Aki Fujimura has been at the forefront of chip design innovations from the beginning of his career and his technology leadership continues today. He serves as Chairman and CEO of D2S, co-founder of the eBeam Initiative, President of BACUS, and a Governing Council member of the ESD Alliance, a SEMI Technology Community. At Tangent (now Cadence), Fujimura and Steve Teig (a chip designer for the last 20 years and now Vice President and Distinguished Engineer at Amazon) built the first commercial over-the-cell routing system dedicated to fully synchronous designs with timing assurance and automated test-scan insertion. Fujimura and Tom Kronmiller developed LEF/DEF for efficient representation of Manhattan routing, both used as standards in the automated place and route (P R) flow to this day. He again teamed with Teig and Kronmiller to develop the X Architecture, an interconnect architecture based on the pervasive use of 45o diagonal routing. I was thinking about his background as I called him to chat about his evolution from chip design before focusing on chip manufacturing via eBeam technology at D2S.Smith: Let’s talk about your journey from focusing on how to do physical design of chips to chip manufacturing. How did this happen?Fujimura: GPUs weren’t a thing until late 1990s. With CPUs, Manhattan design was the obvious choice for computational efficiency. Largely gridded metal n that went up and down, and metal n+1 that went left and right with vias to connect the line segments were how all automated layout worked. PCB routing and packaging (even back then) used diagonal routing and even curved routing. But chip P R was all Manhattan. That was still true when we worked on the X Architecture at Simplex Solutions (now Cadence). ATi (now inside AMD), NVIDIA and several other GPU companies started in the late 1980s to 1990s, but they were targeting video and gaming more than scientific computing at the time. It’s when Teig came up with the idea for the X Architecture that he wanted to know if 60-degree routing was possible “because a hexagon tessellates a plane.” A good question. I set out to try to find out what the actual limits were in manufacturing that create the limitation to Manhattan shapes. I got introduced to the late Bill Arnold of ASML, who then introduced me to a lot of people in manufacturing who helped me get the answer. Naoya Hayashi of DNP was instrumental in helping me understand that mask making is where the limit exists. Hayashi-san kindly explained to me about the two mask writers. I had to dig around a lot more to make sure that that was the only barrier, but that’s how I came to understand that before masks, everything is data, and after masks, everything is physical. Mask making is the key that enables 45 degrees, but not 60 degrees. The lessons I learned then are still very important to me today. That’s when I saw and appreciated the opportunity there is for software for semiconductor manufacturing.Smith: But you still couldn’t use GPUs for the X Architecture work?Fujimura: Right. Way too early. The idea that GPU-accelerated gaming machines can be connected together to do video editing, or that large scientific simulations can be done on a connected set of gaming machines, was being explored in the 1990s already. It was only 20 years ago (2006) when Jensen Huang announced his bet with the CUDA software stack for general purpose GPUs (GP GPUs) for nodes in racks of CPUs, GPUs, memory and communication to create the modern scientific computer. Six years later in 2012, AlexNet won the ImageNet Large Scale Visual Recognition Challenge (ILSVRC) with CUDA, and the rest is history. But no, we didn’t use GPUs at Simplex. But we did help design GPUs, including with the X Architecture.Editor’s Note: ILSVRC evaluates algorithms for object detection and image classification at large scale. Smith: Now, everything you do at D2S is with GPU acceleration. When and how did that change come about?Fujimura: It was back in 2009, two years after D2S was founded. An extraordinary engineer, Harold Zable, noticed that simulation-based manipulation (rather than rules-based manipulation) of mask shapes, both for wafer manufacturing and for mask manufacturing, would be the ideal application for GPU acceleration. Fast-Fourier Transforms (needed for lithography simulation and optical proximity correction (OPC)/inverse lithography technology (ILT)) and Gaussian manipulations (needed for eBeam mask simulation and mask process correction (MPC) are nearly “free” in terms of compute time on GPUs. You still have to get the data in and out efficiently, but you can do pretty sophisticated computing without much overhead. At the same time, multi-beam based eBeam writing was getting momentum, first in wafer direct write applications. In 2007, at the BACUS conference in Monterey, Calif., IMS—then a well-respected research organization in Vienna—published a paper saying that multi-beam for mask writing is what they’d like to do. The wafer market is much bigger, but this technology is more suited for mask writing, where write times are measured in hours per mask. “Wafers Per Hour” is the measure in wafer manufacturing, so mask writing gets to flip the division. We were looking at a mask design and mask manufacturing world that should be doing simulation-based manipulation rather than rule-based. That’s better with GPUs. On top of that, maybe the world is going to go to multi-beam writing, going away from four decades of variable-shaped beam (VSB) writing. And I knew from the X Architecture experience that VSB was the only thing in the eco-structure that restricted mask shapes to be Manhattan or 45 degrees. In fact, with multi-beam, any curvilinear shape within the limits of resolution of a given pixel size can be freely written on the mask. The only barrier then to having curvilinear masks would be the software stack and trying to compute it with CPUs only. We knew GPU acceleration was the answer. Smith: Was it just totally an accident that multi-beam and GP GPUs happened at the same time?Fujimura: Yeah, it was. However, just as when multiple people simultaneously invent the same thing without knowing about each other, the environment and times in which we live have a lot to do with this. So, I guess, it’s not really just “luck.” But GP GPUs in 2006 and IMS Multibeam in 2007, I think that’s luck.Anyway, D2S became the GPU-acceleration partner for the semiconductor manufacturing industry and decided to work only on things that can be accelerated by GPUs in 2012.Smith: What trends do you see going forward in the next three to five years?Fujimura: A move toward curvilinear mask features, as well as an increased interest in curvilinear wafer targets as designers become aware that the manufacturing side has established a solid path for curvilinear mask shapes. We’re leaving a lot of margin on the table to accommodate gridded Manhattan assumptions, and that’s really no longer necessary from a manufacturing standpoint. I think electronic design automation (EDA) should be working on enabling curvilinear designs, because the door is open for the design world to explore curvilinear chip design and to reap compelling benefits in terms of power/performance and reliability.Editor’s Note: While Manhattan geometries are rectilinear shapes aligned to vertical and horizontal axes, curvilinear design introduces smooth, continuous curves into layouts and masks, leveraging advanced computational lithography and mask-writing technologies. This improves pattern fidelity, electrical performance and manufacturability at advanced technology nodes.About Aki FujimuraAki Fujimura is chairman and CEO of D2S, Inc., and managing company sponsor of the eBeam Initiative. Previously, Fujimura was CTO at Cadence Design Systems, President/COO and inside board member of Simplex Solutions, and VP and inside board member at Pure Software. He co-founded Tangent Systems (acquired by Cadence).Fujimura, made a SPIE fellow in 2023, serves as President of the SPIE BACUS Technical Group. He serves on the governing council of the ESD Alliance, a SEMI Technology Community. Fujimura was on the board of HLDS, RTime, Bristol, S7, and Coverity, Inc.Fujimura received his BSEE and MSEE degrees from MIT.Robert (Bob) Smith is executive director of the ESD Alliance, a SEMI Technology Community.