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Reliability Degradation Characteristics of Ultra-thin Gate Dielectrics for Nano-CMOS Application. J.F. Kang. Institute of Microelectronics Peking University Beijing 100871, China. Acknowledgment:. N. Sa, B.G. Yan, H. Yang, J.F. Yang , Z.L. Xia (IME, PKU)

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slide1

Reliability Degradation Characteristics of

Ultra-thin Gate Dielectrics

for Nano-CMOS Application

J.F. Kang

Institute of Microelectronics Peking University Beijing 100871, China

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide2

Acknowledgment:

N. Sa, B.G. Yan, H. Yang, J.F. Yang, Z.L. Xia(IME, PKU)

X.Y. Liu, R.Q. Han, Y.Y. Wang (IME, PKU)

D.-L. Kwong (ECE, UT Austin)

H.Y. Yu (IMEC)

C. Ren, M-F. Li, D.S.H. Chan (SNDL, NUS)

C. C. Liao, Z. H. Gan, M. Liao, J. P. Wang, and W. Wong (SMIC)

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide3

Outline

  • Introduction
  • Reliability characteristics of ultra thin gate dielectrics
    • HfO2 gate stack
      • High temperature annealing effect
      • TDDB, PBTI, and NBTI
    • SiON in pMOS
      • Dynamic NBTI
      • S/D bias effect on NBTI
  • Summary

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide4
Introduction
  • Leading-edge production technology of CMOS has scaled down to sub 90nm nodes.
  • SiON gate dielectrics are used in 90nm and 65nm nodes technology.
  • High-K/metal gate stacks will be required in sub 45nm nodes technology.

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide5
Introduction (SiON)
  • NBTI in p-MOS is a critical reliability issue for CMOS with SiON gate dielectric
    • NBTI is in general attributed to reaction-diffusion (R-D) model involving interfacial bond breaking followed by a diffusion process of hydrogen species (S. Mahapatra et al, IEDM2004, p.105)

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide6

R-D model (S. Mahapatra et al, IEDM2004, p.105; S. Ogawa and N. Shiono, PRB 51, 4218, 1995)

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide7
Introduction (SiON)
  • Mechanisms of NBTI under various operation modes is not clear
    • Release of hydrogen from Si-H bonds followed by the lateral motion of protons along the interface (X.J. Zhou et al, APL 84, p.4394, 2004)
    • Re-passivation effect of interface trap during the post stress phase (T. Yang et al, EDL 26, p.758, 2005)
    • Hot carrier effect on NBTI (D. Saha et al, EDL 27, p.188, 2006)
    • Hole energy effect on NBTI due to broken Si-H and Si-O bonds (D. Varghese et al, EDL 26, p.527, 2005)
    • ……

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide8
Introduction (SiON)
  • The characteristics of NBTI under various operation modes need to be identified
    • Dynamic NBTI has been demonstrated the significant difference with static NBTI (G. Chen et al, IRPS 2003, p.196; M. Ershov et al, APL 83, p.1647, 2003)
    • There is few report on NBTI characteristics in S/D bias mode (N.K. Jha et al, IPRS 2005, p.524)
    • We will address the S/D bias effect on NBTI

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide9
Introduction (HfO2 gate stack)
  • Severe reliability problems exist in high K/metal gate stacks due to high pre-existing charge trapping in the stacks (A. Shanware et al, IRPS 2003; C. Shen et al, IEDM 2004)
  • High temperature RTA ( >900oC) is effective to reduce the preexisting charge trapping in high K gate stack(G.D. Wilk,VLSI 2002)
  • However, high temperature RTA usually causes significant EOT increase(C.S. Kang, VLSI 2002 )

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide10
Introduction (HfO2 gate stack)
  • We have demonstrated the HfN/HfO2 gate stack is robust thermally stable (H. Yu et al, IEDM’03)
    • EOT increase is negligible after a high temperature annealing on the stack (PGA)
  • We could expect the excellent reliability and sub-1 nm EOT to be achieved simultaneously

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide11
In this talk, I will address :
    • HfO2 gate stack
      • High temperature annealing effect on EOT and reliability
      • Intrinsic characteristics of TDDB, PBTI, and NBTI in HfN/HfO2 gate stack fabricated by high temperature process
    • SiON
      • DNBT characteristics and nitrogen effect
      • S/D bias effect on NBTI

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide12

Experiments (HfO2 gate stack)

  • High K gate stack devices were fabricated by using a high temperature process (a gate first process ):
    • DHF-last pre-gate cleaning process
    • Deposition of HfO2 gate dielectrics using a MOCVD cluster tool (deposited at 400oC followed by a 700oC PDA in N2 for 1 min)
    • Deposition of TaN/HfN metal gate stack by PVD
    • Gate patterning by using RIE
    • (Followed by S/D implantations for MOSFET devices)
    • RTA in N2 at 950oC or 1000oC for 30s

