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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.