# Patent

## Title
Semiconductor device and method of manufacturing semiconductor device

## Abstract

A sinker layer is in contact with a first conductivity-type well, and is separated from a first conductivity-type collector layer and a second conductivity-type drift layer. A second conductivity-type diffusion layer (second second-conductivity-type high-concentration diffusion layer) is formed in the surface layer of the sinker layer. The second conductivity-type diffusion layer has a higher impurity concentration than that of the sinker layer. The second conductivity-type diffusion layer and the first conductivity-type collector layer are isolated from each other with an element isolation insulating film interposed therebetween.

## Background
The application is based on Japanese patent application No. 2010-020659, the content of which is incorporated hereinto by reference.
BACKGROUND
1. Technical Field
The present invention relates to a semiconductor device having an insulated gate bipolar transistor (IGBT) and a method of manufacturing the semiconductor device.
2. Related Art
An example of a structure of a semiconductor device having an IGBT in which electrostatic discharge (ESD) resistance is enhanced includes, for example, a structure disclosed in Japanese Unexamined Patent Publication No. H03-211771. This structure is a structure, as shown in FIG. 6, in which a drain diffusion layer of a lateral double-diffused NMOS transistor (LDNMOS) is converted to a reverse conductivity type, an n+ diffusion layer 433 is provided at a position at which it is short-circuited to a p+ diffusion layer 432 functioning as a collector, and then the n+ diffusion layer 433 and the p+ diffusion layer 432 are short-circuited by a collector electrode 434. That is, an n+ diffusion layer 410 serving as an emitter and a p+diffusion layer 412 serving as a back gate are disposed in parallel to each other in a p− substrate 400, and they are connected to a common emitter electrode. In addition, an n− drift layer 430, a p+ diffusion layer 432 serving as a collector, and the n+ diffusion layer 433 are provided in the p− substrate 400. A collector electrode 434 is connected to the p+ diffusion layer 432 and the n+ diffusion layer 433.
In this structure, since a vertical PNP bipolar transistor is added to the p+ diffusion layer 432, a current flows in the longitudinal direction to some extent, which results in an increase in the ESD resistance.
The following analysis is performed by the present inventor. In the semiconductor device shown in FIG. 6, since the n+ diffusion layer 433 is disposed adjacent to the p+ diffusion layer 432, it is difficult to operate a PNP bipolar transistor included in the IGBT. In detail, in order to operate this bipolar transistor, the product of the resistance R1 of the n− drift layer 430 located under the p+ diffusion layer 432 and the electronic current I1 flowing through the n− drift layer 430 is required to be set to be equal to or more than the built-in potential (for example, about 0.7 V) of a pn diode including the p+ diffusion layer 432 and the n− drift layer 430. However, in the structure shown in FIG. 6, since the n+ diffusion layer 433 is disposed adjacent to the p+ diffusion layer 432, R1 is reduced, and thus it is difficult for the product thereof to exceed the built-in potential. In this case, in the IGBT, the bipolar transistor is difficult to operate. In some cases, only the MOS transistor is operated. For this reason, a saturation current is remarkably reduced.
SUMMARY
In one embodiment, there is provided a semiconductor device including: a substrate having a first conductivity-type semiconductor layer in the surface layer; a first first-conductivity-type high-concentration diffusion layer, formed in the surface layer of the first conductivity-type semiconductor layer, which has a higher impurity concentration than that of the first conductivity-type semiconductor layer; a first second-conductivity-type high-concentration diffusion layer, formed in the surface layer of the first conductivity-type semiconductor layer, which is in contact with the first first-conductivity-type high-concentration diffusion layer; a second conductivity-type low-concentration drift layer, formed in the surface layer of the first conductivity-type semiconductor layer, which has a lower impurity concentration than that of the first second-conductivity-type high-concentration diffusion layer; a gate insulating film formed so as to cover the surface of the first conductivity-type semiconductor layer between the first second-conductivity-type high-concentration diffusion layer and the second conductivity-type low-concentration drift layer, and a portion of the second conductivity-type low-concentration drift layer; a gate electrode formed over the gate insulating film; a second first-conductivity-type high-concentration diffusion layer formed in the surface layer of the second conductivity-type low-concentration drift layer; a second conductivity-type sinker layer, of which at least a portion is formed in the surface layer of the first conductivity-type semiconductor layer, and which is separated from both the second conductivity-type low-concentration drift layer and the second first-conductivity-type high-concentration diffusion layer; a second second-conductivity-type high-concentration diffusion layer formed in the surface layer of the second conductivity-type sinker layer; and an interconnect, formed over the first conductivity-type semiconductor layer, which connects the second first-conductivity-type high-concentration diffusion layer and the second second-conductivity-type high-concentration diffusion layer to each other.
