High Temperature Oxidation of TiAlN Thin Films for Memory Devices Sang-Shik Park

Sangju National Univ. Electro-Ceramics Lab.

High Temperature High Temperature OxidationOxidation of TiAlN of TiAlN ThinThin FilmsFilms forfor Memory DevicesMemory Devices

Sang-Shik Park

Dept. of Materials Eng., Sangju National Univ.

Sangju, Kyungbuk 742-711, Korea ([email protected])


IntroductionIntroduction

DRAM cell structure and problems

Required conditions for barrier layers in DRAM applications Withstand at oxygen atmosphere above 650oC, 30min. Prevent oxygen diffusion and remain electrically conductive Total contact resistance after oxidation : 400 Ω

Ref. : Kotecki, et al., IBM J. Res. Develop. Vol.43. No.3 (1999)



Properties of candidate materials

Research trend for barrier layer

Formation of protective layer on surface (TiAlN, TiZrN) Amorphous film (TaSiN, TiSiN, WSiN)

Barrier

Material

Processibility Resistivity

(m Ω-cm)

Oxidation resistance

TiN Easy 0.2 Poor

TaN Easy - Poor

TiAlN, TaAlN Moderate 0.3~0.5 Good

TaSiN, TiSiN Easy 1~10 Good



Crystal Structure

TiN TiAlN

Ti

Al

N

Solubility of Al in TiN (ref.)- Ti1-xAlxN film by sputtering ; x : 0.4 (Ts ; 500 ) - Ti1-xAlxN film by arc evaporation : x ; 0.6 0.7 (T∼ s ; 400~450 )

Objective of this study Properties of TiAlN films with preparation condition

Effects of Al content in TiAlN films

Oxidation behavior of TiAlN films


Experimental Experimental ConditionsConditions

OXIDATION CONDITION :

O2(1 atm), 650~800 oC, 30∼60 min.(RTA)

Deposition condition by sputtering

Target Ti and Al

Substrate poly-Si

D (target-substrate) 50 mm

Base pressure 5.0 ×10-7 torr

Deposition temperature 400 oC

Working pressure 1.0 ×10-2 torr

Rf power 250 W (Ti)

DC power 20~150 W (Al)

Sputtering gas Ar, N2


as-depo. filmsas-depo. films

XRD patterns of Ti1-xAlxN thin films with various Al content.

30 40 50 600

1000

2000

3000

4000

5000

6000

(200)(111)

Ti0.48

Al0.52

N

Ti0.55

Al0.45

N

Ti0.74

Al0.26

N

TiN

Inte

nsi

ty(a

rb.

un

its)

2 theta

Increase of Al content :- Decrease of lattice parameter - Amorphous structure


micro-structuremicro-structure

SEM cross-section images of (a)TiN, (b)Ti0.89Al0.11N and (c) Ti0.48Al0.5

2N thin films.

Increase of Al content :- finer micro-stucture - glass like structure

Difficulty in diffusion of adatom due to compositional defects Decrease of G.B. mobility

(a) (b)

200nm

(b)

(c)


Effects of NEffects of N22 gas ratio gas ratio

XRD patterns of the Ti1-xAlxN films as a function of N2 flow ratio.

30 40 50 60-2000

-1500

-1000

-500

0

500

1000

1500

2000

N2/(Ar+N2) : 83%

N2/(Ar+N2) : 50%

N2/(Ar+N2) : 9%

Inte

nsity

(arb

. uni

ts)

2 theta

83% ; Ti0.82Al0.18N 50% ; Ti0.74Al0.26N 9% ; Ti0.70Al0.30N


ResistivityResistivity

Resistivity of Ti1-xAlxN films as a function of (a) Al content and (b) N2 flow ratio.

0 10 20 30 40 50

800

1200

1600

2000

Res

isti

vity

(¥ì¥

Ø-§

¯)

Al concentration(atomic %)0 20 40 60 80

0

500

1000

1500

2000

Resis

tivi

ty(§

Ù-c

m)

N2 gas ratio(%)

(a) (b)Effect of Al

content


After OxidationAfter Oxidation

XRD patterns of (a)Ti1-xAlxN films annealed at 800oC for 1hr and (b) Ti0.74Al0.26N films annealed at various temp. for 1hr.

30 40 50 60

0

500

1000

1500

2000

2500

3000

3500

TiO

2(11

1)

(200

)

TiO

2(10

1)(1

11)

Ti0.55

Al0.45

N

Ti0.89

Al0.11

N

TiN, 650oC

TiO

2(20

0)

TiO

2(10

1)

Inte

nsity

(arb

. uni

ts)

2 theta30 40 50 60

0

500

1000

1500

2000

2500

3000

3500

4000

(200

)

(111

)

800oC

720oC

650oC

TiO

2(21

1)

TiO

2(11

1)

TiO

2(10

1)

Inte

nsity

(arb

. uni

ts)

2 theta

(a) (b)


micro-structure after oxidationmicro-structure after oxidation

SEM cross-section images of Ti0.74Al0.26N films annealed at (a) 650oC, (b) 720oC and (c) 800oC.

