JPH10284615A - Semiconductor device and manufacture therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable semiconductor device with few device characteristic changes and a method for manufacturing the semiconductor device by providing a simple and short-period process to form high withstand-voltage devices and low withstand-voltage devices having different oxide film thicknesses in a plurality of device formation regions on the same substrate. SOLUTION: Boron ions for controlling a threshold value of a channel layer 19b are injected into a device formation region 16b where a low withstand voltage transistor is formed, while boron ions for controlling a threshold value of a channel layer 19a and oxygen ions for changing an oxide film thickness are injected into a device formation region 16a where a high withstand voltage transistor is formed, and heat oxidation processing is performed. By this arrangement, a thin gate oxide film 24b for a low withstand-voltage transistor is formed uniformly in the device formation region 16b, while a thick gate oxide film 24a for the high withstand-voltage transistor is formed uniformly in the device formation region 16a. Thus, the gate oxide films having differing film thicknesses can be formed by performing the heat oxidation processing only once.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a method of manufacturing a semiconductor device. And a method of manufacturing the same.

[0002]

2. Description of the Related Art In a conventional semiconductor device, for example, in an input / output protection circuit section or a transistor to which a high voltage is applied, if a gate oxide film for insulating between a channel layer and a gate electrode is thin, the gate oxide film is formed. Since the electric field concentration occurs and the dielectric breakdown of the gate oxide film easily occurs, the thickness of the gate oxide film is increased. On the other hand, in a transistor or the like to which a low voltage is applied, it is necessary to reduce the thickness of a gate oxide film in response to a demand for speeding up the element.

For this reason, a transistor to which a high voltage is applied within the same substrate (hereinafter also referred to as a high breakdown voltage transistor)
In a transistor to which a low voltage is applied (hereinafter, also referred to as a low breakdown voltage transistor), the thickness of the gate oxide film is made thinner.

As described above, as a method of manufacturing transistors having different gate oxide thicknesses on the same substrate, for example, as described in JP-A-2-51266, a gate oxide film is formed by first thermal oxidation. Is formed, the gate oxide film in the specific region is removed, and then the gate oxide film is formed again by the second thermal oxidation. According to this method, in the specific region, a transistor (low-breakdown-voltage transistor) having a thin oxide film formed by the second thermal oxidation as a gate oxide film is obtained, and in the other portions, the first and second transistors are formed. A transistor (high breakdown voltage transistor) having a thick oxide film formed by thermal oxidation as a gate oxide film can be obtained.

In the method of manufacturing a semiconductor device described in Japanese Patent Application Laid-Open No. Hei 6-302813, after an ammonia gas is introduced into a silicon substrate to form a nitride at a specific portion, an oxidation process is performed. The growth rate of the oxide film is low in the portion where the oxide film is formed, and the growth speed of oxidation is high in the portion where the oxide film is not formed. As described above, the thickness of the gate oxide film is changed by utilizing the difference in the growth rate of the oxide film due to the nitride.

Further, in the method of manufacturing a semiconductor device described in Japanese Patent Application Laid-Open No. 3-116968, after a pre-gate oxide film is formed on the entire silicon substrate, a silicon nitride film is formed in a region excluding a specific portion. Then, a first thermal oxidation is performed to form a gate oxide film. After the silicon nitride film is removed, a second thermal oxidation is performed to form a gate oxide film again. For this reason, a thick oxide film was formed in a region that was not initially covered with the silicon nitride film, and a thin oxide film was formed in a region that was not covered with the silicon nitride film.

[0007]

However, in such a conventional method for manufacturing a semiconductor device, it is necessary to perform twice the thermal oxidation treatment which requires a long processing time as in the above-described case. In addition, there have been disadvantages that the manufacturing time becomes longer and the manufacturing process becomes complicated.

In the case described above, the nitride is taken in the gate oxide film. Since the nitride easily causes an electron trap, when a film containing the nitride is used as the gate oxide, the threshold value is easily changed, and there is a disadvantage that the reliability of the transistor is reduced.

Further, in the case described above, when removing the oxide film on the nitride film formed during manufacturing and removing the pre-gate oxide film under the nitride film, the previously formed oxide film is removed by two times.
Need to be etched twice. As described above, when a thin oxide film is formed by performing etching a plurality of times, it is very difficult to obtain an oxide film having a uniform film thickness, so that there is a disadvantage that device characteristics are varied and yield is deteriorated. there were.

