Copper Electrodeposition Process Research Articles

Investigating the Effect of Chlorides on the Reaction Kinetics of a Copper Electrodeposition Process

Over the past two decades, the replacement of aluminum interconnects with copper is one of the biggest advances in semi-conductor industry. As the wiring density continues to increase, so does the demand for tighter control on the electrolytic copper deposition process for these industries. Apart from organic additives and other trace metals, one of the crucial component in plating baths mixtures for manufacturing PCB boards and photovolotaic cells is the intermediate cuprous ion composition, which is formed during the copper dispropornation reaction: 2 Cu + (aq) ⇌ Cu(s) + Cu2+ (aq) The cuprous ion is typically unstable in normal acidic solution and it disproportionates into metallic copper and cupric ions. In the presence of chlorides however, the disproportionation reaction equilibrium is shifted and the cuprous ions are stabilized. Cuprous ions are also required in order for the other additives (brightener, suppressor, leveler) used in the process to operate at maximum efficiencies. It is therefore important to know if the Cu2+ intermediate is truly formed and present during the a copper electrodeposition process. In this work, we used Autolab RRDE system to identify mechanisms governing copper electrodeposition process and study the influence of chloride concentration on the generation of intermediates.

Method of Controlling the Morphology of Cathode Deposit by Determining Electrochemical Resistance for Copper Electrodeposition Process

Проблематика . Актуальною проблемою електроекстракційного отримання компактної міді з гідрометалургійних розчинів є інтенсифікація процесу завдяки підвищенню максимально допустимих робочих густин струму при збереженні високої ефектив­ності процесу. Мета дослідження. Розробка способу визначення максимально допустимих робочих густин струму формування компактних осадів міді для процесу електроекстракції на основі використання залежностей електрохімічного опору ( r i ) від робочої густини струму ( i ). Методика реалізації. Застосовувався метод отримання катодних поляризаційних кривих процесу осадження міді із сульфатних розчинів. Морфологію катодної міді, осадженої за умов варіювання концентрації іонів міді, сульфатної кислоти та густини струму, досліджували за допомогою металографічного мікроскопа. Результати дослідження. Показано, що максимальна робоча густина струму осадження компактних осадів міді прийнятної для гідрометалургії якості відповідає початку підйому кривої r i – i після мінімуму. Встановлено, що збільшення концентрації міді зумовлює розширення області мінімуму, а концентрації кислоти – звуження. Аналітично отримано рівняння, яке дає змогу розмежувати міграційну та дифузійну складові граничної густини струму для цієї системи. Висновки . Вперше за допомогою методу диференціювання поляризаційних кривих, з використанням рівняння для умов змішаної кінетики, здійснено визначення максимальної робочої густини струму осадження компактних осадів з врахуванням зміни складу сульфатного розчину електроекстракції міді.

Nonlinear drifting parameters tracking by means of factorized Zakai filter in boundary-controlled electrodeposition process

The Zakai filtering is applied for tracking of nonlinear time-varying parameters on a physical model describing typical electrodeposition process that is fixed on the bulk solution boundary of diffusion layer and is observed-controlled on the electrode surface. The applied boundary control depends on the unknown drifting parameters in a severely nonlinear relationship. A computational algorithm is proposed for drifting parameters estimation based on the factorized Zakai filter. The consistency of estimates is analyzed in simulation on the diffusion type model developed for the copper electrodeposition process

Investigations of solution variables in a contactless copper electrodeposition process for 3D packaging applications

A novel electrochemical method for contactless electrodeposition of copper onto silicon wafers has been investigated. Deposition parameters such as applied current, concentrations of deposition solution and supporting electrolyte were optimized to achieve high deposition rates as well as homogenous deposition of copper. Copper sulfate solution temperature of about 65°C was shown to be suitable for achieving stable and high values of current density that translated to copper deposition rates of~2.4µm/min with good deposition uniformity.

