electric field and temperature effects on copper transport in mos capacitor … · 2006-03-13 ·...

1

ELECTRIC FIELD AND TEMPERATURE EFFECTS ON ELECTRIC FIELD AND TEMPERATURE EFFECTS ON COPPER TRANSPORT IN MOS CAPACITOR WITH COPPER TRANSPORT IN MOS CAPACITOR WITH

COPPER AS THE GATE METAL COPPER AS THE GATE METAL

Prof. Yosi Shacham-DiamandWasedaWaseda UniversityUniversity

2

Surface resistance measurement

R/Ro Vs Oxidation time

0

0.5

1

1.5

2

2.5

3

3.5

0 200 400 600 800

Time (min)

R/R

o

CoMoP/Cu/CoMoPon Co seadCoWP/Cu/CoWP onCo seadCoWP/Cu/CoWP onCu seadCoMoP/Cu on Cusead

3

Co0.9W0.02P0.08

0 200 400 600

60

80

100

120

hcp Co + Co2Phcp Cohcp Co + amorph. Co

Cooling 1st Run

1st Run

2nd Run

Res

istiv

ity (µ

Ω·c

m)

Temperature (oC)

Heating rate ~ 2.8°C/min ; Vacuum ~ 5 × 10-6 Torr

Tracking structural changesIn-situ resistivity as a function of temperature

After anneal:Significant temperature independent

contribution to electron scattering

(imperfections including impurities)Co BulkFilm dT

d dTd ρ

=ρ

BulkFilm ρ>ρ

413.6 14.0 14.4

-14

-13

-12

-11

-10 460 440 420

104/Tc (K-1)

ln[(d

T/dt

)/Tc2 ] (

-)

Tc (oC)

Ea – apparent activation energydT/dt – heating rateTc ≡ dρ / dT is minimal

(maximum rate of crystallization)

Constant kTE

T)dt

dT( ln

C

a2

C

+−=

240 280 320 36090

100

110

120

(e)(c)(d)(b)(a)

Res

istiv

ity (µ

Ωcm

)

Temperature (oC)

(a) 1.4 oC/min(b) 2.8 oC/min(c) 5.6 oC/min(d) 11.2 oC/min(e) 16.8 oC/min

Crystallization and Co2P phase formation processes

16.4 16.8 17.2 17.6 18.0-13

-12

-11

-10

340 320 300Tc (oC)

ln[(d

T/dt

)/Tc2 ] (

-)

104/Tc (K-1)

Ea = 1.6 ± 0.1 eV Ea = 4.7 ± 0.1 eV

hcp Co + amorphous Co(W,P) → hcp Cohcp Co → hcp Co + orthorhombic Co2P

Kissinger analysis:

5

[ ] )t-(tk(T)- exp - 1 )t(f n0⋅=

)0(tf(t)-1

)(tf(t) 1

=ρ+

∞→ρ=

ρ

n = a + b⋅ca = 1 ; Constant nucleation rate (N ~ t )b = 3 ; 3D growthc = 0.5 ; Diffusion controlled growth

0 10 20 30

100

110

120n2 n3n1

Res

istiv

ity (µ

Ω·c

m)

T ~ 260oC

Time (X103 sec)

f(t) – fraction crystallized

k (T) – apparent rate coefficientt0 – incubation timen – J-M-A index

Fraction crystallized as a function of time at a constant temperature:

Crystallization processJ-M-A analysis:

103 104

-4

-2

0

2

n1 = 1.5 ± 0.2

n2 = 2.6 ± 0.2

n3 = 1.3 ± 0.2

ln(-l

n(1-

f)) (-

)

Time (sec)

6

file: “S150n13500KleftisSiO2”

30 35 40 45 50 55

Siλ/2 (004)

εCo(01·0)

εCo(01·1) εCo

(00·2)

Difference

Co seed

Co0.9W0.02P0.08 as-dep.

Inte

nsity

(arb

. uni

ts)

2θ (°)

As-deposited structure?

Powder XRD, Bragg-Brentano geometry

I. Electroless Co0.9W0.02P0.08

II. Sputtered Co (2 nm thick)III. SiO2

Cross sectional phase contrast TEM image – as deposited film

Z.A. [00⋅1]

(10⋅0)

(12⋅0)–5 nm

I.

II.

III.

Fast Fourier transform

7

0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

400oC300oC

l (nm)

α (-

)

8 at. % 10 at. % )

r1)

C1 - 1 (

r1(V

l4 )

rr()

C1 - 1 - (1

1 2pP

2Co

hcp2

p

Co

P

⋅++

⋅=α

α - Fraction coverage of the grain boundaryrCo – Atomic radius of CorP – Covalent radius of PCP – Atomic concentration of P in the filmVhcp – Volume of hcp unit cell

Estimation of grain boundary coverage by Passuming 1 ML of P enveloping hcp Co grains with a side length or diameter, l

Co - PEnrichment of P at the grain boundariesWhy does Co2P nucleate at ~ 420°C?

8

IntroductionIntroduction

Replacing Al with CuCu integration with ILD aroused some problems:

AdhesionCorrosionCu ions transport

The solution: Depositing CoWP as a thin diffusion barrier layer

How to evaluate the quality of the diffusion barrier?Electrical monitoring of MOS capacitorsBTS followed by electrical characterization

T e l A v i v U n i v e r s i t y

9

Ideal MOS CapacitorIdeal MOS Capacitor

Fig. 1: MOS Capacitor

Fig. 2: Energy Diagram of Ideal MOS Capacitor, V=0

Uniform dopingUniform doping

No Currents through the No Currents through the oxideoxide

ΦΦmsms=0=0

There are no oxide charges There are no oxide charges or interface onesor interface ones

Ohmic contact between the Ohmic contact between the semiconductor and the back semiconductor and the back contactcontact


10

Ideal MOS Capacitor Under Voltage (pIdeal MOS Capacitor Under Voltage (p--Type)Type)

•Accumulation (V<0)

•Depletion (V>0)

•Inversion (V>>0)

WqNQ ASC −=

maxWqNQQ ANSC −−=

SSC QQ =


Fig. 3: energy diagram and the charge distribution of MOS Capacitor under v.

