By Debra Vogler, SEMI
If you attended just about any mask making conference in the last five to seven years, you would have heard the lament about exploding data volumes and their impact on mask writing time and, by extension, mask costs. The industry is still concerned with data volumes, whether 193nm immersion or EUVL. “Data volume is significantly increased node by node and requires a faster data transfer rate,” Jongwook Kye, director of the Strategic Lithography Technology Group at GLOBALFOUNDRIES, told SEMI. “We have to support data transfer across multiple continents, and that is a bottleneck.”
So it’s not just that masks are getting more complicated – with large data volumes – but it’s how the data gets transferred from one continent to the other that is becoming more challenging. “Even if you improved the mask writing time, with a multiple e-beam mask writing tool, the problem is still the data transfer rate.” On the subject of multiple e-beam writing tools, Kye noted that they aren’t currently available, and investment in the technology has not been aggressive, so the challenges remain even as the industry goes from node 10 down to node 5. Kye will present at SEMICON West 2015 (July 14-16) in the July 15 Lithography session during the Semiconductor Technology Symposium.
Kye pointed to another sector – the Internet of Things (IoT) – as having the potential to unlock solutions for the data volume/data transfer rate conundrum. “The IoT folks want to solve the data collection problem that arises from having trillions of sensors,” said Kye. “Once the infrastructure is there [to collect sensor data], those solutions can be transferred in some manner to fit the data transfer needs of the mask writing industry.”
One key factor that has changed over the years is that now, edge placement error (EPE) is the most important parameter of concern for lithography, noted Kye (Figure 1). “In traditional lithography, we tried to control overlay (OL) and CDU (critical dimension uniformity),” said Kye. “These days, the OL and CDU are no longer independent parameters, so we unify them together in one word and call it edge placement error.”
Christopher Progler, VP and CTO at Photronics, Inc., told SEMI that, today, EUV masks are being produced that are suitable for wafer technology development and production in limited applications. One relatively new development – pellicles for EUV masks – has taken a major step forward. “The ecosystem is rapidly responding to this new requirement,” noted Progler. “Despite this progress, however, EUV represents a very different mask technology overall when compared to even the most advanced 193nm masks. This presents the industry with new challenges and learning cycles on the path to delivering high yielding production EUV masks.” All in all, however, Progler observed that EUV mask infrastructure continues to advance with progress in a number of critical areas including blank defects, patterning modules, cleaning and validation.
“EUV mask defects will be handled using essentially a multi-sensor approach of inspection and characterization methods knitted together to form sound decisions on an EUV mask for use in particular applications,” Progler told SEMI. He anticipates that eventually, a high-speed, full-field actinic mask inspection tool will be delivered. “Such capability can be enabling for broad adoption of EUV masks, and therefore, EUV lithography.” Progler, however, believes that parallel plans are needed, “One that optimizes and calibrates the multi-sensor approach, and also the collaborative development of the full-field actinic inspection system.”
Addressing the need for greater speed over and above those of single-beam writing tools, Progler told SEMI, “There are a number of mask writer programs underway that would employ a writing engine instead comprised of an array of beams, thereby enabling faster writing time and improved flexibility for real-time pattern correction.” He noted that Photronics has been engaged in an equipment development program at IMS nanoFabrication alongside other industry partners to bring about this type of technology solution.
Rounding out the industry’s “to-do” list for EUVL, the mask industry also faces a challenge in the area of “so-called mask matching.” “Mask matching comprises methods to ensure two masks really are functionally identical for the given use,” Progler told SEMI. “So, driving integrated inspection/metrology/characterization solutions that ensure two masks work equivalently in a given application will continue to evolve.”
In addition to Kye (GLOBALFOUNDRIES) and Progler (Photronics), presenters from Nikon Research, ASML, Canon Nanotechnologies, Sematech and CEA Leti will be featured at the “Making Sense of the Lithography Landscape” (a Semiconductor Technology Symposium session) at SEMICON West 2015, which will be held July 14-16 at Moscone Center in San Francisco, Calif.