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300mm yield awaits perfection in process tools
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Wednesday, December 11, 2002
Semiconductor manufacturing on 300-mm wafers still faces several hurdles before the larger substrates can deliver the expected 30 percent die cost savings over 200-mm wafers, said Henry Chen, deputy director of Taiwan Semiconductor Manufacturing Co.'s 300-mm Fab 12 at Hsinchu, Taiwan.
Moreover, some 300-mm manufacturing equipment needs to be redesigned from scratch, said Chen, who joined several other manufacturing managers in kicking off the 2002 International Electron Devices Meeting (IEDM) here on Sunday (Dec. 8) with a standing-room-only short course on the future of semiconductor manufacturing.
Several key pieces of production equipment remain immature, with an estimated 20 percent overall gap between the targeted productivity and today's throughput, Chen said. The 300-mm lithography wet bench tools and control software are not nearly as efficient as the 200-mm systems, he said, adding that TSMC is expecting a "breakthrough" that he declined to detail from a wet bench equipment supplier. Such tools provide resist and other chemicals to the wafers during the key lithographic steps.
Scanners, chemical-mechanical polishing tools and furnaces must be improved, Chen said, and so must the overall reliability of 300-mm equipment. "There are new features in the CMP tools that are not bug free," he said.
In fact, said Chen, many equipment companies need to completely redesign their 300-mm machines. Some vendors took an efficient 200-mm tool and "just blew up [increased the size of] the chamber or tube. As a result, the uniformity is not as good," he said. "Brand-new designs of 300-mm equipment are needed, but even then it will take several generations before that equipment is mature."
The cost of the control software is an added burden. Because the front-end unified PODs that hold multiple wafers are too heavy for human handlers, 300-mm fabs must be more highly automated. Automation accounts for about 6 percent of the cost of a 300-mm fab, or more than $100 million, double the automation cost burden of a 200-mm production fab, Chen said.
Also, the 300-mm control wafers used to test out process steps are extremely expensive, he said. Production wafers are about five times more costly than 200-mm wafers, at upwards of $500 each, depending on the epitaxial quality.
But the biggest problem is not the equipment but the economy, Chen said. The industry downturn has made it impossible to keep the mammoth 300-mm fabs running at maximum capacity. Though TSMC started work on its Fab 12 in Hsinchu three years ago, that fab is "far from full" and the company has undertaken a "slowdown" in equipping its second 300-mm facility, Fab 14.
Nevertheless, Chen said he expects 300-mm wafers to hit cost parity with 200-mm wafers by the middle of next year at TSMC. For the industry in general, it may be 2006 before the larger wafers hit the 30 percent cost savings projected by International Sematech, he said.
By: DocMemory
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