UltrarapidUltrarapid Thermal Annealing Thermal Annealing Induced by DC Arc Discharge Induced by DC Arc Discharge

Plasma Jet Irradiation Plasma Jet Irradiation

S. HigashiS. Higashi, H. Kaku, T. Okada, T. , H. Kaku, T. Okada, T. YorimotoYorimoto, , H. Murakami and S. Miyazaki,H. Murakami and S. Miyazaki,

Graduate School of Advanced Sciences of Graduate School of Advanced Sciences of Matter Hiroshima University, JapanMatter Hiroshima University, Japan

OutlineOutline1. Background and Objectives2. Experimental

Generation of Thermal Plasma Jet (TPJ) and Its Application to Ultrarapid Thermal Annealing (URTA)

3. Results and DiscussionNoncontact Temperature Measurement Technique with Millisecond Time ResolutionCrystallization of Amorphous Si Films & Its Application to Thin Film Transistor FabricationFormation of Si nanocrystals in SiOx

4. Summary

Background & ObjectivesBackground & ObjectivesUltrarapidUltrarapid Thermal Annealing (URTA) is one of the key process technologiesThermal Annealing (URTA) is one of the key process technologiesULSI Process : Shallow Junction

Giant Microelectronics (TFTs, Solar Cells) : Crystallization, Dopant ActivationExcimer Laser Anneal (ELA)Excimer Laser Anneal (ELA)~10ns

spike annealspike anneal

FLA (Flash Lamp Anneal)FLA (Flash Lamp Anneal)

Laser AnnealLaser Anneal

1s

1ms

1µs

2007 / 65 nm

2010 / 45 nm

2013 / 32 nm

2016 / 22 nm

year / tech. node Annealing Technology

Temperature Measurement in Temperature Measurement in MilliMilli--and Microsecond Time Domainand Microsecond Time Domain

An Alternative High Power Heat An Alternative High Power Heat Source with Simple StructureSource with Simple Structure

>Limit in Output Power (~300W)>Running Cost

Objectives of This Work are Objectives of This Work are ……

To Develop a New URTA Technique and a Temperature Measurement To Develop a New URTA Technique and a Temperature Measurement Technique with Millisecond Time ResolutionTechnique with Millisecond Time ResolutionTo Demonstrate the Application of URTA to Electronic Device FabrTo Demonstrate the Application of URTA to Electronic Device Fabricationication

Thermal Plasma– High density

Thermal Plasma Jet (TPJ) As a Heat Source …– High power density (Thermal

pinch effect) ~100 kW/cm2

– Simple structure– Atmospheric pressure

discharge

About Thermal Plasma Jet (TPJ)About Thermal Plasma Jet (TPJ)

Tem

per

atu

re (

eV)

102011

102

104

106

108

104 108 1012 1016

Plasma Density (cm-3)

10-2

1

102

104

10-4

Tem

per

atu

re (

K) Fusion

Plasma

Inter Planet PlasmaInter Stellar Plasma Ionosphere]

Flame

Glow Discharge Plasma

Solar Corona

ThermalThermalPlasmaPlasma

A comparison of various plasmas in terms of density and temperature.

A photograph of plasma jet generated under atmospheric pressure DC arc discharge.

Thermal Plasma and Its Advantages as a Heat SourceThermal Plasma and Its Advantages as a Heat Source

Concentration of Electric Power

Low Cost URTA Processing

TPJ is a Very Attractive Heat TPJ is a Very Attractive Heat Source for URTASource for URTA

ExperimentalExperimentalApplication of TPJ to RTAApplication of TPJ to RTA Oscillation in Transient ReflectivityOscillation in Transient Reflectivity

Ar：f (L/min)

Cathode (W)

Anode (Cu)

Insulator

Cooling Water

DC Power Supply ：p (kW)

Scan: v (mm/s)

a-Si Film

Photodiode

Gap ：d (mm)

Motion Stage

Filter

TPJ

Quartz(B) (A)

Beam Splitter

Probe Laser (CW )

(before annealing)

(during anneaing)

5102.1 −×=dTdnQ

Experimental set up for thermal plasma jet (TPJ) annealing. Beampaths (A) and (B) are used to measure the temperature and phase transformation of a-Si film during anneal.

