다이아몬드상 카본필름의 잔류응력과 기계적 물성

한국기계연구원2001. 8. 7

한국과학기술연구원이 광 렬

Outline

• 다이아몬드상 카본필름의 소개– 다이아몬드상 카본필름의 일반적 특성– 장단점 및 응용

• 박막의 잔류응력– 잔류응력의 종류– 잔류응력의 측정

• 다이아몬드상 카본필름의 잔류응력– 잔류응력의 발생거동 및 영향– 제삼원소 첨가에 의한 잔류응력의 제어

• 잔류응력을 이용한 박막의 탄성계수평가

Carbon Atomic Bond Structure

What is DLC ?

• Amorphous Solid Carbon Film• Mixture of sp1, sp2 and sp3 Hybridized Bonds• High Content of Hydrogen (20-60%)

• Synonyms– Diamond-like Carbon– (Hydrogenated) amorphous carbon (a-C:H)– i-Carbon– Tetrahedral Amorphous Carbon

a-C:H ta-C

Properties of Solid Carbon

Property Diamond DLC Graphite

Density (g/cm3) 3.51 1.8 – 3.6 2.26

Atomic Number Density (Mole/cm3)

0.3 0.2 – 0.3 0.2

Hardness (Kgf/mm2) 7000 - 10000 2000 - 8000 <500

Friction Coeff. 0.05 0.03 – 0.2

Refractive Index 2.42 1.8 – 2.6 2.15 – 1.8

Transparency UV-VIS-IR VIS-IR Opaque

Resistivity (cm) >1016 1010 - 1013 0.2 – 0.4

Historical Survey

• 1972– Aisenberg and Chabot : Arc Ion Beam

• 1979– Holland and Ohja : PACVD

• 1984– Mori and Namba : Ion Plating

• 1986– Savvides : Sputtering

• 1992– Collins et al : Laser Ablation– Filtered Vacuum Arc

Deposition Methods

Energy

Ion Source

Cold Substrate

Impa

ct E

nerg

y (e

V)

1

10

100

1000

Amorphous Carbon

(sp2)

DenseCarbon

CarbonSource

HydrocarbonSource

DenseHydro-Carbon

PolymerLike

Carbon

PlasmaPolymers

Energy Dependence of DLC

Ion Energy Distribution

PACVDPACVD

Examples of Deposition Methods

Examples of Deposition Methods

합성방법의 특징합성 방법 특징

PECVD (DC, HF, RF,ECR, pulsed DC)

High Productivity, Very Smooth FilmLow Hardness & Thermal StabilityNon Uniform in Complicated Shape

Sputtering : ion beam Process Compatibility for HDD Low Adhesion, Poor Film Quality

Ion Beam Deposition

Medium Hardness, Medium ProductivityUniform Coating for Complicated Shape

High Residual Stress, Poor AdhesionComplicated Deposition System

Laser Ablation High Adhesion & HardnessLow Productivity

FVA(Filtered Vacuum Arc)

High Hardness & Thermal Stability High Residual Stress, Poor Adhesion

Properties of Solid Carbon

Property Diamond DLC Graphite

Density (g/cm3) 3.51 1.8 – 3.6 2.26

Atomic Number Density (Mole/cm3)

0.3 0.2 – 0.3 0.2

Hardness (Kgf/mm2) 7000 - 10000 2000 - 8000 <500

Friction Coeff. 0.05 0.03 – 0.2

Refractive Index 2.42 1.8 – 2.6 2.15 – 1.8

Transparency UV-VIS-IR VIS-IR Opaque

Resistivity (cm) >1016 1010 - 1013 0.2 – 0.4

Major Points of DLC Films

• Low Deposition Temperature (R.T. – 200oC)– No limitation of Substrate Materials

• Smooth Surface– Roughness : few nm

• Wide Range of Physical Properties– Tunability of the Properties

• Uniform Large Area Deposition– High Productivity and Low Cost

AFM Image of DLC coated Si

IR Transmittance of DLC Coated Ge Windows

Courtesy of J&L Tech. Ltd

Minor Points of DLC Films

• Thermal Instability– Degradation at High Temperature (400 – 600oC)

• High Residual Compressive Stress– Max. 10 GPa

• Poor Adhesion– Stable Chemical Bonds

– Especially on Ferrous Materials

Structure and Mechanical Properties

• Hardness– 3-D interlink of the

atomic bond network

• Residual Stress– Distortion of bond angle

and length

• Both are dependent on the degree of 3-D interlinks.2-D Analogy of the Structure

Self Delamination Failure during Tribotest

DLC 필름의 특성과 응용구 분 특 성 응 용

High hardness

Low friction andhigh wear resist.

