Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method
In this paper, we have considered the four-contact method for measurements of the specific contact resistivity of the ohmic contacts (ρc). The presented method for measuring ρc has been compared with several other methods. Limits of applying this method have been shown.
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України
2014
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Цитувати: | Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method / V.N. Sheremet // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 4. — С. 394-397. — Бібліогр.: 8 назв. — англ. |
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irk-123456789-1184262017-05-31T03:07:10Z Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method Sheremet, V.N. In this paper, we have considered the four-contact method for measurements of the specific contact resistivity of the ohmic contacts (ρc). The presented method for measuring ρc has been compared with several other methods. Limits of applying this method have been shown. 2014 Article Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method / V.N. Sheremet // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 4. — С. 394-397. — Бібліогр.: 8 назв. — англ. 1560-8034 PACS 73.40.Ns, 73.40.Cg, 85.40.-e http://dspace.nbuv.gov.ua/handle/123456789/118426 en Semiconductor Physics Quantum Electronics & Optoelectronics Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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In this paper, we have considered the four-contact method for measurements
of the specific contact resistivity of the ohmic contacts (ρc). The presented method for
measuring ρc has been compared with several other methods. Limits of applying this
method have been shown. |
format |
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Sheremet, V.N. |
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Sheremet, V.N. Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method Semiconductor Physics Quantum Electronics & Optoelectronics |
author_facet |
Sheremet, V.N. |
author_sort |
Sheremet, V.N. |
title |
Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method |
title_short |
Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method |
title_full |
Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method |
title_fullStr |
Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method |
title_full_unstemmed |
Metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method |
title_sort |
metrological aspects of researching the specific contact resistivity of ohmic contacts by using the four-contact method |
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Інститут фізики напівпровідників імені В.Є. Лашкарьова НАН України |
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2014 |
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http://dspace.nbuv.gov.ua/handle/123456789/118426 |
citation_txt |
Metrological aspects of researching the specific contact resistivity
of ohmic contacts by using the four-contact method / V.N. Sheremet // Semiconductor Physics Quantum Electronics & Optoelectronics. — 2014. — Т. 17, № 4. — С. 394-397. — Бібліогр.: 8 назв. — англ. |
series |
Semiconductor Physics Quantum Electronics & Optoelectronics |
work_keys_str_mv |
AT sheremetvn metrologicalaspectsofresearchingthespecificcontactresistivityofohmiccontactsbyusingthefourcontactmethod |
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2025-07-08T13:57:49Z |
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2025-07-08T13:57:49Z |
_version_ |
1837087399993147392 |
fulltext |
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 394-397.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
394
PACS 73.40.Ns, 73.40.Cg, 85.40.-e
Metrological aspects of researching the specific contact resistivity
of ohmic contacts by using the four-contact method
V.N. Sheremet
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 03028 Kyiv, Ukraine
Phone: 38(044) 525-61-82; e-mail: VolodymyrSheremet@gmail.com
Abstract. In this paper, we have considered the four-contact method for measurements
of the specific contact resistivity of the ohmic contacts (ρc). The presented method for
measuring ρc has been compared with several other methods. Limits of applying this
method have been shown.
Keywords: ohmic contact, four-contact method, specific contact resistivity.
Manuscript received 19.03.14; revised version received 30.07.14; accepted for
publication 29.10.14; published online 10.11.14.
1. Introduction
Creation of new semiconductor devices and
improvement of existing parameters are impossible
without reducing the resistance of the ohmic contacts.
The main parameter that characterizes the ohmic contact
is the specific contact resistivity ρc. In the case of high
resistance of the metal-semiconductor contact, when a
device operates, an additional heating occurs in the
contact, which negatively impacts on the reliability and
efficiency of the device. It is particularly harmful for
powerful high-frequency devices. To minimize heating,
it is necessary to reduce ρс of the ohmic contact. With
decreasing the ρс value, the requirements to the accuracy
of determining the specific contact resistivity increase.
Promising materials for development of high-power
microwave devices are semiconductor compounds A3B5
such as GaN, InN, InP, etc. The effective use of these
semiconductor materials and increase of the power of
microelectronic devices being based on them are
impossible without creating reliable heat-resistant ohmic
contacts.
