Reduction of moisture and airborne molecular contamination on the purge system of 450 mm Front Opening Unified Pod

Abstract

The Front Opening Unified Pod (FOUP) is used for wafer storage and transport to prevent contamination from internal and external exposure. The FOUP may be contaminated by gases from manufacturing process or by the chemical compounds emitted from the stored wafers in the FOUP. Moisture, oxygen, and Airborne Molecular Contaminations (AMCs) are common sources of many defects and failures of chips. Moisture and Hydrogen Fluoride (HF) are always the most common forms of AMC by virtue of their existence in chemicals. In the past, techniques for removal of these contaminants have used various methods such as purging by nitrogen or compressed dry air (CDA). As the volume of 450 mm FOUP is up to 0.7060 m3, about two and half folds of a 300 mm FOUP, and considering the purge efficiency of purge gas, optimization of FOUP purge technology is urgently needed. In this study, we proposed an alternative method, which combines vacuum technology and purge technology (thereafter referred as "vacuum purge" system). This study aims to evaluate our newly proposed vacuum purge system against the conventional purge system. The Cavity ring-down spectroscopy (CRDS) was used as monitoring system for HF concentration. Results show that with initial Relative Humidity (RH) value of 50% and HF concentration of 9 ppb in the FOUP, RH and HF concentration can be reduced to less than 5% of the initial RH or HF concentration by vacuum purge system in 3 min and 40 s, respectively. For conventional purge system, it took more than 30 min and 80 s to reach that level. For conventional purge system, RH and HF concentration were first-order linearly related to the inversed purge flow rates. Increasing inversed purge flow rate significantly increase purge time.