Chapter 6 Thermal Oxidation _ I

7/25/2019 Chapter 6 Thermal Oxidation _ I

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1. SiO2properties and applications.

2. Thermal oxidation basics.

3. Manufacturing methods and equipment.

4. Measurement methods.

5. eal!gro"e model #linear parabolic model$.

%. Thin oxide gro&th' dependence on gaspressure and cr(stal orientation

). *l!containing gas' 2 gro&th' substratedoping e+ect .

,. -nterface charges' dopant redistribution.

Si(s) + O2(g) SiO2(s)

*hapter % Thermaloxidation and the

SiSiO2interface

1

3 Microfabrication and thin lm technolog(ctor o *ui' 0*0' ni"ersit( of aterloo6 httpece.u&aterloo.ca7bcuio8 Silicon 9:S- Technolog( b( ;lummer' eal and


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;roperties of thermall( gro&n SiO2

-t is amorphous.

Stable' reproducible and

conformal SiO2gro&th Melting point 1)>>*

ensit( 2.21 gcm3#almostthe same as Si that is 2.33gcm3$

*r(stalline SiO2?@uartAB C2.%5gmcm3

Dtomic densit( 2.31>22moleculescm3

#Eor Si' it is 51>22

atomscm3

$ Fefracti"e index nC1.4%

ielectric constant C3.G #&h( notCn2H$

0xcellent electrical insulator

resisti"it( I 1>2>cm' energ(gap 0gC,!G e9.

Jigh brea8do&n electric eld I1>)9cm

*onformalgro&th

2


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3

The perfectinterface bet&een Si and SiO2is one

maKor reason &h( Si is used for semiconductor

de"ices #instead of


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STI

Dpplication of SiO2in -* industr(

4

9er( good etching selecti"it( bet&een Si and SiO2using JE

ST- shallo& trench isolation


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i+usion mas8 for commondopants

SiO2can pro"ide a selecti"e mas8

against

di+usion at high temperatures. #SiO2 si$

Oxides used for mas8ing are >.5!1Nm thic8.

SiO2mas8s for and ;

#not good for


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:ocal Oxidationof Si #:O*OS$

)

Eull( recessed process

attempts to minimiAe birdPspea8.


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Eor nanofabrication oxidationsharpening for sharp DEM tips or eld

emitters for displa(

Si

SiO2

ing' QSilicon Eield 0mission Drra(s ith Dtomicall(Sharp Tips Turn!On 9oltage and the 0+ect of TipFadius istributionR' 2>>2.

Eield emission displa( #E0$

,


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Oxide Structure

asic structure of silica a silicon

atom tetrahedrall( bonds to fourox(gen atoms

The structure of silicon!silicondioxide interface some silicon

atoms ha"e dangling bonds. G

Dmorphous tetrahedral net&or8

ridging ox(gen /on!bridging


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Single cr(stal#quartA$2.%5 gcm3

Dmouphous#thermal oxide$.2.21 gcm3

Oxide Structure

1>


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SiSiO2interface

343 Microfabrication and thin lm technolog(

ructor o *ui' 0*0' ni"ersit( of aterlootboo8 Silicon 9:S- Technolog( b( ;lummer' eal and


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r( and &et oxidation

r( oxidation Si#s$ O2#g$ SiO2#s$6 etsteam oxidation Si#s$ 2J2O#g$

SiO2#s$ 2J2#g$ oth t(picall( G>>!12>>*' &et oxidation is about 1>faster than dr(oxidation.

r( oxide thin >.>5!>.5m' excellent insulator' for gate oxides6 for "er(thin gate oxides' ma( add nitrogen to form ox(nitrides.

et oxide thic8 2.5 m' good insulator' for eld oxides or mas8ing.@ualit( su+ers due to the di+usion of the h(drogen gas out of the lm'&hich creates paths that electrons can follo&.

Foom temperature Si in air creates Qnati"e oxideR "er( thin 1!2nm'poor insulator' but can impede surface processing of Si.

