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

Dorian Minkov,Elias Saugar,George Angelov,Emilio Marquez,Susana Ruano,Gavril Gavrilov

doi:10.3390/ma14164681

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(λ) of the specimen, based on the envelope method. Firstly, it is demonstrated that the accuracy of characterization, of the average film thickness and the thickness non-uniformity ∆d over the illuminated area, increases, employing a simple dual transformation utilizing the product T(λ)xs(λ), where Tsm(λ) is the smoothed spectrum of T(λ) and xs(λ) 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 and ∆d, as this approach is applicable no matter whether the substrate is transparent or non-transparent. Thirdly, the refractive index n(λ) and the extinction coefficient k(λ) are computed, employing curve fitting by polynomials of the optimized degree of 1/λ, instead of by previously used either polynomial of the optimized degree of λ or a two-term exponential of λ. 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 and n(λ) of these films.

Highlights

Optical dielectric and semiconductor thin films have numerous applications in research and development, in applied sciences and engineering [1,2,3]
The main approach for the optical characterization of a thin dielectric or semiconductor film is founded on the analysis of the transmittance spectrum T(λ) of a sample consisting of the film on a substrate, at normal light incidence to the film [16,17,18]
Three issues are investigated for further increasing the accuracy of the characterization of a thin dielectric or semiconductor film on a substrate from T(λ) of the specimen, based on the EM

Summary

Introduction

Optical dielectric and semiconductor thin films have numerous applications in research and development, in applied sciences and engineering [1,2,3]. Such films, with thicknesses of at least 300 nm, are used in solar cells [4,5], thin-film transistors [6,7], photonic circuits [8,9], holography [10,11], and thin-film batteries [12,13]. The primary goal of such analysis of T(λ) is to determine the spectral dependencies of the refractive index n(λ) and the Materials 2021, 14, 4681 of T(λ) is to determine the spectral dependencies of the refractive index n(λ) and the exextinction coefficientk(λ), k(λ),as aswell wellas asthe theaverage averagethickness thickness d ofthe thefilm filmover overthe theilluminated illuminated tinction coefficient d of area area[22,23]

Methods

Results

Discussion

Conclusion