Comparative analysis of the polarization and morphological characteristics of electrochemically produced powder forms of the intermediate metals

The polarization and morphological characteristics of powder forms of the group of the intermediate metals were examined by the analysis of silver and copper electrodeposition processes at high overpotentials. The pine-like dendrites constructed from the corncob-like forms, very similar to each others, were obtained by electrodeposition of these metals at the overpotential belonging to the plateaus of the limiting diffusion current density. The completely different situation was observed by electrodeposition of silver and copper at the overpotential outside the plateaus of the limiting diffusion current density in the zone of the fast increase of the current density with the overpotential. The silver dendrites, very similar to silver and copper dendrites obtained inside the plateaus of the limiting diffusion current density, were obtained at the overpotential outside the plateau. Due to the lower overpotential for hydrogen evolution for copper, hydrogen produced during copper electrodeposition process strongly affected the surface morphology of copper. The same shape of the polarization curves with the completely different surface morphology of Cu and Ag electrodeposited at overpotentials after the inflection point clearly indicates on the importance of morphological analysis in the investigation of polarization characteristics of the electrodeposition systems. Role of hydrogen as crucial parameter in the continuous change of copper surface morphology from dendrites to the honeycomb-like structures was investigated in detail. On the basis of this analysis, the transitional character of the intermediate metals between the normal and inert metals was considered. The typical powder forms characterizing electrodeposition of the intermediate metals were also defined and systematized.

Modeling of electrochemical process in flow 3D electrode with account for distribution of flow velocity of electrolyte in electrode

A mathematical model of the electrochemical metal deposition process in a flow 3D electrode is developed with account for dynamic distribution of the flow velocity of electrolyte, metal mass, potential, porosity, conductivity, specific electrode surface area, and other characteristics in the local volume of the electrode. These characteristics of the process and electrode are considered as functions of time and coordinate within the electrode. The results of experimental studies and calculations of copper electrodeposition process from ammonium sulfate electrolyte onto cathodes of graphitized carbon fibrous materials with different conductivity are presented at different initial flow velocities of electrolyte.

Electrochemical Cell Design with Controlled Hydrodynamics for Uniform Processing

In the manufacture of printed circuit boards (PCBs), copper electrodeposition is the standard fabrication method for metallization of z-axis interconnects.[i] Z-interconnects are important features of the PCB as they facilitate vertical electrical connections, thus eliminating the need for long in-plane interconnects. This in turn enables higher density feature packing and results in smaller and lighter electronic products. This trend has significant implications for the electronics industry which must ensure that the copper electrodeposition process meets the functionality and quality requirements of these advanced device designs. For instance, uneven localized current distribution results in thin barrel plating or voiding in the fill of the z-interconnect. Traditionally, this has been addressed through use of additive chemistry, pulse plating, use of low current densities, surface overplate and in extreme instances reorientation of the panel during the plating process.Faraday Technology has engineered and developed an electrochemical cell geometry[ii],[iii],[iv],[v]that delivers a uniform and reproducible boundary layer thickness across an 18 x 24 inch substrate in order to promote plating uniformity for full size PCB panels. A uniform hydrodynamic boundary layer is achieved with a novel flow scheme (Figure 1) that utilizes eductor flow to enhance solution flow velocity. In addition to the novel flow mechanism, the cell has lateral oscillation and vibration to further improve uniformity of aggressive PCB features as well as insulating shields, which enable uniform deposition of different substrate sizes.The development of the patented cell geometry was initiated to compliment pulse and pulse-reverse waveform development for PCB metallization. Uniform boundary layer conditions allow the full benefits of the pulse/pulse-reverse waveform to be realized. Pulse and pulse-reverse processes may be used with or without additive plating chemistry and improve the throwing power of the deposition process and the quality of the copper deposit as compared to DC electrodeposition at comparable current densities. Use of pulse and pulse-reverse deposition allows control of the deposit characteristics, such as control of the grain size, which is important for thermal cycling considerations. As such, coupling the novel cell geometry with pulse/pulse-reverse deposition provides a manufacturing solution for the continued miniaturization of electronic devices. The cell has been extensively characterized in terms of thickness distribution as a function of cell components, shielding dimensions and substrate dimensions.[vi],[vii],[viii] The boundary layer of the cell has been experimentally calculated revealing a uniform boundary layer across an 18 x 24 inch flat substrate.8 Further, the cell has been validated through the deposition of varying PCB feature dimensions, indicating the cell is an ample tool in the fabrication of PCBs. Finally, the cell has been compared to other plating cell geometries in terms of thickness distribution, tensile strength and feature metallization.[ix] Uniformity of copper deposits as a function of cell components along with examples of metallized PCB features will be discussed. Additionally, Faraday will present preliminary discussions about installation of an industrial cell based on the patented technology in a PCB manufacturing environment, demonstrating the scalability of the technology.The authors wish to acknowledge financial support from the National Science Foundation. [i] P. Dixit, J. Miao and R. Preisser, Electrochem Solid State Lett, 9 (10), G305 (2006).[ii] L.E. Gebhart, J.J. Sun, P.O. Miller, and E.J. Taylor, US Patent 7,553,401 (Issued 6-3-09).[iii] L.E. Gebhart and E.J. Taylor, US Patent 7,947,161 (Issued 5-24-11).[iv] L.E. Gebhart and E.J. Taylor, US Patent 8,226,804 (Issued 7-24-12).[v] L.E. Gebhart, J.J. Sun, P.O. Miler and E.J. Taylor, US Patent 8,329,006 (Issued 12-12-12).[vi] H. Garich, L. Gebhart, S. Snyder, and E.J. Taylor, ECS Trans, 19(6), 11-18 (2009). [vii] S. T. Snyder, H. M. Garich, B. S. Kagajwala, and, E. J. Taylor, Products Finishing, September 2012. [viii] H. Garich, L. Gebhart, E.J. Taylor, M. Inman and H. McCrabb, ECS Trans, 3(16), 1-10 (2007).[ix] J. Sun et al, Effect of Plating Cell Configuration on the Uniformity of Copper Thickness Distribution, Proceedings IPC/APEX 2005, Anaheim, CA.

