U.S. patent application number 13/974939 was filed with the patent office on 2015-02-26 for lateral bipolar junction transistor and fabrication method thereof.
This patent application is currently assigned to United Microelectronics Corp.. The applicant listed for this patent is United Microelectronics Corp.. Invention is credited to Tien-Hao Tang, Pei-Shan Tseng, Chang-Tzu Wang.
Application Number | 20150054132 13/974939 |
Document ID | / |
Family ID | 52479625 |
Filed Date | 2015-02-26 |
United States Patent
Application |
20150054132 |
Kind Code |
A1 |
Wang; Chang-Tzu ; et
al. |
February 26, 2015 |
LATERAL BIPOLAR JUNCTION TRANSISTOR AND FABRICATION METHOD
THEREOF
Abstract
Provided is a lateral BJT including a substrate, a well region,
an area, at least one lightly doped region, a first doped region,
and a second doped region. The substrate is of a first conductivity
type. The well region is of a second conductivity type and is in
the substrate. The area is in the well region. The at least one
lightly doped region is in the well region below the area. The
first doped region and the second doped region are of the first
conductivity type and are in the well region on both sides of the
area. The first doped region is connected to a cathode. The second
doped region is connected to an anode, wherein the doping
concentration of the at least one lightly doped region is lower
than that of each of the first doped region, the second doped
region, and the well region.
Inventors: |
Wang; Chang-Tzu; (Taoyuan
County, TW) ; Tseng; Pei-Shan; (Hsinchu City, TW)
; Tang; Tien-Hao; (Hsinchu City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
United Microelectronics Corp. |
Hsinchu |
|
TW |
|
|
Assignee: |
United Microelectronics
Corp.
Hsinchu
TW
|
Family ID: |
52479625 |
Appl. No.: |
13/974939 |
Filed: |
August 23, 2013 |
Current U.S.
Class: |
257/565 ;
438/353 |
Current CPC
Class: |
H01L 29/6625 20130101;
H01L 27/0259 20130101; H01L 29/861 20130101; H01L 29/735 20130101;
H01L 29/0821 20130101 |
Class at
Publication: |
257/565 ;
438/353 |
International
Class: |
H01L 29/73 20060101
H01L029/73; H01L 29/66 20060101 H01L029/66 |
Claims
1. A lateral bipolar junction transistor, comprising: a substrate
of a first conductivity type; a well region of a second
conductivity type in the substrate; an area in the well region; at
least one lightly doped region in the well region below the area; a
first doped region and a second doped region of the first
conductivity type in the well region on both sides of the area,
wherein the first doped region is connected to a cathode and the
second doped region is connected to an anode, wherein a doping
concentration of the at least one lightly doped region is lower
than a doping concentration of each of the first doped region and
the second doped region, and is lower than a doping concentration
of the well region; and at least one isolation structure in the
area, wherein the at least one isolation structure is adjacent to
the first doped region and the second doped region.
2. The lateral bipolar junction transistor of claim 1, wherein the
first conductivity type is P-type and the second conductivity type
is N-type.
3. The lateral bipolar junction transistor of claim 1, wherein the
first conductivity type is N-type and the second conductivity type
is P-type.
4. The lateral bipolar junction transistor of claim 1, wherein the
at least one lightly doped region is of the first conductivity
type.
5. The lateral bipolar junction transistor of claim 1, wherein the
at least one lightly doped region is of the second conductivity
type.
6. The lateral bipolar junction transistor of claim 1, wherein the
at least one lightly doped region is a single doped region.
7. The lateral bipolar junction transistor of claim 1, wherein the
at least one lightly doped region is a plurality of doped
regions.
8. (canceled)
9. The lateral bipolar junction transistor of claim 8, wherein the
at least one lightly doped region is in contact with the at least
one isolation structure.
10. The lateral bipolar junction transistor of claim 8, wherein the
at least one lightly doped region is separated from the at least
one isolation structure by a distance.
11. The lateral bipolar junction transistor of claim 1, wherein the
at least one isolation structure comprises: a first isolation
structure in the area and adjacent to the first doped region; and a
second isolation structure in the area and adjacent to the second
doped region.
