JP2006066722A - EPITAXIAL SiC FILM, MANUFACTURING METHOD THEREFOR AND SiC SEMICONDUCTOR DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an epitaxial SiC film having no step bunching at its surface, and to provide a device that uses the film wherein a leak current is low and mobility of an MOS interface is high. <P>SOLUTION: In the epitaxial SiC film grown on the off-cut plane of an SiC substrate in a hexagonal crystal structure, the off-cut plane of the SiC substrate has an off-cut angle of ≥0.5° and ≤10°, from a face (0001); and the crystal direction of the off-cut plane is one direction of ≤±7.5°, from any one among 12 kinds of equivalent <21-30> directions ([21-30], [-2-130], [2-310], [-23-10], [12-30], [-1-230], [1-320], [-13-20], [-3120], [3-1-20], [-3210] and [3-2-10]) of the SiC substrate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a single crystal epitaxial substrate of SiC, a manufacturing method thereof, and a semiconductor device manufactured thereon.

  In recent years, research on semiconductors (compound semiconductors) made of light element compounds such as silicon carbide (SiC, silicon carbide) or gallium nitride (GaN) has been actively conducted. Since compound semiconductors are compounds of light elements such as N and C, their binding energy is very strong compared to Si semiconductors. Therefore, it has the advantages and characteristics of a large energy forbidden band (band gap), dielectric breakdown electric field, and thermal conductivity. In particular, taking advantage of the large forbidden bandwidth (wide band gap), materials for high-efficiency and high-voltage electronic devices and their elements (power devices), high-frequency power devices, high-temperature operating devices, or devices emitting blue to ultraviolet light Has attracted attention as.

  In order to use such a compound semiconductor, for example, SiC as a semiconductor device (element), it is necessary to obtain a high-quality single crystal having a certain size. However, as described above, many compound semiconductors such as SiC have a strong binding energy (about 4.5 eV between Si and C), and therefore do not melt even at high temperature at atmospheric pressure and sublimate at 2000 ° C. or higher. For this reason, a method of obtaining a large single crystal upon recrystallization when the melt is solidified by irradiation with an excimer laser used in other semiconductor materials such as silicon (Si), that is, by recrystallization of the melt. Growth of bulk crystals is difficult. Therefore, conventionally, a single piece of SiC single crystal has been obtained by a method using a chemical reaction called the Atchison method and a method using a sublimation recrystallization method called the Rayleigh method.

  Recently, a SiC ingot was grown by a modified Rayleigh method in which a silicon carbide single crystal produced by these methods was used as a substrate and sublimated and recrystallized thereon, and the grown SiC ingot was sliced and sliced. The wafers (substrates of various semiconductor elements including diodes) have been manufactured by mirror polishing. Furthermore, it is possible to grow a SiC single crystal of a target scale on this wafer by vapor phase epitaxial growth or liquid phase epitaxial growth, and to form an active layer with controlled impurity density and film thickness. And SiC semiconductor devices (semiconductor element), such as a pn junction diode, a Schottky diode, and various transistors, were produced using SiC manufactured by such a method (nonpatent literature 1).

However, among the above methods, the Atchison method heats a mixture of silica and coke in an electric furnace and precipitates crystals by spontaneous nucleation, so there are many impurities and it is difficult to control the shape and crystal plane of the crystals obtained. It is. In the Rayleigh method, crystals grow due to spontaneous nucleation, making it difficult to control the crystal shape and crystal plane.
In the modified Rayleigh method, for example, in the invention of Japanese Patent Publication No. 59-48792 (Patent Document 1), a large SiC ingot composed of a single crystal polymorph is obtained. However, large defects called micropipes (small holes penetrating in the <0001> axial direction) are usually included in the crystal at a density of about 1 to 50 cm ⁻² (hereinafter, the display is omitted according to common usage). Yes. Further, there are about 10 ³ to 10 ⁴ cm ^{−2 of} screw dislocations having Burgers vectors in the C-axis direction.

Usually, a SiC {0001} plane or a substrate having an off angle of 3 to 8 degrees in the <11-20> direction or the <1-100> direction from this plane is used for epitaxial growth. At this time, it is known that most of the micropipe defects and screw dislocations existing in the substrate penetrate the SiC epitaxial growth layer, and that the device characteristics are remarkably deteriorated if the SiC device manufactured using the epitaxial growth layer contains micropipe defects. It has been.
Therefore, the micropipe defect is the greatest barrier when manufacturing a large capacity (large current, high breakdown voltage) SiC semiconductor device with a high yield.

  Further, the SiC {0001} plane that is usually used, or an off-angle of several degrees (tilt angle between the growth plane and the axis of the basal plane) in the <11-20> direction or the <1-100> direction from this plane When SiC homoepitaxial growth is performed using a SiC wafer, an atomic step aggregation (step bunching) phenomenon easily occurs on the crystal surface.

