Nondestructive characterization of nitrogen-implanted silicon-on-insulator structures by spectroscopic ellipsometry

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Abstract
Silicon-on-insulator structures implanted by 200-keV nitrogen with a dose of 7.5×1017 atoms/cm2 were studied by spectroscopic ellipsometry (SE). The SE measurements were carried out in the 300–700-nm wavelength (4.13–1.78-eV photon energy) range. For the analysis of the SE data we used the conventional method of assuming appropriate optical models and fitting the model parameters (layer thicknesses and compositions) by linear regression. Calculated data were in good agreement with measurements when a seven-layer model, consisting of surface oxide layer, thick silicon layer, upper two interface layers, thick nitride layer, and lower two interface layers, was applied. Results obtained by SE were compared with those from Rutherford backscattering spectroscopy (RBS) and transmission electron microscopy. In contrast with RBS measurements, we found that the sensitivity of our optical model combined with the fitting technique was good enough to resolve the silicon-rich transition layers at the upper and lower interfaces of the buried nitride layer.