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Article
Microwave Annealing for NiSiGe Schottky Junction
on SiGe P-Channel
Yu-Hsien Lin 1, *, Yi-He Tsai 1 , Chung-Chun Hsu 2 , Guang-Li Luo 3 , Yao-Jen Lee 3 and
Chao-Hsin Chien 2,3
Received: 10 September 2015 ; Accepted: 5 November 2015 ; Published: 10 November 2015
Academic Editor: Jung Ho Je
1
2
3
*
Department of Electronic Engineering, National United University, Miaoli 36003, Taiwan;
[email protected]
Department of Electronics Engineering and Institute of Electronics, National Chiao-Tung University,
Hsinchu 30010, Taiwan; [email protected] (C.-C.H.); [email protected] (C.-H.C.)
National Nano Device Laboratories, Hsinchu 30010, Taiwan; [email protected] (G.-L.L.);
[email protected] (Y.-J.L.)
Correspondence: [email protected]; Tel.: +886-3-738-2533; Fax: +886-3-736-2809
Abstract: In this paper, we demonstrated the shallow NiSiGe Schottky junction on the SiGe
P-channel by using low-temperature microwave annealing. The NiSiGe/n-Si Schottky junction
was formed for the Si-capped/SiGe multi-layer structure on an n-Si substrate (Si/Si0.57 Ge0.43 /Si)
through microwave annealing (MWA) ranging from 200 to 470 ˝ C for 150 s in N2 ambient. MWA
has the advantage of being diffusion-less during activation, having a low-temperature process, have
a lower junction leakage current, and having low sheet resistance (Rs) and contact resistivity. In our
study, a 20 nm NiSiGe Schottky junction was formed by TEM and XRD analysis at MWA 390 ˝ C.
The NiSiGe/n-Si Schottky junction exhibits the highest forward/reverse current (ION /IOFF ) ratio of
~3 ˆ 105 . The low temperature MWA is a very promising thermal process technology for NiSiGe
Schottky junction manufacturing.
Keywords: germanium; microwave annealing; NiSiGe; Schottky junction
1. Introduction
As the devices are being continuously scaled down for logic circuits, higher mobility channel
materials such as Ge or SiGe have been considered to boost the driving current [1–5]. However, most
high mobility materials have a significantly smaller bandgap as compared to Si, which will result in
a higher band-to-band tunneling leakage. Therefore, S/D (Source/Drain) and channel engineering
must play leading roles for boosting device performance. First, the parasitic series resistance should
be reduced. The low dopant solid solubility in Ge results in the large S/D series resistance. A large
S/D series resistance can be restrained by introducing metal germanide S/D. Second, the shallow
junction is needed. The interface between the metal and the semiconductor is abrupt and can be
easily governed by the reactant metal thickness and the process thermal budget, which indicates a
high potential for scalability [6]. Third, simpler device fabrication could be achieved for the Schottky
device without ion implantations and the high temperature annealing for dopant activation [7,8].
NiSiGe is the most promising candidate due to its low resistivity for the junction contact [9–12].
For reducing the thickness of the NiSiGe layer of the Schottky junction, the process temperature
needs to be reduced. However, a lower process temperature results in a higher NiSiGe resistance
due to the small crystallite size of the NiSiGe layer. These are the major challenges of scaling
Ge CMOS (Complementary Metal-Oxide-Semiconductor) into nanoscale devices. Therefore, in
order to avoid the dopant diffusion effect, which is dominant at high annealing temperatures,
Materials 2015, 8, 7519–7523; doi:10.3390/ma8115403
www.mdpi.com/journal/materials
Materials 2015, 8, page–page Materials 2015, 8, 7519–7523
avoid the dopant diffusion effect, which is dominant at high annealing temperatures, low‐temperature annealing with microwave excitation appears to offer a promising microwave annealing (MWA) low-temperature
annealing with
microwave
excitation
appears
to offer
a promising
microwave
process that may be an alternative to other rapid thermal processing methods in silicon annealing
(MWA)
process
that
may
be
an
alternative
to
other
rapid
thermal
processing
methods
in
Materials 2015, 8, page–page processing [13–15]. Microwaves could repair the damage in the Schottky junction formation and silicon processing [13–15]. Microwaves could repair the damage in the Schottky junction formation
avoid the dopant diffusion effect, which is dominant at high annealing temperatures, low‐temperature provide the lower leakage current for the Schottky junction device. and
provide
the lower leakage current for the Schottky junction device.
