JP4152130B2 - Epitaxial film manufacturing method and epitaxial film-coated substrate manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for forming a flat surface suitable for forming an epitaxial film on a silicon carbide substrate. The present invention also relates to an oxide film-coated silicon carbide substrate suitable for an electronic device.
[0002]
[Prior art]
Silicon carbide (SiC) has received much attention as a substrate for optical devices and electronic devices. In the field of optical devices, nitrides such as GaN are made of sapphire (Al₂O₃) And film formation on a silicon carbide substrate.
[0003]
However, as described in Japanese Patent Laid-Open No. 10-270368, when a sapphire substrate is used, the sapphire substrate is electrically insulative, and thus a conductive layer is formed on the substrate. Current must be supplied through the layers. Further, since sapphire and GaN have different cleavage planes, a good cavity cannot be obtained when used as a laser. Therefore, attempts have been made to use conductive silicon carbide substrates instead of sapphire substrates. Since silicon carbide has conductivity, there is an advantage that an electrode can be directly formed on a substrate.
[0004]
In the field of electronic devices, silicon (Si) has been used for a long time. However, the operating temperature is limited to 125 ° C. or less, and power loss due to heat generation during device operation has become a major issue in device design. Electronic devices such as transistors used in mobile phone communication bases, satellite broadcasting communication fields, and traffic and transportation fields where ETC systems and automobile collision prevention function systems are being developed are not only high in temperature but also high withstand voltage. Therefore, there is a demand for a material with low on-resistance and good operating characteristics at high frequencies.
[0005]
Wide bandgap semiconductors are materials that support these technological trends. Wide band gap semiconductors include nitrides such as GaN and AlN, silicon carbide, and diamond. Due to the difficulty in controlling crystal growth, it is difficult to obtain a self-supporting high-quality substrate of GaN or AlN nitride. On the other hand, in addition to the method of depositing a SiC substrate on a Si substrate by CVD, ingot growth using a sublimation method is possible. A wafer is cut out from the ingot-grown silicon carbide, and the wafer can be mirror-polished to be used as a substrate.
[0006]
Although it is difficult to crystallize GaN and AlN alone, it is possible to form a film on the above-described silicon carbide substrate by using a film forming method such as CVD or MBE. In order to form a high-quality GaN film or AlN film, the surface of the silicon carbide substrate is desirably as smooth as possible.
[0007]
It is necessary to mechanically polish and smooth the surface of the silicon carbide wafer cut out from the silicon carbide ingot. The smoothing process called polishing is a method of obtaining a smoother surface by using a polishing agent and changing from rough abrasive grains to fine abrasive grains as polishing progresses. However, the abrasive grains must be harder than silicon carbide or higher. For this reason, a damage layer caused by polishing or polishing scratches called scratches are generated on the entire surface of the silicon carbide substrate. FIG. 2 shows the polished silicon carbide surface observed with an atomic force microscope (AFM).
[0008]
Much of the final device performance depends on the quality of the epitaxial film grown on the silicon carbide substrate. The film quality of the epitaxial film is affected by the silicon carbide substrate as the base. Therefore, in order to obtain a high-quality epitaxial film, it is necessary to remove a damaged layer or scratch on the surface of the silicon carbide substrate to form a flat and clean surface at the atomic level before the epitaxial film is formed.
[0009]
It is known to use hydrogen gas or hydrogen chloride gas in a temperature range of 1300 ° C or higher and 1850 ° C or lower in a CVD apparatus in order to remove polishing scratches on the surface of the silicon carbide substrate and obtain a flat surface. .
[0010]
[Problems to be solved by the invention]
However, since this method uses hydrogen, there is a risk of explosion during operation. In addition, hydrogen chloride is a toxic gas and corrosive, and may corrode the inside of the apparatus. Also, a special device is required for exhausting hydrogen chloride gas. In CVD, the gas pressure is as high as 0.1 to 760 Torr. In such an apparatus, the gas becomes a viscous flow, and when the diameter of a large-diameter wafer or the number of wafers is increased, the etching rate may vary depending on the location or sample of the wafer. .
