U.S. patent application number 13/167058 was filed with the patent office on 2011-10-20 for semiconductor device having non-silicide region in which no silicide is formed on diffusion layer.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Takayuki Hiraoka, Kenji Honda, Tsutomu Kojima, Kuniaki Utsumi.
Application Number | 20110254096 13/167058 |
Document ID | / |
Family ID | 40787573 |
Filed Date | 2011-10-20 |
United States Patent
Application |
20110254096 |
Kind Code |
A1 |
Hiraoka; Takayuki ; et
al. |
October 20, 2011 |
SEMICONDUCTOR DEVICE HAVING NON-SILICIDE REGION IN WHICH NO
SILICIDE IS FORMED ON DIFFUSION LAYER
Abstract
A semiconductor device includes first and second MOSFETs
corresponding to at least first power source voltage and second
power source voltage lower than the first power source voltage, and
non-silicide regions formed in drain portions of the first and
second MOSFETs and having no silicide formed therein. The first
MOSFET includes first diffusion layers formed in source/drain
portions, a second diffusion layer formed below a gate portion and
formed shallower than the first diffusion layer and a third
diffusion layer formed with the same depth as the second diffusion
layer in the non-silicide region, and the second MOSFET includes
fourth diffusion layers formed in source/drain portions, a fifth
diffusion layer formed below a gate portion and formed shallower
than the fourth diffusion layer and a sixth diffusion layer formed
shallower than the fourth diffusion layer and deeper than the fifth
diffusion layer in the non-silicide region.
Inventors: |
Hiraoka; Takayuki;
(Kawasaki-shi, JP) ; Utsumi; Kuniaki;
(Yokohama-shi, JP) ; Kojima; Tsutomu;
(Yokohama-shi, JP) ; Honda; Kenji; (Kawasaki-shi,
JP) |
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
40787573 |
Appl. No.: |
13/167058 |
Filed: |
June 23, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12277456 |
Nov 25, 2008 |
7994584 |
|
|
13167058 |
|
|
|
|
Current U.S.
Class: |
257/368 ;
257/E29.242 |
Current CPC
Class: |
H01L 27/0266 20130101;
H01L 29/105 20130101; H01L 29/0847 20130101; H01L 21/823418
20130101; H01L 29/1083 20130101; H01L 29/665 20130101; H01L 29/7835
20130101; H01L 29/66659 20130101; H01L 27/088 20130101 |
Class at
Publication: |
257/368 ;
257/E29.242 |
International
Class: |
H01L 29/772 20060101
H01L029/772 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2007 |
JP |
2007-333302 |
Claims
1. A semiconductor device comprising: a plurality of metal oxide
semiconductor field-effect transistors (MOSFETs) respectively
corresponding to a plurality of power source voltages, and
non-silicide regions formed in drain portions of the plurality of
MOSFETs and having no silicide formed therein, wherein diffusion
layer resistance regions with the same depth as that of LDD
diffusion layers of that MOSFET which corresponds to highest power
source voltage among the plurality of MOSFETs are formed in the
non-silicide regions of the plurality of MOSFETs.
2. The semiconductor device according to claim 1, wherein the
diffusion layer resistance region is deeper than the LDD diffusion
layers of the MOSFETs other than the MOSFET corresponding to the
highest power source voltage.
3. The semiconductor device according to claim 1, further
comprising those of diffusion layers whose conductivity type is the
same as that of the LDD diffusion layer and diffusion layers whose
conductivity type is different from that of the LDD-diffusion layer
which are formed deeper than the diffusion layer resistance region
in the non-silicide regions of the plurality of MOSFETs.
4. The semiconductor device according to claim 1, wherein the
diffusion layer resistance regions function as ballast resistors.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Division of application Ser. No.
12/277,456 filed Nov. 25, 2008, the entire contents of which are
hereby incorporated herein by reference.
[0002] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2007-333302,
filed Dec. 25, 2007, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] This invention relates to a semiconductor device and more
particularly to a metal oxide semiconductor field-effect transistor
(MOSFET) electrostatic discharge (ESD) protection device for
preventing a current such as electrostatic surge from flowing into
a semiconductor integrated circuit device.
[0005] 2. Description of the Related Art
[0006] Conventionally, semiconductor integrated circuit devices
having ESD protection devices provided thereon have been developed.
