Comparative study on emission characteristics of extreme ultraviolet radiation from CO2 and Nd:YAG laser-produced tin plasmas

Abstract

The direct comparison of the emission characteristics of an extreme ultraviolet (EUV) light between the CO2 and the Nd:YAG laser-produced plasmas (LPP) with a solid tin target is reported. In the case of the Nd:YAG LPP, the conversion efficiency (C.E.) peaked at a laser intensity of about 5×1010W∕cm2 and decreased at higher laser intensity. In the case of the CO2 LPP, the C.E. monotonically increased up to 2×1010W∕cm2, where the C.E. is comparable to the maximum C.E. of the Nd:YAG LPP. The spectral efficiency of the Nd:YAG LPP within the 2% bandwidth around 13.5 nm decreased with laser intensity. The corresponding spectral efficiency of the CO2 LPP was almost constant. This observation indicates the potential of the CO2 laser-produced LPP as the EUV light source for the EUV lithographic systems.

Systematic investigation of self-absorption and conversion efficiency of 6.7 nm extreme ultraviolet sources

“…The spectral behavior is similar to that of Nd:YAG laser-produced xenon (Xe) plasmas, with resonant lines around 11 nm and satellite emission at wavelengths longer than 11 nm, especially around 13.5 nm [19,20]. Figure 2(a) shows the laser intensity dependence on the EUV CE when the laser wavelength of 1064 nm is irradiated according to maximizing 6 the EUV emission in Fig. 1.…”

“…The spectral behavior of Gd and Tb plasmas is expected to be similar to that of Sn plasmas for the 13.5-nm EUV sources [4][5][6][7][8][9][10], because of the similar atomic structure of 4d open-shell ions [11]. Previous work on rare-earth plasma EUV sources has been focused on absorption spectroscopy by generating quasicontinuum spectra at low laser power [12,13].…”

Development of Laser-Produced Tin Plasma-Based EUV Light Source Technology for HVM EUV Lithography

“…To realize this, a double-laser irradiation process is utilized in our system. The theoretical [13] and experimental [14] data have clearly demonstrated the advantage of combining a laser beam at a wavelength of a CO 2 laser with Sn plasma to achieve high CE from driver laser pulse energy to EUV inband energy [15].…”

Scaling of laser produced plasma UTA emission down to 3 nm for next generation lithography and short wavelength imaging

“…To increase the conversion efficiency (CE) in laser-produced Sn plasmas, it is important to reduce both the selfabsorption in the plasmas [4] and the plasma hydrodynamic expansion loss effect [5] at an electron temperature of 20−30 eV. A maximum CE of 3−4% has been predicted for Nd:YAG lasers irradiating at a laser intensity of 10 11 W/cm 2 with pulse durations of a few ns, while for CO 2 lasers, because of reduced opacities, a higher CE should be obtained at a laser intensity of 10 10 W/cm 2 [6][7][8]. The rare-earth elements of gadolinium (Gd) and terbium (Tb), on the other hand, produce strong narrow band emission, which again is attributed to a n = 4−n = 4 UTA, at 6.7 nm.…”