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f Local Valence Electronic States of Silicon Dioxide Ultrathin Films and

Titanium Dioxide Surfaces Using Auger-photoelectron Coincidence Spectroscopy

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i

0h

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otoelectron coincidence spectroscopy : APECS

0c—b

ii

iii

iv Abstract

Recently, the ultra-thin films with a thickness of several atomic layers formed on a substrate are studied actively, because they show the different characters from the solid states (bulk), such as atomic structures, electron states, physical properties, and reactivity. Especially, the local valence states of the ultra-thin films attract attentions from both the basic science and the applied studies, as they are correlation with the appearance of the various device-functions, control of the properties, and reactivity on the ultra-thin films. However, the conventional electron spectroscopy cannot detect the local valence state of only the surface or the interface of the ultra-thin films. Therefore, the author has studied the local valence states of the silicon dioxide (SiO2/Si) ultra-thin film and the titanium dioxide (TiO2(110)) surface using Auger-photoelectron coincidence spectroscopy (APECS) which is very surface-sensitive and can detect only the Auger-electron which is derived from the photoelectron emitted from the atomic site of the specific chemical-state.

At first, the author has improved the electron-electron-ion coincidence (EEICO) analyzer, which can carry out both APECS and electron-ion coincidence (EICO) spectroscopy, and evaluated its performance. The EEICO analyzer consists of coaxially symmetric mirror electron-energy analyzer (ASMA), cylindrical mirror electron-energy analyzer (CMA), and time-of-flight ion-mass spectroscopy (TOF-MS). The electron energy resolution (E/ΔE) of the ASMA and the CMA improved ~80 and ~20 by optimizing the pinhole-size of the ASMA and CMA, the spot-size of the soft X-ray radiation on the sample, and the position of the EEICO analyzer. And the author has succeeded in the high-resolution measurement of the Si-L23VV-Si-2p APECS on the Si(111)-7u7 clean surface and O-KLL-resonance-Auger-electron-H⁺-photoion EICO spectrum of H2O condensed on the Si(111) at hQ =532.9 eV corresponding to the 4a1←O 1s resonance. The APECS and EICO

v

spectroscopy can be measured effectively due to the development of the high-resolution EEICO analyzer.

As the secondary research, the author has studied the local valence states at surface and inter-faces of SiO2/Si ultra-thin films using APECS. The SiO2/Si(100) and SiO2/Si(111) were thermally grown on the Si(100)-2u1 and Si(111)-7u7 surface at 750

vi

corresponding to 2 layers shows that the Si and SiO which desorbed from SiO2/Si interface in the initial oxidation make the VBM-shift about 0.5 eV to the Fermi level because they remain in the SiO2 ultra-thin film. These results contribute to the basic science field to study the local valence state of ultra-thin films less than 1 nm, and give an indicator of a method to produce the high quality gate-oxidation-film, which decreases the leak current, to the Silicon semiconductor device industry.

As the third research, the author has studied the local valence states of the TiO2(110)-1u1 clean surface and its defect surface. The Ti⁴⁺ L2M1M23-L2M23M23-L2M23V Auger-electron spectrum (AES) measured in coincidence with Ti⁴⁺ 2p1/2 photoelectron and the Ti⁴⁺ L3M1M23-L3M23M23-L3M23V AES measured in coincidence with Ti⁴⁺ 2p3/2 photoelecton from the TiO2(110)-1u1 clean surface show that the very fast Coster-Kronig (CK) transition happens. And, the normal AES (Singles AES) from the TiO2(110) defect surface was shifted to the low-kinetic energy side than that of TiO2(110)-1u1 clean surface. In order to reveal the reason of the shift of the Singles AES, the Ti³⁺ L3M1M23-L3M23M23-L3M23V AES were measured in coincidence with Ti³⁺ 2p3/2 photoelectron emitted from TiO2(110) defect surface. As a result, this Ti³⁺ L3M1M23-L3M23M23-L3M23V AES resembles Ti⁴⁺ L3M1M23-L3M23M23-L3M23V AES in the coincidence with Ti⁴⁺ 2p3/2 photoelectron of the TiO2(110)-1u1 in the same kinetic energy region. This result shows that Ti³⁺ L3M23M23-L3M23V AES is unrelated to the shift of the Singles. Therefore, the author concluded that the shift of the Singles AES of the TiO2(110) defect surface is attributed to Ti³⁺ L2L3V giant CK transition, which is the phenomenon that Ti L2L3V CK transition happens with high probability, because the final states of Ti³⁺ L3M1M23-L3M23M23-L3M23V AES via the Ti³⁺ 2p1/2 ionization and Ti³⁺ L2L3V giant CK transition has more than 3-core-holes, they make the Auger line peaks in the lower kinetic energy side of Ti³⁺ L3M1M23-L3M23M23-L3M23V AES via only the Ti 2p3/2 ionization. Generally, the core-hole at Ti 2p1/2 level on the metal Ti is nearly relaxed by Ti L2L3V giant CK transition

