Combining electrothermal vaporization inductively coupled plasma mass spectrometry with in situ TMAH thermochemolysis for the direct determination of trace impurities in a polymer-based photoresist

Abstract

Trace impurities in photoresists are difficult to determine when using electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) because of the presence of excessive amounts of polymeric matrix. In this study, we evaluated the use of tetramethylammonium hydroxide (TMAH) for the removal of the polymeric matrix through the formation of gaseous degradation products. We also investigated the influence that the temperature program had on the separation efficiency. To remove the polymeric matrix to a moderate degree, we performed a pre-reaction step, which was necessary to improve the removal efficiency in order to enhance the thermochemolysis reaction between the photoresist and TMAH. Under the optimized conditions, the signal resulting from the carbon matrix can be suppressed significantly and satisfactory analytical signals can be obtained. The precision of this method was ca. 10% when we used TMAH as a matrix modifier and performed the pre-reaction step during the ETV heating cycle; we confirmed this accuracy by noting the good agreement between the data obtained when using our proposed method and those obtained when using a wet chemical technique. Our method permits the determination of Mn, Zn, Cu, and Pb in photoresists at detection limits within the range from 0.76 to 7.1 ng mL⁻¹.