Plasma physics and radiation hydrodynamics in developing an extreme ultraviolet light source for lithography

Abstract

Extreme ultraviolet (EUV) radiation from laser-produced plasma (LPP) has been thoroughly studied for application in mass production of next-generation semiconductor devices. One critical issue for the realization of an LPP-EUV light source for lithography is the conversion efficiency (CE) from incident laser power to EUV radiation of 13.5-nm wavelength (within 2% bandwidth). Another issue is solving the problem of damage caused when debris reaches an EUV collecting mirror. Here, we present an improved power balance model, which can be used for the optimization of laser and target conditions to obtain high CE. An integrated numerical simulation code has been developed for the target design. The code agrees well with experimental results not only for CE but also for detailed EUV spectral structure. We propose a two-pulse irradiation scheme for high CE, and reduced ion debris using a carbon dioxide laser and a droplet or a punch-out target. Using our benchmarked numerical simulation code, we find a possibility to obtain CE up to 6–7%, which is more than twice that achieved to date. We discuss the reduction of ion energy within the two-pulse irradiation scheme. The mitigation of energetic ions by a magnetic field is also discussed, and we conclude that no serious instability occurs due to large ion gyroradius.

Design of a cone target for fast ignition

“…The wall thicknesses of the cone tip and the wall near the tip are both 10 m. In the simulation, we use tin for the target cone material, instead of gold used in the experiment. This is because we have an accurate tin opacity table, verified by the research of extreme ultra-violet light source [9]. In our simulation, we used two-dimensional radiation hydro code STAR2D [10] with the Euler cylindrical coordinates.…”

High-space resolution imaging plate analysis of extreme ultraviolet (EUV) light from tin laser-produced plasmas

“…In each experiment, a typical EUV spectrum from tin plasma was obtained with a strong peak around 13.5 nm. The emission has been characterized as an unresolved transmission array (UTA) from Sn 8+ to Sn 21+ as 4d-4f transmission 26 typically obtained from laser intensities of 10 10 W/cm 2 from Nd:YAG lasers. 27 The FIG.…”

“…Strong EUV reabsorption is observed when lasers in higher harmonics are used. 26 This meant that the higher coefficients were a direct result of the other radiation species rather than from an optically thick opaque plasma surrounding a 13.5 nm emissive plasma. Another interesting feature was that the cos X θ fitting values for X were similar at both 103 mm and 200 mm distances, where X = 3.7 and X = 3.0, respectively.…”

Development of laser ablation plasma by anisotropic self-radiation

“…Many researchers have devoted their efforts to an accurate prediction of emission from such a target for improving conversion efficiency from the input laser energy to the EUV light by using numerical simulations [1]. Since the ablation plasma is in a highly nonequilibrium state, the emission depends on the atomic models employed in the simulation codes.…”