U.S. patent application number 15/425714 was filed with the patent office on 2017-09-14 for switching device.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. The applicant listed for this patent is TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Takashi KUNO, Akitaka SOENO.
Application Number | 20170263739 15/425714 |
Document ID | / |
Family ID | 59700511 |
Filed Date | 2017-09-14 |
United States Patent
Application |
20170263739 |
Kind Code |
A1 |
SOENO; Akitaka ; et
al. |
September 14, 2017 |
SWITCHING DEVICE
Abstract
A switching device includes a semiconductor substrate having a
first element range including first trenches for gates, and an
ineffective range not including the first trenches. In an
interlayer insulating film, a contact hole is provided within the
first element range, and a wide contact hole is provided within the
inactive range. The first metal layer contacts the semiconductor
substrate within the contact hole and the wide contact hole. The
insulating protective film covers an outer peripheral side portion
of a bottom surface of a second recess which is provided in a
surface of the first metal layer above the wide contact hole. A
side surface of an opening provided in a portion of the insulating
protective film that includes the first element range is disposed
in the second recess. The second metal layer contacts the first
metal layer and the side surface of the opening.
Inventors: |
SOENO; Akitaka; (Toyota-shi,
JP) ; KUNO; Takashi; (Kariya-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOTA JIDOSHA KABUSHIKI KAISHA |
Toyota-shi |
|
JP |
|
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
Toyota-shi
JP
|
Family ID: |
59700511 |
Appl. No.: |
15/425714 |
Filed: |
February 6, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 23/3171 20130101;
H01L 2224/05567 20130101; H01L 2224/26145 20130101; H01L 2924/3512
20130101; H01L 2924/351 20130101; H01L 29/45 20130101; H01L
2224/06181 20130101; H01L 29/1095 20130101; H01L 29/417 20130101;
H01L 29/407 20130101; H01L 2224/04026 20130101; H01L 29/0623
20130101; H01L 29/7397 20130101; H01L 2224/05655 20130101; H01L
29/0638 20130101; H01L 23/5283 20130101; H01L 29/0619 20130101;
H01L 24/05 20130101; H01L 2224/05572 20130101; H01L 2924/13055
20130101; H01L 29/0696 20130101 |
International
Class: |
H01L 29/739 20060101
H01L029/739; H01L 29/06 20060101 H01L029/06; H01L 23/528 20060101
H01L023/528; H01L 29/10 20060101 H01L029/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 9, 2016 |
JP |
2016-046134 |
Claims
1. A switching device comprising: a semiconductor substrate; gate
insulating films; gate electrodes; an interlayer insulating film; a
first metal layer; a second metal layer, and an insulating
protective film, wherein the semiconductor substrate comprises a
first element range and an ineffective range, a plurality of first
trenches is provided in an upper surface of the semiconductor
substrate within the first element range and is not provided within
the ineffective range, the first trenches extending along a first
direction and being arranged at intervals along a second direction
perpendicular to the first direction, the ineffective range is
provided adjacent to the first element range in the second
direction, the gate insulating films cover inner surfaces of the
first trenches, the gate electrodes are disposed inside of the
first trenches, each gate electrode being insulated from the
semiconductor substrate by the corresponding gate insulating film,
the interlayer insulating film covers the upper surface and the
gate electrodes, within the first element range, a contact hole is
provided in a portion of the interlayer insulating film that covers
the upper surface, within the ineffective range, a wide contact
hole is provided in a portion of the interlayer insulating film
that covers the upper surface, the wide contact hole having a width
in the second direction that is wider than a pitch between each
pair of adjacent first trenches in the second direction, the first
metal layer covers the interlayer insulating film, being insulated
from the gate electrodes by the interlayer insulating film, the
first metal layer being in contact with the semiconductor substrate
within the contact hole and the wide contact hole, a first recess
is provided in a surface of the first metal layer above the contact
hole, and a second recess is provided in the surface of the first
metal layer above the wide contact hole, the insulating protective
film covers an outer peripheral side part of a bottom surface of
the second recess, an opening is provided in the insulating
protective film in a range wider than the first element range and
including the first element range, a side surface of the opening
being disposed in the second recess, the second metal layer is in
contact with the surface of the first metal layer in the opening
and is in contact with the side surface of the opening, the second
metal layer having a linear expansion coefficient smaller than a
linear expansion coefficient of the first metal layer, each
semiconductor region interposed between each pair of adjacent first
trenches in the first element range comprises: a first region of a
first conductivity type, being in contact with the first metal
layer in the contact hole, being in contact with the corresponding
gate insulating film; and a body region of a second conductivity
type, being in contact with the first metal layer in the contact
hole, and being in contact with the corresponding gate insulating
film below the first region, the semiconductor region within the
ineffective range comprises a second conductivity type peripheral
region of the second conductivity type, the second conductivity
type peripheral region being in contact with the first metal layer
in the wide contact hole, and extending from the upper surface to a
position deeper than lower ends of the first trenches, the
semiconductor substrate further comprises a second region of the
first conductivity type, the second region being disposed and
extending across below the body region and below the second
conductivity type peripheral region, being in contact with the gate
insulating films below the body region, and being separated from
the first region by the body region.
2. The switching device of claim 1, wherein a plurality of second
trenches is provided in the upper surface, each of the second
trenches extending toward the ineffective range from the first
trench positioned closest to the ineffective range, and each end
surface of the second trenches on an ineffective range side is
covered with the second conductivity type peripheral region.
3. The switching device of claim 1, wherein a second
conductivity-type impurity density of the second conductivity-type
peripheral region is higher than a second conductivity-type
impurity density of a portion of the body region that is positioned
below the first region.
4. The switching device of any one of claim 1, wherein the
semiconductor substrate includes an outer peripheral voltage
resistant range that surrounds a periphery of a range including the
first element range and the ineffective range, and a guard ring of
the second conductivity type is provided in the outer peripheral
voltage resistant range, the guard ring being exposed on the upper
surface, surrounding the range including the first element range
and the ineffective range, and being electrically separated from
the first metal layer.
5. The switching device of claim 4, wherein the semiconductor
substrate further includes a second element range arranged between
the ineffective range and the outer peripheral voltage resistant
range, a plurality of the first trenches is provided at intervals
along the second direction in the upper surface within the second
element range, within the second element range, a contact hole is
provided in a portion of the interlayer insulation film that covers
the upper surface, the first metal layer is in contact with the
upper surface in the contact hole within the second element range,
the insulating protective film covers the first metal layer within
the second element range, the second metal layer is disposed and
extending across from on the first metal layer in the opening and
to on the insulating protective film, an outer peripheral side end
of the second metal layer is positioned on an inner peripheral side
relative to an outer peripheral side end of the first metal layer,
and each of the semiconductor regions interposed between each pair
of adjacent first trenches within the second element range includes
the first region and the body region.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a switching device.
BACKGROUND ART
[0002] Japanese Patent Application Publication No. 2005-116963
discloses a switching device having a semiconductor substrate, an
upper surface of which is connected to a heat sink block by
soldering.
[0003] Further Japanese Patent Application Publication No.
2011-187708 discloses a switching device having a plurality of
trenches that extend linearly in an upper surface of a
semiconductor substrate. Each of the trenches extends parallel to
one another along a certain direction. Inner surfaces of the
trenches are covered with gate insulating films. Gate electrodes
are disposed inside of the trenches. An interlayer insulating film
covers an upper surface of the semiconductor substrate and the gate
electrodes. A contact hole is provided in the interlayer insulating
film above each semiconductor region (hreinafter referred to as an
inter-trench region) interposed between each pair of adjacent
trenches in the semiconductor substrate. An upper electrode covers
the interlayer insulating film, and is in contact with the
semiconductor substrate in the contact holes. Each of the
inter-trench regions includes a first region (emitter region) of a
first conductivity type (n-type), and a body region of a second
conductivity type (p-type). Each of the first regions is in contact
with the upper electrode and the corresponding gate insulating
film. The body region is in contact with the upper electrode, and
is in contact with the gate insulating films below the first
regions. Further, the semiconductor substrate includes a second
region (drift region) of the first conductivity type. The second
region is in contact with the gate insulating films below the body
region, and is separated from the first regions by the body region.
