JPH1154499A - Fabrication of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of steps for depositing a pad oxide and an anti-oxidation film in the process for forming isolation films, of different shapes by repeating thermal oxidation step a plurality of times only for a first oxide layer thereby forming isolation films of different thickness on the bottom face of first and second oxide layers formed on same pad oxide and anti-oxidation film. SOLUTION: A pad oxide 12 and an anti-oxidation film 13 are deposited sequentially from below on the first and second regions 11a, 11b of a semiconductor substrate 11. A first oxide layer 15a is then formed on the pad oxide 12 and the anti-oxidation film 13 in the first region 11a. Subsequently, an oxide 16 is grown on the bottom face of the first oxide layer 15a by thermal oxidation and a second oxide layer 15b is formed on the pad oxide 12 and the anti- oxidation film 13 in the second region 11b. Thereafter, the oxide 16 on the bottom face of the first oxide layer 15a is grown by thermal oxidation to form a first isolation film 16a and a second isolation film 16b is formed of a new oxide grown on the bottom face of the second oxide layer 15b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device in which an element isolation film is formed by a LOCOS method.

[0002]

2. Description of the Related Art In recent years, as semiconductor devices have become more highly integrated and highly functional, LOCOS (Loca (Loca) is located in an internal region where fine functional elements such as memory cells are arranged with a high degree of integration.
lOxidation of Silicon) It is necessary to reduce the buzz beak of the element isolation film formed by the method to narrow the interval between the elements. However, in a peripheral area where a peripheral element to which a high voltage is applied such as a power supply element is arranged, by maintaining a bird's beak of the element isolation film to a certain size,
It is necessary to prevent transistor characteristics and gate oxide film quality from deteriorating due to concentration of an electric field at the bottom of the step due to bird's beak.

Therefore, in the manufacturing process of the semiconductor device, the element isolation film in the internal region and the element isolation film in the peripheral region where different shapes are required as described above are formed in different processes. Here, when the element isolation film is formed by the LOCOS method, the following steps are performed. A step of forming a pad oxide film and an antioxidant film on a semiconductor substrate; a step of etching the antioxidant film and the pad oxide film using a resist pattern formed by lithography as a mask to form an oxide window; This is a step of growing an oxide film to be an element isolation film on the surface of the semiconductor substrate by an oxidation method. For this reason, in the manufacturing process of a semiconductor device in which functional circuits have been highly integrated as described above, for example, after forming an element isolation film in a peripheral region by the above procedure,
A step of removing the antioxidant film and the pad oxide film is performed, and then the above procedure is repeated to form an element isolation film in the internal region.

[0004]

However, in the above-described method for forming a semiconductor device, the element isolation region in the internal region and the element isolation region in the peripheral region are formed in completely different steps as described above. It is necessary to perform the step of forming the pad oxide film and the antioxidant film and the step of thermal oxidation twice,
There is a problem that the number of steps for forming the element isolation region is large.

[0005]

A method of manufacturing a semiconductor device according to the present invention for solving the above-mentioned problems is a method of manufacturing a semiconductor device in which an element isolation region is formed by a LOCOS method. In the method of manufacturing a semiconductor device according to claim 1, when forming the first element isolation film and the second element isolation film having different shapes, the first oxide window for forming the first element isolation film first. Is formed on the pad oxide film and the antioxidant film, and is thermally oxidized. Next, a second oxide window for forming a second element isolation film is formed in the same pad oxide film and antioxidant film, and then thermal oxidation is performed on the bottom surfaces of the first oxide window and the second oxide window. did.

In the method according to the first aspect of the present invention, the thermal oxidation process is performed only on the bottom layer of the first oxidation window a plurality of times, so that each oxidation window is formed on the same pad oxide film and oxidation prevention film. Even if they are formed, element isolation films having different thicknesses are formed on the bottom surfaces of the respective oxidation windows. Therefore, the step of forming the pad oxide film and the antioxidant film when forming the first element isolation film and the second element isolation film having different shapes is reduced to one time.

In the first aspect, between the fourth step and the fifth step, only the surface layer of the semiconductor substrate on the bottom surface of the second oxide window is etched to form a groove on the surface of the semiconductor substrate. May be. In this case, the second element isolation film is formed on the surface layer of the semiconductor substrate in which the groove is formed, and the surface step of the second element isolation film is reduced.

In the method of manufacturing a semiconductor device according to the third or fourth aspect, when forming the first element isolation film and the second element isolation film having different shapes, each oxide window is formed by the same pad oxidation. After forming a groove only on the surface of the semiconductor substrate on the bottom surface of one of the oxidation windows, thermal oxidation is performed on the bottom surfaces of both the oxidation windows.

In the method according to the third or fourth aspect, the grooves are formed only on the surface of the semiconductor substrate on the bottom surface of one of the oxidation windows and thermal oxidation is performed, so that each oxidation window has the same pad oxide film and the same oxide film. Even when the anti-oxidation film is formed, an element isolation film having a different bird's beak is formed in each oxidation window. Therefore, the step of forming the pad oxide film and the antioxidant film when forming the first element isolation film and the second element isolation film having different shapes is reduced to one time.

