Effect of Convection-Dependent Adsorption of Additives on Microvia Filling in an Acidic Copper Plating Solution

Microvia filling of a printed circuit board by acidic copper electroplating was performed to evaluate whether the filling performance of an acidic copper plating solution could be quantified and monitored. The acidic copper plating solution was composed of polyethylene glycol, chloride ions, bis(3-sulfopropyl) disulfide and Alcian Blue. The electrochemical methodology for quantifying the filling performance of the copper plating solution is based on the adsorption and mass transfer of chloride ions. The potential difference that was obtained from galvanostatic measurements at two different rotating speeds of a copper working electrode was confirmed to be an effective indicator of filling performance. A larger potential difference reflected better filling performance. The individual contribution of each additive in the potential difference was explored in detail. The leveler and chloride ion concentrations dominated the potential difference, i.e., the filling performance. When the potential difference was larger than a critical value, i.e., 11 mV, the filling performance was higher than 80%. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.010203jes] All rights reserved

Microvia Filling by Cu Electroplating Over a Au Seed Layer Modified by a Disulfide

A plating process for microvia filling by Cu electroplating, carried out in a plating bath without an accelerator but with a suppressor only, is proposed in this work. The seed layer of microvia used for subsequent Cu-filling plating is Au formed by electroless plating. The surface of the Au seed layer is modified in a solution containing bis(3-sulfopropyl)-disulfide (SPS) and various supporting electrolytes. This pretreatment is similar to the self-assembly monolayer (SAM) of a thiol molecule on a Au substrate. The coverage density of the adsorbed thiolate strongly depends on the presence or the absence of a supporting electrolyte and it crucially determines the filling performance of the plating process. The plating results demonstrate that the thiolate adlayer which is initially formed on the Au seed layer is transferable onto the surface of the plated Cu and then interacts with chloride ions to further facilitate Cu nucleation and growth. According to the results of the filling plating and the electrochemical analysis, an accelerating mechanism of SPS-SAM for copper electrodeposition and its transferring mechanism are proposed in this work

Enhancement of filling performance of a copper plating formula at low chloride concentration

In this work, microvia filling was performed by copper electroplating using two plating formulas with and without a leveler at a low concentration of chloride. The base plating solution contained CuSO4, H2SO4, polyethylene glycol (PEG), his (3-sulfopropyl) disulfide (SPS) and Cl-. When the Cl- concentration was lower than 30 ppm, the plating formula without a leveler became dead for bottom-up filling, resulting in conformal deposition. The addition of I ppm Alcian Blue, used as a leveler, could effectively recover the filling performance of the plating formula with low chloride concentration. Electrochemical analyses revealed possible mechanisms. The results demonstrate that the usage of Alcian Blue can widen the operation window of chloride concentration, since it can assist PEG in competing with SPS in adsorption at low chloride concentration. (c) 2008 Elsevier Ltd. All rights reserved

Modification of Cu nanoparticles with a disulfide for polyimide metallization

Copper metallization on polyimide films was carried out via a wet chemical process. This process included the chemical reaction of KOH with PI to form poly(amic acid) (PAA), ion exchange of doped K(+) with Cu(2+) to form Cu(2+)-doped PAA, doped Cu(2+) reduction by aqueous dimethylamine borane (DMAB) to form copper nanoparticles (CNPs) on PAA, and electroless copper (ELC) deposition catalyzed by CNPs on PAA. An organic additive, namely, bis(3-sulfopropyl)-disulfide (SPS), that can effectively reduce the size of CNPs and significantly enhance the chemical activity of CNPs for ELC deposition was used in this work. For comparison, doped Cu(2+) ions in the PAA were also reduced by hydrogen gas at 350 degrees C. The results show that only aqueous reductants can induce the reduced copper atoms to aggregate on the PAA surface and to form a granular copper layer that acts as a catalyst for the ELC deposition. Mechanisms for the aggregation of copper atoms and for activity enhancement of the CNPs due to SPS addition in the DMAB solution are proposed according to the evidence obtained from Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectrometry (XPS), field emission scanning electron microscopy (FESEM), cross-sectional transmission electron microscopy (TEM), and atomic force microscopy (AFM). The CNP-coated PAA films and the structures of the ELC deposits were characterized by X-ray diffraction (XRD) and UV-visible spectrophotometry (UV-Vis), respectively

Revelation of the spatial structures and polymerization of aniline on Au(100) electrode by in situ scanning tunnelling microscopy

In situ STM imaging of Au(100) electrode in 1 MHClO(4) + 0.03M aniline revealed highly ordered aniline adlattices of (2 root 2 x 4 root 2)R45 degrees and (root 10 x root 10)R18 degrees and polyaniline molecules exhibiting wiggling conformations at potentials negative and positive of 0.95 V ( vs. reversible hydrogen electrode), respectively

