JP2012109599A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superjunction semiconductor device improving an avalanche resistance in a device peripheral part to improve an avalanche resistance of the device as a whole.SOLUTION: In a semiconductor device, a drain drift part 22 has a first parallel pn structure constituted of a first n-type region 22a and a first p-type region 22b by bonding alternately and repeatedly at a pitch P1. A surrounding area of the drain drift part 22 is a device peripheral part 30 consisting of a second parallel pn structure. The device peripheral part 30 is constituted of a second n-type region 30a and a second p-type region 30b by bonding alternately and repeatedly at the pitch P1 so as to be continued from the first parallel pn structure. Impurity concentration of the first and second parallel pn structures are substantially the same as each other. A third parallel pn structure formed on a surface region of the device peripheral part 30 is constituted of a third n-type region 34a and a third p-type region 34b having an impurity concentration higher than that of the third n-type region 34a by bonding alternately and repeatedly at a pitch P2 smaller than the pitch P1. An impurity concentration of the third parallel pn structure is lower than those of the first and second parallel pn structures.

Description

  The present invention can be applied to active elements such as MOSFETs (insulated gate field effect transistors), IGBTs (insulated gate bipolar transistors), and bipolar transistors, and passive elements such as diodes, and achieves both high breakdown voltage and large current capacity. The present invention relates to a vertical power semiconductor element.

In general, semiconductor elements are classified into a horizontal element having electrodes formed on one side and a vertical element having electrodes on both sides. In the vertical semiconductor element, the direction in which the drift current flows in the on state is the same as the direction in which the depletion layer due to the reverse bias voltage extends in the off state. In a normal planar type n-channel vertical MOSFET, the portion of the high resistance n ⁻ drift layer functions as a region through which a drift current flows in the vertical direction when in the on state. Therefore, if the current path of the n ⁻ drift layer is shortened, the drift resistance is lowered, so that an effect that the substantial on-resistance of the MOSFET can be lowered is obtained.

On the other hand, the portion of the high resistance n ⁻ drift layer is depleted in the off state to increase the breakdown voltage. Therefore, when the n ⁻ drift layer is thinned, the width of the drain-base depletion layer that progresses from the pn junction between the P base region and the n ⁻ drift layer becomes narrow, and the critical electric field strength of silicon is quickly reached. The withstand voltage will decrease. On the other hand, in a semiconductor device with a high breakdown voltage, since the n ⁻ drift layer is thick, the on-resistance increases and the loss increases. Thus, there is a trade-off relationship between on-resistance and breakdown voltage.

  This trade-off relationship is also known to hold in semiconductor devices such as IGBTs, bipolar transistors, and diodes. This trade-off relationship is also common to horizontal semiconductor elements in which the direction in which the drift current flows in the on state and the direction in which the depletion layer extends due to the reverse bias in the off state are different.

  As a solution to the above-described problem due to the trade-off relationship, a superjunction semiconductor element having a parallel pn structure in which a drift layer is formed by alternately and repeatedly joining n-type drift regions and p-type partition regions having a high impurity concentration is known. (For example, refer to Patent Document 1, Patent Document 2, and Patent Document 3.) In the semiconductor element having such a structure, even when the impurity concentration of the parallel pn structure is high, the depletion layer extends laterally from each pn junction extending in the vertical direction of the parallel pn structure in the off state, and the entire drift layer Therefore, a high breakdown voltage can be achieved.

  On the other hand, in order to realize a high breakdown voltage of the semiconductor element, an element peripheral part structure is necessary. Without the element termination structure, the breakdown voltage drops at the end of the drift layer, making it difficult to achieve a high breakdown voltage. As a structure for solving this problem, it has been proposed to arrange a parallel pn structure having a smaller pitch than the parallel pn structure of the element active part in a region on the surface side of the outer periphery of the parallel pn structure of the element active part. (For example, refer to Patent Document 4 and Patent Document 5). According to this proposal, the surface electric field in the vicinity of the element active portion is relaxed and high breakdown voltage is maintained.

Further, for improving the avalanche resistance of the drift layer in the super junction semiconductor element, a structure for improving the negative resistance at the time of avalanche breakdown has been proposed (see, for example, Patent Document 6). Further, a structure having an n ⁻ drift layer having an impurity concentration lower than that of the n-type drift region of the parallel pn structure is known between the low resistance layer and the parallel pn structure (see, for example, Patent Document 7).

  FIG. 23 is a schematic partial plan view showing a chip of a conventional vertical MOSFET element, FIG. 24 is a vertical cross-sectional view showing a state cut along the line AA ′ in FIG. 23, and FIG. It is a longitudinal cross-sectional view which shows the state cut | disconnected along B 'line. In FIG. 23, 1/4 of the drain / drift portion (element active portion) is shown (the same applies to FIGS. 1, 7, 10 and 12).

This vertical MOSFET includes a drain / drift portion 22 having a first parallel pn structure formed on a low-resistance n ⁺ drain layer (contact layer) 11 in which the drain electrode 18 on the back side is in conductive contact, and the drain / drift portion. A high impurity concentration p base region (p well) 13a to be an element active portion selectively formed in the surface layer of the portion 22, and a high impurity concentration selectively formed on the surface side in the p base region 13a N ⁺ source region 14, gate electrode layer 16 such as polysilicon provided on the substrate surface via gate insulating film 15, and p base regions 13 a and n via contact holes opened in interlayer insulating film 19 a ^And a source electrode 17 in conductive contact across the source region 14. An n ⁺ source region 14 is shallowly formed in the well-shaped p base region 13a to constitute a double diffusion type MOS portion. Reference numeral 26 denotes a p ⁺ contact region, and a gate electrode wiring of a metal film is in conductive contact with the gate electrode layer 16 in a portion not shown.

The drain / drift portion 22 substantially corresponds to a portion immediately below the p base region 13a of a plurality of wells serving as an element active portion, and a layered vertical first n-type region 22a oriented in the thickness direction of the substrate and in the thickness direction of the substrate. This is a first parallel pn structure in which the oriented layered vertical first p-type regions 22b are alternately and repeatedly joined in the creeping direction of the substrate at a pitch P1. One of the first n-type regions 22 a has an upper end that reaches the interspace region 12 e of the p base region 13 a and a lower end that is in contact with the n ⁺ drain layer 11. The first n-type region 22a reaching the intercostal region 12e is an electric circuit region in the ON state, but the remaining first n-type region 22a is generally a non-electric circuit region. The first p-type region 22 b has an upper end in contact with the well bottom surface of the p base region 13 a and a lower end in contact with the n ⁺ drain layer 11.

  The periphery of the drain / drift portion 22 is an element peripheral portion 30 having a second parallel pn structure. The element peripheral portion 30 is oriented in the thickness direction of the substrate and the layered vertical second n-type region 30a oriented in the thickness direction of the substrate at a repeated pitch P1 continuously to the first parallel pn structure of the drain / drift portion 22. The layered vertical second p-type regions 30b are joined alternately and repeatedly in the creeping direction of the substrate. The first parallel pn structure and the second parallel pn structure have substantially the same repetition pitch and substantially the same impurity concentration.

  A third parallel pn structure is formed in the surface layer region on the substrate surface side in the element peripheral portion 30. This third parallel pn structure is formed by repeatedly joining the layered vertical third n-type region 34a and the layered vertical third p-type region 34b alternately in the creeping direction of the substrate at a repeated pitch P2. The impurity concentration of the third parallel pn structure is lower than the impurity concentration of the second parallel pn structure, and the repetition pitch P2 is narrower than the repetition pitch P1.