Chemical Inertness

Optical Transmittance

2,000 - 8,000Hv(cf. Diamond 10,000Hv)

마찰계수 0.05 - 0.2(cf. Stainless Steel : 0.6 - 0.7)

산 또는 알카리와 반응치 않는다

특히 적외선 영역의 높은 광투과도

비철금속 가공용 공구 ,정밀금형의 표면경화코팅

치구 , GEAR, SURGICALBLADE, HARD DISK 등의 고체 윤활 코팅

부식 방지막 , 인체삽입물의BIO-COMPATIBLE COATING

IR WINDOW, SCANNERWINDOW 의 표면보호 코팅

경질박막의 내마모 윤활특성

DLC

WC

TiN

CrN

TiCN

마모도 마찰계수 .

2.0 1.6 1.2 0.8 0.4 0.2 0.4 0.6 0.8 1.0( 상대비교치 )

DLC 필름의 특성과 응용구 분 특 성 응 용

High hardness

Low friction andhigh wear resist.

Chemical Inertness

Optical Transmittance

2,000 - 8,000Hv(cf. Diamond 10,000Hv)

마찰계수 0.05 - 0.2(cf. Stainless Steel : 0.6 - 0.7)

산 또는 알카리와 반응치 않는다

특히 적외선 영역의 높은 광투과도

비철금속 가공용 공구 ,정밀금형의 표면경화코팅

치구 , GEAR, SURGICALBLADE, HARD DISK 등의 고체 윤활 코팅

부식 방지막 , 인체삽입물의BIO-COMPATIBLE COATING

IR WINDOW, SCANNERWINDOW 의 표면보호 코팅

Applications of DLC Film

Video Cassette Recorder

DLC 코팅 VTR 헤드드럼

Courtesy of Daewoo Electronics Co.

DLC Coated Digital VCR Tape

HDD 용 Hard Disk

DLC coated Head Slider

DLC Coated Razor Blade

Schematic of Diesel Engine

Results of Wear Test under Dry Lubrication Conditions

0 5000 10000 15000

0.2

0.3

0.4

0.5

DLC coated Ring

Hard Cr Ring

No-lubricant conditionLoad 50N

Fric

tion

Coe

ffic

ient

Number of Cycle.

Hard Cr Coated Ring DLC coated Ring

Before Test Before Test

After Test After test

Result of Dynamo Test (900h)

Before Test Before Test

After Test After Test

100m6.5m

5.3m

Hard Cr Coated Piston Ring

DLC/Cr Coated Piston Ring

Sliding Tools for Electron Gun

• Grids (2) manipulate the electron beam.

• Sliding Tools is used to make spacing between the grids (Tolerance is about 4m)

• Smooth grid surface and parallel positioning are important.

DLC Coated Sliding Tools

• Low friction

• Long life time

• Electrical insulation

• No corrosion on the shelves

Courtesy of J&L Tech. Co., Ltd.

IC Packaging

• 반도체 packaging 용 EMC mold cavity 의 이형성 증진 및 수명연장을 위한 코팅

DLC Coating on Packaging Tools

Courtesy of J&L Tech. Co., Ltd.

인공 고관절 및 무릎관절

고관절

무릎관절

DLC Coating for Wear Resistance

Biological Application of DLC

인공 심장 , 수정체

인공심장 판막 인공수정체

DLC Coated Stents

Load

Ruby BallTest disk

Saline

Load :

High &Low

Surroundings :

Wet Condition

Dry Condition

Schematic of Wear Tester

Dry Wet

DLC on Ti

DLC on Ti-Alloy

Condition :

High Load

3000 cycle

Dry Wet

Wear Volume

0.026 mm3

0.021mm3

0.002mm3

0.002 mm3

Wear Volume

Dry Wet Dry Wet

Fracture Cycle

92250 cyc

6750 cyc

10250 cyc

3172 cyc

Condition :

High Load

DLC on Ti

DLC on Ti-Alloy

Life Time of DLC Coatings

IR Windows for Missile and Night Vision System

IR Transmittance of DLC Coated Ge Windows

Sand Blast Type Erosion Rig

J. E. Field, Carvendish Lab. Cambridge University

Solid Particle Impact Erosion

Damage Pattern of Multilayer Coated Ge windows

200 sec

600 sec

Ge

510nm a-Si

1900nm DLC

690nm a-Si

1000nm DLC

Multilayer Structure

DLC Coated CD-R Pressing Die

Courtesy of J&L Tech. Co., Ltd.

