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In
recent years, laser applications have been gaining significance in
the field of micro- and macro-processing. An increasing number of
laser systems are used, and more and more importance is being
placed on these systems. This also holds for optics, in particular
for excimer lasers of shorter wavelengths (193 nm or 157 nm). Optical thin-film
technology is the chosen method for providing the high efficiency and
resolution which is necessary in, for example, laser medicine or semiconductor
lithography. |
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The number of suitable coating
materials is, however, highly restricted in this spectral range.
Apart from the oxides
SiO2 and
Al2O3, only fluoride materials (LaF3,
NdF3,
DyF3,
GdF3,
CaF2,
LiF,
MgF2,
AIF3,
and
Cryolite)
apply. Substrates may well be coated conventionally, but using pure
fluorine, or fluorine compounds as reactive gas components, leads to
a higher quality of the optics. This, however, is associated with
industrial safety and environmental problems. Therefore, LTS
(Chemical) Inc. has conducted investigations on alternative coating
methods in thin-film technology in the UV range. In particular, LTS
has focused on reactive gas processing, which highly dangerous for
the environment and must be replaced. |
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a) One solution is our novel
production method, which allows us to introduce excess fluorine (LaF3) into
the material in a controlled manner.
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b) Another solution to the problem is to mix the existing
fluoride compounds, which makes aggressive reactive gas unnecessary. Fluoride compounds can be combined in multiple ways; this allows for a large variety of
suitable coating materials. The coating properties can be optimally adapted, and adhesion problems on the substrate can be overcome e.g. by adding other suitable fluoride compounds. One way to introduce fluorine is to maintain levels of fluoride in the starter
material through the introduction of a second Halide as a doping component, which is a constituent of liquid phase formulation. As a result of such research, we
offer
for DUV coating. |
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Varied mixing ratios also allow further improvements of the
coatings’ optical properties. The stability of the coatings can be improved
considerably through an optimized adaptation of the structure, and pollutant
deposits in the coating can be reduced. This leads to an improved lifetime of
the optical components. The project was supported by the International SEMATECH
initiative.
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