ALD vs CVD: Saturation, Coverage and Fill

ALD vs CVD: compare the growth mechanism

Atomic layer deposition (ALD) separates complementary surface reactions and seeks saturation in each reaction step. Conventional chemical vapor deposition (CVD) grows a film while reactants are supplied, with growth governed by reaction and transport. Pulses alone do not prove ALD, and an ALD label does not prove complete coverage or void-free fill. Compare the supply sequence, the evidence for self-limitation and the observed film separately. [P1][T1]

ALD belongs to the broader family of chemical vapor deposition processes. The useful distinction here is between alternating, self-limiting growth and conventional CVD growth, rather than a claim that the two share no chemistry. This article uses three observations to show what each kind of evidence can and cannot establish.

Observation one: the reactants arrive in pulses

A typical temporal ALD description separates one reactant exposure from the next and removes excess reactants and products between them. The intended surface reaction stops when the available reactive sites have been consumed. The complementary reaction prepares the surface for a subsequent cycle. [P1]

A pulsed supply record describes timing. It does not, by itself, demonstrate that either reaction saturates. To distinguish the mechanism, look for evidence that extending an exposure no longer increases the intended reaction under the conditions studied, and that the complementary reaction is also self-limiting. That is a stronger statement than “the valves were pulsed.”

The temporal sequence is an explanatory example. The distinction in this article depends on separated, self-limiting reactions; a process name or equipment trace alone does not establish the surface chemistry. For the general mechanism, continue with the ALD overview.

Observation two: growth reaches a plateau

A saturation observation supports self-limited behavior for the reaction, surface and conditions actually examined. It does not automatically establish that all surfaces inside a three-dimensional feature received enough reactant, that the complementary reaction behaved identically, or that an entire film is continuous. Those are additional questions, not consequences of one plateau. [P1]

Conventional CVD also involves surface chemistry and transport. Depending on the regime, the growth rate may be constrained by reaction kinetics or delivery of reactants. A slower reaction is not the same as a reaction that has terminated because reactive sites are exhausted. Keep that distinction when comparing growth curves. [T1]

For example, a reported surface plateau can motivate a saturation claim. A final film thickness alone cannot establish that plateau. This is a distinction between observations and inferred mechanisms, not a procedure for setting exposure conditions.

Observation three: the film follows a feature

Film properties answer different questions. Uniformity asks how thickness or another property varies across a region. Conformality asks how the coating follows a three-dimensional surface. Fill asks whether the intended volume has been occupied without an unwanted seam or void. Electrical function asks whether the resulting material and interfaces perform their intended role. [T1]

Evidence	A supported reading	An unsupported jump
Separated reactant exposures	The supplied reactants were separated in the described sequence	Both surface reactions must have saturated
A plateau for one reaction	Self-limited behavior under the examined conditions	Every recessed surface is completely coated
Coating visible along a sidewall	Coverage at the observed location	The opening is fully filled or electrically acceptable

Consider a coating that follows both walls of an opening but leaves open space between them. It can be a useful conformal coating while still not being a completed fill. Conversely, a filled region does not identify the deposition mechanism. The uniformity versus step-coverage comparison and dielectric versus metal fill discussion examine these geometric requirements.

ALD's self-limiting mechanism can support controlled coating, while CVD can also provide useful coverage. Neither family name replaces evidence from the actual structure. Avoid a universal claim that one always delivers better film quality, faster processing or a better electrical result. [P1][T1]

Locate the film's role before guessing its method

The public 28nm planar-flow overview places film formation and filling within a larger integration sequence. Use it to distinguish a film that establishes an interface or protects a surface from a later stage that fills an opening.

A material name, layer role or node label does not establish whether that particular implementation used ALD or CVD. The learning task is to locate the roles, then state which mechanism evidence remains unspecified. The overview does not provide a deposition recipe; detailed step access follows the site's current permissions.