This paper reports the basic results that have been obtained at the SRC RF TRINITI (the former Branch of the Kurchatov Institute of Atomic Energy). The work deals with the development of high power discharge produced plasma EUV sources that can meet the requirements of high volume manufacturing lithography tools. Solving the problem of extremely high thermal loads on the electrodes of a EUV source by moving away the electrode surfaces from the plasma and using both multi-discharge systems and rotating Sn-covered disc electrodes is discussed.

A small surface wave driven source produces plasma at atmospheric pressure. Microwave power at frequency 2.45 GHz is coupled with the source and a discharge is ignited at power levels below 10 W. The coaxial exciter of the surface waves has a length of 10 mm because its dielectric is a high permittivity discharge tube. The plasma source operates as a plasma jet in the case of plasma columns longer than the tube length. The source maintains stable plasma columns over a wide range of neutral gas flow and applied power in continuous and pulse regimes. An additional advantage of this source is the discharge self-ignition. An electron temperature of Te ∼ 1.9 eV and a density of ne ∼ 3.9 × 1014 cm−3 are estimated by the probe diagnostics method. The emission spectra in the wavelength range 200–1000 nm under different experimental conditions are analysed and they prove the applicability of the source for analytical spectroscopy. The dependences of column length, reflected power and plasma parameters on the gas flow and the input power are discussed.

Plasma parameters of a small surface-wave discharge in argon gas at atmospheric pressure are obtained by optical emission spectroscopy applying the line-ratio method. The microwave discharge is maintained at a frequency of 2.45 GHz in a ceramic tube with an inner diameter of 1 mm and a length of 11 mm. The discharge is ignited at power levels below 10 W. Emission spectra of the argon plasma are measured in the wavelength range 645–825 nm at different gas flows and forward microwave powers. The electron temperature and the plasma density are determined simultaneously through a ‘cross-point’ method using two line-intensity ratios and their values are T e ≅ 1.6 eV and n e = (3.6–4.5) × 1014 cm−3, respectively. The results show a stronger dependence of the plasma parameters on the gas flow rather than on the input power in the case of plasma columns longer than the tube length.

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