A method to measure the mean thickness and non-uniformity of non-uniform thin film by alpha-ray thickness gauge (author's transl)

Abstract

The alpha-ray thickness gauge is used to measure non-destructively the thicknesses of thin films, and up to the present day, a thin film with uniform thickness is only taken up as the object of alpha-ray thickness gauge. When the thickness is determined from the displacement between the absorption curves in the presence and absence of thin film, the absorption curve must be displaced in parallel. When many uniform particles were dispersed as sample, the shape of the absorption curve was calculated as the sum of many absorption curves corresponding to the thin films with different thicknesses. By the comparison of the calculated and measured absorption curves, the number of particles, or the mean superficial density can be determined. This means the extension of thickness measurement from uniform to non-uniform films. Furthermore, these particle models being applied to non-uniform thin film, the possibility of measuring the mean thickness and non-uniformity was discussed. As the result, if the maximum difference of the thickness was more than 0.2 mg/cm2, the non-uniformity was considered to distinguish by the usual equipment. In this paper, an alpha-ray thickness gauge using the absorption curve method was treated, but one can apply this easily to an alpha-ray thickness gauge using alpha-ray energy spectra before and after the penetration of thin film.