Electroplating for high aspect ratio vias in PCB manufacturing: enhancement capabilities of acoustic streaming

This paper considers the copper electrodeposition processes in microvias and investigates whether the quality of the electroplating process can be improved by acoustic streaming using megasonic transducers placed into a plating cell. The theoretical results show that acoustic streaming does not take place within the micro-via (either through or blind-via’s), however it does help improve cupric ion transport in the area close to the mouth of a via. This replenishment of cupric ions at the mouth of micro-via leads to better quality filling of the micro-via through diffusion compared to basic conditions. Experiments showing the improved quality of the filling of vias are also presented.

Initial stages of copper electrodeposition from acidic sulfate solution in the presence of alklpyridinium hydrosulfate ionic liquids

The effect of two alklpyridinium hydrosulfate based ionic liquids (ILs) including N-butylpyridinium hydrogen sulfate (Bpy-HSO4) and N-hexylpyridinium hydrogen sulfate (HpyHSO4) as additives on the nucleation and growth of copper from acidic sulfate bath was investigated using cyclic voltammetry, chronoamperometric and scanning electron microscopy techniques. Results from cyclic voltammetry indicated that the two studied additives had a blocking effect on copper electrodeposition process and this effect initiated by HpyHSO4 was more pronounced in comparison to BpyHSO4. Dimensionless chronoamperometric current-time transients for the electrodeposition of copper from the bath free of additives were in good accord with the theoretical transients for the limiting case of instantaneous three-dimensional nucleation with diffusion-controlled growth of the nuclei. However, the instantaneous nucleation mechanism observed in the additive-free bath was changed to a more progressive one when additives were present in the bath. Surface morphology analysis indicated that alklpyridinium hydrosulfate ILs can induce the formation of leveled and finer grained deposits by the adsorption of additive at the first stages of deposition process, leading to decrease of the nucleation and growth rate of nuclei.

An effective triblock copolymer as a suppressor for microvia filling via copper electrodeposition

In this work, an effective suppressor was found in copper electroplating solution for microvia filling. The suppressor is a triblock copolymer comprised of ethylene oxide (EO)–propylene oxide (PO)–ethylene oxide (EO) with a molecular weight of 2900 (EPE 2900). In terms of the obtained filling performance evaluated by observing the obtained cross-sectional views of the microvias after electroplating, the electroplating solution was systematically studied as functions of Cl− concentration, EPE 2900 concentration, and convection conditions. It was found that filling performance was greatly dependent on these key factors. In the developed copper electroplating formulation, EPE 2900 was able to yield sufficient filling performance in a broad Cl− concentration ranging from 3 to 200ppm, although the optimized value was determined to be about 30ppm in terms of the best filling performance. During the microvia filling process, Cl− concentration, EPE 2900 concentration, and forced convection would affect each other. Their interactions were studied based on the anchor effect of Cl− on the adsorption of EPE 2900 on Cu substrates. In doing so, extensive electrochemical experiments including galvanostatic measurements, linear sweep voltammetry, electrochemical impedance spectroscopy and cyclic voltammetry were employed to study the adsorption behavior of EPE 2900 on the cathode during both the copper electrodeposition and dissolution processes. An adsorbing mechanism of EPE 2900 on cathode was proposed to elucidate the promotional role in improving the microvia filling performance.

