Comparison of Elastic Modulus of Very Thin DLC Films Deposited by

r.f.-PACVD and FVA

Jin-Won Chung, Churl-Seung Lee, Dae Hong Ko*,

Jun-Hee Hahn** and Kwang-Ryeol Lee

Future Technology Research Division, Korea Institute of Science and Technology

* Department of Ceramics, Yonsei University

** Korea Research Institute of Standard Science

Applications of DLC Film

High Residual Compressive Stress of DLC Films

• Causes the Instability of the Coating• Affects the Physical Properties in Some Cases

DLC Coating

Self Delamination of DLC Films

• K.-R. Lee et al., Diam. Rel. Mater. 2 (1993) 208.• M.-W. Moon et al., Acta Mater., 50 (2002) 1219.

Key Idea of the Method

1

E

For Isotropic 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

R

ds

df

ss

ff

f

bf

sfbf

dY

dY

R

dY

3

2

ss

ff

f

bf

sfbf

dY

dY

R

dY

3

2

Measurement of Curvature

dx

dK

sin

dx

dK

sin

Key Idea of the Method

For Isotropic Thin Films

1

E

Preparation of 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

c

c

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

DLC film Deposition

Cleavage along [011] Direction

Si Etching (by KOH Solution) Wet Cleaning

Strain Measurement

Preparation of Free-overhang by Anisotropic Substrate Etching

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

– Completely Exclude the Substrate Effect

– Can Be Used for Very Thin Films

The possibility of elastic modulus measurement in very thin film

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

(G

Pa

)

Thickness (nm)

a-C:H, C6H6 -400V

J.-W. Chung et al, Diam.Rel. Mater. 10 (2001) 2069.

ta-C (-50Vb)

Elastic Modulus of Very Thin Films

Synthesis of DLC Film by r.f.-PACVD

• RF PACVD (13.56MHz)

• Precursor : CH4

• Vb/ P1/2 : 20 ~ 233 Vb/mTorr1/2

• Substrate : P type (100) Si

• Film Thickness : ~ 50nm

Residual Stress & G-peak Position of Raman Spectra

0 50 100 150 200 2501520

1525

1530

1535

1540

1545

1550

1555

G-p

ea

k P

osi

tion

(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

(G

Pa)

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

Biaxial Elastic Modulus

0 100 200 300 400 500 6000

50

100

150

200

Bia

xial

Ela

stic

Mod

ulus

(G

Pa)

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

100

Biaxial Elastic Modulus

0 100 200 300 400 500 6000

50

100

150

200

Bia

xial

Ela

stic

Mod

ulus

(G

Pa)

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

166

100

Biaxial Elastic Modulus

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)

0 100 200 300 400 500 6000

50

100

150

200

Bia

xial

Ela

stic

Mod

ulus

(G

Pa)

Thickness (nm)

20

233

166

100

G-peak Position of Raman Spectra

0 300 600 900 12001520

1530

1540

1550

1560

G-p

eak

Pos

ition

(cm

-1)

Thickness (nm)

20

233

166

100

0 100 200 300 400 500 6000

50

100

150

200

Bia

xial

Ela

stic

Mod

ulus

(G

Pa)

Thickness (nm)

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

(G

Pa)

Thickness (nm)

Synthesis of ta-C Films

• ta-C films on Si (100) Wafer

• Vb : from 0 to –500V

0 100 200 300 400 500 6000

1

2

3

4

5

6

7

Res

idua

l Com

pres

sive

Str

ess

(GP

a)

Negative Bias Voltage (V)

Elastic Modulus of ta-C film

0 100 200 300 400 500100

200

300

400

500

600

700

800

900

35 V 300 V

Bia

xia

l Ela

stic

Mo

du

lus

(GP

a)

Thickness (nm)

0 100 200 300 400 500 6000

1

2

3

4

5

6

7

Res

idua

l Com

pres

sive

Str

ess

(GP

a)

Negative Bias Voltage (V)0 100 200 300 400 500

100

200

300

400

500

600

700

800

900 GND 35 V 300 V

Bia

xia

l Ela

stic

Mo

du

lus

(GP

a)

Thickness (nm)

Elastic Modulus of ta-C film

Raman Spectra

1000 1500 2000 2500

Inte

nsi

ty (

A.U

.)

Raman Shift (cm -1)

16 nm 86 nm 91 nm 132 nm 238 nm 302 nm

Summary

• Presently suggested method for the elastic modulus measurement enabled us to compare the mechanical properites and thus the atomic bond structures of very thin amorphous carbon films.

• ta-C films showed insignificant structural evolution during the initial period of deposition.

• a-C:H showed the significant structural evolution in both polymeric and graphitic film deposition condition.

• a-C:H film deposited in optimum ion energy condition didn’t show the structural evolution.

Applications of DLC Film