Harini Vemu

<a href="https://elearn.maven-silicon.com/"><img class="alignnone size-medium wp-image-18066" src="https://www.maven-silicon.com/blog/wp-content/uploads/2025/07/VLSI-Physical-Design-at-3nm-Innovations-and-Challenges-1024x576.jpg" alt="3nm processor " width="1024" height="576" /></a>

<span style="font-weight: 400;">Picture a tiny city, smaller than a dime, filled with billions of microscopic switches called transistors that run your phone, smartwatch, or even a drone. This is the world of Very Large-Scale Integration (VLSI) physical design, where these switches get arranged on a chip. At 3 nanometers (nm)—a nanometer being a billionth of a meter, like a speck beside a grain of dust—this task is like solving a puzzle with pieces too small to see. Chips at 3nm are super fast and save battery, but they bring big challenges. Let’s dive into what’s new in designing these tiny powerhouses, keeping it clear and easy to follow.</span>
<h2><b>Why 3nm Chips Matter</b></h2>
<span style="font-weight: 400;">A 3nm chip packs more transistors than ever, making devices quicker and more efficient. A 3nm chip in your phone lets you stream videos or play games without the battery draining fast. But working at this scale is tricky, with issues like power, heat, and timing cropping up. New solutions are making it possible to keep these chips running smoothly.</span>
<h2><b>The Big Challenges and Solutions</b></h2>
<h4><b>Energy Supply: Keeping the Chip Running</b></h4>
<span style="font-weight: 400;">Delivering power to billions of transistors in a 3nm chip is like sending electricity through a super-narrow straw to light up a whole town. These thin wires can cause power shortages, making a smartwatch lag when you check a message. To solve this, multi-layered power grids act like stacked highways, moving electricity smoothly. Tiny storage units, like mini batteries, also keep power steady. This ensures a 3nm chip in a fitness tracker keeps tracking your heart rate all day without glitching.</span>
<h4><b>Overheating: Keeping Things Cool</b></h4>
<span style="font-weight: 400;">Squeezing billions of transistors together generates heat, like a packed room with no air conditioning. Too much heat can slow or break a chip, like a tablet crashing during a video. Careful planning places the hottest parts near special vents, like cooling ducts, to let heat escape. This keeps a 3nm chip in a car’s GPS system cool, so it guides you on a road trip without overheating.</span>
<h4><b>Wire Strength: Preventing Breakdowns</b></h4>
<span style="font-weight: 400;">In a 3nm chip, ultra-thin wires carrying electrons can wear out, like a rope fraying under too much strain. This issue, called electromigration, can make the chip fail, like a laptop crashing during a work project. Using tougher materials, like cobalt instead of copper, helps wires handle the electron flow better. Widening some wires also reduces stress, like strengthening a rope. This keeps a 3nm chip in a smartphone running smoothly, so you can browse apps or stream music without interruptions.</span>
<h4><b>Timing: Keeping Everything in Sync</b></h4>
<span style="font-weight: 400;">A chip works like a band, with billions of transistors needing to hit their notes at the right moment. At 3nm, signals can get delayed because wires are so close they interfere, like chatter in a crowded room. Smart tools spread the chip’s “rhythm” evenly to keep everything on track. Computer programs that learn to spot timing issues also help. This ensures a 3nm chip in a gaming console delivers smooth gameplay, so you don’t lag during a fast-paced match.</span>
<h2><b>New Ideas for 3nm Chips</b></h2>
<h4><b>Stacking Chips: Building Up</b></h4>
<span style="font-weight: 400;">Instead of spreading transistors flat like a one-story house, stacking them like a skyscraper saves space and speeds up signals, like taking a quick elevator ride. In a 3nm phone chip, this makes apps open faster, so you can start a video call without waiting.</span>
<h4><b>Smarter Transistors: Better Switches</b></h4>
<span style="font-weight: 400;">Older transistors were like simple light switches, but 3nm chips use Gate-All-Around designs, where the switch is wrapped tightly to control electricity better, like a faucet that doesn’t leak. In a 3nm laptop chip, this lets you edit photos for hours without needing a charger.</span>
<h4><b>Computer Helpers: Smarter Design</b></h4>
<span style="font-weight: 400;">Laying out a 3nm chip is like planning a city with a trillion roads. <a href="https://www.maven-silicon.com/blog/ai-in-vlsi/">Artificial intelligence</a> programs optimize the transistor layout, saving time and power. In a 3nm chip for a security camera, this helps the chip process video quickly, spotting motion to keep your home safe without using too much energy.</span>
<h4><b>Precision Building: Carving Tiny Patterns</b></h4>
<span style="font-weight: 400;">Creating a 3nm chip is like drawing a map on a grain of sugar. Extreme Ultraviolet (EUV) lithography uses special light to carve tiny patterns with precision. In a 3nm chip for a smart speaker, this ensures the chip hears your voice commands clearly, even in a noisy room.</span>
<h2><b>How 3nm Improves Your Life</b></h2>
<span style="font-weight: 400;">These tiny chips make a big impact. A 3nm chip in your earbuds means you can listen to music on a long flight without recharging. In a medical device, it monitors your health in real-time, like a heart tracker that runs smoothly. In a 5G tower, a 3nm chip keeps your phone connected at a busy festival, so you can share photos without a hitch.</span>
<h2><b>What’s Next for Chips?</b></h2>
<span style="font-weight: 400;">Moving below 3nm, maybe to 2nm or 1nm, will bring even bigger challenges. New materials, like ultra-thin carbon sheets, could make chips better. Chips might be built in pieces, like snapping together puzzle pieces, to save time and cost. Ideas from quantum computing could also change how chips work in the future.</span>
<h2><b>Conclusion</b></h2>
<span style="font-weight: 400;">Designing 3nm chips is like building a tiny, super-efficient city under a magnifying glass. It’s tough, but the results are amazing: chips that make your devices faster, longer-lasting, and smarter. From stacked designs to smarter transistors and AI tools, new solutions are tackling the challenges. Next time you use your phone or check a smartwatch, think about the 3nm chips powering it all.</span>

