Willi Dr Neff

Highly repetitive, extreme-ultraviolet radiation source based on a gas-discharge plasma.

An extreme-ultraviolet (EUV) radiation source near the 13-nm wavelength generated in a small (1.1 J) pinch plasma is presented. The ignition of the plasma occurs in a pseudosparklike electrode geometry, which allows for omitting a switch between the storage capacity and the electrode system and for low inductive coupling of the electrically stored energy to the plasma. Thus energies of only a few joules are sufficient to create current pulses in the range of several kiloamperes, which lead to a compression and a heating of the plasmas to electron densities of more than 10(17) cm(-3) and temperatures of several tens of electron volts, which is necessary for emission in the EUV range. As an example, the emission spectrum of an oxygen plasma in the 11-18-nm range is presented. Transitions of beryllium- and lithium-like oxygen ions can be identified. Current waveform and time-resolved measurements of the EUV emission are discussed. In initial experiments a repetitive operation at nearly 0.2 kHz could be demonstrated. Additionally, the broadband emission of a xenon plasma generated in a 2.2-J discharge is presented.

Pinch-plasma radiation source for extreme-ultraviolet lithography with a kilohertz repetition frequency

An extreme-ultraviolet radiation source based on a xenon pinch plasma is discussed with respect to the demands on a radiation source for extreme-ultraviolet lithography. Operation of the discharge in a self-igniting-plasma mode and omitting a switch permits a very effective and low-inductive coupling of the electrically stored energy to the electrode system. The xenon plasma exhibits broadband emission characteristics that offer radiation near 11 and 13 nm. Both wavelengths are useful in combination with beryllium- and silicon-based multilayer mirrors. The plasma emits approximately 74 mW/sr at 11.5 nm and 40 mW/sr at 13.5 nm in a bandwidth of 2% when operated at a repetition frequency of 120 Hz. The source size is less than 500 microm in diameter (FWHM) when viewed from the axial direction. The pulse-to-pulse stability is better than 3.6%. First results with a repetition rate of as much as 6 kHz promise the possibility of scaling to the required emission power for extreme-ultraviolet lithography.