Film uniformity asks how a film property varies across a stated area. Step coverage asks how deposition reaches different surfaces of a local feature, such as its top, sidewall and bottom. Good uniformity across a wafer does not prove good coverage inside a narrow opening.
Always specify the observation scale
A thickness map sampled on open areas can describe lateral variation across those locations. It may say little about surfaces hidden inside trenches. Conversely, a well-coated trench in one cross-section does not establish that every region across a wafer received the same film.
Uniformity also needs a named property. Thickness, composition and electrical behavior can each vary, and agreement in one does not establish agreement in the others. “Uniform film” without a property and sampling region is an incomplete statement.
Process map
This step lives inside the 14nm FinFET course
Examine dielectric deposition inside a three-dimensional gate cavity and the need for surface coverage.
Real step names, layer-by-layer cross-sections, and rationale live inside the 14nm FinFET course, unlocked by account access.
Coverage follows access and surface response
Material must reach a surface and undergo the required growth reaction there. Local geometry changes access, while surface chemistry influences where growth begins and how it proceeds. A film may coat the top well yet be reduced or discontinuous near the bottom.
Self-limiting growth can improve conformality, but does not remove transport limitations. Research modeling ALD in high-aspect-ratio structures explicitly treats incomplete coverage when transport and surface reactions do not produce full conformality. This supports the boundary, not a claim about every ALD process.
| Observation | Supported statement | Unsupported extension |
|---|---|---|
| Similar open-area thickness at several positions | Uniformity at sampled positions | Complete trench-bottom coverage |
| Similar top, sidewall and bottom coating in one feature | Local conformality in that feature | Uniformity over all wafer regions |
| No empty cavity after deposition | The observed cavity is filled | Every interface layer is continuous |
| Similar film thickness | Geometric similarity at measured locations | Identical composition or electrical quality |
Coating and filling are another separate pair
A conformal coating follows existing topography. It does not necessarily eliminate a cavity. As coatings on opposing surfaces grow toward each other, the remaining access path can narrow. The final fill behavior depends on growth evolution, not solely on whether the first coating looked conformal.
This is why a liner can perform its interface role without being the bulk filling material. It is also why evaluating fill alone can miss a discontinuous liner at the bottom. The two materials may have different jobs in the same feature.
A two-scale reading exercise
Imagine that every open-area measurement agrees, but cross-sections show thinner bottom coverage. The contradiction disappears once the sampling scales are named: lateral uniformity is good in the sampled area, while local coverage is incomplete.
Now imagine the reverse: a locally conformal feature appears at one position, but open-area thickness varies elsewhere. The local result remains valid, while the wafer-scale conclusion does not follow. Keeping both statements avoids calling an entire deposition “good” or “bad” from one picture.
Source links
References
Silicon VLSI Technology - Full
James D. Plummer, Michael D. Deal, Peter B. Griffin
Silicon VLSI Technology · ISBN 978-0130850379
Modeling Incomplete Conformality during Atomic Layer Deposition in High Aspect Ratio Structures
Luiz Felipe Aguinsky, Frâncio Rodrigues, Tobias Reiter, Xaver Klemenschits, Lado Filipovic, Andreas Hössinger et al. · arXiv