Planarization of copper layer for damascene interconnection by electrochemical polishing in alkali-based solution

Abstract

Recently, electrochemical-mechanical polishing (ECMP) has been suggested as an alternative to the conventional chemical-mechanical polishing process, in order to overcome the difficulties encountered in the latter. In the ECMP process, Cu ions are electrochemically dissolved by applying an anodic potential to the Cu surface in an electrolyte. The dishing effect, however, still exists for wide-width lines even in the case of the ECMP method. In this study, we focus on minimizing the dishing effect and enhancing the uniformity of the within-wafer profile by applying not only electrochemical dissolution to the wafer, but also mechanical force. First, we studied the alkali-based ECMP process. We reduced the dissolution rate of the Cu ions by using KOH-based electrolyte instead of an acidic-based one, and we fundamentally studied the chemical state of the Cu surface according to the concentration of the electrolyte and the anodic potential using X-ray photoelectron spectroscopy analysis. In this way, we monitored the oxidation of the Cu surface by the anodic potential in KOH electrolyte and found that the oxidation rate was increased by adding H2O2. Also, the uniformity of the within-wafer profile was enhanced by using benzotriazole.