Patent Application
20130240900
The present invention relates to a semiconductor device used for high power switching and a method for producing the semiconductor device, and particularly to a semiconductor device that uses a GaN-based semiconductor among nitride-based semiconductors and a method for producing the semiconductor device.
High reverse breakdown voltage and low on-resistance are required for high current switching devices. Field effect transistors (FETs) that use a group III nitride-based semiconductor are excellent in terms of, for example, high breakdown voltage and high-temperature operation because of their wide band gap. Therefore, vertical transistors that use a GaN-based semiconductor have been particularly receiving attention as transistors for controlling high power. For example, PTL 1 proposes a vertical GaN-based FET whose mobility is increased and whose on-resistance is decreased by forming an opening in a GaN-based semiconductor and forming a regrown layer including a channel of two-dimensional electron gas (2DEG) in the opening. In this vertical GaN-based FET, a structure including a p-type GaN barrier layer and the like is proposed in order to improve the breakdown voltage characteristics and pinch-off characteristics.
PTL 1: Japanese Unexamined Patent Application Publication No. 2006-286942
In the above vertical GaN-based FET, the breakdown voltage characteristics may be improved by a depletion layer formed in a pn junction between the p-type GaN barrier layer and an n−-type GaN drift layer. However, the opening penetrates through the p-type GaN barrier layer and reaches the n−-type GaN drift layer. Therefore, a gate electrode G faces a drain electrode without the p-type GaN barrier layer disposed therebetween. When the semiconductor device is used as a high-power switching device, a voltage of several hundred volts to one thousand and several hundred volts is applied between the source electrode (ground) and the drain electrode in the off-state. A voltage of about minus several volts is applied to the gate electrode in the off-state. Because of the high source-drain voltage, electric field concentration is generated in the bottom portion of the opening, in particular, in a portion of the n−-type GaN drift layer near a ridge (corner in a sectional view) of the bottom portion. As a result, breakdown of a semiconductor occurs from an uneven portion or the like inevitably provided by the ridge of the bottom portion of the opening. The breakdown voltage characteristics in the off-state in the bottom portion of the opening cannot be sufficiently ensured by the above-described p-type barrier layer.
It is an object of the present invention to provide a vertical semiconductor device having an opening and including a channel and a gate electrode in the opening. In the semiconductor device, the electric field concentration near the bottom portion of the opening can be reduced in the off-state. It is another object of the present invention to provide a method for producing the semiconductor device.
A semiconductor device of the present invention is a vertical semiconductor device including a GaN-based stacked layer having an opening. In this semiconductor device, the GaN-based stacked layer includes n-type GaN-based drift layer/p-type GaN-based barrier layer/n-type GaN-based contact layer in that order to the top layer side and the opening extends from a top layer and reaches the n-type GaN-based drift layer. The semiconductor device includes a regrown layer located so as to cover a wall surface of the opening, the regrown layer including an electron drift layer and an electron supply layer; a source electrode that is in contact with the n-type GaN-based contact layer and the regrown layer; a drain electrode located so as to face the source electrode with the GaN-based stacked layer sandwiched therebetween; a gate electrode located on the regrown layer; and a semiconductor impurity adjustment region disposed in a bottom portion of the opening. The impurity adjustment region is a region that promotes a potential drop from the drain electrode side to the gate electrode side in a potential distribution in an off-state.
In the vertical semiconductor device, a high voltage of several hundred volts to one thousand and several hundred volts is applied between the source electrode disposed on one principal surface (a top surface of the GaN-based semiconductor layer) and the drain electrode that faces the source electrode with the GaN-based semiconductor layer sandwiched therebetween. The source electrode is fixed at a ground potential and a high voltage is applied to the drain electrode. The gate electrode is held at minus several volts, such as −5 V, in the off-state for the purpose of opening and closing the channel. That is, in the off-state, the gate electrode has a minimum potential. The voltage difference between the gate electrode and the drain electrode is 5 V higher than the voltage difference between the source electrode and the drain electrode.
According to the above structure, the impurity adjustment region promotes a potential drop from the drain electrode side to the gate electrode side in a potential distribution in an off-state. This decreases the potential difference in the off-state between a semiconductor located in the bottom portion of the opening and the gate electrode. Therefore, a high degree of electric field concentration that has been generated in existing semiconductor devices is not generated in the off-state. Even if a high voltage is applied between the drain electrode and the gate electrode, the electric field concentration in a semiconductor such as the n-type GaN-based drift layer in the bottom portion of the opening is reduced. In particular, the electric field concentration near a ridge (corner in a sectional view) at which the bottom portion of the opening and the wall surface of the opening intersect each other is reduced. Consequently, the breakdown of a semiconductor near the ridge does not readily occur.
