characterization of nickel silicides produced by millisecond anneals

CHARACTERIZATION OF NICKEL SILICIDES PRODUCED BY MILLISECOND ANNEALSPRODUCED BY MILLISECOND ANNEALS

Bruce Adams, Dean Jennings, Kai Ma, Abhilash Mayur, Steve Moffatt, , Stephen Nagy, Vijay Parihar

IEEE RTP 2007 Conference Catania Sicily October 4 2007Catania, Sicily October 4, 2007

FRONT END PRODUCTS GROUP

Overview

Brief Introduction to SilicidesRTP NiSi Formation ProcessRTP NiSi Formation ProcessThe Kinetic Model for NiSi TransformationThe Thermal Model for DSA– What is DSA– DSA Math Modeling

Characteristics and Morphology of DSA NiSi FilmsCharacteristics and Morphology of DSA NiSi Films– Tuning within-wafer uniformity– TEM, XDR Analysis

Predictions and ResultsSummary and Conclusions


2

IntroductionMetallic silicides used to reduce contact resistance in many advanced CMOS processing applications.

Metallic Silicides

TiSi2TiSi2 TiSi2

BPSG

SiO2 SiO2

poly Si

n+ n+p-type Si

gate

2 S 2

gateSiO2


3

Introduction

Limitations /AdvantagesMaterial

Initial use of TiSi2Inability to scaleto narrow lines

Its successor CoSi2Limited by junction leakage, high consumptionts successo CoS 2 g , g pof Si during formation

Low junction resistance, Future generations NiSi small thermal budget, low

consumption of Si duringformation.


4

RTP NiSi Formation2 step process

RTP step 1 RTP step 2

100 Å TiN Å

(200 to 300 °C) (>300 °C)

Thermally stableh i100 Å TiN

oxygen barrier100 Å TiNoxygen barrier

100 Å Ni or Ni

Low sheet resistanceUniform film

Silicon S b t t

Silicon Silicon Silicon

Ni2Si100 Å Ni:Pt (90:10) Ni2Si NiSi

Substrate Substrate SubstrateSilicon Substrate


5

Phase Change Transformation CurvePhase Change Transformation Curve

For a constant temperature (soak) anneal time, the sheet i t b l tt d f ti f diff t lresistance can be plotted as a function of different anneal

temperatures, and thereby quantify the phase change from Ni2Si to NiSi


6

NiSi Transformation Curve 100Å NiNiSi Transformation Curve, 100Å Ni

30.035.0

are) 30 second soak

20.025.0

s/Sq

ua

10.015.0

(Ohm

s

0.05.0

275 300 325 350 375

Rs

275 300 325 350 375Anneal (Soak) Temperature (°C)


7

NiSi Transformation Curves, 100A Ni,

30.035.0

re) 30 second soak

Spike

20.025.030.0

/Squ

a Spike

10.015.020.0

Ohm

s/

0 05.0

10.0

Rs

(O

0.0275 300 325 350 375

Peak Anneal Temperature (°C)


8

p ( )

NiSi Transformation Curves, 100A Ni

30.035.0

are) 30 second soak

Spike

20.025.0

s/Sq

ua

10.015.0

(Ohm

s

0.05.0R

s (

315 8275 300 325 350 375

Peak Anneal Temperature (°C)

315.8


9

Temperature Profiles with same Rs

340360

(°c)

280300320

atur

e

240260280

empe

ra

315 8 °C k

200220240

Te 315.8 °C soak350.0 °C spike

0 25 50 75 100 125Time (Seconds)


10

The Kinetic Model for NiSi TransformationTransformation


11

The Kinetic Model

Equation 1

Fick’s diffusion equation

DtL 2=

L = the diffusion lengthgD (T) = Diffusivity of nickel into silicont = time


12

The Kinetic Model

Equation 2

Diffusivity has an Arrhenius relationship with temperature

aEkT−kTeDD = 0

Do = non thermal pre-exponential constantE = the activation energy barrierEa the activation energy barrierk = Boltzmann’s constantT = absolute temperature


