JP2002289612A - Method for forming oxide film on semiconductor substrate surface and method for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a high quality silicone dioxide film on the surface semiconduc tor substrate with good controllability, and the reduce leak current density. SOLUTION: After cleaning a silicon carbide substrate 1, the substrate is soaked in a heated perchloric acid water solution at 203 deg.C with 72.4 vol.% density for 25 minutes. Thus, the silicon dioxide film 5 is formed on the silicon carbide substrate 1. Thereafter, the substrate is heated in an electric furnace in 900 deg.C nitrogen for 2 hours. An aluminum gate electrode 7 is formed on the silicon dioxide film 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device which can be applied to a gate oxide film, a capacitance oxide film and the like in a device such as a metal-oxide-semiconductor (MOS) transistor or a MOS capacitor used for a semiconductor integrated circuit or the like. The present invention relates to a method for forming an oxide film on a substrate surface and a method for manufacturing a semiconductor device using the oxide film.

[0002]

2. Description of the Related Art An oxide film is usually used as a semiconductor device, particularly as a gate oxide film of a MOS transistor or a capacitance oxide film of a MOS capacitor. These oxide films are required to have high breakdown voltage, high breakdown charge, low fixed charge density, low mobile ion density, and low interface state density.

In the case of a silicon device, conventionally, the gate oxide film of a MOS transistor has been exposed to a high
It has been formed by exposing a semiconductor substrate to an oxidizing atmosphere such as dry oxygen or water vapor (for example, VLSI
Technology (VLSI Technology), SMSze Editing, 19
1984, pp. 131-168). Oxidation at a high temperature is required to form a high-quality oxide film,
Generally, it is formed at a high temperature of 900 ° C. or higher.

[0004] High current, using silicon carbide as a substrate,
Devices operating under high voltage, such as power devices,
An oxide film is usually used also as a gate oxide film or a capacitance oxide film of a high-frequency device or a device operating at a high temperature. MOS formed on silicon carbide substrate
The gate oxide film of the transistor is 1050 to 1150 ° C.
The silicon carbide substrate was formed by exposing the silicon carbide substrate to an oxidizing atmosphere such as dry oxygen or water vapor at a high temperature.

Further, as a method of forming an oxide film at a low temperature, a chemical vapor deposition method for depositing an oxide film on the substrate surface by thermally decomposing monosilane or chlorosilane at 400 to 900 ° C. and reacting with oxygen ( CVD method) has also been used. As another method for forming an oxide film at a low temperature, there is a method of performing oxidation in plasma.
However, in any method for forming an oxide film at a low temperature, it is difficult to form a high-quality oxide film with good controllability and reproducibility regardless of the method used.

At present, a practically used method of forming an oxide film is a method using high-temperature thermal oxidation. In the thermal oxidation method,
The higher the temperature, the better the quality of the oxide film tends to be.
On the other hand, the oxide film / silicon interface or the oxide film / silicon carbide interface becomes rough, which causes a problem that the channel mobility of the MOS transistor is reduced.

Further, in the case of a silicon carbide substrate, graphite is formed at the interface between the oxide film and the silicon carbide in the high-temperature thermal oxidation, which causes problems such as a high interface state density and a high fixed charge density.

Therefore, the present inventors have proposed a method for forming an oxide film on a semiconductor surface that can form a high-quality oxide film on the surface of a semiconductor substrate with good controllability without using high-temperature heating (Japanese Patent Laid-Open Publication No. HEI 9 (1994)]. 10-223629).
There, an oxide film is formed on the surface of the semiconductor substrate by immersing the semiconductor substrate in a solution containing heated perchloric acid or by exposing the semiconductor substrate to a gas containing perchloric acid while heating the semiconductor substrate. I do.

[0009]

An oxide film formed by oxidizing the surface of a semiconductor substrate with perchloric acid can form an oxide film at a lower temperature than a conventional method using high-temperature heating. And has the advantage that it can be formed at low cost. But,
It was found that when a device was formed using the oxide film, the leak current density was increased.

Accordingly, the present invention provides a method of forming an oxide film capable of forming a high-quality oxide film on the surface of a semiconductor substrate with good controllability and lowering a leakage current density when applied to a device. It is an object of the present invention to provide a method for manufacturing a semiconductor device using a film.

[0011]

A first method of the present invention for forming an oxide film on the surface of a semiconductor substrate includes the following steps (A) and (B). (A) a step of immersing the semiconductor substrate in a solution containing heated perchloric acid to form an oxide film on the surface of the semiconductor substrate;
And (B) heat-treating the semiconductor substrate on which the oxide film has been formed.