According to the embodiment of the invention, the first conductivity-type high-concentration diffusion layer functions as a collector of the bipolar transistor included in the IGBT. In addition, the bipolar transistor is formed by the first conductivity-type high-concentration diffusion layer, the second conductivity-type low-concentration drift layer, and the first conductivity-type semiconductor layer. For this reason, it is possible to obtain a high ESD resistance in the semiconductor device.
On the other hand, the first conductivity-type high-concentration diffusion layer and the second conductivity-type sinker layer are short-circuited through the interconnect. In addition, the second conductivity-type low-concentration drift layer and the second conductivity-type sinker layer are isolated from each other. For this reason, the second conductivity-type low-concentration drift layer is in a floating state. Therefore, when a voltage has only to be applied to the first conductivity-type high-concentration diffusion layer by the built-in potential (for example, 0.7 V) of the diode (for example, PN diode) including the first conductivity-type high-concentration diffusion layer and the second conductivity-type low-concentration drift layer, this diode enters an on-state. For this reason, the bipolar transistor of the IGBT is reliably operated.
In another embodiment, there is provided a method of manufacturing a semiconductor device, including: forming a second conductivity-type low-concentration drift layer, located at a portion of the surface layer of a first conductivity-type semiconductor layer, in a substrate having the first conductivity-type semiconductor layer in the surface layer; forming a gate insulating film and a gate electrode located over the gate insulating film in a gate forming region including a portion of the second conductivity-type low-concentration drift layer, and a portion of the surface layer of the portion other than the second conductivity-type low-concentration drift layer in the first conductivity-type semiconductor layer; forming a first second-conductivity-type high-concentration diffusion layer, having a higher impurity concentration than that of the second conductivity-type low-concentration drift layer, in the surface layer of the first conductivity-type semiconductor layer opposite to the second conductivity-type low-concentration drift layer through the gate electrode when seen in a plan view; forming a first first-conductivity-type high-concentration diffusion layer, having a higher impurity concentration than that of the first conductivity-type semiconductor layer, in the surface layer of the first conductivity-type semiconductor layer so as to be in contact with the first second-conductivity-type high-concentration diffusion layer; forming a second first-conductivity-type high-concentration diffusion layer in the surface layer of the second conductivity-type low-concentration drift layer; forming a second conductivity-type sinker layer, within the first conductivity-type semiconductor layer, in a position separated from both the second conductivity-type low-concentration drift layer and the second first-conductivity-type high-concentration diffusion layer; forming a second second-conductivity-type high-concentration diffusion layer in the surface layer of the second conductivity-type sinker layer; and forming an interconnect, which connects the second second-conductivity-type high-concentration diffusion layer and the second first-conductivity-type high-concentration diffusion layer to each other, over the first conductivity-type semiconductor layer.
According to the embodiments of the invention, it is possible to reliably perform an operation of the bipolar transistor (for example, PNP bipolar transistor) included in the IGBT while enhancing the ESD resistance of the IGBT.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which:
FIGS. 1A to 1D are cross-sectional views illustrating a method of manufacturing a semiconductor device according to a first embodiment;
FIG. 2 is a diagram in which an insulating interlayer 200, each contact, and each interconnect are omitted from FIG. 1D, and is a plan view illustrating a layout of element isolation insulating films and each diffusion layer of the semiconductor device shown in FIG. 1D;
FIG. 3 is a graph illustrating an effect of the embodiment;
FIGS. 4A and 4B are cross-sectional views illustrating the configuration of the semiconductor device according to a comparative example;
FIG. 5 is a cross-sectional view illustrating the configuration of the semiconductor device according to a second embodiment;
FIG. 6 is a diagram illustrating the configuration of a semiconductor device disclosed in Japanese Unexamined Patent Publication No. H03-211771.



