JPH05183156A - Semiconductor device and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Purpose] Equipped with a plurality of independently formed gate electrodes,
A part of one gate electrode improves the breakdown voltage of the gate insulating film existing between the gate electrodes in the semiconductor device having a shape overlapping the other gate electrode. [Structure] After forming a first gate electrode 6 on a semiconductor substrate 1 with a first gate insulating film 5 interposed therebetween, a first gate electrode 6 is formed on the exposed semiconductor substrate 1 and a surface of the first gate electrode 6. Second silicon oxide film 7 is formed, the second silicon oxide film 7 is etched until the region of the semiconductor substrate 1 exposed in the above step is exposed again, and then the insulating film and the second polycrystalline silicon film are formed on the entire surface. 12 are sequentially formed, and are patterned and selectively removed to form the second gate electrode 13 with the second gate insulating film 12 interposed therebetween.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a semiconductor device in which the breakdown voltage of a gate insulating film (interlayer insulating film) existing between a plurality of independently formed gate electrodes is improved. Manufacturing method.

[0002]

2. Description of the Related Art Conventionally, a plurality of independently formed gate electrodes are provided on a channel region formed on a semiconductor substrate,
As a semiconductor device having a shape in which a part of one gate electrode overlaps the other gate electrode, for example, a MONOS (Metal Oxide Nitri) is used.
Examples thereof include a de Oxide Semiconductor) type semiconductor non-volatile memory device and a split gate type semiconductor non-volatile memory device.

In these semiconductor devices, for example, as shown in FIG. 7, the gate insulating film 20 is provided at a predetermined position on the semiconductor substrate 1.
Through the first gate electrode 2 made of a polycrystalline silicon film
1 is formed, an oxide film, a nitride film, and an oxide film are sequentially deposited thereon to form an interlayer insulating film having a multilayer structure, and a polycrystalline silicon film is further deposited thereon, and then the above By selectively removing the interlayer insulating film and the polycrystalline silicon film so that the interlayer insulating film and the polycrystalline silicon film overlap a part of the first gate electrode 21, the gate insulating film 23 is removed. The second gate electrode 22 is formed through.

[0004]

In the conventional semiconductor device described above, the gate insulating film 23 existing between the semiconductor substrate 1 and the second gate electrode 22 is deposited on single crystal silicon (semiconductor substrate). Therefore, it has excellent insulation characteristics. Therefore, the gate insulating film 23 existing between the semiconductor substrate 1 and the second gate electrode 22 does not hinder the performance of the semiconductor device even if it is thinned.

However, the first gate electrode 21
A part of the gate insulating film 23 existing between the second gate electrode 22 and the second gate electrode 22 is deposited on the polycrystalline silicon film (first gate electrode 21). Here, as is well known in the art, since the insulating property of the insulating film deposited on the polycrystalline silicon film is inferior to that of the insulating film deposited on the single crystal silicon, the first gate electrode If the gate insulating film 23 existing between the second gate electrode 22 and the second gate electrode 22 is thinned, the withstand voltage (insulation characteristic) of this portion becomes insufficient, which causes a problem in the performance of the semiconductor device.

Particularly, in the MONOS type semiconductor nonvolatile memory element, the film thickness of the ONO (oxide film / nitride film / oxide film) portion is as thin as about 80 to 150Å in terms of oxide film, and will be further thinned in the future. Therefore, it is necessary to provide the gate insulating film 23 with a withstand voltage that can meet the thinning conditions. An object of the present invention is to solve such a problem, and it is provided with a plurality of gate electrodes formed independently, and one gate electrode partially overlaps with the other gate electrode. It is an object of the present invention to provide a semiconductor device having the above-mentioned shape, in which the breakdown voltage of the gate insulating film existing between the gate electrodes is improved, and a manufacturing method thereof.

[0007]

In order to achieve this object, the present invention comprises a plurality of independently formed gate electrodes on a channel region formed in a semiconductor substrate, and one gate electrode is provided with: In a semiconductor device having a shape in which a part of the other gate electrode overlaps, the gate insulating film of the gate electrode that overlaps the one gate electrode has a multilayer structure, and It is intended to provide a semiconductor device characterized in that a film thickness of a region in contact with the electrode is larger than a film thickness of a region in contact with the semiconductor substrate.

