We report on the approach for a high-power high-beam-quality drive laser system that is used for a laser-produced plasma (LPP) EUV source. Cymer has conducted research on a number of solutions for a multi-kW drive laser system that satisfy high volume production requirements. Types of lasers to be presented include XeF at 351 nm and CO<sub>2</sub> at 10.6 micron. We report on a high efficiency XeF amplifier with a 3rd harmonic Nd:YLF master oscillator operated in the 6 to 8 kHz range and a CO<sub>2</sub> laser system with Q-switched cavity dumped master oscillator and RF pumped fast axial flow amplifiers operated in the 10 to 100 kHz range. CO<sub>2</sub> laser short pulse gain and optical isolation techniques are reported. Optical performance data and design features of the drive laser system are discussed, as well as a path to achieve output power scaling to meet high volume manufacturing (HVM) requirements and beyond. Additionally, the electrical efficiency as a component of cost of operation is presented. Development of a drive laser with sufficient output power, high beam quality, and economical cost of operation is critical to the successful implementation of a laser-produced-plasma (LPP) EUV source for HVM applications. Cymer has conducted research on a number of solutions to this critical need. We report our progress on development of a high power system with two gas-discharge power amplifiers to produce high output power with high beam quality. We provide optical performance data and design features of the drive laser as well as a path to output power scaling to meet HVM requirements. Development of a drive laser for LPP EUV source is a challenging task. It requires multi-kW laser output power with short pulse duration and diffraction limited beam quality. In addition, this system needs to be very reliable and cost-efficient to satisfy industry requirements for high volume integrated circuit manufacturing. Feasibility studies of high power laser solutions that utilize proven laser technologies in high power optical gain modules and deliver required beam properties have been performed and are reported.
This paper provides a detailed review of development progress for a laser-produced-plasma (LPP) extreme-ultra-violet (EUV) source with performance goals targeted to meet joint requirements from all leading scanner manufacturers. We present the latest results on drive laser power and efficiency, source fuel, conversion efficiency, debris mitigation techniques, multi-layer-mirror coatings, collector efficiency, intermediate-focus (IF) metrology, mass-limited droplet generation, laser-to-droplet targeting control, and system use and experience. Results from several full-scale prototype systems are discussed. In addition, a multitude of smaller lab-scale experimental systems have also been constructed and tested. This paper reviews the latest experimental results obtained on these systems with a focus on the topics most critical for an HVM source. Laser produced plasma systems have been researched as probable light source candidates for an EUV scanner for optical imaging of circuit features at 32nm and beyond nodes on the ITRS roadmap. LPP systems have inherent advantages over alternative source types, such as Discharge Produced Plasma (DPP), with respect to power scalability, etendue, collector efficiency, and component lifetime. The capability to scale LPP power with repetition rate and modular design is shown. A path to meet requirements for production scanners planned well into the next decade is presented. This paper includes current testing results using a 320mm diameter near-normal-incidence elliptical collector, the first to be tested in a full-scale LPP system. With the collector in-situ, intermediate focus (IF) metrology capability is enabled, and data is presented that describes the quality of light at IF.
In a laser produced plasma (LPP) EUV source the multilayer mirror (MLM) collector optic will be exposed to a flux of energetic ions and neutral atoms ejected from the plasma as well as condensable vapor from excess target material. We are investigating various techniques for reducing the contamination flux and for in-situ removal of the contamination. The protection strategies under investigation must be compatible with gaseous and condensable target materials such as Xe, Sn, In, Li, and other elements. The goal is to develop MLM structures that can withstand elevated temperatures and develop protective barrier coatings that reduce erosion of the mirror surface. Results of MLM exposure to energetic ion beams and thermal atomic sources are presented. Changes in EUV reflectivity of MLM structures after exposure to ions and deposition of target material have been performed on samples cleaned by these developmental processes. In this paper, we will summarize our initial results in these areas and present techniques for mitigation of MLM damage from the source.
