Control of residual stress in extreme ultraviolet multilayer coatings

Study of stress in Mo/Si multilayers is carried out for application of extreme ultraviolet multilayer coatings in the diagnosis of high density plasmas and extreme ultraviolet lithography. Stress generating mechanisms is discussed. Precise measurement of stress is taken by ZYGO interferometer. It is observed that the growth of the Mo component in the multilayers is tensile, while that of the Si component is compressive. The residual stress in a 40-bilayer Mo/Si multilayer coating with high reflectivity is -500 MPa (compressive), stress generation may be attributed to the interfacial diffusion. By varying Mo-to Si thickness ratio(Γ), the stress in multilayers can be compensated to a certain extent. However, the reflectance of Mo/Si multilayers is reduced correspondently.