Testing of ultrapure water is important in maintaining optimal performance in ultrapure water systems (UPW). At ChemTrace, we offer pre-cleaned and prequalified water kits for worry-free collection of water. On-site water collection service is available to customers who are located in the Portland, OR or Fremont, CA areas.
Monitoring Trace Metals in Ultrapure Water
Scheduled monitoring of metals at key points of the UPW system is essential for ensuring optimal performance. For example, Al, Fe, and Mn are highly charged metals that have the potential to coagulate and foul RO membranes. Barium and Sr can cause scaling of the RO and ion-exchange resins. Furthermore, contamination on the wafer surface can be caused by low levels of metals in the UPW. It is particularly critical to monitor certain elements (such as Al, Ca, and Mg) because they can be trapped in the native oxide on the wafer surface. For monitoring trace metals in UPW, ChemTrace employs inductively coupled plasma mass spectrometry (ICP-MS), which can quantify 68 elements in one scan, with detection sensitivities at the parts-per-trillion (ppt) level for most metals.
Silica in Ultrapure Water
An on-line resistivity meter does not provide sufficient sensitivity to detect silica breakthrough of RO membranes when the resin beds are near exhaustion. It is very important, therefore, to monitor silica levels weekly or biweekly to detect early signs of a silica breakthrough. Several test methods are available to detect silica that exists primarily as silicates (dissolved silica) and as polymeric (colloidal or particulate) silica. Because not all forms are detected as dissolved silica, the quantity of total silica in UPW must be verified independently.
Bacteria Counting in Ultrapure Water Systems
Bacterial adhesion occurs naturally in water systems, as pipe walls tend to attract from water the minute quantities of organic nutrients that bacteria need for growth. Bacteria locate these nutrients and attach to the wall, initiating the biofilm process. The formation of biofilms on filters, in membranes, and in ion-exchange resins can be widespread, particularly at inaccessible surfaces of valves and at dead-legs. Bacteria that survive to the point-of-use (POU) pose both a biological and particulate threat to integrated devices. ChemTrace arms clients against these threats by offering several methods to detect bacteria:
- viable bacteria by culture
- total bacteria by epifluorescence
- total viable organisms by Scan RDI
Trace Anions and Cations in Ultrapure Water
Testing of ionics (anions and cations) at the POU in the rinse bath may identify and prevent certain types of haze formation on wafer surfaces. Stable and time-dependent hazes (residues of ammonium chloride, ammonium sulfate, or ammonium ions) may form on wafer surfaces when concentrations of anions and cations exceed 1014 – 1015 atoms/cm2. Poor rinsing of wafers after chemical cleans, as well as inadequate exhaust at wet benches, causes these hazes. Ionic removal in UPW systems can be quantified using ion chromatography that exceeds sensitivity levels specified in SEMI guideline F63-0701.
Characterization of Particles in Ultrapure Water
Ultrapure water used to dilute chemicals and rinse wafers is a potential source of particles that can lead to device failures. At initiation, particles are removed from source water by reverse osmosis (RO), as the RO membranes also act as nanofilters. From there onwards, particle load in the UPW originates from system components such as RO membrane modules, piping components, valves, and tank linings. In most UPW systems, the presence of significant quantities of submicron particles at the final filter may indicate either the breakdown of upstream components, or contamination in the return UPW distribution loop. In addition, dead-legs and system components in tools can be a source of contamination on wafers. ChemTrace characterizes particles using SEM EDX; analysis leads to direct counts and sizes of the particles, and to identification of elemental composition.
Electronics and Nanotechnology
For more information, please contact us
Technology Center and Principal Laboratory
44050 Fremont Blvd
Fremont, California 94538
12130 NE Ainsworth Circle Suite 210
Portland, Oregon 97220