JPH07245395A - High breakdown strength mos transistor and its manufacture - Google Patents

Abstract

PURPOSE:To prevent leak due to creeping of source and drain regions to below a gate electrode in an edge part of a field oxide film without increasing manhour while ensuring high breakdown strength. CONSTITUTION:In a high breakdown strength MOS transistor, a field oxide film 2 is formed on a surface of a P<->-type silicon substrate 1 by a selective oxidation method, a strip-like gate electrode 11 consisting of polysilicon, etc., is formed in a window opening part of the field oxide film 2 of the silicon substrate 1 extending over the field oxide film 2 with a gate oxide film 3 of SiO2, etc., therebetween, and high concentration N<+>-type impurities are selectively diffused by self-alignment in a surface of the silicon substrate 1 at both sides of the gate electrode 11 for forming a source region 5 and a drain region 6. A wide part 12 is therefore formed in the gate electrode 11 in an edge part (m) of the field oxide film 2 along a direction perpendicular to an extension direction of the gate electrode 11.

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 MOS transistor and a manufacturing method thereof, for example, an N channel high breakdown voltage MOS transistor used in various integrated circuits and a manufacturing method thereof.

[0002]

2. Description of the Related Art For example, an N-channel high breakdown voltage MOS transistor has the following specific structure.

[0003] That is, as shown in FIG. 3 (a) (b) P -
A field oxide film 2 is formed on the surface of a silicon substrate 1 by a selective oxidation method, and a strip made of polysilicon or the like is formed in the window opening portion of the field oxide film 2 of the silicon substrate 1 via a gate oxide film 3 such as SiO _2. -Shaped gate electrode 4 is formed so as to straddle the field oxide film 2, and high-concentration N ⁺ -type impurities are self-applied to the gate electrode 4 and the field oxide film 2 on the surface of the silicon substrate 1 on both sides of the gate electrode 4. Source and drain regions 5 and 6 are formed by selective diffusion by aligning. In the figure, 7 is a channel stopper region made of a high concentration P ⁺ -type impurity which is formed under the field oxide film 2 to insulate and separate another semiconductor element adjacent thereto.

[0004]

By the way, in the high breakdown voltage MOS transistor having the above-mentioned structure, as shown in FIG.
By forming the field oxide film 2 as shown in (b),
At the edge portion m [bird's peak] of the field oxide film 2 along the direction intersecting the direction in which the gate electrode 4 extends, boron which is a P-type impurity in the silicon substrate 1 is eroded and its impurity concentration is lowered.

On the other hand, after the gate electrode 4 is formed, N-type impurities are pushed into the surface of the silicon substrate 1 from the window opening portion of the field oxide film 2 by ion implantation and diffused, so that the silicon substrate 1 on both sides of the gate electrode 4 is diffused. The source region 5 and the drain region 6 are formed on the surface. At this time, as shown in FIG. 4A, the source and drain regions 5 and 6 made of the N-type impurities described above are formed below the gate electrode 4 by the lateral diffusion. It is well known that it goes around a little.

Since the amount of sneaking in of the source and drain regions 5, 6 increases as the impurity concentration of the silicon substrate 1 decreases, as described above, the silicon substrate 1 immediately below the gate electrode 4 at the edge portion m of the field oxide film 2. If the impurity concentration in the inside is low, the edge portion m of the field oxide film 2
Then, as shown in FIG. 4B, the wraparound amount of the source region 5 and the drain region 6 directly below the gate electrode 4 becomes large, and the source region 5 and the drain region 6 are close to each other, and between them 5 and 6. There was a problem that a leak occurred. This problem becomes more remarkable as the width dimension [gate length] of the gate electrode 4 becomes smaller as the semiconductor device becomes more highly integrated and faster.

As a means for solving this problem, Japanese Unexamined Patent Publication No.
As disclosed in Japanese Patent Laid-Open No. 3-260178, there is a structure in which a high-concentration layer serving as a channel stopper is exposed inside a field oxide film. In this case, the high-concentration layer has a high-concentration source and drain regions. Therefore, it becomes difficult to secure a high breakdown voltage. In addition, JP-A-62-1
As disclosed in Japanese Patent No. 7148, there is a structure in which a high-concentration layer is formed along the edge portion of a field oxide film and the high-concentration source and drain regions are formed so as not to be in contact with the high-concentration layer. By doing so, it is impossible to form the source and drain regions by self-alignment with the field oxide film, and a dedicated mask for forming the source and drain regions is required, resulting in an increase in man-hours and an increase in cost. .

