Multi-wavelength Raman Characterization of Epitaxial Silicon Wafers for In-Line Process Characterization and Monitoring Applications

We have characterized 200-mm and 300-mm Si wafers with a single epitaxial layer and with a triple epitaxial layer stack atop using multi-wavelength, high-resolution Raman spectroscopy. 96-point wafer mapping measurements were performed on all wafers. Statistics of Raman signal intensity, shift and full-width-at-half maximum (FWEIM) values, under different excitation wavelengths, were extracted and compared with two types of reference Si wafers (prime Si wafers and reclaimed Si wafers). Significant variations in Raman signal intensity, shift and FWEIM were measured between reference wafers and epitaxial wafers indicating potential Si lattice stress and crystallinity variations. Excitation wavelength dependence of Raman signal intensity, shift and FWHM also indicated variations in the Si lattice stress and the crystallinity of epitaxial layers in the depth direction. Non-contact multi wavelength Raman spectroscopy was found to be very sensitive to the quality of epitaxial Si layers which makes this technique very effective in complimentary in-line process characterization and monitoring.