Tensor Evaluation of Anisotropic Stress Relaxation in Mesa-Shaped SiGe Layer on Si Substrate by Electron Back-Scattering Pattern Measurement: Comparison between Raman Measurement and Finite Element Method Simulation

Abstract

A strained SiGe layer will be used in next-generation transistors to improve device performance along with device scaling. However, the stress relaxation of the SiGe layer may be inevitable in nanodevices, because the SiGe layer is processed into a nanostructure. In this study, we evaluated the anisotropic stress relaxation in mesa-shaped strained SiGe layers on a Si substrate by electron backscattering pattern (EBSP) measurement. Moreover, we compared the results of EBSP measurement with those of anisotropic Raman measurement and finite element method (FEM) simulation. As a result, the anisotropic stress relaxation obtained by Raman spectroscopy was confirmed by EBSP measurement. Additionally, we obtained a good correlation between the results of EBSP measurement and FEM simulation. The σ x x and σ y y stresses were markedly relaxed and the σ z z and σ x z stresses were concentrated at the SiGe layer edges. These stresses were mostly relaxed in the distance range from the SiGe layer edges to 200 nm. Therefore, in a SiGe nanostructure with a scale of less than 200 nm, stress relaxation is inevitable. The results of EBSP and Raman measurements, and FEM simulation show a common tendency. We believe that EBSP measurement is useful for the evaluation of stress tensors and is complementary to Raman measurement.

Evaluation of Anisotropic Biaxial Stress in Si1-X Ge x /Ge Mesa-Structure by Oil-Immersion Raman Spectroscopy

“…From the result, the peaks of Si 1-x Ge x were observed on the lower wavenumber side. As is known that strain relaxation in the mesa shaped structure occurs in the range of sub-m [10], it is considered that the stress of the Si 1-x Ge x mesa structures is not relaxed. Therefore, the relaxation of the Si 1-x Ge x was investigated as a function of W for sub-m W. Figure 4(a) and 4(b) show the Raman spectra from the Si 1-x Ge x (x = 0.76) nanostructure with the various Ws in the LO and TO active conditions, respectively.…”

“…In recent years, complicated nanostructure, such as FinFET has emerged for achieving efficient transistors. However, during the nanoscaling processes, stress relaxation in the Si 1-x Ge x is inevitable along both parallel and perpendicular directions to the patterned nanostructure [9,10]. Therefore, control of the strain induced in nano-scaled devices has been strongly desired.…”

Strain distributions in carbon-doped silicon nanowires along [110] and [100] investigated by X-ray diffraction

“…Such strain relaxations around the edge of nanofabricated structures have also been reported for SiGe and SiGe-on-insulator. 14,16,17,22,23) Residual strains in relaxed regions decrease from the bottom to the top layers. The most relaxed positions are both edges on the top layers of all nanowires.…”

“…Local strains in nanostructures have been extensively studied by Raman spectroscopy, 2,4,8,13,16,17,20,21) microbeam X-ray diffraction, 3,7,9,10,12,14,15,19,23) electron backscattering pattern 16,17) and dark field electron holography. 5,6,18,22) These methods give excellent results with very fine spatial resolution but are not suitable for statistical investigations since local and individual characteristics are emphasized By observing samples with many nanowires periodically arranged within a 1.5 mm × 1.5 mm region with X-rays of sub-millimeter beam width, we obtained statistically averaged characteristics while eliminating the effects of individual nanowire differences, as previously reported.…”

Phonon dispersion of bulk Ge-rich SiGe: inelastic X-ray scattering studies

“…We confirmed the orientation distribution and crystallinity of the SiGe sample by EBSP measurement using a field emission scanning electron microscope (SU-70, Hitachi). 22) The accelerating voltage was 20 kV and the measurement step was 10 μm. 2.2.2.…”