Evaluation of Hydrogen-Induced Blistering of Mo/Si Multilayers with a Capping Layer

Mo/Si multilayer mirrors are used for extreme ultraviolet (EUV) lithography. The formation of hydrogen-induced blisters in the Mo/Si multilayer is a problem that reduces the reflectance of the mirror. To evaluate the blister-resistance of EUV mirrors, the blister formation processes of Mo/Si multilayers with a capping layer were investigated using a high-frequency hydrogen plasma system as a hydrogen ion source under varying hydrogen ion exposure conditions. As a result, it was observed that blister formation by low-energy hydrogen ion irradiation of about 10 eV increases the blister-occupied area, depending on the amount of the ion dose. Furthermore, the sample was heated to promote the diffusion of hydrogen atoms, and the activation energy of blister formation was examined using the Arrhenius plot of the ion dose required for blister formation with respect to the heating temperature. The analysis showed that when the ion flux is known, the blister formation time can be predicted.