novel dielectrics for advanced semiconductor devices Cristiano Krug and Gerry Lucovsky Department of Physics North Carolina State University
Dec 30, 2015
novel dielectrics for advanced semiconductor devices
Cristiano Krug and Gerry Lucovsky
Department of Physics North Carolina State University
outline
band edge states - nanocrystalline HfO2 and ZrO2 theory and experiment inherent limitations
engineering solutions
band edge states - non-crystalline Zr and Hf silicate alloys theory and experiment inherent limitations
engineering solutions
novel device structure experimental result
proposed device structures
research plan
band edge states nanocrystalline HfO2 and ZrO2
theory and experiment
inherent limitations
engineering solutions
theory -- crystal field and Jahn-Teller term-splittings model calculation - ZrO2 band edge d-
statestwo issues
can XAS detect mixtures of
tetragonal and monoclinic nano-
crystallites?
and
can mixtures account for range of defect state energies
in electrical measurements ?
-0.5
0
0.5
1
1.5
2
rea
ltiv
e e
ner
gy
(e
V)
C-FJ-T
tetra.J-T
mono.J-T
mono.z-gb x-gb
sphericallysymmetric
Eg
T2gJ-T - orthorhombic
monoclinicC-F cubic
-0.2
-0.1
0
0.1
0.2
0.3
0.4
531 532 533 534 535 536 537 538 539
photon energy (eV)d
eri
vati
ve a
bs
orp
tio
n (
arb
. u
nit
s)
ZrO2
O K1 edgereactive
evaporation
Eg (2) T2g (3) Eg (2) T2g (4+)
as-deposited MO-RPECVD films by IR are
monoclinic similar result for ZrO2
multiple features in T2g region are indicative of mixture of
monoclinic and tetragonal by XRD
nano-crystallite grains - different for different processing Stefan Zollner’s results at Freescale - XRD and SE
theory -- crystal field and Jahn-Teller term-splittings model calculation - ZrO2 band edge d-
statescan XAS detect
mixtures of tetragonal and
monoclinic nano-crystallites?
YES
model predicts at least 4 features in
T2g band
observed for reactive
evaporation, but not for MO-RPECVD-0.5
0
0.5
1
1.5
2
rea
ltiv
e e
ner
gy
(e
V)
C-FJ-T
tetra.J-T
mono.J-T
mono.z-gb x-gb
sphericallysymmetric
Eg
T2gJ-T - orthorhombic
monoclinicC-F cubic
0
500
1000
1500
2000
2500
3000
3500
4000
4.5 5 5.5 6 6.5
ZrO2
V.V. Afanase'vA. Stesmans
photon energy (eV)
[ph
oto
con
du
ctiv
ity]
1/2
(arb
. u
nit
s)
Eg band edgefeature
band edge"defect state"
model calculations indicate band edge defect state is associated with a Jahn-Teller distortion at internal grain boundary and is intrinsic to nano-crystalline thin films
104
105
106
5 5.5 6 6.5 7 7.5 8 8.5 9
ab
sorp
tio
n c
on
sta
nt
(cm
-1)
photon energy (eV)
Eg (2 features)
band edge"defect state"
T2g (1 of
3 features)
nc-ZrO2
B. Rogers,S. Zollner
-bonded d*-states/defects at conduction band edge in absorption constant (2) andconductivity (PC)
onset of strong optical absorption - lowest Eg state -
optical band
gap
optical band
gap
Z . Yu et al., APL 80, 1975 (2002),
in Chap 3.4 - High-K dielectrics, M. Houssa
(ed), IOP, 2004.
localized band edge J-T d*-states inherent asymmetry in transport and trapping
including BTI’s
trap depth 0.5-0.8 eV, same state PC
and band edge abs.
trapping/Frenkel-Poole transport
tunneling but not F-P x'port
crystal field and Jahn-Teller term-splittings model calculation using Zr and O atomic states
can mixtures account for range of defect state energies
in electrical measurements ?
