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Material Dependence of NBTI Stress & Recovery in SiON p-MOSFETs

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Material Dependence of NBTI Stress & Recovery in SiON p-MOSFETs

S. Mahapatra, V. D. Maheta, S. Deora, E. N. Kumar, S. Purawat, C. Olsen1, K. Ahmed1, A. E. Islam2, M. A. Alam2

Department of Electrical Engineering, IIT Bombay, Mumbai, India

1Applied Materials, Santa Clara, CA, USA

2School of Electrical Engineering & Computer Science, Purdue University, W. Lafayette, IN, USA

Email: [email protected]

Outline

Introduction, measurement delay (recovery) issues, fast measurements

Material dependence: Time evolution, time exponent

Material dependence: Field & temperature acceleration

Physical mechanism, isolation of different components

Recovery – material dependence

Conclusion

VDD

VG=0

EOX2, T2

EOX1, T2

VDD

DVT

EOX1, T1

time

What is NBTI?

Issue: p-MOSFET in inversion

VG < (VS, VD, VB)

Parametric shift

Aggravated with –EOX and T

Aggravated for SiON films

What is the N dependence?

Motivation

Proper stress, measurement

Specification

Extrapolation to operating condition

Stress

DVT

Extrapolation to end of life

Lifetime

Operation

Check if passed

time

Need to know physical mechanism for reliable extrapolation to obtain lifetime

NBTI measurement challenge

Stress

-VG (S)

Conventional approach – stress / measure / stress

-VG (M)

Measurement

Recovery of degradation as soon as stress is stopped

Recovery depends on stress to measure voltage difference, time

Stress

-VG (S)

-VG (M)

Measurement

M-time

Lower magnitude, higher slope for higher measurement delay

Impact of Measurement Delay Time

Stress-Measure-Stress (SMS)

Stress

-VG (S)

-VG (M)

Measurement

M-time

Higher recovery & higher slope for lower (absolute) measurement bias

Impact of Measurement Bias

Stress-Measure-Stress (SMS)

DC On-the-fly: Rangan, IEDM 2003

SMU

PGU

On-The-Fly IDLIN (Conventional Scheme)

Start ID sampling

SMU triggers PGU

PGU provides stress pulse at gate

Continue ID sampling without interrupting stress

IDLIN

Uncertainty in IDMAX measurement: t0 ~ 1ms

time

DVT = -DID/IDMAX * VGT0

Rangan, IEDM 2003

IVC

DSO

SMU

PGU

On-The-Fly IDLIN (Fast Scheme)

Start ID sampling

SMU triggers PGU

PGU provides stress pulse at gate

Continue ID sampling without interrupting stress

IDLIN

DVT = -DID/IDMAX * VGT0

Uncertainty in IDMAX measurement: t0 ~ 1ms

time

Captured IDLIN Transients

Peak IDLIN (IDLIN0) captured within 1ms of stress (VG=VGSTRESS)

Gate pulse transition time adjusted to avoid IDLIN overshoot

RTNO shows rapid and larger IDLIN degradation w.r.t PNO

Outline

Introduction, measurement delay (recovery) issues, fast measurements

Material dependence: Time evolution, time exponent

Material dependence: Field & temperature acceleration

Physical mechanism, isolation of different components

Recovery – material dependence

Conclusion

Impact of Time-Zero Delay

Reduction in measured degradation magnitude for higher t0 delay

RTNO shows very large initial and overall degradation and much larger impact of t0 delaycompared to PNO

Time Exponent (Long-time): Impact of t0 Delay

Power law time dependence at long stress time

Lower time exponent (n) for RTNO compared to PNO

Reduction in n with reduction in t0 delay, saturation for t0<10ms

Time Exponent: Impact of Oxide Field and Temperature

EOX independence of n: No bulk trap generation

T independence on n: Arrhenius T activation

PNO shows higher n compared to RTNO

SiON

Poly-Si

Si-substrate

RTNO+PN

N

RTNO

PNO

Shallenberger JVST 99; Rauf, JAP 05

NBTI Transient: PNO / RTNO / RTNO + PN

N density at Si/SiON interface controls degradation transients

Higher Si/SiONN density Higher (short time & overall) NBTI

Time Exponent: PNO / RTNO / RTNO + PN

Lower n (independent of EOX, T) for larger Si/SiON N density

Impact of Post Nitridation Anneal (PNO)

