Computational Fluid Dynamics and 3D Printing towards Nanoscale Thickness Gradients and Scale-up of a Spatial Atomic Layer Deposition System
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Nanoscale functional thin films are integral part of all modern devices. As these devices continue to miniaturize in feature size, better control of film thickness and quality is needed. Atomic Layer Deposition (ALD) is becoming the best option for such devices as it produces high quality ultrathin films that are pinhole-free and conformal by growing the film one atomic layer at a time. However, it remains a slow, expensive and challenging to scale process due to its vacuum chamber requirement. Furthermore, its disadvantages make it inefficient for device prototyping and optimization. Atmospheric Pressure Spatial ALD (AP-SALD) is a novel technique that produces ultrathin films with quality identical to conventional ALD, but at a speed up to 100x faster in open-air without the need of a vacuum chamber, and is scalable to high throughput manufacturing such as roll-to-roll processes. In this work, a customized lab-scale AP-SALD reactor that can deposit thin films with thickness gradients for high throughput combinatorial synthesis and studies is designed, 3D printed and tested. The design of the reactor is guided by Computational Fluid Dynamics (CFD) and design guidelines of Stereolithography (SLA) 3D printing. The reactor was designed with a multimodal feature whereby it can be used to deposit either uniformly thick or graded thin films. It was tested to deposit a uniformly thick zinc oxide film that is 178 nm thick on borosilicate glass with a uniformity of 5%, growth per cycle (GPC) of 1.19 nm/cycle and growth rate of 0.66 nm/s. The same reactor was also used to deposit a zinc oxide film with a thickness gradient of 70 nm (from 150 to 80 nm) with GPC of 0.30 nm/cycle (0.33 nm/s) on the thicker side and GPC of 0.17 nm/cycle (0.19 nm/s) on the thinner side. To validate the scalability of the AP-SALD technique, a heated translating stage that can hold multiple industrial-size substrates (9x larger than lab-scale substrates in area) all at once for high throughput deposition, and a unique reactor for large-area deposition were design and constructed for a pilot-scale AP-SALD system. The heated stage is designed to heat the substrates from room temperature to 300 °C, which is within the ALD window of some common technologically relevant materials such as zinc oxide and aluminum oxide for initial testing. The unique reactor was 3D printed and tested to produce zinc oxide and aluminum oxide films on industrial-size borosilicate glass with thicknesses of 63 nm (uniformity +/- 7%) and 108 nm (uniformity +/- 6%) respectively.
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Jhi Yong Loke (2020). Computational Fluid Dynamics and 3D Printing towards Nanoscale Thickness Gradients and Scale-up of a Spatial Atomic Layer Deposition System. UWSpace. http://hdl.handle.net/10012/16551