Material Simulation of Carbon Thin Film

Kwang-Ryeol Lee

Korea Institute of Science and Technology

Seminar @ Sandia National Lab. (2005. 4. 29)

People

http://diamond.kist.re.kr/DLC

Present Simulation Topics

• Novel diluted magnetic semiconductors : SiC, Diamond, GaN, GaAs, TiN, various Nanowires

• Interfacial intermixing of metallic multilayers : Asymmetry of interfacial intermixing in Al-Co, Co-Cu, Au-Pt

• Field emission simulation of doped CNTs : N and B doped CNT

• Atomic scale analysis of amorphous carbon thin film : Stress control

• Prototype TCAD for nano CMOS devices (just launched)

SiC:TM(Si1-xTMxC) Si-substituted TM

-4 -2 0 2 4-4

-2

0

2

4

DOWN

UP

-SiC:CrSi

64 atom cell

DO

S (

Sta

tes/

eV)

E - EFermi

(eV)

Cr(3d)

-4 -2 0 2 4-4

-2

0

2

464 atom cell

-SiC:MnSi

DOWN

UP

DO

S (

stat

es/e

V)

E - EFermi

(eV)

Mn(3d)

x = 0.03 (3%)

VASP with PAW potential

Search for DMS materials

Deposition in Co-Al System

Co on AlAl on Co

Asymmetric Intermixing

Au on Pt (001)

Pt on Au (001) Co on Cu (100)

Cu on Co (100)

Co on Al

Al on Co

Field Emission from CNT : Calculation

Plane wave

Localized basis

(5,5) Caped CNT, 250atoms

• Ab initio tight binding calc. To obtain self-consistent potential and initial wave function

• Relaxation of the wave functionBasis set is changed to plane wave to emit the electrons

• Time evolutionEvaluation of transition rate by time dependent Schrödinger equation

Coupled states between localized and extended states contribute to the field emssion.

B stateA state C state D state

π*+localized stateLocalized stateπ bond:Extended state

Emission from N doped CNT

Enhanced Field Emssion by Nitrogen Doping

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0 1 2 3 4

Pure CNT

Emitted current(μA)

Total current: 8.8A

En

erg

y st

ate

s (e

V,

E-E

F)

-1.4

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0 1 2 3 4

Nitrogen doped CNT

Emitted current(μA)E

ne

rgy

sta

tes

(eV

, E

-EF)

Total current: 13.2A

AB

C

D

Nitrogen Effect

EF

- N-doped CNT

- Undoped CNTLocalized state

The nitrogen has lower on-site energy than that of carbon atom.T. Yoshioka et al, J. Phys. Soc. Jpn., Vol. 72, No.10, 2656-2664 (2003).

The lower energy of the localized state makes it possible for more electrons to be filled in the localized states.

Doped Nitrogen Position

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

Ban

d sh

ift (

eV)

8

10

12

14

16

18

20

22

Em

ission current (A

)

Present Simulation Topics

• Novel diluted magnetic semiconductors : SiC, Diamond, GaN, GaAs, TiN, Various Nanowires

• Interfacial intermixing of metallic multilayers : Asymmetry of interfacial intermixing in Al-Co, Co-Cu, Au-Pt

• Field emission simulation of doped CNTs : N and B doped CNT

• Atomic scale analysis of amorphous carbon thin film : Stress control

• Prototype TCAD for nano CMOS devices (just launched)

Bond Structure of Carbon Allotropes

1S2 2S22P2

Diamond-like Carbon

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

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

Heart valve Hard disk

a-C:H ta-C

2-D Analogy of Structure

High Residual Compressive Stress

Film Deposition

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

2 4 6 8 10 1210

20

30

40

50

60

70

80

90

100

Fallon Weiler Xu Chhowalla

sp3 f

ract

ion

Stress (GPa)

Ha

rdn

ess

Hardness and Residual Stress

2 4 6 8 10 1210

20

30

40

50

60

70

80

90

100

Fallon Weiler Xu Chhowalla

sp3 f

ract

ion

Stress (GPa)

Ha

rdn

ess

Hardness and Residual Stress

0 10 20 30 40 500

20

40

60

80

100

Stress

Hardness

No

rmal

ized

Pro

per

ties

(%

)

