Plasma-assistedALDofSiliconassisted ALD of...

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Plasma assisted ALD of SiliconPlasma-assisted ALD of Silicon Nitride and Gallium Nitride

Harm KnoopsHarm KnoopsOxford Instruments Plasma Technology

© Oxford Instruments 2014 CONFIDENTIAL

The Business of Science®

SiNx and GaN ALD applicationsThe Business of Science®

ALD spacers for transistors ALD for GaN HEMTs

Oxide

AlGaN

Gatesource drain

Poly-Si

SiNSiN SiO

xHKMG

GaN

buffer

substrate

Koehler et al., IOP Conf. S.: Mater. Sci. Eng. 41, 012006 (2012) • Achieving low defect density at

low deposition temperature.

substrate

• Oxygen and processing barrier• Spacing source and drain

p p• Potential ALD layers

• Al2O3

• HfAlO• HfAlOx

• AlN• SiNx ALD of nitrides

Conformal high-quality ALD of SiNx


• GaN


This presentationThe Business of Science®

Challenges:• ALD f it id ft diffi lt• ALD of nitrides often difficult

(e.g., low reactivity for thermal processes).• Desire for robust process and high material quality.p g q y

This presentation:• Recent SiNx and GaN processes:

• SiNx using BTBAS and N2 plasmaKnoops et al presented at ALD 2013 conference San Diego

• GaN using TEGa and H2/N2 plasma

Knoops et al., presented at ALD 2013 conference San Diego and ALD 2014 conference in Kyoto

Sharp et al., poster at ALD 2013 conference San Diego

• Indentify important plasma parameters:• Pressure gas mixture gas residence time

p , p g


Pressure, gas mixture, gas residence time.


OutlineThe Business of Science®

• IntroductionIntroduction

• ALD of SiNx:

• Process characteristics

• Effect of residence time• Effect of residence time

• ALD of GaN:


• Eff t f H /N ti d l• Effect of H2/N2 ratio and plasma pressure.

• Conclusions



Experimental detailsThe Business of Science®

FlexAL at NanoLab@TU/eALD cycle

N2 plasma10 s

SiH2(NHtBu)2

(BTBAS)

ALD cycle

10 s600 W

40 mTorr

(BTBAS)150 ms50 oC

N N + NN2, N2 , N, etc.

Turbo pump and load-lock for low moisture background.



Saturation curvesThe Business of Science®

0 5 BTBAS dose time N2 plasma exposure

0.4

0.5

e (Å

)

0 6

0.8

e (Å

) 100°C

0.2

0.3

h pe

r cyc

le

0.4

0.6

200°C

th p

er c

ycl

0 0

0.1

Gro

wth

0 0

0.2500°CG

row

t

200 °C0 5 10 15

0.0

N2 plasma exposure time (s)0 100 200 300

0.0

BTBAS dose time (ms)

• ALD behavior (soft saturation)• Growth-per-cycle (GPC) decreases

with increasing temperatures

• GPC shows first fast increase and then a slow decrease to final value


with increasing temperatures. final value


Growth versus temperatureThe Business of Science®

Linear growth Growth versus temperature

40

200 °C

nm)

100 °C1.0

1.2

Å)

g p

20

30

500 °C

ickn

ess

(n

0.6

0.8

per c

ycle

(Å

10

Film

Th

0.2

0.4

Gro

wth

p

0 500 1000 1500 2000 25000

Number of Cycles100 200 300 400 500

0.0

Temperature (°C)

• Linear growth with no growth delay for all temperatures.• Growth-per-cycle (GPC) decreases with increasing temperatures.



Effect of temperature and plasma exposureThe Business of Science®

Substrate temperature Plasma exposure time

20

25

at%

) C 20

25

(at%

)

200 °C10 s plasma

10

15

entra

tion

(a

H 10

15

cent

ratio

n

C

H

0

5

Con

ce

O

0

5 Con

c

O

100 200 300 400 5000

Temperature (°C)0 2 4 6 8 10 12 14 16

0

Plasma exposure time (s)

• Decrease of C and H with temperature and plasma exposure• Decrease of C and H with temperature and plasma exposure• Films are N-rich but become nearly stoichiometric at 500 °C• Decreasing plasma pressure to 10 mTorr less impurities: 6% C, 5% O


Decreasing plasma pressure to 10 mTorr less impurities: 6% C, 5% O


Oxford Instruments FlexAL systemThe Business of Science®

rapidRemote plasma• High radical density at

Plasma gas flow

pplasmastriking

low ion bombardment enabling high material quality Fast saturation

fast ALDvalves

even at low temperatures

APCFast pressure control and turbo pump• Efficient use of precursor

fully open in 150 ms

turbopump

pand fast saturation• Quick removal of reaction products even at

150 ms


pump room temperature


Effect of pressure and residence timeThe Business of Science®

Versus pressure Versus gas residence time

1.9

100 sccm N2 + 200 sccm Ar100 sccm N2

40 sccm N2

(@2e

V)

1.9

100 sccm N2 + 200 sccm Ar100 sccm N2

40 sccm N2

(@2e

V)

1.8

ctiv

e in

dex

1.8

tive

Inde

x

1.7

200 °C10 s plasma R

efra

c

1.7

Ref

rac

200 °C10 s plasma

0 20 40 60 80 100

Plasma pressure (mTorr)0 1 2 3 4

Residence Time (s)

M i l i ff d b h f fl d l• Material properties affected by change of flow and pressure control.• Data from films with different flow, follow residence time trend.

