Diagnosing Asia’s fabs: Copper, 300mm, lithography drive metrology

By Drew Wilson
WaferNews Asian Correspondent

Asia’s big chipmakers have been embracing metrology systems as technology changes come on stream, devices grow in complexity, and time-to-market pressures escalate.

“Today it’s critical to keep fabs operating at optimal yields as much as possible,” says Risto Puhakka, VP of operations for VLSI Research Inc. “That’s the key issue that keeps driving metrology.”

FEI Co., Hillsboro, OR, which makes equipment for structural process management, has its dual beam inspection systems helping TSMC’s Fab 12 go from a few wafer starts/month to 10 times that by year’s end, says Jay Lindquist, VP of FEI’s microelectronics product group. The machines promise to save chipmakers time and money by providing a 3-D view below the surface of the defect area, right on the production line.

“The big push right now is to bring in tools so customers can get a manufacturing line to the point where it’s ready to ramp up,” Lindquist adds.

Asia sales make up more than 30% of FEI’s $376 million in sales and include powerhouses such as UMC, Samsung Electronics, Elpida, and NEC.

Another metrology company, Rudolph Technologies Inc., Flanders, NJ, derives 50% of its $80 million revenue from Asia. Customers include the major Taiwan foundries plus Chartered Semiconductor in Singapore and a list of Japanese and Korean chipmakers.

Rudolph makes metrology tools that essentially improve yield. For example, the company’s sonar-based technology called Metapulse measures the thickness and quality of the films that are involved in the 500-some process steps it takes to turn a silicon wafer into functioning state-of-the-art computer chips, explains George Collins, Rudolph’s VP of marketing.

If the films are too thick or thin, or not laid down or removed properly in the photolithography process, then the wiring that connects maybe 20 million transistors on the chip will create defects.

Asia began buying pulse sonar technology about two years ago. Collins believes sales are still in an early phase.

“Some capacity out there is one or two generations old,” he says. “When high volume production returns, retooling to a new generation will require many metrology tools.”

Technology transitions introduce uncertainty into the chipmaking process and metrology equipment can quickly tell the manufacturer what’s gone wrong and where.

Copper wiring, for example, is problematic, and has high defect rates. While FEI’s systems have the ability to spot voids in a copper structure, Rudolph’s Metapulse helps in laying down the wire properly in the first place.

Collins says Rudolph has sold systems to nearly all of the 20 or so chip companies that announced the adoption of copper.

Another technology change is in lithography, which is pushing the laws of physics by using wavelengths of light much larger than the features that are being printed. FEI’s metrology systems help address phase shifting and proximity correction problems, Lindquist says.

Then there’s the 300mm wafer, which is more costly than 200mm, but can produce 2.4 times more chips that probably carry high ASPs. FEI’s focused ion beam system has been attractive because it doesn’t waste the whole wafer to analyze one chip defect. The system could single out one faulty chip on a 600-chip wafer. In the past, a whole wafer might be cleaved to analyze one defect, losing $5,000 to $20,000 worth of revenue, depending on where it was in the production process.

Rudolph’s Collins adds that a 300mm wafer with microprocessors could be worth about $100,000. Saving only 10 wafers in a 20-wafer cassette by identifying them as good early in the process adds up to $1 million saved.

Typically a fab uses six to 10 of Rudolph’s tools. In a 300mm format, which can run as high as $1.5 million for each tool, the fab can see a payback in six to nine months, Collins claims.

VLSI sees the process diagnostics market, which includes metrology, slightly down in 2002 to $3.4 billion from $3.6 billion last year. But over the long term, the process diagnostics share of all chipmaking equipment is growing, Puhakka says.

“The information you derive from metrology can be used to drive your processes — and that’s why the value is continuously increasing,” he adds.



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