High power gas-discharge and laser-plasma based EUV sources

摘要

In this paper we discuss new results from investigations on high power EUV sources for micro-lithography based on gas discharge produced plasmas and laser produced plasmas. The EUV development is performed at XTREME technologies GmbH, a joint venture of Lambda Physik AG, Goettingen, and Jenoptik LOS GmbH, Jena. For gas discharge EUV sources we report data based on Xenon filled Z-pinches. Prototypes of the EUV source achieve an EUV output power of 10 W in-band in continuous operation. Repetition rates of 1 kHz are possible with liquid cooling of the discharge head. The spectral distribution of the EUV radiation shows a maximum around 13.5nm and matches the reflection characteristics of silicon/molybdenum multilayer mirrors. Conversion efficiencies between 0.25% and 0.7% into a solid angle of 2π sr were achieved with the Z-pinch source depending the discharge geometry. The total EUV average power in the spectral range between 5nm and 50 nm is about 200 W in 1.8 sr. Pulse energy stability data show standard deviation between 1-4 %. Spatial and temporal emission characteristics of the discharge source in dependence on the discharge geometry are discussed. The laser plasma investigations are performed with an experimental setup consisting of a diode pumped laser system coupled to a liquid jet target. Since the conversion efficiency into EUV-power depends critically on the emitter density in the interaction region, we use a Xenon-jet, which is cryogenically liquefied and injected under high pressure into the vacuum vessel. Thus the laser is impinging on a target of solid-state density, which allows the generation of EUV-radiation with high conversion efficiencies of 0.5 % into a solid angle of 2πsr.