Prof. J. Raynien Kwo 郭瑞年

Advances in Oxide Electronics Research:

From High Gate Dielectrics to Diluted Magnetic Oxides

Part I. High Gate Dielectrics

Oxide Electronics

High Tc Superconductors

Memory Devices

DRAM,FRAM

DielectricsHigh

Ferroelectrics

Magnetic Oxides For Spintronics

Epitaxial OxidesMaterials

Integration

Field Effect Devices

Gate oxide

OptoelectronicsTransparent Conductors

Sensors

The Development of Oxide Electronics in Two Decades

近來大力推動奈米科技的背景Moore‘s Law : 摩摩摩摩A 30% decrease in the size of printed dimensions every two years.

來自微電子學可能遭遇瓶頸的考慮

矽晶上電子原件數每兩年會增加一倍

Intel Transistor Scaling and Research Roadmap

High Performance LogicLow Operating Power Logic

CMOS scaling , When do we stop ?

25 22 18 16 Å

15 Å

Reliability:

Tunneling :

In 1997, a gate oxidewas 25 silicon atoms thick.

In 2005, a gate oxidewill be 5 silicon atoms thick, if we still use SiO2

.

.

.

and at least 2 of those 5atoms willbe at theinterfaces.

processing and yield issue

Design Issue: chosen for 1A/cm2 leakageIon/Ioff >> 1 at 12 Å

Bonding: Fundamental Issues--- • how many atoms do we need to get bulk-like properties? EELS -- Minimal 4 atomic layers !!• Is the interface electronically abrupt?• Can we control roughness?

AlAl22OO33 YY22OO33 HfO2 TaTa22OO55 ZrOZrO22 LaLa22OO33 TiOTiO22

3.93.9 9.09.0 1818 20 2525 2727 3030 8080

Band gap (eV)Band gap (eV) Band offset (eV)Band offset (eV)

9.09.0 3.23.2

8.88.8 2.52.5

5.55.52.32.3

5.71.5

4.54.5 1.01.0

7.87.8 1.41.4

4.34.32.32.3

3.03.0 1.21.2

Free energy of formation Free energy of formation MOMOxx+Si+Si22 M+ SiO M+ SiO22

@727C, Kcal/mole of MO@727C, Kcal/mole of MOxx

-- 63.463.4 116.8116.8 47.6 -52.5-52.5 42.342.3 98.598.5 7.57.5

Stability of amorphous Stability of amorphous phasephase

HighHigh HighHigh HighHigh Low LowLow LowLow HighHigh HighHigh

Silicide formation ?Silicide formation ? -- YesYes YesYes Yes YesYes YesYes YesYes YesYes

Hydroxide formation ?Hydroxide formation ? -- SomeSome YesYes Some SomeSome SomeSome YesYes SomeSome

Oxygen diffusivity Oxygen diffusivity @950C (cm@950C (cm22/sec)/sec)

2x 102x 10--

1414 5x 105x 10-25-25 ?? ? ?? 1010-12-12

?? 1010-13-13

Dielectrics

Dielectric constant

Basic Characteristics of Binary Oxide Dielectrics

SiO2

-- Major problems are : High interfacial state density Large trapped charge Low channel mobility Electrical stability and reliability

Electrical characterization / optimization

Low electrical leakage is common . Have Attained an EOT under 1.0-1.4 nm .

-- Good News !!

Low defect high ultrathin films --Interface engineering --Electrical characterization and optimization

Identify new material candidates for metal gate --Metal gate/high integration

Integration of high , and metal gate with Si- Ge strained layer, or with strained Si

High dielectrics for high mobility semiconductors like Ge and III-V semiconductors

Research Programs

oxideoxideMBEMBE

in-situin-situXPSXPS

oxide oxide & metal& metal

MBEMBE

III-VIII-VMBEMBE

Si-GeSi-GeMBEMBE

annealingannealing& metal& metalchamberchamberWafer in

Multi-chamber MBE Within-situ Analysis System

In-situSPM

Functional Functional chamberchamber

metalmetalchamberchamber

Major Research Topics• Novel MBE template approach for ALD

growth • High dielectrics on III-V semiconductors • Enhancement of in the new phase

through epitaxy • Fundamental study by IETS for detections

of phonons and defects in high dielectrics• Diluted magnetic oxide Co-doped HfO2

Novel MBE template for ALD growth

Can you make an excellent HfO2 Film

With low EOT ?

