U.S. patent application number 09/985977 was filed with the patent office on 2002-03-07 for circuit incorporated igbt and power conversion device using the same.
Invention is credited to Kohno, Yasuhiko, Mori, Mutsuhiro, Uruno, Junpei.
Application Number | 20020027253 09/985977 |
Document ID | / |
Family ID | 26572553 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020027253 |
Kind Code |
A1 |
Kohno, Yasuhiko ; et
al. |
March 7, 2002 |
Circuit incorporated IGBT and power conversion device using the
same
Abstract
A circuit incorporated IGBT is provided with a semiconductor
substrate having an IGBT area and a circuit area which are adjacent
to each other. In a semiconductor layer of one conductivity type in
which a circuit element is formed in the circuit area, there is
provided another semiconductor layer of another conductivity type
which adjoins the circuit element and has an impurity concentration
higher than that of the semiconductor layer of the one conductivity
type. An electrode contacts the other semiconductor layer and is
connected to an electrode of the IGBT. Carriers are ejected from
the other semiconductor layer to the electrode of the IGBT, thereby
making it possible to prevent an erroneous operation of the
circuit.
Inventors: |
Kohno, Yasuhiko;
(Hitachi-shi, JP) ; Mori, Mutsuhiro; (Mito-shi,
JP) ; Uruno, Junpei; (Hitachi-shi, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
26572553 |
Appl. No.: |
09/985977 |
Filed: |
November 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09985977 |
Nov 7, 2001 |
|
|
|
09199276 |
Nov 25, 1998 |
|
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Current U.S.
Class: |
257/370 ;
257/E27.015; 257/E29.198 |
Current CPC
Class: |
H01L 29/7395 20130101;
H01L 27/0623 20130101 |
Class at
Publication: |
257/370 |
International
Class: |
H01L 029/76; H01L
029/94 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 1997 |
JP |
09-327572 |
Claims
What is claimed is:
1. A circuit incorporated IGBT comprising a semiconductor substrate
having an IGBT area and a circuit area which are adjacent to each
other, wherein said IGBT area includes a first layer of one
conductivity type extending to said circuit area, a second layer of
another conductivity type adjoining the said first layer and
extending to said circuit area, a third layer of the one
conductivity type formed in said second layer, a fourth layer of
the other conductivity type formed in said third layer, a first
electrode formed through an insulating film on a surface of said
third layer between said second layer and said fourth layer, a
second electrode contacting said third layer and said fourth layer,
and a third electrode contacting said first layer, said circuit
area includes a fifth layer of the one conductivity type formed in
a portion of said second layer extending from said IGBT area, a
circuit element formed in said fifth layer, a sixth layer of the
other conductivity type provided adjacent to said circuit element
and having an impurity concentration higher than that of said fifth
layer, and a fourth electrode contacting said sixth layer, and said
circuit element and said second electrode are electrically
connected through another circuit element, and said second
electrode and said fourth electrode are electrically connected.
2. A circuit incorporated IGBT according to claim 1, wherein said
circuit element formed in said fifth layer includes an MOSFET, said
other circuit element includes a resistor, and said MOSFET and said
resistor form a source follower circuit.
3. A circuit incorporated IGBT according to claim 1, wherein said
circuit element formed in said fifth layer includes a seventh layer
and an eighth layer of the other conductivity type formed in said
fifth layer, a fifth electrode formed through an insulating film on
a surface of said fifth layer between said seventh layer and said
eighth layer, and a sixth electrode contacting said seventh layer,
said other circuit element includes a resistor, and said second
electrode and said sixth electrode are electrically connected
through said resistor, and said sixth layer is adjacent to said
seventh layer.
4. A circuit incorporated IGBT according to claim 3, wherein a
plane pattern of said sixth layer is adjacent to a plane pattern of
said seventh layer and extends along the plane pattern of said
seventh layer.
5. A circuit incorporated IGBT according to claim 4, wherein said
fourth electrode contacts said sixth layer along the plane pattern
of said sixth layer.
