Study On Surface Adsorption And Electrochemical Corrosion In Post CMP Cleaning Of Copper

With the decrease of the feature size of GLSI(Giga large scale integrated circuit),cobalt(Co)is expected to become a novel barrier material due to its low resistivity and adhesion ability.The difference of physical and chemical properties of copper and cobalt results in the possibility of galvanic corrosion defects in the process of chemical mechanical polishing(CMP)and post-CMP cleaning.The main purpose of post-CMP cleaning process for copper interconnection is to remove the residual of polishing slurry on the copper surface.Silica sol as the abrasive could be easily adsorbed on the wafer surface after CMP process,which would directly affect the yield of IC.Therefore,particle removal and control of galvanic corrosion become the key to CMP cleaning.Firstly,the effects of 1H-1,2,3-benzotriazole-5-carboxylic acid(CBT),1,2,4-triazole(TAZ)and 2,2'-[[(meth,yl-1H-benzotriazole-1-yl)methyl]imino]bis ethanol(TT-LYK)on Cu-Co galvanic corrosion were investigated in this paper.The inhibition efficiency and properties of inhibitors was characterized by electrochemical workstation and contact angle detection.The electronic parameters of inhibitors have been studied at the B3LYP/6-31G(d,p)level of theory.The differences in inhibition efficiency of these three inhibitors was investigated by means of chemical reaction parameters and their reaction centers were analyzed on the basis of Fukui indices.The electrophile and nucleophile centers of these three inhibitors were determined.The results show that CBT has the closest adsorption to metal and has the strongest inhibitory capacity.Secondly,three kinds of surfactants,dodecylbenzene sulfonic acid(LABSA),fatty alcohol polyoxyethylene ether ammonium sulfate(AESA)and isomeric alcohol ethoxylates(JFCE),were selected and their effects on Cu/Co galvanic corrosion were studied by means of electrochemical workstation.The effects of different compound ratios and concentrations of composite surfactants on the particle size of silica sol were investigated.The synergistic effect of different surfactants was studied by the interaction parameters of composite surfactants.Through the calculation of the electronic parameters of surfactants and the adsorption energy of the adsorption model of surfactants and silica particles,it was concluded that LABSA has stronger adsorbability on particles,while JFCE can form steric hindrance in water,and the removal of silica sol particles can be realized by the dual functions of surfactant.Finally,the cleaning effect of different kinds and concentrations of inhibitors and different compound ratios of composite surfactants on silica particles adsorbed on the copper surface was studied.The residual silica sol and inhibitors on the surface of copper after cleaning were characterized by scanning electron microscope(SEM),atomic force microscope(AFM)and X-ray photoelectron spectroscopy(XPS).Through the analysis of the action law and synergistic mechanism of the chelating agent,inhibitor and surfactant in the post-CMP cleaning process,the final optimized cleaning solution(p H=9.7)was determined which consists of 150 ppm FA/O? chelating agent,2.5 ppm CBT and 1000 ppm LABSA/JFCE with compound ratio of 2:3.The cleaning solution can effectively inhibit the galvanic corrosion and remove the particles adsorbed on the copper surface,which is suitable for post CMP cleaning of novel barrier layer of copper interconnection.