Optimization of the electrokinetic sample introduction in capillary electrophoresis for the ultra trace determination of anions on silicon wafer surfaces

Summary A capillary electrophoretic method for the ultra trace determination of anions on silicon wafer surfaces is presented. In several sets of experiments designed according to the methodology of Taguchi, electrokinetic sample introduction with transient isotachophoretic preconcentration was simultaneously optimized for peak height, peak area, peak asymmetry, efficiency, peak resolution, and reproducibility of migration time and peak area. The blank reading of the method showed no cross contamination. Thus, a detection limit of 10 nmol L⁻¹ and a linear range from 50 to 500 nmol L⁻¹ were obtained and verified by two independent instruments. Furthermore, the method was applied to the determination of anions on wafers from a regular production line wetting the whole wafer surface with ultrapure water. The capillary electrophoretic results agree with those obtained by ion chromatography. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996.