JP2003133308A - Method and device for manufacturing silicon-carbide oxide film and method of manufacturing semiconductor element using the oxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for manufacturing a silicon-carbide oxide film, with which a silicon-carbide oxide film can be formed efficiently by subjecting a silicon carbide substrate to anodic-oxidation. SOLUTION: The anodic-oxidation is performed on the silicon carbide substrate, by irradiating the substrate with light in a wavelength region having larger energy than the band gap of silicon carbide. Consequently, a thick oxide film can be formed in a short time. In addition, since the anodic-oxidation can be performed at a room temperature unlike the case of thermal oxidation, the oxide film can be formed easily and, at the same time, the quality of the inner part of the silicon carbide substrate not forming the oxide film can be maintained. Moreover, when the method of forming silicon-carbide oxide film is applied to sacrificial oxidation, the formation of an element isolation film, and the formation of a gate oxide film in a semiconductor element manufacturing process, a high-quality semiconductor element can be manufactured efficiently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide film of silicon carbide, which is a semiconductor material, by an anodic oxidation method, an oxide film manufacturing apparatus, and a method for manufacturing a semiconductor element using an oxide film.

[0002]

2. Description of the Related Art Silicon carbide is one of the semiconductor materials expected to be used for electric power and environment resistant devices. As one step for manufacturing a semiconductor device using this silicon carbide, there is a step of forming an oxide film on silicon carbide.

As a method for forming this oxide film, there are a thermal oxidation method, a method using azeotropic perchloric acid, and an anodic oxidation method. The thermal oxidation method creates an acidic atmosphere in the high temperature furnace,
A silicon carbide substrate is put into this furnace to form an oxide film on the surface of the substrate, which is currently most commonly used. Further, the method using azeotropic perchloric acid, for example, H. Kobayashi, T. Sakurai, M. Ni
shiyama and Y. Nishioka: Applied Physics Letters,
78 (2001) p. 2336, 203 ° C.
The oxide film is formed by exposing the silicon carbide substrate to the perchloric acid. Further, the anodic oxidation method is, for example,
JS Shor, XG Zhang and RM Osgood: Journal
As disclosed in Electrochemical Society, 139 (1992) p. 1213, using dilute sulfuric acid as an electrolyte,
A silicon carbide substrate, which is an anode, and a cathode are installed in this electrolytic solution, and a voltage is applied between both electrodes while irradiating the substrate surface with a laser beam to form an oxide film on the surface of the silicon carbide substrate. is there.

[0004]

However, in the thermal oxidation method, the thickness is only 10 nm after the treatment at 1000 ° C. for 1 hour.
However, there is a problem in that only the oxide film of 1) can be formed, and the formation speed of the oxide film is very slow. Further, since the silicon carbide substrate has to be exposed to a high temperature state for a long time, there is a possibility that the influence of heat may reach the inner layer portion that is not directly involved in the formation of the oxide film. In addition, the method using perchloric acid could form only an oxide film having a thickness of only 80 nm in 20 hours of treatment, and was not practical yet.

On the other hand, in the anodic oxidation method, irradiation of laser light has been attempted in order to accelerate the oxidation reaction. However, since the laser beam has high directivity and the area that can be irradiated at one time is very small, there is a limit to the improvement of the oxide film formation rate. Therefore, only a report that an oxide film having a thickness of 20 nm is locally formed has been made, and it has been considered that it is difficult to dramatically increase the oxide film formation rate.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an oxide film manufacturing method and apparatus capable of efficiently performing anodization.

[0007]

Means for Solving the Problems The inventors of the present invention have made extensive studies to develop an oxide film manufacturing method and apparatus capable of efficiently performing anodization, and have found the following findings.

The mechanism of forming an oxide film by the anodic oxidation method is considered to be as follows. Water in the electrolytic solution is ionized and exists as hydrogen ions and hydroxide ions. By placing a silicon carbide substrate as an anode and a cathode in this electrolytic solution and applying a voltage between both electrodes, hydrogen ions are attracted to the cathode electrode and hydroxide ions are attracted to the silicon carbide substrate. become. The hydroxide ions react with holes existing on the surface of the silicon carbide substrate and decompose into oxygen atoms and hydrogen atoms. Then, the oxygen atoms react with silicon atoms or carbon atoms in silicon carbide to form a silicon oxide film and at the same time generate carbon dioxide gas. The remaining hydrogen atoms are paired with two atoms and become hydrogen gas.

