Determination of ultra-trace impurities in high purity gallium arsenide by inductively coupled plasma mass spectrometry after volatilization of matrix

Abstract

Volatilization of Ga and As as their chlorides in a stream of aqua regia vapors is described for the determination of ultra-trace impurities in high purity GaAs wafers. GaAs is treated with vapors of aqua regia at 210 °C using nitrogen as carrier gas. Near-quantitative volatilization (>99.8%) of Ga and As has been achieved in 45 min. The recoveries of Cr, Mn, Fe, Ni, Co, Cu, Zn, Ag, Cd, Ba and Pb after volatilization of matrix elements were found to be 94–101% (80% in case of Ag and Cr). Matrix-free solutions are analyzed using an inductively coupled plasma mass spectrometer with a dynamic reaction cell™ (ICP-DRC-MS). The interferences of 40Ar12C+ and 40Ar16O+ on the determination of 52Cr+ and 56Fe+, respectively, have been reduced in DRC mode using NH3 as the reaction cell gas. Vapor phase sample pretreatment in a closed environment resulted in lower ng g−1 process blank levels. The limits of detection (LOD) computed based on 3σ variation in blank measurements (n = 6) are at the sub-ng g−1 level. The developed method has been applied to the analysis of two high purity GaAs samples. The concentrations of the impurities obtained using the present procedure are compared with the values obtained by sector field ICP-MS (ICP-SFMS) and total reflection X-ray fluorescence (TXRF) after the separation of matrix elements.