Advancements in semiconductors through surface chemistry: an interview with Professor Gregory Herman

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Greg Herman and student in the lab

Gregory Herman, professor of chemical engineering at Oregon State University, is a leading researcher in next-generation oxide semiconductor materials. Herman made the jump to Oregon State after collaborating with the university for many years, first at HP and later at Sharp Laboratories of America. At HP, he was part of the team that secured the patent for indium gallium zinc oxide, a key material used in many of today's consumer electronics. At Sharp, he helped transfer indium gallium zinc oxide into production for display manufacturing. Having developed a great working relationship with Chih-hung Chang, professor of chemical engineering, the move to Oregon State came easily. His move was fueled by the university's strong collaborative efforts with industry, its state-of-the-art facilities, and its forward-looking leadership.

In a recent interview, Herman spoke about his history in industry, how and why he came to Oregon State, and the research he is involved in today.

Can you please tell us a little bit about yourself?

I received my Ph.D. in chemistry at the University of Hawaii, where I did my dissertation on metal semiconductor contacts, and atomic imaging of atoms in semiconductors using photoelectron holography, which was a new technique at the time. I then did a National Research Council Postdoctoral Fellowship at the Naval Research Laboratory. I was based at Brookhaven National Laboratory, at the National Synchrotron Light Source, where I did research related to measuring excited electronic states in gallium arsenide, a high-performance semiconductor. This research was new and exciting, and I found it intellectually stimulating. As a result, I have continued working in surface chemistry and surface physics throughout my career. After my postdoc, I went to work at Pacific Northwest National Laboratory for about eight years. I was one of the early scientists that were part of the Environmental Molecular Sciences Laboratory, a large user facility at PNNL. We were developing new research equipment for studying surface chemistry and surface reactions. My primary focus was looking at surface chemistry on oxide materials, and that included titanium dioxide. The goal was to understand the role of both physical and electronic structures in driving both thermal-induced and photo-induced chemical reactions. We made excellent progress and made insightful discoveries on these topics.

I was then recruited to HP based on my oxide surface chemistry work and started on a solid oxide fuel cell program where we were looking at the miniaturization of solid oxide fuel cells with the goal of replacing lithium-ion batteries. Although we were making really good technical progress on the program, the business case just wasn't there. So, we ended up switching our focus to printed electronics, roll-to-roll processing, and flexible displays. The goal with those efforts was to look at higher-performance semiconductors compared to the organic semiconductors that other companies were focusing on at the time. As part of this effort, we started a collaboration with Oregon State University. We worked on a wide range of technologies, such as low-temperature, solution-processed materials, primarily focused on oxide semiconductors and amorphous high-K dielectrics. During this time we obtained some very impressive results. But what I found most exciting was the work a group of us inside HP were focusing on. We were working on developing the next generation of amorphous oxide semiconductor materials. We started this work by doing combinatorial depositions, where we could study a wide range of compositions of these oxide materials in a short amount of time. At the same time, we were building a patent portfolio around these new material compositions. We ended up getting the foundational patent for indium gallium zinc oxide, typically called IGZO. IGZO is a material used today in cellphones, computer displays, televisions, and similar products. That was a very exciting time with a large impact in consumer electronics.

What would you say is Oregon State’s biggest strength in these programs?

One of the reasons I decided to come to Oregon State is that I saw how well people work together. It’s a very collaborative atmosphere. At other universities that I had considered in the past, I saw that faculty worked in their own silos. And very often, you'd have faculty in a department who wouldn't even talk to each other. What I found during my collaborations with Oregon State, which lasted for almost nine years, is that people liked working together, they felt comfortable discussing ideas with each other, and they worked together on building large programs. I really enjoyed the collaborative atmosphere. When I was part of the National Science Foundation - Center for Sustainable Materials Chemistry, I found that this culture of collaboration extended to other universities as well, where we worked closely with the University of Oregon and others. Often you don't see the two main research universities in a state working as closely together as we did with UO. On other projects I worked closely with Oregon Health & Science University, and these collaborations continue to expand. I really enjoy the collaborative atmosphere in the state, especially across higher education.

Can you take us along your research path at Oregon State?

Oregon State has a lot of collaborations with industry. I continued to work on the oxide semiconductors that we started developing at HP and that I helped transition to commercialization at Sharp. What we have done is focus on different applications, instead of only thin-film transistors. For example, we have used these oxide semiconductors as active elements in field effect biosensors. We published several papers related to fully transparent biosensors, and we were looking at the concept of integrating these biosensors in contact lenses. There are some properties, including high mobility and low leakage currents, that are very good for thin-film transistors and also work well for sensors. We were able to measure glucose concentrations at very low levels, uric acid as well. We were really interested in measuring glucose concentrations in human tears.

