Monday, November 19, 2018

15 nm resolved patterns in Selective Area Atomic Layer Deposition

Here is an impressive and fundamental paper on selective area atomic layer deposition (SA-ALD)or just area selective deposition (ASD) that some prefer to call it.

The researchers at IBM has devleoped a bottom up approach on 300 mm pattern wafers that had been fabricated using standard trench first metal hardmask damascene scheme to create a line pattern of 36 nm pitch with single EUV exposures using low-k OMCTS 2.7 as the dielectric.
By deactivating ond surface with self-assembled monolayers (SAMs, Octadecylphosphonic acid) leaving another surface active for ALD processing (ZnO) they were able to produce 15 nm resolved patterns. One of the biggest challenges in the implementation of SA-ALD is the ability to maintain pattern fidelity and reduce defects during the ALD process (ZnO). 
Thank you Henrik Pedersen for sharing this paper!

Deactivating material is used to block one surface from ALD film growth. (A) ALD eventually leads to overgrowth of the film onto deactivated areas. (B) Defects in the deactivation layer can lead to the formation of locally deposited material. Published with permission from ACS Appl. Mater. Interfaces, 2018, 10 (44), pp 38630–38637 Copyright 2018 American Chemical Society.

Fifteen Nanometer Resolved Patterns in Selective Area Atomic Layer Deposition—Defectivity Reduction by Monolayer Design

Rudy Wojtecki, Magi Mettry, Noah F. Fine Nathel, Alexander Friz, Anuja De Silva, Noel Arellano, and Hosadurga Shobha
ACS Appl. Mater. Interfaces, 2018, 10 (44), pp 38630–38637
DOI: 10.1021/acsami.8b13896
Selective area atomic layer deposition (SA-ALD) offers the potential to replace a lithography step and provide a significant advantage to mitigate pattern errors and relax design rules in semiconductor fabrication. One class of materials that shows promise to enable this selective deposition process are self-assembled monolayers (SAMs). In an effort to more completely understand the ability of these materials to function as barriers for ALD processes and their failure mechanism, a series of SAM derivatives were synthesized and their structure—property relationship explored. These materials incorporate different side group functionalities and were evaluated in the deposition of a sacrificial etch mask. Monolayers with weak supramolecular interactions between components (for example, van der Waals) were found to direct a selective deposition, though they exhibit significant defectivity at and below 100 nm feature sizes. The incorporation of stronger noncovalent supramolecular interacting groups in the monolayer design, such as hydrogen bonding units or pi–pi interactions, did not produce an added benefit over the weaker interacting components. Incorporation of reactive moieties in the monolayer component that enabled the polymerization of an SAM surface, however, provided a more effective barrier, greatly reducing the number and types of defects observed in the selectively deposited ALD film. These reactive monolayers enabled the selective deposition of a film with critical dimensions as low as 15 nm. It was also found that the selectively deposited film functioned as an effective barrier for isotropic etch chemistries, allowing the selective removal of a metal without affecting the surrounding surface. This work enables selective area ALD as a technology through (1) the development of a material that dramatically reduces defectivity and (2) the demonstrated use of the selectively deposited film as an etch mask and its subsequent removal under mild conditions.

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