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24 May 2004 Real-time optics contamination monitoring using surface acoustic wave technology
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The cleanliness of optical components is a critical process parameter in microlithography. Molecular contamination is often the culprit for contaminated optical elements. The increasing use of purge gases and/or gas phase chemical filtration in photolithography tools are methods to help reduce or eliminate airborne molecular contamination (AMC), and is evidence that this form of contamination is problematic. And unfortunately, AMC becomes even more challenging in the transition from 248nm to 193nm and 157nm radiation wavelengths. Because of this, quantitative monitoring techniques and strategies play a crucial role in identifying and resolving molecular contamination that affects optical components. This paper, and the examples within, describe work performed using surface acoustic wave (SAW) technology to monitor and quantify in real-time and with high sensitivity AMC as it adsorbs, desorbs, or reacts with critical optical components. A high frequency oscillating quartz crystal is coated with SiO2 to mimic critical optical component surfaces. As gas phase molecular contamination interacts with the sensor surface, the frequency of oscillation is altered. Contamination information is then extracted from the change in output frequency, including mass, rate, and trending data and correlated to process, equipment, or facility logs in order to determine the contamination source.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Steven Rowley "Real-time optics contamination monitoring using surface acoustic wave technology", Proc. SPIE 5375, Metrology, Inspection, and Process Control for Microlithography XVIII, (24 May 2004);

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