The Challenge: Conformality in Complex Geometries
Atomic Layer Deposition (ALD) is the go-to technique for achieving ultra-thin, conformal films in the deep, narrow features found in advanced semiconductors, batteries, and capacitors.
However, as device designs push into ever-more complex 3D geometries, a hidden challenge emerges: bottlenecks in High Aspect Ratio (HAR) structures can disrupt film growth.
This results in unpredictable conformality, slowing down process development and compromising device reliability.
Understanding and controlling these bottleneck effects is crucial for designing better ALD processes and enabling the next generation of 3D devices.
PillarHall LHAR Chips: A New Window into Bottleneck Effects
Chipmetrics’ PillarHall LHAR5 silicon test chips – containing 28 distinct test structures –offer a powerful platform for experimentally studying bottleneck effects in HAR cavities.
The method:
- Deposit a bottleneck film under ALD conditions that produce poor conformality (short pulse times).
- Follow with a conformal film under optimized ALD conditions.
- Measure the film penetration depth profile.
By separating these layers, researchers can precisely quantify how bottlenecks influence film growth.
Key Findings from our study
- Penetration Depth (PD50%) Difference:
- Bottleneck film: 5–30 µm (Equivalent Aspect Ratio, EAR: 5–30)
- Conformal film: 150–300 EAR
- Film thickness and cavity geometry are factored into Equivalent Aspect Ratio (EAR) calculations using dedicated HAR calculator software.
- Using linear model fits from LHAR experiments allows for accurate prediction of bottleneck effects, with only a +2% error versus experimental data.
- Alternative models were less accurate:
- Bottleneck-throughout-cavity model: −18% error
- Additive-regions model: +12% error
Why This Matters for the Industry
The bottleneck phenomenon in HAR structures is still not fully understood across different materials. This work demonstrates that targeted experiments and statistical modeling can dramatically improve our ability to predict and control ALD conformality in complex 3D structures.
By integrating PillarHall LHAR chip measurements into ALD process development, engineers can:
- Diagnose bottleneck impacts earlier.
- Fine-tune process recipes faster.
- Bring new HAR device architectures to market with more confidence.
Next Steps
The research team emphasizes the need for:
- More experimental studies across diverse material systems.
- Advanced physical modeling to complement statistical fits.
- Broader industry adoption of dedicated metrology test chips for HAR process design.
Takeaway
Bottlenecks in HAR structures aren’t just a nuisance – they’re a key variable in next-gen device manufacturing. With precise test structures like PillarHall LHAR chips, the semiconductor industry now has a sharper tool for decoding and overcoming these hidden barriers.