• Best material properties for short residence time.


Best material properties for short residence time.


Redeposition and saturation of plasma stepThe Business of Science®

0 5 200 °C High redeposition

High C content

0.4

0.5

= 1.7s

High redeposition

Plasma

A B

0 2

0.3

PC (Å

) = 0.58 s

= 0.35 s

0.1

0.2

GP 0.35 s

Plasma

Low redeposition

0 2 4 6 8 10 12 14 160.0

Plasma exposure time (s)

A B

Gas residence time: p ( )Gas residence time:• Long: high GPC due to C from redeposition at short plasma

exposures; long plasma exposure to “clean” surface


• Short: only small effect from redeposition


OutlineThe Business of Science®

• IntroductionIntroduction

• ALD of SiNx:


• Effect of residence time• Effect of residence time

• ALD of GaN:


• Eff t f H /N ti d l• Effect of H2/N2 ratio and plasma pressure.

• Conclusions



Experimental detailsThe Business of Science®

FlexAL system

GaN ALD cycle at 300 °C

H2/N2 plasma30:10 sccm5 s, 300 W

GaEt3 (TEGa)250 ms30 oC ,

5 mTorr30 C

H2, N2, H2+,

N2+, H, N,

NH3, etc.



GaN – achieving saturationThe Business of Science®

• 20:20 H2/N2 plasma (G.R.). 0,6 G.R. G.R.*

• Slow soft saturation.

• 30:10 H2/N2 plasma and APC l d (G R *)

0,4

0,5

ate

(Å/c

ycle

)

closed (G.R.*).

• Faster/normal saturation.

Å0,2

0,3

Gro

wth

Ra

• Lower GPC of ~0.4 Å/cyc

• Comparison dosing methods:

0 500 1.000 1.500 2.000

Dose Time (ms)

• Restricting the flow leads to a shorter half-cycle than in full flow.

Dose

Fl R t i ti

• Increase in precursor consumption efficiency.

Flow Restriction

Purge


0 1 2 3 4 5Time (s)


GaN – plasma gas mix and pressureThe Business of Science®

• Moving to H2-rich plasmas f

2,200,6) G R R Iincreases the refractive index• Also drops growth rate –

implication of increase in film2,00

2,10

0,4

0,5

tive

Inde

x

ate

(Å/c

ycle

) G.R. R.I.

implication of increase in film quality or precursor absorption effect. 1,80

1,90

0,2

0,3

0,0 0,5 1,0

Ref

ract

Gro

wth

Ra

• Decreasing the plasma pressure again shows the same t d

H2:N2 Ratio

2,200,6

e) G R R Itrend• Previous learning is that lower

pressure = higher ion energy =2,00

2,10

0,4

0,5

ctiv

e In

dex

Rat

e (Å

/cyc

le G.R. R.I.

pressure = higher ion energy = higher film quality

• Or redeposition effect.1,80

1,90

0,2

0,3

0 5 10 15 20

Ref

ra

Gro

wth

R

Plasma Pressure (mTorr)


O edepos t o e ect Plasma Pressure (mTorr) H2:N2 20:20


GaN – improving the qualityThe Business of Science®

90

100 C N O Si 90

100 C N OSi 90

100 C N O Si

40

50

60

70

80

Con

cent

ratio

n(%

)

Ga

40

50

60

70

80 Ga

once

ntra

tion(

%)

40

50

60

70

80 Ga

Con

cent

ratio

n(%

)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

10

20

30

Atom

ic C

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

10

20

30

40

Atom

ic C

o

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.00

10

20

30

Atom

ic C

• 15 mTorr for 5

Sputter time(min) Sputter time(min) Sputter time(min)

• 7 mTorr for 5 • 7 mTorr for 30 dseconds

• 15 at% C

seconds• 2 at% C

seconds• 2 at% C

• 10 at% O • 4 at% O • 2 at% O



Effect of temperatureThe Business of Science®

2,200,6

2,10

2,20

0,5

0,6

Inde

x

Å/c

ycle

) G.R. R.I.

1,90

2,00

0,3

0,4

frac

tive

I

h R

ate

(Å

1,800,20 100 200 300 400

Ref

Gro

wth

Temperature (ºC) 10 l

• ALD window found between 150 and 350 ºC

Temperature ( C) 10 s plasma

ALD window found between 150 and 350 C• Increase in temperature yields an increase in R.I. up to

2 11 at 300 ºC


2.11 at 300 C.


High quality materialThe Business of Science®

AES of 65nm ALD GaN layer

Best material obtained so far at:

90

100 C N O Sifar at:

• 350 °C temperature• 10 s plasma at 5 mTorr 60

70

80 Ga

tratio

n(%

)

p• H2/N2 plasma (30:10)• 400W power 30

40

50

Atom

ic C

once

nt

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.00

10

20A

Sputter time(min)Close to GaN stoichiometry



ConclusionsThe Business of Science®

• ALD of SiNx using BTBAS and N2 plasma• Reduced carbon and hydrogen content with longer

plasma exposure or lower pressure.Wid t t i d Cl t Si N f hi h• Wide temperature window. Close to Si3N4 for high temperature deposition.

• Residence time an important “hidden” parameter, p p ,due to redeposition effect.

ALD f G N i TEG d H /N l• ALD of GaN using TEGa and H2/N2 plasma• Higher quality with higher H2:N2 ratio and low

lplasma pressure.• ALD window between 150 °C and 350 °C• Close to GaN composition.


Close to GaN composition.

Plasma-assistedALDofSiliconassisted ALD of...

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