Transcript Document

length scales of order and defects in
nano-crystalline and non-crystalline
Hf-based high/medium-k gate dielectrics
Gerry Lucovsky,
NC State University, Dept. of Physics
students and post doc
S. Lee, JP Long, H Seo and L Fleming
collaborators
J Whitten and D Aspnes (NCSU), J Lüning (SSRL),
G Bersuker and P Lysaght (Sematech)
and M Ulrich (ARO/NCSU)
outline of presentation
research objectives
spectroscopic determination of band edge
electronic structure
conduction and valence band states
intrinsic defects
effects of nano-crystalline grain size on
band edge states
band edge defects
an emerging medium-k non-crystalline on SiON/Si
SiO2 look-alike!- tunneling reduced 102-103 at 1 nm EOT
recent results
Hf-based dielectrics directly on Ge substrates
SiO2 look-alike - lowest tunneling leakage!!
research objectives
correlate electronic structure, pre-existing and
stress-induced defects with different
length scales of order
nano-grain size and intermediate range order, respectively
for
nano- and non-crystalline Hf-based dielectrics
 answer this question!!
is there a higher k dielectric with reduced leakage that
has defect properties qualitatively and quantitatively similar
to SiO2 and/or Si oxynitrides currently in CMOS device??
Glen Wilk and I once believed that the
answer would be either a Zr(GL) or Hf(GW) silicate
but we were both wrong!!
they are unstable wrt to chemical phase separation,
but the answer is YES!!
relative d-state band energies, by
NEXAS, SXPS, vis-VUV SE
interpretation - symmetry adopted linear combinations
(SALCs) of atomic states -- FA Cotton – 1962 monograph
symmetry adopted linear combinations (SALC) of atomic
states define molecular orbitals for 6-fold coordinated Ti
conduction band and
valence band states
symmetry and bonding
coordination of TM and O
parentage of TM d-states in
conduction band is easily
resolved in NEXAS O K1 and
SE, but
valence band states are
broader, but spectra are
consistent with SALCs
crystal-field (C-F) splitting
symmetry and coordination
dependent ~ 1.6 to 5 eV
octahedral bonding of Ti with 6 O
Ti
NEXAS
O K1
edge;
SE
O 2p
UPS,
SXPS
valence
band
cooperative Jahn-Teller bonding distortions - TiO2 - anatase-like,
monoclinic Hf(Zr)O2 - degeneracy removalJ-T term splittings
Eg  2 states and T2g  3 states
d[Eg (2)]~d[T2g (3)] ~ 0.5-1.2 eV
comparison - nano-crystalline TiO2 near NEXAS and
Symmetry Adopted Linear Combination (SALC)
anti-bonding MO conduction band states
0.35
octahedral bonding of Ti with 6 O
absorption (arb. units)
O K1
TiO2
0.3
Ti
0.25
0.2
0.15
T2g(3) Eg(2)
3d5/2 *
525
3d3/2 *
530
535
A1g
T1u
4s *
4p *
540
545
550
NEXAS
O K1
edge;
SE
O 2p
UPS,
SXPS
valence
band
X-ray photon energy (eV)
Ti 3d, 4s and 4p atomic contributions
distinct features in NEXAS O K1
consistent with group theory / SALC MO description
SXPS deconvolution of valence band spectrum
O 2p  non-bonding, Ti 3d -states,
Ti 3d, 4s and 4p -states and band edge defect doublet
octahedral bonding of Ti with 6 O
TiO2
60 eV
photoelectron counts
104
3d5/2
T2g
1000
Ti3+
defect
0
2
3d3/2
Eg
Ti
4p
T1u
O2p
nb

4
4s
A1g

d2p3s
6

8
10

nb 

12
binding energy (eV)
14
16

ordering of valence band states -- ---, etc...
