JP2000294513A - Oxide film forming method of silicon substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a breakdown voltage of an embedded oxide film. SOLUTION: An embedded oxide film 4 is formed in an Si layer 3 by implanting oxygen ions in the Si layer 3. The Si layer 3 is oxidized at a high temperature, an inner oxide film 8 is stacked on the embedded oxide film 4, and an additional embedded oxide film is formed anew. A final embedded oxide film is formed, and an outer oxide film 7 is formed. An additional Si film is newly formed by growing Si on the Si layer 3, which has been formed between the inner oxide film and the outer oxide film, and a final Si film is formed. The film thicknesses of the final embedded oxide film and the final Si film are freely adjusted, and the breakdown voltage of the embedded oxide film is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an oxide film on a Si substrate, and more particularly, to an S film for increasing the withstand voltage.
The present invention relates to a method for forming an oxide film on an i-substrate.

[0002]

2. Description of the Related Art An SOI substrate is known as a silicon substrate. In the method for manufacturing an SOI substrate, it is one of important issues to form a Si layer having a low crystal defect density and a uniform thickness and a buried oxide film having a high electric insulation and a uniform thickness. For such a problem, a method called SIMOX method as shown in FIG. 15 is usually used. According to this method, as shown in FIG. 15 (a), 10 17 (/ cm 2) to 10 18 (/ cm 2)
The oxygen ion implantation layer 102 is formed by performing high-concentration oxygen ion implantation on the order of
By annealing for several hours at a temperature in the range of 300 degrees, an SOI substrate 105 having a uniform thickness of the Si layer 103 and the buried oxide film 104 as shown in FIG.

The SOI substrate 10 thus formed is
3 is called a SIMOX substrate. In a SIMOX substrate in which the implantation dose is set to 5 × (10 17) to 1 × (10 18) (unit omitted), the dielectric strength of the buried oxide film is weak, and the implantation dose is 1 × (10 17). 18th power) ~ 2x
It is known that the SIMOX substrate set to (10 18) has an increased crystal defect density in the Si layer. In order to prevent an increase in dislocation density of the Si layer 101 on the SOI surface and a decrease in oxide film breakdown voltage, a low-dose SIMOX substrate in which the implantation dose is set to 5 × (10 17) or less is considered promising in device application.

In such a low-dose SIMOX substrate,
Particles at the time of ion implantation serve as a mask, and after annealing to form a buried oxide film 104, the buried oxide film 1 is formed.
Since pinholes are likely to be formed in the buried oxide film 104, it is not enough to prevent a decrease in the withstand voltage of the buried oxide film 104.

Japanese Unexamined Patent Publication No. Hei 7-263538 discloses a method of manufacturing a low-dose SIMOX as shown in FIG. 16, and as shown in FIGS. 16 (a) and 16 (b), oxygen ion implantation and annealing are performed. After that, oxidation is performed at a high temperature of 1150 ° C. or higher and lower than the melting point of silicon, and FIG.
As shown in (c), by forming the internal oxide film 106, the thickness of the entire buried oxide films 104 and 106 is increased, the pinhole density is reduced, and the withstand voltage of the buried oxide film is reduced. Is disclosed.

[0006] Such a technique forms an internal oxide film,
Since the pinholes (that is, silicon) of the buried oxide film are oxidized to reduce the pinhole density, there is a certain effect in improving the electrical insulation of the buried oxide film. Thickening of the buried oxide film by this high-temperature oxidation method
For example, in an Ar gas having an oxygen concentration of 30%, for example, 1350 ° C.
In order to form an internal oxide film of about 20 nm by performing high temperature oxidation, an external oxide film 8 of about 500 nm is formed on the surface of the Si layer.
nm, and furthermore, it is necessary to increase the amount of oxidation as the electrical insulation is improved, and the Si layer on the SOI surface becomes thinner. In particular, the implantation energy is limited by the capability of the apparatus, and the implantation of such a high dose, that is, a high beam current, is greatly restricted. Since the thickness is determined, the thickness of the Si layer before high-temperature oxidation is about 400 nm or less, and the amount that can oxidize the Si layer is limited under such a restriction condition. In some cases, both a thick Si layer and a high withstand voltage, that is, a thick oxide film, are required,
There is a problem that it becomes difficult to satisfy such requirements.