11

CC--V Configuration of an Ideal MOS V Configuration of an Ideal MOS Capacitor (pCapacitor (p--Type)Type)

BN0 CC1

C1

1C

++

=

CFB(ψs=0)

Fig. 5:HF C-V of MOS Capacitor

Fig. 4:The Equivalent Electrical Circuit of MOS Capacitor

OOxxiiddee

CCaapp


sOXG VV φ+=

12

CC--V Configuration of an Ideal MOS V Configuration of an Ideal MOS Capacitor (pCapacitor (p--Type)Type)

BN0 CC1

C1

1C

++

=

CFB(ψs=0)

Fig. 5:HF C-V of MOS Capacitor

Fig. 4:The Equivalent Electrical Circuit of MOS Capacitor


sOXG VV φ+=

13

CC--V Measurement (pV Measurement (p--type)type)

dVdQC =

Fig. 6:Low-frequency (LF), high frequency (HH) and deep depletion (DD) capacitance-voltage curves

Our COur C--V Measurement (nV Measurement (n--type)type)


14

Real MOS CapacitorReal MOS Capacitor

OX

sit

OX

Ot

OX

m

OX

fmsFB C

)(QCQ

CQ

CQV ψ

−γ

−γ

−−φ=

FBsOXG VVV +φ+=

( )⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

=γ

=γ

=

=

1

0

)tx(

0x

ox

Fig. 8:The influence of oxide charges and the φms on the C-V curve.

Fig. 7:Charges and their location for thermally oxidized Si.


15

Real MOS Capacitor (pReal MOS Capacitor (p--type)type)

OX

sit

OX

Ot

OX

m

OX

fmsFB C

)(QCQ

CQ

CQV ψ

−γ

−γ

−−φ=

FBsOXG VVV +φ+=

( )⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

=γ

=γ

=

=

1

0

)tx(

0x

ox

Fig. 8:The influence of oxide charges and the φms on the C-V curve.


16

CC--t Measurement & t Measurement & ZerbstZerbsttechniquetechnique

i' g sqndt −τ−=

Fig. 10:Space-charge region (SCR) and quasinetural region generation components of a

deep depletion MOS-C.

A0S

'OXiF

F

OX

A'g

i2

OXNK

SCn21

CC

CC

Nn2

CC

dtd

ε+⎟⎠⎞

⎜⎝⎛ −

τ=⎟

⎠⎞

⎜⎝⎛−

2OXC

Cdtd

⎟⎠⎞

⎜⎝⎛− ⎟

⎠⎞

⎜⎝⎛ −1

CCF

Fig. 11:Zerbst plot of the C-t transient

Fig. 9:Deep depletion MOS-C characteristics: (a) the C-V curve. (b) the C-t transient.


)C/C()n/N(t

FOiDF'

g ⋅≈τ

17

CC--t Measurementt Measurement

Fig. 9:Deep depletion MOS-C characteristics: (a) the C-V curve. (b) the C-t transient.


)C/C()n/N(t

FOiDF'

g ⋅≈τ

18

ZerbstZerbst techniquetechnique'

i'g

FiN sqn)WW(qndt

dQ−

τ

−−=

Fig. 11:Zerbst plot of the C-t transient


A0S

'OXiF

F

OX

A'g

i2

OXNK

SCn21

CC

CC

Nn2

CC

dtd

ε+⎟⎠⎞

⎜⎝⎛ −

τ=⎟

⎠⎞

⎜⎝⎛−

2OXC

Cdtd

⎟⎠⎞

⎜⎝⎛− ⎟

⎠⎞

⎜⎝⎛ −1

CCF

19

Barrier integrity

Questions:

1.How to evaluate the quality of a diffusion barrier?

2.What is the barrier integrity of electroless deposited Co alloy films?

20

Evaluation of barrier integrity depends on the sensitivity of the characterization method

How to evaluate the quality of a diffusion barrier?

MOS capacitor

Most sensitive methods:

Metal – Oxide –Semiconductor (MOS) capacitors and Metal –Semiconductor diodes

MOS is also a functional approach

21

Evaluation of D.B. quality using MOS capacitors: Capacitance-Voltage

∆VFB Cu+ ions in the oxide – requires electric field in order to enhance drift of Cu+ ions→ ∆VFB<0

CINV Decreased minority lifetime as a result of Cu generated deep levels→ CINV increases for a fixed a.c. frequency

f otfb

O

mms

Q QV - CQφ + +

=

-3 -2 -1 0 1 2 3

5

10

15

20

25

30

35

300°C / 30 min 450°C / 4 hrs 450°C / 12 hrs

Cap

acita

nce

(pF)

Voltage (V)

∆Vfb

CINVCu/Co0.9P0.1

Quasi – static C-V measurements (1 MHz)

22

0.0 0.1 0.2 0.3 0.4 0.5 0.60.00

0.05

0.10

0.15

0.20

MOS5_5_1 CoP/Cu/CoP 300C/30min CV1+Ct1

τ' = 630 ± 50 µsecs' = 0.08 ± 0.01 cm/sec

-d(C

0/C)2 /d

t (s

ec-1)

CF/C - 1 (-)

Time

Zerbst plot of a C-t measurement

Cu/Co0.9P0.1 after 300°C /30min

0 50 100 150 200 2505

6

7

8

9

10

Cap

acita

nce

(pF)

Time (sec)

