Preparation Of Ti Or Zr-doped Ceria Abrasives And Their Chemical Mechanical Polishing Performance

Chemical mechanical polishing(CMP) is one of the most efficient planarization technologies in the manufracturing of ultra-large-scale integrate circuits and precision optical devices.Moreover,the development of CMP gives rise to an emergent demand for abrasive particles with controlled physical properties and chemical composition.Thus,the preparation technologies of abrasives are crucial for a desired CMP process.This study was conducted to search a basic route for designing and synthesizing abrasive panicles with perfect polishing performance.Therefore, Zirconium or titanium-doped ceria abrasive panicles were prepared using simple methods,and their polishing properties for semiconductor silicon or precise optical glass wafers were evaluated with respecting to their physical and chemical characteristics change originated from doping.Titanium-doped ceria Ce_1-xTi_xO₂(x = 0 to 0.8 )powders were prepared wet-solid mechanical chemical processing(MCP),and their material removal rate(MRR) values for polishing optical glass were evaluated with respect to their particle chemical composition,sizes,surface charges,crystallinity as well as the suspension stability.Significantly increased MRR values with a particle zeta potential dependence were observed for Ce_1-xTi_xO₂(x≤0.3),indicating that ceria abrasives with high MRR can be designed and synthesized by tuning particle surface charge using the titanium doping method.The XRD and Raman spectroscopic analyses revealed that the large increase in MRR and the surface negative Zeta potentials were attributed to lattice defects due to the formation of CeO₂-TiO₂ solid solutions and the CeTi₂O₆ Phase.A maximum MRR value of 544 nm·min^-1 was obtained using Ce_0.9Ti_0.1O₂ solid solution as a polishing powder for the ZF7 glass.This value is ca. 2.2 times of that obtained from using pure ceria,and its Ra value of glass surface polished is of 0.854 nm.With the x value further increasing to 0.2 and 0.3,the MRR value deceased slightly with the CeTi₂O₆ phase content increasing.This fact reveals that the contribution of CeTi₂O₆ to the MRR increase is less than that of CeO₂-TiO₂ solid solution. Ce_0.8 Zr_0.2O₂ solid solution abrasive particles were successfully synthesized by wet-solid MCP using Ce₂(CO₃)₃·8H₂O and ZrOCl₂·3H₂O as starting reagents, ammonia as precipitant,hydrogen peroxide as reaction accelerant.The minus surface Zeta potential of as-synthesized particles and the MRR for polishing ZF7 optical glass are all higher than that of pure ceia abrasive particles synthesized using same method,illustrating that the increase of MRR value of Ce_0.8Zr_0.2O₂ solid solution abrasives is also derectly related to its minus particle surface Zeta potential increasing. Furthermore,the MRR value of Ce_0.8Zr_0.2O₂ solid solution abrasives polishing ZF7 can further increase by tuning surface zeta potential using sodium hexametaphosphate (SHP) as dispersant,and sodium chloride(NaCl) as electrolyte.And that the average roughness(Ra) of polished glass surface decreases.Monodispersed and nano-sized orbicular CeO₂ and Ce_1-xTi_xO₂(x = 0 to 0.3) powders were successfully synthesized via co-precipitation method in ethylene glycol (EG) followed by azeotropic distillation,using Ce(NO₃)₃ as reagent,ammonia as precipitor,as well as substituting water solvent for ethylene glycol(EG) / water mixed solvent.The optimal parameters for the CMP of P(111) semiconductor Sillicon wafer were determined using nano-sized CeO₂ polishing abrasives slurry.The results show that the polishing performance of as-synthesized Ce_1-xTi_xO₂(x=0.1,0.2) abrasives for Sillicon wafer can be remarkablely enhanced comparing to that of pure CeO₂ slurry.A maximum MRR value of 139 nm·min^-1 with Ra value of 0.254 nm within a 5.0μm×5.0μm area was obtained using Ce_0.8Ti_0.2O₂ as polishing abrasives, which is ca.2.07 times of that obtained using pure ceria(67 nm·min^-1),also demonstrating that doping titania into ceria is a potential method to synthesize abrasive particles with high MRR value of polishing silica wafers.To sum up,doping a mount of titanium or zirconium into ceria can evidently enhance the surface charge of abrasive particles so as to improve its CMP performance,providing a great effective approach to design and synthesize excellent abrasives.