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


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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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


Substrates

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Semiconductor Quantum Well


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LPE (Liquid Phase 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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LPE Melting point ofGaAs = 1238 0C

Ga rich => lower melting point

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LPE (Liquid Phase Epitaxy)

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LPE vs. (VPE and MBE)


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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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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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


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


⇨

⇋

∼ μ /

∼

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MOVPE


Toxic

⇨

TMG (=Trimethyl-gallium)Doping:

(C2H5)2Zn : p-type(C2H5)2Cd : p-typeSiH4 : n-type

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MBE vs. (VPE and LPE)


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


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• 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


Superlattice

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MBE Lab3rd Floor,Electro A Building(same room as Hall Effect measurement)

20 MBE machine at Dept. of Electronics and Telecommunications


Varian Gen II Modular MBE machine

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RHEED patterns from GaAs


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


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Growth Rate from RHEED


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GaInAsSb/AlGaAsSb MQW laser structure


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


-

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Optical detection of trace gases in the Mid-IR range


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


– 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


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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