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Tool limits need for immersion lithography at 45nm

Posted: 20 Sep 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Invarium? Dimension45/32? DimensionPPC? patterning-synthesis software? immersion lithography?

Faced with few other viable choices, many leading-edge chipmakers are reluctantly migrating to immersion lithography for the 45nm node. While immersion will enable them to print the new feature sizes, it is not without its drawbacks, starting with the price tag: An immersion lithography tool is said to cost as much as $40 million.

Enter design-for-manufacturability startup Invarium Inc. The company will roll out new patterning-synthesis software this week, promising, among other things, to limit the number of advanced layers that will require immersion at 45nm. That would allow customers to get more mileage out of existing lithography equipment.

Executives from Invarium do not claim that the tool, Dimension45/32, will eliminate the need for immersion lithography systems. According to Franz Zach, Invarium's VP of applications, the four or five most critical front-end layers in 45nm designs!including diffusion, gate poly and contact layers!are likely to be done on immersion systems at most companies. But, Zach said, there are five or six metal routing layers that can go either way!be patterned using immersion lithography systems or conventional dry tools.

"That's why we thought this was a real opportunity to help with a solution," said Roy Prasad, Invarium's president and CEO. "Immersion is coming. It is an expensive option. There are still some questions about the technology with regard to defects. And there may be a limited number of tools available."

Address patterning challenges
Dimension45/32 is geared to specifically address patterning challenges at the 45- and 32nm nodes, according to Invarium. The tool is designed to help lithography and photomask synthesis teams select and optimize the right combination of exposure strategies and full-chip photomask layout synthesis, along with retargeting if necessary, to achieve desired post-etch results on silicon. According to Invarium, with the right combination of resolution-enhancement technology (RET) features, illumination and polarization techniques, Dimension45/32 can use a dry litho process to deliver a large process window and sufficient stability against process variations for all critical routing layers.

Dimension45/32 embodies the full capabilities of DimensionPPC, Invarium's flagship optical proximity correction (OPC) and RET implementation tool, introduced in February, along with several additional capabilities specifically geared to the 45- and 32nm nodes. They include process setup optimization, printability analysis, dynamic retargeting, enhanced etch models, enhanced process window optimization, model-based subresolution-assist feature synthesis and yield-based optimization, the company said.

Other capabilities of Dimension45/32 include stability/sensitivity analysis, dose-latitude and focus-latitude maximization, mask effects compensation and patterning of critical routing layers.

'Hot spot' analysis
According to the company, the tool's layout-printability analyzer differs from most available "hot spot" analysis programs in at least one respect!no RET/OPC is performed on the layout. Instead, the layout is analyzed for printability at a very fundamental level, Prasad said. "As soon as layout is done, before RET/OPC, you want to know at a fundamental level, 'What is the printability of this layout?'" he said, adding that many patterns will not print accurately even though they have passed a design rule check.

Dimension45/32 implements assist and "clear assist" features that are derived rigorously, instead of rule-based placement, according to the company. The tool's dose-latitude maximization feature optimizes layout to enable the pattern to hold together better under varying conditions. And the dynamic auto-retargeting feature retargets features during lithography correction to improve yield, the company said.

Prasad acknowledged that it is still too early to target in earnest the 32nm node. "It's really a solution for the 45nm node, with the capability to allow us to make future capabilities available for the 32nm node," he said.

Customized services
In addition to offering the new tool, Invarium has also modified its business model around it. The company is now offering services!the Invarium team works with a customer team to develop an optimal patterning-synthesis solution and lithography setup for a given ground rule "with a wide range of flexible deployment options," Prasad said. This service, he added, can be customized based on customer preferences all the way up to a "completely outsourced" patterning service, not unlike a photomask shop.

Invarium said it is currently qualifying Dimension45/32 for customers in North America. A second customer qualification program is scheduled to commence soon in Asia, the company said. Pricing information was not disclosed. Invarium, founded in 2003, maintained a low profile until bursting on the scene with DimensionPPC in February.

- Dylan McGrath
EE Times

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