The Spectra of a Laser-Produced Plasma Source with CO(2), O(2) and CF(4) Liquid Aerosol Spray Target

A laser-produced plasma (LPP) source with liquid aerosol spray target and nanosecond laser was developed, based on both soft X-ray radiation metrology and extreme ultraviolet projection lithography (EUVL). The LPP source is composed of a stainless steel solenoid valve whose temperature can be continuously controlled, a Nd : YAG laser with pulse width, working wavelength and pulse energy being 7 ns, 1.064 mu m and 1J respectively, and a pulse generator which can synchronously control the valve and the laser. A standard General Valve Corporation series 99 stainless steel solenoid valve with copper gasket seals and a Kel-F poppet are used in order to minimize leakage and poppet deformation during high-pressure cryogenic operation. A close fitting copper cooling jacket surrounds the valve body. The jacket clamps a copper coolant-carrying tube 3 nun in diameter, which is fed by an automatically pressurized liquid nitrogen-filled dewar. The valve temperature can be controlled between 77 and 473 K For sufficiently high backing pressure and low temperature, the valve reservoir gas can undergo a gas-to-liquid phase transition. Upon valve pulsing, the liquid is ejected into a vacuum and breaks up into droplets, which is called liquid aerosol spray target. For the above-mentioned LPP source, firstly, by the use of Cowan program on the basis of non-relativistic quantum mechanics, the authors computed the radiative transition wavelengths and probabilities in soft X-ray region for O(4+), O(5+), O(6+), O(7+), F(5+), F(6+) and F(7+) ions which were correspondingly produced from the interaction of the 10(11)-10(12) W . cm(-2) power laser with liquid O(2), CO(2) and CF(4) aerosol spray targets. Secondly, the authors measured the spectra of liquid O(2), CO(2) and CF(4) aerosol spray target LPP sources in the 6-20 run band for the 8 x 10(11) W . cm(-2) laser irradiance. The measured results were compared with the Cowan calculated results ones, and the radiative transition wavelength and probability for the measured spectral lines were obtained.