JP2007305808A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device wherein the increase of its withstanding voltage and the improvement of its ESD resistance can be made compatible with each other. <P>SOLUTION: The semiconductor device 100 has a first conductive first semiconductor layer 1a, a second conductive second semiconductor layer 2 formed to be buried in an SOI layer 1, a second conductive first base region 7 formed in the surface layer of the first semiconductor layer 1a, a second conductive second base region 7a included in the first base region 7 whose end reaches the second semiconductor layer 2, a first conductive source region 8 formed in the surface layer of the first base region 7, a first conductive first drain region 6a intersecting the first base region 7 whose end reaches the second semiconductor layer 2, a first conductive second drain region 6 formed in the surface layer of the first drain region 6a and disposed in the substrate surface of the semiconductor device to be separated from the first base region 7, and a first conductive third drain region 5 formed in the surface layer of the second drain region 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor device having a lateral MOS (Lateral Diffused Metal Oxide Semiconductor) structure in which a source region and a drain region are arranged in a lateral direction of a semiconductor substrate.

  For example, Japanese Laid-Open Patent Publication No. 2001-352070 (Patent Document 1) discloses a lateral MOS structure semiconductor device in which a source region and a drain region are arranged in a lateral direction of a semiconductor substrate.

  FIG. 11 is a schematic cross-sectional view of a conventional semiconductor device 90 having the same cross-sectional structure as the LDMOS disclosed in Patent Document 1. In FIG. 12 to 15 are examples of simulation results of the semiconductor device 90 shown in FIG. FIG. 12 is a diagram showing current-voltage (Id-Vd) characteristics with respect to a surge or the like when the gate voltage Vg is 0V. 13A and 13B are diagrams showing potential distributions in the SOI layer 1 of the semiconductor device 90. FIGS. 13A and 13B show points A (Id = 10A) and B (Id = 50A) in FIG. 12, respectively. It corresponds to the state. FIG. 14 is a diagram showing an electric field intensity distribution in the SOI layer 1 of the semiconductor device 90, and FIG. 15 is a diagram showing a depletion layer formation state in the SOI layer 1 of the semiconductor device 90. 14 and 15, (a) and (b) correspond to the states of point A (Id = 10A) and point B (Id = 50A) in FIG. 12, respectively.

  In the semiconductor device 90 shown in FIG. 11, the first base region 7 of P conductivity type (p) is formed of the first semiconductor layer 1 a of N conductivity type (n−) which is the main body of the SOI layer 1 on the buried oxide film 3. It is formed in the surface layer part. In the semiconductor device 90, an N conductivity type third semiconductor layer 1b having a higher concentration (n +) than the first semiconductor layer 1a is disposed between the buried oxide film 3 and the first semiconductor layer 1a in the substrate cross section.

  On the source side of the semiconductor device 90, a P-conductivity type second base region 7a having a higher concentration (p) than the first base region 7 has a tip formed deeper than the first base region 7 in the cross section of the substrate. Arranged in the surface layer portion of the first semiconductor layer 1 a so as to be included in the first base region 7. An N conductivity type (n +) source region 8 is formed in the surface layer portion of the first base region 7. The source region 8 and a P-conductivity type (p +) region 9 disposed so as to be included in the second base region 7a adjacent thereto are contact regions for the source electrode (not shown). .

  On the drain side of the semiconductor device 90, an N conductivity type second drain region 6 having a higher concentration than the first semiconductor layer 1a is disposed so as to be separated from the first base region 7 within the substrate surface. A third drain region 5 of N conductivity type and higher concentration than the second drain region 6 is formed in the surface layer portion of the second drain region 6. The second drain region 6 is formed so as to increase in concentration as it approaches the third drain region 5. The third drain region 5 is a contact region for a drain electrode (not shown).