An oxide film (insulating film) 33 is formed on the surface of the third parallel pn structure. The oxide film 33 is formed so that its film thickness gradually increases from the drain / drift part 22 to the element peripheral part 30. A field plate electrode FP extended from the source electrode 17 is formed on the oxide film 33 and covers the third parallel pn structure. Further, an n-type channel stopper region 50 connected to the n ⁺ drain layer 11 is formed outside the peripheral edge portion 30, and a stopper electrode 51 is in conductive contact with the surface side of the n-type channel stopper region 50. .

US Pat. No. 5,216,275 US Pat. No. 5,438,215 JP-A-9-266611 JP 2003-224273 A Japanese Patent Laid-Open No. 2004-22716 JP 2004-72068 A JP 2003-273355 A

  However, Patent Document 4 discloses a low on-resistance and a high breakdown voltage, but does not describe an avalanche resistance (breakdown current). Moreover, the above-mentioned Patent Document 6 does not disclose a structure for improving the negative resistance at the time of avalanche breakdown including the element peripheral portion. Even if the avalanche resistance of the element active part is improved, it is difficult to ensure and guarantee the avalanche resistance as a whole unless the avalanche resistance of the peripheral part of the element is improved.

The inventors of the present invention performed a simulation of the current-voltage characteristics of the peripheral portion of the device and the active portion of the device at the time of avalanche breakdown for the 600V class vertical MOSFET device having the structure shown in FIGS. The dimension and impurity concentration of each part of the parallel pn structure used for the simulation have the following values. The drain / drift portion 22 has a thickness (depth direction) of 44.0 μm, the widths of the first n-type region 22a and the first p-type region 22b are 8.0 μm (repetitive pitch P1 is 16.0 μm), The impurity concentration of the first n-type region 22a and the first p-type region 22b is 2.4 × 10 ¹⁵ cm ⁻³ , and the thickness (depth direction) of the second parallel pn structure of the element peripheral portion 30 is 31.degree. 0 μm, the width of the second n-type region 30a and the second p-type region 30b is 8.0 μm (repetitive pitch P1 is 16.0 μm), and the impurities of the second n-type region 30a and the second p-type region 30b The concentration is 2.4 × 10 ¹⁵ cm ⁻³ , the thickness (depth direction) of the third parallel pn structure of the element peripheral portion 30 is 13.0 μm, the third n-type region 34 a and the third p-type region The width of 34b is 4.0 μm (repetition pitch P2 is 8.0 μm), and the third n-type region 4a and the impurity concentration of the third p-type region 34b is 4.8 × 10 ¹⁴ cm ^-3.

  26 to 28 are characteristic diagrams showing simulation results in a portion along the line A-A ′ in FIG. 23. In this simulation, the impurity concentration Nn of each n-type region is set to −10% (FIG. 26), 0% (FIG. 27), and + 10% (FIG. 26) with respect to the impurity concentration Np of each p-type region in consideration of the variation in impurity concentration. FIG. 28). From FIG. 26 to FIG. 28, it can be seen that a negative resistance region exists in the current-voltage characteristics at the periphery of the element in any case.

When entering the negative resistance region, positive feedback is applied in the direction in which the current flows, so that local concentration of the current occurs and the element is destroyed. Therefore, the current (avalanche resistance) that can flow in the element active part before the element active part is destroyed is limited by the avalanche voltage (drain-source voltage) at which the negative resistance at the peripheral part of the element appears. . In view of the variation in the amount of impurities, the avalanche resistance is about 50 A / cm ^{2 in} the element having the conventional structure (see FIG. 28). Therefore, in order to improve the avalanche resistance in a predetermined impurity amount variation range, it is necessary to increase the avalanche voltage at which the negative resistance at the peripheral portion of the element appears to be equal to or higher than that of the element active portion. Alternatively, it is necessary to relax the negative resistance characteristic and to make the resistance positive if possible.

  The present invention has a parallel pn structure as an element peripheral portion around the drift portion which is a parallel pn structure in order to eliminate the above-described problems caused by the prior art, and greatly improves the trade-off relationship between on-resistance and breakdown voltage. An object of the present invention is to provide a semiconductor device capable of improving the avalanche resistance of the peripheral portion of the element in the superjunction semiconductor element that can be improved, thereby improving the avalanche resistance of the entire element. Further, in a superjunction semiconductor device having a parallel pn structure in the drift portion and capable of greatly improving the trade-off relationship between on-resistance and breakdown voltage, the negative resistance at the time of avalanche breakdown is relaxed, whereby the entire device An object of the present invention is to provide a semiconductor device capable of improving the avalanche resistance.

  In order to solve the above-described problems and achieve the object, a semiconductor element according to the present invention includes an element active portion that is present on the first main surface side of a substrate and allows an active or passive current to flow, and a second main portion of the substrate. A low-resistance layer of the first conductivity type existing on the surface side, and a vertical drift that is interposed between the element active portion and the low-resistance layer, and in which the drift current flows in the vertical direction in the on state and is depleted in the off state And an element peripheral portion that is interposed between the first main surface and the low-resistance layer around the vertical drift portion and is substantially a non-electric path region in the on state and depleted in the off state. The vertical drift portion is formed by alternately and repeatedly joining first vertical first conductivity type regions oriented in the thickness direction of the substrate and first vertical second conductivity type regions oriented in the thickness direction of the substrate. A first parallel pn structure and the element; As for the edge, second vertical first conductivity type regions oriented in the thickness direction of the substrate and second vertical second conductivity type regions oriented in the thickness direction of the substrate are alternately arranged with a first repetition pitch. A semiconductor element having a first portion having a second parallel pn structure that is repeatedly bonded to the substrate, wherein the element peripheral portion has a third vertical shape in a surface layer area on the first main surface side of the substrate. The first conductivity type region and the third vertical second conductivity type region having an impurity concentration higher than that of the third vertical first conductivity type region are alternately arranged at a second repetition pitch narrower than the first repetition pitch. It has the 2nd part which consists of a 3rd parallel pn structure formed by joining repeatedly.

  In the semiconductor element according to the present invention, in the above-described invention, the impurity concentration of the third vertical second conductivity type region is 120% or more of the impurity concentration of the third vertical first conductivity type region. And

  The semiconductor element according to the present invention includes an element active portion that is present on the first main surface side of the substrate and allows an active or passive current to flow, and a low resistance layer of the first conductivity type that is present on the second main surface side of the substrate. And a vertical drift portion interposed between the element active portion and the low resistance layer, in which a drift current flows in a vertical direction in an on state and is depleted in an off state, and the first drift around the vertical drift portion. Intervening between the main surface and the low-resistance layer, and having an element peripheral portion that is substantially a non-electric circuit region in the on state and depleted in the off state, and the vertical drift portion is oriented in the thickness direction of the substrate And a first parallel pn structure in which first vertical first conductivity type regions and first vertical second conductivity type regions oriented in the thickness direction of the substrate are alternately and repeatedly joined, and the periphery of the element The second portion is oriented in the thickness direction of the substrate. A first parallel type pn structure in which a first conductive type region and a second vertical second conductive type region oriented in the thickness direction of the substrate are alternately joined at a first repeat pitch. A semiconductor device having a first portion, wherein the peripheral portion of the device has a third vertical first conductivity type region and a third vertical first in the surface layer region on the first main surface side of the substrate. A third parallel pn structure in which third vertical second conductive type regions having a width wider than the conductive type region are alternately and repeatedly joined at a second repeat pitch narrower than the first repeat pitch. It has two parts.

