KLA-Tencor, Nikon collab to corral “mix-and-match” litho setups

December 10, 2007 – KLA-Tencor and Nikon say they have developed a set of fully automated system tools for correcting overlay errors in “mix and match” lithography setups that encompass tools of varying capabilities and from different suppliers.

Most chipmakers using leading-edge (and expensive) lithography equipment only for the most critical levels, and less advanced equipment in other steps. Each of these tools, though, has a different field distortion signature that can cause significant overlay error at 45nm and below process technologies, the companies explain. The codeveloped technology, dubbed “scanner match maker” (SMM), lets users more tightly control different illumination conditions and combinations of these multiple scanner setups — e.g. immersion and dry tools, and/or leading-edge and more mature equipment.

“Today, chipmakers’ overlay budget has almost no margin of error with regard to scanner alignment performance. Mix and match methods can cause scanner fleet alignment performance to be less than half that of dedicated, single-tool overlay operations, and mixing scanners from different suppliers make these errors are even more significant,” said Toshikazu Umatate, GM of development headquarters at Nikon Precision Co., in a statement. “Our SMM toolset is intended to help customers implement sophisticated correction procedures that can overcome inherent overlay errors caused by differences in tool distortion signatures, making it much easier to match a fleet of lithography tools.”

The SMM overlay technology works thusly, according to the companies:

– A reference wafer is exposed by a common planned-maintenance (PM) reticle, measured (by KLA-Tencor’s Archer overlay metrology tool) and analyzed (by the KT Analyzer). Baseline distortion signature data is collected; overlay data is sent to a database server. Meanwhile, the litho scanner sends exposure condition data associated with the overlay metrology data, including machine name and illumination condition. A SMM mix-and-match database is created automatically, with strict user approval and security.

– Incoming production lots to the scanner receive current and previous processing layer information from the SMM database, with distortion and grid signatures from both layers. (Though scanners can adjust stage grid and field distortion for matching based on PM procedures, the current layer usually has a different signature from the previous one.)

– The scanner adjusts the distortion and grid signature using the SMM technology, with Nikon’s “super distortion matching” (which controls field distortion on a scanner’s current layer) and “grid compensation matching” (which controls the stage grid of a current layer) functions to match the target layer’s signatures.

Because the companies eventually plan to connect SMM with scanners from other suppliers, it includes “a built-in security system” to protect the scanner’s proprietary information, stated Ofer Greenberger, VP and GM of KLA-Tencor’s overlay metrology group.

The companies say the SMM technology is currently being evaluated by a “major” Japanese semiconductor manufacturer, where it has demonstrated >30% improvement in overlay performance; automating the procedure also increases accuracy and saves time, they note. The SMM toolset is slated for release in 1Q08.


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