Initial estimation of thin film thickness measurement based on white light spectral interferometry

• The frequency of the nonlinear phase and overall visibility of the signal were applied.
• Both of methods were verified by the simulation and experiments.
• Both of the methods gave better results in shorter time than two commonly used global algorithms.

White-light interferometry has been extended into the spectral domain for many years. The authors discuss a white light spectral interferometer using a Michelson interferometric objective and spectrometer to measure the film thickness and propose two methods for initial estimation which are based on the frequency of the nonlinear phase and the overall visibility of the spectral signal. Both of the methods are capable of obtaining good, rapid, initial estimates in these measurements: our proposed methods are quicker than the commonly used global algorithms (simulated annealing algorithm and genetic algorithm). In terms of the speed and precision, the proposed methods are suited to in-line, high-speed measurement. In general, when the film thickness is more than 1 μm, it is better to use the method based on the nonlinear phase to estimate the initial value, and when the film thickness is < 1 μm, the method based on overall visibility is more applicable.