Preparation And Optical Properties Of HfO₂ Thin Films By DC Magnetron Sputtering

Hafnium dioxide (HfO2) is a photoelectric material with excellent properties. Due to its high hardness, high dielectric constant and good thermal stability in contact with silicon, it has been considered to be one of the most promising candidates to replace silicon dioxide (SiO2) as gate oxide in semiconductor industry. Besides, HfO2 can also be used as optical coatings for optical components and mirrors of high-power lasers. This is because of its large band gap, high refractive index, high damage threshold and wide transparent spectral range from infrared to ultraviolet. Up to now, lots of research efforts have been made to connect the physical properties of the material with the manufacturing conditions.In this dissertation, HfO2 films were deposited by direct current (DC) magnetron reactive sputtering on both n-type Si (100) substrates and fused silica substrates. Deposition parameters such as substrate temperature, O2/Ar ratio and sputtering pressure were changed during deposition process. The influence of deposition parameters on structure, composition and optical properties of the films has been investigated. The main content was summarized as follows:(1) HfO2 films were deposited under substrate temperature ranging from room temperature (RT) to 500℃. The results show that all samples are polycrystalline with monoclinic structure. As the substrate temperature increases, the preferred orientation of (-111) becomes more obvious, and the grain size of HfO2 films increases. In addition, with the substrate temperature increasing, the refractive index increases and the optical band gap decreases. The films have a good transmittance, exceeding 80% in the range from 250nm to 850nm.(2) Hfth films were deposited at different O2/ Ar ratios. The results show that O2/Ar ratio has no significant influence on the structure of deposited films. With the O2/Ar ratio increasing, the deposition rate decreases. When the O2/Ar ratio is about 1:4, the film has a more compact structure and a larger refractive index. In addition, as the O2/Ar ratio increases from 1:9 to 3:2, the ratio of O/Hf decreases from 1.91 to 1.38, and this lead to the decline of optical band gap. An excellent transmittance, exceeding 85% in the range from 200nm to 850nm, is obtained for all samples.(3) HfO2 thin films were deposited under sputtering pressure ranging from 2.5Pa to 8.0Pa. The results show that the preferred orientation of (-111) is more obvious at low sputtering pressure. With the sputtering pressure increasing, the diffraction peak of (111) becomes stronger, while the preferred orientation of (-111) becomes weaker. Moreover, with the sputtering pressure increasing, the deposition rate first increases and then decreases. When the sputtering pressure is 4.0 Pa, the deposition rate has the largest value about 1.8nm/min. The films deposited at high pressure have small band gap.