(Invited) Investigating ALE Approaches for Novel Metal Oxide Patterning at Sub-100 Nm Pitch for High-Density Memory & Compute Applications
Authors: Kundu Shreya , Ghorbani Leila , Lazzarino Frederic , De Gendt Stefan 
Published: December 2024

Atomic layer etching (ALE) continues to garner wide attention as a technique for controlled patterning of different materials.1,2 However, a substantial amount of these studies are carried out on blanket films. It is therefore pivotal to investigate the feasibility of ALE for patterning high-density features as it exhibits the potential to be the preferred etching method for novel materials in the semiconductor industry.
This talk will focus on the impact of ALE in the patterning of complex metal oxides like InGaZnO and MgZnO. These metal oxides are potential contenders as channel materials in high-performing transistors for memory and compute applications.3 Therefore, several critical criteria need to be followed when ALE conditions are being defined.

The channel needs to be patterned with minimal physical and chemical damage such that there is little or no impact on the mobility parameters of the channel.

The etching process should not induce redeposition onto the hard mask which also acts as a top contact in an integrated stack within the chip.

In the case of InGaZnO, ALE-based patterning down to pitch 36 nm will be discussed in a systematic fashion.4 At such scaled pitches, it is observed that the etching challenges highlighted above cannot be resolved completely by ALE itself. Therefore, ALE in conjunction with other patterning approaches such as plasma pulsing needs to be employed to achieve satisfactory etching of the features at pitch 36 nm.
On the other hand, when the metal oxide layer comprises a non-volatile element like Mg (in MgZnO), the etching mechanism tends to be both physical and chemical. In this case, it is still seen that the ALE approach provides a more controlled way of removing the layer without damaging the layer composition when compared to its conventional counterpart – reactive ion etching (RIE) at pitch 90 nm.5

REFERRENCES

(1) Metzler, D.; Bruce, R. L.; Engelmann, S.; Joseph, E. A.; Oehrlein, G. S.; Fluorocarbon Assisted Atomic Layer Etching of SiO2 Using Cyclic Ar/C4F8 Plasma. J. Vac. Sci. Technol. A
2014, 32, 020603.
(2) Metzler, D.; Li, C.; Engelmann, S.; Bruce, R. L.; Joseph, E. A.; Oehrlein, G. S.; Fluorocarbon Assisted Atomic Layer Etching of SiO2 and Si Using Cyclic Ar/C4F8 and Ar/CHF3 plasma. J. Vac. Sci. Technol. A
2016, 34, 01B101.
(3) Belmonte, A.; Oh, H.; Rassoul, N.; Donadio, G. L.; Mitard, J.; Dekkers, H.; Delhougne, R.; Subhechha, S.; Chasin, A.; van Setten, M. J.; Kljucar, L.; Mao, M.; Puliyalil, H.; Pak, M.; Teugels, L.; Tsvetanova, D.; Banerjee, K.; Souriau, L.; Tokei, Z.; Goux, L.; Kar, G. S.; Capacitor-Less, Long-Retention (>400s) DRAM Cell Paving the Way towards Low-Power and
High-Density Monolithic 3D DRAM. 2020 IEEE International Electron Devices Meeting (IEDM)
2020, pp. 28.2.1-28.2.4.
(4) Kundu, S.; Decoster, S.; Bezard, P.; Mehta, A. N.; Dekkers, H.; Lazzarino F.; High-Density Patterning of InGaZnO by CH4: a Comparative Study of RIE and Pulsed Plasma ALE. ACS Appl. Mater. Interfaces
2022, 14, 29, 34029–34039.
(5) Ghorbani, L.; Kundu, S.; De Gendt, S.; Manuscript in preparation.