Inho Song

Miniature hybrid plasma focus extreme ultraviolet source driven by 10 kA fast current pulse

A miniature hybrid plasma focus device, operated in xenon gas medium and driven by a 10kA fast current pulse, has been used to generate extreme ultraviolet radiation in the range of 6–15nm. At present the radiation characteristics from xenon plasma were mainly assessed qualitatively using standard tools such as visible light framing camera, extreme ultraviolet (EUV) pinhole camera, and EUV photodiode. Strong pinching of xenon plasma is indicative from both visible and EUV imagings. The maximum size of the EUV emitting zone is estimated to be of the order of 0.21×1.55mm and the estimated value is within the accepted value as benchmarked by industries. The EUV intensity measurement by photodiode showed fairly isotropic radiation at least in a half solid angle. This device can be developed further as a competent source for EUV metrology or lithography applications.

Highly efficient pulsed power supply system with a two-stage LC generator and a step-up transformer for fast capillary discharge soft x-ray laser at shorter wavelength

Highly efficient and compact pulsed power supply system for a capillary discharge soft x-ray laser (SXRL) has been developed. The system consists of a 2.2 microF two-stage LC inversion generator, a 2:54 step-up transformer, a 3 nF water capacitor, and a discharge section with a few tens of centimeter length capillary. Adoption of the pulsed transformer in combination with the LC inversion generator enables us to use only one gap switch in the circuit for charging the water capacitor up to about 0.5 MV. Furthermore, step-up ratio of a water capacitor voltage to a LC inversion generator initial charging voltage is about 40 with energy transfer efficiency of about 50%. It also leads to good reproducibility of a capillary discharge which is necessary for lasing a SXRL stably. For the study of the possibility of lasing a SXRL at shorter wavelength in a small laboratory scale, high-density and high-temperature plasma column suitable for the laser can be generated relatively easily with this system.

A comparative study on the performance of a xenon capillary Z-pinch EUV lithography light source using a pinhole camera

A pinhole camera has been employed to study the performance of a xenon capillary Z-pinch extreme ultraviolet (EUV) lithography light source driven by different dI/dt discharge current pulses. The performance of the EUV source in terms of dimension, intensity, collection efficiency and stability was specifically investigated by varying the experimental conditions such as the supplying gas pressure and dI/dt of the discharge current. Specific features, such as ring shape (annular profile) pinhole images and symmetrical and stable emission in the high dI/dt discharge current, have been observed or confirmed experimentally. Our results support the fact that the high dI/dt and short discharge currents have better EUV emission characteristics for EUV lithography compared with the low dI/dt discharge current.

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%.

Characteristics of Xenon Capillary Z-Pinch Extreme Ultraviolet Lithography Source Driven by Different dI/dt Discharge Current Pulses

Next-generation lithography will require an extreme-ultraviolet (EUV) light source that ensures high radiation intensities at a wavelength of around 13.5 nm. The characteristics of pinch dynamics and emission in this spectral range were studied experimentally for xenon capillary Z-pinch plasma driven by different dI/dt discharge current pulses. The pinch dynamics of the capillary Z-pinch plasma were examined by employing a high-speed camera, and the spectral emission from plasma was inspected using an EUV photodiode, a mini calorimeter and spectrometers. Our results confirm that high-dI/dt discharge current has better performance in comparison with the low one in terms of plasma dynamics, EUV power output and debris generation.

Extreme Ultraviolet Light Emission from Z‐Pinch Discharge Plasma Source

A capillary Z‐pinch discharge light source for EUV lithography has been developed. Our device is equipped with a water‐cooled ceramic capillary and electrodes, and a solid state pulsed power generator. A stacked static induction thyristors are used as switching elements, which enable high repetition rate operation of pulsed power supply. A magnetic switch is connected in series, which not only assists the semiconductor switch but also provides a preionization current. In the present study, EUV radiation emitted from pinching plasma in a xenon‐filled capillary was quantitatively measured using an in‐band calorimeter. Time‐integrated in‐band source image was also observed using a pinhole camera system. Furthermore, new electrode system using plasma jet has been developed.

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.

Soft X-ray radiation from nitrogen filled capillary z-pinch plasma

Characteristics of soft X-ray radiation from nitrogen Z-pinch plasma column energized by a capillary discharge is reported as a fundamental study for H-like N recombination pumped soft X-ray laser, wavelength of which is 13.4 nm emitted by quantum transition from n = 3 to n = 2. A current pulse of about 15 kA with half-cycle duration of about 110 ns was utilized to excite nitrogen plasma in a 3.0 mm diameter channel. From spectroscopic measurement using a transmission grating spectrometer, ionic charge state of nitrogen in the plasma was analyzed to estimate plasma parameters and the discharge current required for realizing a H-like N recombination soft X-ray laser

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