Sematech gives conveyors a go in fab
09/01/2003
By Hank Hogan
AUSTIN, Texas—International Sematech's latest offering looks a bit like cars racing in slow motion around a track, or perhaps a stately high tech waltz.
But according to Marlin Shopbell, manager of the 300-millimeter (mm) wafer automated material handling program at Sematech, this dance of front opening unified pods (FOUPs) is actually a glimpse of the future.
The research consortium has implemented a demonstration material movement system that combines an overhead hoist with a conveyor. It's a combination that promises to improve material flow and reduce cycle time.
 A combo hoist and conveyor system at International Sematch is designed to improve material flow. |
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Because of the conveyor, the combination is new to semiconductor processing. That, however, doesn't mean that Sematech is championing an untried approach. "Other industries have used conveyors for a long time," says Shopbell. "It's not new technology. It's just new to the semiconductor industry."
Sematech is responding to a 2001 study in which a research consortium concluded that conveyors represented the best solution for material transport within a fab.
Today, this is done using overhead hoists to move lots from tool to tool, with trips to and from a wafer stocker as needed. Usually, the hoists move in one direction and the stocker may be as much as 30 to 40 meters (100 to 130 feet) away. The result is time lost in transit and reduced productivity.
With a conveyor, however, these setbacks can be alleviated. Conveyors move material at a constant speed, regardless of load. A conveyor can have a loop that holds material right at the tool, increasing tool utilization and boosting productivity.
In the demonstration, Sematech used three bi-directional SK Daifuku overhead hoists and a 270-foot-long Middlesex General Industries conveyor to shuttle FOUPs between seven processing tools. It was all done using industry standards and did not require anything new from the hardware. The system is three conveyor tiers deep and out of the way of the manufacturing floor.
"The FOUPs are all overhead," explains Jim Bernardi, project manager at SK Daifuku. "They all, at any time, can be moved around on this conveyor system."
In today's fabs, two overhead hoist loops —one moving clockwise and the other counterclockwise—accomplish the same task. But that requires two loops and storage in a stocker. Bernardi notes that in the Sematech approach, the conveyor is the storage.
Unlike conveyors found in dirtier applications, this cleanroom version is made up of bars that spin in either direction. When no FOUPs are present, the bars are still, reducing the contamination load. Shopbell also notes that the FOUP itself serves to protect the wafers inside from any conveyor-generated particles.
In the Sematech demonstration, a hoist takes a FOUP off the conveyor when needed and moves it to a given tool. When processing is complete, the hoist retrieves the FOUP and places it back on the conveyor. Everything is done under software control.
Although continuous, the conveyor is actually split into many small zones. Each has a sensor that detects when a FOUP enters—information plays an important role. "That's how you keep one FOUP from stacking on top of another," says Shopbell.
Further tests and additional refinements are being made. The conveyor-hoist combination should be ready for industry use within a few years and could be commercially deployed by 2007.