Resistivity of Ni silicide nanowires and its dependence on

Ni film thickness used for the formationo

J. Song1, K. Matsumoto1, K. Kakushima2, Y. Kataoka2, A. Nishiyama2, N.Sugii2,

H.Wakabayashi2, K. Tsutsui2, K. Natori1, H. Iwai1

Tokyo Institute of Technology1

ECS 224th MEETING. 2013

1Frontier Research Center, Tokyo Institute of Technology2Interdisciplinary Graduate School of Science and Engineering

3 Dimensional Devices

・High controllability by Gate-All-Around(GAA) structure

・Suppression of Short Channel Effect

3D devices substitute for planar devices 2

Gate

S D

Planar MOSFETAdvantages

Ni silicide

Gate

S D

GATE

Source Drain

・ Low formation temperature

・Salicide process

Ni silicide

H. Iwai et al., Microelectron. Eng., 60, 157, (2002).

Ni silicide

Vertical of view Si NW FET

・ Low resistivity

Ni silicide

3

Using as contact of S/D in conventional MOSFET

Application for 3D devices such as Si NW FET

ReduceParasitic resistance

Ni silicidation of Si NW

Si-subNi silicide

Si-subNi Annealing

Ni silicidation of bulk Si

18 µΩcm

50 µΩcmSiO2

Z. Hang et al., Appl. Phys. Lett., 88, 213103 (2006).

SiSiO2

Si

RTA: 500 oC

Ni2Si

Annealing

Ni silicidation of Si NW

Ni31Si12

Sensitive to the amountbetween Si and Ni

Difficult to form low resisvitity phase of Ni-silicide for NW

4

Line Width Effect on Resistivity R

esis

tivity

(µΩ

-cm

)

Nanowire width (nm)

RTA 500 oC5 min

050

100

150200250

10 30 50 70 90

Drastic increases in resistivity for line width

narrower than 35nm

5

3. Difference of the phase

Nanowire

NixSiy

1. Line width roughness

(35~80 nm)NiαSiβ

(15~35 nm)

ee e

4. Grain boundary scattering

ee

e

Possible causes2. Surface scattering

K. Matsumoto, et al., ISNE 2013, Kaohsiung City, Taiwan.

Investigation of possible causesR

esis

tivity

(µΩ

-cm

)

Nanowire width (nm)

050

100

150200250

10 30 50 70 90

r = 0.2r = 0.7

Res

istiv

ity (µ

Ω-c

m)

Nanowire width (nm)

0

50

100

150

200

250

0 10 20 30 40 50 60 70 80 90

C = 1.2P = 0.2

Investigation of surface scattering effect

Investigation of roughness effect

Mean free path Calculated as 2 nm

ρbulk = 34µΩ cm

2 nm MFP is short to cause rough surface scattering

実験データ

6K. Matsumoto, et al., ISNE 2013, Kaohsiung City, Taiwan.

Nanowire

Approximation

(Top View) L(1-r)rL

WD/2

D/2

: difference in line width: fraction of nanowire

with wide width

Line width roughness can not be the major reason

LWR and surface scattering have small effect

Purpose of This Study

7

Estimate Ni silicide phase difference as the cause of degradation

Suppression of drastic increased resistivity in narrow line Ni silicide

In order to investigate the different phase formation,change Ni film thickness

Si Sub.BOX

Ni

Deposit different thickness on each sample

Experimental Procedure

Si Sub.BOX

Si Sub.BOX

Si nanowire patterning・SOI height: 30 nm・Nanowire width ranging from 20 to 90 nm

SPM and HF cleaningNi deposition・Ni film thickness：7, 10, 80 and 120 nm・RF sputtering in Ar ambient

1st Rapid thermal annealing (RTA)

Unreacted Ni removal by SPM

Ni silicide

TiN/Ti deposition by RF sputtering・Thickness 50 nm/50 nm

TiN/Ti electrodes patterning by Lift-off technique

Observation and Measurement

・ 270、2 min (N2 ambient)

2nd RTA・ 500、1 min (N2 ambient)

8

・RF sputtering in Ar and N2 ambient

Si Sub.BOX

Ni

NiSi

0

50

100

150

200

250

0 20 40 60 80 100

Nanowire width (nm)R

esis

tivity

(µΩ

cm)

10 nm80 nm120 nm

Experimental Results

Resisvitity of NW increased in narrower line width than 40 nm

Small resistivity can be obtained with Ni film thickness 10 nm

Low resistivity

9

Drastic increase of resistivity

Ni film thickness

Resistivity Dependence on Temperature

0.95

1.00

1.05

1.10

0 25 50 75 100

Temperature()

R/RRT

( ) 1+−= RTRT

TTR

R α

Phase TCR（K-1）

NiSi 0.0022

Ni2Si 0.00096

Ni31Si12 0.00048

Z. Zhang, et al., Appl.Phys.Lett., vol.88, p.043104, 2006.

In order to investigate Ni silicide phase, derive Temperature coefficient of resistance (TCR) α

10

Si-rich

α= TCR

α = Temperature coefficient of resistance (K-1)

0

0.001

0.002

0.003

0.004

0 100 200 300

Resistivity(µΩcm)

