DLTS analysis of amphoteric interface defects in high-k

TiO2 MOS structures prepared by sol-gel spin-coating

Arvind kumar

Dept. of Physics

IISc, Bangalore

11/28/2015 1

arvind9kr@gamil.com

11/28/2015 2

Outline

Why TiO2 ?

The deposition of high- TiO2 films by solution route.

Material characterization and films morphology.

Fabrication of MOS structure.

Interface states density (Dit) analysis by DLTS.

Capture cross – section analysis by IF – DLTS.

Summary

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TiO2 can be used in OFET as an insulator.

TiO2 in DSSC

In Si devices as a dielectric layer.

Anti reflective coating

As Gas sensor

Due to a very high dielectric constant (10 - 170), TiO2 may be a good replacement

for conventional SiO2 ( = 3.9).

Why TiO2 ?

Wang et al, Chem. Rev., 114, 9346 (2014).

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Schematic of important regions of a MOS capacitor

The interfaces with either the gate or

with Si channel region are

particularly important in regard to

device performance.

Wilk et al, J. Appl. Phys., 89, 10 (2001).

888 Isopropyl alcohol (IPA) 8.5 ml

Titanium isopropoxide (TIP) 0.6 ml

Hydrochloric acid (HCl) 20 µL

Ageing for 12 Hour

A transparent solution was obtained

This can be used for spin coating

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Preparation of solution

Arvind et al, Mater. Sci .Semi. Proc. 40, 77 (2015).

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p –Si (100)

TiO2 film

The deposition of high- TiO2 thin films by solution route:

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XRD analysis

XRD analysis suggests a well-crystallized

anatase phase of nc-TiO2 films on Si.

XRD of 600 0C annealed TiO2 film on Silicon.

Arvind et al, Mater. Sci .Semi. Proc. 40, 77 (2015).

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Raman spectrum of 600 0C annealed TiO2 film

on Si and Quartz substrate.

Raman spectrum confirms the presence of

well-crystallized anatase phase of

titanium dioxide film on quartz and Si.

Raman spectrum

The results are in close agreement with

XRD analysis.

Arvind et al, Mater. Sci .Semi. Proc. 40, 77 (2015).

XPS survey scan spectra

Ti2p core level spectra

The separation between the Ti 2p3/2 and the

Ti 2p1/2 peaks is 5.79 eV, which the presence

of Ti in its tetravalent state.

O1s core level spectra Arvind et al, Mater. Sci .Semi. Proc. 40, 77 (2015).

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Cross - sectional SEM : TiO2 layer thickness measurement

tTiO2 = 91 nm

400 500 600 700 800 900

2.3

2.4

2.5

2.6

Refr

acti

ve in

dex (

n)

wavelenght (nm)400 500 600 700 800 900 1000

14

16

18

20

22

24

26

28

30

32

(Experimental)

(fitted)

(Experimental)

(Fitted)

Wavelength (nm)

(

deg)

40

60

80

100

120

140

(

de

g)

2

2

11

1d

nPorosity

n

Ellipsometry Studies

The porosity is 10 %.

Arvind et al, Mater. Sci .Semi. Proc. 40, 77 (2015).

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The RMS surface roughness is 6 Å.

Roughness analysis

Arvind et al, Mater. Sci .Semi. Proc. 40, 77 (2015).

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p –Si (100)

Electrical measurement

MOS capacitor fabrication and measurement

A metal mask having circular hole (d = 288 µ) was used to deposit the Al on

top of TiO2 films. Thermal evaporation technique was used for Al deposition

and thickness was 200 nm.

p-Si (100) T05 header

Device mounted on T05 header for DLTS measurements.

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Schematic diagram of Al/TiO2/p-Si(100) MOS Device.

Estimation of Interface states density (Dit) by DLTS

Voltage-time (V-t) and capacitance time (C-t)

diagrams. VQ is the quiescent voltage and VP is

the majority carrier pulse voltage.

Energy band diagrams of Al/TiO2/p-Si(100) MOS devices

(a) Before (b) on, and (c) after majority carrier pulse. Kundu et al, J. Vac. Sci. Tech B 30, 051206 (2012).