12. A fabrication method of a lateral bipolar junction transistor,
comprising: forming at least one first well region of a first
conductivity type in a substrate; forming a second well region of a
second conductivity type in the substrate, wherein the first well
region is in the second well region, the at least one first well
region is partially overlapped with the second well region, and at
least one lightly doped region is formed after the second well
region is compensated; forming at least one isolation structure in
the area before forming the first well region; respectively forming
a first doped region and a second doped region in the second well
region, wherein the first doped region and the second doped region
are respectively on both sides of an area on the lightly doped
region and the at least one isolation structure is adjacent to the
first doped region and the second doped region; and connecting the
first doped region to a cathode and connecting the second doped
region to an anode.
13. The method of claim 12, wherein the first conductivity type is
P-type and the second conductivity type is N-type.
14. The method of claim 12, wherein the first conductivity type is
N-type and the second conductivity type is P-type.
15. The method of claim 12, wherein the at least one lightly doped
region is of the first conductivity type.
16. The method of claim 12, wherein the at least one lightly doped
region is of the second conductivity type.
17. The method of claim 12, wherein the at least one lightly doped
region is a single doped region.
18. The method of claim 12, wherein the at least one lightly doped
region is a plurality of doped regions.
19. (canceled)
20. The method of claim 12, wherein the at least one lightly doped
region is in contact with the at least one isolation structure.
21. (withdrawn and currently amended) The method of claim 12,
wherein the at least one lightly doped region is separated from the
at least one isolation structure by a distance.
22. The method of claim 12, wherein the step of the at least one
isolation structure comprises: forming a first isolation structure
adjacent to the first doped region; and forming a second isolation
structure adjacent to the second doped region.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to the fabrication of an integrated
circuit, and more particularly, to a lateral bipolar junction
transistor (BJT) and a fabrication method thereof.
[0003] 2. Description of Related Art
[0004] The transistor is a core device in the current electronic
circuit. There are many types of transistors. Based on working
principle, transistors can be divided into bipolar junction
transistors (BJT) and field effect transistors (FET). BJTs are
formed by a pn junction connected in opposite directions and have
an emitter (E), a base (B), and a collector (C) as their three
endpoints.
[0005] One of the main functions of BJTs is to serve as a switch,
wherein there are two main uses. One is to switch a device having
higher power; the other is to construct a digital logic circuit.
Moreover, BJTs can amplify signals and have better power control,
high-speed operation, and endurance ability, and are therefore
frequently used to form amplifier circuits or to drive equipments
such as speakers and electric motors, and are widely applied to the
application products of aeronautics and space engineering, medical
instruments, and robotics.
[0006] BJTs can also be applied to electrostatic discharge
protection circuits. With the development of technology, the
breakdown voltage of the current BJT is insufficient for the needs
of the current device. For instance, in a process for making device
operated between -VDD to 2.5VDD, the output swing is between -3.5
volts and 8.75 volts. It is difficult for traditional electrostatic
discharge protection devices to satisfy the specified range.
Moreover, the breakdown voltage of BJTs is only 7.7 volts, and
therefore a BJT having a high breakdown voltage is needed.
SUMMARY OF THE INVENTION
[0007] The invention provides a plurality of lateral bipolar
junction transistors. The lateral bipolar junction transistors have
a high breakdown voltage.
[0008] The invention provides a plurality of lateral bipolar
junction transistors. The lateral bipolar junction transistors can
confine current in a small region such that the lateral bipolar
junction transistors have a high breakdown voltage.
[0009] The invention provides a plurality of lateral bipolar
junction transistors. The lateral bipolar junction transistors have
a high breakdown voltage, can disperse an electric field, and
increase the effect of heat dissipation.
[0010] The invention provides a fabrication method of the plurality
of lateral bipolar junction transistors. The fabrication method is
compatible with an existing fabrication process and does not need
additional photomasks, and can increase the breakdown voltage of
the lateral bipolar junction transistors.
