Enhancement of EUV reflective multilayer properties by the insertion of Ru barrier layer

Although there are several ways to ensure the high throughput of EUVL process, increasing the EUV reflectivity of the multilayer mirror might be the simplest but still efficient solution for that. Many works to enhance the multilayer reflectivity have been reported and a good deal of them is related to the addition of barrier layers, such as B/sub 4/C and C into Mo/Si multilayer stack. Also, there was a try of sub-multilayering of Mo with Ru insertion to reduce the multilayer stress. In our experiment, we inserted Ru into Mo/Si multilayer to improve the optical property.