MEASUREMENT OF THE REFRACTIVE-INDEX AND THICKNESS FOR INFRARED OPTICAL FILMS DEPOSITED ON ROUGH SUBSTRATES

A novel method is proposed to evaluate the refractive index and thickness of dielectric thin films in the infrared wavelength range. The method is useful for measurement of thin films that are formed on such rough substrates as metal plates, since it utilizes only the wavelengths of interference peaks, which is slightly affected by surface roughness of the sample. The method was applied to the measurement of germanium, zinc selenide, and lead fluoride films deposited on copper substrates. Measured thicknesses agreed well with the values that were obtained by ellipsometry, and refractive indices exhibited a tendency to increase with the film thickness.