[0011]
For example, in Japanese Patent Application Laid-Open No. 2001-77030, “Silicon Carbide Semiconductor Device Manufacturing Method” (Sanyo Electric, Hitachi, Toshiba, National Institute of Advanced Industrial Science and Technology) Surface treatment is performed by flowing 8L / min. The pressure at this time is preferably larger than 2 Torr and not more than 100 Torr. However, when a large number of silicon carbide wafers are to be processed simultaneously under such pressure, there is a possibility that the etching will not be performed uniformly due to the viscosity of the gas flow. In addition, since a large amount of hydrogen gas is used, a sufficient processing apparatus is required for the processing method.
[0012]
In (S. Nakamura, T. Kimoto, H. Matsunami, S. Tanaka, N. Teraguchi and A. Suzuki: “Appl. Phys. Lett.” 76 (2000) No. 23, 3412), 1300 ° C. Surface treatment was carried out by flowing hydrogen chloride gas at 3 sccm (Standard Cubic Centimeter per Minute; flow rate unit) with respect to 1 SLM (Standard Litter per Minute; flow rate unit) of hydrogen at a temperature. (ZYXie, CHWei, LYLi, QMYu and JHEdgar: “J.Cryst.Growth” 217 (2000) 115), 1% hydrogen chloride gas was flowed in hydrogen in the temperature range of 1400-1500 ° C. The surface treatment was carried out. When hydrogen chloride gas is used in such a temperature range, there is a risk that the reactor wall of the reactor will be eroded.
[0013]
Metal oxide semiconductor field effect transistors (MOSFETs) are the key to ultra-high integrated circuits (ULSI) such as high-speed MPUs (microprocessors) and high-density memories that are built into information devices such as personal computers and mobile phones. Is a constituent element. As the material of the MOSFET, Si was overwhelmingly used. According to “Solid physics”, February 2002, page 61 “New picture of silicon thermal oxidation” (Kageshima et al.), The silicon oxide film is an insulating film with a band gap of about 8 eV. The offset (shift of the band gap between Si and the oxide film) is as large as about 3 to 4 eV. A high voltage is applied to the carriers in Si, and the carriers move at high speed in the vicinity of the interface between Si and the oxide film. For this reason, the Si oxide film is used as a gate oxide film of the MOSFET.
[0014]
The reason why Si is used as a material for MOSFET is as follows. Si can be easily oxidized at 600 to 1200 ° C., and the generated oxide film has a uniform thickness, and the interface between Si and the oxide film becomes extremely flat. Another reason is that the carrier mobility can be increased because the charge trap state density is low at the oxide film or at the interface between the oxide film and the Si substrate. It is said that when the oxide film is formed and then annealed in a hydrogen atmosphere, the charge trap level density is further reduced. The charge trap level density is an index indicating an action of trapping carriers. When the charge trap level density is high, the carrier mobility is lowered and the device performance is deteriorated.
[0015]
Recently, however, devices having performance exceeding the theoretical limit of Si materials have been desired. A candidate for such a material is SiC, which is a wide gap semiconductor. If a high-quality oxide film can be formed on the SiC substrate, it is considered that a power electronics device that changes to Si is obtained.
[0016]
Examples of techniques for forming an oxide film on a silicon carbide substrate include the following.
Ryoji Kosugi et al. “J. Appl. Phys.,” 91 (2002) p. 1314
S. Chakraborty et al. “Solid-State Electronics” 45 (2001) 471
JP-A-9-199497
[0017]
However, in these methods, the oxide film is formed in a state where polishing scratches on the surface of the silicon carbide substrate remain. As a result, even when an oxide film is formed, irregularities derived from polishing flaws remain at the interface between the oxide film and the silicon carbide substrate, a charge trap level density is formed, and the device performance deteriorates. .
