Go Where I Send Thee
the technology that the sematech experts picked as runner-up, the Scalpel system being developed by Lucent, uses electrons, rather than light, to make the chips. Electrons are an alluring medium for etching because unlike light, they act more like particles than waves: They tend to go where you point them.
Lucent’s decision to go with Scalpel is a simple matter of risk versus benefit, says Lloyd Harriott, program manager at Lucent. “We had programs in all the next-generation technologies, including EUV,” he says. “In fact, we initiated the EUV technology back in the 1980s.” That was at the old Bell Labs, and money for basic research was becoming tight. As a result, rather than playing the field, Bell Labs had to choose one lithography technique to champion.
Most of the other next-generation lithography technologies will need several breakthroughs before becoming commercially feasible, says Harriott. “If you look at Scalpel, the source is a filament, the optics are not much different from an electron microscope, and the photoresist is the same one currently used with deep UV lithography.” To become feasible, he adds, Scalpel needs just one big advance: “The mask is the most unique problem.” This is because Scalpel’s mask is a radical innovation; the pattern is created in tungsten stuck on a thin membrane of silicon nitride, whereas conventional masks are made of chrome on glass.
Lucent built a proof-of-concept machine in 1996, and a lithography test bed in 1997 that can make features as small as 40 nanometers. The company is developing a commercial system that would be able to reliably make chips with 100-nanometer features that it hopes to market by 2002.
these methods are very promising, and one or more of them will surely be the way to keep Moore’s Law from going bust. Yet chip making is a notoriously conservative and financially competitive business, and companies won’t embrace major change until the industry is painted into a corner. And, with the price of a new fabrication plant starting at around $3 billion, no one can blame them for wanting to be sure before betting all their chips on one particular number.
“If you were starting out today to design a car from scratch, the last thing you might choose to power it is an internal combustion engine,” says Veeco’s Kania. “But that is the current technology, and no automaker is going to change it until they’re forced to.” Likewise, chip makers are working hard to get every last nanometer out of optical lithography before turning to new technology.
Indeed, the most telling scuttlebutt at the Sematech meeting in December was that some in the semiconductor industry are thinking about staying with optical lithography for yet another generation of chips, using light with wavelengths down to 157 nanometers. This would allow them to make feature sizes as small as about 90 nanometers, breaking the 100-nanometer barrier. It would require substantial changes: new fluorine excimer laser technology, and optics made not of sturdy fused silica, but of delicate calcium fluoride. The extension could buy chip manufacturers a few years.
The semiconductor industry’s reluctance to take a chance on new technology is understandable. Intel, the largest chip maker in the world, cranks out 100 million microprocessors every year. Any new technology has to feed this voracious production line reliably and profitably-something that optical lithography has been doing remarkably well for years. “Many times optical lithography has continued to surprise us by always pushing into another generation of chips,” points out Intel’s Gargini.
But sooner or later, the makers of integrated circuits will have to free themselves from optical lithography. That is, if they want to keep Moore’s Law from being put under house arrest.