In the semiconductor device 90 of FIG. 11, the first base region 7 located between the source region 8 and the third drain region 5 is used as a channel region. A portion indicated by reference numeral 10 formed on the channel region is a gate insulating film, and a gate electrode 11 is formed on the gate insulating film 10. In addition, the part of the code | symbol 4 is a LOCOS oxide film.
JP 2001-352070 A

  As shown in FIG. 12, in the current-voltage (Id-Vd) characteristics of the semiconductor device 90, there is a region where the slope of the current Id is negative with respect to the voltage Vd. In the current-voltage characteristics of FIG. 12, the voltage and current at the inflection point S where the slope changes from positive to negative are referred to as a snapback generation voltage Vs and a snapback generation current Is, respectively. A semiconductor device having a higher snapback generation voltage Vs and a snapback generation current Is can be said to be a semiconductor device having a higher ESD tolerance.

  In the semiconductor device 90 of FIG. 11, an electric field such as ESD (Electro Static Discharge) is alleviated by the second drain region 6 that becomes higher in concentration as it approaches the third drain region 5 disposed on the drain side. The ESD tolerance can be improved as compared with the case where 6 is not formed. On the other hand, in order to increase the breakdown voltage in the semiconductor device 90 of FIG. 11, it is necessary to increase the distance between the first base region 7 and the second drain region 6. However, as the distance between the first base region 7 and the second drain region 6 is increased, the on-resistance of the semiconductor device 90 increases. Further, in order to increase the breakdown voltage and improve the ESD tolerance by the second drain region 6, it is necessary to lower the impurity concentration of the first semiconductor layer 1a and the second drain region 6 than in the case of the low breakdown voltage. This also increases the on-resistance of the semiconductor device 90. Therefore, in the structure of the conventional semiconductor device 90 shown in FIG. 11, it is difficult to achieve both high breakdown voltage and improved ESD tolerance.

  Accordingly, an object of the present invention is to provide a semiconductor device having a lateral MOS structure in which a source region and a drain region are arranged in a lateral direction of a semiconductor substrate, and capable of achieving both high breakdown voltage and improvement in ESD resistance. It is said.

  The semiconductor device according to claim 1 is embedded in an SOI substrate having a buried oxide film, a first semiconductor layer of a first conductivity type that is a main body of an SOI layer on the buried oxide film, and embedded in the SOI layer. The second conductivity type second semiconductor layer, the second conductivity type first base region formed in the surface layer portion of the first semiconductor layer, and the surface layer portion of the first semiconductor layer within the substrate surface A second base region of a second conductivity type that is disposed so as to be included in the first base region and formed so that a tip thereof reaches the second semiconductor layer in a cross section of the substrate; and a higher concentration than the first base region; The first conductivity type source region formed in the surface layer portion of the first base region and the surface layer portion of the first semiconductor layer are disposed so as to intersect the first base region within the substrate plane, The tip reaches the second semiconductor layer Formed in the first conductivity type and the first drain region having a higher concentration than the first semiconductor layer, and in the surface layer portion of the first drain region, and separated from the first base region within the substrate surface A first conductivity type higher concentration than the first drain region, and a first conductivity type higher than the second drain region formed in the surface layer portion of the second drain region. A gate insulating film formed on the channel region, and a gate insulating film formed on the channel region, the third drain region having a concentration, and the first base region located between the source region and the third drain region An interface between the first drain region and the second semiconductor layer, comprising: a gate electrode formed thereon; a source electrode connected to the source region; and a drain electrode connected to the third drain region. But In the state projected onto the substrate surface, the second drain region is included inside and formed so as to cross the first base region, and the concentration of the second drain region increases as it approaches the third drain region. It is characterized by being formed as follows.

In the semiconductor device, the second conductivity type second semiconductor layer embedded in the SOI layer and the first base region in the substrate surface are arranged so as to intersect with the second semiconductor layer. The RESURF structure is formed with the first drain region of the first conductivity type formed so as to reach. By appropriately setting the distance between the first base region and the second drain region in the first drain region in this RESURF structure, a semiconductor device with low on-resistance and high breakdown voltage can be obtained.

  In addition, a second drain region is disposed around the third drain region. The second drain region is formed so as to have a higher concentration than the first drain region and a higher concentration toward the third drain region. By using this second drain region, an electric field such as ESD can be relaxed, and the ESD tolerance can be improved as compared with the case where the second drain region is not formed.