Therefore, according to the present invention, the silicon substrate is thermally oxidized as it is in the element formation region of the low breakdown voltage element, and the silicon substrate implanted with oxygen ions is thermally oxidized in the element formation region of the high breakdown voltage element. Accordingly, it is possible to provide a semiconductor device which can easily form oxide films having different thicknesses in respective element formation regions in a short time and can uniformly form a highly reliable oxide film with little change in threshold value or the like. The purpose is.

According to a second aspect of the present invention, a silicon substrate is thermally oxidized as it is in an element formation region where a low breakdown voltage element is formed, and a thermal oxidation treatment is performed after oxygen ions are implanted in an element formation region where a high breakdown voltage element is formed. Accordingly, a method for manufacturing a semiconductor device capable of uniformly forming oxide films having different thicknesses in respective element formation regions in a short time and capable of uniformly forming a highly reliable oxide film with little change in threshold value or the like. It is intended to provide.

According to a third aspect of the present invention, the amount of implanted oxygen ions in the element formation region of the high breakdown voltage element is made larger than that in the element formation region of the low breakdown voltage element. It is an object of the present invention to provide a method for manufacturing a semiconductor device in which oxide films having different thicknesses can be formed with good controllability.

According to a fourth aspect of the present invention, in a device forming region for forming a low breakdown voltage transistor, a silicon substrate is directly thermally oxidized to form a thin oxide film, and oxygen ions are implanted in a device forming region for forming a high breakdown voltage transistor. By thermally oxidizing the silicon substrate to form a thick oxide film,
Provided is a method of manufacturing a semiconductor device in which oxide films having different thicknesses can be easily formed in respective element formation regions in a short time and a highly reliable oxide film having little change in threshold value or the like can be uniformly formed. It is an object.

[0014]

According to a first aspect of the present invention, there is provided a semiconductor device in which a silicon substrate is divided into a plurality of element formation regions by element isolation regions, and an element formation region in which a high breakdown voltage element is formed and a low breakdown voltage element. A first oxide film on a channel layer obtained by thermally oxidizing a silicon substrate in an element formation region in which the low breakdown voltage element is formed; A second oxide film on a channel layer obtained by thermally oxidizing a silicon substrate into which oxygen ions have been implanted into a predetermined region of an element formation region where a high breakdown voltage element is formed; and a conductive film on the first oxide film. The above object is achieved by providing a first electrode patterned and a second electrode patterned with a conductive film on the second oxide film.

Since the second oxide film is an oxide film obtained by thermally oxidizing a silicon substrate into which oxygen ions have been implanted, the first oxide film is obtained by thermally oxidizing a silicon substrate into which oxygen ions have not been implanted. The growth rate of the oxide film is faster than that of the first embodiment, and the thickness of the oxide film can be increased.

According to the above structure, the first oxide film in the element formation region where the low breakdown voltage element is formed thermally oxidizes the silicon substrate, and the second oxide film in the element formation region where the high breakdown voltage element is formed is It is obtained by thermally oxidizing a silicon substrate into which oxygen ions have been implanted, and a first electrode is formed on a first oxide film and a second electrode is formed on a second oxide film. This makes it possible to easily form a high breakdown voltage element and a low breakdown voltage element having different oxide film thicknesses in a short time, and to form a material having a uniform thickness and causing the oxide film to have a change factor such as a threshold value. Since the element is not used, a highly reliable element can be obtained.

According to a second aspect of the present invention, there is provided a semiconductor manufacturing method comprising:
In a method of manufacturing a semiconductor device in which an element isolation region is formed on a silicon substrate and divided into a plurality of element formation regions to form a high breakdown voltage element and a low breakdown voltage element, a predetermined region in the element formation region where the low breakdown voltage element is formed is formed. Implanting impurity ions into a region to form a first channel layer; implanting impurity ions into a predetermined region in an element forming region for forming the high breakdown voltage element to form a second channel layer; Implanting oxygen ions into a predetermined region in a device forming region for forming a high breakdown voltage device; thermally oxidizing the silicon substrate to form a thin oxide film on the first channel layer; The above object is achieved by including a step of forming a thick oxide film on the layer.