  That is, the <11-20> or <1-100> direction of this off-cut is a direction perpendicular to two typical cleavage planes of the hexagonal crystal, and these directions tend to break the crystal bond. . Reflecting such characteristics of the crystal structure, the epitaxial layer on the substrate turned off in these directions has the atomic steps on the surface arranged in order in parallel to the off direction. For this reason, when variations in step speed occur, these steps are combined with each other, and a step with a high step is likely to occur.

As the degree of step bunching increases, the surface roughness of the SiC epitaxial growth layer increases and the flatness of the metal-oxide-semiconductor (MOS) interface deteriorates. Therefore, the channel movement of the inversion layer of the MOS field effect transistor (MOSFET) The degree decreases.
In addition, the flatness of the pn junction and the Schottky barrier interface deteriorates, and electric field concentration occurs at the junction interface, causing problems such as a decrease in breakdown voltage and an increase in leakage current.

  Many crystal polymorphs (polytypes) exist in SiC. Among them, 4H type polytype (Ramsdell notation "4H-SiC". H is a hexagonal crystal. The number indicates the number of layers in which the atomic stacking is described, for example, in the above case, the number of layers, for example, four layers, and indicates a crystal structure that constitutes one period. Has a high mobility, and the ionization energy of donors and acceptors is small, it is considered to be an SiC polytype that is optimal for the production of SiC semiconductor devices.

However, the 4H-SiC {0001} plane, or an epitaxial growth layer on the substrate provided with an off angle of several degrees in the <11-20> direction from this plane (Patent Document 2), or several degrees in the <1-100> direction When an inversion MOSFET is manufactured using an epitaxially grown layer (Patent Document 3) on a substrate provided with an off angle, the channel mobility is as very low as about 1 to 20 cm ² / Vs, and a high-performance transistor cannot be realized.

  In order to solve these problems, in Patent Document 4, growth is performed by an improved Rayleigh method using a seed crystal having a surface other than the (0001) plane of SiC, for example, a (1-100) plane. An SiC ingot with a small number of pipes is obtained.

  However, when epitaxial growth is performed on the SiC (1-100) plane, stacking faults are likely to occur during growth, and it is difficult to obtain a high-quality SiC single crystal sufficient for semiconductor device fabrication. On the other hand, it is known that micropipe defects are also reduced by using a SiC (11-20) substrate, but it is not easy to produce a high-quality SiC epitaxial growth layer on a SiC (11-20) substrate. However, distortion due to the difference in impurity density occurs at the interface between the epitaxial growth and the substrate, which adversely affects the crystallinity of the epitaxial growth layer.

Conventionally, the 6H-polytype 6H—SiC (11-20) surface has been studied. However, when a device is fabricated on this surface, anisotropy of electron mobility becomes a problem. That is, in the 6H—SiC crystal, the electron mobility in the <0001> axis direction is as small as about 20 to 30% of the mobility in the <1-100> and <11-20> directions. For this reason, in the device on the 6H—SiC (11-20) plane, anisotropy of 3 to 5 times occurs in the in-plane electrical conduction.
Japanese Examined Patent Publication No.59-48792 U.S. Pat. No. 4,912,064 Japanese translation of PCT publication No. 2003-502857 Japanese Patent No. 2804860 Edited by Hiroyuki Matsunami, "Semiconductor SiC Technology and Applications" published by Nikkan Kogyo Shimbun in March 2003. Chapter 4.

For this reason, it is hoped to develop a manufacturing method by epitaxial growth of an SiC film in which step defects are promoted and such a defect disappears in a grown film formed or formed even when a micropipe or a spiral transition exists in the substrate. It was rare.
Also, it is desired to develop a manufacturing method by epitaxial growth of a SiC film in which the flatness of the epitaxially grown surface is remarkably improved, mixing of different polytypes is completely suppressed, step bunching is suppressed, and a flat epitaxial surface is obtained. It was.

In addition, as a result of the above, it has been desired to realize an epitaxial SiC film or SiC film substrate having high quality and good surface flatness.
Further, it has been desired to realize a wafer (substrate) or device that uses the above SiC film, has no anisotropy, can be used for a large current, and has excellent high pressure resistance.

  The present invention has been made to solve the above problems, and has an off-cut angle of 0.5 ° or more and 10 ° or less from the (0001) plane in the <21-30> crystal direction of the substrate as a SiC substrate. An epitaxial SiC (silicon carbide) film grown on an offcut surface of a hexagonal SiC crystal substrate is used.

In addition, a buffer layer is formed in order to alleviate distortion due to lattice mismatch caused by a difference in impurity density between the substrate and the epitaxial layer.
The buffer layer and the active layer for device fabrication formed thereon are grown using a chemical vapor deposition method with excellent controllability of film thickness and impurity doping and surface flatness of the growth layer. is there.
The contents and effects of each claim will be described below.