NEXAS
O K1
edge;
SE
O 2p
UPS,
SXPS
valence
band
8
10
TiO2
expsilon 2
7
T2g
1
Eg
defect
states
TiO2 - VUV SE
S Zollner, D Tryoso
epsilon 2, 2 (eV)
imaginary part of dielectric constant (2)
relative d-state energies of final conduction band states from
NEXAS and spectroscopic ellipsometry
6
y = -524.86 + 0.99661x R= 0.98362
5
4
0.1
2
3
4
5
6
photon enegy (eV)
7
8
3
529
530
531
532
533
534
535
OK1 photon energy (eV)
NEXAS -- equivalent to vis-VUV SE for IVB, IIIB TM oxides
wrt energy differences of conduction band d-states
NEXAS faster and more direct
can also be applied to ultra-thin dielectrics for devices (~2 nm )
O K1 edges of 900°C Ar annealed ZrO2 and HfO2
on Si with SiON interfaces - film thickness > 4 nm
Eg
4d3/2
absorption (arb. units)
0.8
O K1
T2g
4d5/2
0.7
0.6
ZrO2
Eg
5d3/2
5s
5p
T2g
5d5/2
7-fold coordinated in
monoclinic structure
sd3p3
SALC* MO labeling pseudocubic (8-fold)
asymmetry in ZrO2, and
features in HfO2
J-T degeneracy removal
0.5
6s
0.4
HfO2
6p
 Eg  (T2g + A1g + T1u)
0.3
528
532
536
540
X-ray energy (eV)
544
7-fold coordinated Hf- black in HfO2
5d3 + 6s1 + 6p3 = 7-  states
sd3 - tetrahedron - p3 - pyramid -
band edge defects in HfO2 and ZrO2 - films > 4 nm thick
vis-VUV SE
SXPS
4.5
SXPS VB
60 eV
HfO2
HfO2
4
900oC anneal
3
photoelectron counts
expsilon 2 (2)
3.5
Eg
Hf 5d3/2
2.5
2
1.5
1
2 band edge
defect states
Eg
Hf 5d3/2
104
7 -bonds
5d35/2 + 6s1 + 6p3
T2g + A1g + T1u
defect
states
1000
2 -bonds
5d3/2
Eg
0.5
4.5
5
5.5
6
6.5
7
7.5
8
0
2
4
6
8
10
12
14
16
binding energy (eV)
photon energy (eV)
2 discrete defect states
below conduction band edge
2 discrete defect states
above valence band edge
defect features in X-ray, visible, UV, VUV enhanced by f-sum rule
energy level diagram for band edge defects from
NEXAS, vis-VUV SE and SXPS spectra for HfO2
same diagram - reduced band gap, 5.5 vs 5.7 eV for ZrO2
7
6
HfO 2 conduction band
energy (eV)
5
electron traps
XAS, SE
4
3
2
hole traps
SXPS
1
0
HfO 2 valence band
-1
0.001
0.01
local
density0.1of states
1
films are
O-deficient - mixture of
HfO2 (Hf4+) and
Hf2O3 (Hf3+)
defects described by
clustered O-atom
vacancies or
equivalently Hf3+ states
clustered at internal
grain boundaries for
nano-grains > 4 nm
diagram verified by
cathodo-luminescence
CLS results
cathodo-luminescence spectra CLS
electrons in - keV’s - photons out from defect transitions
Brillson group at Ohio State University
7
HfO2
104
6
Eb = 4 keV
1000
2, 6
2.7 eV
4
100
3.4 eV
HfO2 CB
Edge (cb)
D(cb)1
5
energy (eV)
CL instensity (arb. units)
900oC RTA
4.2 dV
4
3
D(cb)2
1
2
3
2
5
6
7
a
D(vb)1
Gaussian fits
1, 5
4
1
a
0
D(vb)2
Edge (vb)
5.5 eV
3, 7
HfO2 VB
-1
10
2
3
4
5
photon energy (eV)
deconvolution of spectrum for
bulk excitation in thick HfO2
6
local density of states
mapping of Gaussians onto
edge states - SXPS, SE, XAS
band edge defect spectral features
ZrO2 XAS, VUV SE, PC
absorption constant (cm-1)
0.8
0.7
0.65
0.6
105
defect
absorption
optical gap
~5.5 eV
0.47
0.4
528
0.46
T2g (4d5/2)
state
104
3
gaussian fit
d-state bands
ZrO2
530
532
534
536
538
540
542
0.45
O-atom
defect
vacancy
state
0.43
0.42
0.41
0.4
528
529
530
5
6
7
8
9
4000
photon energy (eV)
Eg (4d3/2)
0.44
4
photon energy (eV)
(arb. units)
0.5
O-atom
defect Eg (4d3/2)
vacancy
Eg (2)
VUV SE
0.55
0.48
0.45
absorption (arb. units)
gaussian fit
d-state bands
ZrO2
O K1
T2g (1 of 3)
[photoconductivity]1/2
absorption (arb. units)
0.75
nc-ZrO2
B. Rogers,
S. Zollner
106
531
532
533
photon energy (eV)
534
535
3500
ZrO2
V.V. Afanas'ev
A. Stesmans
Eg band edge
feature
3000
2500
2000
1500
band edge
"defect state"
