1 Material Dependence of NBTI Stress & Recovery in SiON p-MOSFETs S. Mahapatra, V. D. Maheta, S. Deora, E. N. Kumar, S. Purawat, C. Olsen 1, K. Ahmed 1, A. E. Islam 2, M. A. Alam 2 Department of Electrical Engineering, IIT Bombay, Mumbai, India 1 Applied Materials, Santa Clara, CA, USA 2 School of Electrical Engineering & Computer Science, Purdue University, W. Lafayette, IN, USA

2 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 Conclusion Recovery – material dependence

3 What is NBTI? Issue: p-MOSFET in inversion V G < (V S, V D, V B ) Parametric shift Aggravated for SiON films What is the N dependence? V DD V G =0 Aggravated with –E OX and T E OX1, T 1 V T time E OX1, T 2 E OX2, T 2

4 Motivation Proper stress, measurement V T time Stress Extrapolation to operating condition Operation Extrapolation to end of life Lifetime Check if passed Specification Need to know physical mechanism for reliable extrapolation to obtain lifetime

5 NBTI measurement challenge Conventional approach – stress / measure / stress Recovery of degradation as soon as stress is stopped Recovery depends on stress to measure voltage difference, time Stress Measurement -V G (M) -V G (S)

6 Impact of Measurement Delay Time Stress-Measure-Stress (SMS) Stress Measurement -V G (M) -V G (S) M-time Lower magnitude, higher slope for higher measurement delay

7 Impact of Measurement Bias Stress Measurement -V G (M) -V G (S) M-time Higher recovery & higher slope for lower (absolute) measurement bias DC On-the-fly: Rangan, IEDM 2003 Stress-Measure-Stress (SMS)

8 On-The-Fly I DLIN (Conventional Scheme) SMU PGU Start I D sampling SMU triggers PGU PGU provides stress pulse at gate Continue I D sampling without interrupting stress Uncertainty in I DMAX measurement: t 0 ~ 1ms I DLIN time Rangan, IEDM 2003 V T = - I D /I DMAX * V GT0

9 On-The-Fly I DLIN (Fast Scheme) Start I D sampling SMU triggers PGU PGU provides stress pulse at gate Continue I D sampling without interrupting stress Uncertainty in I DMAX measurement: t 0 ~ 1 s I DLIN time SMU PGU IVC DSO V T = - I D /I DMAX * V GT0

10 Captured I DLIN Transients Peak I DLIN (I DLIN0 ) captured within 1 s of stress (V G =V GSTRESS ) Gate pulse transition time adjusted to avoid I DLIN overshoot RTNO shows rapid and larger I DLIN degradation w.r.t PNO

11 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 Conclusion Recovery – material dependence

12 Impact of Time-Zero Delay RTNO shows very large initial and overall degradation and much larger impact of t 0 delay compared to PNO Reduction in measured degradation magnitude for higher t 0 delay

13 Time Exponent (Long-time): Impact of t 0 Delay Power law time dependence at long stress time Lower time exponent (n) for RTNO compared to PNO Reduction in n with reduction in t 0 delay, saturation for t 0 <10 s

14 Time Exponent: Impact of Oxide Field and Temperature E OX independence of n: No bulk trap generation T independence on n: Arrhenius T activation PNO shows higher n compared to RTNO

15 NBTI Transient: PNO / RTNO / RTNO + PN N density at Si/SiON interface controls degradation transients Higher Si/SiON N density Higher (short time & overall) NBTI SiON RTNO PNO RTNO+PN Poly-Si Si-substrate N Shallenberger JVST 99; Rauf, JAP 05

16 Time Exponent: PNO / RTNO / RTNO + PN D#N DOSE (x10 15 cm - 2 ) N%EOT(Å) A B C Lower n (independent of E OX, T) for larger Si/SiON N density

17 Impact of Post Nitridation Anneal (PNO) PNO without proper PNA: Higher degradation & lower n (like RTNO) D#N DOSE (x10 15 cm -2 )N%EOT(Å) A (Correct PNA) B (Worst PNA) C (Moderate PNA)1620.2

18 Time exponent: Impact of PNO dose Reduction in n with increase in N% D#N DOSE (x10 15 cm -2 )N%EOT(Å) A B C T independence of n for all N% E OX independence of n for all N%

19 Time exponent: Process dependence PNO (proper PNA) trend line Long-time power law time exponent depends on SiON process (PNO, PNA, RTNO) & N%

20 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 Conclusion Recovery – material dependence

21 Temperature Activation RTNO shows higher degradation and lower E A compared to PNO T activation governs by SiON process; shows similar (as time exponent, n) dependence on N% PNO (proper PNA) trend line

22 Field Dependence: PNO / RTNO / RTNO + PN PNO: Increased degradation & lower field dependent slope for higher N% D#N DOSE (x10 15 cm -2 )N%EOT(Å) A B C D E RTNO, RTNO+PN: Very high degradation and low slope Si/SiON interface density governs overall degradation magnitude & oxide field-dependent slope SiON RTNO PNO RTNO+PN Poly-Si Si-substrate N

