Simulation Of Additive Synergistic Effect In Direct Current Electroplating Of Through Silicon Via

TSV(Through Silicon Via),which achieves interconnection by making through-holes between chips and wafers,is the latest interconnect technology.TSV enables maximum three-dimensional staking density,minimum size,considerable speed improvement,and low power consumption,thus becoming one of the most popular three-dimensional packaging technology.Copper filling is key technology of TSV processes.In this dissertation direct current electroplating of TSV is investigated by finite-element simulation method.Additive-assisted copper filling is simulated by CEAC(Curvature Enhanced Accelerator Coverage)model and competitive adsorption model respectively to investigate influence of additive ratio,concentration and potential distribution inside the via on filling profile for the purpose of finding optimal dose of additives and electroplating parameters.To study initial surface coverage of additives,a model is built on the basis of experimental polarization curves to acquire optimal distribution of additive surface coverage inside TSV through a series of calculations.In order to explore effective pre-treatment method,it is assumed that accelerator displaces suppressor while leveler deactives accelerator in a mathematical model,by which adsorption of additives in different pre-treatment methods are calculated and evaluated.CEAC simulations showed that accelerator accumulation at via bottom due to area shrinkage can facilitate superfilling of TSV with aspect ratio of 3:1.However,leveler should take a role in replacing accelerator to inhibit copper deposition especially on via top as to achieve bottom-up filling of high-aspect-ratio vias.Simulations under competitive adsorption theory demonstrated the most suitable doses of additives are 4ppm SPS,300 ppm PEG and 10 ppm JGB for a 50?m×300?m TSV.Simulations indicated the optimal accelerator initial surface coverage inside TSV should be approximately 0.25 at via bottom and 0~0.1 at via top.To meet this requirement,available selections of pre-treatment methods includes immersion in SPS+JGB solution,immersion in SPS solution followed by that in JGB solution,and immersion in SPS+PEG solution followed by that in JGB solution.Simulations in this dissertation provided theoretical analysis for optimization of copper electroplating process as well as development of additive formulation.In combination with experimental data,it could be used as a tool for prediction of via filling profiles,therefore offering guidance for realization of TSV superfilling.