[0018]
For example, in the method of Kosugi et al., A silicon carbide substrate is RCA cleaned, dried and oxidized at 1200 ° C. for 30 minutes to form an oxide film having a thickness of 10 nm, the oxide film is removed with hydrofluoric acid, and then at 400 ° C. An oxide film is formed by chemical vapor deposition using silane gas and oxygen. This oxide film is annealed at 1000 to 1200 ° C. According to this report, the interface state density (D_it: Interface state density) is reduced. This is SiO₂D due to softening in it_itIs reported to have been reduced. However, in the annealing at a temperature of about 1200 ° C., the polishing scratches originally existing in the silicon carbide substrate are not lost, and there are charge trap levels due to the structure of the interface between the oxide film and silicon carbide. It should be.
[0019]
According to a report by S. Chakraborty et al., After RCA cleaning, a silicon carbide substrate was immersed in 1% hydrofluoric acid for 60 seconds, oxidized at 1100 ° C. for 210 minutes in an oxygen atmosphere, and in nitrogen or N₂Annealing is performed in O. Also by this oxide film manufacturing method, the charge trap level derived from the polishing flaw of the substrate is generated at the interface between the oxide film and the silicon carbide substrate.
[0020]
Japanese Patent Laid-Open No. 9-199497 attempts to improve the characteristics of the thermal oxide film by annealing the thermal oxide film in a hydrogen atmosphere or an argon atmosphere. However, the structure of the interface between the oxide film and the silicon carbide substrate is not improved.
[0021]
An object of the present invention is to reduce the fine irregularities such as polishing scratches on the surface of the silicon carbide substrate without using hydrogen gas or hydrogen chloride gas, and to form a surface with extremely good flatness.
[0022]
Another object of the present invention is to provide an oxide film-coated substrate suitable for an electronic device by reducing fine irregularities at the interface between the silicon carbide substrate and the oxide film when an oxide film is provided on the silicon carbide substrate. is there.
[0023]
[Means for Solving the Problems]
  The present invention relates to a method for manufacturing a silicon carbide substrate having a flat surface.It is related.
[0024]
  In the present invention, a substrate made of silicon carbide is used as 10 ^-2 Under atmospheric pressure below Torr or 10 ^-2 Heat treatment is performed at a temperature of 1200 ° C. or higher and 2200 ° C. or lower in an inert gas atmosphere of 7600 Torr to Torr to generate a carbon layer on the surface of the substrate (carbon layer generating step).
[0025]
  And carbon layerOxidationByRemove,By etching the surface of the silicon carbide substrate after removing the carbon layer, a silicon carbide substrate having a flat surface is obtained (etching step). thisOn the surfaceMade of wide band gap semiconductorEpitaxial film is formed(Film formation process).
[0026]
  By this methodEpitaxial filmObtainable.
[0027]
The present invention also provides a substrate made of silicon carbide with 10^-2Under atmospheric pressure below Torr or 10^-2A carbon layer generating step of generating a carbon layer on the surface of the substrate by heat treatment at a temperature of 1200 ° C. or higher and 2200 ° C. or lower in an inert gas atmosphere of 7600 Torr from Torr;
  The carbon layerOxidationByRemoveCarbon layer removal step,
  Next, an etching step of obtaining a silicon carbide substrate having a flat surface by etching the surface of the silicon carbide substrate after removing the carbon layer,and
  On the surfaceMade of wide band gap semiconductorThe present invention relates to a method for manufacturing an epitaxial film-coated substrate, comprising a film forming step for forming an epitaxial film.
[0028]
  By this methodEpitaxial film coated substrateIs obtained.
[0029]
According to the above-described method, polishing scratches on the surface of the silicon carbide substrate can be almost eliminated, and a flat surface can be formed on the atomic order. Moreover, this treatment process is revolutionary in that it does not require hydrogen or hydrogen chloride.
[0030]
  An oxide film-covered substrate comprising a silicon carbide substrate and an oxide film provided on the silicon carbide substrateTo manufacture,
  10 base materials made of silicon carbide^-2Under atmospheric pressure below Torr or 10^-2A heat treatment is performed at a temperature of 1200 ° C. or higher and 2200 ° C. or lower in an inert gas atmosphere from Torr to 7600 Torr to generate a carbon layer on the surface of the substrate. An oxide film is generated by oxidizing the carbon layer.
[0031]
  By this method, an oxide film coated substrateIs obtained.
