Experience The Difference in Oxygen and Moisture Analysis Analyzers measuring oxygen and moisture from Delta F meet the highest standards for innovation, quality and reliability. Delta F strives for complete customer sati......Experience The Difference in Oxygen and Moisture Analysis Analyzers measuring oxygen and moisture from Delta F meet the highest standards for innovation, quality and reliability. Delta F strives for complete customer satisfaction. While Delta F oxygen and moisture analyzers have established the industry benchmark for analytical performance, it is our customer oriented business practices that keep customers coming back. Since 1969, Delta F has been implementing world class business practices in the manufacturing, testing, and support of our oxygen and moisture analysis products. Delta F was the first oxygen analyzer company to receive ISO 9001 certification, passing its first audit by Lloyds Register Quality Assurance, Ltd. in June, 1992. Delta F oxygen and moisture analyzers have achieved the industrys lowest levels of oxygen detection and incorporate innovative designs that offer sophisticated performance with a simple interface. Delta F customer services are second to none and include factory calibration, extended warranties, applications consulting and round-the-clock support lines. As a result of this track record of continuous improvement in oxygen and moisture analysis, companies that require reliable, cost-effective analyzers to measure critical applications keep returning to Delta F years after their first purchase. At Delta F, every analyzer is custom configured and extensively tested . We offer complete support through our headquarters in Woburn, Massachusetts plus a worldwide network of professional representatives and distributors. We log every call and track our responses to ensure a rapid solution to any problem. We even include a Customer Satisfaction Survey Card with every new and repaired analyzer. Customer feedback is very important to us - a key ingredient in our product development and improvement. We invite you to join the ranks of satisfied Delta F users. Introduction Modern semiconductor fabs employ sophisticated gas distribution systems (GDS) to deliver a variety of ultra high purity (UHP) gases from bulk purifiers to the process tools. These GDS are controlled and monitored by Continuous Quality Control (CQC) systems that allow fabs to maintain extremely low levels of contaminants in their process gases, leading to high process yields. The task of controlling contaminants is becoming more demanding as device line sizes decrease at an unprecedented rate and the impurity control points of UHP gases are reduced to their limits. The principal contaminants monitored by CQC systems are oxygen and moisture. Of these, moisture is the most difficult to control due to its adsorption and transport characteristics, particularly at sub-ppb levels. These characteristics not only gate the initial dry down of a GDS but also make leak detection and process trouble shooting of process excursions difficult. The purpose of this Application Note is to familiarize users of CQC systems with the difficulty of making ultra-trace level moisture measurements, to set a practical expectation for moisture analyzer performance and to establish guidelines for the proper use of these analyzers in controlling and monitoring moisture in UHP gases. The following sections of this note will discuss leak mechanisms in gas distribution systems, moisture transport phenomena and behavior in GDS, the implications of these on making moisture measurements and guidelines for the proper use of ultra trace moisture analyzers in CQC systems. Leak Mechanisms in Gas Distribution Systems Leak mechanisms can be characterized in one of two ways: Actual Leak - A direct leak path from atmosphere located directly on an actively flowing UHP line. An actual leak usually produces a fixed rate of atmospheric contaminants entering the UHP system, which enter via back diffusion. Therefore, if the flow of UHP gas increases, the concentration of the contaminants will decrease proportionately due to the dilution effect of the higher UHP gas flow rate. Similarly, if the flow of UHP gas decreases, the concentration of contaminants in the UHP gas downstream of the leak source will increase overall. Virtual Leak - A trapped pocket of contaminated UHP gas which is in a static flow condition (dead leg), but is in direct contact with the active gas distribution system The trapped gas pocket can have an actual leak which is acting as the source of contamination, but that source by this definition is located some distance from the actively flowing UHP gas and is separated by the pocket of trapped gas. Under steady state flow conditions of the actively flowing UHP gas, the contamination is mostly contained within the dead leg. However, some smaller amounts of contamination will continuously diffuse out of the dead leg and into the UHP gas stream. If the pressure of the flowing UHP gas drops slightly at the connection point to the trapped pocket of contaminated gas, then contaminated gas will flow out of the trapped space and into the main flow. In this case, a pressure drop in the flowing line is usually associated with an i