Shielding effect of underlayer against secondary electrons generated in substrate in extreme ultraviolet lithography

Abstract

The wavelength of a radiation exposure source has been reduced to improve the resolution of lithography in the semiconductor industry. The energy of photons reached the ionizing radiation region when using EUV radiation. Because the energy of EUV photons for lithography is 92.5 eV, the EUV photons can ionize all kinds of atom. In this study, the shielding effect of the underlayer against the secondary electrons generated in the substrates was investigated using the bridging risk as an indicator. Secondary electron dynamics was calculated by a Monte Carlo method assuming the resist-underlayer-substrate system. The physical properties of the underlayer were assumed to be the same as those of the resist layer. The secondary electrons generated in the substrate significantly affected the bridging risk when the underlayer thickness was smaller than approximately 5 nm. The resist process should be designed by considering the secondary electrons generated in the substrate.