[0032]
  This wayAccording to the present invention, when an oxide film is provided on a silicon carbide substrate, fine irregularities at the interface between the silicon carbide substrate and the oxide film can be reduced, and an oxide film-coated substrate suitable for an electronic device can be provided.
[0033]
  This wayBy, Height difference when the surface of the silicon carbide substrate is measured with an atomic force microscopeThe5nm or lessAnd can.
[0034]
Thus, an oxide film-coated substrate in which fine unevenness at the interface between the silicon carbide substrate and the oxide film is reduced is suitable as an electronic element. In particular, since the charge trap level along the interface between the oxide film and the substrate is reduced, a high-performance electronic device can be provided.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail. FIG. 1 is a schematic diagram for explaining the process of the present invention.
[0036]
As shown to Fig.1 (a), the base material 1A which consists of silicon carbide is prepared. The surface 2 of the substrate 1 is a polished surface. Here, the crystal system of silicon carbide may be a 6H, 3C, or 4H system. Moreover, it is preferable that the density of silicon carbide is substantially theoretical density. At this time, the surface 2 of the substrate 1 typically has a number of polishing scratches.
[0037]
The crystal plane of the surface 2 is not particularly limited, and may be a Si (0001) plane or a C (000-1) plane. Moreover, it may be the following crystal plane.
(11-20) plane, (1-102) plane
[0038]
Base material 1 made of silicon carbide 10^-2Under atmospheric pressure below Torr or 10^-2In an inert gas atmosphere from Torr to 7600 Torr, heat treatment is performed at a temperature of 1200 ° C. or higher and 2200 ° C. or lower to generate a carbon layer 4 on the surface of the substrate 1 as shown in FIG. Process). Next, when carbon layer 4 is removed (carbon layer removing step), silicon carbide substrate 7 as shown in FIG. 1D is obtained. The surface 8 of the substrate 7 has a flat surface on the atomic order.
[0039]
In the carbon layer generation step, the base material 1 is 10^-2Under atmospheric pressure below Torr or 10^-2By performing heat treatment at a temperature of 1200 ° C. or higher and 2200 ° C. or lower in an inert gas atmosphere from Torr to 7600 Torr, the Si component is sublimated in a vacuum, disappears from the substrate surface, and a carbon layer remains. The form of carbon is not particularly limited, and may be graphite, carbon nanotube, or carbon nanohorn. This process was first reported in (M. Kusunoki et. Al. “Applied physics letters” Vol. 71, Number 18, 3November 1997, pages 2620 to 2622).
[0040]
In the carbon layer generation step, the heating temperature is more preferably 1200 ° C. or higher from the viewpoint of promoting the generation of the carbon layer.
[0041]
The carbon layer generation process is 10^-2Can be performed under atmospheric pressure below Torr, or 10^-2It can be carried out in an inert gas atmosphere from Torr to 7600 Torr.
[0042]
Carbon layer generation process is 10^-2The advantage of performing under atmospheric pressure below Torr is that the disappearance of Si from the substrate surface can be promoted and the carbon layer formation rate can be increased. Although there is no lower limit of the atmospheric pressure, from a practical viewpoint, 10^-10It is preferably at least Torr.
[0043]
On the other hand, if the carbon layer formation rate is too high, the rearrangement of silicon carbide surface atoms cannot follow, and irregularities may remain on the surface. Therefore, by thermally decomposing the substrate surface in an inert gas atmosphere, it is possible to rearrange the atoms on the silicon carbide surface to be flat by suppressing the disappearance of Si and reducing the carbon layer formation rate. . The pressure at that time is 10^-27600 Torr from Torr is suitable. What is necessary is just to change a pressure according to a surface orientation, an impurity, the surface roughness before a process, and the quantity of a polishing flaw. As the inert gas, nitrogen or argon gas is preferable.
[0044]
The thickness of the carbon layer 4 is not particularly limited. From the viewpoint of promoting the surface smoothing of the substrate, the thickness of the carbon layer 4 is preferably 10 nm or more. The upper limit of the thickness of the carbon layer 4 is not particularly limited, but it is difficult to make it thicker to some extent, and it may be practically 200 nm or less.
