JP2012246168A - Silicon carbide substrate, silicon carbide wafer, method for manufacturing silicon carbide wafer, and silicon carbide semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a silicon carbide wafer which prevents complication of a manufacture process, does not restrict a silicon carbide substrate, and is capable of more surely converting a basal plane dislocation to a threading edge dislocation, and also to provide a silicon carbide semiconductor device using the silicon carbide wafer.SOLUTION: The tip part of the basal plane dislocation 20 of the silicon carbide substrate 1 is converted to the threading edge dislocation 30 by heat-treating the silicon carbide substrate 1 at 1,700-2,200°C in an inert gas atmosphere or in a vacuum, and an epitaxial film 2 where the basal plane dislocation 20 is reduced is crystal-grown by carrying out epitaxial growth of silicon carbide on the silicon carbide substrate 1.

Description

  The present invention relates to a silicon carbide substrate, a silicon carbide wafer, a method for manufacturing a silicon carbide wafer, and a silicon carbide semiconductor element, and more particularly to a basal plane dislocation converted into a threading edge dislocation.

  Silicon carbide (SiC) is a semiconductor that has excellent physical properties such as a band gap of about 3 times, a saturation drift velocity of about 2 times, and a breakdown electric field strength of about 10 times that of Si, and a large thermal conductivity. Therefore, it is expected as a material for realizing a next-generation high-voltage / low-loss semiconductor element that greatly exceeds the performance of the currently used Si single crystal semiconductor.

  At present, a sublimation method and an HTCVD method are known as methods for producing a silicon carbide single crystal. According to these methods, a silicon carbide single crystal is obtained as a cylindrical bulk single crystal. A silicon carbide substrate is manufactured by slicing the bulk single crystal to a thickness of about 300 μm to 400 μm. When manufacturing a semiconductor element using this silicon carbide substrate, a single crystal layer having a required film thickness and carrier concentration based on required specifications such as a withstand voltage of the semiconductor element is epitaxially grown from the substrate surface. Often manufactured.

  The silicon carbide substrate is manufactured by the method as described above, but does not have a liquid phase at normal pressure, and does not include crystal defects such as dislocations and stacking faults because of its extremely high sublimation temperature. It is difficult to perform high quality crystal growth.

Currently available silicon carbide substrates include threading screw dislocations propagating in the c-axis direction of about 10 ² cm ⁻² to 10 ³ cm ⁻² and c-axis direction of about 10 ² cm ⁻² to 10 ⁴ cm ^−2. There exist dislocations (basal plane dislocations) propagating in the direction perpendicular to the c-axis of about 10 ² cm ⁻² to 10 ⁴ cm ⁻² . These dislocation densities vary greatly depending on the quality of the substrate.

  These dislocations inherent in the silicon carbide substrate propagate into the epitaxial film when the epitaxial film is grown on the substrate. At this time, it is known that some dislocations may change the extension direction (propagation direction) when propagating into the epitaxial film (for example, see Non-Patent Document 1).

  For example, one or both ends of basal plane dislocation (hereinafter referred to as BPD) appear on the surface of the substrate. When an epitaxial film is grown on the substrate, most of the BPD in the substrate is converted to threading edge dislocation (hereinafter referred to as TED) in the vicinity of the interface between the substrate and the epitaxial film, and a part of the BPD remains as the BPD. Propagate inside.

  Therefore, in the epitaxial film, TED introduced at the time of epitaxial growth is included in addition to BPD propagated as it is from the substrate. These dislocations lower the withstand voltage and reliability of a semiconductor element formed using the epitaxial film. In particular, the BPD contained in the epitaxial film reduces the reliability and performance of the semiconductor element. On the other hand, TED contained in an epitaxial film is said to have a small adverse effect on the reliability and performance of a semiconductor element (see, for example, Non-Patent Document 2).

  Therefore, a method for converting BPD contained in a silicon carbide substrate into TED and increasing the ratio of TED has been studied.

  (1) The substrate surface is etched using molten KOH. By this etching, the front end portion of the BPD on the substrate surface is selectively deeply etched to generate an etch pit. Thereafter, epitaxial growth is performed on the substrate. The presence of etch pits at the tip of the BPD on the substrate surface increases the rate at which BPD in the substrate is converted to TED (see, for example, Patent Document 1, Non-Patent Document 3, and Non-Patent Document 4).