The ESD protection device is provided to prevent a current such as
electrostatic surge from flowing into the semiconductor integrated
circuit device. Some MOSFET ESD protection devices among the above
ESD protection devices are designed to enhance the ESD discharging
ability by forming silicide unformed portions (non-silicide
regions) in drain regions and source regions (see, for example,
Jpn. Pat. Appln. KOKAI Publication No. 2006-339444). That is, since
a current is not concentrated in the silicide portion in a
diffusion layer in the portion formed as the non-silicide region,
the breakdown voltage of the device acting as the ESD protection
device is enhanced.
[0007] In the ESD protection device, a diffusion layer with the
same junction depth as that of a diffusion layer lying below the
gate is formed in the non-silicide region in some cases. However,
if this method is applied to a transistor for low power source
voltage (or low voltage which is hereinafter referred to as LV)
used as the ESD protection device, the junction depth of the
diffusion layer is reduced and junction leakage may occur in the
non-silicide region. In the above document, it is disclosed that
the resistance of the non-silicide region is adjusted by using a
diffusion layer with the same junction depth as that of a diffusion
layer lying below the gate of the LV transistor in the non-silicide
region of a transistor for high power source voltage (or high
voltage which is hereinafter referred to as HV) used as the ESD
protection device.
[0008] However, in the above document, it is not disclosed that a
countermeasure against junction leakage is taken by forming a
diffusion layer with the same junction depth as that of a diffusion
layer lying below the gate of the HV transistor in the non-silicide
region of the LV transistor.
BRIEF SUMMARY OF THE INVENTION
[0009] According to a first aspect of the present invention, there
is provided a semiconductor device which includes first and second
metal oxide semiconductor field-effect transistors (MOSFETs)
corresponding to at least first power source voltage and second
power source voltage lower than the first power source voltage, and
non-silicide regions formed in drain portions of the first and
second MOSFETs and having no silicide formed therein, wherein the
first MOSFET includes first diffusion layers formed in source/drain
portions, a second diffusion layer formed below a gate portion and
formed shallower than the first diffusion layer and a third
diffusion layer formed with the same depth as the second diffusion
layer in the non-silicide region, and the second MOSFET includes
fourth diffusion layers formed in source/drain portions, a fifth
diffusion layer formed below a gate portion and formed shallower
than the fourth diffusion layer and a sixth diffusion layer formed
shallower than the fourth diffusion layer and deeper than the fifth
diffusion layer in the non-silicide region.
[0010] According to a second aspect of the present invention, there
is provided a semiconductor device which includes a plurality of
first metal oxide semiconductor field-effect transistors (MOSFETs)
corresponding to first power source voltage, the plurality of first
MOSFETs including non-silicide regions formed in drain portions
thereof and having no silicide formed therein, first diffusion
layers formed in source/drain portions, second diffusion layers
formed below gate portions and formed shallower than the first
diffusion layer and third diffusion layers formed with the same
depth as the second diffusion layer in the non-silicide regions,
and a plurality of second MOSFETs corresponding to second power
source voltage lower than the first power source voltage, wherein
the plurality of second MOSFETs include non-silicide regions formed
in drain portions thereof and having no silicide formed therein,
fourth diffusion layers formed in source/drain portions, fifth
diffusion layers formed below gate portions and formed shallower
than the fourth diffusion layer and sixth diffusion layers formed
shallower than the fourth diffusion layer and deeper than the fifth
diffusion layer in the non-silicide regions.
[0011] According to a third aspect of the present invention, there
is provided a semiconductor device which includes a plurality of
metal oxide semiconductor field-effect transistors (MOSFETs)
respectively corresponding to a plurality of power source voltages,
and non-silicide regions formed in drain portions of the plurality
of MOSFETs and having no silicide formed therein, wherein diffusion
layer resistance regions with the same depth as that of LDD
diffusion layers of that MOSFET which corresponds to highest power
source voltage among the plurality of MOSFETs are formed in the
non-silicide regions of the plurality of MOSFETs.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0012] FIGS. 1A and 1B are cross-sectional views showing an example
of the structure of a semiconductor device (MOSFET ESD protection
device) according to a first embodiment of this invention.
[0013] FIG. 2 is a diagram showing the relation between the
concentrations of a P-- diffusion layer and a diffusion layer
resistance region of the ESD protection device according to the
first embodiment.
[0014] FIG. 3 is a cross-sectional view showing a manufacturing
method of the ESD protection device according to the first
embodiment.
[0015] FIG. 4 is a cross-sectional view showing a manufacturing
method of the ESD protection device according to the first
embodiment.
