Strains in Si as small as 104 (corresponding to stresses of 10 MPa) have been measured using electron back scatter diffraction (EBSD), with spatial resolution close to 10 nm, and confocal Raman microscopy (CRM) with spatial resolution approaching 100 nm. Analysis of EBSD patterns recorded along a line crossing the mid point of a 20 µm by 2 µm wedge indentation in Si allowed the distortion of the Si crystal to be characterized at each point. Similarly, CRM was used to measure Raman line shifts at each point on a line scan across the indentation, and these shifts were converted to stresses. Comparison of the results show extremely good agreement except very close to the indentation, where the EBSD results, which come from closer to the sample surface than the CRM, indicate greater stresses. Decreasing the CRM laser excitation wavelength to probe smaller sample depths led to convergence of the two measurements as the CRM wavelength and depth probed were decreased. The stress profiles are consistent with an inverse-square power law appropriate to the wedge indentation contact impression acting as an expanding cylinder embedded in the Si surface.
Citation: Applied Physics Letters
Pub Type: Journals
EBSD, Raman, stress, silicon, high resolution