In this switching device, when a potential of the gate electrodes
is controlled to a predetermined potential, channels are formed in
the body region. The first regions and the second region are
electrically connected by the channels. Accordingly, a current
flows between the first regions and the second region.
SUMMARY
[0004] An upper electrode of such a switching device as disclosed
in Japanese Patent Application Publication No. 2005-116963 usually
includes a first metal layer and a second metal layer. The first
metal layer is a metal layer being in contact with the upper
surface of the semiconductor substrate. The first metal layer is
constituted of a material that is less likely to contaminate the
semiconductor substrate and makes contact with the semiconductor
substrate at a low contact resistance. The second metal layer is a
metal layer disposed on the first metal layer and makes contact
with soldering. The second metal layer is constituted of a material
that is easy to be connected to the soldering.
[0005] In a switching device that includes trenches as disclosed in
Japanese Patent Application Publication No. 2011-187708, an upper
electrode may be sometimes constituted of a first metal layer and a
second metal layer to connect the upper electrode to an exterior by
soldering. For example, FIG. 9 shows a cross section of a switching
device having trenches 140. In FIG. 9, an upper electrode 150 is
constituted of a first metal layer 151 and a second metal layer
152. When the first metal layer 151 is formed, recesses 151a are
formed on a surface of the first metal layer 151 above contact
holes 162a of an interlayer insulating film 162. Accordingly, the
first metal layer 151 has a plurality of the recesses 151a on its
upper surface. The second metal layer 152 is disposed on the first
metal layer 151. Accordingly, the second metal layer 152 is filled
in each recess 151a. Further, in a switching device as described in
Japanese Patent Application Publication No. 2011-187708, as shown
in FIG. 9, an upper surface in an outer peripheral portion of a
semiconductor substrate 118 is usually covered with an insulating
protective film 160. The insulating protective film 160 is provided
to cover an outer peripheral side portion of the first metal layer
151 such that no gap is generated between the first metal layer 151
and the insulating protective film 160. The insulating protective
film 160 has an opening 180. The second metal layer 152 covers the
first metal layer 151 in the opening 180. Further, the second metal
layer 152 is provided to make contact with an inner peripheral side
end 160a (a side surface of the opening 180) of the insulating
protective film 160 such that no gap is generated between the
second metal layer 152 and the insulating protective film 160.
Notably, in FIG. 9, a portion of the second metal layer 152 is
disposed above the insulating protective film 160. However, the
second metal layer 152 may not be disposed above the insulating
protective film 160.
[0006] As the switching device in FIG. 9 operates, a temperature of
the semiconductor substrate 118 rises. Then, temperatures of the
first metal layer 151, the second metal layer 152 and the
insulating protective film 160 also rise. A linear expansion
coefficient of the second metal layer 152 is generally smaller than
a linear expansion coefficient of the first metal layer 151.
Further, a linear expansion coefficient of the insulating
protective film 160 is generally equal to or larger than the linear
expansion coefficient of the first metal layer 151. The first metal
layer 151 thermally expands along with the second metal layer 152
in a range where the first metal layer 151 is in contact with the
second metal layer 152. Since the linear expansion coefficient of
the second metal layer 152 is small, thermal expansion of the first
metal layer 151 is suppressed in the range. Especially since the
second metal layer 152 is filled in each recess 151a in the upper
surface of the first metal layer 151, the first metal layer 151 is
firmly restrained by the second metal layer 152. Due to this,
thermal expansion amount of the first metal layer 151 is small in
the range where the first metal layer 151 is in contact with the
second metal layer 152. On the other hand, the first metal layer
151 thermally expands along with the insulating protective film 160
in a range where the first metal layer 151 is in contact with the
insulating protective film 160. Since the linear expansion
coefficient of the insulating protective film 160 is relatively
large, the thermal expansion amount of the first metal layer 151 is
relatively large in this range. The first metal layer 151 directly
below the inner peripheral side end 160a of the insulating
protective film 160 is positioned at a boundary between a range
having a small thermal expansion amount (the range where the first
metal layer 151 is in contact with the second metal layer 152) and
a range having a large thermal expansion amount (the range where
the first metal layer 151 is in contact with the insulating
protective film 160). Due to this, when the temperature of the
switching device changes, stress is likely to concentrate on the
first metal layer 151 directly below the end 160a, and cracks are
thus liable to occur in the first metal layer 151 in this
portion.
[0007] Contrary to this, as shown in FIG. 10, it is conceivable
that an entirety of an upper surface of each inter-trench region
142 (region surrounded by two trenches 140) is covered with the
interlayer insulating film 162 in a vicinity of the inner
peripheral side end 160a of the insulating protective film 160
(that is, the contact holes 162a are not provided in the interlayer
insulating film 162 in the vicinity of the end 160a). An upper
surface of the interlayer insulating film 162 becomes flat in a
range where the contact holes 162a are not provided. Due to this,
the upper surface of the first metal layer 151 also becomes flat on
the interlayer insulating film 162 in this range. That is, the
recesses 151a are not present in the upper surface of the first
metal layer 151 in this range. Accordingly, in this range, the
first metal layer 151 is in contact with the second metal layer 152
at a flat surface. The restraining force of the second metal layer
152 upon the first metal layer 151 is weak at the flat surface. Due
to this, the thermal expansion amount of the first metal layer 151
in the flat surface range is large compared to the thermal
expansion amount of the first metal layer 151 in a range where the
recesses 151a are present (notably, the thermal expansion amount of
the first metal layer 151 even in this flat surface range is small
compared to the thermal expansion amount of the first metal layer
151 in a range where the first metal layer 151 is in contact with
the insulating protective film 160). As a result of this, a
difference in thermal expansion amount of the first metal layer 151
between a range where the thermal expansion amount of the first
metal layer 151 is small (range where the first metal layer 151 is
in contact with the second metal layer 152) and a range where the
thermal expansion amount of the first metal layer 151 is large
(range where the first metal layer 151 is in contact with the
insulating protective film 160) becomes small at a position
directly below the end 160a of the insulating protective film 160.
Due to this, this configuration reduces stress generated in the
first metal layer 151 at the position directly below the end 160a,
and suppresses the occurrence of the cracks in the first metal
layer 151 at this portion.
[0008] However, according to the configuration of FIG. 10, there
occurs a problem that a resistance of the second region 126
increases upon when the switching device turns on. The details will
be explained hereinbelow. In FIG. 10, in each inter-trench region
142 below the interlayer insulating film 162 in a range where no
contact holes 162a are present, the body region 124 is not
connected to the upper electrode 150. Upon when the switching
device turns off, a difference in potential between the second
region 126 and the body region 124 becomes large. Then, a depletion
layer extends from a pn junction at an interface between the second
region 126 and the body region 124. This depletion layer depletes
the second region 126 in a wide range. Further, this depletion
layer partially depletes the body region 124 as well. When the
depletion layer expands in the body region 124, a part of charges
in the body region 124 (e.g., holes) is reunited with charges in
the second region 126 (e.g., electrons) to disappear. Accordingly,
as the depletion layer expands, the charges in the body region 124
reduce.
[0009] After that, when the potential of the gate electrodes 130 is
controlled to a gate-on potential, channels are formed in the body
region 124 in a range adjacent to gate insulating films 132. Then
the potential of the second region 126 becomes substantially equal
to a potential of first regions 122. Charges are then supplied from
the upper electrode 150 to the body region 124 shortly in a range
where the body region 124 is connected to the upper electrode 150.
Due to this, the depletion layer extending from the pn junction at
the interface between the body region 124 and the second region 126
shortly disappears. Accordingly, a current flows between a lower
electrode 154 and the upper electrode 150.
