「富岳」成果創出加速プログラム
省エネルギー次世代半導体デバイス開発のための量子論マルチシミュレーション
第一回ミーティング

2021年7月15日
Zoom meeting

MOVPEによる高純度GaN成長と気相反応解析
名古屋大学 新田 州吾、叶 正、天野 浩

内容背景- GaNパワーデバイスと結晶成長方法- 縦型パワーデバイスエピにおけるMOVPE GaN成長の課題
実験- 飛行時間型質量分析を用いたMOVPE気相反応のその場観察技術- NH3の分解- TMGaの分解 / NH3との反応- TEGaの分解 / NH3との反応
まとめGaNパワーデバイスエピの課題
Anodep+GaNp-GaN

p-GaN layer••

Mg concentration control (~1017 cm-3 )Reduction of compensated by point defectn-GaN
Drift layer

n-GaN Substrate
Cathodn--GaN drift layer• Control of precise donor(Si) concentration• Reduction of compensation point defect• Secure realistic growth rate ( > 2 um/h)

PN diodeSource

GateDrain

AlGaN barrier
2DEG

Barrier structure• Low contact resistance• High carrier density / High mobility• Normally off gate

ud-GaN Chanel
C-doped GaN
S.I.GaN Substrate
AlGaN/GaN HEMT

uid-GaN channel layer• Impurity reduction• Smooth surface[2]Fukushima et al., Appl. Phys. Express 12 (2019) 026502.

p3

GaNの結晶成長 エピタキシャル薄膜成長技術
MBE

MOVPE

HVPE

Growth rate (max.)~2µm/h~10µm/h>200µm/hPressure

Low pressure

10～100kPa～100kPa

Temperature(GaN)

800～900℃

1000～1100℃

1000～1100℃

Ga source

Ga (K-cell)

TMGa (, TEGa)

GaCl

N source

NH3
N2 plasma

NH3

NH3

Dominant impurity

C, O
(Si)

C(Si, O)

(Si, O)n-type doping

Good (Si)Good (Si)Good (Si, Ge)

p-type doping

Good (Mg)Good (Mg)

Difficult(Recently developed (Mg))

Alloys

AlGaN
InGaN
etc.

AlGaN
InGaN
etc.

Difficult

Productivity

not enoughWidely used

Mainly for bulk growth

・MOVPEの・HVPEによる縦型デバイスの高耐圧化、低コスト化

p4縦型パワーデバイスにおける高純度化の必要性Breakdown voltage (V)

絶縁破壊電圧のドーピング濃度依存性[1]4000 25 µm

Non-punch-through縦型p-nダイオードの模式図
アノード
p-GaN

3000

n-GaN

2000
1000
01015

5 µm
1017
1016
−3Doping concentration (cm )

GaN基板
カソード

ドリフト層(=耐圧層)
低不純物濃度制御
Dopant: Si
Background impurity
Donor： Si, O(, CGa),,,Acceptor： CN, Mg, Fe,,,

高耐圧化には低ドーピング濃度かつ厚膜化が必要- MOVPE 成長レートとC濃度のトレードオフ- HVPEのp型GaN:Mgエピ実現により期待大p5

成長条件とC濃度の関係 (経験則)

Danielsson, Ö. et al.,J. Mater. Chem. C 4, 863( 2015).

Pressure ↑[C] ↓Koleske, D. D., et al.,J. Cryst. Growth 242, 55(2002).

Temperature ↑[C] ↓V/III ratio ↑[C] ↓p6

MOVPE炉内では何が起こっているのか？
Ga(CH3)3(g)+ NH3(g) → GaN(s) + 3CH4(g)❓

マルチフィジックスシミュレーションとの連携

成長機構解明による窒化物半導体のポテンシャル拡大
基礎的学理・物性の解明 (シミュレーションへの適用)
膜厚・組成制御、均一性、原料効率の改善
超高純度結晶 (高耐圧・高周波電子デバイス)
高組成InGaN (赤～紫外光デバイス)
高組成AlGaN (深紫外光デバイス、超高耐圧パワー)

p7

飛行時間型質量分析(TOF-MS infiTOF)◆ Time of flight mass spectrometry: TOF-MSｄ∝ resolution

d: flight length of ions◆ High-resolution time-of-flight mass spectrometry “InfiTOF” MSI.TOKYO Inc.
Multiple turn mass analyzer
Orbitalelectroded:Max 500 m✔ resolution≦ 0.002u✔ Measurable range
m/z :1-1000u

p8

QMSとTOF-MS(infiTOF)の比較
Required FWHM resolution to determine absolute species: < 0.0075u

