Sample-standard interaction during trace analysis of semiconductor-grade trimethylindium by inductively coupled plasma atomic emission spectrometry

Abstract

Trimethylindium (TMI), used to make III-V semiconductor compounds, was analyzed by inductively coupled plasma atomic emission spectroscopy. Several calibration approaches were evaluated for the determination of impurities. Oil-based standards dissolved in xylene and in 10% trimethylindium solution in xylene were tested for external and matrix-matched calibrations. Significant differences in the two calibrations were observed for most elements, causing severe determination error. This difference is due to an exchange between the indium in the sample matrix and the metal in the standard analyte compound (i.e., sulfonate, naphthenate, octanoate). An analyte species with enhanced volatility results. The analytes exhibiting highest enhancement are Al, Cd, Pb, Hg, Sn and Zn. Elements showing moderate enhancements are B, Ca, Mg, Mn and Si. Some analytes (i.e., Be, Fe) exhibit no signal enhancement. The sensitivity increased from several to several thousand per cent compared with standard analytes in xylene. Results from a flow merging experiment suggest that interaction between the matrix (TMI) and the standard analyte compound is fast and reaches completion in a few seconds.