lect1 crystal defects

8/4/2019 Lect1 Crystal Defects

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IC Technology

Books:

** The Science and Engineering of Microelectronic

FabricationStephen A. Campbell

VLSI Technology - S.M.Sze

VLSI Fabrication Principles - Sorab K. Gandhi

IC TechnologyMs. Neha Singh

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Lecture # 1


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Syllabus- 7EC4 IC TECHNOLOGYUNIT1:INTRODUCTION TO TECHNOLOGIES- Semiconductor Substrate-Crystal defects,

ElectronicGrade Silicon, Czochralski Growth, Float Zone Growth, Characterization

& evaluation of Crystals; Wafer Preparation- Silicon Shaping, Etching and Polishing,

Chemical cleaning.

UNIT2:DIFFUSION & ION IMPLANTATION- Ficks diffusion Equation in One Dimension,

Atomic model, Analytic Solution of Ficks Law, correction to simple theory ,

Diffusion in SiO2. Ion Implantation and Ion Implantation Systems Oxidation.

Growth mechanism and Deal-Grove Model of oxidation, Linear and Parabolic Rate

co-efficient, Structure of SiO2, Oxidation techniques and system, Oxide properties.

UNIT3:CHEMICAL VAPOUR DEPOSITION AND LAYER GROWTH- CVD for deposition of

dielectric and polysilicon a simple CVD system, Chemical equilibrium and the law

of mass action, Introduction to atmospheric CVD of dielectric, low pressure CVD of

dielectric and semiconductor. Epitaxy-Vapour Phase Expitaxy, Defects in Epitaxial

growth, Metal Organic Chemical Vapor Deposition, Molecular beam epitaxy.

UNIT4:PATTERN TRANSFER- Introduction to photo/optical lithography, Contact/proximity printers, Projection printers, Mask generation, photoresists. Wet etching,

Plasma etching, Reaction ion etching.

UNIT5:VLSI PROCESS INTEGRATION- Junction and Oxide Isolation, LOCOS methods,

Trench Isolation, SOI; Metallization, Planarization. Fundamental consideration for

IC Processing, NMOS IC Technology, CMOS IC Technology, Bipolar IC Technology.

IC TechnologyMs. Neha Singh

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Integrated Circuit (IC)

Technology

3IC TechnologyMs. Neha Singh


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Objectives

After the class, you will be able to:

1. Understand semiconductor manufacturingprocess.

2. Explain the crystal structure and the majordefects in silicon crystal.



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Semiconductor Manufacturing

Processes

Design

Wafer Preparation

Front-end Processes

Photolithography

Etch

Cleaning

Thin Films

Ion Implantation Planarization

Test and Assembly

Thin Films

Photo-lithography

Cleaning

Front-EndProcesses

EtchIon

Implantation

Planarization

Test &Assembly

DesignWafer

Preparation



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Design Process : VLSI Design

Establish Design Rules

Circuit Element Design

Interconnect Routing

Device Simulation

Pattern Preparation

Thin Films

Photo-lithography

Cleaning

Front-EndProcesses

EtchIon

Implantation

Planarization

Test &Assembly

DesignWafer

Preparation



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Wafer Preparation

Polysilicon Refining

Crystal Pulling

Wafer Slicing & Polishing

Epitaxial Silicon

Deposition

Thin Films

Photo-lithography

Cleaning

Front-EndProcesses

EtchIon

Implantation

Planarization

Test &

Assembly

DesignWafer

Preparation



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300 mm

200 mm

150 mm

125 mm

100 mm

75 mm

3 4 5 6 8 12

Wafer Diameter Trends



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88 die

200-mm wafer

232 die

300-mm wafer

Increase in Number of Chips

on Larger Wafer Diameter



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Yield of a Wafer

Yield =66 good die

88 total die

= 75%

Reduction in defect density is a critical aspect for increasing wafer yield.



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Crystal Growth

Shaping

Wafer Slicing

Wafer Lapping and

Edge Grind

Etching

Polishing

Cleaning

Inspection

Packaging

Basic Process Steps for Wafer Preparation



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Why Si?

Because:

No problem of decomposition as with compound

semiconductors. Thus, with Ge, it can be subjected to

variety of processing steps. Si has wider energy gap than Ge thus, can be used at

higher temperatures.

Si lends itself readily to surface passivation (formation

of SiO2) treatment.

But Si has indirect band-gap, so it is not suitable for

applications like lasers, LEDs, photovoltaic devices etc.



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Compound Semiconductor

Mostly used compound semiconductor: GaAs

Properties of GaAs: Higher electron mobility i.e. majority carriers are faster.

Lower saturation field i.e. low power delay product.

It can be made semi-insulating i.e. devices andinterconnects made in the substrate have lower parasiticcapacitances which increases the speed(3-4 timesapprox.).

The lattice structure matches to that of AlAs (energy gap

2.16eV) so ternary alloys AlxGa1-xAs are formed easilywith a wide range of composition (energy gaps).

Thus, AlGaAs compounds are used for heterostructuredevices such as Lasers.



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Crystal Structure

Amorphous Materials

Unit Cells

Polycrystal and Monocrystal Structures

Crystal Orientation



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Atomic Order of a Crystal Structure



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Amorphous Atomic Structure



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Unit Cell in simple cubic (SC) 3-D Structure

Very few crystals exhibit

this structure.

Eg: Polonium

(for a narrow range of

temperature)

Unit cell



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Faced-centered Cubic Body-centered Cubic

(FCC) Unit Cell (BCC) Unit Cell

This structure is exhibited

by a large number of

elements.

Eg: copper, gold, nickel,

platinum and silver.

Eg: Molybdenum, tantalum

and tungsten.



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Silicon Unit Cell: FCC Diamond Structure orZincblende or Sphalerite Structure



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Polycrystalline and Monocrystalline Structures

Polycrystalline structure Monocrystalline structure



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Axes of Orientation for Unit Cells

Z

X

Y

1

1

1

0



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Coordinates for Zincblende cubic

structure

Coordination number (number of neighboring

atoms) is 4.

Distance between two neighboring atoms is (3/4)a,

where a is lattice constant. For Si a=2.351 angstrom.

(1/4,1/4,1/4)

(1/4,/4,1/4)22IC TechnologyMs. Neha Singh


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Miller Indices of Crystal Planes

Z

X

Y

(100)

Z

X

Y

(110)

Z

X

Y

(111)



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Crystal Orientation

The processing characteristics and some materialproperties of silicon wafers depend on itsorientation.

The planes have the highest density of atomson the surface, so crystals grow most easily on theseplanes and oxidation occurs at a higher pace whencompared to other crystal planes.

Traditionally, bipolar devices are fabricated in oriented crystals whereas materials arepreferred for MOS devices.



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Crystal Defects in Silicon

A crystal defect (microdefect) is anyinterruption in the repetitive nature of theunit cell crystal structure. These may occurduring manufacturing process.

Three general types of crystal defects in silicon:1. Point defects - Localized crystal defect at

the atomic level

2. Dislocations - Displaced unit cells

3. Planar or - Defects in crystal structure

areadefects



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Point Defects



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Dislocations in Unit Cells



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Dislocation Movement

Dislocation moves along slip plane.

Climb of an edge dislocation



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Planer Defects : Twins and Grain boundaries

Twinning

X X

29IC TechnologyMs Neha Singh

lect1 crystal defects

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