TOF-MS: FWHM resolution: < 0.002u
m/z=17m/z=28

DMGam/z=44

DM71Ga0.08

0.080.14

MMGa MM71Ga

TMGa TM71Ga

QMS: FWHM resolution: > 1u
Intensity[a.u.]*Not calibrated

020

40m/z 60

80100120

The same mass number molecules are clearly distinguished by TOF-MS.
p9

TOF-MS観察用簡易MOVPE装置
装置模式図TOF-MS

110-3Pa~ 10-5Pa

外観写真
Typical experiment condition
Flow speed：0.02m/s
Total flow rate：1slm
TMGa molar flow rate：29µmol/min
Ⅴ/Ⅲ ratio：100
Sampling position: 20 cm

炉内温度分布p10

マススペクトルの測定例
TMGa / H2 /NH3

✔ Close peaks of mass ✔ Isotopes ✔ Weak adduct signals…

p11

イオン化電圧依存性TMGa
Ga(CH3)3

VFragments generated by high-energy electron impact

Ionization

e-e-TMGa
Ga(CH3)3

DMGa
Ga(CH3)2

MMGa
GaCH3GaCH3・・・・・e-Filament

・Under low ionization voltage
the signal Ga(CH3)3 is weak
Ga(CH3)3 is very easily ionized
・ Under high ionization voltage
clack occurs
all signals are weakened

TMGa/N2;RTFor the convenience of the experiment,
the ionization voltage is set to 14v
p12

TMGa、NH3のイオン化フラグメント
DMGa
Ga(CH3)2Ga(CH3)2HMMGa
GaCH3

NH3
NH2Ga

TMGa
Ga(CH3)3

TMGa/N2

NH3/N2・ Ga(CH3)2 is a major fragment of Ga(CH3)3・ Fragments related with Ga have the same
temperature dependenceGa(CH3)2 and NH2 are treated as Ga(CH3)3 and NH3
p13

NH3の熱分解 (雰囲気ガスの影響)
NH3 decompositon：
He＞N2＞Ar＞H2測定位置：20㎝

NH3NHX＋H

NHx

N＋xH

2N

→

N2

NH3：50sccm

X＝０、１，２Total 1slm

H：Activated hydrogen
N：Activated nitrogen- H2はNH3の分解を抑制- He中は拡散しやすいためNH3分子が会合しやすいかp14

H2およびN2中のTMGa分解 (NH3なし)

Z. Ye et al., Jpn. J. Appl. Phys, 59, 025511(2020).

w/o NH3

In H2

In N2

TMGa decomposition temperature

about 400℃

about 550℃

Main product

CH4

C2H6

p15

H2およびN2中のTMGa分解 (NH3あり)with NH3

In H2

In N2

TMGa decomposition temperature

about 450℃

about 500℃

Main product

CH4CH4

HCN production temperature

about 800°C

about 700°C

p16

TMGa分解におけるH2、N2、NH3の影響
In N2〇 TMGa_N2_w/o NH3

TMGa_N2_w/o NH3 ・ thermally decomposed

・ Slowest decomposition
TMGa_N2_with NH3〇 TMGa_N2_with NH3

TMGa_H2_w/o NH3

・ Decomposition shifted to
TMGa_H2_with NH3

the low temperature
・ NH3 promotes decomposition
In H2〇 TMGa_H2_w/o NH3NH3 has different effects on TMGa

・ Fastest decomposition

decomposition in H2 and N2〇 TMGa_H2_with NH3

白石GによるTMG分解経路シミュレーション⇒ NH3との結合を作りながら分解

・ The decomposition shiftedslightly to the high temperaturep17

H2、N2、NH3雰囲気におけるTMGa分解イメージ
TMGa

C2H4……

C2H6

TMGa/N2C2H6→C2H4＋H2600℃

TMGa
TMGa/N2/NH3500℃

TMGa

800℃

HCN

CH4

CH4＋NH3 →HCN＋3H2
C2H6＋2NH3 →2HCN＋5H2700℃

T

400℃

TMGa/H2/NH3
Products related with C:①
Undecomposed TMGa
(DMGa, MMGa…)

