Tomonao Hosokai

Magnetohydrodynamics control of capillary Z-pinch discharge by using a triangular current pulse for lasing a H-like N recombination soft x-ray laser

In expansion cooling phase of pinched nitrogen plasma generated by fast capillary discharge, it might be possible to realize lasing a Blamer α recombination SXRL, which requires a rapid cooling of nonequilibrium plasma. It is effective to decrease the discharge current rapidly in reducing the additional heating caused by the joule heating and the magnetic compression of plasma as quickly as possible. The shaping of discharge current waveform was demonstrated with a transmission line and its effect on expanding plasma dynamics were investigated through magnetohydrodynamics (MHD) calculation, and validity of the MHD calculation in the expansion phase was shown using the discharge photographs taken by using a high speed camera. As a result, strong radiation from the H-like N ion at the maximum pinch, which is in the current decay phase of the triangular current with peak amplitude of over 70 kA and pulse width of 60 ns, has been confirmed in x-ray photodiode signals at wavelength of less than 2.5 nm, to clar...

Development of Sn-fueled high-power DPP EUV source for enabling HVM

Discharge-produced plasma (DPP)-based EUV source is being developed at Gotenba Branch of EUVA Hiratsuka R&D Center. A high-repetition-rate high voltage power supply (HVPS) was developed and put into operation on the magnetic pulse compression (MPC)-driven DPP source, enabling 8-kHz operation with 15 J/pulse of maximum charging energy and 0.11 % of stability. SnH4 gas was used as a fuel gas in order to obtain high conversion efficiency. SnH4-fueled Z-pinch source demonstrated EUV power of 700 W/2&pgr;sr within 2 % bandwidth around 13.5 nm. Using a nested grazing-incidence collector, EUV power at the intermediate focus which is defined as an interface to the exposure tool reached 62 W with 3.3 mm2sr of etendue. Tin deposition rate on the collector surface, which is the concern in any tin-fueled EUV sources, was decreased by four orders of magnitude as a result of debris-shield development. Cleaning processes were also developed to enhance total lifetime of the collector. A sequence of intentional deposition and cleaning process for the ruthenium grazing-incidence mirror sample was repeated 13 times. By measuring reflectivity of the mirror, it was confirmed that halogen cleaning process worked very effectively and did not get the mirror damaged after such a long-term cleaning experiment.

High brightness extreme ultraviolet (at 13.5 nm) emission from time-of-flight controlled discharges with coaxial fuel injection

Extreme ultraviolet (EUV) emission from discharge produced plasma with the coaxial injection of fuel vapor (tin and lithium) produced by laser ablation is experimentally studied. Multiple plasma pinches preceding a strong and long recombination radiation of EUV are observed in the first half cycle of a sinusoidal discharge current. Due to the time-of-flight control type of the discharge, the shape of pinch radiation pulses is almost identical. With the coaxial injection of time-of-flight controlled discharges, the highest brightness of EUV emission (maximum extracted energy of 244.3 mJ/2π sr per pulse with the emitter size of ∼1×0.3 mm2 in full width at half maximum) is provided with efficiency exceeding 2% of deposited energy into the plasma (or 1% of dissipated energy in the discharge) due to a much better matching with the optimal plasma parameters in the recombination regime and a decrease in the off-duty factor. Stability of emitting plasma of the repetitive pinches is essentially improved with use o...

Elongation of extreme ultraviolet (at 13.5 nm) emission with time-of-flight controlled discharges and lateral fuel injection

A way toward a quasicontinuous extreme ultraviolet (EUV) radiation source is proposed and explored. Tin and lithium vapor discharges with the lateral laser-ablation injection are experimentally studied as possible efficient sources of quasicontinuous emission of EUV radiation at a wavelength of 13.5 nm. It is shown that the time-of-flight control of optimal plasma parameters by means of varying ablating laser pulse parameters provides a considerable elongation of maximal-power EUV emission with an overall efficiency of 0.1% and with an energy output exceeding 1% of the energy deposited in the discharge plasma. Along with a high average power and a stable position, such an emitter may have its size small enough to be used in the projection lithography.

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.

