Mike van de Poll, a researcher at Eindhoven University of Technology, has dedicated his scientific endeavors to exploring the intricacies of spatial Atomic Layer Deposition (ALD). Supervised by renowned experts in the field, Erwin Kessels and Bart Macco, Mike’s research dives deep into understanding fundamental aspects of spatial ALD, leveraging the advanced capabilities of Chipmetrics’ PillarHall test chips.
Unlike traditional temporal ALD, which separates reactants in time within a vacuum chamber, spatial ALD separates reactants in space, allowing substrates to move rapidly between different reaction zones. Mike explains, “Spatial ALD separates reactants in space instead of time, speeding up the ALD process significantly since there’s no need to pump down your vacuum chamber after each reaction.” This approach enables operation at atmospheric pressure, offering advantages for high-volume manufacturing applications like solar cells and batteries.
Mike’s research, particularly enabled by PillarHall test chips, has illuminated how atmospheric pressure affects the conformality and efficiency of plasma-enhanced ALD. Utilizing these test chips, Mike and his team have precisely measured how oxygen radicals—the main workhorse of plasma-enhanced (spatial) ALD—recombine within high-aspect-ratio structures during deposition. Since oxygen radicals no longer contribute towards film growth once they recombine, the probability of recombination is an critical aspect for film conformality. Their studies demonstrated that radical recombination probabilities remain surprisingly consistent across temporal and spatial ALD methods, despite substantial differences in pressure conditions.
However, the pressure does notably impact film conformality. According to Mike, “Atmospheric-pressure spatial ALD starts with a higher concentration of radicals, helping films grow deeper into moderate-aspect-ratio structures quickly. But diffusion rates at atmospheric pressure are slower, making lower-pressure processes better for deeper, more intricate structures.”
The PillarHall chips have proven valuable for delving into the complex growth mechanisms of titanium oxide. This oxide initially deposits amorphously and transitions to crystalline structures as film thickness increases. Mike notes, “Inside 3D structures, where the deposited film thickness typically slightly decreases with the depth, you might see a crystalline film at the start that transitions into an amorphous film deeper in. This change affects subsequent growth rates significantly, influencing overall film conformality.” Such insights are essential for optimizing ALD processes tailored to specific application requirements.
Further leveraging the versatility of PillarHall chips, Mike explored the effects of ions and UV photons from plasma processes. The chips clearly distinguished the influences of these energetic particles, which do not penetrate deeply into lateral trenches, from reactants that diffuse throughout the structures. Understanding these nuances helps in fine-tuning spatial ALD processes to achieve desired material properties.
Looking ahead, Mike is investigating ternary oxides—materials with increasing relevance in advanced technologies. His work compares the co-dosing method (simultaneous introduction of multiple precursors) versus the supercycle method (sequential precursor dosing). Early findings suggest supercycles offer better compositional control within trenches, demonstrating yet again the importance of precise precursor management.
Mike envisions spatial ALD revolutionizing high-volume manufacturing applications. “I’m excited to see spatial ALD adopted in industries like batteries and solar cells,” he says. With startups already leveraging spatial ALD for battery electrode coatings, he anticipates widespread adoption across various industries. Through continued research and innovation facilitated by tools like PillarHall chips, Mike van de Poll remains at the forefront, shaping the future of ALD technologies.