[0045]
Next, by removing the carbon layer 4, a flat surface 8 is obtained. This removal method is not particularly limited. However, in a preferred embodiment, the carbon layer 4 is thermally oxidized to produce CO or CO₂Removed from the substrate surface.
[0046]
The thermal oxidation of the carbon layer 4 is performed by heating in an oxygen-containing atmosphere. The temperature at this time is preferably 1300 ° C. or less, and thereby the carbon layer 4 is removed.
[0047]
The heating temperature is preferably 600 ° C. or higher, and more preferably 1100 ° C. or higher, from the viewpoint of promoting the disappearance of carbon due to thermal oxidation of the carbon layer.
[0048]
The kind of oxygen-containing atmosphere is not particularly limited, and may be air or pure oxygen. Moreover, any mixture of oxygen and an inert gas may be used. Examples of the inert gas include nitrogen, argon, helium, and carbon dioxide.
[0049]
When the carbon layer 4 is thermally oxidized, a thin oxide film 6 is usually formed on the surface of the substrate 1 as shown in FIG. The formation rate of the oxide film 6 varies depending on the thermal oxidation processing time and the plane orientation of the substrate. For example, on the Si surface, an oxide film having a maximum thickness of 300 nm can be formed by thermal oxidation at 1100 ° C. for 12 hours. Also, the oxidation rate on the C surface is faster than that on the Si surface, and it is oxidized up to 500 nm under the same conditions. Depending on the thickness of the carbon layer before thermal oxidation, the oxide film thickness of the silicon carbide substrate can vary.
[0050]
In this way, oxide film-covered substrate 9 including silicon carbide substrate 1 and oxide film 6 formed on the surface of substrate 1 is obtained. Using this oxide film-coated substrate 9, an electronic device can be constructed as will be described later.
[0051]
The oxide film 6 is mainly composed of silicon atoms and oxygen atoms, and is considered to be composed of silicon oxide. However, carbon in silicon carbide may be slightly mixed in the oxide film. Further, the thinner the oxide film 6, the higher the capacitance as a capacitor. Therefore, it is preferable that the oxide film 6 be thin as long as the insulating property can be maintained. In consideration of insulation, the thickness is preferably 1 nm or more. From a manufacturing point of view, it seems to be 500nm or less.
[0052]
Alternatively, the smooth surface 8 can be exposed by etching the oxide film 6. Although this etchant is not limited, hydrofluoric acid, ammonium fluoride aqueous solution, and potassium fluoride aqueous solution are preferable, and hydrofluoric acid is particularly preferable.
[0053]
The roughness of the obtained surface 8 is not limited. However, it is preferably 5 nm or less, more preferably 3 nm or less, when measured with an atomic force microscope (AFM).
Specifically, the substrate surface 8 is observed with an atomic force microscope to obtain a profile of the surface 8. Then, using the scale attached to the microscope, the height difference in the scan range of 2000 nm is measured. This height difference corresponds to the roughness of the surface 8.
[0054]
Depending on the crystal plane of the substrate surface 8, particularly when the crystal plane of the surface 8 is a Si plane, the profile of the surface 8 by an atomic force microscope includes a terrace and a step between the terraces. May be observed. In this case, the size of the step between adjacent terraces (step height) is preferably 5 nm or less, and more preferably 3 nm or less.
[0055]
When the surface of the silicon carbide substrate obtained by the method of the present invention was observed with an atomic force microscope, no regular irregularities were found. Depending on the crystal plane of the substrate surface 8, a terrace having a width of about 200 to 300 nm was observed, but no particular period was found on this terrace. Thus, it is considered that it is preferable from the viewpoint of relaxing the lattice mismatch with the upper epitaxial film that the period is not found in the unevenness.
[0056]
The use of the silicon carbide substrate of the present invention is not particularly limited, and can be used as various members that require a smooth surface. In a preferred embodiment, an epitaxial film can be formed on the surface of the silicon carbide substrate. The material of the epitaxial film may be any of a conductor, a semiconductor, and an insulator. In a particularly preferred embodiment, a semiconductor film is epitaxially grown on the surface of the silicon carbide substrate.