[0016] FIG. 5 is a cross-sectional view showing the manufacturing
method of the ESD protection device according to the first
embodiment.
[0017] FIG. 6 is a cross-sectional view showing the manufacturing
method of the ESD protection device according to the first
embodiment.
[0018] FIGS. 7A and 7B are cross-sectional views showing the
manufacturing method of the ESD protection device according to the
first embodiment.
[0019] FIGS. 8A and 8B are cross-sectional views showing the
manufacturing method of the ESD protection device according to the
first embodiment.
[0020] FIGS. 9A and 9B are cross-sectional views showing an example
of the structure of a semiconductor device (MOSFET ESD protection
device) according to a second embodiment of this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Embodiments of the present invention will be described with
reference to the accompanying drawings. It should be noted that the
drawings are schematic ones and so are not to scale. The following
embodiments are directed to a device and a method for embodying the
technical concept of the present invention and the technical
concept does not specify the material, shape, structure or
configuration of components of the present invention. Various
changes and modifications can be made to the technical concept
without departing from the scope of the claimed invention.
First Embodiment
[0022] FIGS. 1A and 1B show an example of the structure of a
semiconductor device according to a first embodiment of this
invention. In this embodiment, a case wherein this invention is
applied to an ESD protection device having an nMOSFET structure is
explained. FIG. 1A shows an ESD protection device used for high
voltage (HV) corresponding to first power source voltage and
extracted from a plurality of ESD protection devices provided on a
semiconductor integrated circuit device and FIG. 1B shows an ESD
protection device used for low voltage (LV) corresponding to second
power source voltage lower than the first power source voltage and
extracted from the ESD protection devices.
[0023] As shown in the cross-sectional view of FIG. 1A, a plurality
of element isolation regions (shallow trench isolation [STI]) 12a,
13a, 14a are formed on the surface portion of a P-well region (or a
p-type semiconductor substrate formed of silicon, for example) 11a
of an HV ESD protection device 11A. A P+ region 21a for a substrate
contact is formed on that surface portion of the P-well region 11a
which corresponds to a portion between the element isolation
regions 12a and 13a.
[0024] First to third N+ diffusion layers (first diffusion layers)
22a, 23a, 24a with high concentration are selectively formed on
those surface portions of the P-well region 11a which correspond to
a portion between the element isolation regions 13a and 14a. The
first N+ diffusion layer 22a forms a source region and the second
and third diffusion layers 23a and 24a form drain regions. Silicide
layers 31a, 32a, 33a, 34a are respectively formed on the surface
portions of the P+ region 21a and first to third N+ diffusion
layers 22a, 23a, 24a.
[0025] A gate electrode (polysilicon gate) 42a is formed above that
portion of the P-well region 11a which corresponds to a portion
between the first and second N+ diffusion layers 22a and 23a with a
gate insulating film 41a disposed therebetween. Gate sidewall
insulating films 43a are formed on the sidewall portions of the
gate insulating film 41a and gate electrode 42a. A P-- diffusion
layer 25a acting as a channel region is formed on that surface
portion of the P-well region 11a which corresponds to a portion
lying directly below the gate electrode 42a (below the gate), that
is, a portion between the first and second N+ diffusion layers 22a
and 23a. A source-side lightly doped drain (LDD) diffusion layer
(an N- layer acting as a second diffusion layer) 26a used to form
an extension region is formed in a position adjacent to the first
N+ diffusion layer 22a on the surface portion of the P-- diffusion
layer 25a. Further, a drain-side LDD diffusion layer (an N- layer
acting as a second diffusion layer) 27a used to form an extension
region is formed in a position adjacent to the second N+ diffusion
layer 23a on the surface portion of the P-- diffusion layer 25a.
The impurity junctions of the LDD diffusion layers 26a, 27a are
shallower than those of the first to third N+ diffusion layers 22a,
23a, 24a and the depths thereof are controlled according to the
first power source voltage.
[0026] A silicide block 51a used to form a silicide unformed
portion (non-silicide region) is formed above that portion of the
P-well region 11a which corresponds to a portion between the second
and third N+ diffusion layers 23a and 24a. A P-- diffusion layer
28a and a diffusion layer resistance region (an N- layer acting as
a third diffusion layer) 29a acting as a ballast resistor are
formed directly under the silicide block 51a, that is, on that
surface portion of the P-well region 11a which corresponds to the
portion between the second and third N+ diffusion layers 23a and
24a. The P-- diffusion layer 28a is formed with the same impurity
concentration (distribution) and the same junction depth as those
of the P-- diffusion layer 25a. The diffusion layer resistance
region 29a is formed with the same impurity concentration and the
same junction depth as those of the LDD diffusion layers 26a, 27a.
