Ru CMP Slurry for Ru Bottom Elelctrode Formation

Jin-Goo Park

Division of Materials and Chemical EngineeringHanyang University, Ansan, 426-791, Korea

February 12, 2008

LEVITRONIXCPM Users' Conference 2008 February 12, 2008

Summary

4

Introduction1

Objective2

Results

3

- Ru Bottom Electrode Capacitor

- Static etch rate, Film thickness, Contact angle- Effects of pHs and Abrasive Particle on Ru CMP- Removal Rate and Selectivity of Ru disk- Application of Ru slurry on Patterned Wafer

Outline

5

Characterization Methods

Overview on Ruthenium

Ru (Ruthenium)Ru (Ruthenium)

Electrodes in DRAMs and FRAMs (Kwon et al., J. Electrochem. Soc., 151(2) (2004) C127)

Gate electrode in MOSFETs (Zhong et al., J. Electron. Master., 30 (2001) 1493)

Diffusion barrier and Cu seed layer in interconnect metallization(Brusic et al., 2006 ICPT, October 12-13, 2006, Crowne Plaza Hotel, Foster City, CA)

• Application in ICs (Integrated Circuits)

State at RT hard white metal (platinum group)

Melting point 2607 K

Boling point 4173 K

Work function 4.71 eV

Resistivity 7.1 μΩ·cm

Vertical Image

Excessive recess of Ru surface or loss of oxide current leakage, loss of capacitance

(from Samsung Electronics Co.)

Issues in Ru Bottom Electrode Capacitor

Tilt Image

After Dry etch-back method

Fabrication Process of Bottom Electrode

Interlayer dielectric film

contact

TEOS

Formation of Formation of PatternPattern

Ru layer

DepositionDepositionof Bottom Electrodeof Bottom Electrode

Sacrificial Layer (PR or Oxide)

DepositionDepositionof Sacrificial layerof Sacrificial layer

EtchingEtchingof Sacrificial layerof Sacrificial layer Ru CMPRu CMP RemoveRemove

of Sacrificial layerof Sacrificial layer

(from Samsung Electronics Co.)

Ru Bottom Electrode Capacitor

Ru

Ru

after

before

CMP CMP ProcessProcess

Potential-pH equilibrium diagram for system ruthenium-water, at 251)

1) M. Pourbaix, “Atlas of electochemical equilibria in aqueous solutions”, N. A. C. E. Intl., Houston, TX., 1974.2) S. H. Lee, S. H. Lee, Y. J. Kang, I. K. Kim, J. G. Park, KIEEE, 18 (2005) 803

Ru Pourbaix Diagram

(b) Alkaline SolutionKMnO4 + KOHpH 13.24~13.66

Eh 0.6~0.7 V

(a) Acid Solution 2)

CAN + HNO3pH 0~1

Eh 1.6~1.7 V

(a)

(b)

Highly Acidic Slurry- Harmful to Human Body- Generation of Toxic gas- Oxide Residue

Formation on the Pad

Development of

Less Acidic,

Neutral

or Less Alkaline Slurry

Research Objective

Highly Alkaline Slurry- Selectivity Issue due to

High Etch Rate of Oxide- Erosion Issue

Experimental Materials

Characterization methods

Experimental MaterialsSample Ru wafer and disk

Abrasive Particles Alumina, Fumed Silica particles

Etchant and Oxidiant Chemical A

pH adjustor HCl, NH4OH

CMP Poli-500 (GNP Tech.)

XPSCharacterization FESEM

of Ru wafer surface Static Contact Angle Analyzer (SCA)Variable Angle Spectroscopic Ellipsometry (VASE)

Before CMP After CMP

X 100k X 100k

Ru disk before and after CMP

Potential-pH equilibrium diagram for system ruthenium-water, at 25*

* M. Pourbaix, “Atlas of electochemical equilibria in aqueous solutions”, N. A. C. E. Intl., Houston, TX., 1974.

