Thin-film thickness measurement with normal spectral reflectance

Abstract

Thin films are used in many areas for protecting the base, isolating electrons, and so on. Based on the thin-film interference principle and the characteristics of Y-shaped fiber, this paper proposed a reflection objective with annular reflection. With the objective, incident light from the central fiber can be well received for high signal-to-noise ratio. By comparing with the prior-known spectral reflectance of the standard mirror, the absolute spectral reflectance of the thin-film can be achieved. Furthermore, according to the spectral reflectance of the thin-film, film thickness is acquired by the evolutionary genetic algorithm. In the algorithm, the thickness is taken as the independent variable, and the squared difference between the measured spectral reflectance and the preset theoretical spectral reflectance is set as the goal to carry out the global optimization. By testing different silicon-based silica films, the measurement results proved high feasibility and good global fitness. And the total measurement time of a single point is less than 1s. In conclusion, the thin-film measurement system based on the proposed reflection objective and inversion algorithm own excellent performance, which is hopeful for broad usage.