[0010] Contrary to this, charges are hardly supplied from the upper
electrode 150 to the body region 124 in a range where the contact
holes 162a are not present. For example, if the body region 124 in
the range where the contact holes 162a are not present is
electrically separated from the upper electrode 150, charges are
hardly supplied from the upper electrode 150 to the body region 124
in this range. Further, even if the body region 124 in the range
where the contact holes 162a are not present is electrically
connected to the upper electrode 150 at a portion not shown, it
would take time to supply charges to the body region 124 in that
portion since a distance between the connection point and the body
region 124 in the range where no contact holes 162a are present is
long. As such, since charges are hardly supplied to the body region
124 in the range where no contact holes 162a are present, a state
where the depletion layer extends below the body region 124 in this
range is maintained for a while even when the channels have been
formed. That is, even in an ON-state, as shown in FIG. 10, a
depletion layer 159 has spread from the body region 124 in the
range where the contact holes 162a are not present into the second
region 126 for a while. Due to this, in this switching device, a
current path in the second region 126 is narrow and a resistance of
the second region 126 is high just after the turning-ON. As such,
the resistance of the second region 126 is high just after the
tuming-ON.
[0011] Notably, in FIGS. 9 and 10, the switching device including a
collector region 128 (i.e., IGBT: Insulated Gate Bipolar
Transistor) is exemplified. However, a similar problem may occur in
a case of a FET (Field Effect Transistor), which does not include
the collector region 128. The above-described problem may occur
both in an n-channel type FET and a p-channel type FET. Further, in
FIGS. 9 and 10, the electrode 154 is provided on a lower surface of
the semiconductor substrate 118. However the electrode 154 may be
provided in another position.
[0012] The present disclosure provides a technique that can
suppress occurrence of cracks in a first metal layer directly below
a side surface of an opening of an insulting protective film, and
can reduce resistance of a second region when the switching device
being turned on.
[0013] A switching device disclosed herein comprises: a
semiconductor substrate; a gate insulating film; a gate electrode;
an interlayer insulating film; a first metal layer, a second metal
layer, and an insulating protective film. In the switching device,
the semiconductor substrate comprises a first element range, and an
ineffective range. A plurality of first trenches is provided in an
upper surface of the semiconductor substrate within the first
element range and is not provided within the ineffective range. The
first trenches extend along a first direction and are arranged with
intervals along a second direction perpendicular to the first
direction. The ineffective range is provided adjacent to the first
element range in the second direction. The gate insulating film
covers inner surfaces of the first trenches. The gate electrodes
are disposed inside of the first trenches, and each gate electrode
is insulated from the semiconductor substrate by the corresponding
gate insulating film. The interlayer insulating film covers the
upper surface and the gate electrode. Within the first element
range a contact hole is provided in a portion of the interlayer
insulating film that covers the upper surface. Within the
ineffective range a wide contact hole is provided in the interlayer
insulating film in a portion that coves the upper surface, and the
wide contact hole has a width in the second direction wider than a
pitch between each pair of adjacent first trenches in the second
direction. The first metal layer covers the interlayer insulating
film, is insulated from the gate electrode by the interlayer
insulating film, and is in contact with the semiconductor substrate
within the contact hole and the wide contact hole. A first recess
is provided in a surface of the first metal layer above the contact
hole, and a second recess is provided in a front surface of the
first metal layer above the wide contact hole. The insulating
protective film covers an outer peripheral side part of a bottom
surface of the second recess. An opening is provided in the
insulating protective film in a range wider than the first element
range and including the first element range. A side surface of the
opening is disposed in the second recess. The second metal layer is
in contact with the surface of the first metal layer in the opening
and is in contact with the side surface of the opening, and the
second metal layer has a linear expansion coefficient smaller than
a linear expansion coefficient of the first metal layer. Each
semiconductor region interposed between each pair of adjacent first
trenches in the first element range comprises: a first region of a
first conductivity type, being in contact with the first metal
layer in the contact hole and in contact with the gate insulating
film, and a body region of a second conductivity type, being in
contact with the first metal layer and being in contact with the
corresponding gate insulating film below the first region. The
semiconductor region within the ineffective range comprises a
second conductivity type peripheral region of the second
conductivity type, and the second conductivity type peripheral
region is in contact with the first metal layer in the wide contact
hole, and extends from the upper surface to a position deeper than
lower ends of the first trenches. The semiconductor substrate
comprises a second region of the first conductivity type, and the
second region is disposed and extends across below the body region
and below the second conductivity type peripheral region, is in
contact with the gate insulating film below the body region, and is
separated from the first region by the body region.
[0014] In this switching device, the first trenches are not
provided in the upper surface of the semiconductor substrate in the
ineffective range. Further, the wide contact hole is provided in
the interlayer insulating film in the ineffective range. Within the
wide contact hole, the first metal layer is in contact with the
second conductivity type peripheral region. When tuning off the
switching device, depletion layer extends from a pn junction at an
interface between the second conductivity type peripheral region
and the second region. At this occasion, charges in the second
conductivity type peripheral region decrease. Upon when turning on
the switching device, charges are supplied to the second
conductivity type peripheral region from the first metal layer
within the wide contact hole. Due to this, when the switching
device turns on, the depletion layer that had extended from the pn
junction at the interface between the second conductivity type
peripheral region and the second region shortly disappears.
Accordingly, current can flow through the second region in a wide
range. Due to this, in this switching device, the resistance of the
second region is decreased shortly after tuning on. This switching
device is able to operate at a low loss.
[0015] Further, since the first metal layer extends over to the
inside of the wide contact hole, the second recess is formed in the
surface of the first metal layer above the wide contact hole. Since
the width of the wide contact hole is great, the width of the
second recess is also great. Thus, the bottom surface of the second
recess is flat in a wide range.
[0016] In this switching device, the side surface of the opening of
the insulating protective film (an inner peripheral side end of the
insulating protective film) is positioned within the second recess
(i.e., range where the first metal layer has a flat surface). Due
to this, similarly to the case of FIG. 10, stress applied to the
first metal layer at the position directly below the side surface
of the opening of the insulting protective film is mitigated. Thus,
in this switching device, cracks are less likely to occur at the
position directly below the side surface of the opening of the
insulating protective film.
[0017] Further, if the ineffective range where the first trenches
are not present is provided, the electric field may concentrate
around a portion below the first trench disposed closest to the
ineffective range when the switching device is in OFF-state.
However, in this switching device, the second conductivity type
peripheral region extends to a position deeper than the lower ends
of the first trenches. According to this configuration, when the
switching device is in the OFF-state, the lower end of the first
trench disposed closest to the ineffective range is protected by
the depletion layer extending from the second conductivity type
peripheral region. Due to this, the electric field concentration
can be suppressed around the portion of the lower end of the first
trench. According to this switching device, even if the ineffective
range where the first trenches are not present is provided,
sufficient breakdown voltage can be secured.
[0018] As described above, according to the switching device
disclosed herein, occurrence of cracks in the first metal layer
directly below the side surface of the opening of the insulating
protective film can be suppressed. In addition, according to this
switching device, the resistance of the second region can be
shortly decreased upon when tuning on the switching device.
Further, according to this switching device, even if the
ineffective range where the first trenches are not present is
provided, the electric field concentration can be suppressed.
BRIEF DESCRIPTION OF DRAWINGS
[0019] FIG. 1 is a plan view of an IGBT of embodiment 1.
[0020] FIG. 2 is a vertical cross sectional view taken along line
of II-II of FIG. 1.
[0021] FIG. 3 is a vertical cross sectional view taken along line
of III-III of FIG. 1.
[0022] FIG. 4 is an enlarged view of FIG. 2.
[0023] FIG. 5 is a plan view of an IGBT of embodiment 2.
[0024] FIG. 6 is a plan view of an IGBT of variant 1.