Ru Pourbaix Diagram

(b) Alkaline SolutionKMnO4 + KOHpH 13.24~13.66

Eh 0.6~0.7 V

(a) Acid SolutionCAN + HNO3

pH 0~1Eh 1.6~1.7 V

(a)

(b)

(c)

(c) Chemical ApH : 4.5~5

Eh : 0.8 ~ 1 V

Static Etch Rate

The static etch rate and passivation film thickness increased with increase

of chemical A concentration.

The contact angle decreased

due to the formation of Ru oxide.

0.00 0.02 0.04 0.06 0.08 0.100

5

10

15

20

25

30

Chemical A

Chemical A Concentration (M)

Stat

ic E

tch

Rat

e (n

m/m

in)

Contact Angle

0.00 0.02 0.04 0.06 0.08 0.100

10

20

30

40

50

60

70

80

Chemical A

Chemical A Concentration (M)

Con

tact

Ang

le (

O)

0.00 0.02 0.04 0.06 0.08 0.100

5

10

15

20

25

30

Chemical A

Chemical A Concentration (M)

Film

Thi

ckne

ss o

n R

u (n

m)

Passivation film thickness

Static etch rate, Passivation film thickness and Wettability of Ru

XPS Surface Analysis on Ru

In treated Ru in Chemical A,Ru concentration decreasedand O concentration increased.

These results mean that the Ru oxide was formed on Ru surface in Chemical A.

0 1 2 30

102030405060708090

100

Chemical A 0.1 M

Sputtering Time (min)

Ato

mic

Con

cent

ratio

n (%

)

O 1s

Ru 3d

0 1 2 30

102030405060708090

100

Ato

mic

Con

cent

ratio

n (%

)

Sputtering Time (min)

bare Ru

O 1s

Ru 3d

Ru 3d O 1s

As received Ru wafer 97.5 % 2.5 %

Treated Ru wafer(Chemical A 0.1 M)

90 % 10 %

Bare Ru treated Ru

- Chemical A 0.1 M(pH adjustor : HCl, NH4OH)

pH 4 ~ 10Eh 0.7 ~ 1.2 V

- pH 4 ~ 7

Formation of RuO4, H2RuO5

or RuO2·2H2O

- pH 7 ~ 10

Formation of RuO4-

or RuO2 · 2H2O

Eh of Ru as a function of pHsin Chemical A 0.1 M

pH adjustor : HCl, NH4OH

pH

Eh (V

vs.

SH

E)

Chemical A 0.1 M

- Perruthenate (RuO4-) solutions are unstable and decompose into RuO2 · 2H2O and O2

1, 2)

4RuO4- + 6H2O + 4H+

4(RuO2 · 2H2O) (insoluble) + 3O2

- The RuO4 is very soluble in water with the formation of “hyperruthenic acid”, H2RuO5.1, 2)

4RuO4- + 4H+ RuO2.2H2O + 3RuO4

H2O + RuO4 (soluble) H2RuO5

pH 4 ~ 7

pH 7 ~ 10

Representative Reactions

1) M. Pourbaix, “Atlas of electochemical equilibria in aqueous solutions”, N. A. C. E. Intl., Houston, TX., 1974.2) L. Davidson, Y Quinn and D. E Steele, Platinum Metals Rev., 1998, 42, (3), 90-98

Electrochemical Analysis

1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.010.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8Chemical A 0.1 M, pH adjustor : HCl, NH4OH

i (A/cm2)

E

(V v

s. S

HE)

pH 8

pH 10 pH 9

pH 6 pH 4

Increase of Corrosion Current

Decrease of Corrosion Current

- pH 4 ~ 7

The corrosion current increased

up to pH 6 due to the dissolution

of soluble RuO4.

- pH 7 ~ 10

The corrosion current decreased

with increase of pH

due to the formation of

insoluble RuO2 · 2H2O.