Formation of Cu2ZnSnS4 absorber layers for solar cells by electrodeposition-annealing route

This study investigates the electrodeposition process of quaternary copper–zinc–tin–sulfur (CZTS) thin films with a focus on the ability of ligands to bring deposition potentials of the individual elements closer to each other. Our results show that thiocyanate ions (CNS−) can be used as a suitable complexant for the electrodeposition of Cu2ZnSnS4 from aqueous solutions. A complex electrolyte was developed and the composition measurements showed a large potential interval for the deposition of the CZTS thin film material with an appropriate metal ratio. The layers recrystallized in stoichiometric kesterite structure after annealing at 550°C in H2S atmosphere for 60min.

Copper Fractal Growth Pattern in Polymer Systems

This paper presents the effect of polymer (polyvinyl alcohol) on the growth of copper fractal formation. A thin layer electrochemical cell was designed for the study of copper electrodeposition process. The structure and morphology for the copper fractal patterns were investigated by scanning electron microscopy (SEM). The copper fractal dimension was measured by using box counting method. On the basis of diffusion limited aggregation (DLA) model, growth pattern of copper fractal is two dimensional in nature. The copper fractal dimension is affected by the composition of polyvinyl alcohol. The growth pattern of copper fractal formation was measured under constant potential condition.

Influence of the substrate's surface structure on the mechanism and kinetics of the electrochemical UPD formation of a copper monolayer on gold

The copper electrodeposition process was studied onto different gold substrates, single crystal (111) and polycrystalline, using electrochemical techniques. It was found, from the analysis of the experimental current density transients, that the potentiostatic formation of a full copper monolayer onto the gold electrode under UPD conditions follows the same mechanism, regardless of the crystallinity of the substrate. The mechanism involved the simultaneous presence of an adsorption process and of two 2D nucleation processes, progressive and instantaneous, respectively.

In-situ Ellipsometric Study of Lead Electrodeposition on Polycrystalline Cu

Electrodeposition of Pb on polycrystalline Cu surfaces has been investigated by cyclic voltammetry(CV) and in-situ spectroscopic ellipsometry(SE).The ellipsometric parameters Ψ and Δ peak corresponded to both underpotential deposition(UPD) and bulk deposition peak potentials.The "substrate-solution" interface structure was described with a single-layer model,(substrate Cu-deposition Pb layer) and the thicknesses of Pb layer for different scan potentials were obtained by fitting experimental data with the model.Fitting results showed that Pb electrodeposition on the Cu electrode was with three different deposition rates,-0.20 ～-0.35 V,0.003 nm/mV;-0.35 ～-0.48V,0.025 nm/mV;-0.48 ～-0.60 V,0.116 nm/mV.Based on the fitting results,three stages,which were formation of UPD layer,transitional period between the UPD and bulk deposition and formation of bulk deposition layer were proposed for the electrodeposition process of copper in the Pb2 + solution.

Effect of parameters of square-wave pulsating current on copper electrodeposition in the hydrogen co-deposition range

Copper electrodeposition processes in the hydrogen co-deposition range by the pulsating current (PC) regime were examined by the determination of the average current efficiency of hydrogen evolution and by the scanning electron microscopic (SEM) analysis of the morphology of the formed deposits. The two sets of the square-wave PC of the same pause to pulse ratios, but with different duration of deposition pulses and pauses were analyzed. The one set of square-wave PC was with the constant pause duration and different deposition pulses. In the other set, the deposition pulse was constant while the pause duration was varied. The obtained results were compared with those obtained by electrodeposition at the constant overpotential from solutions of different CuSO 4 and H 2SO 4 concentrations. It was found that the effect of the increasing deposition pulse was equivalent to the decreasing CuSO 4 concentration, while the effect of the decreasing pause duration was equivalent to the increasing H 2SO 4 concentration. It is shown that it is possible to achieve a substitution of more solutions of different CuSO 4 and H 2SO 4 concentartions by the use of the only one solution if the appropriate PC parameters were applied, what can be of high technological significance.

