Structure And Performance Study Of CeO₂Films Deposited On Silicon Substrates By Pulsed Laser Deposition

Cerium Oxide (CeO2) has received considerable interest and widely studies because of its excellent characteristics, which make CeO2attractive as an electrolyte material for gate dielectric of MOS devices, buffer layer and optical films. It is of great significance to explore the deposition parameters and performance of CeO2films. In this article, we deposited highly single orientate CeO2films on silicon substrates by PLD method in high vacuum environment, analyzed the relationship between parameters and performance, studied the effects of annealing. The results are showing:(1) CeO2thin films with highly (111) orientation have been deposited on Si(100) substrates. The structure characteristic, surface morphology and electric performance were measured. The results showed that samples grew in two-dimension mode with smooth surface. FWHM value of (111) orientation was larger than which reported in literatures. HRTEM images showed that there was an interface layer between the film and substrate and the sample is polycrystalline. Internal crystal orientations are clutter. Maybe, it was due to the existence of oxygen vacancy. As the substrate temperature raised, dielectric constant increased and some distortion appeared in accumulation part of C-V curves. The right shifting of curves declared that some negative charge existed at the interface. The leakage current density of samples decreased and then increased as the temperature increased. Higher laser power enhanced dielectric constant and there was also distortion in accumulation part of C-V curves. The left shifting indicated the existence of positive charge, and the leakage current density changed little. In order to improve electrical properties, the samples needed to be heat-treated.(2) Physical and electrical properties of samples deposited at different conditions after being treated in argon ambient at different annealing temperatures have been investigated and analyzed. Heat-treatment enhanced the (111) orientation and other orientations did not appear, which was different with the samples deposited by other methods, such as magnetron sputtering technique and so on. The physical results demonstrated that the root-square surface roughness increased as the annealing temperature raised. We calculated the electrical properties of the films deposited at3.5J/cm2and600℃after heat-treatment. All samples showed negative flat band voltage shift owing to the existence of positive effective oxide charges. Sample annealed at900℃has shown the lowest flat band shift, effective oxide charge and leakage current density, besides it had complete regions of inversion, depletion and accumulation in C-V curve. However, as the annealing-temperature raised, the thickness of interface layer increased and the dielectric constant decreased.(3) CeO2thin films with highly (111) orientation have been deposited on Si(111) substrates by PLD in high vacuum. The growth behavior was monitored by reflection high energy electron diffraction in situ. Structure characteristic and surface morphology of the CeO2films were analyzed by X-ray diffractometer and atomic force microscope. The results showed that with the enhancement of substrate temperature and laser energy, orientation relationship and crystallization quality improved and micro-stress released,(111)diffraction peak approached to the standard diffraction peak, surface morphology of samples became smoother. The spectroscopic ellipsometry indicated that the refractive index of the film depends on the crystallization quality. The refractive index of the sample with optimum crystal quality is quite close to that of single crystal CeO2film. HRTEM images showed that the as-prepared sample reveals a good crystal performance, but a slight deviation of orientation exists in some region.