Lighter gas reduces damage to optics in extreme ultraviolet lithography

Sep 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: Tiny particles have big potential in debate over nuclear proliferation

add to favorites email to friend print save as pdf

Related Stories

Freedom of electrons is short-lived

Jun 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 ...

Chemists make first molecular binding measurement of radon

Jul 30, 2011

Even in trace quantities, the radioactive gas radon is very dangerous; it is second only to cigarette smoking as a cause of lung cancer deaths in the United States. The expense and precautions necessary to study it safely ...

Recommended for you

New method for non-invasive prostate cancer screening

7 hours ago

Cancer screening is a critical approach for preventing cancer deaths because cases caught early are often more treatable. But while there are already existing ways to screen for different types of cancer, ...

How bubble studies benefit science and engineering

8 hours ago

The image above shows a perfect bubble imploding in weightlessness. This bubble, and many like it, are produced by the researchers from the École Polytechnique Fédérale de Lausanne in Switzerland. What ...

Famous Feynman lectures put online with free access

9 hours ago

(Phys.org) —Back in the early sixties, physicist Richard Feynman gave a series of lectures on physics to first year students at Caltech—those lectures were subsequently put into print and made into text ...

Single laser stops molecular tumbling motion instantly

13 hours ago

In the quantum world, making the simple atom behave is one thing, but making the more complex molecule behave is another story. Now Northwestern University scientists have figured out an elegant way to stop a molecule from ...

User comments : 0