The invention according to claim 1 is an epitaxial SiC film grown on an off-cut surface of a SiC substrate having a hexagonal crystal structure,
The off-cut surface of the SiC substrate has an off-cut angle of 0.5 ° to 10 ° from the (0001) plane;
The crystal direction of the off-cut surface is 12 equivalent <21-30> directions of the SiC substrate ([21-30], [-2-130], [2-310], [-23-10] , [12-30], [-1-230], [1-320], [-13-20], [-3120], [3-1-20], [-3210] and [3-2-2] The epitaxial SiC film is oriented in one direction of ± 7.5 ° or less from any direction of [10] direction).

  In the invention of this claim, the off-cut surface of the SiC substrate has an off-cut angle of 0.5 ° or more and 10 ° or less from the (0001) plane, and the crystal direction of the off-cut surface is 12 kinds of the substrate. Since it is configured within ± 7.5 ° from any one of the equivalent <21-30> directions, it becomes a two-dimensional offset angle direction and step bunching is eliminated.

In addition, in a semiconductor device using an epitaxial SiC film grown on such an off-cut surface, leakage current is suppressed and the mobility at the MOS interface is increased.
In addition, since step flow growth is promoted, such defects disappear in the growth film even if micropipe or spiral transition exists in the SiC substrate.

  The invention according to claim 2 is the epitaxial SiC film according to claim 1, wherein the SiC substrate is 4H—SiC.

  Since the SiC substrate is 4H—SiC, the epitaxial growth film is also 4H—SiC. This makes it possible to manufacture high-quality single crystal wafers with high electron mobility, forbidden band width, dielectric breakdown electric field, low electrical conduction anisotropy, and relatively shallow donor and acceptor levels. Can be manufactured.

  A third aspect of the present invention is the epitaxial SiC film according to the first aspect, wherein the SiC film is 6H—SiC.

Since the substrate is 6H—SiC, the epitaxial growth film is also 6H—SiC.
6H-SiC is superior in high-performance MOS transistors because it has higher mobility at the MOS interface (electron mobility at the oxide film-semiconductor interface) than 4H-SiC.

  The invention according to claim 4 is the SiC film, wherein a crystal direction of the off-cut surface is ± 5 ° or less from any one of the 12 kinds of equivalent <21-30> directions. The epitaxial SiC film according to any one of claims 1 to 3, wherein the epitaxial SiC film is directed in one direction.

  Since the crystal direction of the off-cut surface is selected to be narrow, a high quality epitaxial SiC film can be obtained.

  The SiC film according to claim 5, wherein a crystal direction of the off-cut surface is ± 2.5 ° or less from any one of the 12 kinds of equivalent <21-30> directions. 5. The epitaxial SiC film according to claim 1, wherein the epitaxial SiC film is directed in one direction.

  Since the crystal direction of the off-cut surface is selected to be narrower, a higher quality epitaxial SiC film can be obtained.

  The invention according to claim 6 is the SiC film, wherein a crystal direction of the off-cut surface is ± 1.5 ° or less from any one of the 12 kinds of equivalent <21-30> directions. 6. The epitaxial SiC film according to claim 1, wherein the epitaxial SiC film is oriented in one direction.

  An even higher quality epitaxial SiC film can be obtained.

The invention according to claim 7 is the SiC film, wherein the SiC substrate has a micropipe defect or a screw dislocation of 10 cm ⁻² or more, and the epitaxial SiC film includes a buffer layer and a buffer layer. Having an active layer provided thereon,
Further, the buffer layer is a buffer layer grown by chemical vapor deposition, having a thickness of 0.3 to 15 μm and having micropipe defects reduced to 80% or less compared to the SiC substrate. It is an epitaxial SiC film characterized by being.

The buffer layer can alleviate distortion due to lattice mismatch caused by the difference in impurity density between the substrate and the epitaxial layer.
This can be used even if the SiC substrate has some defects, leading to an increase in the degree of freedom in obtaining the substrate.
In addition, since the SiC film formed by epitaxial growth does not have step bunching, it is possible to provide a semiconductor device in which leakage current is suppressed and the mobility at the MOS interface is high.
The thickness of the buffer layer is determined in consideration of the time required for formation, energy, and the function of the buffer layer.

  The invention according to claim 8 is the SiC film, wherein the buffer layer is a buffer layer containing at least one impurity atom of nitrogen, phosphorus, aluminum, and boron. The epitaxial SiC film according to claim 7.

  By including impurity atoms in the buffer layer, lattice matching with a substrate having a high impurity concentration can be improved, and distortion at the interface between the epitaxial film and the substrate can be reduced. By promoting the blockage of the pipe, a high quality epitaxial SiC film can be obtained. Nitrogen, phosphorus, aluminum, and boron are particularly effective as such impurity atoms.