annealing with we
microwave appears to offer junction
a promising microwave annealing annealing
(MWA) in
In this paper, we propose a NiSiGe/n‐Si Schottky junction formed by microwave annealing in In
this paper,
propose excitation a NiSiGe/n-Si
Schottky
formed
by microwave
process that may be an alternative to other rapid thermal processing methods in silicon the Si-capped
Si‐capped SiGe Schottky junction devices (Si/Si
xGe
/Si, x shallow junction
junction with aa the
SiGe
Schottky
junction
devices
(Si/Si
x = = 0~1). 0~1). The The shallow
with
x Ge
1´1‐x
x /Si,
processing [13–15]. Microwaves could repair the damage in the Schottky junction formation and eff
20
nm depth has been fabricated with a high effective barrier height (φeff
)
and
low
leakage
current
in

20 nm depth has been fabricated with a high effective barrier height (
) and low leakage current B B
provide the lower leakage current for the Schottky junction device. the
devices.
in the devices. In this paper, we propose a NiSiGe/n‐Si Schottky junction formed by microwave annealing in the Si‐capped SiGe Schottky junction devices (Si/SixGe1‐x/Si, x = 0~1). The shallow junction with a 2.2. Experimental Section Experimental Section
20 nm depth has been fabricated with a high effective barrier height ( eff
B ) and low leakage current Figure
1
shows
the
schematic
diagram
and
process
flow
of
fabricating
the NiSiGe/n-Si Schottky
in the devices. Figure 1 shows the schematic diagram and process flow of fabricating the NiSiGe/n‐Si Schottky junction
structure. The Schottky junction devices were fabricated on a four-inch silicon wafer.
junction structure. The Schottky junction devices were fabricated on a four‐inch silicon wafer. The 2. Experimental Section The
multi-layer
structure of Si/Si
0.57 Ge0.43 (1 nm/2 nm/n-Si) was grown by an ultra-high vacuum
multi‐layer structure of Si/Si
0.57Ge0.43 (1 nm/2 nm/n‐Si) was grown by an ultra‐high vacuum chemical chemical
vapor
deposition
system
(UHVCVD,
CANON
ANELVA
Corporation
(Kanagawa,
Japan))
Figure 1 shows the schematic diagram and process flow of fabricating the NiSiGe/n‐Si Schottky vapor deposition system (UHVCVD, CANON ANELVA Corporation (Kanagawa, Japan)) on an on
anjunction structure. The Schottky junction devices were fabricated on a four‐inch silicon wafer. The n-type Si substrate. The channel was composed of a 1-nm-thick Si cap and a 2-nm-thick
n‐type Si substrate. The channel was composed of a 1‐nm‐thick Si cap and a 2‐nm‐thick SiGe layer multi‐layer structure of Si/Si
0.57Ge0.43strain
(1 nm/2 nm/n‐Si) was grown by an ultra‐high vacuum chemical SiGe
layer with biaxial compressive
and was grown at 420–500 ˝ C and 550 ˝ C, respectively.
with biaxial compressive strain and was grown at 420–500 °C and 550 °C, respectively. The isolation vapor deposition system CANON ANELVA Corporation (Kanagawa, after
Japan)) on surface
an The
filmSiO
of 420
nm (UHVCVD, SiO2 was deposited
on the multi-layer
architecture
series
film isolation
of 420 nm 2 was deposited on the multi‐layer architecture after series surface cleaning. n‐type Si substrate. The channel was composed of a 1‐nm‐thick Si cap and a 2‐nm‐thick SiGe layer cleaning.
Then, the definition of the junction active area was accomplished with lithography and
Then, the definition of the junction active area was accomplished with lithography and wet‐etching. with biaxial compressive strain and was grown at 420–500 °C and 550 °C, respectively. The isolation wet-etching.