  As described above, the semiconductor device is a semiconductor device having a lateral MOS structure in which the source region and the drain region are arranged in the lateral direction of the semiconductor substrate, and is a semiconductor that achieves both high breakdown voltage and improved ESD resistance. It can be a device.

  The ESD tolerance in the semiconductor device is defined as a first conductivity type source region / second conductivity type first base region / first conductivity type third drain region (second drain region) formed in the lateral direction of the substrate cross section. , A first bipolar region).

  Therefore, in the semiconductor device, as described in claim 2, the shortest distance in the channel region direction between the end surface of the second drain region and the end surface of the third drain region is projected onto the substrate surface. In this case, it is preferably set to 1 μm or more and 6 μm or less.

  As a result, the operation of the parasitic bipolar transistor formed in the lateral direction of the substrate cross-section described above is suppressed, and the snap-back generation current, which is a measure of the ESD resistance, is limited to a sufficiently large value to ensure a high ESD resistance. Can do.

  According to a third aspect of the present invention, in the semiconductor device, the first semiconductor layer may be left between the buried oxide film and the second semiconductor layer in a substrate cross section.

  According to a fourth aspect of the present invention, in the semiconductor device, the third conductivity layer of the first conductivity type and higher in concentration than the first semiconductor layer is disposed in contact with the buried oxide film in the substrate cross section. Also good.

  In the above semiconductor device, when the SOI layer (first semiconductor layer) is of the first conductivity type, generally, when the second conductivity type second semiconductor layer is embedded and formed, the first conductivity type in the vertical direction of the substrate cross section. A parasitic bipolar transistor comprising a third drain region (second drain region, first drain region) / second conductivity type second semiconductor layer / first conductivity type first semiconductor layer (third semiconductor layer) is formed. The

  Therefore, as described in claim 5, in the semiconductor device, the SOI layer (first semiconductor layer) is set to the second conductivity type so that the parasitic bipolar transistor is not formed, and the adverse effect thereof is eliminated. can do. In this case, the semiconductor device is configured such that the second semiconductor layer and the first base region are formed at a higher concentration than the first semiconductor layer.

  According to a sixth aspect of the present invention, the second semiconductor layer may be formed directly on the buried oxide film in contact with the buried oxide film.

  In this case, as described in claim 7, the fourth conductivity layer of the second conductivity type and higher in concentration than the second semiconductor layer is interposed between the buried oxide film and the second semiconductor layer in the substrate cross section. It may be arranged.

  In the semiconductor device, for example, as described in claim 8, the first conductivity type is an N conductivity type, and the second conductivity type is a P conductivity type.

  In the semiconductor device, as described in claim 9, the source region and the first drain region, the second drain region, and the third drain region may be arranged in a stripe pattern in the substrate plane. . According to a tenth aspect of the present invention, the source region, the first drain region, the second drain region, and the third drain region may be arranged in a checkered lattice pattern in the substrate surface.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of a semiconductor device 100 as an example of the semiconductor device of the present invention. In the semiconductor device 100 of FIG. 1, the same reference numerals are given to the same parts as those of the semiconductor device 90 of FIG. 2 to 5 are examples of simulation results of the semiconductor device 100 shown in FIG. FIG. 2 is a diagram showing a current-voltage (Id-Vd) characteristic against a surge or the like when the gate voltage Vg is 0V. 3A and 3B are diagrams showing potential distributions in the SOI layer 1 of the semiconductor device 100. FIGS. 3A and 3B show points A (Id = 10A) and B (Id = 50A) in FIG. 2, respectively. It corresponds to the state. FIG. 4 is a diagram showing an electric field intensity distribution in the SOI layer 1 of the semiconductor device 100, and FIG. 5 is a diagram showing a formation state of a depletion layer in the SOI layer 1 of the semiconductor device 100. 4 and 5, (a) and (b) correspond to the states of point A (Id = 10A) and point B (Id = 50A) in FIG. 2, respectively.

