Microvia Filling Of Hdi By Copper Electroplating And Electrochemical Behavior

As the development of electronic products toward miniaturization,lightweight,functional diversification,the high density interconnection(HDI)technology is required for meeting the development of printed circuit board(PCB).The metallization of the micro-blind vias is the key technology in the HDI process.In order to ensure the reliability of the circuit interconnection,the micro-blind vias should be completely filled by electroplating copper.The microvia filling performance of a Cu elelctrolyte can be evaluated by the filling percentage within the microvias and the surface thickness.At present,the advanced technology of Cu electroplating filling for HDI is owned only by the several foreign groups,and has become a technology bottleneck for the PCB industry in China.According to the requirements of HDI electroplating,the filling percentage of microvia should be greater than 85% and the surface deposition thickness should be less than 15?m.Regading that,in this work we aimed to develop a HDI electroplating technology using three kinds of dyes as leveler in the Cu electrolyte.It was shown that in the PEG-SPS-JGB electrolyte the bottom-up filling can be realized in a wide concentration range of the additives.By optimizing the experiment conditions,the filling percentage could be more than 86.8% in one hour and the surface deposition thickness was less than 12.8?m.Also,the bump phnomenon didn't occur at the openings.The allowed current density for obtaining void-free filling effect was 2A/dm2.In comparision,by using the PEG-SPS-MST electrolyte,the filling percentage was more than 86% and the surface deposition thickness was only 1.9?m after plating for 60 min.When the MST concentration was more than 5ppm,it was found that the bumps above the microvia entrances occurred.As the convection force become larger,the the filling percentage become samller,the surface copper thickness become smaller and the the grain size became coarser.In comparision,it is found that the filling rate of the PEG-SPS-MST electrolyte was one times larger than that of the PEG-SPS-JGB electrolyte.In the EPE-SPS-BY electrolyte,the filling percentage was more than 86.8% and the surface deposition thickness was less than 14.3?m in 60 min.The contrast work using PEG-SPS-JGB electrolyte showed that the bottom-up filling could be achieved in a very narrow range of additive concentrations in this electrolyte.When the concentration of SPS was less than 1 ppm,a superconfromal filling mode could be realized.However,as the increase of SPS,the deposition mode was changed into a conformal filling mode.The electrochemical behaviors of all the additives were investigated by means of a rotating disk electrode.The high and low rotation speeds were used to simulate convection environment in the electrolyte.The rotatation speeds of 100 rpm and 1000 rpm represented the convection conditions at the bottom and opening of the microvia respectively.In the linear sweep voltammetry(LSV)curves of thress electrolytes,it was showed that the corresponding current density at 100 rpm was higher than that at 1000 rpm,which sugggsted that the deposition rate at the bottom than that at the opening of the micrvia.It was conclued that a bottom-up fillling mode can be created when this electrochemical requirment is satisfied.The Cl-made the potential in the LSV curve of Cl--PEG system shifted negatively,which meant that Cl-can enhance the suppressing effect of PEG.Also,the Cl-made the potential in the LSV curve of Cl--SPS system shift positively,which meant that Cl-to enhance the accelerating effect of SPS.All of the three levelers could interact with PEG or EPE to form a composite suppressor.It was demonstrated that this composite suppessor was more strongly convection-dependent.It meant that the suppressing effect at the opening or the surface was much stronger,which was the main mechanism for a bottom-up filling mode in this electrolyte using a dye as leveler.In comparision with PEG-SPS-JGB electrolyte,the potential difference(??)of the PEG-SPS-MST electrolyte plating solution at high and low rotational speeds was 10 times larger than PEG-SPS-JGB electrolyte by the pre-dip chronopotential,which suggested that in high convection conditions MST can not deactivate the accelerating effect of SPS.It explained the bump formation very well.In the EPE-SPS-BY electrolyte,it was found that the adsorption of SPS was weaker than that of BY,but stronger than that of BY-EPE.And,the excess SPS could weaken the adsorption of BY-EPE,which was not conducive to the formation of surperfilling mode.