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

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), Al ₂ O₃ (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 (V _dc), and etch time in inductively coupled plasmas. For the fabrication of the attenuated EUVL mask structure proposed herein, the TaN, Al₂ O₃, 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 B Cl₃/Cl₂/Ar plasmas with a V_dc of -100 V 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 V_dc of -25 V even with increasing overetch time.