[0011] The invention provides a fabrication method of the plurality
of lateral bipolar junction transistors. The fabrication method can
be compatible with an existing fabrication process and does not
need additional photomasks, and can confine current in a small
region to increase the breakdown voltage of the lateral bipolar
junction transistors.
[0012] The invention provides a fabrication method of the plurality
of lateral bipolar junction transistors. The fabrication method can
be compatible with an existing fabrication process and does not
need additional photomasks, and can increase the breakdown voltage
of the lateral bipolar junction transistors. Moreover, the
fabrication method can disperse an electric field and increase the
effect of heat dissipation.
[0013] The invention provides a lateral bipolar junction
transistor. The lateral bipolar junction transistor includes a
substrate of a first conductivity type, a well region of a second
conductivity type in the substrate, an area in the well region, at
least one lightly doped region in the well region below the area,
and a first doped region and a second doped region of the first
conductivity type in the well region on both sides of the area,
wherein the first doped region is connected to a cathode and the
second doped region is connected to an anode, and wherein the
doping concentration of the at least one lightly doped region is
lower than the doping concentration of each of the first doped
region and the second doped region, and is lower than the doping
concentration of the well region.
[0014] In an embodiment of the invention, the first conductivity
type is P-type and the second conductivity type is N-type.
[0015] In an embodiment of the invention, the first conductivity
type is N-type and the second conductivity type is P-type.
[0016] In an embodiment of the invention, the at least one lightly
doped region is of the first conductivity type.
[0017] In an embodiment of the invention, the at least one lightly
doped region is of the second conductivity type.
[0018] In an embodiment of the invention, the at least one lightly
doped region is a single doped region.
[0019] In an embodiment of the invention, the at least one lightly
doped region is a plurality of doped regions.
[0020] In an embodiment of the invention, the lateral bipolar
junction transistor further includes at least one isolation
structure in the area, wherein the at least one isolation structure
is adjacent to the first doped region and the second doped
region.
[0021] In an embodiment of the invention, the at least one lightly
doped region is in contact with the at least one isolation
structure.
[0022] In an embodiment of the invention, the at least one lightly
doped region is separated from the at least one isolation structure
by a distance.
[0023] In an embodiment of the invention, the lateral bipolar
junction transistor further includes a first isolation structure in
the area and adjacent to the first doped region, and a second
isolation structure in the area and adjacent to the second doped
region.
[0024] The invention provides a fabrication method of a lateral
bipolar junction transistor. The fabrication method includes
forming at least one first well region of a first conductivity type
in a substrate, forming a second well region of a second
conductivity type in the substrate, wherein the first well region
is in the second well region, the at least one first well region is
partially overlapped with the second well region, and at least one
lightly doped region is formed after the second well region is
compensated, respectively forming a first doped region and a second
doped region in the second well region, wherein the first doped
region and the second doped region are respectively on both sides
of an area on the lightly doped region, and connecting the first
doped region to a cathode and connecting the second doped region to
an anode.
[0025] In an embodiment of the invention, the first conductivity
type is P-type and the second conductivity type is N-type.
[0026] In an embodiment of the invention, the first conductivity
type is N-type and the second conductivity type is P-type.
[0027] In an embodiment of the invention, the at least one lightly
doped region is of the first conductivity type.
[0028] In an embodiment of the invention, the at least one lightly
doped region is of the second conductivity type.
[0029] In an embodiment of the invention, the at least one lightly
doped region is a single doped region.
[0030] In an embodiment of the invention, the at least one lightly
doped region is a plurality of doped regions.
[0031] In an embodiment of the invention, the method further
includes forming at least one isolation structure in the area
before forming the first well region, wherein the at least one
isolation structure is adjacent to the first doped region and the
second doped region.
[0032] In an embodiment of the invention, the at least one lightly
doped region is in contact with the at least one isolation
structure.
[0033] In an embodiment of the invention, the at least one lightly
doped region is separated from the at least one isolation structure
by a distance.
[0034] In an embodiment of the invention, the method further
includes, before forming the first well region, forming in the
area: a first isolation structure adjacent to the first doped
region, and a second isolation structure adjacent to the second
doped region.