Further, in the method of manufacturing a semiconductor device according to the present invention, when forming the first element isolation film and the second element isolation film having different shapes, first, the pad oxide films having different thicknesses are formed. And an antioxidant film are formed on the same semiconductor substrate. Thereafter, a step of forming a first oxide window and a second oxide window provided on the pad oxide film and the antioxidant film, and a step of thermal oxidation for forming each of the element isolation films on the bottom surface of the oxide window. Are performed in the same step.

In the method according to the fifth to seventh aspects, the thickness of the pad oxide film and the thickness of the antioxidant film are different from each other, so that the bottom surface of each oxidation window formed in each thickness portion is different. Even if the same thermal oxidation is performed, element isolation films having different bird's beak sizes are formed in the respective oxidation windows. Therefore, the step of forming each oxide window and the step of thermal oxidation when forming the first element isolation film and the second element isolation film having different shapes are reduced to one time.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. Note that components common to the embodiments are denoted by the same reference numerals, and redundant description will be omitted.

(First Embodiment) FIG. 1 is a sectional process view for explaining a method of manufacturing a semiconductor device according to a first embodiment of the present invention. The method of the first embodiment will be described. First, in the first step, as shown in FIG. 1A, a semiconductor substrate 11 made of, for example, single crystal silicon is prepared. This semiconductor substrate 11
Is provided with a first region 11a and a second region 12b on the surface side. Then, a pad oxide film 12 made of silicon oxide is formed on such a semiconductor substrate 11,
On the pad oxide film 12, an anti-oxidation film 13 made of silicon nitride is formed.

Next, in a second step, as shown in FIG. 1B, a resist pattern 14 is formed on the oxidation preventing film 13 by lithography. The resist pattern 14 has an opening pattern corresponding to the element isolation film forming portion of the first region 11a. Next, the oxidation preventing film 13 and the pad oxide film 12 are etched by using the resist pattern 14 as a mask, thereby
Antioxidant film 13 and pad oxide film 1 in region 11a
Second, a first oxidation window 15a reaching the semiconductor substrate 11 is patterned.

Next, in a third step, as shown in FIG. 1C, after removing the resist pattern (14),
The surface layer portion of the semiconductor substrate 11 exposed on the bottom surface of the first oxidation window 15a is selectively oxidized by a thermal oxidation method. Here, the oxidation prevention film 13 is used as a mask at 900 ° C. to 110 ° C.
A thermal oxidation treatment is performed at 0 ° C.
An oxide film 16 having a thickness of about 00 nm to 500 nm is grown.

Then, in a fourth step, as shown in FIG. 1D, a new resist pattern 1
7 is formed. The resist pattern 17 is formed by the first
The oxide window 15a is buried therein and has an opening pattern corresponding to the element isolation film forming portion of the second region 11b. Next, the oxidation preventing film 13 and the pad oxide film 12 are etched by using the resist pattern 17 as a mask, and thereby the oxidation preventing film 1 in the second region 11b is etched.
A second oxide window 15b reaching the semiconductor substrate 11 is patterned in the pad oxide film 3 and the pad oxide film 12.

Next, in a fifth step, as shown in FIG. 1 (5), after removing the resist pattern (17),
A second thermal oxidation treatment is performed at a temperature of 00C to 1100C. Thereby, the oxide film 16 on the bottom surface of the first oxidation window 15a is formed.
Is further grown to a thickness of about 450 nm to 600 nm, and a first element isolation film 16a made of the oxide film 16 further grown in the first region 11a is formed. With this,
On the bottom of the second oxidation window 15b, a new 250 nm to 400 n
An oxide film having a thickness of about m is grown, and a second element isolation film 16b made of a newly grown oxide film is formed in the second region 11b.

According to the above method, the bottom surface of the first oxidation window 15a is subjected to two oxidation treatments.
Only one oxidation treatment is performed on the bottom surface of the second oxidation window 15b. For this reason, the first element isolation film 16a formed in the first region 11a is thicker than the second element isolation film 16b formed in the second region 11b, and thus has a larger thickness than the second element isolation film 16b. Bird's beak is big. Therefore, the first element isolation film 16a having a large bird's beak suitable for isolating peripheral elements to which a high voltage is applied is formed in the first region 11a. On the other hand, in the second region 11b, the second element isolation film 16b having a small bird's beak which does not hinder high integration of the miniaturized functional element is formed. Moreover, the first area 11
Since the thickness of the first element isolation film 16a disposed on the first element isolation film 16a is larger than the thickness of the second element isolation film 16b, the first element isolation film 16a reliably removes peripheral elements to which a high voltage is applied. It will separate.

In the method of the first embodiment, the same pad oxide film 12 and anti-oxidation film 13 are used for forming the first element isolation film 16a and the second element isolation film 16b.
Therefore, as compared with the case where the first element isolation film 16a and the second element isolation film 16b having different shapes are formed by the conventional method, the step of removing the pad oxide film 12 and the antioxidant film 13 and the step of removing the pad oxide film 12 and the It is possible to reduce the number of steps for forming the antioxidant film 13.