As described above, in the oxidation reaction, it is essential to supply holes from the silicon carbide substrate to the hydroxide ions. The present inventors continuously generate holes on the surface of silicon carbide by anodic oxidation while irradiating the surface of silicon carbide with light having an energy equal to or higher than the band gap of silicon carbide, thereby performing an oxidation reaction. It has been found that can promote. The present invention has been made based on such novel findings.

That is, in the method for producing an oxide film of the present invention, an electrolytic solution is provided with an anode made of a silicon carbide substrate and a cathode forming a pair with the anode, and a potential difference is applied between both electrodes to give a silicon carbide substrate. A method of forming an oxide film on the surface of a silicon carbide substrate, characterized by applying a potential difference between both electrodes while irradiating the silicon carbide substrate with light in a wavelength region having energy larger than the band gap of the silicon carbide. .

The oxide film manufacturing apparatus of the present invention is an oxide film manufacturing apparatus for forming an oxide film on the surface of a silicon carbide substrate by an anodic oxidation method, in which an electrolytic solution is stored.
And a container in which the silicon carbide substrate can be installed, a cathode provided in the container, a power source connectable to the silicon carbide substrate and the cathode, and a wavelength having energy larger than the band gap of the silicon carbide. A light source capable of irradiating the light of the area is provided.

The band gap of silicon carbide differs depending on the crystal structure of silicon carbide. For example, 4H-SiC has 3.2 eV, 6H-SiC has 3.0 eV, and 3C-Si.
It is 2.2 eV in C. The wavelength of light corresponding to these band gaps is represented by the formula λ (nm) = 1240 / Eg (eV) ... Formula (1) (where λ is the wavelength and Eg is the band gap). From this equation, as light having an energy larger than the band gap of silicon carbide described above, 4H-
About 387 nm or less for SiC, about 41 for 6H-SiC
In the case of 3 nm or less and 3C-SiC, near-ultraviolet light having a wavelength of about 563 nm or less can be used.

On the other hand, when irradiating light, it is usual to irradiate from the outside of the container with the silicon carbide substrate immersed in the electrolytic solution in the container. In such a case, the electrolytic solution is used. It is necessary to use light having a wavelength that transmits the light.
The absorption spectrum of the electrolytic solution varies depending on the type and composition of the electrolytic solution. For example, when a mixed solvent of ethylene glycol and water is used, the absorption edge is around 350 nm, and light of wavelengths longer than this Almost 100% transmitted.
Further, in order to allow the reaction to proceed efficiently, it is preferable to use a light source having a wide irradiation area such that the entire region where the oxide film is formed on the silicon carbide substrate can be irradiated at one time. As a light source satisfying these conditions, for example, a mercury lamp, a xenon lamp, a metal halide lamp or the like having an emission wavelength in the near-ultraviolet region can be used. Among them, a mercury lamp (emission wavelength 365 nm, 405 nm, 436 nm) is used.
nm) can be preferably used.

Further, the silicon carbide substrate is installed so that one surface side thereof is in contact with the liquid surface of the electrolytic solution, and anodic oxidation is performed while irradiating light from the other surface side (surface side not in contact with the electrolytic solution). You can also With this configuration, since the electrolytic solution does not exist between the light source and the substrate, it is not necessary to consider the absorption of the irradiation light into the electrolytic solution, and the irradiation light can efficiently contribute to the oxidation reaction.

Further, in order to form the oxide film with good reproducibility, it is preferable that the current density (current value / area of the oxide film forming surface of the silicon carbide substrate) be a constant value.

