Investigation of multilayer structural changes in phase and amplitude-defects correction process

Abstract

Controlling defects on the extreme ultraviolet lithography (EUVL) mask has become a critical issue among many EUVL element technologies. We have conducted experiments to investigate the correctability of two kinds of major defect types, phase and amplitude defects. Phase defects correctability was addressed by using the electron-beam local heating method and amplitude defects correctability were done by using the focused ion-beam (FIB). Additionally, two kinds of multilayers, Mo∕Si and Mo∕Ru∕Si, were used as substrates to inspect the behavior in a comparative way. As a result, the sink brought by electron-beam (e-beam) localized heating on a planar multilayer surface was about 8 and 13.6 nm in Mo∕Si and Mo∕Ru∕Si multilayers, respectively, under the e-beam dose of 250μC∕cm2. However, the heating effect was limited to within a few layers from the surface. FIB etching was also conducted on a planar surface of a multilayer. There are two types of FIB correction methods, image mode and spot mode. The etched area was relatively large (∼3μm×3μm) in image mode. But in the spot mode, the etched area could be confined to a few tens of nanometers in diameter. This FIB method also caused some damage on the multilayer surface.