High Rate Growth of SiO2 by

Thermal ALD Using Tris(di-

methylamino)silane and Ozone

Guo Liu, Ritwik Bhatia, Eric W. Deguns, Mark J.

Dalberth, Mark J. Sowa, Adam Bertuch, Laurent

Lecordier, Ganesh Sundaram, Jill S. Becker

Cambridge NanoTech Inc.

ALD 2011

Cambridge, MA, USA

June 26-29, 2011

Many Existing SiO2 ALD Processes are Unsatisfactory

A few examples

(1) TEOS Process, tetraethoxysilane, Si(OCH2CH

3)4

- Reacts with H2O when catalyzed by NH

3 or amines, even

at room temperature

- 0.07-0.08 nm/cycle at 300 K

J. D. Ferguson,a E. R. Smith,a A. W. Weimer,b and S. M. George, J.

Electrochem. S., 151 (8), G528-G535 (2004)

• Too slow, required large exposures (∼1010 L) for surface

reactions to reach completion (1 L =10-6

Torr-s)

Introduction: Thermal ALD of SiO2

1

(2) 3-aminopropyltriethoxysilane process, O3 and H

2O:

H2N(CH

2)3Si(OCH

2CH

3)3

- Self-catalyzed hydrolysis due to existence of amino group

- 120-250°C, GPC=0.05~0.06nm/cycle

J. Bachmann, R. Zierold, Y. T. Chong, R. Hauert, C. Sturm, R. Schmidt-Grund, B.

Rheinlnder, M. Grundmann, U. Gosele, and K. Nielsch, Angew. Chem. Int. Ed. 47,

6177-6179 (2008).

• High quality SiO2

• Slow process (requires two oxidants H2O and O

3)

• Unreacted precursor caused frequent damages to vacuum

pumps

Introduction: Thermal ALD of SiO2

2

(3) TDMAS (or 3DMAS)-H2O

2 Process:

tris(dimethylamino)silane, [(CH3)2N]

3SiH

- First reported to be a reactive precursor with H2O

2 oxidant

B. B. Burton, S. W. Kang, S. W. Rhee, and S. M. George, J. Phys. Chem. C 113,

8249–8257 (2009)

• Precursor can be used in a wide temperature range: 150-550°C

• Inability of H2O

2 to remove all Si-H bonds at lower temperatures

usable temperature ≥ 450°C

• Low thermal stability of H2O

2

Introduction: Thermal ALD of SiO2

3

The TDMAS – O3 Process

TDMAS, [(CH3)2N]

3SiH

• High vapor pressure at ambient

temperature

BP=145-148°C, 16mmHg at 4°C

no heating needed

• Insoluble in H2O

• No reaction with H2O or O

2 up to 350°C

4

Three Different Reaction Modes

Cambridge NanoTech’s

ALD Reactors

(1) Continuous Mode

• Normal pulse/purge steps for all

precursors

(2) Partial Exposure Mode

• One precursor with an extra hold step

(pulse/hold/purge), staying in reactor

longer to increase residence time

• Different from an extended pulse time

(3) Full Exposure Mode

• All precursors with pulse/hold/purge

steps

0.20

0.30

0.40

0.50

0.60

20 40 60 80 100

Continuous Mode

Pre

ssu

re

Time

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 20 40 60 80

Partial Exposure (pusle 2)

Pre

ssu

re

Time

0.0

1.0

2.0

3.0

4.0

0 20 40 60 80 100 120

Full Exposure (both pulses)

Pre

ssu

re

Time 5

Continuous: very low growth rate ~ 0.02 nm/cycle Partial Expo: TDMAS exposure (28 sec.) key to high growth rate Full Expo: O3 exposure (7 sec.) further increased growth rate Growth rate much lower with H2O2

The TDMAS – O3 Process

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 100 200 300 400

SiO2 from [(CH3)2N]3SiH and O3 in Various ALD Modes

Full ExposurePartial Expo. (TDMAS)Continuous ModeFull Expo. with H2O2

SiO

2G

row

th R

ate

(n

m/c

ycle

)

Deposition Temperature (oC)

6

TDMAS Saturation and Linear Growth

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.000 0.010 0.020 0.030 0.040 0.050

Saturation Curve of [(CH3)2N]3SiH at 250°C

SiO

2G

row

th R

ate

(nm

/cyc

le)

[(CH3)2N]3SiH Pulse Time (sec.)

