Transcript No Slide Title

Introduction.
During the last decade the interest in copper
passivity significantly increased due to the
important role of copper in microelectronic
industry. In resent years copper is being evaluated
as a replacement for aluminum in integrated
circuit interconnects.
Objectives :
• To study copper passivity in alkaline solutions composed of
sodium/potassium sulfate and potassium sorbate.
• To identify the copper repassivation rate in pottasium sorbate
based solutions.
• To investigate the impact of the fatty acid chain length on the
electrochemical behavior of copper.
1 gr/l
SO4 Pottasium
Sorbate,on
scan
1 mV/s
The effect
of KPotassium
Sorbate
Curate
I-V
profile
2
in solutions containing 1 g/l K2SO4
What is Potassium Sorbate?
Potential (VSCE)
0.8
Experimental:
One of the main steps in copper technology is
chemical mechanical planarization (CMP).
Determination of CMP slurry chemical
composition, which could provide rapid and
strong copper passivity, is an important issue for
an efficient CMP. None of Cu CMP commercial
slurries fulfills the requirement for rapid
passivation.
• Electrochemical characteristics of copper was performed in a
three electrode electrochemical cell equipped with Pt counter
electrode and saturated calomel reference electrode.
• The measurements of repassivation rate were conducted on
slurryjet instrument in Max-Plank institute for Iron in
Dusseldorf, Germany.
4
4 g/l K2CO3 + 1g/l Na2SO4, pH=12.6
B
D
F
H
###
###
###
+1gr/l K2CO3
0.2
0.8
Scan rate: 1 mV/s
0.0
-0.2
-5
-4
-3
10
D
2
2
10
5
0
Current (A/cm )
Current (A/cm )
2
Current (A/cm )
200
200
10
0
1000
2000
Time (sec)
3000
Without scratching
0.4
0.2
0.8
0.4
4gr/l
0.2
0.0
-7
0.0
0.6
b
G4
4gr/lG1K2CO3, pH 12.9, =6.82 mS
Positive scan
Backscan at:
0.30 V
1.02 V
0.4
0.2
0.0
-0.2
10
10
-6
10
-5
-4
-3
10
10
10
2
Current (A/cm )
-6
-5
-4
10
10
102
Current (A/cm )
-3
10
-7
10
-6
-5
-4
10
10
10
2
Current (A/cm )
-3
10
-2
10
The reverse scan indicates that at potential
range between-0.1 V and 0.8 V, a protective
layer is formed at the copper surface. At
potentials above 0.8 V, a breakdown of the
protective layer occurs and a further increase
in the anodic currents indicates that copper is
actively dissolved.
AFM images of copper surface exposed at OCP
(-0.15 V) in K2CO3 solution.
Anodic currents obtained from copper in 1
gr/l K2CO3 solution are less than 10-5 A/cm2.
Such low anodic currents can be attributed to
the formation of a protective layer on the
copper surface. Figure b presents reverse
scan at different potentials, indicating the
strong protective characteristics of the formed
layer.
AFM images of copper surface exposed at 0.2V
in K2CO3 solution.
B
Cu, 4 g/l Ka2CO3. Applied Potential -0.2V
2
0
3340
3360 3380
Time (sec)
Upon immersion
5 min. exposure
Upon immersion
0
0.8
0.6
1gr/l
1.0
a
-0.2
6
5
0
G
E
C
A
[K2CO3] (g/l) , pH,  (mS))
1
, 12.5 , 1.88
4
, 12.9 , 6.82
B
Cu, 4 g/l Ka42CO3. Applied Potential -0.2V
250
Positive scan
Back scan at:
2
0.01 A/cm
2
0.001 A/cm
2
0.0001 A/cm
-7
Potentiostatic behavior of copper in
K2CO3 solution.
250
10
-4
10
-3
10
-2
D
B
A
1.0
1.0
4g/l K2CO3 + [KMnO4]
0.8
0.8
0.6
0.4
+1gr/l KMnO4
0.2
+0.05gr/l KMnO4
0.0
Upon imersion
4g/l K2CO3+0.05g/l KMnO7
0.6
KMnO4, g/l:
0.00
0.05
1.00
0.4
Mn1
Mn001
Mn0
0.2
4g/l K CO
name: 1glK2SO4+Diff.Conc.PotSorbate_Pd
-0.2
-7
10
2
3
1 mV/s
-6
-5
-4
10
10
10
2
Current (A/cm )
-3
10
1 mV/s
-2
10
0.0 -7
10
-6
-5
-4
10
10
10
2
Current (A/cm )
1000
2000
Time (sec)
5 min. exposure
3000
Periodically scratched (scriber)
surface
Sharp decrease of anodic current was obtained after
applying +0.2 V. This indicates high rate of copper
passivity K2CO3 solution. High rate of copper
surface re-passivation was observed at periodically
scratched surface.
30 min. exposure
60 min. exposure
30 min. exposure
60 min. exposure
-3
10
-0.2
Breakdown potential of copper in solutions with
K2CO3 concentration above 1 gr/l is ~0.6 V. The
values of anodic currents remained less than 10-5
A/cm2 in wide range of potential.
300
10
-5
-2
10
10
10
2
Current (A/cm )
300
0.6
1.0
Potential (VSCE)
2
1.0
+4gr/l
-6
10
-6
Potentiodynamic behavior of copper in solutions
containing K2CO3 and KMnO4 as a oxidizer.
The effect of K2CO3 on Cu I-V profile
Potential (VSCE)
3
+2gr/l
10
10
-7
Potential (VSCE)
The effect of reverse scan on Cu I-V
profile in 1 gr/l Na2SO4 solution containing
[K CO ] + 1g/l Na SO , pH
4gr/l K2CO3 (pH 12.6)
1gr/l, 12.1
Potential (VSCE)
0.4
10
-8
Increase in potassium sorbate concentration enhances
copper passivity breakdown potential in solutions
containing 1 gr/l Na2SO4 solution. The values of anodic
currents remained less than 10-5 A/cm2 in a wide range of
potential.
2gr/l, 12.4
3gr/l, 12.5
4gr/l, 12.6
+3gr/l
-9
2
[K2CO3] + 1g/l Na2SO4
pH 12.1-12.6
0.6
0.2
Current (A/cm )
Potential (VSCE)
Potential (VSCE)
0.8
0.4
10
2
1.0
0.6
With Potassium Sorbate:
4 g/l (pH 8.2)
10 g/l (pH 9.0)
50 g/l (pH 10)
0.0
The main task of our research is to determine the
parameters controlling copper passivity, such as
chemical composition of slurry, pH range and the
potential region of Cu passivity, which an efficient
CMP can be achieved.
The effect of K2CO3 on Cu I-V profile of
in solutions containing 1 g/l Na2SO4
1 g/l K2SO4(pH 6)
The addition of KMnO4 increases the OCP
potential of copper in 4 gr/l K2CO3 solution.
Increase in KMnO4 concentration shifts the onset
of anodic current to more positive potentials. The
reverse scan indicates high protection
characteristics of the layer which is being formed
on copper.
Conclusions
1. The use of basic solution such as alkaline
and carbonate based slurries can provide
full a passivity to copper surface.
2. The use of carbonate solution with the
addition of oxidizer allows rapid formation
of a compact and thin passive layer.
3. The passive film formed in carbonate
based solution is stable in a wide range of
potential (between -0.15 and 1.00 V).
4. Electrochemical tools in conjugation with
in-situ AFM provide a complete
understanding of copper passivity.