Lighter gas reduces damage to optics in extreme ultraviolet lithography

September 12, 2007

Researchers at the University of Illinois have discovered a way to generate light and reduce damage in a leading candidate for next-generation microelectronics lithography. The technique could help pack more power into smaller computer chips.

In the quest for creating computer chips with ever-smaller feature sizes, chip manufacturers are exploring extreme ultraviolet lithography as the next chip-printing technology. For a light source at the necessary wavelength, scientists have turned to a hot, ionized gas called a plasma, generated within a Z-pinch device. But, energetic ions produced in the plasma can damage the mirror responsible for collecting the light.

“By adding a lighter gas to the plasma, we can significantly reduce the damage and extend the lifetime of the collector optics,” said David Ruzic, a professor of nuclear, plasma and radiological engineering and lead author of a paper that describes the technique in the June issue of the journal IEEE Transactions on Plasma Science.

In a Z-pinch device, xenon is fed into a chamber where it collides with a stream of electrons, producing a low-temperature and low-density plasma. This plasma then flows between two cylindrical electrodes, one positioned inside the other. (The “Z” in Z-pinch refers to the direction of current flow along the cylindrical electrodes.)

Next, a large current pulse heats the plasma, while a magnetic field generated by the pulse compresses and confines the plasma. The plasma becomes hotter and denser until it “pinches,” creating the flash of light needed by the chip industry.

As the pulse passes, internal plasma pressure overcomes magnetic confinement, and the hot, dense plasma flies apart. The resulting fast and energetic ions can damage the delicate collector optics.

However, adding a small amount of a lighter gas, such as hydrogen, “significantly reduces both the number and the energy of xenon ions reaching the collector surface, thereby extending the collector’s lifetime while having a negligible effect on the extreme ultraviolet light production,” Ruzic said. The reduction in xenon energy occurs because the hydrogen ions shield the xenon ions from the high electric field created by the plasma.

“When the plasma flies apart, the less-massive electrons move faster than the hydrogen and xenon ions,” Ruzic said. “The electric field induced by the moving electrons then pulls on the ions and accelerates them. Being much lighter than xenon ions, the hydrogen ions accelerate faster, and shield the xenon ions from some of the electric field.”

By absorbing some of the plasma’s energy, the hydrogen ions prevent the xenon ions from accelerating to the point where they damage the collector surface, thus prolonging the collector’s lifetime.

Xenon is actually the second-best radiator for light at the desired wavelength, Ruzic said. “We can get three times as much light from tin, but tin is a condensable metal and makes quite a mess on the mirrors. We are now looking at ways to clean the mirrors during chip production.”

Source: University of Illinois at Urbana-Champaign

Explore further: Electrons in concert: A simple probe for collective motion in ultracold plasmas

Related Stories

The revolutionary ion engine that took spacecraft to Ceres

March 9, 2015

The NASA spacecraft Dawn has spent more than seven years travelling across the Solar System to intercept the asteroid Vesta and the dwarf planet Ceres. Now in orbit around Ceres, the probe has returned the first images and ...

Diagnostics for super-hot plasmas in fusion reactors

January 30, 2017

In the sun and other fusion plasmas, atoms of hydrogen and its isotopes are the fuel. Plasmas are gases that are so hot that electrons are knocked free of the atom, making the atoms electrically charged ions. The un-ionized ...

Freedom of electrons is short-lived

June 27, 2014

During the interaction of an intense extreme-ultraviolet (XUV) laser pulse with a cluster, many ions and free electrons are created, leading to the formation of a nanoscale plasma. In experiments using XUV/X-ray free electron ...

Recommended for you

ATLAS observes direct evidence of light-by-light scattering

August 15, 2017

Physicists from the ATLAS experiment at CERN have found the first direct evidence of high energy light-by-light scattering, a very rare process in which two photons – particles of light – interact and change direction. ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.