Numerical Model Study On Fabrication Of Vertical Copper Interconnect Of Through Silicon Via

Through-Silicon Via(TSV)is used to fabricate the interconnect of chip in vertical direction.The primary benefit that comes from the used of TSV is reduced interconnect length with short vertical connections.The characteristic of TSV enable smaller device size,reduced latency,low power level communication and so on.With purpose of continuing the“Moore's Law”,TSV plays an important role on technology development of three-dimension electronics packaging.The copper electrodeposition is widely accepted with two outstanding advantages:1)copper has high conductivity and stable performance as conductor;2)electrodeposition has easy control and efficiency as process of TSV fabrication.Usually,multi-additives are added into electrolyte to make the copper filling with void-free for feature of TSV.The synergetic mechanism of multi-additives is still a challenge for researchers.In addition,many processes of TSV fabrication are investigating to satisfy the requirement of 3D packaging which will be used widely in industrial.Hence,the investigation of synergetic mechanism is a key point to improve the present process and research the new process of new type TSV fabrication.In order to improve the investigation,kinetics is usually used to analyze the rate and strength of synergetic performance of multi-additives.And the Finite Element Method(FEA)is used to research the processes of fabrication because of its high efficiency.Combined the kinetics and multi-physics,the copper electrodeposition is investigated efficiently by FEA.In this paper,we study on the synergetic mechanism of multi-additives.Based on investigating the rate of copper deposition adjusted by multi-additives on the sidewall of via,a systematic numerical model has built to interpret these additives behavior on the electrode surface with feature by analyzing the results of Linear Sweep Voltammetry and copper filling experiment.This systematic numerical model is used to predict the defect of copper filling in terms of current density and accelerator concentration.Specific research contents and main conclusions are as follows:1.Combined Curvature-enhanced-accelerator Coverage(CEAC),time-dependent mechanism and compounds of additives with charge,the numerical model has been built to investigate the copper deposition in via.The local reactive current density is calculated by numerical model by describing the additives behavior on the electrode surface with TSV feature.Results of numerical model and copper filling experiment show copper filling in the via with same depth changed from void to void-free,which is corresponding to increase of diameter of via.There are two reasons for this phenomenon:1)Quality of PEG transported into via increasing with the diameter of via increasing.It means more position of sidewall of via is covered by PEG.Considered the adsorptive position of PEG,the copper growth rate decreased obviously on the upper section of via.So copper ion could transported into via more adequately;2)It will take more time to form accumulation of SPS on the bottom of via when via has bigger diameter with same depth.And the time of completed copper filling is prolonged.Compared with results of copper filling experiment,the results of numerical model demonstrate the same trend for different via in different diameter.2.The small peak of results of linear sweep voltammetry is found with a specific condition.The condition is that the electrolyte containing SPS,PEG and Cl~-.It is analyzed by the different coverage of additive which is influenced by the electrode potential.Meanwhile,the potential distribution in via is calculated by numerical model with describing the additives behavior on the sidewall of via.The potential distribution of sidewall of via is used to correspond to the potential area of small peak of linear sweep voltammetry.Compared with the results of copper filling experiment,the results of simulation shows that numerical model could explain the copper filling contour in via for 30 min and 60min.3.Assuming that SPS is main factor to influence the reactive current density,the results of electrochemical measurements are analyzed by numerical model.In the model,two special parameters are implanted,such as normalized coverage and transient time.Based on that the site of electrode is completely occupied by SPS under SPS saturation and non-overpotential condition,the different equilibrium reactive current density and transient time of SPS is investigated by analyzing the results of electrochemical measurement of electrolyte with different SPS concentration.The results show the model containing adsorption,desorption and replace is abundant to explain the behavior of additives on planar electrode.4.Two specific parameters are defined to analyze the result of copper filling,such as transient confront ration and transient aspect ratio.Combined the result of copper filling contour and coverage of SPS,there are four steps for assuring the copper filling with void-free:1)SPS accumulates on the bottom of via;2)V-shape of copper filling contour has been formed on the bottom of via.And new platform is forming on the bottom of V-shape contour;3)The new platform has been formed and the deposition rate on the bottom of V-shape is accelerating;4)Convex is forming on the electrode surface.The evaluation method R<0 is certified by analyzing the relationship between AR and CR of numerical model.5.Combined the external factors and rational value of parameters,the copper filling contour is investigated by analyzing the effect of SPS concentration and inward current density.And an optimal zone has been found for copper filling with void-free.The calculated results are proved by experimental results.And a systematic analytical method is built by the numerical model,which could found the relationship between the results of electrochemistry and copper filling experiments.