Optimizing the photochemistry in extreme ultraviolet (EUV) photoresists due to EUV exposures may enable faster, more efficient resists, leading to a greater throughput in manufacturing. Since the fundamental reaction mechanisms in EUV resists are believed to be due to electron interactions after incident 92 eV photons (13.5 nm) generate photoelectrons during ionization events, understanding how these photoelectrons interact with resist components is critical for optimizing the performance of EUV resists and EUV lithography as a whole. The authors will present an experimental method to measure the cross section of incident electron induced decomposition of three different photoacid generators (PAGs). To study the photoelectrons generated by the EUV absorption and measure their effect within resists, photoresists were exposed to electron beams at electron energies between 80 and 250 eV. The reactions between PAG molecules and electrons were measured by using a mass spectrometer to monitor the levels of small molecules produced by PAG decomposition that outgassed from the photoresist. This methodology allowed us to determine the number of PAG molecules decomposed per incident electron. By combining this result with the average penetration depth of an electron at a given energy, the cross sections of PAG molecules were determined for energies ranging between 80 and 250 eV. Comparing the cross sections of PAG molecules can provide insight into the relationship between chemical structure, reactivity to the electrons, and trends in cross section versus electron energy. This research is a part of a larger SEMATECH research program to understand the fundamentals of resist exposures to help in the development of new, better performing EUV resists.
EUV photons expose photoresists by complex interactions starting with photoionization that create primary electrons (~80 eV), followed by ionization steps that create secondary electrons (10-60 eV).Ultimately, these lower energy electrons interact with specific molecules in the resist that cause the chemical reactions which are responsible for changes in solubility. The mechanisms by which these electrons interact with resist components are key to optimizing the performance of EUV resists. An electron exposure chamber was built to probe the behavior of electrons within photoresists. Upon exposure and development of a photoresist to an electron gun, ellipsometry was used to identify the dependence of electron penetration depth and number of reactions on dose and energy. Additionally, our group has updated a robust software that uses first-principles based Monte Carlo model called "LESiS", to track secondary electron production, penetration depth, and reaction mechanisms within materialsdefined environments. LESiS was used to model the thickness loss experiments to validate its performance with respect to simulated electron penetration depths to inform future modeling work.
This paper describes the synthesis of acid-catalyzed chain-scission polymers and the lithographic results of these polymers in extreme ultraviolet (EUV) resist formulations. These platforms incorporate acid-catalyzed cleavable groups into the polymer backbone. Upon exposure to EUV light and bake, the polymer is transformed from high to low molecular weight segments in the exposed regions. Two polymers were made into resist formulations and tested at Lawrence Berkeley National Laboratories. One of these resists appeared to have highresolution capabilities with modulation down to 14 nm h/p lines.
A novel series of stable, acid amplifiers (AAs) has been designed and tested for use in Extreme Ultraviolet (EUV) lithography, that generate strong, fluorinated polymer bound sulfonic acids. Novel polymer bound and blended AAs were prepared in moderate to good yields and characterized by NMR. We demonstrated by EUV lithography that the polymer bound AA resist has line-edge roughness (LER) values of 3.8 nm and the polymer blended AA resist has LER values of 2.1 nm while the control resist has LER values of 4.6 nm.Although sensitivity comparisons have yet to be made, these new resists using bound and blended AAs are showing remarkable improvements in LER when compared with the control resist without AAs.
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