Enhancement of Dielectric Properties of Nanoscale HfO₂ Thin Films Via Atomic Layer Bombardment

The impacts of the atomic layer bombardment (ALB), which is the in situ layer-by-layer inert gas plasma treatment introduced in each atomic layer deposition (ALD) cycle, is explored to enhance the dielectric characteristics of nanoscale HfO2 thin films. Different ion bombardment modes, including the bombardment after precursor (BAP) and the bombardment after oxidant (BAO), were examined in detail to understand the ALB behaviors. In contrast with the detrimental effects caused by the BAP process, the BAO treatment contributes to an about 3-orders-of-magnitude reduction of the leakage current density (Jg) and an about 26% increase of the dielectric constant (K). The suppression of Jg and the enhancement of K can be attributed to the densification of thin film caused by the BAO process, as revealed by X-ray reflectivity characterizations. As a result, a low equivalent oxide thickness (∼1.1 nm) and a low Jg (6.77 × 10–4 A/cm2) are demonstrated in an ultrathin (∼3 nm) HfO2 high-K gate dielectric prepared by the BAO ALD process. Hence, the ALB treatment is demonstrated as a promising technique to significantly improve the dielectric characteristics of nanoscale thin films, which is critical in semiconductor, energy, and biocompatible applications.