(Invited) Investigations of Interaction and Molecular Structure of Additives on the Copper Electrodeposited Layer By Combination of Cyclic Voltammetry with Time-of-Flight Secondary-Ion Mass Spectrometry (TOF-SIMS)

Abstract

Appropriate additives, such as polyethylene glycol, play the essential role of metal deposition suppressors and are required to control the fabrication process of copper electrodepositionon micro and nanoscale devices. Moreover, brighteners, accelerators and levellers are involved in adjusting of functional properties of the electroplating bath influencing roughness and waviness of deposited copper layer. Our recent studies [1] show that TOF-SIMS measurements under static regime can be conducted successfully for the identification of additives such as PEG, SPS, and Cl, accumulated on the copper electrodeposited layer.Especially, evaluation of molecular structure of the large molecules such as polyethylene glycol is very challenging and out of range for techniques such as SERS, widely applied for in situ studies under copper electrodeposition regime. On the other hand, traditional mass spectroscopy such as electrospray mass spectrometry are oriented on evaluation of composition of electroplating bath. Recently, we have developed a new approach for evaluation of additives on the copper layer by combination of cyclic voltammetry (CV) with TOF-SIMS. To determine the molecular structure of polyethylene glycol and its interaction with chloride and acceleratorson the copper electrodeposited layer CV experiment was conductedwhile a nitinol wire as a working electrode was withdrawn at constant speed from a copper electroplating bath. In that way applied potential during CV corresponds to position of the wire withdrawn from the electroplating bath. This approach allows to evaluate of distribution of chemical species in a function of the applied potential by ex situ TOF-SIMS measurements. Moreover,the thickness of the copper layer was controlled by laser scan micrometer. In the presence of brightener and leveler, the roughness was evaluated by atomic force microscopy in a function of length of wire. In that fashion, CV experiment combined with a molecular analysis, thickness and roughness of copper layer measurements bring complementary knowledge to comprehensively understand the processes occurring on the copper surface. This will have an application for the real-world samples in a wide range of thickness copper layer, applied potential and concentration of additives and copper sulfate.[1] R. Mroczka, R. Łopucki, G. Żukociński, Molecular analysis of additives and impurities accumulated on copper electrodeposited layer by time-of-flight secondary ion mass spectrometry, Applied Surface Science 463 (2019) 412–426