CD Surface Formed by Using Uncoated Mold

RMS roughness = 1.31nm

CD surface formed by using DLC coated mold

RMS roughness = 0.95nm

Residual Stress of Thin Films

• Thin films typically support very high stresses due to the constraint of the substrate to which they are attached– Normally at near failure stress!– Determines mechanical behaviors of the coating and devices

(elastic distortion, plastic deformation, fracture, adhesion)

Substrate Interaction Stresses Intrinsic Stresses

Relative Dimensional Change after Growth

Thermal Stress

Epitaxial Stress

Interfacial Stress

Structure Evolution During Growth

Relative Dimensional Changes

Condition : Adhesion between film and substrate Any process that changes the in-plane dimension of the film relative to that of the substrate

Thermal Stress

Condition : Difference in thermal expansion coeff. Difference in temperature

Epitaxial Strains

Condition : Coherency with different lattice parameters

Interfacial Stresses

Condition : Inherent but significant in very thin film or multilayer

Intrinsic Stress (Growth Stress)

Residual Stress of Thin Films

Measurement of Residual Stress

• Assumption– 1-D Treatment of Elastic

Equilibrium

– Sufficient Adhesion

– df << ds

– ds << R

sff

ssf

ss

ff

f

ssf

ddd

dY

R

dE

dE

d

dY

R

for 6

1

16

1

2

2

sff

ssf

ss

ff

f

ssf

ddd

dY

R

dE

dE

d

dY

R

for 6

1

16

1

2

2

Curvature (R)

dsdf

ss

ff

f

bf

sfbf

dY

dY

R

dY

3

2

ss

ff

f

bf

sfbf

dY

dY

R

dY

3

2

Stress of Multilayer

Ko

K1

K2

11 foKK

212 fKK f1

f1

f2

2

21

14 f

s

f

s

ff d

d

Y

Y 2

21

14 f

s

f

s

ff d

d

Y

Y

Measurement of Curvature

dx

dK

sin

dx

dK

sin

X-ray Strain Measurement : sin2Method

d

sin2

dE

dE

d ff )2

1(sin1 2

Angle between normal vector and scattering vector

d

dEf

2sin/

1

d

dEf

2sin/

1

Typical Behavior of Residual Stress of DLC Films

0 50 100 150 200 250

0.5

1.0

1.5

2.0

2.5

3.0

)V/mTorr(/ 1/2PVb

)V/mTorr(/ 1/2PV b

Res

idua

l Com

pres

sive

Str

ess

(GP

a)

ta-C by FVA a-C:H by rf-PACVD

High Residual Stress

Instability of Coating and Device

The Effect of Stress on Raman G-peak Position

J.K.Shin et al., Appl. Phys. Lett., 78 (2001) 631

Stressed

Stress-relieved

4.1cm-1/GPa

T : Elastic energy

U : Bending strain energy

Δγ : Surface energy

=(- fs+ fv+ sv)

fsT

svfvU

22

2)1(3

B

B

B

ut

tE

22

2)1(3

B

B

B

ut

tE

BB UT

0.22 0.24 0.26 0.28 0.30 0.32 0.34 0.36-10

-5

0

5

10

15

20

25

30

(J

/m2 )

Thickness(m)

Fundamental Adhesion

Energy Dependence of DLC

Synthesis of ta-C:Si

Bias: GroundControl parameter

Ar gas flow 10 ~ 20 SCCM

Pressure B.P.= low 10-6 torr W.P.= mid 10-4 torr

Si was incorporated in the ta-C film by simultaneous magnetron sputtering of Si during the FVA deposition.

Si Incorporation

Si in the film

C

Si in substrate

Composition

9 10 11 12 13 14 15 16 17 18

0

20

40

60

80

100

O

Si

C

Co

nce

ntr

atio

n (

at.