3 4 5 6 7 8 9 10 110

10

20

30

40

50

60

70

80

Ru w afer

Chem ical A 0.1 MpH adjustor : HCl, NH 4OH

pH

Con

tact

Ang

le (

O)

3 4 5 6 7 8 9 10 110

2

4

6

8

10

pH

Ru wafer

Chem ical A 0 .1 MpH adjustor : H Cl, NH 4O H

Film

Thi

ckne

ss o

n R

u (n

m)

In Acid Region- High static etch rate was measureddue to the dissolution of soluble RuO4.- A relatively high passivation film and low contact angle were measured.

Static etch rate, Passivation film thickness and Wettability of Ru

3 4 5 6 7 8 9 10 110

10

20

30

40

50

60

R u w afer

NaIO 4 0.1 M , pH adjustor : H Cl, N H 4O H

pH

Stat

ic E

tch

Rat

e (n

m/m

in)

pH Adjustor : HCl, NH4OHStatic Etch Rate

Passivation film thickness Contact Angle

- Ru Concentration: pH 6 < pH 9

- O Concentration : pH 6 > pH 9

At pH 6, dissolution and oxidation of Ru were higher than those at pH 9

0.0 0.5 1.0 1.5 2.00

102030405060708090

100

Chemical A 0.1 M at pH 6

Sputtering Time (min)

Ato

mic

Con

cent

ratio

n (%

) O1s,ls1

Ru3d

0.0 0.5 1.0 1.5 2.00

102030405060708090

100

Chemical A 0.1 M at pH 6

O1s

Ru3d

Sputtering Time (min)

Ato

mic

Con

cent

ratio

n (%

)

XPS Analysis of Ru as a function of pHs

pH 6 pH 9

pH Ru 3d O 1s

6 89 at% 11 at%

9 97 at% 3 at%

2 4 6 8 10 12-40

-30

-20

-10

0

10

20

30

40γ-Al2O3 500 ppm

No addition Chemical A

0.5 wt%

Ionic Strength : KCl 10-3 MpH Control : HCl and NaOH

Zeta

Pot

entia

l (m

V)

pH of Solution2 4 6 8 10 12

0

500

1000

1500

2000

2500

3000

3500

γ-Al2O3 500 ppm No addition Chemical A

0.5 wt%

Ionic Strength : KCl 10-3 MpH Control : HCl and NaOH

Mea

n Pa

rtic

le S

ize

(nm

)pH of Solution

Zeta Potential Mean Particle Size

In addition of Chemical A- The Decrease of Zeta Potential (The Adsorption of Anion from Chemical A)

: IEP (pH 9 pH 4)- The Migration of the Maximum Point of Particle Size : pH 9.3 pH 4

Alumina with and without Chemical A

2 4 6 8 10 12-50

-40

-30

-20

-10

0

10

20

30

40

50

Ionic Strength : KCl 10-3MpH Control : HCl and NaOH

fumed silica 500 ppm No addition Chemical A

0.5 wt%

Zeta

Pot

entia

l (m

V)

pH of Slurry2 4 6 8 10 12

0

500

1000

1500

2000

2500

3000

3500

fumed silica 500 ppm No addition Chemical A

0.5 wt%

Ionic Strength : KCl 10-3MpH Control : HCl and NaOH

Mea

n Pa

rtic

le S

ize

(nm

)

pH of Slurry

Fumed Silica with and without Chemical A

Zeta Potential Mean Particle Size

In addition of Chemical A

- Little Adsorption of Anion from Chemical A on Silica

: Little Change of Zeta Potential and Particle Size

Removal Rate as a function of pHs

The trend of removal rate of Ru was very similar to that of static etch rate.

The removal rate of Ru was the highest at pH 6 due to high etch rate.

Alumina slurry showed a higher Ru removal rate than silica slurry

due to higher hardness of alumina.