Because of the bulk annealing characteristics of the microwave, the technique was
Because of the bulk annealing characteristics of the microwave, the technique was utilized to form film of 420 nm SiO2 was deposited on the multi‐layer architecture after series surface cleaning. ˝ for 150 s
utilized
to
NiSiGe asSchottky a low-leakage
Schottky
junction
ranging
from for 200150 to 470
NiSiGe as form
a low‐leakage junction ranging from 200 to 470 °C s in C
N2 ambient. Then, the definition of the junction active area was accomplished with lithography and wet‐etching. inThe un‐reacted Ni film was removed, followed by Al deposition as the back contact. N2Because of the bulk annealing characteristics of the microwave, the technique was utilized to form ambient. The un-reacted Ni film was removed, followed by Al deposition as the back contact.
NiSiGe as a low‐leakage Schottky junction ranging from 200 to 470 °C for 150 s in N2 ambient. The un‐reacted Ni film was removed, followed by Al deposition as the back contact. •UHVCVD Si/SiGe (~1 / ~2nm) on n-Si
Al
SiO2
SiO2
Al
SiGe
SiGe
SiO2
SiGe
SiO2
NiSiGe
SiGe
SiGe
NiSiGe
SiGe
(100) n-Si
(100)
Al n-Si
•DHF(HF:H2O = 1:20) surface treatment
•PECVD @
SiO2 (~1
(420
nm) on n-Si
•UHVCVD
Si/SiGe
/ ~2nm)
•Electrode2patterning
by lithography
O = 1:20) surface
treatment and
•DHF(HF:H
wet etch
•PECVD
@ SiO2 (420 nm)
•Sputter @
Ni (10 nm)
and lift-offand
•Electrode
patterning
by lithography
wet etch
•Microwave
Annealing (Splits)
•Sputter
@ Ni
(10 nm)
and lift-off
•Backside
contact
(Al)
•Microwave Annealing (Splits)
•Backside contact (Al)
Al
Figure 1. Schematic diagram and process flow of fabricating the NiSiGe/n‐Si Schottky junction structure. Figure
1. Schematic diagram and process flow of fabricating the NiSiGe/n-Si Schottky
junction structure.
Figure 1. Schematic diagram and process flow of fabricating the NiSiGe/n‐Si Schottky junction structure. 3.3. Results and Discussion Results and Discussion
3. Results and Discussion Figure 2 shows the high resolution TEM images of an approximately 1 nm/2 nm Si/SiGe film Figure
2 shows the high resolution TEM images of an approximately 1 nm/2 nm Si/SiGe film for
Figure 2 shows the high resolution TEM images of an approximately 1 nm/2 nm Si/SiGe film for multi-layer
the multi‐layer Si/Si
0.57
Ge
0.43/n‐Si structure before MWA. The SiGe/Si lattice interface image the
Si/Si0.57
Ge
/n-Si
structure
before
MWA.
The SiGe/Si
lattice interface
image shows
0.43
for the multi‐layer Si/Si
0.57Ge0.43/n‐Si structure before MWA. The SiGe/Si lattice interface image ˝
shows the good polycrystalline The inset figure shows NiSiGe film MWA the
good
polycrystalline
structure.structure. The insetThe figure
shows
the
NiSiGe
film
after
at 390
shows the good polycrystalline structure. inset figure shows the the NiSiGe film MWA
after after MWA at C. Aat 390 °C. A 20‐nm relative uniformity of the NiSiGe film and a distinct interface between the NiSiGe 20-nm
relative
uniformity
of
the
NiSiGe
film
and
a
distinct
interface
between
the
NiSiGe
and
Si
could
390 °C. A 20‐nm relative uniformity of the NiSiGe film and a distinct interface between the NiSiGe and Si could be observed. be
observed.
and Si could be observed. Si Si
Cap
Cap
NiSiGe
SiGe
NiSiGe
SiGe
n-Si
n-Si
in the Si/SiGe/n‐Si Figure 2. The cross‐sectional TEM images show the polycrystalline structure Figure
2. The cross-sectional TEM images show the polycrystalline structure in the Si/SiGe/n-Si
lattice interface image. The inset figure shows the NiSiGe Schottky junction through MWA at 390 °C. Figure 2. The cross‐sectional TEM images show the polycrystalline structure in the Si/SiGe/n‐Si lattice interface image. The inset figure shows the NiSiGe Schottky junction through MWA at 390 ˝ C.
lattice interface image. The inset figure shows the NiSiGe Schottky junction through MWA at 390 °C. 2
2
7520
Materials 2015, 8, 7519–7523
Materials 2015, 8, page–page Materials 2015, 8, page–page The result
the
grazing
incidence
of X-ray
diffraction
(GIXRD)
analysisanalysis was shown
Figure in 3.
