Yoshifumi Ueno

Enhancement of extreme ultraviolet emission from a CO2 laser-produced Sn plasma using a cavity target

We demonstrated enhancement of in-band conversion efficiency (CE) at 13.5nm of the extreme ultraviolet (EUV) emission from a tin (Sn) cavity target irradiated by a CO2 laser pulse. Whereas a planar Sn target produced an in-band CE of around 2%, the use of cavity targets significantly enhanced the EUV emission energy and the EUV CE. An EUV CE of 4% was observed for a Sn cavity target with a depth of 200μm which is one of the highest values ever reported.

Dynamics of laser-produced Sn microplasma for a high-brightness extreme ultraviolet light source

The effect of laser focal spot diameters of 26 and 150 μm on 13.5 nm extreme ultraviolet (EUV) radiation is investigated. Simulations show that the smaller spot size has a shorter electron plasma density scale length and deeper and denser laser energy deposition region. This results in additional time required for plasma expansion and radiation transport to efficiently emit EUV light. This is experimentally observed as an increase in the delay between the EUV emission and the laser pulse. The shorter scale length plasma reabsorbs less EUV light, resulting in a higher conversion efficiency, smaller and slightly brighter light source.

Reduction of debris of a CO2 laser-produced Sn plasma extreme ultraviolet source using a magnetic field

We demonstrated a fivefold reduction in Sn debris deposited on small Mo∕Si multilayer mirrors from a Sn planar target by applying a static magnetic field of 1T. The debris reduction is attributed to the decrease of more than three orders in the number of ions that reach the sample mirror due to their interaction with the applied magnetic field that guides the ions away from the mirror. The remaining deposition is due to neutral Sn atoms that do not interact with the applied magnetic field.

Laser produced EUV light source development for HVM

We develop a laser produced plasma light source for high volume manufacturing (HVM) EUV lithography. The light source is based on a short pulse, high power, high repetition rate CO2 master oscillator power amplifier (MOPA) laser system and a Tin droplet target. A maximum conversion efficiency of 4.5% was measured for a CO2 laser driven Sn plasma having a narrow spectrum at 13.5 nm. In addition, low debris generation was observed. The CO2 MOPA laser system is based on commercial high power cw CO2 lasers. We achieve an average laser power of 3 kW at 100 kHz with a single laser beam that has very good beam quality. In a first step, a 50-W light source is developing. Based on a 10-kW CO2 laser this light source is scalable to more than 100 W EUV in-band power.

Efficient extreme ultraviolet plasma source generated by a CO2 laser and a liquid xenon microjet target

We demonstrated efficacy of a CO2-laser-produced xenon plasma in the extreme ultraviolet (EUV) spectral region at 13.5nm at variable laser pulse widths between 200ps and 25ns. The plasma target was a 30μm liquid xenon microjet. To ensure the optimum coupling of CO2 laser energy with the plasma, they applied a prepulse yttrium aluminum garnet laser. The authors measured the conversion efficiency (CE) of the 13.5nm EUV emission for different pulse widths of the CO2 laser. A maximum CE of 0.6% was obtained for a CO2 laser pulse width of 25ns at an intensity of 5×1010W∕cm2.

Laser-produced-plasma light source for EUV lithography

The status of the next generation lithography laser produced plasma light source development at EUVA is presented. The light source is based on a Xenon jet target and a Nd:YAG driver laser. The laser, having a master oscillator power amplifier (MOPA) configuration, operates at 10 kHz repetition rate and generates an average output power of 1.5 kW. The fwhm pulsewidth is 6 ns. The EUV system currently delivers an average EUV source power of 9.1 W (2% bandwidth, 2π sr) with a conversion efficiency of 0.6 %. Based on the development it is concluded that solid-state Nd:YAG laser technology can be cost efficiently used to produce 10 W level EUV light sources. In order to generate an average power of 115 W for a future extreme ultraviolet (EUV) light source, however, the cost of a Nd:YAG based LPP source will be too high. Therefore RF-CO2 laser technology will be used. The designed CO2 driver laser system has a MOPA configuration. The oscillator has ns-order pulsewidth and the laser system operates at a repetition rate of 100 kHz. Due to its inert cleanliness Xenon droplets will be the target material.

Laser-produced plasma source development for EUV lithography

We are developing a laser produced plasma light source for high volume manufacturing (HVM) EUV lithography. The light source is based on a high power, high repetition rate CO2 laser system, a tin droplet target and a magnetic plasma guiding for collector mirror protection. This approach enables cost-effective high-conversion efficiency and EUV power scaling. The laser system is a master oscillator power amplifier (MOPA) configuration. We have achieved a maximum average laser output power of more than 10 kW at 100 kHz and 20 ns pulse by a single laser beam with good beam quality. EUV in-band power and out-of-band characteristics are measuring with high power CO2 laser and Sn droplet target configuration. This light source is scalable to more than 200 W EUV in-band power based on a 20-kW CO2 laser. Collector mirror life can be extended by using droplet target and magnetic plasma guiding. Effectiveness of the magnetic plasma guiding is examined by monitoring the motion of fast Sn ion in a large vacuum chamber. The ion flux from a Sn plasma was confined along the magnetic axis with a maximum magnetic flux density of 2 T.

Recombination effects during expansion into vacuum in laser produced Sn plasma

The distance over which the charge state distribution evolves during the expansion of laser produced Sn plasma in vacuum is investigated experimentally. This distance is found to be less than 6 cm with a planar target irradiated by a 1.064 μm laser at 8.3×1011 W/cm2 but greater than 60 cm when a 10.6 μm laser at 2.5×1010 W/cm2 is used. The difference is attributed to the laser wavelength dependence of the coronal electron density and the subsequent recombination processes during expansion. Important implications to the extreme ultraviolet x-ray source application are discussed specifically.

CO2 laser-produced Sn-plasma source for high-volume manufacturing EUV lithography

We are developing a laser produced plasma light source for high volume manufacturing (HVM) EUV lithography. The light source is based on a high power, high repetition rate CO2 laser system, a tin target and a magnetic ion guiding for tin treatment. The laser system is a master oscillator power amplifier (MOPA) configuration. We have achieved an average laser output power of 10 kW at 100 kHz by a single laser beam with good beam quality. EUV in-band power equivalent to 60 W at intermediate focus was produced by irradiating a tin rotating plate with 6 kW laser power. This light source is scalable to more than 200 W EUV in-band power based on a 20-kW CO2 laser. Collector mirror life can be extended by using droplet target and magnetic ion guiding. Effectiveness of the magnetic ion guiding is examined by monitoring the motion of fast Sn ion in a large vacuum chamber with a maximum magnetic flux density of 2 T.

CO2 laser-produced Sn plasma as the solution for high-volume manufacturing EUV lithography

We are developing a laser produced plasma light source for high volume manufacturing (HVM) EUV lithography. The light source is based on a short pulse, high power, high repetition rate CO2 master oscillator power amplifier (MOPA) laser system and a Tin droplet target. A maximum conversion efficiency of 4.5% was measured for a CO2 laser driven Sn plasma having a narrow spectrum at 13.5 nm. In addition, low debris generation was observed. The CO2 MOPA laser system is based on commercial high power cw CO2 lasers. We have achieved an average laser power of 7 kW at 100 kHz by a single laser beam with good beam quality. In a first step, a 50-W light source is under development. Based on a 10-kW CO2 laser, this light source is scalable to more than 100 W EUV in-band power.