Special Section on EUV Sources for Lithography

Laser-produced plasma versus laser-assisted discharge plasma: physics and technology of extreme ultraviolet lithography light sources

[+] Author Affiliations
Guido Schriever

XTREME Technologies GmbH, Steinbachstrasse 15, 52074 Aachen, Germany

Science and Technology Consulting, Göttingen, Germany

Olivier Semprez

XTREME Technologies GmbH, Steinbachstrasse 15, 52074 Aachen, Germany

Jeroen Jonkers

XTREME Technologies GmbH, Steinbachstrasse 15, 52074 Aachen, Germany

Masaki Yoshioka

XTREME Technologies GmbH, Steinbachstrasse 15, 52074 Aachen, Germany

Rolf Apetz

XTREME Technologies GmbH, Steinbachstrasse 15, 52074 Aachen, Germany

J. Micro/Nanolith. MEMS MOEMS. 11(2), 021104 (May 29, 2012). doi:10.1117/1.JMM.11.2.021104
History: Received August 24, 2011; Revised November 8, 2011; Accepted January 12, 2012
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Abstract.  Powerful extreme ultraviolet (EUV) sources at 13.5 nm are a prerequisite for the economical operation of lithography scanners for semi-conductor manufacturing. These sources have been under development for more than 10 years. At the beginning, many source concepts were considered. Compact technologies like dense plasma focus or capillary Z-pinch discharges reached very rapidly fundamental limits as far as power scalability and lifetime were concerned. Other complex technologies—like synchrotrons—eventually dropped out of the race as well, exceeding by far the footprint and cost targets. Over time, the technology solidified toward the two source concepts: on one hand, the discharge produced plasmas (DPP), which eventually led to the development of the current laser-assisted discharge plasma (LDP); on the other hand, the laser-produced plasmas (LPP). All these technologies generate hot and dense plasmas of similar properties, which emit EUV radiations efficiently as a black body radiator or Planck emitter, in a pulsed manner. The plasma generation method, however, is quite different. DPP uses a pulsed high-voltage current discharge to generate plasma heating a gaseous or vaporized material up to temperatures close to 200,000°C. As for LPP, microscopic droplets of molten tin are fired through a vacuum chamber, individually tracked, vaporized by a pre-pulse laser, and eventually irradiated by a pulsed high-power infrared CO2 laser at 50 to 100 kHz, creating a high-temperature tin plasma, which radiates EUV light. In the case of LDP the plasma is generated between two rotating discs. Partially immersed in baths filled with liquid tin, the discs are wetted and covered with a thin layer of liquid tin. A pulsed laser beam focused on one of the discs evaporates a small amount of tin and generates a tin cloud between the two discs. Next a capacitor bank, which is connected to the discs via the liquid tin, discharges and converts the tin cloud into a plasma heated up to 200,000°C as well. Pinched by the high current, the plasma emits the EUV radiation. This process is repeated several thousand times per second. The resulting heat-load is cooled away by the liquid tin, which is kept at constant temperature by an external cooler. In this paper, following an overview of the requirements for EUV to transition to high-volume manufacturing (HVM), we compare LDP and LPP at every step of the process of generation of EUV photons and eventually highlight the challenges both technologies respectively face on the path to HVM.

Figures in this Article
© 2012 Society of Photo-Optical Instrumentation Engineers

Citation

Guido Schriever ; Olivier Semprez ; Jeroen Jonkers ; Masaki Yoshioka and Rolf Apetz
"Laser-produced plasma versus laser-assisted discharge plasma: physics and technology of extreme ultraviolet lithography light sources", J. Micro/Nanolith. MEMS MOEMS. 11(2), 021104 (May 29, 2012). ; http://dx.doi.org/10.1117/1.JMM.11.2.021104


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