NaNO3 전해액을 사용한 Copper 부동태층의 전기적 특성에 관한 연구

Abstract

Chemical-mechanical polishing (CMP) is the most commonly used planarization technique in the semiconductor process for ultra-large scale integrated circuit (ULSI) applications. As its name indicates, the CMP process depends on the chemical interaction of the slurry with the polishing wafer and the mechanical down force applied to the wafer. During recent year, the application of CMP has been particularly popular in the fabrication of Cu damascene structures. However, low-dielectric-constant (low-k) materials at 65 nm and below device structures, because of their fragility, require low down-force mechanical polishing to maintain the structural integrity of the underlayer during their fabrication. According to certain recently published reports, it might be possible to achieve low down-pressure polishing of Cu by incorporating voltage-activated electrochemical reactions in the CMP process. This new approach is referred to as electrochemical-mechanical polishing (ECMP). Sato et al. Proposed the ECMP process based on the electrochemical dissolution of Cu, and reported that it could be used to form erosion-free and scratch-free damascene Cu interconnects at a pressure ten times lower than that used for conventional CMP technology. Goonetilleke and Roy studied the chemical effect of additives in a peroxide-based glycine solution by using cyclic voltammetry. Lee et al. characterized electrochemical active, passive, transient, and trans-passive states from the current-voltage (I-V) curve in order to evaluate the optimal process parameters (operating voltage, current density, concentration of electrolyte, operating times, etc.) for the ECMP applications. The purpose of our present study is to focus an certain fundamental aspects of ECMP of Cu. The step of material removal in ECMP is based on the utilization of voltage-activated electrochemical reactions. This voltage is designed to control the anodic dissolution of the surface layer of the working electrode in the form of Cu2+ or Cu+ ions and/or as soluble complexes formed with one or more chemical solution in the electrolyte. In this approach, we can selectively probe the voltage-activated (not mechanically-induced) processes and examine the relative roles of the concentration and the operating voltage used in NaNO3 electrolytes. First, the I-V curves were employed to evaluate the effect of electrolyte concentration on the electrochemical surface reaction of the Cu electrode. From this I-V curve, the electrochemical active, passive and trans-passive states could be characterized. Second, we fundamentally studied the chemical state and the element composition of the Cu surface for variations in the concentration of the electrolyte and the potential by using X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Finally, in this way, we monitored the oxidation and the reduction processes of the Cu surface caused by repetitions of the anodic and the cathodic potential in a NaNO3 electrolyte.