13

The Kinetic Model

Equation 3, Combining equations 1 and 2in integral form

Generalizes the diffusion distance for any arbitrary thermal profile

tkTEa

)(−

∫ dteDL tkT )(02 ∫∝


14

The Kinetic Model

As sheet resistance is related to the diffusion distance, two different thermal profiles will yield the same Rs when the

respective diffusion distances L1 and L2 are equal.p 1 2 q

Equation 4

EE aa

Equating equation 3 for two different thermal profiles T1(t) and T2(t) yields;

dtedte tkTtkTaa

∫∫−−

= )()( 21

We can solve this numerically for EaEa = 1.878 eVCompares favorably with 1.45 to 1.75 eV reported by d’Heurle


15

p y p y

Thermal Model for DSA

What is Dynamic Surface Anneal (DSA)?

Thermal Modeling for DSA.


16

Dynamic Surface AnnealyThermal Budget reduced by decreasing anneal time from ~1 sec (RTP) to ~ 1 msecOptical power densities ~100-500 kW/cm2 cause surface vs. volume heating (RTP: < 0.5 kW/cm2 ) and < 1 msec ramp up time is achieved

Optical power density achieved by focused line from continuous wave laser radiation.

Temperature distribution in wafer

kW/cm2 ) and < 1 msec ramp up time is achieved

laser radiation.Line is scanned relative to the wafer to complete the annealVolume of the wafer acts as heat sink and provides < 1 msec cool

Beam Scan Direction

Beam Scan Direction

Beam Scan Direction

sink and provides < 1 msec cool down timeLine source reduces stress, improves uniformity, and increases th h tthroughput

High Temperature Activation High Temperature Activation


17

without Diffusionwithout Diffusion

General form of the Heat Diffusion Equation

QTkTCp =∇•∇−∂ )(ρ QTk

tCp =∇•∇−

∂)(ρ

Change in bulk heatof unit volume

Heat flux outof unit volume

Net heatof unit volume

Cp = Specific heatρ = Densityρ DensityT = Temperaturet = Timek = Boltzmann’s Constant


18

Q = Heat

Thermal Model

Time dependency is removed by changing the frame of reference. This is accomplished by converting the bulk heating term to a convective

TCQTk ∂+∇∇ )(

g gterm.

xvx

CQTk∂

+=∇•∇− ρ)(

x = direction in the scan direction

vx = velocity in the scan direction


19

Thermal Model

C l d bili bl l i d i l

Steady state solution allows the gridding to beOptimized for high resolution near the beam

Coupled geometry capability enables accurate solution at device scale


20

Thermal Model

Boundary Conditions

( )ασα yx

eeIQ −⎟⎠⎞⎜

⎝⎛ −

=2

2

α o eeIQ =

α = Absorption CoefficientI0 = Peak absorbed irradiance of the Gaussian distributionx = distance in the scan direction away from the Gaussian peaky py = depth into the filmσ = First moment about the Gaussian mean


21

Thermal ModelTh l P fil E ti (8)Thermal Profile Equation (8)

Knowing Ea we can find a new thermal profile which g a pis independent of RTP soak and spike profiles, that has the same diffusion Depth L3

dtkTEa

)(−

∫== 21 LL dteDL tkT )(03

32 ∫=

We expect this new profile to have the samesheet resistance as L1 and L2.


22

Results from ModelingTemperature vs Time Profiles for

Various DSA Powers1400 0

1000.0

1200.0

1400.0

ure

(°C

)

100W125W150W175W200W

600.0

800.0

mpe

ratu 200W

225W250W275W300W325W

200.0

400.0Tem 325W

350W375W400W425W

0.00.02 0.0225 0.025 0.0275 0.03 0.0325 0.035

Time (Seconds)


23

Time (Seconds)

Results from Thermal Modeling

Modeled DSA peak power is adjusted until the thermalModeled DSA peak power is adjusted until the thermal profile equation (8) is satisfied.

This modeling predicts that an absorbed laser power between 225 and 250 Watts is required to achieve thebetween 225 and 250 Watts is required to achieve the correct profile.


24

Film Characteristics and Morphology

Tuning within-wafer uniformity

STEP 1 – Anneal wafer at the steep part of the transformation curve under constant laser power.

