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Monitoring acidic and basic molecular contamination in leading edge lithography and metrology applications: quantitative comparison of solid state and impinger-based sampling methods
Author(s): Sarah Riddle Vogt; Cristian Landoni
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Paper Abstract

Assessing molecular contamination (MC) at part-per-billion (ppbV) or part-per-trillion volume (pptV) levels in cleanroom air and purge gas lines is essential to protect lithography and metrology tools optics and components. Current lithography and metrology tool manufacturer's specifications require testing of some contaminants down to single digit pptV levels. Ideally this analysis would be performed with an on-line analyzer (capable of providing almost instant results): the best analyzers currently available are only capable of providing 100 pptV detection. Liquid impinger sampling has been the dominant sample collection method for sub ppbV acidic and basic MC analysis. Impinger sampling suffers from some inherent problems that can dramatically reduce the collection efficiency such as analyte solubility and evaporative losses. An innovative solid-state trapping technology has been recently developed by SAES Pure Gas along with the CollectTorr sampling system. NIST traceable gas phase standards have been used to compare the collection efficiency of the traditional impinger technology to that of the solid state trapping method. Results varied greatly for the different acid gases with sulfur dioxide showing comparable collection efficiencies while hydrofluoric acid and hydrochloric acid showed much lower recoveries in the impingers than the solid-state traps. Ammonia collection efficiencies were slightly higher for the solid state traps and were improved in the impingers when an acidified solution was used as the collection media. The use of solid-state traps, besides being much simpler from both the handling and logistical stand point, eliminates the analyte solubility and evaporation problems frequently seen with the impinger sampling.

Paper Details

Date Published: 1 April 2010
PDF: 7 pages
Proc. SPIE 7638, Metrology, Inspection, and Process Control for Microlithography XXIV, 763825 (1 April 2010); doi: 10.1117/12.846364
Show Author Affiliations
Sarah Riddle Vogt, SAES Pure Gas, Inc. (United States)
Cristian Landoni, SAES Getters S.p.A. (Italy)

Published in SPIE Proceedings Vol. 7638:
Metrology, Inspection, and Process Control for Microlithography XXIV
Christopher J. Raymond, Editor(s)

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