V. Romanello

Electrodeposition of Cu from Acidic Sulfate Solutions in the Presence of Bis-(3-sulfopropyl)-disulfide (SPS) and Chloride Ions

This paper reports an in situ Raman study of Cu electrodeposition from an acidic sulfate solution in the presence of bis-3- sulfopropyl-disulfide Na salt SPS. In the absence of chloride, in situ surface-enhanced Raman spectra scarcely show few labile features in a narrow range of cathodic potential. When Cl The widely investigated processes of Cu electrodeposition for ultralarge scale integration ULSI fabrication rely heavily on the use of complex blends of organics. Notwithstanding the consider- able number of papers published on the subject and the relatively widespread use of such bath chemistries in the industry, the role of the single additives and the reasons underlying the well-document synergistic actions developing among them have not yet been un- ravelled. The organic additives in acid Cu plating baths are commonly categorised as: i carriers, ii brighteners or accelerators, and iii levellers. Carriers and levellers are sometimes denominated suppres- sors, implying the fact that they hinder the deposition rate and con- sequently enhance the electrodeposition overvoltage. Usually, i carriers are polyethylene glycols, ii brighteners are molecules with thiol RSH and disulfide RSSR bonds and sulfonic acid groups, and iii levellers are molecules with amine functionality or aromatic rings. A host of different chemistries has been proposed in the lit- erature, a review of which is beyond the scope of this paper. In a typical bath chemistry, bis-3-sulfopropyl-disulfide Na salt SPS: NAO3SCH23SSCH23SO3Na acts as the accelerator. 1-28 Accelerators are believed to adsorb on the growing Cu surface and to participate in charge transfer; accelerators coad- sorbed with suppressors would thus offer growth sites on the cath- ode surface, otherwise occupied by other additives exhibiting inhib- iting action. 29 Estimates of the total surface coverage with cathode-blocking species have been evaluated on the basis of electrochemical mea- surements in Ref. 9 for baths containing polyethylene glycol PEG, SPS, and Janus Green B JGB; SPS was shown to lower the total cathode coverage. This scavenging action was reported to be positively correlated with the SPS concentration and to be a function of the potential. If SPS is the sole additive, preferential deposition at the peaks of a saw-tooth profile was found, but use of both SPS and JGB brings about higher deposition rates at the valleys. 3 Enhance- ment of the depolarization effect of SPS in recesses has been dem- onstrated in Ref. 18 by systematic use of through-mask cathodes with different aspect ratios. The accelerating effect has been shown to depend on the pres- ence of Cland to be positively correlated with SPS concentration. 18 The use of SPS in the electrodeposition of Cu for ULSI applications

Electrodeposition of Cu from acidic sulphate solutions in presence of Bis-(3-sulphopropyl)-disulphide (SPS)

Abstract This paper deals with the behaviour of bis-(3-sulphopropyl)-disulphide Na salt (SPS) during Cu electrodeposition from an acidic sulphate solution. This investigation was carried out by cyclic voltammetry and in situ Raman spectroelectrochemistry. Parameters describing nucleation, charge transfer kinetics, mass transport effects and anodic stripping behaviour were derived by quantitative analysis of the cyclic voltammograms. SPS effects have been found on nucleation rate, exchange current density and cathodic Tafel slopes. Voltammetry highlighted the cathodic reactivity of SPS. In situ surface enhanced Raman spectroscopy spectra can be measured only at low cathodic polarisations and for limited electrodeposition times. In situ solution Raman spectroscopy was carried out separately on the catholyte, anolyte and undivided cell. Progressive decrease in the S–S vibration could be followed both in the catholyte and in the anolyte. Cathodic formation and further reaction of thiol and the formation of Cu containing complexes in the undivided cell was assessed.

Study on levellers for Cu electrodeposition from acidic sulphate solution: an in situ spectroelectrochemical approach

Abstract This paper deals with a study of the adsorption behaviour of three molecules which can be employed as levellers in Cu electrochemical plating from acidic sulphate solutions: 4cyanopyridine (4CP), 3-diethylamino-7-(4-dimethylaminophenylazo)-5-phenylphenazinium chloride (Janus Green B, JGB) and a benzyl-phenyl modified polyethyleneimine (BPPEI). This investigation was carried out by in situ surface enhanced Raman spectroscopy (SERS) during electroplating and by in situ electroreflectance spectroscopy (ERS) on electrodeposited Cu layers. Variations of SERS effect with potential and potentiostatic polarisation time were studied. Cathodic reactivity of JGB and BPPEI was highlighted by the analysis of spectral changes as a function of applied potential and by time resolved spectroscopy. The formation of surface electronic states related to the formation of chemisorption bonds between the levellers and the Cu electrode was revealed by ERS.