Thermal ALD Reactor

Thermal ALD, plasma-enhanced ALD (PEALD), and remote-plasma ALD differ in how they drive the second, removal-adjacent half-reaction — pure heat, direct plasma, or plasma generated away from the wafer — and that choice sets the balance between film quality, growth temperature, and process damage for every ALD film a fab deposits.

Surface-saturated precursor from step A
Same first half-reaction across all three modes
Second half-reaction energy source
Thermal ALD
Heat alone drives the reaction, gentlest, often slowest
PEALD
Direct plasma, faster reaction, lower substrate temperature possible
Remote-plasma ALD
Plasma generated upstream, reduces direct ion exposure
Film grown, one atomic layer per cycle
Density, temperature budget, and damage profile set by energy mode

PEALD's biggest practical advantage is lowering the deposition temperature low enough to run on top of structures that can't survive thermal ALD's higher heat budget. Thermal ALD's second half-reaction often needs substrate temperatures that are too high for certain metal interconnects, organic layers, or temperature-sensitive stacks already present on the wafer; PEALD's plasma-driven reaction can proceed at substantially lower substrate temperature because the plasma itself supplies much of the reaction energy instead of relying purely on substrate heat — which is why PEALD has become the standard choice for back-end-of-line and advanced interconnect ALD steps where thermal budget is tightly constrained.

ALD Energy Modes — Thermal, Direct Plasma, Remote Plasma lower temperature and lower damage pull in opposite directions Thermal ALD higher temperature needed no ion damage PEALD — direct lower temperature possible some ion exposure Remote-plasma ALD plasma benefit, less direct ion damage remote-plasma ALD tries to capture most of PEALD's benefit while limiting what reaches the wafer directly

Remote-plasma ALD is the compromise position for films that need plasma assistance but can't tolerate direct ion bombardment at all. By generating the plasma in a separate zone and letting mainly reactive neutral species diffuse to the wafer, remote-plasma ALD captures much of PEALD's lower-temperature advantage while avoiding most of the ion-driven damage a directly coupled plasma would cause — the tradeoff being a somewhat less aggressive reaction than true direct PEALD, since fewer energetic species actually reach the surface.

Thermal, PEALD, and remote-plasma ALD aren't ranked best-to-worst — each sits at a different point on the temperature-versus-damage tradeoff, and the right choice for any given ALD film depends entirely on how much heat the structures underneath can survive and how much ion exposure the growing film itself can tolerate without quality loss.

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