Nitride Superlattice Thin Films Nitride Superlattice Thin Films for Superhard Coatingsfor Superhard Coatings

Ramou Akin-Cole

MRSEC Program 2004

Advisor: Paul Salvador

Graduate Student: Nitin Patel

BackgroundBackground

Hard materials (e.g. TiN, Al2O3) used successfully as coatings to increase tool life by a factor of 4-20.

Diamond and cubic Boron Nitride are the hardest known materials.

Diamond gets oxidized in air at high temperatures.

Cubic Boron Nitride is difficult to produce as thin film.

Cutting tool in operation

How can we design materials that have hardness How can we design materials that have hardness values approaching the hardest known materialsvalues approaching the hardest known materials??

Project ObjectivesProject Objectives Study orientation effects and

hardness with increasing Al content in monolithic Ti1-xAlxN.

Grow Thin Films using Physical Vapor Deposition(PVD) Technique called Pulsed Laser Deposition.

Characterize films using X-Ray Diffraction and Nanoindenter

Grow TiN/Ti1-xAlxN superlattices in both (100) and (111) direction.

Substrate Substrate

TiNTi1-xAlxN

TiNTi1-xAlxN

TiNTi1-xAlx NTiN

ExperimentsExperiments

SrTiO3 (Perovskite) MgO, TiN, AlN(Rocksalt)

TiN AlN MgO STOa(Å) 4.24 4.04 4.21 3.91

Deposition Parameters

PRESSURE : 0.001 - 0.2 Torr

TEMPERATURE: RT - 950 °C

FLUENCE : 2-6 J/cm2

FREQUENCY : 1-10 HzCOOLING: 10-5- 200 Torr

Focusing LensWindow

Deposition Chamber

Target

Plume

Laser Beam

Substrate

Substrate Heater

Target Rotator

Pulsed Laser Deposition

•KrF Excimer Laser:λ = 248 nm

• Energy: ~2 /J cm2

• : 3 Frequency Hz

TiTi1-x1-xAlAlxxN films by alternating N films by alternating depositionsdepositions

Focusing LensWindow

Deposition Chamber

Target

Plume

Laser Beam

Substrate

Substrate Heater

Target Rotator

Pulsed Laser Deposition

•KrF Excimer Laser:λ = 248 nm

• Energy: ~2 /J cm2

• : 3 Frequency Hz

TargetRate

(Å/pulse)# of

pulsesThickness

(Å)

TiN 0.12 9 1.08

AlN 0.29 3/4 1.02

1. Deposit submonolayer of TiN (i.e., 1/4 unit cell thick)

2. Switch target

3. Deposit submonolayer of AlN (i.e., 1/4 unit cell thick)

4. Switch Target

5. Repeat to certain film thickness of Ti1-xAlxN

200 nm Ti0.5Al0.5N : {9Ti / 3Al / 9Ti / 4Al} x 475

10

100

1000

10000

100000

1000000

10000000

100000000

1000000000

10000000000

30 32 34 36 38 40 42 44 46 48 50

SrTiO 3

111

Ti:Al =0:1

Ti:Al =1:3

Ti:Al =1:1

Ti:Al =3:1

10

100

1000

10000

100000

1000000

40 42 44 46 48 50

Monolithic Ti1-xAlxN Films

Inte

nsit

y (

a.u.

)

SrTiO3

100

ST

O (

200)

Ti:Al =1:0

10

100

1000

10000

100000

1000000

10000000

100000000

1000000000

10000000000

30 32 34 36 38 40 42 44 46 48 50

SrTiO 3

111

Ti:Al =0:1

Ti:Al =1:3

Ti:Al =1:1

Ti:Al =3:1

Inte

nsit

y (

a.u.

)

Orientation Intensities and Orientation Intensities and Lattice Parameter versus Lattice Parameter versus

CompositionComposition

1

10

100

1000

10000

0 0.5 1

100 Intensities

111 Intensities

Inte

nsit

y (

a.u.

)

Al:Ti ratio

3.96

4.01

4.06

4.11

4.16

4.21

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Al:Ti ratio

Lat

tice

Par

amet

er (

Å)

111 Substrate

30 35 40 45 50

2-Theta

Intensity

100 Substrate

30 35 40 45 50

2-Theta

TiN/Ti0.25Al0.75N multilayer

MgO

(11

1)

SrTiO3

ST

O (

111)

MgO

Bragg (200) Peak

Bragg (200) Peak

Bragg (111) Peak

MgO

(20

0)Bragg (200) Peak-1

MgO

+1

SrTiO3

Bragg (200) Peak

ST

O (

200)

-1-2

Hardness versus Ti:Al ratioHardness versus Ti:Al ratio

Hardness vs composition

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100

% Al

Conclusion Al was difficult to grow in crystalline form TiN and Ti1-xAlxN grow epitaxially in 100 direction and not

in 111 direction. Superlattices grow well in 100 direction and not in 111

orientation The hardness values of superlattices show significant

enhancement, over individual component Optimizing processing conditions can enable the growth

of (111) oriented monolithic Ti1-xAlxN films and superlattices