Transcript Slide 1

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.
ILD
(a)
(III) Copper deposition: Electroplating
or Electroless.
ILD
(b)
Si
(IV) Global Planarization
of the surface.
ILD
(c)
Si
ILD
(d)
Si
Si
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: To study and understand the electrochemical behavior and compatibility of copper CMP slurry solutions.
Results:
Ammonium hydroxide (NH4OH)
a)
-0.4
30 g/l NH3
-0.5
Potential (VSCE)
2.35 g/l NH3
-0.3
Ecorr (VSCE)
0.4
b)
2.35 g/l NH3
2.35 g/l NH3
30 g/l NH3
0.2
Ecorr
VSCE
2.35 g/l
-0.315
30 g/l
-0.509
0.0
-0.2
-0.4
-0.6
Concentration
NH4OH
30 g/l NH3
2.35 g/l NH3
E
C
A
C
B
B
Icorr
Corrosion
2 NH Rate
2.35 g/l
mA/cm
3
30 g/l NHnm/min
3
1 mV/s
29.76
1.313
51.93
2.29
No pretreatment
Upon immertion
Scan rate 1 mV/s
1 min
In solution
30 g/l NH3
-0.6
0
-5
1000
2000
3000
Exposure Time (sec)
-4
10
60 min
In solution
-3
10
10
2
Current (A/cm )
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)
Icorr
VSCE mA/cm2
%wt HNO3
0.2
1.78
1
1.19
3
0.9
0.02
0.04
0.052
4.468
Additionof
of BTA
Addison
BTA
Addition of BTA
40
13.3
1.658
3 wt% HNO3 + 0.02M BTA
0,2
mm/min
0.604
50
36.6
100.45
Current (mA/cm )
Ecorr
B
D
F
neat 3% wt HNO3
3% wt HNO3 + 0.02M BTA upon immersion
3% wt HNO3 + 0.02M BTA after 1hr in solution
2
pH
Corrosio
n Rate
Potential ( VSCE )
Concentration
Nitric Acid (HNO3) and Inhibitor (benzotriazole)
0,1
3 wt% HNO3
0,0
30
20
10
Potential
0.2V
Potential
0.1V
Potential 0.1V
10
-7
-6
-5
-4
-3
10 10 10 10
2
Current ( A/cm )
10
0
500
-2
550
600
650
Time (sec)
700
750
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)
a)
Without Inhibitor (BTA)
b)
Figure 2: a), b) SEM micrographs obtained after one hour exposure at OCP in 3 vol.% nitric acid solution.
Active Copper Dissolution
Cu, Scan rate(benzotriazole)
1 mV/s, upon immersion
Hydrogen
Peroxide
Cu, 10g/l Na
SO (H SO drop) pH(H
4.3 2O2) and Inhibitor
Hydrogen Peroxide (H2O2)
0.8
0.5 addition of H2O2
3
0.2
Addition 0.01M BTA plus 3 vol% H2O2
0.2
10
10
2
Current (A/cm )
-5
0
a)
3% wt H2O2
Figure 5: Two fragments of copper surface after one hour exposure at the OCP in 3 vol.%
No Pretreatment
peroxide solution.
b
c
2000
3000
4000
B
B
B
a
10
-8
10
-7
10
-6
10
10
0.4
10
10
-7
10
-6
1 mV/s
10
-5
10
-4
10
-3
10
-4
10
-3
10
-2
10
10
2
Current (A/cm )
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).
(d)
0.4V 5min
(e)
0.4V 5min
-2
10
• 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.
-2
Current (A/cm )
-4
10
• All the
slurries (NH4OH, HNO3 and H2O2) do not
provide the conditions required for conventional CMP:
 Copper is actively dissolved with a relatively high
dissolution rate.
2
-6
-5
Conclusions
0.2
-8
0.3V 5min
10g/l Na2SO4 (H2SO4 drop) pH 4.2
Reverse potential:
0.7V
0.6
0.1V
0.2V
0.35V
0.4
0.4V
0.5V
-9
(c)
B
D01
L02
P035
R04
B
proposed
Scan Rate 5mV/s:
3% wt H2O2
3% wt H2O2 + Buffer pH 4
3% wt H2O20.0
+ Buffer pH 4 + 10g/l Na2SO4
0.6
0.3V 5min
b
2
Time (sec)
Current (A/cm )
Figure 7: CorrosionCu,
potential
transient
of copper
in drop) + 0.01M BTApH 4.3
10g/l
Na2SO
(H
SO
Figure 8: Potentiodynamic profiles (scan rate of 1 mV/s) of copper
4
2
4
10 g/l Na2SO4 and 0.01M BTA solution with addition
electrode immersed in three solutions; [a] solutions of Na2SO4 peroxide-free;
of 3 vol.% H2O2. Upon immersion, scan rate 1 mV/s
Na2SO4 with the addition of 0.01M BTA; [c] Na2SO4 solution containing
Different reverse potentials [b]
both BTA (0.01M) and peroxide 3% (vol).
b)
a
1000
(b)
Addition 0.01M BTA
0.0
-6
0.8
c
0.4
0.0
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.
Potential (VSCE)
0.6
Potential (VSCE)
0.3
B
D
F
1 mV/s
0.1
1
10
4
Potential (VSCE)
15 vol.%
-7
2
H2O2 concentration :
0.4
1% wt
3% wt
0.3
15% wt
0.5
0.4
4
0.1V 5min
B
B
D
F
Ecorr (VSCE)
Potential (VSCE)
0.6
2
(a)
Polished
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.
files:CV_x(V)
Active Copper Dissolution
• 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.