Regarding the conductivity type, n-type or p-type, the concentration of an impurity is not limited and may be any concentration from low concentration to high concentration.
The impurity adjustment region can be a region formed by dividing the n-type GaN-based drift layer into a plurality of layers and setting an n-type impurity concentration in one of said plurality of layers to be lower than those in other layers.
In the potential distribution in the off-state in a region from the drain electrode to the gate electrode, a voltage drop is promoted to a greater degree in a region in which the n-type impurity concentration is low than in a region in which the n-type impurity concentration is high. As a result, the potential difference in the off-state between the semiconductor located in the bottom portion of the opening and the gate electrode can be decreased. Furthermore, an increase in on-resistance can be suppressed by disposing a region in which the n-type impurity concentration is low at a position at which electron flow is expanded from the opening toward the drain electrode, that is, at a position closer to the drain electrode.
The n-type GaN-based drift layer can be divided into a second n-type drift layer that forms the bottom portion of the opening and a first n-type drift layer located on the drain electrode side of the second n-type drift layer, and an n-type impurity concentration in the second n-type drift layer can be set to be lower than that in the first n-type drift layer.
By setting the n-type impurity concentration in the second n-type drift layer located closer to the bottom portion of the opening to be low, the voltage drop in the second n-type drift layer is promoted, which can decrease the potential difference between the semiconductor in the bottom portion of the opening and the gate electrode. Consequently, the electric field concentration near the bottom portion of the opening and near the edge (corner or ridge) of the bottom portion is reduced.
The impurity adjustment region can be a bottom p-type region disposed in the bottom portion of the opening so as not to obstruct flow of electrons from the regrown layer. A pn junction can be formed between the bottom p-type region and the n-type GaN-based drift layer located below the bottom p-type region.
According to this, the potential difference between the gate electrode and the semiconductor located above the bottom p-type region can be decreased due to the voltage drop caused by a potential barrier formed in the pn junction and the voltage drop in a depletion layer formed in the pn junction. As a result, the electric field concentration near the bottom portion of the opening, in particular, near the corner can be reduced, which can prevent the breakdown of a semiconductor.
The bottom p-type region can be any one of (1) a plate-shaped bottom region having a plate-like shape and located below the regrown layer that covers the bottom portion of the opening, (2) a ring-shaped bottom region located below the regrown layer that covers the bottom portion of the opening and only at an edge of the bottom portion, and (3) a regrown layer bottom region formed by doping the regrown layer that covers the bottom portion of the opening with a p-type impurity.
According to this, by selecting a suitable bottom p-type region among the above bottom p-type regions in accordance with the usage of the semiconductor device in consideration of on-resistance or the like, the electric field concentration in the bottom portion of the opening, in particular, at the corner can be reduced while at the same time other characteristics can be satisfied.
The plate-like shape and ring shape may have any sectional shape, such as a disc-like shape and an annular shape or an angular plate-like shape and an angular ring shape.
In a method for producing a semiconductor of the present invention, a vertical semiconductor device including a GaN-based stacked layer having an opening is produced. The production method includes a step of forming a GaN-based stacked layer including n-type GaN-based drift layer/p-type GaN-based barrier layer/n-type GaN-based contact layer in that order to the top layer side; a step of forming an opening that extends from the n-type GaN-based contact layer and reaches the n-type GaN-based drift layer; and a step of forming a regrown layer so as to cover a wall surface and a bottom portion of the opening, the regrown layer including an electron drift layer and an electron supply layer. In the step of forming the GaN-based stacked layer, the n-type GaN-based drift layer is formed by successively growing a plurality of layers, and an n-type impurity concentration in one of said plurality of layers is set to be lower than those in other layers.
According to this method, a semiconductor device in which electric field concentration in the bottom portion of the opening is reduced can be produced in a simple manner using existing production equipment only by making a minor change in the process. The reason why the electric field concentration in the bottom portion of the opening is reduced is that, in the potential distribution in the off-state, a potential drop in an n-type region having a low n-type impurity concentration is large.
