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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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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


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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


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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


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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


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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


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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


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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


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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


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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


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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


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  • 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


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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


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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


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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


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  • 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


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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


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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


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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


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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


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  • 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


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  • 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


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  • 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


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  • 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


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  • 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


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  • Under positive stressing, negligible Vt shifts were observed both in nMOS and pMOS

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


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  • Under negative stressing,significant Vt shifts were observed both in nMOS and pMOS devices

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


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Vt shiftsis bias polarity dependent for nMOSFET

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


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Vt shiftsis bias polarity dependent for pMOSFET

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


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  • 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


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  • 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


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  • 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


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  • 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


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  • 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


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  • 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


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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


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  • Frequency dependent NBTI @ AC stressing

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


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  • Frequency dependent NBTI is related to the generation of interface traps

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


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  • 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


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  • 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


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  • 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


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  • 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


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  • 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


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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


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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


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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


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