That is, as the diffusion layer resistance region 29a of the HV ESD
protection device 11A, a region that is the same as the LDD
diffusion layers 26a, 27a lying directly below the gate electrode
42a or a region that is connected to the surrounding second and
third N+ diffusion layers 23a, 24a having deep junctions and formed
with sufficient depth to contain the silicide layers 33a, 34a
without causing any problem associated with the junction leakage is
used.
[0027] Symbols 52a, 53a, 54a in the drawing denote contacts
respectively connected to the silicide layers 31a, 32a, 34a.
[0028] Further, as shown in the cross-sectional view of FIG. 1B, a
plurality of element isolation regions (STI) 12b, 13b, 14b are
formed on the surface portion of a P-well region (or a p-type
semiconductor substrate formed of silicon, for example) 11b of an
IN ESD protection device 11B. A P+ region 21b for a substrate
contact is formed on that surface portion of the P-well region 11b
which corresponds to a portion between the element isolation
regions 12b and 13b.
[0029] First to third N+ diffusion layers (fourth diffusion layers)
22b, 23b, 24b with high concentration are selectively formed on
that surface portion of the P-well region 11b which corresponds to
a portion between the element isolation regions 13b and 14b. The
first N+ diffusion layer 22b forms a source region and the second
and third diffusion layers 23b, 24b form drain regions. Silicide
layers 31b, 32b, 33b, 34b are respectively formed on the surface
portions of the P+ region 21b and first to third N+ diffusion
layers 22b, 23b, 24b.
[0030] A gate electrode (polysilicon gate) 42b is formed above that
portion of the P-well region 11b which corresponds to a portion
between the first and second N+ diffusion layers 22b and 23b with a
gate insulating film 41b disposed therebetween. On the sidewall
portions of the gate insulating film 41b and gate electrode 42b,
gate sidewall insulating films 43b are formed. A P-- diffusion
layer 25b acting as a channel region is formed directly below the
gate electrode 42b (below the gate), that is, on that surface
portion of the P-well region 11b which corresponds to a portion
between the first and second N+ diffusion layers 22b and 23b. A
source-side lightly doped drain (LDD) diffusion layer (an N- layer
acting as a fifth diffusion layer) 26b used to form an extension
region is formed in a position adjacent to the first N+ diffusion
layer 22b on the surface portion of the P-- diffusion layer 25b. A
drain-side LDD diffusion layer (an N- layer acting as a fifth
diffusion layer) 27b used to form an extension region is formed in
a position adjacent to the second N+ diffusion layer 23b on the
surface portion of the P-- diffusion layer 25b. The impurity
junctions of the LDD diffusion layers 26b, 27b are shallower than
those of the LDD diffusion layers 26a, 27a and the depths thereof
are controlled according to the second power source voltage.
[0031] A silicide block 51b used to form a non-silicide region is
formed on that portion of the P-well region 11b which corresponds
to a portion between the second and third N+ diffusion layers 23b
and 24b. A P-- diffusion layer (seventh diffusion layer) 28b and a
diffusion layer resistance region (an N- layer acting as a sixth
diffusion layer) 29b acting as a ballast resistor are formed
directly under the silicide block 51b, that is, on that surface
portion of the P-well region 11b which corresponds to a portion
between the second and third N+ diffusion layers 23b and 24b. The
P-- diffusion layer 28b is formed with the same impurity
concentration and the same junction depth as the P-- diffusion
layer 25b. The diffusion layer resistance region 29b is formed with
the same impurity concentration and the same junction depth as the
diffusion layer resistance region 29a. That is, as the diffusion
layer resistance region 29b of the LV ESD protection device 11B, a
region that is different from the LDD diffusion layers 26b, 27b
lying directly below the gate electrode 42b and is the same as the
LDD diffusion layers 26a, 27a lying directly below the gate
electrode 42a of the HV ESD protection device 11A is used. The
diffusion layer resistance region 29b is formed at the same time as
and in the same formation process as the LDD diffusion layers 26a,
27a and diffusion layer resistance region 29a by use of the same
mask. As a result, the diffusion layer resistance region 29b that
is formed in a small area and does not cause junction leakage can
be easily realized only by using an existing MOSFET formation
process (normal transistor formation process).