The electrolytic solution used in the method for producing an oxide film of the present invention is not particularly limited as long as it is an electrolytic solution usually used in the anodizing method, but a mixed solvent of a solvent having a high relative dielectric constant and water is used. It can be preferably used. Examples of the solvent having a high relative dielectric constant include ethylene glycol, N-methylacetamide, and tetrafurfuryl alcohol (THF). Among them, the use of ethylene glycol makes it possible to form a thick oxide film in a short time. Can be formed. In addition, a salt may be added to the electrolytic solution in order to reduce the electric resistance of the electrolytic solution and accelerate the oxidation. The salt to be added is not particularly limited as long as it is ionized in the electrolytic solution, for example, potassium nitrate, potassium nitrite,
Sodium sulfate and the like can be preferably used.

The oxide film manufacturing method of the present invention can be suitably applied to sacrificial oxidation, formation of an element isolation film, formation of a gate oxide film, etc. in a semiconductor device manufacturing process.

[0018]

EFFECTS OF THE INVENTION AND EFFECTS OF THE INVENTION According to the oxide film manufacturing method and apparatus of the present invention, it is possible to provide an oxide film manufacturing method and apparatus capable of forming an oxide film having a large thickness in a short time.
Further, unlike the thermal oxidation method, since it can be processed at room temperature, an oxide film can be easily formed and the quality of the inner layer portion of the silicon carbide substrate where the oxide film is not formed can be maintained. Furthermore, by applying the oxide film manufacturing method of the present invention to sacrificial oxidation, formation of an element isolation film, and formation of a gate oxide film in a semiconductor device manufacturing process, a good quality semiconductor device can be manufactured efficiently. it can.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment> Next, a first embodiment of the present invention will be described in detail with reference to FIGS.

1) Structure of Oxide Film Manufacturing Apparatus An oxide film manufacturing apparatus 1 of this embodiment is shown in FIG. The container 2 of the oxide film manufacturing apparatus 1 is made of, for example, glass that can transmit light emitted from a mercury lamp 14 described later, and is formed in a rectangular tube shape with a bottom, and the electrolyte solution 3 can be stored therein. ing. Electrolyte 3 is ethylene glycol 300m
1.2 g of potassium nitrate as a salt was dissolved in a mixed solvent obtained by mixing 1 and 7.5 ml of water. As shown in FIG. 2, the electrolytic solution 3 has an absorption edge near 350 nm and transmits almost 100% of light having a wavelength longer than this.

In the container 2, a silicon carbide substrate 4 serving as an anode, a cathode plate 5 (corresponding to the cathode of the present invention), and a support plate 6 for mounting the silicon carbide substrate 4 are installed.

The silicon carbide substrate 4 is fixed by a silicon resin 7 on a support plate 6 which is made of synthetic resin and has a plate shape slightly larger than the silicon carbide substrate 4. At this time, the entire side surface of the silicon carbide substrate 4 is covered with the silicon resin 7 so that only the surface on which the oxide film is formed is exposed. An ohmic electrode 8 made of aluminum is formed on the surface of the silicon carbide substrate 4 facing the support plate 6. The support plate 6 is held by a support arm (not shown) provided near the upper edge of the container 2 and hangs down inside the container 2.

The cathode plate 5 is made of platinum in a plate shape having substantially the same size as the support plate 6. This cathode plate 5 is
It is held by a support arm (not shown) like the support plate 6,
It is suspended in the container 2.

On the ohmic electrode 8 of the silicon carbide substrate 4, one end of the anode side conductive wire 9 is adhered with a silver paste. This anode side conductor 9 is extended to the outside of the container 2 along the support plate 6, and the other end is a DC power source 11
It is connected to the positive terminal 12 (corresponding to the power supply of the present invention). The portion of the anode side conductor 9 that is immersed in the electrolytic solution 3 is insulated by being covered with the silicone resin 7 and is fixed on the support plate 6. Further, one end of a cathode-side conductor 10 is connected to the cathode plate 5, and the other end of the cathode-side conductor 10 is connected to the negative terminal 13 of the DC power supply 11.
It is connected to the.

A mercury lamp 14 (corresponding to the light source of the present invention) is installed on the side of the container 2. The mercury lamp 14 has a larger energy than the band gap of silicon carbide and is capable of emitting light in a wavelength range that passes through the electrolytic solution 3.

