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Journal of the Optical Society of America

Journal of the Optical Society of America

  • Vol. 69, Iss. 8 — Aug. 1, 1979
  • pp: 1143–1152

Polycrystalline silicon film thickness measurement from analysis of visible reflectance spectra

P. S. Hauge  »View Author Affiliations

JOSA, Vol. 69, Issue 8, pp. 1143-1152 (1979)

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An algorithm is described whereby the thickness of polycrystalline silicon (polysilicon) films on oxidized silicon substrates may be determined from the magnitude and wavelength positions of extrema in the visible reflectance spectra. The underlying layer structure, which can consist of two or more layers, is combined mathematically with the silicon into an effective homogeneous substrate to facilitate analysis. Polysilicon layers from about 20 nm to about 1 µm in thickness are measurable for underlying layers in approximately the same range. Proper account is taken of absorption in the polysilicon layer, and interference effects in the underlying layers when they are sufficiently thick. Reflectance lowering caused by scattered light is corrected with the aid of the measured reflectance at 400-nm wavelength, where the polysilicon is opaque. The algorithm is practically insensitive to overlying oxide layers up to 55 nin in thickness, so that buried polysilicon layers are also measurable. When implemented on an automated spectrophotometer, the algorithm provides thickness values in essentially real time, with a precision of about 0.1 nm.

© 1979 Optical Society of America

P. S. Hauge, "Polycrystalline silicon film thickness measurement from analysis of visible reflectance spectra," J. Opt. Soc. Am. 69, 1143-1152 (1979)

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  1. K. L. Konnerth and F. H. Dill, "In-situ Measurement of Dielectric Thickness During Etching or Development Process," IEEE Trans. Electron Devices ED-22, 452–456 (1975).
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  12. Standard deviation is calculated as if the thickness values were normally distributed, while in fact they are not. Spread in these values is more indicative of systematic error than of random error. The quantity is typically less than 1% of the film thickness for measurements of films thicker than about 200 nm.
  13. A wavelength cutoff point is used to eliminate from consideration extrema below a certain wavelength, typically 500 nm, as they are more likely to be inaccurate or extraneous (e.g., produced by noise.)
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