2. Ohmic contact and its resistance
For measuring the contact resistance, both vertical and
planar test structures may be used. In the most complete
manner, the existing methods were considered in the
work [1]. In response to the direct measurement, there
can be obtained a resistance usually presented as the sum
of the resistances [2]:
mpTsc RR+R+R+R=R , (1)
where R is the measured resistance, Rc – the contact
resistance, Rs – resistance of semiconductor, RT –
resistance provoked by current spreading, Rp – resistance
probes and connecting conductors, Rm – resistance of
metallization.
Resistance of metallization, probes, connecting
conductors, and resistance provoked by current
spreading are often small values as compared to the
resistance of semiconductor and that of the contact. If
the contact resistivity is comparable to the resistance of
semiconductor, RT and Rp are infinitely small values in
relation to Rc. With further decreasing ρс, account must
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 394-397.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
395
be also taken of the values of the resistance provoked by
current spreading and that of semiconductor Rp.
In the case of a vertical test structure (Fig. 1a), the
impact of the current spreading is less than in the case of
a planar structure (Fig. 1b), that’s why at first, more
widely used were the methods using a vertical structure,
among which the Cox-Strack method was most widely
applied [1]. However, this method is not applicable in
the case of contact structures to epitaxial films.
Application of a planar structure to study the
specific contact resistivity is preferable because of the
reduced number of processes is required to form a test
structure. But when using a planar test structure, one
should take account of the current spreading that can be
characterized by the transfer length LT – the distance
from the edge of the contact, near which the current
decreases by e times [3-5]. It is determined by the
equation [3-5]:
s
c
T
t
L
. (2)
If the length of contact is longer than the transfer
distance, the contact becomes infinite, and its resistance
does not depend on the length. Since the entire contact
area is not included into the passage of current, it
complicates determining the ρс value. If the contact
length is less than the transfer distance, the total
resistance is increased as a result of reducing the area of
current passage, which must be considered when
determining the specific contact resistivity. Accordingly,
the effective area of the planar contact becomes less than
the actual one.
In the case when the contact length is less than the
width of the diffusion region in semiconductor, there
observed an effect of the surface current spreading, and
the measured total resistance increases to a value
determined in the work [2] as follows:
Fig. 1. Current spreading in the vertical (a) and planar (b) test
structures (d is the diameter of contact, LT – transfer length, t –
thickness of semiconductor).
2
2 1
ln
1
1
ln
1
k
k
k
k
k
R s
w , (3)
where k = W/(W–w) is the correcting parameter, w –
contact width, W – width of the diffusion region.
In these methods, both extrapolative and two-
contact one, with a planar test structure [5], the
resistance caused by current spreading is not taken into
consideration, which results in the increased error of
measurements. One of the most easy-to-implement
planar measurement methods is the four-contact method
of ρс measurements.
3. Principles of measuring ρс
by using the four-contact method
The method consists in measuring the voltage at equal
distances between the current contacts (Fig. 2) [1]. This
method can be used if the transfer length is much larger
than the contact size. Also, a necessary condition is
L >> r, L >> t, where L is the contact length, t – thickness
of the semiconductor film. Under these conditions, the
contact resistivity is determined from the equation [6]:
2ln2
2/12/3ln
0
2
0
12 rL
I
V
I
V
rс . (4)
Disadvantage of the method is that it is necessary
to fulfill the condition L >> r that implies a significant
gap between the contacts, which can result in the
inability to determine the contact resistivity at a certain
ratio ρc /ρs.
Due to simplicity of the test structure formation,
this method is used for large transfer lengths.
In the case of using the four-contact method, the
error of measurements of the specific contact resistivity
can be determined using the partial derivative technique:
.
2
1
2
3
ln1)2(ln321
2
1
2
3
ln
2
2
2
r
L
L
r
r
r
L
r
r
L
L
I
I
V
V
r
r
s
c
c
с
(5)
Fig. 2. The principle of measuring the contact resistivity by
using the four-contact method.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 394-397.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
396
The performed calculations have resulted in the
dependence of the relative error of the measured contact
resistance on the contact radius (Fig. 3). As the obtained
dependence illustrates, when increasing the radius of
contact and increasing the ratio of the specific contact
resistivity to the specific resistance of semiconductor,
the measurement error is reduced.