  In the semiconductor device according to the present invention, the width of the third vertical second conductivity type region is 120% or more of the width of the third vertical first conductivity type region. .

  In the semiconductor device according to the present invention, the impurity concentration of the second portion is lower than the impurity concentration of the first portion in the above-described invention.

  The semiconductor element according to the present invention includes an element active portion that is present on the first main surface side of the substrate and allows an active or passive current to flow, and a low resistance layer of the first conductivity type that is present on the second main surface side of the substrate. And a vertical drift portion interposed between the element active portion and the low resistance layer, in which a drift current flows in a vertical direction in an on state and is depleted in an off state, and the first drift around the vertical drift portion. Intervening between the main surface and the low-resistance layer, and having an element peripheral portion that is substantially a non-electric circuit region in the on state and depleted in the off state, and the vertical drift portion is oriented in the thickness direction of the substrate And a first parallel pn structure in which first vertical first conductivity type regions and first vertical second conductivity type regions oriented in the thickness direction of the substrate are alternately and repeatedly joined, and the periphery of the element The second portion is oriented in the thickness direction of the substrate. A first parallel type pn structure in which a first conductive type region and a second vertical second conductive type region oriented in the thickness direction of the substrate are alternately joined at a first repeat pitch. A semiconductor device having a first portion, wherein the peripheral portion of the device has a third vertical first conductivity type region and a third vertical first in the surface layer region on the first main surface side of the substrate. A third parallel pn structure in which third vertical second conductivity type regions having a carrier concentration higher than that of the conductivity type regions are alternately and repeatedly joined at a second repetition pitch narrower than the first repetition pitch. It has the 2nd part, It is characterized by the above-mentioned.

  In the semiconductor element according to the present invention, in the above-described invention, the carrier concentration of the third vertical second conductivity type region is 120% or more of the carrier concentration of the third vertical first conductivity type region. And

  The semiconductor element according to the present invention includes an element active portion that is present on the first main surface side of the substrate and allows an active or passive current to flow, and a low resistance layer of the first conductivity type that is present on the second main surface side of the substrate. And a vertical drift portion interposed between the element active portion and the low resistance layer, in which a drift current flows in a vertical direction in an on state and is depleted in an off state, and the first drift around the vertical drift portion. Intervening between the main surface and the low-resistance layer, and having an element peripheral portion that is substantially a non-electric circuit region in the on state and depleted in the off state, and the vertical drift portion is oriented in the thickness direction of the substrate And a first parallel pn structure in which first vertical first conductivity type regions and first vertical second conductivity type regions oriented in the thickness direction of the substrate are alternately and repeatedly joined, and the periphery of the element The second portion is oriented in the thickness direction of the substrate. A first parallel type pn structure in which a first conductive type region and a second vertical second conductive type region oriented in the thickness direction of the substrate are alternately joined at a first repeat pitch. A semiconductor device having a first portion, wherein the peripheral portion of the device has a third vertical first conductivity type region and a third vertical first in the surface layer region on the first main surface side of the substrate. A third parallel pn structure in which a third vertical second conductivity type region having a carrier amount larger than that of the conductivity type region is alternately and repeatedly joined at a second repetition pitch narrower than the first repetition pitch. It has the 2nd part, It is characterized by the above-mentioned.

  In the semiconductor device according to the present invention, in the above-described invention, the carrier amount of the third vertical second conductivity type region is 120% or more of the carrier amount of the third vertical first conductivity type region. And

  According to the above-described invention, since the charge imbalance region is provided in the second portion, the avalanche voltage at which the negative resistance at the time of avalanche breakdown appears is increased, and the avalanche current that can flow in the element active portion is improved. Therefore, the avalanche breakdown current (withstand capability) can be increased. Further, according to the above-described invention, the imbalance of the impurity amount or the carrier amount of the third parallel pn structure becomes 20% or more, so that the variation in the avalanche resistance against the variation in the impurity amount or the carrier amount can be reduced. . Further, according to the above-described invention, the lower the impurity concentration of the second portion, the more the surface electric field in the vicinity of the element active portion is relaxed, so that a high breakdown voltage can be easily achieved.

  The semiconductor element according to the present invention includes an element active portion that is present on the first main surface side of the substrate and allows an active or passive current to flow, and a low resistance layer of the first conductivity type that is present on the second main surface side of the substrate. And a vertical drift portion interposed between the element active portion and the low resistance layer, in which a drift current flows in a vertical direction in an on state and is depleted in an off state, and the first drift around the vertical drift portion. Intervening between the main surface and the low-resistance layer, and having an element peripheral portion that is substantially a non-electric circuit region in the on state and depleted in the off state, and the vertical drift portion is oriented in the thickness direction of the substrate And a first parallel pn structure in which first vertical first conductivity type regions and first vertical second conductivity type regions oriented in the thickness direction of the substrate are alternately and repeatedly joined, and the periphery of the element The second portion is oriented in the thickness direction of the substrate. A first parallel type pn structure in which a first conductive type region and a second vertical second conductive type region oriented in the thickness direction of the substrate are alternately joined at a first repeat pitch. A semiconductor element having a first portion, wherein the peripheral edge of the element is formed in a surface layer region on the first main surface side of the substrate, and a second conductivity type region wider than the first repetition pitch. It has a part.

  In the semiconductor device according to the present invention, the impurity concentration of the second portion is lower than the impurity concentration of the second vertical second conductivity type region in the above-described invention. According to the present invention, the avalanche voltage at which the negative resistance at the time of avalanche breakdown appears is increased, and the avalanche current that can flow in the element active portion is improved. Therefore, the avalanche breakdown current (withstand capability) can be increased.

  The semiconductor element according to the present invention is characterized in that, in the above-described invention, the second portion is composed of a first conductivity type impurity and a second conductivity type impurity.

  The semiconductor element according to the present invention is characterized in that, in the above-described invention, a part of the second portion is disposed below an end portion of the second conductivity type region provided in the element active portion. And

  The semiconductor element according to the present invention is characterized in that, in the above-described invention, the thickness of the second portion is 50% or less of the total thickness of the first portion and the second portion. . According to the present invention, it is possible to suppress a decrease in breakdown voltage. Since the decrease in the breakdown voltage with respect to the charge imbalance increases as the connecting portion that becomes the pitch change is thicker, the first portion is thicker than 50% of the total thickness of the first portion and the second portion. Is desirable. In addition, if the first parallel pn structure and the second parallel pn structure are configured to be continuous at the same first pitch, there is no connection portion that becomes a change in pitch, so that a decrease in breakdown voltage in this portion is avoided. Can do.

  The semiconductor element according to the present invention is characterized in that, in the above-described invention, a first-conductivity-type channel stopper region is provided on the outer periphery of the first portion and the second portion.

  The semiconductor element according to the present invention is characterized in that, in the above-described invention, the channel stopper region is connected to the low resistance layer. According to the present invention, the breakdown voltage can be stabilized.

  The semiconductor element according to the present invention is characterized in that, in the above-described invention, the second portion is covered with an insulating film.

  The semiconductor device according to the present invention is characterized in that, in the above-described invention, a part of the second portion is covered with a field plate electrode through the insulating film. According to the present invention, the voltage shared by the insulating film under the field plate electrode compensates for the withstand voltage drop caused by the charge imbalance at the connection portion where the pitch changes, so that the withstand voltage can be easily secured. Can do.

