reaction and formation of la-silicate gate dielectrics on sic ... presen...comparison of basic...

Reaction and formation of La-silicate

gate dielectrics on SiC substrates

Tokyo Tech. FRC 1, Tokyo Tech. IGSSE 2, Mitsubishi Electric Corp.3, ○Y. M. Lei 1, S. Munekiyo 1, K. Kakushima 2,T. Kawanago 2, Y. Kataoka 2, A. Nishiyama 2, N.

Sugii 2, H. Wakabayashi 2, K. Tsutsui 2, K. Natori 1, H. Iwai 1, M.Furuhashi 3, N.Miura 3 and S. Yamakawa 3

Tokyo Insititute of Technology

Iwai・Kakushima labortary

SiC Power Device

Material Si SiC

Eg(ev)

Bandgap1.1 3.2

EBD(106V/cm)

Breakdown field0.3 3

μ(cm2/Vs)

mobility1450 900

Vsat(106cm/s)

Saturated velocity10 22

ĸ(W/cm2K)Thermal conductivity

1.5 5

Comparison of basic parameter of silicon and 4H-SiC Trendency of power conversion intensity

SiC is promising material for high efficiency power device

M. Ohashi et al, IEEE Trans. Electron Devices, vol. 60, no. 2, pp. 528-534

2

The advantage of SiC devices over silicon :

・High operation voltage (×10times) ・High operation frequency

・Better endurance of High temperature ・Low energy loss (1/100)

Issue of SiC power devices

Most report

http://jstshingi.jp/abst/p/10/1

018/naist1.pdf

Improvement of

channel mobility

is necessary

SiC has the ability of forming SiO2 by

thermal oxidation.

Relationship of mobility and Dit

http://www.iisb.fraunhofer.de/de/mobisic.html

Inverse proportional relationship of

mobility with interface state density

Reduction of Dit is critical to make high-speed-SiC power device

3

Approach of Interface Improvement

NO,N2O gas annealing

• Effective passivation of interface trap by annealing the gate

oxide in NO,N2O gas.

SiO2/LaSiOx gate oxides on SiC

• Recently a passivation of interface trap on SiC has been found

by forming LaSiOx interface layer on SiC substrate.

Drain

LaSiOx

SiO2

TaN/W

sicSource

Interface improvement can

be achieved by La-silicate

interface gate dielectrics

[1] X. Yang, et al., ICSCRM Th-2B-5 (2013). 4

Purpose and outline of this presentation

Investigate the interface reaction of La2O3 on 4H-

nSiC substrates to find the best process for gate

dielectric application

1.Introduction

2.Interface reaction of La2O3 on 4H-nSiC substrates

3.SiN barrier layer for La-silicate dielectrics

4.Formation of La-silicate dielectrics by SiO2 capped

annealing.

5.Conclusion

5

1.Introduction




annealing.

5.Conclusion

6

n-SiC(0001)substrate

La2O3 Deposition（EB）

FTIR measurement

Oxidation（5%O2/95%N2）

TEM analysis

Substrate cleaning(SPM, HF)

Sample preparation La2O3/SiC

FTIR measurement n-SiC substrate

La2O3 (2nm)

n-SiC substrate

Sample 1

Sample 2

500oC

1000oC

7

SiC(without La2O3))

5%O2 anneal:500oC—1000oC

12501300 1200 11001150 1050 1000

wavenumbers(cm-1)

Ab

sorb

an

ce (

a.u

.)

(a)

1000oC

600oC

La2O32nm/SiC)

Ab

sorb

an

ce (

a.u

.)12501300 1200 11001150 1050 1000

wavenumbers(cm-1)

(b)5%O2 anneal:500

oC—1000oC

1000oC

950oC

900oC

Oxidation on SiC substrate was enhanced by La2O3 film

Accompanied by La-silicate formation

Si-O-SiLa-O-Si

Si-O-Si

8

FITR spectra of oxidized SiC surface

(SiO2)

(SiO2)

(La-silicate)

SiO2

SiC

La-silicate

SiC

SiO2

sample：La2O3 (2nm)/SiC

SiC(0001) SiC(0001)50nm 10nm

La-silicateSiO2

TEM image of La2O3/SiC oxidized at 1000oC

• Agglomeration of La-silicates above SiO2/SiC interface

• La-silicate grains positioned at bunches of SiC substrate (4o)

