The Effect of Seed Layer on the MgO Thin Film Using the Sol-Gel Method on Si(100)

Abstract

MgO film has many excellent physical and chemical properties. It is widely used as the buffer layer and simple protective layer and so many researchers have been attracted by it due to its huge potential in microelectronics field. According to the existing researches, it is found that growing MgO thin film on Si substrate only by RF magnetron sputtering method is very difficult. The growth rate of growing MgO thin film by using this method is very low. As for this experiment, RF magnetron sputtering and so-gel method were combined together to prepare MgO film and obtained a very good result. The structural properties of MgO film were investigated to optimize growth conditions to obtain high quality MgO film. First, RF magnetron sputtering was used to deposit three different dense buffer layers on Si(100) substrate, which were conducted under various growth conditions. Those three different buffer layers referred to MgO buffer layer, ZnO buffer layer and Mg0.3Zn0.7O buffer layer, respectively. Then by using the sol-gel method, the prepared solution was coated on those different buffer layer by using spin coater to obtain MgO film which had a certain thickness. The structure and surface morphology of the samples were characterized by using atomic force microscopy (AFM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and TEM (Transmission electron microscope).

XRD profiles showed that (111) preferred orientation occurred obviously in the XRD profiles. After annealed at 700 ℃ in oxygen, the MgO film began to crystallize. With the annealing temperature increasing, MgO(111) peak intensity became stronger, while the FWHM became smaller and the crystalline quality of the film was getting better. Compared the MgO film which was prepared only by sol-gel methods, after introducing ZnO and Mg0.3Zn0.7O buffer layer, XRD results showed that the MgO film became much better, while the impact of the introduction of MgO buffer layer film was very weak. Probably due to the low growth rate of MgO film prepared by using RF magnetron sputtering, the MgO buffer layer was too thin or the crystal quality was not good. Those reasons may restrict the effect of the MgO buffer layer. SEM photographs showed that after filtering the solution, the surface of MgO film was very smooth and the phenomenon of surface cracking was reduced significantly. The presence of substances or large insoluble particles existed in the solution can account for it. During spin coating process, these large particles severely affect the uniformity and stability of the film. Furthermore, the coefficient of thermal expansion difference between the particle and the film made such cracking phenomenons occur during the post annealing process. The TEM results showed that the obtained MgO film had dense structure, uniform thickness and a clear boundary over the Si substrates judging by cross-section figures. The diffusion among the Si substrate, buffer layers and the MgO film was not obvious. AFM results showed that the crystalline grain was spherical and crystalline state was obvious. After annealed at a certain temperature limit, the roughness of the surface decreased as the temperature rose. Over the limit, the surface roughness began to increase. As for the grain size, the changes in grain size is inversely related to the change of surface roughness.