Formation Mechanism Of SON Structure And Experimental Verification

The development of very large-scale integrated circuits has enabled terminal products to have the characteristics of high integration,low energy consumption,and high speed.The further reduction of the feature size of integrated circuits puts higher requirements on the device structure.SOI(Silicon-on-Insulator)devices have better electrical performance,stronger anti-interference ability and higher integration density than bulk silicon devices.The SON(Silicon-on-Nothing)structure refers to the cavity formed in the silicon substrate and the monocrystalline silicon film on the cavity during rapid thermal annealing.Compared with the SOI structure,the SON structure has better electrical performance and heat dissipation performance.However,the current technique for fabricating SON structure is not perfect,and the characteristic size of the SON structure cannot be accurately predicted.Therefore,this paper studies the formation mechanism of SON structure and conducts experimental verification.The main research contents and results are as follows:(1)Research on the theoretical model of the formation mechanism of SON structure.Assuming that surface diffusion is the only material transport mechanism,the atomic diffusion phenomenon on the surface of silicon wafer was analyzed theoretically from the perspective of surface morphology evolution caused by the change of free energy.Based on the Nernst-Einstein relation and the Boltzmann distribution,a nonlinear kinetic equation describing the normal velocity of Si atoms along the surface was established.(2)Simulation and analysis of the formation process and influencing factors of the SON structure by COMSOL Multiphysics^?software.Simulations of the formation process of the SON structure were performed by the use of“Level-set”and“General partial differential equation”modules.Based on the simulation results,the relationship between the sizes of regular and irregular trenches and the characteristic sizes of the SON structure and the relationship between the initial trench sizes and the thickness of the step were analyzed.The feasibility of forming multi-layer cavities in the silicon substrate and the temperature dependence of the formation process of the SON structure were discussed.The results show that the thickness of the silicon film Tson increases with the increase of the trench aspect ratio and the distance between neighboring trenches and the decrease of the trench width.The thickness of the cavity Tp increases with the increase of the trench aspect ratio and the trench width and the decrease of the distance between neighboring trenches.Within a certain range,the step thickness Tstep increases with the increase of the trench width and the aspect ratio and the decrease of the distance between neighboring trenches.When the trench aspect ratio exceeds the limit value,multi-layer cavities can be formed in the silicon substrate.In addition,as the annealing temperature increases,the trench morphology changes faster.The S-W's interatomic potential function for silicon was used to simulate the shape evolution of silicon trenches at high temperature by using LAMMPS software.Based on the theories of atom diffusion,grain nucleation growth and grain boundary migration,theoretical derivation was proposed on the migration of Si atoms at each stage of the formation of the SON structure.(3)Experimental preparation and result analysis of SON structure.Auto CAD software was used to complete the layout design and drawing of the SON structure mask.After lithography and etching,the SON structure was fabricated by annealing in a high-temperature vacuum environment based on MSTS(Microstructure transformation of silicon)technology.The SEM images of the cross section and the upper surface of the SON structure were obtained,and the thickness of the silicon film and the cavity were measured.The morphology evolution of silicon trenches was simulated from the macro and micro point of view.The characteristic sizes of the SON structure obtained by the experiments were compared with the simulation results,and the correctness of the simulations was verified through experiments,thus confirming the correctness of the interpretation of the formation mechanism of SON structure by the atomic diffusion theory.