Startup targets mask-making with "patterning synthesis"
By Michael Santarini, Senior Editor -- EDN, February 8, 2006
A new DFM (design for manufacturability) startup called Invarium believes it has one-upped the current generation of RET (reticle enhancement technology) and OPC (optical proximity correction) tools with what it calls "patterning-synthesis" technology.
The company's CEO, industry veteran and former P-CAD co-founder Roy Prasad, said that most RET and OPC tools today perform what is referred to as mask synthesis. Mask-synthesis tools employ a top-down approach, forcing a given layout onto a patterning process and requiring users to tweak OPC models and their layout until their designs print properly in silicon, he said.
Invarium's tool, DimensionPPC (process and proximity correction), employs a bottom-up approach and uses patterning data to ensure the layout will print properly the first time, he said.
"Mask synthesis is still in the domain of making adjustments to a layout, as opposed to synthesizing the mask as a separate entity unto itself," Prasad said. "What we do is patterning synthesis—everything that can and should be done to squeeze out the best patterning results from a fab process, to the extent that it is controllable from a mask level. It's a broader charter than mask synthesis."
The company borrowed the PPC at the end of the product's name from a Toshiba and Samsung technical paper, Prasad said. The abbreviation describes all the things in addition to OPC that need to be accounted for to ensure pattern fidelity when the design is printed in manufacturing.
DimensionPPC includes two technologies: PPC models and a synthesis engine. Invarium has been working with IDM (integrated device manufacturer) customers and more recently foundry customers to characterize their manufacturing flows, Prasad said. The company uses this to create what it calls PPC models, which are essentially physics-based models of the entire patterning process.
Inaccurate process models have become a major cause of respins, Prasad said. "You are not going to achieve without biting the bullet and diagnosing the actual patterning process bottoms up," he said. "We have a proprietary set of experiments and exposure techniques that are designed to separate every process effect that has any kind of impact on process fidelity. We put each of those effects in separate bins without any cross contamination and quantify the things to understand behavior."
In characterizing a process for its PPC models, the company examines mask, photo, optical, resist, etch, and metrology bias, as well as cross-mask effects and wafer-to-wafer variation, he said.
Unlike traditional RET/OPC models, which are typically based on worst-case lumped sum conditions, PPC models are modular, with each module containing data on a specific process effect.
"[The tool] is aware of process window by design—everything that happens in the patterning process by design," Prasad said. "Also, it isn't layout dependant, tuned to specific layout patterns that people typically do today. The tool is somewhat layout agnostic."
The DimensionPPC synthesis engine analyzes the process effects in the PPC model and adds some degree of tolerance to account for random and statistical effects. From these data, the tool then derives its own RET structure and polygons for a design pattern.
The process is totally automated, Prasad said. Users feed the tool GDSII and a layout. The tool generates a new GDSII with patterns targeted to a specific process. "Nobody needs to go through iterations, set parameters, or define rules," Prasad said. "There is no need for an OPC verification step at the end of the process. At the end of it we produce a very manufacturable mask."
DimensionPPC targets the 65-nm and upcoming 45-nm process nodes, Prasad said.
Invarium is based in San Jose and has 25 employees, many of whom have industry backgrounds in either EDA or semiconductor manufacturing. On the executive team with Prasad are CTO Apo Sezginer, formerly with Sensys and Schlumberger, and vice president of engineering Chi-Song Horng, former co-founder of P-CAD, i-Cube, and Si-ID. Invarium's senior vice president of marketing and sales is Ram Ramanujam, a former executive with Sensys and Applied Materials. The company's director of applications engineering is Franz Zach, who has held technical positions at KLA Instruments (now KLA-Tencor) and the Lawrence Berkeley Labs.
Invarium expects DimensionPPC to start at around $200,000.