Interface Engineering !

Deposited by MBE

Structural properties of MBE-grown HfO2

HRTEM

RHEED

HRTEM

atomically order Si(100) surface

amorphous HfO2 surface

IL (1.4 nm)

HfO2(3.6nm)

Deposited by ALD

No IL !!

The MBE Template for ALD Growth

MBE and ALD composite film deposition procedure

Silicon

MBE Al2O3

MBE HfO2

MBE template film growth

ALD Al2O3

ALD HfO2

ALD bulk film growth

Case 1

MBE Al2O3

ALD Al2O3

MBE HfO2

Case 2ALD HfO2

• Low pressure ( <1x 10-8 torr ) maintained during MBE growth• ALD precursors : TMA, H2O, Tsubstrate : 300℃

The structure of ALD Al2O3 with a MBE Al2O3 template

Silicon

ALD Al2O3

MBE Al2O3

AR-XPSTEM

No SiO2 formed at interface for both MBE and MBE+ALD Al2O3

No peak formed at 103.4eV

ALD Al2O3 (1.9nm) with MBE (1.4nm) Al2O3 template

= 8.9EOT=1.41nmVfb= -0.6V

Dit : 2.2 E11 cm-2eV-1

(By conductance method)

Silicon

ALD Al2O3

MBE Al2O3

[1]. CVC model provide by NCSU, Dr. John Hauser

Consistent with twoparallel capacitor plates In series

• High dielectrics on III-V semiconductors • Enhancement of in the new phase through

epitaxy

Can you make even higher ?

Dielectrics SiO2 Al2O3 GGG Gd2O3 Sc2O3 HfO2

Dielectric constant 3.9 9.0 12 14 13 15 - 20

Band gap (eV) 9.0 8.8 5.4 5.4 6.5 5.7

Breakdown field (MV/cm)

10 5 - 8 3 - 5 3.5 ? 5

Hydroxide formation

Slight Some High High Likely Some

Recrytallization temperature

> 1100C

~ 750C > 850C

> 900C

?

~500C

Thermal stability in contact with GaAs at high T

? ~700C ~ 850C ~ 850C ?

?

WSi2 gate

compatibilty

? ? ? Reacted at 530C

? ?

Basic Characteristics of Binary Oxide Dielectrics

HRTEM of Low Temp Growth of HfO2 on GaAs

A very abrupt transition from GaAs to HfO2 over one atomic layer thickness was observed.

Amorphous HfO2 on GaAs (100)

56 Å56 ÅHfOHfO22

GaAsGaAs

High Resolution TEM Images of Pure HfO2 on GaAs (001)

An abrupt transition from GaAs to HfO2 and no interfacial layer

Coexistence of four monoclinic domains rotated by 90º.

The Structure of Pure HfO2 Grown on GaAs(001)

Monoclinic phasea=5.116A, b=5.172A, c=5.295A, =99.180

Coexistence of 4 domains rotated 90º from each other 9.2º

HA

KA

H

K

L

HB

KB

Thickness is about 43A

Can you make even higher ?

Phase transition engineering !

HfO

Crystal structures of HfO2

and the corresponding

The dielectric constant increases when HfO2 structure is changed from monoclinic to other symmetry

Dielectric constants 29 70 16 * 26.17 20 **

* Xinyuan Zhao and David Vanderbrit, P.R.B, VOL. 65, 233106, (2002).

Stable phase temperature >2700oC >1750oC <1750C

** G-M. Rignanese and X. Gonze, P.R.B, VOL. 69, 184301, (2004).

Structure of HfO2 doped with Y2O3

Grown on GaAs(001)

Find many peaks:• (022)(400)(200)(311)(31-1)(113)(420)(133)(20-2)• All peaks of the film match the JCPDS of cubic phase HfO2 • Use the d-spacing formula to fit the lattice parametersHfO2 doped with Y2O3 grown on GaAs(001) is CUBIC

Cubic phasea=5.126A, b=5.126A, c=5.126A

α=90,β=90, γ=903.4 3.6 3.8 4.0 4.2 4.4 4.6 4.810-410-310-210-1100101102103104105106107108109101010111012101310141015

YDH(004)

