JP6295537B2 - Silicon carbide substrate and semiconductor element - Google Patents

Description

    The present invention relates to a silicon carbide substrate used for a high-performance semiconductor element. In particular, it is an object of the present invention to provide a silicon carbide substrate in which the movement is suppressed while including line defects (dislocations) in the crystal, and to enable stable operation of the semiconductor element.

    Silicon carbide has begun to be used as a compound semiconductor crystal serving as a substrate of a semiconductor element used for power control with high efficiency. When silicon carbide is used as a substrate material of a semiconductor element, the semiconductor element can be operated with higher withstand voltage or lower loss than that on a conventionally used silicon substrate because of its high dielectric breakdown electric field strength. However, the silicon carbide substrate contains lattice defects with a higher density than the silicon substrate, and these adversely affect the performance of the semiconductor element. For example, structural defects such as stacking faults and dislocations cause current leakage, dielectric breakdown, or fluctuations in forward voltage, which significantly impairs the performance and reliability of power semiconductor elements. For this reason, a reduction in defect density is desired for a silicon carbide substrate used as a substrate for a semiconductor element.

    Hereinafter, a method for reducing defects in forming a silicon carbide substrate will be described. As a defect density reduction method when epitaxially growing silicon carbide on a silicon substrate, for example, a method of controlling the thickness of silicon carbide described in Japanese Patent Publication No. 6-41400 of Patent Document 1, Shibahara, S .; Nishino, H .; Matsunami, Appl. Phys. Lett. 50 (1987) p. 1888-1890 (Non-patent Document 1) includes an off-angle machining method for slightly tilting the surface normal axis of a silicon substrate. Non-Patent Document 1 specifies a polar plane orientation orientation by using a so-called off-substrate that forms an angle (off angle) of about several degrees in the [011] direction of a silicon (100) substrate, and is a kind of surface defect. A means for eliminating the anti-phase region boundary is described. However, when this off-angle is introduced, stacking faults propagate only in a specific direction, so that their association annihilation mechanism disappears and it is difficult to reduce the stacking fault density.

    Originally, when cubic silicon carbide is grown on the (001) plane, stacking faults propagate in parallel to four equivalent {111} planes, so that opposing stacking faults meet to reduce the stacking fault density. However, when silicon carbide is grown on a silicon (001) substrate in which an off angle is introduced in the [110] direction, the stacking fault that propagates parallel to the (111) plane is blocked by the surface step, and the propagation direction of the stacking fault Is limited to the direction parallel to the (−1-11) plane. As a result, the association annihilation mechanism disappears, and the stacking fault does not completely disappear.

    As a method for solving this problem and reducing both the antiphase region boundary surface and the stacking fault, which are surface defects in silicon carbide, Japanese Patent Laid-Open No. 2001-335935 (Patent Document 2), H. Nagasawa, T .; Kawahara, K .; Yagi, Mater. Sci. Forum 389-393 (2002) pp. As described in 319-322 (Non-Patent Document 2), a technique for epitaxially growing silicon carbide on a silicon substrate on which undulations having ridges parallel to one direction have been developed has been developed. When silicon carbide is heteroepitaxially grown on a undulated silicon (001) substrate having a ridge parallel to one direction, the stacking faults exposing the C phase plane at the antiphase region boundary surface and the substrate surface disappear. However, stacking faults that expose the Si polar face on the surface still remain. One reason for this is that stacking faults that expose the Si polar plane always occur due to lattice distortion during growth, and the other is that dislocations (line defects) that form the remaining stacking faults in the crystal. The reason is that the stacking faults are expanded by the movement. In particular, under a high temperature such as a crystal growth process, distortion due to heat distribution tends to occur inside the silicon carbide crystal, and the generation and expansion of stacking faults is promoted. In particular, since the amount of thermal strain increases depending on the diameter of the crystal, the stacking fault density increases depending on the diameter of the crystal.

