IC layout design is not a trivial task. It requires a high level of skill, creativity, and innovation to cope with the increasing complexity and challenges of IC technology. As the structures on chips shrink in size and the number of transistors on a chip increase, IC layout designers have to deal with various factors such as wire length, cell density, routing congestion, timing closure, power consumption, noise margin, etc. These factors can have a significant impact on the functionality and efficiency of IC circuits, and require careful optimization and trade-offs.
However, IC layout design is not a static process. It involves constant interaction and feedback with other steps in the IC design cycle, such as synthesis, physical verification, testing, etc. It also requires advanced methods and tools to help solve or avoid common problems and errors in IC layout design, such as design rule checking (DRC), layout versus schematic (LVS), parasitic extraction, antenna rule checking, electrical rule checking (ERC), etc. These methods and tools help to boost performance and reduce the costs of IC layout design by ensuring correctness, accuracy, and robustness.
In this article, we will explore the art of semiconductor IC layout design in more detail. We will discuss the key factors that influence the quality of IC layout design, introduce some advanced methods and tools for improving IC layout design, and analyze some case studies of successful IC layout design projects that demonstrate the benefits and best practices of applying these methods and tools. We will also provide some suggestions and recommendations for future research and development in this field.
Key Factors that Influence the Quality of IC Layout Design
IC layout design is a complex and challenging task that requires careful consideration of various factors that can affect the quality of the final product. In this section, we will discuss some of the most important factors that influence the quality of IC layout design, such as:
- Wire length: The total length of the interconnects (wires) that connect the components of an IC. Wire length affects:
- Delay: Longer wires increase the resistance and capacitance, which increase the signal propagation delay and cause timing violations or errors.
- Power: Longer wires consume more power, which increases the overall power consumption and heat dissipation of an IC circuit.
- Area: Longer wires occupy more area on the chip, which increases the overall size and cost of an IC product.
- Cell density: The ratio of the area occupied by cells (components) to the total area available on a chip. Cell density affects:
- Performance: Higher cell density can increase the functionality and performance of an IC circuit, but also introduce more parasitic effects (such as resistance, capacitance, inductance, crosstalk, etc.) that can degrade the performance and reliability of an IC circuit.
- Cost: Higher cell density can reduce the chip size and cost per chip, but also increase the complexity and difficulty of manufacturing and testing an IC product.
- Flexibility: Higher cell density can limit the space for future modifications or enhancements to an IC product design.
- Routing congestion: The degree to which the available routing resources (such as metal layers and tracks) are utilized or saturated by the interconnects. Routing congestion affects:
- Delay: Higher routing congestion can increase the wire length and parasitic effects, which increase the signal propagation delay and cause timing violations or errors.
- Power: Higher routing congestion can increase the power consumption and heat dissipation of an IC circuit.
- Reliability: Higher routing congestion can increase the risk of electromigration and IR drop, which can damage or degrade the interconnects and components over time.
- Timing closure: The process of ensuring that all signals in an IC circuit meet their timing requirements (such as setup time, hold time, clock period, etc.) under all operating conditions (such as voltage, temperature, process variation, etc.). Timing closure affects:
- Functionality: Achieving timing closure is essential for ensuring that an IC circuit works correctly and predictably according to its design specifications and requirements.
- Performance: Achieving timing closure can improve the speed and throughput of an IC circuit by reducing or eliminating timing slack (the difference between the required time and arrival time of a signal).
Advanced Methods and Tools for Improving IC Layout Design
IC layout design is not a one-time or isolated process. It involves constant interaction and feedback with other steps in the IC design cycle, such as synthesis, physical verification, testing, etc. It also requires advanced methods and tools to help solve or avoid common problems and errors in IC layout design, such as design rule checking (DRC), layout versus schematic (LVS), parasitic extraction, antenna rule checking, electrical rule checking (ERC), etc. In this section, we will introduce some of the advanced methods and tools for improving IC layout design, such as:
- Synthesis optimization: The process of transforming a high-level description of an IC circuit (such as a register-transfer level or RTL model) into a low-level description (such as a gate-level netlist) that meets the design specifications and constraints (such as timing, area, power, etc.). Synthesis optimization can improve the quality of IC layout design by generating an optimized netlist that reduces wire length, cell density, routing congestion, power consumption, etc.
- Design rule checking (DRC): The process of verifying that an IC layout design conforms to the rules and specifications of a given technology node or foundry. DRC can ensure the manufacturability and functionality of an IC product by detecting and correcting any violations or errors in the IC layout design, such as minimum feature size, spacing, width, overlap, etc.
- Layout versus schematic (LVS): The process of comparing an IC layout design with its corresponding schematic or netlist to ensure that they are functionally equivalent and consistent. LVS can ensure the correctness and accuracy of an IC product by detecting and correcting any mismatches or discrepancies between the IC layout design and its intended functionality, such as missing or extra components, incorrect connections, wrong orientations, etc.
- Parasitic extraction: The process of extracting the parasitic effects (such as resistance, capacitance, inductance, etc.) of the interconnects and components in an IC layout design. Parasitic extraction can improve the performance and reliability of an IC product by providing accurate information for timing analysis, power analysis, noise analysis, signal integrity analysis, etc.