%)

Ar Flow (sccm)

Mechanical Properties

0 10 20 30 40 50

0

1

2

3

4

5

6

7

Res

idua

l Com

pres

sive

Str

ess

(GP

a)

Si Concentration (at.%)0 10 20 30 40 50

15

20

25

30

35

40

45

50

55

60

65

70

Hardness

Plane Strain Modulus

Si Concentration (at.%)

Har

dnes

s (G

Pa)

50

100

150

200

250

300

350

400

Plane S

train Modulus (G

Pa)

Reduction of Hardness and Residual Stress

0 10 20 30 40 500

20

40

60

80

100

Stress

Hardness

N

orm

aliz

ed P

rope

rtie

s (%

)

Si Concentration (at.%)

I II III

Raman Spectra & G-peak

800 1000 1200 1400 1600 1800 2000

50

37

22

8.5

4

2.5

1

0

Inte

nsity

(a.

u.)

Raman Shift (cm-1)

I

II

III

0 5 10 15 20 40 45 50

1505

1510

1515

1520

1525

1530

1535

1540

1545

1550

1555

1560

1565

1570

1575

G-p

ea

k P

osi

tion

(cm

-1)

Si Concetration (at.%)

Region INo significant changes in atomic bond structure.The stress effect on G-peak position

Atomic Bond Structure

0 10 20 30 40 500

20

40

60

80

100

Stress

Hardness

Nor

mal

ized

Pro

pert

ies

(%)

Si Concentration (at.%)

I II III

Raman Spectra & G-peak

0 5 10 15 20 40 45 50

1505

1510

1515

1520

1525

1530

1535

1540

1545

1550

1555

1560

1565

1570

1575

G-p

ea

k P

osi

tion

(cm

-1)

Si Concetration (at.%)

Region IIThe initial stage of SiC phase appearanceNanocrystalline SiC related peak at 1450 cm-1

800 1000 1200 1400 1600 1800 2000

50

37

22

8.5

4

2.5

1

0

Inte

nsity

(a.

u.)

Raman Shift (cm-1)

I

II

III

The Changes of the Structure

XPSSi 2p

Si-SiC-Si

4000 3500 3000 2500 2000 1500 1000 500

Si-Cstretching

0

37

22

8.5

4

Inte

nsity

(a.

u.)

Wavenumber (cm-1)

0 10 20 30 40 500

20

40

60

80

100

Stress

Hardness

Nor

mal

ized

Pro

pert

ies

(%)

Si Concentration (at.%)

I II III

FTIR

Region IIISiC phase was dominantSi-Si bonding increased 94 96 98 100 102 104 106 108

50 at.%

22 at.%

Inte

nsity

(a.

u.)

Binding Energy (eV)

• ta-C:Si films prepared by hybrid FVA– Si concentration can be controlled by Ar gas flow

• The significant stress reduction by Si addition– Hardness was reduced by 23 % ,while stress was reduce

d by 48 % in low Si concentration. – Weaker Si-C bond sites relieved the stress without brea

king the three dimensional interlink.– When the Si concentration was higher than 22 at.%, the

SiC phase strongly influenced on the structure and mechanical properties.

Conclusions

압축 잔류 응력을 이용한 박막의 탄성계수 평가

• Mechanical properties of thin films are not the same as those of materials having the sample composition in bulk form– High quench rate in deposition process

– High defect densities and textures

– Non-equilibrium compositions

– Confinement of dislocations, craction, etc. in small dimensions

Nano-Indentation

• Initial unloading is pure elastic.

• Sneddon’s elastic contact theory

E1 2

Nano-indentation Results

0 50 100 150 200 250 300 350

100

200

300

400

500

600

700 500nm ta-C on Si 500nm ta-C on Al

CSM

Ela

stic

Mod

ulus

(GPa

)

Displacement (nm)0 50 100 150 200 250 300 350

100

200

300

400

500

600

700 200nm ta-C on Si 200nm ta-C on Al

CSM

Elas

tic M

odul

us (G

Pa)

Displacement (nm)

Sonic Vibration and Laser-Acoustic Technique

Sonic Vibration Laser-Acoustic

Bulge Test

4

3

221 r

hMtc

r

htcP o

)1/( EM For Isotropic Film

Key Idea of the Present Method

1

E

For Isotropic Thin Films

DLC film Deposition

Cleavage along [011] Direction

Si Etching (by KOH Solution) Wet Cleaning

Strain Measurement

Preparation of Freehang

Strain From DLC Bridge by Micro Fabrication

DLC film Deposition ( on SiO2 )

