Conventional transparent film thickness measurement methods such as spectroscopy are essentially capable of measuring only a single point at a time, and their spatial resolution is limited. We propose a film thickness measurement method that is an extension of the global model-fitting algorithm developed for three-wavelength interferometric surface profiling. It estimates the film thickness distribution from an interference color image captured by a color camera with three-wavelength illumination. The proposed method is validated through computer simulations and experiments.

We propose a fast surface-profiling algorithm based on white-light interferometry by use of sampling theory. We first provide a generalized sampling theorem that reconstructs the squared-envelope function of the white-light interferogram from sampled values of the interferogram and then propose the new algorithm based on the theorem. The algorithm extends the sampling interval to 1.425 microm when an optical filter with a center wavelength of 600 nm and a bandwidth of 60 nm is used. The sampling interval is 6-14 times wider than those used in conventional systems. The algorithm has been installed in a commercial system that achieved the world's fastest scanning speed of 80 microm/s. The height resolution of the system is of the order of 10 nm for a measurement range of greater than 100 microm.

A new surface profiling algorithm called the local model fitting (LMF) method is proposed. LMF is a single-shot method that employs only a single image, so it is fast and robust against vibration. LMF does not require a conventional assumption of smoothness of the target surface in a band-limit sense, but we instead assume that the target surface is locally constant. This enables us to recover sharp edges on the surface. LMF employs only local image data, so objects covered with heterogeneous materials can also be measured. The LMF algorithm is simple to implement and is efficient in computation. Experimental results showed that the proposed LMF method works very well.

We have developed a fast and robust surface profiling method by using multi-wavelength single-shot interferometry. The interference patterns are simultaneously captured by a newly developed multi-wavelength imaging system, which is easily and economically constructed by using a commercially available RGB LED illuminator and a color camera. With this imaging system, we first developed a two-wavelength single-shot technique and successfully measured 350 nm step height. Then we expanded it to a three-wavelength and successfully measured 1000 nm step height. For this purpose, we have developed some algorithms including crosstalk compensation and frequency estimation. The algorithms used and experimental results are presented.

As a single-shot interferometric technique, spatial carrier interferometry has been thoroughly investigated, and it has been shown to have some problems, such as low spatial resolution. To overcome the problems, we propose a novel single-shot surface profiling technique that does not require carrier introduction. It is based on a model-fitting algorithm and estimates the model parameters and the heights of plural points simultaneously based on their multi-wavelength intensity data. The validity of the proposed method is demonstrated by computer simulations and actual experiments.