Jul2026
Deionized water is a critical process utility in semiconductor manufacturing. It is used throughout wafer fabrication for cleaning, rinsing, chemical preparation, chemical mechanical planarization, and other wet-process applications where contamination control is essential.
For critical wafer-contact processes, semiconductor facilities use multiple treatment and polishing stages to produce ultrapure water, or UPW. The required water quality depends on the device, the specific process step, and associated contamination risks, but the objective remains consistent: the water must perform its function without introducing material that could affect the wafer surface or interfere with subsequent processing.
Some wet-process applications also require UPW to be supplied at a controlled elevated temperature. In these applications, hot ultrapure water, or HUPW, supports processes such as heated cleaning and rinsing, while the heating equipment becomes part of the high-purity fluid path. It must provide the required temperature and flow without compromising water quality.
As device structures become more complex, water quality must therefore be controlled not only where the water is produced, but throughout its distribution, heating, and delivery to the process tool.
Although the terms DI water and ultrapure water are sometimes used interchangeably, they describe different levels of treatment and control.
Deionization removes dissolved ions from water. Semiconductor-grade UPW requires additional treatment and polishing to control a broader range of contaminants, including particles, organic compounds, dissolved gases, microorganisms, silica, and trace metals.
Electrical resistivity is an important indicator of ionic purity, but it does not provide a complete assessment of water quality. Water with high resistivity may still contain nonionic contaminants or particles that require separate monitoring and treatment.
For this reason, semiconductor UPW systems are designed around multiple treatment, filtration, polishing, and monitoring stages rather than a single purification measurement. SEMI guidance applies these quality considerations to both UPW and hot UPW used in semiconductor processing.
UPW is used extensively in semiconductor wet processing, particularly during wafer cleaning and rinsing.
Wet cleaning processes remove particles, organic residues, metallic contaminants, and materials left by previous manufacturing steps. After chemical treatment, UPW rinses carry residual chemistry and displaced contaminants away from the wafer.
The rinse water must not leave behind material of its own. Contaminants present in the water can be deposited on the wafer during rinsing or become concentrated on the surface as the water dries.
Because wafers move through repeated cleaning, etching, deposition, and rinsing sequences, UPW quality must remain consistent from one process step to the next. Depending on the process, the UPW may be delivered at ambient temperature or heated to a controlled temperature to support cleaning or rinsing performance.
DI water and UPW are also used to dilute concentrated chemicals and prepare solutions for semiconductor wet processes.
Water quality directly affects the purity and consistency of the completed solution. Ionic, metallic, organic, or particulate contamination introduced during dilution becomes part of the process chemistry and may eventually reach the wafer.
This is especially significant in dilute formulations, where water represents most of the finished solution. Consistent water quality supports repeatable concentrations and reduces the possibility that variability in the water supply will alter chemical performance.
When water or a compatible process chemistry must be heated, temperature control and wetted-material selection become part of maintaining consistent process conditions.
Chemical mechanical planarization, or CMP, combines chemical reactions with mechanical action to create a highly uniform wafer surface.
UPW is used in slurry preparation, tool operation, and post-CMP rinsing and cleaning. Because CMP intentionally introduces abrasive particles, the process requires careful control of both the slurry and the water used to remove remaining particles and residues.
Post-CMP cleaning must remove process material without introducing additional contamination. As semiconductor process flows have grown more complex, CMP and wet-bench rinsing have become significant areas of UPW use within the fab.
Producing UPW that meets specification is only one part of water-quality control. Purity must be maintained as the water moves through the facility and into the process tool.
Distribution piping, valves, fittings, filters, sensors, heaters, and other wetted components can affect the quality of the water delivered to the process. Water measured immediately after final purification may not have exactly the same characteristics when it reaches the wafer.
For critical applications, water-quality monitoring may therefore extend beyond the UPW generation system to the point of distribution and point of use. Current SEMI guidance addresses monitoring and controlling UPW quality through the point where the water contacts the wafer.
This system-level approach provides a broader understanding of water quality than resistivity alone. Monitoring programs may evaluate ionic contamination, organic content, particles, microbial activity, and other parameters according to process requirements.
Some contaminants may remain dissolved in UPW and later form particles when the water dries on the wafer. These materials are known as particle precursors.
Particle precursors can originate within UPW treatment and distribution components, including ion-exchange materials and other wetted components. Because they are present in dissolved form, they may not be identified by conventional particle-counting methods.
Once deposited and dried, these compounds can form particles that adhere to the wafer surface and contribute to defects. SEMI F121 provides guidance for evaluating methods used to measure particle precursors in UPW, reflecting increased industry attention to contaminants that may not be detected through traditional water-quality measurements.
Some semiconductor wet processes specifically require UPW to be delivered at an elevated and precisely controlled temperature. Semiconductor industry guidance recognizes hot ultrapure water as part of the UPW system and applies water-quality criteria to both ambient-temperature UPW and HUPW.
Depending on the application, heated UPW may be used during wafer cleaning, rinsing, surface preparation, and other wet-process operations. Temperature can influence cleaning performance, residue removal, chemical behavior, and process repeatability.
Heating equipment must provide the required flow, temperature rise, and outlet-temperature control while preserving the purity of the water. Because the heater directly contacts the UPW, it must be treated as part of the high-purity distribution and point-of-use system.
Wetted components should be selected to minimize the risk of:
Material compatibility becomes particularly important in HUPW service because elevated temperatures can affect interactions between the water and the components used to transport and heat it.
Process Technology offers several systems designed to heat DI water, UPW, and compatible semiconductor process chemistries.
The Lufran® DI Water Heater is a complete, turnkey heating system designed for high-purity semiconductor and flat-panel manufacturing processes.
It incorporates PTFE and PVDF wetted surfaces and an advanced temperature-control system. The Lufran DI Series supports controlled, on-demand heating in applications requiring a high-purity fluid path and precise outlet-temperature control.
The TIH Inline Heater is designed to heat ultrapure DI water and compatible semiconductor process chemistries in single-pass or recirculating systems.
Its PTFE wetted surfaces help protect fluid purity, while multiple plumbing configurations allow the heater to be integrated into a range of process-tool layouts. The system can be selected according to the required flow rate, inlet temperature, temperature rise, and operating configuration.
The TIH Steam Heater provides a steam-powered alternative for facilities that use steam as the available heat source.
The process fluid remains within a PTFE flow path while heat is transferred from the facility steam supply. This configuration separates the steam heating medium from the high-purity water or compatible process chemistry.
DI water and UPW support essential semiconductor manufacturing operations, from chemical preparation and wafer rinsing to CMP and heated wet processing.
Some applications use ambient-temperature UPW, while others depend on HUPW delivered at a precise and repeatable temperature. In those heated applications, the heater is an integral part of the high-purity fluid path rather than a separate utility component.
Distribution design, wetted materials, filtration, monitoring, temperature control, and point-of-use equipment all influence the quality of the water ultimately delivered to the process.
Heating systems designed for high-purity applications help semiconductor manufacturers achieve the required process temperature while protecting the quality of the DI water, UPW, or compatible chemistry moving through the system.