ALD/ALE 2025 Session AS2-WeM: Area Selective Deposition III

Area-selective deposition (ASD) has potential to reduce reliance on costly lithography steps and improve shorting margins for small pitch sizes. ASD has been successfully demonstrated for many material sets, notably dielectric on dielectric (DoD) for fully self-aligned vias,¹ yet the demand for thicker films and new materials continues to grow to enable advanced applications. Selectively depositing a film on a surface of a different type, e.g. a dielectric film on a metal substrate, is inherently more challenging because after the first few cycles of deposition, both the growth and non-growth surfaces are the same type (dielectric in this example), resulting in similar reactivity towards ALD precursors. This work discusses the development of selective dielectric on metal (DoM) deposition from coupon-scale to full wafer patterns.

We utilize inhibitor molecules to selectively block deposition on our desired non-growth surface (dielectric in this case). Numerous inhibitors are screened on both dielectric (SiO₂, SiON, SiOC, etc) and metal (W, Co, Cu, Ru, etc) surfaces using water contact angle (WCA) measurements to characterize hydrophobicity after selective inhibitor adsorption. Inhibitors with the best WCA contrast between dielectric and metal are then evaluated for blocking performance using AlO_x ALD.Ellipsometry, mass, and x-ray reflectivity measurements demonstrate several nm of AlO_x deposition on metal surfaces without any selectivity loss on dielectric. Further verification from TEM and EELS elemental analysis confirm that this selectivity is extended to patterned coupons and full wafers. We demonstrate selective AlO_x on patterned wafers with excellent selectivity (EELS, top-down SEM), which is also extended to other deposited films (e.g. SiN, MoN). These inhibitors are compatible with high volume manufacturing requirements, 3D features, and a wide range of temperatures that accommodates low thermal budget materials as well as high temperature ALD processes. This selective DoM process enables applications such as selective hard masks and etch stop layers and improved shorting margins.

References

As semiconductor devices continue to scale down and increase in complexity, achieving both high performance and reliability has become increasingly critical. Ruthenium (Ru) has emerged as a key material for next-generation interconnects and electrode applications due to its low resistivity (~7.1 μΩ·cm), high work function (~4.7 eV), and excellent chemical stability. To fully utilize these properties, area-selective atomic layer deposition (AS-ALD) is essential for enabling Ru deposition exclusively in growth regions while inhibiting it in non-growth areas. This bottom-up patterning approach mitigates edge placement error (EPE) and enhances overall process yield.

Conventional AS-ALD techniques using self-assembled monolayers (SAMs) as surface inhibitors are inherently limited by their low thermal stability, leading to selectivity degradation over multiple cycles. As the deposition process proceeds, SAM desorption or decomposition leads to unwanted Ru nucleation in non-growth regions, compromising the selectivity of the process. Furthermore, achieving uniform SAM coverage in high-aspect-ratio structures poses additional challenges.

To overcome these limitations, we developed an atmospheric-pressure X plasma surface modification process, which introduces hydrophobic functional groups that effectively suppress Ru nucleation in non-growth areas while maintaining stability throughout multiple ALD cycles. This method demonstrated infinite selectivity, with no Ru deposition detected in non-growth regions even after 200 ALD cycles, while achieving over 30 nm of Ru film growth in targeted areas—exceeding the selectivity performance of conventional AS-ALD approaches.

Additionally, we established a substrate-dependent X plasma effect, demonstrating selective removal of hydrophobic X functional groups based on surface chemistry, which influenced Ru nucleation behavior. Furthermore, we verified that post-deposition atmospheric O₂ plasma treatment effectively eliminates residual X inhibitors from non-growth areas without compromising Ru film integrity in growth regions. These findings highlight plasma-assisted AS-ALD as a scalable, highly selective approach for advanced semiconductor integration.

[Acknowledgment] This research was supported by Korea Institute for Advancement of Technology(KIAT) grant funded by the Korea Government(MOTIE) (RS-2024-00409639, HRD Program for Industrial Innovation. This work was supported by the Technology Innovation Program (RS-2023-00234833) funded By the Ministry of Trade, Industry & Energy(MOTIE, Korea)(NTIS 1415187483).