Understanding surface morphology evolution in magnetron sputtered AlN templates: mitigating tensile stress and enhancing crystal quality†

Abstract

The thickness and surface morphology of aluminum nitride (AlN) templates are crucial for evaluating their quality and suitability for device applications. However, the relationship between these two factors remains unclear for AlN templates grown via magnetron sputtering. This study systematically investigates the surface restructuring mechanisms in AlN films during thickness progression, revealing a stress-driven morphological transition. As film thickness increases, accumulated tensile stress exceeding ∼0.5 GPa triggers the spontaneous formation of “flower-like” surface patterns through stress relief. While mitigating further stress buildup, this morphological transformation degrades crystalline quality post-high-temperature annealing. Through strategic optimization of sputtering thermodynamics, we successfully preset compressive stress in AlN films and extended the critical thickness for morphological degradation to 2 μm. The resulting high-quality thick AlN films exhibit simultaneously improved surface continuity and enhanced crystalline perfection. These results provide valuable insights into the stress-morphology interactions in sputtered AlN films, offering new strategies for optimizing AlN template growth and enhancing the performance of AlN-based devices.