Thirsty chip factories：
Chip manufacturing, is a thirsty industry, the production of a 12-inch silicon wafer, to use up 8 tons of water, can fill a sprinkler, TSMC 150,000 tons of water a day, equivalent to draining 80 swimming pools every day, Intel 34 million tons of water a year, equal to sucking dry 25,000 West Lake every year, chip factories need so much water for what? Part of it, cooling down, part of it, configuring solvents, and more of it is used to bathe the chips.
Before being encapsulated and protected, the delicate chip has a serious cleanliness problem, so there are often thousands of processes in the production of chips, 30% are repeating a thing, wet cleaning, with a large amount of water and chemical solvents, cleaning the silicon wafer, remove the residue of the previous process, to prepare for the next step, photolithography fumigation before cleaning, after exposure development to clean, high-temperature diffusion before cleaning, wet etching after more cleaning, but the chip bath water, not ordinary water.
Water is everywhere in our lives, we often drink drinking water, per litre contains more than 100 mg of metal elements, most of them in ionic form dissolved in water, they are the reason why water is conductive, but also determine the flavor and taste of a glass of water, water is a little bitter, usually high magnesium ions; water is a little astringent, generally excess iron ions; water is a little salty, because sodium ions are salt, water dissolved in addition to metal ions, and gases, as long as the glass of water is still in the atmosphere, it will be dissolved in oxygen, carbon dioxide and other kinds of gases, and impurities not dissolved in water, such as fine particles and various microorganisms.
There are also gases, as long as this glass of water is still in the atmosphere, which will dissolve oxygen, carbon dioxide and other types of gases, and insoluble impurities in the water is more, such as fine particles and a variety of micro-organisms, natural mineral water, there is a certain amount of algae and bacteria, bottled mineral water, although it will undergo additional sterilization, but only to control the total number of bacteria does not exceed the standard.
Despite how many messy things in the water, for humans, a glass of water, as long as the pathogenic bacteria is not excessive, minerals do not exceed the standard, it is called clean and hygienic, but for the chip, the water in this little impurities, really sloppy and deadly, metal ions will affect the threshold voltage of the device; dissolved gas, will interfere with the silicon oxidation coating, bacteria organic matter can cause PN junction short-circuit leakage, fine particles, which can cause surface defects on silicon wafers, so the water that can come into contact with chips must be ultra-pure.
What is ultra-pure water? It is pure water that is cleaner and more hygienic than pure water and more drop pure than distilled water. There are no metal ions, no gas dust, no bacteria or viruses, only water composed of hydrogen and oxygen elements. With our current level of technology, the purest water that can be produced is semiconductor ultra-pure water, which is hundreds of times more stringent than medical sterile injection water in all its indicators.
Neutrino capture：
The most famous ultra-pure water system in the world is in an abandoned mine 1,000 meters underground in Kamioka-cho, Japan, where the University of Tokyo has built a giant 40-meter diameter water barrel with 50,000 tons of constantly circulating ultra-pure water, surrounded by golden spheres that are a photomultiplier tube to capture the universe’s neutrinos. These ghost particles can penetrate everything, and only when the water happens to meet the nucleus or electron of the element hydrogen and oxygen will it trigger Cherenov radiation, producing a glimmer of light.
This little bit of light from the neutrinos is so faint that there can be no impurities in the water, otherwise it will be blocked and absorbed. This is the super Kamioka detector used to observe supernova explosions and study solar neutrinos, which won Japan the 02 Nobel Prize in Physics, and the Kamioka team is still planning to expand a larger detector, to use 260,000 tonnes of ultra-pure water to create an even larger bucket of ultra-pure water in 2027, to peer into even more mysteries of the universe.
Preparation of ultrapure water：
So how does a chip factory produce ultrapure water? The first stage is also called water pretreatment, using multi-media filters and ultrafiltration equipment to remove most of the particulate matter, suspended matter and colloids in the water, in addition to adding activated carbon filters to adsorb organic matter, or sodium bisulfite to remove free chlorine and other oxidizing substances, when the completion of various physical After completion of various physical and chemical softening, the water is also desalinated by two reverse osmosis membranes to remove all kinds of inorganic salts, as well as organic matter and microorganisms that have managed to escape from the filter.
After pretreatment, enter the second step of the main treatment stage, where the water purification method, in addition to the previous filtration and reverse osmosis, also includes UV light irradiation sterilization and oxidative decomposition of organic matter to further reduce the total organic carbon content of the water, but also continuous electrodesalination technology (EDI/CEDI), to solve the remaining anions and cations in the water, and finally the vacuum degasser and multi-stage degassing membrane, to remove all types of dissolved gases in the water, to this point, the chip plant will be refined from the tap water into pure water, temporarily stored in a pure water tank filled with nitrogen.
