JPH0669510A - High-breakdown-strength semiconductor device - Google Patents

Abstract

PURPOSE:To relax that an electric field is concentrated at the tip part of a field plate. CONSTITUTION:A field plate 20a used to prevent that the surface of a substrate is depleted and inverted directly under a metal interconnection 16 is located between the metal interconnection 16 and a substrate 2, and it is extended up to the upper part of a guard ring 12 from the upper part of a drain region 4. The field plate 20a is insulated from both the substrate 2 and the metal interconnection 16, and its base end part is connected to the drain region 4. A P-type low-concentration diffused region 22 which is connected to the guard ring 12 and whose conductivity type is the same as that of the guard ring 12 is formed on the surface of the substrate at the lower side of the field plate 20a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high breakdown voltage MOSFET. The high breakdown voltage MOSFET is used by being integrated with other semiconductor elements on the same semiconductor substrate, or used as an individual element as a power semiconductor device or the like.

[0002]

2. Description of the Related Art In a high breakdown voltage MOSFET in which a source region and a drain region are formed on a surface of a silicon substrate so as to face each other,
For example, when a high breakdown voltage MOS transistor and a low breakdown voltage MOS transistor are mixedly mounted on one semiconductor substrate, when a wiring connected to the source region of the high breakdown voltage MOS transistor is drawn, the wiring crosses the source region and the drain region on the substrate. . When a high voltage is applied to the drain,
The substrate directly under the source wiring may be depleted, causing a short circuit between the source and the drain. It is known that providing a field plate is effective as one means for solving such a problem.

FIG. 3 shows an example of a high breakdown voltage MOSFET provided with a field plate. A high breakdown voltage MOSFET is formed on an N-type silicon substrate 2 separated by a dielectric.
On the side surface and the bottom surface of the substrate 2, a drain region 4 formed of a high concentration N-type diffusion region is formed so as to surround the inside.
In the substrate 2, a source region 8 of a high concentration N type diffusion region is formed in a low concentration P type diffusion region 6. Reference numeral 10 is a contact region of the region 6. A diffusion layer 12 called a guard ring is formed on the surface of the substrate so as to surround the P-type region 6 serving as a channel region, the diffusion layer 12 being a high-concentration P-type diffusion region for preventing extension of the depletion layer.

A gate electrode 14 is formed on the substrate 2 on the channel region via a gate oxide film. Reference numeral 16 denotes an interlayer insulating film 18 which is insulated from both the substrate 2 and the gate electrode 14.
It is a metal wiring formed above and is connected to the source 8 and the contact 10 via the contact hole of the interlayer insulating film 18. The metal wiring 16 has this high withstand voltage MOSFE.
It traverses the upper part of the substrate, which is separated from the semiconductor element for connecting from T to another semiconductor element or the outside. A field plate 20 for preventing depletion and inversion of the substrate surface immediately below the metal wiring 16 is formed of a polysilicon thin film, and the field plate 20 is connected to the drain region 4.

[0005]

In the high breakdown voltage MOSFET provided with the field plate 20 as shown in FIG. 3, the electric field is concentrated at the source side end portion of the field plate 20, and the breakdown of the PN junction occurs at that portion. . Therefore, there is a problem to alleviate the electric field in this portion where the electric field is concentrated. One way to mitigate the electric field concentration by the field plate is to form a sheet of resistive material between the tip of the field plate and the other electrode. However, the method is applied to a bipolar transistor (see Japanese Patent Publication No. 52-24833). However, the means of this reference is the subject of the present invention, M
If applied to the OSFET, there arises a problem that a leak current flows between the source and the drain. It is an object of the present invention to provide a high breakdown voltage MOSFET provided with means for relaxing the electric field concentration at the tip of the field plate by means other than the reference.

[0006]

According to the present invention, a high-concentration diffusion region having the same conductivity type as that of a channel portion is provided on the substrate surface at the source-side end portion of the field plate immediately below the source wiring,
A low concentration diffusion region having the same conductivity type as the high concentration diffusion region and connected to the high concentration diffusion region is provided on the drain side of the high concentration diffusion region. In another aspect of the present invention, a high-concentration diffusion region of the same conductivity type as the channel portion is provided on the substrate surface at the source-side end portion of the field plate immediately below the source wiring, and a portion closer to the drain side than the high-concentration diffusion region is provided. A second diffusion region having the same conductivity type as the high concentration diffusion region and separated from the high concentration diffusion region is provided. In a preferred embodiment, the second diffusion region includes two or more regions which are arranged apart from each other in the drain side direction.

[0007]