• Thick SiO2 of 11nm is formed (enhanced oxidation rate)

9

Enhanced growth rate over thermal oxidation

SiC(0001) 10nm

11.8nm

sample：La2O3 (2nm)/SiCafter oxidation in 1000℃ 5%O2 30min

K. Kita, et al., ECS Trans, vol. 61(2), p. 135-142 (2014).

Higher oxidation rate of 1.5 order of magnitude can been

achieved by La2O3 capped oxidation

However, rough interface/surface may degrade reliability

This study

100

10-1

10-2

10-3

1300oC 1200oC 1100oC 1000oC

Gro

wth

rat

e co

nst

ate(

nm

/min

)

Temperature(oC)

SiO2 Growth rate of thermal oxidation

Oxidation rate comparison

10

1.Introduction




annealing.

5.Conclusion

11

n-SiC substrate

La-silicate

n-SiC substrate

SiO2

SiO2

n-SiC substrate

La2O3

SiN

La2O3 /SiC reaction

La2O3 /SiN reaction

n-SiC substrate

La2O3

SiN barrier layer against agglomeration

La-silicate formation by reaction of La2O3 and SiN layer

(SiN: oxygen barrier to suppress oxidation of SiC)12


EB-La2O3 deposition

FTIR measurement

FTIR measurement

SPM,HF cleaning

PECVD-SiN deposition

AFM, TEM analysis

annealing（5%O2/95%N2）

SiN(2nm, 1.5nm, 0nm)

n-SiC substrate

Sample preparation with SiN barrier

La2O3（4nm）

Sample 500oC ~1000oC

13

La2O3 4nm/SiC)

Ab

sorb

an

ce (

a.u

.)

12501300 1200 11001150 1050 1000

wavenumbers(cm-1)

(C)O2 anneal:500

oC—1000oC

1000゜C

950゜C

900゜C

La2O3 4nm/SiN2nm/SiC)

Ab

sorb

an

ce (

a.u

.)

12501300 1200 11001150 1050 1000

wavenumbers(cm-1)

(A)O2 anneal:500

oC—1000oC1000゜C

950゜C

900゜C

La2O3 4nm/SiN1.5nm/SiC)

Ab

sorb

an

ce (

a.u

.)

12501300 1200 11001150 1050 1000

wavenumbers(cm-1)

(B)O2 anneal:500

oC—1000oC1000゜C

950゜C

900゜C

Formation of La-silicate confirmed above 900oC

Slight suppression of SiO2 with thicker SiN

La-O-Si-O

Si-O-Si

SiN 2nmSiN 1.5nmWithout SiN

Si-O-Si

La-O-Si-OLa-O-Si-O

FTIR spectra of La2O3/SiN/SiC

14

Si-O-Si

10nm

SiC(0001)50nm

Sample： SiO2/La2O3 4nm/SiN 2nm/SiC

Annealing temperature：1000oC

La2O3/SiN/SiC interface section TEM image

SiC(0001)10nm

La-silicate SiO2

• Agglomeration of La-silicates above SiO2/SiC interface

• Thick SiO2 layer is formed (enhanced oxidation rate)

• Little suppression of oxidation variation 15

RMS: 1.80nm RMS: 2.35nm

Oxides surface roughness reduction with SiN barrier layer

has been confirmed by atomic force measurement

La2O3 4nm/SiN2nm/SiC) La2O3 4nm/without SiN/SiC)

RMS:1.80nm RMS:2.35nm

(a) (b)

Reduction of oxides surface roughness

SiN(2nm)

n-SiC

substrate

La2O3（4nm）

n-SiC

substrate

La2O3（4nm）

16

1.Introduction




annealing.