300°C / 30 min 450°C / 4 hrs 450°C / 12 hrs

Inversion

Deep depletion

Evaluation of D.B. quality using MOS capacitors: Capacitance-transient

slopeCNCn2 '

FB

0ig ⋅=τFrom the slope:Effective generation lifetime:

0i

B0S

Cn2interceptNεK s' ⋅

=From the intercept:Effective generation velocity:

∫=W

WscrN

F

dxG q- scr) (bulk dt/dQ

Cu/Co0.9P0.1

Capacitance time measurements (1 MHz)

23

bb

1 – Evaluated by C-t2 – Evaluated by C-V

Evaluation of diffusion barrier quality Results

A. Kohn, M. Eizenberg, Y. Shacham-Diamand

B. Israel, and Y. Sverdlov

Microelectronic Eng. 55, 297 (2001)

Electroless Co0.9P0.1 , 30 nm thick, are stable barriers at 450°C during approximately 10 hours

Current allowed total thermal budget: Thermal cycles equivalent to 400°C, 10 – 60 minutes

Barrier

30 nm thick

Thermal Stress1 Bias and Thermal Stress2

1 MV/cm at 300ºC / 30 min

Co0.96W0.04 Fails after 450ºC / 1hr Fails

Co0.9P0.1 Fails after 450ºC / 10 hr Stable

Co0.9W0.02P0.08 400ºC/30 min: Stable

500ºC/30 min: Fails

N/A

24

Investigation of the structure of electroless Co alloys and its evolution as a result of heat treatments

Questions:1. What is the as-deposited structure?

2. How does the structure change with thermal anneal?

3. What is the structure during failure of the diffusion barrier?

Case study: Co0.9W0.02P0.08Electroless Co0.9W0.02P0.08 10 – 100 nm

Sputtered Co or Cu 2 – 20 nm

(Sputtered Ti) (5 nm)

SiO2 100 nm

Si wafer

25

Most sensitive method: Metal Oxide Semiconductor (MOS) and Metal Semiconductor diodesMOS is also a functional approach

Evaluation of barrier integrity depends on the sensitivity of the characterization method

How to evaluate the quality of a diffusion barrier?

MOS structure

26

Evaluation of D.B. quality using MOS diodes: Capacitance-Voltage

∆VFB Cu+ ions in the oxide→ ∆VFB<0

Cinversion Decreased minority lifetimeas a result of Cu generated deep levels→ increases for a fixed a.c. frequency

Requires electric fieldIn order to enhance drift of Cu+

ions

27

-4 -2 0 2 4

20

40

60

80

Al/SiO2 TS Capacitor 33A no.1

Cap

acita

nce

(pF)

Voltage (Volts)

Vacuum anneal TS 300oC/30 min

-4 -2 0 2 4

20

40

60

80

Al/SiO2 BTS Capacitor 33A no.2

Cap

acita

nce

(pF)

Voltage (Volts)

Vacuum anneal BTS 300oC

2MV/cm 30 min

-4 -2 0 2 4

20

40

60

80

Cap

acita

nce

(pF)

Voltage (Volts)

CV Thermal stress Cap 33B n5 Cu/SiO2

Vacuum anneal TS 300oC/30min

-8 -4 0 4

20

40

60

CV BTS Cap 33B n4 Cu/SiO2

Cap

acita

nce

(pF)

Voltage (Volts)

Vacuum anneal BTS 300oC

2-0.5 MV/cm 30min

Equilibrium capacitance voltage measurements at 1 MHz

Applying bias –enhanced drift of Cu+, and degradation of the dielectric

Reference: Al / SiO2 / n-Si

Cu / SiO2 / n-Si

28

Deep depletion

Strong inversion

Accumulation

0

VG

0

+

t

Evaluation of D.B. quality using MOS diodes: Transient Capacitance

29

Deep depletion MOS-capacitor• Using the expression for capacitance as a function of gate voltage and inversion capacita• For a pulsed capacitor, where dVG/dt = 0,

(dQN/dt ~ -d(Co/C)2/dt)

Thermal generation of electron-hole pairs:

Generation of minority charge carriers

C - capacitance (F/cm2)Co- oxide capacitance (F/cm2)eo - permittivity of free space (F/cm)NB- net doping concentration (cm-3)ni - intrinsic carrier concentration (cm-3)KS- s.c. dielectric constant (Si:11.8) (-)QN- electron surface charge density (Cb/cm2)GSCR- steady-state scr generation rate (cm-3s-1)W - scr width (cm)WF - final scr width for MOS capacitor in heavy inversion (cm)tg - generation lifetime (sec)

30

0 50 100 150 200 250 300 3505

6

7

8

9

10

Cap

acita

nce

(pF)

MOS5_1 CoP/Cu/CoP 300C/30min Ct9

Time (sec)

Zerbst plot of the C-t transientExample: Cu/Co0.9P0.1 after 300°C /30min

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.70.00

0.05

0.10

0.15

0.20τ' = 930 ± 50 µsecs' = 0.10 ± 0.01 cm/sec

MOS5_1 CoP/Cu/CoP 300C/30min CV11+Ct9

-d(C

0/C)2 /d

t (s

ec-1)

CF/C - 1 (-)

Time

B0S

0iF

gFB

0i2

o

NεKs'Cn2 ) 1 -

CC()

'CNCn2 (

dt/C)d(C

+⋅τ

=−

slopeCNCn2 '

FB

0ig ⋅=τFrom the slope:

0i

B0S

Cn2intercept NεK s' ⋅

=From the intercept:

Inversion

Deep depletion

31

MOS Samples

Thermal Stress, 300° - 600°C vacuum anneal (≤10-6 Torr)Bias Thermal Stress 1 MV/cm 300 °C , N2 ambient