[0025] FIG. 7 is a vertical cross sectional view of an IGBT of
variant 2.
[0026] FIG. 8 is a vertical cross sectional view of an IGBT of
variant 3.
[0027] FIG. 9 is a vertical cross sectional view of a switching
device of comparative example 1.
[0028] FIG. 10 is a vertical cross sectional view of a switching
device of comparative example 2.
DETAILED DESCRIPTION
Embodiment 1
[0029] An IGBT 10 of embodiment 1 shown in FIGS. 1 to 3 comprises a
semiconductor substrate 18, electrodes each provided on an upper
surface 18a and a lower surface 18b of the semiconductor substrate
18, and insulating films. Notably, in FIG. 1, illustration of the
electrode on the upper surface 18a of the semiconductor substrate
18 and the insulating films is omitted for easier explanation.
Further, in FIG. 1, for easier view, a terminal region 34 and guard
rings 36 are indicated by hatching. Further, a direction parallel
to the upper surface 18a of the semiconductor substrate 18 will be
denoted as an x direction and a direction parallel to the upper
surface 18a and perpendicular to the x direction will be denoted as
a y direction, hereinbelow.
[0030] As shown in FIG. 1, a plurality of trenches 40 is provided
in the upper surface 18a of the semiconductor substrate 18. The
trenches 40 extend along the x direction parallel to each other,
and arranged at intervals along the y direction. Each region
between each pair of the adjacent trenches 40 will be hereinafter
referred to as an inter-trench region 42. The semiconductor
substrate 18 comprises a first element range 11, a second element
range 12 and a surrounding range 13. The trenches 40 are provided
in the first element range 11, and the second element range 12.
Within the surrounding range 13, no trenches 40 are present Within
the surrounding range 13, any of the trenches are not provided, and
the upper surface 18a of the semiconductor substrate 18 is flat
within the surrounding range 13.
[0031] The first element range 11 is provided in a substantially
center of the semiconductor substrate 18. The trenches 40 are
repeatedly provided at a constant pitch P1 in the first element
range 11 along the y direction.
[0032] The surrounding range 13 is provided on an outer peripheral
side of the first element range 11 (i.e., a range between the first
element range 11 and an outer peripheral end surface 18c of the
semiconductor substrate 18). The surrounding range 13 surrounds a
periphery of the first element range 11. As described above, in the
surrounding range 13, no trenches 40 are provided. A width W1 in
the y direction of the surrounding range 13 in a portion adjacent
to the first element range 11 in the y direction (i.e., an interval
between the first element range 11 and the second element range 12
in the y direction) is greater than twice the above-described pitch
P1. Further, a width W2 in the x direction of the surrounding range
13 in the portion adjacent to the first element range 11 in the x
direction is greater than twice the pitch P1.
[0033] The second element range 12 is provided on an outer
peripheral side of the surrounding range 13 (i.e., range between
the surrounding range 13 and the outer peripheral end surface 18c
of the semiconductor substrate 18). Within the second element range
12, the trenches 40 are repeatedly provided at the constant pitch
P1 along the y direction. The surrounding range 13 (i.e., range
where no trenches are provided) is disposed between the first
element range 11 and the second element range 12. The second
element range 12 is separated from the first element range 11 by
the surrounding range 13. The second element range 12 surrounds a
periphery of the surrounding range 13. Within the second element
range 12 trenches 40 are repeatedly provided along the y direction
at a pitch equal to the above-described pitch P1 (the pitch P1 of
the trenches 40 in the first element range 11).
[0034] An outer peripheral voltage resistant range 14 is provided
on an outer peripheral side of the second element range 12 (i.e.,
between the second element range 12 and the outer peripheral end
surface 18c of the semiconductor substrate 18). No trenches 40 are
present in the outer peripheral voltage resistant range 14. The
outer peripheral voltage resistant range 14 surrounds the second
element range 12.
[0035] As shown in FIGS. 2 and 3, inner surfaces of the trenches 40
are covered with gate insulating films 32. Further, a gate
electrode 30 is disposed inside each trench 40. Each gate electrode
30 is insulated from the semiconductor substrate 18 by the
corresponding gate insulating film 32.
[0036] As shown in FIGS. 2, 3, each inter-trench region 42 in the
first element range 11 includes emitter regions 22 and a body
region 24.
[0037] Each emitter region 22 is an n-type region. The emitter
region 22 is disposed in a range exposed in the upper surface 18a
of the semiconductor substrate 18. The emitter region 22 is in
contact with the corresponding gate insulating film 32 at an
uppermost portion of the corresponding trench 40.
[0038] The body region 24 is a p-type region. The body region 24 is
exposed on the upper surface 18a of the semiconductor substrate 18
in a range where no emitter regions 22 are present. The body region
24 extends from the position exposed on the upper surface 18a to a
position below the emitter regions 22. The body region 24 includes
high density regions 24a and a low density region 24b that has a
lower p-type impurity density than the high density regions 24a.
Each high density region 24a is disposed in a range exposed on the
upper surface 18a. The low density region 24b is disposed lower
than the emitter regions 22. The low density region 24b is in
contact with the gate insulating films 32 below the emitter regions
22.
[0039] Each inter-trench region 42 in the second element range 12
also includes the emitter regions 22 and the body region 24. The
emitter regions 22 and the body region 24 in the second element
range 12 have the same configurations as those of the emitter
regions 22 and the body region 24 in the first element range 11
respectively.
[0040] As shown in FIGS. 2 and 3, a p-type peripheral region 29 is
provided within the surrounding range 13. The p-type peripheral
region 29 is provided in the surrounding range 13 in a range
exposed on the upper surface 18a of the semiconductor substrate 18.
The p-type peripheral region 29 is a p-type region having a p-type
impurity density higher than the p-type impurity density of the low
density regions 24b of the body regions 24. The p-type peripheral
region 29 extends from the upper surface 18a of the semiconductor
substrate 18 to a depth lower than lower ends of the trenches 40.
The p-type peripheral region 29 extends along the surrounding range
13 so as to surround the periphery of the first element range 11.
As shown in FIG. 2, the p-type peripheral region 29 covers a trench
40 (hereinafter referred to as a trench 40a) which is positioned in
the first element range 11 and closest to the surrounding range 13e
in the y direction. More specifically, the p-type peripheral region
29 is in contact with both side surfaces and a bottom surface of
the trench 40a. Further as shown in FIG. 2, the p-type peripheral
region 29 covers a trench 40 (hereinafter referred to as a trench
40b) which is positioned in the second element range 12 and closest
to the surrounding range 13 element range in the y direction. More
specifically, the p-type peripheral region 29 is in contact with
both side surfaces and a bottom surface of the trench 40b. Further,
as shown in FIG. 3, the p-type peripheral region 29 covers an end
in the x direction of each trench 40 in the first element range 11.
More specifically, the p-type peripheral region 29 is in contact
with the side surfaces and the bottom surface of each trench 40 at
the ends in the x direction within the first element range 11.
Further, as shown in FIG. 3, the p-type peripheral region 29 covers
the ends of each trench 40 in the x direction within the second
element range 12. More specifically, the p-type peripheral region
29 is in contact with the side surfaces and the bottom surface of
each trench 40 at the ends of each trench 40 in the x direction
within the second element range 12.
[0041] As shown in FIGS. 1 and 2, a terminal region 34 and a
plurality of guard rings 36 are provided in the outer peripheral
voltage resistant range 14.
[0042] The terminal region 34 is a p-type region, and is positioned
in a range exposed on the upper surface 18a of the semiconductor
substrate 18. The terminal region 34 extends from the upper surface
18a to a lower side than the lower ends of the trenches 40. The
terminal region 34 extends in an annular shape to surround the
first element range 11, the surrounding range 13, and the second
element range 12.