A guard ring has been conventionally provided to prevent a reach-through in which a depletion layer is connected between the source region and the drain region between both regions. However, if a higher breakdown voltage is to be achieved, the guard ring alone is not enough. It is enough. In the present invention, in addition to the guard ring or the diffusion region that plays a role similar to that of the guard ring, a drain region of the depletion layer is formed by providing a diffusion region of the same conductivity type as the channel portion on the substrate surface between the diffusion region and the drain region. Further suppress the spread in the direction.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment. The same parts as those in FIG. 3 are designated by the same reference numerals. In FIG. 1, a high breakdown voltage MOSFET is formed on an N-type silicon substrate 2 separated by a dielectric. A drain region 4 of a high-concentration N-type diffusion region is formed on the side surface and the bottom surface of the substrate 2 so as to surround the inside, and a source of the high-concentration N-type diffusion region is formed in a low-concentration P-type diffusion region 6 in the substrate 2. Region 8 is formed.
Reference numeral 10 is a contact region of the region 6. On the surface of the substrate, a guard ring 12 is formed of a high-concentration P-type diffusion region so as to surround the P-type region 6 serving as a channel region and prevent the extension of the depletion layer. A gate electrode 14 is formed on the substrate 2 on the channel region via a gate oxide film. Reference numeral 16 denotes a metal wiring which is insulated from both the substrate 2 and the gate electrode 14 and is formed on the interlayer insulating film 18, and is connected to the source 8 and the contact 10 through the contact hole of the interlayer insulating film 18. The metal wiring 16 traverses the upper part of the substrate, which is separated from the high-voltage MOSFET to connect to other semiconductor devices and the outside. A field plate 20a for preventing depletion and inversion of the substrate surface immediately below the metal wiring 16 is formed of a polysilicon thin film. The field plate 20a is located between the metal wiring 16 and the substrate 2 and extends from above the drain region 4 to above the guard ring 12. The field plate 20a is insulated from both the substrate 2 and the metal wiring 16, and the base end portion is connected to the drain region 4. On the substrate surface below the field plate 20a, a low concentration diffusion region 22 which is connected to the guard ring 12 and has the same conductivity type as the guard ring 12 is formed.

In the embodiment of FIG. 1, the depletion layer generated when a high voltage is applied to the drain region 4 and the source / drain is reversely biased spreads around the diffusion layers 12 and 22, but the diffusion layer 22. Is present, the radius of curvature of the depletion layer is increased, and the breakdown voltage of the PN junction is increased.

FIG. 2 shows a second embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. As compared with the embodiment of FIG. 1, in FIG. 1, the low concentration N-type diffusion region 22 connected to the guard ring 12 is formed in the field plate 20a.
2, the P-type high concentration diffusion regions 24 and 26 separated from the guard ring 12 are formed on the substrate surface immediately below the metal wiring 16 and the field plate 20a. It is provided between the rain regions 4. P-type diffusion regions 24 and 26 are separated from guard ring 12, and P-type diffusion regions 24 and 26 are also arranged apart from each other. The P type diffusion regions 24 and 26 may be low concentration diffusion regions.

Also in FIG. 2, when a reverse bias voltage is applied between the source and the drain, the depletion layer causes diffusion regions 12, 24,
However, even at this time, the radius of curvature of the depletion layer is increased, the concentration of the electric field is relaxed, and the breakdown voltage of the PN junction is increased. In the embodiment of FIG. 2, the number of P-type diffusion regions arranged on the drain side of the guard ring 12 is 2.
Although it is two as shown by 4 and 26, it may be one or three or more. The larger the number of diffusion regions 24 and 26 is, the larger the radius of curvature of the depletion layer becomes, and the more the electric field concentration is relaxed.

[0012]

According to the present invention, a high-concentration diffusion region of the same conductivity type as that of the channel portion is provided on the substrate surface of the end portion on the source side of the field plate immediately below the source wiring, and a portion closer to the drain side than the high-concentration diffusion region is provided. Since a low-concentration diffusion region having the same conductivity type as that of the high-concentration diffusion region and connected to the high-concentration diffusion region is provided, the radius of curvature of the depletion layer increases when a reverse bias voltage is applied between the source and the drain, and the electric field The breakdown voltage of the PN junction due to concentration is increased,
A higher breakdown voltage MOSFET can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment, (A) is a plan view of a main part, and (B) is a sectional view taken along line XX ′.

2A and 2B are views showing a second embodiment, FIG. 2A is a plan view of a main part, and FIG. 2B is a sectional view taken along the line YY '.

FIG. 3 is a diagram showing a conventional high breakdown voltage MOSFET,
(A) is a plan view of a main part, and (B) is a cross-sectional view taken along the line ZZ '.

[Explanation of symbols]

 2 N-type substrate 4 Drain region 6 P-type region to be a channel 8 Source region 12 P-type diffusion region of guard ring 14 Gate electrode 16 Metal wiring connected to the source 20a Field plate 22 Low-concentration P-type diffusion region 24, 26 High-concentration diffusion region

Claims (3)

[Claims] 1. A first region in which a source region and a drain region are formed facing each other on a surface of a semiconductor substrate and connected to the source region.
The second conductor wiring connected to the drain region is formed immediately below the conductor wiring, and is insulated from the substrate and the first conductor wiring via an insulator, and the first conductor wiring is formed. Immediately below, on the substrate surface of the end portion of the second conductor wiring on the source region side, a high-concentration diffusion region of the same conductivity type as that of the channel portion, and the high-concentration diffusion region on the drain region side of the high-concentration diffusion region. A high-voltage semiconductor device having a low-concentration diffusion region connected to the high-concentration diffusion region of the same conductivity type as that of 1. 2. A first region having a source region and a drain region formed opposite to each other on a surface of a semiconductor substrate and connected to the source region.
The second conductor wiring connected to the drain region is formed immediately below the conductor wiring, and is insulated from the substrate and the first conductor wiring via an insulator, and the first conductor wiring is formed. Immediately below, on the substrate surface of the end portion of the second conductor wiring on the source region side, a high-concentration diffusion region of the same conductivity type as that of the channel portion, and the high-concentration diffusion region on the drain region side of the high-concentration diffusion region. A high withstand voltage semiconductor device having a second diffusion region of the same conductivity type as that of the second diffusion region separated from the high concentration diffusion region. 3. The high breakdown voltage semiconductor device according to claim 2, wherein the second diffusion region includes two or more regions which are arranged apart from each other in the direction of the drain region.