Post on 26-Oct-2014
Episil Technologies Inc.
Silicon Epitaxy
Silicon Epitaxy 2012
EPI – TAXIS = Ordered – onEpitaxy is the growth of a thin layer of single-crystalmaterial on the crystal face of the same (homoepitaxy)or another (heteroepitaxy).
• VPE - Vapor Phase Epitaxy
• LPE - Liquid Phase Epitaxy
• MBE - Molecular Beam Epitaxy
What is EPITAXY ?
Silicon Epitaxy 2012
Typical Epi Wafer Designs(Schottky Diode)
N+ Substrate
N- Epi
Device Structure Epi Layer Structure
Silicon Epitaxy 2012
Typical Epi Wafer Designs(FRED)
N+ Substrate
N- Epi
Device Structure Epi Layer Structure
Silicon Epitaxy 2012
Typical Epi Wafer Designs(Power BJT)
N+ Substrate
N- Epi
Device Structure Epi Layer Structure
Silicon Epitaxy 2012
Typical Epi Wafer Designs(Power MOSFET)
N+ Substrate
N- Epi
Device Structure Epi Layer Structure
Drain
Source Gate
Silicon Epitaxy 2012
Typical Epi Wafer Designs(IGBT)
P+ Substrate
N- Epi
Device Structure Epi Layer Structure
N+ buffer layer
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Typical Epi Wafer Designs(CMOS)
P+ Substrate
P- Epi
Device Structure Epi Layer Structure
P-Epi
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Gemini 2 Reactor
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Gemini 3 Reactor
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NuFlare Reactor
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LPE 3061 Reactor
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ASM E2000 Reactor
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AMAT Centura Reactor
3 Process chambers
Robot
Loadlocks
Cooldown Centerfinder
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Epi Key Parameters
� Thickness
� Thickness variation (within wafer and wafer to wafer)
� Resistivity
� Resistivity variation(within wafer, wafer to wafer and vertical gradient)
Silicon Epitaxy 2012
Process Control ParametersTemperature of the substrate
Pressure within the chamber
Carrier gas flow (H 2)
Flow rate of reactive gases(silicon and dopant)
Flow patterns within the chamber
Temperature profile across the susceptor
Silicon Epitaxy 2012
Chemistry for Epi Deposition
SiCl4 + 2H2 ←→ Si + 4HCl
SiHCl3 + H2 ←→ Si + 3HCl
SiH2Cl2 ←→ Si + 2HCl
SiH4 ←→ Si + 2H2
chemical process for epi depositionin a SiHCl3-H2 system
Silicon Epitaxy 2012
Deposition RateThe growth rate depends on temperature and gas flow
Increasingflow rate
Deposition from SiHCl3 + H2
Activation energy = 22 kcal/mol
Reactioncontrolled
Mass transfer controlled
Temperature (℃)
10,000/ T (K)
Dep
ositi
on r
ate
(um
/min
)
For single wafer reactor, growth rate 4~5um/min
is available
G.R. increases linearlywith square root of gas flow
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TCS Bubbler System
The TCS concentration depends on pressure , temperature and TCS level
TCS Main Tank TCS Bubbler
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Thickness Uniformity Adjustment
Flow patterns within the chamber
Main H2 flow rate
Silicon source flow rate
Deposition Temperature
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Thickness Uniformity Adjustment
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The dopant is co-deposited with silicon. Usually, a lightly doped layer is deposited on a heavily doped substrate.
Doping
dopant precursors :p-type : diborane (B 2H6) in H 2
n-type : phosphine (PH 3) in H 2arsine (AsH 3) in H 2
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Dopant Mix / Delivery System
SRC
DILINJ
mixer
vent line
Chamber A
INJ2
SRC DIL
mixer
INJ3
INJ1
Chamber A
vent lineChamber
BChamber
CChamber
B
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Temperature Dependence of Doping
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Resistivity Uniformity Adjustment
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Resistivity Uniformity Adjustment
Radial lamp array
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Resistivity Uniformity Adjustment
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Autodoping
Lightly doped epi
Heavily doped substrate
Gas-phase autodoping:Dopant fromwafer backsideand edges.
System autodoping:Dopant fromother wafers, susceptor andreactor wall.
Solid-phaseout-diffusion:Dopant diffusion up from substrate.
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Breakdown Voltage Mapping
With light autodoping With serious autodoping
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1 1 1λm+1 λm 2n2d ─── － ─── ＝ ───
� Fourier Transform Infra redSpectrometer(Bio-Rad QS-300)
Epi Thickness Measurements
Silicon Epitaxy 2012
Epi Layer Resistivity Measurements� Capacitance / Voltage
(Hg-CV: SSM 490i/495)
� 4 Point Probe(Tencor RS-35)
Epi layer of at least 3 um are required for reliable 4PP evaluation
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SSM Mercury Probe
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CV Profiling
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Doping Profile Measurements
� Spreading Resistance Probe(SSM 150, SSM 2000)
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Probes and Probe Contacts
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Calibration ChartSpreading Resistance vs. Resistivity (traceable Si bulk standards)
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SR Profile Sample
analysisalgorithms
Rm: resistanceRho: resistivityCC: concentration
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N/N++ SR Profilesfrom different correction methods
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Epi Wafer Visual Inspection
� Human InspectionDiffuse LightHigh Density LightOptical Microscope
� Automatic InspectionLaser Scanner
Wafer Mechanical Inspection
� Multifunction DimensionalMeasurements(ADE 9X00 UltraGage)
ThicknessGlobal ShapeFlatness
D = a + t + bD = a + t + bD = a + t + bD = a + t + b
t = D t = D t = D t = D –––– (a + b)(a + b)(a + b)(a + b)
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TTV(Total Thickness Variation)
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Global Flatness
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Site Flatness
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Site-partitions on 8” Wafer
( 25*25 sq.mm) (20*20 sq.mm)
* 194 mm as diameter for FQA (Fixed Quality Area)
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Stepper Focus at the Edge
Defocus at the edge because of poor edge site flatness
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Bow
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Warp
ASTM F1390entire surface scanned ASTM F657
partial surface scanned
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Taper
T2
T1
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Typical Defects in Epi Layers
Schematic representation of typical epi defects
a) epi stacking faultb) growth hillockc) dislocation (continuation from the bulk)d) stacking fault (continuation from the bulk)e) epi spike
a b c d e
Silicon Epitaxy 2012
Thank you