It is required that the buried oxide film have a higher dielectric strength. Further, it is desired that the crystal defect density of the Si layer is lower. Further, it is preferable that the thicknesses of the Si layer and the buried oxide film can be freely set and designed at the same time.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of forming an oxide film on a Si substrate in which the buried oxide film has a higher withstand voltage. Another object of the present invention is to provide a method for forming an oxide film on a Si substrate in which the crystal defect density of the Si layer is lower. Still another object of the present invention is to provide
It is an object of the present invention to provide a method for forming an oxide film on a Si substrate in which the buried oxide film has a higher dielectric strength and the crystal defect density of the Si layer is lower. Still another object of the present invention is to provide a buried oxide film having a higher withstand voltage, a lower crystal defect density of the Si layer, and a free design of the Si layer and the buried oxide film at the same time. An object of the present invention is to provide a method for forming an oxide film on a Si substrate that can be performed.

[0009]

According to a method for forming an oxide film on a Si substrate according to the present invention, oxygen ions are implanted into a Si layer to form an SI film.
A burying step for forming a buried oxide film inside the layer, and a new additional buried oxide film is formed by superimposing the internal oxide film on the buried oxide film by oxidizing the Si layer at a high temperature and finally filling A first thickening step for forming an embedded oxide film and forming an external oxide film, and newly growing Si by growing a Si layer formed between the internal oxide film and the external oxide film. A second thickening step for forming an additional Si film to form a final Si film. In such thickening steps, the thickness of the Si layer is represented by X, the thickness of the additional Si film is represented by Y, the thickness of the final Si film is represented by x, and the thickness of the final buried oxide film is represented by y. Where the film thickness x of the final Si film and the film thickness y of the final buried oxide film are two-variable conversion functions: (x, y) =
(X (X, Y), y (X, Y)), and is executed according to the design value (x, y) based on the equation, and the film thickness can be freely controlled.

Preferably, the growth of Si is the growth of epitaxial Si. Further, a removing step for removing the external oxide film and a removing step for removing the external oxide film are sequentially added. The first thickening step temporally precedes the second thickening step, and it is effective that the growth of Si is the growth of epitaxial Si. The growth of Si is growth of one or more combinations selected from the group consisting of epitaxial growth, polysilicon growth, and amorphous silicon growth. The dose of the injection is 5 · (10
17) / square cm.

As described above, by performing the high-temperature oxidation for forming the internal oxide film and the additional growth of the Si layer, the thickness of the Si layer of the SOI is increased. By increasing the high-temperature oxidation time for forming the internal oxide film, the thickness of the internal oxide film can be increased as designed, and the final thickness of the Si layer can be increased as designed. The pinhole density of the buried oxide film is low, the withstand voltage of the buried oxide film is high, and the thickness of the Si layer can be increased, so that the degree of freedom in application to devices is high.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the drawings, in an embodiment of a method for forming an oxide film on a Si substrate according to the present invention, oxygen is implanted into a Si substrate. The Si substrate is an SOI substrate. As shown in FIG. 1, oxygen ions O (+) are implanted into the SOI substrate 1 from the upper surface side. The implantation region can be limited to a predetermined depth region. With this injection,
A high-concentration oxygen ion implanted layer 2 and S
An i layer 3 is formed. The Si layer 3 is composed of the oxygen ion implanted layer 2
Is formed on the upper surface side.

The implantation dose is 5 × (10 17) / cm 2 (hereinafter, “/”) in order to prevent an increase in the dislocation density of the Si layer 3 on the surface side of the SOI substrate 1 and a decrease in the withstand voltage of the oxide film.
The square cm "is omitted.) The implantation energy is limited by the capability of the apparatus, and particularly in the case of such a high dose, that is, in the case of high beam current implantation.
Due to severe restrictions, the injection energy is 180 ke
It is set to about V.

The SOI substrate 1 is annealed at a temperature of about 1350 ° C. in an inert gas / Ar atmosphere such as a 0.5% oxygen partial pressure. After crystal stabilization, the oxygen ion implanted layer 2 changes to a buried oxide film 4, as shown in FIG. During the annealing, the surface of the Si layer 3 changes to the oxide film 5. At this point, it is assumed that the thickness of the Si layer 3 is 350 nm and the thickness of the buried oxide film 4 is about 90 nm.

The oxide film 5 is removed with buffered hydrogen fluoride or the like. After the removal, as shown in FIG. 3, the Si gas was mixed with 1200 ° C. mixed gas of SiCl 4 and H 2.
An epitaxial Si layer 6 grows on the surface of the layer 3. It is assumed that the grown film thickness of the epitaxial Si layer 6 is 180 nm.

Next, in an Ar gas having an oxygen concentration of 30%, S
The OI substrate 1 is oxidized at a high temperature of 1350 ° C. S
External oxide film 7 is formed on the surface side of i layer 3. In this case, high-temperature oxidation is performed so that the thickness of the external oxide film 7 becomes about 1000 nm. By such high temperature oxidation, FIG.
, An internal oxide film 8 is formed. Internal oxide film 8 is formed between buried oxide film 4 and Si layer 3.