The invention according to claim 9 is the SiC film, wherein the buffer layer contains at least one impurity atom of nitrogen, phosphorus, aluminum, and boron at 2 × 10 ^{15 to} 3 × 10 ¹⁹ cm ^−3. The epitaxial SiC film according to claim 8, wherein the epitaxial SiC film has a density of

  By including the impurity atoms in the buffer layer at a density in the above range, lattice matching with a substrate having a high impurity concentration can be improved, and distortion at the interface between the epitaxial film and the substrate can be reduced. The high-quality epitaxial SiC film can be obtained by promoting the blockage of the micropipe of the substrate by adding impurities. If the impurity concentration is low, the above effect is not exhibited, and if the impurity concentration is too high, there is a problem that crystallinity is deteriorated.

  The invention according to claim 10 is the SiC film, wherein the buffer layer has an impurity atom density of at least one of nitrogen, phosphorus, aluminum, and boron inside the SiC substrate. The SiC epitaxial wafer according to claim 8 or 9, wherein the buffer layer has a density lower than that of the SiC epitaxial wafer.

  Thereby, the lattice mismatch between the SiC substrate and the active layer having a low impurity concentration can be relaxed, and a high-quality epitaxial SiC film can be obtained.

  The invention according to claim 11 is the SiC film, wherein the buffer layer has a density of at least one impurity atom of nitrogen, phosphorus, aluminum and boron in the active layer from the SiC substrate. 11. The epitaxial SiC film according to claim 8, wherein the epitaxial SiC film is a buffer layer that is gradually decreased toward the surface.

Thereby, it is possible to obtain a high-quality epitaxial SiC film with little distortion and flat at the atomic level.
The impurity density can be gradually decreased from the SiC substrate toward the active layer by gradually decreasing the amount of impurity gas added during epitaxial growth.

  The invention according to claim 12 is the epitaxial SiC film according to claim 2, wherein the SiC substrate and the buffer layer are 4H—SiC. .

  As a result, a 4H type epitaxial SiC film that has no anisotropy in mobility and high drift mobility can be obtained.

  The invention according to claim 13 is characterized in that the active layer is an active layer having a thickness of 2 μm or more grown by chemical vapor deposition. It is an epitaxial SiC film.

  Thereby, an epitaxial SiC film capable of realizing a highly efficient semiconductor device having a breakdown voltage and an operating speed that surpasses that of a Si semiconductor device can be obtained.

  A fourteenth aspect of the present invention is a SiC epitaxial wafer comprising the epitaxial SiC film according to any one of the first to thirteenth aspects.

  By using this SiC epitaxial wafer, it is possible to provide a high-efficiency semiconductor device having a breakdown voltage and operating speed that surpasses that of a Si semiconductor device.

  A fifteenth aspect of the present invention is a SiC semiconductor device manufactured using the epitaxial SiC film according to any one of the first to thirteenth aspects.

  The SiC semiconductor device obtained in this way is a SiC semiconductor device excellent in breakdown voltage characteristics and energy saving characteristics, and can provide a high-quality semiconductor electronic component.

  A sixteenth aspect of the present invention is an SiC semiconductor device manufactured using the SiC epitaxial wafer according to the fourteenth aspect.

  The invention according to claim 17 is the SiC semiconductor according to claim 15 or 16, wherein the SiC semiconductor device has a metal / SiC Schottky barrier on a surface thereof. It is a device.

  Thereby, an excellent Schottky diode can be obtained.

  According to an eighteenth aspect of the present invention, the SiC semiconductor device has a pn junction formed by mixing impurity atoms at the time of epitaxial growth or ion implantation of impurity atoms. Item 18. The SiC semiconductor device according to Item 17.

Thereby, an excellent SiC semiconductor device can be obtained.
For ion implantation, ion doping that is accelerated by voltage and implanted is suitable.

  The invention according to claim 19 is the MOS semiconductor device according to claim 19, wherein the SiC semiconductor device has an oxide film formed by thermal oxidation or chemical vapor deposition as a gate insulating film. The SiC semiconductor device according to any one of claims 15 to 18, characterized by:

Thereby, an excellent SiC semiconductor device can be obtained.
Further, since it is an oxide film, it has excellent cost, voltage resistance, corrosion resistance, heat resistance, etc., and there are few problems with waste during production.

  The invention according to claim 20 is the SiC semiconductor device, wherein the SiC semiconductor device has an oxide film formed by thermal oxidation or chemical vapor deposition as a surface protective film or a part thereof. 20. The SiC semiconductor device according to claim 15, wherein the SiC semiconductor device is a semiconductor device.

  Thereby, an element is protected from external force etc., and it becomes a more excellent SiC semiconductor device.

