Two-Dimensional Strain-Mapping by Electron Backscatter Diffraction and Confocal Raman Spectroscopy
Andrew J. Gayle, Lawrence H. Friedman, Ryan Beams, Brian G. Bush, Yvonne B. Gerbig, Chris A. Michaels, Mark D. Vaudin, Robert F. Cook
The strain field surrounding a spherical indentation in silicon is mapped in two dimensions (2- D) using electron backscatter diffraction (EBSD) cross-correlation and confocal Raman spectroscopy techniques. The 200 mN indentation created a 4 m diameter residual contact impression in the silicon (001) surface. Maps about 50 m × 50 m area with 128 pixels × 128 pixels were generated in several hours, greatly extending the mapping capabilities of both techniques to multiaxial strain states in 2-D. EBSD measurements showed a residual strain field dominated by in-surface normal and shear strains, with alternating tensile and compressive lobes extending about three to four indentation diameters from the contact and exhibiting two- fold symmetry. Raman measurements showed a residual Raman shift field, dominated by positive shifts, also extending about three to four indentation diameters from the contact but exhibiting four-fold symmetry. The 2-D EBSD results, in combination with a mechanical- spectroscopic analysis, were used to successfully predict the 2-D Raman shift map in scale, symmetry, and shift magnitude. Both techniques should be useful in enhancing the reliability of microelectromechanical systems (MEMS) through identification of the 2-D strain fields in MEMS devices.