IBM saves chipmaking kit from an early bath

IBM Research has come up with a way to draw lines in silicon 29.9nm apart with existing chipmaking machines, far closer than on today's chips, a development that could help cut the cost of making chips in the future.

The breakthrough revolves around an enhanced, experimental version of immersion lithography. In immersion lithography, silicon wafers are immersed in purified water. Laser light shining through an intricate mask throws a microscopic shadow pattern onto the wafer, which then becomes permanent through chemical processes similar to the process in which a negative becomes a photographic print.

The wafers are immersed in water because water bends light rays better than air, which in turn can lead to sharper resolution and smaller patterns. Immersion lithography will start getting used commercially in the relatively near future.

In IBM's system, light from the laser is split into two beams. Then, a tool called Nemo weaves the two beams to create an interference pattern that allows for a pattern with more closely etched lines than can be achieved in standard immersion lithography.

The system also swaps out water with a special fluid from JSR Micro, as well as using a specialised prism, and a special photoresist system.

"We can routinely do sub-30nm spacing," said Robert Allen, manager of lithography materials at the Almaden Research Centre, IBM Research.

If the Nemo system ultimately goes commercial, the process could let the industry wring more life out of 193nm lithography systems installed today. Machines based on these standards — which can cost $15m each and get delivered in customised tractor trailers — have been around for years. The name derives from the fact that the wavelength of the laser light measures 193nm.

Replacing them with machines based on new technologies has not been easy. Years ago, IBM was one of the principal backers of x-ray lithography. It worked, but was not economical. In the past decade, Intel — along with AMD and to a lesser extent IBM — has promoted extreme ultraviolet lithography (EUV).

EUV sports light with wavelengths from 1-30nm. The systems, however, have been delayed for years. Back in 1997, proponents expected EUV equipment to be on the manufacturing line for 65nm chips, which just started coming out.

EUV is still in the labs. Although Intel may use it to produce 32nm chips, coming out around 2009 or 2010, researchers there say it is not likely to hit until the chip generation after that, when processors will have an average feature size of 22nm.

Nemo gives IBM confidence that immersion lithography with 193nm systems could be used for the 32nm chips. Pushing it to 22nm, however, will require better fluids, different photoresist materials, and lenses made up of as-yet-unidentified substances, Allen said.

IBM will show off the results at the Microlithography 2006 conference being held in San Jose, California, this week.