High NA EUV Litho May Require Larger Photomask Size

In the meantime, will the mask supply chain have six-inch EUV masks ready by 2015?

With extreme ultraviolet lithography (EUV) potentially being used in pilot production in a few years, it raises the question of larger photomasks sizes—will the industry need them, and if so, when?

Semi EngineeringWhile there has been discussion of late about the possible need to transition to a larger mask size, veterans of the mask business may feel it’s déjà vu all over again. Back in the mid 1990s there was much discussion about transitioning from six-inch to nine-inch masks—so much so that standards were written. Then, as now, the transition (or more accurately, the lack of one) had to do with economics and the choice of lithography technologies used in semiconductor manufacturing.

The forthcoming choice today involves EUV, and as always when the discussion involves EUV, to answer these questions involves a combination of extrapolation and hypothesis. But the industry is finally getting close to putting EUV tools in fabs.

ASML suggested just last week that it is on track to deliver a throughput of 70 wafers per hour (wph) on its first production EUV lithography tool, the NXE:3300B, sometime next year. Ostensibly that will be with an 80 watt power supply, improving on the source in its current development tool, the NXE:3100, which currently can sustain 50 watts over long periods of time, according to the litho tool vendor.

If this holds true, the chip industry could see EUV exposure tools and pilot lines in chipmakers’ fabs within a few years’ time, although the throughput will have to continue to improve for it to move into mainstream production. The current consensus is that widespread use of EUV— assuming current estimates of power source improvements hold true—won’t happen until the end of the decade and beyond at the 10nm and 7nm nodes.

So in terms of the mask industry, it could be looking at a size transition around the 2018 to 2020 time frame. But worrying about that may be putting the cart before the horse, cautions Stefan Wurm, director of lithography for Sematech. “The industry needs to make the decision on doing high NA or not, and if it proves the right choice, it’s got to be a high NA solution that shares multiple nodes,” he said. While the question of high NA EUV is coupled with the need for a larger mask size, “it’s not something that will be decided tomorrow.”

Of more pressing concern is the availability of six-inch EUV photomasks in the 2015 time frame for those pilot lines, Wurm said. “The goal is very simple: make sure there is an adequate supply that supports the yield requirements for EUV ramp up.”

In fact, mask availability is of more concern than source power at this point, he said. Chipmakers are making a huge effort with regard to supporting lithography vendors on EUV source development to ensure success, he noted. Intel’s investment in ASML is a primary example.

“On the mask side it’s a little different because you have to look at the whole supply chain,” Wurm said. While suppliers are waiting to see the outcome of source development, it begs the question: Will they have time and resources to catch up once the source power is there? “We’re more concerned about the mask blanks supply chain than we’re concerned about the source,” he added.

There are still a number of technical issues to address if six-inch EUV masks are going to be ready for pilot production in a few years. “Everything that’s related to yield and masks and mask lifetime and blank defectivity is certainly at the center of that,” Wurm said.

Why larger photomasks?

Even with the adoption of EUV there aren’t necessarily economic or technical reasons for the industry to move to a larger mask size, or at least not right away. It depends largely on which way the industry goes to get to the resolution needed at the 10nm node and beyond, whether it adopts some sort of double patterning scheme with EUV or opts for a higher numerical aperture (NA) EUV exposure technology.

Increasing the NA—seen as necessary if the industry is going to avoid double pattering—will mean increasing the magnification of EUV exposure tools, which means a smaller exposure field size and consequently more exposures (and less throughput), unless a larger mask size is used.

Throughput, and thereby economics, is the key part of the equation. Based on the technical papers presented at SPIE and elsewhere in recent years, it appear the techniques used to achieve the higher NA would cut throughput by as much as 50%. This can be alleviated somewhat with a larger mask size, noted Franklin Kalk, CTO of Toppan Photomasks.

“It’s interesting because the mask size can help the throughput, but it doesn’t bring it back to where it was,” he said.

Furthermore, it all comes back to EUV source power as well. “If we increase the mask size, it won’t improve the throughput without the (EUV source) power,” said Banqui Wu, Applied Materials’ CTO for its photomask etch products business. “People assume we have the power. If we get the power, we can improve both the resolution and the throughput.”