negatively charged
O-atom vacancy
PC
1000
500
0
4.5
5
5.5
photon energy (eV)
6
6.5
correlations between grain-size and defects
nano-scale of order, lcoh (-bonding)
~3-3.5 nm for Hf(Zr)O2
suppression of Jahn-Teller d-state degeneracy splittings
when grain size </~ 2 nm
length scale factor for inter primitive unit cell (PUC) coupling
coherence of -bonding - analog to super exchange in MnO
Mn spins in adjacent PUCs coupled thorugh O’s
-bonding couples metal
atoms, M, in neighboring PUCs
through their nearest neighbor
O-atoms
PUC
1
2
3
primitive unit cells (PUCs)
1/nO-Hf-O1/n (n=3, 4)
labeled as 1, 2 and 3
-bonding orbitals
phase reversal of 2nd nearest
neighbor O-atoms
alternating phase of 2nd
M-atoms
(same phase reversing as for
spins in A-F MnO)
length scale, lcoh, for
J-T splitting
~ 6-7 PUCs or ~3-3.5 nm for
coherent -bonding effects
kinetic and dimensional constraints suppress
Eg - -bond state J-T splittings in O K1 edge spectra
0.45
O K1
HfO2
4 nm
absorption (arb units)
0.4
A1g
0.35
T1u
3 nm
0.3
2 nm
Eg
0.25
0.2
528
530
532
T2g
534
536
538
540
542
544
x-ray photon
photonenergy
energy(eV)
(eV)
X-ray
kinetic
as-dep. 300°C, 500 °C anneal
no J-T splitting
700°C, 900°C anneals J-T splitting
“dimensional”
2 nm thick film no J-T splitting
3 and 4 nm thick films
J-T splitting
differences in band edge defects in HfO2
discrete states and sharp NEXAS edge for tphy > 3nm,
band tail defects and softer edges for tphys ~ 2 nm
0.45
O K1
HfO2
A1g
0.35
T1u
3 nm
0.3
2 nm
Eg
0.25
0.2
528
530
532
T2g
534
536
photoelectron counts
4 nm
0.4
absorption (arb units)
SXPS
60 eV
HfO2
4 nm
104
defects
2 nm
1000
-5d3/22
-5d5/23 + 6s1 + 6p3
538
540
542
544
x-ray photon
photonenergy
energy(eV)
(eV)
X-ray
softer edge for tphys = 2 nm
compared to tphys = 3, 4 nm
100
0
5
10
15
normalized bonding energy (eV)
band tail defects - tphys = 2 nm
discrete defects - tphys = 4 nm
differences in band edge defects
for kinetic constraint
700 oC
300 oC
band
edge
defect
states
5d3/2
Eg
5.5
5
1000
band tail
states
100
40
42
44
46
48
50
52
54
56
soft x-ray photon energy (eV)
absorption (arb. units)
104
HfO2
6 nm
OK1
4.5
4
3.5
3
900oC
700oC
500oC
5.5
HfO2
6 nm
OK1
5
absorption (arb. units)
photoelectron counting rate
HfO2
4 nm
VB spectrum
2.5
5d3/2
Eg
6p
535
540
545
x-ray photon energy (eV)
300, 500°C suppression J-T and
broader features wrt 700&900°C
300°C band tail defect at VB edge
discrete defects after 700°C anneal
3.5 900oC
700oC
500oC
2.5
6s
300oC
530
4
3
5d5/2
T2g
2
slope
1.4
4.5
5d3/2
Eg
slope
1.0
300oC
2
530
531
532
533
534
535
x-ray photon energy (eV)
to obtain electrical defect densities, must apply f(N) sum rule
matrix element enhancement, ~ 50-100x for discrete defects
electrical properties in HfO2 MOSCAPs with
discrete band edge defects (tphys > 4 nm)
C-V and J-V measurments
Si-SiO2-HfO2 gate stacks
Massoun et al., APL 81, 3392 (2002)
Z. Xu et al., APL 80, 1975 (2002)
substrate injection
holes
substrate
injection
electrons
gate
injection
electrons
traps are in high-k material of stack
2x1013 cm -2 --  ~ 1.5x10-17 cm-2
coulombic center - lower x-section
than Pb centers in Si substrate
screened by high dielectric
constant of HfO2
electron trap ~0.5 eV below conduction
band edge HfO2
J-V asymmetry - IMEC model
continuity of E - (SiO2) ~ 3.9 < (HfO2)~20
asymmetry in potential distribution across stack
traps accessible for injection
from n-type substrate using midgap gate metal - TiN
traps not accessible for injection
from mid-gap metal -- TiN
from M. Houssa, IOP, Chapter 3.4
Lucovsky group NCSU
0.01
0.001
>500x
>1000x
0.0001
