Introduction

In the semiconductor manufacturing industry, water plays a pivotal role in the production process. Given its critical nature, ensuring that water is of the highest purity is paramount to maintaining product quality and preventing defects. The journey from raw water to ultrapure water (UPW) involves complex filtration processes designed to remove impurities at each stage. This blog explores the advanced water filtration techniques used in semiconductor fabs, detailing the journey from pre-reverse osmosis (pre-RO) treatment to the production of UPW.

Pre-Reverse Osmosis Treatment

The initial step in water purification for semiconductor fabs is pre-reverse osmosis treatment. This phase focuses on preparing the raw water to undergo further purification processes. Pre-RO treatment usually involves the removal of large particulates, organic materials, and some dissolved solids. Techniques such as sedimentation, coagulation, and flocculation are commonly employed. These processes help in agglomerating suspended particles, making them easier to remove. Additionally, activated carbon filters may be used to eliminate chlorine and organic compounds, which could otherwise damage downstream membranes and affect subsequent filtration stages.

Reverse Osmosis: The Heart of the Process

Reverse osmosis (RO) is the cornerstone of water purification in semiconductor manufacturing. Utilizing a semi-permeable membrane, RO effectively removes a significant portion of dissolved salts, ions, and other impurities from the water. The pressures applied during RO force water molecules through the membrane while retaining the larger molecules and ions. This process significantly reduces the total dissolved solids (TDS), paving the way for the production of high-purity water. However, RO is not perfect; some impurities can still make it through, necessitating further purification steps.

Advanced Filtration Techniques

Beyond reverse osmosis, additional filtration techniques are employed to achieve even higher purity levels required for semiconductor fabrication. Ion exchange is one such method, where unwanted ions are exchanged with hydrogen and hydroxyl ions, effectively demineralizing the water. Mixed-bed deionization, which uses both cation and anion exchange resins in a single vessel, further enhances the removal of ionic contaminants.

Electrodeionization (EDI) is another advanced process that combines ion exchange resins and electricity to remove ionized species. By continuously removing ions with the aid of an electrical gradient, EDI maintains the resins' capacity, resulting in less frequent regeneration and reduced chemical usage. This not only improves efficiency but also aligns with sustainable manufacturing practices.

Ultrapure Water (UPW) Production

Achieving ultrapure water is the ultimate goal of the water filtration journey in semiconductor fabs. UPW is characterized by extremely low levels of impurities, measured in parts per trillion (ppt). The final stages of purification often involve UV oxidation, which breaks down trace organic compounds into carbon dioxide and water, and ultrafiltration to remove any remaining sub-micron particles.

In the UPW system, continuous monitoring and control are critical to maintaining the stringent water quality standards. Online sensors track parameters like conductivity, total organic carbon (TOC), and particle counts, ensuring that the water meets the required specifications. Rigorous quality control measures are essential to prevent any contamination that could affect semiconductor wafer production.

Conclusion

The production of ultrapure water for semiconductor manufacturing is a meticulous and multifaceted process. From pre-reverse osmosis treatment to advanced filtration techniques and the final production of UPW, each step is carefully designed to eliminate impurities and safeguard the integrity of semiconductor products. As technology advances and the demand for high-performance chips increases, the importance of advanced water filtration systems in ensuring the highest water purity standards cannot be overstated. This commitment to purity not only supports the manufacturing process but also underscores the semiconductor industry's dedication to precision, quality, and innovation.