JP2000068266A - Method for forming oxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming an oxide film having good breakdown strength. SOLUTION: A method for forming an oxide film includes a step of forming an oxide film on a semiconductor layer by feeding a wet-type gas after a substrate with the semiconductor layer is stored into an oxidizing furnace, and a step of taking out the substrate from the oxidizing furnace after the feeding of the wet-type gas is stopped and changing the atmosphere to inactive atmosphere by feeding the inert gas into the oxidizing furnace. In this case, an inert gas containing oxygen gas of 0.67 to 20 vol.% for the atmosphere is used during from the time before the substrate is carried to the inside of the oxidizing furnace until the oxide film is formed on the face of the semiconductor substrate.

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 used as a gate oxide film or a tunnel oxide film in the manufacture of a semiconductor device, for example.

[0002]

2. Description of the Related Art For example, in manufacturing a MOS type semiconductor device, it is necessary to form a gate oxide film made of a silicon oxide film on the surface of a silicon semiconductor substrate. Also, EEP
Even in a nonvolatile semiconductor memory cell known as a ROM, it is necessary to form a tunnel oxide film made of a silicon oxide film on the surface of a silicon semiconductor substrate. Further, in manufacturing a thin film transistor (TFT), it is necessary to form a gate oxide film made of a silicon oxide film on the surface of a silicon layer provided on an insulating substrate. It is not an exaggeration to say that such a silicon oxide film is responsible for the reliability of the semiconductor device. Therefore, a silicon oxide film is always required to have high dielectric breakdown voltage and long-term reliability.

[0003] For example, in the case of manufacturing a MOS type semiconductor device, conventionally, NH ₄ OH /
The surface of the silicon semiconductor substrate is cleaned by RCA cleaning in which the surface is washed with an H ₂ O ₂ aqueous solution and further washed with an HCl / H ₂ O ₂ aqueous solution to remove fine particles and metal impurities from the surface. When the RCA cleaning is performed, the surface of the silicon semiconductor substrate reacts with the cleaning liquid to form a silicon oxide film having a thickness of about 0.5 to 1 nm (hereinafter, such a silicon oxide film is referred to as a chemical oxide film). The film thickness of such a chemical oxide film is non-uniform, and a cleaning liquid component remains in the chemical oxide film. Therefore, the silicon semiconductor substrate is immersed in a hydrofluoric acid aqueous solution to remove such a chemical oxide film, and further, a chemical component is removed with pure water. Thereby, it is possible to obtain a surface of the silicon semiconductor substrate that is mostly terminated with hydrogen and extremely partially terminated with fluorine.
In this specification, obtaining a surface of a silicon semiconductor substrate that is mostly terminated with hydrogen and a very small portion is terminated with fluorine is referred to as exposing the surface of the silicon semiconductor substrate in this specification. I do. After that, the silicon semiconductor substrate is carried into an oxidation furnace (processing chamber) of an oxide film forming apparatus, and a silicon oxide film is formed on the surface of the silicon semiconductor substrate.

[0004] As the oxide film forming apparatus, as the gate oxide film becomes thinner and the substrate becomes larger in diameter, a horizontal type vertically holding an oxidizing furnace made of quartz and a vertical type holding it vertically. The transition to is progressing. This is because the vertical-type oxide film forming apparatus is easier to cope with the enlargement of the substrate diameter than the horizontal-type oxide film forming apparatus, and the atmospheric pressure when the silicon semiconductor substrate is transported into the oxidation furnace. This is because a silicon oxide film generated by the entanglement (hereinafter, such a silicon oxide film is called a natural oxide film) can be reduced. However, even when the vertical type oxide film forming apparatus is used, a natural oxide film having a thickness of about 2 nm is formed on the surface of the silicon semiconductor substrate. The natural oxide film contains a large amount of impurities in the atmosphere, and the existence of the natural oxide film cannot be ignored in thinning the gate oxide film. Therefore, (1) a method of flowing a large amount of nitrogen gas into the substrate loading / unloading section provided in the oxide film forming apparatus to form a nitrogen gas atmosphere (nitrogen gas purge method), and (2) once the inside of the substrate loading / unloading section is evacuated. After that, a method has been proposed in which the inside of the substrate loading / unloading section is replaced with an inert gas such as nitrogen gas to eliminate the atmosphere (vacuum load lock method) or the like, and the formation of a natural oxide film is suppressed as much as possible. I have.

Then, the silicon semiconductor substrate is carried into the oxidizing furnace with the inside of the oxidizing furnace being in an inert gas atmosphere, and then the temperature of the oxidizing furnace is changed to an oxidizing atmosphere after the temperature of the oxidizing furnace is raised. Then, a gate oxide film is formed by heat-treating the silicon semiconductor substrate. A method of thermally oxidizing the surface of a silicon semiconductor substrate by introducing high-purity steam into an oxidation furnace maintained at a high temperature (wet oxidation method) is used for forming a gate oxide film. A gate oxide film having higher electrical reliability can be formed than a method of oxidizing the surface of the silicon semiconductor substrate with dry oxygen gas (dry oxidation method). As one of the wet oxidation methods, a pyrogenic oxidation method (also called a hydrogen gas combustion oxidation method) in which a hydrogen gas is mixed with an oxygen gas at a high temperature and burned is used to form a silicon oxide film. Yes, many are adopted. Normally, in this pyrogenic oxidation method, oxygen gas is supplied into a combustion chamber provided outside an oxidation furnace and maintained at 700 to 900 ° C., and then hydrogen gas is supplied into the combustion chamber to obtain a high-temperature gas. The hydrogen gas is burned inside. The wet gas thus obtained is used as an oxidizing species.

FIG. 2 is a conceptual diagram of a vertical type oxide film forming apparatus for forming a silicon oxide film based on a pyrogenic oxidation method. This vertical type oxide film forming apparatus
Oxidizing furnace 10 of double tube structure made of quartz held vertically
And a gas introduction unit 12 for introducing a wet gas and / or gas into the oxidation furnace 10, a gas exhaust unit 13 for exhausting the wet gas and / or gas from the oxidation furnace 10, and a cylindrical soaking tube 16 made of SiC. A heater 14 for maintaining the inside of the oxidizing furnace 10 at a predetermined atmospheric temperature, a substrate carrying-in / out section 20, and a gas introducing section 21 for introducing an inert gas such as nitrogen gas into the substrate carrying-in / out section 20. A gas exhaust unit 22 for exhausting gas from the substrate loading / unloading unit 20, an oxidation furnace 10, and a substrate loading / unloading unit 2.
The shutter 15 is provided to partition the silicon semiconductor substrate into and out of the oxidation furnace 10. A quartz boat 24 for mounting a silicon semiconductor substrate is attached to the elevator mechanism 23. Further, the hydrogen gas supplied to the combustion chamber 30 is mixed with the oxygen gas at a high temperature in the combustion chamber 30 and burned to generate a wet gas. The wet gas is introduced into the oxidation furnace 10 through the pipe 31, the gas flow path 11, and the gas introduction unit 12. In addition, the gas flow path 11
This corresponds to a space between the inner wall and the outer wall of the oxidation furnace 10 having the double tube structure.

An outline of a conventional method for forming a silicon oxide film based on a pyrogenic oxidation method using the vertical type oxide film forming apparatus shown in FIG. 2 will be described below with reference to FIGS. explain.

[Step-10] Nitrogen gas is introduced into the oxidation furnace 10 through the pipe 32, the combustion chamber 30, the pipe 31, the gas flow path 11 and the gas introduction unit 12, and the inside of the oxidation furnace 10 is set to a nitrogen gas atmosphere. At the same time, the ambient temperature of the oxidation furnace 10 is maintained at around 700 ° C. by the heater 14 via the soaking tube 16. In this state, the shutter 15 is closed (see FIG. 15A). The substrate loading / unloading section 20 is open to the atmosphere.

[Step-20] The substrate loading / unloading section 20
Then, the silicon semiconductor substrate 40 is carried in, and the silicon semiconductor substrate 40 is placed on the quartz boat 24. Substrate loading / unloading section 20
After the transfer of the silicon semiconductor substrate 40 to the substrate is completed, a door (not shown) is closed, nitrogen gas is introduced from the gas introduction unit 21 to the substrate carry-in / out unit 20, discharged from the gas exhaust unit 22, and discharged into the substrate carry-in / out unit 20. In a nitrogen gas atmosphere (see FIG. 15B).

[Step-30] When the inside of the substrate loading / unloading section 20 has a sufficient nitrogen gas atmosphere, the shutter 15 is opened (see FIG. 16A), the elevator mechanism 23 is operated, and the quartz boat 24 is operated. Is raised, and the silicon semiconductor substrate 40 is carried into the oxidation furnace 10 (see FIG. 16B). When the elevator mechanism 23 reaches the highest position,
The base of the quartz boat 24 prevents communication between the oxidation furnace 10 and the substrate loading / unloading section 20.

[Step-40] Thereafter, the temperature of the oxidizing furnace 10 in a nitrogen gas atmosphere is increased to 800 to 900 ° C.
(See FIG. 17A). And pipes 32, 3
Oxygen gas and hydrogen gas are supplied into the combustion chamber 30 through the combustion chamber 3, and the wet gas generated by mixing and burning the hydrogen gas and the oxygen gas at a high temperature in the combustion chamber 30 is supplied to the pipe 31 through the gas flow The gas is introduced into the oxidation furnace 10 through the passage 11 and the gas introduction unit 12 and exhausted from the gas exhaust unit 13 (see FIG. 17B). Thereby, the silicon semiconductor substrate 40
A silicon oxide film is formed on the surface of the substrate. The combustion chamber 30
The internal temperature is increased by, for example, 700 heaters (not shown).
Keep at ~ 900 ° C.

