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.
Copper 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 (NH4OH)
ConcentrationNH4OH
Ecorr
VSCE
Icorr
mA/cm2
Corrosion 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 NH3 30 g/l NH3
1 minIn solution
60 minIn solutionActive Copper Dissolution
Nitric Acid (HNO3)
Concentration pH Ecorr IcorrCorrosion Rate
%wt HNO3 VSCE mA/cm2 mm/min
0.2 1.78 0.02 0.604 13.3
1 1.19 0.04 1.658 36.6
3 0.9 0.052 4.468 100.45
Active Copper Dissolution
Nitric Acid (HNO3) 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 wt% HNO3
3 wt% HNO3 + 0.02M BTA
neat 3% wt HNO3
3% wt HNO3 + 0.02M BTA upon immersion
3% wt HNO3 + 0.02M BTA after 1hr in solution
B D F
Pote
ntia
l ( V
SCE )
Current ( A/cm2 )
With Inhibitor (BTA) Without Inhibitor (BTA)
Hydrogen Peroxide (H2O2)
Hydrogen Peroxide (H2O2) and Inhibitor (benzotriazole)
a) b)
10-6 10-4 10-2
0.4
0.6
0.8 cba
3% wt H2O
2No Pretreatment
Scan Rate 5mV/s: 3% wt H
2O
2 3% wt H
2O
2 + Buffer pH 4
3% wt H2O
2 + Buffer pH 4 + 10g/l Na
2SO
4
Pote
ntia
l (V
SCE)
Current (A/cm2)
B B B
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
0.81 mV/s
Addition 0.01M BTA plus 3 vol% H2O2
Addition 0.01M BTA
10g/l Na2SO4 (H2SO4 drop) pH 4.2
Cu, Scan rate 1 mV/s, upon immersion
Pote
ntia
l (V
SCE)
Current (A/cm2)
B D F
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 mV/s
files:CV_x(V)
Cu, 10g/l Na2SO
4 (H
2SO
4 drop) + 0.01M BTApH 4.3
Upon immersion, scan rate 1 mV/sDifferent reverse potentials
Reverse potential: 0.7V 0.1V 0.2V 0.35V 0.4V 0.5V
Pote
ntia
l (V
SCE)
Current (A/cm2)
B D01 L02 P035 R04 B
0 1000 2000 3000 4000
0.0
0.1
0.2
0.3
0.4
0.5
Cu, 10g/l Na2SO
4 (H
2SO
4 drop) pH 4.3
addition of H2O
2
Ecor
r (V
SCE)
Time (sec)
B
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 (NH4OH, HNO3 and H2O2) 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/l NH3
2.35 g/l NH3
1 mV/s
2.35 g/l NH3
30 g/l NH3
No pretreatment Upon immertionScan rate 1 mV/s
Current (A/cm2)
Pote
ntia
l (V
SCE)
E C A C
0 1000 2000 3000-0.6
-0.5
-0.4
-0.3
30 g/l NH3
2.35 g/l NH3 2.35 g/l NH
3 30 g/l NH
3
Ecor
r (V
SCE)
Exposure Time (sec)
B B
Potential 0.2V
500 550 600 650 700 7500
10
20
30
40
50
Curre
nt (m
A/c
m2 )
Time (sec)
B
Addison of BTA
Potential 0.2V
500 550 600 650 700 7500
10
20
30
40
50
Curre
nt (m
A/c
m2 )
Time (sec)
B
Addison of BTA
500 550 600 650 700 7500
10
20
30
40
50
Curre
nt (m
A/c
m2 )
Time (sec)
B
Addison of BTAAddition of BTA
Potential 0.1VPotential 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 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.
Figure 2: 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
H2O
2 concentration : 1% wt 3% wt 15% wt
B D F
Pote
ntia
l (V
SCE)
Current (A/cm2)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.
Figure 5: Two fragments of copper surface after one hour exposure at the OCP in 3 vol.% peroxide solution.
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 7: Corrosion potential transient of copper in 10 g/l Na2SO4 and 0.01M BTA solution with addition of 3 vol.% H2O2.
ab
c
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.
Active Copper Dissolution
(a) 0.1V 5min Polished
(b) (c)
(d) (e)
0.3V 5min 0.3V 5min
0.4V 5min 0.4V 5min