The invention described in claim 21 is an epitaxial SiC film manufacturing method for manufacturing an epitaxial SiC film by growing an epitaxial SiC film on an off-cut surface of a SiC substrate having a hexagonal crystal structure,
The SiC substrate off-cut surface is selected to have an off-cut angle of 0.5 ° or more and 10 ° or less from the (0001) plane,
Further, the crystal orientation of the off-cut surface is the 12 equivalent <21-30> directions ([21-30], [-2-130], [2-310], [-23-10] of the SiC substrate. ], [12-30], [-1-230], [1-320], [-13-20], [-3120], [3-1-20], [-3210] and [3-2] −10] direction), and an off-cut surface selection step for selecting the direction so as to face one direction of ± 7.5 ° or less. .

As a result, step flow growth is promoted by the off-substrate in the above-described direction, so that these defects disappear even if micropipes and screw dislocations are present on the substrate.
In addition, the normal direction of two typical cleavage planes of the (0001) plane, for example, [21-30] of the combined vector of the [11-20] direction and [10-10] vector as specific directions. Since it is turned off in the direction (<21-30> direction in equivalent display), macro undulations of steps occur, and they do not line up in order and in parallel, step bunching is suppressed, and a flat epitaxial surface is formed. can get.
In addition, an epitaxial SiC film having various defects and excellent properties can be efficiently manufactured.

The invention according to claim 22 is the method for manufacturing the SiC film, wherein the SiC substrate selection step is to select a substrate having a micropipe defect or a screw dislocation of 10 cm ⁻² or more as the SiC substrate;
A buffer on which a buffer layer having a thickness of 0.3 to 15 μm and having micropipe defects reduced to 80% or less compared to the SiC substrate is grown by chemical vapor deposition on the SiC substrate. A layer forming step;
The method for producing an epitaxial SiC film according to claim 21, further comprising an active layer forming step of forming an active layer on the buffer layer.

  Thereby, distortion due to lattice mismatch caused by the difference in impurity density between the substrate and the epitaxial layer is alleviated, and an excellent epitaxial SiC film can be manufactured.

  The invention according to claim 23 is the method for manufacturing the SiC film, comprising a donor addition step in which the buffer layer contains at least one impurity atom of nitrogen, phosphorus, aluminum, and boron. A method for producing an epitaxial SiC film according to claim 21 or claim 22.

The invention according to claim 24 is the method for producing the SiC film, wherein impurity atoms are included at a density of 2 × 10 ^{15 to} 3 × 10 ¹⁹ cm ⁻³ by the donor addition step. 24. A method for producing an epitaxial SiC film according to claim 23.

  The invention according to claim 25 is the method of manufacturing the SiC film, wherein the donor addition step is performed such that a density of at least one impurity atom of nitrogen, phosphorus, aluminum, and boron in the buffer layer is 25. The method for producing an epitaxial SiC film according to claim 23 or 24, which is a concentration-controlled donor addition step controlled so as to be lower than an impurity density in the SiC substrate.

  The invention according to claim 26 is the method for manufacturing the SiC film, wherein the donor addition step is performed such that a density of at least one impurity atom of nitrogen, phosphorus, aluminum, and boron in the buffer layer is 26. The epitaxial SiC film according to claim 23, which is a concentration gradient control type donor addition step that is controlled so as to be gradually decreased from the SiC substrate toward the active layer. It is a manufacturing method.

  According to the present invention, unlike the conventional step flow in the <11-20> direction and the <1-100> direction off, that is, in the one-dimensional (eg, X-axis direction) off direction, the direction is between these directions. Therefore, it becomes a two-dimensional off direction, and many kinks are formed along the step, migration is promoted in two dimensions (that is, not only in the X axis but also in the Y axis), and the step flow is performed even at a low off angle. Growth can be realized and a flat epitaxial film can be obtained.

  Further, since there is no step bunching on the epitaxial growth surface, the flatness of the growth surface is remarkably improved, and mixing of different polytypes is completely suppressed. Therefore, a device formed using this SiC film has a pn junction or a shot. Concentration of the electric field at the key barrier interface is greatly reduced, and it becomes easy to increase the breakdown voltage of the device.

Further, since leakage current is suppressed and mobility at the MOS interface is increased, a high-quality SiC semiconductor device is obtained.
Further, since the interface state at the oxide film / SiC MOS interface is reduced, a high-quality MOS interface can be produced, and a high-performance MOS transistor can be realized.
That is, an epitaxial SiC film having high quality and good surface flatness can be produced, and a high-performance power device, a high-frequency device, a high-temperature device, etc. can be produced by using this SiC film.

  Hereinafter, the present invention will be described based on the best mode. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

  Example 1 has an off-cut angle of 8 ° from the (0001) plane in the <21-30> crystal direction in order to investigate the penetration of the micropipe from the SiC substrate to the SiC epitaxial growth layer and the flatness of the growth surface. An n-type SiC layer is grown on a 4H—SiC substrate by a chemical vapor deposition (CVD) method.

