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 det ermined up to an analyte-to-matrix-ratio (ATMR) of 1:10(4) using capil lary zone electrophoresis. On adjusting the mobility and the concentra tion of the co-ion of the electrolyte to an isotachophoretic initial s tate, 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 experi mental silicon wafer surfaces (d = 150 mm) after dissolution of the na tive oxide of silicon in isothermally distilled hydrofluoric acid vapo ur down to the range of 10(9) anions/cm(2). The mobile organic anion o xalate was identified on silicon wafer surfaces for the first time.