Evaluation of Metal Absorber Materials for Beyond Extreme Ultraviolet Lithography

In addition to the development of extreme ultraviolet lithography (EUVL), studies on beyond extreme ultraviolet lithography (BEUVL), which uses radiation with a wavelength of 6.7 nm, are in progress for their application in high-volume manufacturing. The BEUV wavelength, which is much shorter than the EUV wavelength, improves the resolution of patterned features. However, suitable materials for the mask stack of BEUVL are still under development. In this study, the applicability of metallic materials, such as Ni, Co, Ir, W, and Ta, as the absorber in a binary-intensity BEUVL mask was evaluated. The mask-imaging properties were simulated by adopting a thickness that ensured a reflectivity of <1% for each material. Furthermore, we used a multilayered La/B mirror--which exhibited a high reflectivity at a wavelength of 6.7 nm--because BEUV light is absorbed by most materials, and therefore uses reflective optics as desired. The numerical aperture (NA), angle of incidence, and demagnification factor were 0.5 and 0.6, 6 degrees, and 8x, respectively. We confirmed that a line-and-space pattern with a half-pitch of 11 nm can be patterned with metallic absorbers by using a high NA.