lithography

A change is underway in the manufacturing sector as the use of curvilinear shapes on photomasks grows, leading to the real possibility of curvilinear shapes in designs. It may just be the start of a revolution away from Manhattan or rectangular shapes to curvilinear shapes. Changing the physical design infrastructure to be curvilinear seems too daunting a task. Are curvilinear shapes in designs a real possibility? I turned to Aki Fujimura, CEO of D2S, a member of the ESD Alliance, a SEMI Technology Community, to further explain the shape of the future. Smith: What is the difference between Manhattan and curvilinear shapes? Fujimura: Manufactured masks and wafers are all curvilinear, even if the input CAD geometries are rectilinear (shown in Figure 1). It’s always been true that nature can’t make 90-degree turns, so sharp corners were always a matter of how closely you looked. These days, at the leading-edge nodes and their required resolutions, wafers and even masks are all visibly curvilinear as you can see in the graphic on the left in Figure 2. Since the 1980s, both chip design and chip manufacturing systems have used axis-aligned rectangles, or “Manhattan” geometries, because 1) that was sufficient to design transistors and interconnect for the most part, and 2) CPU-based computer algorithms can be made much more efficient for Manhattan geometries. Curvilinear shapes can be piecewise linear polygons of some resolution, or spline-like formats that are curvilinear at any resolution, or specific curved patterns like circles and ovals. Figure 1: All shapes on masks and wafers are curvilinear, even if the input geometries are Manhattan. Source: D2S Smith: What are the benefits of curvilinear masks? Fujimura: The manufacturing side of the semiconductor community knows that the best possible process window for wafer lithography is obtained by using curvilinear correction of mask shapes instead of Manhattan shapes. There have been numerous studies on the topic over several decades. The technique to generate purely curvilinear mask shapes is known as inverse lithography technology or ILT and is an advanced form of optical proximity correction (OPC). At a February 2020 eBeam Initiative event, Micron Technology presented a study showing process window improvement up to 85% for advanced memory designs as a result of using curvilinear ILT (shown in Figure 2). Additionally, Ryan Pearman from D2S presented a study at Photomask Japan 2019 showing that it is preferable to move toward a completely curvilinear paradigm, not only because ILT is better, but because the mask manufactured will have reduced variability. Figure 2: Micron Technology explained the benefits of curvilinear mask shapes for advanced memory at the eBeam Initiative event during 2020 SPIE Advanced Lithography Conference. Source: Micron Technology Smith: If the benefits have been known for decades, why is it happening only now? Fujimura: Several things happened at the same time. Multi-beam mask writing is now available. GPU acceleration for general computing has become mainstream. And wafer process window (resilience to manufacturing variation) is increasingly a problem for the leading-edge nodes as we are in the 5nm node, going to 3nm. Curvilinear ILT is needed much more now than before, will soon be needed for EUV lithography too, and is now possible because of multi-beam mask writing and GPU acceleration. Smith: Curvilinear mask shapes enable curvilinear design shapes too? Fujimura: Adoption of curvilinear mask shapes is the first step in targeting curvilinear shapes on wafers. Without curvilinear masks, it is difficult to target and reliably manufacture curvilinear designs. Curvilinear ILT works in the pixel-space to output the desired mask shape to maximize the process window for wafer lithography. A side effect of curvilinear ILT is that it can also take curvilinear targets as input. ILT, most likely GPU-accelerated ILT, works with rasterized input data, so the ILT algorithm itself is not affected even in runtime by having any amount of curvilinear design data. The resulting mask shapes are written in multi-beam mask writers, which write pixels with doses. They too will write curvilinear masks at the same speed as Manhattan masks. Suddenly now, curvilinear designs can be handled by chip manufacturing equally well for the first time in about 30 years. Smith: But curvilinear designs would be hard, right? There are a lot of tools that depend on the Manhattan assumption. Fujimura: Yes, you’re right. We’re not going to suddenly see chips that have curvilinear routing all over the place, or curvilinear intra-connect in standard cells or memory cells. The entire physical design infrastructure that includes place and route, timing, custom layout, parasitic extraction and design rule checking moving to curvilinear design all at once is extremely unlikely. Could portions of these problems be tackled for specific cases over time as “hot spot” solutions? With GPU-accelerated SPICE being available now, as an example, if GPU acceleration is adopted for design, the same transformation that happened in manufacturing can (gradually) happen in design too. The key question is whether it’s worth the trouble. Smith: Is it worth the trouble? Fujimura: I don’t know if it’s worth the trouble for the entire infrastructure. For hot spots, “hot” for various reasons, there are certainly benefits. Jogging a 32-bit bus by one grid is certainly much more economical space-wise with curvilinear shapes. Inside standard cells or memory cells, there are certain types of features that pack better with curvilinear designs. In general, interconnect is the limiter to chip size of course, but there are always critical areas that could use help to shrink. There are manufacturability benefits as well. In general, when something changes so drastically as this for the first time in 30 years, there’s bound to be some innovation that takes advantage of the discontinuity. Let’s see what the combined capitalistic power of the entire community might be able to come up with. The first thing is to let everyone know that curvilinear designs will be manufacturable today. Hear insights from other leading electronic system design industry CEOs at the SEMI ESD Alliance CEO Outlook on May 18, 2021, 2:00pm-3:00pm PDT. Panelists will discuss the state of the industry along with their views of the outlook for the coming years. Registration is free for SEMI members. About Bob Smith Robert (Bob) Smith is executive director of the ESD Alliance, a SEMI Technology Community. He is responsible for the management and operations of the ESD Alliance, an international association of companies providing goods and services throughout the semiconductor design ecosystem.

