DFM tools help with "lithography-friendly" layouts
By Michael Santarini, Senior Editor -- EDN, May 11, 2006
Mentor Graphics claims that its latest DFM (design-for-manufacturing) offering will help IC designers make "lithography-friendly" IC layouts. The company's new Calibre LFD (lithography-friendly design) is similar to a DRC/LVS (design-rule-checking/low-voltage-signaling) tool. However, rather than check whether a layout conforms to design rules, such as trace widths and spacing, and early schematics, Calibre LFD checks whether a layout conforms to manufacturing-lithography rules that outline the dose and focus of a given manufacturing line. The tool incorporates the same engine as OPCVerify, a similar OPC (optical-proximity-correction) technology that Mentor introduced in January that targets lithography designers.
"Calibre LFD aims to capture process variation to improve design robustness," says Jean-Marie Brunet, product-development manager for LFD products at Mentor. The company has devised the Calibre LFD kit, an encrypted format that allows fab facilities to pass lithography information to layout engineers who are using Calibre LFD. The kit includes manufacturer-defined recipe information and process models with optical processes, resist masks, and, in some cases, etch profiles. After loading the kit into Calibre LFD, layout engineers feed the tool their design layouts. The tool then outputs a set of DRC-like markers, flagging rule violations, which users then have to fix with a separate layout tool. The tool reports different types of error from those that DRC tools do.
The tool also produces a DVI (design-variability index), which helps users identify topologies that are sensitive to variability. The DVI also ranks topology problems to help users make trade-offs when they adjust their layouts or even tweak design rules. A layout modification may have a positive impact on timing and yield, but it can create a problem for power. "For layout engineers to make an optimization, they need to have a reference point ... the ability to compare two layouts without requiring an in-depth understanding of lithography problems," says Brunet. Therefore, the tool assigns a DVI value to a given layout or even a piece of IP (intellectual property), and, the lower the DVI, the less susceptible the design is to variation across parameters.
Future releases of the tool will likely include features for fixing layouts. Mentor will maintain and update fab- and process-specific Calibre LFD kits as manufacturing processes at participating fabs evolve. The price for the tool starts at $246,000 for a one-year subscription.