current (A)
>500x
substrate
electron
injection n-Si
into SiO2/HfO2
F-P hopping
DE~0.5 eV < CB
HfO2
10
-5
10
-6
20x
200oC
25oC
10-7
10-8
10-9
0
0.5
1
1.5
2
2.5
gate voltage (V)
1.0 10-6
substrate hole
injection n-Si
into SiO2/HfO2
interface
EOT~1.7 nm
capacitance (F-cm-2)
EOT~7 nm
8.0 10-7
6.0 10-7
10 khz
4.0 10-7
100 khz
1 Mhz
2.0 10-7
-1
-0.8
-0.6
-0.4
-0.2
gate voltage (V)
C-V -- surface potentials of Si substrate are negative!!  hole injection
0
intrinsic band edge defect states
grain-boundary defects – suboxide bonding - trivalent Hf3+
~/>5x1018 cm-3 - ~/>3x1012 cm-2 clustered on grain boundaries
0.01
7
0.001
HfO2 conduction band
5
electron traps
XAS, SE
4
20x
10-5
trap-assisted
transport of
electrons through
empty states
200oC
10-6
25oC
10-7
10-8
3
10-9
2
1
0
0.5
1
1.5
2
2.5
gate voltage (V)
1.0 10-6
occupied
hole traps
SXPS
8.0
0
HfO2 valence band
0.01
local
density0.1of states
10-7
EOT~1.7 nm hole
trapping into
partially-occupied states
6.0 10-7
-1
0.001
capacitance (F-cm -2)
energy (eV)
empty
>500x
>1000x
0.0001
current (A)
6
1
band edge and paired
band edge defects in HfO2
10 khz
4.0 10-7
100 khz
1 Mhz
2.0 10-7
-1
-0.8
-0.6
-0.4
gate voltage (V)
-0.2
0
electrical properties in Hf Si oxynitride MOSCAPs
electrical measurements and X-ray stress
O1s - d(intensity)/dE (a.u.)
(ZrO2)0.42(SiO2)0.42
(Si3N4) = 0.16
SiO2
Zr (also Ti, Hf) Si oxynitrides
extends EOT to ~0.7-0.8 nm
ZrO2
ZrO2
o
1000 C RTA
high Si3N4 content
Zr(Hf) Si oxynitrides
stable against chemicalseparation
0.0 1.0
o
900 C RTA
0.2
0.8
as-deposited
0.4
538
536
534
532
530
528
binding energy (eV)
0.6
low Si3N4 content
Zr(Hf) Si
oxynitrides
chemicallyseparate
O1s - d(intensity)/dE (a.u.)
0.6
0.4
0.8
1.0
0.0
0.2
0.2
0.4
0.6
0.0
1.0
0.8
Si3N4
SiO2
(ZrO2)0.3(SiO2)0.3
(Si3N4) = 0.40
o
o
900 C RTA
as-deposited
536
534
Cav (0.33,0.33,0.33) = 2.9
Cav (0.30,0.30,0.40) = 3.2
intermed. phase Si3N4 0.33-0.4
fraction strained [SiN4/3]~0.20
below strain percolation limit
however -relative concentration of Hf/Si
~ 16% suggests a percolation
of the low Cav
B'
H'
N'
B
1000 C RTA
538
tetrahedrally-bonded
Zr to O
encapsulated in
Si-N cages
532
530
binding energy (eV)
528
phase-separated Zr/Hf silicates
20 % SiO2
SiO2 "islands"
encapsulated by
connected
Zr/HfO2 grains
limits Zr/HfO2
grain size
5 nm
SiO2 is black
55-65% SiO2
SiO2 partially encapsulates Zr/HfO2 is white/grey
Zr/HfO2 grains
75% SiO2
SiO2 encapsulates
Zr/HfO2 grains
O K1 XAS spectra same before and after 900°C anneal
2nd derviative absorption (arb. units)
0.3
ZrSioxynitride
annealed
0.25
oC Si3N4
900
absorption (arb.units)
0.35 0.2
as-deposited
non-crystalline
0.3 0.1
0.25
0
E T2
-0.1
0.2
900oC anneal
3N4)0.4(ZrO2)0.3
D(SiO
E2g2)0.3(Siphase-separated
1.0 eV nanocrystalline ZrO2
-0.2
0.15
-0.3
530
530
535
532
540
534
536
545
photon energy (eV)
photon energy (eV)
538
550
540
2nd derviative absorption (arb. units)
because of overlap of O, N features in O K1 with Zr d-states
must extract slitting by differentiation
D E()-T
2()
2.2
eV
Eg-Tg
= 2.2DeV
0.15
ZrSioxynitride
0.4 Si3N4
0.1
900oC
anneal
0.05
0
as-deposited
-0.05
no CPS
-0.1
530
532
534
536
538
540
photon energy (eV)
cubic zirconia (Y2O3 alloy)
D E() - T2g() = 4.8 eV
ratio = 2.2±0.3 eV ~ = 8/4 = 2
0.4
analysis of spectral data
N-Si-O
N
Si
O
Zr
order of bonding Zr-O-Si-N
"viewed" from O in O K1
and N in N K1
Cav ~ 3.0 due to chemical
ordering/broken constraints on Si
Si-O
O-Si-N
0.3
0.25
Si-O-Zr
0.2
0.15
0.1
532
534
536
538
540
542
544
546
x-ray photon energy (eV)
0.25
0.24
absorption (arb units)
cavity
0.35
absorption (arb units)
