In this paper two methods of measuring the thickness of a thin film layer on polymer substrate are presented. The first one is based on a polarizing microscope and analyzing the interference spectrum of white light reflected by the specimen. The second is a microscope with a high numerical aperture lens. The interference fringes caused by the birefringence of the polymer substrate can be eliminated, and by a numerical procedure the film index and thickness can be extracted from the measured reflection spectrum. As an example, we made measurements on a single layer UV glue thin film coated on a polymer substrate, polyethylene terephthalate (PET) in this case. We used the Fourier Transform method to analyze the spectrum and confirmed the effect of these methods.
The ellipsometric image contrast for patterned film in whole visible range is simulated and analyzed in this article. By the Fresnel equation and the Jones Matrix, the characteristic wavelength selection method to enhance the image contrast is built. The ellipsometric reflected intensity of specific thin film is nulled into dark by rotating the phase angle of compensator and the azimuth angle of polarizer in whole visible range, which results in higher contrast between non-null and null images after the proper wavelength selection. The approach enables the image defect recognition of patterned film more obvious than recent single wavelength imaging ellipsometry and white light reflective image.
When we used spectrometer with array sensor to calculate thickness or control refractive index, spectrum resolution was the important factor if we measured the reflectance or transmittance as our first step. This situation would be emphasized while the testing sample was the super thick film (>20 μm) which caused the large dense reflectance or transmittance spectrum. In this paper, we developed a method to improve the measurable range of film thickness by use of the different incident angle spectrum. It means the spectrum obtained from thick film would become sparser even we used the same hardware. Some concrete examples would be described here and their results would be shown in this paper.
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