surface engineering semiconductor industry

8/19/2019 Surface Engineering Semiconductor Industry

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CONTENTS:

Sr. No. Topic Page No.

1.

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Surface Engineering in Electronic Industry Semiconductor Doping

Ratandeep Pandeya, As!ay "a!i#aa, $ars!ul Patela, D!rumil Pra#apatia,

aMaster’s Student Mechanical Engineering, University of Ottaa, !" #aurier $ve E, Ottaa, ON%1N &N" 'anada

INTROD%CTION:

(n electronic and (.T sector, se)iconductor are e*tensively used in )anufacturing of ther)istor,

(+ sensors, diodes, transistors, and so forth. The reason of such an e*tensive use of

se)iconductor in electronic euip)ent is due properties such as slope of fi*ation for a dopant in

a su-strate gives distinctive properties, for e*a)ple, varia-le conductivity, light e)anation,

ar) vitality transfor)ation, and so on. The )ost popular )aterials used in su-strate are Silicon

Si/ and 0er)aniu) 0e/, hich are -oth the ele)ents in group ( of the ta-le and have 2

valence electrons in their outer shell.

$istory & De'elopment in Electronic and Semiconductor Industry:

3ith technological i)prove)ents in the telegraph industry during late 14th century industrial era

and in the radio and telephone industries during the early 56th century. 3orld 3ar ( pushed this

develop)ent to an unprecedented scale and a lot of technological leaps ere )ade during this

era. The )odern electronic industry as -orn out of telephone7, radio7, and television7euip)ent

develop)ent and the large a)ount of electronic7syste)s develop)ent during 3orld 3ar (( of

radar, sonar, co))unication syste)s, and advanced )unitions and eapon syste)s. (n the

interar years, the su-8ect as 9non as radio engineering. The ord electronics -egan to -e

used in the 1426s. The electronic la-oratories :ell #a-s in the United States for instance/

created and su-sidi;ed -y large corporations in the industries of radio, television, and telephone

euip)ent, -egan churning out a series of electronic advances. (nvented in 1462 -y


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)!at is 'acuum tu(e*

(n electronics, a vacuu) tu-e or electron tu-e is device that controls electric current -eteen

electrodes in an evacuated container. acuu) tu-es )ostly rely on ther)ionic e)ission of

electrons fro) a hot fila)ent or a heated cathode -y the fila)ent. This type of tu-e is called as a

ther)ionic tu-e or ther)ionic valve. $ phototu-e, though, achieves electron e)ission through

the photoelectric effect only. 0as7filled tu-es are si)ilar devices containing a gas, typically at

lo pressure, hich e*ploit pheno)ena related to electric discharge in gases, usually ithout a

heater.

$o+ it +ors*

$ll )odern vacuu) tu-es are esta-lished on the concept a heated >cathode> -oils off electrons

into a vacuu)? electrons pass through a grid or )any grids, hich control the electron current?

the electrons then stri9e on the anode plate/ and are a-sor-ed into it. The tu-e ill )a9e a s)all

$' signal voltage into a larger $' voltage -y designing the cathode, grids/ and plate suita-ly.

Thus e can a)plify it.

=igure shos a characteristic )odern vacuu) tu-e. (t is a glass -ul- ith ires passing through

its -otto), and connecting to the various electrodes inside. $ poerful vacuu) pu)p suc9s all

the air and gases out -efore the -ul- is sealed. To )a9e a good tu-e, the pu)p )ust )a9e a

vacuu) ith no )ore than a )illionth of the air pressure at sea level. The >harder> the vacuu),

the -etter the tu-e ill or9 and it ill have long life.



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=igure 1@ Sche)atic Aiagra) of vacuu) tu-e

Ad'antages of 'acuum tu(e:

1/ Bigher sound uality.5/ Bighly linear ithout negative feed-ac9, specifically for s)all7signal types.

C/ Easily tolerate large overloads and voltage spi9es.

