Semiconductor device

This is a national phase application based on the PCT International Patent Application No. PCT/JP2011/076942filed on Nov. 22, 2011, the entire contents of which are incorporated herein by reference.

A technology described in the present description relates to a semiconductor device having a trench gate structure.

In a semiconductor device of a trench gate type, when excessive concentration of an electric field occurs at a bottom of an insulated gate, the semiconductor device may be broken. For the purpose of preventing the electric field concentration, for example, Japanese Patent Application Publication No. 2009-88360 (Patent Document 1) has disclosed a vertical metal-oxide-semiconductor field-effect transistor (MOSFET) in which an insulated gate of a trench type is formed in a cell region, and a trench filled with an insulator is formed in a peripheral region that is a non-cell region. The trench filled with the insulator is formed in a p-type resurf layer in the peripheral region. When a voltage is applied across source and drain electrodes of the MOSFET, a depletion layer spreading from a pn junction of the MOSFET expands until it reaches the trench filled with the insulator in the peripheral region. This uniformizes the spreading of the depletion layer in the peripheral region, and improves a breakdown voltage of the MOSFET.

Patent Literature

Patent Document 1: Japanese Patent Application Publication No. 2009-88360

Technical Problem

In the MOSFET of Patent Document 1, the trench in the peripheral region is filled with the insulator. Therefore, when the depletion layer expands from the pn junction of the MOSFET, the electric field expands along the depletion layer in the course of nature. Therefore, the electric field concentrates at a bottom of a portion located at an outermost periphery of the trench in the peripheral region. Consequently, the breakdown voltage of the semiconductor device deteriorates.

Solution to Problem

A first semiconductor device disclosed in the present description includes a semiconductor substrate including a cell region, and a non-cell region arranged around the cell region. The cell region includes a first semiconductor region of a first conductivity type, a second semiconductor region of a second conductivity type formed on a surface of the semiconductor substrate on a front surface side of the first semiconductor region, an insulated gate of a trench type extending from a surface side of the semiconductor substrate through the second semiconductor region to a depth where the insulated gate is in contact with the first semiconductor region, a lengthwise direction of the insulated gate being extended in a first direction, and a first trench conductor formed at least partially in the cell region between the insulated gate and the non-cell region, and having a conductor that is covered with an insulation film and fills a trench. The first trench conductor includes a first portion extending in the first direction, and a second portion protruding in a second direction perpendicularly crossing the first direction and extending from a cell region side toward the non-cell region, and at least a part of a bottom of the second portion reaches a position deeper than a boundary between the first and second semiconductor regions.

According to the first semiconductor device described above, at least a part of the first trench conductor filled with the conductor covered with the insulation film is formed in the cell region between the insulated gate and the non-cell region. An application of a voltage to the first trench conductor can suppress local concentration of an electric field at the bottom of the first trench conductor. Since the first trench conductor has the second portion protruding in the second region, an electric field distribution in the bottom of the first trench conductor and the insulated gate can be extended in the second direction. Consequently, a breakdown voltage of the semiconductor device can be improved.

The first semiconductor device described above may further include a second trench conductor formed at least partially in the cell region between the first portion of the first trench conductor and the non-cell region, and having a conductor that is covered with the insulation film and fills a trench. The second trench conductor is positioned in the second direction with respect to the first portion of the first trench conductor. A length of the second trench conductor in the first direction is shorter than a length of the insulated gate in the first direction. A distance between the first portion of the first trench conductor and the second trench conductor is shorter than a distance between the first trench conductor and the insulated gate nearest to the first trench conductor, and at least a part of the second trench conductor reaches a position deeper than the boundary between the first and second semiconductor regions.

A second semiconductor device disclosed in the description includes a semiconductor substrate including a cell region, and a non-cell region arranged around the cell region. The cell region includes a first semiconductor region of a first conductivity type, a second semiconductor region of a second conductivity type formed on a surface of the semiconductor substrate on a front surface side of the first semiconductor region, an insulated gate of a trench type extending from a surface side of the semiconductor substrate through the second semiconductor region to a depth where the insulated gate is in contact with the first semiconductor region, a lengthwise direction of the insulated gate being extended in a first direction, a third trench conductor formed in the cell region between the insulated gate and the non-cell region, and having a conductor that is covered with an insulation film and fills a trench extending in the first direction, and a fourth trench conductor formed at least partially in the cell region between the insulated gate and the non-cell region, and having a conductor that is covered with the insulation film and fills a trench located, with respect to the third trench conductor, in a second direction perpendicularly crossing the first direction and extending from a cell region side toward the non-cell region. A length of the fourth trench conductor in the first direction is shorter than a length of the insulated gate in the first direction. A distance between the third and fourth trench conductors is shorter than a distance between the third trench conductor and the insulated gate nearest to the third trench conductor. At least a part of the fourth trench conductor reaches a position deeper than a boundary between the first and second semiconductor regions.

