Method and apparatus for determining the thickness and elemental

Abstract

A method and apparatus is presented which applies X-ray fluorescence spectrometry techniques to the problem of determining the elemental composition and thickness of multi-layer structures formed upon a semiconductor substrate. The resulting method and apparatus allows fast, accurate, non-contact, non-destructive, single-measurement determination of the compositions and thicknesses of each thin film on a surface of a measurement sample. Primary X-ray photons emitted by two radioisotopic X-ray sources following defined X-ray paths are incident upon a measurement sample. If the primary X-ray photons have sufficient energy, atoms in the exposed surface of the measurement sample will absorb the energies of the incident primary X-ray photons and emit secondary X-ray photons with characteristic energy levels. Secondary X-ray photons following paths within a defined detection space will reach a sensing face of a lithium-drifted silicon detector and will be detected and counted by a measurement system. The elemental composition of a thin film on an exposed surface of a measurement sample may be determined from the characteristic energy levels of the secondary X-ray photons emitted by the atoms in the thin film. The areas under all corresponding peaks in a graph of the number of secondary X-ray photons detected in predetermined energy ranges (i.e., counts) versus the predetermined energy ranges are directly proportional to the thickness of the thin film.