Selective dry etching of attenuated phase-shift mask materials for extreme ultraviolet lithography using inductively coupled plasmas

Abstract

Among the core extreme ultraviolet lithography (EUVL) technologies, mask fabrication is of considerable importance due to the use of new reflective optics having a completely different configuration from that of conventional photolithography. This study investigated the etching properties of attenuated phase-shift mask materials for EUVL, such as TaN (attenuator layer), Al2O3 (spacer), Mo (phase shifting layer), Ru (buffer/capping/etch-stop layer), and Mo–Si multilayer (reflective layer) by varying the Cl2∕Ar gas flow ratio, dc self-bias voltage (Vdc), and etch time in inductively coupled plasmas. For the fabrication of the attenuated EUVL mask structure proposed herein, the TaN, Al2O3, and Mo layers need to be etched with no loss of the Ru layer on the Mo–Si multilayer. The TaN and Al2O3 layers were able to be etched in BCl3∕Cl2∕Ar plasmas with a Vdc of −100V and the Mo layer was etched with an infinitely high etch selectivity over the Ru etch-stop layer in a Cl2∕Ar plasma with a Vdc of −25V even with increasing overetch time.