The result ofof the grazing incidence of X‐ray diffraction (GIXRD) was inshown From
this
figure,
the
descriptions
of
power
0.5,
power
2,
power
4
are
300
W,
1200
W,
2400
W,
The From result this of the grazing incidence of was in Figure 3. figure, the descriptions of X‐ray power diffraction 0.5, power (GIXRD) 2, power analysis 4 are 300 W, shown 1200 W, ˝ C,
respectively.
thethe temperature
measurements
the above
splits
200 are Figure 3. respectively. From Moreover,
this figure, descriptions of power 0.5, of
power 2, 4 are 300 are
W, 1200 W, 2400 W, Moreover, the temperature measurements of power the power
above power splits ˝ C, and 470 ˝ C, respectively. Many peaks are shown, which correspond to the crystalline nickel
390
2400 W, respectively. Moreover, the temperature measurements of the above power splits are 200 °C, 390 °C, and 470 °C, respectively. Many peaks are shown, which correspond to the crystalline monogermanide;
implementing
390 ˝ C for
MWA
sufficient
to form polycrystalline
NiGe and
200 °C, 390 °C, and 470 °C, respectively. Many peaks are shown, which correspond to the crystalline nickel monogermanide; implementing 390 150
°C sfor 150 is
s MWA is sufficient to form polycrystalline NiSiGe.
The
peaks The corresponding
to (011),
(112),
and
NiSi
and
(111)
NiSiGe
were
nickel and monogermanide; implementing 390 (200),
°C to for 150 (200), s (211),
MWA is (020)
sufficient to form polycrystalline NiGe NiSiGe. peaks corresponding (011), (112), (211), and (020) NiSi and (111) ˝ C for 150 s was sufficient to form the NiSi and
clearly
identified
[16].
Performing
the
MWA
at
390
NiGe and NiSiGe. The peaks corresponding to (011), (200), (112), (211), and (020) NiSi and (111) NiSiGe were clearly identified [16]. Performing the MWA at 390 °C for 150 s was sufficient to form NiSiGe
phase for forming the Schottky junction.
NiSiGe were clearly identified [16]. Performing the MWA at 390 °C for 150 s was sufficient to form the NiSi and NiSiGe phase for forming the Schottky junction. the NiSi and NiSiGe phase for forming the Schottky junction. Figure 3. The GIXRD spectra for MWA with different power splits, confirming the NiSiGe formation. Figure 3. The GIXRD spectra for MWA with different power splits, confirming the NiSiGe formation.
Figure 3. The GIXRD spectra for MWA with different power splits, confirming the NiSiGe formation. Figure 4 shows the I–V characteristics of the fabricated NiSiGe/n‐Si Schottky junction; the Figure
44 shows
the
of
fabricated
NiSiGe/n-Si
Schottky
junction;
Figure shows the I–V
I–V characteristics
characteristics of the
the fabricated NiSiGe/n‐Si Schottky junction; the NiSiGe formation during MWA conditions was at 200 °C, 330 °C, 390 °C, ˝420 °C, and 470 °C the
for ˝
˝
˝
˝
NiSiGe
formation
during
MWA
conditions
was
at
200
C,
330
C,
390
C,
420
C,
and
470
C
for
150
s,
NiSiGe formation during MWA conditions was at 200 °C, 330 °C, 390 °C, 420 °C, and 470 °C for 150 s, respectively. After forming NiSiGe with MWA annealing, the forward currents and reverse respectively.
After
forming
NiSiGe
with
MWA
annealing,
the
forward
currents
and
reverse
leakage
150 s, respectively. After forming NiSiGe with MWA annealing, the forward currents and reverse leakage currents of all NiSiGe/n‐Si contacts gradually decreased from 200 °C to 390 °C. However, ˝ C to 390 ˝ C. However, increasing
currents
of the all NiSiGe/n-Si
contacts gradually
decreased
from°C, 200the leakage currents of all NiSiGe/n‐Si contacts gradually decreased from 200 °C to 390 °C. However, increasing annealing temperature from 200 °C to 470 forward currents and reverse ˝
˝
the
annealing
from 200 C to
470 200 C, the
forward
currents
and reverse
leakage
increasing the temperature
annealing temperature from °C to 470 °C, the forward currents and currents
reverse leakage currents are degraded accordingly. The NiSiGe/n‐Si Schottky junction exhibits the highest are
degraded
accordingly.