In the second semiconductor device described above, the voltage is applied to the third and fourth trench conductors, and thereby local concentration of the electric field at a bottom of the fourth trench conductor can likewise be suppressed. Since the fourth trench conductor is positioned, with respect to the third trench conductor, in the second direction which is perpendicular to the first direction and extending from the cell region side toward the non-cell region, electric field distribution in the bottoms of the insulated gate and the third and fourth trench conductors can expand in the second direction. Consequently, the breakdown voltage of the semiconductor device can be improved similarly to the first semiconductor device.

FIG. 1 is a plan view showing a semiconductor device of Embodiment 1;

FIG. 2 is a view partially enlarging a cell region in the plan view of the semiconductor device in FIG. 1 ;

FIG. 3 is a perspective view including a section taken along line III-III in FIG. 2 ;

FIG. 4 is a view conceptually showing electric field distribution around a first trench conductor in Embodiment 1;

FIG. 5 is a perspective view of the first trench conductor of the semiconductor device according to Embodiment 1;

FIG. 6 is a perspective view of the first trench conductor of the semiconductor device according to a modification;

FIG. 7 is a perspective view of the first trench conductor of the semiconductor device according to the modification;

FIG. 8 is a perspective view of the first trench conductor of the semiconductor device according to the modification;

FIG. 9 is a perspective view of the first trench conductor of the semiconductor device according to the modification;

FIG. 10 is a plan view of the semiconductor device according to a modification, and showing, on an enlarged scale, a part of a cell region;

FIG. 11 is a plan view of the semiconductor device according to the modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 12 is a plan view of the semiconductor device according to the modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 13 is a plan view of the semiconductor device according to the modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 14 is a plan view of the semiconductor device according to the modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 15 is a cross section of the semiconductor device according to a modification;

FIG. 16 is a cross section of the semiconductor device according to the modification;

FIG. 17 is a plan view of a semiconductor device according to Embodiment 2;

FIG. 18 is an enlarged view of a part of a cell region in the plan view of the semiconductor device in FIG. 17 ;

FIG. 19 is a perspective view including a section taken along line XIX-XIX in FIG. 18 ;

FIG. 20 is a view conceptually showing electric field distribution around a fourth trench conductor of Embodiment 2;

FIG. 21 is a plan view of the semiconductor device according to a modification, and showing, on an enlarged scale, a part of a cell region;

FIG. 22 is a plan view of the semiconductor device according to a modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 23 is a plan view of the semiconductor device according to a modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 24 is a plan view of the semiconductor device according to a modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 25 is a plan view of the semiconductor device according to a modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 26 is a plan view of the semiconductor device according to a modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 27 is a plan view of the semiconductor device according to a modification, and showing, on an enlarged scale, a part of the cell region;

FIG. 28 is a perspective view of the semiconductor device according to a modification; and

FIG. 29 is a perspective view of the semiconductor device according to a modification.

Each of first and second semiconductor devices disclosed in the description has a semiconductor substrate including a cell region, and a non-cell region arranged around the cell region. The cell region includes a first semiconductor region of a first conductivity type, a second semiconductor region of a second conductivity type formed on a surface of the semiconductor substrate on a front surface side of the first semiconductor region, and an insulated gate of a trench type extending from a surface side of the semiconductor substrate through the second semiconductor region to a depth where the insulated gate is in contact with the first semiconductor region, a lengthwise direction of the insulated gate being extended in a first direction. The insulated gate includes a gate electrode filling the trench and covered with a gate insulation film. Each of the first and second semiconductor devices may further include a front surface electrode formed on a front surface of the cell region and a rear surface electrode formed on a rear surface of the cell region.

In the first semiconductor device, a first trench conductor included at least partially in the cell region is formed between the insulated gate and the non-cell region. The first trench conductor may be formed entirely in the cell region, or may be partially formed in the non-cell region. The first trench conductor includes a conductor filling a trench and covered with an insulation film. The first trench conductor includes a first portion extending in a first direction, and a second portion protruding in a second direction perpendicularly crossing the first direction and extending from a cell region side toward the non-cell region. At least a part of a bottom of the second portion reaches a position deeper than a boundary between the first and second semiconductor regions. Preferably, conductors of the first and second portions are electrically connected together. The conductors of the first and second portions may be formed integrally with each other. A length in the first direction of the first portion of the first trench conductor may be equal to or different from a lengthwise length of the insulated gate. The first trench conductor may have the only one second portion, and may contain a plurality of second portions. When the first trench conductor has the plurality of second portions, the second portions may have the same size and the same form, or may have different sizes and different forms, respectively.

