Nozomu Kishi

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)

Influence of electrode separation and gas curtain on extreme ultraviolet emission of a gas jet z-pinch source

Extreme ultraviolet (EUV) emission from a gas jet z-pinch source has been examined by employing a photodiode and pinhole camera. Visible images of the pinched plasma have been also recorded. A current pulse of 10kA is used to heat the gas jet, which emits radiation around 13.5nm. Experimental parameters such as electrode separation and gas flow rate are varied to optimize EUV emission. The maximum EUV energy is obtained for 12mm electrode separation and 20Torr xenon pressure and it is estimated to 10.95mJ∕sr per 2% bandwidth per pulse. The presence of gas curtain improves EUV emission by 30%.

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.

Experimental study of xenon and tin discharge produced plasma EUV light source

Recently, a lot of progresses have been made in the field of gas discharge and laser assisted extreme ultraviolet (EUV) light sources. In order to realize the EUV lithography, we have been developing the discharge produced plasma EUV light source with either Xe or Sn fuels. A Xe gas jet Z-pinch discharge system has been developed for generating high quality debris-free EUV emission. A 25kA pulsed power supply system has been constructed and introduced. Observation of optical characteristics are presently in progress. Also, the laser triggered discharge produced plasma with Sn electrode system has been constructed. In our system, after Nd-YAG laser was irradiated on Sn electrode surface for triggering the main discharge, EUV radiation will occur from the generated Sn plasma between electrodes and be collected radially. The maximum discharge current of about 6 kA with a pulse width of 500 ns was supplied to anode-cathode gap. In present study, EUV radiation emitted from gas jet Z- pinch Xe plasma and laser triggered Sn discharge produced plasma was quantitatively measured using an in-band calorimeter. Time-resolved in-band source image measurement was also conducted using a pinhole camera system.

Development of Xe and Sn discharge EUV light source

A high rep-rate, compact and low-debris xenon Z-pinch discharge system has been designed and fabricated as an EUV light source, in which a newly developed gas jet-type Z-pinch source is used. The discharge head has a coaxial double nozzle and diffuser. Xenon Z-pinch plasma that emits EUV light is produced in between the inner nozzle and the corresponding diffuser. An annular shell of a helium gas curtain produced by the outer nozzle is specially designed for shielding the debris and suppressing the inner gas expansion. In this work, in order to get higher EUV output power, a new pulse power supply system has been developed. This power supply delivers a current with amplitude of 22 kA, rise time of 110 ns and pulse duration of 260 ns to a low inductance load. In addition, a laser triggered discharge produced tin 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 found that EUV emissions cannot be obtained when the laser irradiation power is too high.

Optimization of a gas jet-type Z-pinch discharge EUV light source

A high repetitive, compact and low-debris Xenon Z-pinch discharge system has been designed and fabricated as an EUV light source, in which a newly developed gas jet-type Z-pinch source is used. The discharge head has a coaxial double nozzle and a diffuser. Xenon Z-pinch plasma that emits EUV light is produced between the inner nozzle and the corresponding diffuser. An annular shell of a He gas curtain produced by the outer nozzle is specially designed for shielding the debris and suppressing the inner gas expansion. We have succeeded in generating EUV emitting plasma of 0.14 mm FWHM diameter and 0.80 mm FWHM length. We have also developed a new pulse power supply system, which has two magnetic pulse compression stages to achieve higher discharge current

Characteristics of gas jet Z-pinch plasma light source for extreme ultraviolet lithography

Summary form only given. Development of extreme ultraviolet (EUV) light source with enough usable power and long lifetime is key problem of realizing EUV lithography. In order to overcome problems, a Z-pinch discharge light source has been made and demonstrated. In next step, for generating high quality debris-free EUV emission, a new electrode system using gas jet Z-pinch plasma has been proposed and tested. In this system, two cylindrical electrodes are set apart without a discharge tube. One of electrodes acts as a nozzle and the other as a diffuser. The generated EUV radiation from the pinched plasma between electrodes will be collected radially. In present study, EUV radiation emitted from gas jet Z-pinch Xe plasma was quantitatively measured using an in-band calorimeter. Time-integrated in-band source image measurement was also conducted using a pinhole camera system. The details of experimental results will be discussed