0

10

Ref

lect

ivit

y (%

)

Time (ms)0 2010 30 40

p = 2.25 kWf = 9.8 L/mind = 3.0 mmv = 550 mm/s

R′

dnQ′

R

dnQQuartz

Transient reflectivity waveform observed in beam path (A) during TPJ irradiation.

Origin of the OscillationOrigin of the Oscillation

H. Kaku , et.al. Appl. Surf. Sci. 244, (2005) 8.

Noncontact Temperature Measurement TechniqueNoncontact Temperature Measurement Technique

Procedure of AnalysisProcedure of Analysis

Optical Simulation>

> Multiple reflection and interference

( )CTnQ °×+= −5102.15.1

2-d Heat Diffusion Simulation> Effective power transfer efficiency : η (%)> Width of plasma jet : w (mm)

J. H. Wray, et.al. J. Opt. Soc. Am 59 (1969) 774.

Comparison with Experimental Result

Temperature Profile

0

10

0

10

0

10

Ref

lect

ivit

y (%

)

Time (ms)0 2010 30 40

measuredsimulated

v = 900 mm/s

700 mm/s

550 mm/s

R

Position (mm)

Dep

th F

rom

Su

rfac

e (µ

m)

0 5 10

0

100

200

0

100

200

0

100

200

T (K)16001200800400

Plasma Jet

v=900 mm/s

700 mm/s

550 mm/s

(a) (b)

T. Okada, et.al. Jpn. J. Appl. Phys. 45 (2006) 4355.

Temporal Variation of TemperatureTemporal Variation of Temperature

300

600

900

1200

1500

1800

0 20 40 60 80 100 120

Tem

per

atu

re (

K)

Time (ms)

0 (surface)

50

depth (µm)

100

200300 500

p = 2.25 kWf = 9.8 L/mind = 3.0 mmv = 550 mm/s

A Noncontact Temperature A Noncontact Temperature Measurement Technique Measurement Technique with Millisecond Time with Millisecond Time Resolution has been Resolution has been Successfully DevelopedSuccessfully Developed

Accuracy < 30 K @~1670KAccuracy < 30 K @~1670K

Annealing Condition & Surface TemperatureAnnealing Condition & Surface Temperature

300500700900

1100130015001700

0 20 40 60Su

rfac

e T

emp

erat

ure

(K

)

Time (ms)

1.5 mm3 mm

5 mm

Plasma-SubstrateGap d (mm)

300500700900

1100130015001700

0 20 40 60Su

rfac

e T

emp

erat

ure

(K

)

Time (ms)

500

900

1200

Scan Speed v (mm/s)

1200

1400

1600

1800

0

1

2

3

4

5

6

400 600 800 1000 1200

Max

imu

m S

urf

ace

Tem

per

atu

re (

K)

An

nealing

Du

ration

(ms)

Scan Speed v (mm/s)

p = 2.20 kWf = 9.8 L/mind =3.0 mm

1000

1200

1400

1600

1800

0

1

2

3

4

5

6

1 2 3 4 5

Max

imu

m S

urf

ace

Tem

per

atu

re (

K)

An

nealin

g D

uration

(ms)

Plasma-Substrate Gap d (mm)

p = 2.20 kWv = 500 mm/s

: f = 9.8 L/min: f = 4.2 L/min

Scanning Speed (Scanning Speed (vv) Dependence) Dependence

d (mm)

1.53.05.0

T max (K) ta (ms) Rh (x105 K/s) Rc (x105 K/s)

178114881266

2.62.83.0

3.872.932.23

1.471.000.69

PlasPlasmama--Substrate Gap (Substrate Gap (dd) and Ar Flow Rate () and Ar Flow Rate (ff) ) Dependence under constant Dependence under constant vv of 500 mm/sof 500 mm/s

Characteristic Values of TPJ Annealing at Different Gap (Characteristic Values of TPJ Annealing at Different Gap (dd))

Application to Si WaferApplication to Si Wafer

Comparison between Quartz & SiComparison between Quartz & Si

Probe CW LaserIR Laser λ: ~ 1.5 µm

Thermal Properties of Quartz & Si

Oscillation of TransmissibilityOscillation of Transmissibility

0

20

40

60

80

100

300 320 340 360 380

Tra

nsm

issi

vity

(%

)

Temperature (K)

Si (100)d = 1.0 mm

λ = 1510 nm

Transmissivity of d = 1 mm Si wafer measured at a wavelength of 1510 nm under varying temperature. n (T) ~ 2 X 10-4 K-1 was obtained.

