Supression Effect and Additive Chemistry
The excellent additive systems for acid copper sulfate bath developed in the 1960s successfully produce bright copper deposits with smooth surfaces and high ductility. Since then, many applications of copper plating were developed for electronic device an
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Supression Effect and Additive Chemistry Masayuki Yokoi
2.1 Additive Chemistry The excellent additive systems for acid copper sulfate bath developed in the 1960s successfully produce bright copper deposits with smooth surfaces and high ductility. Since then, many applications of copper plating were developed for electronic device and through-hole plating for PCBs as well as conventional decorative plating on steel, electroforming, etc. In 1997, the Copper Damascene Process was developed in improved interconnect material fabrication of ULSIs by IBM. With this turning point, the role of addition agents came under further study using advanced analytical techniques such as Enhanced Raman Spectrometry, QCM, AFM, TEM, EIS, in addition to conventional electrochemical plating research methods. Addition agents in acid copper sulfate bath consist of suppressors, levelers, and accelerators. The former suppress copper deposition on convex regions, and the latter catalyze copper deposition on concave regions in the presence of a small amount of Cl- ions [1–4], resulting in via/trench copper. In the following sections, the roles of the addition agents will be described on the basis of knowledge accumulated by many researchers.
2.2 Role of Suppressors PEG or PEG/PPG copolymers of nonionic surfactants and cationic dyes such as JGB containing nitrogen atoms are widely used as representative suppressors and levelers, respectively. Both of them exert a strong suppression effect on copper deposition reactions in the presence of Cl- ions. The suppressor acts in a relatively
M. Yokoi (&) Osaka Prefecture University, 8-15 Taishi-Cho, 586-0041 Kawachi Nagano Shi, Japan e-mail: [email protected]
K. Kondo et al. (eds.), Copper Electrodeposition for Nanofabrication of Electronics Devices, Nanostructure Science and Technology 171, DOI: 10.1007/978-1-4614-9176-7_2, Springer Science+Business Media New York 2014
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wide copper deposition current region, the leveler plays the role of a surface leveling agent in the low deposition current region, less than a few mA/cm2 [5]. For the suppression mechanism by surfactants of the PEG family, many researchers have studied it in detail since the mid-1980s, and it has basically become clear [6–29]. The action of levelers on copper deposition is under fundamental study for application to via/trench or through-hole copper filling [30–36].
2.2.1 The Role of Peg in Bright Copper Plating by the Hull-Cell Test The Polyoxyethylene family of surface active agents, used as indispensable additives in various metal plating baths, play a decisive role in bright copper plating, through-hole plating, and on-chip wiring copper plating. Kardos [1] indicated in his patent drawing that the appropriate combination of three components, S containing compound, N containing compound, and ethylene oxide polymer give good bright copper plating in the presence of Cl- ions. Mirkova et al. [4] reported that PEG or PPG have a central function in leveling during bright copper plating. In addition, the
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