23, Sep., 2005KAIST

금속이 혼입된 비정질 탄소막(Me-DLC) 에서의 응력감소 거동

; 실험적 분석과 제일원리계산

한국과학기술연구원 미래기술연구본부

최정혜 , 안효신 , 이승철 , 왕애영 , 이광렬

열역학분과 심포지엄

Diamond-like carbon (DLC) films

• High hardness

• High wear resistance

• Low friction coefficient

• Optical transparency

• Chemical inertness

• Smooth surface

• Bio-compatibility

• High hardness

• High wear resistance

• Low friction coefficient

• Optical transparency

• Chemical inertness

• Smooth surface

• Bio-compatibility

Hard disk Video

Head DrumCoronary

Artery Stent Hip Joint

• Protective coating • Bio materials

• Protective coating • Bio materials

Disadvantages of DLC films

Hard disk

Before deposition

After deposition

M. W. Moon, Acta Mater., 50 219 (2002).

High residual compressive stress

(6~20 GPa)

High residual compressive stress

(6~20 GPa)poor adhesionpoor adhesion

Substrate bending Delamination

Stress and sp3 bond fraction

2 4 6 8 10 1210

20

30

40

50

60

70

80

90

100

Fallon Weiler Xu Chhowalla

sp

3 f

ractio

n

Residual Compressive Stress (GPa)

Hard

nes

Hard

nes

ss

To reduce residual comp in DLC films

• Substrate biasing

• Post-annealing

• Metal atom incorporation

; Ti, W, Mo, Cr, Al….

W-incorporated DLC films

1.9 at % W

A.-Y. Wang APL 86 111902 (2005).

Not fully understood yet !!!

Mechanism ?

Purpose of this work

dependency of total energy of the system on the bond angle & the electron density distribution and its effects on the stress reduction behavior of DLC films

DLC; distorted sp3 + sp2, sp bonding

Diamond ; ideal sp3 bonding

109.5o

≠109.5o

Known as a primary cause of the residual stress in DLC structure

Known as a primary cause of the residual stress in DLC structure

Tetrahedron bond model

tetrahedral bonding of carbon(or Me)-carbon structure relaxation total energy calculation ; reference state

tetrahedral bonding of carbon(or Me)-carbon structure relaxation total energy calculation ; reference state

Bond angle distortion bond distance relaxation total energy calculation

Bond angle distortion bond distance relaxation total energy calculation

109.5o

Me

90o~130o

Me

90o~130o

C

109.5o

C

EC-C EMe-C

Calculation condition

Code; DMOL3

Exchange-correlation potential; GGA (PBE)

Atomic orbital; double-zeta polarization basis set

Cutoff radius of atomic orbitals; 9 Å

All electron calculation

Spin consideration

Total energy change by the bond angle distortion

3 4 5 6 7 8 9 10 11 12 13 14 15-1

0

1

2

Fe

Mn

V

ZnCd AlNi

Pd

Co

CuAgAu

MoCrW

Ti

Si

C

E90

o (e

V)

atomic group (# of valence e-)

2nd period 3rd period 4th period 5th period 6th period

Formation energy of Me-C tetrahedron

3 4 5 6 7 8 9 10 11 12 13 14 15

0

2

4

6

8

10

12

14

C

Si

Al

CdZn

AuAg

CuPd

NiCo

Fe

2nd period 3rd period 4th period 5th period 6th period

MnCrMoW

V

Ti

Ef M

e-C(e

V)

atomic group (# of valence e-)

EfM-C = (Etot

M-C + EatomC) - (Etot

C-C + EatomM)Ef

M-C = (EtotM-C + Eatom

C) - (EtotC-C + Eatom

M)

Me

Me

EfM-C

Isosurface of electron density; C-C-tetrahedron

90o

C

1.51.00.5

Inset values are the electron density [Å-3] of the isosurface

109.5o

C

0.5 1.51.0

Isosurface of electron density right before it is separated

Cr 0.72

109.5o

V 0.63 Ti 0.64 Ni 0.67 Si 0.72

Mo 0.72W 0.70Mn 0.70

Co 0.76 Fe 0.82 C 1.50

Isosurface of electron density right before it is separated

109.5o

Ar 0.01 Cd 0.36 Ag 0.40 Au 0.40

Pd 0.58Cu 0.53Zn 0.45Al 0.45

C 1.50

Electron density right before its isosurface is separated (e

s)

Lower es

Lower shape anisotropy of electron density

Lower es

Lower shape anisotropy of electron density

Weaker bonding Lower angular dependency of total energy stress reduction

Weaker bonding Lower angular dependency of total energy stress reduction

3 4 5 6 7 8 9 10 11 12 13 14 150.2

0.4

0.6

0.8

1.4

1.6

C

Al

Si

ZnCd

CuAg/Au

NiPd

CoFe

MnV

Cr/Mo WTi

Ti

2nd period 3rd period 4th period 5th period 6th period

atomic group (# of valence e-)

es (A

-3)

W-incorporated DLC films

W 0.70C 1.503 4 5 6 7 8 9 10 11 12 13 14 15

-1

0

1

2

Al

AgAu

W

Si

C

E90

o (e

V)

atomic group (# of valence e-)

Me-DLC films; Experimental

P. Zhang, J. Vac. Sci. & Tech. A. 20 390 (2002).

Residual stress

By FCVA

Hardness

Young’s modulus

Conclusion

3 4 5 6 7 8 9 10 11 12 13 14 15-1

0

1

2

Fe

Mn

V

ZnCd AlNi

Pd

Co

CuAgAu

MoCrW

Ti

Si

C

E90

o (e

V)

atomic group (# of valence e-)

2nd period 3rd period 4th period 5th period 6th period

C 1.50 Mn 0.70

Au 0.40 Al 0.45