Chapter 32.2 - Automated Material Handling System - Principal Components Of An AMHS

An AMHS is utilized to transport and store carriers within a semiconductor factory. There are a variety
of carriers as well as AMHS components utilized in the semiconductor industry each of which
has particular usage characteristics. The AMHS components can be broken into three categories—
the storage system, the transport system, and the software that controls the overall system.

As wafer sizes have evolved over the last few decades from 3 in or smaller wafers to state-of-the-art
300-mm wafers, the carriers that contain them have also changed. With the advent of 200-mm semiconductor
production in the early 1990s, a significant emphasis was placed on designing carriers that
could be automatically moved through a factory with an AMHS. This philosophy was extended with
the design of 300-mm carriers that were envisioned from the start to be optimized for AMHS.

200-mm Carriers.   There are two cleanroom concept philosophies for 200-mm fabs that dramatically
impact the style of carrier utilized—standard mechanical interface (SMIF) and open cassette.

SMIF.   A SMIF factory utilizes enclosed carriers that are opened by a standard load port on each
tool. In addition, each process tool in a SMIF factory contains a minienvironment that provides a
clean environment for the wafers once they have been removed from the carriers. SMIF carriers are
well suited to AMHS because they have a common automation interface as well as because the
wafers are kept isolated from any potential contamination that might be generated in the movement
of the carriers through the fab.

Open cassette.   Open cassette factories utilize wafer carriers in which the wafers are exposed to
the environment. As such, an open cassette factory must be kept cleaner than a SMIF factory. Open
cassettes may be transported by themselves or placed in a sealed storage box prior to transport. One
of the key disadvantages to open cassettes and their storage boxes is that they were not designed with
automation in mind. Therefore, custom interfaces and custom robots must be utilized to move open
cassettes into and out of automated material handling systems.

300-mm Carriers.  With the transition to 300 mm a significant amount of effort was placed into
standardizing the style of carrier utilized by fabs worldwide. Ultimately, a minienvironment friendly,
automation ready, integrated carrier called a front opening unified pod (FOUP ) was selected as
the industry standard. Similar to the 200-mm SMIF concept, the 300-mm FOUP seals the wafers in
a controlled environment. Additionally, the same style of robotic handle used on SMIF carriers is utilized
to enable FOUPs to be automatically transported through the factory. The difference between
the FOUP and SMIF concepts primarily exists in two areas—(1) the door is on the front of the FOUP
while it is at the bottom of the SMIF carrier and (2) the FOUP contains an integrated wafer cassette,
while a SMIF container has a removable wafer cassette.

An AMHS is utilized to transport and store carriers within a semiconductor factory. There are a variety
of carriers as well as AMHS components utilized in the semiconductor industry each of which
has particular usage characteristics. The AMHS components can be broken into three categories—
the storage system, the transport system, and the software that controls the overall system.

As wafer sizes have evolved over the last few decades from 3 in or smaller wafers to state-of-the-art
300-mm wafers, the carriers that contain them have also changed. With the advent of 200-mm semiconductor
production in the early 1990s, a significant emphasis was placed on designing carriers that
could be automatically moved through a factory with an AMHS. This philosophy was extended with
the design of 300-mm carriers that were envisioned from the start to be optimized for AMHS.

200-mm Carriers.   There are two cleanroom concept philosophies for 200-mm fabs that dramatically
impact the style of carrier utilized—standard mechanical interface (SMIF) and open cassette.

SMIF.   A SMIF factory utilizes enclosed carriers that are opened by a standard load port on each
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