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

Abstract

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 TiO 2 (titanium dioxide), even under mild plasma conditions with lowenergy (<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 TiO 2 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 °C when using short plasma steps and a grounded substrate, providing a low ion-energy dose of ∼1 eV nm −2 cycle −1 , while a high effect is obtained when using extended plasma exposures or substrate biasing (∼100 eV nm −2 cycle −1 ). This work on TiO 2 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.

Atomic layer deposition: An efficient tool for corrosion protection

“…The selection depends on the available equipment, the expected properties and the substrate (topography or temperature sensitivity) on which the deposition is to be made. In the case of non-planar surfaces, the thermal method is often preferred, but recent examples show that it is also possible to achieve conformal films on surfaces with relative high-aspect ratio [28][29][30]. In the car metaphor, it means the driver has more time to find a parking spot.…”

Plasma-Enhanced Atomic Layer Deposition of HfO2 with Substrate Biasing: Thin Films for High-Reflective Mirrors

“…Hafnium dioxide (HfO 2 ) is a widely studied dielectric material due to its application in integrated circuits and optics for its high dielectric constant, high refractive index, and low optical losses in the UV spectral range down to 266 nm wavelength. − Hafnia thin films are typically used as a high refractive index material in interference coatings, especially for high-power laser applications. , HfO 2 thin films for optics are deposited mostly by physical vapor deposition (PVD) ,− and chemical vapor deposition (CVD) ,, techniques. Atomic layer deposition (ALD) has gained importance due to the ability to coat wide-area surfaces with excellent uniformity and grow conformal coatings on high aspect ratio nanostructured substrates. − This technology is a subclass of the CVD technique where gas-phase precursors are sequentially introduced into the deposition chamber. The layer-by-layer growth in a self-limiting manner enables ALD to deposit thin films with a precise thickness control .…”

Our Most Downloaded Papers Published in 2021

“…A number of the top 20 papers focused on material synthesis (Table ). − This emphasis is not new for the journal, but the material classes represented in these manuscripts are broader than in years past. They included metal oxides ranging from TiO 2 prepared by atomic layer deposition (ALD) to ternary oxides and high entropy oxide systems .…”

“… − This emphasis is not new for the journal, but the material classes represented in these manuscripts are broader than in years past. They included metal oxides ranging from TiO 2 prepared by atomic layer deposition (ALD) to ternary oxides and high entropy oxide systems . The latter two reflect a growing interest in high-quality synthetic strategies for materials with increasingly complex compositions.…”