Plasma chamber cuts cost of extreme UV

17 Jun 2002

Researchers in Germany have developed a source of extreme ultraviolet light for photolithography that they believe will cost as little as the lasers used in conventional chip fabrication.

Photolithography is a technique for preparing a silicon wafer for etching. The shorter the wavelength of the light, the finer the structure that can be written onto the chips. For this reason researchers are interested in shorter wavelengths than visible light. Extreme ultraviolet radiation, at a wavelength of about 13 nanometres, is currently very expensive to produce.

The new source is a pulsed plasma, generated by a fast discharge of electrically stored energy that compresses and heats a neutral gas column. No switch is needed between the storage and the electrode system so energies as low as 1 joule are sufficient for the gas discharge.

Klaus Bergmann, one of the researchers involved in this project said that the gas discharge apparatus is quite simple so the radiation source is not expected to cost more than the lasers in conventional photolithography.

Before the new device is suitable for chip manufacture, it must generate radiation at a power of several watts. The bandwidth of the 13 nanometre wavelength must also be reduced to just 0.3 nanometres. The source has already found applications in metrology.

The research team, from the Fraunhofer Institute for Laser Technology and the Technical University of Aachen, have not yet achieved wavelengths below 10 nanometres but they hope to do so in the future. They have already produced wavelengths of around 1 nanometre using hotter plasmas.

SH