Analysis of metal ion impurity in tetraethyl orthosilicate by sector field inductively coupled plasma mass spectrometry

Abstract

A sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) method was developed to directly analyze metal ion impurity in tetraethyl orthosilicate (TEOS). As trace metal ion impurity in TEOS can cause a damaging effect on wafer-product-based electronic devices, it is necessary to develop an efficient analytical method for quantifying the trace metal ions in TEOS for semiconductor manufacturing. The low metal ion content (nanogram per liter level) in a TEOS solution is difficult to be analyzed directly by SF-ICP-MS. Pretreatment such as acidic digestion and direct dilution results in lower concentrations of the metal ions down to picogram per liter level which reaches the instrumental limitation and is not suitable for analysis. In this study, simple liquid liquid extraction (LLE) was applied by adding isopropanol and deionized water to extract the metal ion in TEOS. The interfering compounds can be directly separated from the analyte by SF-ICP-MS with an appropriate resolution, thereby preventing any ambiguity in the identification of metal ions. The maximum concentration factor was 18.94. The applicability of the proposed method has also been validated by the analysis of three TEOS samples for different applications. The concentrations of metal ions with the range from nanogram per liter to microgram per liter can all be determined with good precision (RSD < 9.46%) and good accuracy (spike recoveries from 94% to 113%). This study demonstrates that SF-ICP-MS with LLE pretreatment is a promising approach for analyzing metal ion impurity in TEOS.