AVS 62nd International Symposium & Exhibition
    Nanometer-scale Science and Technology Thursday Sessions
       Session NS+MN-ThM

Paper NS+MN-ThM1
Electron Stimulated Desorption and Raman Investigations of HafSOx Inorganic Resists

Thursday, October 22, 2015, 8:00 am, Room 212B

Session: Nanopatterning and Nanolithography/Nanoscale Mechanics
Presenter: Ryan Frederick, Oregon State University
Authors: R. Frederick, Oregon State University
G. Herman, Oregon State University
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Hafnium oxide hydroxide sulfate (HafSOx) materials are under investigation as inorganic photoresists due to their high patterning fidelity, which is important for next-generation nano-lithography. In order to develop materials with better patterning sensitivity and higher resolution it is critical to understand the underlying mechanisms that result in the soluble/insoluble transition after exposure to radiation. Prior studies have shown that the incorporation of hydrogen peroxide into HafSOx is necessary to provide radiation sensitivity. In this presentation we will demonstrate that electron stimulated desorption (ESD) is a very useful technique for the characterization of radiation-induced mechanisms in HafSOx, and potentially other inorganic photoresists. These ESD studies are being performed with low energy electrons, Ekin = 50 - 500eV, which includes the range of photoemitted and secondary electron energies expected during extreme ultraviolet (EUV) lithography. In the case of HafSOx films we found significant O2 desorption during ESD for films containing hydrogen peroxide, and found no O2 desorption during ESD for films not containing hydrogen peroxide. These studies suggest that O2 is the primary ESD species, and this desorption product can be correlated with the radiation sensitive hydrogen peroxide that is incorporated in the HafSOx films. We have used the Menzel-Gomer-Redhead desorption model to determine the O2 ESD cross-sections over a range of electron energies and doses, and determined that the cross-sections range from 2 ×10-15 to 8 ×10-15 cm2. To confirm that these low energy electrons can drive the soluble/insoluble transition in HafSOx we have measured contrast curves using ellipsometry to measure film thickness after exposing HafSOx to 100eV electrons for various electron doses and after development. The soluble/insoluble transition was found to occur in the electron dose range between 100 to 250 μC/cm2. We have also used Raman spectroscopy to better understand the radiation-induced processes in HafSOx by monitoring the metal coordinated peroxide species after various electron doses. There were very similar reaction kinetics when comparing the increase in O2 desorption signal during ESD and the decrease in the peroxide Raman signal for increasing electron dose. Finally, we will discuss the radiation-induced mechanisms in HafSOx and relate these to other inorganic photoresists being developed for EUV lithography.