Use of Nonvolatile Residue Monitoring in Semiconductor Water Applications
By David Blackford, Ph.D.
Nonvolatile residue (NVR) consists of dissolved inorganic material. NVR is primarily silica (both in dissolved and colloidal forms), but also includes sodium, anions, cations, and trace metals. NVR is not particles. This article reviews NVR and a method for measuring it in high-purity water. The ability to measure NVR is significant because it can be used as a measure of overall water quality. Significant amounts of NVR indicate a possible problem with a high-purity water supply - in fact, NVR is often the first on-line measurement, and therefore the first indicator of a problem in a high-purity water system. An instrumenta has been developed that can measure NVR at parts per trillion (ppt) levels in almost real time. As with other on-line total organic carbon (TOC) monitors and particle counters, the NVR instrument does not identify the residue. However in industries such as semiconductor manufacturing, fast identification of contamination is critical. The primary advantage of the NRM comes from the fact that it gives an almost immediate indicator of the presence of contamination. After the speedy indication of a problem, the technician can then collect and analyze a water sample to identify the contaminant.
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