Research has demonstrated that ozone can offer a more environmentally friendly alternative to existing cleaning processes and, in many instances, can outperform them.
By Christiane Gottschalk, Ph.D., MKS Instruments Inc.
In 1857, Werner Siemens developed the first dielectric barrier discharge technique for the reliable generation of ozone.1-3 Since then, such electrical discharge techniques have become standard in equipment for the production of industrial quantities of ozone for water treatment and in other types of commercial ozone generators for a number of other applications, including semiconductor processing.4 Ozone has a number of industrial uses beyond the disinfection of drinking water and treatment of wastewater. Medical sterilization, odor control, swimming pool water treatment, fish hatcheries, shrimp farms, and low concentrations of ozone in the air to prevent fruit ripening during storage are only some examples.
One of the key advantages for ozone is that its usage provides a safe and environmentally friendly alternative to toxic and corrosive chemical processes. The advent of stricter environmental enforcement made the semiconductor industry acutely aware of the need for environmentally benign chemistries in the different chemical processes associated with device fabrication. Under the heading of “Difficult Challenges,” the 2003 International Technology Roadmap for Semiconductors (ITRS) section on Environmental Safety and Health specifically points out the need for improvements in Chemical Resource Management and Workplace Protection.5 Research over the past decade has demonstrated that ozone can be effectively used in “greener” alternatives to existing cleaning processes and in many instances it actually provides superior process performance for advanced applications. Specifically, research in this area developed ozone alternatives for the wafer cleans based on SPM, H2SO4, and RCA SC-1 and SC-2 that are used for the most critical surface preparation steps in device fabrication processes. This work was greatly assisted by recent improvements to ozonated water delivery systems that provide exceptionally high ozone concentrations and throughputs at the wafer surface (see Figure 1). In the following, a survey of ozone applications in semiconductor device fabrication is given.