In this method, in the step (A), the concentration of perchloric acid in the solution containing perchloric acid is preferably 10 Vol. (Volume)% or more. This is because a lower concentration of the perchloric acid solution lowers the growth rate of the oxide film. The most preferred perchloric acid solution is an aqueous solution of perchloric acid having a concentration of 72.4 Vol.%, And the aqueous solution of perchloric acid has a boiling point of 20%.
It is an azeotrope with water at 3 ° C.

In the step (A), in order to keep the growth rate of the oxide film high, it is preferable that the temperature of the solution containing perchloric acid be 170 ° C. or higher and the boiling point of the solution be lower than the boiling point. .

A second method of the present invention for forming an oxide film on the surface of a semiconductor substrate includes the following steps (A) and (B). (A) a step of exposing a semiconductor substrate to a gas containing perchloric acid while heating to form an oxide film on the surface of the semiconductor substrate; and (B) a step of heat-treating the semiconductor substrate on which the oxide film is formed.

In the second method, in the step (A), the gas containing perchloric acid is preferably a vapor of perchloric acid. In the case of the second method, ozone may be further added to increase the oxidizing power. In the second method, the substrate heating temperature in the step (A) is 17
The temperature is preferably from 0 ° C to 500 ° C.

Step (B) is common to the first and second methods. And the temperature of the heat treatment in the step (B) is preferably in the range of 600 ° C to 1,100 ° C. If the heat treatment temperature is lower than 600 ° C., a chlorine component remains in the oxide film, and the leak current density increases. On the other hand, when the heat treatment temperature exceeds 1,100 ° C., the interface state density increases. In addition, since the heat treatment in the step (B) is intended to remove a chlorine component from the oxide film, it is necessary that the atmospheric gas does not contain chlorine.
As such an atmosphere gas, it is preferable to use one kind of gas selected from the group consisting of nitrogen, argon, oxygen, water vapor and hydrogen, or a mixed gas of two or more kinds thereof, for example, air.

It is considered that by performing this step (B), chlorine and chlorine compounds taken in the oxide film are desorbed, thereby reducing the leak current density when the device is formed. The semiconductor substrate forming the oxide film in the present invention is selected from the group consisting of single crystal silicon, polycrystalline silicon, amorphous silicon, gallium arsenide, indium phosphide, silicon carbide, silicon germanium carbide and silicon germanium. .

According to the oxide film forming method of the present invention, an oxide film having a thickness of 1 to 100 nm can be formed on the surface of a semiconductor substrate. By using perchloric acid as an oxidizing agent, the content of metal impurities in the oxide film becomes extremely small. In particular, when a silicon carbide substrate is used as a semiconductor substrate, the oxide film / silicon The amount of graphite at the carbide substrate interface becomes extremely small. Therefore, the oxide film formed by this method becomes an oxide film having excellent interface characteristics with low interface state density and fixed charge density.

Further, when a silicon carbide substrate is used as a semiconductor substrate, a flat oxide film / silicon carbide interface can be formed, so that when a MOS transistor is used, a large channel mobility can be achieved. The thickness of the oxide film can be easily controlled by adjusting the time of immersion in the solution containing perchloric acid or the time of exposure to the gas containing perchloric acid. Then, through the heat treatment in the step (B), it is possible to reduce the leak current when the device is configured.

The method of manufacturing a semiconductor device of the present invention utilizes an oxide film formed by the method of forming an oxide film of the present invention. That is, after forming an oxide film having a thickness of 1 to 200 nm to be a gate oxide film of a MOS transistor or a capacitance oxide film of a MOS capacitor on the surface of a semiconductor substrate by the oxide film forming method of the present invention, an insulating layer is formed on the oxide film. Alternatively, through a step of forming a conductive layer, or both,
A semiconductor device such as an OS transistor is manufactured. In the semiconductor device manufactured in this manner, an oxide film such as a gate oxide film has excellent interface characteristics such as low interface state density and fixed charge density and low leakage current, so that a high-performance MOS transistor, etc. Semiconductor device can be realized.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to embodiments. <First Embodiment> First, a first embodiment of forming a silicon dioxide film as an oxide film on a silicon carbide substrate according to the present invention will be described with reference to FIG. In the present embodiment, a case where a MOS capacitor is created will be described.

