electro-ceramics lab. preparation and electrical properties of (ba 1-x,sr x )(ti 1-y,zr y )o 3 thin...
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Electro-Ceramics Lab.
Preparation and electrical properties of (BaPreparation and electrical properties of (Ba1-x1-x,Sr,Srxx)(Ti)(Ti1-y1-y,Zr,Zryy)O)O33
thin films for application at high density DRAMthin films for application at high density DRAM
Sang-Shik, Park
Dept. of Materials Engineering, Sangju National University,
Sangju, kyungbuk, 742-711, Korea
Electro-Ceramics Lab.
OUTLINEOUTLINE
- High dielectric Constant
- Low leakage current density
- Fast dielectric response
▶ Requirements of capacitor for high density DRAM
Most promising dielectric material : (Ba1-x Srx )TiO3
BST films by CVD,PLD,Sputtering, MOD showed good properties
▶ Requirements of dielectric films for Gbit-scale DRAM application
≪ 25fF/cell in a cell size smaller than 0.1μm2 ≫ - Lower leakage current at thinner film
- Higher dielectric constant and lower loss compared to BST
- Long life time under dc voltage stress
Electro-Ceramics Lab.
IntroductionIntroduction
Ref. ; IBM J. Res. Develop., 43(3), 367 (1999)
BST- Uniformity- Thickness- Composition- Grain size / Orientation
DRAM cell structure and Key issues
Electro-Ceramics Lab.
IntroductionIntroduction
▶ Ti4+ ; major paths of leakage current in BaTiO3, BST
Zr4+ ; More stable than the Ti4+ with respect to Degradation
Study of Ba(Ti1-xZrx) O3
(R. Waser etal, Integrated Ferroelectrics 17, 141 (1997),
T. B. Wu etal, Thin Soild Films 334, 77 (1998))
▶ In this study, Zr doping in BST thin films
- Composition control of (Ba1-xSrx)(Ti1-yZr y)O3 with variation of
chamber pressure
- Effect of composition on structure and electrical properties
of BSTZ film
Electro-Ceramics Lab.
Deposition ConditionsDeposition Conditions
Target
Target diameterSubstratesTarget-substrate distanceBase pressure of systemWorking PressureR.F. Power densitySputtering gas(Ar:O2)Substrate temperature
(Ba0.65,Sr0.35)(Ti0.65,Zr0.35)O3 with 30mole% excess BaCO3 and SrCO3
5.08 ㎝ (2inch)Pt/Ti/SiO2/Si
40mm1x10-6 Torr
5, 10, 30, 50mTorr3.5W/ ㎠
1:1 600℃
Control of Chamber Pressure ; MFC and main valve
Electro-Ceramics Lab.
RBS AnalysisRBS Analysis
0 100 200 300 400 5000
1000
2000
3000
4000
5000 (a)
(Ba0.66
,Sr0.32
)(Ti0.54
,Zr0.56
)O2.92
Sr
O
Si
Ti
Zr
Ba
Experimental Theoretical
Yie
ld
Channels
0 100 200 300 400 500 600 7000
20
40
60
80
100
Ba;13.20, Sr;6.07, Ti;8.94, Zr;13.34, O;58.45
(b)
Ba
Si
SrTi
Zr
O
Co
nce
ntr
atio
n
Depth(A)
Target (Ba0.65Sr0.35)(Ti0.65Zr0.35)O3.00
5mTorr (Ba0.69Sr0.32)(Ti0.28Zr0.77)O2.96
10mTorr (Ba0.65Sr0.31)(Ti0.39Zr0.66)O2.98
30mTorr (Ba0.65Sr0.30)(Ti0.45Zr0.67)O2.92
50mTorr (Ba0.66Sr0.32)(Ti0.54Zr0.56)O2.92
RBS spectrum(a) and depth profile(b) of BSTZ film deposited at 50mTorr. Table ; composition of films deposited at various pressure.
Electro-Ceramics Lab.
Variation of compositionVariation of composition
Variation of Composition(a) and deposition rate(b) of SBT films as a function of chamber pressure.
0 10 20 30 40 500.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
PRESSURE(mTorr)
(Ba+
Sr)
/(T
i+Z
r)
1.0
1.5
2.0
2.5
3.0
(a)
Zr/T
i
0 10 20 30 40 501.0
1.5
2.0
2.5
3.0(b)
DE
PO
SIT
ION
RA
TE
(nm
/min
.)
