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Polymers as Resists for Lithography
Lithography is a well known technique with great importance
in the manufacture of microelectronic and micromechanic devices. Typical
materials used are organic polymers, and depending on their response
to the exposing radiation they can be classified as positive or negative.
Positive resists have become more soluble in the irradiated regions relative
to the unexposed areas, whereas negative resists become less soluble in
the irradiated regions relative to the unexposed ones.
According the special demands, different wavelength and polymers are
neccessary to create the desired structures. In each case the incident
radiation causes changes in the polymer depending on the dose and wavelength.The
investigation of these changes is of great interest for two goals, as the
precise knowledge of the reaction products helps to develop and optimize
products.
Analytical Methods
In our experiments, we use ultraviolet- as well as white
synchrotron
radiation. The measurements with synchrotron radiation (SYLI
Bonn) have been performed in close cooperation with the research
group of Prof.
Dr. J. Hormes, of the Department of Physics at the University of Bonn.
Detailed investigations of the reaction products require a combination
of different analytical methods. In particular, the establishment of the
new method of in situ Electron Paramagnetic
Resonance (EPR) spectroscopy coupled with synchrotron radiation offers
many additional possibilities and advantages characteristic for in situ
measurements. In order to perform these measurements, we managed to modify
our spectrometer assembly in a way, that allows in situ investigations
at least down to 100 K. In this context EPR spectroscopy has been used
to analyse the structure and dynamics of the radiation-induced free radicals.
Furthermore, a combination of MALDI-TOF-MS-, FT-IR-, and MS-spectroscopy
as well as wet-chemical methods have been applied to proof the identity
of additional reaction products.The MALDI-TOF-MS-measurements were performed
in cooperation with the research group of Prof.
Dr. F. Vögtle, Kekule-Insitute of Organic Chemistry at the University
of Bonn.
In the course of these studies we have been investigated samples of
polymers prepared in part within our own laboratory as well as their corresponding
monomers, both in solution and in the solid state. To proof our hypotheses
pertaining to their modes of radiation-induced decomposition we also tested
some model substances of low molecular weight.
To examine the solubility of irradiated and non irradiated polymers
in different solvents we make use of the quartz microbalance.
The precise identification of the radiation-induced decompostion products
or of reactive intermediates is sometimes not straightforward. For example,
computer-simulations of the obeserved solid-state-EPR-spectra are often
ambiguous, and in such cases the study of model substances is very helpful
in attempting to understand complicated processes.
Contact: Franz-Josef Hünerbein
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