Further Increasing the Accuracy of Characterization of a Thin Dielectric or Semiconductor Film on a Substrate from Its Interference Transmittance Spectrum

Abstract

Three means are investigated for further increasing the accuracy of the characterization

of a thin film on a substrate, from the transmittance spectrum T(l) of the specimen, based on the

envelope method. Firstly, it is demonstrated that the accuracy of characterization, of the average film

thickness d and the thickness non-uniformity Dd over the illuminated area, increases, employing a

simple dual transformation utilizing the product T(l)xs(l), where Tsm(l) is the smoothed spectrum

of T(l) and xs(l) is the substrate absorbance. Secondly, an approach is proposed for selecting an

interval of wavelengths, so that using envelope points only from this interval provides the most

accurate characterization of d and Dd, as this approach is applicable no matter whether the substrate

is transparent or non-transparent. Thirdly, the refractive index n(l) and the extinction coefficient k(l)

are computed, employing curve fitting by polynomials of the optimized degree of 1/ , instead of

by previously used either polynomial of the optimized degree of or a two-term exponential of .

An algorithm is developed, applying these three means, and implemented, to characterize a-Si and

As98Te2 thin films. Record high accuracy within 0.1% is achieved in the computation of d and n(l) of

these films.