  The semiconductor element according to the present invention includes an element active portion that is present on the first main surface side of the substrate and allows an active or passive current to flow, and a low resistance layer of the first conductivity type that is present on the second main surface side of the substrate. And a vertical drift portion interposed between the element active portion and the low resistance layer, in which a drift current flows in the vertical direction in the on state and is depleted in the off state, and provided on the first main surface side of the substrate A plurality of second conductivity type base regions, wherein the vertical drift portion is oriented in the thickness direction of the substrate and the first vertical second orientation oriented in the thickness direction of the substrate. A semiconductor element having a parallel pn structure in which conductive type regions are alternately and repeatedly joined, and in the second conductive type base region provided on the outermost side among the plurality of second conductive type base regions, Relative to the first part having a low impurity concentration A second portion having a high impurity concentration is provided, and a portion of the first portion outside the second portion is covered with an insulating film, and the first portion includes the first portion. The width of the portion covered with the insulating film outside the portion 2 is wider than the repetitive pitch of the parallel pn structure.

  In the semiconductor element according to the present invention, in the above-described invention, in the second conductivity type base region provided on the outermost side, the first portion is covered with the insulating film outside the second portion. The resistance value of the part is 2Ω or more.

  According to the above-described invention, the avalanche current generated at the periphery of the element flows to the source region through the second conductivity type base region provided on the outermost side. Therefore, the negative resistance at the time of avalanche breakdown is relieved by the resistance component of the second conductivity type base region serving as a current path of the avalanche current.

  In the semiconductor device according to the present invention, in the above-described invention, the semiconductor element is interposed between the first main surface and the low-resistance layer around the vertical drift portion. The device peripheral portion further has a depleted device peripheral portion, and the device peripheral portion alternately includes a vertical first conductivity type region oriented in the thickness direction of the substrate and a vertical second conductivity type region oriented in the thickness direction of the substrate. A parallel pn structure formed by repetitive bonding is formed, and in at least a part of the parallel pn structure at the periphery of the element, the repetition pitch in the portion on the first main surface side is larger than the repetition pitch of the parallel pn structure in the vertical drift portion. It is characterized by being narrow.

  In the semiconductor element according to the present invention, in the above-described invention, a part of a portion of the parallel pn structure at the peripheral portion of the element having a repetition pitch smaller than the repetition pitch of the parallel pn structure of the vertical drift portion is provided on the outermost side. The second conductive type base region is disposed below the formed second conductive type base region. According to the present invention, the electric field at the corner portion of the second conductivity type base region provided on the outermost side is relaxed. In addition, the depletion layer tends to spread. Therefore, a high breakdown voltage can be achieved.

  In the semiconductor device according to the present invention, in the above-described invention, between the low resistance layer and the portion of the parallel pn structure at the periphery of the device, the repetition pitch is narrower than the repetition pitch of the parallel pn structure of the vertical drift portion. The vertical first conductivity type regions oriented in the thickness direction of the substrate and the vertical second conductivity type regions oriented in the thickness direction of the substrate alternate with the same repeat pitch as the repeat pitch of the parallel pn structure of the vertical drift portion. It is characterized in that a parallel pn structure formed by repetitively bonding is provided. According to the present invention, since there is no connection portion that changes the pitch between the parallel pn structure of the vertical drift portion and the parallel pn structure of the element peripheral portion, it is possible to avoid a decrease in breakdown voltage in this portion.

  According to the semiconductor device of the present invention, it is possible to increase the avalanche voltage at which the negative resistance at the time of avalanche breakdown appears. Alternatively, the negative resistance characteristic that appears at the periphery of the element at the time of avalanche breakdown can be relaxed. Accordingly, since the avalanche current that can be flown in the element active portion is increased, the avalanche breakdown current (withstand capability) can be improved. In addition, the avalanche resistance variation can be reduced with respect to the impurity amount variation of the parallel pn structure. Therefore, there is an effect that a superjunction semiconductor element having a high avalanche resistance can be obtained.

1 is a schematic partial plan view showing a chip of a vertical MOSFET element according to a first exemplary embodiment of the present invention. It is a longitudinal cross-sectional view which shows the state cut | disconnected along the A-A 'line | wire in FIG. It is a longitudinal cross-sectional view which shows the state cut | disconnected along the B-B 'line | wire in FIG. It is a characteristic view which shows the simulation result of the current-voltage characteristic at the time of avalanche breakdown in the part along the A-A 'line in FIG. It is a characteristic view which shows the simulation result of the current-voltage characteristic at the time of avalanche breakdown in the part along the A-A 'line in FIG. It is a characteristic view which shows the simulation result of the current-voltage characteristic at the time of avalanche breakdown in the part along the A-A 'line in FIG. It is a general | schematic fragmentary top view which shows the chip | tip of the vertical MOSFET element concerning Embodiment 2 of this invention. It is a longitudinal cross-sectional view which shows the state cut | disconnected along the A-A 'line | wire in FIG. It is a longitudinal cross-sectional view which shows the state cut | disconnected along the B-B 'line | wire in FIG. It is a general | schematic fragmentary top view which shows the chip | tip of the vertical MOSFET element concerning Embodiment 3 of this invention. It is a longitudinal cross-sectional view which shows the state cut | disconnected along the A-A 'line | wire in FIG. It is a general | schematic fragmentary top view which shows the chip | tip of the vertical MOSFET element concerning Embodiment 4 of this invention. It is a longitudinal cross-sectional view which shows the state cut | disconnected along the A-A 'line | wire in FIG. FIG. 13 is a characteristic diagram showing a simulation result of current-voltage characteristics at the time of avalanche breakdown at a portion along the line A-A ′ in FIG. 12. FIG. 13 is a characteristic diagram showing a simulation result of current-voltage characteristics at the time of avalanche breakdown at a portion along the line A-A ′ in FIG. 12. FIG. 13 is a characteristic diagram showing a simulation result of current-voltage characteristics at the time of avalanche breakdown at a portion along the line A-A ′ in FIG. 12. It is a longitudinal cross-sectional view which shows the principal part of the vertical MOSFET element concerning Embodiment 5 of this invention. It is a characteristic view which shows the simulation result of the current-voltage characteristic at the time of avalanche breakdown in the part shown in FIG. It is a characteristic view which shows the simulation result of the current-voltage characteristic at the time of avalanche breakdown in the part shown in FIG. It is a characteristic view which shows the simulation result of the current-voltage characteristic at the time of avalanche breakdown in the part shown in FIG. It is a longitudinal cross-sectional view which shows the principal part of the vertical MOSFET element concerning Embodiment 6 of this invention. It is a longitudinal cross-sectional view which shows the principal part of the vertical MOSFET element concerning Embodiment 7 of this invention. It is a general | schematic fragmentary top view which shows the chip | tip of the conventional vertical MOSFET element. It is a longitudinal cross-sectional view which shows the state cut | disconnected along the A-A 'line | wire in FIG. It is a longitudinal cross-sectional view which shows the state cut | disconnected along the B-B 'line | wire in FIG. FIG. 24 is a characteristic diagram showing a simulation result of current-voltage characteristics at the time of avalanche breakdown at a portion along the line A-A ′ in FIG. 23. FIG. 24 is a characteristic diagram showing a simulation result of current-voltage characteristics at the time of avalanche breakdown at a portion along the line A-A ′ in FIG. 23. FIG. 24 is a characteristic diagram showing a simulation result of current-voltage characteristics at the time of avalanche breakdown at a portion along the line A-A ′ in FIG. 23.

