JPH06338610A - Mos transistor - Google Patents

Abstract

PURPOSE:To relieve the field concentration for increasing the element breakdown strength by a method wherein a specific interval is made between a drain electrode and a gate electrode so that the potential contour lines may extend to the interval direction to be aligned perpendicularly to a gate oxide film. CONSTITUTION:For example, an Al source electrode 70 is formed in ohmic contact with a source part 30 likewise an Al drain electrode 80 is in ohmic contact with a drain part 40 while one end 81 thereof 80 overlapped with an oxide film 50 is extended over a drift part 20 separated from the drain part 40 to be arranged making an interval 90 with one end 61 of a gate electrode 60. In such a constitution, the potential contour lines extending over the direction of the interval 90 can be aligned perpendicularly to the gate oxide film 50 due to the existance of the interval 90 between the drain electrode 80 and the gate electrode 60. Accordingly, the bend of the potential contour lines on the surface of a semiconductor substrate 10 and inside the gate oxide film 50 can be straightened up resultantly enabling the field concentration to be relieved for increasing the element breakdown strength.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a MOS (Metal).
Oxide Silicon)
In particular, it relates to improvement of the device characteristics.

[0002]

2. Description of the Related Art Conventionally, a MOS transistor having a structure shown in FIG. 3 is known as a MOS transistor having an improved breakdown voltage. FIG. 3 is a vertical sectional view of a conventional MOS transistor. In FIG. 3, a gate oxide film 53 and a gate electrode 62 overlapping the gate oxide film 53 are formed on a semiconductor substrate substrate 10 made of N-type silicon.

Then, the semiconductor substrate 10 contains P-type impurities.
Ions are self-aligned with the gate electrode 62,
This is thermally diffused and P^-Mold P^-Layer 22 is formed and further
To P ^-P inside the layer 22⁺The mold drain 40 is external
For P⁺Each of the mold source portions 30 is formed.

A source electrode 70 and a drain electrode 82 are formed in ohmic contact with the source portion 30 and the drain portion 40, respectively.

In such a MOS transistor,
When a negative voltage is applied to the drain portion 40 with respect to the gate electrode 62, the source electrode 70, and the semiconductor substrate 10, the depletion layer extends not only inside the semiconductor substrate 10 but also to the P ⁻ layer 22 on the drain portion 40 side. . Therefore, the electric field from the gate electrode 62 is dispersed to the low-concentration P ⁻ layer 22 side without being concentrated in the high-concentration drain part 40, and the breakdown voltage of the element is improved.

[0006]

FIG. 4 shows a gate electrode 62 and a source electrode 70 of the MOS transistor shown in FIG.
6 is a vertical cross-sectional view showing a potential distribution when a negative high voltage is applied to the drain electrode 82 with respect to FIG. Incidentally, in FIG. 4, the dotted lines are contour lines of equipotential.

As shown in FIG. 4, in the conventional MOS transistor, the electric field concentration in the drain portion 40 is alleviated.
There is a problem that the electric field concentration portion 24 still exists on the surface of the P ⁻ layer 22 and inside the gate oxide film 53, and the element breakdown voltage is limited by the electric field concentration.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to reduce the concentration of an electric field and improve the breakdown voltage of the device.
It is to provide an OS transistor.

[0009]

In order to achieve the above object, the present invention provides a drift portion formed on the main surface of a semiconductor substrate of the second conductivity type having a polarity opposite to that of the semiconductor substrate of the first conductivity type. A source portion formed on the main surface of the semiconductor substrate at a second conductivity type having a higher concentration than that of the drift portion, the source portion being separated from one end of the drift portion to the outside and higher than the drift portion. A second conductivity type of concentration, a drain part formed inside the drift part and spaced inward from one end part of the drift part, and formed on the semiconductor substrate, and one end part of which is the drift part. And a gate oxide film that extends to the drain portion and the other end portion extends to the source portion, and is formed on the gate oxide film, one end portion of which extends on the drift portion and the other end portion of the gate oxide film is formed. A gate whose end extends above the source portion. Gate electrode is formed in ohmic contact with the drain part, and one end of the gate electrode overlaps one end of the gate oxide film and extends over the drift part separated from the drain part. A MOS transistor, comprising: a drain electrode that forms a desired distance from one end of the electrode; and a source electrode that is formed in ohmic contact with the source portion.

[0010]

According to the present invention as described above, the potential contour lines extend in the direction of the interval formed between the drain electrode and the gate electrode, and are aligned perpendicular to the gate oxide film. Therefore, the electric field concentration on the surface of the semiconductor substrate and inside the gate oxide film is relaxed.

