FOUP purge performance improvement using EFEM flow converter

Abstract

Front Opening Unified Pod (FOUP) purging with nitrogen or clean dry air (CDA) is well known as the most effective method to protect wafers inside FOUPs from internal as well as external contaminations, e.g. particles, airborne molecular contaminants, humidity and oxygen, which can potentially damage integrated circuits (IC) and significantly impact manufacturing yields. Entegris, Inc. developed a diffuser purging concept that has demonstrated exceptional purge performance over conventional methods under the FOUP door open purging condition, however some unexpected test results were reported in field tests because the diffuser purge performance is significantly affected by Equipment Front End Module (EFEM) flow patterns. Since the EFEM flow is much stronger than the purging flow, in some cases the purging flow cannot overcome the EFEM flow deflected toward the FOUP opening. Furthermore, most of the EFEM flow patterns cannot be easily defined due to the variety of the EFEM designs and operation conditions, which makes it difficult to design a universal diffuser that works with all EFEMs in the field. Therefore, a need exists to develop a simple way to mitigate the effect of the EFEM air flow on the FOUP purging flow. This research was conducted to investigate the feasibility of the EFEM flow converter (EFC) concept, which is a screen mesh installed above the FOUP opening. The test results demonstrated that the EFC can dramatically improve the diffuser purge performance by converting non-uniform EFEM flow in front of the FOUP opening into uniform downward laminar flow that is favorable to FOUP purging.