6. A circuit incorporated IGBT according to claim 3, wherein said
second layer has a first portion which adjoins said first layer and
a second portion which adjoins said first portion and has an
impurity concentration lower than that of said first portion, and a
distance between an end portion of said first electrode nearest to
said circuit area and an end portion of said seventh layer nearest
to said IGBT area and on the IGBT area side is equal to or larger
than the thickness of said second portion of said second layer.
7. A circuit incorporated IGBT according to claim 1, wherein a
further circuit element is formed through an insulating film on a
surface of said semiconductor substrate between said IGBT area and
said circuit area.
8. A circuit incorporated IGBT according to claim 1, wherein said
fourth electrode and a connection location for connecting said
second electrode to an external circuit are connected on the
surface of said semiconductor substrate by a wiring electrode.
9. A power conversion device comprising an input terminal, an IGBT
driven in a turn-on/off switching manner so that a power inputted
to said input terminal is subjected to power conversion by the
turn-on/off switching, and an output terminal for outputting the
power subjected to power conversion, said IGBT including the
circuit incorporated IGBT according to claim 1.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a circuit incorporated IGBT
in which an IGBT and a circuit are formed in a semiconductor
substrate.
[0002] An insulated gate bipolar transistor (hereinafter
abbreviated to IGBT) is a voltage controlled switching element
which can control a current of a main terminal by a voltage of a
control terminal. Since a large current and a switching at a high
frequency are possible, the IGBT's are being used at the present
time in a wide field of applications from household air
conditioners to inverters of electric cars and so forth.
[0003] Hitherto, the contemplation of a low loss and a high speed
was made for IGBT's. In recent years, not only the low loss and the
high speed but also a high functionality have been promoted. A
high-function IGBT includes, for example, an IGBT in which the IGBT
is integrated with a protection circuit so that a protecting
function is possessed by one chip. A problem encountered in
integrating an IBGT with a circuit is an erroneous operation of the
circuit caused by a carrier current or hole current peculiar to the
IGBT. When a hole current injected from a collector layer of the
IGBT flows into a circuit area, an erroneous operation of the
circuit occurs. There has been disclosed a structure in which a
layer for ejecting holes is provided in order to prevent the hole
current from flowing into the circuit area.
[0004] FIG. 11 shows the cross-sectional structure of a circuit
integrated IGBT having a hole ejecting layer. In FIG. 11, reference
numeral 101 denotes a collector layer, numeral 102 a buffer layer,
numeral 103 a drift layer, numeral 104 a channel layer, numeral 105
an emitter layer, numeral 106 a hole ejecting layer, numeral 110 an
emitter electrode, numeral 111 a gate electrode, numeral 112 a gate
oxide film, numeral 114 a source electrode, numeral 115 a MOSFET
gate electrode, numeral 116 a drain electrode, numeral 117 a
collector electrode, numeral 131 a source layer, numeral 132 a base
layer, numeral 133 a drain layer, numeral 150 an IGBT area, numeral
151 a circuit area, and numeral 152 a lateral MOSFET. Though not
shown in FIG. 11, resistors, diodes and so forth are formed as
circuit forming elements other than the MOSFET in the circuit area
151. Similarly, though not shown, the source electrode 114, gate
electrode 115 and drain electrode 116 of the MOSFET are connected
to the other elements formed in the circuit area and the emitter
electrode 110 and gate electrode 111 of the IGBT. In a turned-on
condition of the IGBT, a hole current flows from the collector
layer to the emitter layer, as shown by arrow in FIG. 11. In order
to suppress the flow of this hole current into the circuit area,
the hole ejecting layer 106 is provided to prevent the hole current
from flowing from the IGBT area into the circuit area.
[0005] In recent years, however, the high functionality and high
preciseness of a circuit integrated in an IGBT have been advanced
and there has been generated a problem that an erroneous operation
of the circuit occurs even with a very small leakage current of
holes. This is because even if the hole ejecting layer 106 is
provided, a very small amount of holes may leak into the circuit
area. Such an erroneous operation is remarkable in the case where
an IGBT is integrated with a source follower circuit using a
MOSFET.
[0006] FIGS. 12 and 13 show the cross section and the equivalent
circuit of an IGBT integrated with a source follower circuit. In
FIGS. 12 and 13, the same constituent elements as those in FIG. 11
are denoted by the same reference numerals as those used in FIG.
