Atomic Layer Etching (ALE) is the technique that removes material one atomic layer at a time using self-limiting surface reactions — providing angstrom-level precision for critical patterning at advanced technology nodes where conventional reactive ion etching lacks the control needed for sub-5nm feature dimensions.

How ALE Works

Two-Step Cycle:

• Step 1 — Modification: Reactive gas (Cl2, BCl3) chemisorbs onto the surface, modifying exactly one atomic layer. Reaction is self-limiting — excess gas does not penetrate deeper.
• Step 2 — Removal: Low-energy ion bombardment (Ar+, typically 10–25 eV) sputters only the modified layer, leaving underlying material intact.
• Purge between steps removes by-products and excess reactants.
• Each cycle removes ~0.3–0.5 angstrom of material.

ALE vs. Conventional Etching

Types of ALE

• Directional (Anisotropic) ALE: Ion bombardment provides directionality — used for gate trimming, fin thinning.
• Isotropic (Thermal) ALE: Chemical removal without ion bombardment — used for selective material removal in 3D structures like nanosheet inner spacers.

Applications at Advanced Nodes

• FinFET fin width trimming: Sub-nm precision on fin width for Vt control.
• Nanosheet channel thinning: Precise channel thickness control.
• Self-aligned contact etch: Controlled recess without punching through thin etch stops.
• EUV resist trimming: Smoothing line edge roughness by controlled atomic-scale removal.

Atomic layer etching is the etch counterpart to ALD — together they define the atomic-precision processing paradigm that makes sub-3nm transistor fabrication possible.