Mean free path of electrons in EUV photoresist in the energy range 20 to 450 eV

The blur caused by the nonzero mean free path of electrons in photoresist during extreme ultraviolet lithography has detrimental consequence on patterning resolution, but its effect is difficult to measure experimentally. In this work, a modified substrate-overlayer technique was used to evaluate the attenuation of the photoemission spectra produced in thin chemically amplified photoresist films. The inelastic mean free path of electrons was found to be between 1 to 2 nm in the entire range of interest for EUV lithography (20 to 100 eV kinetic energy). At higher kinetic energy, the mean free path increased consistently with well-known behavior. The presence of photoacid generator and quencher did not change the mean free path significantly (within experimental error).