Dramatic Reduction of Gate Leakage Current of Ultrathin Oxides - - PowerPoint PPT Presentation

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Dramatic Reduction of Gate Leakage Current of Ultrathin Oxides through Oxide Structure Modification

Zhi Zhi Chen Chen, Jun , Jun Guo Guo, and , and Chandan Chandan B.

• B. Samantaray

Samantaray Department of Electrical and Computer Engineering Department of Electrical and Computer Engineering University of Kentucky University of Kentucky Lexington, KY 40506 Lexington, KY 40506

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Outline Outline

• Theory of Hydrogen/Deuterium Isotope Effect

Theory of Hydrogen/Deuterium Isotope Effect

• Experimental Evidence for Origin of Isotope Effect

Experimental Evidence for Origin of Isotope Effect

• Discovery of Phonon Energy

Discovery of Phonon Energy-

• Coupling Enhancement

Coupling Enhancement

• Dramatic Improvement of Quality of Gate Oxides

Dramatic Improvement of Quality of Gate Oxides

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

e- e- Si

H H

Si Si Si Si Si Si

H H H

Si Si Si Si Si Si Si

SiO 2 Si

e- e- Si Si Si Si Si Si

Hot electr ons desorb hydr ogen, cr eating interface states which degrade device performance.

Hydrogen Passivated MOSFET Hydrogen Passivated MOSFET

O O O O O O O O O O O O O

Si Si e-

SiO2 SiO2

n+ n+

p-Si substrate p-Si substrate

Polysilicon Gate Deposited Insulator Metal Drain Contact Metal Source Contact Hot Electrons near Drain

n- n-

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Van de Walle & Jackson Theory (Van de Walle et al., Appl. Phys. Lett. vol. 69, 2441 (1996)) Two competing processes: Two competing processes:

• Hot electron excitation causes

Hot electron excitation causes Si Si-

• H/D bond breaking.

H/D bond breaking.

• De

De-

• excitation is due to energy coupling from

excitation is due to energy coupling from Si Si-

• D to phonon.

D to phonon.

Reason: Reason: ν ν ∝ ∝ 1/m based on

1/m based on IR spectroscopy theory

IR spectroscopy theory

Si Si-

• H

H vibrational vibrational frequency frequency ν ν ~ 650 ~ 650 cm-1. Si Si-

• D

D vibrational vibrational frequency frequency ≈

≈ 460 cm

460 cm-

• 1

1 (

(Si-Si TO phonon mode) De De-

• excitation is more efficient for

excitation is more efficient for Si Si-

• D bonds than for

D bonds than for Si Si-

• H bonds

H bonds

• --This is why

This is why Si Si-

• D bonds are stronger than

D bonds are stronger than Si Si-

• H ones.

H ones.

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Schematic of Hydrogen/Deuterium Effect:

Energy coupling from Si-D bending mode to Si-Si TO phonon mode No coupling from Si-H bending mode to Si-Si TO phonon mode O O

Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si

O O O O O O

D D H H

SiO SiO2

2

Energy Coupling Energy Coupling

Si Si

No Coupling No Coupling

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Direct Measurement of the Vibrational Frequency of Si-H/D Bonds

No experimental data available for No experimental data available for Si Si-

• D

D vibrational vibrational frequency in the frequency in the SiO SiO2

2/Si interface

/Si interface Only in the deuterated amorphous Si (α-Si), the vibrational frequency (510 cm-1) was measured*. However, the chemical environment of the amorphous Si is very different from that of crystal Si. *J.-H. Wei, M.-S. Sun, and S.-C. Lee, Appl. Phys. Lett. 71, 1498 (1997).

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Origin of the Isotope Effect: No Energy Coupling from Si-H to Si-Si TO phonon

0.000 0.002 0.004 0.006 0.008 0.010 425 475 525 575 625 675 725 775 825 875

Wavenumber (cm

• 1)

Absorbance

Si/oxide, hydrogen annealed Si/oxide, unannealed

Si-O LO Si-Si TO X4 point Si-O TO rocking Si-Si LO Si-H Bending Si-O TO bending

No difference between the H-annealed sample and the as-oxidized one, except for the Si-H bending vibration. (Chen et al. Appl. Phys. Lett. 83, 2151-2153, (2003))

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Origin of the Isotope Effect: Energy Coupling from Si-D to Si-Si TO phonon & Si-O TO rocking mode (Chen et al. Appl. Phys. Lett. )

0 .0 0 0 0 .0 0 2 0 .0 0 4 0 .0 0 6 0 .0 0 8 0 .0 1 0 0 .0 1 2 4 1 5 4 6 5 5 1 5 5 6 5 6 1 5 6 6 5 7 1 5 7 6 5 8 1 5 8 6 5

W a v e n u m b e r (c m

• 1)

Absorbance

S i/o x id e , u n a n n e a le d S i/o x id e , d e u te riu m

S i-O T O b e n d in g S i-O T O ro c k in g S i-S i L O S i-S i T O X 4 p o in t S i-O L O S i-D B e n d in g

The absorbance of the Si-Si TO phonon mode and the Si-O TO rocking mode are all enhanced significantly (>25%) after deuterium anneal. (Chen et al. Appl.

