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

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: souvik@ee.iitb.ac.in

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

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%

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

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

Species Slope HO 1/4 H2 1/6 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

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

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

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