Use of Extraction Modeling to Predict Contamination Levels in Ultrapure Water Systems
Gary Van Schooneveld – CT Associates, Inc
Quynh Le – Balazs NanoAnalysis
Bob McIntosh – Enviro-Energy Solutions
Slava Libman – FTD Solutions
Managing ionic, metallic and organic contamination in ultrapure water (UPW) is of critical importance to maintain a robust manufacturing process resulting in high product yield in the semiconductor manufacturing process. Acceptable level of impurities in production, and as such, allowable limits of these and other contaminants in UPW continue to be reduced in the International Roadmap for Devices and Systems (IRDS) in anticipation of advanced devices with smaller dimensions and increasingly complex three-dimensional structures. In order to help the industry respond these needs, a number of SEMI specifications are being developed and revised with new recommendations and performance requirements. Of particular interest to this paper are SEMI F63, Guide for Ultrapure Water Used in Semiconductor Processing and SEMI F57, Specification for Polymer Materials and Components Used in Ultrapure Water and Liquid Chemical Distribution Systems. Aligning these SEMI documents with the UPW quality needs provided within the IRTS roadmap will help the industry meet these challenging objectives.
SEMI F63 provides total concentration guidelines for parameters including metallic, ion and organics levels for UPW systems at the point of dispense (POD). SEMI F57 establishes extraction requirements for most of the same of contaminates as a function of surface area. Historically SEMI F57 was based on the actual level of cleanliness of the best in class high purity polymer materials. In order to align the requirements of SEMI F57 to the guidelines in SEMI F63 and the IRDS, modeling of a typical UPW system and determination of contamination extraction rates as a function of time are required. Models were prepared for both ambient and elevated temperature water systems (Figure 1). The models were used to establish a maximum allowable extraction rate by contaminate based on the SEMI F63 guidelines. To establish extraction rates, PVDF and PFA pipe and tubing samples were subjected to long-term extraction testing at both ambient and 85oC in UPW. The resulting extraction data was used to calculate extraction rates as a function of exposure time assuming diffusion-limited extraction. The measured extraction rate data is compared to the model requirements to determine what adjustments are needed to align SEMI F63 and F57 (Figure 2). This paper will review the details of this analysis and present the proposed revision to SEMI F57.
This project was a highly collaborative industry effort with multiple companies providing materials and funding.
CTA publication #135: Ultrapure Micro 2018, Austin, Texas 2018