High-Density Patterning of InGaZnO by CH4: a Comparative Study of RIE and Pulsed Plasma ALE

Abstract

InGaZnO (IGZO)-based thin-film transistors and selector diodes are increasingly investigated for a broad range of applications such as high-resolution displays, high-density memories, and high-speed computing. However, its potential to be a key material for next-generation devices is strongly contingent on developing patterning processes with minimal damage at nanoscale dimensions. IGZO can be etched using CH4-based plasma. Although the etched by-products are volatile, there remains a concern that passivation -an associated effect arising from the use of a hydrocarbon etchant-may inhibit the patterning process. However, there has been limited discussion on the CH4-based etching of IGZO and the subsequent patterning challenges arising with pitch scaling (< 200 nm). In this work, we systematically investigate dry chemical etching schemes to pattern an IGZO film into densely packed nanostructures using CH4. Straight IGZO lines, similar to 45 nm in width at a pitch of similar to 135 nm, are produced by employing the traditional reactive ion etching method. While the passivating effect of CH4 does not impede the etching process, any further shrinkage of feature and pitch dimensions amplifies reactive ion etching-induced damage in the form of profile distortion and residue redeposition. We show that this is efficiently addressed via atomic layer etching (ALE) of IGZO with CH4 using a pulsed plasma. The unique combination of ALE and plasma pulsing enables controlled reduction of ion-assisted sputtering and redeposition of residues on the patterned IGZO features. This approach is highly scalable and is successfully applied here to achieve well-separated IGZO lines, with critical dimensions down to similar to 20 nm at a dense pitch of similar to 36 nm. These lines exhibit steep profiles (similar to 80 ) and no undesirable change in IGZO composition post-patterning. Finally, ALE of IGZO under pulsed plasma, reproduced on 300 mm wafers, highlights its suitability in large-scale manufacturing for the intended applications.