In the step of forming the GaN-based stacked layer, when the n-type GaN-based drift layer is grown, a first n-type drift layer is grown and then a second n-type drift layer is grown on the first n-type drift layer. An n-type impurity concentration in the second n-type drift layer can be set to be lower than that in the first n-type drift layer.
According to this, the voltage drop in the off-state in the second GaN drift layer can be increased by setting the n-type impurity concentration in the second GaN drift layer that forms the bottom portion of the opening to be low. Thus, the electric field concentration in the bottom portion of the opening, in particular, at the corner can be reduced.
In another method for producing a semiconductor device of the present invention, a vertical semiconductor device including a GaN-based stacked layer having an opening is produced. The production method includes a step of forming a GaN-based stacked layer including n-type GaN-based drift layer/p-type GaN-based barrier layer/n-type GaN-based contact layer in that order to the top layer side; a step of forming an opening that extends from the n-type GaN-based contact layer and reaches the n-type GaN-based drift layer; a step of forming a regrown layer so as to cover a wall surface and a bottom portion of the opening, the regrown layer including an electron drift layer and an electron supply layer; and a step of forming a resist pattern that covers a portion other than a bottom portion of the regrown layer and performing ion implantation with a p-type impurity to convert the bottom portion of the regrown layer into a p-type bottom portion.
According to this method, a semiconductor device in which electric field concentration in the bottom portion of the opening can be reduced can be produced by making a minor change in existing methods for producing a semiconductor device in which a channel is formed of two-dimensional electron gas in the opening. In other words, the electric field concentration can be reduced by forming the regrown layer bottom region obtained by converting the regrown layer in the bottom portion of the opening into a p-type regrown layer.
Before the step of forming the regrown layer and after the opening is formed, a resist pattern that covers a portion other than the bottom portion of the opening is formed and then ion implantation with a p-type impurity is performed in the bottom portion of the opening to form a bottom p-type region, or the bottom portion of the opening is removed by etching and embedded growth of a p-type layer is performed in the bottom portion to form a bottom p-type region; then the regrown layer is formed; and the following step of performing ion implantation with a p-type impurity is not conducted.
According to this method, the p-type region can be relatively easily formed in the bottom portion of the opening below the regrown layer. The shape of the p-type region may be selected from a plate-like shape and a ring shape in accordance with, for example, the usage of the semiconductor device.
According to the semiconductor device of the present invention, in a vertical semiconductor device having an opening and including a channel and a gate electrode in the opening, the electric field concentration in the off-state in the bottom portion of the opening can be reduced.
1 GaN substrate
4 n−-type GaN drift layer
4
a first GaN drift layer
4
b second GaN drift layer
4
c third GaN drift layer
6 p-type GaN barrier layer
7 n+-type GaN contact layer
9 insulating layer
10 semiconductor device (vertical GaN-based FET)
12 gate wiring line
13 gate pad
15 GaN-based stacked layer
22 GaN electron drift layer
26 AlGaN electron supply layer
27 regrown layer
28 opening
28
a wall surface of opening
28
b bottom portion of opening
31 bottom p-type region (plate-shaped p-type region, ring-shaped p-type region, or regrown layer p-type region)
D drain electrode
G gate electrode
K ridge or corner of opening
M1 resist pattern
S source electrode
The n−-type GaN drift layer 4 (first and second GaN drift layers 4a and 4b)/p-type GaN barrier layer 6/n+-type GaN contact layer 7 is successively formed to constitute a GaN-based stacked layer 15. A buffer layer composed of an AlGaN layer or GaN layer may be inserted between the GaN substrate 1 and the n−-type GaN drift layer 4 depending on the type of the GaN substrate 1.
The GaN substrate 1 may be a so-called monolithic, thick GaN substrate or a substrate including a GaN layer that is in ohmic contact with a support substrate. In addition, by forming a GaN layer on a GaN substrate or the like during the growth of a GaN-based stacked layer and then removing a portion having a certain thickness corresponding to the thickness of the GaN substrate or the like, only a thin GaN layer may be left as a base in the form of products. The GaN substrate, the substrate including a GaN layer that is in ohmic contact with a support substrate, and the thin GaN layer left as a base in the form of products may be simply referred to as a GaN substrate.
