Preparation And Chemical Mechanical Polishing Performance Of Ce_1-xM_xO_2-x/2 Abrasives

As the chip manufacturing process continues to shrink,the resolution and the depth of focus of light in the lithography are becoming more and more stringent for the flatness of the substrate.The major negative impact of rough surfaces is the loss of control over line width during lithography,which requires a technique that can meet the high level of flatness,no scratches,and no contamination by impurities to improve its surface.Chemical Mechanical Polishing(CMP)is a technique that uses the synergistic effect of the chemical reaction and mechanical removal to achieve a smooth surface.CMP slurry is an essential factor affecting the performance,in which the abrasive particles are the most crucial core component.CeO2 slurry has considerable research value and economic benefits due to its high polishing performance and wide range of applications.Therefore,this thesis is based on CeO2 abrasives as the research object.The preparation of CeO2 particles by the molten salt method was explored.To improve the efficiency of the abrasives,their polishing activity was enhanced by reducing atmosphere calcination and doping modification.And their CMP performance was investigated by analyzing the polishing experiments of abrasives on quartz glass.In addition,the CMP mechanism of CeO2 abrasives was explored through the comprehensive analysis of abrasive properties and polishing performance.The influence of process parameters on the final product during the preparation of CeO2 particles by the molten salt method was systematically investigated.During the preparation process,the CeO2 crystal increases continuously with the continuous increase of temperature.And the growth rate of crystals increases significantly when the calcination temperature exceeds the eutectic point of the molten salt.In addition,the morphology and size of the final products do not change significantly with the extension of the holding time.The molten salt concentration greatly influences the size of the final product.As the molar ratio of cerium precursor-molten salt increased from 1:2 to 1:14,the size of CeO2 particles increases first and then decreases.In the KCl-NaCl molten salt system,the optimum preparation conditions are obtained when the molar ratio is 1:10.The CeO2 particles were prepared by reducing atmosphere calcination and doping modification to further enhance their reactivity in applications.The analysis of the surface chemical states of the different types of CeO2 particles showed that the surface defects of the CeO2 samples could be enhanced under the conditions of high temperature,ion doping,and reducing atmosphere.And the reducing atmosphere calcination and ion doping significantly improved the defect concentration.The directional attachment,agglomeration,and merging of the crystals formed by the decomposition of cerium precursor are the critical steps for the growth of CeO2 particles.The CeO2 abrasives were prepared by the molten salt method under air and reducing atmospheres,respectively.The morphology of the abrasives changed from spherical to octahedral with the increase of reducing atmosphere,and more oxygen vacancies and Ce3+ were generated on the surface of CeO2 abrasives.CMP experiments showed that the MRRs of CeO2-Air,CeO2-Ar,and CeO2-Ar/H2 abrasives on SiO2 substrates were 337.60,578.74,and 691.28 nm/min,respectively.In particular,the MRR of CeO2-Ar/H2 abrasives was improved by 104.76%compared to CeO2-Air abrasives.In addition,it also confirmed that the substrate surface exhibited low roughness(～0.5 nm)after CMP with all prepared samples.The improvement is mainly attributed to the increase of Ce3+concentration on the abrasive surface and the octahedral morphology of the abrasive,which enhance the chemical reaction and mechanical removal of the abrasives-substrate interface,respectively.A series of CeO2 abrasives with different types(Y3+,La3+,and Pr3+)and amounts(0.00,0.02,0.04,0.06,0.08,0.10)of doping were prepared by the molten salt method to improve the CMP performance.For all types of doped abrasives,the morphology of the abrasive changes from spherical to octahedral with the increase of doping,and particle size decreases continuously.Density functional theory calculation shows that doping reduces the vacancy formation energy of the CeO2 system.Furthermore,XPS also confirmed that the Ce3+ concentration on the surface of the CeO2 abrasive was increased after doping.The mechanism of Ce4+to Ce3+ transformation in the CeO2 system induced by doping is discussed.CMP experiments showed that the polishing efficiency of the doped abrasives was significantly improved.The MRR of Y3+,La3+,and Pr3+ doped CeO2 abrasives increased by 56%,40%,and 44%,respectively,compared with that of pure CeO2 abrasives,in which the Ce0.92Y0.08O2 abrasives has the highest MRR of 626.97 nm/min.The results also show that appropriate doping amount(x=0.08)should be considered to obtain excellent performance.However,the size of the abrasives gradually decreases with the increase of doping,which makes the MRR of the abrasives show a net decrease trend under extensive doping.Meanwhile,it is also confirmed that the substrate surface with almost no damage and low roughness was obtained after polishing.The CMP mechanism of Ce1-xMxO2 abrasives on SiO2 substrate was comprehensively analyzed from the abrasive’s size,morphology,and defects,which provides theoretical support for the design of high-performance CeO2 abrasives.