DETERMINATION OF TRACE AMOUNTS OF IMPURITIES IN HIGH-PURITY SILICON AND SILICATE MATERIALS BY VAPOR-PHASE PRESSURED DECOMPOSITION ICP-AES AND ICP-MS

The determination of trace amounts of impurities in high-purity silicon and silica has been investigated. (1) A sample was decomposed by acid vapor in a pressure bomb. This procedure gave very low blank values at the sub-ppb level and a small amount of sample solution (about 1 ml). The addition of 10 mul of sulfuric acid prevented the loss of impurities (Al and Ti) during the decomposition. (2) A small amount of sample solution (not diluted) was introduced and analyzed utilizing tungsten-filament electrothermal ICP-AES. This technique enables an increase in the efficiency of the sample introduction into the plasma and to improve the sensitivity. As the tungsten filament was eroded by sulfuric acid in the sample solution, the sulfuric acid was removed by cation exchange chromatography. According to this procedure, the detection limit at the ppb to 10 ppb level was obtained. Furthermore, injection(a 300 mul aliquot was introduced into the plasma)-ICP-MS was investigated and high sensitivity (except for iron and calcium; those spectra were interfered by the molecular ions) was obtained. Trace amounts of impurities at the ppb level in the silica crucible and silicon materials could be determined using both of the above two techniques.