23 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

24 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 Si/SiON N density: NBTI magnitude: Time exponent: T activation: E OX acceleration: Low (PNO, proper PNA, lower N, less than 30% at.) Lower High s delay) High (~ eV) High (~0.6 cm/MV) Increase Reduce

25 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 Conclusion Recovery – material dependence

26 Very Long Time Degradation Universally observed very long time power law exponent of n = 1/6 TSMC, IRPS 05 Haggag, Freescale, IRPS 07 Stress time ~ 28Hr TI, IEDM 06

27 Interface Traps: Reaction Diffusion Model Poly Si H H Reaction: Si-H bond breaks into Si + and H Si H Diffusion: Released H diffuse away and leave Si + Si H Jeppson, JAP 1977; Alam, IEDM 2003 SpeciesSlope H O 1/4 H 2 1/6 H + 1/2 Power-law dependence, exponent depends on H Chakravarthi, IRPS 2004; Alam, IRPS (T) 2005 Long time experimental data suggests H 2 diffusion

28 NBTI physical mechanism Tunneling of inversion holes to Si-H Generation of N IT Si H p n-Si SiO N p + -poly Tunneling barrier Tunneling of inversion holes to N related traps Trapping of N h Hole trapping when added to interface traps reduces n & E A of overall NBTI Identical E OX (governs both inversion holes and tunneling) dependence for N IT and N h

29 NBTI Physical Mechanism (Stress) Low Si/SiON N density N IT dominated process, low N h V T (log- scale) stress time (log-scale) Strong T activation Higher Si/SiON N density Significant additional N h component (fast, saturates, weak T dependence) High short-time and overall degradation Low T activation at longer stress time -V G

30 Isolation of Interface Trap Generation and Hole Trapping Total degradation sum of N IT and N h contribution Assumption 1: Fast (t<1s) saturation of N h contribution Assumption 2: Power law n=1/6 dependence for N IT contribution at longer stress time Slides 54 – 56: Mahapatra, TED 2009 (Feb)

31 Field and Temperature Dependence Identical E OX dependence – same barrier controls N IT, N h and hence total degradation Low T activation of N h, when added to higher T activation of N IT lowers T activation of overall degradation

32 Hole trapping – Impact of N% (PNO) Increase in hole trapping with increase in N% causes reduction in n & E A at higher N% Identical T activation of hole trapping over a wide N% range suggests correctness of isolation method

33 T Activation of N IT : Universal Scaling Scheme R-D model solution: V T = (k F.N 0 /k R ) 2/3 (Dt) 1/6 E A (k F ) ~ E A (k R ), V T (T,t) ~ [D(T)t] n E A ~ E D * n X-axis scaling provides E D Identical n at all T Y-axis scaling provides E A

34 Universal T Activation of Diffusion X-axis scaling P1: 1.2nm (14%), P2: 1.2nm (21%) P3: 1.7nm (28%), P4: 2.2nm (29%) Identical E A for PNO & Control Identical E A for Idlin & C-P measurements E D consistent with power law slope (n) from R-D model E A suggest neutral molecular H 2 diffusion* *Reed, JAP 1988

35 T Activation of N IT : Impact of N% (PNO) Validation of E A ~ E D * n for a wide N% range suggests the robustness of isolation method

36 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 Conclusion Recovery – material dependence

37 Recovery Transients (UF-OTF I DLIN ) 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

38 Recovery Analysis Recovery: Hole detrapping (electron capture in bulk traps) Interface trap passivation Stress: Interface trap generation and hole trapping in pre-existing bulk traps Si H p Trap n-Si SiON p + -poly Tunneling barrier (T.B.) Neutralization of interface trap charge by electron capture; valid for recovery at low V G (~ V T ) only [Reisinger, IRPS 2006; Grasser, IRPS 2008] Gate n-Si At stress V G Isolation of components important to model recovery Gate n-Si At recovery V G

39 Recovery Analysis (contd..) Stress Fast hole trapping and gradual interface trap buildup V T (log- scale) stress time (log-scale) Stress recovery time (log-scale) V T (linear- scale) Recovery Recovery Fast hole detrapping and gradual (lock-in) interface trap passivation NhNh N IT Overall recovery spans several orders of time scale

40 Recap: Hole Trap Fraction from Stress Based on N IT & N h isolation scheme Hole trap fraction: Increases with N% Reduces with stress time (N h saturation at short stress time) Reduces with stress T (lower T activation for N h ) Slides 65 – 67: Deora, unpublished

41 Recovery Contribution by Trapped Holes Assumption: Early recovery phase due to hole detrapping Hole detrapping time: Independent of stress time Independent of stress T Find N h fraction (from stress) Find corresponding recovery (hole detrapping) time

42 Recovery: T Dependence Early phase due to hole detrapping weak T dependence Later part due to N IT passivation T activated MSM Larger delay time, T dependent recovery T dependence of n; Not seen for OTF

43 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 Conclusion Recovery – material dependence

44 Summary 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, E OX acceleration Significant contribution from N h (in addition to N IT ) for devices having high Si/SiON N density N IT and N h contributions can be separated consistently N h detrapping and N IT passivation determines early and long-time recovery respectively NBTI recovery impacts measurement lower captured magnitude, higher n & E A uncertain parameters