U.S. patent application number 16/935991 was filed with the patent office on 2021-12-02 for schottky diode with multiple guard ring structures.
The applicant listed for this patent is TAIWAN SEMICONDUCTOR CO., LTD.. Invention is credited to Yao-Wei CHUANG, Syed Sarwar IMAM, Yi-Lung TSAI, Ming-Lou TUNG.
Application Number | 20210376062 16/935991 |
Document ID | / |
Family ID | 1000005968591 |
Filed Date | 2021-12-02 |
United States Patent
Application |
20210376062 |
Kind Code |
A1 |
TSAI; Yi-Lung ; et
al. |
December 2, 2021 |
SCHOTTKY DIODE WITH MULTIPLE GUARD RING STRUCTURES
Abstract
A Schottky diode with multiple guard ring structures includes a
semiconductor base layer, a back metal layer, an epitaxial layer, a
dielectric layer, a first metal layer, a passivation layer and a
second metal layer. The epitaxial layer on the semiconductor base
layer includes a terminal trench structure, a first ion
implantation guard ring, a second ion implantation guard ring and a
third ion implantation guard ring. The dielectric layer is on the
epitaxial layer in a termination area. The first metal layer is on
the terminal trench structure and the dielectric layer. The
passivation layer is on the first metal layer and the dielectric
layer. The second metal layer is on the first metal layer and the
passivation layer. Widths of the first, second and third ion
implantation guard rings decrease in order, so that the voltage can
be distributed step by step.
Inventors: |
TSAI; Yi-Lung; (New Taipei
City, TW) ; IMAM; Syed Sarwar; (New Taipei City,
TW) ; CHUANG; Yao-Wei; (New Taipei City, TW) ;
TUNG; Ming-Lou; (New Taipei City, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAIWAN SEMICONDUCTOR CO., LTD. |
New Taipei City |
|
TW |
|
|
Family ID: |
1000005968591 |
Appl. No.: |
16/935991 |
Filed: |
July 22, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 29/0619 20130101;
H01L 29/66143 20130101; H01L 29/872 20130101 |
International
Class: |
H01L 29/06 20060101
H01L029/06; H01L 29/66 20060101 H01L029/66; H01L 29/872 20060101
H01L029/872 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 2, 2020 |
TW |
109118410 |
Claims
1. A Schottky diode with multiple guard ring structures,
comprising: a semiconductor base layer, having a back surface and a
front surface opposite to the back surface; a back metal layer,
formed on the back surface of the semiconductor base layer; an
epitaxial layer, formed on the front surface of the semiconductor
base layer, having a unit cell area and a termination area,
including: a termination trench structure, disposed at a junction
of the unit cell area and the termination area; a first ion
implantation guard ring, disposed in the termination area by
neighboring to the termination trench structure, having a first
width; a second ion implantation guard ring, disposed in the
termination area, separated from the first ion implantation guard
ring, having a second width less than the first width; and a third
ion implantation guard ring, disposed in the termination area,
separated from the second ion implantation guard ring, having a
third width less than the second width; a dielectric layer, stacked
on the termination trench structure, the first ion implantation
guard ring, the second ion implantation guard ring and the third
ion implantation guard ring in the termination area; a first metal
layer, including: a main body portion, stacked on the termination
trench structure in the unit cell area, extending from the unit
cell area to be stacked on the dielectric layer above the first ion
implantation guard ring in the termination area; and a separation
portion, stacked on the dielectric layer in the termination area,
extending toward the epitaxial layer to penetrate through the
dielectric layer to electrically contact the third ion implantation
guard ring, wherein a trench exposed out of the dielectric layer is
formed between the separation portion and the main body portion; a
passivation layer, stacked on the main body portion in the unit
cell area, extending to be stacked on the main body portion, the
trench, the separation portion and the dielectric layer in the
termination area; and a second metal layer, stacked on the first
metal layer and the passivation layer in the unit cell area,
extending from the unit cell area to be stacked on the passivation
layer above the first ion implantation guard ring in the
termination area.
2. The Schottky diode with multiple guard ring structures of claim
1, wherein the second ion implantation guard ring is separated from
the first ion implantation guard ring by a first spacing, the third
ion implantation guard ring is separated from the second ion
implantation guard ring by a second spacing, and the second spacing
is larger than the first spacing.
3. The Schottky diode with multiple guard ring structures of claim
2, wherein a ratio of the first spacing and the second spacing is
1:1.2.