vii

because the density of the d-character electron at the vicinity of the Ti 2p core-hole is large. Therefore, the author thought that Ti L2L3V CK transition reflects the density of the d-character electron at the vicinity of the core-excited site. This result shows the density of the d-character electron at the vicinity of the Ti³⁺ site is larger than that of the Ti⁴⁺ site.

viii

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39

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41

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43

44

45

46

47

48

49

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600

700

800

900

1000

1100

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53

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4

6

8

10

12

14

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1.0

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55

56

57

58

0 100 200 300 400 500 600 700 800 900

0.0

2.5

5.0

7.5

59

450 460 470 480 490 500 510 520

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0

2

4

6

8

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AEPICO data 10

H

A E P IC O c o u n ts / c p s

Kinetic energy (eV)

J

E

Auger electron spectrum

O K L L A u g er -e le ct ro n c o u n ts 1 0

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60

AMA_MCS-in_electron_KE = 20 – 110 eV (1eV step

61

62

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63

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67

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70

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72

73

74

75

76

77

7 6 5 4 3 2 1 0 -1 -2

P h o to em is si o n I n te n si ty ( A rb . U n it )

Relative binding energy / eV

Experiment

Fit

Si

Si

Si

Si

Si

Si

(a) Detected by ASMA

(b) Detected by CMA

Experiment

Fit

Si

Si

Si

Si

Si

78

79 Si-L23VV-Si³⁺-2p APECS

80

81

82

40 50 60 70 80 90 100

0 2 4 6 8

0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6 0.8 0.0 0.1 0.2 0.3 0.4 0.50.0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

Major peak

Auger-electron kinetic energy / eV

Singles

(a) Si⁰-LVV-Si⁰-2p APECS data

S i

-L V V -S i

-2 p A P E C S c o u n ts / c p s

0 2 4 6 8

Energy loss

Minor peak Major peak

0 2 4 6 8

Energy loss Minor peak ^{Major peak}

A u g er -e le ct ro n c o u n ts 1 0

/ cp s

0 2 4 6 8 10

Minor peak 0

2 4 6 8

(b) Si¹⁺-LVV-Si¹⁺-2p APECS data (c) Si²⁺-LVV-Si²⁺-2p APECS data Energy loss (d) Si³⁺-LVV-Si³⁺-2p APECS data

Major peak

O _D

G J

(e) Si⁴⁺-LVV-Si⁴⁺-2p APECS data

E

83

84

85

86

87

7 6 5 4 3 2 1 0 -1 -2 -3

Si

Si

Si

(a) ~1.5

88

0 20 40 60 80 100 120

0.0

0.2

0.4

0.6

0.8

1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

C M A e le ct ro n c ou n ts 1 0

/ c p s

co A S M A e le ct ro n c o u n ts 1 0

/ c p s

Kinetic energy / eV

89

90

40 50 60 70 80 90

0.0

0.2

0.4

0.6

0.8

1.0

G ^{J E}

A P E C S I n te n si ty / a rb . u n it .