  (2) Reactive ion etching (RIE) is used to form hexagonal or striped grooves on the substrate surface, and then epitaxial growth is performed on the substrate. Due to the presence of square or stripe-shaped grooves on the substrate surface, the ratio of BPD in the substrate converted to TED increases (see, for example, Patent Document 2, Patent Document 3, and Non-Patent Document 3).

  (3) Chemical mechanical polishing (CMP) and hydrogen etching are performed on the substrate surface. Thereby, the damaged layer on the substrate surface is removed, and the substrate surface is flattened. Thereafter, epitaxial growth is performed on the substrate surface. Thereby, the ratio by which BPD in a board | substrate is converted into TED increases (for example, refer patent document 4 and nonpatent literature 5).

  (4) The main surface of the substrate to be epitaxially grown is a (000-1) C plane. Thereby, the ratio in which BPD in a board | substrate is converted into TED increases (for example, refer patent document 5 and nonpatent literature 5).

  (5) The off angle from the {0001} plane of the substrate to be epitaxially grown is reduced from 8 ° to 4 °. Thereby, the ratio in which BPD in a board | substrate is converted into TED increases (for example, refer nonpatent literature 5 and nonpatent literature 6).

(6) During the epitaxial growth on the substrate surface, the supply of the source gas such as SiH ₄ or C ₃ H ₈ is stopped, and the temperature is maintained in the hydrogen stream to stop the epitaxial growth. After a certain period of time, a second epitaxial growth is performed. At this time, a part of BPD propagated in the epitaxial film during the first epitaxial growth is converted to TED during the second epitaxial growth. An epitaxial film having a low BPD density can be obtained by interrupting and restarting such epitaxial growth in the middle or by repeating the interruption and restart in the middle (for example, see Non-Patent Document 7).

  The methods (1) to (3) described above require etching on the substrate surface before epitaxial growth, and the manufacturing process becomes complicated. Since the method (6) requires steps of interrupting and resuming the epitaxial growth, the manufacturing process is similarly complicated.

  In the method (4), the (0001) Si surface cannot be used. In the method (5), a substrate with an off angle of 8 ° cannot be used, and the epitaxial growth rate is limited.

  As described above, in the conventional technique, the manufacturing process is complicated, and it takes time and labor to form the silicon carbide single crystal layer with reduced BPD. In addition, the substrate surface and the off-angle for epitaxial growth are restricted.

US Pat. No. 7,279,115 US Pat. No. 7,226,805 US Pat. No. 7,109,521 JP 2005-311348 A Japanese Patent Laying-Open No. 2005-167035

S. Ha, P. Mieszkowski, M. Skowronski, and L. B. Rowland: J. Cryst. Growth 244 (2002) 257. H. Lendenmann, F. Dahlquist, N. Johansson, R. Soderholm, P. A. Nilsson, J. P. Bergman, and P. Skytt: Mater. Sci. Forum 353-356 (2001) 727. JJ Sumakeris, JP Bergman, MK Das, C. Hallin, BA Hull, E. Janzen, H. Lendenmann, MJ O'Loughlin, MJ Paisley, S. Ha, M. Skowronski, JW Palmour, and CH Carter, Jr .: Mater. Sci. Forum 527-529 (2006) 141. Z. Zhang and T.S.Sudarshan: Appl. Phys. Lett. 87 (2005) 151913. H. Tsuchida, T. Miyanagi, I. Kamata, T. Nakamura, K. Izumi, K. Nakayama, R. Ishii, K. Asano, and Y. Sugawara: Mater. Sci. Forum 483-485 (2005) 97. H. Tsuchida, M. Ito, I. Kamata, and M. Nagano: Phys. Status Solidi B 246 (2009) 1553 R. E. Stahlbush, B. L. VanMil, R. L. Myers-Ward, K-K. Lew, D. K. Gaskill, and C. R. Eddy, Jr .: Appl. Phys. Lett. 94 (2009) 041916.

  The present invention has been made in view of the above situation, and provides a method for manufacturing a silicon carbide wafer that prevents the manufacturing process from becoming complicated, that there is no restriction on the silicon carbide substrate, and that BPD can be more reliably converted to TED. With the goal.

  In addition, the present invention provides a silicon carbide wafer in which the manufacturing process is prevented from being complicated, the silicon carbide substrate is not restricted, and BPD is more reliably converted to TED, and a silicon carbide semiconductor element using the silicon carbide wafer is provided. With the goal.

