Study on Material Removal Mechanism and Polishing Characteristics of Chemical Mechanical Polishing of GaAs Wafer

Author:Yi De Fu

Supervisor:li jian yong


Degree Year:2019





Gallium arsenide single crystal is a second generation semiconductor material developed after monocrystalline silicon,with excellent physical and chemical properties,is an indispensable microelectronics and optoelectronic basic materials in the fields of national defense military industry,aerospace,energy saving and environmental protection.Whether used in the production of integrated circuits or functional deviees,gallium arsenide substrates are required to have excellent smoothness and ultra-smooth surfaces,otherwise the performance of the product will be reduced directly.At present,chemical mechanical polishing is widely used to achieve ultra-smooth machining of gallium arsenide substrates.However,there are many key problems to be solved in the process of chemical mechanical polishing of gallium arsenide substrate,such as:the removal mechanism of polishing process materials at microscopic scale,the influence of polishing process parameters on substrate smoothness,and how to combine the process parameters of ultra-smooth polishing of gallium arsenide substrate,etc.It restricts the development of chemical mechanical polishing technology of gallium arsenide substrate.In this study,the material removal mechanism and polishing process of gallium arsenide substrate chemical mechanical polishing characteristics are systematically studied by the method of combining theoretical analysis,computational simulation and experiment.Molecular dynamics method was used to analyze the deformation mechanism of microscopic materials in the polishing process of gallium arsenide substrate and the effect of rough peaks on substrate surface on material removal.Because gallium arsenide has different atomic structures with different crystal azimuth,the distribution of gallium arsenide sub-surface amorphous and phase change areas under different crystal azimuth under external forces is different,and the material deformation on the microscopic scale of polishing process is mainly phase change and amorphous.Under the action of abrasive particles,complex elastoplastic deformation occurs in the rough peak of the workpiece,the contact area high pressure causes the amorphous and the phase transition from the sphalerite to the rock salt structure,and the obvious anisotropy of the material removal in the polishing process originates from the difference of the atomic surface density and surface spacing of gallium arsenide with different crystalline surfaces.Using the method of finite element simulation and numerical calculation,the surface flatness analysis model of substrate based on material removal process is established,and it is found that the processing condition which has great influence on flatness in the polishing process is the speed of the substrate surface relative to the polishing disc,and the effect of polishing pressure on the flatness change is not significant.In order to reduce flatness and obtain large material removal efficiency,appropriate polishing process parameters should be selected so that the point of substrate surface can obtain higher relative speed.Through the scratch experiment,the material characteristics of gallium arsenide under extemal forces were clarified,and it was found that the elastoplastic removal,processability and material removal rate of gallium arsenide materials had significant anisotropy.At the same time,the preliminary polishing experiment of gallium arsenide substrate was carried out,and the results show that the material removal rate of the substrate surface will converge only after the pressure reaches a certain degree during the polishing process.Only after the rotational speed of the disc was increased to a specific speed,can the ehemical action and mechanieal action of the polishing process be realized,and better surface quality was obtained.The flatness model is verified by chemical mechanical polishing experiment of gallium arsenide substrate,and the experimental results are consistent with the results obtained by the flatness analysis model.Then,the influence of the main process parameters on the surface roughness and flatness of the substrate is analyzed,and the optimum technological parameters for the ultra-smooth machining of gallium arsenide substrates are obtained.