Experts At The Table: Issues In Lithography

By Mark LaPedus
Semiconductor Manufacturing & Design sat down to discuss future lithography challenges with Juan Rey, senior director of engineering at Mentor Graphics; Aki Fujimura, chairman and chief executive at D2S; and Tatsuo Enami, general manager for the sales division at Gigaphoton. What follows are excerpts of that conversation. (Part one can be found here.)

SMD: Let’s re-visit e-beam again. Why is direct-write and maskless so critical for the industry?
Fujimura: Hopefully, people see the benefits. It’s generally not for huge volumes. Let’s say you want to develop a chip and you are not sure it’s going into high volume production yet. It’s getting incredibly difficult to do that now. Innovation in the ecosystem supply chain is being stifled because of cost issues. To help those types of customers, we can do something like direct-write, where there is no mask cost and there are lower volumes. These are important things for the ecosystem to invest in for the sake of the whole semiconductor industry. We are trying to do that with our eBeam Initiative. We were talking about 450mm earlier. With any new technology, in order to get the level of funding you want, you have to appeal to the mass market. But some investments are better for the long term. E-beam investments can be very important not just for the e-beam community, but also the entire semiconductor supply chain.

SMD: How does maskless gain traction?
Fujimura: We also see it in complementary lithography. In complementary litho, you can draw the lines with nanoimprint, EUV or anything else. And then you cut the lines using e-beam. I think that kind of concept being prompted by the major players will be a great way to fund and kick-start the technology into the mass market.
Rey: We have been looking at e-beam direct-write techniques. But we completely agree with Aki about the level of investments in maskless. We have looked at the published information in terms of how much research money has been going in EUV as compared to direct-write. There are orders of magnitude difference between the two of them. In terms of the type of research that we are doing, Mentor has been following the Imagine program with Leti in Europe for direct-write. We see a level of maturity that is still required to even understand the whole magnitude of what the problem is. We don’t have clarity, as compared to what we have for multi-patterning techniques. There is a large gap between the two things.

SMD: When will maskless lithography go into production?
Fujimura: There are people that use direct-write for the 65nm node. But predicting the future has its risks. So that’s a difficult question. It depends on the volumes. In some ways, it’s ready to go.

SMD: Any thoughts on nanoimprint?
Fujimura: One of the things about nanoimprint is that it enables line and space patterns. It seems like they are having some success in being able to print small features very reliably. It’s great for that. It’s also perfect for the complementary lithography idea. Nanoimprint can draw lines. And then e-beam can cut the holes. Something like that can be a good combination. One thing to note is that nanoimprint masters are made with e-beam technology. It’s 1x dimensions, unlike photomask, which are 4x dimensions. It’s basically a direct-write problem to write those masks.
Enami: Nanoimprint is very effective for NAND flash applications. One manufacturer has started pre-production at 11nm by using nanoimprint.
Rey: We are having conversations regarding what is required at 10nm these days. They all seem to be coming from the other techniques and not from nanoimprint.

SMD: DFM is playing a greater role in lithography and in the manufacturing space, right?
Rey: There is something interesting happening. There is increased communications between the manufacturing community and the design community. Many of the barriers have been overcome. This includes discussions to make the process more efficient. And so at least today, the industry is more aware and open to have a dialogue. Many years ago, to get the two sides together was impossible, because everyone was pre-occupied with one’s own worries. They refused to have a discussion. Right now, a dialogue is expected.

SMD: What DFM is needed in litho and other parts of the flow?
Rey: Right now, you see it in double patterning. You see it in the establishment of rules that bring more regularity in design. You see it with several types of things that extend traditional design rule checking. For example, you establish pattern matching techniques that essentially identify the patterns you can manufacture. You can use the information in a way that designs are efficiently done. Each one of these techniques brings all sorts of limitations and needs. But there is a willingness to bring the design and manufacturing communities to the table to discuss them.
Fujimura: Designers want more flexibility. For example, it seems like you should be able to use the techniques like what Tela Innovations is talking about and apply them to SOC designs.

SMD: It’s a cliché, but isn’t there more collaboration in the industry now?
Fujimura: That’s a trend. The whole ecosystem is collaborating together. Even competitors are working together, because the problem is so hard. Making sure the pie continues to grow is the number one issue. But it’s a tough shift. You start with competition. The mindset is if you tell your competitor what you’re doing, then it’s not going to work. But if you don’t talk to other people, then you can’t start the collaboration. If you don’t sell the idea that you have, and try to promote it in a public forum, you can’t make it go. You almost need your competitors to line up with what you are trying to do. That way the industry is working on one thing and investing enough in that. And that way it can actually happen on time.
Rey: A few years back, (IBM fellow) Bernie Meyerson made the point at a keynote at SPIE, where he showed the need for collaboration across the board. This included the process side for developing next-generation technologies, as well as the design side. There must be interaction between the two communities. And at that point, Intel was not that open. But clearly, the industry is moving in the right direction.
Enami: Collaboration is everything. Otherwise, nothing happens.