## 2 Experiment and Apparatus
Most of the surface area of the dummy wafer was removed, as shown in Figure 5, in order to make the FOUP environment approximately empty. The surface of this supporting frame was polished and electroplated in advance, so as to prevent the humidity from being absorbed on it. In addition, Figure 5 depicts the five RH sensors that were embedded on the dummy wafer to measure the RH evolutions at different FOUP locations. For the present study, five dummy wafers were installed at slots 1 (the lowest slot in the FOUP), 7, 13, 19, and 25 (the top slot in the FOUP). Therefore, 25 RH sensors were used in the experiments. The reported RH in the following sections is the mean value from the results of those 25 RH sensors. The measurement range of the RH sensor (DICKSON, model: TK150, IL, USA) was from RH = 0% to 95%, with an accuracy of \(\pm\)3% (for RH >60%) or \(\pm\)2% (for RH <60%). Accordingly, the measurement uncertainty of the mean RH in the FOUP was estimated to be only 0.4%. Figure 6 depicts the testing loop of the experiments for the different purge methods in the FOUP. The purge gas for the FOUP and for the air curtain was the CDA generated from the same system, which was also employed in the previous study [11]. The use of the air curtain reduced the moisture entering the purged FOUP (with an initial RH = 0%) when opening its door in the mini-environment, as reported in our previous study [18]. Here, the air curtain, which had the dimensions of 410 mm (length) \(\times\) 60 mm (height) \(\times\) 60 mm (width), was made of aluminum alloy  
Figure 4: Schematic of a developed FOUP with a panel-purge device. CDA—clean dry air. Figure 5: Dummy wafer embedded with five relative humidity (RH) sensors. 7075, and five UPE ventilation plates were installed inside so as to generate a uniform air flow. For the cases of the conventional-purge and diffuser-purge experiments, the CDA supplied to the FOUP or air curtain, respectively, was controlled by a mass flow controller (Fujikin, model: FCST1500 FC-8F3-F500L, maximum flow rate of 500 L/min, \(\pm\)2% accuracy, Tokyo, Japan) or a digital flow meter (SMC, model: PF2A721, maximum flow rate of 210 L/min, \(\pm\)2% accuracy, Tokyo, Japan), respectively. For the panel-purge experiments, the CDA supplied to both the purge system and the air curtain was controlled by four digital flow meters. More specifically, in order to stabilize the CDA supplied tank and the airflow uniformity to the FOUP, we used three flow meters to control the CDA supplied to the three UPE ventilation plates in this particular case. In the present study, tests were conducted with different CDA flow rates supplied to the FOUP-purge system and air curtain. Table 1 summarizes the details of the experimental conditions. In this table, \(Q_{A}\), \(Q_{C}\), \(Q_{D}\), and \(Q_{P}\) represent the CDA flow rates supplied to the air curtain,  
Figure 6: Testing loops for different purge methods in FOUP: (**a**) conventional purge, (**b**) diffuser purge, and (**c**) panel purge. conventional-purge, diffuser-purge, and panel-purge processes, respectively. Here, the purging flow rate stands for the air flow rate that is purging into the FOUP; such a definition of the purging flow rate is similar, but not identical, to that used in the study of [PERSON] and [PERSON] [PERSON] and [PERSON] (2018). As indicated in Table 1, four different CDA flow rates were supplied to both the air curtain and the FOUP-purge system during the experiments (i.e., 200, 250, 300, and 400 L/min, which were cataloged as cases A, B, C, and D, respectively). The maximum CDA flow rate of 400 L/min was limited by the CDA generation system employed in the present study. In the beginning of the experiments, the FOUP with the door closed was pre-purged using a CDA flow rate of 60 L/min (i.e., 30 L/min for each FOUP-purge inlet or 10 L/min for each panel-purge inlet) for 10 min, so as to ensure that the RH decreased to approximately 0%.