The quantitative characterization of SiGe layers by analysing rocking profiles in CBED patterns

Prior research has shown that strain in semiconductor layers is often affected by surface relaxation effects. Cross-sectional specimens are commonly used, but they introduce complications from surface deformation. Plan-view specimens offer a potential solution by avoiding these distortions. Established methods struggle to achieve monolayer precision in thickness measurements. Strain analysis remains challenging when multiple layers are involved. Existing techniques rely on kinematical approximations, which may not capture all interactions. Energy-filtered convergent beam electron diffraction (CBED) has been proposed for strain quantification. This gap motivated the development of a new approach combining plan-view specimens with rocking curve analysis.

The aim of the study is to improve the accuracy of strain and thickness measurements in Si/SiGe layers. The specific problem is the influence of surface relaxation on cross-sectional measurements. The motivation is to achieve monolayer precision in layer characterization. The study focuses on pseudomorphic systems grown by molecular beam epitaxy. It targets two- and three-layer structures for detailed analysis. The researchers propose using plan-view specimens to eliminate surface effects. They aim to refine strain calculations by comparing experimental and simulated rocking curves. The goal is to validate this method against theoretical strain values.

Plan-view specimens were prepared to avoid surface relaxation effects. Convergent beam electron diffraction (CBED) was used to collect Bragg line data. Energy-filtered CBED patterns were obtained for strain analysis. Rocking curves of Bragg lines were extracted from the diffraction patterns. Experimental rocking curves were compared to kinematical simulations. A computerized fit procedure was applied to refine layer parameters. Dynamical simulations were used to further improve the accuracy of results. The method was tested on Si/SiGe two- and three-layer systems.

Layer thickness was measured with monolayer precision using this method. Strain values matched theoretical predictions within acceptable ranges. The accuracy of strain analysis varied with layer sequence and thickness. Plan-view specimens eliminated surface relaxation effects successfully. Energy-filtered CBED provided clear Bragg line profiles for analysis. Rocking curves were compared to simulations using a computerized fit. The method allowed precise determination of composition and strain. Results demonstrated the feasibility of this approach for multilayer systems.

The authors propose that plan-view specimens improve strain measurements in Si/SiGe layers. They suggest that energy-filtered CBED with rocking curve analysis is effective. The method achieves monolayer precision in thickness measurements. Strain accuracy depends on layer sequence and thickness, as stated. The researchers propose that this approach outperforms cross-sectional methods. They suggest that surface relaxation effects are avoided with this technique. The method was validated against theoretical strain values successfully. The authors propose that this technique is suitable for multilayer systems.