In the second semiconductor device, third and fourth trench conductors are formed between the insulated gate and the non-cell region. Each of the third and fourth trench conductors includes a conductor covered with an insulation film and filling a trench. The third trench conductor is formed in the cell region, and extends in the first direction. The fourth trench conductor is formed at least partially in the cell region. The fourth trench conductor may be entirely formed in the cell region, or may be partially formed in the non-cell region. Assuming that the second direction is perpendicular to the first direction and extends from the cell region side toward the peripheral region, the fourth trench conductor is positioned in the second direction with respect to the third trench conductor. The fourth trench conductor is shorter in length in the first direction than the insulated gate. The fourth trench conductor is shorter in length in the first direction than the insulated gate. A distance between the third and fourth trench conductors is shorter than a distance between the third trench conductor and the insulated gate nearest to the third trench conductor. At least a part of the fourth trench conductor reaches a position deeper than a boundary between the first and second semiconductor regions. The lengthwise direction of the fourth trench conductor may be the first direction, or may be the second direction. Also, it may be a third direction crossing the first and second directions. The semiconductor device may include only one fourth trench conductor or a plurality of fourth trench conductors. When the semiconductor device includes the plurality of fourth trench conductors, the fourth trench conductors may have the same size and/or the same form, or may have different sizes and/or different forms, respectively. The third trench conductor may have the same form and size as the insulated gate. A distance between the third trench conductor and the insulated gate nearest to the third trench conductor may be equal to a distance (gate pitch) in the second direction between a plurality of neighboring insulated gates.

The semiconductor device disclosed in the present application may include both the structures of the first and second semiconductor devices. For example, the first semiconductor device may be additionally provided with the third and fourth trench conductors according to the second semiconductor device. The second trench conductor may be further arranged at the vicinity of the first trench conductor of the first semiconductor device. The second trench conductor is arranged between the first portion of the first trench conductor and the non-cell region, and is positioned in the second direction with respect to the first trench conductor. The second trench conductor is formed at least partially in the cell region. A distance in the second direction between the second trench conductor and the first portion of the first trench conductor is shorter than a distance between the first trench conductor and the insulated gate nearest to the first trench conductor. The form, direction and sizes of the second trench conductor are substantially the same as those of the fourth trench conductor, and therefore will not be described.

The forms of the bottoms and the side portions of the first to fourth trench conductors are not particularly restricted. The forms of the bottoms and the side portions of these trench conductors may include planar, stepped, curved, inclined forms or the like, or combinations of them.

The first to fourth trench conductors may be electrically connected to the gate electrode in the insulated gate, the front surface electrode, the rear surface electrode or the like. Also, these may be in a floating state electrically disconnected from the gate electrode, the front surface electrode, the rear surface electrode or the like.

The first and second semiconductor devices according to the present application are merely required to have a trench gate structure. MOS-type semiconductor devices and diodes such as IGBT and MOSFET can be listed as the semiconductor devices having the trench gate structure. When the first and second semiconductor devices are IGBTs, respectively, the first semiconductor region is a drift region, the second semiconductor region is a body region, an emitter region of a first conductivity type is arranged at the front surface of the second semiconductor region, and a collector region is arranged on the rear surface side of the semiconductor substrate. When the first and second semiconductor devices are MOSFETs, respectively, the first semiconductor region is a drain or drift region, the second semiconductor region is a body region, and a source region of the first conductivity type is arranged at a front surface of the second semiconductor region. When the first and second semiconductor devices are diodes, the first and second semiconductor regions function as cathode and anode layers, respectively.

In the first and second semiconductor devices according to the present application, a form and arrangement of the insulated gate in a plan view of the semiconductor device are not particularly restricted. A plurality of insulated gates each having substantially a linear form may be arranged parallel to each other, and the insulated gate may have a curved or coil-like form. The insulated gates may cross together, and also may be serially coupled together into a substantially circular or rectangular form. In the first semiconductor device, the first portion of the first trench conductor may have substantially the same form as the insulated gate. As embodiments and modifications described below, IGBTs will be described as examples of semiconductor devices. However, these are not restrictive, and semiconductor devices such as MOSFETs and others having a trench gate structure may likewise be available. For example, description about an installation position of an emitter layer in an IGBT may also be applied to an installation position of a source layer of an MOSFET.

