SEMICONDUCTOR FUNDAMENTALS · THIN-FILM DEPOSITION
What Is ALD?
Atomic-scale film growth for precise, conformal layers in advanced logic, memory and three-dimensional structures.
Atomic Layer Deposition, or ALD, grows thin films through alternating, self-limiting surface reactions. Repeating precursor, purge and reactant steps provides excellent thickness control and conformal coverage over complex three-dimensional features.
The ALD cycle
A first chemical precursor enters the chamber and reacts with available sites on the wafer surface. Once those sites are occupied, the reaction stops. Inert gas purges excess precursor and by-products. A second reactant is then introduced and another purge follows. Repeating this sequence builds the target film cycle by cycle.
Why self-limiting reactions matter
Because each half-reaction saturates the surface, film growth is less dependent on small variations in exposure than a continuously reacting process. Engineers can control thickness at extremely small scales and coat the top, sidewalls and bottom of high-aspect-ratio structures more uniformly. The exact growth per cycle still depends on chemistry, temperature and surface condition.
ALD compared with CVD and PVD
Chemical vapor deposition generally exposes the surface to reacting gases continuously or simultaneously and can offer higher throughput for many films. Physical vapor deposition moves material from a target to the wafer and is often more directional. ALD is selected when precise thickness, composition or conformality outweighs its typically slower cycle-by-cycle growth.
Applications in advanced devices
ALD is used for high-k gate dielectrics, metal-gate stacks, spacers, liners, diffusion barriers and capacitor films. Conformal deposition is especially valuable as logic transistors and memory structures become more three-dimensional. Plasma-enhanced ALD can provide reaction energy at lower substrate temperatures for processes with limited thermal budgets.
Why this matters for Japan
ALD connects directly to Japan’s semiconductor-equipment and materials base. Japanese suppliers participate in deposition equipment, vacuum components, gas delivery, valves, precursors and the process-control technologies required for uniform thin films. As logic and memory structures become more three-dimensional, conformal deposition increases the value of precision hardware and high-purity materials. ALD is therefore an example of how Japanese manufacturing capabilities can remain essential to advanced-node production conducted in fabs around the world.
Frequently asked questions
Does ALD deposit exactly one atomic layer per cycle?
The name describes atomic-scale control, but the actual growth per cycle depends on the material system and is often a fraction of a monolayer.
What is PEALD?
Plasma-enhanced ALD uses plasma to activate reactions, which can enable lower processing temperatures or different film properties.
Why is ALD slower than some deposition methods?
The chamber must repeatedly pulse chemicals and purge between reactions, trading throughput for control and conformality.
Official sources
Last reviewed: August 2026. SemiStructure provides independent educational material; specifications and product roadmaps can change.
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