epitaxy - saroj kumar patra - ntnufolk.ntnu.no/jonathrg/fag/tfe4180/slides/epitaxy.pdf · saroj...
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TFE4180 Semiconductor Manufacturing Technology, Epitaxy
EpitaxySemiconductor Manufacturing Technology
Saroj Kumar Patra,Department of Electronics and Telecommunication,
Norwegian University of Science and Technology ( NTNU )
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Epitaxy
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Epitaxy : Process of growing single crystalline film on a crystalline substrate
LPE : Liquid Phase EpitaxyVPE : Vapour Phase EpitaxyMBE : Molecular Beam Epitaxy
The main difference between LPE, VPE and MBE processes is the way the ingradient atoms are brought to the growth-surface.
CVD (including PECVD) is not necessarily epitaxy (may be amorphous or polycrystalline film)
Strain (Deformation) : exx = (ax – a0)/a0
exx negative : compressive strainexx positive : tensile strain
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TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Rf104
Ha105
Sg106
Uns107
Uno108
Une109
IA
IIA
IIIB IVB VB VIB VIIB IB IIB
IIIA IVA VA VIA VIIA
VIIIA
VIIIB
Hydrogen
H1 1.008
Beryllium
Be4 9.012
Na11
Sodium
22.989
Li3
Lithium
6.939
12 24.312
MgMagnesium
19
KPotassium
39.102
Ca20 40.08
Calcium
Sc21
Scandium
44.956
Ti22
Titanium
47.90
V23
Vanadium
50.942
Manganese
Mn25 54.938
Fe26
Iron
55.847
Co27
Cobalt
58.933
Ni28
Nickel
58.71
Rh45
Rhodium
102.91
Zn30
Zinc
65.37
As33
Arsenic
74.922
Se34
Selenium
78.96
Br35
Bromine
79.909
Kr36
Krypton
83.80
Al13
Aluminum
26.981
Si14
Silicon
28.086
P15
Phosphorus
30.974
S16
Sulfur
32.064
Cl17
Chlorine
35.453
Ar18
Argon
39.948
B5
Boron
10.811
C6
Carbon
12.011
N7
Nitrogen
14.007
O8
Oxygen
15.999
F9
Florine
18.998
Ne10
Neon
20.183
He2
Helium
4.0026
Rb37
Rubidium
85.47
Sr38
Strontium
87.62
Y39
Yttrium
88.905
Zr40
Zirconium
91.22
Nb41
Niobium
92.906
Molybde-num
Mo42 95.94
Cr24
Chromium
51.996
Technitium
Tc43 99
Ru44
Ruthenium
101.07
Cd48
Cadmium
112.40
Cu29
Copper
63.54
Palladium
Pd46 106.4
Silver
Ag47 107.87
Sm62
Samarium
150.35
Ga31
Gallium
69.72
In49
Indium
114.82
Ge32 72.59
Germanium
Sn50
Tin
118.69
Sb51
Antimony
121.75
Te52
Tellurium
127.60
I53
Iodine
126.904
Xe54
Xenon
131.30
Cs55
Cesium
132.90
Ba56
Barium
1137.34
La57
Lanthanum
138.91
Hf72
Hafnium
178.49
Ta73
Tantalum
180.95
W74
Tungsten
183.85
Re75
Rhenium
186.2
Os76
Osmium
190.2
Ir77
Iridium
192.2
Pt78
Platinum
195.09
Au79
Gold
196.967
Hg80
Mercury
200.59
Tl81
Thallium
204.37
Pb82
Lead
207.19
Bi83
Bismuth
208.98
Po84
Polonium
210
At85
Astatine
210
Rn86
Radon
222
Uun110
Fr87
Francium
223
Ra88
Radium
226
Ac89 227
Actinium
Ce58
Cerium
140.12
Pr59
Praseodym-ium
140.91 60
NdNeodym-
ium
144.24
Pm61
Prome-thium
147
Europium
Eu63 151.96
Gd64
Gadolin-ium
157.25
Tb65
Terbium
158.92
Dy66
Dyspro-sium
162.50
Ho67
Holmium
164.93
Er68
Erbium
167.26
Tm69
Thulium
168.93
Yb70
Ytterbium
173.04 71
LuLutetium
174.97
Th90
Thorium
232.04
Pa91
Procat-inium
231
U92
Uranium
238.03
Np93
Neptunium
237
Pu94
Plutonium
242
Americium
Am95 243
Cm96
Curium
247
Berkelium
Bk97 247
Cf98
Califor-nium
249
Es99
Einstein-ium
254
Fm100
Fermium
253
Md101
Mendelev-ium
256 102
NoNobelium
253
Lr103
Lawren-cium
257
Transition Metals
Nonmetals
Metalloids(semimetals)
Lanthanides
Actinides
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III-V SemiconductorMaterial System
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Substrates
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Semiconductor Quantum Well
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
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LPE (Liquid Phase Epitaxy)
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
• GaAs substrate mounted on a (graphite) push rod that slides back and forth between Ga-rich GaAs and AlGaAs melts (in graphite container with graphite lids).
• Epitaxial growth occurs on the substrate when the melted GaAs and AlGaAs cools down.
• If the melt is more Ga-rich, then lower temperature is required for deposition of III-V epitaxial material.
• Melting point of GaAs = 1238°C.• Growth occurs at approx. 800°C, and growth rate can be as high as 500
nm/s.