[0043] Each guard ring 36 is a p-type region, and is positioned in
a range exposed on the upper surface 18a of the semiconductor
substrate 18. Each guard ring 36 extends from the upper surface 18a
to a depth lower than the lower end of each trench 40. The terminal
region 34 is surrounded by the multiple guard rings 36. That is,
each guard ring 36 extends in an annular shape to surround the
first element range 11, the surrounding range 13, and the second
element range 12. Each guard ring 36 is separated from the body
regions 24 and the terminal region 34. Further, the respective
guard rings 36 are separated from each other.
[0044] As shown in FIGS. 2, 3, the semiconductor substrate 18
includes a drift region 26, a buffer region 27, and a collector
region 28.
[0045] The drift region 26 is an n-type region having a low n-type
impurity density. The drift region 26 extends across the first
element range 11, the surrounding range 13, the second element
range 12, and the outer peripheral voltage resistant range 14.
Within the first element range 11, the drift region 26 is disposed
below the body region 24 and is in contact with the body region 24
from below the body region 24. Within the first element range 11,
the drift region 26 is separated from the emitter regions 22 by the
body region 24. Within the first element range 11, the drift region
26 is in contact with the gate insulating films 32 at below the
body region 24. Within the surrounding range 13, the drift region
26 is disposed below the p-type peripheral region 29 and is in
contact with the p-type peripheral region 29 from below the p-type
peripheral region 29. Within the second element range 12 the drift
region 26 is disposed below the body region 24, and is in contact
with the body region 24 from below the body region 24. Within the
second element range 12, the drift region 26 is separated from the
emitter regions 22 by the body region 24. Within the second element
range 12, the drift region 26 is in contact with the gate
insulating films 32 at below the body region 24. The drift region
26 is in contact with the terminal region 34 and the respective
guard rings 36 within the outer peripheral voltage resistant range
14. The terminal region 34 is separated from the guard rings 36 by
the drift region 26. Further, the respective guard rings 36 are
separated from each other by the drift region 26.
[0046] The buffer region 27 is an n-type region having a higher
n-type impurity density than the drift region 26. The buffer region
27 extends across the first element range 11, the surrounding range
13, the second element range 12, and the outer peripheral voltage
resistant range 14. The buffer region 27 is disposed below the
drift region 26, and is in contact with the drift region 26 from
blow the drift region 26.
[0047] The collector region 28 is a p-type region. The collector
region 28 extends across the first element range 11, the
surrounding range 13, the second element range 12, and the outer
peripheral voltage resistant range 14. The collector region 28 is
disposed below the buffer region 27, and is in contact with the
buffer region 27 from below the buffer region 27. The collector
region 28 is exposed on the lower surface 18b of the semiconductor
substrate 18.
[0048] As shown in FIGS. 2 and 3, an interlayer insulating film 62,
an ohmic metal layer 51, a plurality of ring electrodes 53, an
insulating protective film 60, and a surface metal layer 52 are
arranged above the semiconductor substrate 18.
[0049] The interlayer insulating film 62 is disposed on the upper
surface 18a of the semiconductor substrate 18. Entireties of upper
surfaces of the gate electrodes 30 are covered with the interlayer
insulating film 62. A contact holes 62a piercing the interlayer
insulating film 62 in a vertical direction is provided above each
of the inter-trench regions 42 within the first element range 11
and the second element range 12. A wide contact hole 62b piercing
the interlayer insulating film 62 in the vertical direction is
provided within the surrounding range 13. The wide contact hole 62b
extends on the upper surface 18a of the semiconductor substrate 18
so as to surround the first element range 11 along the surrounding
range 13. Although within a range shown in FIG. 2, a width W3 of
the wide contact hole 62b in the y direction is slightly narrower
than the width W1 of the surrounding range 13 in the y direction,
the width W3 and width W1 are substantially equal. The width W3 is
wider than twice the above-described pitch P1. Although within a
range shown in FIG. 3, a width W4 of the wide contact hole 62b in
the x direction is slightly smaller than a width W2 of the
surrounding range 13 in the x direction, the width W4 and width W2
are substantially equal. The width W4 is wider than twice the
above-described pitch P1. Contact holes are provided in the
interlayer insulating film 62 within the outer peripheral voltage
resistant range 14 above the terminal region 34 and above the
respective guard rings 36 and the like.
[0050] The ohmic metal layer 51 covers the interlayer insulating
film 62 in the first element range 11, the surrounding range 13,
and the second element range 12. The ohmic metal layer 51 is
constituted of AlSi (alloy of aluminum and silicon). The ohmic
metal layer 51 extends along a surface of the interlayer insulating
film 62 and the upper surface 18a of the semiconductor substrate
18, and has a substantially constant thickness.
[0051] An upper surface of the ohmic metal layer 51 is recessed
following the contact holes 62a within the first element range 11
and the second element range 12. That is, recesses 51a are provided
on the surface of the ohmic metal layer 51 above the respective
contact holes 62a. The ohmic metal layer 51 is in contact with the
upper surface 18a of the semiconductor substrate 18 in each contact
hole 62a. The ohmic metal layer 51 is in ohmic contact with the
emitter regions 22 and the high density region 24a of the body
region 24 in each contact hole 62a.
[0052] The upper surface of the ohmic metal layer 51 is recessed
following the wide contact hole 62b within the surrounding range
13. That is, a recess 51b is provided on the surface of the ohmic
metal layer 51 above the wide contact hole 62b. As shown in FIG. 2,
a width of the recess 51b in the y direction is substantially equal
to the width W3 of the wide contact hole 62b in the y direction.
Further, as shown in FIG. 3, a width of the recess 51b in the x
direction is substantially equal to the width W4 of the wide
contact hole 62b in the x direction. A bottom surface of the recess
51b (i.e., surface of a portion constituting the bottom of the
recess 51b of the ohmic metal layer 51) is flat along the upper
surface 18a of the semiconductor substrate 18. As the recess 51b is
wide, a wide flat surface is formed within the recess 51b. The
ohmic metal layer 51 is in contact with the upper surface 18a of
the semiconductor substrate 18 within the wide contact hole 62b.
The ohmic metal layer 51 is in contact with the p-type peripheral
region 29 within the wide contact hole 62b.
[0053] A part of the ohmic metal layer 51 extends up to above the
terminal region 34. The ohmic metal layer 51 is in ohmic contact
with the terminal region 34 in the contact hole above the terminal
region 34.
[0054] The respective ring-electrodes 53 are disposed on the
respective guard rings 36. The ring-electrodes 53 extend in an
annular shape along the guard rings 36. Each ring-electrode 53 is
in ohmic contact with the corresponding guard ring 36 within the
contact hole above the guard ring 36.
[0055] The insulating protective film 60 is disposed on the ohmic
metal layer 51, the interlayer insulating film 62, and the
ring-electrodes 53 within the second element range 12 and within
the outer peripheral voltage resistant range 14. Entire surfaces of
the second element range 12 and the outer peripheral voltage
resistant range 14 are covered with the insulating protective film
60. A part of the insulating protective film 60 extends over into
the surrounding range 13, and covers an outer peripheral side
portion of the bottom surface of the recess 51b (i.e., the ohmic
metal layer 51 constituting the bottom surface of the recess 51b).
The insulating protective film 60 has an opening 80 at a center of
the upper surface 18a of the semiconductor substrate 18. As shown
in FIG. 1, the opening 80 is provided in a range broader than the
first element range 11 that includes the first element range 11.
That is, the entirety of the first element range 11 and an inner
peripheral portion of the surrounding range 13 are positioned
within the opening 80. As shown in FIGS. 1, 2, an inner peripheral
side end 60a of the insulating protective film 60 (i.e., a side
surface of the opening 80) is positioned within the recess 51b
(i.e., within the surrounding range 13). The insulating protective
film 60 is constituted of resin (e.g., polyimide). A linear
expansion coefficient of the insulating protective film 60 is
slightly greater than a linear expansion coefficient of the ohmic
metal layer 51 (i.e., AlSi).
