Epitaxial Si wafers are widely used for high performance advanced memory devices and CMOS image sensor (CIS) device manufacturing. Surface morphology observation and resistivity measurements are frequently done as quick in-line quality monitoring of epitaxial Si layers. High resolution X-ray diffraction (HRXRD) and etch pit characterizations are done for randomly selected wafers. However, these conventional characterization techniques are not sensitive enough to detect small quality variations in epitaxial Si wafers.

For Si wafers with multiple epitaxial layers and different dopant concentrations, the conventional characterization techniques are even less useful. Introduction of new epitaxial characterization techniques is strongly desired for effective in-line process monitoring. A non-contact, in-line characterization technique, with virtual depth profiling capability, would be beneficial for proper characterization of Si wafers with multiple epitaxial layers.

In this study, we have characterized 200 mm and 300 mm Si wafers with triple epitaxial layers using multiwavelength, high resolution Raman spectroscopy. Ninety three (93)-point wafer mapping measurements were performed on all wafers, Statistics of Raman signal intensity, shift and full-width-at-half-maximum (FWHM) 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 FWHM were measured between reference wafers and epitaxial wafers, indicating potential Si lattice stress and crystallinity. Excitation wavelength dependence of Raman signal intensity, shift and FWHM also indicated variations in Si lattice stress and crystallinity of epitaxial layers in the depth direction. Non-contact multiwavelength Raman measurements are very sensitive to the quality of epitaxial Si layers and are effective as a complimentary in-line process characterization and monitoring technique.