Therefore, the present invention has been proposed in view of the above problems, and an object of the present invention is to secure a high withstand voltage and to increase the number of steps without increasing the man-hours. It is an object of the present invention to provide a high breakdown voltage MOS transistor and a method for manufacturing the same, which can prevent leakage due to the sneak of the source and drain regions under the gate electrode.

[0009]

As a technical means for achieving the above-mentioned object, the present invention forms a field oxide film by a selective oxidation method which leaves an element formation region on the surface of a P-type silicon substrate. A gate electrode is formed in the window opening portion of the field oxide film so as to extend over the field oxide film through the gate oxide film, and a high concentration N-type impurity is added to the gate electrode and the field in the window opening portion on both sides of the gate electrode. In a high breakdown voltage MOS transistor in which source and drain regions are selectively diffused by self-alignment with respect to an oxide film, the gate electrode is widened at the edge portion of the field oxide film along the direction intersecting the direction in which the gate electrode extends. It is characterized in that a part is formed.

Further, the method of the present invention comprises a step of forming a field oxide film by a selective oxidation method while leaving an element formation region on the surface of a P-type silicon substrate, and a window opening portion of the field oxide film which becomes the element formation region. A step of forming a gate electrode having a wide portion at the edge portion of the field oxide film, which is divided into two and spans the field oxide film, through the gate oxide film; and N-type using the field oxide film and the gate electrode as a mask It is characterized by a step of implanting impurities and a step of diffusing the implanted impurities by heat treatment.

[0011]

In the high voltage MOS transistor according to the present invention,
By forming the wide part in the gate electrode at the edge part of the field oxide film along the direction crossing the direction in which the gate electrode extends, the wraparound of the source and drain regions under the gate electrode at the edge part of the field oxide film Even if this occurs, a sufficient space can be secured between the source region and the drain region.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a high breakdown voltage MOS transistor according to the present invention will be described with reference to FIGS. The same parts as those in FIGS. 3 and 4 are designated by the same reference numerals.

For example, in the N-channel high breakdown voltage MOS transistor, as in the conventional case, as shown in FIG. 1A, a field oxide film 2 made of SiO ₂ or the like is formed on the surface of a P ⁻ type silicon substrate 1 by a selective oxidation method. Then, a strip-shaped gate electrode 11 made of polysilicon or the like is formed in the window opening portion of the field oxide film 2 of the silicon substrate 1 via a gate oxide film 3 such as SiO ₂ so as to straddle the field oxide film 2. Then, a high concentration N ⁺ -type impurity is selectively diffused on the surface of the silicon substrate 1 on both sides of the gate electrode 11 by self-alignment with respect to the gate electrode 11 and the field oxide film 2 to form the source region 5 and the drain region 6. Although formed, the high breakdown voltage MOS transistor of the present invention is different from the conventional one in the following points.

The feature of the present invention lies in the shape of the gate electrode 11. That is, both end portions of the gate electrode 11 are made wider than the central portion. In particular, the field oxide film 2 and the edge portion m along the direction intersecting the direction in which the gate electrode 11 extends
Then, the wide portion 12 is provided on the gate electrode 11. The shape of the gate electrode 11 described above is not limited to that shown in FIG. 1A, and for example, as shown in FIG.
The taper shape is widened from the central portion of 1'to both end portions, or as shown in FIG.
It is also possible to have a shape that protrudes on only one side, instead of a shape that protrudes on both sides of.

Here, in the manufacture of a high voltage MOS transistor, after the gate electrode 11 is formed, N-type impurities are ion-implanted into the surface of the silicon substrate 1 from the window opening portion of the field oxide film 2 and then diffused by pushing. Thus, the source region 5 and the drain region 6 are formed on the surface of the silicon substrate 1 on both sides of the gate electrode 11. At this time, as shown in FIG. The regions 5 and 6 slightly go under the gate electrode 11 due to the lateral diffusion.