  A semiconductor device 100 shown in FIG. 1 is a semiconductor device having a lateral MOS (Lateral Diffused Metal Oxide Semiconductor) structure in which a source region 8 and a drain region 5 are arranged in a lateral direction of a semiconductor substrate. For the formation of the semiconductor device 100, an SOI substrate having a buried oxide film 3 is used. The main part of the SOI layer 1 on the buried oxide film 3 is an N conductivity type (n−) first semiconductor layer 1 a, and in the SOI layer 1, a P conductivity type (p) second semiconductor layer 2. Is embedded. In the semiconductor device 100, the third semiconductor layer 1b of N conductivity type and having a higher concentration (n +) than the first semiconductor layer 1a is disposed in contact with the buried oxide film 3 in the cross section of the substrate. 1a is disposed so as to remain between the buried oxide film 3 and the second semiconductor layer 2 in the cross section of the substrate.

  In the semiconductor device 100, the first base region 7 of P conductivity type (p) is formed in the surface layer portion of the first semiconductor layer 1a.

  On the source side of the semiconductor device 100, the second base region 7 a having a P conductivity type and having a higher concentration (p) than the first base region 7 is formed on the surface of the first semiconductor layer 1 a within the substrate surface. It is arranged so as to be included in the substrate, and is formed so that the tip thereof reaches the second semiconductor layer 2 in the substrate cross section. An N conductivity type (n +) source region 8 is formed in the surface layer portion of the first base region 7. The source region 8 and a P-conductivity type (p +) region 9 disposed so as to be included in the second base region 7a adjacent thereto are contact regions for the source electrode (not shown). .

  On the drain side of the semiconductor device 100, a first drain region 6a having an N conductivity type and a higher concentration (n) than the first semiconductor layer 1a is formed on the surface of the first semiconductor layer 1a within the substrate surface. And the tip of the substrate cross section is formed so as to reach the second semiconductor layer 2. A second drain region 6 of N conductivity type and having a higher concentration (n) than the first drain region 6a is formed in the surface layer portion of the first drain region 6a and is separated from the first base region 7 within the substrate surface. Is arranged. Further, a third drain region 5 of N conductivity type and having a higher concentration (n +) than the second drain region 6 is formed in the surface layer portion of the second drain region 6.

  In the semiconductor device 100, the first base region 7 located between the source region 8 and the third drain region 5 is used as a channel region, and a gate insulating film 10 is formed on the channel region. A gate electrode 11 is formed on the gate insulating film 10. The portion 4 of the semiconductor device 100 is LOCOS. Although not shown, the semiconductor device 100 includes a source electrode connected to the source region 8 (and the region 9) and a drain electrode connected to the third drain region 5.

  In the semiconductor device 100 of FIG. 1, the interface between the first drain region 6 a and the second semiconductor layer 2 includes the second drain region 6 inside and intersects the first base region 7 in a projected state on the substrate surface. Is formed. Further, the second drain region 6 is formed so as to increase in concentration as it approaches the third drain region 5.

  In the semiconductor device 100 of FIG. 1, the P-conductivity type second semiconductor layer 2 embedded in the SOI layer 1 and the first base region 7 are arranged so as to intersect the first base region 7 in the substrate surface. A RESURF structure is formed with the first drain region 6 a of N conductivity type formed so as to reach the second semiconductor layer 2. In this RESURF structure, a low on-resistance and high breakdown voltage semiconductor is set by appropriately setting the interval w between the first base region 7 and the second drain region 6 in the first drain region 6a indicated by the double-ended arrows in FIG. It can be a device.

  Further, around the third drain region 5, a second drain region 6 is disposed which has a higher concentration than the first drain region 6 a and a higher concentration as it approaches the third drain region 5. . By using the second drain region 6, an electric field such as ESD can be relaxed, and the ESD tolerance can be improved as compared with the case where the second drain region 6 is not formed.

  As described above, the semiconductor device 100 shown in FIG. 1 is a lateral MOS structure semiconductor device in which the source region 8 and the drain region 5 are arranged in the lateral direction of the semiconductor substrate. It is a semiconductor device that achieves both improvements.

  Next, the semiconductor device 100 of FIG. 1 will be described more specifically.