[0056] The surface metal layer 52 covers the surface of the ohmic
metal layer 51 in a range not covered with the insulating
protective film 60 (i.e., an inner peripheral portion of the ohmic
metal layer 51 within the surrounding range 13, and the ohmic metal
layer 51 in the first element range 11). The surface metal layer 52
is filled in each recess 51a within the first element range 11.
Further the surface metal layer 52 is filled in the recess 51b in
the range not covered with the insulating protective film 60. The
surface metal layer 52 is in contact with the ohmic metal layer 51
in the bottom surface of the recess 51b (i.e., flat surface). As
shown in FIG. 2, a width W5 in the y direction of a range where the
surface metal layer 52 is in contact with the ohmic metal layer 51
at the bottom surface of the recess 51b is wider than the width of
the recess 51a in the y direction, and is wider than the
above-described pitch P1. Further, as shown in FIG. 3, a width W6
in the x direction of the range where the surface metal layer 52 is
in contact with the ohmic metal layer 51 at the bottom surface of
the recess 51b is wider than the width of the recess 51a in the y
direction, and is wider than the above-described pitch P1. A part
of the surface metal layer 52 on the outer peripheral side extends
to above the insulating protective film 60. Thus, the surface metal
layer 52 is in contact with the insulating protective film 60 at
the inner peripheral side end 60a of the insulating protective film
60 (i.e., side surface of the opening 80). The surface metal layer
52 is constituted of Nickel. The surface metal layer 52 (i.e.,
Nickel) has a high solder wettability. The linear expansion
coefficient of the surface metal layer 52 (i.e., Nickel) is smaller
than the linear expansion coefficient of the ohmic metal layer 51
(i.e., AlSi). A soldering layer 55 is bonded to the surface metal
layer 52. The surface metal layer 52 is connected by the soldering
layer 55 to a metal block not shown.
[0057] A lower electrode 54 is disposed on the lower surface 18b of
the semiconductor substrate 18. The lower electrode 54 is in ohmic
contact with the collector region 28.
[0058] Next, operation of the IGBT 10 will be described. The IGBT
10 is used in a state where a voltage that makes the lower
electrode 54 have a higher potential is applied between the ohmic
metal layer 51 and the lower electrode 54. When a potential higher
than a threshold voltage is applied to the gate electrodes 30,
channels are formed in the body regions 24 in ranges adjacent to
the gate insulating films 32. The channels connect the emitter
regions 22 and the drift region 26. Accordingly, electrons flow
from the ohmic metal layer 51 to the lower electrode 54 through the
emitter regions 22, the channels, the drift region 26, the buffer
region 27, and the collector region 28. Further, holes flow from
the lower electrode 54 to the ohmic metal layer 51 through the
collector region 28, the buffer region 27, the drift region 26, and
body regions 24. That is, the IGBT 10 turns on and current flows
from the lower electrode 54 to the ohmic metal layer 51.
[0059] When the potential of the gate electrodes 30 is decreased to
a lower potential than the threshold voltage, the channels
disappear. Then, a reverse voltage is applied to pn junctions 25a
at interfaces between the body regions 24 and the drift region 26
within the first element range 11 and the second element range 12.
Due to this, depletion layers extend from the pn junctions 25a to
the body regions 24 and the drift region 26. Since the n-type
impurity density of the drift region 26 is extremely low, the drift
region 26 is depleted in a wide range. Further, when the depletion
layers spread in the body regions 24, holes existing in the
depleted range are reunited with electrons in the drift region 26
to disappear. Thus, as the depletion layers spread, the holes
existing in the body regions 24 decrease.
[0060] Further, within the surrounding range 13, reverse voltage is
applied to a pn junction 25b of an interface between the p-type
peripheral region 29 and the drift region 26. Due to this,
depletion layer extends from the pn junction 25b to the p-type
peripheral region 29 and the drift region 26. The drift region 26
is depleted by the depletion layer extending from the pn junction
25b as well. Further, as the depletion layer extends to the p-type
peripheral region 29, holes that exist in the depleted region are
reunited with electrons in the drift region 26 to disappear. Thus,
as the depletion layer extends, the holes that exist in the p-type
peripheral region 29 decrease.
[0061] Further, within the outer peripheral voltage resistant range
14, reverse voltage is applied to a pn junction 25c at an interface
between the terminal region 34 and the drift region 26. Due to
this, a depletion layer extends from the pn junction 25c to the
terminal region 34 and the drift region 26. When the depletion
layer extending from the pn junction 25c to the drift region 26
reaches a first guard ring 36, which is positioned on the innermost
peripheral side, the depletion layer extends from the first guard
ring 36 to the drift region 26 around that first guard ring 36.
When the depletion layer extending film the first guard ring 36 to
the drift region 26 reaches a second guard ring 36, which is
positioned next to the first guard ring 36, then the depletion
layer extends from the second guard ring 36 to the drift region 26
around that second guard ring 36. As such, within the outer
peripheral voltage resistant range 14, the depletion layer extends
to the outer peripheral side via the plurality of guard rings 36.
Due to this, within the outer peripheral voltage resistant range
14, the drift region 26 is depleted over to a vicinity of the outer
peripheral end surface 18c of the semiconductor substrate 18.
[0062] As explained above, if the potential of the gate electrodes
30 is lowered to a potential lower than the threshold voltage, the
channels disappear, thereby depleting the drift region 26 in a wide
range. The body regions 24 are separated from the buffer region 27
by the depletion layers. Due to this, when the potential of the
gate electrodes 30 is lowered to a potential lower than the
threshold voltage, the current flowing in the IGBT 10 is stopped.
That is, the IGBT 10 is turned off.
[0063] Equipotential lines 92 in FIG. 4 show an electric potential
distribution within the drift region 26 in a state where the IGBT
10 is off. The drift region 26 is depleted in an entire range shown
in FIG. 4. Further, although the p-type peripheral region 29 and
the body regions 24 are partially depleted in vicinities of the
lower ends thereof most of the p-type peripheral region 29 and the
body regions 24 are not depleted.
[0064] As shown in FIG. 4, in the first element range 11 and the
second element range 12, the trenches 40 protrude to be lower than
the lower ends of the body regions 24, the equipotential lines 92
shift downward at portions below the trenches 40 compared to
portions below the body regions 24. It should be noted that since
the potential of the body regions 24 is substantially equal to the
potential of the gate electrodes 30 and a difference in depth
between the lower ends of the body regions 24 and the lower ends of
the gate electrodes 30 is small, a difference in depth of the
equipotential lines 92 between the portions below the body regions
24 and the portions below the gate electrodes 30 is not
significantly large.
[0065] Within the surrounding range 13, the p-type peripheral
region 29 extends to a depth lower than the lower ends of the
trenches 40. Due to this, the equipotential lines 92 shift downward
at a portion below the p-type peripheral region 29 (i.e., within
the surrounding region 13) compared to the equipotential lines 92
within the first element range 11 and the second element range 12.
When the equipotential lines 92 are distributed as such, the
electric field is alleviated at lower ends of the trenches 40
disposed in the vicinity of the surrounding range 13. In the IGBT
10, the electric field concentration is suppressed in the
surrounding range 13 and its peripheries. Thus, the IGBT 10 has a
high breakdown voltage.
[0066] Further in the cross section shown in FIG. 3, the ends of
the trenches 40 in the x direction are covered by p-type peripheral
region 29. The p-type impurity density of the p-type peripheral
region 29 is adjusted to a level by which a portion covering the
ends of the trenches 40 in the x direction is not completely
depleted (level at least higher than the p-type impurity density of
the lower density regions 24b of the body regions 24). Accordingly,
even when the IGBT 10 is off; the ends of the trenches 40 in the x
direction are covered by the p-type peripheral region 29 that is
not depleted. Due to this, the electric field is less likely to be
applied to the ends of the trenches 40 in the x direction.