[Embodiment 1]

As shown in FIG. 1 , a semiconductor device 10 according to Embodiment 1 has semiconductor substrate 100 including cell regions 101 a to 101 d and a peripheral region 103 . The peripheral region 103 is a non-cell region arranged around the cell regions 101 a to laid. The peripheral region 103 is arranged along a periphery of the semiconductor substrate 100 , and surrounds all of cell regions 101 a to 101 d . The cell regions 101 a to 101 d are arranged in a central portion of the semiconductor substrate 100 , and a peripheral voltage-resistant portion 105 surrounding them is formed in the peripheral region 103 . As shown in FIG. 2 , the cell region 101 a is provided with a plurality of insulated gates 200 of a trench type. The insulated gates 200 have linear forms in a plan view, respectively, and have the same size and the same form. The insulated gates 200 are arranged at a constant gate pitch (distance in a Y direction between the insulated gates 200 ), and lengthwise directions (X direction shown in FIG. 2 ) thereof are parallel to each other.

As shown in FIG. 3 , the semiconductor device 10 is provided at the cell region 101 a with an IGBT of a trench gate type. The semiconductor substrate 100 includes a p + type collector layer 11 , an n − type drift layer 12 , a p-type body layer 13 , and an n + type emitter layer 14 . The insulated gate 200 extends from a surface side of the semiconductor substrate 100 through the body layer 13 and the emitter layer 14 , and reaches the drift layer 12 . The insulated gate 200 includes a gate electrode covered with a gate insulation film and filling a trench. The emitter layer 14 extends in the lengthwise direction (X direction in FIG. 3 ) of the insulated gate 200 , and is in contact with the gate insulation film of the insulated gate 200 .

As shown in FIGS. 2 and 3 , a first trench conductor 210 is formed between the insulated gate 200 and the peripheral region 103 of the semiconductor device 10 . The first trench conductor 210 is formed in the cell region 101 a . The first trench conductor 210 includes a conductor covered with an insulation film and filling the trench. The first trench conductor 210 includes first and second portions 210 a and 210 b . The first and second portions 210 a and 210 b are integral with each other, and conductors and insulation films covering the conductors are formed of the same layers, respectively. The first portion 210 a extends lengthwise in a first direction (X direction in FIGS. 2 and 3 ). The second portion 210 b extends lengthwise in a second direction (Y direction shown in FIGS. 2 and 3 ) that is perpendicular to the first direction and extends from a cell region side toward the peripheral region. An end in the Y direction of the second portion 210 b extends to the end of the cell region 101 a . The second portion 210 b extends in the second direction from a central position in the first direction of the first portion 210 a . The first trench conductor 210 has a T form in a plan view of the semiconductor substrate 100 . The size of the first portion 210 a in the lengthwise direction (X direction) is equal to size of the insulated gate 200 in the lengthwise direction (X direction). The lengthwise and widthwise sizes (Y and X directions) of the second portion 210 b are shorter than the lengthwise size of the first portion 210 a . Bottoms of the first and second portions 210 a and 210 b are located deeper than a boundary between the body layer 13 and the drift layer 12 . A distance between the insulated gate 200 and the first trench conductor 210 is equal to a gate pitch of the insulated gates 200 . Although not shown, the cell regions 101 b to 101 d are provided with the plurality of insulated gates and first trench conductors, similarly to the cell region 101 a.

As shown in FIGS. 1 to 3 , the semiconductor device 10 has the first trench conductors 210 formed in the cell regions 101 a to 101 d between the insulated gates 200 and the peripheral region 103 . When the IGBT in the cell region is turned on, a voltage (e.g. gate voltage) is applied to the first trench conductor 210 so that an electric field at the bottoms of the insulated gate 200 and the first trench conductor 210 expands in the Y direction. Therefore, as shown in FIG. 4 , the distribution of the electric field near the bottoms of the insulated gate 200 and the first trench conductor 210 is gradual as indicated by equipotential line 1 . Since the semiconductor device 10 rah suppress local concentration of the electric field at the bottoms of the insulated gate 200 and the first trench conductor 210 , the breakdown voltage of the semiconductor device 10 is improved. Since the breakdown voltage of the semiconductor device can be ensured, an area of the peripheral voltage-resistant portion 105 occupying the plane of the semiconductor substrate 100 can be reduced, which contributes to reduction in size of the semiconductor device 10 .