    As means for eliminating the above-mentioned residual stacking faults, Japanese Patent Application Laid-Open No. 2002-201099 (Patent Document 3) forms undulations formed on a crystal substrate not only in one direction but also in a direction orthogonal thereto. Yes. In this method, since the step flow formed by one undulation and the step flow formed by the other undulation compete with each other in a perpendicular relationship with each other, it seems that one step flow was dragged as a surface morphology. The morphology disappears and a flat surface is obtained. However, since the tilt is generated not only in one direction but also in the direction orthogonal thereto, the orientation direction control of the polar plane direction as described in Non-Patent Document 2 is impaired, and the antiphase region boundary surface is eliminated. Is not guided.

In Japanese Patent Laid-Open No. 2001-257166 (Patent Document 4), a GaN layer is provided on a sapphire substrate, and an equilateral triangular opening is formed in three <11-20> directions equivalent to SiO ₂ to grow GaN. The triangular pyramid GaN growth layer is formed. When an island GaN layer is formed on the triangular pyramid GaN growth layer and the GaN growth layer is grown on the entire surface of the sapphire substrate, lateral growth is promoted and flattened so as to fill the triangular pyramid. Dislocations extending perpendicularly from the substrate interface are deflected when they reach the slope of the cone structure and do not reach the surface, reducing the dislocation density, but they are deflected and the dislocations gather in the crystalline region on SiO _{2 and} rise again Since it stretches, a high-density dislocation region is formed on the surface. In addition, for plane defects that propagate in parallel to a specific orientation, such as stacking faults in silicon carbide, the defect propagation orientation does not change and low dislocations can be used regardless of the formation of openings or lateral growth. It does not lead to the formation of a density region. Therefore, even if sapphire described in JP-A-2001-257166 is used as silicon carbide and diverted to homoepitaxial growth of silicon carbide, as long as the antiphase region boundary surface and stacking fault of silicon carbide as a substrate are not eliminated, those It is impossible to obtain a silicon carbide surface free from surface defects.

    As a means for eliminating the anti-phase region boundary surface and stacking faults, H.C. Hatta, T .; Kawahara, K .; Yagi, H .; Nagasawa, S .; Reshanov, A .; Schoner, Mater. Sci. Forum 717-720 (2012) pp. As described in 173-176 (Non-patent Document 3), line and space processing is performed on the surface of the silicon carbide substrate, and then epitaxial growth is performed so that voids in the space portion remain, thereby preventing the propagation of stacking faults. There are also known means for terminating at the part, but this method has certain limitations on the relationship between the gap between adjacent gaps and the height of the gaps, and the gap part substantially increases the electrical resistance of the substrate. However, there are problems that dislocations can move freely in the gaps and that the manufacturing process becomes complicated, such as shape processing on the substrate surface and multiple times of epitaxial growth.

Japanese Patent Publication No. 6-41400 JP 2001-335935 A JP 2002-201099 A JP 2001-257166 A

K. Shibahara, S .; Nishino, H .; Matsunami, Appl. Phys. Lett. 50 (1987) p. 1888-1890 H, Nagasawa, T .; Kawahara, K .; Yagi, Mater. Sci. Forum 389-393 (2002) pp. 319-322 H. Hatta, T .; Kawahara, K .; Yagi, H .; Nagasawa, S .; Reshanov, A .; Schoner, Mater. Sci. Forum 717-720 (2012) pp. 173-176

    The present invention has been made in view of the above-mentioned problems, does not perform any processing on the substrate for growing a crystal, prevents the generation and propagation of defects due to thermal strain and lattice mismatch, and has high functionality. It is another object of the present invention to provide a silicon carbide substrate having a low defect density capable of realizing a semiconductor element that operates stably.

In order to achieve the above object, the present invention has the following configuration.
(Configuration 1) A plate-like single crystal silicon carbide substrate composed of a periodic crystal lattice formed by covalent bonding of carbon and silicon. In a part or all of the silicon carbide substrate (impurity added region), carbon or silicon is A silicon carbide substrate characterized in that a part of lattice positions to be arranged is substituted with one or more impurity elements of carbon, silicon, oxygen, iron, cobalt, nickel fluorine, and iodine.