The
NiSiGe/n-Si
Schottky
junction
exhibits
the
highest
forward/reverse
5
leakage currents are degraded accordingly. The NiSiGe/n‐Si Schottky junction exhibits the highest forward/reverse current ratio of ~2.5 × 10 at MWA 390 °C. This result also indicates that the series current
ratio of ~2.5 ˆ 105 at MWA 390 ˝ C.
This result also indicates that the series resistance can be
5 at MWA 390 °C. This result also indicates that the series forward/reverse current ratio of ~2.5 × 10
resistance can be significantly reduced after the SiNiGe formation at the condition of MWA 390 °C. ˝ C. Note that if using
significantly
reduced
after
the
SiNiGe
formation
the condition
of MWA
390°C, resistance can be significantly reduced after the SiNiGe formation at the condition of MWA 390 °C. Note that if using relatively high temperature atMWA annealing at >470 the crystallization ˝ C, the crystallization became more significant
relatively
high
temperature
MWA
annealing
at
>470
Note that if using relatively high temperature MWA annealing at >470 °C, the crystallization became more significant and which was shown by the increased intensity of the GIXRD peak in and
which
was
shown
by
the
increased
intensity
of
the
GIXRD
peak
in
Figure
3.
This
issue
became 3. more which was shown by uniformity, the increased intensity the GIXRD peak in Figure This significant issue will and potentially degrade the cause more of defects induce at will
the potentially
degrade
the
uniformity,
cause
more
defects
induce
at
the
interface,
and
affect
the
leakage
Figure 3. This issue will potentially degrade the uniformity, cause more defects induce at the interface, and affect the leakage current of the junction increase. current
of the junction increase.
interface, and affect the leakage current of the junction increase. 2) 2)
Current
Density
(A/cm
Current
Density
(A/cm
3
10
3
102
10
2
101
10
1
100
10
0
10-1
10
-1
10-2
10
-2
10-3
10
-3
10-4
10
-4
10-5
10
-5
10-6
10
-6
-1.0
10
-1.0
MWA@330C
MWA@390C
MWA@330C
MWA@420C
MWA@390C
MWA@470C
MWA@420C
MWA@200C
MWA@470C
MWA@200C
-0.5
0.0
0.5
-0.5
0.0
Voltage(volt)0.5
Voltage(volt)
1.0
1.0
Figure 4. The I–V characteristics of the NiSiGe/n‐Si Schottky junction annealed at different MWA temperatures. Figure 4. The I–V characteristics of the NiSiGe/n‐Si Schottky junction annealed at different MWA temperatures. Figure 4. The I–V characteristics of the NiSiGe/n-Si Schottky junction annealed at different
Figure 5 shows the effective electron SBH (Schottky barrier height) and ideality factor of MWA temperatures.
