Estimation of film thickness from the background signal in x-ray photoemission spectroscopy

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Abstract
A nondestructive estimation of the thickness of a uniform overlayer has been investigated using x‐ray photoemission spectroscopy (XPS), which is an application of Tougaard’s formalism. It has been shown that it is possible to estimate the thickness of an overlayer existing on a semi‐infinite underlayer, by measuring the ratios of the peak area to the background signal on the high binding energy side of a photoelectron peak produced by an element existing in an underlayer before and after removing the overlayer. Especially when the inelastic mean free path of a photoelectron in an overlayer and an underlayer can be approximated equal, the relation between those ratios and the overlayer thickness is expressed in a very simple mathematical form. This method has been applied to various thickness of a‐Si:H overlayers on SiN x formed by plasma chemical vapor deposition (CVD) method. A good linear correlation has been obtained between the thickness estimated by this method and that estimated from the deposition time, and thus the validity of this method has been shown.

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