Studied in the work [7] was the effect of microwave
treatment on the temperature dependence of the specific
contact resistivity of the ohmic contacts Au(0.2 μm) –
TiBx(0.1 μm) – Ge(0.04 μm) – Au(0.18 μm) – n(2 μm) –
n+(3 μm) – n++(300 μm) – InP within the temperature
range 100 to 400 °C, which were obtained using the
magnetron sputtering of metals and TiBx onto the InP
surface heated up to 100 °C. The specific contact
resistivity was investigated by using the four-contact
method before and after microwave treatment for 10 s at
the frequency 2.45 GHz and power density 1.5 W/cm2.
The radius of contacts was equal to 22.5 μm. Dopant
concentration of n-InP was ~91015 cm–3 in the n-layer,
~51017 cm–3 in the n+-layer, ~1018 cm–3 in the n++-
substrate, the thickness of these layers was 2, 3, and
300 μm, respectively. Ohmic contacts to InP were formed
during the RTA at T = 450 °C.
0 20 40 60 80 100
0.0
0.2
0.4
0.6
0.8
1.0
c
/
s
=1 cm
c
/
s
=0.1 cm
c
/
s
=0.01 cm
c/
c
r, m
Fig. 3. Dependence of the relative error of measuring ρс by
using the four-contact method on the contact radius for
contacts with various ratios ρс /ρs, under the condition of
lithography error ~2.5 μm.
50 100 150 200 250 300 350 400
0.0
0.5
1.0
1.5
2.0
2.5
3.0
init
10s microwave treatment
c, ·
10
-5
·c
m
2
T, K
Fig. 4. Dependence of the specific resistivity of ohmic contacts
Au–TiBx–Ge–Au–n–n+–n++-InP on the temperature before and
after microwave treatment for 10 s [7].
Table. Comparison of relative errors in measurements of
the specific contact resistivity obtained using various
methods.
Methods Δρc /ρc
ρs,
Оhm∙сm
ρc /ρs, сm 0.01 0.1 1 10
Cox-Strack* 0.88 0.27 0.08 –
LTLM
(L < 3LT)*
0.22 0.17 0.17 0.17 10–3
LTLM
(L > 3LT)*
0.16 0.24 – – 10–4
CTLM* 0.27 0.15 0.08 0.05
Four-contact 0.14 0.10 0.10 –
Kelvin* 0.25 0.15 0.05 0.04
Probing the
interface*
0.14 0.07 0.04 0.02
Notes. Asterisk * denotes the results obtained in [8],
LTLM – linear transmission line method,
CTLM – circular transmission line method.
Fig. 4 shows the dependence of ρс(Т) obtained in
[7] before and after microwave treatment. As it follows
from these curves, within the temperature range 80 to
220 K, the ρс value changes not exceeding the
measurement errors. With the temperature increase, the
changes in the specific contact resistivity exceed the
error of the measurement method.
4. Comparison of the measurement methods
Comparison of errors of measuring the specific contact
resistivity was carried out in the work [8]. The errors
were compared under the condition of lithography error
~2.5 μm close to an error produced in an industrial
environment. For the Cox-Strack method, the plate
thickness was 400 μm, for transmission line method
(TLM) the semiconductor thickness was 7 μm, the width
of the pads, as for the method of probing the interface,
was 1000 μm.
If the ratio of the specific contact resistivity to the
specific semiconductor one is equal to unity, the four-
contact method has a higher error than that in the
methods of Cox-Strack, TLM, Kelvin, probing the
interface. In the case of reducing the ratio ρc /ρs down to
0.01 cm, the error in measuring the specific contact
resistivity takes the minimum values as compared with
the abovementioned other methods.
5. Conclusions
In this work, we have considered the four-contact
method of measuring the specific contact resistivity for
planar geometry of pads. The performed calculations
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 394-397.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
397
indicate the promising of using this method for
measuring ρс in the case of the ratio ρc /ρs ≤ 0.01 cm,
provided that the requirements for the use of the four-
contact method are fulfilled.
References
1. D.K. Schroder, Semiconductor Materials and
Devices Characterization. Wiley, N.Y. 2006.
2. Сhung-Yu Ting, Charles Y. Chen, A study of the
contacts of a diffused resistor // Solid State
Electron. 14(6), p. 433-438 (1971).
3. H.H. Berger, Contact resistance and contact
resistivity // J. Electrochem. Soc. 119(4), p. 507-
514 (1972).
4. H.H. Berger, Models for contacts to planar devices
// Solid State Electron. 15(2), p. 145-158 (1972).
5. H. Murrmann, D. Wiedmann, Current crowding on
metal contacts to planar devices // IEEE Trans.
