Page 59 - High Power Laser Handbook

30 G a s , C h e m i c a l , a n d F r e e - E l e c t r o n L a s e r s Excimer Lasers 31

10000

1000
Power (Watt) 100

10

1
1970 1975 1980 1985 1990 1995 2000 2005 2010 2015
Year
Figure 2.12 Power roadmap of commercial excimer laser.

power level reached 1200 W, and higher powers are on the roadmap
to maximize the throughput and overall economics of industrial
applications.

2.3.2 Microlithography
The excimer’s deep UV (DUV) wavelength has a substantial advan-
tage over the 365-nm I line of mercury lamps; this wavelength has
allowed the excimer to achieve smaller features and as such has
helped drive the evolution of large-scale integrated circuits, such
as microprocessors and memory chips. The excimer laser, with its
248-nm wavelength, was chosen for mainstream microlithography
in the early 1990s and, at that time, was considered for 250-nm
features. These lasers are used for microlithography applications
because they can deliver a very narrow spectral width that enables
the high-contrast performance of the stepper lens as well as high
power at a high repetition rate. Today after more than 20 years
deployment of microlithography scanners based on 248 nm (KrF),
the most advanced machines are using 193 nm (ArF) to reach the
65 nm, 45 nm, 32 nm, and 22 nm design nodes.
To achieve a high-resolution image, the laser’s wavelength must
have a very narrow spectrum in order to avoid color aberrations.
Special line-narrowing schemes have been developed that reduce the
output spectrum from the natural width of about 0.5 nm down to
0.1 picometer (pm). For the advanced 193-nm excimer laser used in
microlithography, dual-chamber systems have become the standard.
In these systems, the narrow-output spectrum is achieved by insert-
ing dispersive elements into the resonator of the oscillator. The line-
narrowing module typically consists of a prism beam expander