5.Conclusion

17

SiO2 capped annealing

n-SiC substrate

La2O3

SiO2

n-SiC substrate

La2O3

n-SiC substrate

SiO2

n-SiC substrate

SiO2

n-SiC substrate

SiO2

SiO2

La-silicate

O2 annealing

O2 annealing

Before

SiO2 capped annealing

O2 annealing

SiO2 La2O3

Huge reduction of

oxygen diffusion at

oxidating surface

SiC-Sub

Suppression of oxidation variation by increasing the diffusion length

of oxygen to reduce the amount of oxygen reaching oxidating surface

18

P(O2)

L


EB-La2O3 deposition

SPM,HF cleaning

PECVD-SiO2 deposition

TEM analysis

annealing（5%O2/95%N2）1000℃n-SiC substrate

Sample preparation for SiO2 capped annealing

La2O3 (4nm)

Sample

Sputter-W(50nm) deposition

PMA in F.G for 30 min

Backside Al contact

Al

W

SiO2 (40nm)

19

• Suppression of agglomeration by SiO2 capped annealing

• Some protrusion of La-silicates presented at the interface

SiC(0001) SiC(0001)

Sample： SiO2 40nm/La2O3 4nm/SiC

50nm 10nm

Annealing temperature：1000oC

SiO2La-silicate

SiO2/La2O3/SiC interface section TEM image

protrusion

20

La2O3

O2

O*

・ Thicker La2O3 may suppress the oxidation variation by

generating more radical oxygen

・optimal oxygen pressure may change due to change of

annealing temperature.

Suppression of carbon generation with

higher temperature and low P(O2)

[2]

[2] Y. Song et al., J. Am. Ceram. Soc., 88 [7], p. 1864–1869 (2005)

Modification of SiO2 capped annealing process

Catalytic effect by La2O3 to

generate radical oxygen [1]

[1] K. Kakushima, et al., J. Solid-State Electronic, vol. 54, p. 720-723 (2010).

SiO2

La2O3 SiC-SubSiO2

SiC-Sub

5 20 50 100

W/SiO2(40nm)/La2O3(10nm)/SiC

Oxygen ratio (%)

Hyst

eres

is v

olt

age

ran

ge

(V)

1.6

1.2

0.8

0.4

0

1MHz

L/W =50/50μm

C-V, Hysteresis on different O2 partial pressure

-5 -1 3 7 1511 19 23 270

20

40

60

100

80

120

Gate voltage (V)

Cap

acit

ance

(n

F/c

m-2

)

W/SiO2(40nm)/La2O3(10nm)/SiC

L/W =50/50μm

100%O2

Annealing ambient

50%O220%O25%O2

1MHz

Electrical properties improved by increasing

O2 partial pressure within annealing period

5%100%

22

5% 100%

C-V on annealing temperature of 1050℃

n-SiC substrate

La2O3 (4nm)

Before

Al

W

SiO2 (40nm)


n-SiC substrate

La2O3 (10nm)

After

Al

W

SiO2 (40nm)

}Annealing in

5%O2, 1000℃Annealing in

O2, 1050℃}

23

4H-SiC (1120) 100nm

La-silicate SiO2W

W50nm/SiO235nm/la2O310nm/SiC（gate oxide SiO2/La2O3 1050℃ oxidation）


A uniform La-silicate layer has been achieved by

SiO2 capped annealing in O2 ambient, 1050℃24

100nm 10nm

Light color region distributed in La-silicate layer

4H-SiC (1120) 4H-SiC (1120)


25

Electron diffraction pattern for region 1,2

Both black and light color region in La-silicate

layer are indicated to be La-silicate grain region26

10nm4H-SiC (1120)

*1 *2

c

o

u

n

t

s

c

o

u

n

t

s

c

o

u

n

t

s

c

o

u

n

t

s

500 600 700 800 900 1000

500 600 700 800 900 1000 500 600 700 800 900 1000

500 600 700 800 900 1000

(1) (2)

(3) (4)

Energy loss (eV) Energy loss (eV)

Energy loss (eV) Energy loss (eV)

O

La

O

La

O

La

O

10nm4H-SiC (1120)

*1 *2*4

*3

EELS analysis result of 4 gate oxide region

・Lower Lanthanum density has been detected in light color reigion. ・Existence of Lanthanum atom in thermal growth region (4) has been confirmed by EELS