Tin-Fueled High-Repetition-Rate Z-pinch EUV Source for Semiconductor Lithography

Summary form only given. Extreme ultraviolet (EUV) is the potential candidate for the light source used in next generation semiconductor lithography. In EUV lithography (EUVL), IC pattern as small as 32-nm pitch or below will be realized by using 13.5-nm radiation. There are two major schemes to obtain high-power EUV; laser-produced plasma (LPP) and discharge-produced plasma (DPP). DPP seems to provide more cost-effective source and easier way to obtain necessary EUV power than LPP. EUV is not a coherent radiation so that emitted radiation is collected by optics and transferred to an exposure tool. In volume production, significant amount of IC chip should be yielded. From these points of view, EUV radiation must be emitted from very small volume but have sufficient average power. In our development, Z-pinch plasma is employed to achieve such a high temperature and density micro plasma. It is very important to increase conversion efficiency (CE) of electrical energy input to 13.5-nm radiation. Xe used to be used as fuel material because of its easiness of handling and cleanliness. However, Sn is the best choice from the view point of CE. Despite its handling difficulties, Sn is now being commonly used in many EUV researches. In case of gas-discharge-produced plasma, it is necessary to feed the gas into the discharge region between the electrodes. For this purpose, we utilize SnH4 gas, which is in gaseous state at room temperature and able to be controlled like Xe. EUV source for semiconductor lithography is also required to work at pulse repetition frequency more than 7 kHz. By using high rep-rate (8 kHz) and high-average-power (120 kW) pulsed power driver, and low-inductance Z-pinch load, radiation characteristics of SnH4-fueled Z-pinch were investigated. Radiation energy, radiation stability, plasma image, temporal radiation behavior of Z-pinch were investigated. As a result, EUV power within 2 % bandwidth at 13.5 nm reached 700 W/2 pisr.

Manipulation of elctron beam generation with modified magnetic circuit on laser-wakefield acceleration

Electron beam injection triggered by intense ultrashort laser pulses, which is called as plasma cathode, is presented. We have studied generation of relativistic electrons by interaction between a high intensity ultrashort laser pulse and gas jet. When a static magnetic field of 0.2 T is applied, the modification of the preplasma cavity, and significant enhancement of emittance and an increase of the total charge of electron beams produced by a 12 TW, 40 fs laser pulse tightly focused in a He gas jet, were observed. And very high stability and reproducibility of the characteristics and position of well-collimated electron beams was detected. We performed an experiment with a magnetic circuit that has more intense magnetic field of 1 T.

CTR Bunch Length Measurement of Monoenergetic and Maxwellian Electron Beams from Laser Plasma Cathode

Recently, several plasma cathodes at universities and institutes can generate a monoenergetic electron beam. LBL measured the bunch length by the CTR (Coherent Transition Radiation) interferometer to determine it as about 50 fs (FWHM). We are trying to carry out a single‐shot measurement of the bunch length by a infrared polychromator. As the first step forward it, we measured the CTR spectra emitted at a 300microm‐thick Ti foil by the electron beams from our plasma cathode. The laser parameters are 12 TW, 50fs, 3×1019W/cm2. He gas‐jet is used and the electron density is 6×1019cm−3. By using the liquid He bolometer and several optical low‐pass filter, we measured the spectra of the CTR. We can clearly classify the difference of the spectrum and bunch length for the monoenergetic and Maxwellian beams. The numerical analysis of the bunch elongation due to the energy spread confirms the experimental results. The bunch length of the monoenergetic beam is less than 100 fs at FWHM with about 10 pC per bunch, wh...

Operation of capillary z-discharge pumped soft x-ray laser at shorter wavelength region

We have studied the dynamics of fast capillary Z-discharge to obtain prospects for laser operation in shorter wavelength range. The recent results of our studies indicate that, by preionized fast discharge, the column can implode stably in a wide initial pressure range of 200 - 1000 Pa of argon. These results also suggest that the final plasma parameters and their spatial distributions can be controlled in the stable implosion range. If we can avoid destructive magneto- hydrodynamic (MHD) instabilities over a wide range of implosion parameters, we can make Z-scaling to shorter wavelengths. In order to obtain accurate prospects for the operation in shorter wavelengths, the Z-scaling should be carried out based on a proper modeling including the Z- discharge dynamics and radiation transport.