2/ 'haracteristics are highly independent of te)perature, greatly si)plifying -iasing."/ 3ider dyna)ic range availa-le than transistors circuits, -ecause of higher operating

voltages and overload tolerance.

&/ Aevice capacitances differ only slightly ith signal voltages.!/ 'apacitive coupling can -e done ith s)all, high7uality fil) capacitors, due to

inherently high7i)pedances of tu-e circuits.

D/ Tu-es can -e co)paratively easily replaced -y user.

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Disad'antages of 'acuum tu(e:

1/ :ul9y, hence less suita-le for porta-le products.

5/ Bigher operating voltages generally reuired.

C/ Bigh poer consu)ption? needs heater supply that generates aste heat and produces

loer efficiency, particularly for s)all7signal circuits.

2/ 'athode electron7e)itting )aterials are used up in operation.

"/ So)eti)es higher cost than euivalently poered transistors.

(n 142D ca)e the transistor and in 14&6 the integrated circuit, hich ould revolutioni;e the

electronic industry. Se)iconductors used in integrated circuits facilitated the develop)ent of

)any technologies including ireless telegraphy, radio, television, radar, co)puters and

)icroprocessors.

SE"ICOND%CTOR:

$ se)iconductor is defined as a solid che)ical ele)ent or co)pound that can conduct electricity

under so)e conditions, )a9ing it a decent )ediu) for the control of electrical current.

Aepending on the current or voltage applied to a control electrode its conductance varies, or on

the intensity of irradiation -y infrared (+/, visi-le light, ultraviolet U/, or rays. Most

se)iconductors are crystals )ade of certain )aterials, )ost co))only silicon.

$ se)iconductor is capa-le of functioning of a vacuu) tu-e hich has hundreds of ti)es its

volu)e. $ single integrated circuit ('/ can do the or9 of a set of vacuu) tu-es that ould fill a

large -uilding and reuire its on electric generating plant.

TPES O- SE"ICOND%CTOR DOPIN.:

• N/type semiconductor:

(t is created hen the dopant is an ele)ent that consists of five electrons in its valence layer.

Most co))only used for this purpose is phosphorus.

The phosphorus ato)s -ond ith the crystal structure of the silicon, each one -onding ith

four ad8acent silicon ato)s 8ust li9e a silicon ato). $s phosphorus ato) has five electrons in

its outer)ost shell, and since four of the) are -onded to ad8acent ato)s, the fifth valence

electron is una-le to for) a -ond.



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The e*tra valence electrons in the phosphorous ato)s then start to -ehave li9e the single

valence electron in a regular conductor such as copper. They are free to )ove a-out. Since

this type of se)iconductor has e*tra electrons, itFs called an N7type se)iconductor.

=igure 5@ Microstructure arrange)ent of P7type se)iconductor

• P/type semiconductor:

This type of se)iconductor is created hen the dopant such as -oron/ is left ith three

electrons in its valence shell. 3hen s)all a)ount of dopant is added into the crystal, the

ato) is a-le to -ond ith four silicon ato)s and since it has only three electrons to offer,

a hole is created. This hole -ehaves li9e a positive charge, hence se)iconductors doped in

this ay are called P7type se)iconductors.


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=igure C@ Microstructure arrange)ent of N7type se)iconductor

$s voltage is applied to either an N7type or a P7type se)iconductor, current flos 8ust li9e it

flos in a regular conductor. The negative side of the voltage pushes electrons, and the positive

side pulls the). The outco)e is that the rando) electron and hole )ove)ent hich is alays present in a se)iconductor -eco)es organi;ed in one direction there-y creating )easura-le

electric current.

"ATERIA0S %SED -OR SE"I COND%CTOR DOPIN.:

:y far, silicon is the )ost idely used )aterial in se)iconductor devices. (ts co)-ination of lo

ra )aterial cost, relatively si)ple processing and a useful te)perature range )a9e it currently

the -est co)pro)ise a)ong the various co)peting )aterials. Silicon used in )anufacturing

se)iconductor device is currently fa-ricated into -oules that are large enough in dia)eter to

allo the production of C66)) 15 inch/ afers.

