DETERMINATION OF TRACE AMOUNTS OF ANIONIC IMPURITIES IN HYDROCHLORIC-ACID BY ION CHROMATOGRAPHY

The purity of the hydrochloric acid used in semiconductor processing h as a direct impact on device reliability because ionic impurities adhe re to the wafer's surface during processing, and the impurities must b e monitored in order to avoid both unnecessary wastes and exceeding of the permitted levels. Ion-chromatographic procedures for the determin ation of bromide, nitrate, phosphate, selenate and arsenate in hydroch loric acid are described. The high chloride concentration and the pH o f the sample cause major problems that, for monovalent anions, can be overcome by simply diluting the sample, while matrix elimination in th e presence of potassium permanganate is effective in the determination of polyvalent anions. The optimum pH range, concentration of the matr ix and of the eluent, and working conditions have been investigated. T he use of different eluents has been suggested for the determination o f bromide and nitrate after matrix dilution, as these ions elute very near to the large chloride peak. The procedures described have been su ccessfully used for the routine analysis of hydrochloric acid batches used for cleaning semiconductors.