But what about bigger wafers, too?

As Kalk and Wu suggest, if the source power doesn’t continue to scale as hoped, even if EUV is put into production there would be little need for a larger mask size because high NA EUV wouldn’t be feasible without the requisite source power. But, as Sematech’s Wurm notes, if the source power isn’t available for high NA EUV at the end of the decade, it probably will mean that EUV never made it into production in the first place, and thus it will become a moot point.

Even if high NA EUV proves viable, the smaller exposure field possibly could prove beneficial with high NA EUV at the 10nm and 7nm node, in spite of the extra steps and lower throughput that would result. Yield and defect control conceivably would be easier to manage with the smaller exposure field, Wu noted.

Wrapped up in the argument for larger mask sizes is the transition from 300mm wafers to 450mm wafers, although the wafer size transition wouldn’t necessarily require larger mask sizes, just as the migration from 200mm to 300mm wafers did not. “If the industry doesn’t adopt EUV for production, or it is used on a very limited basis, it seems unlikely the industry would opt to migrate to a larger mask size,” Kalk said. “In principal, on 450mm (wafers), it doesn’t really require a larger mask.”

Applied’s Wu said that a larger mask size in combination with 450mm wafers could provide benefits in terms of wafer etch and chemical-mechanical planarization (CMP). However in terms of throughput, in and of itself a larger mask size wouldn’t really result in any improvements without the adoption of EUV, regardless of wafer size, he said.

Bigger mask size means bigger—much bigger—CapEx

So if high NA EUV is ready for the 10nm node, a transition to a larger mask size, likely nine-inch masks, seems likely. Will the industry be ready? That will remain to be seen, but one thing everyone can agree on: It will require considerable capital investment cycle.

“We’re always used to scaling equipment; we’ve been doing it since the three-inch (mask) days,” said Amitabh Sabharwal, general manager for photomask etch products at Applied. “If there is significant pull and there is an industry demand, we can do it.”

But a transition won’t be cheap.

“The bottom line is it’s going to cost a lot of money to do it,” said Toppan’s Kalk. “We haven’t done a thorough analysis of a nine-inch EUV mask (manufacturing) line or 12-inch EUV capable mask line, but it has to be approximately 200 million,” he said – roughly half the cost of a leading edge manufacturing line today producing photomasks for 28nm manufacturing.

It could mean changes in the photomask supply chain as well. While the big three semiconductor photomask suppliers—Toppan, Photronics and Dai Nippon—have kept their hands in the leading edge by partnering with large IDMs, the pool of those playing at the leading edge dwindles with each technology node. With only a handful of companies likely to be developing chips at the 10nm node, and the considerable capital expense involved, further consolidation among merchant mask suppliers could be in the offing in the years ahead.

Furthermore, with only a small number of chipmakers producing chips at the 10nm node there may not be enough tools sold to justify having two or more suppliers for each piece of equipment. For example, “we’re not going to find multiple providers of writers or etchers,” Kalk said. “I just don’t think that’s going to happen.”

Aside from the economic issues, there will be many technical issues to address when it comes to migrating to a larger mask size along with EUV, such as critical dimension (CD) resolution and mask metrology and defectivity. This is not to mention the technical hurdles that still exist for six-inch EUV masks.

There also is the question of using nine-inch mask sets with six-inch mask sets. While at first glance it may seem plausible to continue to use six-inch mask sets for non-critical layers even as nine-inch masks are used for critical layers, thereby saving costs, this method would introduce its own technical hurdles, such as alignment.

EUV mask availability—be it six-inch or later nine-inch masks—is perhaps indicative of a larger phenomenon in the chip industry beyond EUV and photomasks. “The health of the supply chain in general, not just on the mask side, will need more attention in the industry,” said Wurm. The costs for equipment and materials vendors continues to increase, and their capability to support R&D doesn’t always keep track with what the industry requires of them.

“That’s something the industry needs to keep in mind,” he said. “How can we work together to make sure we have a healthy supply chain in all areas?”

Editor’s Note: As explained at length elsewhere on this site this is a news story written by me for another publication. This originally appeared on Semiconductor Engineering; it holds the copyright, of course.