Further, a condenser lens 15 is attached to the outer peripheral surface 2A of the container 2, and the light emitted from the mercury lamp 14 is condensed by the condenser lens 15 to form the surface of the silicon carbide substrate 4. It is designed to be illuminated.

2) Oxide Film Manufacturing Method Using Oxide Film Manufacturing Apparatus 1 Next, a method of anodizing the silicon carbide substrate 4 using the oxide film manufacturing apparatus 1 configured as described above will be described.

The electrolytic solution 3 is placed in the container 2 of the oxide film manufacturing apparatus 1.
Is poured in so that the entire silicon carbide substrate 4 is dipped. Then, a stirring propeller (not shown) is rotated to stir the electrolytic solution 3, and the mercury lamp 14 is turned on to irradiate the surface of the silicon carbide substrate 4 with light. Then,
Holes are formed on the surface of the silicon carbide substrate 4 by the energy of the irradiation light.

In this state, the DC power supply 11 is turned on to apply a predetermined voltage between the silicon carbide substrate 4 and the cathode plate 5. Then, hydrogen hydroxide ions generated by the ionization of water in the electrolytic solution 3 react with holes to form an oxide film on the surface of the silicon carbide substrate 4.

In this reaction, it is essential to supply holes from the silicon carbide substrate 4 to the hydroxide ions.
By performing anodization while irradiating the surface of the silicon carbide substrate 4 with light having an energy equal to or higher than the band gap of silicon carbide, holes can be continuously generated on the surface of silicon carbide. Further, since the mercury lamp 14 has a larger irradiation area than a laser or the like, the silicon carbide substrate 4
Irradiation light can be radiated at one time over the entire surface of the. As a result, the oxidation reaction can be promoted, and a thick oxide film can be formed in a short time. Furthermore, by irradiating the light in the wavelength region longer than the absorption edge of the electrolytic solution 3, it is possible to prevent the irradiation light from being absorbed by the electrolytic solution 3 and reduce the light amount, and to promote the oxidation reaction efficiently. be able to.

[Examples] 1) Formation of an oxide film on a silicon carbide substrate by the oxide film manufacturing apparatus and method according to the first embodiment. As the silicon carbide substrate 4, an n-type 6H-SiC bulk substrate (0001) on -axis, Si surface polishing (sterling semi
conductor company) was used.

Oxide film manufacturing apparatus 1 configured as described above
The electrolytic solution 3 was poured into the container 2 so that the entire silicon carbide substrate 4 was immersed. Then, while rotating a stirring propeller (not shown) to stir the electrolytic solution 3,
The mercury lamp 14 was turned on to irradiate the surface of the silicon carbide substrate 4 with light. In this state, the DC power supply 11 was turned on to carry out anodization at a current density of 1 mA / cm ² for 20 minutes. At this time, the voltage was measured every 0.5 seconds to examine the change in the applied voltage.

After the voltage application operation was completed, the support plate 6 was pulled up and the silicon carbide substrate 4 was removed. An X-ray photoelectron spectroscopy spectrum was measured for the formed oxide film. In addition, the film thickness of the oxide film was measured by a surface step meter.

Further, as a comparative example, anodic oxidation was performed in the same manner as above except that light was not irradiated, and changes in applied voltage and film thickness were measured.

2) Results and Discussion FIG. 3 shows changes with time in applied voltage during anodic oxidation. In addition, the change over time in the applied voltage when light is not irradiated is also shown.

When no light was applied, the voltage rose to about 62V immediately after the start of anodic oxidation and then dropped sharply to about 42V. After that, the voltage rises slowly,
The voltage remained at about 42 to 54 V until the end of anodization. On the other hand, when irradiated with light, the voltage remained at a low value of about 1 to 2 V and hardly changed. From this, it is understood that by irradiating light to promote the generation of holes on the silicon carbide substrate 4, a current flows at a low voltage, and the oxidation reaction is facilitated. In addition, when light is irradiated, the voltage shows a low value immediately after the start of the reaction. This is because the mercury lamp is turned on and the silicon carbide substrate is irradiated with light prior to turning on the DC power supply, so when the voltage application is started, the surface of the silicon carbide substrate has already been sufficiently filled with holes. It is thought that this is due to the generation of.

