The important role of ultrapure water in the semiconductor and microelectronics industry

Water is the source of life, and its role in modern industrial production is irreplaceable. As far as the semiconductor and microelectronics industries are concerned, water is used in some major processes, such as cleaning, because water is a General solvents are used to clean the surface of silicon wafers at all stages of semiconductor manufacturing. In addition, the feature size of modern microchips is extremely small, and even tiny particles or residues may cause product defects; others include the etching process of the chip, CMP polishing and grinding etc., because water is the carrier of chemicals, and any industry that uses chemical solutions is inseparable from water.

However, natural tap water cannot directly participate in the production and manufacturing of semiconductors, because a variety of substances present in the water will affect the semiconductor and microelectronics manufacturing processes. These substances are often called pollutants and will affect the quality of semiconductors and microelectronics. , reliability and performance, the following are some common substances in water that have significant effects:

1. Particulate matter, particles suspended in water, such as dust, dirt and other solid pollutants, can cause defects and yield losses in semiconductor manufacturing. Current electron beam lithography technology can achieve resolutions below 5nm or even 1nm, so , even small particles can interfere with complex processes such as photolithography, deposition, etching and wafer handling.

2. Dissolved gases. The main effects come from oxygen (O2) and carbon dioxide (CO2), which can react with materials used in semiconductor manufacturing. Oxygen can cause oxidation and corrosion of metal surfaces, while carbon dioxide can cause the formation of carbonic acid and affect pH value etc.

3. Organic pollutants and organic compounds in water, such as hydrocarbons, oils, solvents and surfactants, may pollute the water and interfere with the microelectronics manufacturing process. They will be deposited on the product surface, hindering adhesion and affecting photolithography. properties of the glue, thereby causing defects.

4. Inorganic ions in water. Certain inorganic ions, such as heavy metals (such as copper, lead, mercury), alkali metals (such as sodium, potassium) and transition metals (such as iron, nickel), may exist in water and affect semiconductor manufacturing. These ions can contaminate the wafer surface, introduce impurities during deposition, or cause undesirable chemical reactions.

5. Microorganisms, including bacteria, fungi and spores, may pose a significant threat to semiconductor manufacturing, leading to biofilm formation and microbial-induced corrosion.

Based on the above analysis, due to the precision and sensitivity of these processes, the semiconductor and microelectronics industries have extremely strict standards for process water, such as:

Resistivity standards, typically 18.2 Megohmcm at 25°C, are considered the "theoretical maximum" and indicate very low ion content.

Total organic carbon (TOC) levels are typically below parts per billion (ppb).

Particle count, typically less than 10 particles smaller than 0.05 microns per milliliter.

Bacterial counts are typically less than 1 colony forming unit (CFU) per 1000 ml.

Dissolved gases (e.g. oxygen or carbon dioxide) are controlled/removed according to process specific requirements

Metals and anions/cations can range from parts per billion (ppb) to parts per trillion (ppt) levels and beyond.

Based on the above analysis of water, water must be treated with high purity to be suitable for semiconductor and microelectronics manufacturing applications. A combination of multiple treatment steps is usually used, including filtration, reverse osmosis, deionization, and ultraviolet light to reduce TOC. Irradiation and bacterial control, etc. In special cases, some processes such as dialysis and high-temperature sterilization are also required. Membrane filtration is currently the most commonly used water purification process in manufacturing companies, including microfiltration, nanofiltration, ultrafiltration, and the reverse osmosis mentioned above. , because it is incomparable to other methods in terms of water quality assurance, purity and economic benefits.