Further, a plurality of independently formed gate electrodes are provided on the channel region formed on the semiconductor substrate,
In a method of manufacturing a semiconductor device having a shape in which a part of the other gate electrode overlaps on one gate electrode, a first oxide film and a first polycrystalline silicon film are sequentially formed on the semiconductor substrate. The first step of forming, and the first
Second step of selectively removing the first oxide film and the first polycrystalline silicon film, the semiconductor substrate exposed in the second step, and the first polycrystalline silicon film selectively formed in the third step. A third step of forming a second oxide film on the surface, a fourth step of etching the second oxide film until the semiconductor substrate region exposed in the second step is exposed again, and a fourth step. On the exposed semiconductor substrate region and on the surface of the second oxide film,
A fifth step of forming an insulating film, a sixth step of forming a second polycrystalline silicon film on the insulating film, and a seventh step of selectively removing the insulating film and the second polycrystalline silicon film. The present invention provides a method for manufacturing a semiconductor device, which comprises:

[0009]

According to the semiconductor device of the first aspect, among the film thicknesses of the gate insulating film of the gate electrode which overlaps the one gate electrode, the film thickness of a region in contact with the one gate electrode. Is made thicker than the region in contact with the semiconductor substrate, so that, for example, even if the basic structure of the gate insulating film is an ONO structure capable of being thinned, the gate insulating film existing between the both gate electrodes. It is possible to secure a sufficient withstand voltage. Therefore, it becomes possible to sufficiently cope with the thinning of the gate insulating film.

According to a second aspect of the method of manufacturing a semiconductor device, in the third step, the surface of the first polycrystalline silicon film selectively formed in the second step, and the second step. By forming a second oxide film on the exposed semiconductor substrate, the film thickness of the second oxide film formed on the exposed semiconductor substrate is adjusted to the surface of the first polycrystalline silicon film. It can be made thicker than the film thickness of the second oxide film formed. That is, this difference in film thickness is the rate at which an oxide film is deposited on the polycrystalline silicon film by thermal oxidation (oxidation rate).
Is about 2.5 to 4 times faster than the rate of depositing an oxide film on single crystal silicon (semiconductor substrate) under the same conditions (slightly different depending on the atmosphere of the thermal oxidation).

Then, in the fourth step, the second step
The semiconductor substrate region exposed in the process is re-exposed to the second
By etching the oxide film of, the second oxide film can be formed only on the surfaces of the first oxide film and the first polycrystalline silicon film selectively formed in the second step.
That is, the etching rate of the oxide film formed on the polycrystalline silicon film is about 1 to 1.5 times that of the oxide film formed on the single crystal silicon.
This occurs because the difference is extremely small compared to the difference in the oxidation rate.

Therefore, the insulating film formed in the fifth step is formed on the exposed surface of the semiconductor substrate on the surfaces of the first oxide film and the first polycrystalline silicon film selectively formed in the second step. The thickness of the insulating film can be increased by the amount of the remaining second oxide film. Therefore, as a result of being able to sufficiently secure the breakdown voltage of the insulating film formed on the polycrystalline silicon film, it is possible to sufficiently cope with the thinning of the gate insulating film such as the ONO structure.

[0013]

Embodiments of the present invention will now be described with reference to the drawings. 1 to 6 are partial cross-sectional views showing a manufacturing process of a semiconductor device according to an embodiment of the present invention.
In the step shown in FIG. 1, for example, dry oxidation at 900 ° C. is performed on the semiconductor substrate 1 separated by the field oxide film 2 to deposit a first silicon oxide film 3 having a film thickness of about 200 Å. Then, a first polycrystalline silicon film 4 having a film thickness of about 4000 Å is deposited on this, and, for example,
Phosphorus is diffused to make the first polycrystalline silicon film 4 have electric conductivity.

