What are the Steps in Physical Design?

The physical design process lays the foundation for translating chip designs into tangible products that power our digital landscape. Physical design encompasses a series of meticulously orchestrated steps to optimise chip layouts for performance, power efficiency, and manufacturability. But what exactly are these steps, and how do they contribute to the overall design process? Let’s embark on a journey to unravel the intricacies of physical design and explore the essential steps involved.

Step 1: RTL-to-GDSII Synthesis

The journey begins with the conversion of Register Transfer Level (RTL) descriptions, which represent the logical functionality of the chip, into a physical design representation known as GDSII (Graphic Data System II). This process involves synthesizing the RTL code into a netlist of logic gates and flip-flops, setting the stage for subsequent physical implementation.

Step 2: Floorplanning

Floorplanning establishes the physical boundaries of the chip and defines the placement of logic blocks, memory elements, and I/O pads within the silicon die. By strategically arranging these components, designers aim to optimize chip area, routing congestion, and signal integrity while adhering to design constraints and performance targets.

Step 3: Placement and Routing

Placement involves determining the precise locations of logic gates and other circuit components on the chip’s surface. Routing, on the other hand, involves connecting these components through metal layers to establish electrical pathways. Automated placement and routing algorithms are employed to optimize chip performance, minimize signal delays, and meet timing constraints.

Also read: Practical Placement & Routing Flow

Step 4: Clock Tree Synthesis (CTS)

Clock Tree Synthesis is a critical step in ensuring synchronous operation across the chip by distributing clock signals efficiently and uniformly. Designers carefully design and optimize clock distribution networks to minimize clock skew, reduce power consumption, and enhance signal integrity, thereby facilitating reliable chip operation.

Step 5: Timing Closure

Timing Closure involves verifying that signal paths within the chip meet specified timing constraints to achieve desired performance targets. Static Timing Analysis (STA) tools are utilized to analyze signal propagation delays and identify timing violations, which are then addressed through iterative optimization techniques.

Step 6: Power Optimization

Power Optimization focuses on minimizing power consumption within the chip to enhance energy efficiency and extend battery life in portable devices. Techniques such as clock gating, voltage scaling, and power gating are employed to reduce dynamic and static power dissipation while maintaining design integrity.

Also read: Practical Physical Synthesis Process

Step 7: Design for Manufacturability (DFM)

Design for Manufacturability ensures that the chip design is optimized for successful fabrication and yields high-quality silicon dies. This step involves verifying the layout against foundry-specific design rules, addressing manufacturing constraints, and incorporating features such as metal fill structures to improve planarity and reduce manufacturing variations.

Step 8: Physical Verification and Signoff

Physical Verification encompasses a series of checks and analyses to validate the correctness, integrity, and manufacturability of the chip design. This includes Design Rule Checks (DRC) to ensure compliance with fabrication rules, Layout versus Schematic (LVS) checks to verify layout accuracy, and other verification tasks such as Design for Testability (DFT), Electromigration (EM), and IR Drop Analysis.

Also read: Physical Design Flow

Conclusion

The process of physical design is a meticulously orchestrated journey that transforms abstract chip designs into tangible silicon realities. By following a structured sequence of steps encompassing RTL-to-GDSII synthesis, floorplanning, placement and routing, clock tree synthesis, timing closure, power optimization, design for manufacturability, and physical verification, designers can ensure the successful realization of complex semiconductor chips. With each step playing a crucial role in optimizing chip performance, power efficiency, and manufacturability, physical design remains at the forefront of semiconductor innovation, driving the advancement of technology across diverse industries.