They’re called FOUPs, for front-opening unified pods, they number in the thousands and they’re zipping around continuously overhead.
No, it’s not the climactic invasion scene from Hollywood’s latest space aliens movie. Rather, it’s a real-world scene at a state-of-the-art semiconductor wafer fabrication line operated by IBM Corp., in East Fishkill, N.Y. The 140,000 square foot, $2.5 billion facility, which went operational in mid-2002, is “the first fully automated semiconductor manufacturing line in the world, where the system makes the decisions about what product to run next, how to run it, when to run it and why,” declares Perry Hartswick, senior technical staff member for IBM Microelectronics, in East Fishkill.
The line runs continuously, even when unattended. And the FOUPs—containers that move on overhead monorails to transport semiconductor wafers between processing stations—are a key part of the automated system that leverages real-time information to optimize the complex wafer fabrication process.
High stakes
The stakes are high. A FOUP can carry up to 25 silicon wafers measuring 300 millimeters in diameter, each of which is diced into tiny integrated circuits, or chips, at the end of the wafer fab process. The line produces advanced processor chips, as many as 1,000 to a wafer, says Hartswick. That means that each FOUP can carry up to $2 million worth of finished product—not the kind of payload that IBM wants to lose track of or mishandle.
Wafers typically go through hundreds of operations during processing, says Hartswick, and one wrong step applied to a FOUP’s contents could ruin the entire wafer lot. At IBM’s previous-generation, 200-millimeter wafer fab facilities, employees used bar codes to identify the wafer lots within containers, and then physically carried the containers from tool to tool. And though it didn’t happen often, employees occasionally made costly mistakes, moving containers of wafers into the wrong processing stations.
So when IBM engineers set out to design the East Fishkill 300-millimeter line, they wanted a product tracking system that would eliminate the risk of human error. They also wanted a fully automated facility that would be more labor efficient, more agile and more customer-demand driven.
A big part of the solution involved the use of radio frequency identification, or RFID, says Hartswick. Instead of the previous manual bar code-based approach, the movement of wafers throughout the facility was automated, using the overhead monorail system and the FOUPs, which comply with semiconductor industry standards for 300-millimeter wafer carriers. Each of the FOUPs, made of a polycarbonate material, is embedded with a passive RFID tag that is written with a unique identification number. These numbers can be read by RFID readers located throughout the fabrication facility.
Every processing tool—ranging from chemical etchers and ion implanters to chemical vapor deposition machines and furnaces—contains an RFID reader. Readers are also strategically located next to the monorail system throughout the East Fishkill facility. “There are thousands of RFID readers in this factory,” says Hartswick. The RFID system operates at 134.2 KHz frequency, which provides read distances of three to six inches. Unlike bar codes, a key advantage of RFID is that it requires no line-of-sight for reading, Hartswick points out, which greatly simplified design of the system.
FOUP tracking
The RFID system is used for precise tracking of FOUPs as they travel throughout the facility. Each time a FOUP is loaded with a new set of wafers, the FOUP’s RFID identity is read and the wafers are correlated with the carrier’s ID through a back-end IBM DB2 Universal Database. An IBM manufacturing execution system called SiView Standard then leverages information from DB2 to automatically control each step of the fabrication process.
“We know exactly where every FOUP is,” Hartswick relates. When a FOUP on the overhead track reaches a processing station, it is lowered by a set of cables to the tool loading port. Once the FOUP loads, the tool reads the carrier’s RFID, and downloads the settings or recipes needed for processing the wafers inside. When the processing is finished, the results, including any measurements taken, are sent back to the database, and the FOUP leaves the tool, either to move on to another processing station, or back to a stocker to await additional commands from the system, Hartswick says.
Between 5,000 and 6,000 FOUPs are in circulation at the IBM plant. Wafers can be added to or removed from a FOUP during the fabrication process, and each FOUP travels a different route based on the products being run and on operating conditions. “If the process is running very well, the system may choose to eliminate certain feedback steps, or if the process needs additional feedback, it will automatically trigger those steps,” Hartswick explains.
The system also automatically determines optimal wafer processing sequences, based on incoming customer orders. “If a customer orders X number of wafers by a certain date at a certain priority level, that’s fed directly into the factory,” Hartswick notes. Using real-time order information, the system then schedules the best lot to run next at each tool.
Thanks to the availability of real-time processing data gathered with the help of RFID, customers can also get up-to-the-minute information on the status of their orders, through a Web-based portal system called Customer Connect, Hartswick adds. Further, in the case of problems with chips in the field, the system provides the ability to trace the processing steps performed on the product back to the individual tools used, and the time that each processing step was performed, he observes.
Touch sensitive
IBM lists enhanced employee productivity and more responsive customer service among key benefits of the automation system deployed at East Fishkill. The plant requires fewer employees to operate than would otherwise have been needed, and product errors and delays are reduced due to decreased need for human intervention.
The use of RFID is key to enabling superior traceability and control during the complex fabrication process, Hartswick says. “When we run a product, we need to have full control over every wafer. We need to know that the wafer we’re touching right now within a tool is absolutely the one that we intend to be touching,” Hartswick notes. “There are various ways to do that. But there is no simpler way to do it, and no more accurate way to do it, than with RFID,” he concludes.
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See sidebar to this article: IBM Launches RFID Consulting Services
