Measuring invisible reflections
To make microchips ever more powerful, increasingly harder levels of radiation must be used in photolithography. But conventional optics are unsuitable for use with extreme ultraviolet. Europe's first reflectometer tests special mirrors for use in this part of the spectrum.
The race is on for chip manufacturers. Many of them plan to open chip fabrication facilities employing extreme ultraviolet (EUV) radiation between up until 2010. This trend is being driven by advances in photolithography in which increasingly shorter wavelengths enable the production of even finer microelectronic structures. The result is higher levels of integration and more powerful integrated circuits. Like all things, this also has a catch: Beams with a wavelength of around 13 nanometers, like their close relatives, x-rays, can neither be reflected nor focused with conventional optical systems. One solution is to use curved mirrors that - unlike those in your bathroom - are coated with hundreds of alternating layers of different materials. Each layer reflects a small part of the radiation. Researchers at the Fraunhofer Institute for Material and Beam Technology IWS rejoiced last year when they broke the 70-percent reflectivity barrier.
They're also happy that they don't have to drive to Berlin any longer to use the synchrotron radiation facility BESSY each time they want to measure their EUV optical components. Because meanwhile, the IWS in Dresden has a reflectometer, which is the first measuring instrument of its kind in Europe. In both cases, the EUV radiation is not generated by conventional light sources, as project manager Dr. Ludwig van Loyen explains: "We fire green laser light at gold. A plasma is briefly created on the surface of the metal. This point, only half as thick as a human hair, emits EUV radiation." The beam then passes through a monochromator - derived from the Greek for "single color" - which precisely selects the desired wavelength, in the region between 10 and 16 nanometers.
The now very precisely defined sampling beam then enters the goniometer chamber. This man-high vacuum steel tank contains the object to be tested, such as an EUV mirror. The beam strikes the surface of the mirror and its reflection provides information on the optical quality. "Of course we need to obtain data from every part of the surface, and under various angles," emphasizes van Loyen. "Since the beam is difficult to rotate, the mirror - measuring up to half a meter across and weighing 30 kilos - must be repeatedly moved in every direction under precisely reproducible conditions. This envolves a masterpiece of fine mechanics." The laboratory prototype is currently undergoing trials, and will be transferred to the premises of project partner Carl Zeiss sometime later this year.
Your contact for further information:
Fraunhofer Institute for Material and Beam Technology IWS Dresden
(Fraunhofer-Institut für Werkstoff- und Strahltechnik IWS Dresden)
01277 Dresden, Winterbergstr. 28
Dr. Ludwig van Loyen
Phone: (0351) 25 83 422
Fax: (0351) 25 83 300
Press and Public Relation
Dr. Ralf Jäckel
Phone: (0351) 25 83 444
Fax: (0351) 25 83 300