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Surface Reactions During ALD of TiO2 on GaAs Surfaces Studied by
in situ ATR-FTIR
Liwang Ye, Theodosia Gougousi
Department of Physics, University of Maryland, Baltimore County, Baltimore, MD 21250
University of Maryland, Baltimore County
2 University of Maryland, Baltimore County
Motivation
ALD of high k on III-V has promising applications on MOSFET.
Poor native oxides are the main difficulties for the applications.
Interface self-cleaning has been widely discovered.1
1. P. D. Ye et al. APL 83, 180 (2003), M. M. Frank et al. APL 86, 152904 (2005), D. Shahrjerdi et al. APL 92, 223501 (2008), L. Huang et al. APL 87, 252104 (2005), C.-H. Chang et al. APL 89, 242911 (2006),C. L. Hinkle et al. APL 92, 071901 (2008), Hackley et al. APL 92(16), 162902 (2008) , Suri et al. APL 96, 112905 (2010).
Gougousi et al. TSF 518, 2006 (2010)Gougousi et al. JES, 157(5), H551 (2010)
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Si
TiO2Ti
N(CH3)C2H5(CH3)C2H5N
(CH3)C2H5N N(CH3)C2H5
TEMAT
B. Kan et al., J. Phys. Chem. A 113(16), 3946 (2009).
M. Bouman et al., ECS Transactions, 33 (2) 291-305 (2010).
Si
HfO2
TDMAH HfN(CH3)(CH3)N
(CH3)N N(CH3)
K. Li et al., J. Phys. Chem. C 114, 14061 (2010).
Y. Wang et al., and T. Gustafsson, Chem. Mater. 2007, 19, 3127-3138 3127.
K. Li et al., J. Phys. Chem. C 2011, 115, 18560–18571.
HfN(CH3)C2H5(CH3)C2H5N
(CH3)C2H5N N(CH3)C2H5
HfN(C2H5)2(C2H5)2N
(C2H5)2N N(C2H5)2
TEMAH
TDEAH M. J. Kelly et al., Chem. Mater. 2005, 17, 5305-5314.
In situ FTIR study of high k ALD on Si
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To detector IR incidence IRE (GaAs)
IR detector
IR source
Pump
H2O
TDMAT FTIR ATR cell
Pressure gauge
N2
K. Li, S. Li, N. Li, D. A. Dixon, and T. M. Klein, J. Phys. Chem. C 114, 14061 (2010).
Experiment details: in situ ATR-FTIR setup
University of Maryland, Baltimore County
~12 total reflections on top surface
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• Precursor: TDMAT and H2O 1st
TDM
AT
1st H
2O
Time (min)0 3 4 5 6 7
Pum
p an
d ta
ke sp
ectr
a
Pum
p an
d ta
ke sp
ectr
a
1st Cycle
2nd CycleReac
tor
pres
sure
Note: Y-axis only serves as a guide for understanding the procedure.
Ti
N(CH3)2(CH3)2N
(CH3)2N N(CH3)2
TDMAT
Experimental details: ALD process
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GaAs surface preparation
University of Maryland, Baltimore County
Abs
orba
nce
4000 3000 2000 1000
Wavenumber (cm-1)
CO GaAs F GaAs
H2O
C-H H2O
As-O
As-O
As-O or Ga-O
free OH
“F GaAs” surface: etched in BOE
“CO GaAs” surface:“F GaAs” soaked in (30%)H2O2 at 45°C for 10~30mins.
GaAs
chemical oxide
TiO2
~3nmReference: native oxide GaAs
Reference: F GaAs
M. Rei Vilar et al. Surf. Interface Anal. 37, 673 (2005).
Abs
orba
nce
4000 3500 3000 2500 2000 1500 1000
Wavenumber (cm-1)
TiO2 / CO GaAs 100C
1st TDMAT
1st H2O
2nd TDMAT
2nd H2O
20th TDMAT
20th H2O
1598 14
6614
09
0.004
7
CH3 stretching from TDMAT
ALD of TiO2/CO GaAs(100) at 100°C
University of Maryland, Baltimore County
NC2 stretching from TDMAT
TiO2
8
60x10-3
40
20
0
Inte
grat
ed p
eak
area
20151050 Time(mins)
0.400.300.200.100.00
20151050
Peak areas vs deposition time
1st TD
MA
T
2nd TD
MA
T
3rd TD
MA
T
1st H
2O
2nd H
2O
3rd H
2O
CH stretching
1598 cm-1
IncreaseDecrease
ALD of TiO2/CO GaAs(100) at 100°C
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Possible assignments of the 1598 cm-1: H-O-H bending mode of H2O. OCO stretching of formate (HCOO) . OCO stretching of carbonate (HCO3). N-H bending mode of methylamine (CH3NH2). C=N stretching of Methylmethyleneimine
(CH3N=CH2) (MMI).