(A) The silicon carbide substrate 1 has an n-type conductivity (0001) of a specific resistance of 10 to 15 Ωcm.
6 × 10 ¹⁵ / cm ³ on a silicon single crystal substrate wafer
An epitaxial layer having a thickness of 10 μm and a donor density of 10 μm was used. First, an isolation region 2 and an active region 4 were formed on the silicon carbide substrate 1 by a known selective oxidation technique. In this state, the natural oxide film 3 exists on the surface of the active region 4.

(B) Next, a known RCA cleaning method (W. Ker
n, DA Plutien: RCA Review, Volume 31, 187
After washing the silicon carbide substrate 1 according to the method described on page 1, 1970, the silicon carbide substrate 1 was immersed in a dilute HF solution (0.5 vol.% HF aqueous solution) for 5 minutes to remove the natural oxide film 3 on the surface of the silicon carbide substrate.

(C) Next, the silicon carbide substrate was washed with ultrapure water for 5 minutes, and then heated to 203 ° C. to a concentration of 7%.
A silicon dioxide film 5 was formed on the surface of the silicon carbide substrate 1 by immersing it in a 2.4 vol.% Aqueous solution of perchloric acid for 25 minutes. Then, in an electric furnace 900 in nitrogen
Heated at ° C for 2 hours.

(D) Next, to form an electrode, an aluminum film 6 was deposited to a thickness of 1 μm by sputtering. (E) After forming a gate electrode-shaped resist pattern on the aluminum film 6 by a known photolithography technique, the aluminum film 6 was etched by a known dry etching technique using the resist pattern as a mask to form a gate electrode 7.

FIG. 2 shows a silicon carbide substrate that has been subjected to cleaning by the RCA cleaning method, removal of a natural oxide film by a dilute HF solution, and cleaning by ultrapure water in the same manner as described in the above embodiment. Concentration 72.4v heated to 203 ° C
The X-ray photoelectron spectrum observed after immersion in an ol.% perchloric acid aqueous solution for 120 minutes is shown by a solid line. The horizontal axis represents binding energy (Binding Energy), and the vertical axis represents intensity (Intensity (arb. Units)) in arbitrary units. The X-ray photoelectron spectrum was observed using an ESCALAB220i-XL device manufactured by VG SCIENTIFIC. Photoelectrons were observed in the direction perpendicular to the surface. In FIG. 2, peak (1) is due to photoelectrons from the 2p orbital of Si on the silicon carbide substrate, and peak (2) is due to photoelectrons from the 2p orbital of Si in the silicon dioxide film. The thickness of the silicon dioxide film was calculated to be 3.0 nm from the area intensity ratio between the peak (2) and the peak (1). The dashed spectrum shows that after removing the background from the actually measured spectrum, Si 2p _3/2 and S
i 2p _1/2 component separated into peaks
Only the p _3/2 component is shown.

Between the peak (1) and the peak (2), Si
⁺ , There is only one suboxide peak, and no peaks due to Si ²⁺ or Si ³⁺ .
This indicates that no peroxide is generated because of the strong oxidizing power of perchloric acid. Suboxides can be trap levels and degrade device electrical properties. In the oxidation using perchloric acid, the fact that the amount of generated suboxides is smaller than that of general thermal oxidation is also considered to be one of the factors for good electrical characteristics.

FIG. 3 shows a silicon carbide substrate that has been subjected to cleaning by the RCA cleaning method, removal of a natural oxide film by a dilute HF solution, and cleaning by ultrapure water, as in the above embodiment. Concentration 72.4v heated to 203 ° C
1 is a scanning micrograph showing a cross section of a silicon dioxide film formed by immersion in an aqueous solution of perchloric acid for 1,200 minutes to form a silicon dioxide film. In the figure, the black portion at the upper end is a space, the lower dark region is a silicon carbide substrate, and the upper slightly white region is a silicon dioxide film. From FIG. 3, the thickness of the silicon dioxide film can be estimated to be 80 nm. The thickness of the silicon dioxide film was estimated to be 80 nm even using an ellipsometer. From FIG.
It can be seen that the thickness of the silicon dioxide film is uniform and the interface with the silicon carbide substrate is flat.

As described above, according to the present embodiment, a silicon dioxide film can be formed at a low temperature of about 200 ° C. by oxidizing the surface of a silicon carbide substrate using an aqueous solution of perchloric acid. It was confirmed that there was. Further, by using the perchloric acid aqueous solution in this way, the amount of graphite deposited at the silicon dioxide film / silicon carbide substrate interface becomes extremely small.
It is possible to form a silicon dioxide film having excellent interface characteristics with low interface state density and fixed charge density.