DLTS Theory

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( )exp T V

p p th v

E Ee V N

kT

16

Arrhenius plot obtained from the

peak positions

51000 8.617 10TE slope

Khan et al., Conf. Rec. of the 2006 IEEE 4th World Conf. on (Vol. 2, pp. 1763-1768). IEEE.

DLTS Setup in our lab

17

C-V characteristic of Al/TiO2/Si (100) MOS

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ox FBot

C VQ

q

2high SiO

high

tEOT

The flat – band voltage (VFB) and the density of oxide trapped charges

estimated are – 0.9, – 0.44 V and 5.24×1010, 1.03×1011 cm−2; for the NMOS

and PMOS capacitors, respectively.

EOT was estimated 4.5 nm.

Arvind et al, AIP Advances 5, 117122 (2015).

C-V analysis

DLTS spectra at different rate windows (tw) on N and PMOS.

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The filling pulse is applied from

accumulation to depletion region.

Filling pulse width was taken 5 ms for all

rate windows.

DLTS measurements

51000 8.617 10TE slope

The activation energy of the trap (ET)

is estimated to be 0.30 eV for p-Si

substrate and 0.21eV for n-Si

substrate.

Arvind et al, AIP Advances 5, 117122 (2015).

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Interface analysis

3

0 2 1ln( / )

si ox Ait

C N CD

C kT t t

The interface states (Dit) were estimated 8.73×1011 and 6.41×1011 eV−1 cm−2

for NMOS and PMOS, respectively.

This is an order of magnitude higher than Al/SiO2/Si MOS devices.

Still this is an acceptable value for Si/high-k (non – native Oxide) MOS

devices and consistent with other deposition techniques.

175 200 225 250 275

-160

-140

-120

-100

-80

-60

-40

-20

0

DL

TS

Sig

na

l (f

F)

Temperature (K)

1 us

2 us

4 us

10 us

20 us

40 us

100 us

200 us

400 us

DLTS spectra of TiO2 MOS device as a function of pulse time (tp).

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Capture cross section analysis

[1 exp( )]Pit it

c

td D

max max( ) ( )[1 exp( )]PP LP

c

tC t C t

max

max

( )ln[1 ] .

( )

Pp

LP

C tas a funtion of t gives straight line

C t

DLTS spectra of TiO2 MOS device as a function of pulse time (tp).

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Capture cross section analysis

1p

c thV p

The capture cross – sections estimated

is 5.8×10−23, 8.11×10−23 cm2 for

NMOS and PMOS interface traps.

Arvind et al, AIP Advances 5, 117122 (2015).

Summary

High quality TiO2 thin films have been deposited by combined sol – gel spin – coating

method.

The small surface roughness of 6 Å is achieved.

Reasonably low (Dit) are 8.73×1011 and 6.41×1011 eV−1 cm−2 achieved for NMOS and

PMOS, respectively.

Very low capture cross section indicates that the traps are not aggressive recombination

centers and possibly can not contribute to the device operation to a large extent.

This method might be a good replacement for the expensive high vacuum deposition

techniques in the development of new high-κ dielectrics.

DLTS study provide a better understanding of TiO2/Si interfaces.

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[1] D V Lang, J. Appl. Phys., vol. 45 (1974) 3023.

[2] K Yamasaki et al, Jpn. J. Appl. Phys. 18, 113 (1979).

[3] S Kundu et al, Journal of Vacuum Science Technology B 30,051206 (2012).

[4] E Simoen, ECS Transactions, 41 (4) 37-44 (2011).

[5] S Jeon, Appl. Phys. Letters, vol. 82 (2003) 7.

[6] Hua Min Li et al, Thin Solid Films 518(2010) 6382-6384.

[7] A. Kumar, S. Mondal, and K.S.R.K. Rao, AIP Conf. Proc. 1665, 080015 (2015).

[8] A. Kumar, S. Mondal, S.G. Kumar, and K.S.R. Koteswara Rao, Mater. Sci .Semi. Proc. 40, 77 (2015).

[9] A. Kumar, S. Mondal, and K.S.R.K. Rao, AIP Advances 5, 117122 (2015).

References:

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This work has been done in collaboration with Sandip Mondal.

UGC-CSIR for research scholarship.

We acknowledges the financial support from STC- ISRO.

We thank CeNSE, IISc, for providing various characterization facility.

Acknowledgements

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