Further, FIG. 4 shows the X-ray photoelectron spectroscopy spectrum of the oxide film. Si 2p, 2 at 109.0 eV
Peaks of C 1s appeared at 90.4 eV and O 1s appeared at 538 eV. The oxide film was dissolved by hydrogen fluoride. From these, it is considered that the oxide film contains silicon oxide as the main component and also contains a small amount of carbon atoms.

The film thickness of the oxide film formed was 360 nm when light was irradiated, and 170 nm when light was not irradiated. As described above, it was found that the irradiation of light promotes the oxidation reaction and enables the formation of a thick oxide film.

<Second Embodiment> Next, a second embodiment of the present invention will be described in detail with reference to FIG.

1) Structure of Oxide Film Manufacturing Apparatus 20 The main difference between the oxide film manufacturing apparatus 20 of this embodiment and the oxide film manufacturing apparatus 1 of the first embodiment is that the silicon carbide substrate 25 is used.
However, the one side is installed so as to be in contact with the liquid surface of the electrolytic solution 3. In the present embodiment, the same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the oxide film manufacturing apparatus 20 of the present embodiment, the container 21 is formed in a flat cylindrical shape having upper and lower openings, and its inner diameter is slightly larger than that of the silicon carbide substrate 25. At the upper end and the lower end of this container 21, electrode receiving portions 22A and 22B are provided which are provided so as to project inward.
Is provided.

A disk-shaped cathode plate 23 having the same diameter as the inner diameter of the container 21 is fitted on the bottom surface of the container 21,
It is supported by the lower electrode receiving portion 22A. When the cathode plate 23 is thus fitted in the container 21, the electrolytic solution 3 can be stored inside the container 21. A packing 24 formed of an elastic member such as rubber is fitted under the upper electrode receiving portion 22B. The packing 24 is formed in a donut shape having an outer diameter equal to the inner diameter of the container 21 and an inner diameter substantially equal to the inner diameter of the container 21. An assembling recess 24A is provided outward in a central portion in the vertical direction on the inner peripheral surface of the packing 24. The peripheral edge of the silicon carbide substrate 25 is inserted into the assembling recess 24A and sandwiched from above and below. As a result, it is possible to support the silicon carbide substrate 25.

This silicon carbide substrate 25 and cathode plate 23
The conductors 9 and 10 are connected to the same as in the first embodiment,
These conducting wires 9 and 10 are the positive terminal 1 of the DC power supply 11.
2 and the negative terminal 13 are respectively connected.

A mercury lamp 14 capable of emitting light in a wavelength range having energy larger than the band gap of silicon carbide is installed above the container 21. In the present embodiment, the light of the mercury lamp 14 is directly irradiated onto the silicon carbide substrate 25 without passing through the electrolytic solution 3, so it is not necessary to consider the absorption of the irradiation light by the electrolytic solution 3. .

2) Oxide Film Manufacturing Method Using Oxide Film Manufacturing Apparatus 20 Next, using the oxide film manufacturing apparatus 20 configured as described above, an oxide film is formed on the silicon carbide substrate 25 by anodic oxidation. The method of making it will be described.

The electrolytic solution 3 is poured into the container 21 of the oxide film manufacturing apparatus 20 with the cathode plate 23 fitted therein. Then, the silicon carbide substrate 25 is fitted to the packing 24,
The inner surface 25A side (corresponding to one surface side of the present invention) is brought into contact with the electrolytic solution 3. Then, the mercury lamp 14 is turned on to irradiate the outer surface 25B side of the silicon carbide substrate 25 (corresponding to the other surface side of the present invention) with light. Then, the outer surface 2 of the silicon carbide substrate 25 is changed by the energy of the irradiation light.
Holes are formed in 5B and diffuse toward the inner surface 25A side.

