DETERMINATION OF TRACE IMPURITIES ON SILICON-WAFER SURFACE BY ISOTOPE-DILUTION ANALYSIS USING ELECTROTHERMAL VAPORIZATION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

The feasibility of coupling the isotope dilution (ID) analysis and the electrothermal vaporization/inductively coupled plasma mass spectrome try (ETV-ICP-MS) was studied in order to determine trace impurities on Si-wafer surface precisely. The precision of the isotope ratio measur ement was investigated for single element and sequential two-element d etermination by ETV-ICP-MS. In the case of the single element determin ation, 0.1, ng ml(-1) of Cu in a 20 mu l sample could be measured with relative standard deviation (RSD) less than 6%, and 1 ng ml(-1) of Cu and Zn could be measured with RSD less than 5% in the sequential two- element determination. Coupling of ID and ETV-ICP-MS was applied to de termine trace impurities of Cu, Zn and Pb, which were collected by etc hing a Si-wa fer surface with a vapor mixture of nitric acid and hydro fluoric acid. The amount of etching solution obtained from one Si-wafe r was about 200 mu l. Those impurities were determined at 3x10(8) - 8. 7x10(9) atoms cm(-2) with an RSD of 2% by ID-ETV-ICP-MS. The amount of Cu on the Si-wafer surface was also determined by calibration method with ETV-ICP-MS and by graphite furnace atomic absorption spectrometry . The results obtained by these three different methods agreed well wi th each other.