TCR

(K-1

)

0

50

100

150

200

250

0 20 40 60 80 100

Nanowire width (nm)

Res

istiv

ity (µ

Ωcm

)

10 nm80 nm120 nm

Results of TCR Measurement

・B: Resistivity = About 20 µΩcm, TCR values = 0.0030~38(K-1)

TCR:0.0012-16

TCR:0.0010

It can not conclude that its phase is different because it is close to 0.0012

Ni film thickness

11

・A: Resistivity = About 50 µΩcm, TCR values = 0.0012~16(K-1)Ni2Si (0.00096) < 0.0012~16 < NiSi (0.0022)

TCR:0.0030-38

NiSi (0.0022) < 0.0030~38

・C: High resistivity, TCR value = 0.0010(K-1)

A

B

C B

C

A

Ultrathin Ni silicideMeasured the low resistivities in the Si-rich area

If Ni film thickness decrease more, what will happens?

Overall increases of resistivities

Deposition of 7 nm Ni film thickness

12

50 nm

0

50

100

150

200

250

300

0 20 40 60 80 100

Nanowire width (nm)

Res

istiv

ity (µ

Ωcm

)

7 nm10 nm80 nm120 nm

Ni film thickness

・Ununiform Ni silicide・A lot of contrast and

complicated grain boundary

・Uniform Ni silicide・Monotonous grain boundary

50 nm

30 nm

A

B

A

B

Results of EDS Analysis

13

Ni film thickness: 7 nmNW line width: 45 nm

A B

Ni film thickness: 10 nmNW line width: 27 nm

Si peak

Si peakNi peak

Ni peak

0

50

100

150

200

250

0 50 100 150Thickness of Ni film (nm)

Res

istiv

ity (µ

Ωcm

)

Resistivity Dependence on Ni film thickness

・Resistivity starts to increase with Ni film thickness increasefrom particular place

・In these Si NW size and thermal process condition, （Height 30 nm、Width 20~90 nm）(1st RTA: 270、2nd RTA: 500)

the Ni film thickness around 10nm is an optimum14

10

Si-rich

NW line width 25 nm

NW line width 55 nm

ConclusionInvestigation of resistivity dependence on Ni film thickness

for reducing resistivity increase of Ni silicide NW

・Conformation of resistivity reduction with Ni film thickness reduction

・Measurement of TCR values and investigation of Ni silicide phases

The high TCR value had the low resistivity

・Trying deposition of Ultrathin Ni film thickness

・Measurement of resistivity of Ni silicide NW formed from 10, 80 and 120 nm Ni film thickness

Found the resistivity increase and it is considered agglomeration, complicated grain boundary or excessive Si-rich phase

15Ni film thickness should optimized for NW width

Thank you for your attention!

16

Physical Property Values of Ni silicide

S. P. Murarka, SILICIDES FOR VLSI APPLICATIONS, Academic Press, New York, 1983, Chap. 4.L. J. Chen, Silicide Technology for Integrated Circuits. The IEEE, London, 2004, Chap. 5.J. A. Kittl et al., Appl. Phys. Lett. 91, 232102 (2007).

Phase Resistivity(µΩ・cm)

Crystal structure

Density (g/cm3) Tsilicide / TNi

Si comsunption/ TNi

Ni 7-10 Cubic 8.91 1 0

Ni3Si 80-90 Cubic 7.87 1.31 0.61

Ni31Si12 90-150 Hexagonal 7.56 1.40 0.71

Ni2Si 24-30 Orthorhombic 7.51 1.47 0.91

Ni3Si2 60-70 Orthorhombic 6.71 1.75 1.22

NiSi 10.5-18 Orthorhombic 5.97 2.20 1.83

NiSi2 34-50 Cubic 4.80 3.61 3.66

Si Dopantdependent Cubic 2.33 ― ―

550~900800~950350~750Forming temperature [oC]

＞50＞90~180＜50Applicable line width [nm]

~18~1510.5~18Resistivity[µΩ・cm]

0.821.040.82Si comsunption/Tsilicide

CoSi2TiSi2NiSiSilicide

550~900800~950350~750Forming temperature [oC]

＞50＞90~180＜50Applicable line width [nm]

~18~1510.5~18Resistivity[µΩ・cm]

0.821.040.82Si comsunption/Tsilicide

CoSi2TiSi2NiSiSilicide

J. A. Kittl et al., Microelectron. Eng., 50, 87 (2000). C. Lavoie et al., Microelectron. Eng., 70, 144 (2003).T. Morimoto et al., IEEE Trans. Electron Devices, 42, 915 (1995).

Selecting of Ni silicide

Possibility of Agglomeration

Ting-Hsuan Chen et al., Journal of ECS, 1(2) P90-P93 (2012).

200 nm

Si

NiSi

SEM images of Si nanowiresNi film thickness: 7.5 nm, RTA: 500 for 1 min

200 nm

(a) (b)

Occurred agglomeration by growing NW size

Similarly、it is considered that decreasing Ni film thickness about same NW size

occurs agglomeration also

50 nm 100 nm

SEM Images of Nanowire