Two-dimensional strain-mapping by electron backscatter diffraction and confocal Raman spectroscopy

Area of Science:

• Materials Science
• Solid Mechanics
• Nanotechnology

Background:

• Spherical indentation in silicon creates complex residual strain fields.
• Accurate mapping of these strain fields is crucial for understanding material behavior and device reliability.
• Existing techniques may have limitations in characterizing multiaxial strain states.

Purpose of the Study:

• To map the two-dimensional (2-D) strain field surrounding a spherical indentation in silicon.
• To assess and compare the accuracy of electron backscatter diffraction (EBSD) cross-correlation and confocal Raman spectroscopy for strain mapping.
• To evaluate the potential of these techniques for enhancing the reliability of microelectromechanical systems (MEMS).

Main Methods:

• Two-dimensional (2-D) strain mapping using electron backscatter diffraction (EBSD) cross-correlation.
• Confocal Raman spectroscopy for mapping residual stress.
• Spherical indentation with a 200 mN load on a silicon (001) surface.
• Generation of 50 µm × 50 µm maps with 128 pixels × 128 pixels resolution.

Main Results:

• EBSD revealed a residual strain field with in-surface normal and shear strains, exhibiting two-fold symmetry.
• Raman spectroscopy showed a residual Raman shift field with positive shifts and four-fold symmetry.
• Both strain fields extended approximately three to four indentation diameters from the contact.
• EBSD results, combined with mechanical-spectroscopic analysis, successfully predicted the Raman shift map characteristics.

Conclusions:

• Electron backscatter diffraction (EBSD) and confocal Raman spectroscopy are effective techniques for mapping 2-D strain fields in silicon.
• The study demonstrates the capability of these methods to characterize multiaxial strain states.
• These techniques can enhance the reliability of microelectromechanical systems (MEMS) by identifying critical strain fields.