Applications of Ultra-Pure Water in the Optical Industry

Ultra-pure water, often referred to as high-purity water, plays an increasingly vital role in the field of optics. The quality of water used has become a significant factor affecting the quality of optical components, production yield, and manufacturing costs. Let’s delve into the applications of ultra-pure water in optical manufacturing and the specific water quality requirements for each application.

1. Precision Cleaning:

  • Ultra-pure water is extensively used for precision cleaning in optical manufacturing processes. When water contains impurities like chloride ions, it can lead to electrical leakage in capacitors.
  • In the production of electron tubes, where cathode coatings are critical, even minor impurities can impact electron emission, affecting both amplification performance and the tube’s lifespan.

2. Fluorescent Screen Coating:

  • In the manufacturing of cathode ray tubes (CRTs) and cathode ray oscilloscope tubes, a fluorescent substance composed of sulfides of metals like zinc is applied to the inner walls of the screen using spray or precipitation methods.
  • The preparation of this fluorescent coating requires ultra-pure water. Even trace amounts of copper (>8 ppb) can cause discoloration, while iron (>50 ppb) can lead to color changes, darkening, and flickering. Organic colloids, microparticles, bacteria, and other contaminants can reduce the fluorescence layer’s intensity, adhesive properties to the glass envelope, and result in defects like bubbles, streaks, and light leaks.

3. Semiconductor Manufacturing:

  • In the production of transistors and integrated circuits, ultra-pure water is primarily used for silicon wafer cleaning and as a component in chemical solutions. The quality of water is critical as it directly affects product quality and production yield.
  • Alkali metals (K, Na) in water can compromise insulation film integrity, heavy metals (Au, Ag, Cu) can reduce PN junction breakdown voltage, Group III elements (B, Al, Ga) can deteriorate N-type semiconductor characteristics, and Group V elements (P, As, Sb) can degrade P-type semiconductor characteristics.
  • Phosphorus, a byproduct of high-temperature carbonization of bacteria in water, can lead to localized changes from P-type to N-type silicon on wafers, negatively impacting device performance. Waterborne particles, including bacteria, can cause short circuits or degrade circuit characteristics.

Ultra-pure water is indispensable in ensuring the precision, reliability, and longevity of optical components and semiconductor devices. Its role in maintaining water quality and minimizing impurities cannot be overstated.

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