High power EUV sources for lithography - A comparison of laser produced plasma and gas discharge produced plasma

摘要

Next generation semiconductor chip manufacturing using extreme ultraviolet (EUV) lithography requires a brilliant radiation source with output power between 50 W and 120 W in intermediate focus. This is about five to ten times higher power than that of current DUV excimer lasers used in optical lithography. Lifetime and cost of ownership however, need to be comparable to today's technology. In the present paper experimental results of both laser produced plasma and gas discharge produced plasma EUV source development at XTREME technologies ― the EUV joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena, Germany ― are presented. Source characterization has been performed with calibrated metrology tools for measurement of energy, power, size, spectra and stability of the EUV emission. The laser plasma investigations are performed with a 1st experimental facility comprising a commercial 40 W Nd:YAG laser coupled to a liquid xenon-jet target system, which was developed by XTREME technologies. The EUV in-band power emitted from the 0.25 mm diameter plasma into 2π solid angle is 0.2 W, the conversion efficiency amounts 0.5 %. Estimated EUV emission parameters using a 500 W laser for plasma generation to be installed in spring 2002 are discussed. The gas discharge EUV sources described here are based on efficient Xenon Z-pinches. In the 3rd prototype generation the plasma pinch size and the available emission angle have been matched to the etendue of the optical system of 2-3 mm~2. The solid angle of emission from the pinch of 1.3 mm x 1.5 mm amounts 1.8 sr. The Z-pinch EUV source can be operated continuously at 1000 Hz with an in-band output power of 10 W in 1.8 sr. This corresponds to 4.5 W in intermediate focus, if no spectral purity filter is needed. The power emitted into a solid angle of 2π sr is 35 W. Emission energy stability ranges between 1 % and 4 % standard deviation. Spectral, temporal as well as spatial emission characteristics of the discharge source in dependence on the gas discharge geometry have been evaluated. The potentials as well as limits for power scaling of the two technological source concepts are discussed.