Semiconductor Devices

Abstract

To provide a semiconductor device capable of suppressing a parasitic capacitance and improving a withstand voltage.SOLUTION: A semiconductor device 1A includes: a chip 2 having a first main surface 3; an n type body region 20 (first region) formed on a surface layer portion of the first main surface 3; a p type drift region 21 (second region) formed on a surface layer portion of the body region 20; a drain region 22 formed on a surface layer portion of the drift region 21; a source region 24 formed on the surface layer portion of the body region 20 at a distance from the drift region 21; and a p type floating drift region 31 (floating region) in the body region 20 at a thickness position between a bottom of the body region 20 and a bottom of the drift region 21 and being spaced apart from the bottom of the drift region 21, so as to faces the drift region 21 with a portion of the body region 20 interposed therebetween.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a semiconductor device. [Background technology]

[0002] Patent Document 1 discloses a high-voltage P-channel MOS transistor including an n-type first well diffusion layer, an n-type second well diffusion layer, a p-type third well diffusion layer, a p-type drain diffusion layer, and a p-type source diffusion layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2009 / 267144 Summary of the Invention [Problem to be solved by the invention]

[0004] An embodiment of the present invention provides a semiconductor device capable of suppressing parasitic capacitance and improving breakdown voltage. [Means for solving the problem]

[0005] One embodiment of the present invention provides a semiconductor device including: a chip having a main surface; a first region of a first conductivity type formed in a surface layer portion of the main surface; a second region of a second conductivity type formed in a surface layer portion of the first region; a drain region formed in the surface layer portion of the second region; a source region formed in the surface layer portion of the first region and spaced apart from the second region; and a floating region of a second conductivity type formed in the first region at a thickness position between a bottom of the first region and a bottom of the second region and spaced apart from the bottom of the second region, facing the second region across a portion of the first region.

[0006] The above and other objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the accompanying drawings. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a plan view showing a semiconductor device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged view of region II shown in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III shown in FIG. [Figure 4] FIG. 4 corresponds to FIG. 3 and is a cross-sectional view showing the semiconductor device according to the first embodiment together with the equipotential distribution. [Figure 5] FIG. 5 corresponds to FIG. 3 and is a cross-sectional view showing a semiconductor device according to a second embodiment together with an equipotential distribution. [Figure 6] FIG. 6 corresponds to FIG. 3 and is a cross-sectional view showing the semiconductor device according to the first embodiment together with the equipotential distribution. [Figure 7A] FIG. 7A is a cross-sectional view showing an example of a method for manufacturing the semiconductor device shown in FIG. [Figure 7B] FIG. 7B is a cross-sectional view showing a step subsequent to FIG. 7A. [Figure 7C] FIG. 7C is a cross-sectional view showing a step subsequent to FIG. 7B. [Figure 7D] FIG. 7D is a cross-sectional view showing a step subsequent to FIG. 7C. [Figure 7E] FIG. 7E is a cross-sectional view showing a step subsequent to FIG. 7D. [Figure 7F] FIG. 7F is a cross-sectional view showing a step subsequent to FIG. 7E. [Figure 7G] FIG. 7G is a cross-sectional view showing a step subsequent to FIG. 7F. [Figure 7H] FIG. 7H is a cross-sectional view showing a step subsequent to FIG. 7G. [Figure 7I] FIG. 7I is a cross-sectional view showing a step subsequent to FIG. 7H. [Figure 7J] FIG. 7J is a cross-sectional view showing a step subsequent to FIG. 7I. [Figure 7K] FIG. 7K is a cross-sectional view showing a step subsequent to FIG. 7J. [Figure 7L]FIG. 7L is a cross-sectional view showing a step subsequent to FIG. 7K. [Figure 7M] FIG. 7M is a cross-sectional view showing a step subsequent to FIG. 7L. [Figure 8] FIG. 8 corresponds to FIG. 2 and is an enlarged plan view partially showing the structure of a semiconductor device according to a second embodiment of the present invention. [Figure 9] FIG. 9 corresponds to FIG. 2 and is an enlarged plan view partially showing the structure of a semiconductor device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The accompanying drawings are schematic diagrams, are not strictly illustrated, and are not necessarily to scale. Corresponding structures among the accompanying drawings are given the same reference numerals, and duplicated descriptions are omitted or simplified. For structures whose descriptions are omitted or simplified, the descriptions given before the omission or simplification apply.

[0009] FIG. 1 is a plan view showing a semiconductor device 1A according to a first embodiment of the present invention. FIG. 2 is an enlarged view of region II shown in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III shown in FIG. 2. With reference to FIGS. 1 to 3, semiconductor device 1A includes a rectangular parallelepiped chip 2 (semiconductor chip). In this embodiment, chip 2 is made of a silicon chip. Chip 2 has a first main surface 3 on one side, a second main surface 4 on the other side, and first to fourth side surfaces 5A to 5D connecting first main surface 3 and second main surface 4.

[0010] The first main surface 3 and the second main surface 4 are formed in a quadrangular shape in a plan view seen from their normal direction Z. The normal direction Z is also the thickness direction of the chip 2. The first side surface 5A and the second side surface 5B extend in a first direction X along the first main surface 3 and face each other in a second direction Y that intersects (specifically, is perpendicular to) the first direction X. The third side surface 5C and the fourth side surface 5D extend in the second direction Y and face each other in the first direction X.

[0011] The semiconductor device 1A includes an n-type (first conductivity type) first semiconductor region 6 formed in a surface layer portion of the first main surface 3 of the chip 2. The first semiconductor region 6 is formed in a layer shape extending along the first main surface 3 and is exposed from the first main surface 3 and the first to fourth side surfaces 5A to 5D. In other words, the first semiconductor region 6 has a part of the first main surface 3 and the first to fourth side surfaces 5A to 5D. The n-type impurity concentration of the first semiconductor region 6 is 1×10 14 cm -3 More than 1×10 16 cm -3 The thickness of the first semiconductor region 6 may be 1 μm or more and 15 μm or less. In this embodiment, the first semiconductor region 6 is formed by an n-type epitaxial layer.

[0012] The semiconductor device 1A includes a p-type (second conductivity type) second semiconductor region 7 formed in a surface layer portion of the second main surface 4 of the chip 2. The second semiconductor region 7 may also be referred to as a "base region." The second semiconductor region 7 is formed in a layer extending along the second main surface 4 and is exposed from the second main surface 4 and the first to fourth side surfaces 5A to 5D. In other words, the second semiconductor region 7 has parts of the second main surface 4 and the first to fourth side surfaces 5A to 5D. The second semiconductor region 7 is connected to the first semiconductor region 6 inside the chip 2.