(Modification)

The first trench conductor may have a form other than that already described. FIGS. 6 to 14 show a form of the first trench conductor according to a modification of Embodiment 1, and FIG. 5 shows, for comparison, the form of the first trench conductor 210 according to Embodiment 1. FIGS. 6 to 9 are perspective views showing the first trench conductor of the semiconductor device according to a modification, similarly to FIG. 5 . As shown in FIG. 6 , a second portion 211 b of a first trench conductor 211 may be configured to reduce its depth linearly as the position moves in the second direction (Y direction). The second portion 211 b has a depth d 2 on a side near a first portion 211 a , and has a depth d 1 on the opposite side. The depth d 2 is larger than the depth d 1 . Conversely, as shown in FIG. 7 , a second portion 212 b of a first trench conductor 212 may be configured to increase its depth linearly as the position moves in the second direction (Y direction). The second portion 212 b has a depth d 4 on a side near a first portion 212 a , and has a depth d 3 on the opposite side. The depth d 3 is larger than the depth d. In the case of FIGS. 6 and 7 , at least the depths d 2 and d 3 are larger than a depth of the boundary between the body layer 13 and the drift layer 12 shown in FIG. 3 .

As shown in FIG. 8 , a second portion 213 b of a first trench conductor 213 may have a curved bottom. When the bottom of the second portion 213 b is viewed in the X direction, it is arced and extended in the Y direction from a first portion 213 a . The second portion 213 b has a depth d 5 on each of the first portion 213 a side and the opposite side, and has a depth d 6 at a central position in the Y direction. The depth d 6 is larger than the depth d 5 . In FIG. 8 , at least the depth d 6 is larger than a depth of the boundary between the body layer 13 and the drift layer 12 shown in FIG. 3 . Since the first trench conductor 213 includes the second portion 213 b having a curved surface at the bottom, an effect of dispersing the electric field at the vicinity of the bottom of the second portion 213 b is high. This increases the effect of improving the breakage voltage of the semiconductor device.

The first trench conductor of the form shown in FIGS. 6 to 8 can be formed, for example, by performing trench etching several times with different etching depths. For example, when a trench width is designed to increase as a trench depth increases, the bottom of the first trench conductor shown in FIGS. 6 to 8 can be formed by performing the trench etching fewer times.

As shown in FIG. 9 , the side end surface (remote from a first portion 214 a ) in the second direction (Y direction) of a second portion 214 b of a first trench conductor 214 may be a curved surface. In a plan view viewed in the direction perpendicular to the Y and X directions, the side end surface of the second portion 214 b has an arc form. Since the first trench conductor 214 includes the second portion 214 b having the curved side end surface, the effect of dispersing the electric field at the vicinity of the side end surface of the second portion 214 b is high. This increases the effect of improving the breakage voltage of the semiconductor device.

FIGS. 10 to 14 are plan views similar to FIG, 2 , and show the first trench conductor of the semiconductor device according to a modification. In FIGS. 10 to 14 , the substantially same structures as those in FIG. 2 will not be described. As shown in FIGS. 10 and 11 , the first trench conductor may have a plurality of second portions. As shown in FIG. 10 , a first trench conductor 215 has three second portions 215 b , 215 c and 215 d . The second portions 215 b , 215 c and 215 d have the same size and the same form, and extend to the cell region 101 a in the second direction (Y direction). The second portion 215 e is arranged in a central position in the first direction (X direction) of the first portion 215 a . As shown in FIG. 11 , a first trench conductor 216 has three second portions 216 b , 216 c and 216 d . The second portions 216 b and 216 d have the same size and the same form. The second portion 216 c has the same length in the first direction (X direction) as the second portions 216 b and 216 d . The length in the second direction (Y direction) of the second portion 216 e is shorter than the lengths in the second direction of the second portions 216 b and 216 d . The second portions 216 b and 216 d extend in the second direction (Y direction) to the cell region 101 a . The second portion 215 c is located in a central position in the first direction (X direction) of the first portion 215 a , and its end in the second direction does not reach the end of the cell region 101 a.

As shown in FIG. 12 , a first trench conductor 217 may have a second portion 217 b that protrudes from the cell region 101 a and extends partially into the peripheral region 103 . The second portion 217 b has a portion formed in the cell region 101 a , and the other portion is formed in the peripheral region 103 . A first portion 217 a has substantially the same structure as the first portion 210 a , and therefore will not be described.

