The ALD Process

The Concept

Atomic layer deposition is a gas phase two reaction process. It can be easily explained using bricks as an analogy. Imagine you have green and blue bricks, but there are some rules. Green bricks can only stack on blue, and blue bricks only stack on green. We put down a layer of green bricks, then a layer of blue, and call this one ALD cycle. These cycles are usually around 1 Ångstrom, or 0.0000000001 meters thick. We then repeat these stacks until we get a desired film thickness. The surface would look like this:

ALD, Binary Reactions, Atomic Layer Deposition
One cycle of ALD chemistry.

The Chemistry

To get more technical, replace the green and blue bricks with molecules. For aluminum oxide, our most popular and versatile chemistry, our green bricks are aluminum containing molecules. The blue bricks are oxygen containing molecules, water molecules. When we bring in our aluminum molecules, it reacts to leave aluminum atoms on the surface. Since it can’t react with itself, it only deposits one layer of aluminum atoms on the surface and stops. Then we bring in our oxygen containing molecules and they put down a layer of oxygen.