Co0.9W0.02P0.08 30 nm Co0.9P0.1 / Co0.96W0.04 30 nm

Cu 60 nm Cu 150 nm

Co0.9W0.02P0.08 30 nm Co0.9P0.1 / Co0.96W0.04 30 nm

Co seed 10 nm Co seed 10 nm

Ti (oxidized) 4 nmSiO2 14 nm

SiO2 100 nm

p-Silicon, B doped 1.5×1015 cm-3

p-Silicon, B doped 1.5×1015 cm-3

(a) (b)

32

-3 -2 -1 0 1 2 35

10

15

20

25

300oC / 30 min +450oC / 30 min

Cap

acita

nce

(pF)

Voltage (V)-3 -2 -1 0 1 2 3

5

10

15

20

25

30

35

C

apac

itanc

e (p

F)

Voltage (V)

300oC / 30 min +450oC / 30 min

Evaluation of diffusion barrier quality – 450°CCo0.96W0.04

diffusion barrier Typical example

p-Si

SiO2

Co0.96W0.04

Cu

Co0.96W0.04

Quasi – static capacitance voltage measurements at 1 MHz

33

0 40 80 120 1604

5

6

7

8

300oC / 30 min +450oC / 30 minC

apac

itanc

e (p

F)

Time (sec)

Evaluation of diffusion barrier quality – 450°C

p-Si

SiO2

Co0.96W0.04

Cu

Co0.96W0.04

Co0.96W0.04

diffusion barrier

0 50 100 150 2004

8

12

16

20

C

apac

itanc

e (p

F)

Time (sec)

300oC / 30 min +450oC / 30 min

Typical example

Capacitance transient measurement at 1 MHz

34

-3 -2 -1 0 1 2 3

5

10

15

20

25

30

35

300°C / 30 min 450°C / 4 hrs 450°C / 12 hrs

Cap

acita

nce

(pF)

Voltage (V)0 50 100 150 200 250

5

6

7

8

9

10

C

apac

itanc

e (p

F)

Time (sec)

300°C / 30 min 450°C / 4 hrs 450°C / 12 hrs

Evaluation of diffusion barrier quality – 450°C

Co0.9P0.1

diffusion barrierp-Si

SiO2

Co0.9P0.1

CuCo0.9P0.1

Typical example

35

0 2 4 6 8 10 120.0

0.1

0.2

0.3

0.4

(+order of magnitude)

Anneal time (hr)

Significant increase

V S' (c

m/s

ec)

0 2 4 6 8 10 120

200

400

600

800

Anneal time (hr)

τ g' (µ

sec)

Evaluation of diffusion barrier quality – 450°CTypical example

0 2 4 6 8 10 12-200-150-100-50

050

100150

∆VFB

(mV)

Anneal time (hr)

p-Si

SiO2

Co0.9P0.1

CuCo0.9P0.1

36

-4 -2 0 2 4

5

10

15

20

25

30

Thermal anneal +BTS

Cap

acita

nce

(pF)

Voltage (V)-4 -2 0 2 4

0

10

20

30

Thermal anneal +BTS

Cap

acita

nce

(pF)

Voltage (V)

Quasi-static C-V measurements of MOS capacitors at 1 MHz

Co0.9P0.1 Co0.96W0.04

Bias Thermal Stress - 300oC / 0.5 hr 1 MV/cm, N2 environment :Co0.9P0.1 diffusion barrier stable Co0.96W0.04 diffusion barrier fails

Typical example

37

T

Lower metal layer

Upper metal layer

Interconnectmetal layer

W S

P

CLL

CV = CLG

)TL

P4L ( k 2 RC 2

2

2

2

0 += ερ

ρ – metal resistivity; ε0 – vacuum permittivity; k – relative dielectric constantL – line length; P – line pitch; W – line widthS – line spacing; T – line thickness (the dielectric thickness above and below the interconnect is equal)

0.65 0.5 0.35 0.25 0.18 0.13 0.10

10

20

30

40Gate with Al/SiO2

Gate with Cu/low K

Gate

Del

ay (p

Sec)

Generation

Gate Delay Interconnect Delay: Cu/low K Interconnect Delay: Al/SiO2 Sum of Delays: Cu/low K Sum of Delays: Al/SiO2

Al 3.0 µΩ⋅cm ; Cu 1.7 µΩ⋅cm SiO2 K=4.0 ; Low K K=2.0Al+Cu 0.8 µm thick, 436 µm long

Mark T.Bohr, Interconnect Scaling -The Real Limiter to High Performance ULSII995 International Electron Devices Meeting Technical Digest, (1995) 241-244.

Motivation for Cu metallizationI. Reducing the RC delay time

38

Evaluation of D.B. quality : C-t (MOS)

A: Accumulation

B: Deep depletionAs a result of voltage step

C: Strong inversionEquilibrium state throughehp generation

Deep depletion

Strong inversion

Accumulation

VG

0

0

+

t

39

Electroless deposition of Co alloysProcess:

Co(II)Cit + e- → Co(I)CitadsCo(I)Citads + e- → Co(s) + Cit

Reduction of Co ions (complexed with the citrate)

H2PO2- → HPO2

-ads +

Hads

Reducing agent is hypophosphite:H ?extraction? on the catalytic seed layer

Reaction with OH- ions:

HPO2-ads + OH- → H2PO3

- + e-

Reaction of H atoms is dependant on the catalytic seed layer:

Hads + OH- → H2O + e- Catalytic seed layer: Pd, Pt, Rh 2Hads → H2 Catalytic seed layer: Cu, Au, Ag

In parallel, a competing reaction of hypophosphdeposits P:

H2PO2- + 2H+ + e- → P +

H2O

W deposition? Induced co-deposition: iron group ion + refractory metalProposed Mechanism: Podlaha et al., J. Electrochem. Soc. 144 (1997) 1672

Induced co-deposition of MoO42- and ion M (Fe2+, Co2+, Ni2+) complexed with a ligand L