Exemplary embodiments of a semiconductor device according to the present invention will be explained below in detail with reference to the accompanying drawings. In the following layers and regions where n or p is named, it means that electrons or holes are majority carriers, respectively. Further, “ ⁺ ” and “ ⁻ ” attached to n and p mean a relatively high impurity concentration or a relatively low impurity concentration, respectively. In all the embodiments, n is selected for the first conductivity type and p is selected for the second conductivity type, but this may be reversed. Note that the same reference numerals are given to the same components in all the attached drawings, and redundant description is omitted.

Embodiment 1 FIG.
1 is a schematic partial plan view showing a chip of a vertical MOSFET device according to a first embodiment of the present invention, FIG. 2 is a vertical cross-sectional view showing a state cut along line AA ′ in FIG. 1, and FIG. FIG. 2 is a longitudinal sectional view showing a state cut along line BB ′ in FIG. 1. The vertical MOSFET according to the first embodiment is different from the first embodiment except that the impurity concentration of the third p-type regions 34b, 34ba, 34bb is higher than the impurity concentration of the third n-type regions 34a, 34aa, 34ab. It is the same as the conventional structure shown in FIGS.

  As shown in FIG. 1, in the first embodiment, the first parallel pn structure, the second parallel pn structure, and the third parallel pn structure are planarly striped and arranged in parallel to each other. In the third parallel pn structure, the widths of the third n-type regions 34a, 34aa, 34ab and the third p-type regions 34b, 34ba, 34bb are substantially the same. Further, as shown in FIG. 2, since the second parallel pn structure is continuous with the first parallel pn structure, there is no pitch change portion where the pitch becomes discontinuous. In order to suppress a decrease in withstand voltage against charge imbalance, the thickness of the third parallel pn structure is 50% or less of the total thickness of the second parallel pn structure and the third parallel pn structure. Good.

  Further, in the third parallel pn structure, the inner portions of the third p-type region 34ba and the third n-type region 34aa adjacent to the first parallel pn structure in parallel to the bottom of the p base region 13a. It is formed by sneaking in. Similarly, as shown in FIG. 3, among the third parallel pn structures, the layered vertical third that hits the end faces of the first n-type region 22 a and the first p-type region 22 b of the first parallel pn structure. The inner portions of the p-type region 34bb and the layered vertical third n-type region 34ab are formed so as to penetrate into the bottom of the p base region 13a.

Although not particularly limited, for example, when the vertical MOSFET of the first embodiment has a withstand voltage of 600 V class, the dimensions and impurity concentration of each part take the following values. The drain / drift portion 22 has a thickness (depth direction) of 44.0 μm, the widths of the first n-type region 22a and the first p-type region 22b are 8.0 μm (repetitive pitch P1 is 16.0 μm), The impurity concentration of one n-type region 22a and the first p-type region 22b is 2.4 × 10 ¹⁵ cm ⁻³ . The thickness (depth direction) of the second parallel pn structure of the element peripheral portion 30 is 31.0 μm, and the widths of the second n-type region 30a and the second p-type region 30b are 8.0 μm (repetitive pitch P1 is 16.0 μm), the impurity concentration of the second n-type region 30a and the second p-type region 30b is 2.4 × 10 ¹⁵ cm ⁻³ .

The thickness (depth direction) of the third parallel pn structure of the element peripheral portion 30 is 13.0 μm, and the widths of the third n-type regions 34a, 34aa, 34ab and the third p-type regions 34b, 34ba, 34bb are 4.0 μm (repetitive pitch P2 is 8.0 μm). The impurity concentration of the third n-type regions 34a, 34aa, 34ab is 4.8 × 10 ¹⁴ cm ⁻³ , and the impurity concentration of the third p-type regions 34b, 34ba, 34bb is 7.2 × 10 ¹⁴ cm ⁻³ . is there.

The p base region 13a has a diffusion depth of 3.0 μm, its surface impurity concentration is 3.0 × 10 ¹⁷ cm ⁻³ , the n ⁺ source region 14 has a diffusion depth of 1.0 μm, and its surface impurity concentration is 3.0 μm. × 10 ²⁰ cm ⁻³ , the diffusion depth of the interspace region 12e which is a surface drift region is 2.5 μm, the surface impurity concentration is 2.0 × 10 ¹⁶ cm ⁻³ , and the thickness of the n ⁺ drain layer 11 is 300 μm, The impurity concentration is 2.0 × 10 ¹⁸ cm ⁻³ , the width of the n-type channel stopper region 50 is 30.0 μm, and the impurity concentration is 6.0 × 10 ¹⁵ cm ⁻³ .

  Here, the impurity concentration (impurity amount) of the parallel pn structure means the carrier concentration (carrier amount). Even if the impurity concentration is high, if the carrier concentration is low, a sufficient avalanche resistance improvement effect cannot be obtained. In general, the impurity concentration and the carrier concentration can be regarded as equivalent in a region where sufficient activation has been performed. Similarly, the impurity amount and the carrier amount can be regarded as being equal in a region where sufficient activation has been performed. Therefore, in this specification, for convenience, the impurity concentration includes the carrier concentration, and the impurity amount includes the carrier amount.

  Next, the principle that negative resistance is generated at the time of avalanche breakdown will be described. When a voltage is applied between the drain and source / gate and the corner portion of the p base region 13a reaches a critical electric field, avalanche breakdown occurs and an avalanche current starts to flow. As the avalanche current increases, the number of carriers generated by the avalanche also increases, and holes and electrons are accumulated on the front side and the back side of the device, respectively, causing redistribution of the electric field. At this time, the holes cause electric field redistribution so that the high electric field region moves from the corner of the p base region 13a to the bottom of the p base region 13a. As a result, a product of a vertical electric field distribution and a depletion layer appears as an avalanche voltage.

  Further, when the avalanche current flows and the number of movable carriers generated by the avalanche increases, the vertical electric field has a further downward electric field distribution, and the avalanche voltage decreases. That is, negative resistance appears. Therefore, in order to increase the avalanche resistance, that is, to increase the avalanche voltage at which negative resistance appears, a structure composed of the third parallel pn structure and the second parallel pn structure under the p base region 13a in the element peripheral portion 30. Therefore, the structure may be such that the electric field on the surface side is relaxed when an avalanche current flows.

  Therefore, in the first embodiment, in the third parallel pn structure arranged under the p base region 13a, the impurity concentration of the third p-type region 34ba is higher than the impurity concentration of the third n-type region 34aa. Thus, the electric field on the surface side is relaxed. Specifically, the impurity concentration of the third p-type regions 34b, 34ba, 34bb is set to 150% of the impurity concentration of the third n-type regions 34a, 34aa, 34ab. In order to obtain a sufficient electric field relaxation effect, the impurity concentration of the third p-type regions 34b, 34ba, 34bb should be 120% or more of the impurity concentration of the third n-type regions 34a, 34aa, 34ab. desirable.

  Next, for the 600V class vertical MOSFET device having the structure shown in FIG. 1 to FIG. 3, the present inventors performed a simulation of the current-voltage characteristics of the device peripheral portion and the device active portion at the time of avalanche breakdown. 4 to 6. Note that the dimensions and impurity concentrations of each part of the parallel pn structure used in the simulation are the values described in the first embodiment. As in the prior art, the impurity concentration Nn of each n-type region is set to −10% (FIG. 4), 0% (FIG. 5), and + 10% with respect to the impurity concentration Np of each p-type region in consideration of variations in impurity concentration. Simulation was performed as (FIG. 6).