[Step-50] After a silicon oxide film having a desired thickness is formed, supply of oxygen gas and hydrogen gas into the combustion chamber 30 is stopped. While introducing the active gas, the ambient temperature of the oxidation furnace 10 was lowered to about 700 ° C. (see FIG. 18).
The elevator mechanism 23 is operated to lower the quartz boat 24, and then the silicon semiconductor substrate 40 is unloaded from the substrate loading / unloading section 20.

[0013]

However, by using such a vertical type oxide film forming apparatus, the substrate loading / unloading section 2 is required.
Even if a method of flowing a large amount of nitrogen gas into a nitrogen gas atmosphere (nitrogen gas purge method) is employed, a natural oxide film having many traps may be formed on the surface of the silicon semiconductor substrate. As described above, if the natural oxide film is formed in an uncontrolled state, when the silicon oxide film is formed in the oxidation furnace 10, the thickness of the formed silicon oxide film may vary. . Also,
When the pressure resistance of the silicon oxide film is evaluated based on so-called Coulomb breakdown (Q _BD ) measurement, the silicon semiconductor substrate 40 is loaded into the oxidation furnace 10 in a 100% nitrogen gas atmosphere, and the atmosphere temperature of the oxidation furnace 10 is set to 800 to 900. It has been found that there is room for improvement in the breakdown voltage characteristics of the silicon oxide film obtained through the step of raising the temperature to ゜ C.

Before opening the shutter 15, the oxidation furnace 1
When a silicon semiconductor substrate whose surface has been exposed by washing with a hydrofluoric acid aqueous solution and pure water is transported into a high-temperature nitrogen gas atmosphere, the inside of the oxidation furnace 10 is filled with a silicon oxide film. Is formed, an atomic-level nitride film is locally formed in the silicon oxide film, or the surface of the silicon semiconductor substrate 40 is roughened. These phenomena are caused by the fact that a part of the Si—H bond and a part of the Si—F bond formed on the surface of the silicon semiconductor substrate 40 by the cleaning with the hydrofluoric acid aqueous solution and the pure water increase the temperature of hydrogen or fluorine. It is considered that the loss is caused by the desorption and the etching phenomenon occurs on the surface of the silicon semiconductor substrate 40. For example, when the temperature of a silicon semiconductor substrate is raised to 600 ° C. or more in an argon gas, severe irregularities may occur on the surface of the silicon semiconductor substrate.
Tadahiro Omi, Ultra Clean ULSI Technology, 21st
Page. In order to suppress such a phenomenon, before opening the shutter 15, a nitrogen gas containing 0.5% by volume of oxygen gas is introduced into the oxidation furnace 10 from the gas introduction unit 12, and the inside of the oxidation furnace 10 is reduced to 0%. It is well known that a nitrogen gas atmosphere containing about 0.5% by volume of oxygen gas is used. However, the silicon semiconductor substrate 40 is carried into the oxidation furnace 10 in a nitrogen gas atmosphere containing 0.5% by volume of oxygen gas,
There is still room for improvement in the breakdown voltage characteristics of the silicon oxide film obtained through the process of raising the ambient temperature of the oxidation furnace 10 to 800 to 900 ° C.

In the [Step-50], the oxidation furnace 1
Oxidizing furnace 1 while introducing an inert gas such as nitrogen gas
It has been found that when the temperature of the atmosphere is reduced to 0, the thickness of the silicon oxide film finally obtained may vary in the plane of the silicon semiconductor substrate depending on the atmosphere of the oxidation furnace.

[0016] The above problems occur not only on the surface of a silicon semiconductor substrate but also on the surface of a silicon layer provided on an insulating substrate or an insulating layer.

Therefore, a first object of the present invention is to provide a method for forming an oxide film capable of forming an oxide film having excellent withstand voltage characteristics. Further, a second object of the present invention is to provide:
An object of the present invention is to provide a method for forming an oxide film with less variation in film thickness.

[0018]

Means for Solving the Problems In order to achieve the first object, the method for forming an oxide film according to the first aspect of the present invention comprises the steps of (a) loading a substrate having a semiconductor layer into an oxidation furnace. After that, a step of forming an oxide film on the surface of the semiconductor layer by introducing a wet gas into the oxidation furnace, and (b) stopping the introduction of the wet gas into the oxidation furnace and introducing an inert gas into the oxidation furnace And then carrying out the substrate from the oxidation furnace after the atmosphere of the oxidation furnace is made an inert gas atmosphere, from the time before the substrate is carried into the oxidation furnace until the oxide film is formed on the surface of the semiconductor layer. The atmosphere of the oxidation furnace is an inert gas atmosphere containing oxygen gas at 0.67% to 20% by volume, preferably 3% to 20% by volume, more preferably 5% to 20% by volume. And

In the method of forming an oxide film according to the first aspect of the present invention, in the step (a), the atmosphere temperature of the oxidation furnace before the substrate is carried into the oxidation furnace may be adjusted to adhere to the surface of the semiconductor layer. The temperature at which the removed organic substances react with oxygen gas and are removed is preferably 150 ° C. to 700 ° C., more preferably 30 ° C.
It is desirable that the temperature be 0 ° C to 700 ° C.

In the method of forming an oxide film according to the first aspect of the present invention, in order to simultaneously achieve the second object, an inert gas is introduced into the oxidation furnace in the step (b). In this case, it is desirable to replace the inside of the oxidation furnace from a wet gas atmosphere to an inert gas atmosphere within 5 minutes, preferably within 3 minutes, more preferably within 1 minute. Furnace volume V
(Liter), when the flow rate of the inert gas introduced into the oxidation furnace is F (SLM), F ≧ 0.3 V, preferably F
It is desirable to satisfy ≧ 0.4V.

According to a second aspect of the present invention, there is provided a method of forming an oxide film for achieving the above-mentioned second object, comprising the steps of: (a) loading a substrate having a semiconductor layer into an oxidation furnace; (B) stopping the introduction of the wet gas into the oxidation furnace, introducing an inert gas into the oxidation furnace, and introducing an inert gas into the oxidation furnace. And then carrying out the substrate from the oxidizing furnace after setting the atmosphere to an inert gas atmosphere. In the step (b), an inert gas is introduced into the oxidizing furnace to make the inside of the oxidizing furnace inert from the wet gas atmosphere. It is characterized in that the gas atmosphere is replaced within 5 minutes, preferably within 3 minutes, more preferably within 1 minute.

According to a third aspect of the present invention, there is provided a method of forming an oxide film for achieving the above second object, comprising the steps of: (a) loading a substrate having a semiconductor layer into an oxidation furnace; (B) stopping the introduction of the wet gas into the oxidation furnace, introducing an inert gas into the oxidation furnace, and introducing an inert gas into the oxidation furnace. And then carrying out the substrate from the oxidation furnace. After the step (b), the volume of the oxidation furnace is set to V (liter), and the flow rate of the inert gas introduced into the oxidation furnace is set to F. (S
LM), F ≧ 0.3V, preferably F ≧ 0.
4V.

In the method of forming an oxide film according to the first to third aspects of the present invention, in the step (a), after the substrate having the semiconductor layer is loaded into the oxidation furnace, the atmosphere temperature of the oxidation furnace is reduced. The temperature may be raised to a predetermined temperature, and thereafter, a wet gas may be introduced into the oxidation furnace, and an oxide film may be formed on the surface of the semiconductor layer while the ambient temperature of the oxidation furnace is maintained at the predetermined temperature. it can. In the step (b),
The introduction of the wet gas into the oxidation furnace may be stopped, the temperature of the atmosphere in the oxidation furnace may be lowered while introducing the inert gas into the oxidation furnace, and then the substrate may be carried out of the oxidation furnace.

In the method for forming an oxide film according to the first to third aspects of the present invention, the oxide film may be formed by a batch method or may be formed by a single-wafer method. .

In the method of forming an oxide film according to the first to third aspects of the present invention, examples of the inert gas include a nitrogen gas, an argon gas, and a helium gas. Further, the wet gas is, for example, by reacting hydrogen gas and oxygen gas at a high temperature, that is, by heating pure water by a so-called pyrogenic method,
It can be produced by bubbling heated pure water with oxygen gas or inert gas, by reacting hydrogen gas with oxygen gas under a catalyst, or by reacting oxygen plasma with hydrogen plasma. The wet gas may be generated by combining these wet gas generation methods, or the wet gas may be generated by employing one type of wet gas generation method. The wet gas refers to water vapor or a gas containing water vapor. Examples of the gas include an oxygen gas, an inert gas such as a nitrogen gas, an argon gas, and a helium gas, and a mixed gas of an oxygen gas and an inert gas. Can be mentioned.

In the method of forming an oxide film according to the first to third aspects of the present invention, the wet gas used for forming the oxide film may contain a halogen element. As a result, an oxide film having excellent time-zero dielectric breakdown (TZDB) characteristics and temporal dielectric breakdown (TDDB) characteristics can be obtained. In addition, as the halogen element, chlorine, bromine and fluorine can be mentioned, and among them, chlorine is preferable. As the form of the halogen element contained in the wet gas, for example, hydrogen chloride (HCl), CCl ₄ , C ₂
HCl ₃ , Cl ₂ , HBr and NF ₃ can be mentioned. The content of the halogen element in the wet gas is 0.001 to 10% by volume, preferably 0.005 to 10% by volume, more preferably 0.1 to 10% by volume, based on the form of the molecule or the compound.
02 to 10% by volume. For example, when using hydrogen chloride gas, the content of hydrogen chloride gas in the wet gas is 0.02 to 1
Desirably, it is 0% by volume.

