In Situ Study Of Surface Structure Evolution Of Silicon Oxide And Silicon Carbide Under Thermal Field And Electron Irradiation

Because of the rapid development of information technology,it's urgent to continually scale down the semiconductor devices to meet the needs of high performance.When the size is reduced to nanometer scale,the surface effect will play a dominant role in the performance of devices.Therefore,it's of great significance to explore the surface structure evolution and controllably modify the surface structure at atomic scale,so as to understand the structure-performance relationship for designing high performance device.In this dissertation,we study the surface structure evolution of silicon-base materials?silicon oxide and silicon carbide?under electron beam irradiation and heating using in situ transmission electron microscopy.The main results are summarized as follow:1.In situ study of the growth of crystalline silicon on amorphous silicon oxide surface.?1?Two transformation processes are in situ observed at atomic scale.When the amorphous silicon oxide is exposed to electron shower,amorphous silicon suboxide nanoparticles form firstly and then transform to crystalline silicon nanoparticles.?2?The critical dose for the formation of crystalline silicon decreases from¹0⁸ C m^-2 under300 keV electron irradiation at room temperature to¹0⁵ C m^-2 under 80 keV electron irradiation at600°C,which may give new insights into high-speed direct electron writing.?3?The elastic displacement cross section of silicon oxide is larger than that of crystalline silicon,which significantly reduces the effective free energy of crystalline silicon under electron irradiation,causing the self-organization of silicon atoms and formation of crystalline silicon.2.In situ study of the structure evolution of silicon carbide surface at atomic scale during growth.?1?An experimental methodology is developed for in situ vapor–solid deposition of silicon carbide under electron irradiation and heating.?2?Surface evolution driven by surface energy is revealed.The?-SiC expands mainly along<111>directions layer by layer and its surface tends to form lower energy{111}planes.The formation of multiple stacking faults induces the transformation from?-SiC to?-SiC,and the formation of{111}nano facets on?-SiC surface results in step bunching along<1-100>directions.The hill-and-valley structure,which is consist of inclined{111}nano facets,are preferred to form on?-SiC{1-100}surface,leading to the transformation of the projected shape along[0001]axis from hexagon to triangle.?3?The formation mechanism of the special step structures on?-SiC?6H-SiC and 4H-SiC?surface is uncovered.Due to the formation of{111}nano facets,straight steps with half or one unit cell height are preferable when the surface is inclined to[1-100]direction,whereas zigzag steps with half unit cell height are energetically favorable when the surface is inclined to[11-20]direction.3.In situ study of epitaxial growth of graphene on silicon carbide surface at atomic scale during etching.?1?An experimental methodology is developed to in situ clean the silicon carbide surface by electron-beam-induced etching at high temperature.?2?The growth of epitaxial graphene on silicon carbide?1-100?surface is demonstrated by in situ transmission electron microscopy in combination with ab initio molecular dynamics simulations.Three silicon carbide layers are decomposed successively to form one graphene layer.The sublimation of the first layer results in the formation of carbon clusters containing short chains and hexagonal rings,which can be considered as the nuclei for graphene growth.The decomposition of the second layer causes the appearance of new chains connecting the as-formed clusters and the formation of a network with large pores.The carbon atoms released by the sublimation of the third layer promote the transformation of the chains into hexagonal rings accompanied by the annihilation of the large pores;finally,a large graphene layer is observed.