PNO without proper PNA: Higher degradation & lower n (like RTNO)

Time exponent: Impact of PNO dose

Reduction in n with increase in N%

EOX independence of n for all N%

T independence of n for all N%

Time exponent: Process dependence

PNO (proper PNA) trend line

Long-time power law time exponent depends on SiON process (PNO, PNA, RTNO) & N%

Outline

Introduction, measurement delay (recovery) issues, fast measurements

Material dependence: Time evolution, time exponent

Material dependence: Field & temperature acceleration

Physical mechanism, isolation of different components

Recovery – material dependence

Conclusion

Temperature Activation

PNO (proper PNA) trend line

RTNO shows higher degradation and lower EA compared to PNO

T activation governs by SiON process; shows similar (as time exponent, n) dependence on N%

SiON

Poly-Si

Si-substrate

RTNO+PN

N

RTNO

PNO

Field Dependence: PNO / RTNO / RTNO + PN

PNO: Increased degradation & lower field dependent slope for higher N%

RTNO, RTNO+PN: Very high degradation and low slope

Si/SiON interface density governs overall degradation magnitude & oxide field-dependent slope

Field Acceleration Factor: Process Dependence

PNO (proper PNA) trend line

Field acceleration governs by SiON process; more importantly by N density at Si/SiON interface

Summary: Material Dependence

Si/SiON interfacial N density plays important role

High Si/SiON N density for RTNO process, PNO without proper PNA, or PNO with very high (>30%) N density

Low (PNO, proper PNA, lower N, less than 30% at.)

Lower

High (~0.12 @1ms delay)

High (~0.08-0.09 eV)

High (~0.6 cm/MV)

Si/SiON N density:

NBTI magnitude:

Time exponent:

T activation:

EOX acceleration:

Increase

Increase

Reduce

Reduce

Reduce

Outline

Introduction, measurement delay (recovery) issues, fast measurements

Material dependence: Time evolution, time exponent

Material dependence: Field & temperature acceleration

Physical mechanism, isolation of different components

Recovery – material dependence

Conclusion

Haggag, Freescale,

IRPS ‘07

TSMC, IRPS ‘05

Stress time ~ 28Hr

TI, IEDM ‘06

Very Long Time Degradation

Universally observed very long time power law exponent of n = 1/6

SpeciesSlope

HO1/4

H21/6

H+1/2

Interface Traps:Reaction Diffusion Model

Poly

Reaction: Si-H bond breaks into Si+ and H

Diffusion: Released H diffuse away and leave Si+

H

H

H

H

Power-law dependence, exponent depends on H

Si

Si

Si

Si

Long time experimental data suggests H2 diffusion

Jeppson, JAP 1977; Alam, IEDM 2003

Chakravarthi, IRPS 2004; Alam, IRPS (T) 2005

Tunneling barrier

NBTI physical mechanism

Tunneling of inversion holes to Si-H Generation of NIT

p+-poly

n-Si

SiON

Si

H

p

Tunneling of inversion holes to N related traps Trapping of Nh

Hole trapping when added to interface traps reduces n & EA of overall NBTI

Identical EOX (governs both inversion holes and tunneling) dependence for NIT and Nh

-VG

-VG

NBTI Physical Mechanism (Stress)

Low Si/SiON N density NIT dominated process, low Nh

DVT (log-scale)

Strong T activation

Higher Si/SiON N density Significant additional Nh component (fast, saturates, weak T dependence)

stress time (log-scale)

High short-time and overall degradation

Low T activation at longer stress time

Isolation of Interface Trap Generation and Hole Trapping

Total degradation sum of NIT and Nh contribution

Assumption 1: Fast (t<1s) saturation of Nh contribution

Assumption 2: Power law n=1/6 dependence for NIT contribution at longer stress time

Slides 54 – 56: Mahapatra, TED 2009 (Feb)