In the method for forming an oxide film according to the first to third aspects of the present invention, the atmosphere temperature or a predetermined temperature of the oxidation furnace at the time of forming the oxide film is set at 700 to 1000 ° C., preferably 750 to 900 ° C. C is desirable.
Note that the ambient temperature of the oxidation furnace at the time of forming the oxide film may be hereinafter referred to as an oxidation temperature for convenience. The oxidation temperature or the predetermined temperature may be constant, may be gradually increased, or may be changed stepwise. Further, in the step (b), the atmosphere temperature of the oxidation furnace is set to 700 to 750 ° C. in order to reduce the thermal shock to the semiconductor layer.
It is preferable to lower the temperature to or below.

When the oxidation temperature is changed stepwise, an oxide film is formed on the surface of the semiconductor layer by a wet gas at an ambient temperature at which atoms (eg, silicon atoms) mainly constituting the semiconductor layer do not desorb from the surface of the semiconductor layer. A first oxide film forming step of forming an oxide film while maintaining an atmosphere in an atmosphere temperature range in which atoms mainly constituting the semiconductor layer do not desorb from the surface of the semiconductor layer for a predetermined period after the formation of the oxide film is started. A second oxide film further forming an oxide film by a wet gas at a temperature higher than an atmosphere temperature range in which atoms mainly constituting the semiconductor layer do not desorb from the surface of the semiconductor layer until a desired thickness is obtained. And a forming step. Note that, in this case, the atmosphere temperature at which atoms mainly forming the semiconductor layer do not desorb from the surface of the semiconductor layer does not break bonds between atoms terminating the surface of the semiconductor layer and atoms mainly forming the semiconductor layer. Preferably it is temperature. Further, the temperature at which atoms mainly constituting the semiconductor layer do not desorb from the surface of the semiconductor layer depends on the silicon semiconductor substrate or the silicon layer surface when the semiconductor layer is mainly composed of silicon atoms.
The temperature is preferably a temperature at which the -H bond is not broken, or a temperature at which the Si-F bond on the surface of the silicon semiconductor substrate or the silicon layer is not broken. Plane orientation is (100)
When a silicon semiconductor substrate is used, most of the hydrogen atoms on the surface of the silicon semiconductor substrate are bonded one by one to each of two bonds of silicon atoms, and
It has a -H termination structure. However, a portion where the surface state of the silicon semiconductor substrate is broken (for example, a step formation portion) has a terminal structure in which a hydrogen atom is bonded to only one bond of a silicon atom, or a three-bonded silicon atom. There is a terminal structure in which a hydrogen atom is bonded to each of the hands. Usually, the remaining bonds of silicon atoms are bonded to silicon atoms inside the crystal. The expression “Si—H bond” in this specification refers to a terminal structure in which a hydrogen atom is bonded to each of two silicon atoms, and a hydrogen atom is bonded to only one silicon atom. Termination structure, or silicon atom 3
All of the terminal structures in which a hydrogen atom is bonded to each of the bonding hands are included. The ambient temperature at which the formation of the oxide film on the surface of the semiconductor layer is started is more specifically a temperature at which the wet gas does not condense on the surface of the semiconductor layer, preferably at least 150 ° C, more preferably at least 300 ° C. Is desirable from the viewpoint of throughput. Alternatively, the temperature is higher than the temperature at which the wet gas does not cause condensation on the surface of the semiconductor layer.
A first oxide film forming step of forming an oxide film at an atmosphere temperature of 00 ° C. or less, preferably 450 ° C. or less, more preferably 400 ° C. or less, and an atmosphere temperature higher than that of the first oxide film forming step And a second oxide film forming step of further forming an oxide film by a wet gas until a desired thickness is obtained. In these forms,
The formation temperature of the oxide film in the second oxide film formation step is 7
The temperature is desirably from 00 to 1000 ° C., preferably from 750 to 900 ° C. In addition, the method for generating a wet gas in the first oxide film forming step, the second oxide film forming step, or the first oxide film forming step and the second oxide film forming step is the same as the above-described method (1). It is preferable to use at least one of the above methods. Here, in the first oxide film forming step and the second oxide film forming step, the same method or a different method may be employed as a method for generating a wet gas. As a wet gas in the first oxide film forming step, the second oxide film forming step, or the first oxide film forming step and the second oxide film forming step, an inert gas such as nitrogen gas, argon gas, or helium gas is used. A wet gas diluted with a gas may be used.

The atmosphere in the temperature raising step between the first oxide film forming step and the second oxide film forming step may be an inert gas atmosphere or a reduced pressure atmosphere. Furthermore, the first
The atmosphere in the temperature raising step between the oxide film forming step and the second oxide film forming step may be an oxidizing atmosphere containing a wet gas or an oxidizing atmosphere containing a wet gas diluted with an inert gas. You can also. Here, examples of the inert gas include a nitrogen gas, an argon gas, and a helium gas. The inert gas or the wet gas in the atmosphere in the temperature raising step may contain a halogen element. Thereby, the characteristics of the silicon oxide film formed in the first oxide film forming step can be further improved. That is, when the main atoms constituting the semiconductor layer are silicon, silicon dangling bonds (Si.) And SiOH, which are defects that can occur in the first oxide film forming step, react with the halogen element in the temperature increasing step, As a result of termination or dehydration reaction of the silicon dangling bond, these defects, which are reliability deterioration factors, are eliminated. In particular, the elimination of these defects is effective for the initial silicon oxide film formed in the first oxide film forming step. Examples of the halogen element include chlorine, bromine, and fluorine, and among them, chlorine is preferable. Examples of the form of the halogen element contained in the inert gas or the wet gas include hydrogen chloride (H
Cl), CCl ₄ , C ₂ HCl ₃ , Cl ₂ , HBr, NF ₃
Can be mentioned. The content of the halogen element in the inert gas or the wet gas is 0.001 to 10% by volume, preferably 0.0
It is from 0.05 to 10% by volume, more preferably from 0.02 to 10% by volume. For example, when using hydrogen chloride gas, the content of hydrogen chloride gas in an inert gas or wet gas is 0.02.
Desirably, it is 10 to 10% by volume.

The final thickness of the oxide film after the second oxide film forming step may be a predetermined thickness required for the semiconductor device. On the other hand, the thickness of the oxide film after the first oxide film forming step is preferably as thin as possible. However,
At present, the plane orientation of a silicon semiconductor substrate used for manufacturing a semiconductor device is almost (100), and no matter how the surface of the silicon semiconductor substrate is smoothed, the surface of the silicon semiconductor substrate must be (100). A step called a step is formed. This step is usually for one layer of silicon atoms, but in some cases, a step for two to three layers may be formed. Therefore, the thickness of the oxide film after the first oxide film forming step is (1)
00) When a silicon semiconductor substrate is used, the thickness is preferably 1 nm or more, but is not limited thereto.

In order to further improve the characteristics of the formed oxide film, in the method of forming an oxide film according to the first to third aspects of the present invention, after the formation of the oxide film having a desired thickness is completed, Preferably, the formed oxide film is subjected to a heat treatment.

In this case, it is desirable that the atmosphere for the heat treatment be an inert gas atmosphere containing a halogen element.
By heat-treating the oxide film in an inert gas atmosphere containing a halogen element, time-zero dielectric breakdown (TZD)
B) An oxide film having excellent characteristics and time-dependent dielectric breakdown (TDDB) characteristics can be obtained. Examples of the inert gas in the heat treatment include a nitrogen gas, an argon gas, and a helium gas. Also, as a halogen element, chlorine,
Bromine and fluorine can be mentioned, and among them, chlorine is desirable. Examples of the form of the halogen element contained in the inert gas include hydrogen chloride (HCl),
Examples include CCl ₄ , C ₂ HCl ₃ , Cl ₂ , HBr, and NF ₃ . The content of the halogen element in the inert gas ranges from 0.001 to 0.001 based on the form of the molecule or compound.
It is 10% by volume, preferably 0.005 to 10% by volume, and more preferably 0.02 to 10% by volume. For example, when using hydrogen chloride gas, the content of hydrogen chloride gas in the inert gas is preferably 0.02 to 10% by volume. still,
The heat treatment may be performed in a state in which the atmosphere of an inert gas containing a halogen element is reduced in pressure from atmospheric pressure.

In the method of forming an oxide film according to the first to third aspects of the present invention, the heat treatment may be a single-wafer treatment, but is preferably a furnace annealing treatment from the viewpoint of throughput. Atmospheric temperature of heat treatment is 700 ~ 1
The temperature is 200 ° C, preferably 700 to 1000 ° C, and more preferably 700 to 950 ° C. When the heat treatment is furnace annealing, the heat treatment time is 5 to 60.
Minutes, preferably 10 to 40 minutes, more preferably 20 to 3 minutes.
0 minutes. On the other hand, when the heat treatment is a single-wafer treatment, the heat treatment time is preferably 1 to 10 minutes.

After the heat treatment, the oxide film may be nitrided.
In this case, the nitriding treatment is preferably performed in an N ₂ O gas, NO gas, or NO ₂ gas atmosphere, and particularly preferably in an N ₂ O gas atmosphere. Alternatively, it is preferable to perform the nitriding treatment in an atmosphere of NH ₃ gas, N ₂ H ₄ , and hydrazine derivative, and then perform the annealing treatment in an atmosphere of N ₂ O gas and O ₂ . It is desirable to perform the nitriding treatment at a temperature of 700 to 1200 ° C., preferably 800 to 1150 ° C., and more preferably 900 to 1100 ° C. In this case, the semiconductor layer is heated by infrared irradiation or furnace annealing. preferable.

Alternatively, the atmosphere for the heat treatment may be a nitrogen-based gas atmosphere. Here, as nitrogen-based gas,
Examples include N ₂ , NH ₃ , N ₂ O, NO ₂ , and NO.

