Spatial atomic layer deposition: A route towards further industrialization of atomic layer deposition
(Color online) Schematic representation of the ALD process where the variation in time and position of the substrate (black line) and precursors (colored blocks) are given. (a) In conventional ALD the substrate is at a fixed position, and the precursors are dosed sequentially, separated by a purge step. (b) In spatial ALD, the precursors are dosed simultaneously and continuously, but at different half-reaction zones. The substrate moves between these zones where the half-reactions take place.
Original design for the spatial ALD injector as taken from Ref. 7. Precursors A and B are dosed through slits (number 75 in. drawing), distributed sideways and removed through exhausts (No. 74). The half-reaction zones are separated by gas curtains (No. 73). Reprinted from T. Suntola, J. Antson, U.S. Patent No. 4,058,430 (15 Nov. 1977).
(Color online) (a) Schematic drawing and (b) photograph of the Lotus Applied Technology spatial ALD reactor. The flexible substrate is woven back and forth between two precursor zones separated by an inert gas zone, in a serpentine configuration.
(Color online) (a) Schematic drawing and (b) photograph of the Astral spatial ALD reactor. The flexible substrate is mounted on a central drum and rotated past several precursor injectors, separated by inert gas and exhausts. Reprinted with permission from Chem. Eng. J. 171, 345 (2011).
(Color online) (a) Schematic drawing and (b) photograph of Cambridge Nanotech’s zone separated ALD manifold and cell. (c) Photograph of a prototype 150 mm zone separated ALD cell integrated into a system.
(Color online) Principle of a close proximity spatial ALD reactor concept, where the precursor half-reaction zones are separated by inert gas curtains. By moving the substrate horizontally underneath the injector, the two half-reactions will take place sequentially to form an ALD monolayer. The close proximity between the reactor and the substrate combined with the inert gas flows gives an excellent separation between the precursors.
(Color online) (a) Perspective view of the spatial ALD coating head from Eastman Kodak, showing the gas inlet and exhaust slots as well as a substrate floating on the head. The inset shows the desired gas isolation regions for two inert channels adjacent to a central reactive gas channel. (b) Photograph of the actual reactor.
(Color online) Schematic of the University of Colorado’s test apparatus showing the gas source head manifold, gas source head, micrometers for setting the gap between the substrate and the gas source head, the coupling to the linear translation motor and the frictionless translation table.
(Color online) (a) Schematic of the bottom side of TNO’s rotating spatial ALD reactor head, where the half-reaction zones are integrated into inlets surrounded by exhaust zones and gas bearing planes. (b) Schematic drawing and (c) photograph of the reactor. The reactor head and rotating substrate table with the substrate in between are placed in an oven. The substrate table is rotated by a servo-motor, connected by a drive shaft. The process- and waste gas lines are connected to the reactor head through an opening in the top of the oven.
(Color online) Two double-sided gas bearing spatial ALD concepts used by (a) Levitech and (b) SoLayTec. In both cases, a gas bearing above and below the substrate, forming a narrow slit, makes the substrate float virtually frictionless through the reactor. In the Levitech concept, the substrate is moved along a linear row of repeating half-reaction zones (called “cells”) where the total number of cells determines the overall layer thickness. In the SoLayTec concept, the substrate is moved back and forth in a reciprocating manner under a spatial ALD injector, where the overall thickness is determined by the number of passages underneath the injector. (c) Photograph of the Levitrack spatial ALD reactor from Levitech. (d) Photograph of the Process Development Tool spatial ALD reactor from SoLayTec.
(Color online) Schematic drawing of the roll-to-roll concept currently under development at TNO, consisting of a central drum that contains one or more combinations of TMA and water half-reaction zones. These zones are separated and surrounded by nitrogen gas bearings. The foil to be coated is pulled over this drum, where the gas bearing ensures that the foil is kept at a fixed distance from the surface of the drum outer surface. If the foil is then moved typically clockwise over the drum, ALD deposition will take place, where the total thickness is determined by the rotation frequency of the drum (typically rotating counterclockwise) in combination with the translation speed of the foil.
(Color online) Schematic representation of the current (temporal) “Bosch” deep reactive ion etching process. The etching cycle includes alternating cycles of an isotropic plasma etch and deposition of a chemically inert passivation layer.
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