Physics / mechanism
ALD deposits material one atomic monolayer at a time via sequential, self-limiting surface reactions. A precursor gas chemisorbs onto the substrate; excess is purged; a co-reactant (oxidant, plasma, or reducing agent) reacts with the chemisorbed layer; excess purged again. One cycle = ~0.1–2 Å growth. Self-limiting nature gives exceptional conformality (>99% step coverage in high-aspect-ratio structures) and sub-Ångström thickness control. Typical cycle times 0.5–5 s; throughput is the main industrial constraint. Key materials: Al₂O₃, HfO₂, TiN, ZnO, Ru. State-of-the-art tools (ASM, Lam, Tokyo Electron) run spatial or plasma-enhanced ALD at wafer scales; EUV underlayers and gate dielectrics at <2 nm nodes are ALD-dependent.
Competitive landscape
CVD is the primary alternative—higher throughput, lower conformality, worse thickness control. PVD (sputtering) is faster still but line-of-sight limited, useless for deep trenches. Wet chemical routes (sol-gel, electrodeposition) are cheaper but lack monolayer precision. Molecular beam epitaxy offers crystalline quality but is vacuum-intensive and slow. Area-selective ALD (AS-ALD) is an emerging adjacent that adds patterning functionality, competing with litho-etch steps. Key vendors: ASM International (dominant), Applied Materials, Lam Research, Picosun (AMAT-acquired), Forge Nano (nanoparticle coating niche).
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.