Surface Adsorption of PEG and Cl[sup −] Additives for Copper Damascene Electrodeposition

Abstract

Copper plate was observed by atomic force microscopy ͑AFM͒ after it was immersed in acid electrolyte with polyethylene glycol ͑PEG͒ and chloride ions (Cl Ϫ ). The AFM image confirmed the existence of adsorbed particles, which are in a flat-cone shape with a bottom radius of 15-25 nm and a height of 2-4 nm. The intermediate complex of copper dissolution/deposition was investigated by means of an electrochemical quartz crystal microbalance through detecting the simultaneous mass change of the electrode during cyclic voltammetric ͑CV͒ measurement. The two current peaks in the CV curves illustrate the generation and consumption of intermediate complex Cu ϩ • Cl Ϫ • PEG on the copper electrode.Nanoscale electrodeposition technologies have been applied to on-chip metallization in recent years. 1-4 As the most promising technology, copper damascene electrodeposition has received growing interest because of reduction in signal delay. In this damascene electrodeposition, a suitable combination of bath additives, e.g., polyethylene glycol ͑PEG͒, Cl Ϫ , bis͑3-sulfopropyl disulfide͒ ͑SPS͒, and Janus green B ͑JGB͒, is required for successful via filling. PEG, together with Cl Ϫ , inhibits the Cu deposition; however, the morphology and potential dependency of the intermediate complex is not known in detail.Regarding the study of the mechanism by which PEG affects damascene plating, Yokoi et al. 5 suggested that PEG traps Cu ϩ on the surface to form an adsorbed inhibiting film. The change of surface concentration of Cu ϩ with potential caused the potential dependency of PEG adsorption, while a Cu ϩ • Cl Ϫ • PEG model was proposed to illustrate how the existence of Cl Ϫ widens the potential region of PEG adsorption. To clarify the morphology of this adsorbed film, many efforts have been made. A Raman spectroscopic study 6 showed that the adsorption of PEG is likely to be in two different forms depending on the potential of the electrode. The investigation of J. J. Kelly et al. indicated that Cl Ϫ ions induce the adsorption of PEG to form a monolayer of spherically packed PEG molecules. 7,8 Field-effect scanning electron microscopy ͑FESEM͒ images reported by Kondo et al. 9,10 showed that particles around 30 nm in diam adsorbed on Cu after it was dipped in an electrodeposition bath containing PEG and Cl Ϫ , and the quantity of the adsorbent increased with the dipping time. Recently, Doblhofer et al. 11 investigated the influence of the inhibiting film on Cu/CuCl/Cu 2ϩ reactions. However, they considered that the inhibiting film forms at the moment that the sample was put into the solution, and no changes of the amount of PEG adsorption with potential and time were considered. In this work, AFM was adopted to further examine the morphology of the intermediate.

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

“…This result, however, does not necessarily contradict the present work as the sample analyzed in Ref. 25 was plated at 5 mA cm -2 in a solution with a lower concentration of CuSO 4 . As it is shown in this study, the plating condition could influence the incorporation of PEG + Cl -complex, even in the same solution.…”

“…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.…”

Copper electrocrystallization from acidic sulfate electrolyte containing MPS additive

“…Copper has been widely used as silicon chip interconnect material [1][2][3][4][5][6][7][8][9][10][11][12][13], and for on-chip metallization, damascene is a key technique. In the damascene process, trench and via cavities are first fabricated into a dielectric layer on the wafer.…”

“…To realize void-free electrodeposits, metal electroplating inside high aspect ratio trenches should preferentially occurs at the bottom of trenches. This process, usually called ''superfilling'' or ''superconformal,'' depends largely on the use of complex blends of additives in electrolytes [1][2][3][4][5][6][7][8][9][10][11][12][13]. A typical copper superfilling electrolyte consists of copper sulfate in an aqueous sulfuric acid solution, with the addition of combined additives.…”

“…Accelerators are typically sulfur-based organic molecules, such as 3-mercapto-1-propanesulfonate sodium salt (MPS) [2], which are also called 3-mercapto-1-propanesulfonic acid in some literatures [3][4][5][6], and bis-(3-sodiumsulfopropyl disulfide [6][7][8] (SPS). Typical suppressors are polyethers, such as polyethylene glycol (PEG) [7,[9][10][11][12] and polypropylene glycol [2]. For the leveling agents, thiourea, benzotriazole, and Janus Green B are often used [2,7].…”