11. In FIGS. 12 and 13, reference numeral 140 denotes a source
follower resistor, numeral 201 an n-channel MOSFET corresponding to
a channel portion of the IGBT, numeral 202 an npn transistor
composed of the drift layer, the channel layer and the emitter
layer, numeral 203 a pnp transistor of an MOSFET composed of the
collector layer, the buffer layer, the drift layer and the channel
layer, numeral 204 an npn transistor of a MOSFET composed of the
drift layer, the base layer and the emitter layer, and numeral 205
the lateral MOSFET.
[0007] In the conventional structure, a leakage hole current flows
into the source electrode 114 of the MOSFET through the base layer
132. When the hole current flows into the source electrode, a
voltage generated across the source follower resistor 140 becomes
higher than a desired voltage, thereby causing an erroneous
operation of the circuit.
[0008] The present invention is made taking the above problem into
consideration and provides a circuit incorporated IGBT which can
prevent an erroneous operation of a circuit.
SUMMARY OF THE INVENTION
[0009] A circuit incorporated IGBT according to the present
invention is provided with a semiconductor substrate having an IGBT
area and a circuit area which are adjacent to each other. In a
semiconductor layer of one conductivity type in which a circuit
element is formed in the circuit area, there is provided another
semiconductor layer of another conductivity type which adjoins the
circuit element and has an impurity concentration higher than that
of the semiconductor layer of the one conductivity type. An
electrode contacts such other semiconductor layer and this
electrode is connected to an electrode of an IGBT in the IGBT
area.
[0010] According to the present invention, carriers are ejected
from the second semiconductor layer to the electrode of the IGBT,
thereby making it possible to prevent an erroneous operation of a
circuit.
[0011] The one conductivity type may be p type or n type. The
electrode of the IGBT is, for example, an emitter electrode.
Carriers are holes or electrons.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is the cross section of a first embodiment according
to the present invention;
[0013] FIG. 2 is an equivalent circuit diagram of the first
embodiment according to the present invention;
[0014] FIG. 3 is a plan view of a second embodiment according to
the present invention;
[0015] FIG. 4 is a plan view of the conventional MOSFET;
[0016] FIG. 5 is the cross section of a third embodiment according
to the present invention;
[0017] FIG. 6 is the cross section of the modification of the third
embodiment according to the present invention;
[0018] FIG. 7 is a plan view of the modification of the third
embodiment according to the present invention;
[0019] FIG. 8 is a plan view of a fourth embodiment according to
the present invention;
[0020] FIG. 9 is an equivalent circuit diagram of the fourth
embodiment according to the present invention;
[0021] FIG. 10 is a plan view of the modification of the fourth
embodiment according to the present invention;
[0022] FIG. 11 is the cross section of the conventional circuit
incorporated IGBT having a hole ejecting layer;
[0023] FIG. 12 is the cross section of the conventional IGBT
integrated with a source follower circuit;
[0024] FIG. 13 is an equivalent circuit diagram of the conventional
IGBT integrated with the source follower circuit;
[0025] FIG. 14 is the cross section of a fifth embodiment according
to the present invention;
[0026] FIG. 15 is a plan view of a sixth embodiment according to
the present invention; and
[0027] FIG. 16 is an equivalent circuit diagram of a power
conversion device as a seventh embodiment according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIENTS
[0028] (Embodiment 1)
[0029] FIG. 1 shows the cross-sectional structure of a first
embodiment according to the present invention and FIG. 2 shows an
equivalent circuit thereof. The present embodiment is an example of
a circuit incorporated IGBT in which a source follower circuit is
incorporated.
[0030] In FIGS. 1 and 2, the same constituent elements as those in
FIGS. 11 to 13 are denoted by the same reference numerals as those
in FIGS. 11 to 13. In FIGS. 1 and 2, reference numeral 113 denotes
an earth electrode and numeral 130 denotes an earth layer. In the
following description, symbols p.sup.-, p and p.sup.+ show that the
conductivity type of a semiconductor layer is p type (or one
conductivity type) and the impurity concentration thereof is
relatively high in the mentioned order. Similarly, symbols n.sup.-,
n and n.sup.+ show that the conductivity type of a semiconductor
layer is n type (or another conductivity type) and the impurity
concentration thereof is relatively high in the mentioned
order.
