Contamination control and the next node


By Hank Hogan

Smaller than today’s 65-nanometer state-of-the-art manufacturing, the 45 nm semiconductor processing node looms just a few years ahead. And, when it comes to manufacturing tomorrow’s chips, more than cleanrooms must be ready. Several announcements from July’s SEMICON West trade show illustrate the industry’s response to this challenge and its contamination control requirements.

Laser maker Cymer Inc. (San Diego, Calif.) unveiled its XLR 500i at the show, touting the argon fluoride (ArF) 193 nm wavelength laser as the light source for next-node photolithography. In an announcement, Cymer pointed to laser module modifications that resulted in a 50 percent improvement in energy stability performance and a 20 percent reduction in the cost of ownership for the new product as compared to previous ones.

The Starlith® 1900i system from Carl Zeiss SMT boasts a numerical aperture of 1.35, reportedly the highest NA available on the market. It will be part of ASML’s new TWINSCANTM XT:1900i, which will be shipped mid-2007. Photo courtesy of Carl Zeiss SMT.
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Behind the scenes were other changes. “We have made continuous improvements in a number of contamination technologies,” says Nigel Farrar, Cymer’s vice president of technical marketing.

Farrar notes that, at 193 nm, light can cause surface damage, as well as surface deposits. To minimize both problems, Cymer uses an approved list of low-contamination materials in the product, purges the beam lines and optics with high-purity nitrogen, and filters the purge gas for hydrocarbons. By design, the device filters the chamber gas to minimize particulate contamination and, during operation, Cymer periodically replaces the chamber gas.

In another announcement, Carl Zeiss SMT (Oberkochen, Germany) revealed its Starlith 1900i (see photo). A second generation of the lens system at the heart of immersion steppers, the product reportedly has the highest possible practical numerical aperture, 1.35. The lens is thus capable of imaging 40 nm features. The manufacture of the 1900i requires control of the surface of single lens elements at the scale of a few atoms, notes Wolfgang Rupp, lithography optics division vice president of systems at Carl Zeiss SMT.

Achieving the necessary level of contamination control is accomplished with a number of strategies. These include purging of the assembled lens with an inert gas, as well as manufacturing in cleanrooms with bunny-suit-clad employees. “Additionally, we precisely control the environment, macro- and microenvironments, and temperature during assembly and adjustment of the lenses,” says Rupp.

Finally, filter maker Pall Corp. (East Hills, N.Y.) announced a number of new products designed to help clean up photoresist and other manufacturing chemicals. These new offerings include filters with variable pore sizes, a design that reduces the pressure drop across the material. The company also introduced its tightest filter ever, one with a 10-nanometer rating for use with 193 nm photoresists. Tony Shucosky, vice president of marketing for Pall Microelectronics’ global chemical products, notes that the semiconductor technology roadmap lists the critical particle size as about half the technology node. So for the 45 nm node, that would put the critical size at 22 nm.

Shucosky points out that attention to contamination control during assembly is critical, and that this need extends to the component materials and the final packaging. In the case of Pall’s products, assembly takes place in cleanrooms and often includes post-assembly cleaning. “These steps include flushing with ultrapure water and may also include chemical washing with acid or other proprietary chemical treatments,” he says.

These methods put the total ion metal extractables near one part per billion in a typical 10-inch filter, according to Shucosky. Such cleanliness is essential, he says, given that his company’s semiconductor customers are now measuring contamination as the number of atoms per square centimeter.