Under such conditions, the thickness of the internal oxide film 8 is approximately 40 nm. 40 nm is a determined value. Thus, the final buried oxide film thickness is 130 nm as the determined value. The thickness of the Si layer 3 is 80 nm as a determined value. Here, it is important to note that the epitaxial Si layer 6 shown in FIG. 3 and the external oxide film thickness 7 due to the high-temperature oxidation shown in FIG.
This means that the value is set by calculating back from the i-layer 3 and the thickness of the buried oxide film.

For example, when the desired final thickness of the Si layer 3 is 170 nm, the final buried oxide film thickness (the thickness of the first buried oxide film + the additional buried oxide film) When the film thickness is 130 nm, the epitaxial Si layer 6 grows to 270 nm and the external oxide film 7
Is formed to a thickness of 1000 nm. As a result, the final thickness of the Si layer 3 is 170 nm, and the thickness of the buried oxide film is 130 nm.
nm.

For example, when the desired thickness of the Si layer 3 is 80 nm and the buried oxide film thickness is 150 nm, the epitaxial Si layer 6 is grown to 400 nm.
The external oxide film 7 formed by high-temperature oxidation is formed at 1500 nm,
As a result, the thickness of the Si layer 3 becomes 170 nm, and the thickness of the buried oxide film becomes 130 nm.

In general, the thickness of the Si layer 3 in FIG. 3 is represented by X, the thickness of the additional Si film 6 is represented by Y, and the final Si
If the film thickness of the film 3 is represented by x and the film thickness of the final buried oxide film in FIG. 4 is represented by y, the film thickness x of the final Si film and the film thickness y of the final buried oxide film are represented by a two-variable conversion function. It is represented by the following equation: (x, y) = (x (X, Y), y (X, Y)). x and y are uniquely determined by X and Y. The functional forms of x and y can be approximately determined by experiment. By knowing this functional relationship, the thickness of the final Si film and the thickness of the final buried oxide film can be arbitrarily designed independently.

According to such a manufacturing method, since the thickness of the Si layer is increased by epitaxial Si growth before high-temperature oxidation, the amount of high-temperature oxidation can be increased regardless of the thickness of the Si layer after oxygen implantation and annealing. Thus, the buried oxide film and the Si layer can be made thicker. Therefore, since the thickness of the internal oxide film can be increased, a buried oxide film having a low pinhole density and a high oxide film breakdown voltage can be finally formed, and the thickness of the Si layer can be increased. Therefore, there is an effect that the SOI substrate 1 can be formed by the SIMOX method which has a high degree of freedom in application of the device. Furthermore, oxygen ion implantation is 5 × 1
Since it is set to 0 or less than 17th power, low dose SIM
An SOI substrate having a low defect density, which is a feature of the OX substrate, can be obtained.

In this embodiment, the epitaxial Si
Although growth is used, polysilicon or amorphous silicon growth can be used as long as the grown Si layer is not completely oxidized. However, when epitaxial Si growth is used as described above, the grown Si layer does not need to be completely oxidized.

In the above embodiment, the present invention is applied to the case where Si is grown after oxygen implantation and annealing.
The present invention can also be applied to a case where epitaxial Si is grown after high-temperature oxidation for forming a buried oxide film. The embodiment is shown in FIGS.
FIGS. 5 and 6 correspond completely to FIGS. 1 and 2, respectively.
The steps they show are exactly the same in both embodiments. As shown in FIG. 7, after performing high-temperature oxidation for increasing the thickness of the buried oxide film 4 ', the external oxide film 6' is removed, and epitaxial Si growth is performed as shown in FIG. An additional Si film 5 'is formed so as to increase the thickness of the Si layer 3'.

Also in this embodiment, it is possible to increase the thickness of the buried oxide film and the Si layer. The thickness can be freely adjusted. Regarding the increase in the thickness of the buried oxide film, FIG.
In the manufacturing process, the thickness of the buried oxide film is increased in FIG. 7 and the thickness of the Si layers 3 ′ and 5 ′ is increased in FIG. Since the film is formed, this embodiment is superior in controllability in manufacturing. In this embodiment, since the grown Si layer is used as it is as a Si layer for forming a device, the grown Si layer is not made of polysilicon or amorphous silicon. However, it can be applied to the case where amorphous Si is grown and annealed to form a single crystal.

FIGS. 9 to 14 show still another embodiment of the present invention. It is also possible to adopt a manufacturing method in which epitaxial Si is grown after oxygen implantation and annealing, high-temperature oxidation is performed to increase the thickness of the buried oxide film, and then the Si layer is thickened by epitaxial Si growth. The manufacturing method for that is shown in FIGS.