[0031] As shown in FIG. 1, an IGBT area 150 and a circuit area 151
are provided adjacent to each other in one semiconductor substrate.
The IGBT area 150 includes a collector layer 101 (or a first layer)
of p.sup.+ type adjoining one principal surface of the
semiconductor substrate, a buffer layer 102 (or a first portion of
a second layer) of n.sup.+ type adjoining the collector layer 101,
a drift layer 103 (or a second portion of the second layer) of
n.sup.- type adjoining the buffer layer 102 and the other principal
surface of the semiconductor substrate, a plurality of channel
layers 104 (or third layers) of p type adjoining the other
principal surface of the semiconductor substrate and selectively
formed in the drift layer 103, an emitter layer 105 (or a fourth
layer) of n.sup.+ type adjoining the other principal surface of the
semiconductor substrate and selectively formed in the channel layer
104, and a hole ejecting layer 106 of p type adjoining the other
principal surface of the semiconductor substrate, contacting the
channel layer 104 adjacent to the circuit area 151 and having a
junction depth deeper than that of the channel layer 104. Further,
the IGBT area 150 is provided with a gate electrode 111 (or a first
electrode) formed through a gate oxide film 112 as an insulating
film on an exposed portion of the surface of the channel layer 104
between the drift layer 103 and the emitter layer 105 on the other
principal surface side of the semiconductor substrate, an emitter
electrode 110 (or a second electrode) formed in contact with the
channel layer 104 and the emitter layer 105, and a collector
electrode 117 (or a third electrode) formed on the one principal
surface of the semiconductor substrate in contact with the
collector layer 101. The circuit area 151 is provided with the
collector layer 101, the buffer layer 102, the drift layer 103 and
the collector electrode 117 which extend from the IGBT area. Also,
the circuit area 151 includes a base layer 132 (or a fifth layer)
of p type adjoining the other principal surface of the
semiconductor substrate and selectively formed in the drift layer
103, a source layer 131 (or a seventh layer) and a drain layer 133
(or an eighth layer) of n.sup.+ adjoining the other principal
surface of the semiconductor substrate and selectively formed in
the base layer 132, another gate electrode 115 (or a fifth
electrode) formed through a gate oxide film on an exposed portion
of the surface of the base layer 132 between the source layer 131
and the drain layer 133 on the other principal surface side of the
semiconductor substrate, a source electrode 114 (or a sixth
electrode) formed in contact with the source layer 131, and a drain
electrode 116 (or a seventh electrode) formed in contact with the
drain layer 133. The base layer 132, the source layer 131, the
drain layer 133, the gate electrode 115, the source electrode 114
and the drain electrode 116 forms a lateral MOSFET. The lateral
MOSFET is one circuit element in a circuit such as a protection
circuit of the IGBT formed in the circuit area 151. A resistor 140
as another circuit element or a source follower resistor is
connected between the source electrode 114 of the lateral MOSFET
and the emitter electrode 110 of the IGBT. Namely, a source
follower circuit is formed. The circuit area 151 further includes
an earth layer 130 (or a sixth layer) of p.sup.+ type adjoining the
other principal surface of the semiconductor layer and selectively
formed in the base layer 132, the earth layer 130 being disposed
adjacent to the source layer 131 and having an impurity
concentration higher than that of the base layer 132, and an earth
electrode 113 (or a fourth electrode) formed in ohmic contact with
the earth layer 130. The earth layer 113 is electrically connected
to the emitter electrode 110 by virtue of electrode wiring. A
circuit element other than the lateral MOSFET may be formed in the
base layer 132.
[0032] A feature of the present embodiment lies in that the earth
layer 130 is provided for the lateral MOSFET and this earth layer
130 is connected to the emitter electrode 110 of the IGBT through
the earth electrode 113. With the provision of the earth layer 130,
a hole current flowing from the collector layer 117 into the base
layer 132 can be ejected from the earth layer 130 to the emitter
electrode 110 without passing through the source follower circuit
or the source electrode 114. Accordingly, it is possible to
separate a current flowing through the source follower circuit and
the hole current. Thereby, variations of a voltage generated across
the source follower resistor 140 are suppressed so that an
erroneous operation can be prevented.