Another area of research is display technology. If you look at displays, usually it's just this piece of glass with an array of transistors, and these transistors serve only one function. Usually that's a switch, either on or off. With more advanced displays, what is really wanted was logic on the glass as well as memory. We studied using the same oxide semiconductor materials, but integrating into resistive random access memory devices. We published a couple of articles on this research, and the devices performed fairly well. That said, I don't think this direction is where companies are going right now. But it is a material that has worked well for the application and could have increased the functionality of displays while keeping costs low.

Where are things now, research-wise?

One of the big things I've focused on over the past 10 years is improving the analytical research capabilities on campus. As part of this effort, I was lead on proposals for bringing in a research instrument that does ambient pressure X-ray photoelectron spectroscopy and ambient pressure scanning tunneling microscopy. These techniques allow us to characterize surfaces of materials. With ambient pressure X-ray photoelectron spectroscopy, we can measure oxidation states of materials to see how stable they are under a range of environments. With ambient pressure scanning tunneling microscopy, we can image individual atoms and defects. One area we're really interested in is studying 2D materials as semiconductors. The electronics industry is planning to transition away from silicon to novel materials, and these 2D semiconductors are one path forward. Understanding defects in these 2D materials — how they affect electronic properties, doping, and stability — is critical for future applications. That is one area my group is focused on. Another area my group is studying is extreme ultraviolet photoresists. These EUV photoresists are important for companies like Intel and Micron, which use EUV steppers to make semiconductor devices at the nanoscale. Each of these EUV steppers can cost up to $500 million. Our studies are evaluating the new paradigm of using these metal-organic clusters as the photoresist, as opposed to traditional polymer resists. We are focused on understanding the mechanisms of the photoinduced processes, and how to improve the materials.

Why are you and your team so interested in metal organic clusters?

Inpria, a company in Corvallis that was founded from Oregon State research, is a world leader in developing and manufacturing these metal-organic photoresist materials. The main thing my group is studying is what happens to these materials when they are exposed to EUV radiation.  A range of chemistries take place in these photoresists, and we believe that understanding the mechanisms will allow for a path to improve the performance of the photoresists. The main thing about photoresists is there is a transition between a soluble and insoluble phase, which depends on the material being exposed to radiation. We are trying to understand how to improve the sensitivity of these materials, and how to reduce the amount of radiation to effect this transition. Ultimately, this will allow companies to produce semiconductors more quickly and efficiently, and reduce costs.

Will the next generation of chips take advantage of this particular advent in photoresist technology?

YYes, these metal-organic resists are a critical path forward to make more semiconductor devices on a chip. Of course, there will be different generations of fabs that will not need this technology, since many applications do not need nanosized devices. For example, HP has a big focus on inkjet printing and will not likely need to push the fundamental limits of how small they can make devices. Places like HP make larger devices that can drive more power, so going smaller isn’t the goal. However, smaller devices are critical for Intel, Micron, and many other semiconductor companies and foundries. Nanoscaling is a critical technology on the international semiconductor roadmap, which requires making smaller and smaller devices. Once scaling is below 10 nanometers or so, it will be necessary to use either the Inpria photoresist or one very similar to it.

That is quite an accomplishment.

Yes, it is. Actually, the genesis of this concept was Doug Keszler's research group at Oregon State. I saw some of the results while at HP and we were working jointly on other projects.  HP was not funding this project, but his group was looking at how to make these photoresists from a material that had been developed as a dielectric for our joint project. This was before anyone probably even thought about using inorganic materials as an EUV photoresist. We continued to collaborate when I started at Oregon State in the NSF - Center for Sustainable Materials Chemistry. In the CSMC we had a core group of people looking at how to make the photoresists, what the chemistries are, understanding the reactions, and how to move the technology forward. During this time Inpria worked separately on how to advance the technology. Inpria did very thorough and very important work. I am impressed with what we accomplished in the CSMC. We had a very good group, including May Nyman’s group from chemistry, Rick Garfunkel’s group from Rutgers University, Doug Keszler's group, and my group from chemical engineering. These were the main groups that were part of the nanopatterning group. We also collaborated with groups from UO, specifically Darren Johnson and Jim Hutchison.

Can you speak to the NSF-driven call for advancement in nanotechnology?

