Investigation Of Seedless Copper Plating On Novel Diffusion Barrier Materials For Cu Interconnect

With the continuous shrinkage of IC feature sizes, the currently used adhesion/barrier stack Ta/TaN in the interconnect structure cannot meet the requirement. Some novel barrier materials, such as Co, Mo and their alloys have good potential to be applied in the next generation interconnect due to their low resistivity and good adhesion with Cu. Yet there are few reports about the research on seedless copper plating on these novel barrier materials. In this thesis, the direct copper plating on Co, Mo and CoMo alloys has been investigated systematically.This thesis firstly investigates the direct copper plating on the ultrathin Co film in the acidic bath. The reduction of native Co oxide can be successfully carried out by using a negative potential in tetramethylammonium hydroxide(TMAH) solution prior to the copper plating. Due to the severe corrosion and reaction with copper ion in the acid bath, the copper cannot be deposited onto Co successfully. We then develop a method to apply a negative potential before immersing the sample into the acidic bath and then the copper can be plated on the Co although there are still some voids between the Cu and Co interfaces. A 3 nm seed layer on the Co can decrease the corrosion of Co, yet still with inevitable Co the thickness loss.We further investigate the direct copper plating on ultrathin Co film in an alkaline bath with ethylenediamine(En) as a ligand. The results show the complex of CuEn22+well stop the reaction between the Co and Copper ion and decrease the corrosion of Co. The electrochemical measurement, static corrosion experiments and Transmission electron microscopy (TEM) are used to investigate the Co corrosion in the alkaline bath. The results show that the thickness loss of Co is only 2A. We further study the nucleation mechanism of Cu on Co. Pure instantaneous or progressive nucleation of copper on Co layer is not observed. A high nucleation density about 5xl010cm-2 of Cu is observed on Co. The current density has a great effect on the surface morphology and film resistivity and the electroplated copper layer has a preferential (111) orientation. Finally a uniform copper seed layer is successfully electroplated on the 10 nm Co layer deposited in the MIT 754 patterned wafers.This thesis investigates the seedless copper plating on the ultrathin Mo film. Firstly we study the corrosion of Mo in the the baths with different pH values. The results show that the corrosion in the En bath is very small. The nucleation mechanism of Cu on Mo in the En bath is studied, which seems to more fit the characteristic of instantaneous nucleation at the very initial nucleation time. A Cu nucleation density of l×l010cm-2 can be obtained in the En bath, which is much higher than that in the acidic bath. Finally we successfully electroplate Cu on the patterned wafers with 5nm Mo as adhesion layers using two-step electroplating, first using Cu-En and then using commercial acid bath.In the final part we study the copper plating on the novel barrier material CoMo alloys. The crystallinityand resistivity of the CoMo alloys with different atomic ratio of Co:Mo are investigated. The nucleation density of Cu on the CoMo alloys has an increasing tendency with increase of the Co content in the CoMo films. Also the more Co in the CoMo film, the more smooth Cu film can be electroplated. The self-anneal process for the electroplated Cu is investigated. The Rs drop of Cu on the CoMo alloy films becomes much faster than that on Co and Mo. The Rs of Cu on the Co1Mo3 drops fastest. Finally, uniform copper layer is successfully electroplated on the three kinds of CoMo layers in 5nm in the patterned wafers. The SEM and TEM show the trenches are well filled by copper.We also study the chemical mechanical polishing (CMP) of Co1Mo3 alloy for its real application. The SER of the Co1Mo3 film increases with the increase of H2O2 concentration in both acidic slurry and alkaline slurry. After polishing in a high H2O2 concentration, an over corrosion of Co1Mo3 barrier layer can be observed near the interface with Cu. By reducing the H2O2 concentration, a good Cu surface and Cu/diffusion barrier interface after polishing can be obtained. By adding Glycine into the H2O2 based slurry at pH 3, the removal rate of Co1Mo3 firstly decreases then increases. The galvanic corrosion between the copper and CoMo alloy can be well controlled by adding glycine. The corrosion potential between Cu and CoMo alloy is 0.067 V when 0.1M glycine is added in the 5mL/L H2O2 based slurry.