Computational Fluid Dynamics and 3D Printing towards Nanoscale Thickness Gradients and Scale-up of a Spatial Atomic Layer Deposition System
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Date
2020-12-15
Authors
Loke, Jhi Yong
Journal Title
Journal ISSN
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Publisher
University of Waterloo
Abstract
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.