  Furthermore, an object of the present invention is to provide a silicon carbide substrate in which BPD is converted to TED.

  In a first aspect of the present invention that solves the above-described problems, a silicon carbide substrate is heat-treated at 1700 ° C. to 2200 ° C. in an inert gas atmosphere or in vacuum, so that the tip of the BPD of the silicon carbide substrate becomes a TED. In another aspect of the present invention, there is provided a method for manufacturing a silicon carbide wafer, characterized by performing epitaxial growth of silicon carbide on the silicon carbide substrate.

  In the first aspect, by reducing the BPD, it is possible to manufacture a silicon carbide wafer suitable as a material for a semiconductor element that requires high voltage resistance and high reliability. Further, since the etching process as in the prior art is unnecessary, the surface of the silicon carbide substrate can be kept flat. Further, the etching process and the accompanying planarization process are not necessary, and the manufacturing process can be simplified. Furthermore, it is not necessary to limit the off-angle or crystal plane (Si plane, C plane) of the silicon carbide substrate, and there are no restrictions on the conditions for growing the epitaxial film.

  According to a second aspect of the present invention, there is provided a silicon carbide wafer manufacturing method according to the first aspect, wherein the silicon carbide epitaxial growth and the heat treatment are performed a plurality of times.

  In the second aspect, since the heat treatment is performed every time the epitaxial film is formed, the BPD propagated to the epitaxial film is converted into TED. Thereby, the silicon carbide wafer in which BPD was reduced to the limit can be manufactured.

  According to a third aspect of the present invention, in the method for manufacturing a silicon carbide wafer described in the first or second aspect, epitaxial growth of silicon carbide is further performed once or a plurality of times on the epitaxial film. It exists in the manufacturing method of a silicon carbide wafer.

  In the third aspect, a further epitaxial film can be formed on the epitaxial film obtained by converting BPD into TED by heat treatment.

  According to a fourth aspect of the present invention, in the method for manufacturing a silicon carbide wafer according to any one of the first to third aspects, the silicon carbide substrate is removed after epitaxial growth is performed. It is in the manufacturing method of a wafer.

  In the fourth aspect, after obtaining an epitaxial film with reduced BPD by heat treatment, the silicon carbide substrate in which BPD is present at a high density can be removed.

  According to a fifth aspect of the present invention, in the method for manufacturing a silicon carbide wafer according to the fourth aspect, the epitaxial growth of silicon carbide is further performed once or on the surface of the epitaxial film obtained by removing the silicon carbide substrate. A method of manufacturing a silicon carbide wafer, which is performed a plurality of times.

  In the fifth aspect, after obtaining an epitaxial film with reduced BPD by heat treatment, epitaxial growth of silicon carbide is further performed on the surface of the epitaxial film obtained by removing the silicon carbide substrate in which BPD is present at a high density. Can be performed once or multiple times.

  According to a sixth aspect of the present invention, an epitaxial film made of silicon carbide is formed on a silicon carbide substrate, and the epitaxial film is heat-treated at 1700 ° C. to 2200 ° C. in an inert gas atmosphere or in vacuum. A method of manufacturing a silicon carbide wafer, wherein the tip of the BPD of the epitaxial film is converted to TED, and epitaxial growth of silicon carbide is further performed on the epitaxial film, thereby epitaxially growing the epitaxial film with reduced BPD. It is in.

  In the sixth aspect, BPD can be converted to TED in the epitaxial film. Thereby, a silicon carbide wafer suitable as a material for a semiconductor element that requires high voltage resistance and high reliability can be manufactured. Further, since the etching process as in the prior art is unnecessary, the surface of the silicon carbide substrate can be kept flat. Further, the etching process and the accompanying planarization process are not necessary, and the manufacturing process can be simplified. Furthermore, it is not necessary to limit the off-angle or crystal plane (Si plane, C plane) of the silicon carbide substrate, and there are no restrictions on the conditions for growing the epitaxial film.

  A seventh aspect of the present invention is a method for manufacturing a silicon carbide wafer according to the sixth aspect, wherein the silicon carbide epitaxial growth and the heat treatment are performed a plurality of times.

