Impact of Ions on Film Conformality and Crystallinity during Plasma-Assisted Atomic Layer Deposition of TiO2

This work demonstrates that ions have a strong impact on the growth per cycle (GPC) and material properties during plasma-assisted atomic layer deposition (ALD) of TiO2 (titanium dioxide), even under mild plasma conditions with low-energy (<20 eV) ions. Using vertical trench nanostructures and microscopic cavity structures that locally block the flux of ions, it is observed that the impact of (low-energy) ions is an important factor for the TiO2 film conformality. Specifically, it is demonstrated that the GPC in terms of film thickness can increase by 20 to >200% under the influence of ions, which is correlated with an increase in film crystallinity and an associated strong reduction in the wet etch rate (in 30:1 buffered HF). The magnitude of the influence of ions is observed to depend on multiple parameters such as the deposition temperature, plasma exposure time, and ion energy, which may all be used to minimize or exploit this effect. For example, a relatively moderate influence of ions is observed at 200 degrees C when using short plasma steps and a grounded substrate, providing a low ion-energy dose of similar to 1 eV nm(-2) cycle(-1), while a high effect is obtained when using extended plasma exposures or substrate biasing (similar to 100 eV nm(-2) cycle(-1)). This work on TiO2 shows that detailed insight into the role of ions during plasma ALD is essential for precisely controlling the film conformality, material properties, and process reproducibility.

Automated summary

This study demonstrates that even under low-energy ion conditions, ions have a significant impact on the conformality, film thickness, crystallinity, and wet etch rate of TiO2 films during plasma ALD. The magnitude of this impact depends on various parameters such as deposition temperature, plasma exposure time, and ion energy, which can be utilized to minimize or exploit the effect. Understanding the role of ions in plasma ALD is crucial for precise control over film properties and process reproducibility.