When comparing FIGS. 4 to 6 with FIGS. 26 to 28 (conventional example), in any case, the avalanche voltage at which the negative resistance of the element peripheral portion 30 appears is higher than that of the conventional structure, and it flows in the element active portion. Since the avalanche current that can be increased is increased, the avalanche resistance can be improved. Even if the impurity concentration of the n-type region varies by ± 10%, an avalanche resistance of 250 A / cm ² or more can be obtained (see FIG. 6). Furthermore, since the third p-type region 34b also functions as a guard ring, the breakdown voltage can be easily ensured. In the y direction in FIG. 1, that is, in the direction parallel to the stripe of the parallel pn structure, the third parallel pn structure is sandwiched between the p base region 13a and the n-type channel stopper region 50, so rare.

  Further, since the surface concentration in the vicinity of the element active portion is relaxed because the impurity concentration of the third parallel pn structure is lower than the impurity concentration of the second parallel pn structure, a high breakdown voltage can be easily achieved. . Furthermore, since there is no connection portion that changes the pitch between the first parallel pn structure and the second parallel pn structure, and the third parallel pn structure is thin, a reduction in breakdown voltage in this portion is avoided. Can do. In addition, the breakdown voltage can be stabilized by providing the n-type channel stopper region 50. In addition, since the field plate electrode FP is provided, the voltage shared by the oxide film 33 under the field plate electrode FP compensates for the breakdown voltage drop caused by the charge imbalance at the connection portion where the pitch changes. Therefore, the breakdown voltage can be easily secured.

Embodiment 2. FIG.
FIG. 7 is a schematic partial plan view showing a chip of a vertical MOSFET device according to the second exemplary embodiment of the present invention. FIG. 8 is a vertical cross-sectional view showing a state cut along the line AA ′ in FIG. FIG. 8 is a longitudinal sectional view showing a state cut along the line BB ′ in FIG. 7. The vertical MOSFET according to the second embodiment is a modification of the first embodiment, and is different from the first embodiment as follows. That is, the impurity concentration of the third n-type region 34a and the third p-type region 34b is the same, and the width Wp of the third p-type region 34b is wider than the width Wn of the third n-type region 34a. . For example, the impurity concentration of the third n-type region 34a and the third p-type region 34b is 4.8 × 10 ¹⁴ cm ⁻³ , and the width Wp of the third p-type region 34b is the third n-type region 34b. It is 120% or more of the width Wn of the mold region 34a.

  Further, the direction of the repetition pitch in the third parallel pn structure in the surface layer portion of the element peripheral portion 30 is orthogonal to the direction of the repetition pitch in the first parallel pn structure of the drain / drift portion 22. If the thickness of the third parallel pn structure with a small repetition pitch P2 is sufficiently thinner than the thickness of the first parallel pn structure, the third parallel pn structure is orthogonal to the first parallel pn structure. May also be parallel.

  In the second embodiment, since the charge imbalance is achieved by increasing the width Wp of the third p-type region 34b, the same effect as in the first embodiment can be obtained. In addition, when controlling the impurity amount of the third p-type region 34b, it is easier to control the width of the third p-type region 34b than to control the impurity concentration of the third p-type region 34b. Therefore, the effect that the productivity of the second embodiment is higher than that of the first embodiment is obtained. Furthermore, since the third parallel pn structure and the first parallel pn structure intersect, there is an advantage that the degree of freedom in design is increased.

Embodiment 3 FIG.
FIG. 10 is a schematic partial plan view showing a chip of a vertical MOSFET device according to the third exemplary embodiment of the present invention, and FIG. 11 is a vertical cross-sectional view showing a state cut along the line AA ′ in FIG. The vertical MOSFET of the third embodiment is a modification of the second embodiment, and is different from the second embodiment as follows. That is, the p-type regions 22b ′, 30b ′, 34b ′ and the n-type regions 22a ′, 30a ′, 34a ′ in the first to third parallel pn structures are vertically layered, but are not striped in plan view. The p-type regions 22b ′, 30b ′, and 34b ′ are in the form of hexagonal lattice points in plan, and the remaining portions are n-type regions 22a ′, 30a ′, and 34a ′. Conversely, the n-type region may be in the form of hexagonal lattice points, and the remaining portion may be a p-type region.

  Further, in the third parallel pn structure, if the impurity amount of the third p-type region 34b ′ is larger than the impurity amount of the third n-type region 34a ′, the first to third parallel pn structures. The planar shape is not limited to a hexagonal lattice, and may be a polygonal lattice such as a trigonal lattice or a tetragonal lattice. Furthermore, among the first to third parallel pn structures, any of the parallel pn structures may have a lattice point shape in a plane, and the other parallel pn structures may have a stripe shape in a plane. Also in this example, in the third parallel pn structure, the third n-type region 34aa ′ and the third p-type region 34ba ′ are formed so as to penetrate into the bottom of the p base region 13a. .

In the third embodiment, as shown in FIG. 11, an n-type buffer region 61 is provided between the first and second parallel pn structures and the n ⁺ drain layer 11. Note that the n-type buffer region 61 may not be provided. According to the third embodiment, the voltage value entering the negative resistance at the time of avalanche breakdown can be increased regardless of the planar shape of the parallel pn structure and regardless of the presence or absence of the n-type buffer region 61. Avalanche resistance can be improved.

Embodiment 4 FIG.
FIG. 12 is a schematic partial plan view showing a chip of a vertical MOSFET device according to the fourth exemplary embodiment of the present invention, and FIG. 13 is a vertical cross-sectional view showing a state cut along line AA ′ in FIG. In the vertical MOSFET of the fourth embodiment, a p-type region 34d having a low impurity concentration is disposed in the surface layer region on the substrate surface side of the element peripheral portion 30 instead of the third parallel pn structure. A part of the p-type region 34d is covered with the field plate electrode FP connected to the p base region 13a via the oxide film 33, as in the first embodiment.

In the fourth embodiment, the surface electric field is relaxed in the p-type region 34d. Regarding the impurity concentration of the p-type region 34d, since the breakdown voltage is lowered unless the impurity concentration is such that the p-type region 34d is depleted when a voltage is applied between the source, drain, and gate, It is desirable that the impurity concentration is lower than that of the p-type region 30b. For example, the impurity concentration of the p-type region 34d is 4.8 × 10 ¹⁴ cm ⁻³ . Other dimensions, concentrations, and the like are the same as those in the first embodiment. The p-type region 34d having a high resistance is doped with both n-type impurities and p-type impurities. Since the n-type impurity and the p-type impurity compensate each other, the region doped with almost the same amount acts as a high resistance region. Therefore, a p-type region having high resistance can be easily formed by increasing the amount of the p-type impurity compared to the n-type impurity. Furthermore, since the impurity concentration of the p-type region having high resistance can be easily controlled by the amount of each impurity or the width of the region into which each impurity is introduced, it is possible to manufacture with high productivity.

Next, for the 600V class vertical MOSFET device having the structure shown in FIG. 12 and FIG. 13, the present inventors performed a simulation of the current-voltage characteristics of the device peripheral portion and the device active portion at the time of avalanche breakdown. 14 to FIG. The dimensions and impurity concentrations of the respective parts of the parallel pn structure used in the simulation are the same as those described in the first embodiment except that the impurity concentration of the p-type region 34d is 4.8 × 10 ¹⁴ cm ^−3. It is. As in the first embodiment, the impurity concentration Nn of each n-type region is set to −10% (FIG. 14) and 0% (FIG. 14) with respect to the impurity concentration Np of each p-type region in consideration of the variation in impurity concentration. 15) and + 10% (FIG. 16).