According to the above method, the first channel layer is formed by implanting impurity ions into the element formation region of the low breakdown voltage element, and the second channel layer is implanted by implanting impurity ions into the element formation region of the high breakdown voltage element. After being formed and implanted with oxygen ions, the silicon substrate is thermally oxidized to form the first
A thin oxide film is formed on the channel layer, and a thick oxide film is formed on the second channel layer. As described above, oxide films having different thicknesses can be uniformly formed on each channel layer by performing only one thermal oxidation process, so that the manufacturing process can be simplified and the manufacturing can be performed in a short time. Become. In addition, since a nitride or the like which causes a change in a threshold value or the like during the manufacturing process of the oxide film is not used, a highly reliable element can be formed.

The method of manufacturing a semiconductor device according to the invention according to claim 3, further comprising a step of implanting oxygen ions into a predetermined region in an element formation region for forming the low breakdown voltage element after forming the first channel layer. The above object is achieved by increasing the amount of oxygen ions implanted into the element formation region where the high breakdown voltage element is formed, compared to the amount of oxygen ions implanted into the element formation region where the low breakdown voltage element is formed. .

According to the above method, after the step of forming the first channel layer according to the second aspect of the present invention, a step of implanting oxygen ions into the element formation region of the low withstand voltage element is added. By increasing the amount of oxygen ions implanted into the element formation region of the high-breakdown-voltage element over the amount of oxygen ions implanted into the region, a thin oxide film is formed on the first channel layer and a thick oxide film is formed on the second channel layer Can be formed. As described above, oxygen ions are implanted into both the element formation region of the low-breakdown-voltage element and the element formation region of the high-breakdown-voltage element. Oxide films having different thicknesses can be formed with a uniform thickness. In particular, since the thickness of the oxide film formed in each region can be controlled only by changing the ion implantation amount, the controllability of the oxide film thickness can be improved.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a semiconductor device, wherein a LOCOS oxide film is formed at a predetermined position on a silicon substrate, divided into a plurality of element formation regions, and the surface of the silicon substrate is subjected to a first thermal oxidation process. Forming a thermal oxide film having a predetermined thickness on each element forming region; and implanting impurity ions only into a predetermined region of the element forming region via the thermal oxide film to form a first channel layer And implanting impurity ions through the thermal oxide film into a predetermined region of the element formation region different from the region where the first channel layer is formed to form a second channel layer, and oxygen in the same region. After the step of implanting ions and removing the thermal oxide film,
Forming a thin oxide film on the first channel layer by performing a second thermal oxidation process, and forming a thick oxide film on the second channel layer; Forming an electrode by patterning a conductive film in a predetermined region on the film, forming a high-breakdown-voltage transistor in the element formation region in which the thin-film oxide film is formed, and forming an element in which the thick-film oxide film is formed. The above object is achieved by forming a low breakdown voltage transistor in a region.

According to the above method, the silicon substrate is divided into a plurality of element formation regions by the LOCOS oxide film, and a thermal oxide film for protecting the surface of the silicon substrate is formed. Impurity ions are implanted through the film to form a first channel layer, and impurity ions are implanted through a thermal oxide film into a predetermined region different from the region where the first channel layer is formed to form a second channel layer. At the same time, oxygen ions are implanted into the same region. After removing the thermal oxide film, a second thermal oxidation process is performed to form a thin oxide film on the first channel layer and a thick oxide film on the second channel layer. By forming electrodes on the film and the thick oxide film, a high breakdown voltage transistor and a low breakdown voltage transistor are formed. As described above, it is possible to uniformly form oxide films having different thicknesses on each channel layer by performing only one thermal oxidation process, and to simplify a high breakdown voltage transistor and a low breakdown voltage transistor on the same substrate. Production process in a short time,
A highly reliable transistor in which a threshold value or the like does not easily change can be formed.

[0023]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are preferred embodiments of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. The embodiments are not limited to these embodiments unless otherwise specified.

1 to 7 are process cross-sectional views illustrating one embodiment of a method of manufacturing a semiconductor device according to the present invention. In the present embodiment, a high breakdown voltage transistor having a thick gate oxide film and a low breakdown voltage transistor having a thin gate oxide film are formed on the silicon substrate 12 divided into a plurality of element formation regions.

Next, the manufacturing process of the semiconductor device according to the present embodiment will be described with reference to FIGS.

