Effect of Corrosion Inhibitor (BTA) in Citric Acid based Slurry on Cu CMP
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Effect of Corrosion Inhibitor (BTA) in Citric Acid based Slurry on Cu CMP In-Kwon Kim, Young-Jae Kang, Yi-Koan Hong, Jin-Goo Park Div. of Materials and Chemical Engineering, Hanyang University, Ansan, 426-791, Korea
ABSTRACT In this study, the effect of BTA on polishing behavior was investigated as functions of H2O2, slurry pH and abrasive particles. The addition of BTA effectively prevented Cu from etching by forming the passivation layer of Cu-BTA regardless of pH and H2O2 concentration in slurry. A thinner passivation layer was grown on Cu in BTA added slurry solutions with a higher contact angle of 60o. The dynamic etch rate, the removal rate with abrasive free slurry, also decreased when BTA was added in slurry at pH 2, 4 and 6. The removal rate of Cu was strongly dependent on types of abrasive particles in slurry. The larger hardness of slurry abrasive particles, the higher removal rates of Cu. The reduction of removal rates in BTA added slurry was determined by the competition between chemical dissolution rate and mechanical abrasion rate. INTRODUCTION Copper has been accepted as an interconnection material in integrated circuits because of its low electric resistivity and high electromigration resistance compared with aluminum [1]. Cu CMP is necessary process for global planarization of the wafers. There are issues of dishing, erosion and corrosion on the pattern wafer after Cu CMP process due to its material nature [2,3]. In order to prevent these defects on the Cu wafers, the BTA (benzotriazole, C6H4N3H) was added as a corrosion inhibitor in the Cu CMP slurries [4,5]. BTA is well known as a corrosion inhibitor of Cu in aqueous media by forming a monolayer of Cu-BTA film on Cu to act as a passivating film [6,7,8,9]. Types and thickness of Cu-BTA passivation film depend on pH and BTA concentration in the solutions [10,11]. At acidic pH (below 2), BTA is not effectively adsorbed on Cu surface. At slightly acidic pH, the initially adsorbed molecules of BTA on Cu surface have to ionize prior to the complex formation and their ionization is obviously a slow process. At slightly alkaline, the concentration of free BTA- ions is relatively high. After being adsorbed, they react immediately with Cu [12]. At highly alkaline pH, BTA begins to desorb from the Cu. The thickness of CuBTA film on Cu changes as a function of pH [11]. However, the effect of BTA adsorption is poorly understood in terms of removal rate and dissolution of Cu. In this study, the effect of BTA on polishing and etching behavior was investigated as a function of H2O2, pH and abrasive particles in slurry solutions. EXPERIMENTS Cu films (1.2 µm thickness) were deposited on barrier layer (Ta films) by electrochemical
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deposition method. Cu wafers were cut into 2.0 × 2.0 cm2 for the measurement of film thickness and contact angle on the wafer. Cu disks (99%, 100mm diameter) were used for etching and polishing experiments. Alumina particles (Degussa, 99.99%, 13 nm) and fumed silica particles (Degussa, 99.99%, 30 nm) were used for the
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