Chemical Mechanical Polishing Of Ruthenium And Zirconia Ceramics Under Alkaline Conditions

Chemical mechanical polishing（CMP）is the most widely used technology for the fabrication of multilayer interconnects in semiconductor chips and electronic devices,which can provide a material surface with global sub-nanometer scale planarization.With the development of large-scale integrated circuits,technical nodes have continuously dropped below 22 nm,and the requirements for device planarization have become higher and higher.Ruthenium（Ru）,with high electrical conductivity and good chemical stability,can serve as a barrier to Cu interconnects and a bottom electrode in a dynamic random access memory（DRAM）.With a large refractive index,a high melting point,and strong corrosion resistance,Zirconium oxide（ZrO₂）can be used in various fields,such as sensors,special ceramics,and coating materials.However,the high hardness and chemical inertness of yttrium and zirconia also pose unique challenges to their chemical mechanical polishing process.Due to the poor selectivity,the corrosiveness to the polishing equipment and other shortcomings,acidic polishing fluids are increasingly unable to meet modern process requirements,and therefore have chosen to polish the materials under alkaline conditions.In this paper,for Ru’s CMP study,SiO₂ as abrasive,by using different oxidants,changing polishing pressure and distribution ratio of the slurry,polishing effects influenced by various conditions were analyzed,and function mechanism of the oxidant on Ru was studied by XPS analysis.The results show that Na Cl O has a good corrosion effect on Ru,and different chemical reactions occur under different p H conditions.Under alkaline conditions,Na Cl O oxidizes Ru into soluble RuO₄^2-,RuO₄^-,increasing the material removal rate,obtaining good surface quality,and effectively alleviating the problem that corrosion pits occur on Ru’s surface after polishing by adding BTA as a corrosion inhibitor.Then by changing the concentration of the abrasive,the p H value of the solution,the concentration of the oxidant and the complexing agent,the p H value of the polishing liquid and the influence of the change of the Zeta potential of the abrasive on the stability of the polishing liquid were studied.Through the analysis of different influencing factors,the method that can optimize the stability of the polishing liquid is selected.The results show that when the oxidant and complexing agent concentration are 1%,the abrasive SiO₂ concentration is 3%,p H=9,if adding a small amount of dispersant,the polishing solution can remain stable for at least one week.Finally,in the study of planarization of ZrO₂ ceramics,Al₂O₃ abrasives with higher hardness were used to study the effects of abrasives with different particle sizes,different polishing pressures,p H value of the polishing solution,and oxidant content on the ZrO₂ material removal and surface quality.The results show that the change of the chemical composition in the polishing liquid has little effect on the material removal,while the change of the polishing pressure has a significant influence on the material removal.