[0013] The second semiconductor region 7 may have a substantially constant p-type impurity concentration in the thickness direction. The p-type impurity concentration of the second semiconductor region 7 may be 1×10 13 cm -3 More than 1×10 19 cm -3 The thickness of the second semiconductor region 7 may be 50 μm or more and 400 μm or less. The thickness of the second semiconductor region 7 is adjusted by grinding the second main surface 4. In this embodiment, the second semiconductor region 7 is formed of a p-type semiconductor substrate. That is, the chip 2 has a layered structure including a semiconductor substrate and an epitaxial layer. The second semiconductor region 7 is formed in the semiconductor substrate, and the first semiconductor region 6 is formed in the epitaxial layer.

[0014] The semiconductor device 1A includes a plurality of device regions 8 provided in the first semiconductor region 6. The plurality of device regions 8 are defined inwardly of the first main surface 3 at intervals from the first to fourth side surfaces 5A to 5D in a plan view. The number, arrangement, and shape of the device regions 8 are arbitrary and are not limited to a specific number, arrangement, or shape. The plurality of device regions 8 each include various functional devices. The functional devices may include at least one of a semiconductor switching device, a semiconductor rectifying device, and a passive device.

[0015] The semiconductor switching device may include at least one of a JFET (Junction Field Effect Transistor), a MISFET (Metal Insulator Semiconductor Field Effect Transistor), a BJT (Bipolar Junction Transistor), and an IGBT (Insulated Gate Bipolar Junction Transistor).

[0016] The semiconductor rectifying device may include at least one of a pn junction diode, a pin junction diode, a Zener diode, a Schottky barrier diode, and a fast recovery diode. The passive device may include at least one of a resistor, a capacitor, an inductor, and a fuse. In this embodiment, the plurality of device regions 8 includes at least one MIS region 9 (see region II in FIG. 1 ). In this embodiment, the MIS region 9 is a region including at least one transistor cell 10. In this embodiment, the transistor cell 10 includes a p-channel planar gate LDMISFET (Lateral Double Diffused MISFET). Specific structures of the MIS region 9 and the transistor cell 10 will be described below.

[0017] 2 and 3, the semiconductor device 1A includes a p-type separation region 11 as an example of a region separation structure that separates the MIS region 9 in the first semiconductor region 6. The separation region 11 is formed in a ring shape that surrounds a portion of the first main surface 3 in a plan view, and separates the MIS region 9 of a predetermined shape. The separation region 11 electrically separates the MIS region 9 from other regions. In this embodiment, the separation region 11 is formed in a quadrangular ring shape (specifically, a rectangular ring extending in the second direction Y) in a plan view, and separates the quadrangular-shaped (specifically, rectangular shape extending in the second direction Y) MIS region 9 by its inner peripheral edge. The planar shape of the separation region 11 (the planar shape of the MIS region 9) is arbitrary.

[0018] The isolation region 11 extends in a wall shape from the first main surface 3 toward the second semiconductor region 7 so as to cross the first semiconductor region 6, and is electrically connected to the second semiconductor region 7. In this embodiment, the isolation region 11 has a stacked structure including a first layer 11A and a second layer 11B. The first layer 11A is formed at the boundary between the first semiconductor region 6 and the second semiconductor region 7. The first layer 11A is formed at a distance from the first main surface 3 and the second main surface 4 in the normal direction Z, and is electrically connected to the second semiconductor region 7. The first layer 11A has a higher p-type impurity concentration than the second semiconductor region 7.

[0019] The second layer 11B is formed in the region between the first major surface 3 and the first layer 11A in the first semiconductor region 6 and is electrically connected to the first layer 11A. The second layer 11B may have a p-type impurity concentration equal to or lower than the p-type impurity concentration of the first layer 11A. In this embodiment, one second layer 11B is formed, but the number of second layers 11B (the number of layers stacked) is arbitrary as long as they are electrically connected to the first layer 11A. Therefore, multiple second layers 11B may be stacked in the region between the first major surface 3 and the first layer 11A. Of course, the isolation region 11 does not necessarily have to have a stacked structure including the first layer 11A and the second layer 11B as long as it can define the MIS region 9, and may have a single-layer structure consisting of a single second layer 11B.

[0020] The semiconductor device 1A includes an n-type buried region 12 formed inside the chip 2 across the bottom of the first semiconductor region 6 in the MIS region 9. The buried region 12 may be referred to as a "first buried region." Specifically, the buried region 12 is formed at the boundary between the first semiconductor region 6 and the second semiconductor region 7. The buried region 12 has a higher n-type impurity concentration than the first semiconductor region 6. The n-type impurity concentration of the buried region 12 is 1×10 16 cm -3 More than 1×10 19 cm -3 It may be the following:

[0021] The buried region 12 is formed at a distance from the first main surface 3 and the second main surface 4 in the normal direction Z, and is electrically connected to the first semiconductor region 6. The buried region 12 is formed at a distance from the inner periphery of the isolation region 11 inwardly of the MIS region 9, and exposes a part of the second semiconductor region 7 at the periphery of the MIS region 9. In this embodiment, the buried region 12 is formed in a quadrangular shape (specifically, a rectangular shape extending in the second direction Y) that follows the inner periphery of the isolation region 11 in a plan view.

[0022] The semiconductor device 1A includes an n-type body region 20 (first region) formed in the MIS region 9 in a surface layer portion of the first main surface 3. In this embodiment, the body region 20 is formed by a portion of the first semiconductor region 6 that is surrounded by the isolation region 11. That is, the body region 20 is made of a part of the first semiconductor region 6, and has a bottom formed by the bottom of the first semiconductor region 6. In addition, the body region 20 has a planar shape (in this embodiment, a rectangular shape extending in the second direction Y) that is aligned with the inner periphery of the isolation region 11.

[0023] The semiconductor device 1A includes a p-type drift region 21 (second region) formed in the MIS region 9 in the surface layer portion of the body region 20. The drift region 21 has a p-type impurity concentration higher than the n-type impurity concentration of the body region 20 (first semiconductor region 6). The p-type impurity concentration of the drift region 21 is 1×10 15 cm -3More than 1×10 18 cm -3 The drift region 21 may have a concentration gradient in which the p-type impurity concentration gradually decreases in a direction from the surface portion of the body region 20 toward the bottom portion of the body region 20. The drift region 21 preferably contains boron (B) as the p-type impurity.

