1. Surface reactions and interface evolution
during the ALD of HfO2 on GaAs surfaces
studied by in situ ATR-FTIR
Liwang Ye, Theodosia Gougousi
Department of Physics
University of Maryland, Baltimore County (UMBC),
Baltimore, MD 21250
1
University of Maryland, Baltimore County

2. 2
University of Maryland, Baltimore County
Motivation
 Atomic layer deposition
(ALD) of high-κ on III-V has
promising applications in
MOSFET.
 Poor quality native oxides are
detrimental to MOSFET
applications.
 Interface self-cleaning has
been widely observed.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)
III-V
semiconductor
Metal oxideNative oxide
III-V
semiconductor
Before ALD After ALD
ALD

3. Motivation: understanding the “interface self-cleaning”
3
(1) Ligand exchange 3 HfL4 + 2 A2O3 → 3 HfO2 + 4 AL3
L
(2) Precursor decomposition
N
(3) Oxide conversion 4 GaAs + 3 As2O5 → 2 Ga2O3 + 3 As2O3 + 4 As
GaAs
Native oxide
M
L
L
L
L
GaAs
Native oxide
Decomposition
Byproducts
M: Metal
atom
L
N
A= As
or Ga
or In
S. Klejna and S. D. Elliott, Chem.
Mater. 26, 2427 (2014).
C. H. Chang et al. APL 89,
242911 (2006).
R. P. Vasquez et al. APL 42, 293
(1983).
University of Maryland, Baltimore County

4. 4
Internal reflection element (IRE) (GaAs)
IR
detector
IR
source
Rotary
vane
pump
H2O
TDMAH
FTIR Attenuated total reflection (ATR) cell
Pressure
gauge
N2
In situ ATR-FTIR setup
.
Computer
D2O/
H2
18O
Fixed volume
University of Maryland, Baltimore County
K. Li et al., JVSTA 25, 1389 (2007), K. Li et al., JPCC 114, 14061 (2010).

5. • Precursor: TDMAH and H2O
5
Experimental details: ALD process
University of Maryland, Baltimore County
1stTDMAH
1stH2O
Time (min)0 3 4 5
N2purgeand
spectrataken
1st Cycle
2nd Cycle
Reactor
pressure
N2purgeand
spectrataken
1 2
Hf
N
N
N
N
[Hf(N(CH3)2)4]
TDMAH

6. Absorbance
4000 3000 2000 1000
Wavenumber (cm
-1
)
2920&
2851
1630
1067
843
As-O
H2O
CH
0.01
Absorbance
1000 700
Wavenumber (cm
-1
)
1067
843
As-O
0.01
6
Characterization of the GaAs starting surface
GaAs
Native oxide
GaAs
chemical oxide
Chemical oxide
GaAs(100)
Native oxide
GaAs(100)
 Reference of the spectra are the HF etched GaAs surface. As-O region
University of Maryland, Baltimore County
M. Rei Vilar et al. Surf. Interface Anal. 37, 673 (2005).

7. Absorbance
4000 3500 3000 2500 2000 1500 1000
Wavenumber (cm
-1
)
1470
1410
1572
2777
2855
3630
3240
860
0.002
1
st
TDMAH
2
nd
H2O
20
th
TDMAH
20
th
H2O
1
st
H2O
2
nd
TDMAH
1200
1046
7
ALD of HfO2/CO GaAs(100) at 275°C
GaAs
chemical oxide
Hf
N(CH3)2(CH3)2N
H
O
H
O
Hf
N(CH3)2(CH3)2N
(CH3)2N N(CH3)2
CH3 stretch
O
H
H
TDMAH
O
H
H
chemical oxide
HfO2HfO2
Hf-OH
As-O removal
University of Maryland, Baltimore County

8. 1200 1100 1000 900 800
HfO2/CO GaAs
HfO2/HF GaAs
0.003
1 cycle
2 cycles
3 cycles
10 cycles
20 cycles
8
Interface self-cleaning during the ALD of HfO2 at 275 °C
The references for these spectra are
their respective starting surfaces.
0.5
0.4
0.3
0.2
0.1
0.0
AreaofremovedAs-O
20181614121086420
No. of cycles
As-O region As oxide removal during the deposition at 275 °C
Gradual removal of the arsenic oxide has been
observed during the deposition
L. Ye and T. Gougousi, APL, 105, 121604 (2014).
Removed
As-O
III-V
semiconductor
HfO2chemical oxide
GaAs
ALD
University of Maryland, Baltimore County
Absorbance
Wavenumber (cm-1)

9. 9
Interface self-cleaning during the ALD of HfO2 at 275°CAbsorbance
Wavenumber (cm-1)
The references for these spectra are
their respective starting surfaces.
As-O region
L. Ye and T. Gougousi, APL, 105, 121604 (2014).
As-O-Hf
L : N(CH3)2
Hf
L
L
L
L
As-O-As As
O
Hf
L
L
L
As
L
+
Hf
L
L
L
L
As As
O
Hf
L
L
L
H-L+
O
H
(1)
(2)
Two possible reaction schemes.
University of Maryland, Baltimore County
1200 1100 1000 900 800
HfO2/CO GaAs
HfO2/HF GaAs
0.003
1 cyc
2 cyc
3 cyc
10 cyc
20 cyc
1046

10. 10
Effect of the deposition temperature on the interface self-cleaning
Absorbance
1200 1100 1000 900 800
Wavenumber (cm
-1
)
275 °C
200 °C
0.003 100 °C
250 °C
20 cycles of HfO2 ALD on “CO GaAs” (100) surface.
The spectra have been referenced to the respective starting surfaces.
The arsenic oxide removal
is enhanced at higher
deposition temperatures.
Deposition temperature
Removed As oxides
Suri et al. APL 96, 112905
(2010).
University of Maryland, Baltimore County

11. 1500 1000
860
0.002
1572
1470
1410
1046
Absorbance
Wavenumber (cm-1)
11
Interface self-cleaning during the ALD of HfO2 at 275 °C
HfO2/CO GaAs
CH3-N=CH2
(MMI)
TDMAH
TDMAH
TDMAH
TDMAH
H2O
H2O
H2O
H2O
0.20
0.15
0.10
0.05
0.00
Peakarea
20151050
Time (mins)
CH Stretch
1572 cm
-1
University of Maryland, Baltimore County
1st TDMAH
2nd TDMAH
1st H2O
2nd H2O
3rd H2O
10th H2O
20th H2O
The reference for these spectra is the
starting surface.

12. 12
Possible reaction schemes for the production of MMI
Hf
N(CH3)2
N(CH3)2
+ O
H
H
2
Hf
OH
OH
+ HN(CH3)22(a)
Hf
OH
OH + HN(CH3)2 + + H2N=CH2CH3-
(b)
Hf
OH
OH
+ + HHN=CH2CH3-2 2
(c)
Surface reaction schemes at H2O half cycle during the ALD of HO2 on GaAs surfaces.
University of Maryland, Baltimore County
J. P. A. M. Driessen et al. J. Electrochem. Soc., 148, G178 (2001),
S. Salim et al. Chem. Mater. 7, 507 (1995).

13. Continuous removal of arsenic oxide during the
first 20 ALD cycles has been observed.
Temperature dependence of the arsenic oxide
removal has been confirmed.
Methylmethyleneimine (MMI) is produced during
the H2O exposure and accumulates in the film.
13
Conclusions
University of Maryland, Baltimore County