Real-time trace ambient ammonia monitor for haze prevention

Katsumi Nishimura; Yuhei Sakaguchi; Eric Crosson; Edward Wahl; Chris Rella

doi:10.1117/12.728981

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14 May 2007 Real-time trace ambient ammonia monitor for haze prevention

Katsumi Nishimura, Yuhei Sakaguchi, Eric Crosson, Edward Wahl, Chris Rella

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Proceedings Volume 6607, Photomask and Next-Generation Lithography Mask Technology XIV; 66071Y (2007) https://doi.org/10.1117/12.728981
Event: Photomask and Next-Generation Lithography Mask Technology XIV, 2007, Yokohama, Japan

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.

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Katsumi Nishimura, Yuhei Sakaguchi, Eric Crosson, Edward Wahl, and Chris Rella "Real-time trace ambient ammonia monitor for haze prevention", Proc. SPIE 6607, Photomask and Next-Generation Lithography Mask Technology XIV, 66071Y (14 May 2007); https://doi.org/10.1117/12.728981

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