VLSI Physical Design at 3nm: Innovations and Challenges

<h4><b><img class="alignnone size-medium wp-image-18037" src="https://www.maven-silicon.com/blog/wp-content/uploads/2025/03/Ilyaas-2-1024x576.jpg" alt="" width="1024" height="576" /></b><strong data-start="126" data-end="142">Introduction</strong></h4>
<p class="" data-start="144" data-end="749">As technology advances day by day, it becomes increasingly challenging to transfer patterns onto silicon wafers with high accuracy. To address these challenges, traditional lithography is no longer suitable for fabricating complex designs due to its wavelength limitations. To overcome these challenges, Multi-Patterning (MP) and Optical Proximity Correction (OPC) techniques are extensively used. These techniques ensure that the design layout generated during the Physical Design stage can be accurately fabricated while maintaining yield, performance, and manufacturability.</p>

<h3 class="" data-start="756" data-end="809"><strong data-start="760" data-end="809">Why Do We Have to Use Multi-Patterning &amp; OPC?</strong></h3>
<h6 data-start="811" data-end="840"><strong data-start="811" data-end="840">Impact on Physical Design</strong></h6>
<p class="" data-start="842" data-end="1581">The<a href="https://www.maven-silicon.com/blog/career-opportunities-as-a-physical-design-engineer/"> Physical Design</a> (PD) process consists of various stages like floorplanning, placement, clock tree synthesis (CTS), and routing. During these stages, power, performance, and area requirements must be considered. As the technology node shrinks, the constraints for the layout become more crucial due to lithographic limitations. Multi-patterning (MP) is a technique needed when the pitch becomes smaller than the resolution limit of lithography tools. This requires multiple exposures to correctly define shapes. Optical Proximity Correction (OPC) compensates for pattern distortions that occur during photolithography, ensuring the fabricated wafer matches the intended PD layout.</p>

<h3 class="" data-start="1588" data-end="1630"><strong data-start="1592" data-end="1630">How Are These Used in Fabrication?</strong></h3>
<h6 data-start="1632" data-end="1678"><strong data-start="1632" data-end="1678">Design Rule Constraints in Physical Design</strong></h6>
<p class="" data-start="1680" data-end="1997">At advanced technology nodes, Design Rule Constraints are defined strictly due to multi-patterning limitations. Color-aware routing tracks are defined during the routing stage. Violating multi-patterning constraints can lead to misalignment in the masks, which affects manufacturing yield.</p>

<h6 data-start="1999" data-end="2041"><strong data-start="1999" data-end="2041">Mask Generation and OPC Implementation</strong></h6>
<p class="" data-start="2043" data-end="2195">After completing the Physical Design Signoff process, the layout is provided for mask generation. Different OPC techniques are then applied:</p>

