Thickness and Surface Measurement of Transparent Thin-Film Layers using White Light Scanning Interferometry Combined with Reflectometry

Abstract

Surface profiling and film thickness measurement play an important role for inspection. White light interferometry is widely used for engineering surfaces profiling, but its applications are limited primarily to opaque surfaces with relatively simple optical reflection behavior. The conventional bucket algorithm had given inaccurate surface profiles because of the phase error that occurs when a thin-film exists on the top of the surface. Recently, reflectometry and white light scanning interferometry were combined to measure the film thickness and surface profile. These techniques, however, have found that many local minima exist, so it is necessary to make proper initial guesses to reach the global minimum quickly. In this paper we propose combing reflectometry and white light scanning interferometry to measure the thin-film thickness and surface profile. The key idea is to divide the measurement into two states; reflectometry mode and interferometry mode to obtain the thickness and profile separately. Interferogram modeling, which considers transparent thin-film, was proposed to determine parameters such as height and thickness. With the proposed method, the ambiguity in determining the thickness and the surface has been eliminated. Standard thickness specimens were measured using the proposed method. Multi-layered film measurement results were compared with AFM measurement results. The comparison showed that surface profile and thin-film thickness can be measured successfully through the proposed method.

Depth-resolved local reflectance spectra measurements in full-field optical coherence tomography

“…3(c)). Since the thickness as well as the optical index of the layer are related to the modulation of the spectrum [27,28], the slight difference in the period of the latter can be explained by their values for dispersion used in the program which may be slightly different from the real ones ( Fig. 3(c)).…”

Continuous In-Line Chromium Coating Thickness Measurement Methodologies: An Investigation of Current and Potential Technology

“…As the optical path difference will change relative to the reference mirror and the sample as a function of coating thickness, differing phases based on the optical path difference will provide constructive or destructive interference for the output signal. There are many variants of optical interferometry, such as using differing light sources such as white light or singular wavelength [ 16 , 82 ], differing optical path layouts [ 83 , 84 ], and differing detection elements [ 85 , 86 ]. There are many interferometric solutions for the measurement of thin film thickness which operate on the principle of interference but utilize different components within the system for different applications.…”

Local inspection of refractive index and thickness of thick transparent layers using spectral reflectance measurements in low coherence scanning interferometry

“…The algorithm provides one of them depending on the initial value of the fitting parameters. Some studies were intended to find a good initial estimation of these parameters for quickly converging towards the global minimum [14,15]. In this work, we use an alternative solution which consists in varying the initial values of the pair of parameters ( and ) within one given range and then recording both the local minimum and the final error (difference between the optimized model and the data) provided by the algorithm.…”