4. The Schottky diode with multiple guard ring structures of claim
1, wherein a ratio of the first width, the second width and the
third width is 4:2:1.
5. The Schottky diode with multiple guard ring structures of claim
1, wherein the dielectric layer includes a TEOS film and a BPSG
film, the TEOS film is stacked on the epitaxial layer in the
termination area, and the BPSG film is stacked on the TEOS film in
the termination area.
6. The Schottky diode with multiple guard ring structures of claim
1, wherein the epitaxial layer further includes a plurality of cell
trench structures in the unit cell area.
Description
[0001] This application claims the benefit of Taiwan Patent
Application Serial No. 109118410, filed Jun. 2, 2020, the subject
matter of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
[0002] The invention relates to a Schottky diode, and more
particularly to a Schottky diode with multiple guard ring
structures.
(2) Description of the Prior Art
[0003] Generally speaking, an ideal rectifier should be at least
featured in a low forward voltage drop, a high reverse breakdown
voltage and zero leakage current. For metal-semiconductor junctions
are utilized as Schottky barriers to have characteristics in low
forward voltage drop and high-speed switching, thus the Schottky
diodes are widely applied to power rectifiers. However, since the
Schottky diodes do have shortcomings in lower reverse bias and
larger reverse leakage current, thus the applications of the
Schottky diodes are substantially limited.
[0004] As described, the Schottky diodes are mainly classified into
conventional planar Schottky diodes and trench Schottky diodes. A
typical structure of the planar Schottky diodes is a stacking
structure consisted of interchanging semiconductor layers and metal
layers. As such, properties in the forward voltage drop and the
leakage current shall be balanced. Namely, the topic in enhancing
the breakdown voltage without increasing the leakage current is
definitely welcome to the skilled in the art.
[0005] The trench Schottky diode is mainly formed by filling
polysilicon into an etched trench of a silicon layer, such that the
polysilicon in the trench can be used effectively to deplete drift
electrons in a drift region, and thus the electric field
distribution can be uniformed. In comparison to the conventional
planar Schottky diode, the trench Schottky diode has much lower
forward voltage drop (Low VF) and reverse leakage current (Low
IR).
[0006] Referring to FIG. 1, a schematic cross-sectional view of a
conventional trench Schottky diode is illustrated. As shown, the
trench Schottky diode PA100 includes a semiconductor base layer
PA1, a back metal layer PA2, an epitaxial layer PA3, a dielectric
layer PA4, a first metal layer PA5, a passivation layer PA6 and a
second metal layer PA7.
[0007] The back metal layer PA2 is formed on a back surface of the
semiconductor base layer PA1, while the epitaxial layer PA3 is
formed on a front surface of the semiconductor base layer PA1. The
epitaxial layer is divided into a unit cell area PA3a and a
termination area PA3b adjacent to each other. The epitaxial layer
PA3 further includes a plurality of unit cell structures PA31 (two
shown in the figure), a termination trench structure PA32 and a
guard ring structure PA33. The plurality of unit cell structures
PA31 are separately located in the unit cell area PA3a. The
termination trench structure PA32 is located at a junction of the
unit cell area PA3a and the termination area PA3b, and is separated
from the neighboring unit cell structure PA31 in the termination
area PA3b. The guard ring structure PA33 is adjacent to the
termination trench structure PA32.
[0008] The dielectric layer PA4, disposed in the termination area
PA3b, is stacked on the termination trench structure PA32 and the
guard ring structure PA33. The first metal layer PA5 is stacked on
the epitaxial layer PA3 in the unit cell area PA3a, and extended to
stack the dielectric layer PA4 in the termination area PA3b. The
passivation layer PA6 is stacked on the first metal layer PA5, and
extended to the dielectric layer PA4 in the termination area PA3b
from the unit cell area PA3a. The second metal layer PA7 is stacked
on the first metal layer PA5 and the passivation layer PA6, and
extended from the unit cell area PA3a to the termination area
PA3b.
[0009] As described above, the conventional trench Schottky diode
PA100 is mainly to extend the first metal layer PA5 and the second
metal layer PA7 to the termination area PA3b so as increase the
reverse bias, and to furnish the guard ring structure PA33 to the
epitaxial layer PA3 so as to distribute the voltage level. However,
since the guard ring structure PA33 can only provide limited
ability to buffer the voltage level, thus electric charges of the
trench Schottky diode PA100 would be clustered to the rim of the
termination area PA3b, from which an early breakdown would be
possible.
