Resolution of permeation issues in liquid handling systems
Don Grant – CT Associates, Inc., Bloomington, MN
Dissolved gases and bubbles in liquids can be contaminants. As contaminants, they can reduce manufacturing yield or result in failure of chemical-handling systems. For example, when HCl and HF penetrate equipment they quickly corrode most metals parts if moisture is present. Some components (e.g. valves) in chemical-handling systems often contain metal parts. The metal parts are isolated from the chemical by polymer parts that are chemically resistant. Unfortunately, these polymers often have relatively low resistance to permeation by gases like HCl and HF. The corrosion caused by the permeating gas can cause premature failure.
Dissolved gases in liquids can also cause problems. For example, if photoresist is transported using pressurized gas, the gas will rapidly dissolve into the surface of the photoresist then diffuse into the bulk of the liquid. Eventually the photoresist will become saturated with the gas at the delivery pressure. When the pressure is released, the photoresist will be supersaturated and gas bubbles may form. If bubbles in photoresist are dispensed onto a wafer, they can cause a defect in the wafer and reduce manufacturing yield.
This paper shows how these problems associated with permeating gases can be alleviated. Although permeation of HCl and HF into valves in chemical handling systems cannot be eliminated, it can be controlled. Valves containing metal springs can be designed with diffusion flow paths that allow corrosive gases to move away from the metal springs. Also, the amount of dissolved gases in pressurized liquids can be greatly reduced by surrounding the liquid with a polymer film.
CTA publication #48: In Proceedings of the 22nd Annual Semiconductor Pure Water and Chemical Conference, Sunnyvale, CA, February 2003