Simulated Transient ReflectivitySimulated Transient Reflectivity

G. Cocorullo et. al. Appl. Phys. Lett. 74 (1999) 3338.

κ (Wcm-1K-1)dn/dT (K-1)

QuartzQuartz Si

2.2X102.2X10--22

1.3X101.3X10--55

3.3X103.3X10--11

1.4X101.4X10--44

Higher Sensitivity in SiHigher Sensitivity in SiNoncontact Temperature Measurement Noncontact Temperature Measurement is Applicable to Si Wafer with Higher is Applicable to Si Wafer with Higher Time Resolution of Time Resolution of µµs.s.

Simulated transient reflectivity of Si wafer under URTA.

300

600

900

1200

0.4 0.6 0.8 1 1.2 1.4

Tem

per

atu

re (

K)

Time (ms)

(I) 896 K(II) 1206 K

0

20

40

60

80

0.4 0.6

Ref

lect

ivit

y (%

)

Time (ms)

(I) 896 K

0

20

40

60

80

0.6 0.8 1 1.2 1.4

Ref

lect

ivit

y (%

)

Time (ms)

(II) 1206 K

プローブレーザー（λ=1510 nm）

熱電対

ヒータ

パワーメータ

Siウエハ

Crystallization of aCrystallization of a--Si Films by TPJ IrradiationSi Films by TPJ Irradiation

Crystallinity & Process WindowCrystallinity & Process Window

400450500550

Raman Shift (cm-1)

Sca

tter

ing

Inte

nsi

ty (

arb

. un

its)

c-Si TO

a-Si TO

v (mm/s)

550650800

1000as deposited

p = 2.40 kWtSi = 80 nm

1.5

2

2.5

0 200 400 600 800 1000

Inp

ut

Po

wer

p (

kW)

Scan Speed v (mm/s)

film stripped

amorphous

crystallized

(a)

200 nm0 nm

3.6 nm

(b)

0 nm

20.6 nm

200 nm

(b) Melting and Resolidificationd=300~600 nm, RMS= 3.4 nm

a-Si

poly-Si

Surface MorphologySurface Morphology

(a) Solid Phase Crystallizationd=20~30 nm, RMS=0.5 nm

Crystallization by Step & Repeat MethodCrystallization by Step & Repeat Method

740 760 780 800 820 840

751.5

763.5

772.4 794.8801.5

811.5

826.5

840.8842.5

0

40000

80000

120000

160000

200 300 400 500 600 700 800 900

Emis

sion

Inte

nsity

(a.u

.)

Wavelength (nm)

0

10000

20000

30000

300 350 400 450 500 550

Emis

sion

Inte

nsity

(a.u

.)

Wavelength (nm)

324.8 nm (g)

510.6 nm

Emission Lines Cu I

521.8 nm

Optical emission spectrum of thermal plasma jet.Most of the significant lines are identified to be emission from Ar atoms as indicated in the inset. From the Boltzmann’s plot of the Ar lines, the temperature of the plasma was roughly estimated to be 8300 K.

Identification of emission lines from Cu in thermal plasma jet.No emission lines from Cu was observed in the optical emission spectrum of thermal plasma jet.

OES of Ar Thermal Plasma Jet OES of Ar Thermal Plasma Jet Strong Emission Lines From Atomic Ar are Observed in NIRStrong Emission Lines From Atomic Ar are Observed in NIR

No Emission Lines From Cu was DetectedNo Emission Lines From Cu was Detected

• Total Reflection X-Ray Fluorescence (TXRF)

Impurity Concentrations in TPJ Crystallized Si FilmsImpurity Concentrations in TPJ Crystallized Si Films

• Secondary Ion Mass Spectroscopy (SIMS)

Ato

mic

Den

sity

(cm

-2)

Detection Limit

0 nm

Mn, Zn, Mo, Pd, Sn, Ba, As, Rbwere Below Detection Limit.

