Inductively coupled plasma mass spectrometry (ICP/MS) provides a simple method for the analysis of photoresists used in the manufacture of semiconductors
Agilent Technologies Europe has announced a simple method for analysing photoresist using inductively coupled plasma mass spectrometry (ICP-MS).
A photoresist layer is applied in the manufacture of integrated circuits (ICs) to prevent etching or plating of the area covered.
Constant testing for trace elements at each stage of the IC manufacturing process, and particularly at the critical lithography stage, helps to protect against contamination of the final semiconductor device, as metal impurities can distort electrical properties and diminish final product reliability.
Agilent chemists studied positive photoresists, which become soluble when exposed to ultraviolet light.
Because heavy sample matrices such as these (which have a high carbon content) can cause instrument clogging and signal drift, the chemists used an Agilent 7500s inductively coupled plasma mass spectrometer configured to address these concerns. First, the sample introduction system was optimised to handle high sample matrices over extended periods.
This included using low flow nebulizers, cooling the spray chamber, and using a torch injector designed to minimise sample deposition.
Second, they used a highly efficient plasma 27.12MHz RF generator to produce a robust and stable plasma for complete matrix decomposition and sample ionization.
Finally, they employed an effective plasma grounding device (the Agilent ShieldTorch system) to eliminate polyatomic interferences through high-power (950W), cool plasma operation.
The chemists monitored typical metallic impurities at ultratrace levels - in the range of 1-30ppb per element.
Results show that the special ICP-MS configuration reproducibly measured key analytes at the levels required by the semiconductor industry, effectively breaking down the heavy photoresist matrix and eliminating carbon-based interferences on magnesium and chromium as well as argon-based interferences on potassium, calcium and iron.
These elements would otherwise limit standard quadrupole ICP-MS operation.
For further information, request Agilent application note 'Direct Analysis of Photoresist Using Inductively Coupled Plasma Mass Spectrometry (ICP-MS)', Agilent publication number 5988-7100EN.
This note is available without charge from any Agilent sales office or its website (link above).
