Highly selective dry etching of alternating phase-shift mask (PSM) structures for extreme ultraviolet lithography (EUVL) using inductively coupled plasmas (ICP)

Extreme ultraviolet lithography (EUVL) is the most promising candidate for next generation lithography due to its feature size of 32 nm or below. We investigated the etching properties of materials in an alternating, phase-shift mask (PSM) structure for EUVL, including a Ru top capping layer, Mo-Si multilayer (ML) and Ni etch stop layer (ESL), by varying the Cl2/O2 and Cl2/Ar gas flow ratios, and the dc self-bias voltage (Vdc) in inductively coupled plasma (ICP). The Ru layer could be etched effectively in Cl2/O2 plasmas and Mo-Si ML could be etched with an infinitely high etch selectivity over Ni ESL in Cl2/Ar plasmas, even with increasing overetch time.