Calculation of thin-film optical constants by transmittance-spectra fitting

Determination of thin film refractive index and thickness by means of film phase thickness

“…As it was mentioned above, several alternatives based on equations (10), (13) or (14) λ EX T are also graphically illustrated in Fig. 3.…”

“…As alternatives for two-parameter Cauchy type dispersion (8) three-or more-parameter dispersion equations of power series type (functions of 1 λ 2 or 1 λ ) are used [10,13]:…”

“…Due to interference of light, an oscillating structure with maxima and minima is typical for thin films optical transmittance/reflectance spectra. Optical parameters of thin films can be extracted from optical spectra using several conventional methods [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Most precise information for a thin film may be obtained from transmittance spectra measurements at normal incidence of light [9], because these measurements do not depend on the properties of etalon mirrors and angle of incidence of light (as in case of reflectance measurements).…”

“…Another disadvantage of the envelope methods is the usage of interpolated points (not really measured) between two successive measured maxima or minima [1,2]. Curve fitting methods apply numerical optimisation to fit a theoretical model to measured data in order to find dispersion (λ) and thickness [9][10][11][12][13][14][15]. These methods need specific and flexible software environment for the calculations because of the variety of dispersion equations in literature [9].…”

“…These methods need specific and flexible software environment for the calculations because of the variety of dispersion equations in literature [9]. Curve fitting methods include all measured points of transmittance spectra, but these methods require specific software and very careful selection of the initial data [9][10][11][12][13][14][15]. Thin film phase thickness δ is connected with the optical thickness nd by the relationship δ = 2π λ (for normal incidence of light).…”