Spatial Atomic Layer Deposition (SALD)

In conventional Atomic Layer Deposition (ALD), precursors are sequentially exposed to the substrate via short injections, while being kept physically separated by intermediate purging steps. Spatial ALD (SALD) is a recently developed variation of ALD in which the precursors are continuously sent to different locations, separated by a region or zone containing an inert gas. Film growth is achieved by exposing the substrate to locations containing different precursors. It can also be carried out at ambient pressure, without the need for vacuum. As a result, ALD becomes faster, compatible with high-throughput techniques such as roll-to-roll (R2R), and much more versatile, easier and cheaper to develop on a large scale.

Since the first publications in 2004 and 2008 on the subject, the number of publications has continued to grow, reaching almost 70 articles in 2016. SALD has also made the transition from laboratory to industrial scale, and several commercial systems are already available for both laboratory and production scale.

Because precursors are continuously injected into the SALD, efficient separation by the gas/inert zone flow must be ensured. Analytical fluid dynamics studies and modeling are therefore commonly used when designing reactors and evaluating optimal deposition conditions.

The combination of ALD's unique strengths with much higher deposition rates and the possibility of air deposition, design flexibility and easy large-scale development should make SALD one of the leading thin-film deposition techniques.

This article provides an introduction to the principles and applications of SALD.