The thin GaN layer left as a base may be a conductive or nonconductive layer and a drain electrode can be disposed on the top or bottom surface of the thin GaN layer depending on the production process and the structure of products. In the case where the GaN substrate, the support substrate, or the like is left in a product, the support substrate or the substrate may be a conductive or nonconductive substrate. When the support substrate or the substrate is a conductive substrate, the drain electrode can be disposed directly on the bottom (lower) surface or top (upper) surface of the support substrate or the substrate. When the support substrate or the substrate is a nonconductive substrate, the drain electrode can be disposed above the nonconductive substrate and on a conductive layer located on the lower layer side in the semiconductor layers.
In this embodiment, the p-type GaN barrier layer 6 is used as the p-type GaN-based barrier layer, but any layer composed of a p-type GaN-based semiconductor, such as a p-type AlGaN layer, may be used.
Regarding other layers constituting the stacked layer 15, other GaN-based semiconductor layers may be used instead of the GaN layers described above, if necessary.
In the GaN-based stacked layer 15, an opening 28 is formed so as to penetrate from the n+-type GaN contact layer 7 to the p-type GaN barrier layer 6 and reach the n−-type GaN drift layer 4. The opening 28 is defined by a wall surface (side surface) 28a and the bottom portion 28b. A regrown layer 27 is epitaxially grown so as to cover the wall surface 28a and bottom portion 28b of the opening 28 and the top layer (n+-type GaN contact layer 7) of the GaN-based stacked layer 15. The regrown layer 27 is constituted by an insulating GaN (i-type GaN) electron drift layer 22 and an AlGaN electron supply layer 26. An intermediate layer composed of AlN or the like may be inserted between the i-type GaN electron drift layer 22 and the AlGaN electron supply layer 26. A source electrode S is located on the GaN-based stacked layer 15 so as to be electrically connected to the regrown layer 27, the n+-type contact layer 7, and the p-type GaN barrier layer 6. In
An insulating layer 9 is located below a gate electrode G so as to cover the regrown layer 27. The insulating layer 9 is disposed in order to reduce a gate leak current generated when positive voltage is applied to the gate electrode, which allows high-current operation. Since the threshold voltage can be further shifted in a positive direction, normally-off is easily achieved. Note that the insulating layer 9 is not necessarily disposed.
In the on-state, in the regrown layer 27, two-dimensional electron gas (2DEG) is generated in the i-type GaN electron drift layer 22 at a position near the interface between the i-type GaN electron drift layer 22 and the AlGaN electron supply layer 26. Such two-dimensional electron gas is generated in the i-type GaN electron drift layer 22 at a position near the interface between the i-type GaN electron drift layer 22 and the AlGaN electron supply layer due to, for example, spontaneous polarization or piezoelectric polarization caused by difference in lattice constant. Electrons flow from the source electrode S to the drain electrode D through the two-dimensional electron gas and the n−-type GaN drift layer 4. Since the i-type GaN electron drift layer 22 and the AlGaN electron supply layer 26 in the regrown layer 27 are successively grown in the same growth chamber, the density of impurity level or the like at the interface can be reduced to a low value. Therefore, a high current (per unit area) can be caused to flow with low on-resistance while having a structure in which a high current is caused to flow in a thickness direction by forming the opening 28.
As described above, in the off-state, a high voltage of several hundred volts to one thousand and several hundred volts is applied between the source electrode S held at a ground potential and the drain electrode D. The gate electrode is held at minus several volts, such as −5 V, in the off-state for the purpose of opening and closing the channel. In the off-state, the gate electrode has a minimum potential.
In the case where the n−-type GaN drift layer 4 has a single layer structure as in existing vertical semiconductor devices, the n-type impurity concentration needs to be kept at a certain concentration to achieve low on-resistance. Therefore, in the potential distribution in the off-state in a region from the drain electrode D to the bottom portion of the opening 28, a voltage drop in the n−-type GaN drift layer 4 is not so large. As a result, a large potential difference is held between the gate electrode and the semiconductor 4 near the bottom portion of the opening, which generates high electric field concentration at the semiconductor near the bottom portion 28b of the opening, in particular, at a corner K.
In contrast, in the semiconductor device 10 of this embodiment, the n−-type GaN drift layer 4 is divided into two layers, and the n-type impurity concentration n2 in the second GaN drift layer 4b that forms the bottom portion 28b of the opening is set to be lower than the n-type impurity concentration n1 in the first GaN drift layer 4a located on the substrate side as described above. The n-type impurity concentrations n1 and n2 both fall under the category of n−-type (low concentration) indicated by the n−-type GaN drift layer 4. In particular, the n-type impurity concentration n2 in the second GaN drift layer 4b is set to be lower than the n-type impurity concentration n1 in the first GaN drift layer 4a. As a result, the voltage drop in the second GaN drift layer 4b becomes large in the potential distribution in the off-state. The specific n-type impurity concentrations and thicknesses of the first and second GaN drift layers 4a and 4b can be set in accordance with, for example, the required on-resistance.
