The Effect of Purge Flow Rate and Wafer Arrangement on Humidity Invasion Into a Loaded Front Opening Unified Pod (FOUP)

Abstract

In recent years, the semiconductor industry has continued to advance production techniques and reduce chip feature size. The presence of unwanted moisture during the construction of these features increases the risk of chip defects and reduced yield. During production, smaller integrated circuit (IC) products are more sensitive to the presence of moisture. Therefore, increasing the efficiency of moisture control techniques is very important to decrease the product defect rate. Front opening unified pods (FOUPs) are the plastic enclosure boxes that are designed to provide a cleaner environment for semiconductor wafers during manufacturing and storage. Clean dry air (CDA) or nitrogen (N₂) can purge moist air out from the FOUP. For the first time, in this study the effect of purge flow rate on the moisture removal efficiency of a loaded FOUP was examined accurately via smoke flow visualization, particle image velocimetry (PIV) and relative humidity (RH) measurement. Moreover, two different wafer arrangements of top-empty and bottom-empty FOUP were investigated. The findings show the bottom-empty FOUP arrangement results in higher purge performance compared to the top-empty FOUP arrangement. Four purge flow rates of 130, 200, 300 and 400 LPM were examined. The findings also show that when the purge flow rate was set to 200 LPM, the lowest level of relative humidity was measured inside the FOUP. Therefore, the purge flow rate of 200 LPM and the bottom- empty FOUP arrangement can minimize the humidity invasion into a loaded FOUP. The findings from this study can be beneficial to the industry to optimize the purge flow rate and to define the most efficient arrangement of the wafers inside the FOUP during manufacturing and storage. This can increase the product quality and reduce energy consumption by decreasing product defects and increasing yield.