0er)aniu) 0e/ as idely used early as a se)iconductor )aterial -ut it is less useful than

silicon due to its ther)al sensitivity. Today, 0er)aniu)7Silicon alloy is for)ed for use in very

high speed devices of hich (:M is the largest producer. Silicon is a-undantly availa-le in

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earthFs crust so it is easily availa-le resulting in lo cost. (t had a li)ited usa-le te)perature

range, loer voltage operation ith greater current lea9age. 3ith advance)ent in technology,

silicon proved to -e superior, though at the highest operating freuencies, ele)ents of group (((

and group ( prove to -e superior G eg@ 0alliu) $rsenide. 3ith -etter physical and che)ical

properties and -eing cheaper, Silicon ensured its progress. The only ger)aniu) co)ponents in

the age of silicon as for ger)aniu) signal diodes, here their loer voltage drop as often a

desira-le feature.

0er)aniu) is also used to overco)e the losses hich occur due to silicon. =infets are currently

-eing used in the scaling industry 12n)/ to reduce the lea9age current and to develop

integration density and perfor)ance of chips. (t has -een esta-lished that ger)aniu) finfets give

-etter perfor)ance hen co)pared to silicon and helps in reducing short channel effects to a

greater e*tent.

The )ost i)portant reason hy Si is preferred over 0e is that it for)s Silicon Aio*ide due to

o*idation. SiO5 has very good passivi;ing ualities, have high dielectric constant and can protect

the chip fro) hostile surroundings. (t can -e etched only -y B= acid. On the other hand,

0er)aniu) o*ide can -e easily ashed aay -y ater. (n addition, Si is easily and a-undantly

availa-le and can -e purified to a high degree.

=igure 2@ Ta-le descri-ing valance electronic configuration of dopants



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POP%0AR DOPIN. IN SE"ICOND%CTOR:

Aoping is a process of introducing i)pure ato)s into a se)iconductor in a controlla-le )anner

to i)prove its electrical properties. The doping ith donors and acceptors allos to alter the

electron hole concentration in se)iconductor in a very large range fro) 16 c)7C up to 16 c)

. The carrier concentration can also -e varied uite accurately hich is used to produce PN7

8unctions and -uilt7in electric fields.

TEC$NI1%ES IN SE"ICOND%CTOR DOPIN.:

ION I"P0ANTATION

(n the ion i)plantation process, charged dopants ions/ are accelerated in an electric field and

irradiated onto the afer. The depth of penetration can -e set precisely either -y reducing or

increasing the voltage needed to accelerate the ions. $s the process is ta9ing place at roo)

te)perature, previously added dopants cannot diffuse out. Mas9ing photo resist layer can -e used

to cover the regions that need not to -e doped.$n i)planter consists of the folloing

co)ponents@

• Ion source: To ioni;e the dopants hich are in gaseous state e.g. -oron trifluoride :=C/.

• Accelerator: The ions are dran ith appro*i)ately C6 9ilo electron volts out of the ion

source

• "ass separation: the charged particles are deflected at 46 degrees under the influence of

)agnetic field. ery light particles are deflected )ore and too heavy particles are

deflected less than the desired ions and are trapped ith screens -ehind the separator

• Acceleration lane: the particles are accelerated to their final velocity 566 9e accelerate

ions up to 5.666.666 )Hs/

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• 0enses: lenses are used to focus the ion -ea)

• Distraction: the ions are deflected ith electrical fields to irradiate the desired

destination

• )afer station: 3afers are held into the ion -ea) after placing the) on large rotating

heels.

=igure "@ (llustration of an ion i)planter

Penetrating dept! of ions in t!e +afer: (n contrast to diffusion processes, the particles do not

penetrate into the crystal due to their high velocity. The particles are sloed don -y collisions

ith silicon hich causes da)age to the lattice. Since silicon ato)s are 9noc9ed fro) their

places, the dopants the)selves are )ostly placed interstitial. There, they are not electrically

active as there are is no -onding ith other ato)s that )ay give rise to free charge carriers.

