Emission Control from Semiconductor Wafer Fabrication
(Anguil Environmental Systems, Milwaukee, WI)
Semiconductor wafer fabrication uses a number of chemicals to etch the surface of individual silicon wafers. Many of these chemicals contain VOCs (Volatile Organic Compounds) and HAPs (Hazardous Air Pollutants) which evaporate into the airspace of the tool. To meet EPA (Environmental Protection Agency) regulations the emission laden air needs to be captured and treated before being released into the atmosphere. The fabrication process is extremely pressure sensitive. Pressure fluctuations as low as 0.10” WC can have a negative impact on production, resulting in lost product. Any air pollution control device will be connected directly to the fabrication exhaust duct header, requiring that the control device create no pressure fluctuation within the header. Historically a rotor concentrator wheel in conjunction with a thermal or catalytic recuperative oxidizer has been the technology of choice. The emission laden exhaust from the tools flows through the concentrator wheel, providing two main benefits. The first is the concentrator wheel provides no pressure fluctuation in the exhaust header. The second is it concentrates the relatively large volume, low concentration exhaust into a lower volume, higher concentration stream. This concentrated stream has historically been sent to a smaller thermal or catalytic recuperative oxidizer. While this combination of technologies is dependable and effective, these oxidizers are limited to 65% - 70% thermal efficiencies due to internal metallic heat exchangers. A newer, more fuel-efficient technology called the RTO (Regenerative Thermal Oxidizer) is now being applied in conjunction with concentrator wheels on this application where it was once thought impractical due to pressure pulse issues. The RTO is capable of 99%+ destruction efficiency and upwards of 97% thermal efficiency which dramatically reduces operating costs. However, careful consideration must be given to the design of the system, connection to the concentrator wheel and selection of heat recovery media. If selected, our paper and presentation will examine, in detail, all the benefits and potential hurdles that manufacturers should evaluate before moving to this type of treatment device. In addition, we will identify the Concentrator / RTO features that they should look for in a system. The information will be conveyed using real world examples and case studies from actual emission control projects at several semiconductor facilities.