27

Hypothesis for light color region in La-silicate

La-silicate SiO2

SiO2

*4

*3

SiC-substrate

*2*1

SiO2 protrusion in La-silicate layer by facet

dependent oxidation of SiC substrate 28

Si

O O

O

O

Si

O O

O

OO

OO

O

SiBO

BO

Si Si

Si

BO

BOSi

O O

O

O

Si

O O

O

OO

O

O

O

La NBO

BO

Si Si

La

NBO

BO

La atomBO

NBOSiO4-tetrahedron

BO: bridging oxygen atom

Si-O-Si bonding La-O-Si bonding

NBO:non-bridging oxygen atom

Atomic configuration of La-silicate

La atoms act as the

network modifier to

relax the SiO4 network

The interface between La-silicate/SiC may be modified by

Lanthanum atom in thin grown SiO2

29

Conclusion

• Oxidation with La2O3 capped SiC substrate• Enhanced oxidation rate with radical oxygen atoms generated

by La atoms• Grain growth, agglomeration of La-silicates• Surface roughness due to step enhanced oxidation

• SiN barrier layer for La2O3/SiC substrates• Formation of LaSiON interface layer• Reduction of gate oxides surface roughness

• SiO2 capped annealing for La2O3/SiC substrates• Formation of uniform La-silicate layer• Interface modification with Lanthanum atom relax the SiO4

network of thermal growth layer

30

Thank you very much

Spot 4

Spot 3

Spot 2

Spot 1

Si

CO

La

50 250 450 650 850

c

o

u

n

t

s

Energy loss (eV)

10nm4H-SiC (1120)

*1 *2*4

*3

ＦＦＴ測定結果

格子のデータが一致しています18

sample：La2O3 (2nm)/SiCafter oxidation in 1000℃ 5%O2 30min

ステップ制御エピタキシー

C-face

Si-face

(1120)face

SiC酸化スピードの異方性

オフ角

テラスステップ

(0001)面

テラス面とステップ面の反応スピードが違う

テラスステップ

ステップステップオフ角；4°

[4]

[4] Y. Song et al., J. Appl. Phys. 95 (2004) 4953.

4H-SiC

膜厚不均一

SiO2膜厚不均一性の説明

Tokyo Institute of Technology

160

40

0

Cap

acit

ance

(n

F/cm

2)

80

Gate voltage (V)20-2-4-6 4 6 8 10 161412

120

: 1MHz

: 500kHz

: 100kHz

: 10kHz

W/TEOS-SiO2/La2O3(4nm)/SiC950oC oxidation50mm/50mm

Gate voltage (V)20-2-4-6 4 6 8 10 161412

: 1MHz

: 500kHz

: 100kHz

: 10kHz


Gate voltage (V)20-2-4-6 4 6 8 10 161412

: 1MHz

: 500kHz

: 100kHz

: 10kHz


950oC 1000oC 1050oC

950oC, 1000oCの場合にはslow trapが大きい。

・ La2O3が完全にsilicateに変わっていない

・界面、絶縁膜のバルク欠陥の除去が不十分

1050oCの場合に、その問題は改善

35

熱処理温度増加によるCV特性の変化

La-silicate

n-SiC substrate

La2O3 (10nm)

SiO2 (40nm)

Sufficient oxygen

insufficient oxygen

n-SiC substrate

La-silicate

SiO2 (40nm)

n-SiC substrate

La2O3 (10nm)

SiO2 (40nm)Fixed

charges

Incomplete oxidation by insufficient oxygen generate

fixed negative charges at la2O3/La-silicate interface

SiO2 La2O3

SiC-SubLa2O3

SiC-Sub

SiO2

O2

O*

SiO2 La2O3 SiC-Sub

・ Thicker La2O3 may suppress the oxidation variation by generating more radical oxygen・Prohibition of carbon generation reaction with higher temperature



[2]

[2] Y. Song et al., J. Am. Ceram. Soc., 88 [7], p. 1864–1869 (2005)


Huge reduction of

oxygen diffusion at

oxidating surface

Catalytic effect by La2O3 to generate radical oxygen

radical oxygen

oxygen molecule

21

[1]


La2O3

O2

O*

・ Thicker La2O3 may suppress the oxidation variation by

generating more radical oxygen

・optimal oxygen pressure may change due to change of

annealing temperature.



[2]

[2] Y. Song et al., J. Am. Ceram. Soc., 88 [7], p. 1864–1869 (2005


Catalytic effect by La2O3 to

generate radical oxygen [1]


SiO2

La2O3 SiC-SubSiO2

SiC-Sub

SiC(0001) 10nm

protrusion

[2]

reaction and formation of la-silicate gate dielectrics on sic ... presen...comparison of basic...

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