Cymer Hitting Its EUV LPP Source Goals

Cymer said it is running its laser-produced plasma (LPP) EUV source for eight hours at a time at 50 W of pulsed power. By the end of the year, Cymer expects its source to generate 100 W of sustained power during the time of the exposure of the die, enough power for the pre-production EUV tools expected next year from the major scanner manufacturers, said David Myers, vice president of Cymer's EUV source program.

David Lammers, News Editor -- Semiconductor International, 11/12/2008 9:43:00 AM

Cymer Inc. (San Diego) said it has reached its goal of eight hours of continuous operation of its laser-produced plasma (LPP) source of extreme ultraviolet (EUV) radiation, running its LPP tool for three eight-hour periods over a weekend.

Cymer said its LPP EUV source is able to operate for eight hours.

In May, Cymer was able to run its LPP subsystem for ~90 minutes, said David Myers, the vice president responsible for the EUV source program. In July, Cymer said its year-end goal would be a full shift of operation, or eight hours before scheduled maintenance. Since then, the company has made enough improvements to its debris mitigation system to run for the promised eight hours, Myers said.

“We continue to be executing on our plan to have a system shipped by the end of this year for the first EUV pre-production tools,” he said. “To be a usable development tool, the system has to be able to run for at least a shift. Ultimately it has to run much longer, but for integration and testing it has to be able to run for a full shift.”

Cymer operates one LPP source for mitigation studies, and another full-size tool includes the collection optics, thermal management system, and other components. Both tools are operating for eight-hour periods, Myers said. The tools operate at 50 kHz. As the tin droplets meet the laser pulses at 50,000 times a second, the 13.5 nm radiation is gathered by the collection optics and reflected through the optical path to the mask.

Myers said the eight hours of operation means that Cymer was able to keep the laser running and aligned with the tin droplets, while performing the required debris mitigation. Over the weekend of operation, he said, the LPP system delivered ~1 MJ of dose, sufficient to process 250 300 mm wafers at a resist sensitivity of 10 mJ/cm².

“Most recently, we had on the order of 50 W of power in burst mode, with a duty cycle of 10% on one tool and 30-40% on the other tool. We are still not at the level required for a production tool, but we are getting very close,” he said. By the end of the year, Cymer expects 100 W of sustained power during the time of the exposure of a die, or several seconds, at a nominal duty cycle of 100%.

Although a tin source produces more EUV radiation, tin presents debris mitigation issues. As the 30 µm diameter tin molecules are hit by the laser, the reaction generates atomic tin in vapor form, which can impinge on the surface of the collector optics, degrading the reflectivity. Other “junk materials” must be controlled as well, Myers said, and energetic fast ions and neutrons are an issue.

Although its debris mitigation methods are proprietary and closely held, Cymer uses electrostatic and magnetic fields to deal with the charged particles, as well as optimizing the physical design of the system, Myers said. “We have a few other techniques that we use that we are not disclosing at this time,” he added.

The overall EUV program is making “good progress,” Myers said The alpha EUV tools at IMEC (Leuven, Belgium) and Albany NanoTech (Albany, N.Y.) have processed “well over 500 wafers, resulting in contact patterns that were far better than what would be possible with immersion 193 lithography,” he said.