- Antenna rule checking: The process of checking for antenna effects in an IC layout design. Antenna effects are caused by the accumulation of charge on interconnects during plasma etching in fabrication. Antenna effects can damage or degrade the gate oxide of transistors and affect their functionality and reliability. Antenna rule checking can prevent antenna effects by detecting and correcting any violations or errors in the IC layout design, such as excessive metal area ratio, insufficient diode protection, etc.
- Electrical rule checking (ERC): The process of checking for electrical errors in an IC layout design. Electrical errors are caused by incorrect or incomplete connections or configurations of components in an IC circuit. Electrical errors can affect the functionality and reliability of an IC product by causing short circuits, open circuits, floating nodes, etc. ERC can prevent electrical errors by detecting and correcting any violations or errors in the IC layout design, such as missing power or ground connections
Case Studies of Successful IC Layout Design Projects
IC layout design is not a theoretical or abstract process. It is a practical and applied process that aims to deliver high-quality IC products that meet customer needs and market demands.
Case Study 1: TSMC IC Layout Contest
TSMC is the world’s leading semiconductor foundry that provides advanced process technologies and comprehensive design services for various IC applications. In 2019, TSMC held the first nationwide “IC Layout Contest” in Taiwan, aiming to cultivate top-notch chip layout talent with Design & Technology Co-Optimization (DTCO) expertise.
The contest attracted a total of 1,000 students from 35 universities across the country to compete for generous cash prizes, as well as priority status for selection to TSMC summer internship opportunities. The contest involved designing an IC layout for a 7nm FinFET technology node using Cadence Virtuoso Layout Editor software on the Microsoft Azure cloud platform. The contestants had to optimize their IC layout design according to various criteria, such as wire length, cell density, routing congestion, timing closure, power consumption, noise margin, etc.
The contest also provided extensive online training courses and corresponding EDA IC design tools and virtual environment free of charge. The contestants had the opportunity to learn from TSMC technical experts face-to-face, and benefit from first-hand industry experiences. Through the four-month competition, the contestants gained valuable knowledge and skills in advanced process technology development and chip layout technology.
The contest was a great success and received positive feedback from the participants. A team from Yuan Ze University emerged from the pack and won the championship in the final contest in January 2020. The winning team demonstrated outstanding performance and creativity in their IC layout design, achieving an average wire length reduction of 18%, an average cell density increase of 10%, and an average power consumption reduction of 8%. The winning team also received an offer to join TSMC as full-time employees after graduation.
The contest showcased TSMC’s leadership and innovation in IC layout design and DTCO solutions. It also fostered a strong collaboration and communication between TSMC and academia, as well as among the contestants themselves. The contest created a new model of online learning and competition for IC layout design talent development.
Case Study 2: Siemens EDA 3D IC Design Flow Solutions
Siemens EDA is a leading provider of software solutions for electronic design automation (EDA), enabling customers to design, verify, test, and manufacture electronic systems and semiconductor devices. Siemens EDA offers a comprehensive set of tools and workflows for developing advanced 2.5D/3D IC heterogeneous System-In-Package (SIP) designs.
Siemens EDA’s 3D IC design flow solutions enable customers to explore and deliver product differentiation faster using 3D heterogeneous integration of node and performance-optimized chiplets. The solutions cover various aspects of 3D IC design flow, such as:
- 3D IC Architect workflow: A system-level co-design environment that enables customers to partition their system into multiple chiplets based on performance, power, area, cost, etc., and optimize their interconnects using various packaging technologies (such as wafer-on-wafer or chip-on-wafer).
- 3D IC Designer workflow: A physical design environment that enables customers to create and optimize the layout of their chiplets and interposers using various EDA tools, such as place and route, floorplanning, physical verification, etc.
- 3D IC Analysis workflow: A system-level analysis environment that enables customers to perform various types of analysis and verification for their 3D IC designs, such as thermal analysis, power analysis, signal integrity analysis, etc.
- 3D IC Test workflow: A system-level test environment that enables customers to perform various types of test and diagnosis for their 3D IC designs, such as scan test, memory test, logic test, etc.
- 3D IC Reliability workflow: A system-level reliability environment that enables customers to monitor and optimize the reliability and quality of their 3D IC products throughout their lifecycle, such as aging analysis, fault injection, failure analysis, etc.
Siemens EDA’s 3D IC design flow solutions have been successfully applied by many customers in various domains, such as artificial intelligence, high-performance computing, automotive, etc. For example, one of Siemens EDA’s customers used the 3D IC design flow solutions to design a 2.5D AI accelerator chip with four chiplets on a silicon interposer. The customer achieved the following benefits:
- Reduced the chip area by 40% compared to a monolithic design
- Increased the chip performance by 30% compared to a monolithic design
- Reduced the chip power consumption by 20% compared to a monolithic design
- Reduced the chip development time by 50% compared to a monolithic design
The customer also praised Siemens EDA’s 3D IC design flow solutions for their ease of use, scalability, and accuracy.
Siemens EDA’s 3D IC design flow solutions demonstrate the advantages and potential of 3D IC technology for delivering product differentiation and innovation. They also enable digital transformation for 3D chip design with co-design, co-simulation, and automated system analysis and checking. They provide customers with a proven, complete 3D IC design flow from 3D architecture partitioning to planning, layout, design-for-test, thermal management, multi-die verification, interconnect IP, manufacturing signoff, and post-silicon lifecycle monitoring.