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Source mask optimisation ignites debate

Posted: 03 Mar 2009     Print Version  Bookmark and Share

Keywords:source mask optimisation  lithography  22nm  SMO 

The SPIE Advanced Lithography conference witnessed a sort of war of words between vendors developing source mask optimisation (SMO) tools with the goal of extending 193nm immersion lithography to the 22nm node.

Lithographers have for years used various schemes and computational techniques to optimise the illumination source. Likewise, they have long been optimising the photomask through tricks like reticle enhancement techniques (RETs) and phase-shift approaches. SMO tools are being offered and developed which promise to optimise the source and mask in tandem in order to maximise image contrast in a scanner.

But some say the term is being used for marketing purposes by a number of companies hawking fundamentally different technologies. They liken the situation to that which occurred with DFM, a well-worn acronym that came to be used to promote any technology remotely aimed at design-for-manufacturing.

"DFM is a great analogy" for what is happening with SMO, said Timothy Farrell, a distinguished engineer in computational technology with IBM's systems and technology group.

A number of companies are either developing or offering for sale SMO tools, including IBM, Brion Technologies, Luminescent Technologies Inc., Nikon Corp. and Cadence Design Systems Inc.

But Farrell and an executive from Mentor Graphics Corp., which is working with IBM on SMO for computational scaling, say the work being done by other firms does not truly optimise the mask, instead focusing on optimisation of the illumination source for use with a reticle incorporating standard optical proximity correction (OPC).

"Source optimisation capability has been around a long time," said Charlie Albertalli, a marketing director at Mentor. "We are seeing people use the terminology source-mask optimisation when what they are really doing is source optimisation."

Brion, which is owned by Dutch lithography vendor ASML Holding NV, rolled out this week a new product, Tachyon SMO, which promises to enable full co-optimisation of source and mask. According to the company, the product leverages proprietary illumination capabilities and scanner models from ASML to optimise the source simultaneously with all patterns on the mask.

Executives from Brion acknowledge that the prior generation of Tachyon focused on source illumination and the use of model-based OPC, but say the new product emphasises co-optimisation and that there technology is not dissimilar to the work being done by IBM and its ecosystem partners, including Mentor and photomask maker Toppan Printing.

Moris Kori, president and CEO of Luminescent, said via email that the statements made by Farrell and Albertalli did not accurately characterise his company's technology.

Kori said Luminescent's inverse lithography technology offers the ability to optimise mask patterns in conjunction with illumination patterns, resulting in a free-form, composite or parameterised geometry for the source along with a simultaneously optimised mask pattern including elaborate assist features integrated with main feature corrections.

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