The defining advantage of atomic layer deposition over CVD or PVD in 3D NAND fabrication is its reliance on sequential, self-limiting surface reactions rather than continuous gas-phase decomposition. As described by Lam Research Corporation (2019), a standard ALD cycle consists of four steps: (i) introduction of a precursor that adsorbs onto available surface sites up to a self-limiting monolayer; (ii) purge of excess precursor; (iii) introduction of a co-reactant or oxidant that reacts only with the adsorbed species; and (iv) purge of reaction by-products.

Because the reaction terminates once all reactive surface sites are occupied, the deposited layer thickness per cycle is intrinsically bounded and independent of local precursor flux variation — a critical property when reactants must diffuse deep into narrow, high-aspect-ratio holes. Lam Research (2020) explicitly states that "even in high-aspect-ratio features, ALD can be used to provide highly conformal films with high step coverage," and that uniform material amounts can be deposited between isolated and dense features to minimize critical dimension (CD) loading effects.

Applied Materials (2024) confirms that all exposed surfaces — including high-aspect-ratio features with ratios of approximately 10:1 to 300:1 — will receive the same deposited material quantity. The step coverage superiority of ALD over CVD was established by Samsung Electronics as early as 2006, when they documented that "the step coverage that is typically obtained with CVD-based methods remained less than desired," while ALD could be performed at lower temperatures and still achieve improved step coverage — the baseline advantage on which all subsequent 3D NAND process flows were built.

Thermal ALD is preferred for high-aspect-ratio channel fill. As demonstrated in Lam Research's 2022 patent, thermal ALD with inhibitor-mediated growth cycles fills silicon oxide uniformly into ONON stack channels without the directionality artifacts of plasma-enhanced variants, enabling precise recess-etch alignment. The companion 2023 Japanese filing directly links thermal ALD to the fill requirement in multilayer stacks "with high-aspect-ratio channels arranged within the multilayer stack."

Integrated RIE-ALD cycles are essential for achieving extreme aspect ratios during channel hole etching. Jiangsu Leuven's 2021 RIE-ALD platform patent documents that alternating RIE etch with ALD sidewall passivation layers (3–20 nm thick) is necessary to prevent undercutting and maintain the structural integrity of the channel hole. According to WIPO and EPO filing trends, ALD-etch integration patents have grown substantially across Asian and US jurisdictions.

ALD conformality advantage over CVD has been validated at the device level across decades. Samsung's foundational ALD capacitor work (2006) established that CVD step coverage was insufficient for next-generation devices, and the entire 3D NAND industry has since built on this principle, as confirmed by the Peking University nano-floating gate patent (2026) citing ALD's role in ensuring ultra-thin uniform storage layer deposition at scale. The Semiconductor Industry Association roadmap reflects this consensus.

Area-selective ALD is emerging as a next-generation patterning enabler. SK Hynix's 2025 area-selective ALD patent demonstrates that silicon oxide can be selectively grown on silicon oxide regions but not silicon nitride regions within the same structure by using inhibitor-mediated surface chemistry, enabling sub-10 nm CD adjustments without additional lithography — directly applicable to ONO stack engineering within 3D NAND channel holes. Explore the full landscape on PatSnap's materials intelligence platform.