Electrochemical Aspects of Copper Chemical Mechanical Planarization (CMP) Esta Abelev , D. Starosvetsky and Y. Ein-Eli. 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. opper Metallization Technology: I) Etching trenches and vias in ILD or low-k dielectric. (II) Deposition of diffusion barrier layer. ILD (b) Si (a) Si ILD (III) Copper deposition: Electroplating or Electroless. (c) ILD Si (IV) Global Planarization of the surface. ILD (d) Si Research objectives: To study and understand the electrochemical behavior and compatibility of copper CMP slurry solutions. Results: Ammonium hydroxide (NH 4 OH) Concentrat ion NH 4 OH E corr V SCE I corr mA/cm 2 Corrosi on Rate nm/min 2.35 g/l 0.315 29.76 1.313 30 g/l 0.509 51.93 2.29 2.35 g/l NH 3 30 g/l NH 3 1 min In solution 60 min In solution Active Copper Dissolution Nitric Acid (HNO 3 ) Concentrat ion pH E corr I corr Corrosi on Rate %wt HNO 3 V SCE mA/cm 2 mm/min 0.2 1.7 8 0.0 2 0.604 13.3 1 1.1 9 0.0 4 1.658 36.6 3 0.9 0.0 52 4.468 100.45 Active Copper Dissolution Nitric Acid (HNO 3 ) and Inhibitor (benzotriazole) N N N Cu N N N Cu Cu 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 0,0 0,1 0,2 3 w t% HNO 3 3 w t% HNO 3 + 0.02M BTA P otential( V SCE ) C urrent( A /cm 2 ) With Inhibitor (BTA) Without Inhibitor (BTA) Hydrogen Peroxide (H 2 O 2 ) Hydrogen Peroxide (H 2 O 2 ) and Inhibitor (benzotriazole) a) b) 10 -6 10 -4 10 -2 0.4 0.6 0.8 c b a Potential(V SC E ) C urrent(A /cm 2 ) 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). 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 0.0 0.2 0.4 0.6 0.8 1 m V/s A ddition 0.01M B TA plus 3 vol% H 2 O 2 A ddition 0.01M BTA 10g/lN a 2 SO 4 (H 2 SO 4 drop) pH 4.2 Potential(V SCE ) C urrent(A /cm 2 ) 10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 0.0 0.2 0.4 0.6 1 m V/s R everse potential: 0.7V 0.1V 0.2V 0.35V 0.4V 0.5V Potential(V SCE ) C urrent(A /cm 2 ) 0 1000 2000 3000 4000 0.0 0.1 0.2 0.3 0.4 0.5 addition of H 2 O 2 E corr(V SCE ) Tim e (sec) 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). Conclusions • All the proposed slurries (NH 4 OH, HNO 3 and H 2 O 2 ) do not provide the conditions required for conventional CMP: Copper is actively dissolved with a relatively high dissolution rate. • 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. • The use of oxidizers such as peroxide is not effective in conjugation with inhibitors. -0.6 -0.4 -0.2 0.0 0.2 0.4 10 -5 10 -4 10 -3 30 g/lN H 3 2.35 g/lN H 3 C urrent(A /cm 2 ) Potential(V SC E ) 0 1000 2000 3000 -0.6 -0.5 -0.4 -0.3 30 g/lN H 3 2.35 g/lN H 3 Ecorr(V SCE ) E xposure T im e (sec) Potential 0.2V 500 550 600 650 700 750 0 10 20 30 40 50 Current(m A /cm 2 ) Tim e (sec) A ddison ofBTA Potential 0.2V 500 550 600 650 700 750 0 10 20 30 40 50 Current(m A /cm 2 ) Tim e (sec) A ddison ofBTA 500 550 600 650 700 750 0 10 20 30 40 50 Current(m A /cm 2 ) Tim e (sec) A ddison ofBTA Addition of BTA Potential 0.1V Potential 0.1V Addition of BTA Corrosion & Applied Electrochemistry Laboratory (CAEL) Department of Materials Engineering, Technion, Haifa 32000, Israel. Figure 1: a) Corrosion potential transient of copper in 2.35 g/l (●) and 30 g/l NH 3 g/l (○) solutions at 25 °C, b) Polarization curves of copper electrodes obtained in 2.35 g/l (●) and 30 g/l (○) NH 3 at scan rate of 1 mV/s. : a), b) SEM micrographs obtained after one hour exposure at OCP in 3 vol.% nitric acid solution. a) b) a) b) 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). 10 -7 10 -6 10 -5 0.3 0.4 0.5 0.6 15 vol.% 3 1 Potential(V SCE ) C urrent(A /cm 2 ) 4: Anodic potentiodynamic curves of copper obtained immediately mmersion in 1, 3, and 15 vol % peroxide solutions at a scan rate of 1 mV/s. 5: Two fragments of copper surface after one hour exposure at the OCP in 3 vol.% de solution. Figure 8: Potentiodynamic profiles (scan rate of 1 mV/s) of copper electrode immersed in three solutions; [a] solutions of Na 2 SO 4 peroxide-free; [b] Na 2 SO 4 with the addition of 0.01M BTA; [c] Na 2 SO 4 solution containing both BTA (0.01M) and peroxide 3% (vol). Figure 7: Corrosion potential transient of copper in 10 g/l Na 2 SO 4 and 0.01M BTA solution with addition of 3 vol.% H 2 O 2 . a b c Figure 10: Potentiodynamic profiles (scan rate of 1 mV/s) of copper electrode immersed in solution containing Na 2 SO 4 and 0.01M BTA. Copper electrode potential was swept back at potentials ranging between 0.1-0.7 V. Active Copper Dissolution (a) 0.1V 5m in Polished (b) (c) (d) (e) 0.3V 5m in 0.3V 5m in 0.4V 5m in 0.4V 5m in