[0033] Another feature of the present invention lies in that unit
cell structures of the lateral MOSFET are symmetrically arranged so
that the earth layers 130 are periodically arranged. With the
construction in which the earth layers 130 are periodically
arranged, as shown in FIG. 1, a hole current leaking into the
circuit area is ejected to the earth layers 130, thereby making it
possible to prevent the hole current from flowing into the source
layers 131. Also, since the earth layers 130 are periodically
arranged, it is possible to fix the potential of the base layer to
an earth potential, thereby preventing a substrate bias effect due
to variations in potential of the base layer and so forth to
improve the precision of the circuit.
[0034] The construction of the present embodiment can also be
applied to a circuit other than the above-mentioned source follower
circuit composed of the lateral MOSFET and the resistor. Namely,
the construction of the present embodiment is effective in the case
where a circuit element is formed in the base layer 132, and the
circuit element and the emitter electrode 110 are connected through
another circuit element such as a resistor. In this case, the earth
layer is provided adjacent to the circuit element formed in the
base layer 132, and the earth layer 130 and the emitter layer 110
are electrically connected. Thereby, an erroneous operation caused
by a hole current flowing into the circuit area can be prevented in
a manner similar to that in the embodiment shown in FIG. 1.
[0035] FIG. 3 shows a plane layout of the first embodiment. A-B in
FIG. 3 corresponds to the A-B cross section in FIG. 1. In order to
realize a structure having the earth electrode, the electrode
arrangement of the lateral MOSFET in the present embodiment is
implemented with a structure in which an electrode is folded back
at a terminating portion thereof, as shown in FIG. 3. The drain
electrode 116 and the earth electrode 113 are substantially
comb-like similarly to the conventional MOSFET. The gate electrode
115 and the source electrode 114 are formed between the comb-like
patterns of interdigitally formed drain and earth electrodes 116
and 113 and along the comb-like patterns. The gate electrode 115
and the source electrode 114 lie in zigzag lines on the
semiconductor substrate surface since they are folded back at the
terminating portions of the teeth of the comb-like patterns of the
drain electrode 116 and the earth electrode 113. For comparison, a
plane layout of the conventional MOSFET is shown in FIG. 4. In FIG.
4, a gate electrode 115 is shown by dotted line since the gate
electrode 115 is arranged through an insulating film below the
drain electrode 116 and the source electrode 114. In the
conventional MOSFET, the electrode is a comb-like form shown in
FIG. 4. Therefore, the realization of a construction the periodical
arrangement of earth electrodes cannot avoid the crossing of
wiring. Since the wiring is made of a metal film, the crossing of
wiring requires a multi-layer structure. In the conventional
MOSFET, the gate electrode is actually formed by multi-layer
wiring. The multi-layer structure causes problems including an
increase in cost due to an increase in number of fabrication steps,
the enlargement of unevenness of the surface of a circuit element,
and so forth.
[0036] In the present embodiment, a plane pattern of the earth
layer 130 extends adjacent to a plane pattern of the source layer
131 and along the plane pattern of the source layer 131, as is
apparent from the electrode pattern shown in FIG. 3. Accordingly, a
hole current is difficult to flow into the source layer. In
addition, since the plane pattern of the earth layer 130 extends
along the whole of the plane pattern of the source layer 131, an
effect of preventing the hole current from flowing into the source
layer 131 is large. Further, since the earth electrode 113 contacts
the earth layer 130 along the plane pattern of the earth layer 130,
it is enough to eject the hole current to the emitter
electrode.
[0037] According to the present embodiment, with the structure in
which the electrode of the MOSFET is folded back at its terminating
portion, the four electrodes including the earth electrode, the
gate electrode, the source electrode and the drain electrode can be
laid out without using the multi-layer wiring or the crossing of
wiring. Also, since the folding portion of the electrode is
rounded, as shown in FIG. 3, there is a feature that the
deterioration of the breakdown voltage of a junction between the
base layer and the drift layer can be prevented.