[0035] The lateral bipolar junction transistors of the invention
can increase the breakdown voltage thereof by disposing a lightly
doped region below an area between doped regions connected to a
cathode and an anode.
[0036] The lateral bipolar junction transistors of the invention
can confine current in a small region to increase the breakdown
voltage thereof by disposing a lightly doped region below an
isolation structure, wherein the lightly doped region is separated
from the isolation structure by a distance.
[0037] The lateral bipolar junction transistors of the invention
can increase the breakdown voltage, disperse an electric field, and
increase the effect of heat dissipation by disposing a lightly
doped region below two separated isolation structures.
[0038] The fabrication method of the plurality of lateral bipolar
junction transistors of the invention can be compatible with an
existing fabrication process and does not need additional
photomasks, and can increase the breakdown voltage of the lateral
bipolar junction transistors.
[0039] The fabrication method of the plurality of lateral bipolar
junction transistors of the invention can be compatible with an
existing fabrication process and does not need additional
photomasks, and can confine current in a small region to increase
the breakdown voltage of the lateral bipolar junction
transistors.
[0040] The fabrication method of the plurality of lateral bipolar
junction transistors of the invention can be compatible with an
existing fabrication process and does not need additional
photomasks, and can increase the breakdown voltage of the lateral
bipolar junction transistors. Moreover, the fabrication method can
disperse an electric field and increase the effect of heat
dissipation.
[0041] In order to make the aforementioned features and advantages
of the disclosure more comprehensible, embodiments accompanied with
figures are described in detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
[0043] FIG. 1 illustrates a top view of a lateral bipolar junction
transistor of an embodiment of the invention.
[0044] FIG. 2A illustrates a schematic cross-sectional diagram of
one of the lateral bipolar junction transistors of line I-I of FIG.
1.
[0045] FIG. 2B illustrates a schematic cross-sectional diagram of
another one of the lateral bipolar junction transistors of line I-I
of FIG. 1.
[0046] FIG. 2C illustrates a schematic cross-sectional diagram of
yet another one of the lateral bipolar junction transistors of line
I-I of FIG. 1.
[0047] FIG. 2D illustrates a schematic cross-sectional diagram of
still yet another one of the lateral bipolar junction transistors
of line I-I of FIG. 1.
[0048] FIG. 3A illustrates a top view of yet another lateral
bipolar junction transistor of an embodiment of the invention.
[0049] FIG. 3B illustrates a top view of another lateral bipolar
junction transistor of an embodiment of the invention.
[0050] FIG. 4A illustrates a schematic cross-sectional diagram of
line II-II in FIG. 3A.
[0051] FIG. 4B illustrates a schematic cross-sectional diagram of
line in FIG. 3B.
[0052] FIG. 5 illustrates a top view of a lateral bipolar junction
transistor of an embodiment of the invention.
[0053] FIG. 6A illustrates a schematic cross-sectional diagram of
one of the lateral bipolar junction transistors of line IV-IV of
FIG. 5.
[0054] FIG. 6B illustrates a schematic cross-sectional diagram of
another one of the lateral bipolar junction transistors of line
IV-IV of FIG. 5.
[0055] FIG. 6C illustrates a schematic cross-sectional diagram of
yet another one of the lateral bipolar junction transistors of line
IV-IV of FIG. 5.
[0056] FIG. 6D illustrates a schematic cross-sectional diagram of
still yet another one of the lateral bipolar junction transistors
of line IV-IV of FIG. 5.
[0057] FIG. 7A illustrates a top view of yet another lateral
bipolar junction transistor of an embodiment of the invention.
[0058] FIG. 7B illustrates a top view of another lateral bipolar
junction transistor of an embodiment of the invention.
[0059] FIG. 8A illustrates a schematic cross-sectional diagram of
line V-V in FIG. 7A.
[0060] FIG. 8B illustrates a schematic cross-sectional diagram of
line VI-VI in FIG. 7B.