Electron. Dev. 16(12), p. 1022-1024 (1969).
6. A.S. Holland, G.K. Reeves, New challenges to the
modelling and electrical characterization of ohmic
contacts for ULSI devices // Microelectronics
Reliability, 40(6), p. 965-971 (2000).
7. A.E. Belyaev, A.V. Sachenko, N.S. Boltovets,
V.N. Ivanov, R.V. Konakova, Ya.Ya. Kudryk,
L.A. Matveeva, V.V. Milenin, S.V. Novitskii,
V.N. Sheremet, Effect of microwave irradiation on
resistance of Au–TiBx–Ge–Au–n–n+–n++-GaAs(InP)
ohmic contacts // Fizika tekhnika poluprovodnikov,
46(4), p. 558-561 (2012), in Russian.
8. V.N. Sheremet, Metrological aspects of measuring
the resistance of ohmic contacts // Izvestiya vuzov.
Radioelektronika, 53(3), p. 3-12 (2010), in Russian.
Semiconductor Physics, Quantum Electronics & Optoelectronics, 2014. V. 17, N 4. P. 394-397.
PACS 73.40.Ns, 73.40.Cg, 85.40.-e
Metrological aspects of researching the specific contact resistivity
of ohmic contacts by using the four-contact method
V.N. Sheremet
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 03028 Kyiv, Ukraine
Phone: 38(044) 525-61-82; e-mail: VolodymyrSheremet@gmail.com
Abstract. In this paper, we have considered the four-contact method for measurements of the specific contact resistivity of the ohmic contacts (ρc). The presented method for measuring ρc has been compared with several other methods. Limits of applying this method have been shown.
Keywords: ohmic contact, four-contact method, specific contact resistivity.
Manuscript received 19.03.14; revised version received 30.07.14; accepted for publication 29.10.14; published online 10.11.14.
1. Introduction
Creation of new semiconductor devices and improvement of existing parameters are impossible without reducing the resistance of the ohmic contacts. The main parameter that characterizes the ohmic contact is the specific contact resistivity ρc. In the case of high resistance of the metal-semiconductor contact, when a device operates, an additional heating occurs in the contact, which negatively impacts on the reliability and efficiency of the device. It is particularly harmful for powerful high-frequency devices. To minimize heating, it is necessary to reduce ρс of the ohmic contact. With decreasing the ρс value, the requirements to the accuracy of determining the specific contact resistivity increase. Promising materials for development of high-power microwave devices are semiconductor compounds A3B5 such as GaN, InN, InP, etc. The effective use of these semiconductor materials and increase of the power of microelectronic devices being based on them are impossible without creating reliable heat-resistant ohmic contacts.
2. Ohmic contact and its resistance
For measuring the contact resistance, both vertical and planar test structures may be used. In the most complete manner, the existing methods were considered in the work [1]. In response to the direct measurement, there can be obtained a resistance usually presented as the sum of the resistances [2]:
m
p
T
s
c
R
R
+
R
+
R
+
R
=
R
+
,
(1)
where R is the measured resistance, Rc – the contact resistance, Rs – resistance of semiconductor, RT – resistance provoked by current spreading, Rp – resistance probes and connecting conductors, Rm – resistance of metallization.
Resistance of metallization, probes, connecting conductors, and resistance provoked by current spreading are often small values as compared to the resistance of semiconductor and that of the contact. If the contact resistivity is comparable to the resistance of semiconductor, RT and Rp are infinitely small values in relation to Rc. With further decreasing ρс, account must be also taken of the values of the resistance provoked by current spreading and that of semiconductor Rp.
In the case of a vertical test structure (Fig. 1a), the impact of the current spreading is less than in the case of a planar structure (Fig. 1b), that’s why at first, more widely used were the methods using a vertical structure, among which the Cox-Strack method was most widely applied [1]. However, this method is not applicable in the case of contact structures to epitaxial films.
Application of a planar structure to study the specific contact resistivity is preferable because of the reduced number of processes is required to form a test structure. But when using a planar test structure, one should take account of the current spreading that can be characterized by the transfer length LT – the distance from the edge of the contact, near which the current decreases by e times [3-5]. It is determined by the equation [3-5]:
s
c
T
t
L
r
r
=
.
