Opracowanie technologii cienkich warstw ZnO i...

Opracowanie technologii cienkich

warstw ZnO i optymalizacja

parametrów elektrycznych do złącz

Schottky’ego ZnO/metal

ElŜbieta Guziewicz, Marek GodlewskiT. Krajewski, Ł. Wachnicki, G. Łuka, K. Kopalko,

M. Łukasiewicz, E. Łusakowska, E. Przeździecka, I. Kowalik, W. Paszkowicz, P. Kruszewski, P. DłuŜewski

Institute of PhysicsPolish Academy of Sciences

NANOBIOM 3 luty 2009

Outline

� Atomic Layer Deposition

� ALD laboratory at IF PAN

� ZnO by ALD (precursors, growth rate, structural properties)

� Electrical properties of ZnO-ALD

� Summary


Atomic Layer Deposition


� ALD guarantees flat, uniform and reproducible thickness, low stress, uniform stoichiometry and low defect density.

� Besides the industrial silicon platforms, ALD has proven essential to create gate dielectrics on device substrates without native oxides, such as high mobilityGaAs/AlGaAs heterostructures, organic transistors, nanotubes and many more. Examples of materials include HfO2, ZrO2, Al2O3, LaAlO, GdScO3, their nanolaminates, and others.

Intel has recently announced that their 45 nm generation processors will include a high-k HfO 2 gate dielectric made by ALD .

ALD laboratory at IFPAN


F-120, Microchemistry, FinlandSavannah-100Cambridge NanoTech, USA

ZnO: TMZnO: REII-VI (ZnSe, ZnS,CdS)

ZnOAl2O3HfO2

Zinc precursors:DMZnzinc acetate

Zinc precursor:DEZn

ALD laboratory at IFPAN


Sputtering system Kurt Lesker Co.

Hall effect (RT & LN)

Interferometer(thickness measurement)

Spectrofluorimeter (RT PL)

Access to:

• Nomarski microscope

• X-ray diffractometer

• AFM microscope

•SEM microscope

ZnO grown by ALD


� Atomic Layer Deposition

� ALD laboratory at IF PAN

� ZnO by ALD (precursors, growth rate, structural properties)

� Electrical properties of ZnO-ALD

� Summary

Reactions used in ZnO-ALD growth


� Synthesis reaction� 2Zn + O2 → 2ZnO

� Single exchange reaction� 2ZnCl2 + O2 → 2ZnO + 2Cl2� Zn + H2O → ZnO + H2

� Double exchange reaction� ZnCl2 + H2O → ZnO + 2HCl

� Zn(CH3COO)2 + H2O → ZnO + 2CH3COOH

� Zn(C2H5)2 + H2O → ZnO + 2C2H6

� Zn(CH3)2 + H2O → ZnO + 2CH3

OO

O

O

O O

OO OO

ZnO precursors


� Temperature of the substrates

� 430°C ÷ 500°C for ZnCl2� 300°C ÷ 360°C for Zn(CH3COO)2

� 600C ÷ 300°C for Zn(C2H6)2 (DEZn)� 300C ÷ 300°C for Zn(CH3)2 (DMZn)

� Temperature of the precursors

� 350°C ÷ 400°C for ZnCl2� 230°C ÷ 250°C for Zn(CH3COO)2

� RT for DEZn� -180C for DMZn

High temperature growth

Low temperature growth

ZnO optimization


Each precursor needs its own optimizationALD parameters:

� DEZn pulsing time� DEZn purging time� Water pulsing time� Water purging time� Growth temperature� Precursor’s temperatures� Pressure

~ 205 possibilities !