On the other hand, by forming the field oxide film 2,
At the edge portion m [bird's peak] of the field oxide film 2, boron, which is a P-type impurity in the silicon substrate 1 immediately below the gate electrode 11, is eroded and the impurity concentration is lowered. The wraparound amount of the source region 5 and the drain region 6 increases as the impurity concentration of the silicon substrate 1 decreases, so that the edge portion m of the field oxide film 2 as described above.
Therefore, the impurity concentration in the silicon substrate 1 immediately below the gate electrode 11 is low, and as a result, at the edge portion m of the field oxide film 2 along the direction intersecting the direction in which the gate electrode 11 extends, the gates of the source region 5 and the drain region 6 are The amount of wraparound just below the electrode 11 increases.

However, in the high withstand voltage MOS transistor of the present invention, the wide portion 12 is formed in the gate electrode 11 at the edge portion m of the field oxide film 2, so that FIG.
As shown in (c), even if the amount of the source region 5 and the drain region 6 sneaking directly under the gate electrode 11 is large, a sufficient distance between the source region 5 and the drain region 6 can be ensured. It is possible to prevent a leak from occurring between the drain region 5 and the drain region 6. As a result, even if the width dimension [gate length] of the gate electrode 11 becomes smaller due to the higher integration and higher speed of the semiconductor device, it is possible to reliably prevent the occurrence of leakage.

Although the N-channel MOS transistor using the P-type silicon substrate has been described in the above embodiment, the present invention is not limited to this, and the P-type impurity diffusion layer may be used using the N-type silicon substrate. N channel MO in which a [P well] is formed and an element is formed in the diffusion layer
It is also applicable to the S transistor.

[0019]

According to the present invention, since the wide portion is formed in the gate electrode at the edge portion of the field oxide film along the direction intersecting with the extending direction of the gate electrode, the edge portion of the field oxide film is formed. Even if the source and drain regions go under the gate electrode, a sufficient distance can be secured between the source region and the drain region,
Leakage due to the wraparound can be prevented in advance, a highly reliable MOS transistor can be provided, and the product yield is improved.

[Brief description of drawings]

1A and 1B show an embodiment of a high breakdown voltage MOS transistor according to the present invention, in which FIG. 1A is a plan view thereof, FIG. 1B is a sectional view taken along line AA of FIG. 1A, and FIG. B- in (a)
Sectional view along line B

FIG. 2 is for explaining a modified example of the present invention,
(A) (b) is a top view which shows two examples of the shape of a gate electrode.

3A and 3B are diagrams for explaining a conventional example of a high breakdown voltage MOS transistor, in which FIG. 3A is a plan view thereof, and FIG. 3B is a sectional view taken along line CC of FIG.

4A is a sectional view taken along the line D-D in FIG.
3B is a sectional view taken along the line EE of FIG.

[Explanation of symbols]

 1 P-type silicon substrate 2 Field oxide film 3 Gate oxide film 5 Source region 6 Drain region 11 Gate electrode 12 Wide part m Field oxide film edge part

Claims (2)

[Claims] 1. A field oxide film is formed on a surface of a P-type silicon substrate by a selective oxidation method which leaves an element formation region, and a gate electrode is formed into a field oxide film through a gate oxide film in a window opening portion of the field oxide film. The gate electrode and the gate electrode are formed so as to straddle, and high-concentration N-type impurities are selectively diffused by self-alignment with respect to the gate electrode and the field oxide film in the window opening portions on both sides of the gate electrode to form the source and drain regions. A high breakdown voltage MOS transistor, characterized in that, in the high breakdown voltage MOS transistor, a wide portion is formed in a gate electrode at an edge portion of a field oxide film along a direction intersecting a direction in which a gate electrode extends. 2. A step of forming a field oxide film by a selective oxidation method while leaving an element formation region on the surface of a P-type silicon substrate, and dividing a window opening portion of the field oxide film to be the element formation region into two. Forming a gate electrode across the field oxide film and having a wide portion at an edge portion of the field oxide film through the gate oxide film; and using the field oxide film and the gate electrode as a mask
A method of manufacturing a high breakdown voltage MOS transistor, comprising: a step of implanting a type impurity; and a step of diffusing the implanted impurity by heat treatment.