The n-type impurity concentration n2 in the second GaN drift layer 4b may be, for example, 1×1014 (1E14) cm−3 or more and 5×1016 (5E16) cm−3 or less and the thickness of the second GaN drift layer 4b may be, for example, 0.1 μm or more and 0.3 μm or less. The n-type impurity concentration n1 in the first GaN drift layer 4a may be, for example, 5×10 14 (5E14) cm−3 or more and 5×1017 (5E17) cm−3 or less and the thickness of the first GaN drift layer 4a may be, for example, 0.5 μm or more and 7 μm or less. The thickness of the second GaN drift layer 4b may be smaller than that of the first GaN drift layer 4a for the purpose of maintaining low on-resistance.
The p-type impurity concentration in the p-type GaN barrier layer 6 may be about 1×1017 (1E17) cm−3 to 1×1019 (1E19) cm−3. The p-type impurity may be an impurity, such as Mg, that forms an acceptor in a GaN-based semiconductor. The thickness of the p-type GaN barrier layer 6 is dependent on, for example, the thickness of the n−-type GaN drift layer, and thus the range of the thickness cannot be determined in a general manner. However, the typical thickness often used in many devices is about 0.3 μm to 1 μm. If the thickness is less than 0.3 μm, breakdown voltage characteristics and pinch-off characteristics cannot be sufficiently produced and thus 0.3 μm may be set as the lower limit of thickness. If the p-type GaN barrier layer 6 having a thickness of about 0.3 μm to 1 μm has an excessively high Mg content, straight movement toward the end face of the p-type GaN barrier layer 6 occurs, which adversely affects the channel (increases the on-resistance). The reverse voltage characteristics (breakdown voltage characteristics) at a pn junction between the p-type GaN barrier layer 6 and the n−-type GaN drift layer during channel interruption (off-state) are also degraded.
The thickness of the n+-type GaN contact layer 7 may be about 0.1 μm to 0.6 μm. The length of the n+-type GaN contact layer 7 may be 0.5 μm or more and 5 μm or less.
The perimeter of openings per unit area can also be increased by densely arranging elongated openings instead of employing the hexagonal honey-comb structure. Consequently, the current density can be improved.
A method for producing the semiconductor device 10 according to this embodiment will be described. As shown in
The formation of the above layers may be performed by, for example, metal-organic chemical vapor deposition (MOCVD). By performing growth using MOCVD, a stacked layer 15 having good crystallinity can be formed. In the case where the GaN substrate 1 is formed by growing a gallium nitride film on a conductive substrate using MOCVD, trimethylgallium is used as a gallium raw material. High-purity ammonia is used as a nitrogen raw material. Purified hydrogen is used as a carrier gas. The purity of the high-purity ammonia is 99.999% or more and the purity of the purified hydrogen is 99.999995% or more. A hydrogen-based silane may be used as a Si raw material for an n-type dopant (donor) and cyclopentadienyl magnesium may be used as a Mg raw material for a p-type dopant (acceptor).
A conductive GaN substrate having a diameter of two inches is used as the conductive substrate. The substrate is cleaned at 1030° C. at 100 Torr in an atmosphere of ammonia and hydrogen. Subsequently, the temperature is increased to 1050° C. and a gallium nitride layer is grown at 200 Torr at a V/III ratio of 1500, which is the ratio of the nitrogen raw material and gallium raw material. The formation method of the GaN layer on the conductive substrate is employed for not only the formation of the GaN substrate 1 but also the growth of the stacked layer 15 on the GaN substrate 1.
By employing the above-described method, the first GaN drift layer 4a/second GaN drift layer 4b/p-type GaN barrier layer 6/n+-type GaN contact layer 7 is grown on the GaN substrate 1 in that order.