Normally, before forming a silicon oxide film on a silicon semiconductor substrate or a silicon layer, NH ₄ OH / H ₂
O ₂ was washed with an aqueous solution to wash the surface of the silicon semiconductor substrate or a silicon layer by RCA cleaning of further washed with HCl / H ₂ O ₂ aqueous solution to remove particulate and metal impurities from the surface, hydrofluoric acid aqueous solution Then, the surface of the silicon semiconductor substrate or the silicon layer is cleaned with pure water. However, after that, when the silicon semiconductor substrate or the silicon layer is exposed to the air, the surface of the silicon semiconductor substrate or the silicon layer is contaminated, and moisture and organic substances adhere to the surface of the silicon semiconductor substrate or the silicon layer,
Alternatively, there is a possibility that Si atoms on the surface of the silicon semiconductor substrate or the silicon layer may be bonded to a hydroxyl group (OH) (for example, see “Lily-reliable Gate Oxide Formation f
or Giga-Scale LSIs by using Closed Wet Cleaning Sy
stem and Wet Oxidation with Ultra-Dry Unloading ",
J. Yugami, et al., International Electron Device Me
eting Technical Digest95, pp 855-858). In such a case, when the formation of the silicon oxide film is started as it is, moisture, an organic substance, or Si-OH is taken into the formed silicon oxide film, and the characteristics of the formed silicon oxide film deteriorate or It can cause the generation of defective portions. The defect portion is a portion of a silicon oxide film including a defect such as a silicon dangling bond (Si.) Or a Si-H bond, or a portion of Si-OS.
i-bond is compressed by stress or Si-O-Si
Si-O- such that the bond angle is different from that of the Si-O-Si bond in the thick or bulk silicon oxide film
A portion of a silicon oxide film including a Si bond is meant.
Therefore, in order to avoid occurrence of such a problem, a step of cleaning the surface of the semiconductor layer before forming the oxide film is included, and the semiconductor layer after the surface cleaning is carried into the oxidation furnace without being exposed to the atmosphere. Is preferred. That is, for example, the atmosphere from the cleaning of the semiconductor layer surface to the transfer to the oxidation furnace is preferably an inert gas atmosphere or a vacuum atmosphere. As a result, an oxide film can be formed on a semiconductor layer having a clean surface that is mostly terminated with hydrogen and a very small portion is terminated with fluorine, and the characteristics of the formed oxide film are deteriorated or defects are generated. Can be prevented.

As the semiconductor layer, a silicon semiconductor substrate such as a silicon single crystal wafer can be used. In this case, the base is also a silicon semiconductor substrate. Further, the semiconductor layer includes a semiconductor substrate or a semi-insulating substrate as a base, an epitaxial silicon layer formed on or above the insulating substrate (including an epitaxial silicon layer formed by a selective epitaxial growth method), and polysilicon. Layer or amorphous silicon layer, so called lamination method or SI
A silicon layer in an SOI structure manufactured based on the MOX method, and further a material layer on which an insulating film is to be formed, such as a silicon semiconductor substrate or a semiconductor element formed on these layers, or a Si-Ge mixed crystal. . Forming an insulating film on a semiconductor layer includes not only forming an insulating film on a semiconductor layer formed on or above a semiconductor substrate or the like, but also forming an insulating film on the surface of a semiconductor substrate. In addition, the silicon single crystal wafer can be used for CZ method, MCZ method, DLCZ method, FZ method.
It may be a wafer manufactured by any method such as a method, or may be one to which hydrogen annealing has been added in advance.

The method for forming an oxide film according to the present invention is, for example, an MO method.
Formation of gate oxide film of S type transistor, formation of interlayer insulating film and element isolation region, formation of gate oxide film of top gate type or bottom gate type thin film transistor, EEPROM
For example, the present invention can be applied to formation of an oxide film in various semiconductor devices, such as formation of a tunnel oxide film in a nonvolatile semiconductor memory cell known as a nonvolatile semiconductor memory cell.

Alternatively, in the method of forming an oxide film according to the present invention, not only is the oxide film a gate oxide film, but also the semiconductor layer and the base are formed of a silicon semiconductor substrate, and the oxide film is formed of a silicon semiconductor substrate. An embodiment may be an oxide film formed on the silicon semiconductor substrate before the gate oxide film is formed on the surface. In the latter case, an oxide film formed on the silicon semiconductor substrate before the gate oxide film is formed on the surface of the silicon semiconductor substrate is replaced with an oxide film for forming an element isolation region (that is, an element isolation region having a LOCOS structure or a trench structure). In the process, an oxide film as a base for depositing a silicon nitride film)
Alternatively, it can be a sacrificial oxide film. The element isolation region may have a LOCOS structure, a trench structure, or a form having a LOCOS structure and a trench structure.

In the method for forming an oxide film according to the first aspect of the present invention, the inside of the oxidizing furnace is supplied with oxygen gas of 0.67% by volume.
After the substrate having the semiconductor layer is carried into the oxidation furnace after the inert gas atmosphere containing from 20% by volume to 20% by volume, organic substances attached to the surface of the semiconductor layer react with oxygen gas in the atmosphere and are removed. An oxide film having excellent withstand voltage characteristics can be formed. Further, in the method for forming an oxide film according to the second aspect of the present invention, the inside of the oxidation furnace is promptly brought into an inert gas atmosphere after the formation of the oxide film is completed.
An oxide film with small thickness variation can be formed.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

(Embodiment 1) Embodiment 1 is the first embodiment of the present invention.
The present invention relates to a method for forming an oxide film according to the second and third aspects.
In the first embodiment, the inside of the oxidation furnace is supplied with oxygen gas for 6.25 hours.
After setting the atmosphere to an inert gas atmosphere containing volume%, the substrate having the semiconductor layer is carried into the oxidation furnace. Further, the atmosphere temperature of the oxidation furnace before carrying the substrate into the oxidation furnace is set to 700 ° C., which is a temperature at which organic substances adhering to the surface of the semiconductor layer react with oxygen gas and are removed. After loading the silicon semiconductor substrate, the ambient temperature of the oxidation furnace is increased to a predetermined temperature. After that, wet gas is introduced into the oxidation furnace,
An oxide film is formed on the surface of the semiconductor layer while maintaining the atmosphere temperature of the oxidation furnace at a predetermined temperature. Furthermore, after the formation of the oxide film is completed, the introduction of the wet gas into the oxidation furnace is stopped, and while the inert gas is introduced into the oxidation furnace, the ambient temperature of the oxidation furnace is lowered. Take it out. After the formation of the oxide film is completed, an inert gas is introduced into the oxidation furnace to replace the inside of the oxidation furnace from a wet gas atmosphere to an inert gas atmosphere within 5 minutes. When the furnace volume is V (liter) and the flow rate of the inert gas introduced into the oxidation furnace is F (SLM), F ≧
An inert gas is introduced into the oxidation furnace under a condition satisfying 0.3 V.

In the first embodiment, as described with reference to FIG.
An oxide film was formed by a batch method using a vertical-type oxide film forming apparatus for forming a silicon oxide film based on a pyrogenic oxidation method. The volume V of the oxidation furnace 10 is about 7
It is 0 liter. Further, a silicon semiconductor substrate was used as a base having a semiconductor layer, and nitrogen gas was used as an inert gas. The formed silicon oxide film functions as a gate oxide film.

Hereinafter, a method for forming an oxide film according to the first embodiment will be described with reference to FIGS. 3 to 6 which are conceptual views of an oxide film forming apparatus and the like. FIG. 1 schematically shows an atmosphere temperature profile and the like in Example 1. In FIGS. 1, 9, and 10, "loading" means loading a silicon semiconductor substrate into an oxidation furnace.

[Step-100] First, an N-type silicon wafer doped with phosphorus and having a diameter of 8 inches (prepared by the CZ method)
LOC is formed on a silicon semiconductor substrate 40 by a known method.
An element isolation region having an OS structure was formed, and then well ion implantation, channel stop ion implantation, and threshold adjustment ion implantation were performed. Note that the element isolation region may have a trench structure or a combination of a LOCOS structure and a trench structure. Thereafter, fine particles and metal impurities on the surface of the silicon semiconductor substrate 40 are removed by RCA cleaning, and then the surface of the silicon semiconductor substrate 40 is cleaned with a 0.1% aqueous hydrofluoric acid solution and pure water. The surface was exposed. The surface of the silicon semiconductor substrate 40 is mostly terminated with hydrogen, and a very small portion is terminated with fluorine.

[Step-110] Inert gas (nitrogen gas) and oxygen gas are introduced into the oxidizing furnace 10 through the pipes 32 and 33, the combustion chamber 30, the pipe 31, the gas flow path 11 and the gas introducing section 12, The inside of the oxidation furnace 10 is set to an inert gas atmosphere such as a nitrogen gas (or may be a reduced pressure atmosphere).
The atmosphere temperature of the oxidizing furnace 10 is maintained at 700 ° C. by the heater 14 via the heater (see FIG. 3A). The flow rate of nitrogen gas was 15 SLM, and the flow rate of oxygen gas was 1 SLM. That is, the inside of the oxidation furnace 10 was set to an inert gas atmosphere containing 6.25% by volume of oxygen gas at a temperature of 700 ° C.
In this state, the shutter 15 is closed. The substrate loading / unloading section 20 is open to the atmosphere.
Then, a plurality of (110 in the first embodiment) silicon semiconductor substrates 40 were loaded into the substrate loading / unloading section 20 of the oxide film forming apparatus shown in FIG. 2 from a door (not shown) and placed on the quartz boat 24 ( (See FIG. 3B). In this state, the shutter 15 is kept closed.

