Emerging Issues: Prewetting Filter Technology

Downstream TOC levels during rinse-up for a Emflon PF filter immediately after prewetting with 60/40 IPA./water and a Emflon PF filter. The upstream TOC levels are as shown.
Filter cartridges constructed from all fluorocarbon components are employed to filter high purity chemicals in today's semiconductor fabrication processes. The strict requirements for clean materials, as well as compatibility issues, often need the use of fluorocarbon materials. PTFE is an excellent material for filter membranes and is widely used for bulk, distribution and point-of-use applications. Since PTFE membranes are hydro-phobic, prewetting with low surface tension fluids, such as isopro-panol (IPA), is required. While the prewetting procedure is well established, recent environmental regulations limiting the amount of organic vapors in the workplace air are forcing users to reduce the use of IPA and other solvents for pre-wetting purposes. The permissible exposure limit (PEL) established by OSHA and the threshold limit value (TLV) established by ACGIH for IPA is 400 ppm.

Attempts at prewetting the hydrophobic filters by submerging the filters in water pressurized above the bubble point of the membrane has had limited success. Until now, providing hydrophobic filters prewet so they can be in-stalled directly into tools and distribution systems has been hampered by packaging and fluid shipment and purity issues.

In order to minimize installation difficulties and environmental exposure to organic prewet fluids, Pall Corporation has introduced Emflon PF filter for use in ultra high purity (UHP) semiconductor chemicals and water applications. The prewet manufacturing method yields filters which are packaged in sterile UHP DI water, without any additives, and can be used in chemicals without the need to prewet utilizing a low surface tension fluid.

Prewet Filter Cartridge
Following filter manufacture, they are tested for integrity with an alcohol-based solution by measuring diffusional flow characteristics. The integrity test of every filter ensures 100% integrity of filters from the manufacturing facility. The filters are then rinsed with filtered (0.04 micron) UHP DI water (greater than or equal to 18 megohm-cm), and placed in a fluorocarbon bag filled with 0.04 micron filtered UHP water. The entire package is heat treated in a unique method to provide packaged sterility without any additives. The resultant filter is then delivered in a sealed, sterile fluorocarbon package to the customer in a pre-wet state. There are no materials in the package other than fluorocarbon (for the filter and bag) and UHP water. The benefits of the Emflon PF filter include:
  • Greening of fabs by eliminating the need to prewet filters with low surface tension fluids. The elimination of the prewet step will reduce safety concerns and minimize the associated waste disposal costs.
  • Reduce the time required to change-out all-fluorocarbon filters due to the elimination of the pre-wet step and significantly faster total organic carbon (TOC) rinse-up times. The rapid rinse-up times will minimize process downtime associated with change-out of filters and result in significant savings in volume of UPW required to achieve background TOC levels.
  • Eliminate the possibility of cross-contamination of the process fluid with the prewetting fluid due to inadequate flushing with DI water.
  • Eliminate the possibility of experiencing a high clean differential pressure due to incomplete wetting of the hydrophobic filter. To re-quest a copy of Data Sheet E43, dial Pall Select-A-Fax at 1-800-664-7255, order document #10006 for immediate information on the Prewet Filter Cartridges.

Q&A: What is Pall's guarantee on prewet filter products?

Pall Corporation guarantees that its prewet filter products will remain fully prewet and free from bacteria for as long as the inner packaging remains integral. Pall's prewet filter products are packaged using a proprietary (patent pending) process. The filters are prewet conventionally, using an alcohol-based solution, followed by an ultra high-purity DI water (UPW) flush. The filters are then packaged in an all-fluoro-polymer bag and in-situ sterilized. The sterilization process does not involve any additives to the UPW, so the filter is in contact with and packaged in only 18 Megohm-cm UPW.