• Phys. Lett. 83, 2151-2153, (2003))

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

New finding: Energy is coupled from Si-D bending mode to Si-Si TO phonon mode and also to Si-O TO rocking mode

(Chen et al. Appl. Phys. Lett. 83, 2151-2153, (2003))

O O

Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si

O O O O O O

D D H H

SiO SiO2

2

Energy Coupling Energy Coupling

Si Si

No Coupling No Coupling Energy Coupling Energy Coupling

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Challenge: How to further enhance the energy coupling?

Hypothesis: Hypothesis: Shift the Shift the Si Si-

• D

D vibrational vibrational mode toward mode toward Si Si-

• Si

Si TO phonon mode. TO phonon mode. Method 1: Mechanical stress just a little shift (~6-8 cm-1) Method 2: Electrical stress Method 3: Thermal stress How?

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Surprising Discovery: Phonon Energy-Coupling Enhancement

The absorbance of the Si-Si TO phonon mode,the Si-O TO rocking mode, and Si- Si LO mode are all enhanced significantly (>50%) after rapid thermal processing (RTP). There is further enhancement after deuterium annealing. Tox=23 nm.

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 415 440 465 490 515 540 565 590 615 640

Wavenumbers(cm-1) Absorbance

• 1. Si/Oxide, Unannealed
• 2. Si/Oxide, RTP annealed
• 3. Si/Oxide, RTP plus D2

annealed Si-O TO rocking Si-Si LO Si-Si TO X4 point Si-D Bending 1 2 3

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

The Enhancement is not due to the Surface Plasmon.

It is well-known that the surface plasmon on the nanoscale metallic islands also produces strong surface-enhanced IR spectra. In order to avoid the metallic island- like surface, we used n- wafer (n=2×1014 cm-3 and ρ=20.8 Ω-cm) for experiments.

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 415 435 455 475 495 515 535 555 575 595 615 635

Wavenumbers(cm-1) Absorbance

• 1. Si/Oxide, Unannealed
• 2. Si/Oxide, RTP annealed

1 2 Si-Si TO X4 point Si-O TO rocking Si-Si LO Si-O LO

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Dependence of Enhancement on the Oxide Thickness

For thick oxide (Tox=80 nm), there is almost no enhancement except for the Si-Si LO mode after rapid thermal processing (RTP)---- implying stress-related phenomena. This also suggests that there should be no effect for the polysilicon/oxide stack. 0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 410 430 450 470 490 510 530 550 570 590 610 630 650

Wavenumbers(cm -1)

Absorbance

Si/Oxide, Unannealed Si/Oxide, RTP annealed

Si-O TO rocking Si-Si LO Si-Si TO X4 point

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Dependence of Enhancement on the Cooling Time

The enhancement is strongly dependent on the cooling time ----implying the stress-related phenomena.

0.000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 430 450 470 490 510 530 550 570 590 610 630 650

Wavenumbers(cm-1) Absorbance

• 1. Si/Oxide, Unannealed
• 2. Si/Oxide, RTP annealed,

cooling 10 minutes

• 3. Si/Oxide, RTP annealed,

cooling 5 minutes

• 4. Si/Oxide, RTP annealed,

cooling 20 seconds 1 2 3 4 Si-Si TO X4 point Si-O TO rocking Si-Si LO Si-O LO

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Phonon Energy-Coupling Enhancement: improvement of hot- electron degradation

• 0.01

0.01 0.02 0.03 0.04 0.05 0.06 0.07 10 10

1

10

2

10

3

10

4

10

5

L=2um & W=150 um, Stressed at Vg=4V and Vd=8V

t

Stress Time (s)

D2 anneal only RTP and D2 anneal 200X

• 10

10 20 30 40 50 10 10

1

10

2

10

3

10

4

D2 anneal only, stress Vg=4V Vd=8V RTP+D2 anneal, stress at Vg=9V Vd=18V

Time (s)

• Z. Chen and J.
• Z. Chen and J. Guo

Guo, presented at the 35th IEEE SISC, San Diego, CA, Dec. 9 , presented at the 35th IEEE SISC, San Diego, CA, Dec. 9-

• 11, 2004.

11, 2004.

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Hypothesis: Si-O bonds might be strengthened.