(Second Embodiment) FIG. 2 is a sectional process view for explaining a method of manufacturing a semiconductor device according to a second embodiment of the present invention. A second embodiment will be described. Here, first, the first step described with reference to FIG. 1A to the fourth step described with reference to FIG. 1D are performed similarly to the first embodiment, and the second region of the semiconductor substrate 11 is formed. A second oxidation window 15b is formed on 11b. Thereafter, as shown in FIG. 2A, using the resist pattern 17 used for forming the second oxide window 15b as a mask, the surface layer of the semiconductor substrate 11 on the bottom surface of the second oxide window 15b is etched. Thereby, the semiconductor substrate 11
A groove h having a depth of about 100 nm to 300 nm is formed on the surface of the substrate.

Then, in the next fifth step, as shown in FIG. 2 (2), after removing the resist pattern (17), a second thermal oxidation treatment is performed at a temperature of 900 ° C. to 1100 ° C. This fifth step is the same as that of the first embodiment shown in FIG.
This is performed in the same manner as described using (5).

According to the above method, the second element isolation film 16b is formed by oxidizing and growing the surface layer of the semiconductor substrate 11 in which the groove h is formed. The surface step of the element isolation film 16b is reduced, so that the bird's beak of the second element isolation film 16b can be further reduced. Moreover, the formation of the groove h
Since the etching for forming the second oxide window 15b is performed continuously, the number of manufacturing steps is not particularly increased compared to the first embodiment.

(Third Embodiment) FIG. 3 is a sectional process diagram for explaining a method of manufacturing a semiconductor device according to a third embodiment of the present invention. A third embodiment will be described. Here, first, the first to third steps are the same as the first to third steps described with reference to FIG. 1A in the first embodiment. Then, an oxide film 16 is formed in the first region 11a of the semiconductor substrate 11. However, the thickness of the oxide film 16 is about 100 nm to 300 nm.

Thereafter, in a fourth step, as shown in FIG. 3A, the first oxidation window 15 is formed using the oxidation prevention film 13 as a mask.
The oxide film 16 on the bottom surface of a is removed by etching to form a groove h on the surface of the semiconductor substrate 11.

In the next fifth step, a new resist pattern 31 is formed on the oxidation preventing film 13 as shown in FIG. The resist pattern 31 has an opening pattern that fills the first oxidation window 15a and that corresponds to the element isolation film forming portion of the second region 11b.
Next, the oxidation preventive film 13 and the pad oxide film 12 are etched using the resist pattern 31 as a mask, whereby the oxidation preventive film 13 and the pad oxide film 12 in the second region 11 b reach the semiconductor substrate 11. 2
The oxidation window 15b is patterned.

Then, in a sixth step, as shown in FIG. 3C, after removing the resist pattern (31),
A second thermal oxidation treatment is performed at a temperature of 900C to 1100C. Thereby, the first oxidation window 15a and the second oxidation window 1
The bottom layer of 5b is oxidized to form a first element isolation film 16a made of an oxide film in the first region 11a and a second element isolation film 16b made of an oxide film in the second region 11b. The film thickness of these element isolation films 16a and 16b is 40
It grows to about 0 nm to 600 nm.

According to the above method, the first element isolation film 16a is formed by oxidizing and growing the surface layer of the semiconductor substrate 11 in which the groove h is formed. The surface step of the element isolation film 16a is reduced, so that the first element isolation film 16a having bird's beaks smaller than that of the second element isolation film 16b is obtained. For this reason, the first region 11a has a first bird's beak having a small bird's beak which does not hinder high integration of the miniaturized functional element.
The element isolation film 16a is formed. On the other hand, the second
In the region 11b, a second element isolation film 16b having a large bird's beak suitable for isolating peripheral elements to which a high voltage is applied is formed.

In the method of the third embodiment, the same pad oxide film 12 and oxidation prevention film 13 are used for forming the first element isolation film 16a and the second element isolation film 16b as in the first embodiment. Used. Therefore, compared with the case where the first element isolation film 16a and the second element isolation film 16b having different shapes are formed by the conventional method, the step of removing the pad oxide film 12 and the oxidation preventing film 13 and the step of removing the pad oxide film 12 It is possible to reduce the number of steps for forming the prevention film 13.

Further, the formation of the groove h is performed by the semiconductor substrate 1
Since the etching is performed by removing the oxide film 16 grown on the first surface layer, the depth of the groove h can be controlled more accurately by the thickness of the oxide film 16 as compared with the second embodiment. it can. Further, since the edge of the groove h becomes smooth, the edge of the first element isolation film 16a becomes smooth, and the stress generated in this portion can be suppressed to be small. Further, since both the first element isolation film 16a and the second element isolation film 16b are formed by one thermal oxidation, the thickness can be easily controlled.

(Fourth Embodiment) FIG. 4 is a sectional process view for explaining a method of manufacturing a semiconductor device to which the invention of claim 4 is applied. The fourth embodiment will be described below with reference to FIG. explain. First, in a first step, a pad oxide film 12 and an antioxidant film 13 are formed on a semiconductor substrate 11 as shown in FIG. This step is the first step of the first embodiment.
Performed in the same manner as the process.

