The Effect And Mechanism Of Two Conjugated Structured Inhibitors On Cobalt Filling In Blind Via

With the increasing integration of integrated circuits,the size of transistors has reached the nm level.Due to the influence of size effect,the resistivity of Cu interconnectors increases exponentially when the line width below 14 nm.So new materials are needed to replace metal Cu as interconnects.Metal Co has attracted widespread attention because of its short mean free path of electrons,low resistivity,stable performance and low electromigration.However,due to the short development time of the new chip technology and the immature process of new alternative materials,further analysis and study of the inhibitor and the molecular structure of the inhibitor suitable for the metal Co filling process are still needed.Therefore,studying the seamless filling Co technology has very important theoretical and practical value.According to theoretical calculation and Hull cell experiment,this paper compared the dispersion ability of plating bath after adding additives with different structures and their inhibition ability on Co plating bath,determined the molecular structure suitable for use as a Co plating inhibitor,and discussed the electrochemical behavior and filling effect of the inhibitor in the plating solution.Finally,a metal Co plating process suitable for micron level blind hole filling was verified.The effect of 14 kinds of different additive molecules on Co deposition process was analyzed through Hull cell experiment.It was found that molecular with C=N cyclohexadiene conjugated structure and tetrazole conjugated structure can improve the dispersion ability of Co plating solution.By comparing the filling process,Malachite Green（MG）and Nitro Blue Tetrazolium Chloride（NBT）of the two conjugated structures were used as additives,the deposition rate of Co on the outer surface of the blind hole was significantly inhibited,but the deposition rate at the bottom of the blind hole was not significantly inhibited.According to MD simulation analysis,the special C=N cyclohexadiene conjugated structure in MG molecules could be adsorbed on the cathode surface effectively,occupying the active site and preventing the deposition of Co²⁺.While the conjugated structure of tetrazole in NBT molecule is also easy to be adsorbed on the cathode surface,and NBT has higher adsorption energy than MG.According to the quantum chemical（QC）calculation,the frontier molecular orbital of MG and NBT has a large E_HOMO energy level value,while the?E is low,which ultimately leads to higher adsorption energy of MG and NBT.According to the calculation of molecular electrostatic potential,the surface electrostatic potential of MG and NBT molecules is high and widely distributed,so it is easy to produce adsorption on the cathode surface.In addition,AIM theory analysis shows that these two additives can form complexes with Co ions in solution,and further affect the metal Co nucleation deposition process.The electrochemistry test of the plating solution showed that lower concentrations of MG and NBT（5 mg/L）caused a significant negative shift in the Co reduction potential,and with the increase in inhibitor concentration,the polarization overpotential of the plating solution increased.According to the chronoamperometric curve,increasing the mass transfer rate of the plating solution increases the polarization overpotential of Co,indicating that the adsorption process of inhibitors MG and NBT on the cathode surface is controlled by the mass transfer process.Electrochemical Quartz Crystal Microbalance（EQCM）testing showed that MG and NBT adsorbed on the cathode surface as inhibitors,which hindered the deposition of Co²⁺and reduced the deposition efficiency.Compared with LSV curves,MG and NBT not only inhibited the Co reduction process,but also promoted the hydrogen reduction process.Cyclic voltammetry tests with K⁺to replace Co²⁺showed that MG and NBT promote the hydrogen evolution reaction（HER）,resulting in an increase of p H value in the plating solution.Based on theoretical analysis,it is known that inhibitor molecules adsorb on the cathode surface,occupying active sites,and hindering the nucleation and deposition of Co²⁺;The additive molecules adsorbed on the cathode surface act as active sites for HER,promoting hydrogen precipitation.By comparing the Co reduction current with the total current of the plating solution reduction,the additive promotes the reduction process of H₂O and resulting in a local p H increase,although there is boric acid in the plating solution.According to the filling process analysis,MG and NBT have strong inhibition ability.When 10mg/L MG and NBT are added,the coating deposition rate at the bottom is higher than that at the surface under different voltages.According to the filling effect analysis,the filling mechanism of inhibitor at-1.20 V deposition voltage is different from that at-1.25 V deposition voltage.The plating solution mainly occurs hydrogen reduction process,the increase of p H value causes the higher deposition rate at the bottom is more obvious,obtained.At-1.25 V deposition voltage,the plating rate of the bottom deposition is nearly twice that of the outer surface.When MG and NBT are used as additives,the filling FR value of the micron pore reaches72.6%and 84.5%,respectively.At-1.20 V,the FR values reached 90.3%and 91.9%,respectively.The optimal formulations were 0.4 mol/L Co SO₄,0.5 mol/L H₃BO₃,10mmol/L Na Cl,20 mg/L MPS,10 mg/L MG and 0.4 mol/L Co SO₄,0.5 mol/L H₃BO₃,10 mmol/L Na Cl,20 mg/L NBT,respectively.Compared with the filling conditions of different deposition times,the activation-passivation zone formed in the blind hole is more obvious under low voltage,which is more conducive to the realization of metal Co superfilling.Finally,according to the action mechanism of additives,the adsorption-induction-diffusion filling mechanism was proposed,that is,the inhibitor was adsorbed on the cathode surface to inhibit Co deposition.Inhibitor induced hydrogen precipitation,resulting in the increase of p H,the formation of cobalt hydroxide at the bottom of the intermediate state,improve the bottom deposition rate;Because the inhibitor is controlled by diffusion,it is easy to form an inhibition gradient in the blind hole,thus achieving seamless bottom-up Co filling...