Vertical connectivity is a key element of Advanced Packaging: The implementation of Silicon Interposers and chip stacking allows shorter and more dense electrical connections which reduce signal delay and power low. Through-silicon vias (TSVs) and Through-glass vias (TGVs) are one of the core enablers – especially for 2.5D interposers and many 3D integration schemes.[i]
But TSVs also present process-integration challenges. Typical TSV flows involve deep silicon etch → dielectric liner deposition → barrier/seed deposition→ metal fill (often copper plating) → CMP[ii] → reveal/thinning → CMP. Tiny weaknesses early (like poor barrier/seed coverage) can lead to voids which can cause yield loss or reliability-related failures.[iii]
That’s why TSV R&D doesn’t just need “more metrology.” It needs faster learning cycles – and that’s where dedicated test chips are required.
What makes TSVs hard to develop (and why test chips help)
TSVs are high aspect ratio structures by design. As you push to smaller diameters and deeper vias, you’re fighting:
- Conformality limits (can you coat the sidewalls and bottom uniformly?)
- Sidewall coverage (discontinuous dielectric liners and barrier / seed)[iv]
- Fill defects (voids/seams during electroplating show up later as resistance drift or failures)[v]
- Stress + keep-out zone effects (mechanical stress around TSVs can impact nearby devices)[vi]
The literature is consistent: barrier/seed quality and fill integrity are among the most common TSV risk points, and defects can originate in almost any TSV.
A well-designed test chip lets you turn TSV R&D into something closer to a controlled experiment:
- Run repeatable, known geometry structures through your deposition and fill tools
- Quantify step coverage and continuity across process conditions
- Detect failure modes early – before you’ve burned expensive product wafers and weeks of cycle time
- Overcritical aspect ratios (up to 200:1) allow to explore the limitations of the process and acts as a process corner checkpoint.
Where Chipmetrics VHAR test chips fit in TSV development
Chipmetrics VHAR (Vertical High Aspect Ratio) test chips are a practical way to bring TSV-like geometries into rapid process learning. The key idea is simple:
TSV performance is often decided by how well thin films behave inside deep features. VHAR structures let you measure and optimize that behavior quickly, repeatedly, and at low risk.
1) Dialing in dielectric liner conformality
Most TSV stacks start with an insulating liner (often oxide) to isolate the conductive fill from the silicon. The liner needs to be conformal – especially at the via bottom – because thin spots cause leakage and reliability risks.
How VHAR helps: run the VHAR chip through liner deposition splits (temperature, precursor dose, plasma conditions, pressure), then quantify conformality/coverage trends across the feature depth.
2) Optimizing barrier + seed inside TSV-like features (where PVD often gets pushed)
For copper-filled TSVs, a common metallization approach is:
- Barrier (e.g., Ta/TaN or Ti/TiNy)
- Cu seed
- then Cu electroplating fill
Multiple sources describe this barrier/seed + plating flow as the mainstream route for TSV metallization.
And this is exactly where many teams are leaning into PVD-based approaches for barrier/seed – because PVD is scalable and well understood, but step coverage becomes challenging as aspect ratios increase[vii].
Published work[viii] on ionized and advanced PVD for TSV metallization consistently shows that flux directionality, ionization fraction, and substrate bias strongly influence film redistribution along the sidewalls and the transition from continuous to discontinuous coverage in high aspect ratio features. In extreme aspect ratios, classical PVD may not reach the via bottom at all, making sidewall continuity and thickness gradient control the critical parameters.
How VHAR helps (practically):
- Use the VHAR chip to represent “TSV-class” aspect ratios
- Sweep PVD conditions (ionization strategy, bias, pressure, power, etc.)