During our work with the CSMC we brought in new research equipment to assist in the research. As we were ramping down the CSMC, the NSF came up with a new program called the National Nanotechnology Coordinated Infrastructure. The University of Washington has historically been part of a very similar program with the NSF. Researchers at UW reached out to us to collaborate on this new program. They knew about the new capabilities we brought in as well as the strength of Oregon State’s research in semiconductors. They also knew that we were the only Oregon university that had a user facility with a clean room at the time. It was a natural fit. Therefore, we collaborated with UW on a proposal. We were initially awarded about $5 million, around eight years ago.

In this collaboration we are primarily focused on fabrication and characterization, making nanodevices and nanostructured materials, and measuring their properties. We also focus on mentoring, bringing up the next generation of researchers and providing the research equipment they need. We were renewed on the program about two years ago for another $5 million or so.  Our site, the Northwest Nanotechnology Infrastructure site, is part of a national program with 16 member sites across the country. We have many collaborative programs, with monthly and annual meetings, and we coordinate efforts between the sites. We've been working together on addressing many of the opportunities coming out, like the CHIPS and Science Act, and working to align the future directions of the NNCI to make the largest impact. This includes working with the NSF program managers and hopefully visualizing the changes that we would like to see in the program. We’re looking primarily at expanding and getting more investment into the various sites to make an even larger impact in nanotechnology.

Recently, there was a broad agency announcement from the NSF where they have developed a Regional Innovation Engines program. Oregon State  took the lead on submitting a proposal focused on developing and expanding the ecosystem related to semiconductors and microelectronics in the Northwest, which includes Oregon, Idaho, and Washington. I am the principal investigator on this proposal. We're hoping to hear back on the results in early 2023. Our proposal aligns well with the states’ and universities’ visions for the region’s future in semiconductors and microelectronics. The proposal includes academic institutions, like UW, Boise State University, Oregon State, and UO. Those are the main graduate research-intensive universities. We also included Oregon Institute of Technology and Portland Community College — actually, all community colleges in Oregon. Ultimately we hope all academic institutions in the Northwest will be part of the ecosystem. Also included are Idaho National Laboratory and Pacific Northwest National Laboratory. Both of those labs have unique facilities, capabilities, research expertise, and programs related to semiconductors. Finally, we have midsized and large semiconductor-related companies throughout the Northwest as part of the proposal.

What collaborations have been taking place in your research at Oregon State?

I think what is most exciting is companies like Intel, Micron, Microsoft, Meta, and HP all signed up to be part of the Regional Innovation Engines program. We are also working with smaller companies, like Inpria and American Semiconductor. We probably have 60 or so companies involved and are part of our proposal. Phase one is primarily for pulling the team together and planning how to best make an impact in the region. Our goal is to go after a second phase proposal in two years. The second phase would be about $80 million to $100 million over eight years. This amount of money and the collaborations it will enable will be very beneficial for the region.

What would you say will be the biggest impacts if the funding is granted?

The neat thing about the RIE proposal is that, although it is focused on semiconductors, it covers many items, including workforce development, use-inspired research, and economic development, as well as diversity, equity, and inclusion across the entire site. For the use-inspired research, we are covering nanolithography, semiconductors, memory, More Than Moore, and artificial intelligence. Each of these areas is critical for future generations of consumer products, but the combination will have an even larger impact. One area I am excited about is nanomanufacturing. This is the EUV photoresist work I mentioned earlier, and we will be continuing these efforts as part of the proposal. This is a very important area for Micron and Intel. For example, Micron and Intel buy EUV steppers from AMSL, and they're over $500 million each. Companies need multiples of these EUV steppers, so you can see how expensive it can get. The systems are so expensive that companies need to make sure that they are usable and optimized. That is where photoresists come in. These photoresists have high sensitivity and high resolution. As a result, companies can get more wafers moved through the EUV steppers, increasing production, which affects the bottom line. This is a game-changer.

So you work pretty closely with Intel?

I have worked with Intel through the Semiconductor Research Corporation and have had some smaller projects through the NNCI. Our SRC project was focused on how to improve EUV photoresists, developing methods for characterizing them, understanding the fundamentals, and applying those to practice. In the future, as part of the RIE, we hope to be able to run our chemistries through Intel equipment and to better characterize their performance. We have also done collaborative work, where Intel sent us samples to measure and we hope to expand these efforts. Companies have been using silicon and silicon-germanium since the start of the semiconductor microelectronics industry. If you visualize how these devices are made, it is called two-dimensional integration, because essentially, you are laying these materials out on a flat substrate. Moore's law, where you need to keep increasing the number of transistors on a wafer, which results in reducing the size of the transistors. At some point the transistors cannot get any smaller. For example, devices can't get smaller than an atom. So, the transition is to stack devices on top of each other, so we can fit more transistors on a wafer. This is 3D integration, and both new materials and processes are required. Initially, integration will probably be more like a hybrid, 2.5D approach. But the idea is understanding how to develop these materials, pattern them, and put them in the places where you want them, while getting device performance that's uniform across the entire wafer. This is critical, and understanding the interfacial chemistry is vital to enable this technology transition.