[0067] Thus, electric field concentration is suppressed also in the
ends of the trenches 40 in the x direction. Thus, the IGBT 10 has a
high breakdown voltage.
[0068] When the IGBT 10 is again turned from the OFF state to a
state where the potential of the gate electrodes 30 is raised to a
potential higher than its threshold voltage, channels are formed in
the body regions 24 and the potential of the drift region 26
decreases. Then holes are supplied from the ohmic metal layer 51 to
the body regions 24 via the contact holes 62a. Due to this, the
depletion layers that had extended from the pn junctions 25a at the
interfaces between the body regions 24 and the drift region 26
shrink and disappear. Due to this, electrons and holes become able
to flow in the drift region 26, and thus the IGBT 10 is turned
on.
[0069] Further, when the potential of the drift region 26 is
decreased, holes are supplied from the ohmic metal layer 51 to the
p-type peripheral region 29 via the wide contact hole 62b. Due to
this, the depletion layer that had extended from the pn junction
25b at the interface between the p-type peripheral region 29 and
the drift region 26 shrinks and disappears. Accordingly, electrons
and holes become able to flow also in the drift region 26 below the
p-type peripheral region 29. Due to this, a width of a portion in
the drift region 26 where the electrons and the holes can flow
becomes larger, the resistance of the drift region 26 decreases.
Since the p-type peripheral region 29 is directly connected to the
ohmic metal layer 51 thereon, the holes are shortly supplied to the
p-type peripheral region 29 when the IGBT 10 is tuned on. Due to
this, the resistance of the drift region 26 decreases shortly after
the IGBT turns on. Accordingly, a loss is not likely to be
generated in this IGBT 10.
[0070] Further, by the IGBT 10 repeating to turn ON and OFF, the
temperature of the semiconductor substrate 18 repeatedly changes.
Due to this, the temperatures of the ohmic metal layer 51, the
surface metal layer 52, and the insulating protective film 60 above
the semiconductor substrate 18 repeatedly change as well.
[0071] The ohmic metal layer 51 thermally expands along with the
surface metal layer 52 in the range where the ohmic metal layer 51
is in contact with the surface metal layer 52 (i.e., the first
element range 11 and an inner peripheral portion of the surrounding
range 13). As described above, the linear expansion coefficient of
the surface metal layer 52 (i.e., Nickel) is smaller than the
linear expansion coefficient of the ohmic metal layer 51 (i.e.,
AlSi). Due to this, the thermal expansion of the ohmic metal layer
51 is suppressed in this range. Since the surface metal layer 52 is
filled in each recess 51a in the upper surface of the ohmic metal
layer 51 in the first element range 11, the ohmic metal layer 51 is
firmly restrained by the surface metal layer 52. Due to this,
thermal expansion amount of the ohmic metal layer 51 in the first
element range 11 is small. On the other band, within the
surrounding range 13 (i.e., within the wide recess 51b) the upper
surface of the ohmic metal layer 51 (i.e., bottom surface of the
recess 51b) is flat. As such, since the upper surface of the ohmic
metal layer 51 is flat in such a wide range, and the surface metal
layer 52 is in contact with such a flat upper surface, restraint
force of the surface metal layer 52 on the ohmic metal layer 51 is
small in the recess 51b. Accordingly, thermal expansion amount of
the ohmic metal layer 51 is larger in this range than the thermal
expansion amount of the ohmic metal layer 51 in the first element
range 11.
[0072] The ohmic metal layer 51 thermally expands along with the
insulating protective film 60 in the range where the ohmic metal
layer 51 is in contact with the insulating protective film 60
(i.e., on an outer peripheral side of the surrounding range 13, the
second element range 12, and the outer peripheral voltage resistant
range 14). As described above, the linear expansion coefficient of
the insulating protective film 60 (i.e., polyimide) is slightly
larger than the linear expansion coefficient of the ohmic metal
layer 51 (i.e., AlSi). Due to this, in this range the ohmic metal
layer 51 has the largest thermal expansion amount within a range
shown in FIG. 2.
[0073] As described above, in the IGBT 10 of embodiment 1, the
inner peripheral side end 60a of the insulating protective film 60
(i.e., the side surface of the opening 80) is positioned in the
surrounding range 13 (i.e., on the flat ohmic metal layer 51). Due
to this, a portion of the ohmic metal layer 51 having a relatively
large thermal expansion amount (i.e., the inner peripheral side of
the surrounding range 13) is adjacent to a portion of the ohmic
metal layer 51 having the largest thermal expansion amount (i.e.,
the outer peripheral side of the surrounding range 13). Due to
this, a difference in the thermal expansion amount of the ohmic
metal layer 51 is not significantly large around the inner
peripheral side end 60a of the insulating protective film 60. Due
to this, an extremely large stress is not likely to be generated in
the ohmic metal layer 51 below the end 60a. Accordingly, occurrence
of cracks in the ohmic metal layer 51 below the end 60a is
suppressed. The IGBT 10 of embodiment 1 has a high reliability.
[0074] Notably, in the IGBT 10 of embodiment 1, the surface metal
layer 52 is formed by sputtering (hereinbelow referred to as a mask
sputtering) through a stencil mask (mask plate prepared separately
from the semiconductor substrate 18). Since high precision cannot
be achieved by the mask sputtering, fluctuation in positions of an
outer peripheral side end 52b of the surface metal layer 52 in FIG.
2 is large. If the outer peripheral side end 52b of the surface
metal layer 52 extends toward the outer peripheral side than an
outer peripheral side end 52c of the ohmic metal layer 51, a
potential distribution in the drift region 26 in the outer
peripheral voltage resistant range 14 is disturbed, and breakdown
voltage of the IGBT 10 decreases. Further, if the outer peripheral
side end 52b of the surface metal layer 52 is positioned on an
inner peripheral side than the inner peripheral side end 60a of the
insulating protective film 60, the ohmic metal layer 51 is exposed,
leading to a lower reliability of the IGBT 10. Accordingly, a wide
interval may preferably be provided between the outer peripheral
side end 52c of the ohmic metal layer 51 and the inner peripheral
side end 60a of the insulating protective film 60, and the outer
peripheral side end 52b of the surface metal layer 52 may
preferably be arranged in the wide interval. In this design, by
providing the second element range 12 (i.e., range operating as a
switching device) between the outer peripheral side end 52c of the
ohmic metal layer 51 and the surrounding range 13, the
semiconductor substrate 18 can be effectively utilized, and current
capacity of the IGBT 10 can be increased.
[0075] Further as in the IGBT 10 of the embodiment 1, a gate
capacity (capacity between the gate and the emitter and capacity
between the gate and the collector) becomes small by removing the
trenches within the surrounding rage 13. Due to this, a switching
speed of the IGBT 10 can be improved.
[0076] Further; in the configuration as in the IGBT 10 of the
embodiment 1, in which the ohmic metal layer 51 is in contact with
the semiconductor substrate 18 at below the inner peripheral side
end 60a of the insulating protective film 60, the stress generated
in the ohmic metal layer 51 can be decreased compared to the
configuration in which the metal layer 151 is in contact with the
interlayer insulating film 162 at below the inner peripheral side
end 160a of the insulating protective film 160 as in FIG. 10.
Embodiment 2
[0077] In an IGBT 10 of embodiment 2, as shown in FIG. 5, a
plurality of trenches 41 extending in the y direction is provided
in the upper surface 18a of the semiconductor substrate 18. The
trenches 41 are arranged in the first element range 11 and the
second element range 12, and are not arranged in the surrounding
range 13.