[0024] The drift region 21 is formed at a distance inward from the separation region 11 in a plan view. The drift region 21 is formed within a region surrounded by the periphery of the buried region 12 in a plan view. Specifically, the drift region 21 is formed within a region surrounded by the periphery of the buried region 12 at a distance inward from the periphery of the buried region 12 in a plan view. In other words, the entire drift region 21 faces the buried region 12 in a plan view. In this embodiment, the drift region 21 is formed in a band shape extending in the second direction Y in a plan view. The drift region 21 has both ends that are curved in an arc shape facing outward in the second direction Y.

[0025] The drift region 21 is formed at a distance from the bottom of the body region 20 toward the first main surface 3 in the normal direction Z. Specifically, the drift region 21 is formed at a distance from the buried region 12 toward the first main surface 3 in the normal direction Z. The drift region 21 has a cross-sectional shape whose width in the direction along the first main surface 3 gradually narrows toward the thickness direction. The drift region 21 may have a thickness of 0.5 μm or more and 3 μm or less.

[0026] The semiconductor device 1A includes a p-type drain region 22 (first impurity region) formed in the MIS region 9 in a surface layer portion of the drift region 21. The drain region 22 has a higher p-type impurity concentration than the drift region 21. The p-type impurity concentration of the drain region 22 is 1×10 19 cm -3 More than 1×10 21 cm -3The drain region 22 may be formed at a distance inward from the periphery of the drift region 21 in plan view. In this embodiment, the drain region 22 is formed in a strip shape extending along the drift region 21 in plan view. The drift region 21 has both end portions that are curved in an arc shape outward in the second direction Y. The drain region 22 is formed at a distance from the bottom of the drift region 21 toward the first main surface 3 in the thickness direction.

[0027] The semiconductor device 1A includes at least one n-type well region 23 (in this embodiment, multiple n-type well regions 23) formed in the surface layer of the body region 20 in the MIS region 9. Each well region 23 has an n-type impurity concentration that exceeds the n-type impurity concentration of the body region 20. The n-type impurity concentration of each well region 23 is 1×10 16 cm -3 More than 1×10 18 cm -3 The well region 23 may have a concentration gradient in which the n-type impurity concentration gradually decreases from the surface layer portion to the bottom portion.

[0028] In this embodiment, the multiple well regions 23 include a first well region 23A on one side (the third side surface 5C side) and a second well region 23B on the other side (the fourth side surface 5D side). The first well region 23A is formed at an interval on one side (the third side surface 5C side) in the first direction X from the drift region 21. The second well region 23B is formed at an interval on the other side (the fourth side surface 5D side) in the first direction X from the drift region 21. The second well region 23B faces the first well region 23A across the drift region 21. In this embodiment, the multiple well regions 23 are each formed in a strip shape extending in the second direction Y in a plan view. Each of the multiple well regions 23 has both ends curved in an arc shape facing outward in the second direction Y.

[0029] The multiple well regions 23 are formed at intervals from the bottom of the body region 20 toward the first main surface 3 in the normal direction Z. The multiple well regions 23 may be formed deeper than the drift region 21, or may be formed shallower than the drift region 21. The multiple well regions 23 may be formed at intervals from the buried region 12 toward the first main surface 3, or may be connected to the buried region 12. The multiple well regions 23 each have a cross-sectional shape whose width along the first main surface 3 gradually narrows in the thickness direction.

[0030] The semiconductor device 1A includes p-type source regions 24 (second impurity regions) formed in the surface layer of each of the multiple well regions 23 in the MIS region 9. Each source region 24 has a higher p-type impurity concentration than the drift region 21. The p-type impurity concentration of each source region 24 is 1×10 19 cm -3 More than 1×10 21 cm -3 The p-type impurity concentration of each source region 24 is preferably approximately equal to the p-type impurity concentration of the drain region 22.

[0031] Each source region 24 is formed at a distance inward from the periphery of each well region 23 in plan view. In this embodiment, each source region 24 is formed in a strip shape extending along each well region 23 in plan view. Each source region 24 is formed at a distance from the bottom of each well region 23 toward the first main surface 3 in the thickness direction. Each source region 24 faces the drain region 22 in the first direction X, and forms a channel 25 of the transistor cell 10 between itself and the drain region 22 (specifically, the drift region 21). Each source region 24 has both end portions curved outward in an arc shape in the second direction Y.

[0032] The semiconductor device 1A includes n-type contact regions 26 formed in regions different from the source regions 24 in the surface layer portions of the multiple well regions 23. Each contact region 26 has a higher n-type impurity concentration than each well region 23. The n-type impurity concentration of each contact region 26 is 1×10 19 cm -3 More than 1×10 21 cm -3 It may be the following: Each contact region 26 is formed at a distance inward from the periphery of each well region 23 in plan view. In this embodiment, each contact region 26 is formed in a region opposite the drain region 22 with respect to each source region 24, and is formed in a strip shape extending along each well region 23 in plan view. Each contact region 26 is formed at a distance from the bottom of each well region 23 toward the first main surface 3 in the thickness direction. Each contact region 26 has both end portions curved in an arc shape outward in the second direction Y.

[0033] The semiconductor device 1A includes a p-type floating drift region 31 (floating region) formed inside the body region 20 in the MIS region 9. The floating drift region 31 may also be referred to as a "second buried region" or a "buried drift region." The floating drift region 31 has a p-type impurity concentration higher than the n-type impurity concentration of the body region 20. The p-type impurity concentration of the floating drift region 31 is 1×10 15 cm -3 More than 1×10 18 cm -3 The peak value of the p-type impurity concentration in the floating drift region 31 is preferably 0.9 to 1.1 times the peak value of the p-type impurity concentration in the drift region 21. The peak value of the p-type impurity concentration in the floating drift region 31 is preferably approximately equal to the peak value of the p-type impurity concentration in the drift region 21.