Next, in a second step, as shown in FIG. 4B, a resist pattern 41 is formed on the antioxidant film 13 by lithography. The resist pattern 41 has an opening pattern corresponding to an element isolation film forming portion of the first region 11a and the second region 11b. Next, the oxidation preventive film 13 and the pad oxide film 12 are etched using the resist pattern 41 as a mask, whereby the oxidation preventive film 1 in the first region 11a is etched.
3 and the pad oxide film 12 are formed with a first oxidation window 15a reaching the semiconductor substrate 11, and at the same time, the second region 11 is formed.
A second oxidation window 15b reaching the semiconductor substrate 11 is formed in the oxidation preventing film 13 and the pad oxide film 12 in FIG.

Thereafter, in a third step, as shown in FIG. 4C, after removing the resist pattern (41),
By performing a thermal oxidation process at 900 ° C. to 1100 ° C., an oxide film 16 having a thickness of 400 nm to 500 nm is grown on the bottom layer of the first oxide window 15a and the second oxide window 15b.

Next, in a fourth step, a resist pattern 42 covering the first region 11a is formed on the semiconductor substrate 11, as shown in FIG. Then, using the resist pattern 42 and the oxidation preventing film 13 as a mask,
Oxide film 16 on bottom surface of second oxide window 15b in region 11b
Only etching is removed. Thus, a groove h is formed on the surface of the semiconductor substrate 11 at the bottom surface of the second oxidation window 15b.

Then, in a fifth step, as shown in FIG. 4 (5), after removing the resist pattern (42),
A second thermal oxidation treatment is performed at a temperature of 900C to 1100C. Thereby, the oxide film 16 on the bottom surface of the first oxidation window 15a is formed.
Is further grown to a thickness of about 450 nm to 600 nm, and a first element isolation film 16a made of the oxide film 16 further grown in the first region 11a is formed. With this,
On the bottom of the second oxidation window 15b, a new 250 nm to 400 n
An oxide film having a thickness of about m is grown, and a second element isolation film 16b made of a newly grown oxide film is formed in the second region 11b.

As described above, in the first area 11a, 2
The first element isolation film 16a is formed by thermal oxidation twice,
A second element isolation film 16b having a smaller thickness than the first element isolation film 16a is formed in the second region 11b by one thermal oxidation. In addition, since the second element isolation film 16b is formed by oxidizing and growing the surface layer of the semiconductor substrate 11 in which the groove h is formed, the second element isolation film 16b
The bird's beak is smaller than that of the second element isolation film 16b formed in the first embodiment. Therefore, the first
In the region 11a, a first element isolation film 16a having a large bird's beak suitable for isolation of a peripheral element to which a high voltage is applied is formed, and in the second region 11b, high integration of miniaturized functional elements is not hindered. Thus, the second element isolation film 16b having a small bird's beak is formed. And the first
Since the thickness of the first isolation film 16a disposed in the region 11a is larger than the thickness of the second isolation film 16b,
The first element isolation film 16a reliably isolates a peripheral element to which a high voltage is applied.

In the method of the fourth embodiment, the same pad oxide film 12 and oxidation prevention film 13 are used for forming the first element isolation film 16a and the second element isolation film 16b.
In addition, the first oxidation window 15a that requires high alignment accuracy
And the formation of the second oxidation window 15b are performed in the same step. Therefore, compared with the case where the first element isolation film 16a and the second element isolation film 16b having different shapes are formed by the conventional method, the step of removing the pad oxide film 12 and the oxidation preventing film 13 and the step of removing the pad oxide film 12 and the oxidation The step of forming the prevention film 13 and the step of forming the oxidation window can be reduced.

Further, the formation of the groove h is performed by the semiconductor substrate 1
Since the removal is performed by etching the oxide film 16 grown on the surface layer of the first element, the depth of the groove h can be controlled with high precision as in the third embodiment, and the edge of the second element isolation film 16b can be smooth. Thus, the stress generated in this portion can be reduced.

(Fifth Embodiment) FIG. 5 is a sectional process view for explaining a method of manufacturing a semiconductor device according to a fifth embodiment to which the invention of claim 5 is applied. A fifth embodiment will be described. First, in the first step, FIG.
As shown in (1), a pad oxide film 12 is formed on a semiconductor substrate 11. Thereafter, a resist pattern (not shown) is formed to cover the pad oxide film 12 in the first region 11a, and the entire surface of the pad oxide film 12 in the second region 11b is removed by using this resist pattern as a mask.
Here, the damage caused by the etching is the second region 11b.
In order to prevent the active region of the semiconductor substrate 11 from being added to the above, wet etching using an aqueous solution of hydrogen fluoride as an etching solution is performed.