    (Structure 2) A silicon carbide substrate according to Structure 1, wherein the impurity concentration is substituted at a ratio of 0.1 ppm or more and 10 ppm or less of the silicon concentration in the impurity added region.

    (Structure 3) Carbonization characterized in that it is a silicon carbide substrate according to structures 1 and 2, and the boundary between the impurity-added region and the impurity-free region described in structure 1 is not parallel to the densest surface of the substrate crystal lattice. Silicon substrate.

    (Structure 4) A silicon carbide substrate having two or more electrodes, wherein the impedance is different between different electrodes depending on applied current, voltage, pressure, and light, and is described in Structure 1 to Structure 3. A semiconductor element characterized by being provided above.

    Conventionally, the propagation and expansion of defects was suppressed by association annihilation and voids, but the probability of association annihilation is proportional to the stacking fault density, so as the number of stacking faults decreases, the density reduction effect (per unit thickness) Decreasing stacking fault density) decreases, and it is difficult to reduce it to a certain value or less. In order to reduce stacking faults and dislocation density regardless of such association annihilation and termination at voids, in the present invention, as shown in FIG. 1, the movement of dislocations is prevented in the impurity added region (101) in the silicon carbide crystal. Impurities are added as follows. The added impurities are carbon (104), silicon (105), oxygen (106), iron (107), cobalt (108), nickel (109) at the lattice positions of carbon (102) and silicon (103) constituting silicon carbide. , Fluorine (110), or iodine (111).

    The position where oxygen, iron, cobalt, nickel fluorine, and iodine are substituted is not limited to the original carbon position or silicon position, but when carbon is an impurity, the original silicon position is replaced and silicon is an impurity. Must replace the original carbon position. The atomic radius of the impurity to be substituted is smaller than the atomic radius of carbon (0.79 angstrom) or larger than the atomic radius of silicon (1.11 angstrom), so that the original silicon position or carbon position is replaced with the impurity. The substituted impurities increase the Peierls-Navarro force against dislocations moving in the crystal, immobilizing them and preventing the extension of stacking faults. Therefore, it is desirable that the region where the impurities are replaced is the entire crystal, but the effect is exhibited if at least the width of the region is equal to or larger than the average size of the stacking fault.

    In addition, the shape of the region in which the impurity has replaced the crystal lattice is not particularly limited, but at least it is not necessary to be parallel to the closest dense surface (112) where the dislocation moves, which is a necessary condition for causing dislocation immobilization. .

    Also, as long as the impurity atoms remain in the crystal lattice, the dislocation movement is hindered. For example, even when an electric field, current, pressure, or light is applied, the dislocation is kept immobilized, and the operating characteristics of the semiconductor element are Stabilize. Therefore, the addition of impurities may be performed during the production of the crystal, and the effect of the present invention is exhibited even after the production of the crystal or the production of the semiconductor element.

    When impurities are added during crystal growth, a gas containing impurities may be mixed into a silicon carbide raw material (a gas containing carbon and a gas containing silicon). In this case, the gas containing carbon and silicon are included. If the gas flow ratio is changed, the lattice position where the impurities are replaced can be selected, and if the supply amount of the gas containing impurities is changed, the impurity concentration in the silicon carbide can be controlled. Further, it is possible to add impurities by ion implantation or thermal diffusion after the crystal is grown.

    It is sectional drawing of the silicon carbide substrate which concerns on this invention.

Mode for carrying out the present invention

    The present invention is effective for any of the silicon carbide crystal polymorphs, but the effect is remarkable in a cubic silicon carbide substrate having a large number of {111} faces, which is the most dense surface. Further, if the main surface (the portion of the surface of the crystal that has the largest exposed area) is parallel to the (001) plane and is a plate-like crystal having a back surface parallel to the (001) plane, impurities are added. It is optimal because the region is parallel to the substrate surface and not parallel to any dense surface.

    The added region of the impurity may be the entire substrate, but since the impurity changes the electrical resistance of the substrate, if it is not desired to greatly change the specific resistance of the substrate, it may be added in a layer parallel to the substrate surface. The effect of. In particular, since the depletion layer of the semiconductor element expands in the region of about 20 micrometers near the surface of the substrate, it is desirable to exclude it from the impurity added region from the viewpoint of controlling the breakdown voltage and resistance of the semiconductor element.

