ALD (Atomic Layer Deposition)

Notes

ALD is indispensable for high-k gate dielectrics, barrier liners and the tight gaps in nanosheet devices.

Overview

ALD (atomic layer deposition) is a thin-film deposition method that builds a film roughly one atomic layer at a time by exposing the wafer to two or more chemicals in separate, alternating pulses, each of which reacts with the surface only until the surface is saturated. Because every cycle adds a fixed, tiny amount, ALD gives very precise thickness control and coats the inside of deep, narrow structures evenly. It is used for the thinnest and most critical layers in logic, memory and packaging.

How it works

A basic cycle has four steps. The first precursor is pulsed into the chamber and reacts with the available surface sites until none are left; inert gas then purges the excess; the second reactant is pulsed in and reacts with the new surface; and a second purge clears the by-products. In the classic example, trimethylaluminium and water deposit aluminium oxide at about 0.1 nanometres per cycle, and the required thickness is reached by repeating the cycle.

Because each step stops by itself, growth depends little on exactly how much precursor reaches each point, so films grow evenly over complex three-dimensional shapes. Each process has a temperature window in which the growth per cycle stays nearly constant; outside it, growth can rise or fall. Plasma-enhanced ALD (PEALD) uses a plasma to supply the reaction energy, which allows lower temperatures for layers that cannot tolerate much heat.

The main drawback is speed. Depositing even a few tens of nanometres takes many cycles, so ALD is kept for thin films where its precision is needed, although spatial ALD variants can be much faster. Precursors must be volatile yet stable, and many are sensitive to air, which adds cost and handling care.

Examples

• High-k gate dielectrics in logic transistors; Intel reported using ALD for the high-k gate dielectric of its 45 nm technology.
• Dielectric films in DRAM capacitors, where very deep, narrow structures must be coated evenly.
• Spacer dielectrics for multiple patterning, one of the applications ASM lists for its ALD tools.
• Thin titanium nitride or tantalum nitride barriers around copper interconnects.

Why it matters

As transistors and memory cells have become three-dimensional and critical films only a few nanometres thick, ALD has become essential for layers that must be both very thin and even over complex shapes. ALD process engineers develop and run the processes, precursor chemists design the chemicals, and integration engineers rely on ALD films for gate stacks, spacers and barriers that shape device behaviour.

In the chip lifecycle, ALD processes are developed alongside each new process technology, qualified on test wafers, and then run in volume production, where film thickness and uniformity are monitored throughout.

It matters most to: Advanced Node Process Integration Engineer, ALD and CVD Precursor Chemist, ALD Process Engineer, Process Technician (Diffusion and Thin Film), Thin Film Deposition Process Engineer

Common confusions

Not the same as CVD

In chemical vapour deposition the precursors react together continuously, so growth depends on gas flow and temperature across the wafer. ALD is a form of CVD that splits the reaction into separate self-limiting steps, trading speed for control.

Not the same as atomic layer etching

Atomic layer etching uses a similar cyclic, self-limiting idea to remove material a few atomic layers at a time instead of adding it.

Not the same as atomic layer epitaxy

Atomic layer epitaxy is the original name Tuomo Suntola gave the technique when he devised it in Finland in 1974. The abbreviation ALE is now more often used for atomic layer etching.

Sources

1. ALD (Atomic Layer Deposition) (opens in a new tab), ASM, 2026-10-22
2. Deposition (opens in a new tab), Lam Research, 2026-10-22
3. Etch (opens in a new tab), Lam Research, 2026-10-22
4. Atomic layer deposition (Wikipedia) (opens in a new tab), Wikimedia Foundation, 2026-10-22

Related terms

• CVD
• HKMG
• Work function metal
• Barrier layer

Where it appears on the Hub

Used on 18 pages of the Hub. In each group, the pages that mention it most come first.