  In the seventh aspect, since the heat treatment is performed every time the epitaxial film is formed, the BPD propagated to the epitaxial film is converted into TED. Thereby, the silicon carbide wafer in which BPD was reduced to the limit can be manufactured.

  According to an eighth aspect of the present invention, in the method for manufacturing a silicon carbide wafer according to the sixth or seventh aspect, the epitaxial growth of silicon carbide is further performed once or a plurality of times on the epitaxial film. It exists in the manufacturing method of a silicon carbide wafer.

  In the eighth aspect, a further epitaxial film can be formed on the epitaxial film obtained by converting BPD into TED by heat treatment.

  According to a ninth aspect of the present invention, in the method for manufacturing a silicon carbide wafer according to any one of the first to eighth aspects, a gas containing a dopant is used for the dopant in the epitaxial film when the epitaxial growth is performed. In a method for manufacturing a silicon carbide wafer, wherein

  In the ninth aspect, a silicon carbide wafer containing a p-type or n-type dopant can be manufactured.

  According to a tenth aspect of the present invention, in the method for manufacturing a silicon carbide wafer according to any one of the sixth to ninth aspects, after the epitaxial growth is performed, the silicon carbide substrate is removed, or the silicon carbide substrate And a method of manufacturing a silicon carbide wafer, wherein the epitaxial film subjected to the heat treatment is removed.

  In the tenth aspect, after obtaining an epitaxial film with reduced BPD by heat treatment, the silicon carbide substrate in which BPD exists at a high density is removed, or the silicon carbide substrate and the epitaxial film subjected to the heat treatment are removed. be able to.

  An eleventh aspect of the present invention is obtained by removing the silicon carbide substrate or the silicon carbide substrate and the epitaxial film subjected to the heat treatment in the method for manufacturing a silicon carbide wafer according to the tenth aspect. Further, the present invention provides a method for manufacturing a silicon carbide wafer, wherein epitaxial growth of silicon carbide is further performed once or a plurality of times on the surface of the epitaxial film.

  In the eleventh aspect, after obtaining an epitaxial film with reduced BPD by heat treatment, the silicon carbide substrate having a high density of BPD is removed, or the silicon carbide substrate and the epitaxial film subjected to the heat treatment are removed. Further, epitaxial growth of silicon carbide can be performed once or a plurality of times on the surface of the obtained epitaxial film.

  A twelfth aspect of the present invention resides in a silicon carbide substrate in which 20% or more of BPD is converted into TED in a region of 0.1 μm or more and 10 μm or less from the surface of the silicon carbide substrate.

  The twelfth aspect is suitable as a material for semiconductor elements that require high voltage resistance and semiconductor elements that require high reliability.

  In a thirteenth aspect of the present invention, an epitaxial film is formed on a silicon carbide substrate, and the silicon carbide substrate has a BPD region in a region within a range of 0.1 μm to 10 μm from the interface between the silicon carbide substrate and the epitaxial film. The silicon carbide wafer is characterized in that 20% or more of them are converted to TED.

  In the thirteenth aspect, a silicon carbide wafer with reduced BPD is provided. Silicon carbide wafers are suitable as materials for semiconductor elements that require high voltage resistance and semiconductor elements that require high reliability. Further, the silicon carbide wafer is not limited to the off-angle or crystal plane (Si plane, C plane) of the silicon carbide substrate. Accordingly, a silicon carbide wafer having an off angle and a crystal plane suitable for manufacturing a semiconductor element is provided.

  In a fourteenth aspect of the present invention, a first epitaxial film and a second epitaxial film are formed on a silicon carbide substrate, and BPD is converted to TED by the first epitaxial film, and is included in the second epitaxial film. The silicon carbide wafer is characterized in that the density of BPD is 80% or less of the density of basal plane defects contained in the first epitaxial film.

  In the fourteenth aspect, a silicon carbide wafer is provided in which the BPD contained in the second epitaxial film on the substrate surface side is 80% or less of the BPD contained in the first epitaxial film.

  According to a fifteenth aspect of the present invention, in the silicon carbide wafer described in the fourteenth aspect, the dopant concentration contained in the second epitaxial film is lower than the dopant concentration contained in the first epitaxial film. In a silicon carbide wafer.

  In the fifteenth aspect, a silicon carbide wafer containing a p-type or n-type dopant can be manufactured.