Next, after the resist pattern is removed, as shown in FIG. 5 (2), a pad oxide film 12 in the first region 11a is further grown by performing a thermal oxidation process, thereby forming a first pad oxide film. While forming the film 12a, an oxide film is newly grown on the surface layer of the semiconductor substrate 11 in the second region 11b, and this is used as the second pad oxide film 12b. As described above, the first pad oxide film 12a and the second pad oxide film 12b having a smaller thickness are formed without causing damage due to etching.

If the pad oxide films 12a and 12b are damaged by etching, nitrogen enters the semiconductor substrate from the antioxidant film through the damage in the subsequent step of forming an element isolation film and nitrides. Are formed, and this nitride causes deterioration of the device. However, when it is not necessary to consider these inconveniences, a silicon oxide film is formed on the semiconductor substrate 11 and only the silicon oxide film portion in the second region 11b is entirely etched back to a predetermined depth. Pad oxide films having different thicknesses may be formed in the first region 11a and the second region 11b.

Thereafter, in a second step, as shown in FIG. 5C, an oxidation preventing film 13 is formed on the first pad oxide film 12a and the second pad oxide film 12b.

Next, in a third step, as shown in FIG. 5D, a resist pattern 51 is formed on the antioxidant film 13 by lithography. The resist pattern 51 has an opening pattern corresponding to an element isolation film forming portion of the first region 11a and the second region 11b. After that, using the resist pattern 51 as a mask, the oxidation preventing film 13, the first pad oxide film 12a, and the second pad oxide film 12b are etched. As a result, the first oxidation window 1 reaching the semiconductor substrate 11 reaches the antioxidant film 13 and the first pad oxide film 12a in the first region 11a.
5a is formed, and at the same time, a second oxidation window 15b reaching the semiconductor substrate 11 is formed in the antioxidant film 13 and the second pad oxide film 12b in the second region 11b.

Thereafter, in a fourth step, as shown in FIG. 5 (5), after removing the resist pattern (51),
By performing a thermal oxidation process at 900 ° C. to 1100 ° C., an oxide film having a thickness of 400 nm to 600 nm is grown on the bottom layer of the first oxide window 15a and the second oxide window 15b.
The first element isolation film 16a made of the oxide film is formed in the region 11a.
Is formed, and a second element isolation film 16b made of the oxide film is formed in the second region 11b.

In the manufacturing method according to the fifth embodiment, the first element isolation film 16a is formed in the first region 11a where the first pad oxide film 12a is formed, and is thinner than the first pad oxide film 12a. A second element isolation film 16b is formed in the second region 11b where the second pad oxide film 12b is formed. For this reason, the first element isolation film 16a is
Bird's beak is larger than b. Therefore, in the first region 11a, the first element isolation film 1 having a large bird's beak suitable for isolating a peripheral element to which a high voltage is applied.
6a is formed, while a second element isolation film 16b having a small bird's beak which does not hinder high integration of miniaturized functional elements is formed in the second region 11b.

The first element isolation film 16a and the second element isolation film 16b are formed by the same thermal oxidation process. In addition, the formation of the first oxidation window 15a and the formation of the second oxidation window 15b that require high alignment accuracy are performed in the same step. Therefore, as compared with the case where the first element isolation film 16a and the second element isolation film 16b having different shapes are formed by the conventional method, the step of the thermal oxidation process for forming the element isolation film and the step of forming the oxidation window are performed. The number of forming steps can be reduced to one.

(Sixth Embodiment) FIG. 6 is a sectional process diagram for explaining a method of manufacturing a semiconductor device according to a sixth embodiment of the present invention. A sixth embodiment will be described. First, in the first step, FIG.
As shown in (1), a pad oxide film 12 is formed on the semiconductor substrate 11.

Next, in a second step, a first silicon nitride film 61 is formed on the pad oxide film 12 as shown in FIG. Thereafter, a resist pattern (not shown) having a shape covering the first silicon nitride film 61 in the second region 11b is formed, and the entire surface of the first silicon nitride film 61 in the first region 11a is removed by etching using the resist pattern as a mask. I do. Here, the damage due to the etching is applied to the pad oxide film 12 in the first region 11a, whereby the first
When forming the element isolation film in the region 11a, the semiconductor substrate 11
Is wet-etched to prevent nitriding. At this time, by using hot phosphoric acid as an etching solution, the first silicon nitride film 61 is etched while maintaining a good selectivity with respect to the pad oxide film 12, and the thickness of the pad oxide film 12 is maintained.

Thereafter, as shown in FIG. 6C, a second silicon nitride film 62 is formed on the pad oxide film 12 in the first region 11a and on the first silicon nitride film 61 in the second region 11b. . Thus, a first oxidation preventing film 13a made of the second silicon nitride film 62 is formed in the first region 11a. On the other hand, in the second region 11b, a second oxidation prevention film 13b including the first silicon nitride film 61 and the second silicon nitride film 62 is formed. As described above, the first antioxidant film 13a and the second antioxidant film 13b having a larger thickness are formed without causing damage due to etching and with good controllability of the film thickness.