Kinetic energy / eV

13

91

92

93

94

95

96

6 5 4 3 2 1 0 -1 -2

In te n si ty / a rb . u n it

Relative binding energy / eV

Experiment

Fit

Si

site

Si

site

Si

site

Si

site

Si

site

97

98

65 70 75 80 85 90 95

0.0

0.2

0.4

0.6

0

2

4

0

2

4

0

2

4

0

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VV-Si

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A u g er -e le ct ro n c o u n ts 1 0 3 / c p s

A P E C S c o u n ts / c p s

Auger electron kinetic energy / eV

(a)

0.0

0.2

0.4

0.6

0.8 _(b)

Si-L

VV-Si

-2p APECS

0.0

0.1

0.2 ^(c)

Si-L

VV-Si

-2p APECS

0.0

0.2

0.4

0.6 (d)

Si-L

23

^VV-Si

3+

-2p APECS

0.0

0.1

0.2

0.3 _(e)

Si-L

^VV-Si

4+

-2p APECS

Singles

99

100

7 6 5 4 3 2 1 0 -1 -2

Si

site

Si

site

Si

site

Si

site

Experiment

Fit

Si

site

In te n si ty / a rb . u n it

Relative binding energy / eV

101

50 60 70 80 90

A P E C S i n te n si ty / a rb . u n it

Auger electro kinetic energy / eV

1.5-

102

103

104

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105 0¿

V

mol m^-2 min^-1)

0n

[

6.2, 3]

106

107

108

109

110

111

112

113

114

115

116

117

118 SrTiO3

119

120 Ti 2p1/2

121

122

123

340 360 380 400 420

0

1

2

3

4

0.00

0.05

0.10

0.15

0.20

0.25

0.30

A P E C S c o u n ts / c p s

A u g er -e le ct ro n co u n ts / k cp s

Auger electron kinetic energy / eV

Singles

b

b

a

a

b

b

b

a

a

b

(a) Ti-L

M

M

-L

M

M

-L

M

V-Ti-2p

APECS

(b) Ti-L

M

M

-L

M

M

-L

M

V-Ti-2p

APECS

124

450 455 460 465 470 475 480 485

In te n si ty / a rb . u n it .

Photon energy / eV

Total electron yield

(TEY)

125

126

127

340 360 380 400 420

0.00

0.03

0.06

0.09

0

1

2

3

4 0

1

2

3

4

0

1

2

3

4

a

a

a

a

a

a

Auger electron kinetic energy / eV

Ti

2p

trigger

(a) a

1

0.0

0.1

0.2

0.3 b

^b

c

c

b

b

A u g er -e le ct ro n c o u n ts / k cp s

(b)

A P E C S c o u n ts / c p s

Ti

2p

trigger

b

0.00

0.05

0.10

0.15

c

c

c

(c) Ti

2p

trigger

Singles

128

129

130

131

132 15919 (1997).

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133

C

O

0

A

PECS

0f+

0O

134

135 A

00W

ICO

ˆÅ

0Ã

5

136

137

138

139

140

200 400 600 800 1000

0

2

4

6

8

10

H ⁺ signal ^{h Q} = 532.9 eV

Electron kinetic energy

= 516.5 eV

301 ns

141

460 480 500 520

0

100

200

300

400

500

600

700

0

10

20

30

40

50

60

142

143

e

n

I

_³

O

D

O

V

n

I 

_³

Si

SiO SiO SiO

Si SiO

D

O

O

V

O

V

n n I I

2

2 I c

d

O D

（

144

145

,

N. Fujita, M. Tanaka, and K. Mase,

Analytical Sciences

, 87 (2008).

on ion coincidence

(EICO) spectroscopy _”, T. Kakiuchi, E. Kobayashi, N. Okada, K. Oyamada, M.

Okusawa, K. K. Okudaira, and K. Mase, J. Electron Spectrosc. Relat. Phenom.

,

164 (2007).

0

mm

u

ter Diameter of 70 mm _”,

Takuhiro Kakiuchi and Kazuhiko Mase, J. Vac. Soc. Jpn.

, 1 (2008).

a

l Wafer Holder with a Cold Trap and a Direct Heating Mechanism

Mounded on a Conflat Flange with an Outer Diameter of 70 mm ”, E. Kobayashi, A.

Nambu, T. Kakiuchi, and K. Mase, Shinku

, 57 (2007). )

ÿ

and Kazuhiko Mase, PF

Activity Report 2006, Part A, Highlights 55 (2007).

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147

148

2006

149