In this state, the DC power supply 11 is turned on to apply a predetermined voltage between the silicon carbide substrate 25 and the cathode plate 23. Then, the hydroxide ions generated by the ionization of water in the electrolytic solution 3 react with the holes that have moved to the inner surface 25A side of the silicon carbide substrate 25 to form an oxide film on the surface of the silicon carbide substrate 25. To generate. As described above, also in this embodiment, similarly to the first embodiment, it is possible to continuously generate holes on the surface of silicon carbide to promote the oxidation reaction and form a thick oxide film in a short time. it can. Further, since it is not necessary to consider the absorption of the irradiation light into the electrolytic solution 3, the energy of the irradiation light can be used more efficiently for promoting the oxidation.

<Third Embodiment> Next, a third embodiment of the present invention will be described in detail with reference to FIGS. In the present embodiment, the oxide film manufacturing method of the present invention is applied to the sacrificial oxidation in the manufacturing of the semiconductor devices 35, 45, 55, the formation of the element isolation film 44, and the formation of the gate oxide film 53.

1) Sacrificial Oxidation FIG. 6 is a process diagram of sacrificial oxidation to which the oxide film manufacturing method of the present invention is applied. First, a nitride film is formed on the entire surface of the silicon carbide substrate 30 by using, for example, a well-known CVD (chemical vapor deposition) method. Next, a photoresist film having a predetermined pattern is formed on this nitride film. Then, by using this photoresist film as a mask, the nitride film in the electrode formation region 31 is selectively removed by dry etching using plasma, for example. Then, the photoresist film is removed. In this way, the element isolation film 32 having the electrode formation region 31 opened is formed.

Then, a sacrificial oxide film 33 is formed on the exposed surface of the electrode formation region 31 (FIG. 6A). The sacrificial oxide film 33 is formed by, for example, the anodic oxidation method using the oxide film manufacturing apparatus 1 of the first embodiment described above. Specifically, the support plate 6 to which the silicon carbide substrate 30 is attached and the cathode plate 5 are set in the electrolytic solution 3 filled in the container 2. Then, the electrode forming region 3 of the silicon carbide substrate 4
1, while irradiating light with the mercury lamp 14, the DC power supply 11 is turned on, and the silicon carbide substrate 30-cathode plate 5
Apply voltage between them. As a result, the sacrificial oxide film 33 can be formed efficiently in a short time.

After that, the sacrificial oxide film 33 is removed by etching using hydrofluoric acid, for example, and the electrode forming region 31
Clean the surface of (FIG. 6B). Then, the electrode 34 is formed on the electrode formation region 31 by a known method (FIG. 6).
C). In this way, the semiconductor element 35 is manufactured.

2) Formation of inter-element isolation film FIG. 7 shows a process diagram of formation of an inter-element isolation film to which the oxide film manufacturing method of the present invention is applied. First, an oxide film 41 is formed on the entire surface of the silicon carbide substrate 40 (FIG. 7A). The oxide film 41 is formed by the anodic oxidation method using, for example, the oxide film manufacturing apparatus 1 of the first embodiment described above. Specifically, the support plate 6 to which the silicon carbide substrate 40 is attached and the cathode plate 5 are set in the electrolytic solution 3 filled in the container 2. Then, while the mercury lamp 14 irradiates the entire surface of the silicon carbide substrate 40 with light, the DC power supply 11 is turned on to apply a voltage between the silicon carbide substrate 40 and the cathode plate 5. Thus, the thick oxide film 41 can be formed in a short time.

Next, a photoresist film 42 having a predetermined pattern is formed on the oxide film 41 (FIG. 7B). Then, using the photoresist film 42 as a mask, the oxide film 41 in the electrode formation region 43 is selectively removed by etching using hydrofluoric acid. After that, the photoresist film 4
2 is removed to form an element isolation film 44 (see FIG. 7).
C). In this way, the semiconductor element 45 is manufactured.

3) Formation of Gate Oxide Film FIG. 8 shows a process diagram of gate oxide film formation to which the oxide film manufacturing method of the present invention is applied. First, a nitride film is formed on the entire surface of the silicon carbide substrate 50 by using, for example, a well-known CVD method. Next, a photoresist film having a predetermined pattern is formed on this nitride film. Then, by using this photoresist film as a mask, the nitride film in the electrode formation region 51 is selectively removed by dry etching using plasma, for example. Then, the photoresist film is removed. In this way, the inter-element isolation film 52 having the electrode formation region 51 opened is formed (FIG. 8A).