When the antioxidant films 13a and 13b are damaged by etching, there is a case where the antioxidant film does not partially become an oxidation-resistant mask in the subsequent step of forming an element isolation film. is there. However, when it is not necessary to consider such a problem, a silicon nitride film is formed on the pad oxide film 12, and only the silicon nitride film portion in the first region 11a is entirely etched back to a predetermined depth. The first oxidation preventing film 1 made of the silicon nitride film
3a and the second antioxidant film 13b may be formed.

Next, in a third step, as shown in FIG. 6D, the first oxidation preventing film 13 is formed by lithography.
a and a resist pattern 63 on the second oxidation preventing film 13b.
To form This resist pattern 63 is formed in the first region 1
It has an opening pattern corresponding to an element isolation film forming portion of the first region 1a and the second region 11b. Thereafter, the first oxidation preventing film 13 is formed by using the resist pattern 63 as a mask.
a, the second antioxidant film 13b and the pad oxide film 12 are etched. Thus, a first oxidation window 15a reaching the semiconductor substrate 11 is formed in the first antioxidant film 13a and the pad oxide film 12 in the first region 11a, and at the same time, the second antioxidant film 13b and the second antioxidant film 13b in the second region 11b are formed. Second reaching the pad oxide film 12 to the semiconductor substrate 11
An oxidation window 15b is formed.

Thereafter, in a fourth step, as shown in FIG. 6 (5), after removing the resist pattern (63),
By performing a thermal oxidation process at 900 ° C. to 1100 ° C., an oxide film having a thickness of 400 nm to 600 nm is grown on the bottom layer of the first oxide window 15a and the second oxide window 15b.
The first element isolation film 16a made of the oxide film is formed in the region 11a.
Is formed, and a second element isolation film 16b made of the oxide film is formed in the second region 11b.

In the manufacturing method according to the sixth embodiment, the first element isolation film 16a is formed in the first region 11a where the first oxidation prevention film 13a is formed, and has a thickness larger than that of the first oxidation prevention film 13a. The second element isolation film 16b is formed in the second region 11b where the second oxidation prevention film 13b is formed. Therefore, the first element isolation film 16a has a larger bird's beak than the second element isolation film 16b. Therefore, the first element isolation film 16a having a large bird's beak suitable for isolating peripheral elements to which a high voltage is applied is formed in the first area 11a, while the second area 11b is provided with a miniaturized functional element. The second element isolation film 16b having a small bird's beak which does not hinder high integration is formed.

Here, as in the fifth embodiment, the first element isolation film 16a and the second element isolation film 16b are formed by the same thermal oxidation treatment, and the first oxidation window 15
The formation of a and the formation of the second oxidation window 15b are performed in the same step. For this reason, the first element isolation films 16 having different shapes are used.
Compared with the case of forming the device isolation film 16a and the second device isolation film 16b by the conventional method, the number of steps of the thermal oxidation process for forming the device isolation film and the process of forming the oxidation window can be reduced to one. become.

(Seventh Embodiment) FIG. 7 is a sectional process view for explaining a method of manufacturing a semiconductor device to which the invention of claim 7 is applied. The seventh embodiment will be described below with reference to FIG. explain. First, in a first step, a first silicon oxide film 71 is formed on the semiconductor substrate 11 as shown in FIG.
And a first silicon nitride film 72 is formed on the first silicon oxide film 71. Thereafter, a resist pattern (not shown) having a shape covering the first silicon nitride film 72 in the second region 11b is formed, and the first silicon nitride film 72 and the first oxide film in the first region 11a are formed using this resist pattern as a mask. The entire surface of the silicon film 71 is removed by etching. Here, after the first silicon nitride film 72 is wet-etched using hot phosphoric acid, the first silicon oxide film 71 is wet-etched using hydrogen fluoride water. Thus, a second pad oxide film 12b made of the first silicon oxide film 71 is formed on the semiconductor substrate 11 in the second region 11b.

Next, after removing the resist pattern, the first silicon nitride film 72 is formed as shown in FIG.
By performing a thermal oxidation process using
The first pad oxide film 12a is formed by oxidizing and growing the surface layer of the semiconductor substrate 11 in the region 11a. The first pad oxide film 12a is formed so as to be thicker than the second pad oxide film 12b. As described above, the first pad oxide film 12a and the second pad oxide film 12b are formed in the individual steps with good controllability of the film thickness.

Thereafter, a second silicon nitride film 73 is formed on the first pad oxide film 12a in the first region 11a and on the first silicon nitride film 72 in the second region 11b. Thus, a first oxidation preventing film 13a made of the second silicon nitride film 73 is formed on the first pad oxide film 12a in the first region 11a. On the other hand, the first silicon nitride film 72 is formed on the second pad oxide film 12b in the second region 11b.
Anti-oxidation film 1 composed of and second silicon nitride film 73
3b is formed. The second antioxidant film 13b is thicker than the first antioxidant film 13a.