YES
3x energy scale ~ 0.5 - 0.8 eV
-0.5
0
0.5
1
1.5
2
rea
ltiv
e e
ner
gy
(e
V)
C-FJ-T
tetra.J-T
mono.J-T
mono.z-gb x-gb
sphericallysymmetric
Eg
T2g
-0.5
0
0.5
1
1.5
2
rea
ltiv
e e
ner
gy
(e
V)
C-FJ-T
tetra.J-T
mono.J-T
mono.z-gb x-gb
sphericallysymmetric
Eg
T2gJ-T - orthorhombic
monoclinicC-F cubic
engineering solutions
NEC solution limit applied bias so that injection into
band edge defect states is not possible
modify band tail states by alloying with divalent (MgO) or trivalent oxides (Y2O3)
e.g. Y2O3 in cubic zirconia introduces vacancies random distribution gives cubic structure and eliminates J-T term
splittings, but evidence for absorption associated with excitations to/from midgap state issue: is this state electrically active ?
study has just been undertaken
VUV spectroscopic ellipsometry and UV-VIS
transmission
term-spitting removed - but new absorption band at ~4.1 eV
sub-band-gap absorption - O vacancies
Jahn-Teller term-split d-states of nc-ZrO2 not in Y-Zr-O, but edge
broadened
0
50
100
150
200
3.5 4 4.5
, ab
so
rpti
on
co
nst
ant
(cm
-1)
photon energy (eV)
ZrO2-9.5%Y2O3
"cubic zirconia"ZrO2-9.5%Y2O3
cubic zirconia
4.1 eV
0
1
2
3
4
5
6
7
5 5.5 6 6.5 7 7.5 8 8.5 9
A
ima
gin
ary
par
t o
f d
iele
ctr
ic c
on
sta
nt
(2)
photon energy (eV)
bulk x'tal-90.5% ZrO2
9.5% Y2O3
6.3 eV
5.3 eV
0
2
4
6
8
5 5.5 6 6.5 7 7.5 8 8.5 9
ima
gin
ary
par
t o
f d
iele
ctri
c c
on
sta
nt
(2)
Eg (2 features)
T2g (1st feature)
nc-ZrO2
photon energy (eV)
nanocrystalline ZrO2
5.7 eV
6.2 eV
7.0 eV
8.5 eV
outline
band edge states non-crystalline Zr and Hf silicate alloys
theory and experiment
inherent limitations
engineering solutions
IR results - GB Rayner - PhD thesis, NCSU
Si-O-1 group shoulder ~ 950 cm-1
grows with increasing x in
as-films deposited
changes continuously with annealing in inert
ambient, Ar
SiO2 features at 1068, 810 and 450 cm-1 sharpen up
with increasing Tann
chemical phase separation “non-crystalline” by XRD, but, x=0.23 nano-crystalline by TEM
and EXAFS
4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0
W a v e n u m b e rs (cm -1)
Ab
sorb
ance
(a
.u.)
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
a s d e p .
6 0 0 °C
8 0 0 °C
7 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
x = 0 .1 0 1 0 6 6
8 1 0
4 5 0
4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0
W a v e n u m b e rs (cm -1)
Ab
sorb
ance
(a
.u.)
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
a s d e p .
6 0 0 °C
8 0 0 °C
7 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
x = 0 .1 0 1 0 6 6
8 1 0
4 5 0
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
a s d e p .
6 0 0 °C
8 0 0 °C
7 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
x = 0 .1 0 1 0 6 6
8 1 0
4 5 0
4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0
W a v e n u m b e rs (cm -1)
Ab
sorb
ance
(a.
u.)
F ig u re 3 .7 T h e (a ) IR a b s o rp t io n s p e c tra a n d (b ) X R D re s u lts o f x = 0 .2 3 a llo y a s a fu n c t io n o f a n n e a lin g te m p e ra tu re u p to 9 0 0 C .
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
x = 0 .2 3
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
1 0 6 8
8 1 0
4 5 0
(a )
(b )
4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0
W a v e n u m b e rs (cm -1)
Ab
sorb
ance
(a.
u.)
F ig u re 3 .7 T h e (a ) IR a b s o rp t io n s p e c tra a n d (b ) X R D re s u lts o f x = 0 .2 3 a llo y a s a fu n c t io n o f a n n e a lin g te m p e ra tu re u p to 9 0 0 C .
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
x = 0 .2 3
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
1 0 6 8
8 1 0
4 5 0
(a )
(b )
4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0
W a v e n u m b e rs (cm -1)
Ab
sorb
ance
(a
.u.)
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
a s d e p .
6 0 0 °C
8 0 0 °C
7 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
x = 0 .1 0 1 0 6 6
8 1 0
4 5 0
4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0
W a v e n u m b e rs (cm -1)
Ab
sorb
ance
(a
.u.)
