Bubble-free ozonated Di water for wafer cleaning

12/01/1998

Bubble-free ozonated DI water for wafer cleaning

The presence of residual ozone gas bubbles during critical cleans, such as ozonated deionized (DI) water rinses following dilute HF cleans, can generate streaky particle patterns on the water surface. De-bubblers can remove only large bubbles at low liquid flow rates and carryover of small bubbles at high liquid flows is a problem in wafer cleaning. Particles tend to adhere to small bubbles and collect at hydrophobic wafer surfaces, possibly leading to wafer defects.

Scientists at W. L. Gore & Associates Inc. reported on a new commercial approach to introduce bubble-free DI water at the 1998 IEEE/SEMI Advanced Semiconductor Manufacturing Conference in Boston, MA. The new technique uses a fluoropolymer membrane contactor that consists of a large bundle of small tubes made of microporous polytetrafluoroethylene (PTFE). Water is directed through the tubing bundle, while ozone gas is passed around the outside of the bundle. Ozone diffuses through the porous PTFE tubing, while the hydrophobic surface of PTFE prevents water from penetrating the pores and directly mixing with the gas stream.

The cleanliness and performance of PTFE has been well established in high-purity gas and liquid filtration. It is also corrosion resistant and ensures good mechanical strength and toughness. Since the gases and liquids are not mixed directly, the ozonated water produced is free of bubbles, and additional downstream de-bubbling equipment is no longer necessary. When used in conjunction with a high output ozone generator, the dissolved ozone concentrations (2-20 ppm) and flow rates (2-10 standard liters/min) are within the requirements of critical cleaning processes. Results show that using bubble-free dissolved ozone can considerably reduce particulate-related wafer defects. - M.Y.M.L.