DETAILED DESCRIPTION
The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes.
Hereinafter, the embodiments of the invention will be described with reference to the accompanying drawings. In all the drawings, like elements are referenced by like reference numerals and descriptions thereof will not be repeated.
FIGS. 1A to 1D are cross-sectional views illustrating a method of manufacturing a semiconductor device according to a first embodiment. FIG. 1D in these drawings shows a cross-sectional view of the semiconductor device manufactured by this method of manufacturing the semiconductor device.
The semiconductor device shown in FIG. 1D includes a substrate 10, a first conductivity-type semiconductor layer (first conductivity-type well) 102, a second conductivity-type low-concentration drift layer (second conductivity-type drift layer) 104, a first second-conductivity-type high-concentration diffusion layer (second conductivity-type emitter layer) 106, a second first-conductivity-type high-concentration diffusion layer (first conductivity-type collector layer) 108, a first first-conductivity-type high-concentration diffusion layer (first conductivity-type well extracting diffusion layer) 107, a gate insulating film 110, a gate electrode 112, a sinker layer 115, and an interconnect 220.
The surface of the substrate is formed of a first conductivity-type, for example, p-type semiconductor layer. The first conductivity-type well 102 is formed in the surface layer of the substrate 10. The second conductivity-type drift layer 104 is a second conductivity-type, for example, an n-type. The second conductivity-type drift layer 104 is formed in the surface layer of the first conductivity-type well 102, and is separated from the first conductivity-type well 102. The second conductivity-type emitter layer 106 is formed in the surface layer of the first conductivity-type well 102, is separated from the second conductivity-type drift layer 104 when seen in a plan view, and has a higher impurity concentration than that of the second conductivity-type drift layer 104. The first conductivity-type well extracting diffusion layer 107 is formed in the surface layer of the first conductivity-type well 102, has a higher impurity concentration than that of the first conductivity-type well 102, and is connected to the second conductivity-type emitter layer 106. The first conductivity-type collector layer 108 is formed in the surface layer of the second conductivity-type drift layer 104, and has a higher impurity concentration than that of the first conductivity-type well 102. The gate insulating film 110 is formed on a portion of the second conductivity-type drift layer 104, and on a region located between the second conductivity-type drift layer 104 and the second conductivity-type emitter layer 106 in the first conductivity-type well 102. The gate electrode 112 is formed on the gate insulating film 110. The sinker layer 115 is a second conductivity-type diffusion layer formed in the substrate, and the impurity concentration thereof is higher than that of the second conductivity-type drift layer 104. The sinker layer 115 is in contact with the first conductivity-type well 102, and is also separated from any of the second conductivity-type drift layer 104 and the first conductivity-type collector layer 108. The interconnect 220 is formed on the substrate 10, and is connected to the sinker layer 115.
A second conductivity-type diffusion layer (second second-conductivity-type high-concentration diffusion layer) 116 is formed in the surface layer of the sinker layer 115. The second conductivity-type diffusion layer 116 has a higher impurity concentration than that of the sinker layer 115. An element isolation insulating film 16 is formed in the surface layer of an epitaxial layer 14. The element isolation insulating film 16 is located between the second conductivity-type diffusion layer 116 and the first conductivity-type collector layer 108. That is, the second conductivity-type diffusion layer 116 and the first conductivity-type collector layer 108 are isolated from each other by the element isolation insulating film 16.
Meanwhile, the element isolation insulating film 16 is also located between the first conductivity-type collector layer 108 and the second conductivity-type emitter layer 106. A portion of the gate electrode 112 is also located on the element isolation insulating film 16 which is located at this portion. However, the element isolation insulating film 16 and the second conductivity-type emitter layer 106 are separated from each other.
An insulating interlayer 200 is formed on the substrate 10. The interconnect 220 is formed on the insulating interlayer 200. The interconnect 220 is connected to the second conductivity-type diffusion layer 116 through a contact 211 buried in the insulating interlayer 200. In detail, an electrode is formed in the surface of the second conductivity-type diffusion layer 116, and the electrode and the contact 211 are electrically connected to each other. In addition, the interconnect 220 is also connected to the first conductivity-type collector layer 108 through a contact 212 buried in the insulating interlayer 200. In detail, an electrode is formed in the surface of the first conductivity-type collector layer 108, and the electrode and the contact 212 are electrically connected to each other. That is, the first conductivity-type collector layer 108 and the second conductivity-type diffusion layer 116 (that is, sinker layer 115) are connected to each other through the contact 212, the interconnect 220, and the contact 211.