MoO42- + M(II)L + 2H2O + 2e- → [M(II)LMoO2]ads + 4OH-

[M(II)LMoO2]ads + 2H2O + 4e- → Mo(s) + M(II)L + 4OH-

40

Periodicity in P depth profile

AES depth profiles

SiSiO2

TiCo

Co0.9W0.02P0.08

as-deposited

3000C

5000C

7000C

4000C

~12 nm

41

Chemical binding statesCo, W – no observable change in chemical binding (XPS, EELS)P – significant changes

X-ray photoelecton spectroscopySuggested fitting of 2p3/2 and 2p1/2 P states :P1 and P2 2p binding states1. p3/2 and p1/2 ∆E = 0.84 eV Goodman et al., Phys. Rev B 27, 7440 (1983)2. p3/2 and p1/2 area ratio = 2:13. FWHM, G/L ratio equal for p3/2 and p1/2 for P1, P24. 0.2 ≤ G/L ≤ 0.8Results:1. P1 and P2 – equal B.E., FWHM, G/L ratio for all samples

→ validates assumptions2. Area ratio of P1:P2 → ratio of binding states

as-dep Data Fitting

P2

P2

P1P1

400oC

P1 P1P2

P2

P1 P1P2

P2

600oC

132 130 128 126

P1P1P2

P2

Co2P

Binding Energy (eV)

Inte

nsity

(arb

. uni

ts)

Sample

Area ratio P1/P2 (-) ±10%

Co0.9W0.02P0.08 as-dep 1:1.1 Co0.9W0.02P0.08 400oC 1:2 Co0.9W0.02P0.08 600oC 1:4.9 Co2P Reference 1:5

42

Same results on Co and Cu seed layer

No phase reaction between Cu and the electroless film up to 700°C

Structure of Co0.9W0.02P0.08 and its evolution with thermal treatmentsCu : Influence of seed layer and / or phase interaction?

Powder XRD, Bragg-Brentano geometry

Thermal anneal:1 hourVacuum ≤ 10-6

Torr

Copper seed

30 35 40 45 50 55

5x102

2x103

3x103

4x103

5x103

2θ (°)

as depInte

nsity

(a.u

.)

300oC

500oC

700oC

Cu (111)

αCo(200)

εCo(01·1)

Co2P (201)

Siλ/2 (004) αCo

(111)

εCo (00·2)

εCo (01·0)

43

The Main GoalsThe Main Goals

The effectiveness of CoWP as a Barrier The effectiveness of CoWP as a Barrier Layer against Cu transportLayer against Cu transport

Failure characterizationFailure characterization

Comparison between the various kinds of Comparison between the various kinds of electrical measurements electrical measurements

The effect of the temperature and the bias The effect of the temperature and the bias on the Cu transporton the Cu transport

Calculation of the Calculation of the DDeffeff of Cu under BTS of Cu under BTS

44

CapacitorsCapacitors’’ typetype

Oxide

Semiconductor

Metal

n-Si-360µ

SiO2-1000Å

CoWP-300Å

Cu-600Å

CoWP-300Å

Al-1000Å

Co-100Å

Ti-20Å

1. Test capacitors: CoWP/Cu/CoWP/Co/Ti/SiO2 2. Reference capacitors #1: CoWP/Cu/Co/Ti/SiO23. Reference capacitors #2: CoWP/Cu/SiO2

45

Experimental SetupExperimental Setup

Annealing at 300°C for 1/2hr

Annealing at 300°C for 1/2hr

performing C-V, C-t and I-VMeasurements at 25°C

performing CC--VV, CC--tt and II--VVMeasurements at 25°C

I-t measurement in-situ

II--tt measurement in-situ

Going down to room temperature and performing C-V, C-t and I-V measurements

Going down to room temperature and performing CC--VV, CC--tt and II--VV measurements

BTS at 250-300°C, undervarious fields; 0.3-1.4MV/cm

BTSBTS at 250-300°C, undervarious fields; 0.3-1.4MV/cm

The main parameters, that were derived from the electrical measurements, are:

CC--VV curve: CFB, Nd, Qit, Qm, dox

CC--tt curve: τg’, s’

II--VV curve: Ecritical, Conduction mechanism,

II--tt curve: tf, Leakage currents

46

Results presentation methodologyResults presentation methodology

I. TS and BTS measurements under:

low electriclow electric fieldfield.

high electric fieldhigh electric field.

II. Data of BTS results under wide range of temperatures and fields.

III. Calculating the effective diffusion coefficient

IV. Proposing a model for Cu+ transport in the oxide.

47






III. Modeling using the effective diffusion coefficient

IV. Proposing a model for Cu transport in the oxide.

48

CC--VV of test cap.: CoWP/Cu/CoWP/Co/Ti/SiOof test cap.: CoWP/Cu/CoWP/Co/Ti/SiO22

TS4/BTS497

TS3/BTS325.83

TS2/BTS22.5

TS1/BTS11

Stress No.Accumulate Time(hr)

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

0

50

100

150

200

250

300

350

400

b

C(pF)

V(v)

PreAnn. TS1 TS4

-10 -8 -6 -4 -2 0 2 4

0

50

100

150

200

250

300

350

400

a

C(pF)

V(v)

PreAnn. TS1 TS4

TS: 250TS: 250°°CC

-10 -8 -6 -4 -2 0 2 4

0

50

100

150

200

250

300

350

400

a

C(pF)

V(v)

PreAnn. BTS1 BTS2 BTS3 BTS4

-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

0

50

100

150

200

250

300

350

400

b

C(pF)

V(v)

PreAnn. BTS1 BTS2 BTS3 BTS4BTS: 250BTS: 250°°C, C,

0.3MV/cm0.3MV/cm

49

∆∆VVFBFB vs. timevs. time of ref. #1 of ref. #1

0 10 20 30 40 50-0.7

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

VFB [V]∆

time [hr]

