Strain maps on statically bend (001) silicon microbeams using AFM-integrated Raman spectroscopy

Material characterization at the micron-scale is of great importance in the design phase and for the estimation of the reliability of micro and nanoelectromechanical systems (MEMS/NEMS). We present a coupled technique for extracting material property information based on a defined force application on silicon beams in combination with a mapping of the resulting strains using an atomic force microscope integrated in a Raman spectroscope. Experimental data are compared to analytical predictions from the theory of elasticity. This technique will be useful, e.g., for the identification of stress concentrations in micro machined devices. The experiment is based on a bidirectional polarized micro-Raman diffraction in a backscattering configuration from a (001) silicon surface of a [001] parallel loaded micro-cantilever. A scalar-based relationship of the shift of the Raman frequency and strain is developed, taking into account the penetration depth of the laser into the silicon, as well as the drift of the optomechanical construction of the spectroscope. An effect of frequency shifts, induced by the laser energy, has been observed along the axis of the micro-cantilever.