GaAs(040)YDH(040)

YDH(400)

GaAs(004)

YDH(004) L-scan YDH(400) H-scan YDH(040) K-scan

I det/I m

on

L/H/K(r.l.u_GaAs)

GaAs(400)

h

l

k

(004)

(400)(040)

0 90 180 270 360

1E-3

0.01

I de

t/I mon

Phi(degree)

FWHM~3.091(degree)

YDH(040)/(400) phi scans

1x 1.1x

Comparison between Monoclinic phase and Cubic phase of HfO2

Without doping Y2O3

Monoclinic phase

200 & 220 L scan

With doping Y2O3

Cubic phase

200 L scan

220 Lscan

x

yA

AB

C

DD

B

A

B

CD

D

B

C

The Electrical Property of HfO2 doped with Y2O3 Grown on GaAs(001)

=32T=110A

GaAs(001)

Y2O3+HfO2

-1 0 1 2 3 40.00.51.01.52.02.53.03.54.04.5

100k 50k 30k 10k

C(

F/cm

2 )

V (volts)

-6 -4 -2 0 2 4 610-9

10-7

10-5

10-3

10-1

101

YDH/GaAs HfO

2/GaAs

J (A

/cm

2 )E (MV/cm)

MBE-HfO2 (0.8) /Y2O3 (0.2)

Electrical properties - MBE-HfO2 (0.8) /Y2O3 (0.2)

Increase of from 15 to over 30 !

Annealing Temperature effects

-2 -1 0 1 2 30

25

50

75

100

125

150

175

200-2 -1 0 1 2 3

0

25

50

75

100

125

150

175

200

TiNMBE-HfO2 +Y2O3

P-Si(100)

10 nm

TiNMBE-HfO2 +Y2O3

P-Si(100)

10 nm

TiN/MBE-HfO2 (0.8)/Y2O3 (0.2)(~10nm)/P-Si FG 400oC 30min

1k 10k 100k

Cox

(pF)

V (voltage)-3 -2 -1 0 1 2 3 4 5

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8-3 -2 -1 0 1 2 3 4 5

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.010-8

10-6

1x10-4

10-2

100

102

E (MV/cm)

J g (A

/cm

2 )

k ~ 10

k ~ 17.9

k ~ 30.1

As-deposited RTP 800oC 20s N2

RTP 900oC 20s N2

MOS diodes of TiN/HfO2(0.8)

/Y2O

3(0.2)/p-Si(100)

Different RTP conditions

V(voltage)C

(uF/

cm2 )

HRTEM image of yttrium-doped HfO2 films 11 nm thick on GaAs (001).

HRTEM image of yitturm-doped HfO2 films 7.5 nm thick on Si (111).

Cross Sectional HRTEM Study of The Y-doped HfO2 Films in Cubic Phase

5nm

[001]YDH

[1-10]YDH

[001]GaAs

GaAs

YDH

11nm

⊙ =[110]YDH

⊙ =[110]GaAs

Interfaces of YDH(100)/GaAs, and YDH(111)/Si are atomically sharp

The Enhancement of through “Phase Transition Engineering”

Change of molar volume of Y doping HfO2

m/ Vmm/ Vm

Clausius-Mossotti Relation

The high materials, such as HfO2, ZrO2, TiO2, or Ta2O5, commonly have a high temperature phase with a high dielectric constant. We plan to achieve the enhancement through phase transition engineering by additions of dopants such as lower valence cations, followed by proper post high temperature anneals.

IETS Study to Detect Phonons and Defects in High Dielectrics

But what is inside of high ?

Degradation of Mobility in High Gate Stack

Phonons may have reduced mobility seriously !

Correction from the charge trapping effect

Fechetti et al, JAP90, 4587, (2001).

Elastic tunnel current increases linearly with the potential difference biased on both electrodes; while, inelastic electron tunneling occurs at the characteristic energy of vibrational levels.

(b) The I-V curve, conductance-V curve, and the IETS spectrum would result from both elastic processes and the inelastic tunneling channels.

