Evaluating operating conditions for continuous atmospheric atomic layer deposition using a multiple slit gas source head

Abstract

Continuous atmospheric atomic layer deposition (ALD) is based on the separation of ALD reactants in space rather than in time. In this study, operating conditions for continuous atmospheric ALD were evaluated using a multiple slit gas source head. A test apparatus was constructed consisting of a gas source head that sits above a substrate that is driven by a programmable stepper motor. The gas source head was composed of a series of rectangular channels that spatially separate the ALD reactants. With Al2O3 ALD as the model system, the trimethylaluminum (TMA) reactant channel was positioned in the center and the H2O reactant channels were located on both sides of the TMA channel. This design allowed for deposition of two Al2O3 ALD cycles during one complete back-and-forth translation of the substrate. The gap spacing between the gas source head and substrate was fixed and controlled using micrometers. A series of experiments was conducted using He as a tag gas to determine operating conditions that prevent reactant cross diffusion. There was a wider range of suitable exhaust pumping speeds at a 30 μm gap spacing than at a 100 μm gap spacing. However, mechanical tolerances were not sufficient to allow back-and-forth translation of the substrate at a gap spacing of 30 μm. For Al2O3 ALD at a 100 μm gap spacing, the best Al2O3 film uniformity was achieved when there was a slight vacuum of ∼−5 Torr beneath the gas source head relative to ambient. A larger vacuum beneath the gas source head occurred if the pumping speed of the exhaust channel was higher relative to the N2 supplied to the gas source head. These conditions produced a smaller footprint of Al2O3 deposition resulting from an influx of N2 from the higher pressure ambient. The gas source head had a higher pressure than ambient if the exhaust pumping speed was too low relative to the N2 supply. Under these conditions, reactant gas leaked out the sides and formed Al2O3 powder around the perimeter of the gas source head resulting from the chemical vapor deposition reaction of TMA with ambient moisture. A response surface model was generated to predict the dependence of the pressure beneath the gas source head relative to ambient on the various operating conditions.

Roll‐to‐Roll Atmospheric Atomic Layer Deposition of Al2O3 Thin Films on PET Substrates

“…In our experimentation, a constant growth rate of 0.98 Å per cycle was recorded, which means that one pass (five ALD cycles) would result in a film thickness of ∼4.9 Å. This achieved growth rate of 0.98 Å per cycle is slightly lower than in conventional ALD systems, but it is comparatively higher than other reported values of the latest ALD technologies . The study also demonstrated that the amount of Al 2 O 3 deposited during the starting cycles of ALD is virtually the same as in the later ALD cycles.…”

“…Scientific studies have reported that the cycle time may be as long as many minutes and result in deposition of films with thickness of approximately one angstrom, which greatly reduces the efficiency of ALD technology . Apart from that, the conventional ALD is a vacuum‐based technology and has rarely been reported to be used for the fabrication of thin films under atmospheric pressure conditions . The size and design of the ALD reactor also affects the processing parameters of the ALD process.…”

“…Levy et al demonstrated spatial ALD using a multiple‐slit gas‐source head . Fitzpatrick et al utilized a multiple‐slit gas‐source head to deposit Al 2 O 3 films on silicon substrates . Unlike the conventional ALD process, in which the two precursors are separated in time, in spatial ALD, the exposure of precursors has been separated in space.…”

Roll-to-roll atomic layer deposition process for flexible electronics encapsulation applications

“…1. SALD processes have been described by a number of authors, [9][10][11][12] and concepts for developing these into a roll-to-roll process have been proposed. [13][14][15] Previously, only one implementation has been constructed, which enables narrow webs to be coated in a roll-to-roll basis with a very restricted number of deposition cycles in one pass.…”

Spatial atomic layer deposition for coating flexible porous Li-ion battery electrodes

“…Spatial ALD can be performed using a number of different designs based primarily on the gap between the gas source head and the substrate. 14 These designs include a translating gas source head or substrate moving horizontally back-and-forth with a gap of $30-100 lm defined either by mechanical separation or a gas bearing; [15][16][17] a substrate spinning underneath a gas source head with the gap of $20 lm defined by a gas bearing; 18 and a rotating cylinder design with the gap of $1 mm defined by two concentric cylinders. [19][20][21][22] Another design is based on a "serpentine" web moving through spatially separated reactants 23 or a "closed loop" flexible web moving under a gas source head.…”