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
a s d e p .
6 0 0 °C
8 0 0 °C
7 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
x = 0 .1 0 1 0 6 6
8 1 0
4 5 0
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
a s d e p .
6 0 0 °C
8 0 0 °C
7 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
x = 0 .1 0 1 0 6 6
8 1 0
4 5 0
4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0
W a v e n u m b e rs (cm -1)
Ab
sorb
ance
(a.
u.)
F ig u re 3 .7 T h e (a ) IR a b s o rp t io n s p e c tra a n d (b ) X R D re s u lts o f x = 0 .2 3 a llo y a s a fu n c t io n o f a n n e a lin g te m p e ra tu re u p to 9 0 0 C .
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
x = 0 .2 3
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
1 0 6 8
8 1 0
4 5 0
(a )
(b )
4 0 06 0 08 0 01 0 0 012 0 01 40 01 6 0 0
W a v e n u m b e rs (cm -1)
Ab
sorb
ance
(a.
u.)
F ig u re 3 .7 T h e (a ) IR a b s o rp t io n s p e c tra a n d (b ) X R D re s u lts o f x = 0 .2 3 a llo y a s a fu n c t io n o f a n n e a lin g te m p e ra tu re u p to 9 0 0 C .
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D eg re es )
Co
un
ts (
a.u
.)
x = 0 .2 3
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
9 0 0 °C
9 0 0 °C
a s d e p .
6 0 0 °C
7 0 0 °C
8 0 0 °C
1 0 6 8
8 1 0
4 5 0
(a )
(b )
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)
Fourier Transform
(a.u.)
x ~ 0.25
As Dep.
900°C
Zr–O
Zr–Zr
(a)
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)
Fourier Transform
(a.u.)
x ~ 0.25
As Dep.
900°C
Zr–O
Zr–Zr
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)
Fourier Transform
(a.u.)
x ~ 0.25
As Dep.
900°C
Zr–O
Zr–Zr
(a)
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)Fourier Transform
(a.u.)
x ~ 0.55
As Dep.
900°C
Zr–O Zr–Zr
(b)
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)Fourier Transform
(a.u.)
x ~ 0.55
As Dep.
900°C
Zr–O Zr–Zr
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)Fourier Transform
(a.u.)
x ~ 0.55
As Dep.
900°C
Zr–O Zr–Zr
(b)
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)
Fourier Transform
(a.u.)
x ~ 0.25
As Dep.
900°C
Zr–O
Zr–Zr
(a)
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)
Fourier Transform
(a.u.)
x ~ 0.25
As Dep.
900°C
Zr–O
Zr–Zr
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)
Fourier Transform
(a.u.)
x ~ 0.25
As Dep.
900°C
Zr–O
Zr–Zr
(a)
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)Fourier Transform
(a.u.)
x ~ 0.55
As Dep.
900°C
Zr–O Zr–Zr
(b)
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)Fourier Transform
(a.u.)
x ~ 0.55
As Dep.
900°C
Zr–O Zr–Zr
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Radius (Angstroms)Fourier Transform
(a.u.)
x ~ 0.55
As Dep.
900°C
Zr–O Zr–Zr
(b)
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D e g re e s )
Co
un
ts (
a.u
.)
As D e p .
6 0 0 o C
9 0 0 o C
8 0 0 o C
7 0 0 o C
(a )x = 0 .2 3
1 0 1 8 2 6 3 4 4 2 5 0 5 8 6 6
2 (D e g re e s )
Co
un
ts (
a.u
.)
( b )
As D e p .
