Airborne molecular contamination (AMC) is responsible for crystalline defects and has an impact on final yield for 300 mm CMOS sub 90nm technology. In this paper, we describe our investigation on a vacuum purge system designed to suppress post etch issues. Moisture and volatile acids released in slot-to-slot space inside FOUP during queue time were found to be essential elements for crystal growth on patterned wafers. Vacuum purge was proven as the most efficient way to suppress those compounds in FOUP and on wafers. Results of this new containment method show successful and persistent crystal growth prevention as well as yield enhancement (up to 7%).