[0034] That is, the dose of p-type impurities in the floating drift region 31 is preferably approximately equal to the dose of p-type impurities in the drift region 21. The floating drift region 31 preferably has a concentration gradient in which the p-type impurity concentration gradually decreases in the direction from the bottom of the body region 20 toward the surface of the body region 20. That is, the floating drift region 31 preferably has a concentration gradually decreasing direction opposite to the concentration gradually decreasing direction of the drift region 21. The floating drift region 31 preferably contains boron (B) as the p-type impurity. That is, the floating drift region 31 preferably contains the same type of p-type impurity as the drift region 21.

[0035] The floating drift region 31 is formed inside the body region 20 at a thickness position between the bottom of the body region 20 and the bottom of the drift region 21. The floating drift region 31 is spaced apart from the bottom of the drift region 21 and faces the drift region 21 across a part of the body region 20. The floating drift region 31 is spaced apart from the bottom of the body region 20 towards the drift region 21. The floating drift region 31 is preferably formed at a thickness position closer to the bottom of the drift region 21 than to the bottom of the body region 20.

[0036] In this embodiment, the floating drift region 31 is spaced from the buried region 12 toward the drift region 21 and faces the buried region 12 across a portion of the body region 20. The floating drift region 31 is formed at a thickness position closer to the bottom of the drift region 21 than the buried region 12. It is preferable that the floating drift region 31 does not face the multiple well regions 23 in the direction along the first main surface 3 (first direction X in this embodiment). In other words, it is preferable that the floating drift region 31 is located on the bottom (buried region 12) side of the body region 20 relative to the depth positions of the bottoms of the multiple well regions 23.

[0037] The floating drift region 31 is formed at a distance inward from the isolation region 11 in a plan view. The floating drift region 31 is formed within a region surrounded by the periphery of the buried region 12 in a plan view. Specifically, the floating drift region 31 is formed within a region surrounded by the periphery of the buried region 12 at a distance inward from the periphery of the buried region 12 in a plan view. In other words, the entire floating drift region 31 faces the buried region 12 in a plan view.

[0038] The floating drift region 31 is further formed within a region surrounded by the periphery of the drift region 21 in a plan view. Specifically, the floating drift region 31 is formed within a region surrounded by the periphery of the drift region 21, with a gap inward from the periphery of the drift region 21 in a plan view. In other words, the entire floating drift region 31 faces the drift region 21 in a plan view.

[0039] The floating drift region 31 faces the drain region 22 in plan view. Preferably, the floating drift region 31 faces the entire drain region 22 in plan view. In this embodiment, the floating drift region 31 is formed in a strip shape extending in the second direction Y in plan view. In plan view, the floating drift region 31 has both ends that are curved in an arc shape outward in the second direction Y. Preferably, the floating drift region 31 has a width in the first direction X that is less than the width of the drift region 21. The floating drift region 31 may have a thickness of 0.5 μm or more and 3 μm or less.

[0040] The floating drift region 31 has an upper end portion 31a on the upper surface side of the body region 20 and a lower end portion 31b on the bottom side of the body region 20. The upper end portion 31a of the floating drift region 31 is formed at a first distance L1 from the bottom of the drift region 21. The lower end portion 31b of the floating drift region 31 is formed at a second distance L2 from the buried region 12. It is preferable that the second distance L2 exceeds the first distance L1 (L1 < L2). The first distance L1 may be 0.1 μm or more and 5 μm or less. The first distance L1 is preferably 0.5 μm or more and 2 μm or less. The second distance L2 may be 0.2 μm or more and 10 μm or less. The second distance L2 is preferably 2 μm or more and 5 μm or less.

[0041] The lower end portion 31b of the floating drift region 31 is formed at a third distance L3 from the bottom of the drain region 22. It is preferable that the third distance L3 is less than the distance LS between the drain region 22 and the source region 24 (L3 < LS). That is, in a cross-sectional view, the floating drift region 31 is preferably formed such that at least a part thereof is located within a semi-circular region defined by the drain region 22 and an arc having a radius of the distance LS.

[0042] It is particularly preferable that the floating drift region 31 is formed such that at least a part or all of the lower end portion 31b is located within the semi-circular region. The third distance L3 may be less than the width of the drift region 21. The third distance L3 may belong to a range of 0.9 times or more and 1.1 times or less of the distance LD between the drain region 22 and the periphery of the drift region 21 (0.9×LD ≦ L3 ≦ 1.1×LD). The third distance L3 may be approximately equal to the distance LD.

[0043] The semiconductor device 1A includes a first pn junction P1 and a second pn junction P2. The first pn junction P1 is formed at the boundary between the body region 20 and the drift region 21. The first pn junction P1 extends a first depletion layer into the body region 20 and the drift region 21. The second pn junction P2 is formed at the boundary between the body region 20 and the floating drift region 31. The second pn junction P2 extends a second depletion layer into the body region 20 and the floating drift region 31.

[0044] The second depletion layer from the second pn junction P2 is connected to the first depletion layer from the first pn junction P1 in a region between the drift region 21 and the floating drift region 31 in the body region 20. In other words, the drift region 21 is configured so that the first depletion layer extends from the boundary with the body region 20 into the body region 20. On the other hand, the floating drift region 31 is configured so that the second depletion layer extends from the boundary with the body region 20 into the body region 20 so as to be connected to the first depletion layer from the drift region 21.

[0045] The semiconductor device 1A includes a field insulating film 40 that selectively covers the first main surface 3 inside and outside the MIS region 9. The field insulating film 40 preferably includes a silicon oxide film. The field insulating film 40 covers the periphery of the drain region 22 (the inner part of the drift region 21) and the isolation region 11 on the first main surface 3. The field insulating film 40 includes a first opening 41 and a plurality of second openings 42. The first opening 41 exposes the drain region 22. In this embodiment, the first opening 41 is formed in a strip shape (oval shape) extending along the drain region 22 in a plan view.

[0046] One second opening 42 is formed in a region between the drain region 22 and the first well region 23A, exposing the channel 25 on the first well region 23A side. The other second opening 42 is formed in a region between the drain region 22 and the second well region 23B, exposing the channel 25 on the second well region 23B side. Specifically, each second opening 42 exposes the periphery of the drift region 21, the well region 23, the source region 24, and the contact region 26. In this embodiment, each second opening 42 is formed in a strip shape (rectangular shape) extending along the drift region 21 in a plan view.

[0047] The semiconductor device 1A includes a planar gate structure 50 formed on the first main surface 3 so as to cover the channel 25 in the MIS region 9. The planar gate structure 50 controls the on / off of the channel 25. The planar gate structure 50 has a stacked structure including a gate insulating film 51 and a gate electrode 52. The gate insulating film 51 preferably includes a silicon oxide film. The gate electrode 52 preferably includes conductive polysilicon.