6 0 0 oC
7 0 0 oC
8 0 0 oC
9 0 0 oC
te t rag o n a lZ rO 2
x = 0 .5
comparison of extended x-ray absorption fine structure and x-ray diffraction
crystallite size
difference for x ~ 0.25 and
x ~ 0.5
from HRTEM
x~0.25, ~3 nm
x~0.5, ~10 nm
chemical phase separation (CPS) in Zr silicate and ZrSiON alloys after 900°C annealing
doubly degenerate Eg feature in non-crystalline Zr silicate alloys independent of alloy composition
after 900°C anneal, chemical phase separation and crystallization Eg narrowed/shifted 0.5 eV in Zr silicate, asymmetric in
ZrSiON
6
8
10
12
14
16
18
530 532 534 536 538 540photon energy (eV)
abso
rpti
on
(ar
b. u
nit
s)
Zr silicate alloys
x = 35% ZrO2 non-crystalline
x = 60%ZrO2
phase-separated
non-crystalline
E~0.5 eV
n-c
0
1
2
3
4
530 532 534 536 538 540
Zr, Si oxynitride~20% ZrO2
900oC anneal
Zr 4d*
derivativeabsorption
Si 3s* (Si-O)
photon energy (eV)
abso
rpti
on
(ar
b. u
nit
s)
SiO2
CPS
i) metal ions, Na1+, Ca2+, Y3+,
Zr4+, etc.. disrupt network converting bridging Si-O-Si to
terminal Si-O1- group
ii) number of terminal groups valence of metal ion, 1 for Na, 2 for Ca, 3 for Y and 4 for Zr
iii) connectedness of network defined by shared corners,
Cs between SiO4/2 units
iv) Cs = 4 perfect 3 D network, Cs= 1,0 completely
disrupted mixture of SinOm molecular ions and metal
ions
statistical/mean field disruption of SiO2 network 1:1 representation of silicate alloys
0
1
2
3
4
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
(CaO)x(SiO2)1-x
(ZrO2)x(SiO2)1-x
(NaO1/2)x(SiO2)1-x
(YO3/2)x(SiO2)1-x
corn
ers
sh
are
d/S
i ato
m
alloy composition, x
rate of network disruption increases with valence of metal ion when normalized on a per/atom basis
for x > xo for Cs = 0, silicate is “inverted” and SinOm are minority species
xo
cs = 0
cs
1500 1200 900 600 300
1100C
1000C
900C
as dep.
[a]
abso
rpti
on
(a.
u.)
wave number (cm-1)538 536 534 532 530 528
[b]
sig
nal
leve
l (a.
u.)
O 1s core state energy (eV)
1000C
900C
as dep.
538 536 534 532 530 528
[b]
sig
nal
leve
l (a.
u.)
O 1s core state energy (eV)
1000C
900C
as dep.
(SiO2)0.4(Si3N4)0.25(ZrO2)0.35
pseudo-ternary (SiO2)1-x-y(Si3N4)y(ZrO2)x alloys remote plasma enhanced chemical vapor deposition
as-deposited amorphous alloy – significant Si oxynitride bonding
after anneal at 1000°C – chemical phase separation into SiO2, nanocrystalline ZrO2 with N-bonding
pseudo-ternary (SiO2)1-x-y(Si3N4)y(ZrO2)x alloys remote plasma enhanced chemical vapor deposition
(SiO2)0.3(Si3N4)0.4(ZrO2)0.3
as-deposited amorphous alloy – significant Si oxynitride bonding
after anneal at 1000°C – no chemical phase separation and self-organization encapsulating ZrSiO4
bonding groups
viable engineering solution, k~9-10, EOT to 0.7-0.8 nm
538 536 534 532 530 528
[d]
sig
nal
str
eng
th (
a.u
.)O 1s core level energy (eV)
900C
as dep.
1000C
538 536 534 532 530 528
[d]
sig
nal
str
eng
th (
a.u
.)O 1s core level energy (eV)
900C
as dep.
1000C
1500 1200 900 600 300
1100C
1000C
900C
as dep.
[c]
abso
rption (a.
u.)
wave number (cm-1)
novel device structures (one example)
experimental results for Ge-SiO2
no preoxidation C-V is as good as the best discussed by
Saraswat of Stanford Univ. at Workshop on Future Electronics
2005
two approaches
i) 15 oxidation followed by plasma nitridation
ii) grow 3-5 atomic layers of pseudo-morphic Si on Ge and
oxidize surgically to prevent Ge-O bond formation use on-line
AES
this worked in mid-late 80's, but was not followed-up
Ge – direct deposition of SiO2 with & without pre-oxidation, 0.5-0.6 nm
same as RPAO step for GaN
pre-oxidation of Ge leads to an
increase in Dit, but a decrease in negative fixed charge – next step
interface nitridation!
-Qf
Dit
~Vfb
0.4 -cm n-type - Al
research plans
device testing - ZrO2-Y2O3 and atomically engineered ZrSiON alloys
nitrided Ge interfaces - two approaches
nano-scale vertical p-n junctions (~25 nm diameter!) a precursor to vertical MOS devices
(SRC patent application in process)