    The impurity to be added may be any of carbon, silicon, oxygen, iron, cobalt, nickel fluorine, and iodine. However, from the viewpoint of easy addition of impurities and avoiding contamination in the semiconductor device manufacturing process, any of carbon, silicon, and oxygen may be added. It is desirable to use an element selected from these. Further, substitution of a large amount of carbon at the silicon position or substitution of a large amount of silicon at the carbon position causes the occurrence of an antiphase region interface, so oxygen is the most desirable as an impurity.

    If the impurity concentration is 0.1 ppm or more and 10 ppm or less of the silicon concentration constituting silicon carbide, the effect of the present invention is exhibited. However, when the impurity concentration is low, the effect of suppressing the movement of dislocations is reduced, and the impurity concentration is low. If it is high, impurities may be deposited or the electrical resistance may be increased. Therefore, it is preferably 0.2 ppm or more and 10 ppm or less, more preferably 0.5 ppm or more and 5 ppm or less.

  Impurity elements can be added by ion implantation or thermal diffusion, but the impurity addition region is limited to the ion range in ion implantation, and the diffusion coefficient of impurities in silicon carbide is low in thermal diffusion. Therefore, it is desirable to add impurities by mixing impurities into the silicon carbide raw material gas during crystal growth. When oxygen is added as an impurity source, oxygen gas may be mixed into the raw material gas. However, in general, hydrogen is used as a carrier gas in vapor phase growth, so there is a risk of oxygen and hydrogen reacting to cause an explosion. Therefore, it is desirable to use a gas that does not explode even when mixed with hydrogen, such as carbon dioxide or nitrogen oxides.

A method for realizing the best mode is, for example, as follows.
Cubic silicon carbide is epitaxially grown using a commercially available silicon single crystal wafer (001) surface as a substrate. For the growth of silicon carbide, CVD (Chemical Vapor Deposition), MBE (Sensitive Line Epitaxy), LPE (Liquid Phase Epitaxy), etc. can be used. It is desirable that the supply amount can be adjusted individually, and further, it is desirable to change the supply ratio of the Si source and the C source by precisely adjusting the flow rate as a gas, so that the CVD method is optimal. In the CVD method, by appropriately adjusting the supply ratio of the Si source and the C source, it becomes possible to orient the specific crystal plane in the specific crystal orientation by making a difference in the growth rate of the Si plane and the C plane. For example, it arrange | positions so that Si surface may become (111) and (-1-11) surface, and C surface may become (-111) and (1-11) surface. By adjusting the orientation azimuth in this way, it is possible to arrange carbon at a location where silicon should originally be located in the crystal lattice, or to place silicon at a location where carbon should be originally located in the crystal lattice. When oxygen is added, in addition to Si source and C source gas, carbon oxide (CO, CO ₂ ) or nitrogen oxide (NO, NO ₂ ) gas is mixed, and Si source and C source are mixed. By appropriately adjusting the gas supply ratio, the lattice position where oxygen is arranged can be arbitrarily controlled. The amount of impurities to be added can be controlled by the flow rate of carbon dioxide or nitrogen oxide gas, and the concentration of the added impurities increases as the flow rate is increased. The optimum impurity source gas flow rate varies depending on the ratio of the decomposition efficiency of the impurity source gas and the carbon and silicon source gas at the temperature at which silicon carbide is grown, but these can be obtained experimentally. Thus, the additive impurity concentration can be arbitrarily controlled by adjusting the gas supply amount and the supply amount ratio.

    Further, the position and thickness of the layer to which the impurity is added can be controlled by the supply start time and the supply continuation time of the impurity source gas. For example, assuming that the growth rate of silicon carbide is 50 micrometers / hour, the oxygen-added layer is controlled to be in the range of 100 micrometers to 150 micrometers from the interface between the silicon substrate and silicon carbide. In this case, the supply of the impurity source gas may be started after two hours have passed after the growth of silicon carbide is started, and then the supply may be continued for one hour. In this case, since the layer to which the impurity is added is substantially parallel to the (001) plane of cubic silicon carbide, dislocations are immobilized by crossing the {111} plane which is the dense plane.

