NEWSLETTER SEPTEMBER 2001

Why is MEDEA+ focussing on Extreme Ultra Violet (EUV) Lithography in its Technologies subprogramme ?

For decades the semiconductor industry has kept up with Moore's Law - doubling every 18 months the number of transistors on the most advanced silicon chips. Now it looks as if silicon chips would require feature sizes which are beyond the limits of the traditional optical-projection lithography. One priority of MEDEA+ is to pave the way for the new, unconventional "optical" EUV lithography through maximum cooperation of Europe's key actors in this domain.

One of the main steps in semiconductor manufacturing is the transfer of patterns from a mask to the silicon wafer. Every time the feature sizes of the lines in these patterns are reduced to start new semiconductor technology generations, new imaging tools also have to be developed.

In the 1970s the light sources and the lenses were believed to be usable only down to feature sizes of 1?m, maybe 0.5?m. So new approaches to lithography using electrons, ions and x-rays were extensively investigated.
The "optical" lithography equipment makers did not give up and invested a lot of work in basic research of the imaging process and in developing new lens systems with higher numerical apertures for shorter wavelengths. Optical lithography manufacturers know very well that wafer-fab managers would like to keep optical lithography as long as possible alive to protect the vast know-how and long experience of their engineers and operators in that field.

In 1996 the equipment companies finally succeeded to transfer structures from a mask to a wafer that had the same dimensions as the wavelength used in the imaging system. And today it is even possible to print structures which are only half of the wavelength. All this progress has been achieved through skillfull special manipulation in the illumination system, special preparation of the masks (optical proximity correction, various types of phase-shifting), and through special resist systems and treatment of the resist after exposure.

Today it seems possible that with a wavelength of 157 nm, the 70 nm technology node could still be realised with "optical" techniques. But the next technology node in the ITRS, 50nm or even 45 nm, does not seem to be achievable with this technique.
For some years ISMT has been organising a yearly workshop on "Next Generation Lithography". At the end of the workshop the participants have always been asked: "If you had to choose one imaging option today, which one would you choose?" During the last two workshops an increasing majority voted for EUV (Extreme Ultra Violet) as the lithography technology of choice for 50nm and below.

Lithography in MEDEA+

Since progress in semiconductor technology depends to a large extent on future-proof lithography systems and techniques, R&D in lithography has been selected as one of the key working areas in the MEDEA+ Technologies sub-programme.

Development of optical lithography with a wavelength of 193 and 157 nm for processes down to 70 nm or so was already started during MEDEA, and will be continued in MEDEA+. As an alternative for structures below 70 nm, ion projection was also investigated during the MEDEA programme.

But, for any new Next Generation Lithography system very heavy investments are required. Moreover, for a new system to become economical, it must be widely accepted and used for at least two upcoming technology generations. The industry's limited resources therefore must be concentrated on one single new system. After very thorough discussions the European partners finally decided to focus their resources on EUV lithography.

Why R&D for EUV in MEDEA+

The primary goal of MEDEA+ is to initiate R&D co-operation in Europe in those fields of Microelectronics, where a large well coordinated effort on a European level has the best chances of success for the benefit of European partners.
In the field of EUV a particularly strong effort is required because there are many technical problems for which solutions have to be found and innovation must be generated.
MEDEA+ is therefore the catalyst for a well defined cooperation involving all major European research institutes and companies whose strengths have to be bundled.

MEDEA+ knows that all the actors in this environment carry a heavy responsibility for the large amount of resources focused on this development. We are convinced that knowledge and competence, together with the concentrated co-operation within the MEDEA+ Programme will benefit the European suppliers and users of EUV-lithography, and will definitely improve their positions in the global competition.