Filling mechanism in microvia metallization by copper electroplating

This work explores the mechanism of microvia filling by copper electroplating using a printed circuit board (PCB) with a specific pattern design. The microvias employed in this work had no sidewall copper layer. The outer and inner copper layers of these microvias that had no sidewall copper layer were together connected to the cathode during electroplating in order to clarify the mechanism of bottom-up filling. A plating formula that was composed Of CuSO4, H2SO4, polyethylene glycol (PEG), bis(3-sulfopropyl) disulfide (SPS), Cl- and Janus Green B (JGB) was employed as a model formula for studying the filling mechanism. The results showed that bottom-up filling stemmed from two crucial factors. One was the sidewall growth of the microvia, increasing the surface coverage of an accelerator; the other was the convection-dependent adsorption (CDA) of additives, leading to different copper deposition rates on the outer and inner copper layers. When a leveler was present in the plating solution, CDA behavior dominated the filling mechanism, regardless of whether a sidewall copper layer was present. On the other hand, the mechanism of coverage accumulation of the accelerator was dominant only when the microvia possessed a sidewall copper layer and no leveler was present in the plating solution. (C) 2008 Elsevier Ltd. All rights reserved

Copper Fill of Microvia Using a Thiol-Modified Cu Seed Layer and Various Levelers

Microvia filling by copper electroplating was carried out using a plating bath containing a suppressor and a leveler without an accelerator. The required accelerator was adsorbed onto the copper seed layer of the microvia in a predipping bath before the filling plating. This pretreatment is similar to the self-assembled monolayer of thiol molecules that forms on a copper surface. The suppressor was poly(ethylene glycol) (PEG), and five levelers, namely, Janus green B, diazine black, methylene violet, safranine O, and Alcian blue, were employed to screen for the best plating formula suitable for a plating process in which no accelerator was present in the plating solution. The thiol molecule employed in this work was 3-mercapto-1-propanesulfonate (MPS). The electrochemical behaviors of various plating formulas were characterized using a galvanostatic measurement on a copper electrode at different rotating speeds. Results indicated that the MPS adlayer is transferable onto the surface of the copper deposit and can be displaced by the PEG-Cl-leveler. The displacement rate depends on the molecular structure of the added leveler. This plating process has the potential to greatly reduce the plating time of microvia filling

In Situ Scanning Tunneling Microscopy Study of 3-Mercaptopropanesulfonate Adsorbed on Pt(111) and Electrodeposition of Copper in 0.1 M KClO4+1 mM HCl (pH 3)

In situ scanning tunneling microscopy (STM) was used to examine the spatial structure of adsorbed 3-mercaptopropanesulfonate (MPS) molecules on a Pt(111) electrode in 0.1 M KClO4 + 1 mM HCl + 10(-7) M MPS (pH 3). Two ordered MPS structures, Pt(111) (2 x 2) (theta = 0.25) and (root 3 x root 3)R30 degrees (theta = 0.33) structures were observed at -0.25 V (vs Ag/AgCl). The former (latter) was more important at more negative (positive) potentials. These MPS structures became a disordered adlayer at E > 0.1 V. These restructuring events could result from a progressive increase of the surface coverage of MPS with potential. Shifting the potential negatively could restore the ordered structures of (root 3 x root 3)R30 degrees and (2 x 2), but the rather strong Pt-MPS made it difficult for MPS admolecules to desorb from the Pt(111) electrode. By contrast, the MPS adlayer seen in 0.1 M HClO4 was always disordered, regardless of the potential of Pt(111) electrode. (Tu et al., J. Electrochem. Soc. 2010, 157, D206.) It is reasonable to state that potential control, pH, and/or countercations to the sulfonate group of the MPS admolecule could be important in guiding the adsorption of MPS molecules on Pt(111) electrode. Strongly adsorbed MPS molecules on the Pt(111) electrode could impede the rate of Cu2+ reduction, thereby inhibiting rather than accelerating electrodeposition of copper under the present conditions. Real-time STM imaging revealed random nucleation of copper adatoms on Pt(111), followed by lateral growth of Cu nuclei upon further deposition. Segregated domains of (root 3 x root 3)R30 degrees, ascribable to MPS and chloride adspecies, were observed atop a monolayer of Cu deposit prior to the commencement of bulk Cu deposition. With a small overpotential (eta < 20 mV), multilayer copper was electroplated on Pt(111) in a layered manner, producing atomically smooth Cu deposit capped by patches of (3 x 3) MPS. By contrast, the Cu deposit on MPS-modified Pt(111) in 0.1 M HClO4 was decidedly rough, as reported earlier