Study of standard sample preparation for total reflection X-ray fluorescence spectrometry and of its application to high-accuracy analysis

Abstract

Metallic impurities on the surface of semiconductor wafers deteriorate the electrical properties of LSI devices. In recent years, total reflection X-ray fluorescence(TXRF) spectrometry has come into wide use in semiconductor industry for the analysis of metal impurities. In TXRF analysis, the properties of a standard sample, especially the depth distribution of the analyte, are significant for accurate quantification. First, requirements for standard samples are discussed. Next, a study of metal adsorption in ammoniac hydrogen peroxide cleaning solution through equilibrium analysis is considered. It has been found that the properties of the wafers, on which metals are adsorbed in the solution, are suitable for standard samples of TXRF. This method was named “immersion in alkaline hydrogen peroxide(IAP).” The depth distribution of analyte on IAP wafers was evaluated by fitting angle scan data. After carrying out the above-mentioned studies, cross-check experiments between TXRF and other methods at a level of 1012 atoms cm-2 were conducted by using the IAP standard samples. The study clarified that the IAP standard samples are suitable for crosscheck experiments. Finally, the accuracy of TXRF below a level of 1011 atoms cm-2 was examined. With IAP standard samples, the determination values of TXRF agreed with those of AAS with an accuracy of 20%.