Next, a gate oxide film 53 is formed on the exposed surface of the electrode formation region 51 (FIG. 8B). The gate oxide film 53 is formed by an anodic oxidation method using, for example, the oxide film manufacturing apparatus 1 of the first embodiment described above. Specifically, the support plate 6 to which the silicon carbide substrate 50 is attached and the cathode plate 5 are set in the electrolytic solution 3 filled in the container 2. Then, the DC power supply 11 is turned on while irradiating the electrode formation region 51 of the silicon carbide substrate 50 with light from the mercury lamp 14, and a voltage is applied between the silicon carbide substrate 50 and the cathode plate 5. Thereby, the gate oxide film 53 can be formed efficiently in a short time. Then, the gate electrode 5 is formed on the gate oxide film 53 by a known method.
4 are formed (FIG. 8C). In this way, the semiconductor element 55 is manufactured.

As described above, the oxide film manufacturing method of the present invention is
The semiconductor element can be efficiently manufactured by applying it to the sacrificial oxidation in the manufacturing process of the semiconductor element, the formation of the element isolation film, and the formation of the gate oxide film. Further, since it can be processed at room temperature, an oxide film can be easily formed, and the quality of the inner layer portion of the silicon carbide substrate where the oxide film is not formed can be maintained, so that a good-quality semiconductor element can be manufactured.

The technical scope of the present invention is not limited to the above-mentioned embodiments, and the following technical scope is also included in the technical scope of the present invention.
In addition, the technical scope of the present invention extends to an equivalent range. (1) In the first embodiment, the irradiation light from the mercury lamp 14 is condensed by the condenser lens 15 and applied to the silicon carbide substrate 4. However, according to the present invention, the irradiation light is not necessarily condensed. It is not necessary to irradiate the silicon carbide substrate directly. In addition, in the second embodiment, the mercury lamp 1
Although the irradiation light from 4 is directly irradiated onto the silicon carbide substrate 4 without being condensed, it may be irradiated via a condensing lens. (2) In the first embodiment, the ohmic electrode 8 is made of aluminum, but according to the present invention, the material of the ohmic electrode is not limited to that of the present embodiment, and may be made of nickel, for example. (3) According to the second embodiment, the container 21 has a cylindrical shape, but according to the present invention, the shape of the container is not limited to that of this embodiment, and for example, a silicon carbide substrate to be anodized, such as a rectangular tube shape. Various shapes can be used according to the shape of. (4) In the sacrificial oxidation step and the gate oxide film formation step in the third embodiment, the element isolation film 32,
Although 52 is formed of a nitride film, according to the present invention, the composition of the element isolation film is not limited to that of this embodiment, and may be formed of, for example, an oxide film. Further, in forming the inter-element isolation film, the oxide film manufacturing method of the present invention can be suitably applied, and any method that is generally applied in the formation of the inter-element isolation film may be applied.

[Brief description of drawings]

FIG. 1 is a schematic view showing an oxide film manufacturing apparatus of a first embodiment.

FIG. 2 is a graph showing an absorption spectrum of an electrolytic solution.

FIG. 3 is a graph showing changes with time in applied voltage during anodization.

FIG. 4 X-ray photoelectron spectroscopy spectrum of oxide film

FIG. 5 is a schematic view showing an oxide film manufacturing apparatus of a second embodiment.

FIG. 6 is a process diagram of sacrificial oxidation to which the oxide film manufacturing method of the present invention is applied.

FIG. 7 is a process chart of forming an element isolation film by applying the oxide film manufacturing method of the present invention.

FIG. 8 is a process chart of forming a gate oxide film by applying the oxide film manufacturing method of the present invention.

