Qiushi Zhu

Investigation of the dynamics of the Z-pinch imploding plasma for a laser-assisted discharge-produced Sn plasma EUV source

Dynamics of the imploding plasma and its relations to the 13.5nm EUV emissions have been experimentally investigated for a laser-assisted Sn based discharge-produced plasma EUV source. The behaviours and two-dimensional electron density distributions of the EUV-emitting plasma were obtained using the time-resolved shadowgraph and Nomarski interferometric techniques. Observation of the plasma piston in the prepinch phase justified the validity of the zero-dimensional thin-shell model, from which the ion charge state of the prepinch plasma in the cathode region was estimated. The sausage (m = 0) instability that usually enhances the EUV emission was observed, with the radial electron density distribution that displays a concave shape at the crest of the plasma and a bell shape at the neck; the maximum of the electron density is located at one peak of the concave distribution at the crest instead of the neck. Intense EUV emission was produced by the Z-pinch plasma with the electron density (2.0‐3.0) × 10 18 cm −3 . Moreover, the shock waves generated in the anode region can also produce in-band EUV emission with the intensity of 30% of that from the Z-pinch plasma. (Some figures in this article are in colour only in the electronic version)

Structure and Expansion Characteristics of Laser Ablation Tin Plasma into a Vacuum

The internal structure and expansion characteristics of a laser ablation tin plasma into a vacuum have been investigated. A Q-switched Nd:YAG laser with the power density of 1011 W/cm2 at the focal spot on the tin bulk target was employed to create the ablation plasma. The ion velocity distribution calculated from the time-of-flight measurements displays a multimodal structure; shifted-Maxwell–Boltzmann fitting indicates ions with multiple charge states exist in the ablation plume, and the temperature of the Knudsen layer was estimated to be ~4.0×105 and ~8.3×105 K for the laser energy of 77 and 129 mJ, respectively. Particle acceleration mechanisms were discussed according to the time resolved, two-dimensional images of the Sn I and Sn II plasma plume. The unstable adiabatic expansion with the formation of Knudsen layer was found dominates the expansion behavior of Sn I, and the Knudsen layer temperature was calculated to be 6.68×105 K according to the front edge velocity of the Sn I plume.

Estimation of electron temperature and density of the decay plasma in a laser-assisted discharge plasma extreme ultraviolet source by using a modified Stark broadening method

In order to investigate the plasma expansion behaviors and the electrical recovery process after the maximum implosion in our tin fueled laser-assisted discharge plasma (LDP) 13.5 nm EUV source, we developed and evaluated a cost-efficient spectroscopic method to determine the electron temperature Te and density ne simultaneously, by using Stark broadenings of two Sn II isolated lines (5s24f2F°5/2 – 5s25d2D3/2 558.9 nm and 5s26d2D5/2 – 5s26p2P°3/2 556.2 nm) spontaneously emitted from the plasma. The spatial-resolved evolutions of Te and ne of the expansion plasma over 50 to 900 ns after the maximum implosion were obtained using this modified Stark broadening method. According to the different ne decay characteristics along the Z-pinch axis, the expansion velocity of the electrons was estimated as ∼1.2 × 104 ms− 1 from the plasma shell between the electrodes towards the cathode and the anode. The decay time constant of ne was measured as 183 ± 24 ns. Based on the theories of plasma adiabatic expansion and e...

Pinch dynamics of the 13.5 nm EUV-emitting plasma in a LA-DPP source

Pinch dynamics of the imploding plasma and its relations with the 13.5 nm extreme ultraviolet (EUV) emissions have been experimentally investigated for a laser assisted Sn based discharge produced plasma (LA-DPP) EUV source. Plasma behaviors during the discharge are clarified using the laser aided shadowgraphic technique. Temporally and spatially resolved electron density distributions obtained by using Nomarski interferometry reveal that the maximum EUV emission corresponds to the electron density of (2.0–3.0)×1018 cm−3. The ion fraction and electron temperature of the pre-pinch plasma are estimated using a stationary collisional-radiative model.

Behavior of laser assisted tin discharge EUV emitting plasma

Extreme Ultraviolet (EUV) lithography is considered as the most promising candidate of the next generation of lithography for manufacturing ever smaller and faster chips. In our laboratory, a laser assisted tin target discharge produced plasma EUV source has been studied[1]. The system comprises an Nd:YAG laser, focusing on a tin (Sn) rod embedded in one of electrodes to create plasma; and a power supply system to generate a sinusoidal discharge current of 22 kA amplitude, 250 ns half cycle that flows through the plasma between the electrodes to pinch the plasma and produce EUV radiation.

Extreme ultraviolet light sources and soft x-ray laser based on discharge produced plasma

Due to the demand to realize shorter wavelength light sources, extreme ultraviolet (EUV) sources and soft x-ray laser (SXRL) are under development. The development of EUV sources at the wavelength of 13.5 nm started to realize light sources to be used for next generation lithography. Xenon was used at the beginning of development, however, to attain higher conversion efficiency, tin is now used as fuel. As a coherent light source, capillary discharge SXRL is under development. After the demonstration of Ne-like Ar SXRL by using electron collisional excitation scheme, the effort to shorten the wavelength has been made by adopting recombination scheme such as H-like N. Though the challenge has not yet been successful, the source has potential to be used as a SXR source in the water window wavelength region. Current status of EUV and SXR sources based on discharge produced plasma will be given.

EUV and SXR sources based on discharge produced plasma

EUV sources based on discharge produced plasma (DPP), one of which is based on xenon gas jet discharge and the other is based on laser assisted tin discharge, are being developed for the next generation lithography. To get a high power source demanded by manufacturers, the understanding of pinch dynamics corresponding to emission is important and hence fundamental investigation, such as the simulation of gas density distribution or the measurement of electron temperature and density, is conducted. Soft X-ray laser using recombination scheme is also being studied to realize a shorter wavelength nitrogen laser at 13.4 nm. The results of spectroscopic measurement are shown.

Development of Extreme Ultraviolet Radiation Source using Laser Triggered Vacuum Spark Discharge Plasma

A laser triggerd discharge produced Sn plasma light source has been developed. Experimental parameters such as electrode separation and laser irradiation power are varied to optimize EUV emission power. It is clear that the maximum EUV radiation was occurred in the position where the pinch was observed.