DLC PatterningSiO2 Isotropic Wet Etching

Wet Cleaning

Strain Estimation

Microstructure of DLC Bridges

C6H6, 10mTorr, -400V, 0.5m

150m

Strain of the Buckled Thin Films (I)

xco

E

)1(

t

D

xAxW

x

Wt

x

WD

c

o

c

x

WWx

x

WWx

2

2

2

2

4

4

4

2cos1)(

0

0 ,2

at

0 ,2

at

Z

X

2A0

Stain of the Buckled Thin Films (II)

2

2

2

2

2 2

11

2

1

ox

x

x

A

dxx

W

x

W

cooA

E

2

1

0

131

1

13

1

,4

From

2

22

2

2

2

t

A

t

E

t

D

oo

c

c

c

ooA

E

2

1

Elastic Modulus for Various Ion Energies

0 100 200 300 400 500 600 700 800

0

50

100

150

200

250

Pla

ne

Str

ain

Mod

ulus

(G

Pa

)

Negative Bias Voltage (V)

Nanoindentation t>1.0 ㎛

100 200 300 400 500 600

0

50

100

150

200

Bridge Method

Freehang Method

E/(1

-)

(GPa

)

Negative Bias Voltage (V)

Advantages of This Method

– Simple Method

– Completely Exclude the Substrate Effect

– Can Be Used for Very Thin Films

The possibility of elastic modulus measurement in very thin film

Elastic Modulus of Very Thin Films

0 200 400 600 800 1000 1200

25

50

75

100

on Si on W / Si on SiO

2/ Si

Bia

xial

Ela

stic

Mod

ulus

(GPa

)

Thickness (nm)

a-C:H, C6H6 -400V

J.-W. Chung et al, Diam.Rel. Mater. in press (2001)

ta-C (Ground)

Residual Compressive Stress & G-peak Position of Raman

0 50 100 150 200 2501520

1525

1530

1535

1540

1545

1550

1555

G-p

eak

Pos

ition

(cm

-1)

Vb / P1/2 (V/mTorr1/2)

0 50 100 150 200 250

0.5

1.0

1.5

2.0

2.5

3.0

Res

idua

l Com

pres

sive

Stre

ss (G

Pa)

Vb / P1/2 (V/mTorr1/2)

Biaxial Elastic Modulus

0 100 200 300 400 500 6000

50

100

150

200

Bia

xial

Ela

stic

Mod

ulus

(GP

a)

Thickness (nm)

0 50 100 150 200 250

0.5

1.0

1.5

2.0

2.5

3.0

Res

idua

l Com

pres

sive

Str

ess

(GP

a)

Vb / P1/2 (V/mTorr1/2)

20

233

166

100

G-peak Position of Raman

0 300 600 900 12001520

1530

1540

1550

1560

G-p

eak

Pos

ition

(cm

-1)

Thickness (nm)

0 50 100 150 200 250

0.5

1.0

1.5

2.0

2.5

3.0

Res

idua

l Com

pres

sive

Str

ess

(GP

a)

Vb / P1/2 (V/mTorr1/2)

20

233

166

100

0 300 600 900 12001520

1530

1540

1550

1560

G-p

eak

Pos

ition

(cm

-1)

Thickness (nm)

233

166

100

20

Schematic Film Structure

Si Substrate

Si Substrate

Si Substrate

0 100 200 300 400 500 6000

50

100

150

200

Bia

xial

Ela

stic

Mod

ulus

(GP

a)

Thickness (nm)

Conclusions

Using the free overhang method, we could accurately measure the biaxial elastic modulus of very thin DLC film.

(down to 50nm).

The structural evolution in the initial stage of the film growth depended on the deposition conditions.

- At the optimum ion energy, the film exhibited a fixed elastic modulus and G-peak position regardless to the film thickness.

- On the other hand, the structural evolution during the initial stage of the film deposition was significant in the films of high content of polymeric or graphitic component.

Acknowledgement

• Financial Support– 과기부 한러협력기술개발사업 (91-94) – 과기부 선도기술개발사업 (94-01)– 과기부 중소기업지원사업 (97)– 산자부 산업기반기술개발사업 (99-01)– KIST 기관고유사업 (92-00)– 산업체 : 대우전자 , 대우중공업 , 제이엔엘테크

• Researchers– Postdoc : 오제욱 , 최준엽 , 신진국– 위촉연구원 : 김성화 , 김종국 , 김명근– 학생연구원 : 조성진 , 이철승 , 박세준 , 정진원