Nucleation and Area-selective ALD/MLD

As advanced nanoelectronics shrink into the sub-10 nm regime with complex 3D structures, conventional lithographic patterning is becoming extremely challenging to scale down.^[1] It requires multiple lithography and etch steps, which can result in many issues including rising costs. Accordingly, area-selective atomic layer deposition (AS-ALD) has attracted worldwide attention as a new reliable bottom-up method to overcome current fabrication challenges.^[2] AS-ALD allows growth of materials only in the areas of interest, reducing the number of the fabrication steps and improving the accuracy of feature patterning.

AS-ALD can be achieved by 1) inherent selectivity (using substrates as-is), 2) pre-functionalization of target substrates before ALD cycles (selective passivation or activation), or 3) periodic correction steps during ALD cycles (deposition/etch or deposition/passivation).^[2] For example, several ALDs for inorganic materials (W, Co, HfO₂, TiO₂) show substrate-dependent nucleation.^[3-3.2] Furthermore, beyond inorganic materials, ASD of various organic materials including poly(3,4-ethylenedioxythiphene) (PEDOT)^[4] is studied by oxidative molecular layer deposition (oMLD). To better achieve AS-ALD, our work focuses on understanding nucleation mechanisms that occur during dielectric and metal ALD on various substrates. Our functional model for ALD nucleation helps to estimate the nucleation mechanism out of experiment data.^[5] Based on the theoretical and experimental analysis, we devise schemes to modify and control film nucleation and thereby expand the process “window” available for AS-ALD processes.

The image below shows one of our recent results (AS-ALD of TiO₂ on SiO₂ vs Si-H by ALD/ALE). TiO₂ ALD is inherently selective to SiO₂ vs Si-H but is limited to ~1.2 nm more growth on SiO₂. Periodic ALE cycles added to the ALD cycles effectively remove unfavorable nucleation on Si-H with minimal film loss on SiO₂, leading to improved selective deposition (~15 nm TiO₂).^[6] Better improved selective deposition (32.7~ nm) was also demonstrated by controlling exposure of H₂O in this system.^[7]

Reference

[1] Clark et al. APL Mater. 2018, 6, 058203

[2] Parsons et al. Chem. Mater. 2020, 32, 4920

[3] Kalanyan et al. Chem. Mater. 2016, 28, 117

[3.1] Lemaire et al. J. Chem. Phys. 2017, 146, 052811

[3.2] Atanasov et al. J. Vac.Sci. Technol. A, 2016, 34, 01A148

[4] Atanasov, Chem. Mater. 2014, 26, 3471

[5] Parsons et al. J. Vac. Sci. Technol. A. 2019, 37, 020911

[6] Song et al. Chem. Mater. 2019, 31, 4793

[7] Holger et al. J. Appl. Phys. 2020, 128, 105302