[Step-120] Then, the substrate loading / unloading section 2
0, the door (not shown) is closed, and the gas introduction unit 21 is inserted into the substrate carry-in / out unit 20.
The nitrogen gas was introduced from the gas exhaust unit 22 and exhausted from the gas exhaust unit 22, and the inside of the substrate loading / unloading unit 20 was set to a nitrogen gas atmosphere. The oxygen gas concentration in the substrate loading / unloading section 20 is monitored, and if the oxygen gas concentration becomes, for example, 100 ppm or less, it is determined that the inside of the substrate loading / unloading section 20 has a sufficient nitrogen gas atmosphere. Thereafter, the shutter 15 is opened (see FIG. 4A), and the elevator mechanism 23 is operated to operate the quartz boat 24.
(Ascending speed: 100 mm / min), and the silicon semiconductor substrate 40 was carried into the oxidation furnace 10 having a double tube structure made of quartz (see FIG. 4B). When the elevator mechanism 23 reaches the highest position, the base of the quartz boat 24 stops communication between the oxidation furnace 10 and the substrate loading / unloading section 20. The ambient temperature of the oxidation furnace 10 is set to 70 by the heater 14.
It is kept at 0 ° C.

[Step-130] Thereafter, inert gas (nitrogen gas) and oxygen gas are supplied to the pipes 32 and 33,
0, the atmosphere temperature of the oxidizing furnace 10 of the oxide film forming apparatus is maintained at 850 by the heater 14 through the soaking tube 16 while continuously introducing the oxidizing furnace 10 into the oxidizing furnace 10 through the pipe 31, the gas flow path 11 and the gas introducing section 12. The temperature was raised to ゜ C (see FIG. 5A). The heating rate was 5 ° C / min.

In [Step-120], the inside of the oxidation furnace 10 is set to an inert gas atmosphere containing 6.25% by volume of oxygen gas, and then the silicon semiconductor substrate 40 is loaded into the oxidation furnace 10; Step-130], the oxidation furnace 1
Since the temperature of the atmosphere of 0 is raised to a predetermined temperature (850 ° C.), organic substances, particularly carbon-containing organic substances, attached to the surface of the silicon semiconductor substrate 40 react with oxygen gas in the atmosphere of the oxidation furnace 10, It is removed as CO _2.

[Step-140] After the ambient temperature of the oxidizing furnace 10 reaches a predetermined temperature (850 ° C. in the first embodiment), the oxidizing furnace 1
A silicon oxide film was formed on the surface of the silicon semiconductor substrate 40 by introducing a wet gas into the inside. Specifically, the supply of the nitrogen gas to the oxidation furnace 10 is interrupted, and the supply amount of the oxygen gas from the pipe 32 to the combustion chamber 30 is increased.
Supplies hydrogen gas into the combustion chamber 30 and burns the hydrogen gas in the combustion chamber 30. The wet gas generated in the combustion chamber 30 is oxidized through the pipe 31, the gas passage 11, and the gas introduction unit 12. Then, a silicon oxide film having a thickness of 5 nm was formed on the surface of the silicon semiconductor substrate 40 by a pyrogenic oxidation method (see FIG. 5B). The supply amounts of oxygen gas and hydrogen gas to the combustion chamber 30 are respectively
10 SLM and 10 SLM were set.

[Step-150] Since the formation of the silicon oxide film on the surface of the silicon semiconductor substrate 40 is completed as described above, the inside of the oxidation furnace 10 is set to an inert gas atmosphere such as a nitrogen gas. At this time, the flow rate (F) of the inert gas introduced into the oxidation furnace 10 was set to 30 SLM. That is, F / V = 3
0/70 = 0.43. Further, the inside of the oxidizing furnace 10 was replaced from a wet gas atmosphere to an inert gas atmosphere within 5 minutes, and in Example 1, about 3 minutes (see FIG. 6). The cooling rate was 3 ° C / min. Then, when the ambient temperature of the oxidizing furnace 10 reached 700 ° C., the elevator mechanism 23 was operated to lower the quartz boat 24, and then the door (not shown) was opened to carry out the silicon semiconductor substrate 40.

Comparative Example 1 In Comparative Example 1, the atmosphere of the oxidation furnace 10 in [Step-110] and [Step-120] of Example 1 was a 100% nitrogen gas atmosphere. Except for this point, a silicon oxide film was formed under the same method and conditions as in Example 1.

The silicon obtained in Example 1 and Comparative Example 1
Q of oxide film_BDThe properties were measured. In addition, Q_BDFor measurement samples
Here, the formation of the element isolation region was omitted. Specifically
Are 59 on each of the three silicon semiconductor substrates 40
Was manufactured. In addition, MOS capacity
5.0mm gate area^TwoAnd And in FIG.
The circuit shown in the figure is made schematically, and a constant current is applied to the gate electrode 42.
(J = 0.1 A / cm^Two) Constant current switch to apply stress
The so-called Coulomb breakdown (Q _BD)
It was measured. In FIG. 7, reference numeral 41 denotes a silicon oxide film.
It is. Where Q_BDIs J (A / cm^Two) And insulation break
Time t to break_BDIt is expressed by the product of FIG. 8 shows the cumulative
Failure rate P and time t to dielectric breakdown_BDRelationship Wai
It is the figure which showed the bull probability distribution. In addition, in FIG.
Marks, black circles, and black squares indicate the silicon obtained in Example 1.
The evaluation results of the oxide film are shown, with white triangles, white circles, and white squares.
Shows the evaluation results of the silicon oxide film obtained in Comparative Example 1.
You. As is clear from FIG. 8, the system obtained in Example 1 was used.
In the silicon oxide film, the time t until the dielectric breakdown occurs is t
_BDIs longer than Comparative Example 1 and the initial reliability is improved.
I understand. Further, regarding the wear failure area, the first embodiment
The silicon oxide film obtained by shifting to longer life side
Therefore, the silicon oxide film obtained in Example 1 is longer
It turns out that it has reliability. In Comparative Example 1,
Same as [Step-110] and [Step-120] in Example 1.
In the same process, the surface of the silicon semiconductor substrate 40 is
Organic substances, especially organic substances containing carbon, are not removed.
Because Q_BDIs thought to decrease.

The same method as in Example 1 except that the atmosphere of the oxidation furnace 10 in [Step-110] and [Step-120] of Example 1 was changed to a 100% oxygen gas atmosphere.
A silicon oxide film was formed under the conditions, and _QBD characteristics of the obtained silicon oxide film were measured. As a result, a result similar to that of Comparative Example 1 was obtained. When the atmosphere of the oxidation furnace 10 is a 100% oxygen gas atmosphere, [Step-110] and [Step-12] of the first embodiment are included in the formed silicon oxide film.
[0], it is considered that the _QBD decreases as a result of an increase in the proportion of the dry silicon oxide film (silicon oxide film formed by high-purity dry oxygen gas) formed in the same step as in [0].

(Comparative Example 2) In Comparative Example 2, the oxidation furnace 1 was used in the same step as [Step-150] of Example 1.
0 was set to an inert gas atmosphere such as nitrogen gas. At this time, the flow rate F of the inert gas
SLM. That is, F / V = 15/70 = 0.21. Further, the inside of the oxidation furnace 10 was replaced from the wet gas atmosphere to the inert gas atmosphere in about 6 minutes. The cooling rate is 3 ゜ C /
Minutes. Then, when the ambient temperature of the oxidizing furnace 10 reached 700 ° C., the elevator mechanism 23 was operated to lower the quartz boat 24 and unload the silicon semiconductor substrate 40.

The thickness of the silicon oxide film obtained in Example 1 and Comparative Example 2 was set at 49 per silicon semiconductor substrate.
It was measured at ellipsometers at several places. The measurement results are shown in Table 1 below. In Table 1, "Average silicon oxide film"
In one silicon semiconductor substrate, [(maximum thickness of silicon oxide film) − (minimum thickness of silicon oxide film)] /
It is a value obtained from (silicon oxide film average value × 2) × 100 (%). Compared to Comparative Example 2, the thickness variation of the silicon oxide film obtained in Example 1 was about １ ／. In Comparative Example 2, a rich amount of wet gas remains in the oxidation furnace for a considerable time immediately after the completion of the formation of the oxide film. for that reason,
Even when the ambient temperature of the oxidation furnace is lowered, a wet gas exists with a certain distribution in the plane of the silicon semiconductor substrate, and the formation of the oxide film proceeds by the wet gas, and a new oxide film is formed. As a result, it is considered that the in-plane variation of the thickness of the oxide film is increased. On the other hand, in the first embodiment, since a large amount of inert gas is introduced into the oxidation furnace, the atmosphere of the oxidation furnace is promptly replaced with the inert gas atmosphere, so that the progress of forming an oxide film is suppressed. Therefore,
It is considered that the in-plane variation of the thickness of the oxide film is reduced.

[0057]

[Table 1]

(Embodiment 2) Embodiment 2 is a modification of Embodiment 1. In Example 2, a heat treatment was performed on the formed silicon oxide film following [Step-140] of Example 1 using the vertical type oxide film forming apparatus shown in FIG. That is, after [Step-140] is completed, the introduction of the wet gas into the oxidation furnace 10 is stopped, and while the nitrogen gas is introduced into the oxidation furnace 10 from the gas introduction unit 12, the atmospheric temperature of the oxidation furnace 10 is reduced by the heater 14. To 900 ° C, and then
Nitrogen gas containing 1.3% by volume of hydrogen chloride gas was introduced into the oxidation furnace 10 from the gas introduction unit 12 and heat-treated for 30 minutes. Specifically, the flow rate of nitrogen gas is set to 15 SLM,
The flow rate of the hydrogen chloride gas was 0.2 SLM. FIG. 9 schematically shows an atmosphere temperature profile and the like in the second embodiment.