  The ESD tolerance in the semiconductor device 100 of FIG. 1 is the N conductivity type source region 8 / P conductivity type first base region 7 / N conductivity type third drain region 5 (the first conductivity region) formed in the lateral direction of the substrate cross section. This relates to a parasitic bipolar transistor comprising two drain regions 6 and a first drain region 6a).

FIG. 6 shows the shortest distance w in the channel region direction between the end face of the second drain region 6 and the end face of the third drain region 5 shown in FIG. It is a figure which shows the relationship of the snapback generation | occurrence | production current Is. From the result of FIG. 6, it can be seen that the snapback generation current Is takes a maximum value with respect to the interval w. Therefore, in the semiconductor device 100 of FIG. 1, the shortest distance w in the channel region direction between the end surface of the second drain region 6 and the end surface of the third drain region 5 is 1 μm or more and 6 μm or less in the projected state on the substrate surface. It is preferable to set to. As a result, the operation of the parasitic bipolar transistor formed in the lateral direction of the substrate cross section is suppressed, and the snapback generation current Is, which is a measure of the ESD resistance, is limited to a sufficiently large value of 15 A / mm ² or more. High ESD tolerance can be ensured.

  7 to 9 are schematic cross-sectional views of the semiconductor devices 101 to 104 as examples of another semiconductor device according to the present invention. 7 to 9, the same reference numerals are given to the same parts as those of the semiconductor device 100 of FIG. 1.

  In the semiconductor device 101 of FIG. 7, unlike the semiconductor device 100 of FIG. 1, the main part of the SOI layer 1 on the buried oxide film 3 is a first semiconductor layer 1c of P conductivity type (p−). Further, the N-conductivity (n +) third semiconductor layer 1b that is in contact with the buried oxide film 3 is also not disposed. Note that the second semiconductor layer 2 and the first base region 7 in the semiconductor device 101 are formed at a higher concentration than the first semiconductor layer 1c.

  In the case where the first semiconductor layer 1a, which is the main body of the SOI layer 1, is an N conductivity type as in the semiconductor device 100 shown in FIG. In the longitudinal direction of the cross section, a third drain region 5 of N conductivity type (second drain region 6, first drain region 6a) / second semiconductor layer of P conductivity type 2 / first semiconductor layer 1a of N conductivity type (third An NPN-type parasitic bipolar transistor composed of the semiconductor layer 1b) is formed. On the other hand, as in the semiconductor device 101 shown in FIG. 7, the first semiconductor layer 1c, which is the main body of the SOI layer 1, is made of P conductivity type so that the NPN-type parasitic bipolar transistor is not formed. Can be eliminated.

  In the semiconductor device 102 of FIG. 8A, the SOI layer 1 is thinner than the semiconductor device 100 of FIG. 1, and the second semiconductor layer 2 of P conductivity type (p) embedded in the SOI layer 1 is used. Is formed so as to contact the buried oxide film 3. Further, in the semiconductor device 103 of FIG. 8B, the second semiconductor layer 2 of P conductivity type (p) is deeply diffused by heat treatment, so that the second semiconductor is formed in the same manner as the semiconductor device 102 of FIG. The layer 2 is formed in contact with the buried oxide film 3. As described above, in the semiconductor devices 102 and 103, the second semiconductor layer 2 is formed on the buried oxide film 3 in contact with the buried oxide film 3. 8A and 8B, as in the semiconductor device 101 of FIG. 7, the N-conductivity type (n +) third semiconductor layer 1b in contact with the buried oxide film 3 is also formed. Not placed.

  In the semiconductor device 104 of FIG. 9, the fourth semiconductor layer 1 d having P conductivity type and higher concentration (p +) than the second semiconductor layer 2 is disposed between the buried oxide film 3 and the second semiconductor layer 2 in the substrate cross section. Yes. The fourth semiconductor layer 1d can be formed by, for example, partial ion implantation.

  The semiconductor devices 102 to 104 shown in FIGS. 8 and 9 are configured such that no NPN-type parasitic bipolar transistor is formed, similarly to the semiconductor device 101 of FIG.