DESCRIPTION OF THE EMBODIMENTS
[0061] Regarding the lateral bipolar junction transistors (BJT) of
the invention, in addition to forming two doped regions connected
to a cathode and an anode in a well region, a lightly doped region
is further formed below an area between the two doped regions. The
conductivity type of the lightly doped region can be the same or
different from the conductivity type of the well region. A single,
two, or a plurality of isolation structures can be formed in the
area between the two doped regions. The lightly doped region can be
in contact with the one or a plurality of isolation structures or
be separated from the one or a plurality of isolation structures by
a distance. Since the doping concentration of the lightly doped
region is lower than the doping concentration of each of the two
doped regions and is lower than the doping concentration of the
well region, the breakdown voltage of the lateral bipolar junction
transistors can be increased. The invention is explained through a
plurality of embodiments below. However, the lateral BJT of each of
the embodiments is not limited thereto.
[0062] In the embodiments below, in the lateral BJTs, a first
conductivity type is, for instance, P-type and a second
conductivity type is, for instance, N-type (as shown in FIGS. 1 to
8B). However, the invention is not limited thereto. In another
embodiment, in the lateral BJT, the first conductivity type is, for
instance, N-type and the second conductivity type is, for instance,
P-type. The P-type dopant is, for instance, boron or boron
trifluoride. The N-type dopant is, for instance, phosphorous or
arsenic.
[0063] FIG. 1 illustrates a top view of a lateral BJT of an
embodiment of the invention. FIG. 2A illustrates a schematic
cross-sectional diagram of a lateral BJT of line I-I of FIG. 1.
[0064] Referring to FIG. 1 and FIG. 2A, the lateral BJT includes a
substrate 10, a well region 20, doped regions 22 and 24, a lightly
doped region 26, a well region 30, and a doped region 32.
[0065] The substrate 10 can be a semiconductor substrate such as a
silicon substrate. The substrate 10 is of the first conductivity
type.
[0066] The well region 20 is of the second conductivity type and is
in the substrate 10. The doped regions 22 and 24 are of the first
conductivity type and are in the well region 20.
[0067] The doped regions 22 and 24 are of the first conductivity
type and are respectively connected to a cathode and an anode. In
an embodiment, the doped region 22 is separated from an area 40 and
surrounds the doped region 24.
[0068] The area 40 has a single isolation structure 50 therein. The
isolation structure 50 is, for instance, a shallow trench isolation
structure.
[0069] The lightly doped region 26 is of a second conductivity type
and is in the well region 20 below the isolation structure 50 of
the area 40. The doping concentration of the lightly doped region
26 is lower than the doping concentration of each of the doped
region 22 and the doped region 24 and is lower than the doping
concentration of the well region 20. In the present embodiment, the
lightly doped region 26 is a single region and is in contact with
the isolation structure 50. However, the embodiments of the
invention are not limited thereto.
[0070] The well region 30 is of the first conductivity type and is
in the periphery of the well region 20. In an embodiment, the well
region 30 surrounds the well region 20.
[0071] The doped region 32 is of the first conductivity type and is
in the well region 30. In an embodiment, the doped region 32
surrounds the periphery of the doped region 22. The doped region 32
and the doped region 22 can be separated by an isolation structure
52.
[0072] In the lateral BJT, since the lightly doped region 26 and
the well region 20 are of the same conductivity type and the doping
concentration of the lightly doped region 26 is lower than the
doping concentration of the well region 20, the resistance of the
lightly doped region 26 can be increased to increase the voltage
across thereof and increase the breakdown voltage of the
device.
[0073] FIG. 2B illustrates a schematic cross-sectional diagram of a
lateral BJT of line I-I of FIG. 1.
[0074] In the embodiment of FIG. 2A, the lightly doped region 26 is
a single region; however, the embodiments of the invention are not
limited thereto. In another embodiment, as shown in FIG. 2B, there
can be a plurality of lightly doped regions 26 below the isolation
structure 50. In an embodiment, the lightly doped region 26 is
juxtaposed below the isolation structure 50. In the present
embodiment, by disposing a plurality of lightly doped regions 26
below the isolation structure 50, the breakdown voltage of the
junction of the lightly doped region 26 and the well region 20 can
be further increased.
