Investigation On Chemical Mechanical Polishing Performance Of Novel Copper Diffusion Barrier Of Ru,Ru-Ta Alloy And Mo Film

The research on ultra-thin diffusion barrier materials and processes has always been hot topics in the copper interconnect research. In sub-16nm node, novel barrier materials besides current Ta/TaN bilayer need to be investigated. Due to the lower resistivity, good adhesion with Cu and directly plating property of Cu onto the barrier surface without using Cu seed layers, Ru, Ru-Ta alloy and Mo are potential alternative adhesion/barrier layer in the copper interconnect. Although thermal and electrical stabilities of these metals and alloys have been report, there are few reports focused on the chemical mechanical polishing (CMP) of these metals. The study of CMP performance and process of these novel materials has important scientific value and broad application prospects.This thesis first investigates the effect of glycine in KIO4based polishing solution on Ru CMP. The results show that, the polishing rates of Ru and Cu increase as the KIO4concentration increases. The Ru polishing rate decreases while Cu polishing rate increases with increased glycine concentration. Thus by adjusting the concentration of glycine, Ru and Cu polishing rate can be adjusted to1:1. The fact that glycine in KIO4-based solution can inhibit Ru corrosion is mainly because of the adsorption of the neutral ion generated during glycine dissociation, i.e.+H3NCH2COO-, onto the surface of oxidized Ru, thus suppressing the Ru corrosion. The insitu OCP scanning and XPS measurement results also prove this conclusion. It is found that after addition of glycine less RuO2formed on the Ru surface. The addition of glycine accelerating Cu corrosion is mainly due to its chelation with Cu oxide.The thesis also carries out a preliminary study on the polishing of RuTa alloy (9:1) in KIO4-based polishing slurry. Experimental results show that the slurry has a fairly good polishing effect on the RuTa alloy, and the static etch rate is nearly zero. So the polishing efficiency is significantly greater than that for pure Ru. However, galvanic corrosion between RuTa alloy and Cu still occurs as that on pure Ru polishing.The thesis then studied the CMP of Mo in the H2O2-based slurry. It is found that the main oxidation product MoO3and MOO2, and there are more MoO3in the alkaline conditions. The polishing rate of Mo increases with higher concentrations of H2O2. In the acidic media, the polishing rate of Mo is lower because of the less soluble oxide formed. In alkaline media, both the polishing rate and static etch rate of Mo are high, arising from the more easily dissolved MoO3oxide under alkaline conditions.AS was added in the H2O2-based slurry and the polishing rate and static etch rate of Mo increases under alkaline conditions, which is due to that NH4+can chelate with molybdate to form more soluble ammonium molybdate. Under acidic conditions AS does not promote Mo corrosion. It is found that the polishing rate and static etch rate decrease with increase of SiO2abrasive concentrations, indicating that SiO2abrasive can inhibit Mo corrosion in the H2O2solution. The adsorption of SiO2abrasive particles onto Mo surface is observed. The addition of glycine in H2O2-based polishing solution can effectively inhibit the corrosion of Mo, improving the polishing efficiency and surface roughness.The thesis investigated CMP of Mo using the KIO3-based polishing solution of Mo CMP for the first time. It is found that MoO3, Mo2O5and MoO2formed when the Mo was dipped into the KIO3solution. In the KIO3solution at pH2, the main oxidation product of Mo is MoO3, together with Mo2O5and few MoO2. As the pH value of the slurry increases, the polishing rate of Mois reduced, which is due to formation of more insoluble MoO2and Mo2O5oxides. The polishing rate of Mo increases with more content of KIO3and SiO2abrasive. It is found that in0.1M KIO3at pH2the SER of Mo is substantially zero, but the polishing rate is highest, showing the best polishing efficiency. We also compare the surface roughness of Mo after polishing by using KIO3or H2O2as oxidant. It is found that the Mo surface after polishing by KIO3slurry is much smoother than that by H2O2slurry with abrasives.