FIGS. 9 and 10 show the same steps as those of the first embodiment to increase the thickness of the buried oxide film.
As shown in FIG. 3, after removing the oxide film, as shown in FIG. 14, a re-added Si layer 5 ″ is grown to increase the thickness of the Si layer to a desired thickness.

According to this method, the thickness of the internal oxide film 3 can be increased, so that a buried oxide film having a lower pinhole density and a higher oxide film breakdown voltage can be formed, and the thickness of the Si layer can be increased. Since film formation is possible, an SOI substrate by a SIMOX method, which has a higher degree of freedom in device application, can be formed.

In particular, since epitaxial Si growth is performed before the high-temperature oxidation treatment for increasing the thickness of the buried oxide film, FIG.
The thickness of the buried oxide film can be further increased by increasing the amount of high-temperature oxidation regardless of the thickness of the Si layer in the state of (1).
This has a synergistic and special effect that the film thickness can be formed with good controllability.

In this embodiment, epitaxial Si growth is used in the step shown in FIG. 11, but polysilicon or amorphous silicon growth can be used before the grown Si layer is completely oxidized. However, when epitaxial Si growth is used, the grown Si layer does not need to be completely oxidized. In the step of FIG. 14, since the grown Si layer is used as it is as a Si layer for forming a device, the grown Si layer is not made of polysilicon or amorphous silicon. However, amorphous S
It can be applied to the case of i-growing, annealing and single crystallization.

[0030]

According to the method for forming an oxide film on a Si substrate according to the present invention, the objects of the present invention can be achieved freely and freely.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a method for forming an oxide film on a Si substrate according to the present invention.

FIG. 2 is a sectional view showing a step subsequent to FIG. 1;

FIG. 3 is a sectional view showing a step subsequent to FIG. 2;

FIG. 4 is a sectional view showing a step subsequent to FIG. 3; .

FIG. 5 is a sectional view showing another embodiment of the method for forming an oxide film on a Si substrate according to the present invention.

FIG. 6 is a sectional view showing a step subsequent to FIG. 5;

FIG. 7 is a sectional view showing a step subsequent to FIG. 6;

FIG. 8 is a sectional view showing a step subsequent to FIG. 7; .

FIG. 9 is a sectional view showing still another embodiment of the method of forming an oxide film on a Si substrate according to the present invention.

FIG. 10 is a sectional view showing a step subsequent to FIG. 9;

FIG. 11 is a sectional view showing a step subsequent to FIG. 10;

FIG. 12 is a sectional view showing a step subsequent to FIG. 11; .

FIG. 13 is a sectional view showing a step subsequent to FIG. 12;

FIG. 14 is a sectional view showing a step subsequent to FIG. 13; .

FIG. 15 is a sectional view showing a known method.

FIG. 16 is a sectional view showing a step subsequent to FIG. 15;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Si substrate 2 ... Oxygen ion implantation layer 3 ... Si layer 4 ... Buried oxide film 5 ... Oxide film 6 ... Epitaxial Si layer 7 ... External oxide film 8 ... Internal oxide film

Claims (8)

[Claims] A buried step for implanting oxygen ions into the Si layer to form a buried oxide film inside the SI layer; and burying the internal oxide film by oxidizing the Si layer at a high temperature. A first thickening step for forming a final buried oxide film by newly forming an additional buried oxide film on the film, and forming an external oxide film; the internal oxide film and the external oxide film A second thickening step for forming a new additional Si film by forming Si on the Si layer formed during the second step to form a final Si film. 2. The method according to claim 1, wherein the thickness of the Si layer is represented by X, the thickness of the additional Si film is represented by Y, and the thickness of the final Si film is represented by x. If the thickness of the film is represented by y, the thickness x of the final Si film and the thickness y of the final buried oxide film are two-variable conversion functions: (x, y) = (x (X (X , Y), y (X, Y)), and the step of executing the steps according to the design value (x, y) based on the above equation. Oxide film forming method. 3. The method for forming an oxide film on a Si substrate according to claim 1, wherein said growing of Si is growing of epitaxial Si. 4. The method according to claim 1, further comprising a removing step for removing the external oxide film. 5. The method according to claim 4, further comprising a removing step for removing the external oxide film, wherein the first thickening step temporally precedes the second thickening step. The method for forming an oxide film on a Si substrate, wherein the growth is growth of epitaxial Si. 6. The method according to claim 1, wherein the second thickening step temporally precedes the first thickening step. 7. The method according to claim 6, wherein the growth of Si is selected from the group consisting of epitaxial growth, polysilicon growth, and amorphous silicon growth.
Or S or more combinations of growth
A method for forming an oxide film on an i-substrate. 8. The method according to claim 1, wherein the dose of the implantation is 5 · (10 17) / square c.
m. A method for forming an oxide film on a Si substrate, the method comprising: