Electrochemical Aspects of Copper Chemical Mechanical Planarization (CMP )

1. Cu Addition of BTA Cu N N N N Potential 0.1V N N Cu a) b) Addition of BTA Potential 0.1V Electrochemical Aspects of Copper Chemical Mechanical Planarization (CMP) Esta Abelev, D. Starosvetsky and Y. Ein-Eli. Corrosion & Applied Electrochemistry Laboratory (CAEL) Department of Materials Engineering, Technion, Haifa 32000, Israel. Introduction: Copper is used as a replacement of aluminum in integrated circuit interconnections. The advantages of copper interconnectors are based on two important properties of copper; higher electric conductivity and stronger electromigration resistance. Copper Metallization Technology: (II) Deposition of diffusion barrier layer. (I) Etching trenches and vias in ILD or low-k dielectric. (III) Copper deposition: Electroplating or Electroless. • Global Planarization • of the surface. Planarization is an important technological step in copper metallization. This research work is focused on problems associated with copper planarization technique-Chemical Mechanical Planarization (CMP). Research objectives: Tostudy and understand the electrochemical behavior and compatibilityof copper CMP slurry solutions. Results: Ammonium hydroxide (NH4OH) 30 g/l NH3 2.35 g/l NH3 b) a) 1 min In solution 60 min In solution Active Copper Dissolution Figure 1: a) Corrosion potential transient of copper in 2.35 g/l (●) and 30 g/l NH3 g/l (○) solutions at 25 °C, b) Polarization curves of copper electrodes obtained in 2.35 g/l (●) and 30 g/l (○) NH3 at scan rate of 1 mV/s. Nitric Acid (HNO3) Nitric Acid (HNO3) and Inhibitor (benzotriazole) Figure 3: a) Anodic potentiodynamic curves (scan rate 1 mV/sec) of copper in 3 vol.% nitric acid without (●) and with (○) 0.02 M BTA, b) Anodic current transient of copper measured in 3 vol.% nitric acid containing 0.02 M BTA (at applied voltage of 0.1 V). With Inhibitor (BTA) Without Inhibitor (BTA) a) b) Active Copper Dissolution Figure 2: a), b) SEM micrographs obtained after one hour exposure at OCP in 3 vol.% nitric acid solution. Hydrogen Peroxide (H2O2) Hydrogen Peroxide (H2O2) and Inhibitor (benzotriazole) c b a Figure 7: Corrosion potential transient of copper in 10 g/l Na2SO4 and 0.01M BTA solution with addition of 3 vol.% H2O2. Figure 8: Potentiodynamic profiles (scan rate of 1 mV/s) of copper electrode immersed in three solutions; [a] solutions of Na2SO4 peroxide-free; [b] Na2SO4 with the addition of 0.01M BTA; [c] Na2SO4 solution containing both BTA (0.01M) and peroxide 3% (vol). Figure 4: Anodic potentiodynamic curves of copper obtained immediately upon immersion in 1, 3, and 15 vol % peroxide solutions at a scan rate of 1 mV/s. Conclusions • All the proposed slurries (NH4OH, HNO3 and H2O2) do not provide the conditions required for conventional CMP: •  Copper is actively dissolved with a relatively high • dissolution rate. Figure 5: Two fragments of copper surface after one hour exposure at the OCP in 3 vol.% peroxide solution. • The active dissolution of Cu proceeds non-uniformly, with deep intergranular penetration. This may lead to a damage of the thin Cu layer, resulting in severe dents and fractures in the copper interconnects. • Copper protection with the use of inhibitors is not effective for CMP processes, [which continue only for a period of 2 minutes], under rapid surface abrading. Figure 10: Potentiodynamic profiles (scan rate of 1 mV/s) of copper electrode immersed in solution containing Na2SO4 and 0.01M BTA. Copper electrode potential was swept back at potentials ranging between 0.1-0.7 V. • The use of oxidizers such as peroxide is not effective in conjugation with inhibitors. Active Copper Dissolution Figure 6: Anodic potentiodynamic curves (Scan rate of 1 mV/s) of copper immersed in 3 vol% peroxide Solutions with and without the addition of buffer and Na2(SO4) additives: (a) without additives; (b) with 5 ml addition of buffer (pH 4); (c) with buffer and 10 g/l Na2SO4 (pH 4).