(2)
If the length of contact is longer than the transfer distance, the contact becomes infinite, and its resistance does not depend on the length. Since the entire contact area is not included into the passage of current, it complicates determining the ρс value. If the contact length is less than the transfer distance, the total resistance is increased as a result of reducing the area of current passage, which must be considered when determining the specific contact resistivity. Accordingly, the effective area of the planar contact becomes less than the actual one.
In the case when the contact length is less than the width of the diffusion region in semiconductor, there observed an effect of the surface current spreading, and the measured total resistance increases to a value determined in the work [2] as follows:
Fig. 1. Current spreading in the vertical (a) and planar (b) test structures (d is the diameter of contact, LT – transfer length, t – thickness of semiconductor).
÷
÷
ø
ö
ç
ç
è
æ
-
+
-
+
p
r
=
2
2
1
ln
1
1
ln
1
k
k
k
k
k
R
s
w
,
(3)
where k = W/(W–w) is the correcting parameter, w – contact width, W – width of the diffusion region.
In these methods, both extrapolative and two-contact one, with a planar test structure [5], the resistance caused by current spreading is not taken into consideration, which results in the increased error of measurements. One of the most easy-to-implement planar measurement methods is the four-contact method of ρс measurements.
3. Principles of measuring ρс
by using the four-contact method
The method consists in measuring the voltage at equal distances between the current contacts (Fig. 2) [1]. This method can be used if the transfer length is much larger than the contact size. Also, a necessary condition is L >> r, L >> t, where L is the contact length, t – thickness of the semiconductor film. Under these conditions, the contact resistivity is determined from the equation [6]:
(
)
[
]
ï
þ
ï
ý
ü
ï
î
ï
í
ì
-
÷
÷
ø
ö
ç
ç
è
æ
-
p
»
r
2
ln
2
2
/
1
2
/
3
ln
0
2
0
1
2
r
L
I
V
I
V
r
ñ
.
(4)
Disadvantage of the method is that it is necessary to fulfill the condition L >> r that implies a significant gap between the contacts, which can result in the inability to determine the contact resistivity at a certain ratio ρc /ρs.
Due to simplicity of the test structure formation, this method is used for large transfer lengths.
In the case of using the four-contact method, the error of measurements of the specific contact resistivity can be determined using the partial derivative technique:
(
)
.
2
1
2
3
ln
1
)
2
(ln
3
2
1
2
1
2
3
ln
2
2
2
÷
÷
ø
ö
ç
ç
è
æ
÷
ø
ö
ç
è
æ
-
÷
ø
ö
ç
è
æ
-
-
-
÷
÷
ø
ö
ç
ç
è
æ
+
r
r
÷
ø
ö
ç
è
æ
-
´
´
÷
ø
ö
ç
è
æ
D
+
D
+
D
+
D
+
D
»
r
r
D
r
L
L
r
r
r
L
r
r
L
L
I
I
V
V
r
r
s
c
c
ñ
(5)
Fig. 2. The principle of measuring the contact resistivity by using the four-contact method.
The performed calculations have resulted in the dependence of the relative error of the measured contact resistance on the contact radius (Fig. 3). As the obtained dependence illustrates, when increasing the radius of contact and increasing the ratio of the specific contact resistivity to the specific resistance of semiconductor, the measurement error is reduced.
Studied in the work [7] was the effect of microwave treatment on the temperature dependence of the specific contact resistivity of the ohmic contacts Au(0.2 μm) – TiBx(0.1 μm) – Ge(0.04 μm) – Au(0.18 μm) – n(2 μm) – n+(3 μm) – n++(300 μm) – InP within the temperature range 100 to 400 °C, which were obtained using the magnetron sputtering of metals and TiBx onto the InP surface heated up to 100 °C. The specific contact resistivity was investigated by using the four-contact method before and after microwave treatment for 10 s at the frequency 2.45 GHz and power density 1.5 W/cm2. The radius of contacts was equal to 22.5 μm. Dopant concentration of n-InP was ~9(1015 cm–3 in the n-layer, ~5(1017 cm–3 in the n+-layer, ~1018 cm–3 in the n++-substrate, the thickness of these layers was 2, 3, and 300 μm, respectively. Ohmic contacts to InP were formed during the RTA at T = 450 °C.
0
20
40
60
80
100
0.0
0.2
0.4
0.6
0.8
1.0
r
c
/
r
s
=1 cm
r
c
/
r
s
=0.1 cm
r
c
/
r
s
=0.01 cm
Dr
c
/
r
c
r,
m
m
Fig. 3. Dependence of the relative error of measuring ρс by using the four-contact method on the contact radius for contacts with various ratios ρс /ρs, under the condition of lithography error ~2.5 μm.