  For comparison, evaluation is also performed by simultaneously growing SiC layers on SiC substrates in the <11-20> direction and the <1-100> direction having an off-cut angle of 8 ° from the (0001) plane of 4H—SiC. did.

The SiC substrate was prepared by slicing and mirror polishing an ingot grown by the modified Rayleigh method. The SiC substrates are all n-type, the effective donor density determined from the capacitance-voltage characteristics of the Schottky barrier is 1 to 3 × 10 ¹⁸ cm ⁻³ , and the thickness is 400 μm. As a result of etching these SiC substrates with molten potassium hydroxide (KOH) at 500 ° C. for 10 minutes, the micropipe density was 10 to 100 cm ⁻² and the screw dislocation density was 5 × 10 ³ to 2 × 10 ⁴ cm ^−. It was found that there were about ² defects.

  Next, the SiC substrate subjected to KOH etching was repolished, mirror-finished, and subjected to CVD growth on the surface. These substrates were washed with an organic solvent, aqua regia, and hydrofluoric acid, then rinsed with deionized water, placed on a graphite susceptor covered with a SiC film, and set in a CVD growth apparatus.

For CVD growth, a normal pressure horizontal CVD apparatus using hydrogen (H ₂ ) as a carrier gas was used, and the susceptor was heated by high frequency induction heating. After placing the SiC substrate in the reactor, gas replacement and high vacuum evacuation were repeated several times, and then a H ₂ carrier gas was introduced to enter the CVD growth program.

First, vapor phase etching with HCl / H ₂ gas was performed at 1300 ° C., then the temperature was raised to 1500 ° C. and growth was started by introducing source gases (silane: SiH ₄ , propane: C ₃ H _8, etc.). . In CVD growth, an n-type SiC buffer layer having an effective donor density of 3 to 4 × 10 ¹⁷ cm ⁻³ is first grown by 2.6 μm, and then an n-type active layer having an effective donor density of 1 to 2 × 10 ¹⁶ cm ⁻³ is formed. Grow 12 μm. During growth, nitrogen gas was added to control n-type conductivity.
The growth conditions of the buffer layer and the active layer at this time were as follows.

For the buffer layer, the SiH ₄ flow rate is 0.30 sccm, the C ₃ H ₈ flow rate is 0.20 sccm, the N ₂ flow rate is 6 × 10 ⁻² sccm, the H ₂ flow rate is 3.0 slm, the substrate temperature is 1500 ° C., and the growth time. Was 60 minutes.

For the active layer, the SiH ₄ flow rate is 0.50 sccm, the C ₃ H ₈ flow rate is 0.50 sccm, the N ₂ flow rate is 2 × 10 ⁻² sccm, the H ₂ flow rate is 3.0 slm, the substrate temperature is 1500 ° C., and the growth time. Was 180 minutes.

  As a result of observing the sample surface epitaxially grown under the above conditions with a differential interference optical microscope, it was found that a mirror surface was obtained on any surface. However, in the <1-100> direction off substrate, streaky irregularities and grooves partially running in the <11-20> direction were observed. This streak defect can be reduced by optimizing the substrate surface treatment method before the growth or by performing the CVD growth under a low supersaturation growth condition, for example, a low raw material gas flow rate. Still, the range of optimum conditions was narrow.

Next, the result of measuring the surface profile with an atomic force microscope (AFM) is shown in FIG. The photograph on the left is an atomic image of each sample. The lower right indicates the reference density of the surface roughness, and the flatness is better as there is no color shading.
It can be seen that there are stepped irregularities due to atomic step aggregation (step bunching) on the 8 ° off-plane in the <11-20> direction. Step bunching was also observed on the <1-100> direction 8 ° off-plane, and also on the part where the mirror surface was obtained, but the degree of unevenness was small.
On the other hand, on the substrate having an off-cut angle of 8 ° from the (0001) plane in the <21-30> crystal direction, no grooves, hillocks, steps, etc. were observed, and a very flat surface was obtained.

  The root mean square (Rms) of the surface roughness when the range of 2 μm × 2 μm is observed by AFM is 0.24 nm in the <11-20> direction 8 ° off plane, and the <1-100> direction 8 ° off plane. Then, it was 0.19 nm, and it was 0.17 nm in the <21-30> direction 8 ° off-plane. For this reason, the substrate which is 8 ° off in the <21-30> direction was the most excellent.

The grown sample was etched with molten KOH to examine structural defects in the growth layer.
In the growth layer on the 8 ° off-plane in the <11-20> direction, the micropipe density is 18 cm ⁻² and the screw dislocation density is 8 × 10 ³ cm ⁻² , which is almost the same as the value of the substrate before growth and is generated by etching. The positions of the pits were in good agreement with those before the growth.
In the <1-100> direction 8 ° off substrate, the streak defect was further deepened in the portion where the streak defect was seen. Since these streak-like grooves always extend in the <11-20> direction, it is considered to be caused by stacking faults.