Field and Temperature Dependence

Identical EOX dependence – same barrier controls NIT, Nh and hence total degradation

Low T activation of Nh, when added to higher T activation of NIT lowers T activation of overall degradation

Hole trapping – Impact of N% (PNO)

Increase in hole trapping with increase in N% causes reduction in n & EA at higher N%

Identical T activation of hole trapping over a wide N% range suggests correctness of isolation method

T Activation of NIT:Universal Scaling Scheme

Identical n at all T

Y-axis scaling provides EA

R-D model solution:DVT = (kF.N0/kR)2/3 (Dt)1/6

EA(kF) ~ EA(kR), DVT(T,t) ~ [D(T)t]n

X-axis scaling provides ED

EA ~ ED * n

EA suggest neutral molecular H2 diffusion*

*Reed, JAP 1988

Universal T Activation of Diffusion

X-axis scaling

Identical EA for PNO & Control

Identical EA for Idlin & C-P measurements

ED consistent with power law slope (n) from R-D model

P1: 1.2nm (14%), P2: 1.2nm (21%) P3: 1.7nm (28%), P4: 2.2nm (29%)

T Activation of NIT: Impact of N% (PNO)

Validation of EA ~ ED * n for a wide N% range suggests the robustness of isolation method

Outline

Introduction, measurement delay (recovery) issues, fast measurements

Material dependence: Time evolution, time exponent

Material dependence: Field & temperature acceleration

Physical mechanism, isolation of different components

Recovery – material dependence

Conclusion

Recovery Transients (UF-OTF IDLIN)

Low N% (low hole trapping) – delayed start of recovery

High N% (high hole trapping) – fast start of recovery

Difference in recovery shape certainly not ~log(t)

Kapila, IEDM 2008

Gate

n-Si

At recovery VG

Recovery Analysis

Stress: Interface trap generation and hole trapping in pre-existing bulk traps

n-Si

p+-poly

SiON

H

Si

p

Recovery:

Hole detrapping (electron capture in bulk traps)

Interface trap passivation

Trap

Trap

Tunneling barrier (T.B.)

Gate

Neutralization of interface trap charge by electron capture; valid for recovery at low VG (~ VT) only [Reisinger, IRPS 2006; Grasser, IRPS 2008]

n-Si

Isolation of components important to model recovery

At stress VG

Stress

DVT (log-scale)

stress time (log-scale)

Recovery Analysis (contd..)

Recovery

DVT (linear-scale)

NIT

Nh

recovery time (log-scale)

Stress Fast hole trapping and gradual interface trap buildup

Recovery Fast hole detrapping and gradual (lock-in) interface trap passivation

Overall recovery spans several orders of time scale

Recap: Hole Trap Fraction from Stress

Based on NIT & Nh isolation scheme

Hole trap fraction:

Increases with N%

Reduces with stress time (Nh saturation at short stress time)

Reduces with stress T (lower T activation for Nh)

Slides 65 – 67: Deora, unpublished

Recovery Contribution by Trapped Holes

Assumption: Early recovery phase due to hole detrapping

Find Nh fraction (from stress)

Find corresponding recovery (hole detrapping) time

Hole detrapping time:

Independent of stress time

Independent of stress T

Recovery: T Dependence

Early phase due to hole detrapping weak T dependence

Later part due to NIT passivation T activated

MSM Larger delay time, T dependent recovery T dependence of n; Not seen for OTF

Outline

Introduction, measurement delay (recovery) issues, fast measurements

Material dependence: Time evolution, time exponent

Material dependence: Field & temperature acceleration

Physical mechanism, isolation of different components

Recovery – material dependence

Conclusion

Summary

NBTI recovery impacts measurement lower captured magnitude, higher “n” & EA uncertain parameters

N density at Si/SiON interface plays important role PNO better than RTNO, proper PNA important for PNO

Higher N at Si/SiON higher degradation magnitude, lower time exponent, T activation, EOX acceleration

Significant contribution from Nh (in addition to NIT) for devices having high Si/SiON N density

NIT and Nh contributions can be separated consistently

Nh detrapping and NIT passivation determines early and long-time recovery respectively