[0057]
The type of such a semiconductor is not limited, but is preferably a wide band gap semiconductor, particularly aluminum nitride, gallium nitride, and a mixed compound of aluminum nitride and gallium nitride (Al_xGa_1-xN), zinc oxide is preferred. Examples of film forming methods include chemical vapor deposition, molecular beam epitaxy, organometallic chemical vapor deposition, vapor deposition, and sputtering.
[0058]
Moreover, the use of the oxide film-coated substrate 9 of the present invention is not limited. However, an electronic device using an oxide film as an insulating film is preferable. Examples of such an electronic element include an insulating element that uses an oxide film as an insulating film and a transistor that uses an oxide film as a gate electrode.
[0059]
For example, as shown in the schematic diagram of FIG. 8, the oxide film-coated substrate of the present invention can be used as a material for the MOSFET 10. The MOSFET 10 of this example includes a silicon carbide substrate 11, a source electrode 12 formed on the surface of the substrate 11, and a drain electrode 13. The oxide film 15 of the present invention is formed on a part of the surface 11 a of the substrate 11, and the gate electrode 14 is provided on the oxide film 15. The oxide film 15 acts as an insulating film, and carriers move as indicated by an arrow A from the source 12 toward the drain 13. Here, in the oxide film-coated substrate of the present invention, there are few fine irregularities due to polishing flaws at the interface 17 between the substrate 11 and the oxide film 15, which reduces the charge trap level for carrier movement. The
[0060]
【Example】
[Example 1]
10^-2Silicon carbide substrate 1 was housed in a furnace that can be evacuated to Torr or less. The base material 1 was a 6H—SiC (0001) substrate, and the Si surface 2 was processed. When the roughness of the surface 2 was observed with an atomic force microscope, high-density and fine polishing scratches were observed. FIG. 2 shows this image. The depth of the polishing scratch was 10 to 50 nm. Further, a reflection high-energy electron diffraction (RHEED) photograph was taken on the surface 2 of the substrate 1 from the [11-20] direction. The result is shown in FIG. The three diffractive rods correspond to (0-1), (00), and (01) in order from the left.
[0061]
(Carbon layer generation process)
The inside of the furnace was heated at 500 ° C./h and heated at 1700 ° C. for 4 hours. During heating, a vacuum was drawn with a rotary pump and an oil diffusion pump. Thereby, the carbon layer 4 was produced. The carbon layer 4 in this example is mainly made of graphite. A reflection high-energy electron diffraction (RHEED) photograph of the carbon layer 4 was taken in the same manner as described above. The result is shown in FIG. In FIG. 6, it can be seen that each diffractive rod is thinner than in FIG. 5, and the flat terrace region at the atomic level is larger. The reason why the distance between the diffractive rods is changed as compared with FIG. 5 is that a carbon layer is newly formed on the surface. The lattice constant of silicon carbide is 3.07 angstroms, and the lattice constant of graphite is 2.46 angstroms. Since the lattice constant of graphite is smaller than that of silicon carbide, the distance between the diffraction rods of graphite is larger on the diffraction pattern representing the reciprocal space.
[0062]
(Carbon layer removal process)
Thereafter, the sample was held in a tubular furnace at 1150 ° C. for 10 hours, and thermally oxidized while flowing 100 cc of oxygen gas containing saturated water vapor per minute, thereby producing a thermal oxide film 6 shown in FIG. . The oxide film 6 was mainly composed of silicon atoms and oxygen atoms. The thickness of the oxide film was about 25 nm.
[0063]
Next, the sample was immersed in a 5% aqueous hydrofluoric acid solution at room temperature for 10 minutes. The surface 8 of the substrate thus treated was observed again with an atomic force microscope. The result is shown in the upper left photograph of FIG. A terrace having a width of 200 to 300 nm was formed in the [11-20] direction, and the step height was 1.5 nm. The right column of FIG. 3 shows the form of irregularities when viewed along the line of the photograph.