When forming a high breakdown voltage transistor and a low breakdown voltage transistor on a silicon substrate in the same step, first, an element isolation region for isolating each element formation region is formed. In this embodiment, in forming the element isolation region, LOCOS (Local Oxidation of Silico) is used.
n) method is used. This LOCOS method uses a silicon substrate 1
This is a technique of forming an element isolation region by selectively thermally oxidizing a part of the element 2. The specific steps include:
As shown in FIG. 1, a silicon nitride film (Si ₃ N ₄ ) (not shown), which is an oxidation-resistant film, is formed on a silicon substrate 12 to form an element isolation insulating film (Si) as an element isolation region.
O ₂ ) The silicon nitride film in the regions where 14a, 14b, and 14c are to be formed is removed by etching to expose the silicon substrate 12, and selectively thermally oxidized in high-temperature (1000 ° C. or higher) water vapor to obtain a thick heat. Element isolation insulating films (SiO ₂ ) 14a, 14b, 14c made of an oxide film are formed. Thus, the element isolation insulating film (SiO ₂ ) 14a,
The element formation regions 16a and 16b on the silicon substrate 10 are separated by 14b and 14c. Then, in a H ₂ / O ₂ atmosphere in which hydrogen and oxygen are mixed, a thermal oxidation treatment is performed at a temperature of 800 ° C. for 15 minutes to thereby protect the silicon substrate surfaces of the element formation regions 16a and 16b. Oxide film 18 is formed to 150 Å.

Next, as shown in FIG. 2, a photoresist 20 is patterned and formed so that the element forming region 16b for forming the low breakdown voltage transistor is opened. Then, in order to adjust the threshold value in the channel layer 19b as the first channel layer, boron ions (B) are applied here to the element forming region (for example, 16b) where the photoresist 20 is not formed. Ion implantation is performed under the conditions of an acceleration voltage of 15 KeV and an implantation amount of 2e12 / cm ² (a cross mark in the figure indicates a boron ion implantation position in the silicon substrate 12).

Then, as shown in FIG. 3, after removing the photoresist 20 in FIG. 2, a photoresist 22 is formed by patterning so that an element forming region 16a for forming a high breakdown voltage transistor is opened. . Then, boron ions (B) for adjusting the threshold are applied to the channel layer 19a as the second channel layer of the element formation region (16a) where the photoresist 22 is not formed under the same conditions (accelerating) as described above. Voltage 15 KeV,
Ion implantation is performed at an implantation dose of 2e12 / cm ² ).

Next, as shown in FIG. 4, while keeping the photoresist 22 as it is,
Under the conditions of 0 to 80 KeV and an implantation amount of 1 to 2e18 / cm ² , an element formation region 16a for forming a high breakdown voltage transistor
Ion implantation. This step is a characteristic manufacturing step of the present invention. Even if thermal oxidation is performed under the same conditions, a region where oxygen ions are not implanted into the silicon substrate 12 (the element formation region 16b ) Than the region into which oxygen ions have been implanted (the element formation region 16).
Using the fact that the growth rate of the thermal oxide film is faster in a),
Oxide films having different thicknesses can be formed uniformly by one thermal oxidation treatment. This is because, in a region into which oxygen ions are introduced (element formation region 16a), when thermal oxidation is performed, a reaction between oxygen (O ₂ ) and silicon (Si) proceeds, and more silicon dioxide (SiO ₂ ) is produced. This is because a thick oxide film can be formed to be formed. Therefore, formation of oxide films having different film thicknesses can be performed not only with or without oxygen ion implantation but also by changing the amount of oxygen ion implantation.

Referring back to FIG. 4, the photoresist 22 is removed, and the element forming regions 16a,
The sacrificial oxide film 18 formed on the surface of
F) Remove with solution. Thus, the sacrificial oxide film 18
FIG. 5 shows a state after the removal of.

In the state of FIG. 5, the surface of the silicon substrate 12 is heated at 800 ° C. in an H ₂ / O ₂ atmosphere at a temperature of 15 ° C.
As shown in FIG. 6, by performing the thermal oxidation treatment for one minute, the element formation region 16b for forming the low breakdown voltage transistor is formed.
150 Å thin gate oxide film 24 b
Is formed, and a thick gate oxide film 24a of 300 Å is formed in the element forming region 16a where the high breakdown voltage transistor is to be formed. The above-described gate oxide film 24b
Is formed by thermally oxidizing the surface of the silicon substrate 12 as it is, and has a uniform thickness. The gate oxide film 24a is obtained by thermally oxidizing the silicon substrate 12 into which oxygen ions have been implanted. If implanted, a uniform film thickness can be obtained.

