What is source-mask optimization?

SANTA CLARA, Calif. — A war of words of sorts emerged this week at the SPIE Advanced Lithography conference among vendors developing source mask optimization (SMO) tools in hopes of extending 193-nm immersion lithography to the 22-nm node.

Lithographers have for years used various schemes and computational techniques to optimize the illumination source. Likewise, they have long been optimizing the photomask through tricks like reticle enhancement techniques (RETs) and phase-shift approaches. SMO tools are being offered and developed which promise to optimize the source and mask in tandem in order to maximize 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 optimize the mask, instead focusing on optimization of the illumination source for use with a reticle incorporating standard optical proximity correction (OPC).

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