Si Concentration (at.%)

Stress Reduction by Si Incorporation

C.-S. Lee et al, Diam. Rel. Mater., 11 (2002) 198-203

S.-H. Lee et al, to be Submitted (2005)

Molecular Dynamics Simulation

• Brenner force field for C-C bonds• Tersoff force field for C-Si and Si-Si bon

ds• Diamond substrate : 6a0 x 4.75a0 x 6a0

– 1,368 atoms with 72 atoms per layer• Deposition

– Total 2,000 atoms– Incident Kinetic Energy : 75 eV for both

C and Si– Si concentration : 0.5 % ~ 20 %

Fixed Layer

FullyRelaxedLayer

Deposited atomscreated on this plane

Snapshots after Deposition

0.0 %

0.5 %

1.0 %

2.0 %

3.0 %

5.0 %

10.0 %

20.0 %

0 5 10 15 20 250

1

2

3

4

5

6

7

Resid

ual S

tress[G

Pa]

Si Concentration [at.%]

Experiment

MD Simulation

Experiment : C.-S. Lee et al, Diam. Rel. Mater., 11, 198 (2002).

Residual Compressive Stress

Atomic Bond Structure

0 5 10 15 20

0

10

20

30

40

50

60

70

80

sp

sp3

sp2

Bo

nd

Ratio

[%

]

Si Concentration [at.%]

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

eak

Pos

ition

(cm

-1)

Si Concetration (at.%)

Experiment : C.-S. Lee et al, Diam. Rel. Mater., 11 (2002) 198-203

Raman G-peak PositionMD Simulation

2.54 Å

1.54 Å

1.0 1.5 2.0 2.5 3.0 3.5 4.0

0

2

4

6

C- CSatellite

C- C1st:1.54 A

Rad

ial D

istr

ibutio

n F

unc.

[g

(r)]

Distance [A]

C- C2nd:2.54 A

Radial Distribution of Pure a-C and Diamond

Radial Distribution Function

1.0 1.5 2.0 2.5 3.0 3.5 4.0

0

3

6

9

12

15

18

212.54 A

20 at.%

5 at.%

3 at.%

1 at.%

0.5 at.%

C- C satellite

Si- Si1st,C- C2ndSi- C1st

Rad

ial D

istr

ibutio

n F

unc.

[g

(r)]

Distance [A]

C- C1st

Pure ta- C film0 5 10 15 20 25

0

1

2

3

4

5

6

7

Resid

ual S

tress[G

Pa]

Si Concentration [at.%]

Experiment

MD Simulation

Carbon for Satellite Peak

93.1°94.2°

2.184 A

2.185 A

60 80 100 120 140

0

20

40

60

80

100

120

0.5 at.% Si Incorporation

No

rmalized

Co

unt

Ratio

[%

]

Angle [Degree]

Pure ta- C

109.5° 120.0°

Bond Angle Distribution

W-DLC by Hybrid Ion Beam Deposition

Sputter gun: Third elements addition to DLC (W, Ti, Si …);

Ion gun: Easy controlling the ion bombardment energy with high ion flux.

Wn+

H+, Cm+

A.-Y. Wang et al, Appl. Phys. Lett., 86, 111902 (2005).

0 2 4 6 8 101.0

1.5

2.0

2.5

3.0

3.5

Res

idua

l str

ess

(GP

a)

W concentration (at.%)

(a)

-1 0 1 2 3 4 5 6 7 8 9 1015

20

25

30

35

40

45

100

120

140

160

180

200

Ela

stic

mod

ulus

(GP

a)

Har

dnes

s (G

Pa)

W concentration (at.%)

hardness

elastic modulus(b)

Stress & Mechanical Properties

21±3 GPa

170±15 GPa

TEM Microstructures

8.6

4 nm

-W2C(102)

-W2C(101)

1.9

4 nm

W atoms are dissolved in a-C:H matrix.

Nano-crystalline -W2C phases evolve.