40 80 120 160 200 2400.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

grow

th r

ate

[A/c

ycle

]

growth temperature [oC]

ALD window

ALD growth window

DEZn+H2O

DEZn + H2O

ZnO precursors

� ZnCl2 4300C-5000C

� Zn(CH3COO)2 3000C-3600C

� Zn(C2H5)2 600C-3000C

� Zn(CH3)2 300C-3000C


ZnO by ALD at High Temperature


� Zn(CH3COO)2 , growth temperature 400°C – 280°C

� ZnCl2 , growth temperature 4300C – 5000C

20 30 40 50 60 70 80

100

1000

10000 10000

Inte

nsity

(ar

b. u

nits

)

TS= 300 2000 cycles

Polycrystalline, rough surface (10-30 nm), high n concentration

ZnO/GaN - monocrystalline growth achieved @ T = 4800C

FWHM = 650 arcsec (for GaN = 530 arcsec)

Smooth surface (1-2 nm) with growth rate about 0.5 nm/cycle

ZnCl2 + H2O → ZnO + 2HCl

Zn(CH3COO)2 + H2O → ZnO + 2CH3COOH

Low Temperature ZnO by ALD


� DEZn, growth temperature 600C-2500C

Zn(C2H5)2 + H2O → ZnO + 2C2H6

� DMZn, growth temperature 300C-3000C

Zn(CH3)2 + H2O → ZnO + 2CH3

Low Temperature growth → important for hybrid structures ZnO/organic material

Low Temperature ZnO by ALD

� DEZn

Zn(C2H5)2 + H2O → ZnO + 2C2H6


LT ZnO-ALD grown with DEZn

� DEZn, growth temperature 600C-2400C

� Substrate: Si, glass, Al2O3


b)

100 120 140 160 180 200

1,0

1,5

2,0

2,5

3,0

3,5

4,0

Rou

ghne

ss [

nm ]

Temperature [ 0C ]

ZnO/Si(001)

70 80 90 100 110 120

1,0

1,5

2,0

2,5

3,0

3,5

4,0

Rou

ghne

ss [

nm ]

Film Thickness [nm]

ZnO/Si(001)

a)

100°°°°C 130°°°°C 190°°°°C

RMS = 3.9 nm RMS =0.9 nmRMS = 1.4 nm

AFM scans from 2×2 µm ZnO(DEZn) samples

0 100 200 300 400 500

10

20

30

40

50

Col

umn

Wid

th [

nm ]

Film Thickness [ nm ]

ZnO/Si (001)

AFM – E. Łusakowska

TEM – P. DłuŜewski


� XRD results


(10.0)(11.0) 30 40 50 60 70

0.0

3.0x103

6.0x103

9.0x103

1.2x104

1.5x104

1.8x104

ZnO/Si

370 nmSi

2400C

00.2

2ΘΘΘΘ angle30 40 50 60 70

0

1x103

2x103

3x103

4x103

5x103

6x103

7x103

1865 nm

1300C

10.0

00.2

11.0

2ΘΘΘΘ angle

(00.2)

80 100 120 140 160 180 2000

20

40

60

80 10.0

00.2

Growth Temperature [0C)

Orientation [%]

Preferential orientation depends on:• growth temperature• precursors’ pulsing and purging time• thickness

I.A. Kowalik et al, J. Cryst. Growth (in print)

XRD – W. Paszkowicz



350 400 450 500 550 600 650 700 750 8000.000

0.005

0.010

0.015

0.020

0.025 ZnO (S128/ZnO/Si(p)/60

oC)

T = 300 K (RT)

λexc. = 300 nm

Slitexc. = 5 nm

Slitemm.

= 5 nm

PL Intensity, a.u.

Wanelength, nm

T= 60oC

S128ZnO/Si(p)

350 400 450 500 550 600 650 700 750 8000,00

0,01

0,02

0,03

0,04

0,05 ZnO (S110/ZnO/Si/100

oC)

T = 300 K (RT)

λexc. = 300 nm

Slitexc. = 5 nm

Slitemm.

= 5 nm

PL Intensity, a.u.

Wanelength, nm

T=100oC

S110ZnO/Si

350 400 450 500 550 600 650 700 750 8000,00

0,03

0,06

0,09

0,12

0,15

0,18

0,21

0,24

0,27 ZnO (S114/ZnO/Si/200

oC)

T = 300 K (RT)

λexc.

= 300 nm

Slitexc.

= 5 nm

Slitemm.

= 5 nm

PL Intensity, a.u.

Wanelength, nm

T=200oC

S114ZnO/Si

350 400 450 500 550 600 650 700 750 8000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6 ZnO (S132/ZnO/Si/130

oC)

T = 300 K (RT)

λexc. = 300 nm

Slitexc. = 5 nm

Slitemm.

