Ozonated water processes promise greener, cost-effective cleaning
John Haystead
Leuven, Belgium — The Inter uni versity Microelectronics Research Center (IMEC; Leuven, Belgium) and Semitool Inc. (Kalispell, MT) have announced a collaboration aimed at replacing conventional H2SO4/H2O2 photoresist-removal and cleaning processes used in semiconductor fabrication with lower-cost, environmentally friendly technology. The removal of H2SO4 and H2O2 from the manufacturing process promises to both reduce chemical and disposal costs as well as reduce deionized water usage. Ozonated water processes may also potentially enable new manufacturing technologies for the production of next-generation devices. According to Marc Heyns, group leader of IMEC`s ultraclean processing group, “The process should lead to environmental as well as economic benefits.”
Dana Scranton, Semitool`s surface preparation division director of marketing, says that, although the collaboration is structured on a yearly basis, it`s expected to continue for several years. “The first goal is to eliminate sulphuric acid and hydrogen peroxide from the baths, followed by the elimination of ashers at certain steps in the fabrication process.”
As part of the agreement signed in January, IMEC will work to enhance Semitool`s patent pending HydrOzone ozonated-water cleaning process. According to Scranton, HydrOzone`s combination of dry ozone gas, water and spray technology provides an “aggressive organic cleaning and resist removal capability without the limitations experienced by immersion systems where the concentration of ozone dissolved in water is critical.” Ian Sharp, general manager of Semitool`s surface preparation division, says “The HydrOzone process has been shown to be five to 10 times more effective than other ozonated water processes currently in use in the semiconductor industry.”
IMEC will apply technology from its own patented moist vapor ozone cleaning process to the HydrOzone system. “Although at the molecular level, the fundamental concepts are similar, the delivery mechanism is different between the two approaches,” Scranton describes. The IMEC method involves bubbling ozone through warm water, which saturates the cleaning environment with a warm, moist, ozone-containing vapor. In contrast, the HydrOzone process first sprays hot water across the semiconductor wafer followed by the introduction of dry ozone gas to the process chamber, diffusing it through a thin layer of water. Still, says Scranton, “Their process was close enough to ours in performance to make collaboration beneficial.”
The collaboration with IMEC is expected to further improve the HydrOzone photoresist stripping capability. Although the HydrOzone process has already been demonstrated to remove various resist types, including those implanted at 70KeV and 1.0E14, according to Scranton, the goal is to further enhance its aggressiveness. “Right now we can strip certain types of photoresist, but we want to also be able to tackle high-energy, high-dose implants.” In addition, says Sharp, “The collaboration will add significantly to our process development efforts as well as provide a more rapid transition of the technology to the production environment.”