[0048] The gate insulating film 51 is formed in the multiple second openings 42 of the field insulating film 40, and covers the region between the drain region 22 and the source region 24 (i.e., the channel 25) in each second opening 42. Specifically, the gate insulating film 51 covers the periphery of the drift region 21, the body region 20, the periphery of the well region 23, the source region 24, and the contact region 26 in each second opening 42. The gate insulating film 51 has a thickness less than that of the field insulating film 40, and is continuous with the field insulating film 40.

[0049] The gate electrode 52 is formed on the gate insulating film 51 and faces a region between the drain region 22 and the source region 24 (i.e., the channel 25) with the gate insulating film 51 interposed therebetween. Specifically, the gate electrode 52 is formed in a plurality of second openings 42 in the field insulating film 40 and faces the channel 25 in each second opening 42 with the gate insulating film 51 interposed therebetween. Specifically, the gate insulating film 51 faces the periphery of the drift region 21, the body region 20, the periphery of the well region 23, the source region 24, and the contact region 26 in each second opening 42 with the gate insulating film 51 interposed therebetween.

[0050] In this embodiment, the gate electrode 52 is formed in a ring shape surrounding the drain region 22 in a plan view. The gate electrode 52 includes an outer peripheral wall 52a on the isolation region 11 side and an inner peripheral wall 52b on the drain region 22 side. The outer peripheral wall 52a is formed at a distance from the periphery of the drift region 21 toward the isolation region 11 in a plan view, and surrounds the drift region 21. In this embodiment, the outer peripheral wall 52a has a planar shape that differs from the planar shape of the periphery of the drift region 21 in a plan view. In this embodiment, the outer peripheral wall 52a is formed in a rectangular shape extending along the inner periphery of the separation region 11. Of course, the outer peripheral wall 52a may be formed in an oval shape extending along the separation region 11 in a plan view.

[0051] Inner peripheral wall 52b is formed at a distance from the periphery of drift region 21 toward drain region 22 in plan view, and surrounds drain region 22. In this embodiment, inner peripheral wall 52b is formed at a distance from the periphery of floating drift region 31 toward the periphery of drift region 21, and surrounds floating drift region 31. Of course, inner peripheral wall 52b may also be formed at a distance from the periphery of floating drift region 31 toward the periphery of drift region 21 in plan view.

[0052] That is, the inner circumferential wall 52b may be located in a region between the periphery of the floating drift region 31 and the periphery of the drift region 21 in a plan view. In this embodiment, the inner circumferential wall 52b has a planar shape similar to the planar shape of the periphery of the floating drift region 31 in a plan view. In this embodiment, the inner circumferential wall 52b is formed in an elliptical shape extending along the floating drift region 31 in a plan view. Of course, the inner circumferential wall 52b may also be formed in a rectangular shape extending along the inner periphery of the floating drift region 31 in a plan view.

[0053] In this embodiment, the gate electrode 52 includes a lead-out portion 53 that is led out from above the gate insulating film 51 onto the field insulating film 40. The lead-out portion 53 forms an outer peripheral wall 52a of the gate electrode 52. The lead-out portion 53 is formed at an interval from the drain region 22 toward the peripheral edge of the drift region 21 in plan view, and faces the drift region 21 with the field insulating film 40 interposed therebetween.

[0054] Thus, the transistor cell 10 includes a drift region 21 , a drain region 22 , a plurality (two) of well regions 23 , a plurality (two) of source regions 24 , a plurality (two) of contact regions 26 , and a planar gate structure 50 . Semiconductor device 1A includes a drain contact electrode 60, a plurality of source contact electrodes 61, and a gate contact electrode 62. Drain contact electrode 60 is electrically connected to drain region 22 on first main surface 3. Drain contact electrode 60 may be formed in a strip shape extending along drain region 22 in a plan view.

[0055] The plurality of source contact electrodes 61 cover the plurality of well regions 23 on first main surface 3, respectively, and are electrically connected to the source regions 24 and contact regions 26 in the plurality of well regions 23. The plurality of source contact electrodes 61 may be formed in a strip shape extending along the plurality of well regions 23 in a plan view. The gate contact electrode 62 is electrically connected to the gate electrode 52 on the planar gate structure 50. The gate contact electrode 62 is electrically connected to one or both of the ends of the gate electrode 52 in the second direction Y. The gate contact electrode 62 preferably faces the field insulating film 40 with the lead portion 53 of the gate electrode 52 interposed therebetween.

[0056] 4 corresponds to FIG. 3 and is a cross-sectional view showing a semiconductor device 71 according to the first reference embodiment together with equipotential distribution. Referring to FIG. 4, the semiconductor device 71 according to the first reference embodiment has a structure similar to that of the semiconductor device 1A according to the first embodiment, except that it does not have a floating drift region 31. In the semiconductor device 71, equipotential lines become dense near the bottom of the drift region 21. That is, in the semiconductor device 71, the breakdown voltage (specifically, the breakdown voltage) decreases due to electric field concentration at the bottom of the drift region 21.

[0057] 5 is a cross-sectional view corresponding to FIG. 3 showing a semiconductor device 72 according to a second reference embodiment together with equipotential distribution. Referring to FIG. 5, the semiconductor device 72 according to the second reference embodiment has a structure similar to that of the semiconductor device 1A according to the first embodiment, except that it does not have a floating drift region 31 and that the drift region 21 is formed deep. In the semiconductor device 72, the deep drift region 21 pushes and spreads the equipotential lines in the thickness direction of the body region 20.

[0058] As a result, in the semiconductor device 72, electric field concentration near the bottom of the drift region 21 is suppressed, and a decrease in breakdown voltage due to the electric field concentration is suppressed. However, in the semiconductor device 72, the junction area of ​​the drift region 21 with respect to the body region 20 increases, resulting in an increase in parasitic capacitance. Specifically, the parasitic capacitance is the output capacitance between the drain region 22 and the source region 24. When the output capacitance increases, the switching characteristics deteriorate due to a delay in the charging and discharging time of the output capacitance during on / off switching.