<First Embodiment>
First, an extremely thin silicon carbide layer is formed on the surface of a silicon (001) substrate having a diameter of 6 inches in a CVD apparatus. Carbon source gas C ₂ H ₂ and carrier gas H ₂ are supplied to the substrate surface from room temperature, and then the substrate temperature is raised to a predetermined growth temperature of 1350 ° C. The gas supply amount and pressure are as shown in Table 1.

Immediately after the substrate surface temperature reaches 1350 ° C., SiH ₂ Cl ₂ as Si raw material, C ₂ H ₂ and H ₂ as C raw material are supplied to vapor-phase grow silicon carbide. The growth conditions in this case are as shown in Table 2. The growth pressure is adjusted with a throttle valve installed between the reaction chamber and the exhaust system.

    Growth is performed for 8 hours under the above conditions, and 450 μm cubic silicon carbide is grown on the silicon substrate.

    After the growth, the silicon substrate is etched with a mixed acid of hydrofluoric acid and nitric acid to obtain a single cubic silicon carbide substrate. Next, the cubic silicon carbide substrate is again inserted into the CVD apparatus, and 240 micrometer silicon carbide is grown in 3 hours under the conditions shown in Table 3.

Oxygen is mixed in the silicon carbide by growing by adding CO ₂ as an oxygen source. It is determined from the energy spectrum and intensity of the X-ray photoelectron spectroscopy that the mixed oxygen is originally contained in the lattice position where the carbon should be disposed and that the concentration is 0.21 ppm of the silicon concentration.

    Next, in order to measure the defect density on the surface of the grown cubic silicon carbide substrate, it is immersed in KOH melted at 500 ° C. for 5 minutes. Thereafter, by observing the surface of the substrate on which the stacking fault is manifested as an etch pit with an optical microscope, it is found that the line density of the stacking fault exposed on the surface is 150 / cm.

For comparison, the oxygen concentration in silicon carbide is changed by changing only the CO ₂ supply amount from 0 cc / min to 1500 cc / min under the conditions shown in Table 4. Then, in order to measure the defect density of the grown cubic silicon carbide substrate, it was immersed in KOH melted at 500 ° C. for 5 minutes, and the linear density of stacking faults exposed on the surface as etch pits was obtained. Dependencies as shown in Table 4 are obtained. Table 4 also shows the resistivity of silicon carbide that can be obtained from the four-terminal resistance measurement.

    As described above, when the original carbon position in silicon carbide is replaced with oxygen, a stacking fault reduction effect is brought about at a concentration of 0.1 ppm or more, and the effect becomes more remarkable at an oxygen concentration of 0.2 ppm or more. However, since the resistivity rapidly increases when the oxygen concentration exceeds 10 ppm, the oxygen concentration is preferably 10 ppm or less.

    As described above, the effect of reducing defects by adding impurities is clear. In this example, cubic silicon carbide was used as the crystal substrate. However, since the {111} plane, which is a dense surface, is comparable to the {0001} plane of hexagonal crystal, the same defect reduction effect can be obtained in hexagonal silicon carbide. It is clear that In this case, if the {11-20} plane or the {03-38} plane is used as the surface of the substrate, the impurity-added region intersects with the {0001} plane which is a dense plane, so that the effect of reducing defects becomes high.

Also, SiH ₄ , SiCl ₄ , SiHCl ₃ or the like may be used as a Si source gas for use in growing silicon carbide. As the C source gas, CH ₄ , C ₂ H ₄ , C ₂ H ₆ , C ₃ H _8, or the like can be used. Further, although CO ₂ is used as the oxygen source, any molecule that releases oxygen thermally may be used, and oxygen gas, CO, NO, NO _2, etc. can be appropriately adjusted by adjusting the gas flow rate. Similar effects can be obtained. In particular, it is preferable to use nitrogen oxide as an impurity raw material because nitrogen substitutes at a carbon position and acts as a donor, thereby suppressing an increase in resistivity due to oxygen atoms.