This article is the fifth and final in a series highlighting the vital importance of SEMI Standards to commemorate the publication of the 1000th SEMI Standard in July 2019. Find the entire series here.As we define industry standards for managing data in the fab and beyond, we are creating a virtuous circle. More data create better processes. Better processes generate more good data, and more good data lead to better processes. It becomes a cycle of continuous improvement, and we are only just beginning to realize its potential. To dive deeper we interviewed Alan Weber, vice president, New Product Innovations at Cimetrix, and an active member of SEMI Standards Information and Control Committee (IC C).“Industry standards are critical in allowing us to collect information across the fab and use it in increasingly sophisticated control algorithms for the equipment,” said Weber. “The last few years have been about analysis applications that leverage big data in the fab. What started at the lot level is now applied at the wafer level, and for a process like lithography, it’s down to the shot or die level. We’re now collecting enough data variables at individual process and recipe steps to model for predictive maintenance and virtual metrology.”The migration from using data as rearview mirror for identifying and addressing fab issues to using data to head off issues preemptively represents a paradigm shift with immense advantages. This is the starting point for realizing a virtuous data circle.The benefits of a virtuous data circle are simple and compelling: higher yields, faster time to market, more revenue and greater profitability. Our optimism, however, is tempered by major obstacles to this promising future.Multilingual ManufacturingWeber points out that the electronics industry is becoming a multilingual standards world with more than 1,000 fab equipment vendors and several layers of protocols that present the challenge of seamlessly handling multiple protocols. His IC C Committee is out to tackle this challenge.“While SEMI Standards efforts first began in the front end, our standards program now encompasses the back end with test and packaging as well as other device areas including MEMS, sensors and displays,” said James Amano, senior director, International Standards and EHS, SEMI. “We’re going to see data connectivity from the front end to the back end to the final assembly of multi-chip products and that needs standards,” Weber explained. “We’ll need more connected equipment throughout the global, multi-site manufacturing process if we are to support the full traceability requirements of the most demanding markets such as automotive.”The industry will benefit from greater collaboration. Weber predicts that companies will team to create integrated supply chains within broader industry supply chains.Getting the Right People at the Right Time“As we lead the development cycle of a standard from concept to realization, one of the most important jobs of our standards task forces and committees is to coordinate competing companies and build an industry consensus,” Amano said. “This is the case for data in particular, where we rely on industry professionals like Weber and his colleagues, who are working to bring people together to collaborate on developing standards for connectivity and data sharing. It is that critical human element that allows SEMI to sustain our commitment to introducing standards that move the industry forward.”Will Companies Share Data If It Is Secure? Weber contends that when it comes to securing and sharing the data, the biggest challenge is to change the industry’s information-sharing culture.“Finance and defense are already finding ways to deal with data security,” said Weber. “While we will always have problems that require technology fixes, like dealing with new types of computer viruses, I am confident that we will be able to create standards that enable the free, secure flow of information. The key to making progress and better leveraging data is to get companies to see the potential of sharing data while investing in the standards.”SEMI recently launched a project to optimize data sharing across two critical process steps – lithography and plasma etch – to accelerate the adoption of data-driven AI methodologies. The results will help to establish data transfer and management standards crucial to the trusted exchange of trade secrets, IP and other sensitive information. Tools and materials from several SEMI members will be used for the project at Cornell University’s NanoScale Science Technology Facility (CNF). SEMI members are invited to join the project review team. Contact Pushkar Apte at SEMI ([email protected]) for more information on the initiative.Advantages Are Too Great to IgnoreTraditional cultural obstacles aside, the advantages of creating virtuous data circles are simply too great to ignore. Now that it’s accepted wisdom for fabs, factories and supply chains to continuously leverage interconnected data to get smarter, the time has come to extend those advantages throughout the full manufacturing process. Without these data circles, we’ll slow the development of new technologies and applications.We can only speculate where the lines of sharing data are drawn and will be redrawn in the future. But, without doubt, technology innovations such as AI will spawn new information business models that vertically and horizontally integrate companies in ways previously unimaginable. Data standards will underpin this structural transformation.Use your voice to affect standardization in and around the microelectronics industry. Learn about SEMI International Standards – and become part of the solution. Heidi Hoffman is senior director of technology communities marketing at SEMI. Hoffman and her team shine a spotlight on the work of the more than 20 technology communities under the SEMI electronics manufacturing supply chain collaboration platform. Actively engaging community members in marketing programs that showcase their unique value, Hoffman’s team helps companies to grow and prosper through the power of connection, collaboration and innovation.