Comparing FIGS. 14 to 16 with FIGS. 26 to 28 (conventional example), in any case, the avalanche voltage at which the negative resistance of the element peripheral portion 30 appears is higher than that of the conventional structure, and it flows in the element active part. Since the avalanche current that can be increased is increased, the avalanche resistance can be improved. Further, even if the impurity concentration in the n-type region varies by ± 10%, an avalanche resistance of 340 A / cm ² or more can be obtained (see FIG. 15).

Embodiment 5 FIG.
FIG. 17 is a longitudinal sectional view showing a state in which a chip of a vertical MOSFET element according to the fifth embodiment of the present invention is cut. This vertical cross section corresponds to a cut surface when the chip of the vertical MOSFET element according to the fifth embodiment is cut along a cutting line corresponding to the AA ′ line in FIG. 1, for example.

In the vertical MOSFET of the fifth embodiment, the outermost p base region (hereinafter referred to as the outermost peripheral p base region) 13 b is outside the p ⁺ contact region 26 that contacts the source electrode 17 and is formed by the oxide film 33. Except for the fact that the width Wb of the covered portion is wider than the repetition pitch P1 of the first parallel pn structure consisting of the first n-type region 22a and the first p-type region 22b, FIG. This is the same as the conventional configuration shown. In the outermost peripheral p base region 13b, the p ⁺ contact region 26 corresponds to a second portion having a relatively high impurity concentration, and the other p regions correspond to a first portion having a relatively low impurity concentration. To do.

  As shown in FIG. 17, in the fifth embodiment, as in the first embodiment, the second parallel pn structure including the second n-type region 30a and the second p-type region 30b is the first parallel pn. The structure is continuous and there is no pitch transition where the pitch becomes discontinuous. As a result, a decrease in breakdown voltage due to charge imbalance is alleviated.

Although not particularly limited, for example, when the vertical MOSFET of the fifth embodiment has a withstand voltage of 600 V class, the size and impurity concentration of each part take the following values. The drain / drift portion 22 has a thickness (depth direction) of 44.0 μm, the widths of the first n-type region 22a and the first p-type region 22b are 8.0 μm (repetitive pitch P1 is 16.0 μm), The impurity concentration of one n-type region 22a and the first p-type region 22b is 2.4 × 10 ¹⁵ cm ⁻³ .

The thickness (depth direction) of the second parallel pn structure of the element peripheral portion 30 is 31.0 μm, and the widths of the second n-type region 30a and the second p-type region 30b are 8.0 μm (repetitive pitch P1 is 16.0 μm), the impurity concentration of the second n-type region 30a and the second p-type region 30b is 2.4 × 10 ¹⁵ cm ⁻³ . The thickness (depth direction) of the third parallel pn structure of the element peripheral portion 30 is 13.0 μm, and the widths of the third n-type region 34a and the third p-type region 34b are 4.0 μm (repetitive pitch P2 is 8.0 μm). The impurity concentration of the third n-type region 34a and the third p-type region 34b is 4.8 × 10 ¹⁴ cm ⁻³ .

The diffusion depth and surface impurity concentration of the p base region 13a are 3.0 μm and 1.0 × 10 ¹⁷ cm ⁻³ , respectively, and the diffusion depth and surface impurity concentration of the p ⁺ contact region 26 are 1.0 μm and 4.0 respectively. × 10 ¹⁹ cm ^-3 . The diffusion depth and the surface impurity concentration of the n ⁺ source region 14 are 1.0 μm and 3.0 × 10 ²⁰ cm ⁻³ , respectively, and the diffusion depth and the surface impurity concentration of the interspace region 12e serving as the surface drift region are 2.5 μm, respectively. And 2.0 × 10 ¹⁶ cm ⁻³ .

The thickness and impurity concentration of the n ⁺ drain layer 11 are 300 μm and 2.0 × 10 ¹⁸ cm ⁻³ , respectively, and the width and impurity concentration of the n-type channel stopper region 50 are 30.0 μm and 6.0 × 10 ¹⁵ cm ^{−, respectively. 3} . In the outermost peripheral p base region 13b, the diffusion depth, the width Wb of the portion covered with the oxide film 33 outside the p ⁺ contact region 26, and the surface impurity concentration are 3.0 μm, 50 μm, and 1.0 ×, respectively. 10 ¹⁷ cm ⁻³ .

  In the first embodiment, in order to increase the avalanche resistance based on the principle of generation of negative resistance at the time of avalanche breakdown, the electric field on the surface side is relaxed when an avalanche current flows in the element peripheral portion 30. I explained that it should be a simple structure. In addition, according to the above principle, it is understood that the resistance of the outermost peripheral p base region 13b through which the avalanche current flows may be increased in order to increase the avalanche resistance. Therefore, in the fifth embodiment, the negative resistance is relaxed by reducing the impurity concentration of the outermost peripheral p base region 13b and increasing the width Wb of the portion through which the avalanche current flows.

  Here, in order to avoid the negative resistance at the time of avalanche breakdown, the resistance value of the outermost peripheral p base region 13b may be 2Ω or more in the entire outermost peripheral p base region 13b. This is because, in the conventional example, when the impurity concentration Nn of the n-type region is higher than the impurity concentration Np of the p-type region, the negative resistance value at the periphery of the element is around 2Ω. For example, in the fifth embodiment, when the total peripheral length (full length), sheet resistance, and width Wb of the outermost peripheral p base region 13b are about 16 mm, 800Ω / □, and 50 μm, respectively, The resistance value is about 2.5Ω. In this case, even if an avalanche is locally generated in a part of the outermost peripheral p base region 13b, the current concentration is alleviated.

  On the other hand, when the element is in the ON state, the outermost peripheral p base region 13b is an invalid region where no current flows. Therefore, in order to improve area efficiency, it is desirable that the width of the outermost peripheral p base region 13b be as narrow as possible. However, in order to avoid the negative resistance at the time of avalanche breakdown, it is necessary to widen the width of the outermost peripheral p base region 13b to some extent. Specifically, the width of the outermost peripheral p base region 13b only needs to be wider than the repetition pitch P1.

  Next, the present inventors conducted simulations of the current-voltage characteristics of the element peripheral part and the element active part at the time of avalanche breakdown for the 600 V class vertical MOSFET element having the structure shown in FIG. 20 shows. Note that the dimensions and impurity concentration of each part of the parallel pn structure used in the simulation are the values described in the fifth embodiment. As in the prior art, the impurity concentration Nn of each n-type region is set to −10% (FIG. 18), 0% (FIG. 19), and + 10% with respect to the impurity concentration Np of each p-type region in consideration of variations in impurity concentration. (FIG. 20) was simulated.

  As is clear from comparison between FIG. 20 and FIG. 28 (conventional example), when the impurity concentration Np of the p-type region is lower than the impurity concentration Nn of the n-type region, the negative resistance is relaxed and becomes a positive resistance. Therefore, the avalanche resistance can be improved. On the other hand, as apparent from the comparison between FIG. 18 and FIG. 26 (conventional example) and the comparison between FIG. 19 and FIG. 27 (conventional example), the impurity concentration Np of the p-type region is higher than the impurity concentration Nn of the n-type region. Is high, and when both are equal, the negative resistance is hardly relaxed. This is because the avalanche current flows only in the middle or part of the outermost peripheral p base region 13b.