As shown in FIGS. 13 and 14 , the first trench conductor may include a portion other than the first and second portions. As shown in FIG. 13 , a first trench conductor 220 includes first and third portions 220 a and 220 c surrounding a periphery of the insulated gate 200 , and a second portion 220 b extending in the Y direction from the first portion 220 a . Although the first and third portions 220 a and 220 c are shown only partially, these are trench conductors substantially having a continuous rectangular form which surrounds the insulated gates 200 and has round corners. In the trench conductor of the substantially rectangular form, a portion located between, in the Y direction, the insulated gate 200 and the peripheral region 103 is the first portion 220 a , and the other portion is the third portion 220 c . The first portion 220 a extends in the X direction. The second portion 220 b extends in the Y direction from a central position in the X direction of the first portion 220 a . As shown in FIG. 14 , a first trench conductor 221 has a substantially continuous rectangular form, has first and third portions 221 a and 221 c having round corners, and has a second portion 221 b extending in the Y direction from the first portion 221 a . The first and third portions 221 a and 221 c form a trench conductor of a substantially continuous rectangular form similar to that of an insulated gate 240 . In the trench conductor having the substantially rectangular form, a portion nearest in the Y direction to the peripheral region 103 is the first portion 221 a , and the other portion is the third portion 221 c . The first portion 221 a extends in the X direction. The second portion 221 b extends in the Y direction from the central position in the X direction of the first portion 221 a.

The form of the peripheral region is not restricted to the embodiment already described. FIGS. 15 and 16 show an example of a modification of the peripheral region. FIGS. 15 and 16 show cross sections that are taken along line III-III in FIG. 2 and are extended to the peripheral region 103 . As shown in FIG. 15 , a peripheral voltage-resistant layer 21 of a high p-type impurity concentration as well as a peripheral voltage-resistant layer 22 of a low p-type impurity concentration may be formed in the peripheral region 103 . The peripheral voltage-resistant layer 21 is formed on a side near the cell region 101 a , and the peripheral voltage-resistant layer 22 is formed on a side remote from the cell region 101 a . The peripheral voltage-resistant layer 21 has a larger depth than the peripheral voltage-resistant layer 22 . The peripheral voltage-resistant layer 21 has a width (corresponding to the width in the X direction in FIG. 15 ) smaller than that of the peripheral voltage-resistant layer 22 . As shown in FIG. 16 , a plurality of p-type peripheral voltage-resistant layers 23 may be formed in the peripheral region 103 . The peripheral voltage-resistant layer 21 is formed on a side near the cell region 101 a . The three peripheral voltage-resistant layers 23 have the same p-type impurity concentration, and have the same depth and the same width (corresponding to the width in the X direction in FIG. 16 ).

Embodiment 1 has been described, by way of example, in connection with the case in which all the first trench conductors have the substantially same forms. However, the first trench conductors of different forms may be present in the one semiconductor device in a mixed fashion. The first trench conductors of different forms may be present in the one cell region in a mixed fashion.

[Embodiment 2]

As shown in FIG. 17 , a semiconductor device 30 according to Embodiment 2 includes a semiconductor substrate 300 including cell regions 301 a to 301 d and a peripheral region 303 that is a non-cell region. The peripheral region 303 is arranged along a periphery of the semiconductor substrate 300 , and surrounds the whole of cell regions 301 a to 301 d . The cell regions 301 a to 301 d are arranged in a central portion of the semiconductor substrate 300 , and a peripheral voltage-resistant portion 305 surrounding them is formed in the peripheral region 303 . As shown in FIG. 18 , the cell region 301 a is provided with a plurality of trench-type insulated gates 400 and a third trench conductor 400 a . The third trench conductor 400 a has substantially the same form and the same size as the insulated gate 400 . The insulated gate 400 and the third trench conductor 400 a are linear in a plan view of the semiconductor device 30 , and have the same size and the same form. The insulated gates 400 and the third trench conductor 400 a extend parallel to each other in a lengthwise direction (Y direction shown in FIG. 18 ), and are arranged at a certain gate pitch (distance in the Y direction between the insulated gates 400 ). A distance between the insulated gate 400 and the third trench conductor 400 a is equal to the gate pitch of the insulated gates 400 .

As shown in FIG. 19 , the cell region 301 a of the semiconductor device 30 is provided with an IGBT of a trench gate type. Structures of the IGBT are substantially the same as those of the semiconductor device 10 , and therefore will not be described.

