Litho vendors flirt with double patterning, but no date yet

by M. David Levenson, Editor-in-Chief, Microlithography World

Although double patterning (DPT) was the talk of the litho panels during SEMICON West, none of the scanner makers offered fully-fledged tools, which would have extraordinary overlay capability and throughput sufficient to be profitable.

The ASML Twinscan XT:1950i came closest — but it was advertised as the “ultimate” single-patterning tool. Still, the 3.5nm single-tool overlay spec (4nm without dedicated chucks) comes close to what is needed to begin 32nm DPT production. In a single exposure, resolution was reported as 38nm half-pitch by Jan Smits, SVP of ASML’s Twinscan unit. Getting that resolution and overlay required implementing two distortable lens elements to control aberrations, elements which can be retrofitted to existing 1900 and 1700 series tools, according to Smits. With a 30mJ/cm2 resist and 125 shots/wafer, the 1950i’s throughput was 148 wafers/hour (WPH), implying about 70WPH in a DPT mode. Other improvements included the iClean option, a flush sequence during idle time, and a liquid particle counter to warn when contamination is about to occur. Smits indicated that ASML was now shipping one Twinscan a week, but the 1950i would not be shipped until 1Q09.

Canon’s long awaited response to the XT:1900i, the FPA-7000AS7, was also in evidence, but seemed more like last year’s tool with a ≤6nm overlay and ≤45nm nominal resolution. Still, the throughput was claimed to be 133 WPH, and upgrades are coming for the DPT era, according to Phil Ware, senior fellow, strategic lithography. The system features a continuous flow immersion nozzle (like Nikon but unlike ASML) coupled with twin wafer stages and an NA=1.35 lens.

Not in evidence was Nikon’s DPT tool, rumored to be titled the NSR-620C. It is expected to be an extension of the current NSR-610D system with better overlay and throughput, possibly linked to a recently delivered 90W laser source. Nikon’s reticent corporate culture, however, releases new tool information only when deliveries are imminent. — M.D.L.

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