On the other hand, when a sample grown on an off-cut surface of 8 ° from the (0001) plane in the <21-30> crystal direction is etched with molten KOH, the density of polygonal pits reflecting dislocations is 2 × 10 ³ cm ^−2. The stacking fault density was as small as 10 cm ⁻¹ or less.
Moreover, it turned out that the micropipe density estimated by etching the surface which carried out the diagonal grinding | polishing of this sample is less than 10 cm ^<-2 >, and a screw dislocation density is also less than 500 cm ^<-2 >.

  That is, by using the <21-30> crystal direction off substrate, it is possible to grow a high quality SiC epitaxial crystal that suppresses the penetration of micropipes and screw dislocations from the substrate and has very few stacking faults. This is because, in the <21-30> crystal direction, a number of kinks are formed along the steps, migration is promoted in two dimensions (that is, not only in the X axis but also in the Y axis), and stable step flow growth is achieved. It is because it is realizable.

  Next, in order to confirm whether or not the same effect can be obtained even in an equivalent direction, the same method as in Example 1 was used except that a substrate that was 8 ° off in the <3-1-20> direction was used. did. As a result, the root mean square (Rms) of the surface roughness when observed with AFM was 0.18 nm. This value is substantially the same plane roughness as the root mean square of 0.17 nm when the <21-30> direction is 8 ° off, and even in the <3-1-20> direction 8 ° off substrate. It was confirmed that the effects described in the present specification were obtained.

Example 2 has the same conditions as Example 1 except for the off-cut angle.
Epitaxial growth was performed by gradually reducing the off-cut angle from 8 ° to 0.5 °, and it was examined how the off-cut angle changed with a change in the off-cut angle.
First, it was confirmed that a mirror surface was obtained at the naked eye level when the off-cut angle was about 4 °, even when turned off in any direction from the (0001) plane. Next, evaluation was performed by reducing the off-cut angle to 0.5 °.
Specifically, an n-type SiC layer was grown by chemical vapor deposition (CVD) on a substrate having an off-cut angle of 0.5 ° from the (0001) plane in the <21-30> crystal direction. As a result, as in Example 1, a mirror surface was obtained.

On the other hand, for comparison, the 4H-SiC (0001) plane <11-20> direction 0.5 ° offcut plane and the 4H-SiC (0001) plane <1-100> direction 0.5 ° offcut plane are also used. Grown at the same time. However, no mirror surface was obtained.
This indicates that in the comparative example, step flow growth cannot be sufficiently realized if the off-cut direction is small.

  In Example 3, the direction of the off-cut surface is turned off in the directions deviated by 7.5 °, 5 °, 2.5 °, and 1.5 ° from the equivalent direction to the <21-30> crystal direction. The same epitaxial growth was performed.

  As a result, the root mean square (Rms) of the surface roughness when AFM observation of the 2 μm × 2 μm range was 7.5 °, 5 °, 2.5 °, and 1.5 °, respectively, 0.23 nm, It was 0.20 nm, 0.18 nm, and 0.17 nm, and the smaller the deviation from the <21-30> crystal direction, the flatter the surface.

It is a figure which shows the result of having measured the surface shape profile about the SiC film of Example 1 with an atomic force microscope (AFM).

Claims (26)