    The impurity is not necessarily oxygen, and may be any of carbon, silicon, iron, cobalt, nickel fluorine, and iodine as long as the lattice position of carbon or silicon is substituted. In this embodiment, the chemical vapor deposition method is used as the crystal growth method. However, if a predetermined amount of a predetermined impurity can be added to a predetermined lattice position, a sublimation recrystallization method, solution growth, or the like can be used. The effect of.

Second Embodiment
An ultrathin silicon carbide layer is formed on the surface of a 6-inch diameter silicon (001) substrate in a CVD apparatus under the conditions shown in Table 1. Next, silicon carbide is epitaxially grown under the conditions shown in Table 2 by supplying SiH ₂ Cl _{2 as} a Si raw material, C ₂ H ₂ and H _{2 as} a C raw material at a temperature of 1350 ° C. The growth pressure is adjusted by a throttle valve installed between the reaction chamber and the exhaust system. Vapor phase growth is performed for 12 hours under the above conditions to grow 675 micrometer cubic silicon carbide on the silicon substrate.

After the growth, the silicon substrate is etched with a mixed acid of hydrofluoric acid and nitric acid to obtain a single cubic silicon carbide substrate. Thereafter, oxygen ions are implanted in a direction of 7 degrees in the [110] direction with respect to the normal axis of the main surface. The acceleration energy of oxygen is changed between 200 keV and 400 keV, and the dose at each acceleration energy is changed from 10 ¹⁴ / cm ² to 10 ¹⁷ / cm ² . As a result, a layer in which oxygen is added to a 0.1 micrometer layer on the surface of silicon carbide is formed. It is identified from the energy position of the energy spectrum of X-ray photoelectron spectroscopy that oxygen is originally contained in the lattice position where carbon should be arranged, and the concentration is calculated from the peak intensity of the energy spectrum of X-ray photoelectron spectroscopy.

    A 5 micrometer cubic silicon carbide growth is then performed over 5 minutes under the conditions listed in Table 2. Thereafter, the silicon carbide substrate is immersed in 500 ° C. molten KOH for 5 minutes to reveal stacking faults. When this substrate surface is observed with an optical microscope, the stacking fault density on the substrate surface shows the tendency shown in Table 5 with respect to the added oxygen concentration.

    As described above, when the original carbon position in silicon carbide is replaced with oxygen, a remarkable stacking fault reduction effect is obtained at a concentration of 0.1 ppm or more, and thus the defect reduction effect of the present invention is clear. However, when the oxygen concentration exceeds 10 ppm, the crystal lattice is significantly disturbed by ion implantation, and the etch pit density increases rapidly. Therefore, the oxygen concentration is preferably 10 ppm or less.

    In this example, a cubic silicon carbide (001) plane was used as the crystal substrate, but the {110} plane or the {211} plane is not parallel to the {111} plane which is a dense plane. Defect reduction similar to the example is brought about. Furthermore, since the {111} plane, which is a dense surface of cubic silicon carbide, is comparable to the {0001} plane of hexagonal crystal, the same defect reduction effect can be achieved in hexagonal silicon carbide. In this case, if the {11-20} plane or the {03-38} plane is used as the surface of the substrate, the impurity-added region intersects the {0001} plane which is a dense plane, so that the effect of reducing defects becomes high.

    The impurity is not necessarily oxygen, and may be any of carbon, silicon, iron, cobalt, nickel fluorine, and iodine as long as the lattice position of carbon or silicon is substituted. Further, the addition method is not limited to ion implantation, and the same effect can be obtained by thermal diffusion as long as impurities can be substituted at the lattice positions of carbon or silicon.