PRESSURE(mTorr)
Electro-Ceramics Lab.
XRD AnalysisXRD Analysis
X-ray diffraction patterns of the BSTZ films as a function of chamber pressure.
20 30 40 50 60
Ti3Pt (211)
Pt
Pt
Pt
(110)
5mTorr
10mTorr
30mTorr
50mTorr
Inte
nsity
(arb
.)
2 theta
20 25 30 35 40 45 50 55 60
Inte
nsity
(arb
.)
(211)
(210)
(200)
(111)
(110)
(100)
2 theta
Target
Electro-Ceramics Lab.
SEM images SEM images
SEM surface images of BSTZ films; (a) 50mTorr, (b) 30mTorr, (c) 10mTorr and (d) 5mTorr.
200nm
(a)
(c) (d)
(b)
200nm
(d)
(d)
(d)
(d)
200nm
Electro-Ceramics Lab.
AFM imagesAFM images
AFM images of BSTZ films as a function of chamber pressure.
0 10 20 30 40 502
3
4
5
6
7
Ave
rag
e r
ou
gh
ne
ss(n
m)
Chamber pressure(mTorr)
50mTorr(Ave. rough. ; 7.08Å)
5mTorr(Ave. rough. ; 2.63Å) 10mTorr(Ave. rough. ; 3.18Å)
30mTorr(Ave. rough. ; 5.21Å)
Electro-Ceramics Lab.
rr and tan and tan vs. Frequency vs. Frequency
Variation of dielectric constant and dissipation factor of BSTZ films as a function of chamber pressure.
102
103
104
105
106
0
100
200
300
400
500
600
700 50mTorr 30mTorr 10mTorr 5mTorr
FREQUENCY(Hz)
DIE
LE
CT
RIC
CO
NS
TA
NT
0.00
0.05
0.10
0.15
0.20
DIS
SIP
AT
ION
FA
CT
OR
Electro-Ceramics Lab.
C-V & P-E characteristicsC-V & P-E characteristics
Capacitance-voltage(a) and polarization-voltage(b) behaviorof BSTZ films as a function of chamber pressure.
-6 -4 -2 0 2 4 60.5
0.6
0.7
0.8
0.9
1.0(a)
50mTorr 30mTorr 10mTorr 5mTorr
C/C
ma
x
VOLTAGE(V)
-6 -4 -2 0 2 4 6
-30
-20
-10
0
10
20
30 (b) 50 mTorr 30 mTorr 10 mTorr 5 mTorr
PO
LAR
IZA
TIO
N(
C/c
m2 )
VOLTAGE(V)
Electro-Ceramics Lab.
Leakage current densityLeakage current density
Current-voltage(a) and current-E1/2 plot(b) of BSTZ films as a function of chamber pressure.
-400 -200 0 200 40010
-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
50mTorr
30mTorr
10mTorr
5mTorr
(a)
LEA
KA
GE
CU
RR
EN
T D
EN
SIT
Y(A
/cm
2 )
ELECTRIC FIELD(kV/cm)
0 10 2010
-12
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
(b) 50mTorr 30mTorr 10mTorr 5mTorr
LE
AK
AG
E C
UR
RE
NT
DE
NS
ITY
(A/c
m2 )
E1/2
(kV/cm)1/2
Electro-Ceramics Lab.
SummarySummary
(Ba1-x,Srx)(Ti1-yZry)O3 thin films were deposited by r.f. magnetron sputtering
Zr/Ti ratio of films decreased significantly with increasing chamber pressure. This variations affected microstructure and electrical properties.
▶when increasing chamber pressure - Decrease of Zr content - Decrease of Crystallinity - Increase of grain size and roughness - Increase of dielectric constant due to decrease of Zr - Increase of leakage current density
▶ Electrical properties of BSTZ thin films
- Dielectric constant and dissipation factor : 380~525 and 0.03~0.05 @ 100kHz - Leakage Current Density : 10-7 ~ 10-8A/cm2 order @ 200kV/cm - Paraelectric properties and schottky emission conduction
▶ BSTZ films appeared to be attractive for high density DRAM and should be further studied together BST.