  According to a sixteenth aspect of the present invention, a plurality of epitaxial films are formed on a silicon carbide substrate, and two adjacent epitaxial films among the plurality of epitaxial films, the first epitaxial layer on the side close to the silicon carbide substrate. A silicon carbide wafer having an epitaxial film and a second epitaxial film on the far side, wherein 20% or more of BPD is converted to TED in the first epitaxial film, and the thickness direction in the first epitaxial film is 2 μm. In the region within, 60% or more of the conversion from BPD to TED is performed.

  In the sixteenth aspect, there is provided a silicon carbide wafer in which BPD is intensively converted to TED in a region within about 2 μm in the thickness direction of the epitaxial film.

  According to a seventeenth aspect of the present invention, in the silicon carbide wafer described in the sixteenth aspect, in the region of 0.1 μm or more and 10 μm or less from the interface with the second epitaxial film in the first epitaxial film, In the silicon carbide wafer, 80% or more of the conversion from TED to TED is performed.

  In the seventeenth aspect, there is provided a silicon carbide wafer in which BPD is intensively converted to TED in a region of 0.1 μm or more and 10 μm or less from the interface.

  According to an eighteenth aspect of the present invention, there is provided the silicon carbide wafer according to any one of the thirteenth to seventeenth aspects, wherein the silicon carbide substrate is removed.

  In the eighteenth aspect, a silicon carbide wafer made of an epitaxial film in which BPD is reduced by heat treatment is obtained by removing the silicon carbide substrate having a high density of BPD.

  According to a nineteenth aspect of the present invention, there is provided the silicon carbide wafer according to the eighteenth aspect, wherein an epitaxial film is formed on the surface on the side where the silicon carbide substrate is removed.

  In the nineteenth aspect, the silicon carbide substrate in which the BPD is present at a high density is removed, and the silicon carbide wafer in which the epitaxial film is further formed on the epitaxial film in which the BPD is reduced by the heat treatment is obtained.

  A twentieth aspect of the present invention resides in a silicon carbide semiconductor element manufactured using the silicon carbide wafer described in any one of the thirteenth to nineteenth aspects.

  In the twentieth aspect, since it is manufactured from a silicon carbide wafer having a reduced BPD, a reduction in reliability and performance is prevented, and a high-performance semiconductor element utilizing the excellent characteristics of silicon carbide is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the silicon carbide wafer which can prevent complication of a manufacturing process, has no restrictions of a silicon carbide substrate, and can convert BPD to TED more reliably is provided.

  Also provided are a silicon carbide wafer in which the manufacturing process is prevented from becoming complicated, the silicon carbide substrate is not restricted, and BPD is more reliably converted to TED, and a silicon carbide semiconductor element using the silicon carbide wafer.

  Furthermore, a silicon carbide substrate in which BPD is converted to TED is provided.

1 is a cross-sectional view of a silicon carbide wafer according to Embodiment 1. FIG. 3 is a cross-sectional view showing the method for manufacturing the silicon carbide wafer according to the first embodiment. FIG. 3 is a cross-sectional view showing the method for manufacturing the silicon carbide wafer according to the first embodiment. FIG. 3 is a cross-sectional view showing the method for manufacturing the silicon carbide wafer according to the first embodiment. FIG. It is sectional drawing of the silicon carbide substrate for demonstrating the principle by which BPD is converted into TED. 6 is a cross-sectional view of a silicon carbide wafer according to Embodiment 2. FIG. 10 is a cross-sectional view showing a method for manufacturing the silicon carbide wafer according to the second embodiment. FIG. 10 is a cross-sectional view showing a method for manufacturing the silicon carbide wafer according to the second embodiment. FIG. 10 is a cross-sectional view showing a method for manufacturing the silicon carbide wafer according to the second embodiment. FIG. 10 is a cross-sectional view showing a method for manufacturing the silicon carbide wafer according to the second embodiment. FIG. 5 is a cross-sectional view showing a method for manufacturing a silicon carbide wafer according to Embodiment 3. FIG. 6 is a cross-sectional view of a silicon carbide wafer according to Embodiment 4. FIG. It is a topography image concerning a comparative example. It is a topography image concerning a comparative example and an example. It is a figure showing the frequency | count of the conversion from BPD to TED which occurred in the epitaxial film.

<Embodiment 1>
FIG. 1A is a cross-sectional view of a silicon carbide wafer according to this embodiment, and FIG. 1B is a cross-sectional view of a silicon carbide substrate according to this embodiment.

