What is a ultrapure water production system? Manufacturing process from primary pure water [Basic knowledge]
Ultrapure water is refined through preprocessing, primary pure water, subsystems, and multiple stages. This explains the role of each process and the reason for placing ion exchange after ultraviolet treatment.
The ultrapure water production system is a facility that produces water with highly removed impurities, including not only ionic components in water but also organic substances, fine particles, viable bacteria, and dissolved oxygen. It is used in semiconductor manufacturing, such as for cleaning silicon wafers. If impurities from the water used for cleaning remain on the surface of the wafers, it can lead to pattern anomalies and potentially lower the yield of the products. ■ How is the process divided? 1. Pre-treatment: Mainly removes turbidity components using sand filtration, etc. 2. Primary ultrapure water system: Mainly removes ionic components (deionization). 3. Secondary ultrapure water system (subsystem): Highly removes trace impurities remaining in the primary ultrapure water. ■ Primary ultrapure water is sent through a tank. Primary ultrapure water is temporarily stored in a pure water tank and then pumped to the secondary ultrapure water system. ■ What is inside the primary ultrapure water system? It combines RO membranes, ion exchange resins, and degassing devices that remove dissolved gases from water. The RO membrane also removes some organic substances along with salts, thus playing a role in reducing TOC (total organic carbon). For degassing, membrane-type devices that create a vacuum on the outside of the membrane to extract dissolved gases are also used. Please feel free to consult us first.
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■Main Configuration of the Subsystem The basic configuration is to arrange the ultraviolet oxidation device, the ion exchange device (non-regenerable polisher) used without on-site regeneration, and the ultrafiltration membrane device in that order. ■Does Ultraviolet Light Not "Eliminate" Organic Matter?! When exposed to ultraviolet light that includes a wavelength of 185 nm, highly reactive hydroxyl radicals are generated from water, and trace amounts of organic matter are decomposed into organic acids and carbon dioxide. However, the decomposed substances still remain in the water. Since organic acids and carbonates become ions, they can be removed by the subsequent ion exchange device. This is why ion exchange is placed after ultraviolet treatment. ■Why Place the Ultrafiltration Membrane at the End? At the end of the process, fine particles containing viable bacteria are removed using the ultrafiltration membrane and sent to the use point. Fine particles can also be released from the ion exchange resin in the previous stage, and development of resins that produce fewer particles has been ongoing. ■Ultraviolet Lamps Are Consumables Too! To decompose trace amounts of organic matter, the ultraviolet oxidation device continuously exposes the water to ultraviolet light. The lamps are regularly replaced as part of the device's maintenance.
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■Where does the unused water go? The ultrapure water that is not used at the use points (such as cleaning devices) is returned to the tank and circulated while being processed again. This is because stagnant areas where the flow of water stops are more likely to promote bacterial growth. ■Is the equipment itself the source of contamination?! At the level of ultrapure water, contamination from the equipment used for purification becomes a concern. It has been pointed out that exposing it to ultraviolet light can produce hydrogen peroxide as a byproduct. Hydrogen peroxide can damage finishing resins, so a method has been developed to decompose it using resins that carry catalysts. Additionally, choosing ion exchange resins with low elution or using materials like PVDF (polyvinylidene fluoride) for piping are also measures to maintain water quality. ■The quality of primary pure water is the foundation The subsystem is responsible for the trace impurities remaining in the primary pure water. Stable operation of the pretreatment and primary pure water system is a prerequisite for producing ultrapure water. At Torii, we offer consultations on pretreatment for pure water systems and the replacement and maintenance of ion exchange resins. Please feel free to contact us first.
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