An epitaxial SiC film grown on an off-cut surface of a SiC substrate having a hexagonal crystal structure,
The off-cut surface of the SiC substrate has an off-cut angle of 0.5 ° to 10 ° from the (0001) plane;
The crystal direction of the off-cut surface is 12 equivalent <21-30> directions of the SiC substrate ([21-30], [-2-130], [2-310], [-23-10] , [12-30], [-1-230], [1-320], [-13-20], [-3120], [3-1-20], [-3210] and [3-2-2] The epitaxial SiC film is oriented in one direction of ± 7.5 ° or less from any direction of [10] direction).   The epitaxial SiC film according to claim 1, wherein the SiC substrate is 4H—SiC.   The epitaxial SiC film according to claim 1, wherein the SiC substrate is 6H—SiC.   The crystallographic direction of the off-cut surface is oriented in one direction of ± 5 ° or less from any one of the 12 types of equivalent <21-30> directions. Item 4. The epitaxial SiC film according to any one of Items 3.   2. The crystal direction of the off-cut surface is directed to one direction of ± 2.5 ° or less from any one of the 12 types of equivalent <21-30> directions. The epitaxial SiC film according to claim 4.   2. The crystal direction of the off-cut surface is directed to one direction of ± 1.5 ° or less from any one of the 12 types of equivalent <21-30> directions. The epitaxial SiC film according to claim 5. The SiC substrate has a micropipe defect or a screw dislocation of 10 cm ⁻² or more,
Further, the epitaxial SiC film has a buffer layer and an active layer provided on the buffer layer,
Further, the buffer layer is a buffer layer grown by chemical vapor deposition, having a thickness of 0.3 to 15 μm and having micropipe defects reduced to 80% or less compared to the SiC substrate. An epitaxial SiC film characterized by being.   8. The epitaxial SiC film according to claim 1, wherein the buffer layer is a buffer layer containing at least one impurity atom of nitrogen, phosphorus, aluminum, and boron. 9. The buffer layer according to claim 8, wherein the buffer layer includes at least one impurity atom of nitrogen, phosphorus, aluminum, and boron at a density of 2 × 10 ^{15 to} 3 × 10 ¹⁹ cm ^−3. The epitaxial SiC film described.   9. The buffer layer according to claim 8, wherein the density of at least one impurity atom of nitrogen, phosphorus, aluminum, and boron in the buffer layer is lower than the density of impurity atoms in the SiC substrate. The SiC epitaxial wafer according to claim 9.   The buffer layer is a buffer layer in which the density of at least one impurity atom of nitrogen, phosphorus, aluminum, and boron therein is gradually decreased from the SiC substrate toward the active layer. The epitaxial SiC film according to claim 8.   12. The epitaxial SiC film according to claim 2, wherein the SiC substrate and the buffer layer are 4H—SiC. 13.   The epitaxial SiC film according to any one of claims 1 to 12, wherein the active layer is an active layer having a thickness of 2 µm or more grown by a chemical vapor deposition method.   An SiC epitaxial wafer comprising the epitaxial SiC film according to claim 1.   A SiC semiconductor device manufactured using the epitaxial SiC film according to any one of claims 1 to 13.   A SiC semiconductor device manufactured using the SiC epitaxial wafer according to claim 14.   The SiC semiconductor device according to claim 15 or 16, wherein the SiC semiconductor device has a metal / SiC Schottky barrier on a surface thereof.   18. The SiC semiconductor device according to claim 15, wherein the SiC semiconductor device has a pn junction formed by mixing impurity atoms during epitaxial growth or ion implantation of impurity atoms. Semiconductor device.   The SiC semiconductor device according to any one of claims 15 to 18, wherein the SiC semiconductor device is a MOS type SiC semiconductor device having an oxide film formed by thermal oxidation or chemical vapor deposition as a gate insulating film. SiC semiconductor device.   20. The SiC semiconductor device according to any one of claims 15 to 19, wherein the SiC semiconductor device has an oxide film formed by thermal oxidation or chemical vapor deposition as a surface protective film or a part thereof. The SiC semiconductor device as described. An epitaxial SiC film manufacturing method for manufacturing an epitaxial SiC film by growing an epitaxial SiC film on an off-cut surface of a SiC substrate having a hexagonal crystal structure,
The SiC substrate off-cut surface is selected to have an off-cut angle of 0.5 ° or more and 10 ° or less from the (0001) plane,
Further, the crystal orientation of the off-cut surface is the 12 equivalent <21-30> directions ([21-30], [-2-130], [2-310], [-23-10] of the SiC substrate. ], [12-30], [-1-230], [1-320], [-13-20], [-3120], [3-1-20], [-3210] and [3-2] The method for producing an epitaxial SiC film, comprising an off-cut surface selection step of selecting the direction so as to face one direction of ± 7.5 ° or less from any direction of [−10] direction). A SiC substrate selection step of selecting a substrate having a micropipe defect or a screw dislocation of 10 cm ⁻² or more as the SiC substrate;
A buffer on which a buffer layer having a thickness of 0.3 to 15 μm and having micropipe defects reduced to 80% or less compared to the SiC substrate is grown by chemical vapor deposition on the SiC substrate. A layer forming step;
The method for producing an epitaxial SiC film according to claim 21, further comprising an active layer forming step of forming an active layer on the buffer layer.   23. The method of manufacturing an epitaxial SiC film according to claim 21, further comprising a donor addition step of including at least one impurity atom of nitrogen, phosphorus, aluminum, and boron in the buffer layer. 24. The method of manufacturing an epitaxial SiC film according to claim 23, wherein impurity atoms are included in the donor addition step at a density of 2 × 10 ^{15 to} 3 × 10 ¹⁹ cm ⁻³ .   The donor addition step is a concentration-controlled donor addition performed by controlling the density of at least one impurity atom of nitrogen, phosphorus, aluminum, or boron in the buffer layer to be lower than the impurity density in the SiC substrate. The method of manufacturing an epitaxial SiC film according to claim 23 or 24, wherein the method is a step. The donor addition step is performed by controlling the density of at least one impurity atom of nitrogen, phosphorus, aluminum, and boron in the buffer layer so as to gradually decrease from the SiC substrate toward the active layer. 26. The method for producing an epitaxial SiC film according to claim 23, wherein the step is a gradient-controlled donor addition step.