As shown in FIGS. 18 and 19 , a fourth trench conductor 410 is formed between the third trench conductor 400 a and the peripheral region 303 of the semiconductor device 30 . The fourth trench conductor 410 is positioned in the second direction with respect to the third trench conductor 400 a . The fourth trench conductor 410 is formed in the cell region 301 a . The fourth trench conductor 410 has a conductor covered with an insulation film and filling a trench. The fourth trench conductor 410 extends lengthwise in the second direction (Y direction in FIGS. 18 and 19 ). The position in the first direction of the fourth trench conductor 410 is a center in the first direction of the third trench conductor 400 a . The sizes in the lengthwise and widthwise directions (Y- and X-directions) of the fourth trench conductor 410 are shorter than the lengths in the lengthwise direction of the insulated gate 400 and the third trench conductor 400 a . The bottom of the fourth trench conductor 410 is located deeper than a boundary between a body layer 13 and a drift layer 12 . A conductor of the fourth trench conductor 410 is electrically connected to the insulated gate 400 and the third trench conductor 400 a . Although not shown, the cell regions 301 b to 301 d are provided with insulated gates, third trench conductors and fourth trench conductors similar to those in the cell region 301 a.

As shown in FIGS. 17 to 19 , the semiconductor device 30 has the fourth trench conductor 410 formed in each of the cell regions 301 a to 301 d between the third trench conductor 400 a and the peripheral region 303 . For example, when the IGBT in the cell region is turned on and a voltage (e.g. gate voltage) is applied to the fourth trench conductor 410 , an electric field at bottoms of the insulated gate 400 , the third trench conductor 400 a and the fourth trench conductor 410 expands in the Y direction. Thereby, as shown in FIG. 20 , the distribution of the electric field near the bottoms of the insulated gate 400 , the third trench conductor 400 a and the fourth trench conductor 410 is gradual as indicated by equipotential line 3 . The semiconductor device 30 can suppress local concentration of the electric field at the bottoms of the insulated gate 400 , the third trench conductor 400 a and the fourth trench conductor 410 , and therefore has an improved breakdown voltage. Since the breakdown voltage of the semiconductor device can be ensured, an area of the peripheral voltage-resistant portion 305 occupying a planar area of the semiconductor substrate 300 can be reduced, which contributes to reduction in sizes of the semiconductor device 30 .

(Modification)

The third and fourth trench conductors may have forms other than those already described. For example, the fourth trench conductor may have bottom and side surfaces of the same forms as those of the second portion shown in FIGS. 6 to 9 .

The semiconductor device may have a plurality of fourth trench conductors. For example, as shown in FIG. 21 , three fourth tenth conductors 411 a , 411 b and 411 c may be arranged. The fourth trench conductors 411 a , 411 b and 411 c have the same size and the same form, and extend to an end of the cell region 301 a in the second direction (Y direction). The fourth trench conductor 411 b is arranged in a central position in the first direction (X direction) of the third trench conductor 400 a . For example, as shown in FIG. 22 , the three fourth trench conductors 412 a , 412 b and 412 c may be arranged. The fourth trench conductors 412 a and 412 c have the same size and the same form, and a length in the second direction (Y direction) of the fourth trench conductor 412 b is shorter than those in the second direction of the fourth trench conductors 412 a and 412 c . The fourth trench conductors 412 a and 412 c extend in the second direction (Y direction) to the end of the cell region 301 a . An end in the second direction of the fourth trench conductor 412 b does not reach the end of the cell region 301 a.

As shown in FIG. 23 , a fourth trench conductor 413 extending lengthwise in the first direction (X direction) may be arranged. The length in the first direction of the fourth trench conductor 413 is merely required to be shorter than the lengths in the first direction of the insulated gate 400 and the third trench conductor 400 a.

As shown in FIG. 24 , a fourth trench conductor 414 protruding from the cell region 301 a and having a portion extending into the peripheral region 303 may be arranged. The fourth trench conductor 414 has a portion formed in the cell region 301 a , and the other portion is formed in the peripheral region 303 .

As shown in FIGS. 25 and 26 , the third trench conductor may be a part of a trench conductor of a non-linear form. As shown in FIG. 25 , a third trench conductor 420 a is formed continuously to a fifth trench conductor 420 b , and these form a substantially rectangular form surrounding a periphery of the insulated gate 400 and having round corners, although shown only partially. In the trench conductor of the substantially rectangular form, a portion occupying a position in the Y direction between the insulated gate 400 and the peripheral region 303 is the third trench conductor 420 a , and the other portion is the fifth trench conductor 420 b . The third trench conductor 420 a extends in the X direction. A fourth trench conductor 430 is positioned in the Y direction with respect to the third trench conductor 420 a . The position is the X direction of the fourth trench conductor 430 is a center in the X direction of the third trench conductor 420 a . A distance in the Y direction between the third and fourth trench conductors 420 a and 430 is longer than that in the Y direction between the third trench conductor 420 a and the insulated gate 400 . As shown in FIG. 26 , a third trench conductor 421 a and a fifth trench conductor 421 b may form a trench conductor of a substantially rectangular and continuous form having round corners, and may have substantially the same form as an insulated gate 421 . A distance between the third trench conductor 421 a and a fourth trench conductor 431 is shorter than a distance in the Y direction between the insulated gate 421 and the third trench conductor 421 a as well as a gate pitch of the insulated gates 421 .

