An SERS study of the galvanostatic sequence employed for the electrochemical deposition of Copper in the fabrication of Interconnects

TL;DR

This study employs surface-enhanced Raman spectroscopy to analyze the interfacial behavior during galvanostatic copper electrodeposition, revealing additive interactions and their effects on deposit morphology.

Contribution

First application of SERS to monitor organic additive interactions during copper electrodeposition in real-time.

Findings

Additives co-adsorb at open circuit.

PEG scavenges SPS during polarization.

Organic additives influence deposit microstructure.

Abstract

This paper reports the first study carried out by surface-enhanced Raman spectroscopy (SERS) during the galvanostatic electrodeposition (ECD) of copper from an acidic sulphate solution, in the presence of polyethylene glycol (PEG), bis-(3-sulfopropyl)-disulfide Na salt (SPS), benzyl-phenyl modified polyethyleneimine (BPPEI) and chloride ions. The analysis of SERS spectra recorded during electrodeposition allowed to get an insight into the complex interfacial behaviour of the organic blend, in terms of co-adsorption and reactivity. At open-circuit (OC), the additives co-adsorb on the copper cathode. Upon increasing the cathodic polarization, progressive SPS-scavenging action of PEG was observed. BPPEI is adsorbed in the entire process window and cathodic reaction products of PEG were identified. The joint action of the organic additives yields a continuous deposit with crystallites of submicron dimensions, as revealed by Scanning Electron Microscopy (SEM).