From pure water to ultra-pure water, there is a third step, the polishing of water (polish), which is the refining stage. This part is simply the second degree of the first two steps, where the various water purification devices that have appeared before are assembled again in a piping system, in which pure water is circulated at high speed for another billion times to ensure that pure water becomes ultra-pure water and maintains its purity in an infinite cycle until it is taken out at the point of use and used to make chips，
After so much tossing and turning, tap water in the purification process, to lose 3-4% of the water to become ultra-pure water, while the chip production process, extremely water-intensive, a large amount of ultra-pure water is not only used for wet cleaning, but also includes submerged lithography, configuration of etching solution, chemical mechanical polishing (CMP), silicon wafer cutting and cooling processes, so that chip manufacturing is a thirsty industry, for water quality and water requirements are extremely high，
The distribution of chip factories in China, mainly in the south, especially concentrated in the Yangtze River Delta region, which water resources is one of the reasons, the location of the chip factory is very important, to consider a variety of factors, including the environment, the same machinery and equipment and processes, moved to different places, production yields and chip quality may not be the same, this is not what metaphysics, but the feng shui of each place is different, the wind refers to the airflow circulation, that is, the chip The clean room of the production, through the fan filtration unit (FFU), constantly circulating the external supplemental air to maintain cleanliness, if the local air pollution is serious, it will affect the quality of air inside the plant, water is also the same, if the quality of the original water is not high, then the quality of purified ultrapure water will also be different.
In addition, the temperature of the plant location, altitude, ground micro-vibration and other factors, may have a southern impact on the chip yield, so located in the Pacific Rim seismic zone of the treasure island of Taiwan, the lack of large rivers and rainfall rely on the typhoon (monsoon), from a geographical point of view, is not the ideal base for chip plants, last year in the spring and summer, no typhoon on the island, resulting in a serious drought, so TSMC had to use more than 100 trucks a day to transport water, just to barely maintain the chip production.
Testing ultrapure water：
Going back to the production of ultrapure water, it is not enough to have various means of purification and filtration, how do you know that all the impurities in the water have been removed? This requires extremely precise testing of water quality: for example, measuring the PH value, the chip is neither acid nor alkali resistant, and then for example, measuring the concentration of dissolved oxygen and carbon dioxide, the chip hates dissolved oxygen in water, it will lead to the formation of a layer of silicon oxide on the surface of the silicon, affecting the performance and yield of the device, for the chip, everything in the water chemical composition, almost all toxic, for example, silicon will lead to silicon defects; boron will lead to silicon wafer doping; chlorine affects chemical deposition; and various metal ions, which change the electrical properties of the transistor，
So the ultra-pure water system of the chip factory, to be equipped with a variety of water quality analyzer, the trace components of the water for real-time detection. For example, the resistivity of water, is a direct reflection of water quality parameters, life we often say that water is conductive, but the actual conductive substances are mainly metal minerals in the water, the less impurity components of the water, the higher the resistivity of water, seawater resistivity of about 20Ω.cm, tap water resistivity of about 200Ω.cm, medical sterile injection water resistivity higher than 770KΩ.cm, and semiconductor grade The resistivity of ultra-pure water needs to be greater than 18.18MΩ.cm, which is an insulator，
So the ultra-pure water system of the chip factory, to be equipped with a variety of water quality analyzer, the trace components of the water for real-time detection. For example, the resistivity of water, is a direct reflection of water quality parameters, life we often say that water is conductive, but the actual conductive substances are mainly metal minerals in the water, the less impurity components of the water, the higher the resistivity of water, seawater resistivity of about 20Ω.cm, tap water resistivity of about 200Ω.cm, medical sterile injection water resistivity higher than 770KΩ.cm, and semiconductor grade The resistivity of ultra-pure water needs to be greater than 18.18MΩ.cm, which is an insulator，
Compared to the measurements mentioned above, the most problematic is the microbial content testing, because it is usually necessary to first sample the water body, on a petri dish, cultivate colonies, and then indirectly determine the water quality by the number of colonies, this petri dish method has a large sample error, takes several days, and can not be monitored in real time, more advanced technical means, is the spectral measurement method, using the metabolites in the body of microorganisms, such as coenzyme 1 and riboflavin, when exposed to a specific wavelength of light to release a special fluorescence, to directly measure and count microorganisms，
Detection technology and instrument accuracy are important because they determine the limit of water purification, the semiconductor industry in the development of ultra-quasi-water standards, often limited by the detection limits of the instrument, such as the minimum range of TOC, is 1 part per 20 billion (0.05ppb), below this value even the most sophisticated analyzer, can not be detected, there is no way to do further control of water quality and purification, and As the chip process continues to advance towards 2nm and 1nm, the industry’s requirements for ultrapure water purity will continue to rise, driving us to explore the limits of water purification.
Is it good？
OK, finally, to answer the most important question, is ultrapure water good to drink? I have not drunk the water in the fab, but I have tasted the ultrapure water in the lab, and it is not good at all, no taste at all, the reason why water tastes like water, or water as we know it, does not come from the water, but depends on the trace minerals in the water, the ultrapure water with all impurities removed, is a strange to the taste buds of monotony and extreme boredom, because the migration rate of substances in water, depends on the concentration difference. Since the concentration of impurities in ultrapure water is zero, it is extremely soluble and cleansing, very suitable as chip bath water, which can easily take away all kinds of things from the silicon wafer in one wave.
But as drinking water, although it is non-toxic, it can drain you dry. This water walks around the human digestive tract and sucks away minerals and trace elements from the body, and if you only occasionally steal a little bit in the lab, as long as you don’t get caught by your tutor, it’s generally not life-threatening, but drinking ultra-pure water for a long time or in large quantities can cause serious electrolyte imbalances in the body and is life-threatening. This is why it is important to drink clean water, but not completely clean, as our old ancestors have long said, water until it is clear is no fish.
