Tiny mountains are calling
Atomic layer deposition for high aspect ratio (HAR) structures
It’s a small world, and it’s rapidly getting smaller, especially in emerging technologies. The tiny parts of today's nanotechnology solutions may be just barely visible, but they have mountainous differences in surface structures, with sharp edges, steep slopes, deep trenches and gate oxides concentrated in a single area. These types of complex surfaces with high aspect ratio (HAR) features require incredibly precise processing; you want those steep slopes and deep trenches conformally protected, too.
HAR and nanotubes
Surfaces with HAR features are found for example in nanotubes. Nanotubes made from TiO2 are widely used, especially on photocatalytic applications and water purification systems. The geometry of these types of nanotubes approach very high aspect ratios, and their widely varying surface structures need conformal coatings to increase lifetime and efficiency.
Reliable coating is not only crucial, it’s also demanding, and the best results are achieved with ALD coating.
Figure 1. Top of TiO2 nanotubes coated with a Beneq HAR module.
Figure 2. Bottom of TiO2 nanotubes coated with a Beneq HAR module.
In figures 1 and 2 above are example results of Al2O3 deposition on TiO2 nanotubes with an aspect ratio of 1:1088 using the Beneq HAR module. The thickness of the ALD layer is 38.8 +/- 4 nm at the middle of the nanotube and 39.8 +/- 5.7 nm at the bottom of the nanotubes. Figure 3 below shows the height of the coated nanotubes. Images courtesy of J. Prikryl et al. AVS-ALD 2016, 19.7.2016, Ireland.
Figure 3. Height of nanotubes coated with Al2O3.
Why choose ALD for High Aspect Ratio structures?
The answer is simple, only ALD can ensure a confoirmal coating on HAR structures.
You could choose, let’s say, CVD coating, but you’ll only get the flatter surfaces coated, not the trenches, tunnels, steep slopes, or sharp edges. In a CVD coating process, all the chemicals are sent at once. This means that not only will you have a totally non-conformal end result, but you’ll also have gas phase reactions and uncontrolled growth.
With ALD coating processes, a gas at a time is sent in pulses. This means that everything, even the deepest tunnels, are saturated and conformally coated. Conformal ALD coating is brilliantly suited for HAR structures due to its self-limiting characteristic. This characteristic restricts the reaction at the surface to no more than one monolayer of precursor. By increasing the precursor pulse time, the precursor can disperse into those steep slopes and deep trenches, allowing for complete reaction with the entire surface.
At Beneq, we provide four unique qualities with our Beneq TFS 200 and HAR module combination for the best ALD coating results:
1. No cross-contamination
Our inert gas valve (IGV) system keeps even the most minor traces of precursor flow out of the reaction chamber. You don’t have to worry about contamination.
2. Wide process temperature range
Chemicals are different, and so are the processing temperatures. We deliver processing ranges from 0°C to 500°C.
3. Different gas flow configuration options
Surfaces vary; you may need cross flows, or shower head flows, or both. You have the option to choose.
4. Easy maintenance of reaction chambers
The reaction chamber is held together by pressure differentials and seals, it’s not bolted down. You can easily remove it, clean it, and put it back.
We’ll be looking more closely at the actual technology behind Beneq HAR modules in our future blog posts.
If you would like to hear more now, you are more than welcome to talk to Beneq specialists, they will happily answer your questions and queries!
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Bottom DBR for LEDBeneq developed a multi-layer DBR structure on a patterned surface for a leading LED manufacturer.
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Anti-corrosion coating for sensorsThe highly conformal and pin-hole free ALD coating solved a leading sensor manufacturer's sensor corrosion problems without compromising sensor sensitivity.
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Diffusion barrier for Li-ion batteriesBeneq's ultra-thin ALD coating solved a leading Li-ion battery manufacturer's battery corrosion challenges by reducing the fading of battery capacity caused by repeated charge and unload cycles.
Anti-tarnishing coating for jewelryBeneq helped Kalevala Jewelry in preventing the discoloration of silver surfaces by providing the patented nSilver industrial-scale protection solution for an ultra-thin, totally conformal, and fully transparent anti-tarnish coating.
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Optical coatings for lenses in high power lasersBenq developed a conformal high- and low-index multilayer optical coating for a leading provider of high power laser optics and coatings using the TFS 500 batch ALD system.
Coating of Microchannel Plates (MCP)Beneq developed an ALD coating solution for microchannel plates (MCP) for Incom, Inc., the world’s largest supplier of rigid fused fiber optics, to allow for significantly greater secondary electron emission .
Thin-film encapsulation of OLED lightingBeneq developed a conformal, dense, and pinhole-free Al2O3 and TiO2 barrier coating for a leading OLED lighting panel manufacturer to protect OLED panels from humidity.
Thin-film encapsulation of scintillator plates for X-ray imagingBeneq developed a conformal, dense, and pinhole-free low temperature Al2O3 and TiO2 barrier coating for a leading scintillator plate manufacturer to protect scintillator materials from moisture and increase product lifetime and reliability.