In Situ Ellipsometric Study of PEG∕Cl[sup −] Coadsorption on Cu, Ag, and Au

Abstract

Spectroscopic ellipsometry was used to examine the adsorption of poly͑ethylene glycol͒ ͑PEG͒ and Cl − on polycrystalline Cu, Ag, and Au electrodes in sulfuric acid. In halide-free sulfuric acid, PEG adsorption on Cu and Ag is minimal at potentials positive of the estimated potential of zero charge ͑pzc͒. PEG adsorption on Au was also negligible in halide-free environments positive of the pzc, but slight adsorption was evident near the pzc. In contrast, in the presence of adsorbed halide, PEG coadsorption is clearly evident at potentials near or positive of the pzc for all metal samples studied. The PEG/Cl − coadsorbed film does not provide a significant barrier to outer-sphere electron-transfer reactions ͓i.e., Ru 3+/2+ ͑NH 3 ͒ 6 ͔, although inner-sphere reactions associated with electrodeposition of copper are effectively inhibited. The implications of these observations with respect to the role of Cu + ions in the PEG-induced inhibition of Cu electrodeposition is discussed.

Influence of plating parameters and solution chemistry on the voiding propensity at electroplated copper–solder interface

“…Yet, in the damascene process, PEG is known as an inhibitor. But, it is known this inhibition effect becomes stronger in the presence of Cl -ion in the solution [23][24][25]. In fact, substantially different results are obtained upon the combination of PEG and Cl -into the H 2 SO 4 + CuSO 4 solution.…”

Superconformal Electrodeposition for 3‐Dimensional Interconnects

“…Upon immersion, a PEG layer rapidly forms as a co-adsorbate on top of the halide layer, inhibiting the metal deposition reaction by blocking access of aquo Cu 2 + ions to the Cl --terminated surface. [13,14] A leakage current is associated with local desorption and re-adsorption of PEG ligaments forming the blocking layer. The more dilute SPS species compete for PEG-free surface sites and, once adsorbed, the sulfonate end group of SPS disrupts, displaces, and prevents the readsorption of the PEG layer.…”

Applications to Magnetic Recording and Microelectronic Technologies

“…On the basis of SERS spectra, complementary modeling of a three-coordination Cu with two ether oxygen ligands from PEG and one chloride ligand is proposed, as illustrated in Figure 27.25b. In contrast to Raman spectroscopy, electrochemical quartz crystal microbalance (EQCM) [86,134] and recent in situ spectroscopic ellipsometry (SE) studies [105,135,136] indicate that Cu ions (neither Cu þ nor Cu 2 þ ) are not essential for the formation of PEG-Cl inhibiting layer. A recent in situ SE study [105] shows that the PEG adsorption alone is very weak and does not vary with the potential, which is consistent with Raman [129] and EQCM [86,134] measurements.…”

“…Studies of electronic properties [105] showed that the PEG-Cl layer does not significantly affect the outer sphere electron-transfer reduction. However, a significant decrease of the interfacial capacitance is observed, which is in agreement with results of electrochemical impedance spectroscopy (EIS) that reported a capacitance reduction to almost a half value upon PEG-Cl layer formation [130].…”

“…The exchange current density values suggest that copper deposition kinetics was hindered by almost two orders of magnitude in the presence of PEG-Cl additives. The insignificant changes of respective transfer coefficients suggest that the copper reduction is unaltered by the PEG-Cl layer; that is, this layer behaves as a physical barrier blocking the access of cupric ions to the electrode surface [105].…”