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ASML readies EUVL demo tools

IMEC has much to show for its efforts over the past two decades. At its founding in 1984, the Belgian research institute received the bulk of its funding from the government of Flanders, had one associated lab (at Ghent University), and submitted its first patent application. Today, it receives more than 80% of its funding from private sources, maintains relations with universities all over Europe, and holds approximately 50 patents. Twenty years ago, IMEC's staff numbered 70 people; today, nearly 1400 people are on the payroll.

How will the semiconductor industry tackle the difficult lithography challenges looming on the post-45-nm horizon? As part of IMEC's Annual Research Review Meeting in mid-October, ASML execs offered their views on the lithography roadmap and extreme UV lithography (EUVL) during meetings at the company's facility in Veldhoven, The Netherlands.

Making the case for EUVL to fabricate 32-nm and smaller half-pitch device features, ASML executive vice president Martin van den Brink argued that alternatives to EUVL would require the development of new glass materials and liquids, which, in his words, would take a "miracle." Furthermore, new liquid and glass materials would lower the k1 value, decreasing resolution. In air-based lithography systems, the highest numerical aperture (NA) that can be attained is 0.93, which would only support device nodes down to the 60––65-nm range. A hyper-NA immersion system with an NA of 1.20 would support the 45-nm node, van den Brink added.

Since manufacturing 32-nm devices using 193-nm immersion lithography would entail costly double patterning and pose significant technical difficulties (e.g., the need to develop new liquids), ASML, together with IMEC, is developing EUVL. The new lithography's most unique feature, stated Noreen Harned (ASML's vp of marketing, technology, and new business), is its vacuum environment. That environment enables the use of either a laser-produced plasma source or an electrical discharge source that, when subjected to a high-voltage charge or high-energy photons, produces light with a very short wavelength of 13.5 nm, approximately 14 times shorter than that used in 193-nm lithography. ASML's two alpha demo tools, which will be shipped in 2Q06 to IMEC in Leuven, Belgium, and the Albany NanoTech center in Albany, NY, will use an electrical discharge source based on tin. Using EUVL, lithographers hope to achieve the 32-nm node with an NA of 0.25 and a k1 value of 0.59.

While progress has been made in tin source development, optics fabrication, and reticle handling, the development and implementation of EUVL faces several other challenges. In the area of radiation generation, issues remain with collectible in-band EUV power, the lifetime of discharge-source electrodes, and the lifetime of the collecting optics. In the EUVL mask area, mask-blank defects generated during deposition must be decreased. The current level of one defect per mask measured at 80-nm resolution must be reduced to zero defects measured at 25-nm resolution by 2009 (see "Sematech North Advances EUV Technology by Reducing Defects in Mask Blanks," Finally, in the photoresist area, resists with <30-nm resolution have been demonstrated, but meeting line-edge-roughness, resolution, and sensitivity requirements simultaneously remains problematic.

In short, Harned noted, "EUVL is still in early development and will require a major effort to be available in time for pilot production tool use in 2009 for the 32-nm technology node."—BM

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