<Third Embodiment>
A pn diode is formed on the surface of the silicon carbide substrate manufactured in Example 2 as follows. First, nitrogen ions having a dose of 3 × 10 ¹⁵ / cm ² are implanted into the entire surface of the substrate at an acceleration energy of 400 keV to form an n layer having a thickness of 1 μm and a donor concentration of 1 × 10 ¹⁶ / cc. Next, a photoresist having a thickness of 5 micrometers is applied to the substrate surface, and a circular opening having a diameter of 10 micrometers is provided by a photolithography process. Further, aluminum ions having a dose of 7 × 10 ¹⁵ / cm ² at an acceleration energy of 300 keV are implanted to form a p layer having a thickness of 0.3 μm and an acceptor concentration of 3 × 10 ¹⁷ / cc. An aluminum electrode is vacuum-deposited on the surface of the p layer, and a nickel electrode is deposited on the back side of the substrate to form an anode and a cathode, respectively.

    When a constant current of 1 mA is applied for 12 hours from the anode to the cathode at room temperature, and the change in potential difference between the anode and the cathode after the start of application is measured, the oxygen concentration dependency as shown in Table 6 is obtained.

    As described above, when the original carbon position in silicon carbide is replaced with oxygen, the fluctuation of the potential difference between the electrodes is suppressed at a concentration of 0.1 ppm or more, so that the stable operation of the semiconductor element provided by the present invention is ensured. The However, since the voltage drop between the electrodes rapidly increases when the oxygen concentration exceeds 10 ppm, the oxygen concentration is desirably 10 ppm or less.

    Further, in this embodiment, the effect of the stable operation in the pn diode is shown. However, since the same effect appears as long as an electric field is applied to the defect, the present invention is a Schottky diode, JFET, bipolar transistor, MOSFET, IGBT, etc. It is clear that the effect is exerted on any semiconductor element.

    The impurity is not necessarily oxygen, and the same effect can be obtained with any of carbon, silicon, iron, cobalt, nickel fluorine, and iodine as long as the lattice position of carbon or silicon is substituted. The addition method is not limited to the ion implantation method described in Example 2, and even when the addition is performed during the vapor phase growth described in Example 1, the movement of dislocation is suppressed, so that it is clear that stable operation of the device is brought about. It is.

    Further, in this example, a cubic silicon carbide (001) plane was used as the crystal substrate, but the {110} plane or the {211} plane is not parallel to the {111} plane which is a dense plane. Defect reduction similar to the present embodiment is brought about. Furthermore, since the {111} plane, which is a dense surface of cubic silicon carbide, is comparable to the {0001} plane of hexagonal crystal, the same defect reduction effect can be achieved in hexagonal silicon carbide. In this case, if a {11-20} plane or a {03-38} plane is used as the surface of the substrate, the impurity-added region intersects with the {0001} plane which is a dense plane, thereby realizing stable operation of the element.

101; impurity doped region in silicon carbide crystal 102; carbon atom 103 at lattice position; silicon atom 104 at lattice position; carbon atom 105 at silicon lattice position; silicon atom 106 at carbon lattice position; oxygen atom 107; iron atom 108; Cobalt atom 109; Nickel atom 110; Fluorine atom 111; Iodine atom 112; A plane parallel to the most dense surface of the crystal lattice

Claims (3)

A plate-like single crystal silicon carbide substrate composed of a periodic crystal lattice formed by covalent bonding of carbon and silicon, and a lattice in which carbon or silicon is to be arranged in a part or all of the region (impurity added region) of the silicon carbide substrate A silicon carbide substrate, wherein a part of the position is substituted with one or more impurity elements of oxygen, fluorine, and iodine at a ratio of 0.1 ppm to 10 ppm with respect to the silicon concentration .   A plate-like single crystal silicon carbide substrate having a periodic crystal lattice formed by covalent bonding of carbon and silicon. In a partial region (impurity-added region) of the silicon carbide substrate, the lattice position where carbon or silicon is to be disposed A silicon carbide substrate partially substituted with one or more impurity elements of carbon, silicon, oxygen, iron, cobalt, nickel, fluorine, iodine, and the boundary between the impurity-added region and the impurity-free region is A silicon carbide substrate characterized by not being parallel to the close-packed surface of the substrate crystal lattice. It is a semiconductor element which has two or more electrodes, and the impedance between different electrodes changes with applied current, voltage, pressure, and light, and is provided on the silicon carbide substrate according to claim 1 or 2 . A semiconductor element characterized by this.

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