# Electolytically Ionized Abrasive-Free CMP (EAF-CMP) for Copper
## 1 Introduction  
Chemical-mechanical polishing (CMP) is a semiconductor manufacturing process applied to planarize highly integrated devices [1; 2; 3]. It uses both chemical reactions and mechanical material removal to planarize the surface of a semiconductor. Recently, the importance of CMP has been increasing with the rise of integration and diversity of devices. Copper (Cu) wires, which are widely used in semiconductor devices, are manufactured using a damascene technique that uses CMP [4; 5; 6]. The material removal in Cu CMP is known to be mostly affected by chemical reactions rather than mechanical material removal using abrasive particles [7; 8]. A Cu CMP slurry contains abrasives, oxidizers, complexing agents, and corrosion inhibitors, which react chemically with Cu to create a chemically reacted layer on the surface of the Cu [9; 10]. In a Cu CMP slurry, the oxidizer creates Cu ions by oxidizing the Cu surface [11; 12]. The Cu ions combine with the complexing agent to form a Cu complex [13; 14; 15]. Corrosion inhibitors reduce the corrosion reaction in the trench at the wafer pattern, enabling global and local planarization [16; 17; 18]. Many researchers have studied the chemical composition of Cu CMP slurries from a chemical reaction perspective. Hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) is commonly used as an oxidizer in Cu CMP because of its high oxidization capability [19]. H\({}_{2}\)O\({}_{2}\) generates Cu ions from the Cu surface via oxidation. [PERSON] et al. [20] proposed citric acid (C\({}_{6}\)H\({}_{8}\)O\({}_{7}\)) as a complexing agent in H\({}_{2}\)O\({}_{2}\)-based Cu CMP slurry. Citric acid is also widely used for post-Cu CMP cleaning. Complexing agents, including citric acid, are known to combine with Cu ions generated by oxidizers to prevent Cu ions from being re-absorbed into the Cu surface or produce a Cu complex layer on the surface of the Cu. [PERSON] et al. [21] reportedthat the wear resistance of the Cu complex layer, generated by citric acid and H\({}_{2}\)O\({}_{2}\) in Cu CMP, decreased as the citric acid concentration increased, making it easier to remove mechanically. Benzotriazole (BTA) is the most common corrosion inhibitor in Cu CMP [22] techniques. The addition of BTA to the CMP slurry formed a Cu-BTA complex layer to prevent excessive dissolution of the copper [23]. The abrasive serves to mechanically remove material from the interface of the wafer and the polishing pad, ensuring a high material removal rate (MRR) during CMP [24; 25]. The common abrasives for Cu CMP are silica (SiO\({}_{2}\)) and alumina (Al\({}_{2}\)O\({}_{3}\)), and many researchers have studied Cu CMP results based on abrasive characteristics. [PERSON] et al. [26] investigated the influence of abrasive size in Cu CMP. They stated that in a Cu CMP slurry, if the particle size is small, then the particle concentration should be high. [PERSON] et al. [27] studied the frictional behavior during Cu CMP by understanding the particle adhesion characteristics. They expressed that in a Cu CMP slurry, silica particles have a higher adhesion force, a higher friction force, and a higher MRR with Cu compared to alumina particles. According to [PERSON] et al. [24], the friction force tends to increase as the colloidal silica concentration increases. High particle concentrations have been reported to help increase the MRR in CMP. However, abrasive particles can also be a scratch-inducing source instead of guaranteeing a high MRR [28]. In particular, a high particle concentration and agglomerated particles are the main factors that cause scratches during CMP. For this reason, several researchers have proposed the study of an abrasive-free CMP solution. [PERSON] et al. [29] proposed an abrasive-free solution for Cu CMP using oxalic acid (C\({}_{2}\)H\({}_{2}\)O\({}_{4}\)) and H\({}_{2}\)O\({}_{2}\). The adjustment of H\({}_{2}\)O\({}_{2}\) concentration is efficient in controlling the MRR of Cu removed with an abrasive-free CMP (AF-CMP) solution. They observed the MRR to be the highest when the solution's pH was 3.