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Abstract
To meet various physical property requirements of materials for advanced applications for specific devices, combinations of Si/Ge, Ge/Si, Si1-xGex/Si, are frequently introduced in the device fabrication process. Epitaxy, condensation and annealing processes are commonly used. Since a small variation in composition, strain and crystallinity can result in reduced device performance or failure, the composition, strain and crystallinity must be carefully monitored and controlled throughout the manufacturing process. We have studied the dependence of Ge and Si intermixing on annealing temperature and Raman excitation wavelength. Using multiwavelength Raman spectroscopy, we found Ge and Si intermixing in epitaxially grown Ge(100)/Si(100) after successive thermal anneals. Very strong dependence of signal-to-noise (S/N) ratio measurements on excitation wavelength and film structure was observed. Suitable excitation wavelengths must be chosen to properly characterize Si and Ge-based heteroepitaxial layers based on the thickness, stacking order and composition of epitaxial films having different optical properties at different wavelengths.
Highlights
The origin of tensile strain in Ge(100) film is speculated to be the difference between coefficients of thermal expansion (CTE) of Ge and Si
As material property enhancement techniques, combinations of Si/Ge, Ge/Si, Si1-xGex/Si are frequently introduced in the device fabrication process to meet various physical property requirements of materials for advanced application-specific devices
Heteroepitaxy, condensation and annealing processes are commonly used in advanced device manufacturing
Summary
514.5 nm excitation Raman spectra.— A 514.5 nm Ar+ ion laser line is frequently used for Raman characterization of semiconductor materials due to its availability, intensity and stability as an excitation source.[9,25,26,27,28] Figure 2 shows 514.5 nm excited linear and log scale Raman spectra from reference Si, reference Ge, reference thin (0.2 μm thick) epitaxial Ge(100)/Si(100) and epitaxially grown 1.0 μm thick Ge/Si wafers after thermal annealing in the temperature range of 800 ∼ 875◦C. The peak position shifts under the presence of strain/stress and isotopic variations.[4,5,9,27,28,29,30,31] Alloys of Si and Ge (Si1-xGex) typically show three Raman peaks of Ge-Ge (∼300 cm−1), Si-Ge (∼400 cm−1) and Si-Si (∼500 cm−1). The alloy composition can be estimated from Raman spectra
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