SUMMARY OF THE INVENTION
[0010] In order to increase the reverse bias of the conventional
trench Schottky diode, the first metal layer and the second metal
layer thereof are extended into the termination area, and thus
surface charges would be easy to be accumulated on the epitaxial
layer. Though the conventional trench Schottky diode is furnished
with the guard ring structure to avoid severe variations in voltage
levels, yet the corresponding improvement is still limited anyway.
Accordingly, it is an object of the present invention to provide a
Schottky diode that can reduce accumulation of surface charges
through structural changes, such that an early breakdown can be
avoided.
[0011] In the present invention, a Schottky diode with multiple
guard ring structures includes a semiconductor base layer, a back
metal layer, an epitaxial layer, a dielectric layer, a first metal
layer, a passivation layer and a second metal layer.
[0012] The semiconductor base layer has a back surface and a front
surface opposite to the back surface. The back metal layer is
formed on the back surface of the semiconductor base layer. The
epitaxial layer, formed on the front surface of the semiconductor
base layer, has a unit cell area and a termination area. The
epitaxial layer includes a termination trench structure, a first
ion implantation guard ring, a second ion implantation guard ring
and a third ion implantation guard ring.
[0013] The termination trench structure is disposed at a junction
of the unit cell area and the termination area. The first ion
implantation guard ring, disposed in the termination area by
neighboring to the termination trench structure, has a first width.
The second ion implantation guard ring, disposed in the termination
area and separated from the first ion implantation guard ring, has
a second width less than the first width. The third ion
implantation guard ring, disposed in the termination area and
separated from the second ion implantation guard ring, has a third
width less than the second width.
[0014] The dielectric layer is stacked on the termination trench
structure, the first ion implantation guard ring, the second ion
implantation guard ring and the third ion implantation guard ring
in the termination area.
[0015] The first metal layer includes a main body portion and a
separation portion. The main body portion, stacked on the
termination trench structure in the unit cell area, extends from
the unit cell area to be stacked on the dielectric layer above the
first ion implantation guard ring in the termination area. The
separation portion, stacked on the dielectric layer in the
termination area, extends toward the epitaxial layer to penetrate
through the dielectric layer to electrically contact the third ion
implantation guard ring. Further, a trench exposed out of the
dielectric layer is formed between the separation portion and the
main body portion.
[0016] The passivation layer, stacked on the main body portion in
the unit cell area, extends to be stacked on the main body portion,
the trench, the separation portion and the dielectric layer in the
termination area. The second metal layer, stacked on the first
metal layer and the passivation layer in the unit cell area,
extends from the unit cell area to be stacked on the passivation
layer above the first ion implantation guard ring in the
termination area.
[0017] In one embodiment of the present invention, the second ion
implantation guard ring is separated from the first ion
implantation guard ring by a first spacing, the third ion
implantation guard ring is separated from the second ion
implantation guard ring by a second spacing, and the second spacing
is larger than the first spacing. Preferably, a ratio of the first
spacing and the second spacing is 1:1.2.
[0018] In one embodiment of the present invention, a ratio of the
first width, the second width and the third width is 4:2:1.
[0019] In one embodiment of the present invention, the dielectric
layer includes a TEOS film and a BPSG film, the TEOS film is
stacked on the epitaxial layer in the termination area, and the
BPSG film is stacked on the TEOS film in the termination area.
[0020] In one embodiment of the present invention, the epitaxial
layer further includes a plurality of cell trench structures in the
unit cell area.
[0021] As stated, the Schottky diode with multiple guard ring
structures provided by the present invention divides the first
metal layer into the main body portion and the separation portion
to successfully avoid accumulation of surface charges by the
separation portion. In addition, since the Schottky diode with
multiple guard ring structures of the present invention is further
furnished with the first ion implantation guard ring, the second
ion implantation guard ring and the third ion implantation guard
ring in the termination area, with individual widths to become
smaller from the unit cell area toward the termination area. Thus,
the voltage levels of the entire Schottky diode with multiple guard
ring structures can present a stepwise variation, and thus possible
early breakdown can be effectively avoided.