TS BTS

0 5 10 15 20 25 30 35 40 4545

50

55

60

65

70

75

80

85

90

a

C(pF)

t(sec)

PreAnn. BTS1 BTS2 BTS3 BTS4 BTS5 BTS6

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

0

0.5

1

1.5

2

2.5Zerbst Plot

(Cf/C -1)[-]

-d(C

o/C

)2 /dt,

[1/s

ec]

t=26.12 1e-6 sec

Vs=0.63457 cm/sec

b

PreAnn.τg

'=26 µsS'=0.63 cm/sec

cd

CC--t t of ref. #1 under BTS: 250of ref. #1 under BTS: 250°°C, 0.3MV/cmC, 0.3MV/cm

50

CC--V & CV & C--tt of ref. #1 :of ref. #1 : CoWP/Cu/Co/Ti/SiOCoWP/Cu/Co/Ti/SiO22

-10 -8 -6 -4 -2 0 2 40

50

100

150

200

250

300

350

400

a

C(pF)

V(v)


-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.00

50

100

150

200

250

300

350

400

b

C(pF)

V(v)


45BTS6

26BTS5

20.5BTS4

3.5BTS3

2.5BTS2

1BTS1

Accumulate Time(hr)Stress No.

BTS: 250BTS: 250°°C, 0.3MV/cmC, 0.3MV/cm

0 5 10 15 20 25 30 35 40 4545

50

55

60

65

70

75

80

85

90

a

C(pF)

t(sec)


0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

0

0.5

1

1.5

2

2.5Zerbst Plot

(Cf/C -1)[-]

-d(C

o/C

)2 /dt,

[1/s

ec]

t=26.12 1e-6 sec

Vs=0.63457 cm/sec

b

PreAnn.τg

'=26 µsS'=0.63 cm/sec

cd

51

II--V & IV & I--t t of ref. #1 :of ref. #1 : CoWP/Cu/Co/Ti/SiOCoWP/Cu/Co/Ti/SiO22

45BTS6

26BTS5

20.5BTS4

3.5BTS3

2.5BTS2

1BTS1


0 5 10 15 20 25 30 35 40 45 50 55-2.0µ

0.0

2.0µ

4.0µ

6.0µ

8.0µ

10.0µ

12.0µ

14.0µ

16.0µ

18.0µ

20 40

0.0

200.0n

I(A)

V(v)I(A)

V(v)

PreAnn. BTS6


52

CC--V & IV & I--tt of ref. #2: CoWP/Cu/SiOof ref. #2: CoWP/Cu/SiO22

8BTS6

6BTS5

4BTS4

3BTS3

1.5BTS2

0.5BTS1



-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.050

100

150

200

250

300

350

400

b

C(pF)

V(v)

Theory PreAnn. BTS1 BTS2 BTS3 BTS4 BTS5 BTS6

-10 -8 -6 -4 -2 0 2 450

100

150

200

250

300

350

400

a

C(pF)

V(v)

Theory PreAnn. BTS1 BTS2 BTS3 BTS4 BTS5 BTS6

53

Temperature effect under Temperature effect under lowlow electric fieldelectric fieldin ref. #1in ref. #1

250 275 3000.0

0.1

0.2

0.3

0.4

0.5

0.6

VFB| [V]|∆

T(C0)

A B

0 10 20 30 40 50

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

∆VFB [V]

time [hr]

TS=2500C TS=2750C BTS=2500C, 0.3MV/cm BTS=2750C, 0.3MV/cm BTS=3000C, 0.3MV/cm

-0.5729.38B300°C ,0.3MV/cm3

-0.3233.50B

-0.2519.15A275°C ,0.3MV/cm2

-0.2026.00B

-0.1520.50A250°C ,0.3MV/cm1

∆VFB(V))hr(Stress timetypeBTS

* * AA--flatflat--band shift after 20 hours.band shift after 20 hours.

* B* B--critical change in the Ccritical change in the C--V curve after 26V curve after 26--33 hours33 hours..

54








55

CC--V, CV, C--t & It & I--t t of ref. #1: of ref. #1: CoWP/Cu/Co/Ti/SiOCoWP/Cu/Co/Ti/SiO22

2.2hrBTS4

22.5BTS3

9.5BTS2

4.5BTS1

Accumulate Time(min)Stress No.


-45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 150

50

100

150

200

250

300

350

400

a

C(pF)

V(v)


-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.00

50

100

150

200

250

300

350

400

b

C(pF)

V(v)


0 20 40 60 80 100 120 140

50

100

150

200

250

300

a

C(pF)

t(sec)


c0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8Zerbst Plot

(Cf/C -1)[-]

-d(C

o/C

)2 /dt,

[1/s

ec]

t=143.8209 1e-6 sec

Vs=0.47689 cm/sec

b d

PreAnn.τg

'=143 µsS'=0.48 cm/s

e

56

CC--V & IV & I--t t of test cap.:of test cap.: CoWP/Cu/CoWP/Co/Ti/SiOCoWP/Cu/CoWP/Co/Ti/SiO22


-10 -8 -6 -4 -2 0 2 4

0

50

100

150

200

250

300

350

400

C(pF)

V(v)

PreAnn. BTS

*BTS - accumulate stress time of 27.5hr

57

CC--V V of ref. #2:of ref. #2: CoWP/Cu/SiOCoWP/Cu/SiO22

BTS437.66

BTS322.33

BTS29

BTS14.5

Stress No.Accumulate Time(min)


-2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.050

100

150

200

250

300

350

400

C(pF)

V(v)


-10 -8 -6 -4 -2 0 2 450

100

150

200

250

300

350

400

C(pF)

V(v)


