Abstract
In order to reduce costs and increase the yields of wafer device, chip manufacturers are using wafers with ever-larger diameters and ever-narrower line widths, which has led to a demand for ever-lower levels of trace-element contamination in high-purity process chemicals. While ten years ago Semiconductor Equipment and Materials International (SEMI) deemed that 10-ppb purity levels were adequate for many chemicals. Today 100-ppt levels are typical, and for some of the more critical materials, 10-ppt levels are being proposed. Traditionally, inductively coupled plasma mass spectrometry (ICP-MS) has been the technique of choice for ultralow trace-element determinations in high-purity chemicals. In terms of the report of literature, a continuous aspiration of concentrated acids would result in a highly unstable, rapid deteriorating performance, sever interference problems and harmful to the instrument. In this regard, dilution of sample matrix prior to instrumental analysis are frequently used currently. However, that would enervate the detection power of trace elements, slow down routine analysis or introduce contamination. Therefore, a novel analytical system was developed to meet that challenge resulted from the need to determine ultralow trace-element in high-purity and concentrated acids. In this study, two on-line neutralizer-(micro-column)-ICP-MS system were developed to analyze not only alkaline and alkaline-earth metal ions, but also transition metal ions in concentrated acids. In order to on-line remove the concentrated acid matrix prior to the ICP-MS measurement, a high capacity neutralizer was employed as guard device. During the on-line neutralization process, water was used as stripping solution and electrolyzed to produce hydroxide ions which serve to neutralize the acidic portion of the sample by way of an electrodialysis procedure. For purpose of maximizing the efficiency of removal of acid matrix and enhancement of analytes, several parameters, such as sample flow rate, acid concentration, the volume of sample loop, and buffer concentration were optimized. Up to now, 40% for nitric acid and hydrochloric acid, 20% for sulfuric acid can be on-line neutralized under the optimized condition and trace cationic impurities in concentrated acids can be determined by proposed hyphenated system.