tetrahedrally-bonded Zr (Ti,Hf) in
high Si3N4 Si oxynitrides
ls ~1 nm
O K1
Zr SiON
N K1
Zr SiON
N-Si-O
N-Si
0.23
0.22
N-Si-O-Zr
0.21
0.2
0.19
0.18
398
400
402
404
406
408
x-ray photon energy (eV)
410
105
16% Si3N4
occupied
defects
hole traps
40% Si3N4
consistent with
high level of
defects observed
in C-V trace
Ti Si oxynitrides
as-deposited
SXPS
60 eV
104
1000
2
4
6
8
10
12
16% Si3N4 alloy
shows high defect
level alloy
spectroscopically
14
energy (eV)
40% Si3N4 alloy shows sharper valence band
edge and lower defects spectroscopically
consistent with high level of defects
observed in C-V trace
normalized capacitance, C/Cox
counting rate (arb units)
106
1.1
1
Hf Si oxynitrides
(a): 40% Si3N4
(b): 18% Si3N4
0.9
(a) 40% Si3N4
Vfb = -0.026+/-0.03 V
(b) 18% Si3N4
Vfb = 0.035+/-0.03 V
0.8
0.7
DVfb= -0.06+/-0.005 eV
0.6
0.5
Qif = 0.5+/-0.05x10-12 cm-2
(b)
(a)
0.4
-1.5
-1
-0.5
0
0.5
1
gate voltage (V)
1.5
2
0.7
normalized capacitance, C/Cox
spectroscopic detection of
defects by soft X-ray XPS
valence band spectroscopy
0.65
Hf Si oxynitrides
(a) 40% Si3N4
(b) 18% Si3N4
0.6
0.55
(b)
10 kHx to
1 MHz
DV= 0.14 eV
dit = 1.1x10-12 cm-2
0.5
(a)
0.45
-1
100 kHx and
1 MHz
-0.8
-0.6
-0.4
gate voltage (V)
-0.2
J-V measurements sharp
minimum in gate leakage, direct
tunneling consistent with low
level of trap-assisted tunneling
gate leakage current (A-cm-2)
0.001
measurements at VU have
demonstrated
ii) only positively charged defects
by X-ray stressing
iii) rate of defect level generation
approximately same as SiO2
0.0001
10-5
(e)
10-6 (a)
(b)
(c)
10-7
10-8
0.5
(d)
1
1.5
Vg-Vfb (V)
2
2.5
10-5
reduced gate leakage current (A-cm-2)
i) defect levels in 40% alloy films
comparable to SiO2
Hf Si oxynitrides
(a) 18%, (b) 25%, (c) 30%
(d) 40%, (e) 58% Si 3N4
(e)
(a)
(b)
10-6
(c)
10-7
Hf Si oxynitrides
(a) 18%, (b) 25%, (c) 30%
(d) 40%, (e) 58% Si 3N4
10-8
(d)
10-9
0.1
0.2
0.3
0.4
0.5
Si3N4 content (fraction)
0.6
preview radiation induced defects (DK Chen, VU, later in program)
low
Si3N4
high
Si3N4
D(Vfb) vs stress time for
high/low Si3N4 H SiON with
Vg = 1.5 V
injected charge 104 s ~7 x 1015
C/cm2
these plots indicate improved performance of
high Si3N4 HfSiON wrt
i) low Si3N4 HfSiON, and ii) Hf silciates
high
Si3N4
Hf
silicates
total-dose-induced midgap
voltage shifts DVmg's for
high Si3N4 HfSiON
compared with
larger DV's for Hf silicates
HfO2 and TiO2 on Ge – no detectable Ge-N
interfacial transition regions
approach
resonant atom-specific near edge X-ray absorption
spectroscopy (NEXAS) and vis-UV spectroscopic
ellipsometry
O K1 spectra
MO anti-bonding states with Hf, Ti
d, s and p contributions - 2 to 6 nm thick films
N K1 spectra
“buried” nitrided interfaces between
Si (SiON) and Ge (Ge-N) and HfO2 and TiO2
as function of process temperature
comparisons O K1 and vis-UV SE
emphasis of differences/process induced changes
in band edge defects Ge(100) and Ge(111)
buried interface studies - resonant atom-specific
near edge X-ray absorption spectroscopy (NEXAS)
resonant photoemission for O-Hf, O-Ti
anti-bonding states
O K1 525-555 eV
X-rays
HfO2 or TiO2
HfO2 or TiO2
SiON
GeN
Si substrate
Ge substrate
resonant photoemission for Ge-N, Si-N
anti-bonding states
N K1 395-425 eV
X-rays
HfO2 or TiO2
HfO2 or TiO2
SiON
GeN
Si substrate
Ge substrate
HfO2 and TiO2 films are "transparent" to N K1 X-rays and
to decay products after x-ray excitation
N K1 spectra - remote plasma assisted nitridation of Ge (100)
(a) Ge substrate nitridation for
all Ge samples
(b) buried interfaces for
2 nm and 6 nm thick HfO2 films
after 800C anneal.