In the embodiment, the semiconductor device includes a second conductivity-type buried layer 114. The second conductivity-type buried layer 114 is formed under the sinker layer 115 and the first conductivity-type well 102, respectively, and is connected to the sinker layer 115 and the first conductivity-type well 102, respectively. The impurity concentration of the second conductivity-type buried layer 114 is higher than that of the first conductivity-type well 102. That is, the lateral side and the bottom of the first conductivity-type well 102 are surrounded by the sinker layer 115 and the second conductivity-type buried layer 114.
The substrate 10 is configured such that the first conductivity-type epitaxial layer 14 is epitaxially grown on a first conductivity-type semiconductor substrate 12 such as a silicon substrate. The second conductivity-type buried layer 114 is formed across the epitaxial layer 14 from the semiconductor substrate 12 when seen in the thickness direction of the substrate 10.
The first conductivity-type well extracting diffusion layer 107 is adjacent to the second conductivity-type emitter layer 106. The first conductivity-type well extracting diffusion layer 107 and the second conductivity-type emitter layer 106 are connected to each other through a silicide layer 109 formed in these surface layers. The silicide layer 109 is connected to an interconnect 222, formed in the surface layer of the insulating interlayer 200, through a contact 213 buried in the insulating interlayer 200.
In addition, a contact 214 is buried in the insulating interlayer 200. The contact 214 connects an interconnect 224 formed in the surface layer of the insulating interlayer 200 to the gate electrode 112. A sidewall is formed at a sidewall of the gate electrode 112.
Meanwhile, two sets of the second conductivity-type drift layer 104 and the first conductivity-type collector layer 108 are formed in the first conductivity-type well 102. That is, two IGBTs are formed in the first conductivity-type well 102. These two IGBTs are line-symmetrically disposed with reference to a set of the first conductivity-type well extracting diffusion layer 107 and the second conductivity-type emitter layer 106, and share the first conductivity-type well extracting diffusion layer 107, the second conductivity-type emitter layer 106, and the first conductivity-type well 102. In addition, the gate insulating film 110 and the gate electrode 112 having the same structure are line-symmetrically disposed.
FIG. 2 is a plan view illustrating a layout of the element isolation regions 16 and each diffusion layer of the semiconductor device shown in FIG. 1D, and is a diagram in which the insulating interlayer 200, each contact, and each interconnect are omitted from FIG. 1D. As shown in these drawings, the second conductivity-type drift layer 104 is not in contact with any of the edges of the first conductivity-type well 102. That is, the second conductivity-type drift layer 104 is not in contact with the sinker layer 115. In addition, the sinker layer 115 and the second conductivity-type diffusion layer 116 are formed so as to surround the first conductivity-type well 102 when seen in a plan view. In the element isolation region 16, a region 105 in which the element isolation region 16 is not formed exists in the center of the region surrounded by the second conductivity-type diffusion layer 116. The second conductivity-type emitter layer 106 and the first conductivity-type well extracting diffusion layer 107 are formed within the region 105. When seen in a plan view, the region 105 also extends onto a region adjacent to the second conductivity-type emitter layer 106 in the second conductivity-type drift layer 104. In addition, the first conductivity-type collector layers 108 are formed at the positions separated from the region 105 in both sides of the region 105.
Next, references are made to FIGS. 1A to 1D to describe the method of manufacturing the semiconductor device shown in FIG. 1D and FIG. 2. First, as shown in FIG. 1A, the semiconductor substrate 12 is prepared. Next, a second conductivity-type (n-type) impurity, for example, As or P is implanted into the semiconductor substrate 12. Thereby, the second conductivity-type buried layer 114 is formed in the semiconductor substrate 12.
Next, the first conductivity-type (p-type) epitaxial layer 14 is grown on the semiconductor substrate 12. At this time, since the semiconductor substrate 12 and the epitaxial layer 14 are heated, the second conductivity-type buried layer 114 formed in the semiconductor substrate 12 is diffused into the epitaxial layer 14. Thereby, the second conductivity-type buried layer 114 is formed across the epitaxial layer 14 from the semiconductor substrate 12 when seen in the thickness direction of the substrate 10.