[0078] The plurality of trenches 41 extending parallel to each
other along the y direction are formed in the first element range
11. The trenches 40 and the trenches 41 are connected to each
other. That is, a trench extending in a grid-shape (hereinafter
referred to as a grid-shape trench) is formed by the trenches 40
and the trenches 41. The semiconductor region in the first element
range is partitioned into rectangular regions by the grid-shape
trench. Each of the rectangular semiconductor regions partitioned
by the grid-shape trench will be hereinafter referred to as a cell
region 43. A plurality of the trenches 41 extending parallel to
each other along the y direction is provided also in the second
element range 12. A grid-shaped trench is formed by having trenches
40 and the trenches 41 connected to each other also in the second
element range 12. Cell regions 43 partitioned by the grid-shaped
trench are provided also in the second element range 12. The IGBT
10 of the embodiment 2 has the same configurations as those in the
IGBT 10 of the embodiment 1 except for having the trenches 41.
[0079] A cross section taken along line A-A in FIG. 5 (position
traversing the trenches 40 in the y direction) is similar to the
cross section shown in FIG. 2 (embodiment 1). A cross section taken
along line C-C in FIG. 5 (position traversing the trenches 41 in
the y direction) is similar to the cross section shown in FIG. 3.
That is, an end of each trench 41 in the y direction is covered by
the p-type peripheral region 29. Accordingly, the electric field
concentration is suppressed also in the positions of the line A-A
and the line C-C as in embodiment 1. Further, a cross section taken
along line B-B in FIG. 5 (position traversing the trenches 41 in
the x direction) is approximately similar to the cross section
shown in FIG. 2. In addition, a cross section taken along line D-D
in FIG. 5 (position traversing the trenches 40 in the x direction)
is similar to the cross section shown in FIG. 3. Accordingly, the
electric field concentration is suppressed also in the position of
line B-B and the position of line D-D similarly to embodiment 1.
Further, also in embodiment 2, since the inner peripheral side end
60a of the insulating protective film 60 is positioned in the wide
recess 51b, cracks in the first metal layer 51 is suppressed
similarly to embodiment 1. Further, also in embodiment 2, since the
p-type peripheral region 29 is connected to the first metal layer
51 via the wide contact hole 62b, resistance of the drift region 26
is shortly decreased when the IGBT turns on.
[0080] It should be noted that in the above-described embodiment 2,
the trenches 41 extend linearly in the y direction. However, the
trenches 41 may extend offset to each other as shown in FIG. 6.
[0081] Further, in the above-described embodiments land 2, the
trenches 40a and 40b, which are closest to the surrounding range
13, are covered by the p-type peripheral region 29. However the
trenches 40a and 40b closest to the surrounding range 13 may not be
covered by the p-type peripheral region 29, as shown in FIG. 7. It
should be noted that, in FIG. 7, the p-type peripheral region 29
(i.e., p-type region extending deeper than the lower ends of the
body regions 24) may preferably be positioned as close as possible
to the trenches 40a and 40b closest to the surrounding range 13 in
order to ensure high breakdown voltage. For example, an interval
between the p-type peripheral region 29 and the trench 40a (or the
trench 40b) may preferably be smaller than the above-described
pitch P1.
[0082] It should be noted that in the above-described embodiments 1
and 2, the surface metal layer 52 is formed by mask sputtering.
However, the surface metal layer 52 may be formed by plating. In
this case, as shown in FIG. 8, the outer side end 52b of the
surface metal layer 52 makes contact with the inner side end 60a of
the insulating protective film 60 (i.e., side surface of the
opening 80) without extending to above the insulating protective
film 60. This configuration as well may bring the same advantageous
effect as that in the above-described embodiments.
[0083] Further, in the above-described embodiments 1 and 2, the
IGBT is explained. Alternatively, the technique disclosed herein
may be applied to other switching devices including MOSFET. By
providing an n-type region (drain region) which is in ohmic contact
with the lower electrode 54, instead of the collector region 28 of
the embodiments, an n-channel type MOSFET can be obtained. Further,
a p-channel type MOSFET can be obtained by reversing the n-type
regions and the p-type regions in the n-channel type MOSFET.
[0084] Corresponding relationships of the constituent features of
the semiconductor devices of the above-described embodiments and
the constituent features of the claims will be described. The ohmic
metal layer 51 in the embodiments is one example of a first metal
layer in the claims. The surface metal layer 52 of the embodiments
is one example of a second metal layer in the claims. The emitter
region 22 of the embodiments is one example of a first region in
the claims. The drift region 26 of the embodiments is one example
of a second region in the claims. The p-type peripheral region 29
of the embodiments is one example of a second conductivity-type
peripheral region in the claims. The portion of the surrounding
range 13 that is adjacent to the first element range 11 in the y
direction in the embodiments is one example of an inactive region
in the claims. The trenches 40 of the embodiments are one example
of first trenches in the claims. The trenches 41 of the embodiments
(more specifically, a portion of the trenches 41 extending from the
trenches 40 toward the surrounding range 13) is one example of
second trenches in the claims.
[0085] Some technical elements disclosed herein will be listed.
Notably, each of the following technical elements is useful
independently.
[0086] In a configuration example of the present disclosure, a
plurality of second trenches may be provided in the upper surface,
and each of the second trenches may extend toward the ineffective
range from the first trench positioned closest to the ineffective
range. An end surface of each second trench on the ineffective
range side may be covered by the second conductivity-type
peripheral region.
[0087] According to this configuration, a trench having a
complicated shape can be constituted by the second trenches and the
first trenches. Further, in this configuration, since the end
surfaces of the second trenches on an ineffective range side are
covered with the second conductivity-type peripheral region,
electric field concentration around these end surfaces can be
suppressed.
[0088] In a configuration example of the present disclosure, a
second-conductivity type impurity density of the second
conductivity type peripheral region may be higher than a
second-conductivity type impurity density of a portion of the body
region that is positioned below the first regions.
[0089] According to this configuration, since the second
conductivity type peripheral region is less likely to be depleted,
the electric field concentration can be more efficiently suppressed
around the trenches in the vicinities of the ineffective range.
[0090] In a configuration example of the present disclosure, the
semiconductor substrate may include an outer peripheral voltage
resistant range that surrounds a periphery of a range including the
first element range and the ineffective range. A guard ring of the
second conductivity type may be provided in the outer peripheral
voltage resistant range. The guard ring may be exposed in the upper
surface, may surround the range including the first element range
and the ineffective range, and may be electrically separated from
the first metal layer.
[0091] According to this configuration, the breakdown voltage of
the switching device can be further improved.
[0092] In a configuration example of the present disclosure, the
semiconductor substrate may further include a second element range
arranged between the ineffective range and the outer peripheral
voltage resistant range. A plurality of the first trenches may be
provided at intervals along the second direction in the upper
surface within the second element range. Within the second element
range, a contact hole may be provided in a portion of the
interlayer insulation film that covers the upper surface. The first
metal layer may be in contact with the upper surface in the contact
hole in the second element range. The insulating protective film
may cover the first metal layer in the second element range. The
second metal layer may be disposed and extend across on the first
metal layer in the opening and on the insulating protective film.
An outer peripheral side end portion of the second metal layer may
be positioned on an inner peripheral side relative to an outer
peripheral side end portion of the first metal layer. Each of the
semiconductor regions interposed between each pair of the adjacent
first trenches within the second element range may include the
first region and the body region.
[0093] For ensuring reliability of the switching device, an
interval may be provided between the inner side end portion of the
insulating protective film and the outer side end portion of the
first metal layer, and an outer side end portion of the second
metal layer may be disposed in the interval. By providing the
second element range (range functioning as the switching device) in
this interval portion, current capacity of the switching device can
be increased.
[0094] While specific examples of the present invention have been
described above in detail, these examples are merely illustrative
and place no limitation on the scope of the patent claims. The
technology described in the patent claims also encompasses various
changes and modifications to the specific examples described above.
The technical elements explained in the present description or
drawings provide technical utility either independently or through
various combinations. The present invention is not limited to the
combinations described at the time the claims are filed. Further,
the purpose of the examples illustrated by the present description
or drawings is to satisfy multiple objectives simultaneously, and
satisfying any one of those objectives gives technical utility to
the present invention.
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