= 5 nm

PL Intensity, a.u.

Wavelength, nm

T=130oC

S132ZnO/Si

Optimization of the growth process results in ZnO-ALD thin films in which we do not observe PL from deep dopants levels.

RT PL – Ł. Wachnicki, M. Łukasiewicz

„as grown samples”

Low temperature PL


2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4

20 K

Energy (eV)

7 meV

D0X

He-Cd 325 nm laser

P

L In

tens

ity (

arb.

uni

ts)

Energy (eV)

140 meV

3.27 eV300 K

LT PL – E. Przeździecka

„as grown”

Growth T = 1300C

Electrical properties


For electronic applications a stable and reproducible n- and p-type doping is

obligatory.

nominally undoped ZnO is heavily n-type

Electrical properties


� nominally undoped ZnO is heavily n-type

� EG(RT) ≅ 3.37 eV → intrinsic free carrier n(RT)~106cm-3

� 1017-1021 cm-3 reported for ZnO grown by different techniques!

� very high level of n-doping has been attributed to different types of defects

� carbonates, hydrogen carbonates, zinc interstitials, oxygen vacancies, hydrogen

often introduce very shallow donor levels at ~ 10÷50 meV below the CV minimum

ZnO-based Schottky junction

� Modeling - material requirements

High mobility – high forward current Low n concentration – low reverse current

n electron concentration ~ 1017 cm-3`

Electron mobility ≥ 10 cm2/Vs


Electrical properties of LT-ZnO


60 80 100 120 140 160 180 200 220 240 2601E16

1E17

1E18

1E19

1E20

1E21C

arrie

rs' c

once

ntra

tion

[cm

-3]

Growth temperature [°C]

Series 4 (DEZn) 1000 cycles Series 5 (DEZn) 1000 cycles

n, µ - Hall measurement in the van der Pauwconfiguration (RH2035 system, PhysTech GmbH)

Free carrier concentration can be regulated in a wide range without any intentional doping.

Mobility:µ = 10-50 cm2/Vs

Hall – T. Krajewski

Carrier concentration and mobility good for a Schottky junction

Low Temperature ZnO with DMZn


� difficult ALD precursor (unclear growth window, ZnO quality very different for similar process parameters)

� interesting electrical parameters

� at 2800C-3200C we obtained good monocrystalline ZnO

-39500 -39000 -38500 -38000Qx*10000(rlu)

48000

48200

48400

48600

48800

49000

49200

49400

Qy*10000(rlu)

S

L

F174_m-1-14_DAslit1i8.xrdml

1.5

2.5

4.1

6.9

11.5

19.1

31.8

53.0

88.2

146.7

244.2

406.4

676.4

1125.7

1873.6

3118.1

5189.5

8636.8

14374.1

23922.7

39814.2

RSM , -1-14 refl.

ZnO

GaN

ZnO FWHM =335”GaN FWHM =220”

ZnO has slightly bigger SCREW dislocations

33.6 33.8 34.0 34.2 34.4 34.6 34.8 35.0 35.2 35.42Theta/Omega (°)

0.1

1

10

100

1K

10K

100K

1Mcounts/s

ZnO GaN

XRD – J. Domagała

Optimization of growth temperature

� Low temperature → lower n concentration, polycrystalline films

� High temperature → monocrystalline films, high n concentration


Co wiemy

� Jak kontrolować parametry strukturalne i elektryczne ZnO

� Jak otrzymać monokrystaliczne ZnO (pierwsze wyniki)

� Jak zrobić struktury hybrydowe ZnO/ materiał organiczny

� Jak robić kontakty do n-ZnO (do diod Schottky’ego)


Jak dalej optymalizować wzrost?

� Własności warstw ZnO dopasowane do danego typu funkcjonalizacji

� Optymalizacja kontaktów

� Problem ZnO p-typu

� Struktury ZnO/GaN oraz GaN/ZnO

� Tlenki podbramkowe do struktur HEMT


Opracowanie technologii cienkich warstw ZnO i...

Documents

Transcript of Opracowanie technologii cienkich warstw ZnO i...