Ultrapure water is used in the electronics and pharmaceutical industries. Water is not the first thought when we talk about electronics, but several key processes in the manufacturing of semiconductors require ultrapure water.
Characteristics of ultrapure water
Ultrapure water is water that is highly purified to suit stringent specifications. Unlike normal water, ultrapure water contains no electrolytes. It is completely deionized and contains nothing but H2O molecules. All traces of natural salts, sodium potassium, bacteria, organic compounds, metallic impurities, and anionic compounds are removed from the water
A key characteristic of ultrapure water is its high electrical conductivity or low resistivity. To put it in perspective, the resistivity of seawater stands at 0.2 whereas drinking water could have around 2. On the other hand, the resistivity of ultrapure water stands at 18.2.
Why does the electronics industry require ultrapure water?
Microchips are constructed in layers. After each step in the manufacturing process, the chip must be thoroughly cleaned of the debris and solvents, one layer at a time. The catch is that these chips have fine pathways that are narrower than the wavelength of visible light and can be seen only under certain electron microscopes. Even the tiniest debris and impurity could hamper the proper functioning of the chip. Additionally, any contaminants might also damage the sensitive machinery used to manufacture these chips. Even the slightest damage to these machines could be costly to repair.
Ultrapure water is also used to cool capacitors and transistors after manufacturing. If normal water was used, these components would be corroded and rendered unusable.
It is especially important to remove particulate, ionogenic, and organic contaminants for the following reason: in order to meet the highest quality requirements, some ingredients in ultrapure water may only be present in the ppt range (parts per trillion). To achieve this demanding processing goal, adapted treatment steps and a selection of the right materials are required.
How is ultrapure water obtained?
Filtering water to the ultrapure level involves using a combination of water filtration technologies. Pre-treatment first turns raw water into pure-grade water (different from ultrapure water). After this, the water is put through a number of different filtration methods to obtain ultrapure water.
Pre-treatment
In the pre-treatment process, chemicals are added to the water to remove contaminants, and the water is then run through a filtration system such as RO system. Next, chlorine is added to the water. The pre-treatment process depends on the nature of the raw water being used. In the pre-treatment phase, the water is softened, and its pH is adjusted to suit further treatment. Other conventional filtration systems can also be added to the pre-treatment process depending on the nature of the water.
Water management experts at Inovar closely study the customer’s application requirement and the properties of available raw water to design a suitable pre-treatment system.
Primary treatment
As mentioned before, the primary or main treatment mechanism for ultrapure water involves a combination of various water filtration technologies.
Activated carbon
Post-pre-treatment, the water is passed through cartridges of activated carbon. Activated carbon removes the organic constituents and residual disinfectants in water. This is essential for protecting the ion exchange system from possible damage due to oxidation of organic fouling.
Ion exchange
In the ion exchange filtration, water passes through two tanks that bear cation exchange resin and anion exchange resin respectively. HCL and H2SO4 are used to facilitate the removal of cations while NaOH is used to remove anions from the water. In the ion exchange process, the impure ions in water are replaced with hydrogen ions. All the suspended gas ions are also removed from the water.
Microfiltration
In the microfiltration process, water is forced through racks of vessels that contain thousands of hollow fibers. The fibers are around 0.4 microns in size. Which is 300 times smaller than the width of human hair. The fibers filter out microscopic particles, such as protozoan cysts, bacteria, and even viruses. Microfiltration vessels are backwashed every 30 minutes to remove the buildup of particles on the membrane walls.
UV light treatment
UV light treatment further removes any bacteria, viruses, and other living microorganisms from the process water. The UV light damages the nucleic acids of the microorganisms so that they are incapable of multiplying and infecting.
Ultrafiltration
After UV treatment, water passes through the ultrafiltration membranes with a fine size of 0.25 microns. These membranes are specifically designed as per the requirements for ultrapure water. They remove any impurities that might still remain from all of the previous processes.
Final treatment/polishing
In the polishing system, water s passed through mixed bed system which purifies the water further in a semicircle loop system.
Conclusion
Obtaining ultrapure water is a critical process that also entails high costs. 6000 liters of pure grade water will yield around 3800 liters of ultrapure water. A single 200-millimeter semiconductor wafer could require around 5600 liters of ultrapure water for cleaning. Thus, it is vital that the user work closely with experts in water treatment.
Inovar is focused on developing technologies for efficient and cost-effective water treatment. We water purification systems for highly pure water needs in electronics. These include Low Conductivity Water for various surface finish operations, Low BOD, Low TDS Water for testing manufactured equipment, and other key processes. Water from various processes is reused and recycled within key process parameters and regulatory norms.