SiO2 SiO2 Glass Sub.

No Metal No Metal Contamination was Contamination was Detected from TPJ Detected from TPJ Crystallized Si FilmsCrystallized Si Films

ExperimentalExperimentalApplication of TPJ to RTAApplication of TPJ to RTA Oscillation in Transient ReflectivityOscillation in Transient Reflectivity

Ar：f (L/min)

Cathode (W)

Anode (Cu)

Insulator

Cooling Water

DC Power Supply ：p (kW)

Scan: v (mm/s)

a-Si Film

Photodiode

Gap ：d (mm)

Motion Stage

Filter

TPJ

Quartz(B) (A)

Beam Splitter

Probe Laser (CW )

(before annealing)

(during anneaing)

5102.1 −×=dTdnQ

Experimental set up for thermal plasma jet (TPJ) annealing. Beampaths (A) and (B) are used to measure the temperature and phase transformation of a-Si film during anneal.

0

10

Ref

lect

ivit

y (%

)

Time (ms)0 2010 30 40

p = 2.25 kWf = 9.8 L/mind = 3.0 mmv = 550 mm/s

R′

dnQ′

R

dnQQuartz

Transient reflectivity waveform observed in beam path (A) during TPJ irradiation.

Origin of the OscillationOrigin of the Oscillation

H. Kaku , et.al. Appl. Surf. Sci. 244, (2005) 8.

20

30

40

50

60

70

600

800

1000

1200

1400

1600

1800

7 8 9 10 11 12

Ref

lect

ivity

(%

)

Tem

per

atu

re (

K)

Time (ms)

0.2 ms(SPC)

1278 K

1.3 ms(melting)

1660 Kp = 2.10 (kW)

Crystallization of aCrystallization of a--Si FilmsSi FilmsInIn--situsitu Observation of Solid Phase Observation of Solid Phase Crystallization (SPC)Crystallization (SPC)

20

30

40

500

1000

5 10 15

Ref

lect

ivit

y (%

)

Su

rfac

e T

emp

erat

ure

(K

)

Time (ms)

p (kW)1.89

20

30

40

500

1000

5 10 15

Ref

lect

ivit

y (%

)

Su

rfac

e T

emp

erat

ure

(K

)

Time (ms)

p (kW)1.892.10

20

30

40

500

1000

5 10 15

Ref

lect

ivit

y (%

)

Su

rfac

e T

emp

erat

ure

(K

)

Time (ms)

p (kW)1.892.102.10

0.6 ms (SPC)

20

30

40

600

800

1000

1200

5 10 15

Ref

lect

ivit

y (%

)

Su

rfac

e T

emp

erat

ure

(K

)

Time (ms)

p (kW)1.892.102.10

0.6 ms (SPC)

1221 K

Annealing conditions :

f = 7.0 L/min, d = 3.3 mm, v = 770 mm/s

InIn--situsitu Observation of Melting & Observation of Melting & ResolidificationResolidification

Annealing conditions :

f = 7.0 L/min, d = 0.8 mm, v = 770 mm/s

> Solid Phase Crystallization (SPC)> Solid Phase Crystallization (SPC)

> 1220 K, 0.6 ms> 1220 K, 0.6 ms

> SPC at 1278 K within 0.2 ms > SPC at 1278 K within 0.2 ms followed by melting and followed by melting and resolidification at 1660 K within 1.3 resolidification at 1660 K within 1.3 ms.ms.

Electrical Properties of TPJ Crystallized Si FilmsElectrical Properties of TPJ Crystallized Si FilmsElectrical Conductivity of TPJ Crystallized lightlyElectrical Conductivity of TPJ Crystallized lightly--doped Si Filmsdoped Si Films

Electrical conductivity as functions of annealing temperature

Defects localized at grain boundary work as carrier trap sites.

