APPLICATION OF CAPILLARY ZONE ELECTROPHORESIS WITH AN ISOTACHOPHORETIC INITIAL-STATE TO DETERMINE ANIONIC IMPURITIES ON AS-POLISHED SILICON-WAFER SURFACES

Mobile inorganic anions such as chloride, sulfate and nitrate were determined up to an analyte-to-matrix-ratio (ATMR) of 1:10(4) using capillary zone electrophoresis. On adjusting the mobility and the concentration of the co-ion of the electrolyte to an isotachophoretic initial state, the detection limit of the analytes was improved by a factor of 2 by increasing the plate numbers through the isotachophoretic state. The ATMR could be increased to 1:6 . 10(4). These optimized conditions were applied to the determination of anionogenic impurities on experimental silicon wafer surfaces (d = 150 mm) after dissolution of the native oxide of silicon in isothermally distilled hydrofluoric acid vapour down to the range of 10(9) anions/cm(2). The mobile organic anion oxalate was identified on silicon wafer surfaces for the first time.