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Reco'ery t!e crystal lattice and acti'ation of dopants: ())ediately after the i)plantation

process, a-out " I of the dopants are still -onded in the lattice. $t te)peratures a-out 1666 J',

the dopants )ove on lattice sites. The lattice da)age due to the collisions ere already cured at

a-out "66 J'. These steps are carried out only for a very short ti)e -ecause the dopants )ove

inside the crystal during high te)perature processes

C!anneling: The su-strate is present as a single crystal due to hich the silicon ato)s are

regularly arranged and for) >channels>. The dopant ato)s in8ected -y ion i)plantation can

)ove parallel to these channels and are sloed don slightly, hence penetrate deeply into the

su-strate. (n order to overco)e this, so)e of the possi-ilities are as follos@

• )afer alignment: +egarding the ion -ea), the afers ould -e deflected at angle of !

degrees. Thus the radiation is not parallel to the channels and the ions are decelerated

i))ediately -y collision.

• Scattering: $ parallel arrival is prevented -y a thin o*ide layer hich deflects the ions

=igure &@ (on ()plantation 'hanneling Process

C!aracteristic:



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• The precision of ion i)plantation is very high.

• the outard diffusion of other dopants is prevented -y carrying out the process at roo)

te)perature

• spin coated photo resist as a )as9 is sufficient, an o*ide layer, , is not necessary

• ion i)planters are very e*pensive, the costs per afer are relatively high

• the dopants do not spread laterally under the )as9 only )ini)ally due to collisions/

• 3ide range of ele)ents can -e i)planted in the crystal ith highest purity

• Aopants hich ere previously used to deposit on alls or screens inside the i)planter

and later -e carried to the afer.

• three7di)ensional structures e.g. trenches/ cannot -e doped -y ion i)plantation

• the i)plantation process ta9es place under high vacuu), hich )ust -e produced ith

several vacuu) pu)ps

There are several types of i)planters for s)all to )ediu) doses of ions 16 11 to 161" ionsHc)5/ or

for even higher doses of 161" to 161! ionsHc)5. The ion i)plantation has replaced the diffusion

)ostly due to its advantages.

234 Ad'antage and Disad'antage

Ad'antages:

1/ (t is a lo te)perature process.

5/ The dose of the ions can -e controlled.

C/ (t is possi-le to control the precise depth.

2/ This process can -e used to i)plant ions through thin layers of o*ide.

"/ This )ethod can -e used to o-tain e*tre)ely lo as ell as high dope.

&/ (t is a fast process.



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=igure !@ Aifferent parts of ion i)plantation euip)ent

Disad'antages:

1/ The )a8or disadvantage is that ion i)plantation process causes physical da)age to the

surface.

5/ $nnealing is reuired to relieve the stresses and re)ove physical da)age to the )aterial.

C/ $)orphous regions are for)ed in the crystal lattice.2/ 'hanneling causing irregular distri-ution of ions.

"/ (t is an e*pensive process.

&/ (t is one of the )ost ha;ardous process tools availa-le in the se)iconductor industry.

DI--%SION

Aiffusion is defined as the )olecular )ove)ent fro) a region of higher concentration to one of loer concentration -y rando) )otion of )olecules. The result of diffusion is a gradual )i*ing

of )aterials. =or e*a)ple, a drop of in9 in a glass of ater is evenly distri-uted after a certain

a)ount of ti)e. The diffusion can -e perfor)ed in different ays@



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• Empty space diffusion: the e)pty spaces in the crystal are filled -y the i)purity ato)s

hich are alays present, even in perfect single crystals

• Inter lattice diffusion: the i)purity ato)s )ove in7-eteen the silicon ato)s in the

crystal lattice.

• C!anging of places: the i)purity ato)s are located in the crystal lattice and are

e*changed ith the silicon ato)s.

