Gigaphoton Confirms Debris Mitigation Technology
OYAMA, Japan, July 14, 2011 — Gigaphoton Inc., a lithography light source manufacturer, announced that it has confirmed its original technology for mitigating debris with magnetic fields for laser-produced plasma (LPP) light sources. It plans to push forward with a mass-production model in the beginning of 2012.
Gigaphoton has been working on the development of LPP light sources for EUV lithography in pursuit of higher output and better cost of operation since 2002. In production-level light sources, the company said its technology of debris mitigation with magnetic fields can remove 92 percent of debris, enabling greater reduction in Sn (tin) deposited on the collector mirror as well as in damage to the multilayer film of the mirror. Gigaphoton considers that this will become indispensable for full-production models of LPP light sources for EUV lithography.
The LPP light source allows radiation by a CO2 laser of the Sn target (droplets) to cause emission of EUV. Sn debris, such as Sn fragments and Sn atoms, deposits on the collector mirror, and Sn ions damage the multilayer film on the collector mirror. As a result, the reflectance of the collector mirror is lowered within a short period, reducing the output. This is a serious problem for full-production light sources.
The Gigaphoton-proposed technology for debris mitigation with magnetic fields uses an optimum combination of the prepulse generated by a solid-state laser and the main pulse generated by a CO2 laser to suppress the generation of Sn fragments and neutral Sn atoms and to ionize most of the Sn in each droplet. Ionized Sn is guided to the Sn catcher by magnetic power and then removed to minimize deposition on and damage to the collector mirror.
During the verification experiment, the main pulse of the CO2 laser radiates each 20-µm-diameter droplet following the prepulse by a solid-state laser to completely eliminate Sn fragments. As a result, it is has been confirmed that 93 percent of droplets are ionized. Optimum magnetic power then is applied to the droplets, guiding more than 99 percent of Sn ions to the Sn catcher. This allows the minimization of damage to the multilayer film on the collector mirror surface. It also becomes a clue for making the mirror reusable.
Although the remaining 7 percent of nonionized Sn atoms after laser radiation may slowly deposit on the collector mirror, the company uses etching gas to allow regular cleaning to remove them.
As double-pattern lithography with a 193-nm immersion lithography tool approaches its resolution limit, an EUV light source with a much shorter wavelength is considered to be the next-generation lithography solution that can support Moore's Law for multiple device generations to come. To implement the EUV lithography tool, stabilized operation of the light source has been the major challenge among the technology elements. Overcoming this challenge, therefore, has been considered worthy of attention.
For more information, visit: www.gigaphoton.com