- Measure which settings preserve continuous barrier/seed down the sidewalls and at the bottom
- Choose a process window that maximizes continuity while minimizing thickness/stress penalties
This is also where you can align with what a major equipment supplier has publicly emphasized for TSV PVD: improving ion density/directionality and tunable energy to enable continuous barrier + seed in HAR TSVs while reducing excessive thickness.[ix]
3) De-risking plating by qualifying deposition first
Bottom-up copper fill in TSVs depends strongly on feature geometry and pattern density. A standard VHAR structure, with its high pattern density, is not representative of practical TSV layouts and therefore can rather be viewed as an overcritical layout which can act as a process corner. The aspect ratio of the VHAR structures can be adjusted by customer request, typically between values of 10 and 200. This covers even the most extreme cases in the foreseeable future.
Electroplating performance depends critically on the integrity of the underlying barrier and seed layers. Incomplete bottom coverage, discontinuities, or excessive resistivity in the seed layer often manifest later as voids or seams during fill. VHAR test chips allow teams to rigorously tune and qualify barrier/seed conformality in TSV-like aspect ratios before committing to costly TSV integration lots.[x]
In this way, VHAR structures function as a deposition process screen: they ensure the metallization stack is robust enough to support plating, while plating optimization itself is validated on dedicated TSV density monitors.
Why this matters specifically for advanced packaging R&D
Advanced packaging R&D is under pressure to do two things at once:
- Shrink interconnect dimensions and increase density
- Keep reliability high across thermal cycling, warpage, and mechanical stress
High aspect ratio TSV concepts and dense arrays are actively being pushed in the research community to improve integration density (while managing stress and performance).
In that environment, the value of a VHAR test chip is that it becomes a standardized learning vehicle:
- Run it frequently (per tool PM, per target material change, per recipe rev)
- Use it to compare deposition technologies (PVD vs ALD vs alternatives) for specific TSV modules
- Shorten the time from “interesting idea” → “measured result” → “process window”
A simple TSV-R&D workflow using Chipmetrics VHAR test chips
Here’s a practical loop many teams aim for:
- Define the TSV risk module (liner, barrier/seed, or fill)
- When possible, validate on the actual target TSV dimensions; in parallel, map key geometric parameters (aspect ratio and feature size regime) to VHAR structures to accelerate process learning. Run designed splits. (power/bias/pressure; temp/dose; chemistry variants)
- Quantify conformality + continuity and identify process cliffs
- For HAR films, Chipmetrics also highlights test-structure-based approaches designed to measure conformality behavior in HAR features.
- Confirm with one integration check (a small TSV monitor lot), instead of iterating blindly at full scale
The outcome is fewer “integration surprises,” and more TSV learning per week.
Closing thought
TSVs aren’t just a single “via step” – they’re a chain of tightly coupled modules. In advanced packaging R&D, the teams that win are the ones that can learn fastest about thin-film behavior in deep features and then translate that learning into stable integration.
Chipmetrics VHAR test chips are built for that exact job: turning TSV challenges (liner, barrier/seed, fill readiness) into measurable, repeatable experiments – so process development becomes systematic instead of speculative.
[i] https://www.sciencedirect.com/science/article/pii/S0167931714004511
[ii] https://pubs.aip.org/avs/jva/article/38/3/031202/1023659/Tutorial-on-forming-through-silicon-vias
[iii] https://www.sciencedirect.com/science/article/pii/S0167931724000509
[iv] https://link.springer.com/content/pdf/10.1007/s12540-015-4546-z.pdf
[v] https://www.researchgate.net/publication/4344277_High_aspect_ratio_TSV_copper_filling_with_different_seed_layers
[vi] https://www.mdpi.com/2072-666X/13/7/1147
[vii] https://tohoku.elsevierpure.com/en/publications/impact-of-super-long-throw-pvd-on-tsv-metallization-and-die-to-wa/
[viii] https://imapsource.org/api/v1/articles/57175-highly-ionized-sputtering-for-tsv-lining.pdf
[ix] https://www.mdpi.com/1996-1944/16/24/7652
[x] https://www.acmr.com/electroplating-of-metal-for-tsv-formation/
