Schott Claims Progress in LuAG Absorption for High-Index Lithography

Staff -- Semiconductor International, 2/22/2008

Schott Lithotec (Jena, Germany) today announced it has made “significant progress” toward meeting its absorption targets for lutetium aluminum garnet (LuAG), moving from a development factor of 22 last October to a factor of 10 from the final target of 0.005 cm^-1.

With improved transmission of the 193 nm light and progress with the supply of high-purity materials needed to make the high-index lens elements, Schott executives said they are confident that high-index lithography can meet its targets.

At an October 2007 Sematech-organized immersion lithography conference in Keystone, Colo., Schott technologists made headlines by saying they were behind schedule with the key LuAG program. To make high-index lithography feasible, a high-index fluid is required, as well as a bottom lens element with a refractive index of >1.8.

Schott Lithotec said it has improved the absorption properties of LuAG, a crystalline lens material required for high-index immersion lithography.

Together, the materials could improve the numerical index (NA) of the optics and intersect the semiconductor industry’s needs for 2009, when leading-edge companies are expected to be in development of the 22 nm half-pitch technology. High-index lithography also could be used for the 32 nm node, obviating the need for expensive double patterning.

Lutz Parthier, head of development at Schott Lithotec, said that when the LuAG development program started in 2006, Schott’s researchers realized that the challenges would involve raw material purity and transmission properties, among others. “We now feel confident that we will be able to overcome these technical challenges and deliver to the lithography industry the material they need to bring semiconductor production to a new stage,” he said.

Schott also reported progress in other areas of its LuAG program, including guarantees from suppliers that they will be able to deliver commercial quantities of purified lutetium oxide (Lu₂O₃), one of the key raw materials needed to make LuAG.

For the other essential material, purified aluminum oxide (Al₂O₃), Schott said they have established development targets with its suppliers.

The company has also “demonstrated successful reproduction of its LuAG crystal growth processes. This indicates that Schott Lithotec will be able to commercially produce LuAG with the needed absorption values.”

At the Keystone Immersion Symposium, Schott presented its success in growing a 280 × 80 mm boule of LuAG with a flat interface. The recent progress “moves Schott Lithotec one step closer to meeting its goal of commercially producing 160 mm diameter LuAG for the lithography industry by the fourth quarter of 2009,” the company said.

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