Next, in the second step, as shown in FIG. 7C, the first oxidation preventing film 13 is formed by lithography.
a and a resist pattern 74 on the second oxidation preventing film 13b.
To form The resist pattern 74 is formed in the first region 1
It has an opening pattern corresponding to an element isolation film forming portion of the first region 1a and the second region 11b. Thereafter, the first oxidation preventing film 13 is formed using the resist pattern 74 as a mask.
a, the second oxidation preventing film 13b, the first pad oxide film 12a, and the second pad oxide film 12b are etched. As a result, the first oxidation preventing film 13a in the first region 11a
A first oxidation window 15a is formed in the first pad oxide film 12a to reach the semiconductor substrate 11, and at the same time, the second oxidation prevention film 13b and the second pad oxide film 12b in the second region 11b extend to the semiconductor substrate 11. Second oxidation window 1 reached
5b is formed.

Thereafter, in a third step, as shown in FIG. 7D, after removing the resist pattern (74),
By performing a thermal oxidation process at 900 ° C. to 1100 ° C., an oxide film having a thickness of 400 nm to 600 nm is grown on the bottom layer of the first oxide window 15a and the second oxide window 15b.
The first element isolation film 16a made of the oxide film is formed in the region 11a.
Is formed, and a second element isolation film 16b made of the oxide film is formed in the second region 11b.

According to the manufacturing method of the seventh embodiment, the first element isolation film 16a is formed in the first region 11a where the first pad oxide film 12a and the first oxidation prevention film 13a are formed.
The second element isolation is formed in the second region 11b where the second pad oxide film 12b thinner than the first pad oxide film 12a and the second antioxidant film 13b thicker than the first antioxidant film 13a are formed. The film 16b is formed. Therefore, the first element isolation film 16a has a larger bird's beak than the second element isolation film 16b. Therefore, the first region 11a
Is formed with a first element isolation film 16a having a large bird's beak suitable for isolation of a peripheral element to which a high voltage is applied. On the other hand, in the second region 11b, high integration of miniaturized functional elements is prevented. Thus, the second element isolation film 16b with no bird's beak is formed.

Then, similarly to the fifth and sixth embodiments, the first element isolation film 16a and the second element isolation film 1 are formed.
6b is formed by the same thermal oxidation treatment, and the formation of the first oxidation window 15a and the formation of the second oxidation window 15b are performed in the same step. From this, the first shape of the different shape
Compared to the case where the element isolation film 16a and the second element isolation film 16b are formed by a conventional method, the number of steps of a thermal oxidation process for forming an element isolation film and the step of forming an oxidation window are reduced to one. It becomes possible.

[0061]

As described above, according to the first aspect of the present invention, the same pad oxide film and the same anti-oxidation film are obtained by performing the thermal oxidation process only a plurality of times on the first oxidation window. Since the element isolation films having different thicknesses are formed on the bottom surfaces of the first oxidation window and the second oxidation window formed in the step, the pad oxide film and the antioxidant film when the element isolation films having different shapes are formed. Can be reduced to one time.

Further, according to the second aspect of the present invention,
By forming a groove in the surface layer of the semiconductor substrate on the bottom surface following the formation of the second oxide window in the above-mentioned claim 1 and then performing a thermal oxidation process on the second oxide window, without increasing the number of manufacturing steps The surface step of the second element isolation film can be reduced.

According to the third or fourth aspect of the present invention, the grooves are formed only on the surface of the semiconductor substrate at the bottom of one of the oxide windows, so that the same pad oxide film and the same antioxidant film are formed. Since the element isolation films having different shapes are formed on the bottom surfaces of the first and second oxidation windows, the pad oxide film and the antioxidant film are formed when the element isolation films having different shapes are formed. The number of steps can be reduced to one.

Further, according to the present invention, since the respective oxide windows are provided in portions where the thicknesses of the pad oxide film and the antioxidant film are different, even if the same thermal oxidation is performed. Since the element isolation films having different bird's beak sizes are formed in each of the oxidation windows, the formation process of each oxidation window and the heat generation when forming the first and second element isolation films having different shapes are performed. The number of oxidation steps can be reduced to one.

As described above, according to the first to seventh aspects of the present invention, the number of steps for manufacturing a semiconductor device can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional process view illustrating a method for manufacturing a semiconductor device of a first embodiment.

FIG. 2 is a sectional process view illustrating a method for manufacturing a semiconductor device of a second embodiment.

FIG. 3 is a sectional process view illustrating a method for manufacturing a semiconductor device of a third embodiment.

FIG. 4 is a sectional process view illustrating a method for manufacturing a semiconductor device of a fourth embodiment.

FIG. 5 is a sectional process view illustrating a method for manufacturing a semiconductor device of a fifth embodiment.

FIG. 6 is a sectional process view illustrating a method for manufacturing a semiconductor device of a sixth embodiment.

FIG. 7 is a sectional process view illustrating a method for manufacturing a semiconductor device of a seventh embodiment.

[Explanation of symbols]

 Reference Signs List 11 semiconductor substrate 11a first region 11b second region 12 pad oxide film 12a first pad oxide film 12b second pad oxide film 13 antioxidant film 13a first antioxidant film 13b second antioxidant film 15a first oxidation window 15b 2 oxide window 16 oxide film 16a first element isolation film 16b second element isolation film h groove

Claims (7)

[Claims] A first step of sequentially forming a pad oxide film and an antioxidant film on a first region and a second region of a semiconductor substrate from a lower layer, and the pad oxide film and the antioxidant film in the first region. A second step of patterning a first oxide window reaching the semiconductor substrate on the film; a third step of growing an oxide film on a bottom layer of the first oxide window by a thermal oxidation method; A fourth step of patterning a second oxide window reaching the semiconductor substrate on the pad oxide film and the antioxidant film; and growing the oxide film on the bottom surface of the first oxide window by a thermal oxidation method to form a first element. Forming a separation membrane;
Forming a second isolation film made of an oxide film newly grown on the bottom surface of the oxide window. 2. The method for manufacturing a semiconductor device according to claim 1, wherein only the surface layer of the semiconductor substrate on the bottom surface of the second oxide window is etched between the fourth step and the fifth step. Performing a step of forming a groove in the surface of the substrate. 3. A first step of sequentially forming a pad oxide film and an antioxidant film on a first region and a second region of a semiconductor substrate from a lower layer, and the pad oxide film and the antioxidant film in the first region. A second step of patterning a first oxide window reaching the semiconductor substrate on the film; a third step of growing an oxide film on a bottom layer of the first oxide window by a thermal oxidation method; The oxide film on the bottom is etched, and the first
A fourth step of forming a groove in the surface of the semiconductor substrate on the bottom surface of the oxidation window; and a fifth step of patterning a second oxidation window reaching the semiconductor substrate in the pad oxide film and the antioxidant film in the second region. An oxide film is grown on a bottom layer of the first oxidation window and the second oxidation window by a thermal oxidation method, and a first element isolation film made of the oxide film is formed in the first region;
Forming a second element isolation film made of the oxide film in the region. 4. A first step of sequentially forming a pad oxide film and an antioxidant film on a first region and a second region of a semiconductor substrate from a lower layer, and the antioxidant film and the pad in the first region. Patterning a first oxide window reaching the semiconductor substrate in the oxide film and patterning a second oxide window reaching the semiconductor substrate in the antioxidant film and the pad oxide film in the second region; A third step of growing an oxide film on the bottom layer of the first and second oxide windows by a thermal oxidation method; and etching only the oxide film on the bottom surface of the second oxide window to form the second oxide window. A fourth step of forming a groove in the surface of the semiconductor substrate in the two regions; and growing the oxide film on the bottom surface of the first oxide window by thermal oxidation to form a first element isolation film and forming the second element isolation film.
Forming a second element isolation film made of a newly grown oxide film on the bottom surface of the oxidized window in the region. 5. A first pad oxide film is formed on a first region of a semiconductor substrate, and the first pad oxide film is formed on a second region of the semiconductor substrate.
A first step of forming a second acid pad oxide film thinner than the pad oxide film; a second step of forming an antioxidant film on the first pad oxide film and the second pad oxide film; A first oxidation window reaching the semiconductor substrate is formed in the antioxidant film and the first pad oxide film in the first region by patterning, and the antioxidant film and the second pad oxide film in the second region are formed in the first region. A third step of patterning a second oxide window reaching the semiconductor substrate, and an oxide film is grown on a bottom layer of the first oxide window and the second oxide window by a thermal oxidation method, and is formed on the first region. Forming a first element isolation film made of the oxide film and the second element isolation film;
A fourth step of forming a second element isolation film made of the oxide film in the region. 6. A first step of forming a pad oxide film on a first region and a second region of a semiconductor substrate, and forming a first antioxidant film on the pad oxide film in the first region. A second step of forming a second anti-oxidation film thicker than the first anti-oxidation film on the pad oxide film in the second region; and the first anti-oxidation film in the first region and the second anti-oxidation film. A first oxide window reaching the semiconductor substrate is patterned in the pad oxide film, and the second oxide window in the second region is formed.
A third step of patterning a second oxide window reaching the semiconductor substrate on the antioxidant film and the pad oxide film, and an oxide film on a bottom layer of the first oxide window and the second oxide window by a thermal oxidation method. Is grown, a first element isolation film made of the oxide film is formed in the first region, and the second element isolation film is formed.
A fourth step of forming a second element isolation film made of the oxide film in the region. 7. A first pad oxide film and a first antioxidant film are sequentially formed from a lower layer on a first region of a semiconductor substrate, and a film is formed on a second region of the semiconductor substrate more than the first pad oxide film. A first step of sequentially forming a second pad oxide film having a smaller thickness and a second antioxidant film having a thickness larger than that of the first antioxidant film from a lower layer, and the first antioxidant film and the first antioxidant film in the first region. First
A first oxide window reaching the semiconductor substrate is patterned in the pad oxide film, and a second oxidation window reaching the semiconductor substrate in the second antioxidant film and the second pad oxide film in the second region is formed. A second step of forming a pattern, an oxide film is grown on a bottom layer of the first oxide window and the second oxide window by a thermal oxidation method, and a first element isolation film made of the oxide film is formed in the first region. And forming the second
A third step of forming a second element isolation film made of the oxide film in the region.