xing sheng, ee@tsinghua principles of micro-and ... · xing sheng, ee@tsinghua 1 xing sheng盛兴...
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Xing Sheng, EE@Tsinghua
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Xing Sheng盛兴
Department of Electronic EngineeringTsinghua University
Film DepositionPart IV: CVD
Principles of Micro- and Nanofabrication for Electronic and Photonic Devices
Xing Sheng, EE@Tsinghua
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Film Deposition
PVD: Physical Vapor DepositionCVD: Chemical Vapor Deposition
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Film Deposition
PVD: Physical Vapor DepositionCVD: Chemical Vapor Deposition
Xing Sheng, EE@Tsinghua
CVD Si
poly-Si
W, SiO2, ...
PVD Al, Ti
...
Electrodeposition Cu
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Thin Film in CMOS
Xing Sheng, EE@Tsinghua
APCVD Atmosphere Pressure CVD
LPCVD Low Pressure CVD
UHVCVD Ultrahigh Vacuum CVD
MOCVD Metal Organic CVD
PECVD Plasma Enhanced CVD
ALD Atomic Layer Deposition
...
CVD: Chemical Vapor Deposition
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Xing Sheng, EE@Tsinghua
Example:
CVD: Chemical Vapor Deposition
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SiH4 (g) = Si (s) + 2H2 (g)
SiH4 (g) + O2 (g) = SiO2 (s) + 2H2 (g)
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CVD
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Process Parameters Time
Temperature
Gas type
Gas pressure
Flow rate
...
Control Parameters Film thickness
Crystallinity
Film quality (defects, dielectric strength, ...)
- gas transport- surface reaction
Q: differences between CVD and oxidation?
Xing Sheng, EE@Tsinghua
Crystallinity
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temperature
deposition rate
Deposit Si on Si
Monocrystalline Polycrystalline Amorphous
SiH4 (g) = Si (s) + 2H2 (g)
800 oC 600 oC
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Crystallinity
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temperature
efficiency
Silicon Solar Cells
Monocrystalline Polycrystalline Amorphous
price
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Deposition Rate vs. Temperature
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2/3~ TR
kT
ER exp~
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Deposition Rate vs. Gas Flow
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Issues of Gas Transport
14tilt the samples to improve uniformity
Xing Sheng, EE@Tsinghua
Issues of Gas Transport
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better to operate at surface reaction limited zone(low T, high flux rate)
Xing Sheng, EE@Tsinghua
Gas Types
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Si CVD
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LPCVD
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Low Pressure CVD at low pressure,
- Increased rate- Increased zone for surface reaction- reduce cost
why ??
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LPCVD
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Low Pressure CVD
pr
kT22
molecular mean free path
p
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PECVD
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Plasma Enhanced CVD
plasma enhances the ion energy:
- higher dep. rate- lower temperature
Xing Sheng, EE@Tsinghua
SiO2 Growth Methods
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dry oxidation
Si + O2 ~ 1100 oC
wet oxidation
Si + H2O ~ 1000 oC
APCVD / LPCVD
SiH4 + O2 400~600 oC
PECVD
SiH4 + N2O 200~400 oC
Sputter or Evaporation
substrate at room temperaturegrowth
temperaturefilm
quality
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Step Coverage
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surface reaction controlled diffusion/transport controlled
- LPCVD, UHVCVD, oxidation- ALD- ...
- PECVD- PVD (sputter, evaporation)- ...
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MOCVD
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Metal-Organic CVD
Ga(CH3)3 (g) + AsH3 (g) = GaAs (s) + 3CH4 (g)
Ga(CH3)3 (g) + NH3 (g) = GaN (s) + 3CH4 (g)
Xing Sheng, EE@Tsinghua
ALD: Atomic Layer Deposition
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precursor
reactant
- self limited growth- layer by layer - high uniformity- accurate thickness control
2Al(CH3)3 + 3H2O = Al2O3 + 6CH4
Si(OCH2CH3)4 + H2O = SiO2 + ...
Hf(N(C2H5)(CH3))4 + H2O = HfO2 + ...
TiO2 / Al2O3 multilayer
Xing Sheng, EE@Tsinghua
ALD: Atomic Layer Deposition
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thickness t is already ~ nmhigh -> large C -> large ID
t
AC
VVC
L
WI thG
SatD
0
2
,2
)(
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Selective Deposition
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non-selective (everywhere)
Tungsten (W) via by CVD
WF6 (g) + 3H2 (g) = W (s) + 6HF (g)
2WF6 (g) + 3Si (s) = 2W (s) + 3SiF4 (g)
selective, only on Si, not SiO2
Q: why do we use CVD for W vias?
Xing Sheng, EE@Tsinghua
Step Coverage
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surface reaction ballistic transport
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Localized CVD
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higher T --> higher rate
B. Sosnowchik, et al., J. Appl. Phys. 107, 051101 (2010)heated region
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Graphene by CVD
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Grephene likes to nucleate at Cu grain boundariesHow to get single crystal graphene?
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Graphene by CVD
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Single Crystal Substrate
Single Crystal Graphene
X. Xu, et al., Science Bulletin 62, 1074 (2017)
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Diamond by CVD
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