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  1. 101 Quartzite
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  3. 103 Wafering
  4. 104 Pillar 6 · Plasma Etching
  5. 105 BEOL
  6. 106 Packaging

Silicon University / Pillar 06 · Plasma Etching & Atomic-Scale Material Removal / Topic 6.2 · Atomic Layer Etching

Tier 2 · Equipment & Kinematics 16 min read

ALE Tool Architecture: High-Speed Gas Pulsing, Fast-Switching Plasmas & Cycle Control

Hardware mechanics of ALE chambers capable of sub-hundred-millisecond gas pulsing, ultra-fast vacuum purge valves, atomic radical generator modules (Ar, F, Cl), and synchronized RF power pulsing.

Etch Equipment EngineersProcess Integration SpecialistsHardware Designers
Dimitri AlbinoProject Leader, Advanced Wet Processing Equipment Manufacturing & Deployment

01Hardware Demands for Atomic Precision

While conventional RIE chambers maintain steady-state gas flows and continuous RF plasma discharges for minutes at a time, Atomic Layer Etching (ALE) tools must execute hundreds of discrete, highly synchronized chemical cycles within tight timeframes.

To make ALE commercially viable in high-volume manufacturing (HVM), tool manufacturers (such as Lam Research, Applied Materials, and TEL) engineered specialized hardware capabilities:

Process schematicSchematic · source diagram
FAST GAS INJECTION PULSE VALVES(Sub-50ms Response Times / ALD Style)MINIMIZED CHAMBER VOLUME(Rapid Gas Exchange / High Purge Rates)SYNCHRONIZED RF BIAS / SOURCE PULSING(Precise Control of Ion Energy Window: 20-50eV)

02Fast-Switching Gas Delivery & Chamber Purge Kinematics

The overall throughput of an ALE process is dominated by the duration of the purge steps (Step 2 and Step 4). If gas purging takes 5 seconds per step, a 100-cycle etch sequence requires over 15 minutes per wafer.

Process schematicSchematic · source diagram

CONVENTIONAL RIE GAS PANEL ADVANCED ALE FAST-PULSE PANEL

Gas Flow: Continuous (sccm) Gas Flow: Millisecond Injections

Chamber Residence: ~1-3 sec Chamber Residence: < 100-200 ms

Key Hardware Innovations

  1. Ultra-Fast ALD-Style Injector Valves: Piezoelectric or high-speed solenoid pulse valves deliver precise chemical micro-doses with response times under .
  2. Cross-Flow Small-Volume Chambers: Reduced internal chamber volume () combined with high-capacity turbomolecular pumps enables complete gas exchange in under .
  3. Pulsed Inert Sweep Systems: High-velocity argon sweep flows continuously clear unreacted species from dead-volume zones near showerhead ports.
Figure 1
FIG. 1

03Ion Energy Window Tuning & Synchronized RF Bias

The critical challenge in Directional Plasma ALE is maintaining ion kinetic energies strictly within the ALE Operating Window:

Sputtering & Damage RegimeSchematic · source diagram
Material Sputter Threshold (~50-80 eV)No Self-Limiting ControlALE OPERATING WINDOW (20 e50 eV)Modified Layer Removal Threshold (~20 eV)Self-Limiting Monolayer EtchNO ETCH REGIME (< 20 eV)

Precise Energy Control

  • Low-Frequency Bias Pulsing: RF bias power supplied to the wafer pedestal is pulsed in millisecond bursts during Step 3, producing an narrow Ion Energy Distribution Function (IEDF) centered between and .
  • ICP Source Synchronization: The top ICP source plasma is maintained at low power to provide uniform ions without generating energetic high-voltage ions that would breach the bulk sputter threshold.
Figure 2
FIG. 2
Figure 3
FIG. 3

→Prerequisites & continue reading

Prerequisites: ["p06-t6.2-t1-atomic-layer-etching-ale-fundamentals"]

Also in Topic 6.2, Atomic Layer Etching:

Tier 1 · Atomic Layer Etching (ALE): Core Principles & Sub-Na…Tier 3 · Directional Plasma vs. Thermal Isotropic ALE: Surfac…