Removal Rate

3 4 5 6 7 8 9 10 110

20

40

60

80

100

120

140

160

180

Fumed Silica

Alumina

Chemical A 0.1 M + Abrasive Particle 2 wt% pH adjustor : HCl, NH4OH

pH

Rem

oval

Rat

e (n

m/m

in)

fumed Silica Slurry

0

10

20

30

40

50

60

0

20

40

60

80

100

120

140

160

180Chemical A 0.1 M + fumed Silica 2 wt% pH adjustor : HCl, NH4OH

Rem

oval

Rat

e (n

m/m

in)

Ru TEOS

Selectivity

109864

pH

Selectivity

Selectivity

Alumina Slurry- At pH 8 ~ 9 : High Selectivity (Ru : TEOS = 22 : 1)

Fumed Silica Slurry- At pH 6 ~ 8 : High Selectivity (Ru : TEOS = 22 : 1)

0

10

20

30

40

50

60

0

20

40

60

80

100

120

140

160

180Chemical A 0.1 M + Alumina 2 wt% pH adjustor : HCl, NH4OH

Rem

oval

Rat

e (n

m/m

in)

Ru TEOS

Selectivity

109864

pH

Selectivity

Alumina Slurry fumed Silica Slurry

※ Low pH (4 ~ 7)

Removal Mechanism of Ru

- The Formation of Soluble RuO4

- High Chemical Removal by the dissolution of Soluble RuO4

- Mechanical Removal of RuO4 by Abrasive Particle and Pad

Chemical Removal >> Mechanical Removal

Ru

Pad

Ru oxide (soluble RuO4)

Abrasive Particle

Dissolved Ru Oxide

※ High pH (7 ~ 10)

Removal Mechanism of Ru

- The Formation of thin Insoluble RuO2·2H2O- Low Chemical Removal due to the Insoluble RuO2·2H2O- Mechanical Removal of RuO4 by Abrasive Particle and Pad

Chemical Removal << Mechanical Removal

Ru

Pad

Ru oxide (insoluble H2RuO5)

Abrasive Particle

Dissolved Ru Oxide

Reference Ru Patterned wafer

38 nm

RuTEOSReference Ru Patterned Wafer

- Thickness of deposited Ru layer wasabout 38 nm.

- The each capacitor was connectedby deposited Ru layer.

X 30K

X 100K, Tiling : 60°

Slurry : Chemical A 0.1 M + Alumina 2 wt% (pH 4) CMP time : 1 min

Ru

TEOS

X 30K X 100K

X 100K, Tiling : 60°

In the case of slurry at pH 4- Each capacitor was isolated after CMP.

- Ru over etching was generated due to

high etch rate of Ru.

Ruover etching

Slurry : Chemical A 0.1 M + Alumina 2 wt% (pH 6)CMP time : 1 min

RuTEOS

Ruover etching

In the case of slurry at pH 6- Each capacitor was isolated after CMP.

- Ru over etching was become seriously.

X 30K X 100K

X 100K, Tiling : 60°

Slurry : Chemical A 0.1 M + Alumina 2 wt% (pH 9)CMP time : 1 min

RuTEOS

In the case of slurry at pH 9- Ru over etching was prevented

due to low etch rate of Ru.- The plarnarity and isolation of each

capacitor were acquired successfully after CMP.

X 30K X 100K

X 100K, Tiling : 60°

We successfully developed Ru CMP slurry at alkaline pH.

Optimized Slurry- Chemical A 0.1 M, Alumina 2 wt%, pH 9- Removal Rate

Ru : 70 nm/min, SiO2 : 3.2 nm/min- Selectivity

Ru : SiO2 ( 22 : 1 )

The Mechanism of Ru CMP can be explained.- In slurry at pH 4 ~ 7,

Chemical effect is dominant on Ru CMPdue to the dissolution of soluble RuO4.

- In slurry at pH 8 ~ 10,Mechanical effect is dominant on Ru CMP

due to the formation of insoluble RuO2·2H2O.

Summary

Acknowledgments

Lab of Excellence in the Ministry of Education and Human

Resources Development (MOE), the Ministry of Commerce,

Industry and Energy (MOCIE) , and the Ministry of Labor

(MOLAB)

Post BK21 program

Hynix Semiconductor