Raman microprobe determination of local crystal orientation

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The analysis of local crystal orientation with micron spatial resolution is of prime importance in understanding the dynamics of crystal growth processes with potential for device applications. Examples of such processes are laser annealing, lateral epitaxial growth over oxides, and molecular-beam-epitaxial growth over structured substrates. We present here a nondestructive technique for obtaining such information based on polarization selective Raman scattering from near-diffraction limited O(1 μm) regions of the sample. Depth resolution is limited by the optical penetration depth at the laser wavelength, which is on the order of 1.0 μm for Si at visible wavelengths. By rastering the sample with respect to the probe laser beam, maps of the local crystal orientation can be obtained. Abrupt changes in crystal orientation at grain boundaries are readily apparent. This paper details the experimental apparatus and the method for extracting local crystal orientation information for the particular case of Si. Experiments on single crystals of known orientation are presented which confirm our theoretical predictions and serve to calibrate the technique. Practical examples of mapping of laser annealed silicon-on-oxide structures are given. The analysis shows the loss of the lateral epitaxial seed, with many grains exhibiting 〈110〉 surface normals, in agreement with qualitative results obtained from a destructive selective chemical-etching procedure. Signal intensities are such that orientation information at a single point can be recorded in less than 30 s, thus providing the potential for a real time in situ monitor of slow growth processes.

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Journal of Applied Physics

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