Next, in the step shown in FIG. 2, the semiconductor substrate 1 obtained in the step shown in FIG. 1 is patterned to selectively etch the first silicon oxide film 3 and the first polycrystalline silicon film 4. To do. In this way, on the semiconductor substrate 1,
The first gate electrode 6 was formed via the first gate insulating film 5. Next, in the step shown in FIG. 3, the semiconductor substrate 1 obtained in the step shown in FIG. 2 is thermally oxidized in a steam atmosphere at 850 ° C. to form a second silicon oxide film 7. here,
Since the rate of the thermal oxidation is different between single crystal silicon and polycrystalline silicon, the semiconductor substrate 1 shown in FIG.
A second silicon oxide film 7 having a film thickness of about 200 Å is formed on the semiconductor substrate 1 region (single crystal silicon) exposed in the step shown in FIG.
A second silicon oxide film 7 of about 0Å is deposited.

Next, in the step shown in FIG. 4, the second silicon oxide film 7 obtained in the step shown in FIG. 3 is etched using hydrofluoric acid, and the semiconductor substrate exposed in the step shown in FIG. Re-expose one area. Here, since the etching rates of the second silicon oxide film 7 for hydrofluoric acid are different,
When a predetermined region of the semiconductor substrate 1 is exposed, a second film having a film thickness of about 500 to 600Å is formed on the surface of the first gate electrode 6.
The silicon oxide film 7 is left.

Next, in the step shown in FIG. 5, a silicon oxide film 8 having a film thickness of about 20Å and a silicon nitride film 9 having a film thickness of about 70 to 150Å are formed on the semiconductor substrate 1 obtained in the step shown in FIG. Deposit one after another. Then, the silicon nitride film 9 is formed.
Is thermally oxidized to deposit a silicon oxide film 10 having a film thickness of about 40 to 80Å, and then a second film having a film thickness of about 4000Å is deposited.
Then, the polycrystalline silicon film 11 is deposited. After that, for example, phosphorus is diffused in the second polycrystalline silicon film 11 so as to have electric conductivity.

Next, in the step shown in FIG. 6, the semiconductor substrate 1 obtained in the step shown in FIG. 5 is patterned to form a second polycrystalline silicon film 11, a silicon oxide film 10, a silicon nitride film 9 and a silicon oxide film. The film 8 and the second silicon oxide film 7 are selectively etched. In this way, the second gate electrode 13 was formed via the second gate insulating film 12.
Here, the second gate including the second silicon oxide film 7, the silicon oxide film 8, the silicon nitride film 9, and the silicon oxide film 10 is provided between the first gate electrode 6 and the second gate electrode 13. The insulating film 12 is the second gate insulating film 1 including the silicon oxide film 8, the silicon nitride film 9, and the silicon oxide film 10 between the semiconductor substrate 1 and the second gate electrode 13.
2 was formed. That is, the film thickness of the second gate insulating film 12 formed on the polycrystalline silicon film is smaller than the film thickness of the remaining second silicon oxide film 12 formed on the single crystal silicon. The thickness of the film 7 (500 to 600
Å) It can be formed thick. Therefore, the breakdown voltage of this portion can be sufficiently secured. Furthermore, the second gate insulating film 13 existing between the semiconductor substrate 1 and the second gate electrode 13 has an ONO structure, and thinning is achieved.

After that, the source / drain regions, wirings, etc. are formed by a known method to complete the semiconductor device.
In the process shown in FIG. 3 of this embodiment, the semiconductor substrate 1 is
Although the second silicon oxide film 7 is formed by thermal oxidation in a water vapor atmosphere at 50 ° C., the present invention is not limited to this method, and the second silicon oxide film 7 may be thermally oxidized in another atmosphere such as a dry oxygen atmosphere.

In the step shown in FIG. 4, the second silicon oxide film 7 is etched with hydrofluoric acid. However, the present invention is not limited to this, and the second silicon oxide film 7 is formed on the surface of the first gate electrode 6. Other etchants may be used provided they can be left behind. Then, in the present embodiment, a method of manufacturing a semiconductor device having a shape in which a part of the second gate electrode 13 overlaps the first gate electrode 6 has been described, but the present invention is not limited to this. Is independently formed on a channel region formed on a semiconductor substrate, such as a semiconductor device having a shape in which a part of the second gate electrode and a part of the third gate electrode overlap each other. Needless to say, a semiconductor device having a plurality of gate electrodes, and a part of one gate electrode overlapping the other gate electrode can be applied to a semiconductor device having another structure.