Inelastic Electron Tunneling Spectroscopy

Trap-Related Signatures in IETSI

V

V

Trap Assisted Tunneling

Background I-V

Charge Trapping

Charge Trapping

Trap Assisted Tunneling

2

2

dVId

Wei He and T.P.Ma, APL 83,2605, (2003) ; APL 83, 5461, (2003)

Interactions Detectable by IETS

Substrate Silicon Phonons Gate Electrode Phonons Dielectric Phonons Chemical Bonding (Impurities) Defects (Trap States)

Al/HfO2(40 A)/n-type Si

Electrical stress induced traps in Al/HfO2/Si structure

Determination of trap energy and location in staked HfO2/Y2O3/Si structure

IETS of Si MOS Devices made of High Gate Dielectrics

IET spectrum of Al/HfO2/Si MOS structureIET spectra of the MBE-grown HfO2(~25Å)annealed at 600oC in vacuum for 3 minutes

0 25 50 75 100 125 150 175 200

Voltage (mV)

d2 I/dV

2 (A

rbitr

ary

Uni

ts)

InitialAfter 200 sec 400 sec 800 sec -1.2 V, DC stress1

Forward-bias (gate positive)

The features of trap-assisted tunneling

0 25 50 75 100 125 150 175 200 Voltage (mV)

Electrical stress induced traps in Al/HfO2/Si MOS structure annealed at 600oC in vacuum

•The IETS spectra of HfO2 change slightly after electrical stress.

•The trap assisted tunneling are observed in IETS spectra after

400 sec DC stress at -1.2V.

Substrate Si(100)

Y2O3 ~2nm

HfO2 ~2nm● ● ● Charge trapping

dt

Determination of Physical Locations and Energy Levels of Trap in Stacked HfO2/Y2O3/Si Structure

rfrft VVVVV /

rfft VVVdd /0

Vf and Vr are the voltages where the charge trapping features occur in forward bias and reverse bias.

d0

M. Wang et al,APL. 86, 192113 (2005)APL, 90, 053502 (2007)

Major Accomplishments First demonstration of atomically abrupt high HfO2/Si interface by the MBE process, and employed as a MBE template for ALD.

With a novel MBE template for ALD growth, we have achieved excellent electrical properties (ID of 240 mA/mm and gm of 120 mS/mm) in HfO2 MOSFETs, compared very favorably to the results reported by other major groups.

Passivation of the GaAs surface by high dielectrics HfO2 in both amorphous and epitaxial films with sharp interfaces. Stablization of the cubic HfO2 phase with Y doping by epitaxy at 600C on GaAs (100) as well as on Si (111) to achieve an enhanced over 33.

Major Accomplishments• IETS has detected phonons, defects (traps), and interfacial

structures in ultra-thin HfO2/Si, and stacked HfO2/Y2O3/Si bilayer.

• IETS is capable of monitoring the defect formation with electrical stress applied to dielectrics.

• By using a simple mode, we are able to estimate the energy and physical location of traps in dielectrics.

• MBE grown GGG on n-Ge(100) demonstrated abrupt interface between oxide and substrate. The GeO2 was notably suppressed in the MBE growth process.

• For 600°C annealing, GGG remains good dielectric property, but HfO2 becomes leaky. The better thermal stability of GGG makes it promising for GGG based devices.

Part II: Diluted Magnetic Oxides

Can you make HfO2 magnetic ?

---Observation of Room Temperature Ferromagnetic Behavior in

Cluster Free, Co doped HfO2 Films

Introduction and motivation Both injection and transport of spin-polarized carriers are necessary for the spintronic

devices. Using diluted magnetic semiconductor (DMS) as the ferromagnetic contact is one way to achieve this goal.

Several models such as Zener’s model, bound magnetic polaron, F-center theory and impurity band exchange model were used to describe the

ferromagnetism.

The potential usage of HfO2 as alternative high- gate dielectrics in replacing SiO2 for nano CMOS.

Giant magnetic moment in Co doped HfO2 was reported recently.

Oxygenvacancy

Fe3+ Fe3+

F-center

HR-TEM Images of the High-T and Low-T Grown Films

High-T (700°C) grown film Low-T (100°C) grown film

Characterization of High T (700ºC) Grown Films

EXAFS of the high-T grown samples showed a progressive formation of Co clusters in the film (Co = 1-20 at.%). Superparramagnetic temperature dependence. Saturation moment increases with increasing Co doping concentration.2.04A 2.49A

1st O shell + 2nd Co shell

Structural Characterization of Low-T Grown Films

YSZ

Co:HfO2 1000Å

RHEED pattern shows that Co doped HfO2 film grown at low-T is a poly-crystalline structure. No sign of Co clusters was detected by EXAFS. Co is likely to be at the interstitial site with 2+ sate.