[0064]
Further, a reflection high-energy electron diffraction (RHEED) photograph was taken on the surface 8 of the substrate in the same manner as described above. The result is shown in FIG. In FIG. 7, it can be seen that each diffractive rod is thinner than in FIG. 5, and the surface irregularities are reduced to the atomic level. Moreover, the space | interval between diffractive rods is the same as that of FIG. 5, and it turns out that silicon carbide is exposed.
[0065]
[Example 2]
The silicon carbide base material was housed in the same furnace as in Example 1 in a nitrogen atmosphere of 760 Torr. This base material was a 6H—SiC (0001) substrate, but its C surface was treated.
[0066]
(Carbon layer generation process)
Heat treatment was performed at 1900 ° C. for 4 hours. A vacuum pump is not used during heating. A carbon layer was formed on the surface by this heat treatment. When the cross section was observed with an electron microscope, the carbon layer was mainly formed of graphite. The film thickness of the carbon layer was about 100 nm. On the other hand, when the C-plane substrate was heat-treated in vacuum at 1900 ° C. for 4 hours for comparison, carbon nanotubes were formed with a thickness of about 350 nm. By heating in a nitrogen atmosphere, the carbon layer formation rate could be suppressed.
[0067]
(Carbon layer removal process)
The heat-treated substrate was thermally oxidized in a tubular furnace at 1150 ° C. for 3 hours while flowing 100 cc of oxygen gas containing saturated water vapor per minute. This oxide film was mainly composed of silicon atoms and oxygen atoms. The thickness of the oxide film was about 40 nm.
[0068]

Next, the sample was immersed in a 5% aqueous hydrofluoric acid solution at room temperature for 10 minutes. The surface of the substrate thus processed was observed with an atomic force microscope. The result is shown in FIG. No steps as observed on the Si surface were observed. However, the height difference of the surface profile was within 2 nm in the 2000 nm scan range.
[0069]
[Example 3]
About 0.2 μm of AlN was formed on the surface 8 of the silicon carbide substrate manufactured in Example 1 by molecular beam epitaxy (MBE). The unevenness of the AlN surface was 3 nm or less. An atomic force microscope image of the AlN film is shown on the left side of FIG. Moreover, the cross-sectional roughness curve of the dotted line part of an atomic force microscope image is shown on the right side of FIG.
[0070]
The substrate 6H—SiC has a hexagonal crystal, and the lattice constants thereof are a = 3.07 angstroms and c = 15.1 angstroms. On the other hand, AlN has a hexagonal wurtzite type crystal system, and the lattice constants thereof are a = 3.11 angstroms and c = 4.98 angstroms. The lattice mismatch in the a-axis is 1.3%. By smoothing the surface of the silicon carbide substrate, a good AlN epitaxial film could be generated.
[0071]
In addition, a gallium nitride film was formed instead of the aluminum nitride film, and the same results as above were obtained.
[0072]
[Example 4]
10^-2Silicon carbide substrate 1 was housed in a furnace that can be evacuated to Torr or less. The base material 1 was a 6H—SiC (0001) substrate, and the Si surface 2 was processed. This substrate is the same as in Example 1.
[0073]
(Carbon layer generation process)
The inside of the furnace was heated at 500 ° C./h and heated at 1700 ° C. for 4 hours. During heating, a vacuum was drawn with a rotary pump and an oil diffusion pump. Thereby, the carbon layer 4 was produced. The carbon layer 4 in this example is mainly made of graphite. As a result of taking a reflection high-energy electron diffraction (RHEED) photograph of the carbon layer 4 in the same manner as described above, the same result as in Example 1 was obtained.
[0074]
(Thermal oxide film generation process)
Thereafter, the sample was held at 1150 ° C. for 12 hours in a tubular furnace, and thermally oxidized while flowing 100 cc of oxygen gas containing saturated water vapor per minute. As a result, an oxide film mainly composed of Si atoms and oxygen atoms was obtained. The thickness of the oxide film was about 30 nm.