Tin, lithium, and xenon laser-produced plasmas are attractive candidates as light sources for extreme ultraviolet lithography (EUVL). Simulation of the dynamics and spectral properties of plasmas created in EUVL experiments plays a crucial role in analyzing and interpreting experimental measurements, and in optimizing the 13.5 nm radiation from the plasma source. Developing a good understanding of the physical processes in EUVL plasmas is challenging, as it requires accurate modeling for the atomic physics of complex atomic systems, frequency-dependent radiation transport, hydrodynamics, and the ability to simulate emergent spectra and images that can be directly compared with experimental measurements. We have developed a suite of plasma and atomic physics codes to simulate in detail the radiative properties of hot plasmas. HELIOS-CR is a 1-D radiation-magnetohydrodynamics code used to simulate the dynamic evolution of laser-produced and z-pinch plasmas. Multi-frequency radiation transport can be computed using either flux-limited diffusion or multi-angle models. HELIOS-CR also includes the capability to perform in-line non-LTE atomic kinetics calculations at each time step in the simulation. Energy source modeling includes laser energy deposition, radiation from external sources, and current discharges. The results of HELIOS-CR simulations can be post-processed using SPECT3D to generate images and spectra that include instrumental effects, and therefore can be directly compared with experimental measurements. Results from simulations of Sn laser-produced plasmas are presented, along with comparisons with experimental data. We discuss the sensitivity of the 13.5 nm conversion efficiency to laser intensity, wavelength, and pulse width, and show how the thickness of the Sn radiation layer affects the characteristics of the 13.5 nm emission.
Over the past several years, a continuous improvement of the performance parameters of discharge produced plasmas as potential sources of 13.5 nm radiation for commercial EUV lithography systems has been achieved. At Cymer we have continued developing the dense plasma focus (DPF) discharge as an EUV source. The majority of the data presented here is focused on DPF operation with xenon gas. We have recently started investigating the DPF operation with Sn, as well. A significant improvement in conversion efficiency (CE) was observed. We have investigated DPF configurations with different polarity of the drive voltage. Central to both configurations is the pulsed power system, which is being developed to operate in continuous mode at 5 kHz while delivering approximately 10 J to the load. Significant differences have been observed for the energy deposition profiles in the positive and negative polarity systems. Calorimetric data show that the fraction of energy deposited into each discharge electrode depends on the polarity. The thermal engineering of the central electrode remains a major challenge. With the present generation DPF we have demonstrated operation at 5 kHz in burst mode and at 2.3 kHz in continuous mode, with 76 W of in-band energy generated at the source. We observed that certain transient effects in the EUV output were correlated with the degree of energy coupling during the burst. However, we found that the pulsed power system is well matched to the load with >90% of the stored energy coupled to the discharge and electrodes. The conversion efficiency of the DPF operated with Xe is near 0.5% for both polarities, while measurements with Sn show a CE ~1.7%. Plasma modeling supported the optimization of the pinch dynamics and electrodes. Debris mitigation studies were also carried out and the carbon contamination was reduced.
A commercially viable light source for EUV lithography has to meet the large set of requirements of a High Volume Manufacturing (HVM) lithography tool. High optical output power, high-repetition rate, long component lifetime, good source stability, and low debris generation are among the most important parameters. The EUV source, being developed at Cymer, Inc. is a discharge produced plasma source in a dense plasma focus (DPF) configuration. Promising results with Xe as a working gas were demonstrated earlier. To scale the DPF parameters to levels required for HVM our efforts are concentrated on the following areas: (1) thermal engineering of the electrodes utilizing direct water cooling techniques; (2) development of improved pulsed power systems for > 4 kHz operation; (3) study of erosion mechanisms for plasma facing components; (4) development of efficient debris mitigation techniques and debris shields; (5) studies of plasma generation and evolution with emphasis on improving conversion efficiency and source stability; (6) development of EUV metrology techniques and instrumentation for measurements of source size; and (7) development of an optimized collector optic matched to our source parameters. In this paper, we will present results from each of these key areas. The total in-band EUV output energy now approaches 60 mJ/pulse into 2πsr and the conversion efficiency has been increased to near 0.5 %. Routine operation at 4 kHz in burst-mode, and continuous operation at 1 kHz has been demonstrated. Improved at-wavelength source metrology now allows a determination of EUV source size utilizing imaging, and monitoring of key features of the spectrum on a pulse-to-pulse basis. With effective suppression of debris generated from the anode by several orders of magnitude, UV/EUV-catalyzed carbon growth now presents the limit in producing a clean source.