Microelectronics Technology NERIST 09 Aug

8/14/2019 Microelectronics Technology NERIST 09 Aug

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Anirban Bhattacharyya

Talk at NERIST, August

2009


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Introduction to High Electron Mobility Transistors (HEMTs)

Semiconducting Materials

Processing Steps

Substrate Growth

Epitaxy

Molecular Beam Epitaxy

Vapor Phase Epitaxy

Characterization of Materials

Chemical Composition

Doping

Photolithography

Etching Metallization

Bonding and Packaging

2


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- High electron mobility

Transistor


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Some Scattering Mechanisms Ionized Impurity Scattering

Neutral Impurity Scattering

Acoustic Phonon Scattering

Optical Phonon Scattering


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Depends on Coulombic Interaction between electronsand ionized atoms (donors) Increases with increasing impurity concentration

(but not linearly, due to screening effects)

Where


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Large BandGap

Narrow Band Gap

Eg (Wide) Eg (Narrow)


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Eg (Wide)Eg (Narrow)


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LargeB

andGap

Material

Narrow

Ban

dGap

Material


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Large Bandgap Material, undoped

Narrow Bandgap Material

Buffer Material

Substrate Material

Large Bandgap Material, doped

Cap Layer


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GaAs Substrate

GaAs (600nm)

In0:15Ga0:85As (90nm)

Al0:24Ga0:76As (spacer)

AlAs/GaAs Superlattice

Al0:24Ga0:76As (undoped Schottky, 30 nm)

GaAs (cap layer, Si doped)

Si- Doping level 5 x 1012 cm-3

2 D Electron Gas


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Silicon: Starting material: Silica Sand

Silica Sand + Carbon Silicon (95%-97%) Electric arc furnace in

reducing ambient

Silicon (95-95%) Trichlorosilane

Fractional Distillation of Trichlorosilane

Trichlorosilane Silicon (Electronic

Grade)


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Starting Materials Germanite

Arsenopyrite

Formation of Gallium Arsenide

Evacuated Quartz Sealed Tube

Arsenic 600C -620CGallium 1220 1240C


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Water CooledEnclosure

Stirred Melt

Graphite Crucible

Gas Outlet

Seed Crystal

INGOT

RF POWER


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Grinding

Slicing

Wafer preparation

Lapping Chemo-mechanical Polishing


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Molecular Beam Epitaxy (MBE)

Metallorganic Chemical Vapor Deposition

(MOCVD)


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To Pump


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To Pump


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To Pump


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ChamberWall

RHEEDGUN

RHEED

Screen

TransferRod

EffusionCell

Shutter


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Gallium Source: Triethylgallium Aluminum Source: Trimethylaluminum

Arsenic Source: Arsine, Tertiarybutylarsenic

P-type dopant: DiethylZinc

N-type dopant: Sulphur (H2S), Selenium (H2Se), Silicon (SiH4)

Carrier Gas: Hydrogen

SUSCEPTOR

GAS INLET VENT

R. F. COIL


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3


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SHEET Carrier Density of 2DEG

= 2.1x1012 / cm2

Mobility of 2DEG

= 6100 / cm2


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Photoresist

Developer

Exposure


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1 micronfeature size

436 nm light

0.5 micron

feature size

436 nm light

0.5 micron

feature size

365 nm light


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Contact printing is capable of high resolution buthas higher defect densities

Proximity printing cannot easily print small features(except for x-ray systems)

Projection printing provides high resolution and lowdefect densities and dominates today in the industry

Typical projection systems use reduction optics (2X-5X), step and repeat or step and scan mechanicalsystems


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GaAs Substrate

GaAs


In0:15Ga0:85As

Al0:24Ga0:76As

Al0:24Ga0:76As

GaAs

Photolithography

MESA Isolation by

Wet Chemical Etching

Metallization: Ni/Ge/Au/Ti/Au

Rapid Thermal Annealing


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Increasing Directionality

Isotropic Anisotropic


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Dissociation : CF4 + e- CF3 + F + e

-

Ionization: CF3

+ e- CF3

+ + 2e-

Dissociative Ionization: CF4 + e- CF3 + F + e

-

Excitation: CF4 + e- CF4

* + e-


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GaAs Substrate

GaAs


In0:15Ga0:85As

Al0:24Ga0:76As

Al0:24Ga0:76As GaAs etching byCitric Acid + Hydrogen

peroxide

Metallization: Ti/Pt/Au

Passivation with SiN


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GaAs

Co-Polymer

PMMA

E-BEAM


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GaAs

Develop PMMA and Co-polymer

GaAsMetallization

GaAsLiftoff


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Silicon

Silicon Dioxide

PMMAPMMA-MMA

E-Beam


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Silicon

Silicon Dioxide

Cr

Ni

Cr

Silicon

Silicon Dioxide

E-beam Exposure and Developing Metallization


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Silicon

Silicon Dioxide

Cr

Ni

Cr

Formation of T-gate

Silicon

Cr

Ni

Cr

Reactive Ion Etching of SiO2


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Silicon

Removal of Ni by NH3

Silicon

RIE Etching of Silicon Dioxide


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Wafer level testing will be carried out


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Dicing to separate individual Devices High Speed Saw

Laser

Crystallographic Cleaving

Bonding Ball Bonding (Thermasonic)

Wedge Bonding (stitching)

Packaging


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Substrate Development

Epitaxy

Photolithography

Etching

Metallization

Packaging


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Microelectronics Technology NERIST 09 Aug

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