Making An Impression with Nanoimprint

By Mark LaPedus
Semiconductor Manufacturing & Design sat down to discuss the trends in lithography with Mark Melliar-Smith, president and chief executive of Molecular Imprints Inc. (MII), a supplier of nanoimprint lithography tools.

SMD: How do you view the IC industry now?
Melliar-Smith: It’s truly incredible work that this industry continues to do. The industry will see its way for the next 10 years. But to some extent, there are storm clouds on the horizon. This incredible complexity eventually looks like it may get a little out of control. We have to see what happens.

SMD: What will drive the demand for ICs in the future?
Melliar-Smith: There is a never-ending demand for more complex capabilities coming from the consumer. For example, there is an increasing amount of memory that needs to be stored in the cloud or on a mobile system. In addition, there is an enormous demand for bandwidth.

SMD: Why are lithography costs soaring out of control?
Melliar-Smith: We are in an era of increasing complexity and cost. The complexity comes in two varieties. The first complexity comes in the restrictions placed on the designers. That makes the designs less efficient and more difficult. The other part of the complexity comes just from the fact that you are starting to do double patterning. There are more steps to do it all. The complexity, of course, always comes with increased costs.

SMD: So is lithography heading for a train wreck?
Melliar-Smith: If I take a larger view of lithography, I could charge lithography the extraneous costs, including the inefficiencies of designs. Now, you are getting to the point where the productivity is beginning to come off the tracks in terms of how many millions of transistors per dollar I get. It’s not a train wreck, but it’s more of a challenge to really get the same learning curves we had before.

SMD: Any comments on EUV?

Melliar-Smith: EUV is a very difficult technology. I admire the people and what they’ve been able to do. The challenges get exponentially more difficult every year it’s late.  It’s been so delayed now that the dimensions that people want to use it for are down to well below 20nm. And at that point, you have a tough problem. The number of photons is much less than what you have at 193nm. It’s like by a factor of 30 less. So you have these very energetic photons flying in and the chemical debris goes into different directions. So it is not easy to solve that problem at 15nm. You also worry about shot noise and line-edge roughness.

SMD: What is the progress of nanoimprint lithography?
Melliar-Smith: We are actually making good progress. Obviously, as you know, if you want to go in and turn over the existing litho technology in today’s fabs, then that’s probably the toughest challenge you could have. People are justifiably conservative. The reason why we are getting a lot of traction now is that the benefits are becoming very noticeable.

SMD: What are the benefits of nanoimprint?
Melliar-Smith: First of all, we have no wavelength imaging issues. So, we can do single imprints or single patterning down towards 10nm. Second, we have far fewer design rule restrictions. We are not in the position of giving a design rule book that is like a telephone book, with all of the things you can’t do. We also don’t use high-speed photo chemistry to image. If you are imaging on a wafer, you are shining this image down and must do some chemistry on a resist. But as you get to smaller and smaller features, the problem gets tougher. So you get shot noise and line-edge roughness problems. We don’t have any of this. We bring the potential for much lower cost.

SMD: What markets are you targeting in semiconductors?
Melliar-Smith: Our target for initial production would be the memory space, particularly flash. The resolution requirements are the most extreme.

SMD: Toshiba is one of your customers. Is Toshiba in NAND production using nanoimprint yet?

Melliar-Smith: No. They are not in production yet. You have to ask them what their plans are. But clearly, they see the potential for the technology. In the memory space, people don’t talk very much about what they are doing. It’s hard to get our customers to stand up and champion us publicly.

SMD: The knock on nanoimprint is defectivity, overlay and throughput. What’s the latest on that?

Melliar-Smith: The long pole in the tent has always been defectivity. In the last couple of years, we’ve made huge progress. We are now down to the point where we believe our defectivity is close enough, that there is significant consideration for production in memory using nanoimprint. The advantage in memory, of course, is that you have redundancy built into the device. So the acceptable defect level is much higher than it is in logic. We believe the defect issues, and the ability to make 1X masks, looks like they are well under way for a solution.

SMD: What are the other challenges?
Melliar-Smith: The only challenge we’ve got is to make these very high-resolution masks. At present, the electron-beam pattern generators that write our masks are resolution limited to about 25nm, which is not enough.

SMD: What are the solutions?

Melliar-Smith: There were a couple of papers from SPIE. One is from IMS, which is developing a multi-beam mask writer. IMS is going to bring out a 12nm beta tool in 2015. The other one is from DNP. They showed results using double patterning on the mask to imprint a mask. You do all of the expensive patterning on the master mask. And then you use the master to create a replicate mask. And then you use a replicate mask in the factory. The cost of the master mask is irrelevant in the cost-of-ownership. DNP showed 15nm master masks made by double patterning.

SMD: You are also targeting the 450mm market. You sold a 450mm nanoimprint tool to Intel, right?
Melliar-Smith: We had a 450mm tool, which was billed and accepted by a customer. The customer wants to accelerate the transition to 450mm. To do that, they’ve got to provide patterned wafers to companies like Lam, Applied and TEL.

SMD: MII also has been talking about the disk drive industry. Nanoimprint is targeted for the shift towards bit-patterned media. What’s the status on that?
Melliar-Smith: Given the dynamics of that industry like consolidation and other things, the (disk drive makers) have actually slowed their density roadmap down. So that opportunity for us has been pushed out a couple of years. It’s a matter of if and not when. Hitachi, Seagate and Western Digital all have programs with patterned media using nanoimprint.

SMD: What other markets are you looking at?

Melliar-Smith: Another area we are interested in is working with the polarizers in flat-panel displays. They use polarizers in front of the light source and after the switching matrix. Today, they use organic film polarizers. They’ve known for a long time that a so-called wide-grid polarizer is a better polarizer. That’s an aluminum film on the glass, which is etched into 15nm lines and spaces. It has better transmission. That solution plays to our strengths.