[0011]

Embodiments of the present invention will now be described with reference to the drawings. Hereinafter, description will be made taking a P-type channel MOS transistor as an example. In addition, in the following drawings, FIGS.
The same parts as those in FIG.

FIG. 1 is a vertical sectional view showing a specific embodiment of the present invention. In FIG. 1, the drift portion 20 is formed by thermally diffusing low concentration boron, for example, as a second conductivity type P type impurity on the main surface of a semiconductor substrate 10 made of, for example, N type silicon. There is.

In the source portion 30, for example, boron as the P-type impurity is contained in the semiconductor substrate 1 at a higher concentration than the drift portion 20.
It is formed by being thermally diffused on the main surface of No. 0 and separated from the end portion 21 of the drift portion 20 to the outside.

In the drain portion 40, for example, boron as a P-type impurity is thermally diffused into the drift portion 20 in a concentration higher than that of the drift portion 20, and an end portion 41 thereof is separated from an end portion 21 of the drift portion 20 inward. Is formed.

Gate oxide film 50 is formed on the main surface of semiconductor substrate 10 with one end portion 51 extending to drift portion 20 and drain portion 40 and the other end portion 52 extending to source portion 30. ing.

Then, for example, a polysilicon gate electrode 60 in which N-type impurities are diffused at a high concentration is formed on the gate oxide film 50, and one end portion 61 thereof extends on the drift portion 20, The other end portion 62 extends to the source portion 30.

The source electrode 70 made of, for example, aluminum metal (containing several% of silicon) is formed in ohmic contact with the source portion 30, and is made of, for example, aluminum metal (several%).
The drain electrode 80 (containing silicon) makes ohmic contact with the drain portion 40, and one end portion 81 thereof overlaps with the gate oxide film 50 and extends on the drift portion 20 separated from the drain portion 40 to extend to the gate electrode 60. The end portion 61 and the end portion 61 are provided with a gap 90 of, for example, about several μm.

Next, the operation of the MOS transistor shown in FIG. 1 will be described with reference to FIG. FIG. 2 shows the MO shown in FIG.
FIG. 6 is a vertical cross-sectional view showing a potential distribution when a negative high voltage is applied to a drain electrode 80 with respect to a gate electrode 60 and a source electrode 70 of an S transistor.

In FIG. 2, since there is a gap 90 between the drain electrode 80 and the gate electrode 60, the potential contour line extends in the direction of the gap 90, and is aligned perpendicular to the gate oxide film 50. Therefore, the bending of the potential contour line on the surface of the semiconductor substrate 10 or inside the gate oxide film 50 is eliminated, and as a result, the electric field concentration is alleviated and the breakdown voltage of the element is improved.

Further, the present invention is not limited to the P-type channel MOS transistor described above, but can be applied to an N-type channel MOS transistor whose conductivity type is reversed.

[0021]

As described above, according to the present invention, a desired space is provided between the drain electrode and the gate electrode, and the contour lines of the potential extend in the direction of the space and are aligned perpendicular to the gate oxide film. Since it is configured, it is possible to provide a MOS transistor in which the electric field concentration is further alleviated and the device breakdown voltage is improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a specific embodiment of the present invention.

FIG. 2 is a vertical sectional view for explaining the operation of the MOS transistor shown in FIG.

FIG. 3 is a vertical sectional view of a conventional MOS transistor.

FIG. 4 is a vertical cross-sectional view explaining the operation of the MOS transistor shown in FIG.

[Explanation of symbols]

 10 semiconductor substrate 20 drift part 30 source part 40 drain part 50 gate oxide film 60 gate electrode 70 source electrode 80 drain electrode 90 interval

Claims (1)

[Claims] 1. A drift region formed on the main surface of the semiconductor substrate, which has a second conductivity type having a polarity opposite to that of the first conductivity type semiconductor substrate, and a second conductivity type having a higher concentration than the drift unit, A source part formed on the main surface of the semiconductor substrate and spaced apart from one end of the drift part; a second conductivity type having a higher concentration than the drift part; and one end of the drift part. A drain portion that is formed inside the drift portion, and is formed on the semiconductor substrate, with one end portion extending to the drift portion and the drain portion and the other end portion being the source portion. A gate oxide film extending to the gate oxide film, a gate electrode formed on the gate oxide film, one end of which extends on the drift part and the other end of which extends on the source part; Shaped by ohmic contact with the drain part And one end of the gate oxide film overlaps one end of the gate oxide film and extends over the drift part separated from the drain part and has a desired distance from one end of the gate electrode. And a source electrode formed in ohmic contact with the source portion.