9olume expansion b( 2.2#C1>.4%$' so SiO2lm has compressi"e

stress.

=>.4%

Si &afer Uoxis nal oxide thic8ness


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SiSiO2interface




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Thermal silicon oxidation methods

D three!tubehoriAontalfurnace&ith multi!Aonetemperature control

9erticalfurnace

#not popular$ 14

et oxidation using J2and O2is

more popular #cleaner$ than using


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The tubular reactor made of quartA or glass' heated b(resistance.

Ox(gen or &ater "apor Vo&s through the reactor and pastthe silicon &afers' &ith a t(pical "elocit( of order 1cms.

Thermal oxidation equipment

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1. *lean the &afers #F*D clean' "er( important$

2. ;ut &afers in the boat

3. :oad the &afers in the furnace4. Famp up the furnace to process temperature in /2#pre"ents oxidation

from occurring$

5. StabiliAe

%. ;rocess #&et or dr( oxidation$

). Dnneal in /2. Dgain' nitrogen stops oxidation process.,. Famp do&n

Thermal oxidation in practice

1!


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4. Measurement methods #mechanical' optical'electrical$.





1)


SiSiO2interface




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Oxide etched a&a( b( JE

o"er part of the &afer and amechanical st(lus is draggedo"er the resulting step.

Surface prolometr( #e8ta8$mechanical thic8ness

measurement

Stylus

1,

Mirror image of st(lus

st(lus

can also be used for thic8ness measurement. atomic force microscop($


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Thic8ness determination b( loo8ing the color

Oxide thic8ness for constructi"e interference #"ie&ed from abo"e C>o$UoC82n' nC1.4%' 8C1' 2' 3L

Our e(e can tell the color di+erence bet&een t&o lms ha"ing 1>nmthic8ness di+erence.

Eilm thic8ness #nm$

Felati"eillum

inationintensit(

1!

O i l hi 8 lli


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L igh t

source F il te r P o la r ize r

Q u a r t e r

w a v e p l a te

S ubs t r a t e

F i l m b e in g

me a su r e d

D e t e c t o rA n a l y z e r

Dfter quarter &a"e plate' the linear polariAed light becomes circularpolariAed' &hich is incident on the oxide co"ered &afer.

The polariAation of the reVected light' &hich depends on the thic8nessand refracti"e index #usuall( 8no&n$ of the oxide la(er' is determinedand used to calculate the oxide thic8ness.

Multiple &a"elengthsincident angles can be used to measurethic8nessrefracti"e index of each lm in a multi!lm stac8.

Optical thic8ness measurement ellipsometr(

er( accurate #1nm accurac($

2>


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0lectrical thic8ness measurement *!9 of MOSE0T

Substrate is /!t(pe. 0lectron ismaKorit( carrier' hole is minorit(carrier.

a. Dccumulation positi"e gate"oltage attracts electrons to

the interface.b. epletion negati"e gate

bias pushes electrons a&a(from interface. /o charge atinterface. T&o capacitance inseries.

c. -n"ersion further increase

SmallAC"oltage is

applied on top of the* "oltage forcapacitancemeasurement.

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0+ t f f f D* it


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;!t(pe substrate here#pre"ious slide /!t(pe$

0+ect of frequenc( for D* capacitance measureme

Dtafter in"ersion

Eor lo& frequenc(' #minorit($ charge

generation at the interface canfollo& the D* eld to balance thecharge at the gate' so *in"C*ox.

Eor high frequenc(' the gate chargehas to be balanced b( the carrierdeep belo& the interface' so *in"

!1C

*ox!1

*Si!1

.eep depletion for high scanningspeed #the DC"oltage scan fast intolarge positi"e "oltage$' depletiondepth Udmust increase to balance

the gate charge.

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;arameter from *!9measurement ielectric constant of Si W

SiO2 *apacitor area Oxide thic8ness -mpurit( prole in Si

Threshold "oltage of MOScapacitor

Chapter 6 Thermal Oxidation _ I

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Transcript of Chapter 6 Thermal Oxidation _ I