[0075] FIG. 2C illustrates a schematic cross-sectional diagram of
yet another one of the lateral bipolar junction transistors of line
I-I of FIG. 1. FIG. 2D illustrates a schematic cross-sectional
diagram of yet another one of the lateral bipolar junction
transistors of line I-I of FIG. 1.
[0076] In the embodiment of FIG. 2A, the lightly doped region 26 is
in contact with the isolation structure 50. However, the
embodiments of the invention are not limited thereto. In the
embodiment of each of FIG. 2C and FIG. 2D, the lightly doped region
26 and the isolation structure 50 are separated by a distance d1
and are not in contact. The distance d1 is, for instance, 0.05
.mu.m to 1 .mu.m. Similarly, the lightly doped region 26 can be a
single region as shown in FIG. 2C; and the lightly doped region 26
can also be a plurality of regions as shown in FIG. 2D. In
comparison to a situation without the lightly doped region 26, in
the present embodiment, the lightly doped region 26 is separated
from the isolation structure 50 by the distance d1. As a result,
the channel is smaller and current is confined in a small region,
thereby increasing the breakdown voltage of the lateral bipolar
junction transistor.
[0077] In the embodiment of each of FIG. 2A to FIG. 2D, a single
isolation structure 50 is disposed in the area 40. However, the
embodiments of the invention are not limited thereto.
[0078] FIG. 3A and FIG. 3B respectively illustrate a top view of
another lateral BJT of an embodiment of the invention. FIG. 4A
illustrates a schematic cross-sectional diagram of line II-II in
FIG. 3A. FIG. 4B illustrates a schematic cross-sectional diagram of
line in FIG. 3B.
[0079] Referring to FIG. 3A and FIG. 4A, in the present embodiment,
two separate isolation structures 62 and 64 are disposed in the
area 40. The isolation structure 62 is in contact with the doped
region 22 and the isolation structure 64 is in contact with the
doped region 24. The area 40 reserved between the isolation
structure 62 and the isolation structures 64 is a portion of the
area 20. The lightly doped region 26 is disposed below the area 40,
is not in contact with the isolation structures 62 and 64, and is
separated from the isolation structures 62 and 64 by a distance d2.
The distance d2 is, for instance, 0.05 .mu.m to 1 .mu.m. Similarly,
the lightly doped region 26 can be a single region as shown in FIG.
3A and FIG. 4A; and the lightly doped region 26 can also be a
plurality of regions as shown in FIG. 3B and FIG. 4B. In comparison
to a situation without the lightly doped region 26, in the present
embodiment, the lightly doped region 26 is separated from the
isolation structure by the distance d2. As a result, the channel is
smaller and current is confined in a small region, thereby
increasing the breakdown voltage of the lateral bipolar junction
transistor. However, in comparison to the situation of the
embodiment of each of FIGS. 2C and 2D, in the present embodiment,
the area 40 reserved between the isolation structure 62 and the
isolation structure 64 can disperse an electric field to increase
the effect of heat dissipation.
[0080] In the embodiment of each of FIG. 2A to FIG. 2D, FIG. 4A,
and FIG. 4B, the conductivity type of the lightly doped region 26
below the area 40 is the same as the conductivity type of the well
region 20 and is of the second conductivity type. However, the
embodiments of the invention are not limited thereto. The
conductivity type of the doped region below the area 40 can also be
different from the conductivity type of the well region 20 and be
of a first conductivity type as shown in FIG. 5, FIG. 6A to FIG.
6D, FIG. 7A, FIG. 7B, FIG. 8A, and FIG. 8B.
[0081] FIG. 5 illustrates a top view of a lateral BJT of an
embodiment of the invention. FIGS. 6A to 6D respectively illustrate
a schematic cross-sectional diagram of one of the lateral BJTs of
line IV-IV of FIG. 5. FIG. 7A and FIG. 7B respectively illustrate a
top view of another lateral BJT of an embodiment of the invention.
FIG. 8A illustrates a schematic cross-sectional diagram of line V-V
in FIG. 7A. FIG. 8B illustrates a schematic cross-sectional diagram
of line VI-VI in FIG. 7B.