<ul>
 	<li data-start="2199" data-end="2267"><strong data-start="2199" data-end="2217">Rule-Based OPC</strong>: Applies predefined rules to correct distortions.</li>
 	<li data-start="2270" data-end="2376"><strong data-start="2270" data-end="2289">Model-Based OPC</strong>: Uses lithography simulations to predict pattern distortions and optimize mask shapes.</li>
 	<li data-start="2379" data-end="2475"><strong data-start="2379" data-end="2408">Inverse Lithography (ILT)</strong>: An advanced, AI-driven technique that enhances mask accuracy.</li>
</ul>
<h6 data-start="2477" data-end="2528"><strong data-start="2477" data-end="2528">Lithography and Multi-Patterning in Fabrication</strong></h6>
<ul>
 	<li data-start="2532" data-end="2626"><strong data-start="2532" data-end="2559">Double Patterning (DPT)</strong>: Uses two masks for a single layout, improving feature resolution.</li>
 	<li data-start="2629" data-end="2740"><strong data-start="2629" data-end="2668">Self-Aligned Quad Patterning (SAQP)</strong>: Ensures the accuracy of the interconnect routing of critical nets.</li>
 	<li data-start="2743" data-end="2898"><strong data-start="2743" data-end="2776">Post-Fabrication Verification</strong>: Ensures that the printed wafer matches the layout extracted from the <a href="https://www.maven-silicon.com/blog/why-physical-design-in-vlsi-is-important/">physical design</a> using lithographic simulations.</li>
</ul>
<h3 class="" data-start="2905" data-end="2968"><strong data-start="2909" data-end="2968">Advantages of Multi-Patterning &amp; OPC in Physical Design</strong></h3>
<ul>
 	<li data-start="2972" data-end="3050">Ensures all designs in advanced technology nodes maintain design accuracy.</li>
 	<li data-start="3053" data-end="3140">Helps meet DRC (Design Rule Check) rules by ensuring correct feature alignment.</li>
 	<li data-start="3143" data-end="3266">Prevents fabrication-induced distortions that can alter interconnect parasitics, leading to timing distortions.</li>
 	<li data-start="3269" data-end="3314">Improves yield and manufacturability.</li>
 	<li data-start="3317" data-end="3378">Enables high-density routing and interconnect layers.</li>
</ul>
<h3 class="" data-start="3385" data-end="3403"><strong data-start="3389" data-end="3403">Conclusion</strong></h3>
<p class="" data-start="3405" data-end="3931">Multi-Patterning and OPC techniques are critical in the journey from <a href="https://www.maven-silicon.com/blog/is-physical-design-in-vlsi-a-good-career/">Physical Design</a> to Fabrication. As these techniques become more complex, AI-driven OPC tools are being explored to reduce the need for multi-patterning. However, until EUV (Extreme Ultra Violet) lithography becomes fully mature, multi-patterning-aware physical design methodologies will remain essential for ensuring successful timing closure, area optimization, and manufacturability in advanced semiconductor nodes.</p>

Multi-Patterning and  (Optical Proximity Correction) Challenges in Physical Design

<img class="aligncenter size-medium wp-image-17233" src="https://www.maven-silicon.com/blog/wp-content/uploads/2024/10/Significance-of-RC-Parasitics-in-Physical-Design-1024x576.jpg" alt="Significance of RC Parasitics in Physical Design" width="1024" height="576" />

The main goal of VLSI technology is to pack billions of transistors onto a single chip to create advanced devices and system-on-a-chips. Several sectors, including data centers, telecommunications, consumer electronics, automotive, defense, and industrial automation, among others, depend extensively on the chips. Manufacturing these small chips, which are made of billions of transistors and their interconnects to form very complex circuitry.

For a chip to be launched into the consumer market, it must meet the standards of area, performance, and power. As a result, depending on the application, the area and power of a design may vary from one to another. However, all designs must consider performance as a critical component.