[0022] All these objects are achieved by the Schottky diode with
multiple guard ring structures described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The present invention will now be specified with reference
to its preferred embodiment illustrated in the drawings, in
which:
[0024] FIG. 1 is a schematic cross-sectional view of a conventional
trench Schottky diode;
[0025] FIG. 2 is a schematic cross-sectional view of a preferred
embodiment of the Schottky diode with multiple guard ring
structures in accordance with the present invention;
[0026] FIG. 3 demonstrates schematically voltage distribution
curves of the Schottky diode with multiple guard ring structures of
FIG. 2; and
[0027] FIG. 4 demonstrates schematically reverse bias curves of the
Schottky diode with multiple guard ring structures of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] The invention disclosed herein is directed to a Schottky
diode with multiple guard ring structures. In the following
description, numerous details are set forth in order to provide a
thorough understanding of the present invention. It will be
appreciated by one skilled in the art that variations of these
specific details are possible while still achieving the results of
the present invention. In other instance, well-known components are
not described in detail in order not to unnecessarily obscure the
present invention.
[0029] Referring to FIG. 2, a schematic cross-sectional view of a
preferred embodiment of the Schottky diode with multiple guard ring
structures in accordance with the present invention is shown. As
illustrated, the Schottky diode with multiple guard ring structures
100 includes a semiconductor base layer 1, a back metal layer 2, an
epitaxial layer 3, a dielectric layer 4, a first metal layer 5, a
passivation layer 6 and a second metal layer 7.
[0030] The semiconductor base layer 1, having a back surface 11 and
a front surface 12 thereof opposite to each other, is an N-type
heavily-doped silicon layer. The back metal layer 2, formed on the
back surface 11 of the semiconductor base layer 1, can contain
titanium, nickel, silver or any combination of the above elements.
The epitaxial layer 3, formed on the front surface 12 of the
semiconductor base layer 1, has a unit cell area 3a and a
termination area 3b neighboring to the unit cell area 3a. In this
embodiment, the epitaxial layer 3 is an N-type lightly-doped
silicon layer, in which the light doping of the epitaxial layer 3
is compared to the heavy doping of the semiconductor base layer 1.
In addition, the epitaxial layer 3 includes a plurality of cell
trench structures 31 (one labeled in the figure), a termination
trench structure 32, a first ion implantation guard ring 33, a
second ion implantation guard ring 34 and a third ion implantation
guard ring 35.
[0031] The plurality of cell trench structures 31 are disposed in
the unit cell area 3a by being separated to each other. The
termination trench structure 32 is disposed at the junction of the
unit cell area 3a and the termination area 3b. In other words, the
termination trench structure 32 is across the unit cell area 3a and
termination area 3b. In this embodiment, the termination trench
structure 32 further includes a gate oxide layer 321 and a
polysilicon layer 322, in which the gate oxide layer 321 and the
polysilicon layer 322 are formed by forming a groove on the
epitaxial layer 3, then oxidizing an inner wall of the groove so as
to form the gate oxide layer 321, and finally the polysilicon is
fed into the groove so as to form the polysilicon layer 322. In
addition, the cell trench structure 31 is structurally resembled to
the termination trench structure 32. Thus, the cell trench
structure 31 includes also a gate oxide layer (not labeled in the
figure) and a polysilicon layer (not labeled in the figure).
[0032] The first ion implantation guard ring 33, disposed in the
termination area 3b by neighboring to the gate oxide layer 321 of
the termination trench structure 32, has a first width w1. The
second ion implantation guard ring 34, disposed in the termination
area 3b and separated from the first ion implantation guard ring 33
by a first spacing dl, has a second width w2 less than the first
width w1. The third ion implantation guard ring 35, disposed in the
termination area 3b and separated from the second ion implantation
guard ring 34 by a second spacing d2 larger than the first spacing
d1, has a third width w3 less than the second width w2. In this
embodiment, a ratio of the first width w1, the second width w2 and
the third width w3 is 4:2:1, and another ratio of the first spacing
d1 and the second spacing d2 is 1:1.2. In particular, the first
width w1 is 8 .mu.m, the second width w2 is 4 .mu.m, the third
width w3 is 2 .mu.m, the first spacing d1 is 10 .mu.m, and the
second spacing d2 is 12 .mu.m.
[0033] In addition, in practical applications, each of the first
ion implantation guard ring 33, the second ion implantation guard
ring 34 and the third ion implantation guard ring 35 is formed by
implanting boron ions onto the epitaxial layer 3 in the termination
area 3b. In this embodiment, each of the first width w1, the second
width w2 and the third width w3 is the instant width while in
implanting the boron ions. Practically, the width after the
implanting would be larger due to a diffusion effect.
