Virtuosity: Are Your Layout Design Mansions Correct-by-Construction?

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Imagine your dream mansion that was constructed last year starts to show up flaws in just a year of being constructed. This annoys you a lot and you call up your architect, John. John comes over next morning to inspect your mansion, and guess what he has to say? The contractor did not take care of the details during construction and John suggests a renovation. This annoys you all the more.

Similar to your mansion, for a layout engineer, a design is no less than a mansion. It's best to be correct-by-construction in the first place. Especially, in advanced node designs that have quite complex design rules, focusing on the width-dependent spacing is very important. Layout engineers may be presented with hundreds of lines of DRC rules for a single layer to find a legal spacing configuration. To increase the productivity and to reduce the difficulty of layout engineer’s day-to-day job, it is beneficial to predetermine the sets of specific width and spacing values that are DRC clean when routed. This is the methodology for ensuring that designs are correct-by-construction. 

Are you still using a workflow where you draw routing, check it, and then clean up the DRC violations? This is definitely not as efficient because changing the width of a shape or changing its space relative to its neighboring shapes can cause a ripple effect of creating more DRC violations that need to be cleaned. In this scenario, finding a legal set of width and spacing values afterwards can be a very challenging task.

Introducing Width Spacing Patterns (WSPs)

You might already be aware, but if not, we wanted to share with you a more efficient way to work in this scenario. You can use WSPs, which are track lines that provide guidance for quickly creating wires. Defining WSPs that capture the width-dependent spacing rules and snapping the pathSegs of a wire to them, ensures that the wires meet the width-dependent spacing rules. In contrast to the previous implementation of tracks which used a uniform space, you can use WSPs to easily define variable width and spacing tracks.

When pathSegs are drawn, they snap to the WSP track location and inherit the specified width. You can also use WSP tracks to assign color to those pathSegs. WSPs are paired with Width Spacing Snap Pattern Defs (WSSPDefs) that are a container that associate the WSP width and space values with specific layers and directions. You can define WSPs and WSSPDefs in the technology file, or attach them to the design. 

Related Resources

User Guide

Virtuoso Width Spacing Patterns User Guide

Using the WSP Manager

Working with the Track Pattern Assistant

Rapid Adoption Kits 

WSP Manager Workshop

Color Aware Design and Width Spacing Patterns

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Happy Reading!

Andrew Young and Komal Johar