After the completion of the heat treatment, the inside of the oxidation furnace 10 was set to an inert gas atmosphere such as a nitrogen gas. At this time, the flow rate F of the inert gas introduced into the oxidation furnace 10 was set to 30 SLM. That is, F / V = 0.43. Further, the inside of the oxidizing furnace 10 was replaced from a wet gas atmosphere to an inert gas atmosphere within 5 minutes, and in Example 2, about 3 minutes. 3 ℃ lowering rate
/ Min. Then, the ambient temperature of the oxidation furnace 10 is set to 700
When the temperature reached ゜ C, the elevator mechanism 23 was operated to lower the quartz boat 24, and then a door (not shown) was opened to carry out the silicon semiconductor substrate 40.

Third Embodiment The third embodiment is also a modification of the first embodiment. In Example 3, an oxide film was formed based on the first oxide film forming step and the second oxide film forming step. FIG. 10 shows the ambient temperature profile and the like in the third embodiment. Hereinafter, an oxide film forming method according to the third embodiment will be described.

[Step-300] First, after a device isolation region and the like are formed in a silicon semiconductor substrate in the same manner as in Example 1, fine particles and metal impurities on the surface of the silicon semiconductor substrate are removed by RCA cleaning. Next, the surface of the silicon semiconductor substrate was washed with a 0.1% aqueous solution of hydrofluoric acid and pure water to expose the surface of the silicon semiconductor substrate.

[Step-310] Next, the plurality of silicon semiconductor substrates 40 are loaded into the substrate loading / unloading section 20 of the oxide film forming apparatus shown in FIG.
Placed on In addition, nitrogen gas and oxygen gas are introduced into the oxidation furnace 10 from the gas introduction unit 12, and the inside of the oxidation furnace 10 is set to an inert gas atmosphere such as a nitrogen gas (a reduced pressure atmosphere may be used).
Further, the oxidation furnace 1 is heated by the heater 14 through the soaking tube 16.
The atmosphere temperature of 0 was maintained at 400 ° C. In this state, the shutter 15 is closed. The flow rate of nitrogen gas was 15 SLM, and the flow rate of oxygen gas was 1 SLM.
That is, the inside of the oxidation furnace 10 was set to an inert gas atmosphere at a temperature of 400 ° C. containing 6.25% by volume of oxygen gas.

[Step-320] Then, the substrate loading / unloading section 2
0, the door (not shown) is closed, and the gas introduction unit 21 is inserted into the substrate carry-in / out unit 20.
The nitrogen gas was introduced from the gas exhaust unit 22 and exhausted from the gas exhaust unit 22, and the inside of the substrate loading / unloading unit 20 was set to a nitrogen gas atmosphere. Thereafter, the shutter 15 is opened, and the elevator mechanism 23 is operated to raise the quartz boat 24 (elevation speed: 250 mm /
Minute), the silicon semiconductor substrate 40 was carried into the oxidation furnace 10 having a double tube structure made of quartz. Since the temperature of the inert gas atmosphere containing 6.25% by volume of oxygen gas in the oxidizing furnace 10 is maintained at 400 ° C. by the heater 14, that is, silicon atoms, which are atoms mainly constituting the semiconductor layer, are removed. Oxidizing furnace 10 is heated to an ambient temperature at which the
Is held in the silicon semiconductor substrate surface.
Since the i-H bond is not broken or the Si-F bond on the surface of the silicon semiconductor substrate is not broken, generation of roughness on the surface of the silicon semiconductor substrate 40 can be suppressed.

[Step-330] Next, an oxide film is formed on the surface of the semiconductor layer by a wet gas at an ambient temperature (oxidation temperature) at which atoms (silicon atoms) mainly constituting the semiconductor layer do not desorb from the surface of the semiconductor layer. Began to form. Alternatively, the temperature is higher than the temperature at which the wet gas does not cause condensation on the surface of the semiconductor layer.
At an atmosphere temperature (oxidation temperature) of 00 ° C. or less, formation of an oxide film on the surface of the semiconductor was started by a wet gas. Then, after the formation of an oxide film on the surface of the semiconductor layer by the wet gas at an ambient temperature at which atoms (silicon atoms) mainly constituting the semiconductor layer do not desorb from the surface of the semiconductor layer,
During a predetermined period, a first oxide film forming step of forming an oxide film while maintaining an atmosphere in an atmosphere temperature range in which atoms mainly constituting the semiconductor layer do not desorb from the surface of the semiconductor layer was performed. Specifically, while maintaining the ambient temperature (oxidation temperature) at a temperature at which silicon atoms do not desorb from the surface of the silicon semiconductor substrate 40 (specifically, in the third embodiment, the ambient temperature is set to 400 ° C.). Setting), an oxide film was formed on the surface of the semiconductor layer by wet gas. In the third embodiment, oxygen gas and hydrogen gas are supplied into the combustion chamber 30 via the pipes 32 and 33, and the wet gas generated in the combustion chamber 30 is supplied to the pipe 3
1. Oxidizing furnace 1 via gas flow path 11 and gas introduction unit 12
Then, a silicon oxide film having a thickness of 1.2 nm was formed on the surface of the silicon semiconductor substrate 40 by a pyrogenic oxidation method. The thickness of this silicon oxide film is SiO ₂
And a thickness sufficient to function as a protective film even in consideration of steps on the surface of the silicon semiconductor substrate.

[Step-340] Thereafter, the introduction of the wet gas into the oxidation furnace 10 is stopped, and an inert gas (nitrogen gas) is introduced.
Is introduced into the oxidation furnace 10 through the pipe 32, the combustion chamber 30, the pipe 31, the gas flow path 11, and the gas introduction unit 12, and the atmosphere temperature of the oxidation furnace 10 of the oxide film forming apparatus is set to The temperature was increased to 800 ° C. by the heater 14 via the heater. The heating rate was 10 ° C./min. [Step-3
30], a silicon oxide film which also functions as a protective film is already formed on the surface of the silicon semiconductor substrate.
In this [Step-340], the surface of the semiconductor layer (silicon semiconductor substrate 40) is not roughened.

[Step-350] The oxidation furnace is heated to an atmosphere temperature (800 ° C. in Example 3) higher than the atmosphere temperature range in which atoms (silicon atoms) mainly constituting the semiconductor layer do not desorb from the surface of the semiconductor layer. After the atmospheric temperature of 10 was reached, a second oxide film forming step of forming a silicon oxide film with a wet gas was performed while maintaining the atmosphere at this atmospheric temperature (oxidation temperature). Specifically, oxygen gas and hydrogen gas are again supplied into the combustion chamber 30 via the pipes 32 and 33, and the wet gas generated in the combustion chamber 30 is supplied to the pipe 31, the gas flow path 11 and the gas introduction section 12 again. Then, a silicon oxide film having a total thickness of 4.0 nm was formed on the surface of the silicon semiconductor substrate 40 by a pyrogenic oxidation method.

As described above, since the formation of the silicon oxide film on the surface of the silicon semiconductor substrate 40 is completed, the flow rate (F) is passed through the same steps as [Step-150] of the first embodiment, ie, into the oxidation furnace 10. An inert gas of 30 SLM was introduced into the oxidation furnace 10, and the inside of the oxidation furnace 10 was replaced with a inert gas atmosphere from a wet gas atmosphere within 5 minutes. The cooling rate was 3 ° C / min. And the ambient temperature of the oxidation furnace 10 is 70
When the temperature reached 0 ° C., the elevator mechanism 23 was operated to lower the quartz boat 24, and then a door (not shown) was opened to carry out the silicon semiconductor substrate 40. As in the second embodiment, after forming the silicon oxide film, heat treatment may be performed on the silicon oxide film.

(Embodiment 4) In Embodiment 4, a heating means for heating the semiconductor layer, which is provided outside the oxidation furnace and substantially parallel to the surface of the semiconductor layer, is provided in the oxidation furnace. A horizontal oxide film forming apparatus provided with was used. A schematic diagram of an example of the oxide film forming apparatus used in Example 4 is shown in FIG.
As shown in FIG. This oxide film forming apparatus includes an oxidation furnace 50,
A resistance heater 51 is provided as heating means for heating the semiconductor layer. The volume V of the oxidation furnace 50 is about 70 liters. The oxidation furnace 50 includes a furnace tube made of quartz,
In order to form an oxide film on the semiconductor layer, a semiconductor layer (specifically, for example, a silicon semiconductor substrate) is housed therein. The resistance heater 51 serving as a heating unit includes an oxidation furnace 50.
And is arranged substantially parallel to the surface of the semiconductor layer. The semiconductor layer (for example, the silicon semiconductor substrate 40) is placed on a wafer table 52, and is oxidized through a gate valve 53 provided at one end of the oxidizing furnace 50.
It is carried in and out of 0. An oxidation furnace 50 is provided in the oxide film forming apparatus.
A gas introduction unit 54 for introducing a wet gas and / or a gas and a gas exhaust unit 55 for exhausting the wet gas and / or the gas from the oxidation furnace 50 are further provided. The temperature of the semiconductor layer (specifically, for example, a silicon semiconductor substrate)
It can be measured by a thermocouple (not shown). still,
As in the first embodiment, a wet gas is generated by mixing hydrogen gas supplied to the combustion chamber with oxygen gas at a high temperature in the combustion chamber and burning the mixture. The wet gas is introduced into the oxidation furnace 50 through the pipe and the gas introduction unit 54. Illustration of the combustion chamber and piping is omitted.

Alternatively, a horizontal oxide film forming apparatus of the type schematically shown in FIG. 12 can be used. This figure 1
In the horizontal oxide film forming apparatus shown in FIG. 2, the heating means comprises a plurality of lamps 51A emitting infrared or visible light.
It is composed of The temperature of the silicon semiconductor substrate is measured by a pyrometer (not shown). Other structures can be basically the same as those of the oxide film forming apparatus shown in FIG. 11, and a detailed description thereof will be omitted.