[0038] (Embodiment 2)
[0039] FIG. 5 shows a second embodiment according to the present
invention. In FIG. 5, the same constituent elements as those in
FIGS. 1 to 4 are denoted by the same reference numerals as those in
FIGS. 1 to 4. In FIG. 5, reference numeral 500 denotes a cut-off
layer.
[0040] A feature of the present embodiment lies in that a cut-off
area is provided between the IGBT and the MOSFET and the width or
distance L of the cut-off area is made equal to or larger than the
thickness d of the drift layer 103. The distance L is a distance
between the termination of the channel of the IGBT nearest to the
circuit area or the terminating portion of the gate electrode 111
and the IGBT area side terminating portion of the source layer 131
of the lateral MOSFET nearest to the IGBT area.
[0041] A hole current injected from the collector layer 101
progresses in the drift layer 103 by virtue of a drift
electric-field. At this time, the progressing direction of the hole
current is scattered at 45 degrees at the greatest due to the
scattering by crystals of the drift layer 103, a lateral
electric-field in the drift layer 103, and so forth. Thus, in the
present embodiment, this scattering is taken into consideration so
that the distance L between the IGBT and the MOSFET is set to be at
least equal to or larger than the thickness d of the drift layer.
Thereby, the cut-off area is wider than the scattering distance of
the hole current in a lateral direction. Therefore, it is possible
to suppress the arrival of the hole current at the MOSFET. At this
time, holes injected from the collector layer 101 are ejected from
the earth layer 130 to the emitter electrode 110 in a manner
similar to that in the first embodiment.
[0042] Though the effect of prevention of a hole current from
flowing into the MOSFET becomes larger as the distance L of the
cut-off area is made wider, there is a problem that the breakdown
voltage is deteriorated. Therefore, L must be set within a range in
which the breakdown voltage is not deteriorated. Alternatively,
there is preferable a structure in which the cut-off layer 500 is
formed as shown in FIG. 5, thereby preventing the deterioration of
the breakdown voltage.
[0043] (Embodiment 3)
[0044] FIG. 6 shows a third embodiment according to the present
invention.
[0045] The structure of FIG. 5, in which the width of the cut-off
area is made equal to or larger than the thickness of the drift
layer, has a problem that the circuit area is correspondingly
increased, thereby making the chip size large. In the present
embodiment shown in FIG. 6, a circuit element such as a resistor or
diode is disposed in the cut-off area, thereby making the effective
use of the space of the circuit area to suppress an increase in
chip area. The circuit element disposed in the cut-off area must be
a circuit element free from the influence of a hole current. For
example, a resistor, diode or the like formed on an oxide film is
preferable. In the present embodiment, there is provided a resistor
element including a resistor 120 of a polycrystalline semiconductor
which is formed on an oxide film 801 and electrode terminals 121
which contact opposite ends of the resistor 120. Also, a hole
ejecting layer 106 of the same conductivity type as that of the
earth layer and a cut-off layer 600 are provided in a drift layer
of the cut-off area under the oxide film 801. With the provision of
the cutoff layer 600, it is possible to further suppress the flowin
of a hole current from the IGBT and to prevent the deterioration of
the breakdown voltage. Further, it is preferable that the cut-off
layer 600 is formed in not only the cut-off area but also a region
in the circuit area between the MOSFET and the other circuit
element. Since the cut-off layer is connected to an earth
potential, there is an effect that the potential of the circuit
area is stabilized, thereby improving the reliability of the
circuit operation.
[0046] FIG. 7 shows a plane layout of the third embodiment. In FIG.
7, the same constituent elements as those in FIGS. 1 to 6 are
denoted by the same reference numerals as those in FIGS. 1 to 6. In
FIG. 7, reference numeral 700 denotes a gate pad which serves as a
connection location for connecting an external circuit to the gate
electrode 111 and to which the gate electrode 111 is connected,
numeral 701 a MOSEFT formation area, numeral 702 a cut-off area,
numeral 703 denotes an emitter pad which serves as a connection
location for connecting an external circuit to the emitter
electrode 110 and to which the emitter electrode 110 is connected,
numeral 704 an IGBT area, and numeral 705 a termination area.