5.31·108

2.51·107

Cu+[ions/cm2·sec]

1.2·10121.2MV/cm

7.24·10110.3MV/cm

Cu+[ions/cm2]E

0.05.0k 10.0k15 .0k20.0k 25.0k30.0-6-5-4-3-2-1V FB [V]∆ time( sec) [ ] overall2 tSlopeAqcmCu ∆⋅⋅⋅−=⎥⎦⎢⎣ dtSlope=

∆∆VVFB FB vs. timevs. time of ref. #2 under low and high electric fieldof ref. #2 under low and high electric field

58

Temperature effect under Temperature effect under highhigh electric fieldelectric fieldin ref. #1in ref. #1

9.16min10-2A16.5min-8.32300°C 1MV/cm

3

31.28min10-2A40min-9.29275°C 1MV/cm

2

3.99hr10-2A4.05hr-12.61250°C 1MV/cm

1

Arrival time to the current threshold

Current threshold

Arrival time to a significant

shift

∆VFB

From I-tFrom C-VBTS

02468

10121416182022

300275250

|∆VFB| [V]

T(C0)

0 1 2 3 4

-10-9-8-7-6-5-4-3-2-101

time [hr]

∆VFB [V]

BTS=2500C, 1MV/cm BTS=2750C, 1MV/cm BTS=3000C, 1MV/cm

59

Electric field effect on the Electric field effect on the flatbandflatband shift in ref. #1 and shift in ref. #1 and #2#2

0 5 10 15 20 25 30 35

-10-9-8-7-6-5-4-3-2-101

VFB [V]∆

time(hr)

Cu/SiO2=0.3MV/cm,2500C

Cu/Co/Ti/SiO2=0.3MV/cm,2500C

Cu/SiO2=1.2MV/cm,2500C

Cu/Co/Ti/SiO2=1.2MV/cm,2500C

Cu/Co/Ti/SiO2=1MV/cm,2500C

High

LowCu/SiO2

High

Low

Electric field

strength

Cu/Co/Ti/SiO2

Advance stress time

Initial stress time

type

Gradual increase in ∆VFB

Exponential increase in ∆VFB

••Under low electric field the flat band Under low electric field the flat band shift is gradualshift is gradual

••The CO/Ti seed layer serves as a barrier The CO/Ti seed layer serves as a barrier layer against Cu at low electric fieldslayer against Cu at low electric fields

60

Our observations concerning to the electric field and Our observations concerning to the electric field and temperaturetemperature

Capacitors without a barrier layer (ref. #2):lllLinear increase in the flat band shift under low and high IIIelectric fields.

Capacitors with a seed layer (ref. #1):lllLinear increase in the flat-band shift only under low IIIelectric fields. A sudden increase in progress steps of IIIthe BTS under high electric fields.

Capacitors with the full stack (test cap.) or capacitors IIIthat were subjected to TS only:lllMinor shifts.

The temperature effect becomes significant in a lower IIIvalue at BTS under high electric field, comparing to IIIBTS under low electric field.

61








62

BTS under different kind of fields and temperaturesBTS under different kind of fields and temperatures

kTQ

GGf e

Vd

Vdt

0

22

µ=

µ=

1.7x10-31.8x10-31.8x10-31.8x10-31.9x10-31.9x10-32.0x10-3102

103

104

105

106

T [0C]

tƒ [sec]

1/T [k-1]

E=0.3MV/cm E=0.6MV/cm E=1.0MV/cm E=1.2MV/cm

2500C2750C3000C

63

The activation energy vs. electric field The activation energy vs. electric field comparing to the literaturecomparing to the literature

0.0 0.5 1.0 1.50.60.70.80.91.01.11.21.31.41.51.61.71.81.9

3.0 3.5 4.0 4.5 5.00.6

0.9

1.2

1.5

1.8

Raghavan [16]

E [MV/cm]

Q [eV]

Miyazaki [53]

Shacham-Diamand [14]

McBrayer [15]

E [MV/cm]

Q [eV]

[14] Y. Shacham-Diamand, A. Dedhia, D. Hoffsetter and W. G. Oldham, J. Electrochem. Soc., Vol. 140, No. 8 (1993) 2427-2432.[15] J. D. McBrayer, R. M. Swanson, and T. W. Sigmon, J. Electrochem. Soc., Vol. 133, No. 6 (1986) 1242-1246.[16] G. Raghavan, C. Chiang, P. B. Anders, S. Tzeng, R. Villasol, G. Bai, M. Bohr, D. B. Fraser, Thin Solid Films, Vol. 262 (1995), 168-176.[53] H. Miyazaki, H. Kojima, A. Hiraiwa, K. Murakami and Y. Homma, J. Electrochem. Soc., Vol. 139, No. 11 (1992) 3264-3267.

64

The effective time to failure vs. fieldThe effective time to failure vs. field

D

xtdiff 2

2.

4α≈

Extdrift µ

≈

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

4E+5

2E+5

6E+3

2E+3

8E+3

3E+3

1E+3

4E+2

1E+2

5E+1

2E+1

1E+1

0.18MV/cm, 4hr

E [MV/cm]

tf [sec]

tf(2750C)

tf-Diff.(2750C)

tf-Drift(2750C)

3.03e-3 [1/eV]0.5

EQf eddEt

0µ=

µ=

The slope:

driftdifff ttt111

.+∝

65






III. Calculating the effective diffusion coefficient


66

Calculating the effective diffusion coefficient of Calculating the effective diffusion coefficient of Cu in the oxideCu in the oxide

22

,

/

/),,(

⎟⎟⎟⎟⎟

⎠

⎞

⎜⎜⎜⎜⎜

⎝

⎛+α+α−

=

qkTtE

xqkT

E

ETxD BTSeff

t-time,

x-distance,

µ−mobility,

Deff,BTS-effective diffusion coefficient,

k-Boltzman constant,

T-temperature in Kelvin,

q-electron charge

67

The effective diffusion The effective diffusion coefficientcoefficient

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.41E-17

3E-17

9E-17

2E-16

6E-16

2E-15

5E-15

1E-14

3E-14

BTS

TS

E [MV/cm]

Deff [cm2/sec] 2500C (BTS) 2750C (BTS) 3000C (BTS) 2500C (TS) 2750C (TS) 3000C (TS) 3000C (Ref.14)

68

Diffusion under electric fieldDiffusion under electric field

Experimental result: Experimental result:

-- Cu diffusivity in oxide depends on the electric field at high eCu diffusivity in oxide depends on the electric field at high electric fieldslectric fields

Problem:Problem:

-- How to take into consideration the electric field effect ?How to take into consideration the electric field effect ?

