SEMI C79 - Guide to Evaluate the Efficacy of Sub-15 nm Filters Used in Ultrapure Water (UPW) Distribution Systems
This Document is a recommended guide to evaluate the efficacy of filter elements used in ultrapure water (UPW) fluid streams, providing particle control as risk mitigation for particle contamination on the wafer.
Due to the lack of adequate on-line particle detection metrology at the particle sizes addressed by this Guide, however off-line filter performance testing can be used to validate filter retention efficiency. Off-line filter performance testing will help mitigate the risks related to particle control in flowing UPW streams that make contact with silicon wafers.
This Document provides a guide to the test method to evaluate filter elements used in UPW fluid streams.
This Document is a guide rather than a standard. Additional data is necessary to correlate the results tested in the procedure using high challenge particle concentrations with the actual filter’s performance to evaluate particle behavior under much lower particle concentrations in real world UPW. That is to say, in the method described in this Guide, filters are challenged at high particle concentrations not representative of real-world conditions because current particle-detection metrology cannot detect low particle concentrations.
This Guide applies to UPW-system final filters and other UPW distribution filters intended for use in semiconductor manufacturing tools and ancillary equipment.
This Guide applies to advanced semiconductor facilities requiring control of the UPW particles from 5 to 15 nm. The guide may also be used for large particles not covered by existing particle-detection metrology.
Four aspects in evaluating filter performance are considered in this Guide:
- Ability of the filter to retain influent particles is assessed with a particle challenge test. The filter is tested under single pass filtration of water or challenge particle solution—with no recirculation applied.
- Possible contribution of particles by the filter is evaluated during initial rinse of the filter
- Filter performance stability is addressed by repeating the performance test throughout the operating lifetime of the filter. Different representative filters from the same group of filters are tested during filter life time in order to confirm the frequency of the filter change out.
- Initial filter cleanliness.
This Guide describes procedures for measuring filter particle retention while using UPW as the test media. UPW parameters, for the intents and purposes of this Guide, is defined in § 7.6.
This Guide uses commercially available colloidal silica with a mean particle size of 5 to 15 nm. Using polystyrene latex spheres (PSL) as a filter challenge does not work at the 5 to 15 m size range because the PSL size distribution is too broad and using white spherical plastic beads is an unrealistic challenge for filter testing. Colloidal silica is a superior challenge material because it is commercially available (and inexpensive) in the 5 to 15 nm size range. Colloidal silica has a relatively narrow size distribution and has lower interaction with filter material; therefore it is primarily removed by a filter’s sieving mechanism.
The filter-performance evaluation procedure described in this Guide uses a combination of grab-sample lab analysis and in situ liquid particle measurement (using an aerosol particle detection technique).
Referenced SEMI Standards
SEMI E49 — Guide for High Purity and Ultrahigh Purity Piping Performance, Subassemblies, and Final Assemblies
SEMI F57 — Specification for Polymer Materials and Components Used in Ultrapure Water and Liquid Chemical Distribution Systems
SEMI F61 — Guide for Ultrapure Water System Used in Semiconductor Processing