Determination of Na and Al Ions in Semiconductor Cleaning Solution Using Capillary Electrophoresis

Abstract

most common process chemical used in the manufacturing process is a standard cleaning (SC) solution, a mixture of ammonia and hydrogen peroxide in deionized water. Since the purity of the SC solution used in the process has been required to the level of sub-ppb range, accurate and reliable determination of ionic contaminants becomes increasingly difficult. In order to satisfy the requirement of impurity control, inductively coupled plasma-mass spectrometer (ICP-MS), graphite furnace atomic absorption spectrometer (GFAAS), and ion chromatography (IC) are currently the most common analytical instruments used in the process. 3 However, those instruments are not designed for on-line monitoring but rather for off-line analysis. Recently, separation and detection of various particles, such as cells and nanoparticles, with capillary electrophoresis (CE) was reported, although the application of CE has been mostly limited to organic or biological samples. 4-6 Capillary electrophoresis has been emerging as an alternative to ICPAES and AAS for trace metal analysis. In CE, some analytes such as inorganic cations and anions do not absorb at all or only very weakly absorb the light in the UV range. Therefore, an indirect UV absorption technique, in which the analyte displaces a mobile phase additive in the eluted band, has been used successfully in capillary electrophoresis. 7-13 The displacement causes a decrease in the absorption or fluorescence signal, because the concentration of the mobile-phase additive is lower in the eluted bands when compared with its steady-state concentration. Recently, separation and detection of various kinds of metal ions, including, alkali, alkaline earth, transition metals, and even lanthanide ions by CE in the presence of UV absorbing complexing agent were reported. 14-18 For semiconductor application, method development and applications of capillary electrophoresis for determination of cations in the highest purity grades of hydrogen peroxides that has been utilized widely in critical wafer processing steps were reported. 3 However, no article for the determination of trace metals in SC solution was reported so far. In this work, a labmade CE with a movable pinhole for optical adjustment was built and demonstrated for the determination of Na and Al ions in SC solution for semiconductor application.