This paper overviews the application of multivariate curve resolution (optimized by alternating least squares) to spectroscopic data acquired by monitoring chemical reactions and other processes. The goals of the resolution methods and the principles for understanding their applications are described. Some of the problems arising from these evolving systems and the limitations of the multivariate curve resolution methods are also discussed. This article reviews most of the applications of multivariate curve resolution applied to reacting systems published between January 2000 and June 2007. Some basic papers dated before 2000 have also been included.

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A physicochemical model for the effect of the additives polyethylene glycol ͑PEG͒ and Cl − on Cu 2+ reduction onto a rotating-disk electrode in acidic sulfate solutions has been developed and fit to experimental potential scans to estimate kinetic parameters. The model, which applies to either transient or steady-state conditions, incorporates diffusion, convection, and a reaction mechanism that explicitly includes the effects of both additives. Very good agreement between the fitted model and experimental data is obtained. The model captures the range of voltammogram shapes experimentally observed over a wide range of additive levels ͑i.e., from the gradual loss of Cu 2+ reduction inhibition with increasing overpotential at high PEG and Cl − concentrations to the sudden and complete breakdown of the inhibiting film at a critical potential when intermediate additive levels are used͒. An impedance model has also been derived and solved to generate impedance spectra using the previously obtained kinetic parameters. The predicted impedance spectra show good agreement with measured ones. Key aspects of the reaction mechanism are PEG desorption from the electrode, which occurs due to displacement by depositing copper, and the distinction made between the situations when the electrode is completely and partially covered by the inhibiting film.Polyethylene glycol ͑PEG͒ and chloride ions are commonly added to electroplating baths used in the electrodeposition of copper to improve the filling of trenches and vias in the Damascene processes for microelectronic circuit fabrication. 1-3 These two additives form a complex responsible for the selective inhibition of Cu 2+ reduction in particular regions of these features. There is not universal agreement concerning the structure of the inhibiting complex. Some researchers have presented evidence or interpreted experimental results on the basis that the complex contains PEG, Cl − , and Cu + , 4-8 whereas others have reported data supporting the view that copper is not necessarily a constituent of the complex. 9-11 Two different roles have been attributed to the inhibiting complex during copper electrodeposition: ͑i͒ blockage of sites available for the reduction of Cu 2+ and ͑ii͒ intermediate for the reduction of Cu 2+ . Some researchers have suggested that the inhibiting complex only blocks the substrate and does not participate as an intermediate in Cu 2+ reduction. [12][13][14][15][16] Other researchers have proposed mechanisms by which the complex fulfills both inhibiting and intermediate roles by being continually reformed during cathodic polarization. [17][18][19][20][21] It should be noted that if the second role applies, then Cu + necessarily is a constituent of the inhibiting complex.Numerous studies have been conducted to investigate the effect of PEG and Cl − concentration on the voltammetric response during Cu 2+ reduction. Broadly speaking, the cathodic scans fall into one of three categories, depending on additive concentration: ͑i͒ responses similar to those obs...