Merchant Photomask Makers Remain Relevant

They still have roles to play, but economies of scale may force further consolidation in the long run.

For many years the trend in the semiconductor industry with regard to photomasks and chipmakers was to shed captive mask operations in favor of merchant photomask suppliers. This reflected a larger trend all along the supply chain with many companies moving away from vertical integration as, consequently, the foundry model grew.

Semi Engineering“This was mainly driven by cost considerations,” said Franklin Kalk, CTO of merchant photomask supplier Toppan Photomasks. “The cost of R&D to stay current made it difficult to justify maintaining an internal (photomask) business—that really was the impetus for consolidation into large mask merchants.” It was only natural for merchant photomask suppliers to flourish.

Over the course of the last several industry cycles, however, a converse trend has emerged as leading-edge production technology has become ever more complex and costly. Captive mask shops have become a competitive necessity among first-tier device makers, which tend to be more vertically integrated.

“Now there are so few semiconductor companies at the leading edge, and they have scale,” Kalk said. “Those companies have enough scale to justify having a captive mask shop.” These large companies—IDMs like Samsung and Intel or foundries like Taiwan Semiconductor Manufacturing Co. (TSMC) and GlobalFoundries—all use huge numbers of masks. They have the economies of scale to maintain what has become a differentiator between first- and second-tier chipmakers.

So what are the implications for the merchant photomask industry? More consolidation? As the industry closes in on the 10nm node at the end of the decade will it still need merchant mask suppliers?

The answer is, as it always is in the semiconductor industry, an educated guess at best. But it’s clear that the big three photomask suppliers, Toppan, Photronics Inc. and Dai Nippon Printing Co. Ltd., aren’t going away anytime soon.

Leading edge drives merchant photomasks

Semiconductor Equipment and Materials International (SEMI) has forecast the worldwide photomask market to reach $3.5 billion in 2014. After reaching a market peak in 2011, the photomask market contracted 4% in 2012 to $3.2 billion. SEMI anticipates the market to grow again by 3% this year and another 3% next year, driven by advanced technology (sub-45nm manufacturing) and the growth of manufacturing in Asia-Pacific, namely Taiwan.

Meanwhile, photomask suppliers are seeing the uptick in the second half of 2013 that is being reported elsewhere in the supply chain. In reporting its quarterly earnings for the fiscal quarter ended April 28, Photronics CFO Sean Smith said the company was accelerating the installment of advanced photomask production tools in North America and Asia as the result of projected demand for advanced photomasks in Q4 of this year and into 2014.

“We are very optimistic as we get into Q4 about our growth prospects as a result of the high-end capacity, the leading-edge IC products coming online and with new opportunities for node migration and increased share,” Smith said. “And we expect that to continue into 2014.”

Toppan’s Kalk said his company was observing similar trends. “There appears to be traction out of the recent semi industry downturn,” he said. “I would say we’re optimistic about the second half of the year. It seems like what people thought was an upturn at the beginning of the year has pushed out a little bit.”

Kalk noted that today the merchant photomask business tends to mirror the chip industry in general much more closely than it did before. Driven by design starts, in the past photomask industry cycles tended to lag the chip industry by six months or more to as much as a year. “Now what we see is that the supply chain has become much tighter; people don’t let their inventories stretch as much as they did in the past.” Consequently, mask business cycles are both more moderate and much closer in terms of timing to those of chip manufacturing, due partly to the capital-intensive nature of industry in general and leading-edge photomasks in particular.

Size—and proximity—matter

It is this capital-intensive nature of manufacturing at the leading edge, perhaps more than anything other factor, that has caused the reversal of captive and merchant mask trends. But coupled with this is the changing nature of end markets, namely an increasing reliance on consumer devices, which puts pressure on development and manufacturing cycle times.

Over the last two years, both leading foundry and logic companies have invested heavily in and expanded their captive operations quite rapidly, said Amitabh Sabharwal, general manager for mask etch products at Applied Materials. With the cost of a 45nm mask manufacturing line costing anywhere from $200 million to half a billion dollars, these are mammoth investments. “It’s not something you do on a whim,” he said.

Therefore having the economies of scale that Kalk mentioned, not to mention the deep pockets of companies such as Intel or TSMC, makes it easier for them to invest in mask production.

