Characterization of Mechanical Properties of Thin Film Using Residual Compressive Stress

2004. 2. 16.

Sung-Jin Cho, Jin-Won Chung, Myoung-Woon Moon and Kwang-Ryeol Lee

Korea Institute of Science and Technology

미세구조 Workshop, 강원도 평창군 피닉스파크

Residual Stress of Thin Films

• Thin films typically support very high stresses due to the constraint of the substrate to which they are attached

Residual Compressive Stress of DLC Film

Film Deposition

Telephone Cord Buckling

M.W.Moon et al , Acta Mater., 50 (2002) 1219.

Off-Piste Run in Hoghfügen

Buckling Configurations

Quantitative Analysis

K.-R. Lee et al , Diam. Rel. Mater., 2 (1993) 218.

What can we do with this phenomenon?

• Can be a useful tool to estimate the fundamental interface toughness (adhesion) and the mechanical properties of thin films

What can we do with this phenomenon?

1

E

For Isotropic Thin Films

Measurement of Residual Stress

f

s

s

s

d

dE

R

2

21

1

Curvature (R)

DsDf

What can we do with this phenomenon?

1

E

For Isotropic Thin Films

DLC Bridges by Micro Fabrication

DLC film Deposition ( on SiO2 )

DLC PatterningSiO2 Isotropic Wet Etching

Wet Cleaning

Strain Estimation

C6H6, 10mTorr, -400V, 0.5m

150m

Microstructure of DLC Bridges

Strain of the Buckled Thin Films

xco

E

)1(

Z

X

2A0

2

2

2

2

11

2

1

2

2

o

x

x

A

dxx

W

x

W

cooA

E

2

1

ooA

E

2

1

Effect of Bridge Length

60 80 100 120 140 1600

40

80

120

160

200

E/(

1-)

(G

Pa)

Bridge Length (m)

m

Dependence of Film Thickness

0.0 0.3 0.6 0.9 1.2 1.50

40

80

120

160

200

E/(

1-)

(G

Pa)

Thickness (m)

V

V V

V

DLC Bridges

Biaxial Elastic Modulus

0 100 200 300 400 500 600

0

50

100

150

200

SiO2 etching techniqueE

/(1-

) (

GP

a)

Negative Bias Voltage (V)

DLC film Deposition

Cleavage along [011] Direction

Si Etching (by KOH Solution) Wet Cleaning

Strain Measurement

Preparation of Free Overhang

Free Overhang Method

• Biaxial elastic modulus

• Strain of the free overhang

2

0

)(1 A

E

20 )( A

A0 / λof Free-hang at 546 nm

4 8 12 16 20 24

0.02

0.04

0.06

0.08

0.10

0.12

0.14

A0

/

Etching Depth (m)

I II III

a-C:H, C6H6 -400V

5.6 ㎛ 11.3 ㎛

2 ㎛ 11 ㎛

Effect of Etching Depth

546 nm

55 nm

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

Nano-indentation

Substrate Effect is Significant.

The elastic strain field >> the plastic strain field

Substrate

Substrate Effect on the Measurement

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

Elas

tic M

odul

us (G

Pa)

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)

Advantages of This Method

• Simple Method• Completely Exclude the Substrate Effect• Can Be Used for 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

(G

Pa

)

Thickness (nm)

a-C:H, C6H6 -400V

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

ta-C (Ground)

Elastic Modulus of Very Thin Films

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

0 300 600 900 12001520

1530

1540

1550

1560

G-p

eak

Pos

ition

(cm

-1)

Thickness (nm)

233

166

100

20

Structural Evolution of DLC Films

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)

J.-W. Chung et al, Diam.Rel. Mater., 11, 1441 (2002).

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)

Residual Stress of ta-C film

0 100 200 300 400 500 600 7000

100

200

300

400

500

600

700

800

900

Bia

xia

l Ela

stic

Mo

du

lus

(GP

a)

Thickness (nm)

Biaxial Elastic Modulus of ta-C film

Conclusions

• Can be a useful tool to estimate the fundamental interface toughness (adhesion) and the mechanical properties of thin films

What can we do with this phenomenon?

• Can be a useful tool to estimate the fundamental interface toughness (adhesion) and the mechanical properties of thin films

Fundamental Adhesion

B fsT

B f sU

s f fs

B fs B s f

B B

T U

T U

22

2)1(3

B

B

B

ut

tE

22

2)1(3

B

B

B

ut

tE

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

DLC on Glass

Conclusions

• Can be a useful tool to estimate the fundamental interface toughness (adhesion) and the mechanical properties of thin films