Michael B. Petach

Xenon target performance characteristics for laser-produced plasma EUV sources

Laser-produced plasmas (LPPs) are being developed as light sources for EUV lithography. To meet the requirements for high-volume manufacturing, LPP EUV sources must generate intense EUV output in the 13.5 nm band, and minimize source-induced degradation of EUV optics allowing hundreds of hours of clean operation. Xenon has been identified as a promising target material for LPP EUV light sources, with the potential for both high-efficiency EUV generation, and low optics contamination. Several dense xenon target configurations have been tested including aerosol sprays, continuous liquid streams, condensed xenon droplets, and frozen solid xenon. Important LPP performance characteristics, such as conversion efficiency, EUV radiation distribution, EUV optics degradation by material erosion and/or deposition, and the physical interface to the EUV optical system, are strongly influenced by the xenon target design. The performance of xenon targets with measured conversion efficiencies in the 0.4 percent to 1.4 percent range is reported. Prospects for xenon targets to reach the EUV power generation and contamination goals for production lithography tools are addressed.

Laser-produced plasma (LPP) scale-up and commercialization

An EUV light source, created when a high-average power (750 W) Nd:YAG laser forms a plasma in a xenon liquid-spray jet, has been characterized. This source has shown improved conversion from laser to EUV, and a more uniform angular distribution, as the laser pulse energy and average power are increased. System performance has been analyzed and compared with the requirements for future EUV microlithography tools for semiconductor manufacturing. EUV power scaling requirements and factors influencing Cost-of-Ownership are discussed.

Miniature Long-Life Space-Qualified Pulse Tube and Stirling Cryocoolers

Cryogenic coolers for small satellites require low power and minimum weight. In this paper we report on the status of both our miniature flight-qualified pulse tube cooler as well as our miniature flight-qualified Stirling cooler. Both integral linear coolers are small, efficient, low-power, and vibrationally balanced, and incorporate Oxford-type single flexure-bearing compressors. Vibrational balance is achieved with a motor-driven balancer. The Stirling cooler cold head incorporates a colinear flexure-bearing suspended displacer/regenerator with a motor drive used for phase control. The larger capacity pulse tube cooler uses a completely passive cold head which contains no cold moving parts. Nonwearing clearance seals in both coolers advance the long 10-year life projections.

Laser-produced plasma light source for extreme ultraviolet lithography

Pulsed Nd:YAG lasers have been developed to achieve high peak power and high pulse repetition rate. These systems are being used as drivers for laser-produced plasmas which efficiently convert the 1064-nm laser output to extreme ultraviolet (EUV) light at 13.5 nm for future microlithography systems. The requirements for laser-produced plasma EUV light sources and their integration in lithography tools for high-volume manufacturing are reviewed to establish the key design issues for high-power lasers and plasma targets. Xenon has been identified as a leading target material to realize the goals of intense EUV emission and clean operation. Recent progress in high-power diode-pumped Nd:YAG lasers and xenon targets for EUV generation is reviewed, showing that laser-produced plasma sources meet the needs for current EUV lithography development tools. Future directions to meet EUV source requirements for high-volume manufacturing tools are discussed.

Xenon Target and High-Power Laser Module Development for LPP Sources

This chapter gives an overview of LPP EUV source development work at Northrop Grumman Corporation (NGC). The chapter covers development of the laser module, xenon target, and overall system. The volume editor (V. Bakshi) prepared this chapter as a summary of information provided to him by NGC. Lasers for LPP EUV sources are expected to produce tens of kilowatts of high-pulse-rate, high-pulse-energy, short-pulse-width, near-diffraction-limited output. Such lasers will be focused onto a condensed jet of cryogenic xenon or tin targets to produce a plasma with sufficient temperature to generate EUV radiation. For the generation of the EUV-producing plasma, pulse widths of around 10 ns and pulse energies in the range of 0.5 to 1 J are required. High beam quality and low pointing error are required to maintain constant high intensity on the EUV source target so that the radiated EUV power and consequent exposure doses on the semiconductor wafer are uniform. Depending on the choice of target material, eventually pulse rates of at least 7500 Hz and laser powers of 10–30 kW will be required to ensure the required power collection at the intermediate focus (IF). In 1999, NGC constructed a 1700-W diode-pumped Nd:YAG phase-conjugated master oscillator-power amplifier (MOPA) laser, designated EUV-Alpha, which was used in a lithography testbed at Sandia Labs in Livermore (see Chapter 24 for further description). Later NGC built an EUV-Beta laser (Fig. 25.1) that produced 4500 W and was operated at NGCs EUV source development facility at Cutting Edge Optronics (CEO). The Beta laser, a modular design for better maintainability, was twice as efficient and had two-thirds the footprint of the Alpha laser. For this laser, NGC selected a MOPA architecture (Fig. 25.2) using stimulated Brillouin scattering (SBS) phase conjugation to compensate for aberrations, figure error, and thermal distortions in the Nd:YAG gain media. The output of a custom 12-W master oscillator (MO) was split in two with a polarizer and directed to two amplifier trains. Each amplifier train consisted of two diode-pumped zigzag slab amplifiers, image relay telescopes, shaping optics, and an SBS cell. After round trips through the two slab amplifiers, the two MO beams were brought to their full 750-W power in each train, and then polarization-combined for a total of 1500 W. In the Beta laser, there were three such 1500-W modules, which yielded a system total of 4500 W at 7500 Hz.