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Determination of Dopant Density Profiles of Heavily Boron-Doped Silicon From Low Temperature Microphotoluminescence Spectroscopy

Low temperature microphotoluminescence spectroscopy (μ-PLS) is employed to determine the inhomogeneous doping profiles for heavily boron-doped regions on silicon wafers. Samples having various Gaussian function doping profiles, in terms of surface dopant density and depth factor, are prepared via two-step thermal boron diffusion on high resistivity n-type silicon wafers. Measured PL spectra are normalized to the Si band–band luminescence peak, and PL components of undiffused Si are subtracted to resolve the doping peak. We show that the wavelength of the doping peak has a reliable and simple linear relationship with the measured surface dopant density on a semilog plot, and so establish a calibration curve which can be applied to estimate the surface dopant density. A second calibration curve for estimating the depth factor is also established after correcting the measured doping peak intensity to account for incomplete dopant ionization. We show the effectiveness of this method by reconstructing independently measured doping profiles using the surface dopant density and depth factors estimated from the PL spectra. Furthermore, by performing two-dimensional mapping, with μ-PLS measurements at 2 μm spatial resolution, we are able to map the surface dopant density and diffusion depth factor of micron-scale, locally diffused features.