Evaluation of impurity migration and microwave digestion methods for lithographic materials

In the section of incoming quality (IQC) or quality reliability analysis (QRA) of advanced semiconductor fabrication company, it is inevitable to regulate the strict standard for the incoming materials to ensure the reliability. In our radioactive tracer study, it is interestingly found the various amounts of metal and trace element impurities in the lithographic materials may migrate into the substrate. Based on the complex organic matrix in lithographic materials such as bottom anti-reflective coating (BARC), I-line resist and DUV resist, it is not easy to direct determine the multi-elements by the instrumentation. In this work, the lithographic materials are first decomposed by the close-vessel and open-focused microwave oven, and the digest is evaporated to incipient dryness. After adding water, the sample solutions are used either for evaluating the completeness of the digestion process by UV-VIS spectrometer, or for the determination of eleven elements using inductively coupled plasma mass spectrometry (ICP-MS). In addition, the digestion efficiency is also evaluated by the weight of total dry residual after various digestion recipes. By the complementary digestion method, the method detection limits for analytes can be achieved at lower than ng/g level. For evaluation of data accuracy, the results obtained by the two independent degestion methods are in good agreement. Moreover, the spiking recovery tests for all the elements are of 70 to 130%. According to the microcontamination control limit predicted by the SIA roadmap, the established method can meet the requirements for the quality control of lithographic materials in the future ten years.