Introduction
During semiconductor fabrication, N-Methyl-2-pyrrolidone (NMP) is typically used as a photoresist stripper, due to its low vapor pressure and relatively high boiling point (80 °C), which improves its efficiency in stripping off the photoresist. NMP easily dissolves organic impurities without damaging the photoresist itself, making it the best solvent for this application. Semiconductor fabrication requires ultra-high purity reagents, so NMP must be analyzed for trace-metal contamination. The presence of contaminants would have detrimental effects on the reliability of memory devices. SEMI Standard SEMI C33-0213 specifies the contamination limit for high-purity NMP Grade 4 to be less than 100 ppt for each element.
Inductively coupled plasma mass spectrometry (ICP-MS) has been widely used for the determination of ultra-trace impurity levels in various chemicals. However, it can be subjected to interferences originated from the plasma and/or matrix species.
This work demonstrates the ability of the NexION® 2200 ICP-MS to eliminate interferences, allowing precise measurement of trace impurities in NMP using only hot plasma conditions in a single analysis. By utilizing Reaction mode on the proprietary UCT, argon- and carbon-based polyatomic spectral interferences are effectively reduced. This enables the determination of traditionally problematic elements by ICP-MS with good accuracy and precision, demonstrating the suitability of the NexION 2200 ICP-MS for the routine quantification of ultra-trace impurities at the ppt level in organic solvents critical to semiconductor applications.
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