0.146
3.6
N K1 edge
Ge (100)
(a)
3.5
absorption (arb. units)
absorption (arb. units)
0.144
0.142
0.14
0.138
0.136
395
6 nm HfO2
3.4
800oC anneal
3.3
3.2
2 nm HfO2
800oC anneal
3.1
400
405
410
X-ray photon energy (eV)
strong N-feature for all buried asdeposited interfaces
415
(b)
N K1 edge
Ge (100)
3
395
400
405
410
X-ray photon energy (eV)
no N-feature after 800C
anneal - for both 2 & 6 nm
415
O K1 spectra for HfO2 on Ge(100) with Ge-N interface
as-deposited at 300C - after an 800C 1 min anneal in Ar
(a) 2 nm thick
O K1 edge
Ge (100)
(a)
5d5/2
T2g
4
3.6
5d3/2
Eg
3.2
2 nm HfO2
800oC anneal
6s
A1g
6p
T1u
2.8
2.4
2 nm HfO2
as-deposited
2
1.6
530
5
535
540
X-ray photon energy (eV)
545
absorption (arb. units)
absorption (arb. units)
4.4
(b) 6 nm thick
4.5
4
3.5
(b)
O K1 edge
Ge (100)
5d5/2
T2g
5d3/2
Eg
6 nm HfO2
800oC anneal
6s
A1g
6p
T1u
3
2.5
2
530
6 nm HfO2
as-deposited
535
540
X-ray photon energy (eV)
broad, but different spectra as-deposited -- no J-T Eg splitting
similar sharp spectra after 800C anneal -- J-T Eg splitting
545
O K1 spectra for HfO2 on Si(100) with SiON interface
as-deposited at 300C - after a 900C 1 minute anneal in Ar
(a) 2 nm
(b) 6 nm
5
2.4
900oC
anneal
(a)
4.5
5d5/2
T2g
2
1.8
6s
1.6
6p
as-deposited
1.4
1.2
1
530
5d3/2
Eg
535
540
X-ray photon energy (eV)
absorption (arb. units)
absorption (arb. units)
2.2
O K1 edge
2 nm HfO2
SiON-Si
O K1 edge
6 nm HfO2
SiON-Si
4
(b)
5d5/2
T2g
3.5
3
900oC
anneal
6s
5d3/2
Eg
6p
as-deposited
2.5
545
no J-T degeneracy removal
some sharpening after anneal
dimensional constraint > kinetics
2
530
535
540
X-ray photon energy (eV)
545
J-T degeneracy removal after
800C anneal
kinetic constraint - as-dep
2 nm thick TiO2 on Ge(100) as-deposited at 300C after an 800C 1 minute anneal in Ar
(a) N K1 spectra
(b) O K1 spectra.
4
1.08
1.04
3.5
absorption (arb. units)
absorption (arb. units)
1.12
as-deposited
300oC
800oC
anneal
1
0.96
N K1 edge - 2 nm TiO2
plasma-nitrided Ge (100)
3
2.5
2
1.5
400
405
410
X-ray energy (eV)
as-deposited
300oC
hwhm ~1 eV
1
0.5
395
annealed
800oC
hwhm ~0.5 eV
415
nitrogen removal - 800C anneal
same effect as for HfO2 films
also for N-loss for 6 nm TiO2
O K1
2 nm TIO2
Ge (100)
530
535
540
545
X-ray photon energy (eV)
550
spectral changes - 800C anneal
features sharper - edge hwhm
hwhm on SiON ~0.7 eV
comparison of O K1
spectra for HfO2
5.5
absorption (arb. units)
5
O K1 edge
6 nm HfO2
4.5
4
in contact with noncrystalline SiON interfacial
transition region on Si
Ge
800oC
5d5/2
Eg
5d5/2
T2g
6s
3.5
6p
SiON-Si
900oC
3
2.5
530
535
540
X-ray photon energy (eV)
HfO2
SiON
Si substrate
545
in direct bonding contact
with Ge after elimination of
Ge-N interfacial transition
region
significant Eg differences
qualitatively different
-bonding Hf-O-Hf-O......
