Atomic Layer Deposition

Atomic Layer Deposition (ALD) or Pulsed-Enhanced Atomic Layer Deposition (PEALD) is the most advanced material processing technique which enables the deposition of highly conformal films on semiconductor wafers. This technology provides accurate thickness control and robust film properties, and this is extremely beneficial when it comes to semiconductor applications as the industry continues to evolve to greater die density and lighter weight packaging with increased sensitivity to environmental conditions.

Figure 1 Schematic diagrams of the conventional CCP VHF PEALD system (DOI:https://linkinghub.elsevier.com/retrieve/pii/S2468023022004862 )

Figure 2 Schematic representation of the general structure of an ALD process. ( Functional analysis of retarding field energy analyzers for ion energy distribution measurements in plasma enhanced atomic layer deposition, Buiter, J. W.  2018)

In general, Atomic Layer Deposition consists of a cycle of 4 steps that is repeated as many times as necessary to achieve the required deposited thickness as shown below in figure 3. Each step is a self-limiting reaction and thus provides excellent control on thickness.

1. First step is the dosing of the substrate with a process specific precursor leading to its adsorption and reaction with substrate.
2. Next is the purging step to prevent the reactants from reacting with each other.
3. In this step a remote plasma exposure to the substrate is provided with activate radicals
4. Again, purging is carried to remove the reaction products.

ALD technique is used to deposit a vast variety of materials ranging from oxides, nitrides, carbides, metals, biomaterials to polymers. ALD offers following advantages:

1. Precise control of film thickness in nano meter scale with high uniformity
2. Low temperature process (50-500 ℃)
3. Excellent adhesion and superior surface passivation
4. Conformal coating on any shape, geometry, 3D structures and sensitive substrates
5. A highly repeatable and scalable process