Xe laser-plasma EUV radiation source with a wavelength near 11 nm—Optimization and conversion efficiency

Abstract

Xe laser-produced plasma with a gas-jet target is considered a promising λ = 11.2-nm radiation source for a possible extension of the EUV (Extreme UltraViolet) lithography. EUV spectra of the plasma radiation obtained with the aid of both a grating spectrograph and Bragg mirrors are presented. The absorption of the EUV radiation in the cold peripheral gas has been eliminated in another experiment by means of irradiating the target with a wide defocused laser beam that resulted in an increase of the EUV output by an order of magnitude. In that experiment, the conversion efficiency at λ = 11.2 nm amounted to 3.9%.

Absorption of laser radiation in a laser-produced plasma of Xe: hydrodynamic effects and nonequilibrium ionization

“…Simultaneously to the absorption measurements, the EUV radiation intensity was also measured as a function of the target position on the Y-axis, thereby reproducing, in part, experiments described in [20,21,23]. In these experiments, a turnable Be/Mo multilayer mirror was used at a grazing angle of incidence/reflection of 76 • , so that the wavelength of the reflected radiation was λ = 11.4 nm at the bandwidth (FWHM) of 0.27 nm and the reflection coefficient of 67%.…”

“…The experimental setup described in [23] was adapted to measure the absorption of the laser radiation in the LPP (figure 1). The plasma was generated by a beam of a pulsed multimode solid-state Nd:YAG laser (λ = 1.064 µm) operating in a single-pulse mode.…”

“…This idea had inspired several newly undertaken studies of EUV emission from laser sparks on a Xe gas-jet target, the results of which were recently published in [19][20][21][22][23]. The laser-lightto-EUV conversion efficiency, CE = 3.9% at λ ∼ = 11.2 nm, reported in [23] looks rather encouraging for a possible '11 nm extension' of EUV lithography in the future. An additional hope is given by recent advances in the development and production of Be-based optics [24,25].…”

“…In the experiment described in [20,21,23], the Xe gas-jet target was illuminated by a laser beam of a variable diameterfrom ϕ beam ∼ = 40-50 µm, when it was sharply focused onto the target, up to ϕ beam ∼ = 350-400 µm in the case of a defocused beam. Accordingly, the EUV radiation output from the plasma increased four times at λ = 11.4 nm and 11 times at λ = 13.5 nm.…”

Измерение Геометрических Параметров Мощного ИК Лазерного Луча В Прифокальной Области Для Применений В Лазерно-Плазменном Источнике Коротковолнового Излучения

“…Предложение [5] о разработке варианта литографии на длине волны λ = 11.2 nm с Be-содержащими интерференционными зеркалами [6,7] инициировало новую волну интереса к источнику с лазерной Xe-плазмой, поскольку интенсивность его излучения на " новой" длине волны ожидается примерно на порядок более высокой, чем на λ = 13.5 nm. Первые экспериментальные исследования такого источника с λ = 11.2 nm были опубликованы в [8][9][10][11].…”