0

10

20

30

40

50

60

70

80

0 100 200 300 400 500 600 700

Full EXPO SiO2 from [(CH3)2N]3SiH and O3 at 200°C

SiO

2Th

ickn

ess

(nm

)

Number of Cycles

• Deviation from a flat saturation curve with TDMAS dose could be

due to less than full saturation from limited exposure time

• Growth is linear without nucleation delay

• Process completely repeatable

7

Electrical Properties by mercury probe

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

0 100 200 300 400

SiO2 from [(CH3)2N]3SiH and O3 Full Expo

Leak

age

Cu

rre

nt a

t 2

MV

/cm

(A/c

m2)

Deposition Temperature (°C)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0 100 200 300 400

SiO2 from [(CH3)2N]3SiH and O3 Full Expo

Bre

akd

ow

n F

ield

(MV

/cm

)

Deposition Temperature (°C)

Leakage Current and Breakdown Strength

• Data scattered due to changing properties with time

• 80-120°C process produced SiO2 films with lowest leakage

current and highest breakdown strength; 200°C the worst

8

SiO2 films absorb H

2O in air

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

0 2 4 6 8 10 12

Full Expo SiO2 from [(CH3)2N]3SiH and O3 at 100°C

5 days laterNext dayfreshD

iele

ctri

c C

on

stan

t at

10

kHz

Voltage (V)

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

0 1 2 3 4 5 6 7

Full Expo SiO2 from [(CH3)2N]3SiH and O3 at 100°C

Fresh

5 days later

Cu

rre

nt (

A/c

m2)

Electric Field (MV/cm)

Change in Dielectric Constant, Leakage Current and

Breakdown Field with Time

• Dielectric constant of fresh 100°C SiO2 close to ideal value of 3.9

• It increased with air exposure time until reached a saturated state

9

SIMS Analysis

0

5

10

15

20

25

0 100 200 300 400

H

C

N

Deposition Temperature (°C)

H, C

, N C

on

cen

trat

ion

(at

%)

Imprity Levels in SiO2 from

[(CH3)2N]3SiH and O3 by SIMS

1.0E+18

1.0E+19

1.0E+20

1.0E+21

1.0E+22

1.0E+23

1.0E+24

0 100 200 300 400 500 600 700

SIMS Profiles of SiO2 deposited at 350°C

C N O Si H

Inte

grat

ed

Co

un

ts

Depth (Å)

• Very Low C impurity (highest at 0.2 at% with 100°C SiO2)

• Low N at high temperatures (highest at 3.6 at% with 100°C SiO2)

• High concentrations of H (highest with 200°C SiO2)

10

30

32

34

36

38

40

42

-5 0 5 10 15 20 25 30 35

300°C annealed in NH3

80C SiO2

100C SiO2

150C SiO2

Thic

kne

ss (

nm

)

# of days after anneal

Before anneal

immediately after anneal

1.37

1.39

1.41

1.43

1.45

1.47

-5 0 5 10 15 20 25 30 35

300°C annealed in NH3

80C SiO2

100C SiO2

150C SiO2R

efr

acti

ve I

nd

ex

n a

t 6

33

nm

# of days after anneal

Before anneal

immediately after anneal

• Annealing at ≥300°C led to 3-5% decrease in thickness and a

slight drop in refractive index

• Refractive index partially reversible upon re-exposure to air

H2O-saturated SiO

2 films:

annealing in vacuum or NH3

11

0

2

4

6

8

10

12

-5 0 5 10 15 20 25 30 35

300°C annealed in vacuum

80C SiO2100C SiO2 150C SiO2

Die

lect

ric

Co

nst

ant

at

10

kHz

# of days after anneal

Before anneal

immediately after anneal

0

2

4

6

8

10

12

-5 0 5 10 15 20 25 30 35

300°C annealed in NH3

80C SiO2100C SiO2150C SiO2

Die

lect

ric

Co

nst

ant

at10

kHz

# of days after anneal

Before anneal

immediately after anneal

Before anneal

H2O-saturated SiO

2 films:

annealing in vacuum or NH3

• 300°C anneal in NH3 was more effective than vacuum anneal

Dielectric constant dropped to 3.9 for NH3-annealed 80-120°C SiO

2

• NH3 facilitates removal of OH groups?

• Reversible dielectric constant with re-exposure to air

12

Summary

• TDMAS-O3 a good ALD process for SiO

2

• Full exposure mode helps growth saturation

• 80-120°C SiO2 films have better electrical properties

• Uncapped ALD SiO2 absorbs H

2O in air

• Annealing of H2O-absorbed SiO

2 films in NH

3 at 300-

350°C restores electrical properties

13