[0059] 6 corresponds to FIG. 3 and is a cross-sectional view showing the semiconductor device 1A according to the first embodiment together with the equipotential distribution. Referring to FIG. 6, the semiconductor device 1A includes a chip 2, a body region 20, a drift region 21, a drain region 22, a source region 24, and a floating drift region 31. The chip 2 has a first main surface 3. The body region 20 is formed in a surface layer portion of the first main surface 3. The drift region 21 is formed in a surface layer portion of the body region 20. The drain region 22 is formed in a surface layer portion of the drift region 21. The source region 24 is formed in a surface layer portion of the body region 20, spaced apart from the drift region 21.

[0060] The floating drift region 31 is formed in the body region 20 at a thickness position between the bottom of the body region 20 and the bottom of the drift region 21 and spaced apart from the bottom of the drift region 21. The floating drift region 31 faces the drift region 21 with part of the body region 20 in between. With this structure, the equipotential lines on the drift region 21 side are spread in the depth direction of the body region 20 by the floating drift region 31. This suppresses electric field concentration near the bottom of the drift region 21 and suppresses a decrease in breakdown voltage due to the electric field concentration.

[0061] Furthermore, the floating drift region 31 is separated from the drift region 21 with a part of the body region 20 interposed therebetween. This prevents the junction area of ​​the drift region 21 to the body region 20 from being expanded due to the junction area of ​​the floating drift region 31 to the body region 20. This prevents an increase in output capacitance due to an increase in the junction area of ​​the drift region 21 to the body region 20. Therefore, the semiconductor device 1A can improve the breakdown voltage while suppressing the output capacitance (parasitic capacitance).

[0062] 7A to 7M are cross-sectional views showing one example of a method for manufacturing the semiconductor device 1A shown in FIG. 1. Referring to FIG. 7A, a disk-shaped p-type wafer 80 that serves as a base for the second semiconductor region 7 (semiconductor substrate) is prepared. Next, an MIS region 9 is defined in the wafer 80, and p-type impurities are introduced into a region in which the first layer 11A of the isolation region 11 is to be formed. Furthermore, n-type impurities are introduced into a region in the MIS region 9 in which the buried region 12 is to be formed.

[0063] 7B, an n-type first epitaxial layer 81, which will become part of the first semiconductor region 6, is formed on the wafer 80 by epitaxial growth. In this process, the n-type impurities and p-type impurities introduced into the wafer 80 diffuse into the wafer 80 and the first epitaxial layer 81 during the silicon crystal growth. This forms the first layer 11A of the isolation region 11 and the buried region 12.

[0064] 7C, a first resist mask 82 having a predetermined pattern is formed on the first epitaxial layer 81. The first resist mask 82 exposes the region where the floating drift region 31 is to be formed and covers the other regions. Next, p-type impurities are introduced into the surface layer of the first epitaxial layer 81 by ion implantation via the first resist mask 82. The first resist mask 82 is then removed.

[0065] 7D, an n-type second epitaxial layer 83, which will become part of the first semiconductor region 6, is formed on the first epitaxial layer 81 by epitaxial growth. In this process, the p-type impurities introduced into the first epitaxial layer 81 diffuse into the first epitaxial layer 81 and the second epitaxial layer 83 during silicon crystal growth. This forms the floating drift region 31.

[0066] Next, referring to FIG. 7E, a second resist mask 84 having a predetermined pattern is formed on the first semiconductor region 6. The second resist mask 84 exposes a region where the second layer 11B of the isolation region 11 is to be formed, and covers the other regions. Next, p-type impurities are introduced into the first semiconductor region 6 by ion implantation via the second resist mask 84. This forms the isolation region 11 including the first layer 11A and the second layer 11B. The second resist mask 84 is then removed.

[0067] Next, referring to FIG. 7F, a third resist mask 85 having a predetermined pattern is formed on the first semiconductor region 6. The third resist mask 85 exposes regions where multiple well regions 23 are to be formed and covers the remaining regions. Next, n-type impurities are introduced into the surface layer of the first semiconductor region 6 by ion implantation via the third resist mask 85. This forms multiple well regions 23. The third resist mask 85 is then removed.

[0068] Next, referring to FIG. 7G, a fourth resist mask 86 having a predetermined pattern is formed on the first semiconductor region 6. The fourth resist mask 86 exposes the region where the drift region 21 is to be formed and covers the other regions. Next, p-type impurities are introduced into the surface layer portion of the first semiconductor region 6 by ion implantation via the fourth resist mask 86. This forms the drift region 21. The step of forming the drift region 21 may be performed prior to the step of forming the multiple well regions 23. The fourth resist mask 86 is then removed.

[0069] 7H, a field insulating film 40 is formed on the first semiconductor region 6. The field insulating film 40 is formed by selectively oxidizing the first semiconductor region 6 (second epitaxial layer 83) by an oxidation process (for example, a thermal oxidation process). The field insulating film 40 has a first opening 41 that exposes an inner portion of the drift region 21 and a plurality of second openings 42 that expose the plurality of well regions 23. The first opening 41 exposes a region where the drain region 22 is to be formed, and the plurality of second openings 42 expose regions where the source region 24 and the contact region 26 are to be formed, respectively.

[0070] 7I, a gate insulating film 51 is formed on the first semiconductor region 6. The gate insulating film 51 is formed by selectively oxidizing the portions of the first semiconductor region 6 exposed from the first opening 41 and the plurality of second openings 42 of the field insulating film 40 by an oxidation treatment method (for example, a thermal oxidation treatment method). 7J, a base electrode layer 87 that will become gate electrode 52 is formed on field insulating film 40 and gate insulating film 51. Base electrode layer 87 includes conductive polysilicon. Base electrode layer 87 may be formed by a CVD (Chemical Vapor Deposition) method.

[0071] Next, referring to FIG. 7K, a fifth resist mask 88 having a predetermined pattern is formed on the base electrode layer 87. The fifth resist mask 88 covers the region where the gate electrode 52 is to be formed and leaves the other regions exposed. Next, unnecessary portions of the base electrode layer 87 are removed by etching through the fifth resist mask 88. The etching may be wet etching and / or dry etching. As a result, the gate electrode 52 is formed. The fifth resist mask 88 is then removed.

[0072] 7L, a sixth resist mask 89 having a predetermined pattern is formed on the field insulating film 40 and the gate electrode 52. The sixth resist mask 89 exposes regions where the drain region 22 and the plurality of source regions 24 are to be formed, and covers the other regions. Next, p-type impurities are introduced into the surface layer portion of the first semiconductor region 6 by ion implantation via the sixth resist mask 89.