This is because energy is also coupled from Si-O rocking mode to Si-Si TO phonon mode and also to Si-D bending mode O O

Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si Si

O O O O O O

D D

SiO SiO2

2

Energy Coupling Energy Coupling

Si Si

Energy Coupling Energy Coupling

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Hydrogen/Deuterium Effect on Gate Oxide: No Effect

10

• 12

10

• 11

10

• 10

10

• 9

10

• 8

10

• 7

10

• 6

10

• 5

2 4 6 8 10 12

D2 anneal D2 anneal D2 anneal H2 anneal H2 anneal

Gate Voltage (V)

10

• 3

10

• 4

10

• 5

10

• 6

10

• 7

10

• 8

10

• 2

T

• x=10.2nm

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Direct Rapid Thermal Processing Only: Improvement of Breakdown Voltage (15%) and Reduction of Leakage Current (10X)

10

• 12

10

• 11

10

• 10

10

• 9

10

• 8

10

• 7

10

• 6

10

• 5

2 4 6 8 10 12 14

Gate Voltage (V)

H

2 anneal only

RTP+H

2 anneal

10

• 3

10

• 4

10

• 5

10

• 6

10

• 7

10

• 8

10

• 2

T

• x=11.1nm

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Direct Rapid Thermal Processing Plus D2 Annaeal: Improvement of Breakdown Voltage (30%) and Reduction of Leakage Current (100X)

10

• 12

10

• 11

10

• 10

10

• 9

10

• 8

10

• 7

10

• 6

10

• 5

5 10 15

Gate Voltage (V)

D

2 anneal only

RTP+D

2 anneal

10

• 3

10

• 4

10

• 5

10

• 6

10

• 7

10

• 8

10

• 2

T

• x=10.2nm

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Direct Rapid Thermal Processing Plus D2 Anneal: Improvement of Breakdown Voltage (30%) and Reduction of Leakage Current (100X)

10

• 12

10

• 11

10

• 10

10

• 9

10

• 8

10

• 7

10

• 6

10

• 5

1 2 3 4 5 6

Gate Voltage (V)

D

2 anneal only

RTP+D

2 anneal

10

• 3

10

• 4

10

• 5

10

• 6

10

• 7

10

• 8

10

• 2

T

• x=3.7nm

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Direct Rapid Thermal Processing Plus D2 Anneal of Thin Oxides: Reduction of leakage current (105X)

This is similar to that of HfSiON (Gusev et al., IEDM Technical Digest, 451-454 (2001))

10

• 10

10

• 8

10

• 6

10

• 4

10

• 2

10 0.2 0.4 0.6 0.8 1 1.2 Control sample: D

2 anneal (30 min)

RTP (1 min) plus D

2 anneal (30 min)

10

5 X

T

• x=2.2nm

Gate Voltage (V)

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Capacitance-Voltage Curves and oxide thickness of oxide measured before and after RTP

• 2
• 1

1 2

Control-1MHz RTP1min-1MHz-S1 RTP1min-1MHz-S2 RTP1min-1MHz-S3

350 300 200 150 100 50 T

• x=3.0 nm

250

Gate Voltage (V)

Table: Comparison of oxide thickness measured Table: Comparison of oxide thickness measured using using ellipsometry ellipsometry before and after RTP before and after RTP

There is only a slight flat There is only a slight flat-

• band voltage shift and thickness remains unchanged after RTP.

band voltage shift and thickness remains unchanged after RTP.

Sample No. Oxidation Parameters Tox before RTP Tox after RTP #1110051 N2 @1000sccm, O2 @20 sccm, 9000C for 20 s 22.4 Å 23.3 Å #0628052 N2 @1000sccm, O2 @20 sccm, 9000C for 10 s 19.8 Å 20.9 Å #1110052 N2 @2000sccm, O2 @20 sccm, 9000C for 20 s 19.5 Å 20.09Å

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Summary Summary

• We discovered a new effect, phonon energy

We discovered a new effect, phonon energy-

• coupling

coupling enhancement, i.e. the energy coupling from the enhancement, i.e. the energy coupling from the Si Si-

• D bond to the

D bond to the Si Si-

• Si

Si TO mode and the TO mode and the Si Si-

• O rocking mode is dramatically

O rocking mode is dramatically enhanced after the RTP processing directly on the oxide. enhanced after the RTP processing directly on the oxide.

• In addition to strengthening Si-D bonds, Si-O bonds are also
• strengthened. The breakdown voltage of oxides after RTP

processing is improved by 30%.

• The leakage current of thin oxide (2.2 nm) after direct RTP

processing is reduced by 105 times, similar to that of high-k

• xides.

• Dept. of Electrical and Computer Engineering

University of Kentucky University of Kentucky

2005 ISDRS, Bethesda, MD 2005 ISDRS, Bethesda, MD

Acknowledgements Acknowledgements

• This research is supported by National Science Foundation

This research is supported by National Science Foundation ECS-0093156 and EPS- 0447479.