FIG. 4 is a graph in which the thickness of the formed silicon dioxide film is plotted with respect to the time of immersion in a perchloric acid aqueous solution heated to 203 ° C. and having a concentration of 72.4 vol.%. The horizontal axis is Immersion Time (mi
n)), and the vertical axis indicates the thickness (Thickness (nm)). In order to form a silicon dioxide film, the silicon carbide substrate was washed, a natural oxide film was removed with an aqueous solution of hydrofluoric acid (HF) having a concentration of 1.0 vol.%, And then a concentration of 72.4 vol. % Perchloric acid aqueous solution.
The thickness of the silicon dioxide film was determined from an X-ray photoelectron spectrum for a silicon dioxide film having a thickness of 5 nm or less, and was determined by ellipsometry for a silicon dioxide film having a thickness greater than 5 nm. As shown in FIG. 4, the thickness of the silicon dioxide film increases linearly with time, and the thickness of the silicon dioxide film can be easily controlled by adjusting the immersion time in the aqueous solution of perchloric acid. It turns out that it can be done.

FIG. 5 shows cleaning by the RCA cleaning method and dilute HF.
The silicon carbide substrate having been subjected to the removal of the natural oxide film with the solution and the cleaning with the ultrapure water was heated at a temperature of 203 ° C. in a 72.4 vol.
The current-voltage curve of a sample in which an aluminum electrode is formed on a silicon dioxide film formed by immersion for a MOS structure is shown. The horizontal axis is the gate voltage (Gate Voltage) applied to the aluminum electrode, and the vertical axis is the current density (Current Densit).
y). (A) is a sample in which an aluminum electrode is formed on a silicon dioxide film without performing a heat treatment after forming the silicon dioxide film, and has a high leak current density. on the other hand,
(B) is a sample in which an aluminum electrode was formed on a silicon dioxide film after a silicon dioxide film was formed and then subjected to a heat treatment at 900 ° C. for 2 hours in nitrogen. The leak current density was 10 when the gate voltage was 2 V. ^It is sufficiently low at ^-10 A / cm ² .

From this experimental result, it can be seen that a silicon dioxide film formed at 203 ° C. using an aqueous solution of perchloric acid becomes effective as a MOS capacitor and a gate insulating film of a MOS transistor through heat treatment. Understand.

<Second Embodiment> A second embodiment for forming a silicon dioxide film as an oxide film on a silicon substrate according to the present invention will be described. In the present embodiment,
A case where a MOS capacitor is created will be described. The steps are the same as those in FIG. 1 showing the first embodiment. In this embodiment, the substrate 1 is read as a silicon substrate. As the silicon substrate 1, a p-type conductive single crystal silicon wafer having a (100) plane orientation and a specific resistance of about 1 Ωcm was used.

A silicon dioxide film 5 was formed in the same manner as in the first embodiment, and an aluminum gate electrode 7 was formed on the silicon dioxide film 5. That is, after forming the isolation region 2 and the active region 4 on the silicon substrate 1 by a known selective oxidation technique, the silicon substrate 1 is cleaned by a known RCA cleaning method, and a natural oxide film is removed by a dilute HF solution. Further, it was washed with ultrapure water. Thereafter, the silicon substrate 1 is immersed in an aqueous solution of perchloric acid having a concentration of 72.4 vol.
A silicon dioxide film 5 was formed on the surface of the substrate. Then, it heated in nitrogen using the electric furnace.

In order to form a MOS capacitor, an aluminum film 6 is deposited on the silicon dioxide film 5 by a sputtering method, and the aluminum film 6 is etched by a photolithography technique and a dry etching technique to form a gate electrode 7.

For the silicon dioxide film formed in the second embodiment, Cl 2p was measured in the same manner as in FIG.
FIG. 6 shows an X-ray photoelectron spectrum due to photoelectrons from the orbit. (A) is for a silicon dioxide film as formed by immersion in an aqueous solution of perchloric acid, and (b) is for after heating at 800 ° C. in nitrogen. 208.5 eV and 201.5 are applied to the silicon dioxide film (a) before the heat treatment.
A peak is seen at eV. The peak at 208.5 eV is C
lO ₄ ^- due to photoelectrons from the 2p orbital of Cl in the ion peak of 201.5eV is Cl ^- is due photoelectrons from 2p orbit of the ion. As a result of measurement while reducing the thickness of the silicon dioxide film by etch back, C
The concentrations of IO ₄ ^- ions and Cl ^- ions were almost constant throughout the entire thickness of the silicon dioxide film. For it,
As shown in (b), these peaks disappeared after heat treatment at 800 ° C. in nitrogen.

