Group of 10 to Tackle Killer Particles
Peter Singer, Editor-in-Chief -- Semiconductor International, 8/31/2007 11:48:00 AM
Ex-IBMer turned consultant Paul Castrucci is taking aim at what he thinks will be a yield limiter for the 45 nm generation: killer nanoparticles that are held to the wafer surface by strong Van der Waals forces. Such particles, measuring 20-25 nm, are difficult to remove with traditional wafer cleaning equipment and could result in major yield problems on ultrahigh-density ICs. He believes his research will show that supercritical cleaning will provide the solution.
Castrucci worked at IBM from 1956 until 1988, where he was the plant manager for the Essex Junction, Vt., facility, which led the transition to 200 mm wafers, and then was a member of the corporate technology committee in Armonk, N.Y. He was the chief operating officer at Sematech in 1988-1989 before starting his own company in 1989.
“One billion transistor ICs, when processed with conventional cleaning solutions, will experience a yield barrier,” Castrucci said. “The barrier is due to the inability to remove absorbed nanoparticles.”
Castrucci’s goal is to form a “Group of Ten” made up of companies and government labs, preliminarily identified as IBM, Applied Materials, KLA-Tencor, Northeastern University’s Center for Nano and Microconamination Control, Los Alamos National Labs, NIST, Sematech, Nestec and Arizona State University. The work would be done at Albany Nanotech and be led by Castrucci’s company, Paul Castrucci & Associates (Burlington, Vt).
Castrucci said the group members would be confirmed in the next few weeks. The study would be completed in about a year. Sematech’s involvement would be to determine “rules and regulations” required for collaborative research as opposed to technical involvement.
The challenge of removing nanoparticles is that they “pancake” and become flattened, making them more difficult to remove. In a related study by Phadon Avouris and colleagues at IBM Research, it was shown that when small carbon nanotubes cross each other they deform with a force equivalent to the forces experienced by carbon when converted to diamond.
Castrucci said the Van der Waals forces are similar in scale. “The smaller the nanoparticle, the stronger the Van der Waals forces and the more difficult it will be to remove,” he said..
This is compounded by the varying surface roughness of different types of materials. Individual wafer surfaces have an atomic roughness of about 1-30 Å.
Supercritical cleaning, which operates at high pressures where matter looks like a liquid but acts like a gas — a fourth state not typically found in nature — has some distinct advantages. Supercritical carbon dioxide (SCCO2), for example, has a density that is much larger than that of air, thereby dramatically increasing the drag on the particle. SCCO2 is also able to dissolve organic materials.
