Inhibition of Copper Deposition by Polyethylene Glycol and Chloride

Abstract

A physicochemical model for the effect of the additives polyethylene glycol ͑PEG͒ and Cl − on Cu 2+ reduction onto a rotating-disk electrode in acidic sulfate solutions has been developed and fit to experimental potential scans to estimate kinetic parameters. The model, which applies to either transient or steady-state conditions, incorporates diffusion, convection, and a reaction mechanism that explicitly includes the effects of both additives. Very good agreement between the fitted model and experimental data is obtained. The model captures the range of voltammogram shapes experimentally observed over a wide range of additive levels ͑i.e., from the gradual loss of Cu 2+ reduction inhibition with increasing overpotential at high PEG and Cl − concentrations to the sudden and complete breakdown of the inhibiting film at a critical potential when intermediate additive levels are used͒. An impedance model has also been derived and solved to generate impedance spectra using the previously obtained kinetic parameters. The predicted impedance spectra show good agreement with measured ones. Key aspects of the reaction mechanism are PEG desorption from the electrode, which occurs due to displacement by depositing copper, and the distinction made between the situations when the electrode is completely and partially covered by the inhibiting film.Polyethylene glycol ͑PEG͒ and chloride ions are commonly added to electroplating baths used in the electrodeposition of copper to improve the filling of trenches and vias in the Damascene processes for microelectronic circuit fabrication. 1-3 These two additives form a complex responsible for the selective inhibition of Cu 2+ reduction in particular regions of these features. There is not universal agreement concerning the structure of the inhibiting complex. Some researchers have presented evidence or interpreted experimental results on the basis that the complex contains PEG, Cl − , and Cu + , 4-8 whereas others have reported data supporting the view that copper is not necessarily a constituent of the complex. 9-11 Two different roles have been attributed to the inhibiting complex during copper electrodeposition: ͑i͒ blockage of sites available for the reduction of Cu 2+ and ͑ii͒ intermediate for the reduction of Cu 2+ . Some researchers have suggested that the inhibiting complex only blocks the substrate and does not participate as an intermediate in Cu 2+ reduction. [12][13][14][15][16] Other researchers have proposed mechanisms by which the complex fulfills both inhibiting and intermediate roles by being continually reformed during cathodic polarization. [17][18][19][20][21] It should be noted that if the second role applies, then Cu + necessarily is a constituent of the inhibiting complex.Numerous studies have been conducted to investigate the effect of PEG and Cl − concentration on the voltammetric response during Cu 2+ reduction. Broadly speaking, the cathodic scans fall into one of three categories, depending on additive concentration: ͑i͒ responses similar to those obs...

Stochastic Modeling of Polyethylene Glycol as a Suppressor in Copper Electroplating

“…At steady state, the conservation of mass requires: r c1 − r a1 = D(c bCu(I I) − c Cu(I I) )/δ [4] r c1 − r a1 + r a2 − r c2 = D(c bCu(I ) − c Cu(I ) )/δ [5] where the same diffusion coefficient D is assumed for both Cu 2+ and Cu + , δ is the diffusion layer thickness. As Cu + is unstable in the presence of dissolved O 2 , the bulk concentration of Cu + is assumed to be zero.…”

Revisiting the Polyethylene Glycol-Chloride Adsorption Structure on Cu Electrode in Sulfuric Acid Solution by Wide-Frequency ATR-SEIRAS

“…9−13 It is known that chloride ions actively participate in forming the inhibition layer from conventional electrochemical measurements. 7,14 The adsorption−desorption behavior 15−17 and the inhibition effect 6,18,19 of the PEG-Cl − adlayer on the Cu electrode have been investigated by electrochemical and spectroscopic methods. At a mesoscopic scale, the inhibition layer is composed of PEG with Cl − and/or Cu + with spherical morphology as deduced by quartz crystal microbalance (QCM) 20 and electrochemical impedance spectroscopy (EIS), 21 or with flat-cone mound morphology as directly observed by in situ atomic force microscopy (AFM).…”

“…PEG whose chemical structure is relatively simpler often serves as a model suppressor for Cu electrodeposition in fundamental studies. − It is known that chloride ions actively participate in forming the inhibition layer from conventional electrochemical measurements. , The adsorption–desorption behavior − and the inhibition effect ,, of the PEG-Cl – adlayer on the Cu electrode have been investigated by electrochemical and spectroscopic methods. At a mesoscopic scale, the inhibition layer is composed of PEG with Cl – and/or Cu + with spherical morphology as deduced by quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS), or with flat-cone mound morphology as directly observed by in situ atomic force microscopy (AFM). , Despite these advancements, the microscopic intricacies of the PEG-Cl – inhibition layer continue to pose questions, which warrant further investigation through molecular spectroscopies.…”

“…The accelerator promotes Cu reduction on the bottoms of vias or trenches, while the suppressor and the leveler restrain Cu deposition on the sides of vias or trenches and the superfluous Cu bumps. Among them, the suppressor plays an indispensable role in achieving “bottom-up” filling in Cu interconnects in the presence of chloride ions. − In most cases, suppressors are large alkyl-ether polymers or copolymers, such as polyethylene glycol (PEG), polypropylene glycol (PPG), or triblock copolymer composed of ethylene oxide (EO)–propylene oxide (PO)–ethylene oxide (EO) …”

Modeling of the Coadsorption of Chloride and Hydrogen Ions on Copper Electrode Surface

“…[1][2][3][4][5][6] The working mechanism of chloride ions has been extensively studied both experimentally and theoretically. [7][8][9][10][11][12][13][14][15][16][17] Commonly, the electrolytes used for the electrochemical copper deposition are highly acidic. 1,2 Thus, it seems likely that the adsorption of hydrogen ions competes with the adsorption of chloride ions at certain potentials of the copper electrode.…”