It is no exaggeration to say that without water, there would be no semiconductor factories. Semiconductor manufacturing is one of the most water-intensive industrial processes on Earth. An advanced chip manufacturing facility (Fab) can consume as much water in a day as a small city (for instance, in Taiwan, where water scarcity is an annual issue, the water consumption of wafer fabs is several times that of the local population). The reason behind this is not poor management or waste, but rather the extremely high precision and complex physical and chemical processes inherent in semiconductor manufacturing. So why is so much water needed?
1. Extreme Cleanliness Requirements: Wafer Cleaning
The cleaning of wafers is the most water-consuming step in semiconductor manufacturing, accounting for over 50% of the total water usage in the process. Why do wafers need to be cleaned so frequently? Manufacturing chips is akin to constructing a super skyscraper on a fingernail, with each room being only a few nanometers in size. Even a tiny speck of dust or a molecular-level contaminant can be like a meteorite striking the building, leading to the entire chip being scrapped. Therefore, wafers must be cleaned before entering the next stage of processing, whether they are incoming wafers or after etching, primarily to remove chemical residues, particulate contaminants, and metal ions. Cleaning is typically not done with cloths but by soaking the wafers in chemical solutions or rinsing them with ultra-pure water. To ensure that contaminants are completely washed away, a large and continuous flow of ultra-pure water is required for rinsing, making this process very water-intensive.
2. Preparation of Ultra-Pure Water (UPW)
The preparation of ultra-pure water itself is very water-intensive; the water used for cleaning chips is not ordinary tap water, nor is it drinking water, but ultra-pure water that meets extremely high standards (this is not the same as bottled purified water; ultra-pure water is not safe to drink). Ultra-pure water is theoretically the cleanest water in the world, containing almost no impurities, including ions, organic substances, particles, bacteria, or dissolved gases. The efficiency of producing ultra-pure water is low, typically requiring multiple stages of filtration, reverse osmosis, ion exchange, and ultraviolet sterilization. In this process, to obtain one unit of ultra-pure water, usually 1.5 to 2 units of raw water (tap water) are consumed. The water that is filtered out, which contains a high concentration of impurities (referred to as “concentrated water”), must be discharged, resulting in a low “water yield” in the production of ultra-pure water, making it a water-intensive process.
3. CMP Manufacturing Process
Chemical Mechanical Polishing (CMP) is the core process for creating multi-layer structures within chips, akin to “nano-level floor polishing,” and it accounts for about 20-30% of water usage. The water used in the CMP process serves as a primary component of the polishing slurry and is also responsible for rinsing and cooling the wafers. During polishing, the wafers generate heat that needs to be dissipated promptly, and a significant amount of particulate matter is produced that must be cleaned up quickly to prevent surface defects on the wafers.
4. Cooling Systems: Supporting Massive Infrastructure
Chip manufacturing facilities operate 24/7 and are filled with various large machines (such as diffusion furnaces, ion implanters, etchers, etc.), which generate substantial heat during operation. These machines require water for cooling; although this water can be recycled, a significant amount evaporates as steam, leading to considerable water loss and necessitating continuous replenishment.
In summary, the enormous water consumption in semiconductor manufacturing is an inevitable result of its pursuit of extreme precision and purity, which are intrinsic properties of the technology itself. As global demand for chips increases and environmental awareness grows, how to use water more efficiently has become a major challenge and core competitive advantage for all chip manufacturers.