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide13

Experiment (SiON)

  • P+ poly-Si MOSFETs were fabricated using a 90nm CMOS technology.
  • SiON gate dielectrics: RTO+ Plasma Nitridation+PDA
  • Static and Dynamic stresses were performed @ RT and 125oC
    • S/D bias=0
    • Various S/D biases

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide14

Outline

  • Introduction
  • Reliability characteristics of ultra thin gate dielectrics
    • HfO2 gate stack
      • High temperature annealing effect
      • TDDB, PBTI, and NBTI
    • SiON in pMOS
      • Dynamic NBTI
      • S/D bias effect on NBTI
  • Summary

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide15

High temperature annealing effect

    • High temperature process causes the significant reduction of bulk charge trapping in HfN/HfO2 gate stack (J.F. Kang et al, ESL 8 : G311-G313 2005)
  • After a high temperature

(>900oC) process :

    • Hysteresis-

Significant reduction

    • Extra inversion capacitance-

Disappearance

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide16

High temperature annealing effect

Scalability of HfN/HfO2 gate stack (MOSC) (J.F. Kang et al, ESL 8 ; H. Yu et al, IEDM’03)

0.75 nm EOT (W/ SN) and 0.91 nm EOT (W/O SN) were achieved in MOSC undergoing a 1000oC PGA process

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide17

HfN

HfN

HfO2~2.0nm

HfO2~2.2nm

IL~0.9 nm

IL~0.7 nm

1000oC

RTA

FGA

  • High temperature annealing effect

Scalability of HfN/HfO2 gate stack (MOSC)

The robust thermal stability could be attributed to barrier effect of HfN layer against oxygen diffusion into HfO2/Si interface, which effectively suppresses the growth of IL during high temperature RTA

1000oC RTA

FGA

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide18

IL ~0.8 nm

  • High temperature annealing effect

Scalability of HfN/HfO2 gate stack (MOSFET) (J.F. Kang et al, EDL 26 ,2005;)

0.95 nm EOT and low gate leakage (9.7X10-5A/cm2 @VFB+1V and 1.3X10-3A/cm2 @VFB-1V ) are achieved in HfN/HfO2 gated nMOSFET

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide19
High temperature annealing effect

Well-behaved device performances are achieved in the 0.95 nm EOT nMOSFET (J.F. Kang et al, EDL 26, p.237, 2005)

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide20
Reliability of HfN/HfO2 gate stack
    • TDDB
  • Polarity dependent TDDB had been reported in devices with high-k dielectrics(*,**,***)
  • Two mechanisms were proposed for TDDB
    • Interfacial layer initiated breakdown
    • Bulk layer initiated breakdown
  • E-field dependent TDDB will be shown

*R. Degraeve, et all; IRPS 2003.

** Wei Yip Loh, et all; IEDM 2003.

*** Y. H. Kim, et all; Device Research Conference, 2003.

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide21
Reliability of HfN/HfO2 gate stack
    • Intrinsic TDDB characteristics (J.F. Kang et al, submitted to T-ED)
  • Nearly constant slopes for different areas are the indication of the intrinsic TDDB (A. S. Oates, IEDM, p.923, 2003 )
  • Observed TDDB in the HfO2 gate stack fabricated by a high temperature process is intrinsic

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide22
Reliability of HfN/HfO2 gate stack
    • E-field dependent TDDB (J.F. Kang et al, submitted to T-ED)
  • Under low E-fields, constant weibull slope indicates IL initiated breakdown
  • Under high electric field, the E-field dependent weibull slope indicates bulk initiated breakdown

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide23
Reliability of HfN/HfO2 gate stack
    • E-field dependent TDDB (J.F. Kang et al, submitted to T-ED)
  • Under high E-fields, hole trapping behavior was observed
  • Under low E-fields, electron trapping behavior was observed

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide24
Reliability of HfN/HfO2 gate stack
    • E-field dependent TDDB (J.F. Kang et al, submitted to T-ED)
  • High energetic holes or electrons trapping dominate the dielectric breakdown (K. Torii et al, in IEDM p.129-132, 2004 )
  • Under a high CVS, hole trapping in HfO2 bulk is dominant
  • Under a low CVS, electron trapping in IL layer is dominant due to the higher E-field in IL layer based on Gauss law εILEIL=εBulkEBulk

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide25
Reliability of HfN/HfO2 gate stack
    • BTI (J.F. Kang et al, submitted to T-ED)
  • Under positive stressing, negligible Vt shifts were observed both in nMOS and pMOS

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide26
Reliability of HfN/HfO2 gate stack
    • BTI (J.F. Kang et al, submitted to T-ED)
  • Under negative stressing,significant Vt shifts were observed both in nMOS and pMOS devices

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide27
Reliability of HfN/HfO2 gate stack
    • BTI (J.F. Kang et al, submitted to T-ED)

