ALD Reactors

Pulse-purge systems, spatial ALD, and batch vs single-wafer designs

ALD Reactor Designs

ALD reactors must efficiently deliver, react, and purge precursors in rapid cycles:

Temporal (pulse-purge) ALD: The standard approach. Precursor A is pulsed, then purged with inert gas, then precursor B is pulsed and purged. One cycle = one atomic layer. Cycle time: 1–10 seconds.
Spatial ALD: Instead of time-sequenced pulses, the wafer physically moves between different gas zones separated by inert gas curtains. Much faster — cycle times under 0.1 seconds. Used for high-throughput applications.
Batch ALD: Process 100+ wafers simultaneously in a vertical furnace. Lower throughput per cycle but high total throughput. Used for films where absolute thickness control is less critical.
Plasma-enhanced ALD (PEALD): Uses plasma in the second half-cycle for better reactivity at lower temperatures. Critical for BEOL applications.

Key Concept: ALD Throughput Challenge

ALD's main weakness is speed — depositing 10 nm at 0.1 nm/cycle requires 100 cycles. At ~5 seconds/cycle, that's over 8 minutes per wafer for a single film. Equipment makers address this with multi-station designs (4 wafers simultaneously) and faster purge systems.

PVD Systems

Epitaxy Systems

Knowledge Check

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What is spatial ALD?

The wafer moves between separate precursor zones instead of time-sequenced pulsesALD performed in outer spaceALD on multiple wafers stacked verticallyALD with variable chamber pressure