Discussion: the possible assignments
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D2O H218O D2O
Or H218O
Species Liquid H2OMMA
CH3NH2 on TiO2
Formate HCOO
Bidentate carbonateHOCOOTi
MMI(CH3N=CH2)
Modes Scissoring NH2 scissoring
Anti. Sym. OCO
stretchingOCO Sym. stretching
N=C stretching
Peak (cm-1) ~1620 1607 1607 1582 ~1590
Peak with isotope
D2O CH3ND2 HC18O18O H18OC18O18O CH3N=CH2
~1200 1205 1587 1570 ~1590
Shift (cm-1) 400 ~400 20 ~12 0
ReferencesR. Nakamura, et al.
Langmuir 17, 2298(2001)
Li. –F. Liao et al. J. Phys. Chem. B 105,
5928(2001).
L.-F. Liao et al., J. Phys. Chem. B, 106(43), 11241
(2002).
L.-F. Liao et al., J. Phys. Chem. B, 106(43), 11241
(2002).
C. M. Truong et al. J. Phys. Chem. 99,
8831(1995).
Isotope exchange experiments
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Abs
orba
nce
4000 3500 3000 2500 2000 1500 1000
Wavenumber (cm-1)
1598 14
6614
09
10 cyc of TiO2 on CO GaAs 100C
ALD with H216O
ALD with H218O
0.001
• D2O exchange excludes the assignments of H2O and CH3NH2.• H2
18O exchange experiment excludes the possibilities of formate and carbonate species.
Abs
orba
nce
4000 3500 3000 2500 2000 1500 1000
Wavenumber (cm-1)
1598
1466
1409
10 cyc of TiO2 on CO GaAs 100C
2400
ALD with D216O
ALD with H216O
0.001
Isotope exchange experiments
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OHHO O
TiN
(CH
3) 2
N(C
H3) 2
+ N=CH2CH3-
+ O OTi
O-HO-H HN(CH3)2
O OTi
N(C
H3) 2
N(C
H3) 2
-N(CH3)2 + HN=CH2CH3- + H2
O OTi
O-HO-H
+O OTi
N(C
H3) 2
N(C
H3) 2
+
HN(CH3)2
Mechanism ?
2 -N(CH3)2+N=CH2CH3-
+
Ref. 2
1. J. P. A. M. Driessen et al., J. Electrochem. Society, 148(3), G178(2001).2. S. Salim et al., Chem. Mater. 7, 507(1995).
((CH3)2N)xE + H ((CH3)2N)x-1E + H2 + H2C=NCH3 E: As, P, Sb; x=1,2,3
Ref. 1+H2 2 + H2
Reaction scheme
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OHH
OHH
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OHHO O
TiN
(CH
3) 2
N(C
H3) 2
+ N=CH2CH3-
+O OTi
O-HO-H
HN(CH3)2
O OTi
N(C
H3) 2
N(C
H3) 2
-N(CH3)2 + HN=CH2CH3- + H2
O OTi
O-HO-H
+O OTi
N(C
H3) 2
N(C
H3) 2
+
HN(CH3)2
Mechanism ?
2 -N(CH3)2+ N=CH2CH3-+
Ref. 2
1. J. P. A. M. Driessen et al., J. Electrochem. Society, 148(3), G178(2001).2. S. Salim et al., Chem. Mater. 7, 507(1995).
((CH3)2N)xE + H ((CH3)2N)x-1E + H2 + H2C=NCH3 E: As, P, Sb; x=1,2,3
Ref. 1
+H2 2 + H2
Reaction scheme for revison
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OHH
OHH
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Effect of ALD temperature and surface preparation
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Abs
orba
nce
4000 3500 3000 2500 2000 1500 1000 Wavenumber (cm-1)
20 cyc of TiO2 on GaAs
CO GaAs 100 C
CO GaAs 200 C
1598
1466
1409
0.002
F GaAs100 C
F GaAs 200 C
Abs
orba
nce
4000 3500 3000 2500 2000 1500 1000
Wavenumber (cm-1)
1st TDMAH
2nd TDMAH
30th TDMAH
1st H2O
2nd H2O
30th H2O
ALD HfO2/CO GaAs at 275C Reference: CO GaAs 1
598
146
6 1
409
0.004
• The spectrum of 30 cycles of HfO2 resembles the one from ALD of TiO2 on GaAs. A broad negative peak is growing at As-O region.
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ALD HfO2/CO GaAs
University of Maryland, Baltimore CountyA
bsor
banc
e
1200 1100 1000 900 800
Wavenumber (cm-1)
0.004
As-O region
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As oxide removal was observed during the deposition at 275°C but was not observed at 200°C.
GaAs oxide removal
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Abs
orba
nce
1400 1300 1200 1100 1000 900 800
Wavenumber (cm-1)
As-O
B: As-prepared CO GaAs (RT)
A: After 30cyc HfO2 cooled down to RT
As-O
A-B: Difference of two spectra
0.01
ALD HfO2/CO GaAs at 275C Reference: etched GaAs surface
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For the deposition of TiO2 on GaAs surface, Methylmethyleneimine (MMI) was produced during the H2O exposure and accumulates in the film.
As oxide removal was observed during the deposition on HfO2 on chemical oxide GaAs surface at 275°C but was insignificant at 200°C.
Conclusions
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Acknowledgements
University of Maryland, Baltimore County
DMR-0846445
Alex Henagar