Investigation On Chemical Mechanical Polishing Of Metal Ruthenium

Ruthenium (Ru) may be used as new barrier materials in copper interconnects of integratedcircuit (IC) and has been used as bottom electrode material in dynamic random access memory(DRAM), the surface of the barrier layer and the bottom electrode should be leveled. At present,Chemical Mechanical Polish (CMP) technique has become as a technology to achieve globalplanarity of wafer surface, it is of great importance to study the CMP of Ru. In this paper, chemicalmechanical polishing behaviors of Ruthenium(Ru) were studied by using home-made slurries indifferent systems, the composition of slurries affects material removal rate and surface quality wereinvestigated, and the effect of the slurries on the corrosion behaviors were investigated byelectrochemical methods and X-ray photoelectron spectroscopy(XPS).Firstly, chemical mechanical polishing experiments and investigation of electrical chemistrywere done on ruthenium in CH3COOH and salicylic acid based slurries. Results show that thematerial removal rate (MRR) for ruthenium CMP can reach7.1nm/min under the followingconditions: the down force is6.9kPa, the rotation speed of the table is50circles per minute, the flowrate of the slurry is50mL/min, the constituents of the slurry are SiO2concentration1%, H2O2concentration1%and CH3COOH concentration1%(mass fraction). CH3COOH and salicylic acidcan accelerate the anode reaction and enhance the chemical action of the slurry on the surface of Ru.H2O2at low concentration promotes the chemical corrosion ability to corrode Ru surface andincreases MRR, the increasing of H2O2concentration may promote the formation of a thick oxidefilm on Ru surface, which reduces the corrosion rate and the MRR at higher concentration of H2O2inCH3COOH based slurries. The increasing of the concentration of salicylic acid to Ru surface passivefilm formation, the material removal rate (MRR) of Ru increases and tends to be gently. The XPSresults suggest that the formation of RuO2and RuO4on the Ru surface just after the immersion of Ruinto the H2O2–based slurry with CH3COOH, and the formation of RuO2、Ru2O3and RuO4on the Rusurface just after the immersion of Ru into the salicylic acid-H2O2system slurry.Then, the CMP experiments were done on Ruthenium using home-made slurry, effect ofimidazole in the chemical mechanical planarization of ruthenium was investigated. The results showthat the MRR could attain6.2nm/min when pH value is8.0in the slurry which comprises1%H2O2,1%H3PO4and1%SiO2, and the surface roughness (Ra) of the polished ruthenium can reach10.7nm;The MRR for Ru CMP could reach3.9nm/min, the constituents of the slurry are1%H2O2,1%H3PO4,1%SiO2,0.5mol/L imidazole, the pH value of the slurry is8.0, under the followingconditions: the down force is6.9kPa, the rotation speed of the table is50circles per minute, the flowrate of the slurry is50ml/min, the roughness Rawas1.0nm under these conditions. Midazole canpromote the formation of the passive film on the surface of Ru and the corrosion current and the MRR are decreased by inhibiting cathode reaction, but obtain better surface quality. The XPS resultssuggest that the formation of RuO2and RuO3on the Ru surface just after the immersion of Ru intothe H3PO4slurries.Finally, nano-CeO2abrasives were prepared by liquid phase precipitation and the phasecomposition of the samples was characterized by X-ray diffraction (XRD). The effects of thedispersant species, and the heat-treatment temperature on the average particle sizes and the zetapotentials of CeO2suspensions were investigated by means of nano particle size analyzer. Thenano-CeO2abrasive slurry was used for chemical mechanical polishing (CMP) of ruthenium, thesurface of ruthenium was characterized by atomic force microscopy (AFM). The results show thatthe prepared powders are nano-CeO2with cubic fluorite structure, the average particle size of CeO2powder increases with the increasing of the heat-treatment temperature; the dispersibility ofnano-CeO2in the suspension is best when the dispersing agent is sodium hexametaphosphate(SHMP); the material removal rate (MRR) for ruthenium CMP and the surface roughness (Ra) of thepolished ruthenium can reach9.0nm/min and2.2nm/min under the following conditions: the downforce is6.9kPa, the rotation speed of the table is50circles per minute, the flow rate of the slurry is50mL/min, the constituents of the slurry are CeO2concentration1%,(NH4)2S2O8concentration1%,SHMP concentration0.01%(mass fraction), the pH value of the slurry is10.0.