By Caroline Hayes, Senior Editor
The industry prepares to embrace the all-encompassing FinFET validation model – a view from the supply chain.
TSMC’s 16nm FinFET reference flow has made headlines recently, and EDA and IP companies are responding with supporting products. It is not a simple support role, however, it demands a rigorous, all-encompassing model.
In response, Apache Design has announced that its RedHawk and Totem have completed methodology innovations for the thee-dimensional transistor architecture and TSMC has certified Mentor’s Olympus-SoC place and route system and its Calibre physical verification platform.
The first reaction has to be one of surprise as the excessive interest in FinFET. Apache Design’s vice president product engineering & customer support, Aveek Sarkar, provides the answer: “[FinFET] can manage voltage closely and lower the supply voltage considerably,” he told System Level Design. “Power is a quadratic formula, so to lower voltage from 1V to 0.7V reduces the dynamic power by 50%,” he adds, explaining the appeal of FinFET.
System Level Design asked if lower supply voltages can outweighed the obstacles FinFET poses to EDA? It has a more complex structure, with more restrictive design rules than planar structures and poses challenges in extraction. It seems these have not proved to be deterrents, judging by the industry’s activity.
For example, TSMC has given certification to the Mentor Olympus-SoC place and route system, and its Calibre physical verification platform. Avrind Narayanan, product marketing manager Place & Route division, Mentor Graphics, explains that the Olympus-SoC for 16nm FinFET enables efficient double patterning (DP) and timing closure. “It also has comprehensive support for new design rule checks and multi-patterning rules, fin grid alignment for standard cells and macros during placement, and Vt min-area rule and implant layer support during placement,” he adds.
Explaining the Calibre product, Michael Buehler-Garcia, senior director, marketing, Calibre Design Solutions, Mentor Graphics, tells System Level Design that it supports 16nm FinFET advanced design rule definition and litho hotspot pre-filtering. The Calibre SmartFill facility has been enhanced to support the TSMC-specified filling requirements for FinFET transistors, including support for density constraints and multilayer structures needed for FinFET layers.
Significantly, SmartFill also provides double patterning support for back end layers and, says Buehler-Garcia, “goes beyond simple polygons to automatically insert fill cells into a layout based on analysis of the design”.
He continues to point out the new challenges of 16nm FinFET designs. “[They] require careful checking for layout features that cannot be implemented with current lithography systems—so-called litho hotspots. They also require much more complex and accurate fill structures to help ensure planarity and to also help deal with issues in etch, lithography, stress and rapid thermal annealing (RTA) processes”. The value of place and route layout tools will be in implementing fin grid alignment for standard cells and macros during placement, he notes, as well as in Vt min-area rules and implant layer support during placement.
Apache has enhanced its PathFinder, which verifies ESD (electrostatic discharge) at the SoC level for the technology. Since FinFET lacks snapback protection, diodes have to be used, to protect against ESD. However, using diodes brings the drawback of degraded performance due to a higher current density. FinFET means that instead of one supply domain, there are now hundreds of voltage islands across the chip, says Sarkar, explaining Apache’s approach. These islands have to be protected individually, and the designer needs to be able to predict what problems will happen on each of the islands, which means that layout-based SoC sign-off is critical, he concludes. “It is no longer a visual check, but electrical analysis,” he says.
TSMC and Mentor Graphics introduced a fill ECO (Engineering Change Order) flow as part of the N16 reference flow. This enables incremental fill changes, which reduce run time and file size while supporting last minute engineering changes. “By preserving the vast majority of the fill, the ECO flow limits the timing impact of fill to the area around the ECO changes,” says Buehler-Garcia.
Sarkar agrees that FinFET requires more attention to fill and its impact on capacity, and the time needed for design and verification. The company works with the foundry for certification to ensure that the tool is ready in terms of capacity, performance and turnaround time. However, he warns that accuracy for the full chip is only possible by simulating the whole chip in the domain analysis. This means examining how much change is needed, and where the voltage is coming from. “Every piece has to be simulated accurately,” he says, predicting more co-design with different aspects will need to be brought into the design flow. Expanding on the theme, he says that one environment may focus on the package and the chip simultaneously, while another environment may include the package, the chip and the system. “There will be less individual silo-based analysis and more simulations that looks across multiple domains.”
For Buehler-Garcia, the main difference for 16nm FinFET was that new structures brought a new set of requirements that had to be developed and carefully verified throughout the certification process. He describes the collaboration between the foundry and the company as “an evolutionary step, not revolutionary”.
In the next Deeper Dive (December 5) System Level Design will look at the role of double patterning in FinFET processes and how different EDA tools address its IP validation.