Subsequently, as shown in
Subsequently, the resist pattern Ml is removed and the wafer is cleaned. The wafer is inserted into an MOCVD apparatus and a regrown layer 27 including an electron drift layer 22 composed of undoped GaN and an electron supply layer 26 composed of undoped AlGaN is grown as shown in
Subsequently, the wafer is taken out of the MOCVD apparatus. An insulating layer 9 is grown as shown in
The plate-shaped bottom p-type region 31 is in contact with the regrown layer 27 on the opening 28 side and forms a pn junction with the n−-type GaN drift layer 4 on the substrate 1 side. At the pn junction, a depletion layer is formed under the application of reverse bias voltage in the off-state and a voltage drop can be provided at the pn junction. Furthermore, a potential barrier formed at the pn junction also contributes to the voltage drop with certainty under the application of reverse bias voltage, which decreases the electric potential in a portion of the plate-shaped bottom p-type region 31 on the substrate 1 side. Consequently, the potential difference between the bottom portion 28b of the opening and the gate electrode G decreases and thus the electric field concentration in the bottom portion 28b of the opening is reduced. The electric field concentration at the corner K is also reduced with certainty.
A method for producing the semiconductor device shown in
The process (i) or (ii) of (S3) is a production process unique to the semiconductor device 10 of this embodiment. After that, the same production process as that in the first embodiment is performed, that is, a step of forming a regrown layer is performed.
An effect of reducing the electric field concentration in the bottom portion of the opening using the ring-shaped bottom p-type region 31 is produced with the same mechanism as that of the bottom p-type region disposed in the semiconductor device in
In short, in the semiconductor device 10 in
A method for producing the semiconductor device 10 in
Points to keep in mind are as follows. The regrown layer bottom region 31 in the modification 2 is obtained by converting the regrown layer into a p-type regrown layer. If the regrown layer bottom region 31 is formed in the entire bottom portion 28b, the regrown layer bottom region 31 obstructs the flow of electrons. Therefore, the diameter of the regrown layer bottom region 31 is preferably set to be smaller than that of the bottom portion 28b of the opening in order to maintain low on-resistance.
The production method has the following difference, which is not significant difference. The bottom p-type regions 31 in the semiconductor devices 10 in
Regarding the semiconductor device of the first embodiment shown in
In the test specimens (A1) to (A3), the n-type impurity concentration in the second GaN drift layer 4b is lower than the n-type impurity concentration in the first GaN drift layer 4a. The test specimens (A1) to (A3) are treated as Invention Examples A1 to A3. In a strict sense, the test specimen (A3) having an n-type impurity concentration of 1×1016 (1E16) cm−3 cannot be treated as Invention Example. However, the test specimen (A3) was treated as Invention Example by interpreting the n-type impurity concentration in the second GaN drift layer 4b as a concentration only slightly lower than the n-type impurity concentration in the first GaN drift layer 4a. Other test specimens are treated as Comparative Examples (B1) and (B2). In Comparative Examples B1 and B2, the n-type impurity concentration in the second GaN drift layer 4b is higher than that in the first GaN drift layer 4a.
The simulation was evaluated by determining the electric field strength (arbitrary unit) at the corner K of the bottom portion 28b of the opening. The electric field strength of Invention Example A1 is assumed to be 5 (referred to as a reference value), and the electric field strengths of other test specimens are shown as relative values.
Referring to
It was confirmed from the simulation results that the electric field concentration in the bottom portion 28b of the opening could be reduced by decreasing the n-type impurity concentration in the second GaN drift layer 4b. Accordingly, the n−-type GaN drift layer 4 is divided into two layers and the n-type impurity concentration in the second GaN drift layer 4b that forms the bottom portion 28b of the opening is set to be lower than the n-type impurity concentration in the first GaN drift layer 4a located below the second GaN drift layer 4b, whereby the electric field concentration in the bottom portion 28b of the opening can be reduced.
The structures disclosed in the above embodiments of the present invention are mere examples and the scope of the present invention is not limited to these embodiments. The scope of the present invention is defined by the appended claims, and all changes that fall within the scope of the claims and the equivalence thereof are therefore embraced by the claims.
According to the semiconductor device or the like of the present invention, in a vertical semiconductor device having an opening, the breakdown voltage characteristics in the off-state can be improved by disposing an impurity adjustment layer that promotes a voltage drop from the drain electrode side to the gate electrode side in the potential distribution in the off-state. The breakdown voltage characteristics in the off-state can be stably improved by employing a simple structure in which, for example, the impurity adjustment layer is formed by dividing a drift layer into two layers and setting the n-type impurity concentration of a drift layer that forms a bottom portion of an opening to be low.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-247719 | Nov 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/073826 | 10/17/2011 | WO | 00 | 5/3/2013 |