In digital design, timing analysis is a crucial stage, particularly in VLSI (Very Large Scale Integration), where it ensures that a device or system works correctly at the desired clock frequency. It ensures that every path satisfies the necessary timing requirements, allowing data to flow across the circuit free of violations. To ensure that the circuit meets requirements in terms of area, power and speed, reliability, and functional criteria, there are various types of essential factors to take into account during timing analysis in VLSI design. Operating conditions are among them, and in addition, RC parasitics during the timing analysis, are the most significant elements. The significance of these parasitics, in affecting the timing, power, and performance of a VLSI design increases as technology progresses to nanoscale nodes in terms of overall chip behavior and signal integrity.

<em><strong>Also read: <a href="https://www.maven-silicon.com/blog/what-is-a-buffer-in-vlsi/" target="_blank" rel="noopener">What is a Buffer in VLSI?</a></strong></em>

The sources for the RC parasitics are Interconnect Resistance and Interconnect Capacitance.
<h2><strong>Interconnect Capacitance </strong></h2>
Interconnect wires can hold electrical charge because they are placed close to each other. When a signal moves through a wire, it acts like a surface that holds a lot of charge (Plate).

<img class="aligncenter wp-image-17238 " src="https://www.maven-silicon.com/blog/wp-content/uploads/2024/10/Image-1.png" alt="Significance of RC Parasitics in Physical Design" width="546" height="340" />

There can be three types of capacitance available in the designs. They are:
<ol>
 	<li>Coupling Capacitance C<sub>c</sub> = ε*T/S</li>
 	<li>Area Capacitance per Unit length C<sub>a</sub> = ε*W/H</li>
 	<li>Fringe Capacitance C<sub>f</sub></li>
</ol>
The values of the capacitances are dependent on the below parameters
<ol>
 	<li>Dielectric Constant (ε)</li>
 	<li>Width of Metal (W)</li>
 	<li>Thickness of Metal (T)</li>
 	<li>Spacing between the metals (S)</li>
 	<li>Thickness of Dielectric (ILD –Interlayer Dielectric) (H)</li>
</ol>
<em><strong>Also read: <a href="https://www.maven-silicon.com/blog/3d-integration-in-vlsi-circuits/" target="_blank" rel="noopener">3D Integration in VLSI Circuits</a></strong></em>
<h2><strong>Interconnect Resistance</strong></h2>
All materials resist the flow of electricity to some extent. Conductors have low resistance, materials like highly doped silicon have moderate resistance, and insulators have very high resistance. In CMOS circuits, different materials are used based on their level of resistance.

"Resistivity depends on the material of the metal layer. Resistance is directly proportional to delay; when the resistance increases, the delay also increases."

Resistance per unit length = p*W/T
<ol>
 	<li>Resistivity of the metal layer (p)</li>
 	<li>Width of Metal (W)</li>
 	<li>Thickness of Metal (T)</li>
</ol>
By considering the above interconnect parasitics, the RC corners (combinations of R and C) will be taken for timing analysis.

<strong>RC corners</strong> refer to different combinations of <strong>resistance (R)</strong> and <strong>capacitance (C)</strong> values used during timing analysis and circuit simulation. These variations are introduced to account for the inherent manufacturing process variations, temperature changes, and voltage fluctuations that can affect the performance of an integrated circuit (IC).
<h2>Why RC Corners in Timing Analysis?</h2>
The RC parasitics (resistance and capacitance) associated with interconnects and transistors influence signal propagation delay in a chip. To ensure robust design, designers use different RC corners, typically grouped into:
<ul>
 	<li>Metal layers are connected with the help of via’s. Between two metal layers, there is a material known as dielectric.</li>
 	<li>All the metals as per the technology have to follow certain design rules and the rules are the minimum width of the metal layer and minimum spacing between two metal layers.</li>
</ul>
Based on the above parameters, two RC extraction corners are defined which are called conventional RC corners.
<ul>
 	<li>C<sub>best</sub> (also known as C<sub>min</sub>) - minimizes capacitance, maximizes the resistance</li>
 	<li>C<sub>worst</sub> (also known as C<sub>max</sub>) - maximizes capacitance, minimizes the resistance</li>
</ul>
<em><strong>Also read: <a href="https://www.maven-silicon.com/blog/what-is-skew-in-vlsi/" target="_blank" rel="noopener">What is Skew in VLSI?</a></strong></em>

