Physics / mechanism
Thin films are material layers deposited at nanometre-to-micrometre scale onto substrates, where bulk properties no longer dominate — quantum confinement, interface effects, and stress states govern behaviour. Key deposition methods: PVD (sputtering, evaporation), CVD/PECVD, ALD (Ångström-level thickness control, ±1–2% uniformity across 300mm wafers), and sol-gel. Critical parameters: thickness uniformity, step coverage, stoichiometry, residual stress (<500 MPa target for optical stacks), and adhesion. ALD is now indispensable below 5nm nodes for high-k dielectrics (HfO₂, Al₂O₃) and barrier layers (TaN, TiN). Optical thin films achieve <0.1% reflectance or >99.99% reflectivity in narrowband laser mirrors.
Competitive landscape
PVD and CVD compete directly on throughput vs. conformality trade-offs. Epitaxial growth (MBE, MOCVD) overlaps in III-V and nitride device layers but at far higher cost. Electroplating and electroless deposition address thick copper interconnect where ALD is uneconomic. Atomic layer etching (ALE) is the functional inverse and increasingly co-optimised with ALD in gate-all-around flows.
| Method | Conformality | Throughput | Cost/wafer |
|---|---|---|---|
| ALD | Excellent | Low | High |
| PECVD | Moderate | High | Low–mid |
| Sputtering (PVD) | Poor–moderate | High | Low |
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