The use of any solid material as a fuel and the discharge stability make a laser triggered discharge-produced-plasma (LT-DPP) an attractive light source. Density, size, uniformity, and so on of a fuel control the pinch process by a Lorentz force, and understanding the plasma dynamics in the initial stage is the most important in the LT-DPP study. This work reports how a material for a pinch is supplied and how a laser-produced-plasma (LPP) generated on the electrode behaves before the main discharge current. Our study revealed that the material of a pinch plasma is mainly supplied by laser ablation of a cathode not by current heating of the electrodes. The delay time of a discharge is determined by the velocity of an LPP generated on the cathode, and the traveling velocity of about 1 × 105 m/s of LPP is determined by two factors: the pressure of LPP and acceleration by the electric field. Before the main discharge current starts to flow, two X-ray pulses are generated. The first X-ray pulse is generated on the cathode where a laser is irradiated. The second X-ray pulse is generated on the anode when the LPP generated on the cathode arrives, and the arrival of the LPP triggers the main discharge current. The material for the pinch is not the LPP, but supplied by laser ablation. A faintly bright region appears between electrodes several tens of ns after the start of the main discharge current and this region is slowly imploded and a pinch plasma is formed at the current peak.

For effective use of a laser-produced-plasma (LPP) light source, an LPP is desired to emit a narrow spectral peak because the reflection spectrum of multilayer mirrors for guiding emission from the source is very narrow. While a Gd plasma has been studied extensively as an extreme ultraviolet (EUV) light source at around 6.8 nm, where La/B4C multilayer is reported to have a high reflectivity with a bandwidth of about 0.6 %, all previous works using an Nd:YAG laser reported very broad spectra. This paper reports the first narrowing of the 6.8 nm peak in the case of using an Nd:YAG laser to generate a Gd plasma by using a pre-pulse. The best peak narrowing is observed when a pre-formed plasma is heated by a 1064 nm main laser pulse with a duration of 10 ns at the irradiation density of 4x 1011 W/cm2 at a delay time of 50 ns after the pre-pulse irradiation. The observed spectral width of about 0.3 nm is about one fifth of the value for no pre-formed plasma. The peak wavelength of the 6.8 nm band shifted to a longer wavelength side and the peak was broadened both for lower and higher laser irradiation density. It is discussed that this robustness of the peak position of the 6.8 nm Gd peak against temperature change is suitable to achieve a narrow bandwidth from an LPP generated on solid. The observed spectra are compared with those previously reported in various conditions.

In applying a laser-triggered discharge-produced plasma (LT-DPP) as a light source, the most important issues are the supply of fuel and the suppression of a large-scale nonuniformity called the zippering effect. This paper reports pinch formation in LT-DPP under various electrode separations from 4 mm to 10 mm, which provides information for suppressing the zippering effect. Spherically expanding fuel ablated from the cathode becomes visible when the discharge current becomes large. By 100 ns after the laser trigger, the laser-ablated fuel extends 5 mm from the cathode. The width of the fuel reduces gradually with the increase of the current and forms a pinch at the current peak at 200 ns for the case of a 5mm electrode separation. When the electrode separation is larger, neck-like fuel distribution is observed and the pinched portion propagates toward the anode. The condition for reducing the zippering effect is discussed.

The extreme ultraviolet (EUV) lithography technology, which is required for high-end chip manufacturing, is the first of 35 "neck stuck" key core technologies that China is facing currently. The EUV source with high conversion efficiency is an important part of EUV lithography system. The experiment on dual-pulse irradiated Gd target is carried out to realize the stronger 6.7 nm EUV emission output. Firstly, we compute the contribution of transition arrays of the form 4p–4d and 4d–4f from their open 4d subshell in charge states Gd¹⁸⁺–Gd²⁷⁺, and transition arrays of the form 4d–4f from their open 4d subshell in charge states Gd¹⁴⁺–Gd¹⁷⁺ on the near 6.7 nm EUV source. Subsequently, the experimental results of the dual pulse laser irradiated Gd target show that the intensity of 6.7 nm peak EUV emission decreases first, then increases and drops again due to the plasma density decreasing gradually when the delay time between the pre-pulse and main-pulse increases from 0–500 ns. The strongest intensity of 6.7 nm peak EUV emission is generated when the delay time is 100 ns. At the same time, the spectrum efficiency is higher when the delay time is 100 ns, which is 33% higher than that of single pulse laser. In addition, the experimental results show that the half width of EUV spectrum produced by dual pulse in the delay between 10–500 ns is narrower than that of signal laser pulse due to the fact that the method of dual pulse can suppress the self-absorption effect. The half width is the narrowest when the delay is 30 ns, which is about 1/3 time of EUV spectrum width generated by a single pulse. At the same time, the narrowing of Gd EUV spectrum improves the spectral utilization efficiency near 6.7 nm wavelength (within 0.6% bandwidth).

The extreme ultraviolet (EUV) lithography technology, which is required for high-end chip manufacturing, is the first of 35 "neck stuck" key core technologies that China is facing currently. The high conversion efficiency EUV source and low out-of-band radiation play a significant role in the application of the EUV lithography system. In this paper, the EUV source and out-of-band radiation are studied by using laser irradiated solid Sn and low-density SnO₂ targets. The result shows that a strong EUV radiation at the wavelength of 13.5 nm was generated when the laser irradiated the two forms of Sn target. Due to the self-absorption effect of the solid Sn target plasma, the maximum intensity of the wavelength was not located in the center of 13.5 nm, which is working wavelength of EUV lithography system. However, the peak radiation spectrum was located at 13.5 nm with low-density SnO₂ target due to its weaker plasma self-absorption effect. In addition, the satellite lines are weaker in low-density SnO₂ target compared with the solid Sn target, so that the spectrum efficiency of the EUV at 13.5 nm(2% bandwidth) increased by about 20%. On the other hand, the experimental study of the out-of-band radiation was carried out. The out-of-band radiation spectral results show that the out-of-band radiation is mainly dominated by the continuum spectrum. Compared with the solid Sn target, the low-density SnO₂ target contains a part of the low Z element O (Z=8), resulting in a low intensity of the continuum spectrum. In addition, the collision probability of ion-ion and electron-ion becomes short when the laser irradiated the low-density SnO₂ target, which resulted in a short out-of-band radiation duration time. Therefore, the out-of-band radiation generated by the laser irradiated on the low-density SnO₂ target was weak based on above reasons. The angular distribution of out-of-band radiation measurement results show that the intensity of out-of-band radiation decreases with an increasing of the angle. A cosine function fitted to the angular distribution of the total the radiation by <i>A</i>cos^<i>α</i><i>θ</i>.