(c) (c)


Oxidation of TiN filmOxidation of TiN film

AES depth profile of TiN film annealed at 650oC for 30min.

0 100 200 300 400 500 600 7000

20

40

60

80

100

N Ti O Si

Ato

mic

co

nce

ntra

tion

(%)

Etch time(sec)


Oxidation vs. temperatureOxidation vs. temperature

AES depth profile of Ti0.74Al0.26N films annealed at (a) 650oC, (b) 720oC and (c) 800oC for 1hr.

0 200 400 600 800 1000 1200 1400 1600

0

20

40

60

80

100(a) Ti

O Al Si N

Ato

mic

con

cent

ratio

n(%

)

Etching time(sec)

0 200 400 600 800 1000 1200 1400 1600 18000

20

40

60

80

100(b)

Ato

mic

con

cent

ratio

n(%

)

Etching time(sec)

0 200 400 600 800 1000 1200 1400 1600 1800 2000

0

20

40

60

80

100(c)

Ato

mic

con

cent

ratio

n(%

)

Etching time(sec)


Oxidation vs. Al contentOxidation vs. Al content

AES depth profile of Ti1-xAlxN films annealed at 800oC for 1hr.

0 400 800 1200 1600 2000 24000

20

40

60

80

100

Ti0.55

Al0.45

N Al Si N Ti O

Ato

mic

con

cent

ratio

n(%

)

Etching time(sec)

0 400 800 1200 1600 2000

0

20

40

60

80

100

Ti0.89

Al0.11

N

Ato

mic

con

cent

ratio

n(%

)

Etching time(sec)

0 400 800 1200 1600 2000

0

20

40

60

80

100

Ti0.74

Al0.26

N

Ato

mic

con

cent

ratio

n(%

)

Etching time(sec)


Oxidation behaviorOxidation behavior

RBS spectra of Ti0.70Al0.30N and (b) Ti0.82Al0.18N films annealed at 800oC for 1hr.

100 200 300 400 5000

1000

2000

3000(a)

NO

Al

Ti

As-depo. Oxidized

Yie

ld

Channels

100 200 300 400 5000

1000

2000

3000

Bulk Si

N O

Al

Ti

(b) As-depo. Oxidized

Yie

ld

Channels

Film with higher Al content :- Decrease of oxide thickness- Oxide form ; AlTiNO (Incease of Al content)


Oxidation KineticsOxidation Kinetics

Oxidation kinetics

dox = 2 (Dt)1/2

D = D0 exp (- Ea / kT)

dox ; oxide thickness, D ; diffusion coefficient, t ; oxidation time,

Ea ; activation E., k ; Boltzmann’s const., T ; temperature

Ti-richAlTiNO

TiAlN

Si

TiO2 TiO2

TiAlN

Si

Al-richAlTiNO

650 oC / lower Al content 720 oC / higher Al content


Oxidation KineticsOxidation Kinetics

(a) Dependence of the thickness of oxide layer on oxidation time and (b) Arrhenius plot of diffusion coefficient.

2 4 6 8 10 12

10

20

30

40

50

60

70

80

90

923oK

993oK

1073oK

Oxi

de th

ickn

ess(

nm)

Time(min)1/2

0.9 1.0 1.1 1.2 1.3

10-16

10-15

10-14

10-13 TiN(ref.)Ea = 2.0-2.1eV

TiAlNEa = 2.12eV

Diff

usio

n C

oeff

icie

nt,

D(c

m2 /s

ec)

1000/T(oK)

(a) (b)

Ti0.74Al0.26N films

ref. : Wittmer, et al., JAP. .52, 11 (1981)


TiZrN film for comparisonTiZrN film for comparison

AES depth profile of Ti0.73Zr0.27N films annealed at 720oC for 30min.

0 400 800 1200 1600

0

20

40

60

80

100

Si Zr N Ti O

Ato

mic

con

cent

ratio

n(%

)

Etching time(sec)annealed

As depo.

Annealed


SummarySummary

Ti1-xAlxN barrier layer was deposited by reactive magnetron sputtering

Effects of Al content - Resistivity increases with Al incorporation - Excess Al(x=0.52) reduce the crystallinity of films due to lattice defects - N2 flow rate affects the Al/Ti ratio of films

- Oxidation resistance increases with increasing the Al content

Oxidation Kinetics of TiAlN thin films

- Diffusion rate of Al ion to the surface is higher at high temperature - Protective layer on the surface is AlTiNO layer - Films with higher Al content forms thicker protective layer - Thinner Al-rich surface layer results in easier O diffusion - Oxidation of TiAlN layer is diffusion limited process - Ti0.74Al0.26N layer show diffusion coefficient of ~10-15 /s at 800oC and

activation Energy of 2.12eV

Documents

High Temperature Oxidation of TiAlN Thin Films for Memory Devices Sang-Shik Park