(Invited) Ultrapure Water for Advance Semiconductor Manufacturing: Challenges and Opportunities
Authors: Libman Slava , Wilcox Daniel , Zerfas Bernard 
Published: February 2020

High purity water is one of the most critical chemicals used in semiconductor manufacturing for critical rinses, chemical dilution, immersion lithography, and cooling medium. It is probably the most complex utility in the fab: fully automated system, processing millions gallons a day via dozens of treatment steps. UPW technology has become mature over last three decades of its development. It is believed to be effective to address UPW quality and reliability needs. Nevertheless, increasing complexity driven by “Moore and More” (ITRS, 2013) continuously challenging UPW process capabilities. The “killer” particle size has reached 10nm for the most advanced semiconductor processes, which is smaller than the capability of the most advanced UPW metrology. Furthermore, the most advanced filtration technology becomes marginal in its ability to remove completely particles at this size. Recently obtained data suggest that 10 nm particles in UPW may significantly exceed currently defined ITRS concentration limits.

New SEMI standards have been recently developed to help coping with the particles challenge. It was found that ion exchange resin may generate up to 1E+9 particles per milliliter of 10nm diameter particles. Those levels can be substantially reduced by effectively pre-cleaned resin while the quality of the resin can be verified by the new SEMI guide (recently approved for publication). The importance of managing the particle challenge to the UPW final filters is growing as the killer particles size approaches the limits of the best available technology. The most advanced ultra-filters are expected to remove approximately 2-3 orders of magnitude of the incoming 10nm particles. SEMI C079 method of filter performance testing helps to better understand filtration capability at the killer particles size range. The presentation will include details of potential additional origin of the particles challenging the filters and the ways to monitor and control particles using new and advanced methods and techniques. The discussion will include potential impact to the yield for the cases when final filters are challenged or when filters integrity is compromised.

In addition to particles, other trace contaminant may pose risks to the most advanced manufacturing. It was demonstrated that Ultraviolet (UV) treatment of UPW to control TOC may produce concentrations of hydrogen peroxide potentially exceeding those of dissolved oxygen at the limits of UPW ITRS.

Effect of dissolved organics to the advanced IC manufacturing is another area of concern. Some of the organics, such urea originating from incoming city water, is very difficult to treat due to its small size and weak charge. Some other organics can be contributed by ion exchange resin or other UPW system materials. The level of the organics may vary seasonally or with the age of the materials in the system.

Better understanding the effects of UPW impurities to the manufacturing can help to mitigate risks to the wafer manufacturing and reduce costs associated with UPW systems construction and operation. It may help with decisions for UPW recycling that would improve environmental footprint and reduce impacts to the infrastructure local.