Fourier transformation mode infrared ray film thickness measuring method

摘要

PURPOSE:To obtain a Fourier transformation type infrared film thickness measuring apparatus available for accurate measurement of film thickness even if the specimen is covered with the film of high absorbability. CONSTITUTION:The apparatus is provided with an infrared polarizer 16 between infrared interference filler 14, specimen 17 and light source 9. When a reflection infrared spectrum is measured by a Brewster's angle, a vertical polarized light measurement assumes pronouncedly overlapped interference spectrums caused by the thickness of the thin film and a horizontal polarized light measurement does not include this feature at all and consequently, when the difference spectrum of both measurements is obtained, the spectrum obtained shows only an interference spectrum by the thickness of the film. By Fourier conversion of this difference spectrum, a noiseless cepstrum including only the side burst caused by the film thickness can be obtained. The higher calculation accuracy of the Fourier conversion, the narrower the wave length range of the infrared light. Further, many thin films do not show absorbability in the range of 2,700-1,800cm and by using an interference filter 14 transmitting the beams of light of this range, considerations not only of the calculation accuracy of the Fourier conversion, but also of the absorption by the thin film can be eliminated.