Ultrapure water for microelectronics FAQs
The role of ultrapure water in semiconductor manufacturing
Ultrapure water plays a vital role in semiconductor manufacturing, where even the smallest impurities can affect product quality and performance. Here, we've answered some of the most common questions about how ultrapure water is produced, the industry standards it must meet, and the role it plays in supporting efficient, sustainable microelectronics manufacturing.
Frequently asked questions
Ultrapure water (UPW) is essential throughout semiconductor manufacturing where even trace contaminants can impact chip performance and yield. It is primarily used in multiple stages of wafer fabrication to ensure surfaces remain free of particles, organic compounds and dissolved impurities. It is used across several key applications, including cleaning, surface preparation, and chemical dilution.
- Cleaning - Ultrapure water is primarily used for cleaning wafers throughout the manufacturing process. It removes particles, organic residues, and chemical contaminants left after steps such as etching, deposition, and polishing. Effective cleaning with UPW is essential to prevent defects and maintain high production yields.
- Surface preparation - In surface preparation, ultrapure water ensures wafers are fully free from impurities before critical processes like lithography and thin-film deposition. This enables precise layer formation and strong material adhesion, which are vital at the micro- and nanoscale.
- Chemical dilution - Ultrapure water is used to dilute chemicals such as acids, bases, and etchants used in fabrication. Because UPW contains virtually no impurities, it ensures that dilution does not introduce contaminants that could interfere with sensitive reactions or damage micro-scale structures.
Ultrapure water used in microelectronics must meet extremely stringent quality standards defined by industry organisations such as SEMI (Semiconductor Equipment and Materials International).
Key standards include:
- SEMI F63 / F63-0701 – Defines performance criteria and guidelines for UPW systems
- SEMI F57 – Specifies materials used in UPW distribution systems to prevent contamination
- ASTM Type E-1 water – Covers high-purity water requirements, often aligned with semiconductor needs
Typical UPW quality parameters include:
- Resistivity: 18.2 MΩ·cm (maximum purity)
- Total organic carbon (TOC): <1 ppb
- Dissolved oxygen: tightly controlled depending on process
- Silica, particles, metals: ultra-low or near-detectable limits
These standards ensure consistent water quality to protect sensitive semiconductor manufacturing processes.
Ultrapure water is produced through a multi-stage purification process designed to remove dissolved salts, organic compounds, particles, and gases to extremely low levels. In microelectronics applications, achieving the highest water quality relies on advanced technologies such as reverse osmosis (RO), continuous electrodeionisation (CEDI) and UV treatment, alongside other filtration steps.
Ultrapure water systems support sustainability by enabling water reuse and reducing waste. Technologies like CEDI eliminate the need for chemical regeneration, while efficient system design lowers energy consumption, maintenance and operating costs, helping fabs meet environmental targets.
Continuous electrodeionsation (CEDI) replaces traditional chemical-based processes such as mixed bed deionisation (MBDI) with a safer, chemical-free process. Xylem’s innovative Ionpure® CEDI system works by combining resin, electricity, and ion-exchange membranes to remove ionised or ionisable impurities – including carbon dioxide, boron, and silica. This continuous low energy consuming process avoids the need for chemical regenerants, eliminating the handling and storage of hazardous chemicals, delivering vital safety benefits.
Silica and boron are particularly difficult to remove during deionisation because they are weakly ionised in water. Unlike many dissolved salts, they don’t respond as effectively to conventional ion exchange processes, making it more difficult to remove to the extremely low concentrations required by semiconductor manufacturing. The answer is advanced CEDI technology. Xylem’s Ionpure VNX-Ultra has been developed and optimised for the microelectronics industry for this purpose. It’s extremely effective at removing boron from UPW, with boron and silica removal ≥ 99.8% and sodium and chloride removal ≥ 99.9%. It can effectively hit 1 ppt boron with a one system set-up configuration and no requirement for boron selective resin.