STEP 2 – Map the sheet resistance of the wafer.STEP 2 Map the sheet resistance of the wafer.

STEP 3 – Develop a corrected laser power map using the sensitivity curveusing the sensitivity curve


25

Millisecond Anneal Transformation curve

3 040.0

qNo Tuning

Chamber tuning for within-wafer uniformity

25.030.035.0

ohm

/sq With Tuning

1 9% 1σ

10 015.020.0

ean

Rs,

As Deposited1.9% 1σ

0.05.0

10.0

Me

Error bars represent +/- 1σ

120 140 160 180 200 220 240 260 280

Absorbed Laser Power, Watts


26

Millisecond Anneal NiSi Transformation Curve

40.0qLocations for TEM and XRD Analysis

25 030.035.0

ohm

/sq

A

15.020.025.0

n R

s, o

As Deposited B

0.05.0

10.0

Mea A, B, C = Samples for XRD andTEM

C0 0

120 140 160 180 200 220 240 260 280

Absorbed Laser Power, Watts


27

,

TEM Analysis

A B C

No Pitting or voids in silicide layer.

Smooth contact area at silicide / nickelsubstrate interface.


28

TEM of poor NiSi film for comparison

During low temperature annealing epitaxial NiSi2During low temperature annealing, epitaxial NiSi2growth may occur.


29

XRD analysis on the same three wafersG l a n c i n g I n c i d e n c e X R D ( G I X R D ) a t a f i x e d i n s i d e n c e o f 0 . 5 °

2 0 0 0

2 5 0 0

S a m p le C ( R s 8 . 6 o h m s / s q )

S a m p le B ( R s 1 7 o h m s / s q )

S a m p le A ( R s 2 6 o h m s / s q )

NiS

i(112

)

1 0 0 0

1 5 0 0

ensi

ty (c

ount

s)

S a m p le A ( R s 2 6 o h m s / s q )

0)

5 0 0

1 0 0 0

Inte

NiS

i(103

)

NiS

i(122

) or (

104)

NiS

i(200

)

NiS

i(210

)

NiS

i(020

)

NiS

i(201

)

Ni 2Si

(002

)

NiS

i(121

)

Ni 3Si

(402

) or N

i 3Si(2

00

Ni 2Si

(311

)

Ni 2Si

(112

)

03 0 3 5 4 0 4 5 5 0 5 5 6 0 6 5 7 0

2 t h e t a ( d e g r e e )

The evolution of the mono silicide phase (NiSi) as aThe evolution of the mono-silicide phase (NiSi) as a function of higher laser power is consistent with the electrical measurements.


30

Comparison of Results with Predictions

1) Output power of the laser is measured directly with an in-situpower meter.

2) The absorbed power is calculated by measuring the2) The absorbed power is calculated by measuring the reflectivity of the wafer surface – for example, The reflectivity of 100Å TiN / 100Å Ni on Silicon is 59% ± 2% at the laser wavelength and angle of incidence Therefore 41% of thewavelength and angle of incidence. Therefore 41% of the laser power is absorbed into the surface.

3) The Rs at the steep portion of the RTP transformation curve 21 2 Ω/ Thi R l d t 245 W ttwas 21.2 Ω/sq. This Rs value corrorsponds to 245 Watts on

the millisecond transformatioon curve.4) Compares well with the range of 225 to 250 Watts predicted

by the model.


31

Summary and Conclusions

We investigated the formation of NiSi in RTP and DSA from 30 second to millisecond time frame.OOur models predicted reasonably well the experimental results.Detailed numerical modeling predicts the steepest slope of the g p p pmillisecond transformation curve at 580 °C ± 10 °C. This is equivalent to 350 °C for spike, and 315 °C for a 30 second soak.Using this technique allows for tuning the laser power to optimize Rs uniformity for NiSi.We ha e demonstrated the formation of NiSi films bWe have demonstrated the formation of NiSi films by millisecond anneal with interface quality and within wafer uniformity that meet all state-of-the-art requirements.


32

Thank You.


33

characterization of nickel silicides produced by millisecond anneals

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