Can you tell us more about advancements in memory and where things are headed?

Our group has done memory research as well. Micron is a world leader in memory and has evaluated essentially every memory technology and has commercialized 3D vertical structures for memory. My group has been studying resistive random access memory, which can also be integrated into these vertical structures, while integrating other functionality is important for future technology nodes. The use-inspired research area covered in the RIE is impactful and I believe it encompasses the future of where the semiconductor industry is heading.

The other thing underlying just about everything in the research that we will be doing is artificial intelligence and machine learning. These new computational approaches include new programs that can identify what material systems make the most sense to use, what are the best architectural structures of the devices that we are creating, and how to develop processes to better understand how everything can fit together. I'm really excited about these five research areas all coming together. Combining very good experiments with very good theory is critical for the future direction of the semiconductor industry and will be an area that the team will focus on.

Given all of that, what do you see as the biggest challenges in the field?

For my personal research interests, I believe that the biggest challenges are trying to find the optimal semiconductor materials to allow the three-dimensional scaling. In my past experience in industry, I've found that a lot of time is focused on making sure that the research is scalable. I think a lot of researchers don't really worry about scalability. Rather, they believe that if they can make one transistor that works well, then someone else can worry about making tens of millions of transistors that are identical. What I’ve found is that it's so critical to have that uniformity. So, trying to find ways of controlling defects and getting uniformity across the entire wafer for these new semiconductor materials is really going to be critical for advancing them. If we can't get that under control, these three-dimensional integration structures with 2D materials just aren't going to happen.

Anything else that you're working on that you're excited about?

In my group we work on a lot of different things, where some areas are somewhat unrelated to semiconductor research. For example, we're doing research looking at single-atom catalysis, which is really understanding chemistry that can be dictated by a single atom at a surface. We are finding ways to get a single atom pinned at a specific defect at the surface of a material. This research is primarily related to catalysis, where we are working to make more efficient catalysts through a detailed understanding of surface reactions. These concepts can be directly applied to semiconductors as well. My group has expertise in surface characterization and modification, which helps us better understand reactions at surfaces. These concepts can be applied to a variety of other systems.

The Jen-Hsun Huang and Lori Mills Huang Collaborative Innovation Complex is projected to open in 2025. What opportunities will that open up?

I really am excited about the Huang Collaborative Innovation Complex, because it's not just an Engineering building, it’s not just a Science building, and it’s not just focused on Earth, Ocean, and Atmospheric Sciences. It's meant to be collaborative between these three colleges and the rest of the university. We're going to have collaborative research working together on complex programs in the the complex. We will have a clean room and a supercomputer. We will also have modular lab space available. Early on, when the university was putting together a proposal to the donors, Brady Gibbons (associate dean for research) and I co-led a team of scientists and engineers in coming up with concepts of what the the complex would enable us to do. We had people from across Engineering, across Science, and across Earth, Ocean, and Atmospheric Sciences. There were just so many good ideas that came out of these brainstorming sessions that we sent up to College of Engineering Dean Scott Ashford, and went all the way up to the provost and the president. In the end, it's exciting to see that the the complex is happening and that it's moving forward as quickly as it is. I think it's not only going to pull together researchers at the university; I can see that it will also get companies from across the state interested in collaborating. The the complex is going to be awesome, and the faculty are extremely excited. We are already talking to Intel about aspects of the cleanroom, along with HP. I think they are as excited as we are to see this building moving forward.

Fantastic. 2025 can’t come soon enough.

Also, when you asked about the the complex, there's something else that came to mind. Oregon State’s new president, Jayathi Murthy, is an engineer. She has a vision of what Oregon State can become and the impact that we can make. She's really good at meeting with industry, working with industrial partners in the state, especially in the semiconductor industry, and promoting the university as well as our faculty, staff, and students. She was a great hire, and will be able to leverage the goodwill throughout the state and help expand industry and academic research programs. Ultimately this will advance the university’s and state’s missions.

To explore collaborative opportunities, or the semiconductor program in general, get in touch with us at: semi-osu@oregonstate.edu.

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Jan. 30, 2023