[0073] This forms the drain region 22 and a plurality of source regions 24. In this embodiment, the drain region 22 is formed in a self-aligned manner with respect to the first opening 41 in the field insulating film 40. In this embodiment, the plurality of source regions 24 are formed in a self-aligned manner with respect to a portion (a portion extending in the second direction Y) of the outer peripheral wall 52a of the gate electrode 52. The sixth resist mask 89 is then removed.

[0074] Next, referring to FIG. 7M, a seventh resist mask 90 having a predetermined pattern is formed on the field insulating film 40 and the gate electrode 52. The seventh resist mask 90 exposes regions where the plurality of contact regions 26 are to be formed and covers the remaining regions. Next, n-type impurities are introduced into the surface layer of the first semiconductor region 6 by ion implantation through the seventh resist mask 90. ​​This forms the plurality of contact regions 26. In this embodiment, the plurality of contact regions 26 are formed in a self-aligned manner with the plurality of second openings 42 in the field insulating film 40. The step of forming the contact regions 26 may be performed prior to the step of forming the drain region 22 and the source region 24. The seventh resist mask 90 is then removed.

[0075] Thereafter, drain contact electrode 60, source contact electrode 61, and gate contact electrode 62 are formed. Wafer 80 is then selectively cut, and a plurality of semiconductor devices 1A are cut out from wafer 80. Through the steps including those described above, semiconductor device 1A is manufactured. 8 is an enlarged plan view corresponding to FIG. 2 and partially illustrating the structure of a semiconductor device 1B according to a second embodiment of the present invention. In the semiconductor device 1A according to the first embodiment, a contact region 26 is formed adjacent to the source region 24 in the first direction X in a plan view. In contrast, referring to FIG. 8, in the semiconductor device 1B according to the second embodiment, a contact region 26 is formed adjacent to the source region 24 in the second direction Y.

[0076] Specifically, a plurality of source regions 24 and a plurality of contact regions 26 are formed in each well region 23. The plurality of source regions 24 are formed at intervals in the second direction Y in each well region 23. Each source region 24 faces the drain region 22 in the first direction X. The plurality of contact regions 26 are formed alternately with the plurality of source regions 24 at intervals in the second direction Y in each well region 23. As described above, the semiconductor device 1B also achieves the same effects as the semiconductor device 1A.

[0077] 9 corresponds to FIG. 2 and is an enlarged plan view partially showing the structure of a semiconductor device 1C according to a third embodiment of the present invention. In each of the above-described embodiments, one transistor cell 10 is formed in the MIS region 9. However, multiple (two or more) transistor cells 10 may be formed in the MIS region 9. In this case, the isolation region 11 may be formed in a square ring shape (rectangular ring shape) extending in the first direction X, the buried region 12 and the body region 20 may be formed in a square shape (rectangular shape) extending in the first direction X, and the multiple transistor cells 10 may be arranged in a line along the first direction X.

[0078] With respect to two adjacent transistor cells 10, the first well region 23A of one transistor cell 10 may be formed integrally with the second well region 23B of the other transistor cell 10. In other words, the two adjacent transistor cells 10 may share one well region 23 (including the source region 24 and the contact region 26) located between two adjacent drift regions 21. As described above, the semiconductor device 1C also achieves effects similar to those of the semiconductor device 1A.

[0079] The present invention may be embodied in other forms. For example, in the above-described embodiments, the second semiconductor region 7 is of p-type. However, the second semiconductor region 7 may be of n-type. Furthermore, in the above-described embodiments, the first conductivity type is n-type and the second conductivity type is p-type. However, the first conductivity type may be p-type and the second conductivity type may be n-type. A specific configuration in this case can be obtained by replacing the n-type region with a p-type region and the p-type region with an n-type region in the above description and the accompanying drawings.

[0080] Below, examples of features extracted from this specification and drawings are shown. Below, we provide a semiconductor device that can suppress parasitic capacitance and improve breakdown voltage. Below, alphanumeric characters in parentheses represent corresponding components in the above-mentioned embodiments, but are not intended to limit the scope of each item to the embodiments. [A1] A semiconductor device (1A, 1B, 1C) including: a chip (2) having a main surface (3); a first region (20) of a first conductivity type formed in a surface layer portion of the main surface (3); a second region (21) of a second conductivity type formed in a surface layer portion of the first region (20); a drain region (22) formed in a surface layer portion of the second region (21); a source region (24) formed in the surface layer portion of the first region (20) and spaced apart from the second region (21); and a floating region (31) of a second conductivity type formed in the first region (20) at a thickness position between a bottom of the first region (20) and a bottom of the second region (21) and spaced apart from the bottom of the second region (21), facing the second region (21) across a portion of the first region (20).

[0081] [A2] The semiconductor device (1A, 1B, 1C) according to A1, wherein the floating region (31) is spaced apart from a bottom of the first region (20). [A3] A semiconductor device (1A, 1B, 1C) according to A1 or A2, wherein the floating region (31) is formed at a thickness position closer to the bottom of the second region (21) than to the bottom of the first region (20).

[0082] [A4] A semiconductor device (1A, 1B, 1C) described in any one of A1 to A3, wherein the second region (21) is configured to extend a first depletion layer from its boundary with the first region (20) into the first region (20), and the floating region (31) is configured to extend a second depletion layer from its boundary with the first region (20) into the first region (20) so as to be connected to the first depletion layer of the second region (21).

[0083] [A5] The semiconductor device (1A, 1B, 1C) according to any one of A1 to A4, wherein the floating region (31) is formed narrower than the second region (21). [A6] The semiconductor device (1A, 1B, 1C) according to any one of A1 to A5, wherein the entire floating region (31) faces the second region (21) in plan view. [A7] A semiconductor device (1A, 1B, 1C) according to any one of A1 to A6, further including a well region (23) of a first conductivity type formed in a surface layer portion of the first region (20) spaced apart from the second region (21) and having a higher impurity concentration than the first region (20), and the source region (24) is formed in a surface layer portion of the well region (23).

[0084] [A8] The semiconductor device (1A, 1B, 1C) according to A7, further comprising a contact region (26) formed in a surface layer portion of the well region (23) in a region different from the source region (24). [A9] A semiconductor device (1A, 1B, 1C) according to A8, wherein the floating region (31) is formed on the bottom side of the first region (20) relative to the depth position of the bottom of the well region (23), and does not face the well region (23) in a direction along the main surface (3).

