AVS 69 Session AP+PS-FrM: Atomic Scale Processing Late Breaking Atomic Layer Etching and Area Selective Deposition

Due to the scaling down in the Si device fabrication, the aspect ratio and complexity of 3D device structures is rapidly increased, leading to the limitation of the conventional fabrication process including deposition, etching, lithography and so on. Area selective deposition (ASD) has received great attentions from the Si industry as one of the unit processes to overcome the limitations. ASD is developed based on the atomic layer deposition (ALD) which has the unique self-saturation surface reaction mechanism. The surface chemical properties are modified by using the promoter or inhibitor which promotes or inhibits the thin film growth, respectively. Accordingly, the ALD thin films are selectively deposited on the desired area. At the beginning of the ASD research, the self-assembled monolayers (SAMs) were commonly used as an inhibitor. But the inherent size of SAMs has potential problems for the pattern interference in nm-size scale. In this study, we investigated the ASD using a small molecule inhibitor (SMI). We selected the aldehyde molecules as SMI to inhibit the nitride surface but not on oxide surface. By using density functional theory (DFT) calculation, adsorption behaviors and energetics of the aldehydes was studied on nitride and oxide surfaces. From the experiments, it was observed that the aldehyde selectively adsorbs on only nitride surface but not on oxide surface and block the HfO₂ deposition until 15 cycles. The inhibition of nitride surface using SMI can contribute to many unit processes of Si device fabrication by simplifying the process scheme.

As the semiconductor device dimensions continue to shrink, area-selective atomic layer deposition (AS-ALD), which is a bottom-up technique, can address the challenges associated with device fabrication. SiO₂ and SiN_x are two of the most commonly used dielectrics in semiconductor devices, and deposition on one dielectric with minimal deposition on the other can simplify processing. For example, in 3D-NAND structures, there are alternating layers of SiO₂ and SiN_x, and during processing, it is desirable to grow a metal oxide on SiO₂ with no growth on SiN_x. In AS-ALD, inhibitor molecules can be used to functionalize SiN_x because very few ALD precursors have an inherent binding selectivity to SiO₂ over SiN_x. Finding inhibitor molecules that selectively adsorb on SiN_x over SiO₂ is also challenging since on SiO₂ films contain SiOH groups, which react readily with many compounds such as chlorosilanes, alkoxides, and aminosilanes. We have previously shown that aldehydes selectively adsorb on SiN_x with minimal adsorption on SiO₂.

Anisotropic patterning process of metal layers in complex nanostructures is a big challenge. Pt is a promising material, but it is a hard-to-etch material. Dry etching of Pt thin film has been developed by using halogen-based plasmas of SF₆, CF₄, or Cl₂ gas. However, the anisotropic etch profiles of Pt films in most cases have not achieved due to the redeposition of the etch residues that produces fences or tapered sidewall. Recently, non-halogen chemistry for noble metal etching has been developed using atomic layer etching (ALE) with surface modification by oxidation and removal of the oxide layer by vapor of organic compounds [1].

Our developed floating wire-assisted high-density plasma at medium pressure significantly increases the chemical reaction rate to the sample surface, that was applied in the reduction of SnO₂ [2] and dry etching of TiAlC [3]. Here, we have demonstrated ALE of Pt via high-density plasma oxidation and removal of the modified layer by organic acid vapor or organic acid plasma. High-density nitrogen-oxygen based plasma (N-O plasma) was generated to fully oxidize Pt surface and form a dominant oxidation state (Pt⁴⁺). Surface modifications after the reactions of Pt with N-O plasmas and the modified layer with organic acid vapor or plasma were analyzed by X-ray photoelectron spectroscopy. The film thickness was characterized by ellipsometry and X-ray reflectivity. Surface roughness was analyzed by atomic force microscopy, and patterning profiles were observed by transmission electron microscopy. The N-O plasmas and organic acid plasmas were diagnosed by high-resolution optical emission spectroscopy.

The formation and desorption of organometallic compounds on Pt surface are able to be atomic-level controlled at low temperature (less than 100 ^oC). A smooth surface of Pt film was obtained with the etch depth per cycle from 0.3 to 0.7 nm/cycle. The exposure of Pt film to N-O plasmas determines the dominant oxidation state, surface roughness, and thickness of the modified layers, that strongly affects to etching performance of Pt film. The non-halogen atomic layer etching of Pt has been successfully developed in this study.

[1] J. Chang and J.P. Chang, J. Phys. D: Appl. Phys.50, 25 (2017).

[2] T.T.N. Nguyen et al., Plasma Process. Polym. 19, 6 (2022).

[3] T.T.N. Nguyen et al., Sci. Rep. 12, 1 (2022).