Next, as shown in FIG. 1B, the element isolation insulating film 16 is formed in the epitaxial layer 14 using a LOCOS oxidation method. Meanwhile, the element isolation insulating film 16 may be formed by a separate method, for example, an STI method. Next, a first conductivity-type impurity, for example, B is selectively implanted into a region serving as the first conductivity-type well 102 in the epitaxial layer 14, and a second conductivity-type impurity, for example, As or P is selectively implanted into a region serving as the sinker layer 115 in the epitaxial layer 14. Thereafter, the impurities implanted into the epitaxial layer 14 are diffused into the inside of the epitaxial layer 14 by performing high-temperature heat treatment, and the first conductivity-type well 102 and the sinker layer 115 are formed.
Next, as shown in FIG. 1C, the second conductivity-type impurity, for example, As or P is selectively implanted into the epitaxial layer 14. Thereby, the second conductivity-type drift layer 104 is formed. Meanwhile, the portion located under the element isolation insulating film 16 in the second conductivity-type drift layer 104 is formed more shallowly than other regions because implanted ions penetrate the element isolation insulating film 16.
Next, as shown in FIG. 1D, the gate insulating film 110 and the gate electrode 112 are formed in a gate forming region of the epitaxial layer 14. The gate forming region includes a portion of the second conductivity-type drift layer 104, and a portion of the surface layer of the portion other than the second conductivity-type drift layer 104 in the first conductivity-type well 102. A portion of the gate electrode 112 is located on the element isolation insulating film 16. Next, the first conductivity-type impurity, for example, B is selectively implanted into a region serving as the first conductivity-type well extracting diffusion layer 107 and a region serving as the first conductivity-type collector layer 108. In addition, the second conductivity-type impurity, for example, As or P is selectively implanted into a region serving as the second conductivity-type emitter layer 106 and a region serving as the second conductivity-type diffusion layer 116. Thereby, the second conductivity-type emitter layer 106, the first conductivity-type well extracting diffusion layer 107, the first conductivity-type collector layer 108, and the second conductivity-type diffusion layer 116 are formed. Meanwhile, the second conductivity-type emitter layer 106 is formed in the surface layer of the first conductivity-type well 102, which is opposite to the second conductivity-type drift layer 104, through the gate electrode 112 when seen in a plan view. Here, the first conductivity-type well extracting diffusion layer 107 and the first conductivity-type collector layer 108 may not be formed by the same process. In addition, the second conductivity-type emitter layer 106 and the second conductivity-type diffusion layer 116 may not be formed by the same process.
Next, a metal layer is formed on the epitaxial layer 14, on the element isolation insulating film 16, and on the gate electrode 112, and this metal layer and the epitaxial layer 14 are heat-treated. Thereby, the silicide layer 109 is formed in the surface layer of the second conductivity-type emitter layer 106 and the surface layer of the first conductivity-type well extracting diffusion layer 107. In this process, the silicide layer is also formed in the surface layer of the gate electrode 112, the surface layer of the first conductivity-type collector layer 108, and the surface layer of the second conductivity-type diffusion layer 116.
Next, the insulating interlayer 200 is formed on the epitaxial layer 14, on the element isolation insulating film 16, and on the gate electrode 112. Next, connection holes serving as the contacts 211, 212, 213, and 214 are formed by selectively removing the insulating interlayer 200. Next, the contacts 211, 212, 213, and 214 are formed by burying a metal, for example, tungsten (W) in these connection holes. Next, the interconnects 220, 222, and 224 are formed in the surface layer of the insulating interlayer 200.
Next, operations and effects of the embodiment will be described. According to the embodiment, the first conductivity-type collector layer 108 functions as a collector of the bipolar transistor included in the IGBT. In addition, a vertical PNP bipolar transistor which causes a current to flow in the longitudinal direction is formed by the first conductivity-type collector layer 108, the second conductivity-type drift layer 104, and the first conductivity-type well 102. For this reason, it is possible to obtain a high ESD resistance in the semiconductor device.
