Quantitative 3-D Flow Visualization of Conventional Purge Flow Within a Front Opening Unified Pod (FOUP)

The front opening unified pod (FOUP) is a carrier that transports multiple wafers as it moves between numerous processing facilities. It is inevitably exposed to air humidity coming from the equipment front end module (EFEM), which leads to the formation of harmful residual particles on the wafer surfaces due to the reaction of moisture with airborne molecular contamination (AMC). This can cause serious defects, and thus there is a need to understand the complex flow structure inside the EFEM and FOUP. Magnetic resonance velocimetry (MRV) is hereby employed to qualitatively and quantitatively measure the 3D flow when conventional load port purge (LPP) is utilized to protect the wafers. The front LPP forms a barrier between the FOUP and EFEM, blocking the EFEM flow from entering the FOUP. Additionally, at the rear of the FOUP, flow from the rear and front LPP collide and then travels between the wafers toward the FOUP entrance, thereby protecting the wafers. Using computational fluid dynamic (CFD) simulations, various combinations of flow rates from different purge ports were simulated, leading to an optimal flow condition. These findings suggest that independent control of the flow rates can be a practical way to protect the wafers from defects.