Characterization of Cleanroom Dry Wipers for Trace Metal Contaminations

摘要

In this work, metal contamination of cleanroom dry wipers was characterized by ICP-MS analysis using various sample preparation methods. Trace metals extracted by ultrapure water were limited even with sonication and results from nitric acid extraction were orders of magnitude higher, possibly due to improved solubility of metal species. Results from high temperature ashing process provided an overall picture of all non-volatile metal impurities in these wipers and served as a reference point for the study. By varying acid composition, acid concentration, and/or extraction temperature, metal impurity information reflecting real-world applications could be attained. The study found titanium and antimony constituted approximately 0.25% (as TiO_2) and 0.015% (as Sb_2O_3) of wiper weight with other trace metals at 5-15 ppm; Hydrofluoric acid - hydrogen peroxide mixture extracted more impurities than dilute nitric acid; and 80℃ 1-hour extraction was more effective than 20℃ 24-hour extraction. Replicate measurements found significant wiper piece-to-piece variation for some metals. Time study for acid extraction of these wipers suggested 6-12 hours extraction duration needed for metals to reach concentration plateau at room temperature. The study demonstrated that ICP-MS based methods are effective and viable techniques for wiper evaluation and qualification, process monitoring, and quality control.