On the other hand, the first conductivity-type collector layer 108 and the sinker layer 115 are short-circuited through the interconnect 220. In addition, the second conductivity-type drift layer 104 and the sinker layer 115 are isolated from each other with the first conductivity-type well 102 interposed therebetween. For this reason, the second conductivity-type drift layer 104 is in a floating state. Therefore, the voltage applied between the first conductivity-type collector layer 108 and the second conductivity-type drift layer 104 reaches a voltage required to turn on the diode including the first conductivity-type collector layer 108 and the second conductivity-type drift layer 104, without raising the voltage applied to the first conductivity-type collector layer 108. For this reason, the PNP bipolar transistor included in the IGBT is reliably operated.
Additionally, in the step of forming the second conductivity-type emitter layer 106, the second conductivity-type diffusion layer 116 is formed in the surface layer of the sinker layer 115. For this reason, the number of processes for manufacturing the semiconductor device shown in FIG. 1D and FIG. 2 does not increase from the number of processes for manufacturing the semiconductor device shown in FIG. 6. Therefore, it is possible to suppress an increase in the manufacturing cost.
In addition, since the first conductivity-type well 102 is surrounded by the sinker layer 115 and the second conductivity-type buried layer 114, the substrate 10 and the back gate of the MOS transistor can be isolated from each other. Therefore, when the voltage between the collector and the emitter is raised, it is possible to suppress an increase in the substrate leakage current.
FIG. 3 is a graph illustrating an effect of the embodiment. This graph shows the characteristics (or characteristics of Id (drain current)—Vds (voltage between the drain and the source)) of Ic (collector current)—Vce (voltage between the collector and the emitter) of the semiconductor device shown in FIG. 1D and FIG. 2 and the semiconductor device according to the comparative example shown in FIGS. 4A and 4B, respectively. The semiconductor device shown in FIG. 4A is configured such that the sinker layer 115, the second conductivity-type diffusion layer 116, and the second conductivity-type buried layer 114 are omitted from the semiconductor device shown in FIG. 1D and FIG. 2, and the second conductivity-type diffusion layer 150 is added thereto. However, the semiconductor device operates as the IGBT. The semiconductor device shown in FIG. 4B is configured such that the sinker layer 115, the second conductivity-type diffusion layer 116, and the second conductivity-type buried layer 114 are omitted from the semiconductor device shown in FIG. 1D and FIG. 2, and a second conductivity-type impurity layer 160 is provided in place of the first conductivity-type collector layer 108. The semiconductor device functions as a LDNMOS.
As shown in FIG. 3, Ic (Id) of the IGBT shown in FIG. 4A is larger than that of the LDNMOS shown in FIG. 4B in the vicinity of 4 V. This is because the bipolar transistor included in the IGBT is turned on in the vicinity of 4 V. On the other hand, Ic (Id) of the IGBT according to the embodiment is larger than that of the LDNMOS shown in FIG. 4B in the vicinity of 0.7 V. This is because the bipolar transistor included in the IGBT is turned on in the vicinity of 0.7 V. That is, in the IGBT according to the embodiment, the bipolar transistor is turned on by a lower collector voltage than that of the IGBT according to the comparative example. In addition, the saturation current value of Ic of the semiconductor device according to the embodiment considerably rises by approximately twice that of the LDNMOS according to the comparative example.
FIG. 5 is a cross-sectional view illustrating the configuration of the semiconductor device according to a second embodiment. This semiconductor device has the same configuration as that of the semiconductor device shown in the first embodiment except for the following point.
First, a silicon-on-insulator (SOI) substrate is used as the substrate 10. That is, the substrate 10 is configured such that an insulating layer 13 such as a silicon oxide layer and a semiconductor layer 15 are laminated on the semiconductor substrate 12 in this order. The first conductivity-type well 102 and the sinker layer 115 are formed within the semiconductor layer 15 in the depth direction, and the lower ends thereof reach the insulating layer 13. The second conductivity-type buried layer 114 is not formed in the semiconductor device shown in FIG. 5.
According to the embodiment, it is possible to obtain the same effect as that of the first embodiment. In addition, the first conductivity-type well 102 is surrounded by the sinker layer 115 and the insulating layer 13. That is, the lower surface of the first conductivity-type well 102 is covered by the insulating layer 13 in place of the second conductivity-type buried layer 114, thereby allowing the substrate leakage current to be further suppressed.
As described above, although the embodiments of the invention have been set forth with reference to the drawings, they are merely illustrative of the invention, and various configurations other than those stated above can be adopted.
It is apparent that the present invention is not limited to the above embodiment, and may be modified and changed without departing from the scope and spirit of the invention.

