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Coating a through silicon via’s (TSV’s) interior can push a deposition process to its limits. Material must reach deep into the feature, covering scalloped, nearly vertical sidewalls and delivering consistent film properties throughout the finished device.
As developers look to scale superconducting quantum hardware, they add a new dimension to that fundamental challenge. Coverage alone is not enough; the film lining the via must also retain the device’s required superconducting properties, one more constraint in an unforgiving deposition step.
Why Is Superconducting Via Coating So Demanding?
The shape of the via alone creates significant deposition challenges. High-aspect-ratio features can extend hundreds of microns into a substrate, while remaining only a fraction as wide. When they are etched using the Bosch process (as many are), the sidewalls end up with microscopic scallops.
Nearly vertical walls receive less material from directional deposition, and the scallops create additional areas that are difficult to reach. The deeper the via becomes, the harder it is to get consistent coverage.
In superconducting quantum hardware, the deposited film must remain continuous through the entire feature while maintaining the properties needed for superconducting performance at cryogenic temperatures. Research has demonstrated that high-aspect-ratio superconducting TSVs in quantum integrated circuits are possible. Translating that capability into a repeatable manufacturing process means controlling film coverage and quality through a geometry that is difficult to coat consistently.
What Does a Scalable Superconducting Via Process Need to Deliver?
Denton’s PIB-CVD is as much a research tool as a production process. As quantum designers settle on new superconductors and dielectrics, the same tunable system can develop and optimize the materials those devices will require.
A viable process has to satisfy several requirements at once. First is conformality: the need for continuous film coverage along the sidewalls and through the depth of the via, including any difficult geometry left behind in the etching process.
The film also has to preserve the electrical characteristics the quantum device depends on. In demonstrated superconducting TSV designs, a continuous, low-loss path through the substrate that does not compromise qubit performance is critical. Reproducing that performance consistently puts tight demands on both film quality and process control.
Finally, the deposition process has to fit the realities of manufacturing. That means working within the device’s thermal budget, adapting to the materials and geometries a given design calls for, and keeping tool cost and complexity in check. Speed reflects yet another vital input. These often-conflicting needs create an inherent tradeoff: methods that excel at conformal coverage tend to be slow and expensive to run, while faster directional methods struggle to reach deep sidewalls.
Can a Single Process Balance Coverage, Flexibility, and Cost?
For demanding geometry, ALD is the benchmark. Its conformality is the gold standard, and nothing matches its control over thickness and composition. However, speed remains a concern. Temporal ALD builds films one atomic layer at a time through repeated precursor and purge cycles, which makes it slow, and the spatial ALD systems that speed it up tend to be larger, more complex, and more expensive; for films thick enough to serve as functional superconducting layers, that combination is hard to reconcile with practical manufacturing.
Denton’s Plasma Ion Beam Chemical Vapor Deposition (PIB-CVD) approaches ALD’s conformality on nearly vertical structures while adding the flexibility ALD lacks. Ion energy, ion current density, plasma chemistry, pressure, and substrate conditions can each be tuned independently, so a single system can engineer film density, crystallinity, composition, and electrical properties to the needs of a given device, including materials that are difficult or impossible to produce with ALD. Denton is making continued progress toward the production of superconducting titanium nitride films on vertical structures, a material whose properties can be tailored over a wide range by adjusting deposition conditions.
So far, Denton has demonstrated dense, uniform, highly conformal films on trenches up to a 6:1 aspect ratio, with sidewall coverage between 15 and 30 percent of the field thickness, and is working to extend that to 10:1 and beyond. We achieve this in a more compact and economical platform than spatial ALD, creating a significant cost-of-ownership advantage to go with deposition rates far beyond those of ALD. Quantum manufacturing is still early enough that throughput is not yet the main constraint, but as the field moves toward volume production, speed will become a decisive factor.
Put PIB-CVD Against Your Device Requirements
Denton has taken PIB-CVD from concept to demonstrated results on real high-aspect-ratio features. The next step is proving it against the specific via geometries, substrate materials, film specifications, material properties, and thermal limits that real quantum devices demand.
If your team is developing superconducting vias or related advanced packaging, Denton is ready to develop the coating process against your device requirements.