[0034] The dielectric layer 4 includes a tetraethyl orthosilicate
(TEOS) film 41 and a borophosphosilicate glass (BPSG) film 42. The
TEOS film 41 is stacked on the termination trench structure 32, the
first ion implantation guard ring 33, the second ion implantation
guard ring 34 and the third ion implantation guard ring 35 of the
epitaxial layer 3 in the termination area 3b, while the BPSG film
42 is stacked on the TEOS film 41 in the termination area 3b.
[0035] The first metal layer 5, includes a main body portion 51 and
a separation portion 52. The main body portion 51 is stacked on the
termination trench structure 32 in the unit cell area 3a, and
extended from the unit cell area 3a to the termination area 3b by
stacking on the dielectric layer 4 above the first ion implantation
guard ring 33. As shown, in the unit cell area 3a, the main body
portion 51 includes a nickel-platinum alloy layer 511, a titanium
layer 512, a titanium-tungsten alloy layer 513 and an aluminum
layer 514. The nickel-platinum alloy layer 511 is stacked on the
epitaxial layer 3 and contacting the polysilicon layer (not labeled
in the figure) of the cell trench structure 31. The titanium layer
512 is stacked on the nickel-platinum alloy layer 511 in the unit
cell area 3a, and extended from the unit cell area 3a to the
termination area 3b for stacking onto the dielectric layer 4 above
the first ion implantation guard ring 33. The titanium-tungsten
alloy layer 513 is stacked on the titanium layer 512 in the unit
cell area 3a, and extended from the unit cell area 3a to the
termination area 3b for stacking on the titanium layer 512. The
aluminum layer 514 is stacked on the titanium-tungsten alloy layer
513 in the unit cell area 3a, and extended from the unit cell area
3a to the termination area 3b for stacking on the titanium-tungsten
alloy layer 513.
[0036] The separation portion 52 is stacked on the dielectric layer
4 in the termination area 3b, and extended toward the epitaxial
layer 3 by penetrating the dielectric layer 4 to electrically
contact the third ion implantation guard ring 35. Between the
separation portion 52 and the main body portion 51, a trench (not
labeled in the figure) exposed out of the dielectric layer 4 is
formed. The separation portion 52 further includes a titanium layer
521, a titanium-tungsten alloy layer 522 and a aluminum layer 523.
The titanium layer 521 is the BPSG film 42 stacked on the
dielectric layer 4. The titanium-tungsten alloy layer 522 is
stacked on the titanium layer 521. The aluminum layer 523, stacked
on the titanium-tungsten alloy layer 522, further extends toward
the epitaxial layer 3 to penetrate through the titanium layer 521,
the titanium-tungsten alloy layer 522 and both the BPSG film 42 and
the TEOS film 41 of the dielectric layer 4 so as to electrically
contact the third ion implantation guard ring 35. Practically, the
third spacing d4 of the TEOS film 41 can be 2 .mu.m.
[0037] In a manufacturing process, the titanium layer 512 and the
titanium layer 521 are formed by the same sputtering process, the
titanium-tungsten alloy layer 513 and the titanium-tungsten alloy
layer 522 are formed by the same sputtering process, and also the
aluminum layer 514 and the aluminum layer 523 are formed by the
same sputtering process. In addition, the aluminum layer 523, the
titanium-tungsten alloy layer 522 and the titanium layer 521 are
introduced to penetrate through the dielectric layer 4 so as to
have the titanium layer 521 further to electrically contact the
third ion implantation guard ring 35. Thereby, the aluminum layer
523 can be electrically connected to the third ion implantation
guard ring 35 via the titanium-tungsten alloy layer 522 and the
titanium layer 521. Before the titanium layer 521, the
titanium-tungsten alloy layer 522 and the aluminum layer 523 are
formed, the dielectric layer 4 above the third ion implantation
guard ring 35 is grooved by etching or a laser means, such that the
titanium layer 521, the titanium-tungsten alloy layer 522 and the
aluminum layer 523 can penetrate through the dielectric layer 4 to
electrically contact the third ion implantation guard ring 35.
[0038] In addition, after the titanium layers 512, 521, the
titanium-tungsten alloy layers 513, 522 and the aluminum layers
514, 523 are formed, another etching process is applied to form
grooves for separating the main body portion 51 and the separation
portion 52.