## Claims

1. A semiconductor device comprising:
a substrate having a first conductivity-type semiconductor layer in the surface layer;
a first first-conductivity-type high-concentration diffusion layer, formed in the surface layer of said first conductivity-type semiconductor layer, which has a higher impurity concentration than that of said first conductivity-type semiconductor layer;
a first second-conductivity-type high-concentration diffusion layer, formed in the surface layer of said first conductivity-type semiconductor layer, which is in contact with said first first-conductivity-type high-concentration diffusion layer;
a second conductivity-type low-concentration drift layer, formed in the surface layer of said first conductivity-type semiconductor layer, which has a lower impurity concentration than that of said first second-conductivity-type high-concentration diffusion layer;
a gate insulating film formed so as to cover the surface of said first conductivity-type semiconductor layer between said first second-conductivity-type high-concentration diffusion layer and said second conductivity-type low-concentration drift layer, and a portion of said second conductivity-type low-concentration drift layer;
a gate electrode formed over said gate insulating film;
a second first-conductivity-type high-concentration diffusion layer formed in the surface layer of said second conductivity-type low-concentration drift layer;
a second conductivity-type sinker layer, of which at least a portion is formed in the surface layer of said first conductivity-type semiconductor layer, and which is separated from both said second conductivity-type low-concentration drift layer and said second first-conductivity-type high-concentration diffusion layer;
a second second-conductivity-type high-concentration diffusion layer formed in the surface layer of said second conductivity-type sinker layer; and
an interconnect, formed over said first conductivity-type semiconductor layer, which connects said second first-conductivity-type high-concentration diffusion layer and said second second-conductivity-type high-concentration diffusion layer to each other.

2. The semiconductor device according to claim 1, further comprising:
an element isolation insulating film, formed in the surface layer of said first conductivity-type semiconductor layer, which is disposed so as to isolate said second first-conductivity-type high-concentration diffusion layer and said second second-conductivity-type high-concentration diffusion layer from each other.