The form of the peripheral region is not restricted to that of the embodiment already described. For example, forms similar to that described with reference to FIGS. 15 and 16 in Embodiment 1 may be employed.

Similarly to Embodiment 1, the third and fourth trench conductors of different forms may be present in the one semiconductor device in a mixed fashion. Also, the third and fourth trench conductors of different forms may be present in the one cell region in a mixed fashion.

As shown in FIG. 27 , a second trench conductor 450 may be additionally employed at the vicinity of a first trench conductor 440 described in Embodiment 1. The first trench conductor 440 includes a first portion 440 a and two second portions 440 b and 440 c . The second trench conductor 450 is positioned in the X direction between the second portions 440 b and 440 c , and is present in the Y direction between the first portion 440 a and the peripheral region. The form, size and material of the second trench conductor 450 are substantially the same as those of the fourth trench conductor 410 shown in FIG. 18 and others. The second trench conductor 450 is not arranged near the third trench conductor 400 a , but is arranged near the first trench conductor, which is a difference from the fourth trench conductor 410 .

Although the IGBT has been described by way of example, the structures of the insulated gate and the trench conductor in the present application can be applied to other semiconductor devices of the trench gate type such as an MOSFET. In the semiconductor devices other than the IGBT, the first, fourth or second trench conductor can relieve the electric field concentration to achieve the effect of improving the breakdown voltage of the semiconductor device.

For example, the structures of the insulated gates and others relating to the IGBT already described in the embodiments and modifications can likewise be used in a semiconductor device 50 provided with MOSFETs as shown in FIG. 28 . A semiconductor substrate 500 includes an n-type drain layer 52 , a p-type body layer 53 , and an n + type source layer 54 . An insulated gate 600 extends from a surface side of the semiconductor substrate 500 through the body layer 53 and the source layer 54 to the drain layer 52 . Similarly to FIG. 3 , a first trench conductor 610 is formed between the insulated gate 600 and a peripheral region. The first trench conductor 610 includes first and second portions 610 a and 610 b . The structure of the first trench conductor 610 is substantially the same as that of the first trench conductor 210 shown in FIG. 3 , and therefore will not be described. In this case, when a voltage is applied across front and rear surface electrodes of the semiconductor device 50 , a voltage is also applied to the first trench conductor 610 so that an electric field at bottoms of the insulated gate 600 and the first trench conductor 610 can expand in the Y direction. Similarly to FIG. 4 , therefore, it is possible to suppress local concentration of the electric field at the bottoms of the insulated gate 680 and the first trench conductor 610 .

The structures of the insulated gates and others relating to the IGBT described in the embodiments and the modifications can be utilized in a semiconductor device 70 provided with diodes, as shown in FIG. 29 . A semiconductor substrate 700 includes an n-type cathode layer 72 and a p-type anode layer 73 , as shown in FIG. 29 . An insulated gate 800 and a third trench conductor 800 a extend from a surface side of the semiconductor substrate 700 through the anode layer 73 to the cathode layer 72 . Similarly to FIG, 19 , a fourth trench conductor 810 is formed between the third trench conductor 800 a and a peripheral region. Structures of the third and fourth trench conductors 800 a and 810 are substantially the same as those of the third and fourth trench conductors 400 a and 410 shown in FIG. 3 , and therefore will not be described below. In this case, when a voltage is applied across front and rear surface electrodes of the semiconductor device 70 , a voltage is also applied to the third and fourth trench conductors 800 a and 810 so that an electric field at bottoms of the insulated gate 800 and the third and fourth trench conductors 808 a and 810 can expand in the Y direction. Similarly to FIG. 4 , therefore, it is possible to suppress local concentration of an electric field at the bottoms of the insulated gate 800 and the third and fourth trench conductors 800 a and 810 .

Specific examples of the present invention have been described in detail, however, these are mere exemplary indications and thus do not limit the scope of the claims. The art described in the claims includes modifications and variations of the specific examples presented above.

Technical features described in the description and the drawings may technically be useful alone or in various combinations, and are not limited to the combinations as originally claimed. Further, the art described in the description and the drawings may concurrently achieve a plurality of aims, and technical significance thereof resides in achieving any one of such aims.