Role of Molecular Structure of Complexing/Chelating Agents in Copper CMP Slurries
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Role of Molecular Structure of Complexing/Chelating Agents in Copper CMP Slurries Udaya B. Patri, S. Pandija and S.V. Babu Department of Chemical Engineering, Center for Advanced Materials Processing, Clarkson University, Potsdam, NY 13699 ABSTRACT The role of the molecular structure - different functional groups, the length of the carbon chain and the relative positions of different functional groups – of several complexing/chelating agents (acetic acid, glycine, ethylene diamine, succinic acid, alanine and amino butyric acid (ABA)) in controlling copper (Cu) removal rates was investigated. The results are consistent with the known activity of –COOH groups at acidic conditions and that of –NH2 groups in an alkaline environment. In comparison with glycine, it was also observed that an increase in the carbon chain length increased the removal rates at acidic pH values and decreased the removal rates at alkaline pH values. Also, Cu removal rates decreased with an increase in the distance between the –NH2 and –COOH groups in an amino acid at all pH values except at 4. INTRODUCTION Chemical mechanical planarization (CMP) is widely used to planarize metal and dielectric films during integrated circuit fabrication [1, 2]. With the introduction of low-k dielectric materials, integration of Cu/low-k dielectrics has become a challenge due to the weak mechanical properties of the low-k materials. In order to overcome this problem, Cu CMP needs to be performed at low pressures. If throughput is not to be sacrificed, this requires increasing the chemical activity of the CMP slurries. A better understanding of the roles of various chemicals used in typical Cu CMP slurries along with the search for novel chemicals is helpful to achieve this goal. Typically Cu CMP slurries are composed of an oxidizer, the most preferred one being hydrogen peroxide (H2O2), a corrosion inhibitor like benzotriazole (BTA), a complexing/chelating agent, and other additives along with abrasives like silica or alumina. Glycine [3-10], citric acid [7, 9, 11, 12], ethylene diamine [13], ethylene diamine tetra acetic acid [14], etc., are some of the many complexing/chelating agents that have been investigated in Cu CMP slurries. However, there has been no definitive elucidation of the role of the molecular structure of the complexing agents - different functional groups (eg: -NH2 vs. -COOH), their relative positions, the length of the carbon chain, etc., - in controlling the material removal rates. Recent work from our group [8-10] on the role of complexing agents showed that –COOH groups are active under acidic conditions whereas –NH2 groups are more active in an alkaline environment. In continuation of that study, several complexing agents containing amine and/or carboxyl groups (acetic acid, succinic acid, ethylene diamine, glycine, alanine, amino butyric acid) have been studied in this present work to understand better the role of the molecular structure in determining Cu removal rates. EXPERIMENTAL DETAILS Cu disks (99.99%), 3 mm thick and 1.2
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