Sensitivity Enhancement for Quantitative Electrochemical Determination of a Trace Amount of Accelerator in Copper Plating Solutions

Abstract

An accelerator is an indispensable organic additive for the bottom-up filling of copper electroplating in nano- or micro-scale features. However, its effective concentration is too low to be easily determined and controlled. Herein, a new electrochemical analysis method based on self-assembly monolayers of thiol molecules on a gold electrode was developed to accurately determine a trace amount of accelerator. The accelerator employed in copper plating solutions is bis-(3-sulfopropyl) disulfide (SPS), which is the most common accelerator for the filling of vias and trenches of interconnects. The SPS concentration in copper plating solutions ranged from 0.3 to 9.0 ppm. Following selective chemisorption of SPS onto the gold electrode, the SPS-modified gold electrode was transferred into a specific electrolyte composed of CuSO4, H2SO4, polyethylene glycol and chloride ions to run cyclic voltammetry (CV) for copper deposition and stripping. A specific peak current of copper reduction formed in the CV, and its peak area depended on the SPS concentration in the copper plating solution. A good linear calibration line was obtained by using this electrochemical analysis method, which can determine a trace amount of SPS in a concentration range of 0.3-1.0 ppm, which is a significant challenge for traditional instruments

Accelerator Screening by Cyclic Voltammetry for Microvia Filling by Copper Electroplating

“…SPS adsorption is a secondorder process because one SPS molecule contains two sulfonate terminal groups. 51 This result is in agreement with the adsorption kinetics results of TBPS because one TBPS molecule also contains two sulfonic groups, which can trap two Cu 2+ ions simultaneously, as illustrated in Fig. 4.…”

“…Only TBPS induced a large number of CuNPs on the TBPS-modified Au electrode, which is similar to the result obtained with the SPS-modified Au electrode. 51 Neither MPA nor MPO facilitated CuNP formation and gave rise to a significant change in the cathodic surface composition under the same conditions. Therefore, no α peak and no hysteresis loop was formed on the MPA-or MPO-modified Au electrode during the reduction analysis.…”

“…3e and 3f; this result is the same as that previously observed with SPS. 51 According to the schematic acceleration mechanism illustrated in Fig. 4, neither MPA nor MPO has any capability for accelerating copper electrodeposition because they do not contain an end group with a negative charge and because their gauche conformation leads to a double-adsorption bonding to the copper surface.…”

“…The accelerating effect on copper electrodeposition caused by the accelerator combines with its floatability and transferability on the as-deposited copper surface. 39,51 Herein, we examined five organosulfides, as shown in Fig. 1, using the CV method to test their accelerating effect on copper deposition.…”

Multiphysics coupling simulation of RDE for PCB manufacturing

“…In this metallization technique, copper is directly filled into the vias using a base cupric sulfate/sulfuric acid electrolyte containing special additives (Dow et al, 2008a(Dow et al, , 2009aChiu et al, 2011;Tenno and Pohjoranta, 2008). These additives function synergistically to cause either bottom-up filling or superfilling of copper deposits in the vias.…”