Controlled film growth at the atomic level
Atomic layer deposition (ALD) is a thin film growth technique based on sequential, self-limiting surface reactions. With this method, it is possible to have control of film growth at the atomic level. It is also possible to conformally deposit thin films on very high aspect ratio structures, while retaining a much higher level of uniformity than with any other method of film deposition.
Coupled with the continuous development of precursors, ALD can be used to deposit a wide variety of materials at many different conditions, which opens the possibility for applications to a huge range of substrates.
ALD is also flexible and can be performed in various types of reactor configurations under a variety of conditions that include chamber pressures up to atmospheric pressures. Under high vacuum, ALD reactors enable plasma ALD processing.
In most implementations mentioned thus far, the reactants are pulsed in the chamber one at a time and then removed by purging or vacuum pumping. The substrates remain fixed in one location and the reactants pumped one at a time and then completely removed before the introduction of the next reactant to avoid any gas phase reactions that may lead to CVD.
Separate precursors in space with spatial ALD
An alternative approach to separating precursors in time is to separate them in space. In this case, the two reactants are no longer delivered at the same point, but rather the substrate moves relative to the reactant sources. The reactants flow continuously because the substrate movement sets the coating parameters. This is what we call spatial ALD and one example of such embodiment is the roll-to-roll system, where a flexible substrate moves continuously under several ALD zones.
Continuous roll-to-roll for large area substrates
Continuous roll-to-roll is significant because it allows application in many large area substrates in a cost-effective manner.
The original idea of moving the substrate through zones of constant precursor flows has been around since 1977. It involved rotating the substrate among alternating chemically reactive zones separated by purge regions.
A natural extension of this approach is based on moving the substrate close to several chemically reactive regions. The precursors continually flow through orifices on the gas delivery heads that are separated by inert gas purging and vacuum zones. Gas phase reactions between the zones are prevented both by the inert gas curtains and the vacuum pumping zones that separates the precursor delivery regions.
Roll-to-roll for cost-effective ALD
The implementation of roll-to-roll is important for cost-effective ALD in several areas. One of the most important applications areas is ALD coatings as barriers for polymer substrates. The barrier films are critical for encapsulation and moisture barrier protection for flexible organic light emitting diodes (OLED) displays and thin film solar cells.
Internal Beneq results confirmed by independent laboratories have shown that Al2O3 ALD coatings using TMA and ozone form excellent gas barriers with WVTR values of about 1×10-5 g/m2/ at 38C/85% relative humidity.
Beneq WCS 600
The Beneq WCS 600 is the ideal option for customers looking for a large and cost-effective ALD roll-to-roll system. Typical non-uniformities are less than 2% across the web width for a typical Al2O3 coating. A WVTR of 10-4 g/m2 day can be expected at a web speed of 0.25 meters/minute.