Abstract
The damascene process for fabrication of copper interconnects requires void-free deposition into submicron or vias. Since these trenches and vias are always of high aspect ratio, void-free (or, superfilling) deposition can be realized only when the deposition rate is higher in the bottom of the via than at the entrance. The achievement of void-free deposition requires the use of additives in the plating bath. A conventional solution for copper electroplating contains additives. Among various additives, PEG functions as the suppressor because it can inhibit deposition kinetics, especially when chloride ion is present.In this laboratory, a single additive system was developed based on the characteristics of current-potential response of acid copper sulfate bath containing PEG and chloride ion. The filling experiments were carried out by the acid copper bath containing PEG of different molecular weights in various concentrations. The filling results show that better filling results can be obtained as the molecular weight of PEG increases. Several electrochemical methods have been employed, including chronopotentiometry, linear sweep voltammetry (LSV) and cyclic voltammetry (CV), to study the PEG adsorption and diffusion behavior.Besides the above electrochemical analyses, related properties of the as-deposited copper film have also been measured by the atomic force microscopy (AFM), field emission gun scanning electron microscopy (FEGSEM), and the X-ray diffraction (XRD) methods. The results obtained by AFM and SEM show that both the grain size of Cu deposit and the uniformity of metal distribution decreases as the mol. wt. of PEG increases. From the results of XRD, we find that the ratio of (111-200) orientation in the case of the electrolyte containing PEG3200 is much lower than that containing no additives.