Cross sections of EUV PAGs: influence of concentration, electron energy, and structure

Abstract

Optimizing the photochemistry of extreme ultraviolet (EUV) photoresists should provide faster, more efficient resists which would lead to greater throughput in manufacturing. The fundamental reaction mechanisms in EUV resists are believed to be due to interactions with energetic electrons liberated by ionization. Identifying the likelihood (or cross section) of how these photoelectrons interact with resist components is critical to optimizing the performance of EUV resists. Chemically amplified resists utilize photoacid generators (PAGs) to improve sensitivity; measuring the cross section of electron induced decomposition of different PAGs will provide insight into developing new resist materials.To study the interactions of photoelectrons generated by EUV absorption, photoresists were exposed to electron beams at energies between 80 and 250 eV. The reactions between PAG molecules and electrons were measured using a mass spectrometer to monitor the levels of small molecules produced by PAG decomposition that outgassed from the film. Comparing the cross sections of a variety of PAG molecules can provide insight into the relationship between chemical structure and reactivity to the electrons in their environments. 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].…”

“…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].…”

“…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.…”

“…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.…”