Measuring extreme-ultraviolet secondary electron blur (Conference Presentation)

Abstract

Extreme-ultraviolet (~13.5 nm) lithography is much different than the previous lithographic wavelength such that chemical reactions within the resist are caused by electrons generated from ionization. As the lithographic community moves towards printing more advanced nodes, the secondary electron blur from extreme-ultraviolet photons becomes more critical. Understanding the range of the secondary electrons from the photoionization site would provide insight into patterning capabilities for different photoresists and aid in the development of improved models. Here, we aim to determine the range of electrons by measuring the thickness loss due to top-down electron beam exposure. More importantly, this work focuses on measuring the thickness loss due to incident electrons with energies less than 80 eV for two different resist systems: (1) a chemically amplified photoresist where acid diffusion affects the depth of solubility changing reactions, and (2) a non-chemically amplified photoresist, PMMA, where no acid diffusion occurs. Photoresists are exposed to electrons, baked, and developed; subsequent ellipsometry is used to quantify the depth at which solubility changing reactions occur based on the incident energy and dose. Quencher concentration and post-exposure bake parameters are varied to mitigate acid diffusion to extrapolate the electron range. The results are then compared to the thickness loss of the non-chemically amplified photoresist.