  FIGS. 10A and 10B are schematic diagrams showing examples of arrangement patterns of source cells and drain cells in the substrate plane for the semiconductor devices 100 to 104 shown in FIGS. 1 and 7 to 9, respectively. is there. 10A and 10B, the same reference numerals are given to the same parts as those of the semiconductor devices 100 to 104 shown in FIG. 1 and FIGS. Further, the cross-sectional views of the semiconductor devices 100 to 104 shown in FIG. 1 and FIGS. 7 to 9 correspond to the cross sections taken along the alternate long and short dash line A-A in FIGS.

  In FIG. 10A, source cells (source region 8) and drain cells (first drain region 6a, second drain region 6 and third drain region 5) are arranged in stripes. In FIG. 10B, source cells (source region 8) and drain cells (first drain region 6a, second drain region 6 and third drain region 5) are arranged in a checkered lattice pattern. As described above, the arrangement pattern of the source cells and the drain cells in the substrate surface of the semiconductor devices 100 to 104 shown in FIGS. 1 and 7 to 9 may be a stripe shape or a checkered lattice shape. There may be. Further, any other repeated pattern may be used.

  As described above, each of the semiconductor devices 100 to 104 shown in FIGS. 1 and 7 to 9 is a semiconductor device having a lateral MOS structure in which the source region and the drain region are arranged in the horizontal direction of the semiconductor substrate. Thus, the semiconductor device can achieve both higher breakdown voltage and improved ESD resistance. The semiconductor devices 100 to 104 shown in FIGS. 1 and 7 to 9 are all N-channel lateral MOS structure semiconductor devices. However, the semiconductor device of the present invention is not limited to this, and may be a P-channel lateral MOS structure semiconductor device in which the conductivity types of the respective parts of the semiconductor devices 100 to 104 shown in FIGS. 1 and 7 to 9 are all reversed. The same effect can be obtained.

1 is a schematic cross-sectional view of a semiconductor device 100 as an example of the semiconductor device of the present invention. It is an example of the simulation result of the semiconductor device 100, and is a diagram showing current-voltage (Id-Vd) characteristics with respect to a surge or the like when the gate voltage Vg is 0V. FIGS. 5A and 5B are diagrams showing potential distributions in the SOI layer 1 of the semiconductor device 100, and FIGS. ing. FIGS. 3A and 3B are diagrams showing electric field intensity distributions in the SOI layer 1 of the semiconductor device 100, wherein FIGS. 2A and 2B are respectively in a state of point A (Id = 10 A) and point B (Id = 50 A) in FIG. It corresponds. FIGS. 3A and 3B are diagrams illustrating a state where a depletion layer is formed in the SOI layer 1 of the semiconductor device 100. FIGS. 2A and 2B are states at points A (Id = 10A) and B (Id = 50A) in FIG. It corresponds to. It is a figure which shows the relationship between the space | interval w between the 2nd drain region 6 end surface shown in FIG. 1, and the snap back generation | occurrence | production current Is shown in FIG. FIG. 6 is a schematic cross-sectional view of a semiconductor device 101 as another example of the semiconductor device according to the present invention. In another example of the semiconductor device according to the present invention, (a) and (b) are schematic cross-sectional views of the semiconductor devices 102 and 103, respectively. FIG. 6 is a schematic cross-sectional view of a semiconductor device 104 as another example of the semiconductor device according to the present invention. (A), (b) is a schematic diagram which shows the example of arrangement pattern of the source cell and drain cell in a substrate surface about the semiconductor devices 100-104, respectively. 10 is a schematic cross-sectional view of a conventional semiconductor device 90. FIG. It is an example of a simulation result of the semiconductor device 90, and is a diagram illustrating a current-voltage (Id-Vd) characteristic against a surge or the like when the gate voltage Vg is 0V. FIGS. 9A and 9B are diagrams illustrating potential distributions in the SOI layer 1 of the semiconductor device 90, and FIGS. ing. FIGS. 9A and 9B are diagrams showing the intensity distribution of an electric field in the SOI layer 1 of the semiconductor device 90, where FIGS. It corresponds. FIGS. 9A and 9B are diagrams showing the formation state of a depletion layer in the SOI layer 1 of the semiconductor device 90, wherein FIGS. 12A and 12B are states at points A (Id = 10A) and B (Id = 50A) in FIG. It corresponds to.