Hereinafter, a method for forming the silicon oxide film of the fourth embodiment will be described. The atmosphere temperature profile in Example 4 was the same as that in FIG.

[Step-400] First, an element isolation region and the like are formed in a silicon semiconductor substrate in the same manner as in the first embodiment, and then fine particles and metal impurities on the surface of the silicon semiconductor substrate are removed by RCA cleaning. Next, the surface of the silicon semiconductor substrate was washed with a 0.1% aqueous solution of hydrofluoric acid and pure water to expose the surface of the silicon semiconductor substrate.

[Step-410] Next, the silicon semiconductor substrate 40 placed on the wafer table 52 is placed in the oxidation furnace 50 by opening the gate valve 53 of the oxide film forming apparatus shown in FIG. 11 or FIG. After carrying in, the gate valve 53 was closed. The atmosphere of the oxidation furnace 50 was previously set to an inert gas atmosphere (oxygen gas concentration: 6.25% by volume) heated to about 700 ° C. by a heating means.

[Step-420] Then, an oxygen gas is introduced into 6.
While continuously introducing nitrogen gas containing 25% by volume into the oxidation furnace 50, the ambient temperature of the oxidation furnace 50 was raised to 850 ° C. by a heating means. In Example 4,
Since the heating means is disposed substantially parallel to the surface of the semiconductor layer, it is possible to suppress, for example, the occurrence of in-plane temperature variations of the silicon semiconductor substrate when the temperature of the silicon semiconductor substrate is raised.

[Step-430] Oxidizing furnace 50 at 850 ° C.
After the ambient temperature was reached, a wet gas was introduced into the oxidation furnace 50 while maintaining the atmosphere at this temperature to form a silicon oxide film on the surface of the silicon semiconductor substrate 40.
Specifically, a wet gas generated in the combustion chamber is introduced into the oxidation furnace 50 through a pipe and a gas introduction unit 54, and a 4.0 nm silicon oxide film is formed on the surface of the silicon semiconductor substrate 40 by a pyrogenic oxidation method. Formed.

[Step-440] Since the formation of the silicon oxide film on the surface of the silicon semiconductor substrate 40 is completed as described above, the inside of the oxidation furnace 50 is set to an inert gas atmosphere such as a nitrogen gas. At this time, the flow rate (F) of the inert gas introduced into the oxidation furnace 50 was set to 30 SLM. That is, F / V =
0.43. Further, the inside of the oxidizing furnace 50 was replaced from a wet gas atmosphere to an inert gas atmosphere within 5 minutes, and in Example 4, about 3 minutes. The cooling rate was 3 ° C / min.
Then, when the ambient temperature of the oxidation furnace 50 reached 700 ° C., the silicon semiconductor substrate 40 was unloaded from the oxidation furnace 50 via the gate valve 53.

In the fourth embodiment, the heat treatment may be performed in the oxidation furnace 50 as in the second embodiment, or the silicon semiconductor substrate may be loaded into another batch-type heat treatment apparatus, and the batch-type heat treatment may be performed. The heat treatment may be performed by an apparatus.

Although the present invention has been described based on the preferred embodiments, the present invention is not limited to these embodiments. Various conditions including the temperature conditions described in the embodiments and the structure of the oxide film forming apparatus are merely examples, and can be changed as appropriate. The oxide film is formed not only by the pyrogenic oxidation method, but also by an oxidation method using a wet gas generated by heating pure water, and an oxidation method using a wet gas generated by bubbling heated pure water with an oxygen gas or an inert gas. Alternatively, a method using these oxidation methods in combination can be used.

Alternatively, the oxide film may be formed by a wet gas generated by a reaction between hydrogen gas and oxygen gas based on a catalytic action. In this case, as a catalyst to be used, for example, a Ni-based catalyst such as NiO, a Pt-based catalyst such as Pt or PtO ₂ , a Pd-based catalyst such as Pd or PdO, an Ir-based catalyst, a Ru-based catalyst such as Ru or RuO _2, or an Ag-based catalyst Catalysts such as Ag and Ag ₂ O, Au catalysts, Cu catalysts such as CuO, Mn
Examples thereof include a Mn-based catalyst such as O _{2 and} a Co-based catalyst such as Co ₃ O ₄ . The catalyst is placed inside the wet gas generator, and heated to a desired temperature by a heater provided inside the wet gas generator. Hydrogen gas and oxygen gas (if necessary) are supplied to the wet gas generator from piping. If an inert gas is supplied to the gas, a wet gas can be generated by the reaction between the hydrogen gas and the oxygen gas.

Alternatively, a wet gas can be generated by a reaction between oxygen plasma and hydrogen plasma. In the oxidation method using a wet gas generated by a reaction between oxygen plasma and hydrogen plasma, oxygen plasma generated by microwave discharge is converted into ground state O ₂ (X ³ Σg
^- ) Is excited into an excited state O ₂ (A ³ Σu ⁺ ) or O ₂ (B ³ Σu ⁻ ) by electron collision, and dissociates into oxygen atoms as in the following formulas.

[0080]

Embedded image O ₂ (X ³ -g ⁻ ) + e → O ₂ (A ^{3 +} u ⁺ ) + e Formula (1-1) O ₂ (A ³ Σu ⁺ ) + e → O ( ³ P) + O ( ³ P) + e Formula (1-2) O ₂ (X ³ Σg ⁻ ) + e → O ₂ (B ³ Σu ⁻ ) + e Formula (1-3) O ₂ (B ³ Σu ⁻ ) + e → O ( ^{3 P) + O (1 D} ) + e equation (1-4)

Therefore, excited oxygen molecules and oxygen atoms are present in the oxygen plasma, and these become reactive species. When hydrogen H ₂ is introduced here, the following plasma is generated.

[0082]

H ₂ + e → 2H Formula (2)

In the oxygen plasma, for example, the formula (1)
The oxygen plasma generated in -2) reacts with the hydrogen plasma generated in equation (2) to generate a wet gas. And
The surface of the heated semiconductor layer is thermally oxidized by the wet gas, and an oxide film is formed on the surface of the semiconductor layer.

[0084]

Embedded image 2H + O ( ³ P) → H ₂ O Formula (3)

FIG. 13 is a conceptual diagram of an oxide film forming apparatus based on an oxidation method using a wet gas generated by a reaction between oxygen plasma and hydrogen plasma. This apparatus includes an oxidation furnace 60 and a wet gas generator 70. The wet gas generating device 70 includes a wet gas generating chamber 71 made of quartz, a microwave waveguide 72, and a magnetron 73 attached to the microwave waveguide 72. In the magnetron 73, a microwave having a frequency of 2.45 GHz is generated. The microwave is applied to the microwave waveguide 7.
2 and is introduced into the wet gas generating chamber 71. Hydrogen gas and oxygen gas are introduced into the wet gas generation chamber 71 via pipes 74 and 75. Microwaves (electromagnetic waves) are applied to the hydrogen gas and the oxygen gas introduced into the wet gas generation chamber 71. As a result, the reactions shown in Equations (1-1) to (1-4) and Equation (2) proceed, and oxygen plasma and hydrogen plasma are generated. As a result of the reaction shown in Equation (3), Wet gas is generated. Wet gas generation chamber 7
1, a heater 77 is disposed outside the wet gas generating chamber 7.
1 is at a desired temperature (for example, 200 to 300 ° C.)
Is held. The wet gas generated in the wet gas generation chamber 71 is introduced into the oxidation furnace 60 from a pipe 78. It is preferable that a heater 79 is provided outside the pipe 78 in order to prevent dew condensation of the wet gas in the pipe 78, and for example, the inside of the pipe 78 is maintained at 200 to 300 ° C. Also,
A pipe 76 for introducing an inert gas (for example, nitrogen gas) into the wet gas generation chamber 71 is provided in the wet gas generation chamber 71. Oxidation furnace 60 showing only some components
Can have the same structure as the oxide film forming apparatus shown in FIG. 2, FIG. 11 or FIG. 12, such as the heater 14, and form a silicon oxide film on the surface of the silicon semiconductor substrate 40 in the oxidation furnace 60. Can be.

Alternatively, after cleaning the surface of the silicon semiconductor substrate 40 with a 0.1% aqueous solution of hydrofluoric acid and pure water in Examples 1 to 4, the silicon semiconductor substrate 40 is carried into the oxide film forming apparatus. However, the atmosphere from the surface cleaning of the silicon semiconductor substrate 40 to the transfer into the oxide film forming apparatus may be an inert gas (eg, nitrogen gas) atmosphere. In this case, for example, the atmosphere of the apparatus for cleaning the surface of a silicon semiconductor substrate is made an inert gas atmosphere, and the silicon semiconductor substrate 40 is placed in a transport box filled with an inert gas to form an oxide film. A method for loading the substrate into and out of the substrate loading / unloading section 20 and the oxidation furnace 50, and a surface cleaning device, an oxide film forming device,
Using a transport tool, a cluster tool device including a loader and an unloader, connecting the surface cleaning device of the silicon semiconductor substrate to the substrate loading / unloading section 20 of the oxide film forming device or the oxidation furnace 50 by a transport route, and the surface cleaning device. In addition, it can be achieved by a method in which the atmosphere of the transport path is an inert gas atmosphere.

