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.

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.

The main task of our research is to determine theparameters 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.

AFM images of copper surface exposed at 0.2V in K2CO3 solution.

AFM images of copper surface exposed at OCP (-0.15 V) in K2CO3 solution. Conclusions

Upon immersion 5 min. exposure

30 min. exposure 60 min. exposure

Upon immersion 5 min. exposure

30 min. exposure 60 min. exposure

0 1000 2000 30000

5

10

200

250

300

Cur

rent

(A

/cm

2 )

Cu, 4 g/l Ka2CO

3. Applied Potential -0.2V

Time (sec)

D

0 1000 2000 30000

5

10

200

250

300

3340 3360 33800

2

4

6

Cur

rent

(A

/cm

2 )

Time (sec)

B

Cu, 4 g/l Ka2CO

3. Applied Potential -0.2V

Cur

rent

(A

/cm

2 )

Time (sec)

B

Without scratching Periodically scratched (scriber) surface

Potentiostatic behavior of copper in K2CO3 solution.

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.

Potentiodynamic behavior of copper in solutions containing K2CO3 and KMnO4 as a oxidizer.

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

10-7 10-6 10-5 10-4 10-3 10-2

4g/l K2CO

3

+1gr/l KMnO4

+0.05gr/l KMnO4

Upon imersion4g/l K2CO

3 + [KMnO

4]

KMnO4, g/l:

0.00 0.05 1.00

Current (A/cm2)

Pot

entia

l (V

SC

E)

Mn1 Mn001 Mn0

0.0

0.2

0.4

0.6

0.8

1.0

10-7 10-6 10-5 10-4 10-3

4g/l K2CO3+0.05g/l KMnO7

4g/l K2CO

3+0.05g/l KMnO

7

Current (A/cm2)

Pot

entia

l (V

SC

E)

Mn005

1 mV/s 1 mV/s

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.

What is Potassium Sorbate?

The effect of Potassium Sorbate on Cu I-V profile in solutions containing 1 g/l K2SO4

The effect of K2CO3 on Cu I-V profile of in solutions containing 1 g/l Na2SO4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

10-7 10-6 10-5 10-4 10-3 10-2

4 g/l K2CO

3 + 1g/l Na

2SO

4, pH=12.6

Positive scanBack scan at:

0.01 A/cm2

0.001 A/cm2

0.0001 A/cm2

Current (A/cm2)

Pote

ntia

l (V S

CE)

G E C A

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

10-7 10-6 10-5 10-4 10-3

4gr/l1gr/l

[K2CO

3] (g/l) , pH, (mS))

1 , 12.5 , 1.88 4 , 12.9 , 6.82

Current (A/cm2)

Pot

entia

l (V

SC

E)

G4 G1

The effect of K2CO3 on Cu I-V profile

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

10-7 10-6 10-5 10-4 10-3

Positive scanBackscan at:

0.30 V 1.02 V

4gr/l K2CO

3, pH 12.9, =6.82 mS

Current (A/cm2)

Pot

entia

l (V

SC

E)

D B A

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.

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.

Experimental:• 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.

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.

The effect of reverse scan on Cu I-V profile in 1 gr/l Na2SO4 solution containing

4gr/l K2CO3 (pH 12.6)

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.

a b

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.

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.

10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2

0.0

0.2

0.4

0.6

0.8

name: 1glK2SO4+Diff.Conc.PotSorbate_Pd

1 gr/l K2SO

4 Pottasium Sorbate, scan rate 1 mV/s

Pote

ntia

l (V

SC

E)

Current (A/cm2)

1 g/l K2SO

4(pH 6)

With Potassium Sorbate: 4 g/l (pH 8.2) 10 g/l (pH 9.0) 50 g/l (pH 10)