FIG. 7 shows an X-ray photoelectron spectrum of the silicon dioxide film formed in the above embodiment, which was formed by immersing the silicon substrate in a perchloric acid aqueous solution for 90 minutes in the same manner as in FIG. Show. In the figure, the peak (1) is due to photoelectrons from the 2p orbital of Si on the silicon substrate, and is divided into two peaks of 2p _3/2 level and 2p _1/2 level. The broad peak (2) is due to photoelectrons from the 2p orbital of Si in the silicon dioxide film. The dashed spectrum shows that after removing the background from the actually measured spectrum, Si 2p _3/2 and Si
Si 2p for peak separated into 2p _1/2 components
Only the _3/2 component is shown. There is no suboxide peak between peak (1) and peak (2),
This is considered to be one factor of favorable electric characteristics shown in FIGS. 8 and 9 below.

When a silicon dioxide film was formed on a silicon substrate with perchloric acid, the thickness of the silicon dioxide film was uniform and the interface with the silicon substrate was flat. It was also found that the thickness of the formed silicon dioxide film can be controlled by the time of immersion in the aqueous solution of perchloric acid.

FIG. 8 shows a current-voltage curve of a sample having a MOS structure in which a silicon dioxide film was formed to a thickness of 18 nm and an aluminum electrode was formed thereon in this embodiment. (B) is a sample in which an aluminum electrode is formed on a silicon dioxide film without performing a heat treatment after the formation of the silicon dioxide film, and has a high leak current density. On the other hand, (a)
Is a sample in which an aluminum electrode is formed on a silicon dioxide film after performing a heat treatment at 900 ° C. for 2 hours in nitrogen after a silicon dioxide film is formed. It is sufficiently low at 10 ^-9 A / cm ² .

From this experimental result, it was found that a silicon dioxide film formed on a silicon substrate at 203 ° C. using an aqueous solution of perchloric acid was also subjected to heat treatment to obtain a MOS capacitor and a MOS capacitor.
It turns out that the film is effective as a gate insulating film of a transistor.

FIG. 9 shows a capacitance-voltage curve measured using the same MOS structure sample used for measuring the current-voltage curve of FIG. The horizontal axis is the gate voltage (Gate Voltage) applied to the aluminum electrode, and the vertical axis is the capacitance (Capacitance).
It is. The thick line is a capacity-voltage curve measured using a high frequency, and the thin line is a capacity-voltage curve measured using a low frequency. From the comparison between these two curves, the interface state density at the mid gap was estimated to be 1.5 × 10 ¹⁰ cm ⁻² eV ⁻¹ . This interface state density is M
The OS capacity is very low.

In the above embodiment, the concentration is 72.
The case where a 4 vol.% Aqueous solution of perchloric acid is used has been described as an example, but the present invention is not necessarily limited to a perchloric acid solution having this concentration. If the concentration of perchloric acid is 10 vol. To achieve the intended purpose.

In the above embodiment, an aqueous solution of perchloric acid is used to form an oxide film.
Perchloric acid is not necessarily limited to a solution, and a similar oxide film can be formed by reacting gaseous perchloric acid with a semiconductor substrate such as silicon carbide or silicon.

In the method of forming an oxide film using gaseous perchloric acid, a reaction device having a horizontally long chamber is used. The semiconductor substrate can be supported horizontally in the chamber, the semiconductor substrate can be heated by a halogen lamp or resistance heating from the outside of the chamber, the inside of the chamber is depressurized, a predetermined gas is supplied from one end, and the other end is supplied from the other end. Make sure it can be drained.

A semiconductor substrate is supported in a chamber, and anhydrous HF gas is first supplied into the chamber to remove a natural oxide film on the surface of the semiconductor substrate. Next, while heating so that the surface temperature of the semiconductor substrate becomes 170 to 500 ° C., for example, 300 ° C., vapor of perchloric acid is introduced into the chamber to form a silicon oxide film on the surface of the semiconductor substrate.

As a gas for forming a silicon oxide film, it is sufficient that the concentration of perchloric acid is 10 vol.% Or more.
Ozone gas may be added to the vapor of perchloric acid in order to increase the oxidizing power. In the present invention, by heating the oxide film formed of liquid or gaseous perchloric acid in the range of 600 ° C. to 1,100 ° C., the leak current density when applied to a device is reduced.

