Growth properties and optical properties for HfO₂ thin films deposited by atomic layer deposition

Research on HfO₂ thin film deposition by atomic layer deposition for growth properties and laser damage resistance is rare. In this paper, its related properties have been investigated with various deposition cycles. Microstructure of the thin films was investigated by X-ray diffraction. Film cross-sections were measured by the Transmission Electron Microscope. In addition, film morphology was studied under an atomic force microscope. Laser-induced damage threshold was tested by a damage test system. The results show that with the increase of cycle number, the refractive index of the HfO₂ film deposited by ALD increases gradually. Growth rate was no longer keeps a constant, and there was a jump at the 500 cycles. Moreover, film roughness increases gradually with the deposition cycles increased, especially when the cycle numbers were 500 and 1000, film roughness were 2.16 nm and 2.03 nm, respectively. Based on the results of XRD and TEM, crystallization was found to occur when the deposition cycle was larger than or equal to 500 with mainly polycrystalline structure. With the film thickness increased, film exhibited preferred orientation of (2, 0, 0). All it shows that with the film cycle number increased, three processes of the film growth appeared: gathered, island and nucleation crystalline phases. The damage threshold of the films decreased from ∼28 J/cm² to ∼16 J/cm² while the crystallinity of films increased, indicating that the presence of grain boundaries led to the reduction of the damage threshold of the films.