eBeam Initiative: A voice for the photomask industry during rapid evolution

As the group approaches its 15th anniversary, the shift to curvilinear masks tops the agenda.

By Jan Willis, Co-Founder, eBeam Initiative

•Founded in early 2009, the eBeam Initiative is an industry group that provides a forum for educational and promotional activities regarding new design-to-manufacturing approaches that help reduce photomask costs for semiconductor devices based on electron beam (eBeam) technologies. The eBeam Initiative quickly established itself as a powerful collaborative forum for the semiconductor manufacturing community, with member companies presenting papers starting in late 2009.

While the early focus of the eBeam Initiative was on eBeam direct write (EBDW) where designs are written directly to wafer using advanced eBeam technology, the group quickly shifted to focus on the mask industry and to the technologies that could improve mask quality and lower mask cost. Historically, the mask industry has been depended upon to provide the accuracy needed for advanced nodes (though it has tended to be underappreciated), and with the scaling challenges facing the semiconductor industry starting in the early 2000s, the mask industry was positioned to play an even larger role. Within a few years of its inception, the eBeam Initiative had become a voice for the mask community, helping to communicate its interests and achievements to the rest of the ecosystem.

To support the mission of education and promotion for the mask industry, the eBeam Initiative established multiple annual meetings, which take place each year during the SPIE Advanced Lithography Conference (usually held in February) and the SPIE Photomask Technology Conference (organized by BACUS, usually held in September).

Figure 1: Logos of current eBeam Initiative member companies and design advisory team

In the years since its founding with 20 members, the organization has expanded its membership to include more than 50 member companies across the semiconductor manufacturing and design ecosystem (see Figure 1).

Over the years of the eBeam Initiative’s existence, the mask industry has seen multiple major shifts in technologies as the industry worked to keep advanced semiconductor node roadmaps viable as 193-nm immersion (193i) lithography was pushed to its limits and implementation of extreme ultra-violet (EUV) lithography was delayed. The eBeam Initiative’s philosophy is to work closely with industry luminaries to curate technical and business insights for the mask community as it works with the rest of ecosystem to keep roadmaps in place. As the eBeam Initiative approaches its 15th anniversary in 2024, it is poised to help the mask industry make the next big shift coming for masks: curvilinear mask targets.

In the beginning: Extending 193i while waiting for EUV
As the semiconductor industry entered the 2010s, anxiety was high regarding extending 193i lithography through new advanced nodes while the industry was waiting for EUV lithography to reach maturity. The mask industry had a key role to play in providing solutions that would bridge this gap and produce masks that could meet the technical requirements of new advanced nodes and deliver them at a practical cost.

Mask customers were interested in making a balanced trade?off between the wafer quality achievable with complex optical proximity correction (OPC)/inverse lithography technology ILT)/source-mask optimization and the turnaround time of mask manufacturing. At 20-nm-and-below process nodes, both the main features of photomasks and the sub?resolution assist features (SRAFs) – which help preserve depth of focus (DOF) and critical dimension uniformity (CDU) for the main mask feature they support, but which do not print themselves – need to be increasingly complex in shape to ensure optimal patterning.

However, the number of eBeam shots required using variable-shaped beam (VSB) eBeam mask writers to create these complex features caused mask write-times – and mask costs – to increase significantly.

For several years, the eBeam Initiative focused its educational programming on the potential of using overlapping shots with VSB writers. One of the key solutions for this challenge was the addition of model-based mask data preparation (MB-MDP) to mask makers’ technology toolkits.

Conventional mask data preparation simply fractured target mask shapes into adjoining rectangles, each representing a single eBeam shot of the same dosage. MB-MDP models enabled the use of overlapping shots that resulted in accurate mask shapes with fewer eBeam shots, and therefore faster write times.

Figure 2: eBeam Initiative 2015 Luminaries Survey results on the use of EUV in HVM

In 2012, the question of whether EUV would ever be ready for high-volume manufacturing (HVM) was still on the minds of leaders in the mask community. That year, the eBeam Initiative embarked on its first industry survey of business and technology experts throughout the semiconductor ecosystem, which has become known as the Luminaries Survey and conducted annually. The idea was to capture the opinions of the luminaries to provide early insight into key market and technology trends. In the fourth survey¹ conducted in 2015, the Luminaries’ opinions on EUV provided the insight that the turning point on EUV had been reached (see Figure 2) and signaled to the entire community the need to prepare for EUV masks.

A Milestone innovation: Readying the ecosystem for multi-beam mask writers
More than ten years ago, multiple companies were working on several technologies that split eBeams into multiple beams of constant size to effectively form a pixel array of eBeams to speed up mask write times and address the mask turnaround time issue. IMS Nanofabrication presented printing results of their multi-beam mask writing solution as early as the eBeam Initiative meeting at the 2012 SPIE Photomask Technology Conference². NuFlare Technology followed with the introduction of their multi-beam mask writer at the eBeam Initiative’s meeting at the 2016 SPIE Advanced Lithography Conference³.

As development of EUV lithography progressed, it became clear that VSB mask writers would not support the resolution requirements of EUV, so multi-beam mask writer development became a strategic imperative for the entire industry. In the 2018 eBeam Initiative Survey⁴ (see Figure 3), the majority of luminaries surveyed were signaling that the resolution needs of EUV would make multi-beam mask writers a requirement for both EUV and for 193i lithography at very advanced nodes.

Figure 3: eBeam Initiative 2018 Luminaries Survey results regarding adoption of multi-beam mask writers

The eBeam Initiative becomes a forum for introduction of emerging trends
Over the years, eBeam Initiative member companies – and even some non-member companies – have used the forum provided by the eBeam Initiative to introduce emerging trends to the mask industry. Several times – as with multi-beam mask writer development – an eBeam Initiative meeting was the venue for the first introduction of an idea or technology.

One trend introduced through an eBeam Initiative event was the resurgence of ILT in part due to multi-beam mask writers’ capability to deliver constant write time, independent of mask complexity and density. Tom Cecil, now a principal engineer at Synopsys, described this at the 2017 eBeam Initiative meeting at SPIE Advanced Lithography. His presentation⁵ provided some of the very first insights on how ILT could improve EUV process variability (PV) bands as shown in Figure 4.

Another example of eBeam Initiative meetings being a forum for discussion of emerging technology was provided by David Lam, Chairman of Multibeam Corporation, at the annual meeting at SPIE Advanced Lithography Conference in 2023. Dr. Lam’s presentation6 focused on new applications for eBeam direct-write technology, including internet of things (IoT) security applications. IoT security is a topic of concern for the entire semiconductor ecosystem, and it was interesting to see how eBeam technology could play a role in addressing this challenge.