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Proceedings Paper

Real-time trace ambient ammonia monitor for haze prevention
Author(s): Katsumi Nishimura; Yuhei Sakaguchi; Eric Crosson; Edward Wahl; Chris Rella
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Paper Abstract

In photolithography, haze prevention is of critical importance to integrated circuit chip manufacturers. Numerous studies have established that the presence of ammonia in the photolithography tool can cause haze to form on optical surfaces resulting in permanent damage to costly deep ultra-violet optics. Ammonia is emitted into wafer fab air by various semiconductor processes including coating steps in the track and CMP. The workers in the clean room also emit a significant amount of ammonia. Chemical filters are typically used to remove airborne contamination from critical locations but their lifetime and coverage cannot offer complete protection. Therefore, constant or periodic monitoring of airborne ammonia at parts-per-trillion (ppt) levels is critical to insure the integrity of the lithography process. Real time monitoring can insure that an accidental ammonia release in the clean room is detected before any optics is damaged. We have developed a transportable, highly accurate, highly specific, real-time trace gas monitor that detects ammonia using Cavity Ring-Down Spectroscopy (CRDS). The trace gas monitor requires no calibration gas standards, and can measure ammonia with 200 ppt sensitivity in five minutes with little or no baseline drift. In addition, the high spectral resolution of CRDS makes the analyzer less susceptible to interference from other gases when compared to other detection methods. In this paper we describe the monitor, focus on its performance, discuss the results of a careful comparison with ion chromatography (IC), and present field data measured inside the aligner and the reticule stocker at a semiconductor fab.

Paper Details

Date Published: 14 May 2007
PDF: 11 pages
Proc. SPIE 6607, Photomask and Next-Generation Lithography Mask Technology XIV, 66071Y (14 May 2007); doi: 10.1117/12.728981
Show Author Affiliations
Katsumi Nishimura, Horiba Ltd. (Japan)
Yuhei Sakaguchi, Horiba Ltd. (Japan)
Eric Crosson, Picarro, Inc. (United States)
Edward Wahl, Picarro, Inc. (United States)
Chris Rella, Picarro, Inc. (United States)

Published in SPIE Proceedings Vol. 6607:
Photomask and Next-Generation Lithography Mask Technology XIV
Hidehiro Watanabe, Editor(s)

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