MICRO: Tool/Fab Support

Wayne Curcie and Marcel Choudhury, Infineon Technologies; and Semiconductor fab clean dry air (CDA) system designs have received increasing attention because of the requirements of photolithography tools. Technology developments in the IC industry have led to the use of lithography tools with higher purity, flow, and pressure requirements, placing new demands on CDA system design. This article discusses traditional CDA system design, the role of vendors in supplying CDA to fabs, and lithography tool requirements. It presents measures that existing and future fabs can take to meet their CDA needs and discusses the potential impact of those measures on the manufacturing process. CDA is used in many applications throughout the fab and support areas, including in pneumatic controls and tools, purging equipment, air cylinders for machine actuation, product cleaners and blow-off devices, and air-driven pumps. A fab's CDA system is typically located in the central utility plant and is configured along the lines of the simplified schematic in Figure 1. The system is normally designed to provide –80° to –100°F dew-point air with 0.01–0.003-µm filtration. Delivered pressure to the point of use is generally 100 psig. Generally, multiple compressors are needed to generate CDA, and an additional unit (n + 1) serves as a standby. Design data from many fabs indicate that CDA consumption can vary significantly from 25 to 50 std cu ft/min per 1000 sq ft of production cleanroom area. CDA consumption in newer fabs seems to be closer to a nominal 40 std cu ft/min per 1000 sq ft of cleanroom area. Typically, more than 80% of the CDA system is used to support manufacturing equipment, while the remaining 20% is used for instrument air and utility applications. In the manufacturing area, wet and lithography applications are the largest consumers of CDA, each using 15% of the facility's