Highly sensitive strain detection in silicon by reflectance anisotropy spectroscopy

Abstract

Reflectance anisotropy spectroscopy (RAS) measurements were performed on strained silicon (Si) stripes cut from crystalline silicon wafers. Strains were externally applied using a device developed especially for the study of layers and layered structures. The dependence of the RAS signal intensity on strain was measured for (100), (110), and (111) silicon wafers strained along [001] and [011]. In these configurations, the RAS spectra show a derivativelike structure at 3.4 eV, which increases in amplitude linearly with strain. While RAS line shapes depend on the orientation of the Si wafer and the crystallographic directions along which strains are applied, RAS intensities depend on strain magnitude. Strains as low as ${10}^{\ensuremath{-}5}$ can be measured, which is two orders of magnitude smaller than those detected with standard techniques such as Raman, piezoelectroreflectance spectroscopy (PERS), or x-ray diffraction (XRD). The experimental RAS spectra are found to be in good agreement with spectra calculated on the basis of the spectral response of the published piezo-optical tensor components. It is concluded that RAS provides a highly sensitive tool for the detection of strain induced bulk anisotropies. Strain calibrated RAS spectra can be used for strain-stress characterization of semiconductor layers and microstructures with a higher efficiency than that achieved by Raman, PERS, and XRD. Combined with growth techniques, RAS spectroscopy can be also used for in situ control of strain during semiconductor growth.