Research On CMP Of Cobalt Barrier In Integrated Circuit Copper Interconnection Technology

The integrated circuit technology node has been developed to 14 nm and below.The traditional barrier layer material(Ta/Ta N)has a series of problems such as poor adhesion to copper(Cu)and reduced reliability,which can no longer be required for the barrier layer.The metallic material cobalt(Co)has extremely low resistivity and excellent step coverage,it can effectively block the diffusion of copper,so it has great potential for development in barrier materials.However,there are few reports on chemical mechanical planarization(CMP)of Co,especially the research on acid slurry,and the lack of research on the CMP process parameters and polishing mechanism of Co in acid slurry.Therefore,this paper optimizes the CMP process parameters of Co under acidic slurry conditions,and discusses the polishing mechanism of Co under acidic conditions.In this paper,the Co film was deposited by magnetron sputtering method,and the influence of different DC power conditions on the Co film thickness and root mean square(RMS)roughness was compared by a surface profiler and an atomic force microscope.It is found that the two powers of 100W and 150W have little effect on the deposition rate of Co,and the film roughness obtained under low power conditions is lower.The feasibility of the acid slurry was confirmed by studying the effect of two complexing agents of different concentrations of acetic acid and citric acid on the CMP of the Co film,and it was found that when the acetic acid concentration is 0.2wt%,a lower RMS roughness can be obtained,which is about 5.16nm.After that,malic acid with better complexing ability and higher safety was selected as the complexing agent to optimize the two process parameters of downforce and speed,and the Preston equation was revised.When the composition of the polishing liquid is 5wt%Si O₂,1wt%H₂O₂ and 0.05mol/L malic acid and at p H=5,the sub-nanometer RMS roughness of0.49nm and faster removal rate 327 nm/min is obtained under the conditions of 2psi down pressure and 60rpm,at the same time,the study found that the influence of down pressure and rotation speed on material removal rate is mainly realized by changing the contact amount of slurry and film.Finally,the electrochemical methods such as open circuit potential,Tafel curve and impedance spectroscopy,potential-p H diagram and X-ray photoelectron spectroscopy(XPS)test were used to analyze the polishing mechanism of Co in the above-mentioned slurry.When p H=5,Co will form a passivation layer on its surface under the action of oxidant to slow down the corrosion of metal,and the addition of complexing agent can effectively complex the ionized Co²⁺in the solution,strengthen the effect of chemical corrosion and improve the material removal rate,and the chemical reaction equation that may occur.