[0032] Symbols 52b, 53b, 54b in the drawing denote contacts
respectively connected to the silicide layers 31b, 32b, 34b.
[0033] FIG. 2 shows the relation between the concentrations of the
P-- diffusion layer and the diffusion layer resistance region. When
the LDD structure (HV LDD) of the HV ESD protection device 11A is
used as the ballast resistor of the LV ESD protection device 11B,
it is rather preferable than in a case wherein the LDD structure
(LV LDD) of the LV ESD protection device 11B is used. As is clearly
understood from the drawing, this is because the junction leakage
in the non-silicide region of the LV ESD protection device 11B can
be reduced by using a gentle and deep junction, for example,
between the P-- diffusion layer 25a and the LDD diffusion layers
26a, 27a of the HV ESD protection device 11A. Thus, the ESD
discharging ability can be enhanced by forming the ballast resistor
of the HV LDD structure that is formed of the diffusion layer
resistance region 29b in the non-silicide region of the LV ESD
protection device 11B.
[0034] The junction depth of the diffusion layer below the gate of
the transistor is set to approximately 1/4 the gate length in order
to suppress the short channel effect. For example, if it is
supposed that the gate length of an HV transistor of an
input/output portion is set to approximately 400 nm with the
transistor technique in which the gate length of an LV transistor
is set in a 90 nm-generation, the junction depth of a diffusion
layer below the gate of the LV transistor is set to 20 to 25 nm and
the junction depth of a diffusion layer below the gate of the HV
transistor is set to approximately 100 nm.
[0035] Next, a manufacturing method of the ESD protection device
(FIGS. 11A, 11B) with the nMOSFET structure described above is
simply explained with reference to FIG. 3 to FIGS. 8A and 8B.
[0036] First, for example, as shown in FIG. 3, a plurality of
element isolation regions 12a, 13a, 14a and 12b, 13b, 14b are
formed on the surface portions of P-well regions 11a, 11b by use of
an existing MOSFET formation process. Then, P+ regions 21a, 21b for
substrate contacts and P-- diffusion layers 25a, 25b are
respectively formed on the surface portions of the P-well regions
11a, 11b. After this, gate insulating films 41a, 41b and gate
electrodes 42a, 42b are formed on the P-well regions 11a, 11b. A
reference symbol 61 in the drawing denotes a mask used at the
ion-implantation time in a simplified form.
[0037] Next, for example, as shown in FIG. 4, LDD diffusion layers
26b, 27b are formed in self-alignment with the gate electrode 42b
in the LV ESD protection device 11B.
[0038] Then, for example, as shown in FIG. 5, LDD diffusion layers
26a, 27a are formed in self-alignment with the gate electrode 42a
in the HV ESD protection device 11A.
[0039] At this time, for example, as shown in FIG. 6, a diffusion
layer resistance region 29b having the same junction depth as the
LDD diffusion layers 26a, 27a of the HV ESD protection device 11A
is formed in an area in which a silicide block 51b is to be formed
in the LV ESD protection device 11B by using the mask 61 having an
opening with the width determined by taking the mask misalignment
and spread of the diffusion layer into consideration.
[0040] Next, for example, as shown in FIGS. 7A and 7B, gate
sidewall insulating films 43a and silicide block 51a of the HV ESD
protection device 11A are formed and, at the same time, gate
sidewall insulating films 43b and silicide block 51b of the LV ESD
protection device 11B are formed by using the existing MOSFET
formation process.
[0041] Next, for example, as shown in FIGS. 8A and 8B, deep N+
diffusion layers 22a, 23a, 24a with high concentration are formed
in the source/drain regions of the HV ESD protection device 11A
and, at the same time, deep N+ diffusion layers 22b, 23b, 24b with
high concentration are formed in the source/drain regions of the LV
ESD protection device 11B by using the existing MOSFET formation
process.
[0042] At this time, deep diffusion layers with high concentration
are prevented from being formed in portions directly under the
silicide blocks due to the presence of the silicide blocks 51a,
51b.
[0043] After this, silicide layers 31a, 32a, 33a, 34a and 31b, 32b,
33b, 34b and contacts 52a, 53a, 54a and 52b, 53b, 54b are formed to
complete the HV ESD protection device 11A and LV ESD protection
device 11B with the structures shown in FIGS. 1A and 1B.