Next, the gate oxide films 24a,
4b, a chemical vapor deposition (CVD)
position) to deposit polycrystalline silicon 26 to a thickness of 3500 angstroms, on which resist patterns 28a and 28b for forming a gate electrode to be described later are formed.
Is formed, and the polycrystalline silicon 26 is dry-etched using this as an etching mask to form gate electrodes 30a and 30b of the transistor. Then, the resist patterns 28a and 28b are removed to form an element as shown in FIG. Structure can be obtained.

Since the manufacturing process of the transistor after FIG. 7 is not directly related to the present invention and is similar to the conventional manufacturing process, detailed description is omitted, but the gate electrode 30a,
Self-alignment (self-alignment) using 30b as a mask
Impurity ions are implanted to form source / drain regions, not shown, respectively.
An S (Metal Oxide Semiconductor) type high voltage transistor is formed, and a MOS type low voltage transistor is formed in the element forming region 16b.

As described above, according to the present embodiment, it is possible to uniformly form gate oxide films having different thicknesses in each element formation region on the same silicon substrate.
A high breakdown voltage transistor and a low breakdown voltage transistor can be formed. Moreover, in this embodiment, when forming oxide films having different thicknesses, the growth rate of the thermal oxide film is increased by setting the presence or absence of oxygen ion implantation or the difference in the amount of oxygen ion implantation for each element formation region. To achieve the film thickness difference, the controllability of the film thickness becomes good,
Since oxide films having different thicknesses can be simultaneously formed by one thermal oxidation treatment, there is an advantage that the manufacturing time is shortened, the throughput is improved, and the manufacturing process is simplified.

Further, since the generated gate oxide film does not contain a substance such as a nitride which changes the threshold value, a transistor having a highly reliable oxide film can be formed.

As described above, the invention made by the inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to the above, and various modifications can be made without departing from the gist of the invention. It goes without saying that it is possible.

For example, in the above embodiment, a description has been given of an example in which a transistor having two types of withstand voltage characteristics, that is, a high withstand voltage transistor and a low withstand voltage transistor, is formed on the same silicon substrate. May be formed. In that case, it is necessary to appropriately adjust the presence or absence of oxygen ion implantation and the amount of oxygen ion implantation so that a gate oxide film having a thickness corresponding to the thickness resistance characteristics of the transistor formed in each element formation region is formed. is there.

Further, in the above-described embodiment, an example is shown in which one high-breakdown-voltage element and one low-breakdown-voltage element are formed in each element formation region. However, the present invention is not limited to this. Of course, the case of forming the low-breakdown-voltage transistor described above may be good.

[0039]

According to the semiconductor device of the present invention, the silicon substrate is thermally oxidized as it is in the element formation region of the low breakdown voltage element, and the silicon substrate implanted with oxygen ions is used in the element formation region of the high breakdown voltage element. Since thermal oxidation is performed, oxide films having different thicknesses can be easily formed in each element formation region in a short time, and a highly reliable oxide film with little change in threshold value or the like can be uniformly formed. .

According to the method of manufacturing a semiconductor device of the second aspect of the present invention, the silicon substrate is thermally oxidized as it is in the element formation region where the low breakdown voltage element is formed, and oxygen ions are removed in the element formation region where the high breakdown voltage element is formed. Since the thermal oxidation treatment is performed after the implantation, oxide films having different thicknesses can be easily formed in each element formation region in a short time, and a highly reliable oxide film with little change in threshold value or the like can be formed uniformly. it can.

According to the method of manufacturing a semiconductor device according to the third aspect of the present invention, the implantation amount of oxygen ions in the element formation region of the high breakdown voltage element is larger than in the element formation region of the low breakdown voltage element. Oxide films having different thicknesses can be formed in each element formation region with good controllability.

According to the method of manufacturing a semiconductor device of the present invention, the silicon substrate is thermally oxidized as it is in the element formation region where the low breakdown voltage transistor is formed to form a thin oxide film on the first channel layer. In the element formation region for forming a high breakdown voltage transistor, a silicon substrate implanted with oxygen ions is thermally oxidized to form a thick oxide film, so oxide films having different thicknesses can be easily formed in each element formation region in a short time. As a result, a highly reliable oxide film with little change in threshold value or the like can be formed uniformly.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an element isolation step according to a method for manufacturing a semiconductor device of the present invention.

