4/17/2002

1

Comparison of electrochemical and chemical oxidizing agents for copper CMP

SFR Workshop & ReviewApril 17, 2002

Serdar Aksu, Ling Wang, Amnuaysak Chianpairotand Fiona M. Doyle,

Berkeley, CA

2002 GOAL: Integrate initial chemical models into basic CMP model by 9/30/2002

4/17/2002

2

Problem formulation and motivation• Work to date has focused on electrochemical studies

of the behavior of copper in slurries containing organic complexing agents– Existing electrochemical theory is mature field– Lends itself to development of models for copper

planarization behavior– Facilitates integration into basic CMP model

• During commercial CMP, however, metals are oxidized chemically, not electrochemically– Literature suggests different behavior with chemical

oxidants– Hence, it is necessary to compare chemical and electro-

chemical oxidation of copper, and elucidate any differences

4/17/2002

3

Our Approach• Direct comparison of electrochemical and chemical

behavior of copper under chemical conditions representative of CMP

• Characterization of copper/solution interfacial species formed during electrochemical and chemical oxidation, to elucidate mechanistic reasons for differences in behavior

• Rigorous characterization of (electro)chemical and mechanical contributions to material removal

• Incorporation of results into general model for CMP

4/17/2002

4

Implementation - Electrochemical Measurements

Magnetic stirrer

Rotating diskelectrode for ex-situ

polarization

In-situ Electrochemical Polarization

Pt Counter Electrodes

Luggin Probe & Reference Electrode

Polish pad

Copper Working Electrode

Slurry poolP

Rotator Frame

ω

Fritted glassgas bubbler

Rotating CuDisk electrode

4/17/2002

5

Results - Electrochemistry of Copper in AqueousGlycine Solutions

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0 2 4 6 8 10 12 14 16pH

E, V

vs.

SH

E

Cu2+

CuL2Cu

L+

Cu

O2

2-

Cu

OCu2O

Cu

i, A/m2

10-4 10-3 10 -2 10-1 100 101 102 103

E m

V v

s. S

HE

-800

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

1800

pH 4pH 9pH 12

{CuT} = 10-5, {LT} = 10-2{LT} = 10-2

Polarization curves are consistent with stabilities of different phases – passivation is seen at pH 12, where solid CuO forms a protective film

4/17/2002

6

Results – Effect of Polishing on Electrochemistry of Copper in Aqueous Glycine Solutions

i, A/m2

10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1

E m

V v

s. S

HE

-800

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

1800

No abrasionPolishing with pad onlyPolishing with pad and5 % alumina particles

i, A/m2

10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1E

mV

vs.

SH

E-800

-600

-400

-200

0

200

400

600

800

1000

1200

1400

1600

1800

No abrasionPolishing with pad onlyPolishing with pad and5 % alumina particles

pH 4 pH 12

Abrasion eliminates passivity; this will facilitate planarization

4/17/2002

7

Implementation – Chemical Oxidation of Copper

• Dissolution Rate Experiments– Cleaned, weighed, copper coupons (50 x 25 x 1 mm,

99.999%) suspended in stirred solutions– After tests, dried and weighed– Copper removal rate determined by weight loss

• Polishing Rate Experiments– Used same equipment used for in-situ polarization tests– Electrochemical information unstable with peroxide– Polishing rates determined from weight loss measurements

4/17/2002

8

Results – Chemical Oxidation of Copper

Aqueous 10-2 glycine, pH 4, 27.6 kPa, 200 rpm

0

20

40

60

80

100

120

140

160

0 1 2 3 4 5 6H2O2 , wt%

Rem

oval

Rat

e, n

m/m

in Dissolution Rate

Polish Rate

0

100

200

300

400

500

600

700

0.1 1 10 100

Current density, A/m 2

Eoc

, V (

SH

E) Polishing

Dissolution

Dissolution

Equivalent polarization curve

Clear evidence of passivation, even though no solid phases are

stable under these conditions

4/17/2002

9

Results – Chemical Oxidation of Copper

Aqueous 10-2 glycine, pH 9, 27.6 kPa, 200 rpm

Dissolution

Equivalent polarization curve

Clear evidence of passivation, even though no solid phases are

stable under these conditions0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6H2O2, wt%

Rem

oval

Rat

e, n

m/m

in

Dissolution Rate

Polish Rate

-500

50100150200250300350400450

0.1 1 10 100

Current density, A/m2

Eo

c, V

(S

HE

)Dissolution

Polishing

4/17/2002

10

Future Research – Elucidate Differences Between Electrochemical and Chemical Oxidation

• Use a copper rotating disk to simulate the transport phenomena occurring during real CMP– Polarize a copper rotating disk electrode into the passive

and active regimes– “Polarize” chemically with peroxide to attain equivalent

rest potentials• Characterize and compare the films formed in the

passive and active regime in each case– Characterization methods will include Raman scattering,

XPS, TEM.• The nature of the films will provide information on

the interaction between hydrogen peroxide and copper; this will allow processes to be modeled

4/17/2002

11

Future Research – Coupling of Mechanical and (Electro)chemical Removal Processes

• Preliminary results suggest that during CMP, the predominant material removal mechanism is mechanical– Electrochemical contribution, assessed from current

densities at the electrode, are relatively minor

• However, the mechanical removal rates appear to increase with increasing potential– Mechanistically, probably due to differences in the

mechanical properties of surface films formed at different potentials

• This coupling must be well understood for effective modeling, and will be explored in depth

4/17/2002

12

2002 and 2003 Goals

• Integrate initial chemical models into basic CMP model, by 9/30/02

• Comprehensive chemical and mechanical model. Experimental and metrological validation, by 9/30/03