[0085] [A10] A semiconductor device (1A, 1B, 1C) according to any one of A1 to A9, further including a buried region (12) of a first conductivity type formed inside the chip (2) across the bottom of the first region (20) and having a higher impurity concentration than the first region (20), and the floating region (31) is spaced apart from the buried region (12). [A11] The semiconductor device (1A, 1B, 1C) according to A10, wherein the buried region (12) is formed to be wider than the second region (21).

[0086] [A12] The semiconductor device (1A, 1B, 1C) according to any one of A1 to A11, further comprising: a gate insulating film (51) covering a region on the main surface (3) between the second region (21) and the source region (24); and a gate electrode (52) formed on the gate insulating film (51). [A13] A semiconductor device (1A, 1B, 1C) according to A12, further comprising a field insulating film (40) covering the periphery of the drain region (22) on the main surface (3), the gate insulating film (51) having a thickness less than the thickness of the field insulating film (40) and connected to the field insulating film (40), and the gate electrode (52) including a portion (53) extending from above the gate insulating film (51) onto above the field insulating film (40).

[0087] [A14] A semiconductor device (1A, 1B, 1C) according to any one of A1 to A13, further comprising a second conductivity type separation region (11) formed in a surface layer portion of the main surface (3) so as to define a device region (8, 9) in a part of the main surface (3), and the first region (20) is formed in the surface layer portion of the main surface (3) in the device region (8, 9). [A15] The semiconductor device (1A, 1B, 1C) according to A14, wherein the isolation region (11) is formed in a ring shape surrounding a part of the main surface (3) in a plan view.

[0088] [A16] A semiconductor device (1A, 1B, 1C) according to A14 or A15, further including a base region (7) of a second conductivity type formed in a region directly below the first region (20) within the chip (2), and the isolation region (11) is electrically connected to the base region (7). [A17] The distance (L3) between the drain region (22) and the floating region (31) is less than the distance (LS) between the drain region (22) and the source region (24) (L3 < LS), the semiconductor device (1A, 1B, 1C) according to any one of A1 to A16.

[0089] [A18] The distance (L3) between the drain region (22) and the floating region (31) is less than the width of the second region (21), the semiconductor device (1A, 1B, 1C) according to any one of A1 to A17. Although the embodiments of the present invention have been described in detail, these are merely specific examples used to clarify the technical content of the present invention, and the present invention should not be construed as being limited to these specific examples, and the scope of the present invention is limited by the appended claims.

Explanation of Signs

[0090] 1A Semiconductor device 1B Semiconductor device 1C Semiconductor device 2 Chip 3 First main surface 7 First region 8 Device region 9 MIS region 11 Isolation region 12 Buried region 20 Body region (first region) 21 Drift region (second region) 22 Drain region 23 Well region 24 Source region 26 Contact region <000040​​​​​​​​​

Claims

1. a chip having a major surface; a first region of a first conductivity type formed in a surface layer portion of the main surface; a second region of a second conductivity type formed on a surface layer portion of the first region; a drain region formed in a surface layer portion of the second region; a source region formed in a surface layer portion of the first region and spaced apart from the second region; a floating region of a second conductivity type formed in the first region at a thickness position between a bottom of the first region and a bottom of the second region and spaced apart from the bottom of the second region, and facing the second region with a part of the first region in between; The floating region is formed at a thickness position closer to a bottom of the second region than to a bottom of the first region.

2. The semiconductor device according to claim 1 , wherein the floating region is spaced apart from a bottom of the first region.

3. the second region is configured to extend a first depletion layer from a boundary with the first region into the first region, 3. The semiconductor device according to claim 1, wherein the floating region is configured to extend a second depletion layer into the first region from a boundary with the first region so as to be connected to the first depletion layer of the second region.

4. 4. The semiconductor device according to claim 1, wherein the floating region is formed to be narrower than the second region.

5. 5. The semiconductor device according to claim 1, wherein the entire floating region faces the second region in a plan view.

6. a well region of a first conductivity type formed in a surface layer portion of the first region at a distance from the second region and having a higher impurity concentration than the first region; 6. The semiconductor device according to claim 1, wherein the source region is formed in a surface layer of the well region.

7. 7. The semiconductor device according to claim 6, further comprising a contact region formed in a surface layer portion of said well region in a region different from said source region.

8. 8. The semiconductor device according to claim 7, wherein said floating region is formed on the opposite side of said main surface side with respect to a depth position of the bottom of said well region, and does not face said well region in a direction along said main surface.

9. a gate insulating film covering a region on the main surface between the second region and the source region; 9. The semiconductor device according to claim 1, further comprising: a gate electrode formed on said gate insulating film.

10. a field insulating film covering a periphery of the drain region on the main surface; the gate insulating film has a thickness less than a thickness of the field insulating film and is connected to the field insulating film; 10. The semiconductor device according to claim 9, wherein said gate electrode includes a portion extending from above said gate insulating film onto above said field insulating film.

11. a second conductivity type isolation region formed in a surface layer portion of the main surface so as to define a device region in a part of the main surface; 11. The semiconductor device according to claim 1, wherein the first region is formed in a surface layer portion of the main surface in the device region.

12. The semiconductor device according to claim 11 , wherein said isolation region is formed in a ring shape surrounding a part of said main surface in a plan view.

13. a second conductivity type base region formed in the chip in a region immediately below the first region; 13. The semiconductor device according to claim 11, wherein the isolation region is electrically connected to the base region.

14. 14. The semiconductor device according to claim 1, wherein the distance between the drain region and the floating region is less than the distance between the drain region and the source region.

15. 15. The semiconductor device according to claim 1, wherein the distance between said drain region and said floating region is less than the width of said second region.

16. a chip having a major surface; a first region of a first conductivity type formed in a surface layer portion of the main surface; a second region of a second conductivity type formed on a surface layer portion of the first region; a drain region formed in a surface layer portion of the second region; a source region formed in a surface layer portion of the first region and spaced apart from the second region; a floating region of a second conductivity type formed in the first region at a thickness position between a bottom of the first region and a bottom of the second region and spaced apart from a bottom of the second region, and facing the second region with a part of the first region interposed therebetween; a buried region of a first conductivity type formed inside the chip across a bottom of the first region and having a higher impurity concentration than the first region; The floating region is spaced apart from the buried region.

17. 17. The semiconductor device according to claim 16, wherein said buried region is formed to be wider than said second region.

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