10-5

10-4

10-3

10-2

1300 1400 1500Ele

ctri

cal C

on

du

ctiv

ity

(S/c

m)

Maximum Surface Temperature (K)

d = 3 mm

d = 4 mm

d = 5 mm

p = 2.04~2.10 kW f = 9.8 L/minv = 350 ~ 900 mm/s

(a)(b)

(c)

Average P Concentration : 4.3 x 10Average P Concentration : 4.3 x 101717 cmcm--33

> Carrier Concentration in TPJ Crystallized Si Films Increases w> Carrier Concentration in TPJ Crystallized Si Films Increases with Increasing ith Increasing Annealing Temperature.Annealing Temperature.

> Defect density in Si Films is Decreases with Annealing Tempera> Defect density in Si Films is Decreases with Annealing Temperatureture

Grain Grain Boundary

Defects

(a) High Defect Density(a) High Defect Density

(b) Low Defect Density(b) Low Defect Density

EC

Free Electrons

EV

Ei

EEFF

Trapped Electrons

ED

EC

EV

Ei

EEFFED

Electrical Properties of TPJ Crystallized Si FilmsElectrical Properties of TPJ Crystallized Si FilmsElectrical Conductivity of TPJ Crystallized lightlyElectrical Conductivity of TPJ Crystallized lightly--doped Si Filmsdoped Si Films

Electrical conductivity as functions of annealing temperature

10-5

10-4

10-3

10-2

10-1

2.6 2.8 3 3.2 3.4Ele

ctri

cal C

on

du

ctiv

ity

(S/c

m)

1000 / T (K-1)

p = kW f = 9.8 L/mind = 4 mm

[450, 1526]

[v (mm/s), Tmax

(K)]

[500, 1448]

[600, 1340]0.58 eV

0.38 eV

0.26 eV

(a)

(b)

(c)

Average P Concentration : 4.3 x 10Average P Concentration : 4.3 x 101717 cmcm--33

> Carrier Concentration in TPJ Crystallized Si Films Increases w> Carrier Concentration in TPJ Crystallized Si Films Increases with Increasing ith Increasing Annealing Temperature.Annealing Temperature.

> Defect density in Si Films is Decreases with Annealing Tempera> Defect density in Si Films is Decreases with Annealing Temperatureture

Defects localized at grain boundary work as carrier trap sites.

Grain Grain Boundary

Defects

(a) High Defect Density(a) High Defect Density

(b) Low Defect Density(b) Low Defect Density

EC

Free Electrons

EV

Ei

EEFF

Trapped Electrons

ED

EC

EV

Ei

EEFFED

Electrical Properties of TPJ Crystallized Si FilmsElectrical Properties of TPJ Crystallized Si Films

Electrical conductivity of TPJ & ELA crystallized Si films before and after hydrogenation

10-6

10-5

10-4

10-3

10-2

10-1

100

101

1300 1400 1500

300 350 400

Ele

ctri

cal C

on

du

ctiv

ity

(S/c

m)

Maximum Surface Temperature (K)

Laser Energy Density (mJ/cm 2)

TPJ

ELA

: as crystallized

: Hydrogenated100nm

2.6

0

(a)

RMS=0.4 nm

100nm

12.8

0

(b)

RMS=2.4 nm

> TPJ Crystallized Films Have Lower Defect Density Compared to E> TPJ Crystallized Films Have Lower Defect Density Compared to ELA FilmsLA Films

> Defect Reduction Process Works Efficiently to TPJ Si Films> Defect Reduction Process Works Efficiently to TPJ Si Films

Defect Reduction by Hydrogen Plasma Treatment @ 250C, 60sDefect Reduction by Hydrogen Plasma Treatment @ 250C, 60s

AFM images of (a) TPJ & (b) ELA crystallized Si films

Average P Concentration : 4.3 x 10Average P Concentration : 4.3 x 101717 cmcm--33

Spin density NS in (a) TPJ & (b) ELA crystallized Si films

1017

1018

1019

1450 1500

200 250 300 350

Sp

in D

ensi

ty N

s (cm

-3)

Maximum Surface Temperature Tmax

(K)

Laser Energy Density (mJ/cm2)