Then there are the pressures on turnaround times in a tight supply chain. Even as market pressures demand the time from design to tapeout to be as short as possible, mask production times are a continuing headache for the industry. Extending optical lithography has required increased resolution enhancement techniques for more and more layers in devices, which consequently impacts mask write times, and not for the better.

Thus it further behooves leading-edge device makers to have a captive shop to provide masks for critical layers. EDA vendor Synopsys devotes a lot of time and effort in optimizing and reducing mask write times at their customers, according to Tom Ferry, the group’s senior director of marketing. When it comes to working with a captive mask shop at a chipmaker, given the complexity and the enormity of the data involved, the turnaround time in mask production is quicker when everything is handled in house; with an outside merchant mask shop more challenges arise.

“Clearly the captive model…is a more beneficial model for them,” Sabharwal said of the large IDMs and foundries that maintain captive mask operations. He further noted with regard to cycle times that chipmakers with captive mask shops gain an edge when it comes to testing new mask sets. “A merchant can produce it but can’t test it. That’s a huge capability that captives have,” he said. “The cycle time is rapid with a captive.”

Merchants still have roles to play

At first glance it might seem there is a dwindling place for merchant photomask makers at the leading edge, given the cost involved and the competitive benefits a captive mask operation provides. But this isn’t really the case, and the big three, Toppan, Photronics and Dai Nippon, aren’t likely to consolidate or otherwise leave the market anytime soon.

“What role do the big mask merchants have? I would say we have two roles,” said Toppan’s Kalk. One role is to provide standard photomask sets, he explained. The bulk of chip production, even on leading-edge devices, still involves non-critical layers with features above 45nm. Device makers consequently still find it cost-effective to rely on merchant shops for these standard mask sets; this part of the market remains solidly in the province of merchant suppliers.

The second role is that of partner. It’s a matter of strategy—the so-called earthquake strategy, as Kalk put it. Or to use a much older metaphor, chipmakers don’t want to have all their eggs in one basket. Thus the industry has seen a number of close strategic partnerships in recent years among merchant photomask suppliers and chipmakers—Photronics and Micron and Toppan and IBM, for example—spreading the development of leading-edge photomasks economically as well as geographically.

Having a merchant supplier capable of supplying photomasks for critical as well as non-critical layers—a second source—provides two primary benefits for chipmakers with captive mask shops. First, it provides the ability to handle capacity overflow. Second, it provides a source of photomasks should something catastrophic happen to their captive operations. Given the global nature of the chip industry, having a second source clearly makes sense. Moreover, it’s arguably essential in terms of business strategy.

But production won’t get any easier…or cheaper
So merchant photomask suppliers still clearly have roles to play. But with each technology node the number of leading-edge chipmakers dwindles, even as the remaining ones grow larger still. As the industry closes in on the 10nm node at the end of the decade, will there still be room for three major mask merchants? Or will the industry see further consolidation?

Toppan’s Kalk characterized the answer as coming down to who can afford to play at the leading edge. He noted that for the last decade or so, with every succeeding technology node, one or more companies drops out, choosing to go fabless. Assuming this trend continues, at 10nm there may be as few as six chipmakers with their own leading-edge production fabs, split between between foundries and IDMs.

How many will remain at the 7nm node? “Who knows, but the number is dwindling rapidly,” Kalk said.

This begs a further question: Will there still be a need for three merchant makers at 10nm and beyond? The last major consolidation in the merchant photomask space occurred in 2005, when Toppan merged with DuPont Photomasks. Then, as now, the question came down to economic scale.

“Is the scale enough right now, and does each company have the scale required to supply the market? That’s the question,” Kalk said. He further noted that while leading-edge mask technology is already expensive, if extreme ultraviolet technology proves commercially viable, the related mask technology will be more expensive still.

“If you don’t have scale, you’re less attractive to a semiconductor company as a potential partner.” If that proves to be the case for one of today’s big mask merchant companies, then just as we see the number of companies involved at leading-edge production dwindle, further consolidation could be coming for merchant photomask companies.

Editor’s Note: As explained at length elsewhere on this site this is a news story written by me for another publication. This originally appeared on Semiconductor Engineering; it holds the copyright, of course.