[Explanation of symbols]

1, 20 ... Oxide film manufacturing equipment 2, 21 ... Container 3 ... Electrolyte 4, 25, 30, 40, 50 ... Silicon carbide substrate 5, 23 ... Cathode plate (cathode) 11 ... DC power supply (power supply) 14 Mercury lamp (light source) 31, 43, 51 ... Electrode forming region 32, 44, 52 ... Element separation film 33 ... Sacrificial oxide film 35, 45, 55 ... Semiconductor element 41 ... Oxide film 54 ... Gate oxide film 55 ... Gate electrode

Continued front page    (72) Inventor Eisuke Arai             Meijo House, 3-1 Meijo, Kita-ku, Nagoya City, Aichi Prefecture             2-107 F-term (reference) 5F032 AA11 CA01 CA05 CA09 DA24                       DA54                 5F058 BC02 BF70 BF71 BF78                 5F140 AA19 AA40 BA02 BA20 BD06                       BE07 CB00

Claims (11)

[Claims] 1. An electrolytic film is provided with an anode made of a silicon carbide substrate and a cathode forming a pair with the anode, and a potential difference is applied between both electrodes to form an oxide film on the surface of the silicon carbide substrate by an anodic oxidation method. A method for producing an oxide film, which comprises forming a potential difference between both electrodes while irradiating the silicon carbide substrate with light in a wavelength region having energy larger than a band gap of silicon carbide. Production method. 2. The oxide film manufacturing method according to claim 1, wherein the light is light in a wavelength region longer than a wavelength of an absorption edge in the electrolytic solution. 3. The method for producing an oxide film according to claim 1, wherein the electrolytic solution contains ethylene glycol and water. 4. The method for producing an oxide film according to claim 1, wherein the electrolytic solution contains a salt ionizable in the electrolytic solution. 5. An oxide film production apparatus for forming an oxide film on the surface of a silicon carbide substrate, wherein a container in which an electrolytic solution is stored and in which the silicon carbide substrate can be installed, and a container provided in this container are provided. A cathode, a power source connectable to the silicon carbide substrate and the cathode, and a light source capable of irradiating light in a wavelength region having energy larger than a band gap of the silicon carbide, Oxide film manufacturing equipment. 6. The silicon carbide substrate is installed such that one of the front and back surfaces thereof is in contact with the liquid surface of the electrolytic solution, and the other surface of the silicon carbide substrate is irradiated with the light. The oxide film manufacturing apparatus according to claim 5, wherein a light source is provided. 7. A semiconductor device comprising an oxide film manufactured by the method for manufacturing an oxide film according to claim 1. Description: 8. A semiconductor device manufactured by a method including the method for manufacturing an oxide film according to claim 1. 9. (a) a step of forming an inter-element isolation film having an electrode formation region opened on the surface of a silicon carbide substrate; (b) a step of forming a sacrificial oxide film in the electrode formation region; c) A method of manufacturing a semiconductor device, comprising: a step of removing the sacrificial oxide film by etching; and (d) a step of forming an electrode in the electrode forming region, wherein the sacrificial oxide film is formed in the step (c). An anode composed of the silicon carbide substrate in the electrolytic solution and a cathode paired with the anode are provided, and the electrode formation region is irradiated with light in a wavelength region having energy larger than the band gap of silicon carbide. A method for manufacturing a semiconductor element, which is formed by applying a potential difference between electrodes. 10. A semiconductor device including (e) a step of forming an oxide film on the surface of a silicon carbide substrate, and (f) a step of forming an element isolation film by etching the oxide film in a predetermined pattern. In the step (e), the sacrificial oxide film is provided with an anode made of the silicon carbide substrate and a cathode forming a pair with the anode in the electrolytic solution, and the surface of the silicon carbide substrate is provided. A method for manufacturing a semiconductor element, which is formed by applying a potential difference between both electrodes while irradiating with light in a wavelength region having energy larger than the band gap of silicon carbide. 11. (g) A step of forming an inter-element isolation film having an opening in an electrode formation region on the surface of a silicon carbide substrate, (h) a step of forming a gate oxide film in the electrode formation region, i) A method of manufacturing a semiconductor device, which comprises a step of forming a gate electrode on the gate oxide film, wherein in the step (i), the gate oxide film is an anode made of the silicon carbide substrate in an electrolytic solution. , A cathode that forms a pair with this anode is provided, and the electrode formation region is formed by applying a potential difference between both electrodes while irradiating light in a wavelength region having energy larger than the band gap of silicon carbide. A method for manufacturing a characteristic semiconductor device.