[0047] In the present embodiment, the MOSFET formation area is
disposed at the central portion of the circuit area and is
surrounded by the cut-off area, thereby suppressing the flow-in of
a hole current from the IGBT. As mentioned above, a resistor, diode
or the like through an insulating film is disposed in the cut-off
layer in order to make the effective use of the space. Though not
shown in FIG. 7, the cut-off layer 600 is disposed in a region of
the circuit area having not the MOSFET, thereby stabilizing the
potential of the circuit. In the present embodiment, the circuit
area is disposed beside the gate pad, thereby minimizing a delay of
the circuit operation for an IGBT control signal inputted to the
gate.
[0048] (Embodiment 4)
[0049] FIG. 8 shows a cross-sectional structure of a fourth
embodiment according to the present invention.
[0050] A feature of the present embodiment lies in that the emitter
pad 703 and the earth electrode 113 or the earth layer 130 are
connected by a wiring electrode 800. The emitter electrode of the
IGBT has a resistance component Re, as shown in FIG. 8.
[0051] In the equivalent circuit shown in FIG. 2, the resistance
component Re is shown by a resistor 900. Since a reference
potential of the circuit is derived from the emitter electrode of
the IGBT, the reference potential of the circuit may change due to
a voltage produced across the resistor Re 900 of the emitter
electrode by the flow of a current in the IGBT, thereby bringing
about an erroneous operation of the circuit. According to the
present embodiment, the earth layer 130 providing a reference
potential of the circuit is connected to the emitter pad 703 by the
wiring electrode 800 independent of the emitter electrode 111 of
the IGBT, thereby making it possible to prevent a change in earth
potential which may be caused by the resistor Re.
[0052] An equivalent circuit is shown in FIG. 9. Since the earth
layer of the circuit is directly connected to the emitter pad 703,
it is possible to eject a hole current without being passed through
the resistor Re. As a result, an erroneous operation of the circuit
can be prevented.
[0053] FIG. 10 shows the modification of the fourth embodiment. In
FIG. 10, the same constituent elements as those in FIGS. 1 to 9 are
denoted by the same reference numerals as those in FIGS. 1 to 9. In
FIG. 10, reference numeral 1000 denotes an earth pad.
[0054] A feature of this modification lies in that the earth pad is
provided and the earth layer is connected to the earth pad. In the
construction of the fourth embodiment, it is not possible to
prevent a change in earth potential which may be caused due to the
resistance of a wiring which connects the external circuit of the
chip and the emitter pad. In the present modification, a wiring for
the exclusive use of earth is provided for the earth pad and is
directly connected to an earth potential point of the external
circuit, thereby stabilizing the circuit operation.
[0055] (Embodiment 5)
[0056] FIG. 14 shows a cross-sectional structure of a fifth
embodiment according to the present invention. In FIG. 14, the same
constituent elements as those in FIGS. 1 to 13 are denoted by the
same reference numerals as those in FIGS. 1 to 13. In the present
embodiment, a diode as a circuit element is formed in a
semiconductor layer corresponding to the base layer 132 of the
circuit area in the foregoing embodiment. In a diode base layer
1003 of p type, a cathode layer 1002 of n.sup.+ type having an
impurity concentration higher than that of the diode base layer
1003 and an anode layer 1004 of p.sup.+ type having an impurity
concentration higher than that of the diode base layer 1003 are
provided adjoining the other principal surface of the semiconductor
substrate. A cathode electrode 1000 is provided in ohmic contact
with the cathode layer 1002, and an anode electrode 1001 is
provided in ohmic contact with the anode layer 1004. A diode is
formed by the cathode layer 1002, the diode base layer 1003, the
anode layer 1004, the cathode electrode 1000 and the anode
electrode 1001. The cathode electrode 1000 and an emitter electrode
110 of an IGBT are electrically connected through a resistor 140.
