Front Opening Unified Pod / FOUP: boxes for wafers
Submitted by SDRAM Technology on Fri, 08/07/2009 - 12:23
A FOUP (Front Opening Unified Pod) is a closed and transportation safe box for wafers within a semiconductor factory. The main purpose of a FOUP is to isolate the wafers from the clean room environment. The FOUP concept allows to save investments needed for a class 1 clean room. Due to the fact that inside the FOUP a special microclimate/micro-clean-room is generated/maintained and the wafers are isolated from the clean room atmosphere, the class of the clean room itself can be higher(=worse), e.g. 1000, as would be necessary without the FOUP concept. Investments and maintenance for a class 1000 clean room are much lower as compared with a class 1 clean room. Due to this reasons, FOUPs are indispensable accessories in modern 300mm microelectronic factories. Examples of FOUPs can be seen in Figure 1 and 2.
Figure 1: Front Opening Unified Pod Example 1
Figure 2: Front Opening Unified Pod Example 2
In modern microelectronic factories the tools are also isolated from the clean room environment, i.e. they are also inside special “boxes” which have the same micro-climate/micro-clean-room conditions as inside the FOUPs. In order to avoid tool and FOUP contamination with the “dirty” clean-room air (during the process of wafer transfer from the FOUP into the tool), the modern microelectronic tools have special docking stations for FOUPs (see Figure 3).
In order to maintain constant the micro-clean-room conditions (without any contaminations) inside the FOUPs, they have to be periodically cleaned. While processing the wafers, e.g. during an etching process, the wafers are treated with different gaseous, liquid, plasma etc. substances. Much of the species from the used chemicals can be found on the wafers also after the process was finished. Due to the fact that after the process the wafers should be transferred into the FOUP, they can outgas and contaminate the FOUP with different kinds of chemicals. In turn, the undesired chemical species can attack uncontrolled the wafers inside the FOUP and destroy the micro/nano structures on them. Due to this, the so called haze effect, the FOUPs shall be changed (and cleaned) several times during wafer processing in a Front End factory. FOUP cleaning is a relatively expensive logistic step.
A usual FOUP (Front Opening Unified Pod) has a capacity for 25 wafers, weights more than 5 kg (without wafers) and more than 8 kg with wafers inside (a Silicon wafer weights ~120 g). The price of a FOUP is certainly dependent on the supplier, but is in the range of 1000 USD/unit. A FOUP has a life time of ~5 years.
Figure 3: At tool docked FOUPs