T

CH4

TMGa/H2
TMGa

T

CH4

HCN
CH4＋NH3 →HCN＋3H2450℃

800℃②Hydrocarbons(CH4, C2H2, C2H4, C2H6)

T
③HCN

p18

TMGa分解における流速の効果
Compare the decomposition of TMGa at different flow rates
Speculated result（~1m/s）
0.2m/s_H2

Flow rate：0.02→0.2m/s(Partial pressure constant)

Shifted byflow speed

0.2m/s_N2

0.02m/s_N2

Ⅴ/III:100

0.02m/s_H2

Reaction shift
to high temperature side

〇 reactions[high flow rate，high temperature][Low flow rate，low temperature]〇 In the actual MOVPE growth conditions (~1 m/s，1000 ℃)
Undecomposed TMGa in gas phasep19

MOVPE高流速下におけるTMGa濃度分布
Quartz Reactor in this work
Heater range:30cm
Flow rate: 0.02m/s
heater〇Real MOVPE 2-inch reactor
Flow rate: ~1m/s
Heater range:5cm
heatertray
substrate

Decomposition image of TMGa in MOVPEDistribution of TMGa in gas phase

TMGa concentration〇

TMGa_N2_w/o NH3
TMGa_N2_with NH3
TMGa_H2_with NH3
Flow speed: ~1m/s
Surface 1000℃

substrate

heater

TMGa_H2_w/o NH3

tray

Position

In real MOVPE reactor: High flow rate, shorter heater range
The actual distribution corresponds to our results in the low temperaturep20

CH4およびHCNからのC取り込み

p21

TMGa気相反応解析から得られた結論
Two important conclusions from this work:① Main source of C :undecomposed TMGa

② NH3 promotes
the decomposition

The dependence of carbon and growth conditions can be explained

measured dataDanielsson, Ö. et al., J. Mater. Chem. C 4, 863( 2015).

Koleske, D. D., et al., J. Cryst. Growth 242, 55(2002).

High temperature, High pressure, High V/III ratiop22

重水素(D2)を用いたTMGa分解反応の切り分け
NH3なし

NH3あり？

Ga(CH3)2

CH3D

CD4

CH4
CH2D2
CHD3Ga(CH3)2CH4CH3D

CD4CH2D2CHD3DCN

TMGa/D2 w/o NH3〇TMGa+D2→CH3D✔H2 promotes the decomposition of TMGa
〇 CH4 is unstable in high temperature(H-D exchange)

TMGa/D2 with NH3

In TMGa/D2/NH3
With the decomposition of TMGa
Intensity:CH4>CH3Dp23

重水素(D2)を用いたTMGa分解反応の切り分け

TMGa/D2 with NH3

H2/NH3NH3Ga(CH3)2NH2DND3NHD2CH4

CH3D

CH2D2CD4CHD3NH3 is quite active even at 400 oC
The priority of TMGa with NH3 is higher than that with D2 (H2)p24

重水素(D2)を用いたTMGa分解反応の切り分け
TMGa/H2 w/o NH3H

H

HCGa
H

CH C

H
H

H

H

HCGaH

H

H CCH

HH

H HCH HH

H2 and CH3(methyl) react to form CH4H

H

Ha high activity state

TMGa/H2 with NH3H

H

HCGa
HC

H
H

H

H C
H

H

H

H

HC
Ga
H

C

H

H C
H

NH

H

H
H

N

H

NH3NH2 + H

H H
C
H H

H
H
HH

TMG reacts preferentially with NH3
p25

TMGa分解における分解種の分圧比導出
RTでの強度で規格化

TMG：5 cc (29 µmol/min)
H2：9955 cc
大気圧

DMG強度で規格化

本データは寒川・草場G 「データ同化による気相反応モデルの高精度化」に利用

p26

まとめ
TMGaの気相反応解析から得られた主な知見- NH3は流れがある場合1000℃においてもほぼ分解しない
ただし400℃以上では活性となり、反応しやすい- H2、NH3はTMGaの分解(-CH3脱離)を促進- H2中でもNH3と優先的に反応する- C取り込みの主な経路はTMGa未分解種(DMGa、MMGa、GaH)