SEMATECH News
Laser-Based EUV Source Technology Gains Ground at SEMATECH Workshop
Baltimore, MD (21 May 2007) — A former “dark horse” technology appears capable of taking the lead as the most promising power source for extreme ultraviolet (EUV) lithography, according to scientists at a recent SEMATECH-sponsored workshop here.
The emerging power source – laser produced plasma (LPP) using tin as fuel – can now produce up to 130 watts of power for short periods, which could result in more than 40 watts of power at the intermediate focus using highly efficient collectors, suppliers of EUV source systems reported at the EUV Source Workshop held here in early May.
If commercial versions of these sources can be integrated into a reliable source-collector module on time, that’s enough power to meet the minimum requirements of 40W-60W for beta level EUVL scanners scheduled for delivery in 2009, noted Vivek Bakshi, workshop chair and senior member of technical staff at SEMATECH.
“LPP-based EUV sources, using tin as fuel, are shining brighter and show increasing promise of meeting power requirements for EUV-based lithography scanners,” Bakshi said. “This is good news, since tin-based LPP EUV source technology has many positive features that make it an attractive choice for high-volume microchip manufacturing.” Bakshi added that the reported power availability is based on suppliers’ estimates of the performance of their own in-house prototypes, which will be developed into commercial products to support EUV lithography.
EUV lithography is widely regarded as the most promising patterning technology for the commercial production of advanced microchips in the next decade. With a wavelength of only 13.5 nm, EUV light could be used to define circuit lines and features much smaller than those being placed on chips today.
In an LPP-based system, EUV light is produced by bombarding a sliver of tin with a high-power laser. The light is then gathered by specially engineered EUV mirrors, which then focus an EUV beam in the EUV scanner to produce microchip patterns.
LPP-based sources are rivaled by discharge-produced plasma (DPP) sources, which currently generate more power, consume less energy, are less expensive, and are being integrated into alpha-level EUVL scanners. The lower power version of DPP-based EUV sources has been used to support EUV microexposure tools and industry-wide EUV metrology and EUV resist development projects.
However, the heat and debris that result from EUV sources, which can seriously damage EUVL scanner components, are more difficult to control in a DPP-based system. These disadvantages, coupled with recent progress in high power lasers, are increasing the feasibility of LPP-based sources, Bakshi noted.
At the SEMATECH workshop, 12 suppliers and R&D groups described the readiness and development plans of three types of high power laser systems designed to bombard tin to produce EUV light. Presenters showed that:
- Pulsed CO2 lasers generate the most power (7 kilowatts), but are still being developed and have not been subjected to continuous operation
- Nd:YAG laser modules with 1500 W power capable of continuous operation are already available as commercial products, with 3000 W modules in development. (Nd:YAG systems utilize a neodymium yttrium aluminum garnet crystal as the lasing medium.)
- Fiber-based lasers require less electricity, cost less and can be easily scaled but are also less developed than CO2 and Nd:YAG lasers.
Although each of these LPP-based approaches falls short of the 10-20 kilowatts of laser power that will be needed for commercial EUV scanners, the necessary wattage can be obtained by “multiplexing” less powerful systems – much as batteries can be linked in parallel to produce more electricity, Bakshi explained. “The feasibility of linking laser modules in this way has been demonstrated for some time,” he said. “And as the power and reliability improve for individual laser modules, fewer modules will be needed to achieve sufficient power in an LPP-based source.”
The workshop also included a panel discussion on the challenges of developing a source collector module (SoCoMo), which consists of an EUV source, debris mitigation devices, spectral purity filters and collector mirrors, to channel clean EUV photons to a EUV scanner.
“Most of the panelists agreed that the success of SoCoMo depends on collaboration among all parties: source, collector, and scanner manufacturers, research institutions, and end users,” Bakshi said. “It appears likely that in the near future, instead of source suppliers, there will be suppliers who will provide an optimized SoCoMo developed in collaboration with scanner manufacturers.”
“Efficient collaborations among stakeholders will be critical to demonstrate EUV beta tool sources with power levels of 40-60 watts at the intermediate focus, and with reliable operation over weeks by the end of 2008,” noted Stefan Wurm, EUV Strategy Program Manager for SEMATECH “This will ensure that the industry can be confident that mature beta tool sources will be ready for integration into beta EUVL scanners in 2009,” Wurm said.