4 nm

3.6-W2C (101)

-W2C 4 nm

2.8

0 2 4 6 8 101.0

1.5

2.0

2.5

3.0

3.5

Res

idu

al s

tres

s (G

Pa)

W concentration (at.%)

(a)

Amorphous to crystalline WC1-x transition occurs.

Raman & EELS Spectra

400 600 800 1000 1200 1400 1600 1800 2000

3.6

2.8

W 1.9 at.%

6.0

4.7

Inte

nsity

(a.u

.)

Wave number (cm-1)

8.6

(a)

0 1 2 3 4 5 6 7 8 9 10

1551

1554

1557

1560

1563

1566

1569

G-P

eak

posi

tion

(cm

-1)

W concentration (at.%)

(b)

I/I = 0.550.1

TEM Microstructures

8.6

4 nm

-W2C(102)

-W2C(101)

1.9

4 nm

W atoms are dissolved in a-C:H matrix.

Nano-crystalline -W2C phases evolve.

4 nm

3.6-W2C (101)

-W2C 4 nm

2.8

0 2 4 6 8 101.0

1.5

2.0

2.5

3.0

3.5

Res

idu

al s

tres

s (G

Pa)

W concentration (at.%)

(a)

Amorphous to crystalline WC1-x transition occurs.

90 100 110 120 130

0.00

0.08

0.16

0.24

0.32

0.40

0.48

0.56

0.64

Tota

l ene

rgy

vari

atio

ns, (

eV)

Bond angle (degree)

C-C bond W-C bond

Role of W atoms- ab initio calculation

C

CH

W

CH

Conclusions

• Various properties of a-C films generated by MD simulation agrees well with those of experimentally obtained a-C films.– Brenner force field for C-C bond– Tersoff force field for Si-Si and Si-C bond

• Stress reduction mechanism based on the atomic scale structure analysis– Small amount of Si incorporation in a-C network effectively

relaxes the distorted bonds. – W atoms dissolved in a-C matrix play a role of pivot site w

here the atomic bond distortion can occur without inducing a significant increase in elastic energy.

Newly Launched Project @ KIST

• Massive MD/MC simulation technology to understand atomic scale phenomena of 100 million atoms system.

• Electron transport analysis technology to characterize nano-device.

Next Generation Prototype TCAD for nano CMOS FET simulation

Next Generation Prototype TCAD for nano CMOS FET simulation

Effect of atomic scale interfacial structureon the performance of nano-scale CMOS device

Technology Oriented CAD (TCAD)

• using computer simulations to develop and optimize semiconductor processing technologies and devices

• Process CAD + Device CAD

• using computer simulations to develop and optimize semiconductor processing technologies and devices

• Process CAD + Device CAD

Process CAD Device Structure Device CAD

Device Properties

Next Generation TCAD for Nano-devices

• Atomic scale description of the devices • Electron transport in subatomic scale

and via non-continuum media

• Atomic scale description of the devices • Electron transport in subatomic scale

and via non-continuum media

Device StructureDevice CAD

Process CAD

Device Properties

CMOS FET : Scale down issue

1~3nm

0.13 m

<10 nm

1. Atomic scale oxide-channel structure simulation

2. Device characterization for various interface structures

1. Atomic scale oxide-channel structure simulation

2. Device characterization for various interface structures

Research Flow

3 Tflop Cluster Supercomputing Environment (KIST)

Process SimulationBased on Massice MD/MC simulation

Device Simulation Based on TB Theory and Electron Drift Theory

KIST KIAS

KIST Supercomputer : grand.kist.re.kr

• Calculation Nodes : 512 nodes– Intel Xeon 2.4GHz Dual – RedHat7.3 Kernel 2.4.20 SMP– Myrinet PCI-X D/Cisco Gigabit SW– 2G PC2100 ECC SDRAM– IDE 80GB HDD

Storage Node

512 Computing Nodes

Myrinet

Public Network

Head Node

3.07 TFlops

What we have to do

• Have a massive MD/MC code with wide range of applicability, which can cover various processes such as deposition, oxidation, diffusion, implantation and other nano-scale processes.

• Obtain oxide potentials for Si-O and Hf-O and integrate into the massive MD code.

• Visualize the 100 million atoms assembly and characterize the atomic scale structures (bulk and interface).