HfO2
Ge substrate
changes in absorption (bottom) are qualitatively
the same as changes in CLS (top)
HfO2
1000
CL instensity (arb. units)
CL instensity (arb. units)
900oC RTA
Eb = 4 keV
100
2.7 eV
3.4 eV
HfO2
104
as-deposited 300oC
4.2 dV
Gaussian fits
comparisons
between 2 of HfO2
and TiO2 and
CLS response
Eb = 4 keV
1000
2.7 eV
3.4 eV
4.2 dV
Gaussian fits
100
5.5 eV
5.1 eV
10
10
2
3
4
5
2
6
3
4
5
6
photon energy (eV)
photon energy (eV)
5
0.5
HfO2 on GeN
as-deposited
300oC
0.45
HfO2 on Ge
annealed
800oC
4
defect states
D(vb)2-D(cb)2
epsilon 2 (2)
epsilon 2 (2)
vb-D(cb)1,2
0.4
0.35
0.3
3
vb-D(cb)2
2
D(vb)2-D(cb)2
vb-D(cb)1,2
D(vb)1-D(cb)2
0.25
open circles
Ge(100)
filled circles
Ge(111)
1
0.2
2
2.5
3
3.5
4
4.5
photon energy (eV)
5
5.5
3
3.5
4
4.5
photon energy (eV)
5
5.5
as-deposited on GeN
with interfacial transition
layer
and after 800°C
indirect bonding contact
on
Ge(100) and Ge(111)
surfaces
5
0.5
HfO2 on GeN
as-deposited
300oC
4
defect states
vb-D(cb)1,2
0.4
D(vb)2-D(cb)2
epsilon 2 (2)
epsilon 2 (2)
0.45
HfO2 on Ge
annealed
800oC
0.35
0.3
3
vb-D(cb)2
vb-D(cb)1,2
D(vb)1-D(cb)2
open circles
Ge(100)
filled circles
Ge(111)
2
D(vb)2-D(cb)2
0.25
1
0.2
2
2.5
3
3.5
4
4.5
5
3
5.5
3.5
photon energy (eV)
4
4.5
photon energy (eV)
5
5.5
as-deposited on GeN
with interfacial
transition layer
and after 800°C
indirect bonding
contact with
Ge on both Ge(100)
and Ge(111) surfaces
qualitatively similar changes – as-deposited
to annealed 800°C
10
TiO2 on Ge
annealed
800oC
open circles
Ge(100)
filled circles
Ge(111)
1
epsilon 2 (2)
epsilon 2 (2)
TiO2 on GeN
10 as-deposited
300oC
T2g
open circles
Ge(100)
filled circles
Ge(111)
1
defect
states
T2g
0.1
0.1
vb-D(cb)1
vb-D(cb)1
vb-D(cb)2
2.5
3
3.5
4
4.5
5
photon energy (eV)
vb-D(cb)2
5.5
6
2.5
3
3.5
4
4.5
5
photon energy (eV)
comparisons
between 2 of HfO2
and TiO2
5.5
6
preliminary results
first try I-V for HfO2 and Hf SiON on Ge after anneal
physical thickness ~ 2nm
nominal nrea ~ 0.50E-4cm 2
0.001
HfO2 0n Ge (111)
HfO2 0n Ge (100)
20-30x
0.0001
current (A)
~10x
10-30x lower tunneling
than for HfO2
Hf SiON better dielectric
even though keff is
smaller by ~1.5-2
Eb and m*e are larger
Hf Si oxynitride
10-5
10-6
0
0.5
1
voltage (V)
1.5
difference between Ge(111)
and Ge(100) for HfO2
higher Ge(111) symmetry
more column-like growth
habit  more leakage
checking by TEM
2
Jdt = ~exp(-ak[Eb me*]0.5)
summary of experimental results
length scale, lcoh - coherent Hf d – O p -bond inter-PUC coupling
5.5
HfO2
6 nm
OK1
nano-crystalline
thin films
1.1
phaseseparated
Hf silicates
80% HfO 2
1.08
1.04
1.02
3.5 900oC
500oC
4.5
3.5
slope
1.0
300oC
3
0.5
1
1.5
2
2.5
3
3.5
Eg
Hf 5d3/2
2
1.5
4
length scales, ls
J-T splitting
1.2 eV
2.5
1
0.98
0
HfO2
4
900oC anneal
thin films
bond-lengths,
bond-angles
0.15-0.35 nm
1
700oC
2
530
< 700oC
chemical bonding
Hf Si
self-organizations
oxynitrides
0.6 to 0.8 nm
rings of
bonded atoms
non-crystalline
0.4 - 0.6 nm
4
2.5
type II
tphys
>3 nm
Tproc
>/=700oC
5d3/2
Eg
4.5
3
type I
tphys
<2 nm
Tproc
1.06
slope
1.4
type II
lcoh > 3 nm or > 6 PUCs
J-T splittings and
discrete band-edge
defects
1.12
2 band edge
defect states
Eg
Hf 5d3/2
0.5
106
531
532