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TFE4180 Semiconductor Manufacturing Technology, Epitaxy
LPE Melting point ofGaAs = 1238 0C
Ga rich => lower melting point
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TFE4180 Semiconductor Manufacturing Technology, Epitaxy
LPE (Liquid Phase Epitaxy)
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LPE vs. (VPE and MBE)
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Positive:• Short production time (high growth rate)• Less Ga vacancies (non-radiative centers)• Cheaper (both equipment and operation)
Negetives:• Blurred hetero-interfaces (approximately 10 ML to 1 ML of MBE)• Inhomogeneous film thickness (due to convective flow in the melt)• Poor control of the thickness of thin layers (due to poor control over
growth rate )• Inhomogeneous composition with film thickness for the ternary (e.g.,
AlGaAs) and quaternary (e.g., InGaAsSb) III-V semiconductors.• Poor morphology. Rarely flat/smooth surfaces.
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TFE4180 Semiconductor Manufacturing Technology, Epitaxy
VPE (Vapor Phase Epitaxy)
• Epitaxial film formed by chemical reaction of gases on a hot surface. The driving force of deposition is the change in free energy due to chemical reaction.
• Cold wall or hot wall reactor system.• At high substrate temperatures, the growth rate is determined by mass
transfer rate to the surface.• At low substrate temperatures, the growth rate is determined by chemical
reaction rate on the surface.
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TFE4180 Semiconductor Manufacturing Technology, Epitaxy
VPE (Vapor Phase Epitaxy)Si VPE
Si on SiSi on SiffireSi on GaAs
⇄ ∶
Reaction
⇨ ∶
Pyrolysis
Doping : B2H6, PH3, AsH3
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Boundary Layer at Wafer Surface
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Continuous gas flow
Deposited film
Silicon substrate
Boundary layer
Diffusion of reactants
Figure 11.15 Quirk and Serda
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III-V VPE
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
⇨
⇋
∼ μ /
∼
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MOVPE
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Toxic
⇨
TMG (=Trimethyl-gallium)Doping:
(C2H5)2Zn : p-type(C2H5)2Cd : p-typeSiH4 : n-type
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MBE vs. (VPE and LPE)
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Positives:
• Good control over composition, doping and thickness (sharp interfaces). It is quite useful for structures involving QWs (Quantum Wells) and SLs (Superlattices).
• Use of UHV implies analysis equipment inside the chamber (ideal for surface analysis studies).
Negetives:
• Lower growth rate (hence longer production time).
• Expensive (both equipment and operating expenses).
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Molecular Beam Epitaxy
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
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Molecular Beam Epitaxy
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
• Be for p-type doping in III-As, III-Sb and III-AsSb (Be sits in the Grupe-III (Al, In and Ga) sites in the structure).
• Si for n-type doping in III-As (Si sits in the Group-III sites in arsenide structures, but it can sit in both Group-III and Group-V sites in antimonide structures).
• Te for n-type doping in III-Sb and in III-AsSb(Te sits in the As or Sb sites in the structure).
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Molecular BeamEpitaxy
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Superlattice
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Molecular Beam Epitaxy
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
MBE Lab3rd Floor,Electro A Building(same room as Hall Effect measurement)
20 MBE machine at Dept. of Electronics and Telecommunications
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Varian Gen II Modular MBE machine
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RHEED patterns from GaAs
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
GaAs(001) 2x4 reconstruction E-beam along [100]:
GaAs(001) c(4x4) reconstructionE-beam along [100]:
Diffracted spots will oscillate during MBE growth.
One oscillation = 1 ML GaAs grown.
RHEED = Reflection High-Energy Electron Diffraction
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RHEED Oscillations
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
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Growth Rate from RHEED
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
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GaInAsSb/AlGaAsSb MQW laser structure
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
References:
Choi & Eglash (MIT Lincoln Lab.) APL 61 (1992) p.1154.
Menna et al. (Sarnoff Corp.) SPIE 3284 (1998) p.238.
Emmision wavelength determined by the effective band gap of the quantum wells
Compressively strained quantum wells reduce the laser threshold current density due to
• removal of the degeneracy in the valence band (strain splits the heavy and light hole bands)
• reduced Auger recombination rates(split-off band pushed out of resonnance)
==> Higher laser power and higherworking temperatures
Not included in Syllabus
-
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GaInAsSb/AlGaAsSb MQW laser structure
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
-
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Optical detection of trace gases in the Mid-IR range
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Sensitivity increased by about 150 !
wavelength sensitivity
1.57 m 4 ppm-m
2.33 m 0.03 ppm-m
1.4 1.6 1.8 2.0 2.2 2.4 2.60.0
0.2
0.4
0.6
0.8
1.0
Tra
nsm
issi
on (%
)
Wavelength (m)
Molecules have a set of absorption lines.
Gas concentrations can be determined by measuring the attenuation of a laser tuned to an absorption line.
Increased sensitivity in the mid-IR
Example CO:
Not included in Syllabus
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Mid Infra-red Diode Laser for Gas Detection Applications
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
– Gas molecules absorb laser light.– The absorption is measured and the gas concentration is calculated
Metal contactSi3N4 (isolation)Active Layer
Substrate Gas molecule(e.g., CH4)
Cladding LayerTo Detector and Computing
Source
28 GRINSCH DQWLASER Layer Structure
TFE4180 Semiconductor Manufacturing Technology, Epitaxy
Contact Metals:Example of MBE grown laser structurewith AuGe/Ni metal contact to thesubstrate backside and Ti/Pt/Au metalcontact to the laser structure top side.
• Ti for good for adhesion.
• Pt acts as the barrier layer so that Au doesn’t diffuses into the semiconductor material
• Au for outside contact
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TFE4180 Semiconductor Manufacturing Technology, Epitaxy