TuD2
Laser-Produced Plasma EUV Sources Harry Shields, Richard H. Moyer, Fernando Martos, Stuart McNaught, Randall St. Pierre, Steven W. Fornaca, and Mark Michaelian, Northrop Grumman Space Technology, Redondo Beach, CA 90278 Telephone: 310-813-2608 Fax: 310-812-1684 Email:
[email protected]
Abstract: Progress in laser-produced plasma EUV generation for advanced micro-lithography is reviewed and compared with industry requirements. Performance of a high power diode-pumped Nd:YAG laser and a xenon target is presented, demonstrating that intense emission and clean operation are feasible, and these sources can meet EUV power requirements for high-volume manufacturing. 2003 Optical Society of America OCIS codes: (140.0140) Lasers and optics; (260.7200) Ultraviolet, extreme
Summary: Pulsed Nd:YAG lasers have been developed to achieve high peak power and high pulse repetition rate. These lasers are being used as drivers for laser-produced plasmas (LPPs) that efficiently convert the 1064 nm laser output wavelength to EUV light at 13.5 nm for future microlithography systems. The continued reduction in microelectronic feature sizes demanded by Moore’s Law has driven the development of lithography tools based on light sources of increasingly shorter wavelength. The 13.5 nm wavelength has been adopted because of the availability of Mo-Si multilayer mirrors that can achieve reflectivity of 65% to 70% in the 13 to 14 nm band. Using projection optics with a numerical aperture (NA) of 0.25, and process parameter k = 0.65 enables circuit features to be printed at a resolution of R = kλ/(NA) = 35 nm. This is the target feature size for insertion of EUV systems in manufacturing. For cost-effective, high-volume manufacturing it has been estimated that a collected EUV power of greater than 100 W will be needed. This presents significant challenges for high power pulsed laser development, efficient conversion to EUV output, and effective thermal management in the plasma source. Xenon has been identified as a promising target material for LPP EUV light sources, with the potential for both high-efficiency EUV generation, and minimal contamination of EUV optics allowing hundreds of hours of clean operation. Efficient absorption of the laser pulse energy requires that the xenon target has a high density. A condensed xenon stream target has been developed, demonstrating conversion efficiency from laser to in-band EUV pulse energy of about 1%. This xenon target system can support laser pulse rates exceeding 20 kHz. For high power EUV generation, a diode-pumped Nd:YAG laser system has been developed with a 4.5 kW average power output at a pulse rate of 7.5 kHz. The laser system consists of three modules, each generating pulses at 2.5 kHz, and the beams from these modules are directed to a common focus at the xenon target where the focused laser intensity is about 1012 Wcm-2. The average EUV power generated by this LPP system is 45 W in a 2% bandwidth at 13.5 nm. This paper will discuss the requirements for LPP sources for manufacturing-scale EUV lithography, and the current status of high power laser and target technology. Measurements of EUV power generation and source characteristics such as radiation distribution, spectrum, stability, etc. will be presented. Prospects for using LPP sources to reach the EUV power and contamination goals for production lithography tools will be addressed.
