Effect of post-etch cleaning on Ru-capped extreme ultraviolet lithography photomask

Ru-capped extreme ultraviolet lithography photomasks require cleaning after patterning of the absorber layer. In this study, it was confirmed that, during Cl2 dry etching to remove the absorber layer, RuCl3 was formed on the Ru capping layer surface, and the surface roughness thereby deteriorated. Therefore, the changes in RuCl3 formation and surface roughness with various cleaning processes were investigated. Among the treatments used, i.e., sulfuric peroxide mixture, an ammonia peroxide mixture or ozonated water (DIO3), DIO3 exhibited the most effective Cl removal efficiency and surface roughness recovery. DIO3 treatment successfully reduced the Cl-terminated Ru surface to its original state and decreased the surface roughness to the pre-Cl2-etched Ru value.

► Formation of RuCl3 on the Ru surface after Cl2 etching. ► Increases in Ru surface roughness after Cl2 etching. ► Removal of Cl and recovery of surface roughness after ozonated water cleaning.