Current status of EUV lithography

It is undeniable that extreme ultra-violet lithography has progressed in an extraordinary way in the last 12 months.

Until recently, it was not commonly agreed upon in the lithography industry whether EUV litho would have made it to full production or HVM (high-volume manufacturing) at all.

Naysayers were pointing to the fact that the power of the light source was lagging much behind the level needed for HVM and that the issues in mask defectivity control and in resist development were far from being addressed properly.

Fortunately enough, in the last 12 months huge progress has been made in most if not all areas of EUV litho:

1. Light source development

Most of EUV pundits believe that light source power is the single most important issue for successful EUV lithography development and most resource investment related to EUCV has been focused in achieving a light source powerful enough to sustain high-volume manufacturing requirements.

Only one year ago, TSMC was having problems in breaking the 10W barrier while now the same company made public their results and claimed they were able to achieve an impressive 1000 wafers processed in a single day with a 80W source.

The two major companies behind EUV light source development, Cymer and Gigaphoton, are both claiming to be on track to achieve a 125W power source by the end of this year with a 250W light source on the horizon for next year.

Cymer claims to have a 100W power source running in their labs with 3.5% conversion efficiency and based on a 15KW laser which they hope to be able to upgrade to 5.5% conversion efficiency using a 27KW laser by next year at latest, which would mean 250W of light source power, well enough for high volume manufacturing

Gigaphoton, on the other hand, recently issued a press release announcing to have a light-source running at 142W with 50% duty cycle (=71W at 100% duty cycle), a significant improvement from last December when they claimed to have a 120W working at 50% duty cycle. Gigaphoton made clear that they are now looking for achieving 250W in “burst mode” before being able to expand the source availability.

While neither Gigaphoton nor Cymer have any plans for light sources beyond the 500W mark, Free Electron Lasers are now being considered by other players as a viable route to step into the 500W~10000W range which is what will be needed for high-NA scanner machines.

2. High-NA scanners

Carl Zeiss is currently working on improving the optics quality and based on this, ASML is now hoping to be able to achieve numerical aperture (NA) of 0.5 up from the current mark of 0.33 which would allow to reach a couple of nodes beyond 10nm without the need of multiple patterning using EUV.

3. Resists

Resist development has been an issue mostly disregarded by EUV pundits until recently as all the attention went to what was considered as the major hurdle for full development of EUV litho, that is, the availability of a light source powerful enough for HVM.

Since now the problems with light source development seem to be on track to be solved, attention is back to other aspects of EUV litho development such as resist.

Due to strict requirements it takes quite some time, even 1~3 years at least, to have a resist validated for full production so it has now become imperative to address this issue as well.

Much of the recent work is now behind negative-tone CAR resists, while Intel is working with resist makers on HfO2-based resists trying to improve their shelf-life from the current range of few weeks to a few months or more.

The advantage of metal oxide-based resists is that they have high absorption properties and therefore they can allow the use of light sources with lower power.

Other areas of development where control in EUV mask defectivity, with Hoya showing promising results in reducing the mask blank defects, and mask defect inspection, with Carl Zeiss announcing their upcoming tool specifically targeted at EUV mask inspection by the end of this year .

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