Additives inhibiting electrodeposition

The inhibition-acceleration mechanism. Moffat et al. (37) proposed the inhibition-acceleration mechanism to explain the experimentally observed comer rounding (inversion of curvature. Fig. 19 in Ref. 37) and general shape evolution in superconformal electrodeposition of copper in vias and trenches of nanometer dimensions (37,38). These authors also smdied a three-additive system composed of two inhibitors and one accelerator. They concluded that superconformal deposition and comer rounding may be attributed to competitive adsorption of inhibitor and accelerator. This model is based on the assumption of curvature (in vias and trenches) -enhanced accelerator coverage. 

The electrodeposition of Zn-Co and Zn-Fe alloys in an aqueous bath is classified as an anomalous codeposition [44] because the less noble Zn is preferentially deposited with respect to the more noble metal. This anomaly was attributed to the formation of Zn(OH)+ which adsorbs preferentially on the electrode surface and inhibits the effective deposition of the more noble metal. This anomaly was circumvented by using zinc chloride-n-butylpyridinium chloride ([BP]+C1 / ZnCf ) [27] or [EMIMJ+Ch/ZnCh [28] ionic liquids containing Co(II). The Zn-Co deposits can be varied from Co-rich to Zn-rich by decreasing the deposition potential or increasing the deposition current. XRD measurement reveals the presence of CosZ i in the deposited Zn-Co alloys and that the Co-rich alloys are amorphous and the crystalline nature of the electrodeposits increases as the Zn content of the alloys increases. Addition of propylene carbonate cosolvent to the ionic liquid decreases the melting temperature of the solution and allows the electrodeposition to be performed at a lower temperature. The presence of CoZn alloy is evidenced by the XRD patterns shown in Figure 5.2. 

Unfortunately, the electrodeposition of metals summarized in Table 4 is accompanied by increased HTSC degradation under cathodic polarization [53, 55]. In nonaqueous media, electrocrystallization processes can be inhibited due to the peculiarities of the intermediate Cu+ species solvation [286]. Moreover, the surface morphology of deposits can be adversely affected by the formation of dendrites this can be overcome by the addition of a brightening agent [497]. 

K. (2004) Role of Additives for Copper Damascene Electrodeposition Experimental Study on Inhibition and Acceleration Effects. J. Electrochem. Soc., 151, C250-C255. 

It was proposed by Andricacos et al This mechanism considers one-additive system. It is noted in Ref. 47 (Ch. 10, Sections 10.4 and 10.5) that in general, adsorption of additives (inhibitor) at the cathode affects the kinetics and growth mechanism of electrodeposition. The surface coverage of the additive (inhibitor), 0, is a function of the diffusion controlled rates of the adsorption-desorption processes. In the differential-inhibition mechanism it is assumed that a very wide range of additive fluxes over the micro-profile (vias and trenches) exists, that is, extremely low flux in deep interior comers, low flux at the bottom center, moderate flux at the sidewalls, and high flux at shoulders. 

Our model has the quantitative capability to predict the superfilling behavior and also the capability to predict conditions for which superfilling breaks down and voiding occurs for both trenches and vias. The essence of the model lies in the assumption that the rate constant for electrodeposition, i0, is higher at point B than at point A due to differential inhibition. The surface concentration of adsorbate species varies along the feature because it is influenced by the diffusive transport of the additive/inhibitor. Diffusion is sustained because the additive is consumed at the surface by reaction or incorporation into the deposit. It is assumed that the kinetic inhibition is a function of the adiitive flux and so the... 

These are the roles of additives for corrosion inhibition and the modification of electrodeposits. For electrode reactions where the overall sequence includes chemical steps, however, the role of the adsorbate layer may be quite different. Rather it may be to create an environment which is more favourable than the bulk solution for a particular reaction. For example, the proton availability may be different it is not unusual for an adsorbate layer to be relatively aprotic compared with an aqueous electrolyte and such modifications of electrode processes have been used in the following. 

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