3. The semiconductor device according to claim 1,
wherein said second conductivity-type sinker layer is provided so as to surround said second conductivity-type low-concentration drift layer, said first second-conductivity-type high-concentration diffusion layer, and said first first-conductivity-type high-concentration diffusion layer, when seen in a plan view, and
said first conductivity-type semiconductor layer has a higher impurity concentration of the portion located at the internal side of said second conductivity-type sinker layer than the impurity concentration of the portion located at the external side of said second conductivity-type sinker layer.

4. The semiconductor device according to claim 3, further comprising:
a second conductivity-type buried layer, formed under said second conductivity-type sinker layer and said first conductivity-type semiconductor layer, respectively, which is in contact with said second conductivity-type sinker layer and said first conductivity-type semiconductor layer, respectively.

5. The semiconductor device according to claim 4,
wherein said substrate includes:
a semiconductor substrate; and
an epitaxial layer epitaxially grown over said semiconductor substrate, and
said second conductivity-type buried layer is formed across said epitaxial layer from said semiconductor substrate.

6. The semiconductor device according to claim 1,
wherein said substrate is a silicon-on-insulator (SOI) substrate in which an insulating layer and a semiconductor layer are laminated over a semiconductor substrate in this order, and
said second conductivity-type sinker layer is formed within said semiconductor layer in the depth direction, and the lower end thereof reaches said insulating layer.

7. A method of manufacturing a semiconductor device, comprising:
forming a second conductivity-type low-concentration drift layer, located at a portion of the surface layer of a first conductivity-type semiconductor layer, in a substrate having said first conductivity-type semiconductor layer in the surface layer;
forming a gate insulating film and a gate electrode located over said gate insulating film in a gate forming region including a portion of said second conductivity-type low-concentration drift layer, and a portion of the surface layer of the portion other than said second conductivity-type low-concentration drift layer in said first conductivity-type semiconductor layer;
forming a first second-conductivity-type high-concentration diffusion layer, having a higher impurity concentration than that of said second conductivity-type low-concentration drift layer, in the surface layer of said first conductivity-type semiconductor layer opposite to said second conductivity-type low-concentration drift layer through said gate electrode when seen in a plan view;
forming a first first-conductivity-type high-concentration diffusion layer, having a higher impurity concentration than that of said first conductivity-type semiconductor layer, in the surface layer of said first conductivity-type semiconductor layer so as to be in contact with said first second-conductivity-type high-concentration diffusion layer;
forming a second first-conductivity-type high-concentration diffusion layer in the surface layer of said second conductivity-type low-concentration drift layer;
forming a second conductivity-type sinker layer, within said first conductivity-type semiconductor layer, in a position separated from both said second conductivity-type low-concentration drift layer and said second first-conductivity-type high-concentration diffusion layer;
forming a second second-conductivity-type high-concentration diffusion layer in the surface layer of said second conductivity-type sinker layer; and
forming an interconnect, which connects said second second-conductivity-type high-concentration diffusion layer and said second first-conductivity-type high-concentration diffusion layer to each other, over said first conductivity-type semiconductor layer.

8. The method of manufacturing a semiconductor device according to claim 7, further comprising:
forming an element isolation insulating film in the surface layer of said first conductivity-type semiconductor layer so as to isolate said second second-conductivity-type high-concentration diffusion layer and said second first-conductivity-type high-concentration diffusion layer.

9. The method of manufacturing a semiconductor device according to claim 7,
wherein said step of forming said first first-conductivity-type high-concentration diffusion layer and said step of forming said second first-conductivity-type high-concentration diffusion layer are performed by the same process.

10. The method of manufacturing a semiconductor device according to claim 7,
wherein said step of forming said first second-conductivity-type high-concentration diffusion layer and said step of forming said second second-conductivity-type high-concentration diffusion layer are performed by the same process.