=igure D@ (llustration of Aiffusion Process

The dopant ill continue to diffuse till concentration gradient is -alanced, or the te)perature asloered, so that the ato)s can no longer )ove. The speed of the diffusion process depends on

several factors@

• Aopant

• 'oncentration gradient

•

Te)perature

• Su-strate

• 'rystallographic orientation of the su-strate



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DI--%SION "ET$ODS:

Diffusion +it! an e5!austi(le source

(t )eans that the dopant is in li)ited uantity. $s the diffusion process continues, the

concentration at the surface decreases, hence the depth of penetration into the su-strate increases.

The diffusion coefficient of a su-stance indicates ho fast it )oves in the crystal. $rsenic ith a

lo diffusion coefficient penetrates sloer into the su-strate.

Diffusion +it! an ine5!austi(le source

(t )eans the dopant is in unli)ited uantity, hence the concentration at the surface re)ains

constant during the process hich results in continuous replenish)ent of the particles that have

penetrated into the su-strate. (n the su-seuent processes the afers are placed in a uart; tu-e

that is heated to a certain te)perature.

Diffusion from t!e gas p!ase

$ carrier gas nitrogen, argon etc./ that is )i*ed ith the desired dopant also in gaseous for),

e.g. phosphine PBC or di-orane :5B&/ leads to the silicon afers, on hich the concentration

-alance can ta9e place.

Diffusion +it! solid source

Slices containing the dopants are placed -eteen the afers. $s the te)perature in the uart;

tu-e is raised, the dopant fro) the source discs diffuses into the at)osphere. 3ith a carrier gas,

the dopant ill -e distri-uted unifor)ly, hence reaches the surface of the afers.

Diffusion +it! li6uid source

:oron -ro)ide ::r C or phosphoryl chloride PO'lC are used as liuid sources. $ carrier gas is led

through the liuids transporting the dopant in gaseous state. 'ertain areas can -e )as9ed ith

silicon dio*ide since the entire afers should not -e doped. The dopants cannot penetrate



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through the o*ide, and therefore no doping ta9es place at these locations. To avoid tensions or

even fractions of the discs, the uart; tu-e is gradually heated e.g. K16 J' per )inute/ till

466 J'. Su-seuent the dopant is led to the afers. To set the diffusion process in )otion, the

te)perature is then increased up to 1566 J'.

C$ARACTERISTICS:

• Since )any afers can -e processed si)ultaneously, this )ethod is uite favora-le

• (f there already are dopants in the silicon crystal, they can diffuse out in later processes

due to high process te)peratures

• Aopants can deposit in the uart; tu-e, and -e transported to the afers in later processes

• Aopants in the crystal are spreading not only in perpendicular orientation -ut also

laterally, so that the doped area is enlarged in a unanted )anner

Ad'antages and Disad'antages

Ad'antages:

1/ The diffusion process doesn’t da)age the surface of the parent se)iconductor.5/ :atch fa-rication is possi-le.

C/ #o overall cost of the process.

2/ :eing an isotropic process, the properties in the hole Silicon crystal is sa)e.

Disad'antages:

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1/ Aiffusion process is -ased upon solid solu-ility of the parent )aterial and the i)purity.

This )a9es the process li)ited to a narro range of )aterials.5/ Shallo 8unctions are difficult to fa-ricate.

C/ The process cannot -e carried at roo) te)perature.

2/ #o dose doping is difficult to carry out.

NE) E7PERI"ENTA0 "ET$ODS:

$ lot of research has -een carried out in field of )anufacturing se)iconductors to reduce the cost

of production and increase uality of se)iconductor. $ lot of ne e*peri)ental )ethods have

-een discovered. Once Such )ethod hich is gaining popularity is 0as i))ersion laser doping

0(#A/.

.as Immersion 0aser Doping 8.I0D9:

(n this process a thin Silicon afer is i))ersed in :oron gas hile a pulsed laser repeatedly

)elts and cools the afer. The :oron ato)s in the gas diffuse into the )olten parts of the Silicon

and stay there hen the Silicon solidifies, thus producing a P7type Silicon afer ith :oron

i)purities.

