures
are at the very heart of
many modern technologies, including aggressively scaled complementary
metal oxide semiconductor transistors for high performance computing
and laser diodes for low power solid state lighting applications.
The control of structural and compositional homogeneity of these semiconductor
heterostructures is the key to success to further develop these state-of-the-art
technologies. In this article, we report on the lateral distribution
of tilt, composition, and strain across step-graded SiGe strain relaxed
buffer layers on 300 mm Si(001) wafers treated with and without chemical–mechanical
polishing. By using the advanced synchrotron based scanning X-ray
diffraction microscopy technique K-Map together with micro-Raman spectroscopy
and Atomic Force Microscopy, we are able to establish a partial correlation
between real space morphology and structural properties of the sample
resolved at the micrometer scale. In particular, we demonstrate that
the lattice plane bending of the commonly observed cross-hatch pattern
is caused by dislocations. Our results show a strong local correlation
between the strain field and composition distribution, indicating
that the adatom surface diffusion during growth is driven by strain
field fluctuations induced by the underlying dislocation network.
Finally, it is revealed that a superficial chemical–mechanical
polishing of cross-hatched surfaces does not lead to any significant
change of tilt, composition, and strain variation compared to that
of as-grown samples
Nanoscale Mapping of the 3D Strain Tensor in a Germanium Quantum Well Hosting a Functional Spin Qubit Device
A strained Ge quantum
well, grown on a SiGe/Si virtual substrate
and hosting two electrostatically defined hole spin qubits, is nondestructively
investigated by synchrotron-based scanning X-ray diffraction microscopy
to determine all its Bravais lattice parameters. This allows rendering
the three-dimensional spatial dependence of the six strain tensor
components with a lateral resolution of approximately 50 nm. Two different
spatial scales governing the strain field fluctuations in proximity
of the qubits are observed at 1 μm, respectively.
The short-ranged fluctuations have a typical bandwidth of 2 ×
10–4 and can be quantitatively linked to the compressive
stressing action of the metal electrodes defining the qubits. By finite
element mechanical simulations, it is estimated that this strain fluctuation
is increased up to 6 × 10–4 at cryogenic temperature.
The longer-ranged fluctuations are of the 10–3 order
and are associated with misfit dislocations in the plastically relaxed
virtual substrate. From this, energy variations of the light and heavy-hole
energy maxima of the order of several 100 μeV and 1 meV are
calculated for electrodes and dislocations, respectively. These insights
over material-related inhomogeneities may feed into further modeling
for optimization and design of large-scale quantum processors manufactured
using the mainstream Si-based microelectronics technology