Vt shiftsis bias polarity dependent for nMOSFET

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide28
Reliability of HfN/HfO2 gate stack
    • BTI (J.F. Kang et al, submitted to T-ED)

Vt shiftsis bias polarity dependent for pMOSFET

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide29
Reliability of HfN/HfO2 gate stack
    • NBTI in pMOS
  • DCIV indicates increasing interfacial traps under NBT;
  • Increasing hysteresis indicates the generation of new bulk traps during NBT stressing

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide30

Reliability of HfN/HfO2 gate stack

    • NBTI in p-MOS
  • NBTI well fitted by R-D model was observed (S. Zafar et al, VLSI’04 p.208)
  • Intrinsic NBTI similar to SiO2-devices could be attributed to the breaking of Si-H bonds followed by the H species diffusion

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide31
Reliability of HfN/HfO2 gate stack
    • PBTI in n-MOS (N. Sa et al, EDL 26, p.610, 2005 )
  • At room temperature, a “turn-around” phenomenon was observed. (left)
  • Negative Vt shifts was observed and shows strong
  • dependence on temperature and electrical field. (right)

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide32
Reliability of HfN/HfO2 gate stack
    • PBTI in n-MOS (N. Sa et al, EDL 26, p.610, 2005 )
  • The increased S with stressing time indicates the increased interfacial trap density
  • PBTI fitted by R-D model was observed and the slop was ~0.6 corresponding to the process of the charged species diffusion

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide33

Reliability of HfN/HfO2 gate stack

    • PBTI in n-MOS (N. Sa et al, EDL 26, p.610, 2005 )
  • Intrinsic PBTI fitted by R-D model is observed
  • PBTI can be explained by the breaking mechanism of Si-O bonds in IL induced by the injected electrons

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide34

Reliability of HfN/HfO2 gate stack

    • PBTI in n-MOS (N. Sa et al, EDL 26, p.610, 2005 )
  • The breaking mechanism of Si-O bonds induced by the injected electrons was confirmed by the measurement on activation energy

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide35

Outline

  • Introduction
  • Reliability characteristics of ultra thin gate dielectrics
    • HfO2 gate stack
      • High temperature annealing effect
      • TDDB, PBTI, and NBTI
    • SiON in pMOS
      • Dynamic NBTI
      • S/D bias effect on NBTI
  • Summary

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide36
Reliability of SiON gate dielectric
    • DNBTI characteristics
  • Frequency dependent NBTI @ AC stressing

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide37
Reliability of SiON gate dielectric
    • DNBTI characteristics
  • Frequency dependent NBTI is related to the generation of interface traps

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide38
Reliability of SiON gate dielectric
    • DNBTI characteristics
  • Process of Nit generation and passivation associated with Si-H bonds meets the R-D model in DC and AC modes

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide39
Reliability of SiON gate dielectric
    • DNBTI characteristics
  • Origin of frequency dependent DNBTI could be attributed to the nitrogen trapping effect on diffused H species
  • The trapped H species will not be responsible for the re-passivation of Si-H bonds during recover phase

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide40
Reliability of SiON gate dielectric
    • S/D bias effect on NBTI
  • In low Vds region, NBTI is consistent with one predicted by R-D model (S. Mahapatra et al, EDL 51, p.1371, 2004)
  • Anomalous E-field dependent NBTI was observed in high Vds region
  • More severe NBTI with S/D bias was observed in the short channel devices

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide41
Reliability of SiON gate dielectric
    • S/D bias effect on NBTI
  • Time evolution of △Vthobeys a power law depicted by generalized reaction-diffusion (R-D) model
  • The mechanism involving the release of hydrogen from Si-H bonds followed by H species diffusion is responsible for the NBTI
  • We guess that the energetic holes are responsible for the anomalous E-field dependence of NBTI

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide42
Mechanism of S/D bias enhanced NBTI
  • S/D bias causes the formation of energetic holes in the channel inversion layer;
  • Energetic holes are captured by Si-H bonds causing weakened Si-H bond;
  • Additional energies of the captured holes causes Si-H bond breaking

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide43
Summary (1)
  • High temperature process could effectively reduce the pre-existing charge trapping in HfO2 gate stacks
  • For HfN/HfO2 gate stack, sub-1 nm EOT could be achieved even after a high temperature process

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide44
Summary (2)
  • Intrinsic characteristics of TDDB, NBTI and PBTI could be observed in the HfN/HfO2 with low pre-existing charge trapping
  • The combination of high temperature process and HfN/HfO2 gate stack is a potential solution for the application in sub-45 nm nodes technology

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006

slide45
Summary (3)
  • Nitrogen trapping effect on the diffused H species is critical for DNBTI
  • S/D bias effect on NBTI is significant, especially in the short channel devices
  • New models on reliability evaluation, including nitrogen effect and S/D bias effect, is required

SINANO Workshop, Montreux, Switzerland Sept. 12~16, 2006