[0044] As described above, the LDD structure (HV LDD) of the HV ESD
protection device 11A is used in the drain portion (non-silicide
region) of the LV ESD protection device 11B. That is, the diffusion
layer resistance region 29b having the same junction depth as the
LDD diffusion layers 26a, 27a of the HV ESD protection device 11A
is formed directly under the silicide block 51b of the LV ESD
protection device 11B. Thus, the LV ESD protection device 11B can
be formed with the structure of a small area without causing a
junction leakage problem. Therefore, a MOSFET ESD protection device
that corresponds to low power source voltage and enhances the ESD
discharging ability without providing an additional step to the
existing MOSFET formation process can be realized.
Second Embodiment
[0045] FIGS. 9A and 9B show an example of the structure of a
semiconductor device according to a second embodiment of this
invention. In the present embodiment, a case wherein this invention
is applied to an ESD protection device having an nMOSFET structure
is explained. In this case, FIG. 9A shows a high power source
voltage (HV) ESD protection device that corresponds to first power
source voltage and is extracted from a plurality of ESD protection
devices provided on a semiconductor integrated circuit device and
FIG. 9B shows a low power source voltage (LV) ESD protection device
that corresponds to second power source voltage lower than the
first power source voltage and is extracted from the ESD protection
devices. In this example, portions that are the same as those of
the first embodiment (see FIGS. 1A and 1B) are denoted by the same
reference symbols and detailed explanation thereof is omitted.
[0046] In the case of this embodiment, diffusion layer resistance
regions (N- layers) 29a, 29b acting as ballast resistors and N--
diffusion layers (eighth layers) 71a, 71b used for the formation of
pMOSFETs (not shown) are respectively formed directly under
silicide blocks 51a, 51b that constitute drain portions. That is,
for example, as shown in FIG. 9A, an HV ESD protection device 11A'
is formed with the structure in which the N-- diffusion layer 71a
for the channel region of the pMOSFET is formed as the diffusion
layer directly below the silicide block 51a and the diffusion layer
resistance region 29a that is formed at the same time as and in the
same formation step as the LDD diffusion layers 26a, 27a by use of
the same mask is superimposed on the above diffusion layer.
[0047] Further, for example, as shown in FIG. 9B, an LV ESD
protection device 11B' is formed with the structure in which the
N-- diffusion layer 71b for the channel region of the pMOSFET is
formed as the diffusion layer directly below the silicide block 51b
and the diffusion layer resistance region 29b that is formed at the
same time as and in the same formation step as the LDD diffusion
layers 26a, 27a and diffusion layer resistance region 29a of the HV
ESD protection device 11A' by use of the same mask is superimposed
on the above diffusion layer.
[0048] The N-- diffusion layers 71a, 71b are formed at the same
time in the same formation step by use of the same mask when the
channel regions of pMOSFETs (not shown) are formed.
[0049] Thus, according to the present embodiment, the diffusion
layer resistance region that is formed in a small area and has
preset resistance without causing a junction leakage problem can be
formed only by using the existing MOSFET formation process and the
ESD discharging ability can be enhanced.
[0050] Particularly, with the structure as shown in the second
embodiment, a deep junction can be attained directly below the
silicide block without significantly lowering the diffusion layer
resistance. Therefore, for example, the junction resistance of the
diffusion layer can be further enhanced and a MOSFET ESD protection
device having more preferable ESD protection ability can be
realized.
[0051] In each of the above embodiments, a case wherein this
invention is applied to the ESD protection device with the nMOSFET
structure is explained as an example, but this invention is not
limited to this case. For example, this invention can be similarly
applied to an ESD protection device with a pMOSFET structure.
[0052] Further, this invention is not limited to the MOSFET ESD
protection device with the LDD structure that corresponds to two
types of HV and LV power source voltages. For example, this
invention can be applied to a MOSFET ESD protection device with an
LDD structure that corresponds to three or more types of power
source voltages. In this case, an LDD diffusion layer of the ESD
protection device that corresponds to the highest power source
voltage may be formed as a diffusion layer of a drain portion
(directly under the silicide block) of another ESD protection
device whose power source voltage is lower than that of the above
ESD protection device.
[0053] Further, as the diffusion layer resistance region 29b formed
directly under the silicide block 51b, any region whose junction is
shallower than that of the second N+ diffusion layer 23b and deeper
than those of the LDD diffusion layers 26b, 27b can be used.
[0054] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *