The Quality of Ultrapure Water Should Be Taken Seriously in IC Manufacturing

In modern electronics manufacturing, the most obvious characteristic of integrated circuits is the continuous miniaturization of product size. This change leads to increasingly higher requirements for ultrapure water quality in the production process, and thus increasingly stringent requirements for equipment such as water purifiers. Especially in electronics factories, pure water supply is a crucial aspect of cleanroom design, as the quality and quantity requirements for pure water vary across different electronic product manufacturing processes.

In electronic product manufacturing, the selection of an ultrapure water system should be based on a techno-economic comparison, considering the raw water quality, the water quality requirements of the product manufacturing process, system scale, and the availability of materials and equipment. The quality of raw water for pure water systems varies greatly depending on the region and city. Some cities use rivers as their water source, and even river water varies in quality depending on the source and the geology and topography of the areas it flows through. Other cities use well water, and the depth, location, and geological structure of the wells all contribute to significant differences. Currently, many cities use a combination of river, lake, and well water sources, and the water quality can vary between different districts and sections within a city. Therefore, the selection of a pure water system varies greatly depending on the quality of the raw water. Whether or not to use raw water pretreatment, and the type and scale of pretreatment equipment, are all related to the raw water quality. Thus, the selection of an ultrapure water system for a cleanroom in an electronics factory should be determined through a comprehensive techno-economic comparison, considering the raw water quality, the water quality requirements of the electronic product manufacturing process, the water production capacity of the pure water system, and the availability of pure water equipment and materials at the time and place.

In ultrapure water for very large-scale integrated circuits, the priority water quality indicators are: resistivity, particulate matter, TOC (total organic silicon), silicon, alkali metals, alkaline earth metals, heavy metals, and dissolved oxygen.

Aqueous solutions conduct electricity because various dissolved salts in water exist in ionic states. During integrated circuit chip manufacturing, the more ions the water in contact with silicon wafers contains, the greater the impact on product yield. Resistivity reflects the ion content in ultrapure water; the higher the resistivity of ultrapure water, the higher its purity. Generally speaking, at 25℃, the theoretical resistivity of pure water is 18.24 MΩ·cm.

Particle count is also an indicator of ultrapure water purity. If the cleaning water used in the photolithography process of integrated circuits contains impurities or particles, it will lead to uneven gate oxide film thickness, product pattern defects, and deteriorated withstand voltage performance. Generally, a particle size of 1/10 of the pattern size is used as the evaluation standard. Trace organic matter in ultrapure water affects the insulation and withstand voltage performance of the gate oxide film. Alkali metals, alkaline earth metals, and heavy metals cause poor crystallization and deteriorate the insulation and withstand voltage performance of the gate oxide film. Dissolved oxygen in ultrapure water promotes the premature natural formation of the oxide film on the silicon wafer surface. Reports indicate that even nitrogen dissolved in the water affects the cleaning effect. In ultrapure water, the impact of bacteria is essentially the same as that of TOC and particles, mainly because their proliferation within the system makes it a source of organic matter and particles.