ELA

TPJ

RC~1010 K/s

RC~105 K/s

ELAELA

TPJTPJ

TFT Fabrication Process FlowTFT Fabrication Process Flowa-Si Deposition> S/D n+ a-Si (PECVD)

> Channel a-Si deposition(PECVD)

Crystallization> Thermal Plasma Jet

2.3kW 700mm/s (SPC condition)

> Excimer Laser Annealing (ELA) :Reference

Channel Isolation> Dry Etching (SF6)

Source/Drain Electrode Formation> Thermal Evaporation Al

Gate SiO2 Formation> SiO Evaporation in Oxygen Radical

Gate Electrode Formation> Al Evaporation

Defect Reduction

> High-Pressure H2O Vapor Anneal

quartz substrate

n+ a-Si a-Si 20nm

Ar

poly-Si

Gate SiO2 100 nm

Al

TFT PerformancesTFT Performances

0

20

40

60

0 2 4 6

Dra

in C

urr

ent

(X10

-6 A

)

Drain Voltage (V)

VG=5V

4V

3V

1V 2V

v : 700mm/sd : 2.0 mmf : 9.8 L/minp : 2.29 kW

TPJ annealing condition

10-11

10-10

10-9

10-8

10-7

10-6

10-5

-5 0 5 10

Dra

in C

urr

ent

(A)

Gate Voltage (V)

Vd=0.1 V

W/L=2tSiO2

=100nm

2.29

2.11

1.86

v : 700mm/sd : 2.0 mmf : 9.8 L/min

ELA (350 mJ/cm2 )

TPJ annealing condition

p (kW) :

Output CharacteristicsOutput Characteristics Transfer CharacteristicsTransfer Characteristics

62

3.4

µFE (cm2V-1s-1)

Vth (V)

ION / IOFF >106

Process Temperature (C) 260

S. Higashi , et.al. Jpn. J. Appl. Phys. 44, (2005) L108.

Formation of Formation of NanocrystalsNanocrystals in in SiOxSiOxRaman Scattering Spectra of TPJ Raman Scattering Spectra of TPJ Annealed Annealed SiOSiOxx FilmsFilms

PL Spectra of TPJ Annealed PL Spectra of TPJ Annealed SiOxSiOxFilms (excitation : 325 nm )Films (excitation : 325 nm )

Ramanshift (cm-1)550700 600 500 400650 450

as deposited

1200 mm/s, 1444K

1000 mm/s, 1566K

800 mm/s, 1673K

700 mm/s, 1673K

Wavelength (nm)600 800 1000 1200

1200 mm/s,1212K

1000 mm/s, 1369K

800 mm/s, 1527K

700 mm/s, 1664KAs deposited

1 cm

NanocrystallineNanocrystalline MirocrystallineMirocrystalline

Formation of Formation of NanocrystalsNanocrystals in in SiOxSiOxCross sectional TEM of a TPJ Cross sectional TEM of a TPJ annealed annealed SiOxSiOx filmfilm

Large lateral grain growth from Large lateral grain growth from SiOxSiOx film with trench structurefilm with trench structure

Si Si nanocrystalsnanocrystals are formed in TPJ are formed in TPJ annealed annealed SiOxSiOx

Lateral crystalline growth as long as 3 Lateral crystalline growth as long as 3 µµm m is achieved.is achieved.

5 nmCross sectional TEM

NanocrystallineNanocrystalline MirocrystallineMirocrystalline

ConclusionsConclusions1. A New RTA Technique Utilizing Thermal Plasma Jet

(TPJ) and Noncontact Temperature Measurement Technique with Millisecond Time Resolution have been Developed.

2. Substrate Surface Temperature is Controlled From 960 to 1781 K with Typical Annealing Duration of 3 ms.

3. Amorphous Si (a-Si) Films are Crystallized Through Solid Phase or Melting & Resolidification Depending on the Annealing Condition.

4. TFTs Fabricated Using TPJ Crystallization Technique Show Good Electrical Performance with µfe of 62 cm2/Vsand Vth of 3.4 V.

5. Nano- and Micrometer Sized Si Crystalline Growth is Achieved by TPJ Annealing of SiOx Films.