Atomic Layer Etching

Our group actively works on developing and characterizing atomic layer etching (ALE) processes for various materials, including metal oxides (such as TiO₂, HfO₂, Al₂O₃, ZnO₂) and metals (W, Co, Cu).  Atomic layer etching is also described as “inverse ALD” as material is etched a single monolayer at a time using self-limiting reactions. This emerging technique is not only useful for precise thickness control, but also enables highly selective, isotropic etching with minimal damage to the sample. In addition, intermittent ALE cycles can be combined with an ALD process to achieve area-selective deposition as described in more detail in the Area Selective ALD and MLD section.

In the example process imaged we have developed a process for atomic layer etching of TiO₂ using WF₆ and BCl₃ as reactants. WF₆ reacts with the surface, creating WO_xF_y/TiO_yF_z species, which subsequently react with BCl₃, creating volatile WOCl₄, TiCl₄, and BF₃ species and therefore removing a monolayer of the thin film. This cycle can be repeated as many cycles as needed to achieve the desired film thickness.

You can read more about this method and results in these journal publications:

• Xie W, Lemaire PC, Parsons GN. Thermally Driven Self-Limiting Atomic Layer Etching of Metallic Tungsten Using WF₆and O₂. ACS Appl Mater Interfaces. 2018, 10, 10:9147-9154. doi:10.1021/acsami.7b19024
• Lemaire PC, Parsons GN. Thermal Selective Vapor Etching of TiO₂: Chemical Vapor Etching via WF₆and Self-Limiting Atomic Layer Etching Using WF₆ and BCl₃. Chem. Mater. 2017, 29, 16:6653-6665. https://doi.org/10.1021/acs.chemmater.7b00985