Acceleration Kinetics of PEG, PPG, and a Triblock Copolymer by SPS during Copper Electroplating

Abstract

Three copper-plating suppressors are examined in three-additive baths: a polyethylene glycol ͑PEG͒, a polypropylene glycol ͑PPG͒, and a triblock copolymer of the two. Bis͑3-sulfopropyl͒-disulfide ͑SPS͒ is found to transition each to a state of nonsuppression, i.e., accelerate each, at a rate dependent on the suppressor molecule, the SPS concentration, and, to a lesser extent, the suppressor concentration. Using a planar microscale working electrode ͑d = 100 m͒, the kinetic currents of the plating reactions are observed without the influence of ohmic resistance, revealing far higher current densities than previously reported. Potentiostatic and galvanostatic experiments of additive adsorption at short times, t Ͻ 20 s, are compared quantitatively using a surfaceblocking model to transform the data to effective surface coverage, EFF , vs time. A major difference is found in SPS acceleration between galvanostatic and potentiostatic experiments, with the rate of change in suppression being proportional to the current density. This results in a constant rate of change in EFF under constant current but a self-reinforcing rate of change in EFF at constant potential. A simple additive model is introduced to characterize the results.The chosen material for interconnect manufacture in the semiconductor industry is electrodeposited copper, switched from aluminum in the late 1990s to achieve architecture scales below 250 nm. 1,2 The drive for increasing computing power continues, following the relation known as Moore's Law, and the characteristic scale of interconnects has fallen below 100 nm, approaching 30 nm and lower in the coming years. Electrodeposition of copper in highaspect-ratio features on this scale requires plating bath additives, which suppress and enhance deposition rates at the feature mouth and floor, respectively, to achieve bottom-up, void-free copper filling. This is referred to as superconformal filling or superfill.The additives required for superfill are a halide-ion promoter such as Cl − , a polyether suppressor such as polyethylene glycol ͑PEG͒, and a sulfur-containing molecule such as bis͑3-sulfopropyl͒-disulfide ͑SPS͒. Superfilling behavior results from an interaction of these additives, and this study focuses on plating behavior as a function of bath composition in order to formulate for decreasing feature sizes. It has been shown that the polyether suppressor and chloride ions coadsorb on the copper electrode surface, raising the overpotential required for a constant plating current. 3-7 This suppression becomes minor if the halide is not present and is a function of both halide and polyether concentration. 5 Other polyether molecules besides PEG ͓polypropylene glycol ͑PPG͒ and pluronic triblock copolymers of ethylene oxide ͑EO͒ and propylene oxide ͑PO͔͒ display the same characteristic suppression, although its degree is a function of the molecular structure. 8,9 A proportional increase of PO repeat units in the chain causes an increase in suppression. However, the presence of long, hydrophobic PO...

Triblock Copolymers as Suppressors for Microvia Filling via Copper Electroplating

“…That meant the more PO segments in the molecules would lead to the stronger suppression strength of the suppressors. This result was in line with that observed by West et al 21 Using the optimized Cl − concentrations for each suppressor, GMs were performed for evaluating the filling performances of the plating baths containing suppressors at a low concentration of 20 ppm suppressors, as shown in Fig. 7.…”

Further studies in the electrochemical/mechanical strength of printed microbatteries

“…To emulate the latter condition, a microfluidic device was used to observe in-situ changes on the electrode structure: the electrolyte flow is a medium to induce shear stress on the electrode surface. [10][11][12] This shear stress was correlated with the shear stress observed on the electrode surface during the flexing of the battery. Learning from these studies, we demonstrated a flexible battery electrode based on a mesh embedded architecture.…”

Pulse-Reverse Electrodeposition of Cu for the Fabrication of Metal Interconnection

“…[1][2][3][4][5][6][7][8][9][10][11][12] The main mechanism of superfilling is the local promotion of Cu deposition at the bottom of the features. This controlled deposition rate according to the location within the feature, is enabled by the adsorption of different types of organic additives, and the changes in their surface coverage.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12] In contrast, various polyethers in combination with chloride ions are employed as the suppressor, and polyethylene glycol (PEG), polypropylene glycol (PPG), and their block copolymers are the typical suppressors. [1][2][3][4][5][6][7][8][9][10][11][12] The superfilling mechanism has been understood based on the Curvature Enhanced Accelerator Coverage (CEAC) model. [13][14][15] This model emphasized the accumulation of accelerators, through area reduction at the bottom corners of filling features, as the electrodeposition progresses.…”