Explanation of symbols

90, 100 to 104 Semiconductor device 1 SOI layer 1a First semiconductor layer (n−)
1b Third semiconductor layer (n +)
1c 1st semiconductor layer (p-)
1d Fourth semiconductor layer (p +)
2 Second semiconductor layer (p)
3 buried oxide film 4 LOCOS
5 (Third) drain region (n +)
6 Second drain region (n)
6a First drain region (n)
7 First base region (p)
7a Second base region (p)
8 Source region (n +)
9 region (p +)
10 Gate insulating film 11 Gate electrode

Claims (10)

An SOI substrate having a buried oxide film;
A first semiconductor layer of a first conductivity type that is a main body of an SOI layer on the buried oxide film;
A second semiconductor layer of a second conductivity type embedded in the SOI layer;
A first base region of a second conductivity type formed in a surface layer portion of the first semiconductor layer;
A second conductivity type, which is disposed in the surface layer portion of the first semiconductor layer so as to be included in the first base region within the substrate surface, and is formed so that a tip thereof reaches the second semiconductor layer in the substrate cross section. And a second base region having a higher concentration than the first base region,
A source region of a first conductivity type formed in a surface layer portion of the first base region;
In the surface layer portion of the first semiconductor layer, the first conductivity type is disposed so as to intersect the first base region within the substrate surface, and is formed so that a tip thereof reaches the second semiconductor layer in the substrate cross section. A first drain region having a higher concentration than the first semiconductor layer;
A second drain region of a first conductivity type and having a higher concentration than the first drain region, which is formed in a surface layer portion of the first drain region and is spaced apart from the first base region within the substrate surface;
A third drain region of a first conductivity type and having a higher concentration than the second drain region, formed in a surface layer portion of the second drain region;
A gate insulating film formed on the channel region, the first base region located between the source region and the third drain region as a channel region;
A gate electrode formed on the gate insulating film;
A source electrode connected to the source region;
A drain electrode connected to the third drain region,
The interface between the first drain region and the second semiconductor layer is formed so as to include the second drain region inside and intersect the first base region in a projected state on the substrate surface.
2. The semiconductor device according to claim 1, wherein the second drain region is formed so that the concentration is higher as the second drain region is closer to the third drain region.   The shortest distance in the channel region direction between the end surface of the second drain region and the end surface of the third drain region is set to 1 μm or more and 6 μm or less in a projected state on the substrate surface. Item 14. The semiconductor device according to Item 1.   3. The semiconductor device according to claim 1, wherein the first semiconductor layer is left between the buried oxide film and the second semiconductor layer in a cross section of the substrate.   4. The semiconductor device according to claim 3, wherein a third semiconductor layer of the first conductivity type and having a higher concentration than the first semiconductor layer is disposed in contact with the buried oxide film in a cross section of the substrate. The first semiconductor layer is of a second conductivity type;
4. The semiconductor device according to claim 3, wherein the second semiconductor layer and the first base region are formed at a higher concentration than the first semiconductor layer.   3. The semiconductor device according to claim 1, wherein the second semiconductor layer is formed directly on the buried oxide film in contact with the buried oxide film.   The fourth semiconductor layer of the second conductivity type and having a higher concentration than the second semiconductor layer is disposed between the buried oxide film and the second semiconductor layer in a cross section of the substrate. Semiconductor device.   The semiconductor device according to claim 1, wherein the first conductivity type is an N conductivity type, and the second conductivity type is a P conductivity type.   9. The source region according to claim 1, wherein the source region, the first drain region, the second drain region, and the third drain region are arranged in a stripe shape within the substrate surface. Semiconductor device.   9. The source region according to claim 1, wherein the source region, the first drain region, the second drain region, and the third drain region are arranged in a checkered grid pattern in the substrate surface. The semiconductor device according to item.

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