Sources of error in spectroscopic low-level integrated light scattering measurements

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Abstract
A wavelength scanning, total integrated scattering instrument has been constructed for backward and forward light scattering studies in the 400 - 1000 nm wavelength range. In both modes calibration can be made with two references, one diffuse and one specular. The two types of calibration give similar results in reflectance mode, but in transmittance mode, some discrepancies were noted. Correctly positioned apertures suppress stray light from the source. A detailed study has been made on the effects of this arrangement when low level scattering samples are studied. Small amounts of scattering from the source optics can be erroneously registered as originating from the sample. This stray light can have a dramatic impact on the determination and interpretation of scattering from low scattering multilayer samples. It is shown that a diffuse reflectance spectrum of a thermally oxidized silicon wafer, where the stray light has not been considered, would be interpreted as due to correlated interface roughness. When the stray light was blocked the spectra implied uncorrelated interface roughness. It is recommended to combine reflectance and transmittance measurements of scattered light to ensure correct interpretation.

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