Dynamic Analysis on Particle Concentration Induced by Opening the Door of a Front Opening Unified Pod ( FOUP ) that Loaded with 25 Pieces of 300 mm Wafer Manufacturing Processes

This study investigates experimentally and numerically the influences of FOUP door opening speed (Vdoor) and the pressure difference (dP) on the dynamic distributions of the averaged nondimensional particle concentration in the FOUP (Cave), which is defined as averaged particle concentration in the FOUP (cave) divided by the particle concentration in the clean room (cCR). Here dP is the difference between the mini-environment pressure and the clean-room pressure. Results show that when Vdoor lies between 0.05 m/s~0.15 m/s and dP within 0.3 Pa-12.7 Pa, Cave proportional to 1/2ρVdoor and inversely proportional to dP. This can be expressed by a stepwise multiple regression equation: Cave = 4.56 × 10 (1/2ρVdoor) – 4.6 × 10 dP + 4.96 × 10.


INTRODUCTION
The entire module is composed of three main components, namely, a mini-environment, a LPU and a FOUP, as illustrated in Fig. 1.
Their main functions are detailed as follow.
In line with improvement in production techniques, the rise in the number of 300 mm wafer manufacturing factories is a natural trend.As opposed to factories producing the smaller 200 mm wafer, these factories use wafer loading/unloading modules with FOUP/LPU combined with mini-environment.

Mini-environment
Mini-environment is a small-scale clean environmental mechanism housing the entire wafer production facilities to ensure that the processing of wafer is carried out in a controllable high level of cleanliness.Each production tool has its individual minienvironment whose clean air is provided by a  Hsiao, 2003) and airborne molecular contaminant (Chien et al., 2007;Li et al., 2007).According to the technical manual published by SEMATECH (1996), the design criteria stipulate that the air velocity in a minienvironment for producing 300 mm wafer must be between 0.2 m/s and 0.45 m/s while the pressure difference (between the minienvironment and the clean room) must be maintained at above 1.27 Pa but below 100 Pa.
As the mini-environment is created by the isolation technique, the air space to be controlled is largely reduced and therefore relatively easy to achieve higher level of cleanliness compared with the several technical problems faced in maintaining cleanliness in a large ballroom environment.

Load Port Unit (LPU)
The   processing.This study focuses on process 3, in which the wafer is most likely to be contaminated.The ISO and IEST publish the methods or protocols on construction and operation of minienvironments and clean rooms (Tannous et al., 1997;ISO 14644-1, 1999;Hu et al., 2002).For the 8 inch wafermanufacturing, some studies or benchmarking activities addressed the impact of production yields by adopting minienvironments (IEST, 1995;Rothman et al., 1995).Xu (2007) indicates that at a steady state, pressure differentials as low as under 0.2 Pa can be sufficient for achieving a high level of air cleanliness to meet environmental control expectation and requirements.

Experimental Approach
The experiment was carried out in a cleanroom.By adjusting the frequency of the inverter of supply air fan, various cleanliness levels ranging from ISO Class 1 to ISO Class 6 were achieved.The temperature and relative humidity were maintained at 22 ± 1°C and 55 ± 5% R.H., respectively.The multi-point laser particle counter (Mini-Net 310 PMS) was used to monitor particle concentration in the FOUP.
The multi-point laser particle counter used an "ensemble manifold" to draw particle samples simultaneously from seven sampling points, at a combined rate of 1 ft 3 /min.A particle counter then samples this mixed air.As a result, the particle counts represent the total number of particles from all sites, rather than from one site at a time.The results provide more meaningful data than the common single-point monitoring.

CFD Approach
The CFD study was performed by using a where n and n + 1 denote the respective Where φ represents each of the velocity components v and u, the turbulence kinetic energy (k), the dissipation rate of the turbulence kinetic energy (ε), and the particle concentration (c).ρ is the fluid density, while u is the flow velocity vector, g u is the grid elocity of the moving mesh, Γ is e diffusion coefficient for the dependent variable quantities at the current and next time levels.opening period for different door-opening speeds when dP is 9 Pa.
Fig. 1.Components of a FOUP/LPU loading/unloading module main function of the LPU is to open/close the door of the FOUP such that the wafer stored in the FOUP can be loaded into the manufacturing machine.Its main components are a FOUP Stage and a Frontopening Interface Mechanism (FIM).FOUP This is the container storing the wafer and is air-tight sealed to shelter the wafer from any contact with the environment in the conveying process to prevent particle contamination.A FOUP can store up to 25 pieces of wafer.The operating procedure of the FOUP/LPU loading module can be illustrated by five main processes as shown in Fig. 2.
Through an Automated Material Handling Module (AMHS) or an operator, a FOUP wafer-containing is first positioned on the stage with a kinematic coupling pin.In the second process, the stage will convey the FOUP forward until the latch on the FOUP door and the latch key on the front-opening interface mechanism are securely fastened.The third process, the latch key then rotates to open the door of the FOUP and moves backwards towards its initial position, completing the full opening operation of the FOUP door.In fourth process, the entire frontopening interface mechanism moves downwards into the LPU.In the final process, each wafer is then moved into the minienvironment to be loaded in sequence into the processing tool chamber by a robotic arm for The operating procedure (processes 1~5 (from left to right)) of unloading of a wafer.

FigFig. 7 .
Fig. 7 shows the simulated particle concentration values for 05 m/s to 0.15 m/s and dP ranging from 0.3 pa to 12.7 Pa.By applying the Stepwise Multiple Regression method, the following regression equations are obtained from the simulated data.It shows the influences of door opening velocity energy 1/2ρV door 2 and system pressure dP on the non-dimensional particle concentration C ave, where the determinant R 2 = 0.895 and corrected value is R 2 = 0.872.