[0020]

As described above, according to the first aspect of the invention, one of the gate electrode film thicknesses of the gate insulating film of the gate electrode overlapping the one gate electrode is the one gate electrode. By making the film thickness of the region in contact with the semiconductor substrate thicker than that in the region in contact with the semiconductor substrate, it is possible to sufficiently secure the breakdown voltage of the gate insulating film existing between the both gate electrodes. It becomes possible to sufficiently cope with the thinning of the film. Therefore, it is possible to provide a semiconductor device having improved reliability and high integration.

According to the second aspect of the invention, the difference in thermal oxidation rate between the polycrystalline silicon film and the single crystal silicon, and the oxide film and the single crystal silicon deposited on the polycrystalline silicon film By utilizing the difference in etching rate of the oxide film deposited on the gate electrode, the thickness of the insulating film formed on the gate electrode made of the polycrystalline silicon film is changed to that of the insulating film formed on the semiconductor substrate (single crystal silicon). It can be thicker than the film thickness. Therefore, the breakdown voltage of the gate insulating film existing between the plurality of independently formed gate electrodes can be improved, and as a result, the reliability of the semiconductor device is improved. Furthermore, since the thickness of the gate insulating film existing between the gate electrode and the semiconductor substrate can be reduced, high integration can be achieved.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a manufacturing process of a semiconductor device according to an embodiment of the invention.

FIG. 2 is a partial cross-sectional view showing the manufacturing process of the semiconductor device according to the embodiment of the invention.

FIG. 3 is a partial cross-sectional view showing the manufacturing process of the semiconductor device according to the embodiment of the invention.

FIG. 4 is a partial cross-sectional view showing the manufacturing process of the semiconductor device according to the example of the invention.

FIG. 5 is a partial cross-sectional view showing the manufacturing process of the semiconductor device according to the embodiment of the invention.

FIG. 6 is a partial cross-sectional view showing the manufacturing process of the semiconductor device according to the embodiment of the invention.

FIG. 7 is a partial cross-sectional view showing a conventional semiconductor device.

[Explanation of symbols]

 1 semiconductor substrate 2 field oxide film 3 first silicon oxide film 4 first polycrystalline silicon film 5 first gate insulating film 6 first gate electrode 7 second silicon oxide film 8 silicon oxide film 9 silicon nitride film 10 Silicon Oxide Film 11 Second Polycrystalline Silicon Oxide Film 12 Second Gate Insulating Film 13 Second Gate Electrode

Claims (2)

[Claims] 1. A semiconductor having a plurality of independently formed gate electrodes on a channel region formed on a semiconductor substrate, and a shape in which a part of the other gate electrode overlaps one gate electrode. In the device, the gate insulating film of the gate electrode that overlaps the one gate electrode has a multi-layered structure, and a film thickness of a region in contact with the one gate electrode is in contact with the semiconductor substrate. A semiconductor device characterized by being thicker than a film thickness of a region to be formed. 2. A semiconductor having a plurality of independently formed gate electrodes on a channel region formed on a semiconductor substrate, and a shape in which one gate electrode partially overlaps with the other gate electrode. In the method of manufacturing the device, a first step of sequentially forming a first oxide film and a first polycrystalline silicon film on the semiconductor substrate, and a step of forming the first oxide film and the first polycrystalline silicon film. The second step of removing selectively, the semiconductor substrate exposed in the second step, and the surface of the first polycrystalline silicon film selectively formed in the third step,
Forming an oxide film, a fourth step of etching the second oxide film until the semiconductor substrate region exposed in the second step is exposed again, and a semiconductor substrate region exposed in the fourth step A fifth step of forming an insulating film on the upper surface of the second oxide film, a sixth step of forming a second polycrystalline silicon film on the insulating film, and the insulating film and the second polycrystalline film. A seventh step of selectively removing the crystalline silicon film, and a method of manufacturing a semiconductor device.