electronic industry_semiconductor doping

8/19/2019 Electronic Industry_Semiconductor Doping

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SURFACE ENGINEERING IN ELECTRONICS INDUSTRY

1

SEMICONDUCTOR DOPING

Akshay Makhija

Dhrumil PrajapatiHarshul Patel

Ratandeep Pandey


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Introduction

• Semiconductor plays key role in the applications in area

of thermostat, diodes, transistors etc.

• The gradient of concentration of a dopant in a sustrate

pro!ides different properties like !ariale conducti!ity,

light emission etc.

• Most popular material used in sustrate are silicon and

germanium.


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Type of seiconductors

T"o kind of semiconductors#$• Intrinsic seiconductor$ %ntrinsic semiconductor is pure.

%t has poor electric conduction.

• E!trinsic seiconductor$ &'trinsic semiconductor is also

kno"n as impurity semiconduc

a. %t is lightly or moderately doped and it has great capacity

of electric conduction.

. A semiconductor doped to high le!els such as it acts likeconductor called degenerate.


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%mpurity semiconductor is classified in t"o types

• ($type

• P$type


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• )or ($type semiconductor , impurities are chosen from range of

pentads, mostly phosphorus

•

)or P$type semiconductors , the selected impurities should e tri!alentelements, mostly oron

• The follo"ing tale sho"s the !arious materials used in

semiconductor industry


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Tec"ni#ues of Seiconductor Dopin$

There are numerous techni*ues eing follo"ed in theindustry for doping, most "idely used techni*ues are

• %on implantation

•

Diffusion• +'idation

e are going to focus on t"o major techni*ues#$

Diffusion and Ion ip%&nt&tion


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Diffusionhat is Diffusion-

•

The mo!ement of impurity atoms dopant/ at high temperature into a

semiconductor material due to concentration gradient is kno"n as

diffusion.• Diffusion of impurities in the silicon lattice takes place at

temperatures in the range of 011$2211o 3.


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There are t"o major "ays in "hich diffusion

doping process can e carried out#

•

Predeposition# The impurities diffuse into the parent material "ith aconstant concentration gradient.

• Dri!e$in# A layer of the dopant is deposited on the surface. %n this

case, the impurity gradient at the surface of the sustrate decreases

"ith time.

Pre$deposition Dri!e$%n


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Diffusion &t Microscopic Le'e%

Sustitution diffusion

%nterstitial Diffusion


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Diffusion Process P&r&eters

• Temperature

• Type of impurity

• Diffusion time

• Defects in silicon crystal

Ad'&nt&$es()• (o damage to surface• 4atch farication is possile• An isotropic process• 3ost associated "ith process is

lo"

Dis&d'&nt&$es()• 5o" Dose doping is difficult to

carry out

• Shallo" junctions are difficult to

faricate• 3ant e carried out at room

temperature


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Ion ip%&nt&tion

•hat is ion implantation-

%ons of the desired dopant are first accelerated using

an electric field resulting in formation of a eam of

ions. The eam is then projected upon the parentlattice material causing a omardment of the ions

on the sustrate resulting in a uniform deposition of

dopant on the parent lattice.


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T"e Process

•

%n order to form a eam of ions, the first step is togenerate ions.

• The dopants are heated on a hot filament causing

generation of ions.

• The ions generated are accelerated a"ay from thesource y electric field.

• The ions then pass through a magnetic field "hich

di!erts the ions and separates them according to their

si6e or according to the re*uirement using a

predesigned aperture.


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The separated ions are rought to the desired energy y accelerating them

again using an electric field and are omarded on the sustrate after passing

through a focusing lens.

The focused accelerated ions strike the sustrate and get implanted in the areae'posed to the eam.


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P&r&eters Effectin$ Ion Ip%&nt&tion Process()

• The energy of the incoming impurity

• %ntensity

• Project range


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Ad'&nt&$es()• %t is a lo" temperature process

and fast process.• The dose of ion can e

controlled• Precise depth control possile• %t can e used to implant ions

through thin layers of o'ide• The method can e used to

otain e'tremely lo" as "ell

as e'tremely high dope.

Dis&d'&nt&$es()• %t causes physical damage to

the surface• Annealing is re*uired to

reli!e the stresses and remo!e

physical damage to the

material

• Amorphous regions are

formed in the crystal lattice• 3hanneling occurs, causing

irregular distriution of ions.• %t is e'pensi!e and one of the

most ha6ardous process.


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Cop&r&ti'e study()Parameter: Diffusion Ion Implantation

Cost: It is relatively cheaper It is expensive

Batch Formation: Possible Not Possible

Reproducibility: Not Possible Possible

Very i!h

Concentration Dopin!:

Not Possible Possible

"emperature: It is a high temperature

process (900-10000C)

It is relatively a lo# temperature process

Process "ype: It is a natural process It is a forced process

Drivin! Force: Concentration Dierence $lectric Field %acceleration&

'hallo# (unction: Not Possible PossibleDopin! Concentration: Cannot be controlle! Can be controlled precisely

Dopin! Depth: Cannot be controlle! Can be controlled easily

Parent )aterial

'urface:

Doesn"t un!ergo any !amage Dama!e in form of distortion may

occur

Directional: Isotropic Process *nisotropic Process

Post do in rocess: No #nnealin is re uire! *nnealin is re uired


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Conc%usion()

• The dri!ing force in the diffusion process is the difference

et"een the concentrations of the materials in!ol!ed, is carried

out at high temperature. %t is a non$destructi!e process and

causes no damage to the material surface. 4atch formation is

possile "ith diffusion process, increasing the o!erall output

• The %on %mplantation process offers etter doping concentration

control, precise junction depth control, and easy reproduciility

and doesn7t re*uire high temperature for eing carried out. The

ion implanted product has to undergo annealing process to repair

the damage "hich makes this process relati!ely e'pensi!e.


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G&s Iersion L&ser Dopin$ *GILD+(

• Thin Silicon "afer is immersed in 4oron gas "hile a pulsed laser

repeatedly melts and cools the "afer.• The 4oron atoms in the gas diffuse into the molten parts of the Silicon

and stay there "hen the Silicon solidifies.

• 8%5D producing a P$type Silicon "afer "ith 4oron impurities.


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• GILD process could be an alternative to ion implantation as it usesrapid annealing for making ultra-shallow junctions.

Advantages:. GILD process can be used for large scale manufacturing and low

cost manufacturing.

!. GILD provides process control over concentration as well as depthof doping process.


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