Monitoring the Influence of Gelatin and Thiourea on Copper Electrodeposition Employing Electrochemical Noise Technique

The copper electrodeposition from sulphuric acid electrolytes in the presence of thiourea and gelatin as additives was investigated using Electrochemical Noise (EN) and Linear Sweep Voltammetry (LSV) in conjunction with the scanning electron microscopy technique. This study was oriented to examine the utility of using EN technique to characterize the electrowinning process and the deposit structure morphology was compared to LSV, an electrochemical method generally used industrially. Both EN and LSV techniques were successful in revealing the effect of different concentrations of thiourea and gelatin on the copper electrodeposition process. In this study, LSV detected an excess of thiourea leading to porous deposit; while the EN analysis in the time domain (skewness and kurtosis parameters) detected the presence of nodules and has provided useful information concerning the morphology of the deposit closely related to the macroscopic and microscopic studies.

Advanced TSV Copper Electrodeposition for 3D Interconnect Applications

Robust and manufacturable processes are needed to enable a smoother and faster transfer of TSV technology from development to production. There are several steps involved with TSV technology application. Either if it is done before or after thinning the wafer, as a via first, middle or via last approach, the main steps are: via etching, lining with insulator/barrier and copper seed, deep via fill and chemical mechanical planarization (CMP), chip dicing and stacking. Deep via fill is one of thee most critical steps in forming the TSV electrodes, and copper electrodeposition process has been identified to be the most appropriate and cost effective method of filling the vias. Various critical factors with significant effect on the process performance were found: seed layer uniformity, via profile and size, stability and performance of the chemicals and equipment design. The amount and quality of the copper at the top of the vias and over the entire surface of the wafer is very important for the CMP processing. A more uniform deposition and lower overburden could significantly decrease the complexity and cost of the CMP step. The copper thickness profile between deposition and CMP can be cross-optimized to reduce dishing, increase throughput and reduce cost. This paper will focus on the deep via fill, the critical factors associated with this step and integration aspects of Cu TSV deposition step that need to be taken in consideration for successful application of this technology. A significant amount of work has been performed to develop processes that can successfully fill features of various sizes in a cost effective way. Some of the chemistries available commercially today, although have very good super-fill characteristics, have the disadvantage of forming nodular and high-stress deposits which could have a negative impact on CMP processing. An innovative process with strong bottom-up capability that significantly reduces the overburden while increasing the speed of deposition has been developed at Semitool and the characteristics of this process and advantages over previous generation processes will be presented. The effect of copper stress and copper extrusion observed during annealing step as well as approaches taken to minimize this effect will be described.

Electrode kinetics parameters estimation using Zakai equation

The Zakai filtering method is applied on a physical model describing electrode kinetics in a voltammetric analysis, and which is substantially nonlinear in the parameters. The model parameters are estimated using a direct sample path integration method developed for the Zakai equation and pathwise filtering equation. Convergence of the estimates is analysed numerically on two electrode kinetics models. The proposed path integration method is applied for description of the measured data in the copper electrodeposition process and compared with the direct search method.

Characterization of Iron Mediated Copper Electrodeposition Process for Semiconductor Interconnect Metallization

not Available.

Effect of solution flow rate and direction on copper electrodeposition process from sulfuric acid electrolyte on porous electrode with high electric conductivity

The effect of solution flow direction and rate on the dynamics of copper electrodeposition onto a premetallized coal-graphite VINN-250 material from a dilute copper sulfate sulfuric acid solution is experimentally studied in the direct-flow mode. A light effect of solution supply on the copper deposit final mass for high and low solution flow rates is found, while the effect of this parameter on the metal distribution within the porous electrode is significant. The most uniform copper deposit distribution throughout the porous electrode is observed in the case of intermediate solution flow rates at its rear supply. The obtained experimental data agree qualitatively with the earlier published mathematical simulation results. Small systematic deviations from numeric calculations can be due to the process disregarded in the mathematical model: the effect of gas phase formed within the porous cathode due to the simultaneous hydrogen evolution.