[0039] The passivation layer 6 is stacked on the main body portion
51 in the unit cell area 3a, and extended to be stacked on the main
body portion 51, a trench between the separation portion 52 and
main body portion 51, the separation portion 52 and the dielectric
layer 4 in the termination area 3b. In this embodiment, the
passivation layer 6 is a silicon nitride layer.
[0040] The second metal layer 7 is stacked on the first metal layer
5 and the passivation layer 6 in the unit cell area 3a, and
extended from the unit cell area 3a to be stacked on the
passivation layer 6 above the first ion implantation guard ring 33
in the termination area 3b. The second metal layer 7 includes a
titanium layer 71, a nickel layer 72 and a silver layer 73. The
titanium layer 71 is stacked on the aluminum layer 514 of the first
metal layer 5 and the passivation layer 6. The nickel layer 72 is
stacked on the titanium layer 71. The silver layer 73 is stacked on
the nickel layer 72.
[0041] Refer to FIG. 3 and FIG. 4; where FIG. 3 demonstrates
schematically voltage distribution curves of the Schottky diode
with multiple guard ring structures of FIG. 2, and FIG. 4
demonstrates schematically reverse bias curves of the Schottky
diode with multiple guard ring structures of FIG. 2.
[0042] As shown in FIG. 1 through FIG. 3, Curve C1 of FIG. 3 is
accounted for the conventional trench Schottky diode PA100 of FIG.
1, while Curve C2 thereof is accounted for the Schottky diode with
multiple guard ring structures 100 provided by the present
invention as shown in FIG. 2. The conventional trench Schottky
diode PA100 applies the guard ring structure PA33 to maintain the
voltage level of Curve C1 at around 35V. However, after passing the
guard ring structure PA33, the voltage level would quickly rise to
250V. On the other hand, in the Schottky diode with multiple guard
ring structures 100 of the present invention, the first ion
implantation guard ring 33 is applied to firstly maintain the
voltage level at around 35V, then the second ion implantation guard
ring 34 is applied to maintain the voltage level at around 100V,
and finally the third ion implantation guard ring 35 is applied to
maintain the voltage level at around 200V. Thus, with the Schottky
diode with multiple guard ring structures 100 of the present
invention to apply the first ion implantation guard ring 33, the
second ion implantation guard ring 34 and the third ion
implantation guard ring 35, the corresponding voltage levels can
present a stepwise variation, and so the voltage levels can be more
effectively distributed, such that possible early breakdown can be
avoided.
[0043] In addition, since the Schottky diode with multiple guard
ring structures 100 of the present invention is further furnished
with the separation portion 52 to top and thus electrically contact
the third ion implantation guard ring 35, thus the accumulation of
surface charges can be effectively avoided.
[0044] On the other hand, as shown in FIG. 4, Curve C3 of FIG. 4 is
accounted for variation in reverse voltages of the conventional
trench Schottky diode PA100 of FIG. 1, while Curve C4 thereof is
accounted for another variation in reverse voltages of the Schottky
diode with multiple guard ring structures 100 provided by the
present invention as shown in FIG. 2. It is obvious that the
Schottky diode with multiple guard ring structures 100 of the
present invention can maintain almost the same response in reverse
bias, with respect to the conventional trench Schottky diode
PA100.
[0045] In summary, in comparison with the conventional trench
Schottky diode who extends both the first metal layer and the
second metal layer into the termination area so as to increase the
reverse bias but inevitably lead to accumulate excessive surface
charges on the epitaxial layer, the Schottky diode with multiple
guard ring structures provided by the present invention divides the
first metal layer into the main body portion and the separation
portion to successfully avoid accumulation of surface charges by
the separation portion. In addition, since the Schottky diode with
multiple guard ring structures of the present invention is further
furnished with the first ion implantation guard ring, the second
ion implantation guard ring and the third ion implantation guard
ring in the termination area, with individual widths to become
smaller from the unit cell area toward the termination area. Thus,
the voltage levels of the entire Schottky diode with multiple guard
ring structures can present a stepwise variation, and thus possible
early breakdown can be effectively avoided.
[0046] While the present invention has been particularly shown and
described with reference to a preferred embodiment, it will be
understood by those skilled in the art that various changes in form
and detail may be without departing from the spirit and scope of
the present invention.
* * * * *