[0082] Referring to FIG. 5 and FIG. 6A, the area 40 has a single
isolation structure 50 therein, and a lightly doped region 126 is
below the isolation structure 50. The lightly doped region 126 is
of the first conductivity type. The doping concentration of the
lightly doped region 126 is lower than the doping concentration of
each of the doped regions 22 and 24. In the present embodiment, the
lightly doped region 126 is in contact with the isolation structure
50. Punch through occurs when the depletion region of the cathode
covers the lightly doped region 126, thereby increasing the
breakdown voltage of the lateral bipolar junction transistor.
[0083] Referring to FIG. 5 and FIG. 6B, the lateral BJT of each
thereof is similar to the lateral BJT of FIG. 6A, but a plurality
of lightly doped regions 126 of the first conductivity type are
below the isolation structure 50 in each of the lateral BJTs of
FIG. 5 and FIG. 6B. Since the conductivity type of the lightly
doped region 126 is different from the conductivity type of the
well region 20, it is similar to that plural PNPs are connected in
series. Therefore, the breakdown voltage of the junction of the
lightly doped region 126 and the well region 20 can be further
increased.
[0084] Referring to FIG. 5, FIG. 6C, and FIG. 6D, the lateral BJT
of FIG. 6C is similar to the lateral BJT of FIG. 6A; the lateral
BJT of FIG. 6D is similar to the lateral BJT of FIG. 6B, but the
isolation structure 50 and the lightly doped region 126 of the
first conductivity type below the isolation structure 50 are
separated by a distance d3 and are not in contact. The distance d3
is, for instance, 0.05 .mu.m to 1 .mu.m. In comparison to a
situation without the lightly doped region 126, in the present
embodiment, the lightly doped region 126 is separated from the
isolation structure 50 by the distance d3. As a result, the channel
is smaller and current is confined in a small region, thereby
increasing the breakdown voltage of the lateral bipolar junction
transistor.
[0085] Referring to FIG. 7A, FIG. 7B, FIG. 8A, and FIG. 8B, in the
present embodiment, two separate isolation structures 62 and 64 are
disposed in the area 40. The isolation structure 62 is in contact
with the doped region 22 and the isolation structure 64 is in
contact with the doped region 24. The area 40 reserved between the
isolation structure 62 and the isolation structure 64 is a portion
of the area 20. The lightly doped region 126 of the first
conductivity type is disposed below the region 40, is not in
contact with the isolation structures 62 and 64, and is separated
from the isolation structures 62 and 64 by a distance d4. The
distance d4 is, for instance, 0.05 .mu.m to 1 .mu.m. Similarly, the
lightly doped region 126 can be a single region as shown in FIGS.
7A and 8A; and the lightly doped region 126 can also be a plurality
of regions as shown in FIG. 7B and FIG. 8B. In comparison to a
situation without the lightly doped region 126, in the present
embodiment, the lightly doped region 126 is separated from the
isolation structure by the distance d4. As a result, the channel is
smaller and current is confined in a small region, thereby
increasing the breakdown voltage of the lateral bipolar junction
transistor. However, in comparison to the situation of the
embodiment of each of FIGS. 6C and 6D, in the present embodiment,
the area 40 reserved between the isolation structure 62 and the
isolation structure 64 can disperse an electric field to increase
the effect of heat dissipation.
[0086] The lateral BJT of each embodiment above can be compatible
with current fabrication process. Both the lightly doped region 26
of the same conductivity type as the well region 20 and the lightly
doped region 126 of a different conductivity type from the well
region 20 can be formed by a method of ion implantation and without
additional photomasks.
[0087] The fabrication method of each of the lateral BJTs of the
invention is explained in the following through FIG. 2A and FIG.
6A.