[0047]

As described above, according to the present invention,
By oxidizing the surface of a semiconductor substrate such as a silicon carbide substrate or a silicon substrate using perchloric acid, a high-quality oxide film having excellent interface characteristics can be formed. Further, by performing a heat treatment, the leakage current density when the device is used for a device can be reduced. Therefore, by using these oxide films as a gate oxide film, a high-performance MOS device can be realized.

[Brief description of the drawings]

FIG. 1 is a process sectional view for explaining a manufacturing method of the present invention.

FIG. 2 shows a silicon carbide substrate having a silicon dioxide film formed thereon according to the first embodiment of the present invention.
It is an X-ray photoelectron spectrum of a 2p area.

FIG. 3 is a cross-sectional scanning micrograph of a silicon carbide substrate having a silicon dioxide film formed thereon according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a dipping time of a silicon carbide substrate in a perchloric acid aqueous solution and a thickness of a silicon dioxide film to be formed in the first embodiment of the present invention.

FIG. 5 is a current-voltage curve for a MOS structure in which a silicon dioxide film is formed on a silicon carbide substrate according to the first embodiment of the present invention, and an aluminum electrode is further formed on the silicon dioxide film. Curve (b) shows the case where the heat treatment was performed in nitrogen at 900 ° C. for 2 hours when the heat treatment was not performed after the formation of the silicon dioxide film.

FIG. 6 shows a second embodiment of the present invention, in which a silicon dioxide film is formed, and Cl 2 is formed on a silicon substrate.
It is an X-ray photoelectron spectrum of a p region.

FIG. 7 is an X-ray photoelectron spectrum of a Si 2p region using a silicon substrate on which a silicon dioxide film is formed according to the second embodiment of the present invention.

FIG. 8 is a current-voltage curve for a MOS structure in which a silicon dioxide film is formed on a silicon substrate according to a second embodiment of the present invention and an aluminum electrode is formed thereon, and curve (a) is a curve of FIG. When the heat treatment is not performed after the formation of the silicon film, the curve (b) shows
This is the case where heat treatment was performed at 2 ° C. for 2 hours.

9 is a diagram showing a capacitance-voltage curve measured using the same MOS structure sample used for the measurement of the current-voltage curve of FIG. 8;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon carbide substrate (silicon substrate) 2 isolation region 4 active region 5 silicon dioxide film 7 aluminum electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference)

Claims (10)

[Claims] 1. A method for forming an oxide film, comprising the following steps (A) and (B). (A) a step of immersing the semiconductor substrate in a solution containing heated perchloric acid to form an oxide film on the surface of the semiconductor substrate;
And (B) heat-treating the semiconductor substrate on which the oxide film has been formed. 2. In the step (A), the solution containing perchloric acid has a perchloric acid concentration of 10 vol.% Or more.
3. The method for forming an oxide film according to item 1. 3. The method for forming an oxide film according to claim 1, wherein in the step (A), the temperature of the solution containing perchloric acid is set to 170 ° C. or higher and equal to or lower than the boiling point of the solution. 4. A method for forming an oxide film including the following steps (A) and (B). (A) a step of exposing a semiconductor substrate to a gas containing perchloric acid while heating to form an oxide film on the surface of the semiconductor substrate; and (B) a step of heat-treating the semiconductor substrate on which the oxide film is formed. 5. The method for forming an oxide film according to claim 4, wherein in the step (A), the gas containing perchloric acid is vapor of perchloric acid. 6. The method for forming an oxide film according to claim 1, wherein in the step (B), the temperature of the heat treatment ranges from 600 ° C. to 1,100 ° C. 7. The method for forming an oxide film according to claim 1, wherein the atmosphere of the heat treatment is a gas containing no chlorine. 8. The oxide film according to claim 7, wherein the atmosphere of the heat treatment is one kind of gas selected from the group consisting of nitrogen, argon, oxygen, water vapor and hydrogen, or a mixed gas of two or more kinds thereof. Formation method. 9. The semiconductor substrate according to claim 1, wherein the semiconductor substrate is selected from the group consisting of single crystal silicon, polycrystalline silicon, amorphous silicon, gallium arsenide, indium phosphide, silicon carbide, silicon germanium carbide, and silicon germanium. Item 10. The method for forming an oxide film according to any one of Items 1 to 8. 10. A method for manufacturing a semiconductor device, comprising a step of forming a conductive layer on an oxide film formed by the method according to claim 1. Description: