byeongbyeong--joo lee joo lee - postech · scope cvd 1. too much changeable results depending on...
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Byeong-Joo Leewww.postech.ac.kr/~calphad
ByeongByeong--Joo LeeJoo Lee
POSTECH POSTECH -- MSEMSE
[email protected]@postech.ac.kr
ScopeScope
CVD
1. Too much changeable results depending on the condition
2. Beyond Scientific Explanation for long time
3. Process development has been mostly empirical
Approach (by Nong Moon Hwang, KRISS/SNU)
1. How to define the driving force of CVD
2. Low pressure synthesis of Diamond
Byeong-Joo Leewww.postech.ac.kr/~calphad
2. Low pressure synthesis of Diamond
3. Charged Cluster Model in CVD
References
N.M. Hwang et al., Diamond and Related Materials, 1 (1992)
191-194.; 3 (1993) 163-167.
N.M. Hwang et al., J. Crystal Growth 135 (1994) 165-171;
143 (1994) 103-109; 160 (1996) 87-97; 160 (1996) 98-103;
162 (1996) 55-68.
Homogeneous NucleationHomogeneous Nucleation
Nucleation of liquid from vapor
assume spherical nucleus
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Homogeneous NucleationHomogeneous Nucleation
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CVD Diamond CVD Diamond -- N.M. Hwang et al., J. Crystal Growth 162, 55 (1996)N.M. Hwang et al., J. Crystal Growth 162, 55 (1996)
Byeong-Joo Leewww.postech.ac.kr/~calphad
Diamond deposited on silicon substrate Soot deposited on the iron substrateDiamond deposited on silicon substrate Soot deposited on the iron substrate
CVD Si CVD Si -- N.M. Hwang et al., J. Crystal Growth 218, 27 (2000)N.M. Hwang et al., J. Crystal Growth 218, 27 (2000)
Byeong-Joo Leewww.postech.ac.kr/~calphad
CVD Si Nanowire CVD Si Nanowire -- N.M. Hwang et al., J. Crystal Growth 218, 33 (2000)N.M. Hwang et al., J. Crystal Growth 218, 33 (2000)
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※ Example: Deposition of Silicon CarbideSiH4 + CH4 = SiC + 4H2
Driving force of CVD DepositionDriving force of CVD Deposition
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Diamond formation with simultaneous graphite etchingDiamond formation with simultaneous graphite etching
in low pressure synthesis of diamondin low pressure synthesis of diamond
Thermodynamic ParadoxThermodynamic Paradox
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∆−
∆=
kT
G
kT
GOqI co
**
exp
σπ
πµ 3/2
3/2
4
34 nnG solidgas
Ω+∆=∆ →
323216 ΩΩ σπσπ
Nucleation of clusters in gas phase Nucleation of clusters in gas phase -- Diamond/GraphiteDiamond/Graphite
∆−∆⋅=
kT
GGA
I
I diagra
gra
dia **
exp
Byeong-Joo Leewww.postech.ac.kr/~calphad
2
32
2
32
**
)(3
16
)(3
16
diagas
diadia
gragas
gragra
diagra GG→→ ∆
Ω−
∆
Ω=∆−∆
µσπ
µ
σπ
The nucleation ratio is very sensitive to the variation of the surface energy
ranging from 1010 to 10-6 with σdia = 3.7 and 4.1 J/m2
at 1200K and σgra = 3.1 J/m2
→ There must be some factor that modifies the surface energy of diamond
→ Creation of the Charged Cluster Model