Further, an earth layer 130 of p.sup.+ type adjoining the other
principal surface of the semiconductor substrate and having an
impurity concentration higher than that of the diode base layer 130
is formed in the diode base layer 1003. An earth electrode 113 is
provided in ohmic contact with the earth layer 130. The earth
electrode 113 and the emitter electrode 110 are electrically
connected by wiring.
[0057] According to the present embodiment, a hole current injected
from a collector layer 117 is ejected from the earth layer 130 to
the emitter electrode 110. Accordingly, the hole current does not
flow into the cathode layer 1002 of the diode, thereby making it
possible to prevent an erroneous operation of the circuit.
[0058] (Embodiment 6)
[0059] A plane structure of a sixth embodiment according to the
present invention is shown in FIG. 15. The figure shows a plane
pattern of a lateral MOSFET formed in a circuit area of a circuit
incorporated IGBT. Though electrodes are omitted from the
illustration, the electrode pattern shown in FIG. 3 exists as an
example of an electrode pattern. In FIG. 15, an elongated
stripe-like drain layer 133 is disposed at a central portion of a
ring-like source layer 131. The source layer 131 is surrounded by
an earth layer 130. Accordingly, holes trying to flow into the
source layer can effectively be ejected from the earth layer.
Further, since the whole of the periphery of the source layer 131
is surrounded by the earth layer 130, little erroneous operation
occurs.
[0060] (Embodiment 7)
[0061] FIG. 16 is an equivalent circuit diagram of a power
conversion device as a seventh embodiment according to the present
invention. The present embodiment corresponds to a three-phase
inverter device.
[0062] In FIG. 16, reference numerals 1400 and 1401 denote DC input
terminals, numeral 1405 a plurality of sets of circuit incorporated
IGBT's of the present invention, each set including two circuit
incorporated IGBT's connected in series between the DC input
terminals, numerals 1402 to 1404 AC output terminals connected to
the respective series connection points of the sets of circuit
incorporated IGBT's, and numeral 1406 a freewheeling diode
connected in anti-parallel to each circuit incorporated IGBT.
Anyone of the circuit incorporated IGBT's in the foregoing
embodiments can be used as the circuit incorporated IGBT 1405. The
circuit incorporated IGBT's 1405 are driven in a turn-on/off
switching manner. With this on/off switching, a DC power inputted
from the DC input terminals 1400 and 1401 is converted into an AC
power. The AC power is outputted from the AC output terminals 1402
to 1404 to drive an AC load such as a three-phase induction motor
which is connected to the AC output terminals.
[0063] In the present embodiment, a protection circuit for
protecting the IGBT from an over-current is formed in the circuit
area of the circuit incorporated IGBT 1405. According to the
present embodiment, since a hole current flowing into the circuit
area is ejected from the earth layer at the time of over-current
protecting operation, it is possible to suppress the influence of
the hole current on a circuit element in the circuit area.
Therefore, the circuit incorporated IGBT becomes difficult to make
an erroneous operation. As a result, a high-precision over-current
protecting operation is enabled. Accordingly, it is possible to
realize an inverter device which has a high-reliability
over-current protecting function.
[0064] The circuit incorporated IGBT according to the present
invention is applicable to inverter devices as well as various
power conversion devices such as converter devices, chopper devices
and various switching power supplies in which an input power is
subjected to power conversion through the switching of the IGBT and
the power subjected to power conversion is outputted.
[0065] In the foregoing, the present invention has been described
in conjunction with the case where the n-channel IGBT is integrated
with the emitter follower circuit including the n-channel MOSFET.
However, a similar effect can also be obtained by the combination
of a p-channel IGBT and a p-channel MOSFET. Namely, the present
invention provides a similar effect even in the case where the
conductivity type of each semiconductor layer in the foregoing
embodiments is reversed.
[0066] Also, the circuit construction is not limited to the emitter
follower circuit and a similar effect can be obtained so long as
the circuit construction is a circuit integrated with a MOSFET.
[0067] Further, the present invention is not limited to the IGBT.
For example, a similar effect can be obtained in the case where a
circuit is integrated with a bipolar element as in a MOS controlled
thyristor or the like.
[0068] According to the present invention described above, it is
possible to prevent an erroneous operation of a circuit integrated
with an IGBT.
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