Cell delay is calculated as the product of RC i.e., (R*C). The connection delay plays a major role in a timing path below the 90nm node. At a timing path’s endpoint, the coupling capacitance component (Cc) in the net delay can alter the slack levels. RC corners have been divided into two types, depending upon the contribution of each component like ground capacitance (Cg) and the coupling capacitance (Cc). Based on this, the foundry came up with two more additional corners on top of conventional corners.
<ul>
 	<li>RC<sub>best</sub> (XTALK corner) - Cc is max and Cg x R is min.</li>
 	<li>RC<sub>worst</sub> (Delay corner) - Cc is min and Cg x R is max.</li>
</ul>
The below figure shows the graphical representation of RC parasitic corners: Parasitic capacitance and parasitic resistance are the values that the foundry will provide in the PDK for the previously mentioned properties, such as Cbest, Cworst, RCbest, and RCworst. These are the maximum and minimum reference values for resistance and capacitance, respectively. These values are not design-specific since they change according to the length of the metal layers.
<h3>1) <strong>C<sub>best</sub>:</strong></h3>
<ul>
 	<li>This corner will have the lowest capacitance and highest resistance and will be also called as <strong>Cmin</strong></li>
 	<li>Results in the shortest delay for paths with short nets, ideal for <strong>min-path analysis</strong>.</li>
</ul>
<h3>2) C<sub>worst</sub>:</h3>
<ul>
 	<li>This is the corner where the capacitance will be high and the interconnect resistance will be lower than the typical corner and this corner will be called as the <strong>Cmax</strong></li>
 	<li>Results in the longest delay for paths with short nets, useful for <strong>max-path analysis</strong>.</li>
</ul>
<h3>3) RC<sub>best</sub>:</h3>
<ul>
 	<li>Refers to corners that minimize the interconnect RC product, also called <strong>RC-min</strong></li>
 	<li>Typically results from smaller etch widths, increasing trace width, which lowers resistance but slightly increases capacitance.</li>
 	<li>Results in the shortest path delay for long interconnects, ideal for <strong>min-path analysis</strong>.</li>
</ul>
<img class="aligncenter wp-image-17239 " src="https://www.maven-silicon.com/blog/wp-content/uploads/2024/10/Image-2.png" alt="Graphical representation of Parasitic corners" width="547" height="346" />

<strong>Example</strong>: Assume a VLSI design with a long connecting wire. The wire is widened in the RC<sub>best</sub> corner to reduce resistance, which allows electrons to pass through more readily and speeds up signal transmission. Because a larger wire can hold more charge, the greater width somewhat increases capacitance; nevertheless, the reduced resistance is more significant and leads to quicker signal timing. This scenario is commonly employed in min-path analysis for calculating the circuit's traversal speed of signals. This corner will be used for performing the timing analysis for the faster signals.
<h3>4) RC<sub>worst</sub>:</h3>
<ul>
 	<li>Refers to corners that maximize the interconnect RC product, also known as <strong>RC-max</strong></li>
 	<li>Typically results from larger etch widths, decreasing trace width, which increases resistance but reduces capacitance.</li>
 	<li>Results in the longest path delay for long interconnects, useful for <strong>max-path analysis</strong>.</li>
</ul>
Consider the same length connecting wire, but narrower at the RC<sub>worst</sub> corner to increase resistance. Higher resistance slows the current and causes the signal to travel more slowly. Although reduced width reduces capacitance (since a thinner wire stores less charge), increased resistance dominates, resulting in delayed signal timing. This is used for maximum-path analysis, determining how long signals can travel across the circuit in the worst-case scenario. RCworst is useful for ensuring that the circuit will match timing requirements even in the most adverse situations, such as in paths with lengthy interconnects or under high-resistance scenarios.
<h3>5) Typical:</h3>
Represents the <strong>nominal values</strong> for interconnect resistance and capacitance.
<h2><strong>Summary of RC Corners in addition to PVT Corners</strong></h2>
As stated in this article, the following RC corners, in addition to the PVT corners, can be used for time analysis.

<img class="aligncenter wp-image-17240 " src="https://www.maven-silicon.com/blog/wp-content/uploads/2024/10/Image-3.png" alt="RC corners &amp; PVT corners" width="590" height="316" />

Harini Vemu

All Posts

VLSI Physical Design at 3nm: Innovations and Challenges

Multi-Patterning and (Optical Proximity Correction) Challenges in Physical Design

Significance of RC Parasitics in Physical Design

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Harini Vemu

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VLSI Physical Design at 3nm: Innovations and Challenges

Multi-Patterning and (Optical Proximity Correction) Challenges in Physical Design

Significance of RC Parasitics in Physical Design

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