Carbon/boron multilayer for beyond EUV lithography

In 2019, EUV lithography technology with a wavelength of 13.5 nm was first applied to mass production of 7 nm+ node logic devices. In the future, since semiconductor devices with higher-density electronic circuits are required, beyond EUV (BEUV) lithography technology with an exposure wavelength around 6.7 nm is expected to utilize as the next generation lithography. The development of multilayer with high reflectivity is a critical issue for BEUV lithography. La/B-based multilayers were reported as a high theoretical reflective multilayer. However, the stability of the reflectance of La/B-based multilayers is low because of the high reactivity of La material. Thus, we propose carbon/boron (C/B) multilayer for BEUV multilayer. The C/B multilayer has a high theoretical reflectance of approximately 80%, which is comparable to the La/B multilayer. The optical constant of the carbon film depends on its density, and high density is required to obtain high reflectance and wide reflection bandwidth. For the C/B multilayer performance estimation, we deposited carbon and boron monolayer films and measured the actual optical constants at BEUV light using a reflectometer at the NewSUBARU synchrotron light facility. We discuss the performance of the C/B multilayer using the measured optical constants.