Alternatively, a 0.1% hydrofluoric acid aqueous solution
Instead of cleaning the surface of the semiconductor layer with pure water and
Gas using anhydrous hydrogen fluoride gas under the conditions exemplified in FIG.
The surface of the semiconductor layer may be cleaned by a phase cleaning method.
Methanol is added to prevent the generation of particles
I do. Alternatively, under the conditions exemplified in Table 3, hydrogen chloride
Surface cleaning of semiconductor layer by gas phase cleaning method using gas
May go. Before starting the surface cleaning of the semiconductor layer or
Atmosphere and transport path of surface cleaning equipment after surface cleaning is completed
Atmosphere may be an inert gas atmosphere.
1.3 × 10 ^-1Pa (10^-3Torr) vacuum atmosphere
It may be. In addition, the atmosphere of the transfer path, etc.
In this case, when the semiconductor layer is carried in,
The atmosphere of the substrate loading / unloading section 20 or the oxidizing furnace 50 is, for example,
1.3 × 10^-1Pa (10^-3Torr) vacuum atmosphere
After the loading of the semiconductor layer is completed, the substrate loading / unloading section 20 is opened.
Or the atmosphere of the oxidizing furnace 50 is set to an oxygen gas of 0.67 volume.
% To 20% by volume of an inert gas at atmospheric pressure (eg,
A nitrogen gas atmosphere may be used.

[0088]

[Table 2] Anhydrous hydrogen fluoride gas: 300 sccm Methanol vapor: 80 sccm Nitrogen gas: 1000 sccm Pressure: 0.3 Pa Temperature: 60 ° C

[0089]

[Table 3] Hydrogen chloride gas / nitrogen gas: 1% by volume Temperature: 800 ° C

In these cases, the oxide film forming apparatus shown in FIGS. 2, 11 and 12 can be used. This makes it possible to keep the surface of the semiconductor layer terminated with hydrogen or fluorine free of contamination or the like before the oxide film is formed. As a result, moisture, organic substances, or Si-OH Can be effectively prevented from deteriorating the properties of the formed oxide film or generating defective portions.

Further, following the formation of the oxide film, a polysilicon layer or an amorphous silicon layer containing impurities is formed on the oxide film to form, for example, a gate electrode. Activation annealing treatment can be performed on impurities contained in the layer.

[0092]

According to the method for forming an oxide film according to the first aspect of the present invention, organic substances adhering to the surface of the semiconductor layer carried into the oxidation furnace are removed by reacting with oxygen gas in the atmosphere of the oxidation furnace. As a result, the intrinsic defect rate shifts in the direction of more retaining the charge amount, and an oxide film having a low initial defect rate and excellent withstand voltage characteristics can be formed. As a result, high reliability can be imparted to the semiconductor device. Further, it is possible to eliminate the influence of air entrapment when the silicon semiconductor substrate is carried into the oxidation furnace. Furthermore, in the method for forming an oxide film according to the second aspect of the present invention, since the inside of the oxidation furnace is immediately brought into an inert gas atmosphere after the formation of the oxide film is completed, the oxide film having a small thickness variation is small. Can be formed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an ambient temperature profile and the like in Example 1.

FIG. 2 is a schematic sectional view of a vertical type oxide film forming apparatus (thermal oxidation furnace).

FIG. 3 is a conceptual diagram of an oxide film forming apparatus and the like for explaining a method of forming an oxide film in Example 1.

FIG. 4 is a conceptual diagram of an oxide film forming apparatus and the like for explaining a method of forming an oxide film in Example 1, following FIG. 3;

FIG. 5 is a conceptual diagram of an oxide film forming apparatus and the like for explaining a method of forming an oxide film in Example 1 following FIG. 4;

FIG. 6 is a conceptual diagram of an oxide film forming apparatus and the like for explaining a method of forming an oxide film in Example 1, following FIG.

FIG. 7 is a schematic diagram of a circuit for measuring Q _BD characteristics.

FIG. 8 is a diagram showing a Weibull probability distribution of the relationship between the cumulative failure rate P and the time t _BD up to dielectric breakdown in the silicon oxide films obtained in Example 1 and Comparative Example 1.

FIG. 9 is a diagram showing an ambient temperature profile and the like in Example 2.

FIG. 10 is a diagram showing an ambient temperature profile and the like in Example 3.

FIG. 11 is a schematic cross-sectional view of a horizontal oxide film forming apparatus suitable for carrying out an oxide film forming method of the present invention.

FIG. 12 is a schematic cross-sectional view of a horizontal oxide film forming apparatus suitable for carrying out an oxide film forming method of the present invention, which has a structure slightly different from that of FIG.

FIG. 13 is a conceptual diagram of an oxide film forming apparatus for forming an oxide film using a wet gas generated by a reaction between oxygen plasma and hydrogen plasma.

FIG. 14 is a schematic view of a cluster tool device.

FIG. 15 is a schematic sectional view of an oxide film forming apparatus and the like for explaining a conventional method for forming a silicon oxide film.

FIG. 16 is a schematic cross-sectional view of an oxide film forming apparatus and the like for explaining a conventional method of forming a silicon oxide film, following FIG.

FIG. 17 is a schematic cross-sectional view of an oxide film forming apparatus and the like for explaining a conventional method of forming a silicon oxide film, following FIG. 16;

FIG. 18 is a schematic cross-sectional view of an oxide film forming apparatus and the like for explaining a conventional method of forming a silicon oxide film, following FIG. 17;

[Explanation of symbols]

10, 50, 60: oxidation furnace, 11: gas flow path,
12 ... gas introduction part, 13 ... gas exhaust part, 14.
..Heater, 15 ... Shutter, 16 ... Heat equalizing tube, 20 ... Substrate carry-in / out part, 21 ... Gas introduction part,
22: gas exhaust unit, 23: elevator mechanism, 2
4 ... quartz boat, 30 ... combustion chamber, 31, 32,
33 ... piping, 40 ... silicon semiconductor substrate, 51
... Resistance heater, 51A ... Lamp, 52 ...
・ Wafer table, 53 ・ ・ ・ Gate valve, 54 ・ ・ ・ Gas introduction part, 55 ・ ・ ・ Gas exhaust part, 70 ・ ・ ・ Wet gas generator, 71 ・ ・ ・ Wet gas generation chamber, 72 ・ ・ ・ Micro Wave waveguide, 73 ... magnetron, 74, 75, 7
6, 78: piping, 77, 79: heater

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F045 AA20 AB32 AC11 AC13 AC15 AC18 AD11 AD12 AD13 BB02 BB16 CA05 DP04 DP19 EB08 EB13 EK06 EN04 EN05 HA04 HA16 5F058 BA06 BA11 BA20 BC02 BE02 BF37 BF55 BF63 BF68 BH01 BJ01

Claims (8)

[Claims] (A) a step of introducing a substrate having a semiconductor layer into an oxidation furnace and then introducing a wet gas into the oxidation furnace to form an oxide film on the surface of the semiconductor layer; Stopping the introduction of the wet gas into the oxidizing furnace, introducing an inert gas into the oxidizing furnace to change the atmosphere of the oxidizing furnace to an inert gas atmosphere, and then carrying out the substrate from the oxidizing furnace. The atmosphere of the oxidizing furnace from before carrying in the substrate to before forming the oxide film on the surface of the semiconductor layer is an inert gas atmosphere containing 0.67% by volume to 20% by volume of oxygen gas. A method for forming an oxide film. 2. In the step (a), after carrying the substrate having the semiconductor layer into the oxidation furnace, the ambient temperature of the oxidation furnace is raised to a predetermined temperature, and thereafter, a wet gas is introduced into the oxidation furnace. 2. The method as claimed in claim 1, wherein an oxide film is formed on the surface of the semiconductor layer while maintaining the ambient temperature of the oxidation furnace at the predetermined temperature. 3. In the step (b), the introduction of the wet gas into the oxidation furnace is stopped, and while the inert gas is introduced into the oxidation furnace, the ambient temperature of the oxidation furnace is lowered. 3. The method according to claim 2, wherein the substrate is carried out. 4. In the step (a), the atmosphere temperature of the oxidizing furnace before carrying the substrate into the oxidizing furnace is a temperature at which organic substances adhering to the surface of the semiconductor layer react with oxygen gas and are removed. The method for forming an oxide film according to claim 1, wherein: 5. In the step (b), an inert gas is introduced into the oxidation furnace, whereby the inside of the oxidation furnace is changed from a wet gas atmosphere to an inert gas atmosphere within 5 minutes. Item 3. The method for forming an oxide film according to Item 1. 6. In the step (b), when the volume of the oxidation furnace is V (liter) and the flow rate of the inert gas introduced into the oxidation furnace is F (SLM), F ≧ 0.3V is satisfied. The method for forming an oxide film according to claim 1, wherein: 7. A method comprising: (a) carrying a substrate having a semiconductor layer into an oxidation furnace; and introducing a wet gas into the oxidation furnace to form an oxide film on the surface of the semiconductor layer. Stopping the introduction of the wet gas into the oxidizing furnace, introducing an inert gas into the oxidizing furnace to change the atmosphere of the oxidizing furnace to an inert gas atmosphere, and then removing the substrate from the oxidizing furnace. 3. The method for forming an oxide film according to claim 1, wherein an inert gas is introduced into the oxidizing furnace to replace the inside of the oxidizing furnace from a wet gas atmosphere to an inert gas atmosphere within 5 minutes. 8. A method comprising: (a) carrying a substrate having a semiconductor layer into an oxidation furnace; and introducing a wet gas into the oxidation furnace to form an oxide film on the surface of the semiconductor layer. Stopping the introduction of the wet gas into the oxidizing furnace, introducing an inert gas into the oxidizing furnace to change the atmosphere of the oxidizing furnace to an inert gas atmosphere, and then carrying out the substrate from the oxidizing furnace. , The volume of the oxidation furnace is V (liter),
A method for forming an oxide film, wherein F ≧ 0.3V, where F (SLM) is a flow rate of an inert gas introduced into the oxidation furnace.