Humidity Control for Front Opening Unified Pod after Opening Its Door in a Mini-Environment

Abstract

Wafers are usually placed in a front opening unified pod (FOUP) while waiting in the line of manufacturing processes; a conventional way for preventing (or removing) contamination is to purge an FOUP with a gas, so as to maintain the cleanliness level. This study investigates the effect of the flow rate of clean dry air (CDA), supplied to the purge system and air curtain, on the moisture prevention performance, while opening the FOUP door in a mini-environment. An initial relative humidity (RH) in the pre-purged FOUP was approximately 0%, whereas an RH in the mini-environment was about 43%. Conventional, diffuser, and panel purge approaches were tested. The results showed that the moisture in the surroundings rapidly entered the FOUP when the door was opened, without using either the purge system or air curtain. When the CDA was then supplied to both the purge system and the air curtain, the RH values decreased significantly; the drop slope of the RH for the diffuser- and panel-purge processes was much larger than that of the conventional-purge process. In addition, the moisture prevention performance when the developed panel-purge system was used was slightly lower than when using the diffuser-purge system. However, the use of the panel-purge method could sufficiently suppress the vibration problem. In the present study, the case with CDA flow rates of 150 L/min to the air curtain and 250 L/min to the panel-purge device had the best moisture prevention performance, because of the smallest values for both the mean and maximum RH values (i.e., 1.3% and 9.5%, respectively) in the FOUP.