INDUSTRY NEWS

Ohmi: Rapid ramp-ups, 100% recycling, ‘dry-in/out’ CMP tools are 2001 needs

SAN JOSE—Rapid process line ramp-ups, 100% recycling, and drastically shortened wafer flow paths will be standard requirements for successful chipmakers in 2001, according to one of the world’s leading experts in ultraclean semiconductor manufacturing technology.

Tadahiro Ohmi gave an audience at the 44th American Vacuum Society meeting his considered views of manufacturing come the millennium. Additional requirements for ULSI processes, said Ohmi, will include low-cost production, high productivity, and 100% yields. Meeting these three goals will require global standardization, process simplification, and around-the-clock fab operations.

Ohmi, a professor of engineering at Tohoku University in Sendai, Japan, delivered the keynote address on manufacturing requirements in 2001 during an AVS seminar hosted by the Ultra Clean Society. Japan-based UCS is a 235-member R&D organization whose mission is to develop new technology for future semiconductor manufacturing needs. Ohmi’s prescriptions were based on work conducted at his Tohoku University lab in conjunction with UCS member companies. UCS has eight committees which oversee what Ohmi called “science-based engineering.”

Ohmi said UCS’s work is grounded in three principles: ultraclean wafers, an ultraclean processing environment, and perfect parameter-controlled processes, particularly plasma processing. A “new production line concept” has been a UCS priority, noted Ohmi, particularly with the coming 300-mm transition. “Many people are anxious over costs,” he noted, adding that researchers are “eager to establish a compact manufacturing line . . . equal to 200-mm lines.” Minimizing the 300-mm wafer flow path from a conventional “job shop system” of 15 kilometers to a “modified” system reduces the length of travel to 800 meters, Ohmi said. Converting the process line to this “flow-shop” system raises technical concerns about stepper/ scanner compatibility, chemical vapor— free wet cleaning, chemical vapor—free resist removal, and a process Ohmi called “dry-in, dry-out CMP.”

In a later interview, Ohmi elaborated on some of the main points he raised in his address. The technology directions he brought up involve interlocking technological requirements. Among the more important needs are short wavelength lithography using excimer lasers operating at 248 and 157 nm and x-ray lithography to 1 nm, complete wafer uniformity on a single-wafer process at high throughputs, and ultramultilayer metallization.

Ohmi also discussed the following points:

• He noted that for the past five to six years his lab has developed “wet chemical cleaning technologies that are totally room-temperature processes, requiring only H^₂O^₂ for the cleaning.”

• Room-temperature processing is a “key issue” that ties into the establishment of dry-in, dry-out CMP processing. “At present, all semiconductor manufacturers are using high- temperature liquid procedures. If the liquid chemical temperature is increased to 80° or 100°C, they generate too many liquid chemical vapors. Our room-temperature chemical cleaning procedures do not generate any liquid chemical vapor, only water vapor, so we can arrange the wet chemical station any place in the factory. . . and we can establish the dry-in, dry-out type of CMP equipment adjacent to the successive processing equipment.”

• UCS is evaluating reactive ion etching for 300-mm wafers. After the RIE “we can obtain the contact holes at 0.15- and 2-µm depths. At present we can evaluate the process result only by cutting the wafer. Obviously, it’s very expensive. So you can imagine how important it is to develop nondestructive, three-dimensional profilers. We’re working with a supplier to do that.”

• Metrology advances figure high on Ohmi’s list: “It is key for us to come up with very developed metrologies.” He noted that UCS is working on a three-electron-beam system to reduce evaluation time. “So far we are evaluating the process result from the structure itself. There is some contamination or particles, but right now electrical performance must be evaluated simultaneously. The main reason for yield reduction is electrical characteristics, not defects. We cannot find any defects from variations in device structure.”

• In the ULSI era newly constructed fabs will need to come on-line very quickly and operate around the clock. Chipmakers will need to modify their methods of using high-temperature sterilization or HP sterilization for their DI-water systems. They will be able to avoid having to stop the circulation process through the use of in-line ozone injection sterilization.

• Present steppers and scanners from different manufacturers have distinct “personalities and optical characteristics . . . so we must establish completely compatible steppers. This means providing a completely similar lens material. Unfortunately, the material itself and the surface microstructures are different for individual lenses.” For the past five years Ohmi’s lab team has focused on developing systems of measuring lens performance ֻso the distortion of patterns is decreased very drastically.”

• Ohmi emphasized that problems in gas-delivery lines caused by “external leakage or particle generation are completely overcome.” He noted, however, that the introduction of corrosives such as HCl to a gas line causes “the inner surface of the gas tubing system to generate too much metallic contamination on the wafer surface.” Several Japanese suppliers are seeking to solve these remaining “corrosion difficulties” by coating the inner surface of the tubes with Cr^₂O^₃ film.

Most of the research conducted at his lab is paid for by corporate backers, Ohmi said, adding that it receives very little support from the Japanese government. Many of the developments he mentioned in his presentation “will be ready for volume production use within the next two years.” Chipmakers need to develop “compact manufacturing lines” for 300-mm wafer processing, Ohmi says.

MicroHome | Search | Current Issue | MicroArchives
Buyers Guide | Media Kit