[0088] Referring to FIG. 2A, a well region 226 of the first
conductivity type is formed in the substrate 10 by a method of ion
implantation. Then, the well region 20 of the second conductivity
type is formed in the substrate 10, wherein the well region 226 is
in the well region 20, the well region 226 is partially overlapped
with the well region 20, and the well region 226 can form the
lightly doped region 26 (FIG. 2A) or the lightly doped region 126
(FIG. 6A) after the well region 20 is compensated. When the doping
concentration of the well region 226 is lower than the doping
concentration of the well region 20, after dopants of two different
conductivity types are compensated, a portion of the doping of the
second conductivity type of the well region 20 still can not be
compensated, and therefore the lightly doped region 26 of the
second conductivity type is formed. When the doping concentration
of the well region 226 is higher than the doping concentration of
the well region 20, after dopants of two different conductivity
types are compensated, a portion of the doping of the first
conductivity type of the well region 226 still can not be
compensated, and therefore the lightly doped region 126 of the
first conductivity type is formed.
[0089] Then, the doped regions 22 and 24 are formed in the well
region 20, the well region 30 is formed in the substrate 20, the
doped region 32 is formed in the well region 30, the isolation
structure 50 is formed in the area 40, and the isolation structure
52 is formed between the doped regions 22 and 32. Then, the doped
region 22 is connected to the cathode and the doped region 24 is
connected to the anode.
[0090] The above embodiment is exemplified as forming a single
lightly doped region 26 and 126; however, if the lateral BJT has a
plurality of lightly doped regions 26 and 126 as shown in FIGS. 2B,
2D, 6B, and 6D, then a plurality of well regions 226 of the first
conductivity type can be formed in the substrate 10 with a
fabrication method similar to the above.
[0091] In the above embodiment, the lightly doped regions 26 and
126 are in contact with the isolation structure 50; however, if the
lightly doped regions 26 and 126 of the lateral BJT are not in
contact with the isolation structure 50 and are separated by the
distance d1, d2, d3, or d4 as shown in FIGS. 2C, 2D, 4A, 4B, 6C,
6D, 8A, and 8B, then the well region 226 can be formed by
controlling the parameter (such as energy or dose) of the ion
implantation.
[0092] The formation method of each of the isolation structures 50,
52, 62, and 64 can be the same as the formation method of a known a
shallow trench isolation structure and is not repeated herein.
[0093] Simulation experiments show that, in comparison to a BJT
device without a lightly doped region, the breakdown voltage of the
lateral BJTs of the invention can be increased from 8.5 volts to
9.2 volts, and therefore the lateral BJTs of the invention can be
applied in high-speed devices or complementary metal-oxide
semiconductor radio frequency devices.
[0094] Based on the above, the breakdown voltage of the lateral
BJTs of the invention is increased by disposing a lightly doped
region below an area between two doped regions. The conductivity
type of the lightly doped region can be the same or different from
the conductivity type of the well region. When the conductivity
type of the lightly doped region is the same as the conductivity
type of the well region, since the doping concentration of the
lightly doped region is lower than the doping concentration of the
well region, resistance can be increased. As a result, the voltage
across the lightly doped region can be increased, and therefore the
breakdown voltage of the lateral BJTs is increased. Punch through
occurs when the conductivity type of the lightly doped region is
different from the conductivity type of the well region and the
depletion region of the cathode covers the lightly doped region,
thereby increasing the breakdown voltage of the lateral BJTs.
[0095] The lightly doped region can be a single one or a plurality.
When the lightly doped region is a plurality and the conductivity
type of the lightly doped region is different from the conductivity
type of the well region, it is similar to that plural PNPs are
connected in series. Therefore, the breakdown voltage of the
junction of the lightly doped region and the well region can be
further increased.
[0096] Moreover, the lightly doped region is separated from the
isolation structure by a distance, and therefore current can be
confined in a small region to increase the breakdown voltage.
[0097] Furthermore, when the lightly doped region is disposed below
the area between two isolation structures, in addition to
increasing the breakdown voltage, electric fields can also be
dispersed, thereby increasing the effect of heat dissipation.
[0098] Moreover, the fabrication methods of the lateral BJTs of the
invention can be compatible with current fabrication process. The
lightly doped region can be formed by a method of ion implantation
and does not need additional photomasks.
[0099] Although the invention has been described with reference to
the above embodiments, it will be apparent to one of the ordinary
skill in the art that modifications and variations to the described
embodiments may be made without departing from the spirit and scope
of the invention. Accordingly, the scope of the invention will be
defined by the attached claims not by the above detailed
descriptions.
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