533
534
535
x-ray photon energy (eV)
Hf Si oxynitrides- high Si3N4 %
no inter-group Hf d-O p-bonding
no phase-separation, but only for
small range of compositions
very low tunneling, ~12 (to 16-18)
counting rate (arb units)
absorption (arb. units)
5
asymmetric h/e trapping
+/- defects X-ray stress
expsilon 2 (2)
phase-sep. silicates
and type I
lcoh ~ 2 nm or < 5 PUCs
no J-T splittings
and band-tail defects
105
16% Si3N4
occupied
defects
hole traps
4.5
5
5.5
6
6.5
7
7.5
8
photon energy (eV)
40% Si3N4
Ti Si oxynitrides
as-deposited
SXPS
60 eV
104
1000
2
4
6
8
10
energy (eV)
12
14
positive charge defects
- X-ray stress
HfO2 and Hf silicates
both positive/negative
charged defects
direct bonding on Ge(100/111)
electricals being studied and
measurements extended to Ge(111)
HfO2 or TiO2
absorption (arb. units)
1.12
1.08
HfO2 or TiO2
SiON
GeN/GeO
Si substrate
Ge substrate
resonant photoemission for Ge-N, Si-N
anti-bonding states
N K1 395-425 eV
X-rays
as-deposited
300oC
1.04
resonant photoemission for O-Hf, O-Ti
anti-bonding states
O K1 525-555 eV
X-rays
HfO2 or TiO2
800oC
anneal
HfO2 or TiO2
SiON
GeN/GeO
Si substrate
Ge substrate
1
N K1 edge - 2 nm TiO2
plasma-nitrided Ge (100)
0.96
395
400
405
410
X-ray energy (eV)
415
GeO and GeN removed during anneal substrate specific -bonds Ge (100/111)
resonant X-rays reveal buried interface SiON interface Ge-direct different T2g 
10
5.5
4.5
4
5d5/2
Eg
5d5/2
T2g
6s
3.5
6p
SiON-Si
900oC
physical thickness ~ 2nm
nominal area ~ 0.50E-4 cm-2
0.001
open circles
Ge(100)
filled circles
Ge(111)
1
defect
states
0.0001
current (A)
Ge
800oC
epsilon 2 (2)
absorption (arb. units)
5
TiO2 on Ge
annealed
800oC
O K1 edge
6 nm HfO2
T2g
0.1
10-5
annealed HfO2/Ge(100)
annealed HfO2/Ge(111)
annealed HfSiON/Ge(100)
3
2.5
530
10-6
535
540
X-ray photon energy (eV)
545
2.5
3
3.5
4
4.5
5
photon energy (eV)
5.5
6
0
0.5
1
gate voltage (V)
1.5
2
plans for next year
comparisons of HfO2 and ZrO2 with
different length scales on Si/SiON and Ge substrates
Ge work with include deposition of in-situ homo-epi Ge on Ge
to improve surface quality and
hetero-epi of Ge on Si, and GaAs
NEXAS, SXPS and SE spectroscopy
J-V and C-V
compare electrical stress
SILC and N and PBTI with x-ray stress
i) d-state electronic structure of elemental TM oxides
symmetry adopted linear combinations (SLACs) of
atomic orbitals – FA Cotton, 1962 text
ii) conduction band or anti-bonding states in NEXAS
same relative energies as in vis-VUV SE
iii) band edge defects in SXPS, NEXAS and SE
matrix element enhancement of 50-100 - N-sum rule
0.5 eV widths compared with 24-40 eV for band to band
iv) d-state degeneracies suppressed - nano-grains < 3 nm,
band edge defects are changed from discrete states
to band tails and defects reduced > 20-50x
defect densities as low as mid-1011 cm-2
band tails - asymmetric - like discrete states
possible show stopper for CMOS -- different NBTI and PBTI's
v) dielectrics that work Hf Si oxynitrides, high Si3N4
stable to 1100 C, compatible with poly Si (Si,Ge) gates defects
and defect precursors ~ same as SiO2,
very low tunneling current, k's to 16-18 are possible
in Hf,Ti Si oxynitrides