Dow Corning taking collaborative route to photoresist goals

by James Montgomery, News Editor, Solid State Technology

Feb. 25, 2008 – Dow Corning exec Jeff Bremmer talks with WaferNEWS about how his company has turned to a new business model, development partnerships with litho materials suppliers, for its push into the world of photoresist resins.

Last week Dow Corning said it has more than doubled production capacity for silicon polymer resin used in a bilayer photoresist developed with TOK in late 2006, that uses a silicon polymer in the imaging layer to improve etch selectivity and eliminate the need for a separate hardmask layer, targeting 193nm immersion lithography processes. (As of last Dec. they said the technology is being used in production by a leading unidentified memory chipmaker.)

The silicon resin, when combined with photosensitive materials, enables use of thinner photoresist layers, which in turn improves pattern resolution, and thus enables smaller circuit patterns, explained Jeff Bremmer, global market manager with Dow Corning’s silicon lithography solutions business, in an interview with WaferNEWS. “The silicon resin etches at a different rate than organic photoresists,” so a thinner film can be laid down and still survive the etch process, he said. “You don’t need as thick a layer to transfer the pattern to the underlying layer.” Going with thinner layers allows for better imaging, better pattern transfer, finer features, “and in many cases a better process window and process latitude,” he added. “That’s what end user device manufacturers are trying to get to.”
Bremmer noted that one well-known problem with thick photoresist layers is tall features that tend to collapse, a problem alleviated by a thinner resist. “At 65nm it’s becoming an issue, and certainly beyond 65nm,” he said, so the company is targeting “65nm and below” as an entry point for its silicon resins, first targeting the memory sector. He added that the company is actively developing silicon resin for trilayer antireflective coating (ARC) as well, working with “several leading lithography materials suppliers” targeting the 65nm-45nm window.

Before 2004, Dow Corning had no photoresist market position, but felt its skills in supplying interconnect and spin-on dielectrics were applicable to supplying resins for lithography applications, according to Bremmer. But the company also came to recognize the difficulty in doing a lot of the application development on its own (including the huge investment in leading-edge lithography tools), and that customizing the photoresist materials would be best approached by a change in business model — to collaborative development partnerships with lithography materials suppliers. “It’s not just simply, purchase the silicon resin and make it work,” he told , noting that it “requires a lot of optimization” to zero in on the best-performance resin. Going the route of development partnerships with the litho materials suppliers helps Dow “improve our probability of success, and lower our risk of participating in this market.”

Such customization requirements that dictate the choice of bi- or trilayer resist also play out within Dow’s work with individual lithography materials suppliers (e.g., TOK, Rohm & Haas). “They understand what end-users need for performance,” Bremmer noted, and “we offer customization to get that performance with each partner.” Dow’s resins become part of those firms’ photoresist schemes, formulated with additional additives (e.g. photoacid generators), which are then sold to the end-user (e.g. memory manufacturer), he explained.

And the development partnerships will help expand Dow Corning’s target markets beyond memory into logic as well, Bremmer noted. “We learn more every day with our collaboration with partners,” he said. “My understanding is at this point, a lot of ARC or photoresists can be transferred to logic as well.” — J.M.

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