Cross sections of photoacid generators at low electron energies

Abstract

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.

Acid Generation Efficiency of EUV PAGs via Low Energy Electron Exposure

“…An example of a possible acid generation pathway for a select PAG molecule. In this reaction pathway benzene is created as a product and can be used to monitor the number of acid generation events in the resist due to exposure [1,[6][7][8].…”

“…It is well known that when a photoresist is exposed to EUV photons that molecules will outgas [1,[4][5][6][7]. For select PAGs, some of these outgassing molecules correlate to an acid generation event (Fig.…”

“…For select PAGs, some of these outgassing molecules correlate to an acid generation event (Fig. 1) [1,6,7]. Photochemistry in EUV exposures is dominated by the secondary electron cascade after ionization.…”

“…Here, a third method is utilized to measure acid generation efficiency that involves measuring the outgassing products as a means to quantify the number of reactions occurring within the photoresist during exposure [6,7]. It is well known that when a photoresist is exposed to EUV photons that molecules will outgas [1,[4][5][6][7].…”

“…The PAG is a photon-or electron-sensitive molecule that is capable of producing an acid which catalyzes numerous chemical transformations in the surrounding resist [1][2][3][4][5][6][7]. Further improvement of chemically amplified photoresists for use with EUV is crucial to meet the lithographic requirements of the microelectronics industry, or an innovative nonchemically amplified resist must be developed to satisfy this need.…”