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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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