Measurement of the thickness distribution and optical constants of non-uniform thin films

In this paper, an original method for the complete optical characterization of thin films exhibiting area thickness non-uniformity is presented. This method is based on interpreting experimental data obtained using an original imaging spectroscopic photometer operating in the reflection mode at normal incidence of light. A CCD camera is employed as a detector of the photometer. The spectral dependences of the reflectance measured simultaneously by individual pixels of the CCD camera correspond to the local reflectance of small areas of the non-uniform thin films characterized. These areas form a matrix along a relatively large part of the substrate covered with the non-uniform film. The spectral dependences of the local reflectance measured by the individual pixels are treated separately by means of the formulae for the reflectance valid for uniform thin films. The reason is that the local areas corresponding to the pixels are sufficiently small so that the film characterized can be considered to be uniform within these local areas. Using this approach, it is possible to determine the values of the local thickness and local optical constants for every small area of the matrix. Thus, in principle it is possible to determine the distributions (maps) of the local thickness and the local optical constants of the non-uniform films simultaneously. This method is used to characterize carbon-nitride thin films exhibiting only the thickness area non-uniformity.