Materials innovation has always been vital to the semiconductor industry. In the past, it was high-κ gate dielectrics. Today, Cobalt is seen as a replacement for Tungsten in middle-of-line (MOL) contacts.What materials innovation will the future bring?A likely answer is Graphene, the wonder material discovered in 2004.Graphene is one atomic layer of carbon, the thinnest and strongest material that has ever existed. It is 200 times stronger than steel and the lightest material known to man (1 square meter weighing around 0.77 mg). It is an excellent electrical and thermal conductor at room temperature with an electron mobility of ~ 200,000cm2.V-1.s-1. At one atomic layer, graphene is flexible and transparent. Other notable properties of Graphene are its uniform absorption of light across the visible and near infrared spectrum and its applicability towards spintronics-based devices.Graphene and Moore’s LawMoore’s Law scaling can be broken down into 4 key areas: Lithography FET Advanced Packaging (2.5D and 3D IC) Interconnect Material Solutions for upcoming nodes are starting to emerge in the first two areas (EUV and Nanowire- or Nanosheet-based FET respectively). Graphene play an important role in the latter two areas. For advanced packaging, Graphene can be used as a heat spreader (to lower overall thermal resistance), or as an EM shield (to lower crosstalk) as part of a 3D IC package.Active Graphene device layers can potentially be stacked on top of each other using a low-temperature transfer process ( 400°C) to allow for a dense heterogeneous “memory near compute” configuration. This is an area DARPA is actively researching as part of its new $1.5 billion Electronics Resurgence Initiative.Regarding interconnects, Copper interconnects are running out of steam and becoming a major IC bottleneck (projected 40% total delay for 7 nm node). Graphene’s high electron mobility and thermal conductivity make it an attractive interconnect material for MOL and back-end-of-line (BEOL), especially at line widths 30 nm.Graphene Device ApplicationsGraphene-based semiconductor applications are already starting to hit the market. A fully integrated optical transceiver (with a Graphene modulator and photodetector) operating at 25 Gb/s/channel was on display at the recent Mobile World Congress in Barcelona. San Diego-based Nanomedical Diagnostics is selling a medical device that uses a Graphene biosensor. Europe-based Emberion is building Graphene optoelectronic sensors that might find a home in LIDAR applications, where there is currently a focus on improving sensing in low-light conditions.What will the overall Graphene roadmap in the semiconductor industry look like? The history of ion implantation serves as a good example of how a fundamental scientific discovery moves from the lab to the foundry floor.The dominant view in the semiconductor industry at the time was that ion implantation would not work in practice (vs. thermal diffusion) and that, if it did, it would only marginally improve the manufacturing yields of existing products. There was nothing obvious about the transfer of ion bombardment techniques from nuclear physics research to semiconductor production.Varian (led by British physicist Peter Rose) built a new, advanced ion implant tool that Mostek (DRAM manufacturer based in Texas) was able to use to create MOS ICs with clear competitive advantages. The successful collaboration between Varian and Mostek was the turning point in the development of ion implantation as a major semiconductor manufacturing process. Over the next few years, semiconductor firms used ion implantation in a growing number of process steps and, by the late 1970s, it became one of the main processes used in semiconductor manufacturing.Likewise, the Graphene world needs to work closely with the semiconductor industry to develop the tools and techniques required to solve fundamental issues around Graphene growth (good uniformity over large area, low defect density) and Graphene transfer (high throughput, CMOS compatible). It is only then will we fully realize a future that includes 2D materials.The first step in this process is cross-industry education and initiating the dialogue between semiconductor industry and graphene companies. The National Graphene Association will be hosting the largest gathering of graphene companies and commercial stakeholders at the Global Graphene Expo Conference, October 15-17, 2018, in Austin, Texas.Learn more about graphene at the upcoming Global Graphene Expo Conference with dedicated panels of experts and investors, and roundtable discussions on how Graphene will impact the semiconductor industry. The event promo code is SEMINGA. About the AuthorAnand Chamarthy is the CEO and Co-Founder of Lab 91, an Austin-based startup that is working towards Graphene/CMOS integration at the foundry level. Anand can be reached at [email protected]. About the National Graphene AssociationThe National Graphene Association is the main organization and body in the U.S. promoting and advocating for commercialization of graphene and addressing critical issues such as standards and policy development.