[0075]
(Thermal oxide film removal process)
The thermal oxide film was removed by etching in the same manner as in Example 1. About the obtained sample, as a result of performing the same measurement as Example 1, the result similar to Example 1 was obtained. In particular, a terrace with a width of 200 to 300 nm was formed in the [11-20] direction, and the step height was 0.7 to 2.3 nm. As described above, the lattice constant of silicon carbide in the c-axis direction is 15.1 angstroms (1.51 nm), and this step height is half to 1.5 times as high as the unit cell of silicon carbide. It is thought that it corresponds to.
[0076]
【The invention's effect】
As described above, according to the present invention, fine unevenness such as polishing scratches on the surface of the silicon carbide substrate is reduced without using hydrogen gas or hydrogen chloride gas, and a surface with extremely good flatness is formed. be able to.
[0077]
In addition, according to the present invention, when an oxide film is provided on a silicon carbide substrate, it is possible to reduce fine irregularities at the interface between the silicon carbide substrate and the oxide film and provide an oxide film-coated substrate suitable for an electronic device. it can.
[Brief description of the drawings]
FIGS. 1A, 1B, 1C and 1D are explanatory views of a surface treatment process of a silicon carbide substrate according to the present invention.
FIG. 2 shows an atomic force micrograph of the surface 2 of the substrate 1 before treatment.
FIG. 3 shows an atomic force micrograph of a surface 8 of a silicon carbide substrate and a cross-sectional roughness curve.
FIG. 4 shows an atomic force micrograph and a cross-sectional roughness curve of an epitaxial film formed on surface 8 of a silicon carbide substrate.
FIG. 5 shows a reflection high-energy electron diffraction (RHEED) photograph of the surface 2 of the substrate 1 before treatment.
6 shows a reflection high-energy electron diffraction (RHEED) photograph of the carbon layer 4. FIG.
FIG. 7 shows a reflection high-energy electron diffraction (RHEED) photograph of the surface 8 of the substrate.
FIG. 8 is a schematic view showing a MOSFET 10 using the oxide film-coated substrate 10 of the present invention.
FIG. 9 shows an atomic force micrograph of a surface 8 of a silicon carbide substrate and a cross-sectional roughness curve.
[Explanation of symbols]
1 Base material made of silicon carbide before treatment 2 Surface of base material 1
4 Carbon layer 6, 15 Oxide film 7, 11 Silicon carbide substrate
8, 11a Surface of silicon carbide substrate 7 9 Oxide film coated substrate
10 MOSFET 17 Interface between oxide film and silicon carbide substrate

Claims (6)

A substrate made of silicon carbide ¹⁰ -2 Torr or less under atmospheric pressure or ¹⁰ -2 Torr 1200 ° C. or higher in an inert gas atmosphere of 7600Torr from, heat treatment at 2200 ° C. below the temperature on the surface of the substrate A carbon layer generating step for generating a carbon layer;
Removing the carbon layer by oxidizing the carbon layer;
Etching process for obtaining a silicon carbide substrate having a flat surface by etching the surface of the silicon carbide substrate from which the carbon layer has been removed , and forming an epitaxial film made of a wide band gap semiconductor on the surface The manufacturing method of an epitaxial film characterized by having a process. Wherein the carried out in an oxygen-containing atmosphere at a temperature of 1300 ° C. or less oxidation method of claim 1, wherein. And performing said etching by hydrofluoric acid, the process of claim 1. A substrate made of silicon carbide ¹⁰ -2 Torr or less under atmospheric pressure or ¹⁰ -2 Torr 1200 ° C. or higher in an inert gas atmosphere of 7600Torr from, heat treatment at 2200 ° C. below the temperature on the surface of the substrate A carbon layer generating step for generating a carbon layer;
Removing the carbon layer by oxidizing the carbon layer;
An etching process for obtaining a silicon carbide substrate having a flat surface by etching the surface of the silicon carbide substrate from which the carbon layer has been removed, and an epitaxial film made of a wide band gap semiconductor on the surface of the silicon carbide substrate. A method for producing an epitaxial film-coated substrate, comprising a film forming step of forming a film. Wherein the carried out in an oxygen-containing atmosphere at a temperature of 1300 ° C. or less oxidation method of claim 4. The method according to claim 4 , wherein the etching is performed with hydrofluoric acid.

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