FIG. 2 is a cross-sectional view illustrating a step of implanting impurity ions into a channel region of a low breakdown voltage transistor according to the method for manufacturing a semiconductor device of the present invention.

FIG. 3 is a cross-sectional view illustrating a step of implanting impurity ions into a channel region of a high breakdown voltage transistor according to the method for manufacturing a semiconductor device of the present invention.

FIG. 4 is a cross-sectional view illustrating an oxygen ion implantation step of adjusting an oxide film thickness of a high breakdown voltage transistor according to the method for manufacturing a semiconductor device of the present invention.

FIG. 5 is a cross-sectional view showing a state after removing a sacrificial oxide film according to the method for manufacturing a semiconductor device of the present invention.

FIG. 6 is a cross-sectional view illustrating a step of forming a gate electrode by performing a thermal oxidation process according to the method for manufacturing a semiconductor device of the present invention.

FIG. 7 is a cross-sectional view showing a state after forming a gate electrode according to the method for manufacturing a semiconductor device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Silicon substrate 14a-14c Element isolation insulating film (element isolation region) 16a, 16b Element formation region 18 Sacrificial oxide film (oxide film) 19a Channel layer (second channel layer) 19b Channel layer (first channel layer) 24a Gate oxidation Film (thick oxide film) 24b Gate oxide film (thin oxide film) 26 Polycrystalline silicon 30a Gate electrode (second electrode) 30b Gate electrode (first electrode)

Claims (4)

[Claims] A semiconductor substrate divided into a plurality of element formation regions by an element isolation region, and having at least one element formation region in which a high breakdown voltage element is formed and at least one element formation region in which a low breakdown voltage element is formed; In the device, a first oxide film on a channel layer obtained by thermally oxidizing a silicon substrate in an element formation region where the low breakdown voltage element is formed, and oxygen in a predetermined region of the element formation region where the high breakdown voltage element is formed. A second oxide film on the channel layer obtained by thermally oxidizing the ion-implanted silicon substrate; a first electrode obtained by patterning a conductive film on the first oxide film; and a conductive film on the second oxide film. A second electrode having a patterned conductive film. 2. A method of manufacturing a semiconductor device in which an element isolation region is formed on a silicon substrate and divided into a plurality of element formation regions to form a high breakdown voltage element and a low breakdown voltage element. Forming a first channel layer by implanting impurity ions into a predetermined region in the formation region, and forming a second channel layer by implanting impurity ions into a predetermined region in an element formation region for forming the high breakdown voltage device Performing a step of implanting oxygen ions into a predetermined region in an element formation region for forming the high breakdown voltage element; and forming a thin film oxide film on the first channel layer by thermally oxidizing the silicon substrate. Forming a thick oxide film on the second channel layer. 3. The method according to claim 1, further comprising, after forming the first channel layer, implanting oxygen ions into a predetermined region in an element formation region for forming the low breakdown voltage element. 3. The method of manufacturing a semiconductor device according to claim 2, wherein the amount of oxygen ions implanted into an element forming region for forming the high breakdown voltage element is larger than the amount of oxygen ions implanted into the semiconductor device. 4. A LOCOS oxide film is formed at a predetermined position on a silicon substrate to divide it into a plurality of element formation regions, and the surface of the silicon substrate is thermally oxidized to a predetermined thickness on each element formation region by a first thermal oxidation treatment. Forming a film, forming a first channel layer by implanting impurity ions only in a predetermined region of the element forming region via the thermal oxide film, and forming the first channel in the element forming region. Implanting impurity ions through the thermal oxide film into a predetermined region different from the region where the layer is formed to form a second channel layer, and implanting oxygen ions into the same region; Forming a thin oxide film on the first channel layer by performing a second thermal oxidation process after the removal, and forming a thick oxide film on the second channel layer; On the thick oxide film Forming an electrode by patterning a conductive film in a constant region, and forming a high withstand voltage transistor in the element formation region where the thin oxide film is formed, and a low voltage transistor in the element formation region where the thick oxide film is formed. A method for manufacturing a semiconductor device, comprising forming a breakdown voltage transistor.