Improvement in Linearity of Calibration Curves Using of Palladium Modifier in Electrothermal Vaporization/ICP-MS and Determination of Ultratrace Metallic Impurities on Silicon Wafers

Abstract

An electrothermal vaporization (ETV)/inductively coupled plasma mass spectrometry (ICP-MS) technique has been developed to determine the ultratrace metallic impurities of 10 elements (Na, Mg, Al, Cr, Mn, Fe, Ni, Cu, Zn, and Pb) in the natural oxide layer on a Si wafer. SiO2 reacts to form SiF6 2- with hydrofluoric acid in vapor-phase decomposition. The pyrolysis temperature (150°C) for eliminating SiF6 2- was added to the ETV operating conditions, because the existence of 28Si, 28Si2, and 28SiO2 due to SiF6 2- influences the ion intensities of 27Al, 56Fe, and 60Ni, respectively. Furthermore, adding 25 ng of a palladium modifier improved the linearity of each calibration curve. As a result, it was possible to determine the 10 elements in concentration ranges of 20 (40)-10000 pg ml-1. The recovery percentages obtained by adding the mixed standard solution to the sample solution were 95-105%, showing that the ETV/ICP-MS measurements are accurate. The detection limit (3σ) was approximately 106 (Pb)-108 (Na) atoms cm-2 for a Si wafer with a diameter of 130 mm. This method can be applied to the above wafer to determine the 10 metallic elements (109-1011 atoms cm-2).