However, in any case, since the avalanche voltage at which the negative resistance of the element peripheral portion 30 appears is high, a high avalanche resistance can be ensured. 18 to 20, an avalanche resistance of about 300 A / cm ² can be secured even if the impurity concentration in the n-type region varies by ± 10% (see FIG. 19).

  Note that Patent Document 4 describes a cross-sectional view (for example, FIG. 14) in which the width of the portion on the element peripheral side is slightly wider than the high concentration p region in the outermost peripheral p base region. However, in the said patent document, the negative resistance which appears at the time of avalanche breakdown is not considered. Further, as can be seen with reference to FIG. 14 of Patent Document 4, for example, the width of the outermost peripheral p base region closer to the element periphery than the high-concentration p region therein and the portion covered with the oxide film is Not particularly wide. The fifth embodiment is different from the element described in Patent Document 4 in that the width of the portion is extremely wide compared to, for example, FIG. 14 of Patent Document 4.

Embodiment 6 FIG.
FIG. 21 is a longitudinal sectional view showing a state in which a chip of a vertical MOSFET element according to the sixth embodiment of the present invention is cut. This vertical cross section corresponds to a cut surface when the chip of the vertical MOSFET element according to the sixth embodiment is cut along a cutting line corresponding to the AA ′ line in FIG. 1, for example.

The vertical MOSFET according to the sixth embodiment is a modification of the fifth embodiment, and is different from the fifth embodiment as follows. That is, the third parallel pn structure composed of the third n-type region 34a and the third p-type region 34b is not connected to the outermost peripheral p base region 13b. Even in such a structure, when the impurity concentration Np of the p-type region is lower than the impurity concentration Nn of the n-type region, an avalanche is generated at the corner portion of the outermost peripheral p base region 13b, and an avalanche current is generated in the outermost peripheral p base region. 13b flows through the wide portion outside the p ⁺ contact region 26 to the source electrode 17, so that the negative resistance at the time of avalanche breakdown is relaxed. Therefore, the same effect as in the fifth embodiment can be obtained.

Embodiment 7 FIG.
FIG. 22 is a longitudinal sectional view showing a state in which the chip of the vertical MOSFET element according to the seventh embodiment of the present invention is cut. This vertical cross section corresponds to a cut surface when the chip of the vertical MOSFET element according to the seventh embodiment is cut along a cutting line corresponding to the AA ′ line in FIG. 1, for example.

The vertical MOSFET according to the seventh embodiment is a modification of the fifth embodiment, and is different from the fifth embodiment as follows. That is, the third parallel pn structure composed of the third n-type region 34 a and the third p-type region 34 b reaches the n ⁺ drain layer 11. That is, in the seventh embodiment, the second parallel pn structure including the second n-type region 30a and the second p-type region 30b is not provided. Even in such a structure, as in the fifth embodiment, the negative resistance at the time of avalanche breakdown when the impurity concentration Np of the p-type region is lower than the impurity concentration Nn of the n-type region is mitigated. The same effect as 5 is obtained.

  As described above, the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, instead of applying the field plate structure to the surface edge structure, a guard ring may be used, and the surface edge structure may sufficiently relax the curvature of the p base region 13b located at the outermost peripheral portion of the element active portion. As long as the structure can be used, not only the field plate structure and the guard ring structure, but also a structure using both of them may be used. In addition, the element active portion formed on the first main surface side of the substrate is, for example, a vertical MOSFET, a switching portion including a channel diffusion layer and a source region forming an inversion layer on the first main surface side, and a bipolar transistor In this case, the switching part includes an emitter or a collector region, and refers to an active part or a passive part having a selection function of conduction and non-conduction on the first main surface side of the drift part. Therefore, the present invention is not limited to a MOSFET, but an IGBT, The present invention can also be applied to a bipolar transistor, FWD, or Schottky diode.

  As described above, the present invention is useful for high-power semiconductor devices, and in particular, it is possible to achieve both high breakdown voltage and large current capacity of MOSFETs, IGBTs, bipolar transistors, etc. having a parallel pn structure in the drift portion. Suitable for semiconductor devices that can be used.

FP field plate electrode 11 low resistance layer of first conductivity type (n ⁺ drain layer)
13b Outermost peripheral p base region 22 Vertical drift portion (drain drift portion)
22a, 22a ′ first vertical first conductivity type region (first n-type region)
22b, 22b ′ first vertical second conductivity type region (first p-type region)
30 Element peripheral portion 30a, 30a ′ Second vertical first conductivity type region (second n-type region)
30b, 30b ′ second vertical second conductivity type region (second p-type region)
33 Insulating film (oxide film)
34a, 34aa, 34ab, 34a ′, 34aa ′ Third vertical first conductivity type region (third n-type region)
34b, 34ba, 34bb, 34b ', 34ba' Third vertical second conductivity type region (third p-type region)
34d Second conductivity type region (p-type region)
50 n-type channel stopper region

Claims (5)

An element active portion that is present on the first main surface side of the substrate and allows an active or passive current to flow, a low-resistance layer of a first conductivity type that is present on the second main surface side of the substrate, the element active portion, A vertical drift portion interposed between the low resistance layer and flowing in the vertical direction in the on state and depleted in the off state, and a plurality of second conductivity types provided on the first main surface side of the substrate And a vertical first drift type conductive region that is oriented in the thickness direction of the substrate and a first vertical second conductivity type region that is oriented in the thickness direction of the substrate alternately. A semiconductor element having a parallel pn structure formed by bonding,
In the second conductivity type base region provided on the outermost side among the plurality of second conductivity type base regions, a first portion having a relatively low impurity concentration and a second portion having a relatively high impurity concentration are present. The first portion of the first portion outside the second portion is covered with an insulating film, and the first portion outside the second portion is insulated from the second portion. The width of the portion covered with the film is wider than the repetition pitch of the parallel pn structure.   In the second conductivity type base region provided on the outermost side, the resistance value of the portion of the first portion covered by the insulating film outside the second portion is 2Ω or more. The semiconductor device according to claim 1.   An element peripheral portion that is interposed between the first main surface and the low-resistance layer around the vertical drift portion and is substantially a non-electric path region in the on state and depleted in the off state; The peripheral portion has a parallel pn structure in which a vertical first conductivity type region oriented in the thickness direction of the substrate and a vertical second conductivity type region oriented in the thickness direction of the substrate are alternately and repeatedly joined. 3. The repetitive pitch in the first main surface side portion is narrower than the repetitive pitch of the parallel pn structure of the vertical drift portion in at least a part of the parallel pn structure of the peripheral portion. Semiconductor element.   A part of the portion of the parallel pn structure of the peripheral portion of the element having a repetition pitch narrower than the repetition pitch of the parallel pn structure of the vertical drift portion is below the second conductivity type base region provided on the outermost side. The semiconductor element according to claim 3, wherein the semiconductor element is arranged.   A vertical first conductive material oriented in the thickness direction of the substrate between a portion of the parallel pn structure of the peripheral edge of the element and a portion where the repetition pitch is narrower than the repetition pitch of the parallel pn structure of the vertical drift portion and the low resistance layer. A parallel pn structure is provided in which a mold region and a vertical second conductivity type region oriented in the thickness direction of the substrate are alternately and repeatedly joined at the same repetition pitch as that of the parallel pn structure of the vertical drift portion. The semiconductor device according to claim 3, wherein the semiconductor device is a semiconductor device.

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