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 spectrometry (ETV-ICP-MS) was studied in order to determine trace impurities on Si-wafer surface precisely. The precision of the isotope ratio measurement was investigated for single element and sequential two-element determination by ETV-ICP-MS. In the case of the single element determination, 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 determine trace impurities of Cu, Zn and Pb, which were collected by etching a Si-wa fer surface with a vapor mixture of nitric acid and hydrofluoric acid. The amount of etching solution obtained from one Si-wafer 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 with each other.