Highly reliable DUV light sources are required for semiconductor applications such as a photomask inspection. The
mask inspection for the advanced devices requires the UV lightning wavelength beyond 200 nm. By use of dual fiber
lasers as fundamental light sources and the multi-wavelength conversion we have constructed a light source of 198nm
with more than 100 mW. The first laser is Yb doped fiber laser with the wavelength of 1064 nm; the second is Er doped
fiber laser with 1560 nm. To obtain the robustness and to simplify the configuration, the fundamental lights are run in
the pulsed operation and all wavelength conversions are made in single-pass scheme. The PRFs of more than 2 MHz
are chosen as an alternative of a CW light source; such a high PRF light is equivalent to CW light for inspection
cameras. The light source is operated described as follows. Automatic weekly maintenance within an hour is done if it is
required; automatic monthly maintenance within 4 hours is done on fixed date per month; manufacturer's maintenance is
done every 6 month. Now this 198 nm light sources are equipped in the leading edge photomask inspection machines.
A novel continuous-wave blue-green laser was developed by the second-harmonic generation of the emission from Yb doped gain fiber. The laser cavity consists of a fiber Bragg grating (FBG), a gain fiber, an aspheric lens, a dichroic mirror for output coupling of second harmonic, a periodically-poled LiNbO3 (PPLN), and a high reflector. The intracavity-doubled fiber laser was pumped by a 580-mW, fiber pigtailed laser diode at 974 nm through the FBG. The Yb laser emission from the fiber end was focused onto the high reflector, providing optical feedback and forming the resonator. The PPLN was placed near the flat end mirror, where the waist is formed, in order to increase the fundamental intensity. The emission wavelength can be selected by changing the FBG within the bandwidth of the gain fiber. An FBGs for 1017.6 nm was selected for the experiment. Circulating power of the fundamental wave in the cavity was measured to be approximately 1500 mW when a 5% output coupler was placed instead of high-reflecting mirror. Stable output in excess of 30 mW at 508.8 nm was obtained. The optical-optical efficiency from the pump power to the visible output was about 5%. The fluctuation of the laser output power was less than 0.5% for more than 2 hours without a power feedback loop. The M2 value was measured to be 1.2. Wavelength-selectable lasers will be useful for applications including fluorescent microscopy, biological imaging, flow cytometry and spectroscopic analysis.
The optical emission spectra of the plasma produced by infrared and ultraviolet laser ablation of graphite in a vacuum were observed. The fundamental output of an Nd: YAG laser was used as the infrared laser. The fourth harmonic output of an Nd: YAG laser and a KrF excimer laser were used as the ultraviolet lasers. The emission intensity of the ionic carbon as well as C2 and C3 from the plasma produced by the infrared laser were stronger than that produced by the UV lasers at the same fluences. The C2 and C3 emission intensities decreased rapidly with increasing the distance from the target. The emission intensity of atomic carbon at 247.8 nm from the plasma produced by the KrF excimer laser was much stronger than that produced by the other lasers at the same laser fluence, due to the wavelenght of the KrF laser being so close to that of atomic carbon's emission line as to raise its electrical state.
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