=igure 16@ (llustrates #aser (nduced Aiffusion Process

Process: 0(#A is perfor)ed in a high vacuu) cha)-er 167! )-ar/ on Si and SO( afers, using

ho)ogeni;ed e'l e*ci)er laser C6D n), C6 ns, 566 )< per pulse, 1G5" B;/.$fter cleaning and

re)oving native o*ide the su-strate is introduced in the cha)-er. The dopant precursor gas

:'lC/ is in8ected and che)isor-ed on the su-strate -efore each laser pulse.

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=igure 11@ Stages of 0(#A process.

0(#A process could -e an alternative to ion i)plantation as it uses rapid annealing for )a9ing

ultra7shallo 8unctions. Luantity :oron ato)s incorporated per laser shot depends on the laser

energy density and te)perature gradient.

Ad'antages:

1. 0(#A process can -e used for large scale )anufacturing and lo cost )anufacturing.

5. 0(#A provides process control over concentration as ell as depth of doping process.

-uture Scope of )or:

0(#A still reuires a lot of research to precisely deter)ine the laser energy density and the

nu)-er of laser shots to )a9e an ultra7thin 8unction. The use of 0(#A techniue has only -een

tested on a select group of se)iconductor )aterials. This techniue still reuires a lot of research

to )a9e it usa-le for large scale production of se)iconductor

Ta(le of Comparati'e Study

Parameter: Diffusion Ion Implantation



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Cost: (t is relatively cheaper (t is e*pensive

atc! -ormation: Possi-le Not Possi-le

Reproduci(ility: Not Possi-le Possi-le

;ery $ig!

Concentration

Doping:

Not Possi-le Possi-le

Temperature:(t is a high te)perature

process 4667

16666'/

(t is relatively a lo te)perature

process

Process Type: (t is a natural process (t is a forced process

Dri'ing -orce: 'oncentrationAifference

Electric =ield acceleration/

S!allo+


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causes no da)age to the )aterial surface. Though relatively cheaper the diffusion process has its

on dra-ac9s hich include ina-ility to control the 8unction depth and difficulty in )aintaining

precise doping concentration. The (on ()plantation process offers -etter doping concentration

control, precise 8unction depth control, and easy reproduci-ility and doesn’t reuire high

te)perature for -eing carried out

(n se)iconductors, the doping depth and concentration decide the uality of the se)iconductor.

(on i)plantation process not only offers e*cellent doping unifor)ity -ut also precise control over

depth and profile of the ion distri-ution of doping. (on i)plantation can also -e used for -oth

high and lo concentration doping and is carried out in a closed and controlled environ)ent,

reducing the possi-ility of any unanted conta)ination due to i)purities. (n co)parison to ion

i)plantation process, diffusion process offers pea9 concentration of the dopants near surface.

Easy reproduci-ility of the product is also an advantage of the ion i)plantation process.

$lthough ion i)plantation is e*pensive -ut it produces -etter uality se)iconductor as co)pared

to Aiffusion Process. (on i)plantation has so)e dra-ac9s li9e for)ation of a)orphous regions,

physical distortion of the su-stance -ut it is preferred over diffusion process as these da)ages

can -e re)oved -y annealing the product. $n i)prove)ent to the ion i)plantation process is the

plas)a i))ersion ion i)plantation P(((/.

RE-RENCES:

1. 'arrier gas diffusion for gas phase/U+#@ [email protected]

5. Aiffusion of dopantsfor gas phase and liuid/

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U+#@ [email protected])Hdiffusion7of7i)purities7for7ic7fa-rication

C. Mas9ing o*ideion i)plantation/

U+#@ [email protected]&1.5"5."!HipciHcoursesHtechnologyHinde14".ht)2. Aoped se)iconductor

U+#@ [email protected])l

". (on i)plantation syste) U+#@[email protected])Hion7i)plantation&. 0.%errien, T.Sarnet, A.A-arre,

surface engineering semiconductor industry

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