40-100℃

Magnetic Property of low-T grown films

At 10K, the low T-grown Hf0.953Co0.047O2 thin film showed a Ms of 0.47 μB /Co and a Hc of 170 Oe. At 300 K, the Ms and Hc decrease to 0.43 μB /Co and 50 Oe, respectively.

Para + FerromagneticTemp. dependence

Magnetic Property of low-T grown filmsSubstrateTemperature ( ) ℃

40~100 40~100 40~100

Doping concentration (at.%)

4.7 5.5 10

Ms at 10K (μB/Co) 0.47 0.36 0.13

Ms at 300K(μB/Co) 0.43 0.29 0.1

Ferromagnetic behavior was observed at both 10K and 300K. The magnetic moment decreases with increasing Co doping due to enhanced dopant dopant associations.

The magnetic properties are stable after annealing in O2 at 350oC. Correlation between saturationmagnetization with the concentration of oxygen vacancies

F-center Exchange Mechanism: --An electron orbital created by an oxygen vacancy with trapped

electrons is expected to correlate with magnetic spins dispersed inside the oxides.

Impurity-band Exchange Model : --The hydrogenic orbital formed by donor defect (like oxygen

vacancy) associated with an electron overlaps to create delocalized impurity bands.

-- If the donor concentration is large enough and interacts with the magnetic cations with their 3d orbitals to form bound magnetic polarons leading to ferromagnetism.

γ3δp ≈ 4.3, where γ = ε(m/m*)δp : polaron percolation threshold Xp : cation percolation threshold H : hydrogenic radius

Theoretical Analysis Using the Impurity Band Exchange Model

Material ε m*/m γ γH

(nm)δP

(10-6)ZnO 4 0.28 14 0.76 1500TiO2 9 1 9 0.48 5900

SnO2 3.9 0.24 16 0.86 1000

HfO2 15 0.1 150 7.95 1.27

Al2O3 9 0.23 39 2.07 72

δpandxp are two landmarks on the magnetic phase diagram. Ferromagnetism occurs when δ > δp and x < xp.

The δp of HfO2 based DMO was deduced approximately from 1.27×10-6 to 8.15×10-5

The appearance of ferromagnetic insulator behavior in the TM doped HfO2 is more likely than the widely studied TM doped ZnO, TiO2 and SnO2 .

δp : polaron percolation thresholdXp : cation percolation thresholdhydrogenic orbital radius

Major Accomplishment Uniformly doped Co in HfO2 thin films without clusters or second

phases were achieved by low-T MBE growth as confirmed by EXAFS, and are stable up to 350℃ anneals under most ambient.

Ferromagnetic behavior in B-H loops and temperature dependence was observed at both 10K and 300K, and magnetic moment of Mn decreases with increasing Mn concentration (4-10 at.%).

Have ruled out the reported “giant magnetic moment effect”. Found qualitative correlations between the values of saturation

magnetization with the concentration of oxygen vacancies. Consistent with a recently proposed F-center exchange mechanism, or a impurity band exchange model to account for the apparent

ferromagnetism. The appearance of ferromagnetic insulator behavior in the Co doped

HfO2 is more likely than Co doped ZnO, TiO2, and SnO2 systems for doping concentrations under cation percolation threshold.

Acknowledgement

NTHU---Prof. Minghwei Hong, Prof. T. B. Wu Prof. Y. L. SooNSRRC---Dr. Chia-hong Hsu, Dr. H. Y. LeeCCMS---Dr. M. W. Chu, Dr. S. C. Liou, Dr. C. H. ChenNTU---Prof. C. W. LiuNCTU---Prof. A. ChinA.S.---Dr. S. F. Lee

And All of Our Group Students

Group Members: 何信佳博士、 J. P. Mannaerts、吳彥達、李昆育、 李威 縉、朱其新、李毅君、潘欽寒、徐雅玲、邱亦欣、黃建中、杭孟琦摩張宇行、洪宏宜 、游璇龍 、謝政義

Acknowledgement : Thanks to the Support of the NSC National Nano Project

UST/CNST Project , and ITRI/ERSO Project.