Industry weighs shift to 157-nm lithography
By David Lammers, EE Times
May 18, 2000 (9:26 AM)
URL: eetimes.com
AUSTIN, Texas ? Equipment vendors are hustling to ready the 157-nm lithography generation in time for introduction at
the 100-nm process technology generation. At the First International Symposium on 157-nm Lithography, held earlier
this month in Dana Point, Calif., vendors agreed that the equipment, resists, and other pieces of the 157-nm puzzle
need to be ready by the first quarter of 2003. According to Richard Harbison, 157-nm program manager at International
Sematech and the organizer of the symposium, "insertion timing" is the most critical issue facing the semiconductor
industry. The goal is to have a full 157-nm optical lithography solution, based on a fluorine laser, ready by the first
quarter of 2003, when many companies are readying 100-nm lines.
"We are not going to have 50 tools ready at that point in time, it will not be for full-blown manufacturing. But we have a commitment from the suppliers to be ready by then," Harbison said. He called the shift "a high-risk thing, and all the nickels must land on their edges to get there. But I think we can do it."
Among the four full-field scanner manufacturers, Silicon Valley Group Lithography (Wilton, Conn.) has the most
aggressive 157-nm schedule, with a plan to have a prototype system ready by the fourth quarter of 2001 and a
commercial-grade tool shipping by the first quarter of 2003. Gerhardt Gross, director of lithography at International Sematech, said that ASM Lithography (Bilthoven, Netherlands) expects to ship its first scanner by the third or fourth quarter of 2003, and Canon Inc. expects to be ready a year later. Nikon Corp. has yet to reveal its schedule, Gross
said.
IC makers are now "buying slots from the main tool vendors," Gross said, with advance payments made in return for
early systems shipped. And the 157-nm tools demand big bucks: Estimates for a single scanner range from $12 million to an eye-popping $20 million for a system with a high numerical aperture.
If the schedule slips badly, the suppliers of 157-nm tools and support infrastructure could miss their main window of
opportunity: the 70-nm technology node, starting in 2005. Most IC companies expect the 193-nm tools, based on an
argon fluoride laser, to share the 100-nm node with the new 157-nm tools. So the 70-nm node is likely to be the prime
opportunity of the 157-nm tools.
Essential to the success of the 157-nm program is cost. If IC makers discover they can get by with 193-nm tools and
phase shift masks, they may do so. "There will be specific combinations of techniques for specific applications," Gross
said.
The leading technical issue continues to be development of a resist that is transmissive at 157-nm wavelengths, and
which can withstand the etch steps.
Platform promise
Harbison said several large resist manufacturers report that they have established "platforms" ? the basic chemistry ?
needed to develop a commercial 157-nm resist. Sumitomo Chemical has committed to having a commercial resist ready
by the final quarter of 2002, and others have devised polymer-based chemistries that show promise. "We had nothing
before, so these developments are very promising," Gross said.
A remaining concern is the supply of the basic calcium fluoride material for the lenses from suppliers such as Bicron, Corning, Korth and Schott.
"At the supply line we are getting conflicting information about the calcium fluoride supply," Harbison said. "There is
another material, barium fluoride, which can be used in corrective elements for the refractive lenses. That could take some of the pressure off."
The scanner makers have different strategies. Silicon Valley Group Lithography is experienced with catadioptic systems,
which combine mirrors and refractive lenses and which use less calcium fluoride. However, such systems require an
off-axis illumination scheme, which can be difficult to align.
The three other scanner makers are more comfortable with refractive lenses, in which the laser, lens, mask and wafer
are all vertically aligned. But refractive systems put more pressure on the laser suppliers to deliver a narrower
bandwidth of light, Harbison said.
The pellicle, a soft membrane that serves to keep defects at the mask level out of focus, has become an essential tool
for IC makers, who are struggling to keep mask costs down. Harbison said one encouraging presentation at the 157-nm
symposium came from a manufacturer that has developed a pellicle with high transmissivity and good durability. That
vendor is expected to deliver samples to the MIT Lincoln Laboratory for characterization purposes.
Gross said the industry has learned "never to say never" about the ability to extend a lithography generation with phase shift masks, off-axis illumination and other technologies.
"The next step is that the lens makers now believe that they will be able to offer lenses with what to me are incredibly
good numerical apertures," he said. A high numerical aperture delivers more depth of focus at the wafer plane. If that becomes the case, there is a possibility 157-nm lithography could be extended to the 50-nm (0.05-micron) process node. "We just don't know yet," said Gross. |
