Other EUV progress has also been reported in the past week:
• On source power: Nigel Farrar, vice president of technical marketing at Cymer, said Cymer has now achieved about 50 watt expose power on its HVM I source using a pre-pulse—which conditions the target prior to the main pulse—at full repetition rate using closed loop controls. (Back in February, Cymer also reported average power of 50 watts, but that was in open loop testing, minus the power-reducing controls placed on systems in the field to improve stability.)
• Meurice said the potential for 105 watts has been confirmed in lab experiments, supporting ASML's roadmap to volume production starting at 70 wafers per hour in 2014 and upgradable to 125 wafers per hour in 2016. He cautioned that in-situ experiments, as opposed to lab experiments, are still necessary to confirm this roadmap. Even if ASML stopped development now, Meurice said the lab data demonstrated that ASML's NXE:3300—the production tool successor to the pre-production NXE 3100 systems installed at several customer sites—would support throughput of 30 to 40 wafers per hour based on its superior architecture and energy efficiency. (Halting development, of course, is not the plan).
• Source availability: Farrar said Cymer's HVM I sources have been running at about 70 percent availability for the past two quarters, up from 50 percent in prior quarters. Only about 10 percent of the downtime was unscheduled, the rest was for planned maintenance.
• Source collector durability: Cymer has demonstrated stable reflectivity for its EUV source collector over more than 30 billion pulses. Collector reflectivity is a key issue because replacing the collector is a major undertaking and the collector's performance will degrade over time. Cymer does not know how long the source can last between replacements, but 30 billion pulses over more than a year is considered encouraging.
• Mask defectivity: Kalk acknowledged that EUV masks will not be defect-free. Due to the complexity involved, every EUV mask blank will have defects, an multi-layer mask blank defects cannot be repaired, Kalk said. But masks must be "defect free enough" to work, he said. In the case of memory, design patterns are redundant enough that the mask can be shifted and rotated accordingly in order to write the pattern around the defects—if mask makers know where they are, according to Kalk. Improvement in both blank and mask inspection tools, as well as mask writer accuracy, is required, Kalk said.
• Mask durability: No one will know exactly how long an EUV mask will last until they are used in high volume production. Kalk said different mask durability issues—including the appearance of haze on a mask and, later, mask absorber degratdation—arose in the first six years or so after the introduction of 193-nm lithography, depending on the number of exposures for a mask. "We are going to encounter issues," Kalk said. 'I don't even know what they are yet, but we are going to encounter them."
• Tools needed: The full tool kit for EUV masks won't be ready until about 2018, according to Kalk. He said development is needed on blank and mask inspection tools, as well as the Carl Zeiss EUV actinic aerial image metrology system (AIMS) for reticle defect and printability analysis. Kalk said that EUV insertion can occur before the full mask tool kit is in place, but that a "bridge strategy" will be required. As manufacturing eventually ramps up, new issues will arise he said.