Fast thickness measurement of thin films using two-dimensional Fourier transform-based structured illumination microscopy

Effective measurement of the surface and thickness variation of thin films are important to achieve a special function and better performance for a coated optical device. In this research, we propose a new incoherent technique named Fourier transform based structured illumination microscopy (FTSIM) to detect the surface topography and thickness distribution. In this technique, a sinusoidal fringe pattern produced by digital micro-mirror devices (DMD) is projected onto the sample. The modulation estimation which depends on the surface and thickness of thin films is obtained by two-dimensional Fourier transform algorithm. Further, separating the reflected signals from the film boundaries, the surface finish of the film, as well as a film thickness map, can be achieved at the same time. With this method, only one pattern is required to determine the modulation value of a whole field. The measurement system is relatively simple and only an ordinary objective is enough to achieve imaging of the sample. Both theory and experiments are conducted in detail to demonstrate that the availability of this method.