50
100
150
200
250
300
350
400
0.0
0.5
1.0
1.5
2.0
2.5
3.0
init
10s microwave treatment
r
c
, ·10
-5
W
·cm
2
T, K
Fig. 4. Dependence of the specific resistivity of ohmic contacts Au–TiBx–Ge–Au–n–n+–n++-InP on the temperature before and after microwave treatment for 10 s [7].
Table. Comparison of relative errors in measurements of the specific contact resistivity obtained using various methods.
Methods
Δρc /ρc
ρs, Оhm∙сm
ρc /ρs, сm
0.01
0.1
1
10
Cox-Strack*
0.88
0.27
0.08
–
LTLM
(L < 3LT)*
0.22
0.17
0.17
0.17
10–3
LTLM
(L > 3LT)*
0.16
0.24
–
–
10–4
CTLM*
0.27
0.15
0.08
0.05
Four-contact
0.14
0.10
0.10
–
Kelvin*
0.25
0.15
0.05
0.04
Probing the interface*
0.14
0.07
0.04
0.02
Notes. Asterisk * denotes the results obtained in [8],
LTLM – linear transmission line method,
CTLM – circular transmission line method.
Fig. 4 shows the dependence of ρс(Т) obtained in [7] before and after microwave treatment. As it follows from these curves, within the temperature range 80 to 220 K, the ρс value changes not exceeding the measurement errors. With the temperature increase, the changes in the specific contact resistivity exceed the error of the measurement method.
4. Comparison of the measurement methods
Comparison of errors of measuring the specific contact resistivity was carried out in the work [8]. The errors were compared under the condition of lithography error ~2.5 μm close to an error produced in an industrial environment. For the Cox-Strack method, the plate thickness was 400 μm, for transmission line method (TLM) the semiconductor thickness was 7 μm, the width of the pads, as for the method of probing the interface, was 1000 μm.
If the ratio of the specific contact resistivity to the specific semiconductor one is equal to unity, the four-contact method has a higher error than that in the methods of Cox-Strack, TLM, Kelvin, probing the interface. In the case of reducing the ratio ρc /ρs down to 0.01 cm, the error in measuring the specific contact resistivity takes the minimum values as compared with the abovementioned other methods.
5. Conclusions
In this work, we have considered the four-contact method of measuring the specific contact resistivity for planar geometry of pads. The performed calculations indicate the promising of using this method for measuring ρс in the case of the ratio ρc /ρs ≤ 0.01 cm, provided that the requirements for the use of the four-contact method are fulfilled.
References
1. D.K. Schroder, Semiconductor Materials and Devices Characterization. Wiley, N.Y. 2006.
2. Сhung-Yu Ting, Charles Y. Chen, A study of the contacts of a diffused resistor // Solid State Electron. 14(6), p. 433-438 (1971).
3. H.H. Berger, Contact resistance and contact resistivity // J. Electrochem. Soc. 119(4), p. 507-514 (1972).
4. H.H. Berger, Models for contacts to planar devices // Solid State Electron. 15(2), p. 145-158 (1972).
5.
H. Murrmann, D. Wiedmann, Current crowding on metal contacts to planar devices // IEEE Trans. Electron. Dev. 16(12), p. 1022-1024 (1969).
6. A.S. Holland, G.K. Reeves, New challenges to the modelling and electrical characterization of ohmic contacts for ULSI devices // Microelectronics Reliability, 40(6), p. 965-971 (2000).
7. A.E. Belyaev, A.V. Sachenko, N.S. Boltovets, V.N. Ivanov, R.V. Konakova, Ya.Ya. Kudryk, L.A. Matveeva, V.V. Milenin, S.V. Novitskii, V.N. Sheremet, Effect of microwave irradiation on resistance of Au–TiBx–Ge–Au–n–n+–n++-GaAs(InP) ohmic contacts // Fizika tekhnika poluprovodnikov, 46(4), p. 558-561 (2012), in Russian.
8. V.N. Sheremet, Metrological aspects of measuring the resistance of ohmic contacts // Izvestiya vuzov. Radioelektronika, 53(3), p. 3-12 (2010), in Russian.
© 2014, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine
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