Synthesis And Polishing Properties Of Cerium-based Oxide Materials And Their Precursors

Cerium oxide is one of the main abrasives for chemical mechanical polishing（CMP）of semiconductor devices and integrated circuit chips,and its particle size,morphology and purity are closely related to the polishing performance.In order to get rid of the passive situation of excessive dependence on imports of integrated circuit chips,it is necessary to develop cerium oxide-based polishing materials with own intellectual property rights.In this paper,the effects of cerium source and precipitating agents,dosage ratio of carbonate to cerium,precipitation temperature and time,aging temperature and time,rare earth doping etc on the morphology and phase composition of cerium-based carbonates were investigated in detail.It was found that when the amorphous precipitate（AP）formed by the reaction between cerium ion and ammonium bicarbonate with molar ratio of 6 at temperature from 10℃to 70℃is aged at temperature around 60℃,two special precursors can be obtained:The first is a amorphous gel state which formed by a aging time of around 2 h;The second is a broom-like crystalline state formed after aging for more than 24 h.The later one is a characteristic product which can only be slowly formed in the presence of excessive ammonium bicarbonate with cerium ion.The broom-like crystalline product was characterized by means of DTA-TG,XRD,IR,XPS,F-SEM and H-TEM,and was proved to be composed of Ce₂（C₂O₄）₃·10H₂O and Ce（CO₃）₂:It is rare earth ions with variable valence of 4⁺/3⁺that catalyze the oxidation-reduction reaction between ammonium and bicarbonate which guides the crystalline growth toward broom-like morphology by the formation of oxalate.More important,this characteristic reaction can occur in the case of cerium and praceodymium with other rare earths doping and shows great potential in the preparation of rare earth materials.Meanwhile,a flaky cerium-based precursors was obtained by aging the AP above at room temperature.Three cerium based oxides（CBO）with different morphology of broom-like,small particle aggregates and flaky were prepared by calcining the three precursors with morphology of broom-like,gel-like and flaky in a muffle furnace.Their slurries with solid content of 1%were prepared and used to polish ZF7 glass.The effects of precursors and calcination temperatures on the morphology,particle size,crystallinity of CBOs on their polishing performance were investigated based on the results of zeta potential,p H,material removal rate（MRR）,and roughness（Ra）during the polishing process.The results showed that the MRR of the three CBOs for ZF7 glass follows the order of 321.9 nm/min for small particle aggregate>272.23 nm/min for broom-like>168.5 nm/min for flaky.The Ra of the polished glasses showed the order of 0.76 nm for nanoaggregate<0.87 nm for the broom-like<1.129 nm for flake.