1994 Volume 43 Issue 1 Pages 57-60
In FT-IR microreflection spectroscopy, interference spectra often obstruct the analysis of the sample spectra. The interference spectra occur when the following conditions are satisfied: 1) the difference between the refractive index of a sample layer and that of its substrate is large; 2) the surface of the film and the substrate are optically smooth; 3) the thickness of the film is about 0.3100 μm. One may prevent the occurrence of the interference spectra by avoiding the above conditions. Unfortunately the first and second conditions cannot be changed because the refractive indices are constant, and it is difficult to process the sample surface when the substrate is hard and its area is very small. The third condition can be prevented by putting a transparent material, which has almost the same refractive index, on the sample to increase the film thickness. However, when we put a thin KBr crystal on the sample, another interference spectra occured due to the air gap between the KBr crystal and the sample surface. This problem was solved by filling this gap with liquid paraffin. By applying this method to the measurement of a photoresist resin layer on a silicon substrate, a good result was obtained.