Figure 5 shows the effective electron SBH (Schottky barrier height) and ideality factor of NiSiGe/n‐Si Schottky junctions with different MWA temperatures. For a typical or moderate doped NiSiGe/n‐Si Schottky junctions with different MWA temperatures. For a typical or moderate doped semiconductor, the I–V characteristics of the Schottky diode could be described by: 7521
semiconductor, the I–V characteristics of the Schottky diode could be described by: 3
3
Materials 2015, 8, page–page Materials 2015, 8, 7519–7523
 qVa

I  I S exp
 1
(1) Figure 5 shows the effective electron SBH (Schottky
nK BT barrier height) and ideality factor of
NiSiGe/n-Si Schottky junctions with different MWA temperatures. For a typical or moderate doped
with semiconductor, the I–V characteristics of the Schottky diode could be described by:
 q Beff˙ 
qV
a
IIS “ IAA
T exp ´ 1 
S exp
nK B T K BT 
*
ˆ
2
(2) (1)
with Is is the saturation current, A is the diode area, the applied voltage, A* is the effective where ˜ Vae is ¸
ff
eff
qφ
Richardson constant [17,18], B is the SBH, n is the Bideality factor. The ideality factor n and IS “
AA˚and T 2 exp
(2)
KB T
eff
SBH B can be derived as: where Is is the saturation current, A is the diode area, Va is the applied voltage, A* is the effective
 q  V  factor. The ideality factor n and SBH
Richardson constant [17,18], φeff
B is the SBH,
 n  and n isthe ideality
(3) eff
φB can be derived as:
 K BT˙ˆ[ln I ]˙
ˆ
q
BV
n“
(3)
and KB T
BrlnIs
and
eff
ef f 
φ B “
B
K
T ˆ AT 2 ˙
K BBT ln A˚ T 2  ln 

qq
 JJSS 
(4) (4)
1.6
0.75
1.5
0.70
1.3
0.60
1.2
0.55
1.1
0.50
Ideal Factor
1.4
0.65
1.0
270 300 330 360 390 420 450 480
°
Effective Barrier Hieght(ev)
eff from each MWA sample of a
By using Equation (3), we extract the ideal factor n and SBH φeff
By using Equation (3), we extract the ideal factor n and SBH BB from each MWA sample of a different temperature in the I–V characteristics of Figure 4. From Figure 5, we can observe that the
different temperature in the I–V characteristics of Figure 4. From Figure 5, we can observe that the SBH and the ideality factor of the MWA 390 ˝ C condition are 0.63 eV and 1.01, and it shows good
SBH and the ideality factor of the MWA 390 °C condition are 0.63 eV and 1.01, and it shows good electrical characteristics of Schottky junctions.
electrical characteristics of Schottky junctions. Temperature( C)
Figure 5. SBH and ideality factor of NiSiGe/n‐Si Schottky contact with different MWA temperatures. Figure 5. SBH and ideality factor of NiSiGe/n-Si Schottky contact with different MWA temperatures.
4. Conclusions 4. Conclusions
This paper realized the shallow NiSiGe Schottky junction on the SiGe P‐channel by using low‐
This paper realized the shallow NiSiGe Schottky junction on the SiGe P-channel by using
temperature microwave annealing. The formation of junction defects could be suppressed and low-temperature microwave annealing. The formation of junction defects could be suppressed and
prevent the agglomeration due to the lower forming temperature. The microwave‐annealed NiSiGe prevent the agglomeration due to the lower forming temperature. The microwave-annealed NiSiGe
Schottky junction exhibited a superior ION/IOFF ratio of about 3 × 105 formed at 390 °C as well as more Schottky junction exhibited a superior ION /IOFF ratio of about 3 ˆ 105 formed at 390 ˝ C as well as
stable off‐current characteristics with an SBH of 0.63 eV and an ideality factor of 1.01. We believe more stable off-current characteristics with an SBH of 0.63 eV and an ideality factor of 1.01. We believe
our microwave annealing NiSiGe Schottky junction is promising for high performance logic circuits our microwave annealing NiSiGe Schottky junction is promising for high performance logic circuits
and will enable SiGe channel devices to be integrated on the Si substrate for the future applications. and will enable SiGe channel devices to be integrated on the Si substrate for the future applications.
Acknowledgments: Acknowledgments: The The authors authors thank thank the the National National Science Science Council Council of of the the Republic Republic of of China, China, Taiwan, Taiwan, for for
supporting this research (104‐2221‐E‐239‐017). National Nano Device Laboratories (NDL), Taiwan, supporting this research (104-2221-E-239-017). National Nano Device Laboratories (NDL), Taiwan, is is highly highly
appreciated for its technical support.
appreciated for its technical support. Author Contributions: Contributions: Yu‐Hsien Yu-Hsien Lin Lin organized organized the the research research and and wrote wrote the the manuscript; manuscript; Yi‐He Yi-He Tsai Tsai and and
Author Chung-Chun
Hsu
performed
the
experiments
and
performed
data
analysis;
Yu-Hsien
Lin,
Guang-Li
Luo,
Chung‐Chun Hsu performed the experiments and performed data analysis; Yu‐Hsien Lin, Guang‐Li Luo, Yao-Jen Lee, and Chao-Hsin Chien discussed the experiments and the manuscript.
Yao‐Jen Lee, and Chao‐Hsin Chien discussed the experiments and the manuscript. 4
7522
Materials 2015, 8, 7519–7523
Conflicts of Interest: The authors declare no conflict of interest.
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