Beta testing an in-line monitor for moisture measurement in inert gas lines

David A. Zatko and David F. Yesenofski, ; and Manfred Schneegans and Johann Helneder, A significant stage in the development of new products, beta-site testing enables manufacturers and potential users to collaborate on studies that complement the manufacturers' laboratory and in-house evaluations. Beta-site participants have an opportunity to learn about technological advances and have an impact on how a new system is finally configured for production, while the manufacturer gains insights into the ways the tool performs in the field. As shrinking device sizes and increasing numbers of process steps increase the risks associated with moisture contamination, the semiconductor industry needs new techniques for controlling gas purity. Extensive beta-site collaboration is needed to develop products that can minimize contamination-related downtime, provide more knowledge about the moisture levels that are acceptable for a given process, and allow purge cycles to be determined with precision. This article reports on the beta tests performed at two sites for an in-line moisture detection device based on a new monitoring technology developed by Millipore (Bedford, MA), which was described in an earlier issue of Designed to measure moisture levels in ultra-high-purity (UHP) nitrogen and argon gases, the monitor uses a piezoelectric quartz crystal microbalance (QCM) sensor. The quartz crystal is coated with a thin film of barium metal, with which moisture reacts irreversibly: The speed of this chemical reaction enables the sensor to respond rapidly. As moisture reacts with the barium, the mass of the coating increases, causing a decrease in the frequency of crystal oscillation. The rate of change in oscillation frequency is correlated to moisture concentration through a one-time factory calibration. A calibration constant is programmed into the monitor's onboard electronics for use in calculating the moisture level (in parts per billion by volume, or ppbv) from the frequency change per unit of