Principle of a new reflectometer for measuring dielectric film thickness on substrates of arbitrary surface characteristics

A reflectometer is described that can make accurate measurements of the thickness of a dielectric film on a large‐area substrate. The measured value does not depend on the surface characteristics of the substrate. Two basic principles that the new reflectometer invokes are: (i) the wavelength dependence of the integrated reflectance exhibits a minimum at a wavelength which can be related to the film thickness; and (ii) the reciprocity principle for integrated reflectance (i.e., the sample is illuminated with a light of wide angular distribution and the component of light reflected normal to the sample is measured). The instrument has applications in semiconductor industry in general and, in particular, in solar energy device fabrication. This instrument can also be used to measure the absolute reflectance.