Model:Model:

-- Assume that the electric field modifies the energy barrier for Assume that the electric field modifies the energy barrier for emission of emission of the Cu ions that are trapped in the oxide.the Cu ions that are trapped in the oxide.

EE

69

What affects the diffusivity at high fields ?What affects the diffusivity at high fields ?

D, Diffusivity = D, Diffusivity = λλ22 νν00 Exp[Exp[--qEqEaa/kT/kT]]

νν0 0 = lattice vibration frequency= lattice vibration frequency

EEaa = Activation energy for de= Activation energy for de--trappingtrapping

λλ= jump distance ( between trapping sites)= jump distance ( between trapping sites)

•• Ea is a function of the electric fieldEa is a function of the electric field

•• It is a local effect, hence it affects diffusivity directlyIt is a local effect, hence it affects diffusivity directly

Diffusivity definition in a 3D random Diffusivity definition in a 3D random walk model between trapswalk model between traps

70

Modifying PooleModifying Poole--FrenkelFrenkel emissionemission

φ∆φ∆−φ−== kT

qkTq

eDAeTEDB

0)(

),(

20 SiO

qEεπε

=φ∆

4.02e-3From the Deff vs.

4.50e-3From Poole- Frenkel

The slope [1/eV]0.5

20 SiO

qkTqslope

επε=

( D-diffusion coefficient, A-constant, φB-barrier height, ∆φ-barrier lowering, D0-diffusion constant, T-temperature in Kelvin, E-electric field,

k-boltzman constant, q-electron charge, ε0−permittivity in vacuum, εSiO2-dielectric constant )

E

71







IV. Proposing a model for Cu+ transport in the oxide.

72

CuCu++ transport in the oxide under BTStransport in the oxide under BTS

300

265

220

165

17.5

D/D0 eB/BE [MV/cm], T=300°C

5471.2

2871

1420.8

650.6

16.10.3

(r-the distance between the sites, E-electric field, θ-the angle projection on x, ∆φ-barrier lowering, ν0- jumping frequency, f-statistic function, εsIo2−permettivity dielectric constant, k-boltzman constant, T-temperature in Kelvin, q-electron charge)

•The barrier to Cu+ movement is anisotropic

•Assuming Poole-Frenkel model modification

Our assumptionsOur assumptions::

SiOSiO22

CopperCopper

SiSi

Bfor>>)1(00)(IeDED==

The

average

effective

Di

ν∝θefdI)(000I=

The

potenti

al:

πε=4)(xVSiO

The

power:

⎢⎢⎣=kTB

73

The effective time to failureThe effective time to failure

D

xtdiff 2

2.

4α≈

Extdrift µ

β≈

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

4E+5

2E+5

6E+3

2E+3

8E+3

3E+3

1E+3

4E+2

1E+2

5E+1

2E+1

1E+1

0.18MV/cm, 4hr

E [MV/cm]

tf [sec]

tf(2750C)

tf-Diff.(2750C)

tf-Drift(2750C)

••The time to failure, depending on the componentsThe time to failure, depending on the components’’ diffusiondiffusion::

••The time to failure, as depending on the componentsThe time to failure, as depending on the components’’ driftdrift::

1ft≈

diftt11∝

ft1≈

ffoorr

tdiff.<<

tdrift tthh

ffoorr

tdiff.>>

tdrift tthh

••TThhee

ttiimmee

ttoo

ffaaiilluurree

iinn

tthh

3.03e-3 [1/eV]0.5

EQf eddEt

0µ=

µ=

The slope:

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛−+++≈ 1

41

21111 .

.. drift

diff

diffdriftdifff tt

tttt driftdifff ttt111

.+∝⇒

74

DISCUSSIONDISCUSSIONThe capacitance techniquescapacitance techniques are more sensitive to the penetration of Cu into the oxide than current measurements.

The transient capacitance measurementhave been proven to be the most sensitive in identifying the penetration of Cu onto the Si substrate.

The I-t measurement let us know the exact time to failure and control the stress in-situ.


75

SummarySummaryThe major effects that indicate a coming failure are:

C-V curve:The curve distortion and a noticeable shift of the flat-band voltage.Hysteresis effectsAn increase In the inversion capacitance and a decrease in the accumulation capacitanceApart of the capacitors looses his ability to form an inversion layer so a deep depletion layer appears

C-t curve:Minority’s lifetime decreased sharply

I-V, I-t curves:The leakage currents become stronger, exceeding to values greater than 10-6A


76

ConclusionsConclusionsThe effectiveness of CoWP as a Barrier Layer against Cu transport was demonstrated.

In BTS under low electric field the temperature assists the Cu transport, while during BTS under high electric field the magnitude of the phenomenon determines mainly by the electric field.

The Deff of Cu under BTS was calculated and correlated under various conditions.

Cu+ transport though the oxide under BTS in a modification of the Poole-Frenkel mechanism.


electric field and temperature effects on copper transport in mos capacitor … · 2006-03-13 ·...

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