  As shown in FIG. 1A, a silicon carbide wafer (hereinafter referred to as a wafer) 10 includes a silicon carbide substrate (hereinafter referred to as a substrate) 1 and an epitaxial film 2 provided on the substrate 1.

  The substrate 1 is obtained by slicing a cylindrical bulk silicon carbide single crystal to a thickness of about 300 μm to 400 μm. The bulk silicon carbide single crystal is produced by a sublimation method, an HTCVD method, or the like. The substrate 1 has a crystal growth surface 5 (see FIG. 2A) having an inclination angle (off angle) of 0 ° to 10 ° with respect to the basal plane (0001). The polytype of the substrate 1 is preferably 4H, but is not particularly limited.

  Epitaxial film 2 is a thin film made of silicon carbide formed by performing epitaxial growth of silicon carbide on substrate 1.

  The substrate 1 has a plurality of basal plane dislocations (hereinafter referred to as BPD) 20. In the figure, five BPDs 20 are illustrated. The basal plane dislocation is a dislocation that propagates through a crystal plane (basal plane) perpendicular to the c-axis and has a Burgers vector of a / 3 <11-20>.

  Three of the BPDs 20 are converted into threading edge dislocations (hereinafter referred to as TED) 30 in the substrate 1. The threading edge dislocation is a dislocation that propagates in a direction substantially parallel to the c-axis and has a Burgers vector of a / 3 <11-20>. As will be described in detail later, the conversion from the BPD 20 to the TED 30 is performed by heating the substrate 1 in an inert gas or in a vacuum for a predetermined temperature for a predetermined time.

  In the epitaxial film 2, three TEDs 30 that have been converted by the substrate 1 propagate, and two BPDs 20 that have not been converted into the TED 30 in the substrate 1 propagate.

  Of the substrate 1, a region R is 0.1 μm or more and 10 μm or less from the interface between the substrate 1 and the epitaxial film 2. The conversion from BPD 20 to TED 30 performed on the substrate 1 is performed in the region R. Further, 20% or more of the BPD 20 included in the substrate 1 is converted to the TED 30. In the illustrated example, three of the five BPDs 20 have been converted to TED, and therefore 60% of all BPDs 20 have been converted to TED30.

  Although not particularly illustrated, one or more epitaxial films may be further laminated on the wafer 10, that is, on the epitaxial film 2.

  FIG. 1B shows the substrate 1 before the above-described epitaxial film 2 is formed. Also for the substrate 1, the conversion from the BPD 20 to the TED 30 is performed in the region R as described above, and 20% or more of all the BPDs 20 included in the substrate 1 are converted to the TED 30.

  As described above, in the wafer 10, the BPD 20 is converted into the TED 30 in the substrate 1.

  In conventional techniques such as Non-Patent Document 1 and Non-Patent Document 7, the conversion from BPD 20 to TED 30 is performed at the interface between substrate 1 and epitaxial film 2.

  On the other hand, also in the silicon carbide wafer according to the present embodiment, BPD 20 is converted to TED 30 at the interface between substrate 1 and epitaxial film 2. In addition, in the region R in the substrate 1, 20% or more of all the BPDs 20 are converted to the TED 30. Therefore, the wafer 10 according to the present embodiment has a further reduced BPD 20.

  Thus, since the BPD 20 is reduced, the wafer 10 according to the present embodiment is suitable as a material for a semiconductor element that requires high voltage resistance and a semiconductor element that requires high reliability. Similarly, the substrate 1 shown in FIG. 1B is also suitable as a material for a semiconductor element that requires high voltage resistance and a semiconductor element that requires high reliability. Furthermore, since the conversion from the BPD 20 to the TED 30 is not performed at the interface between the substrate 1 and the epitaxial film 2 as in the prior art, but is performed inside the substrate 1 which is an inactive region of the semiconductor element, high reliability is achieved. Is more suitable as a material for obtaining a conductive semiconductor element.

  The wafer 10 is not limited to the off-angle of the substrate 1 or the crystal plane (Si plane, C plane). Therefore, a wafer 10 having an off angle and a crystal plane suitable for manufacturing a semiconductor element is provided.

  FIG. 2 is a cross-sectional view illustrating the method for manufacturing the silicon carbide wafer according to the first embodiment.

  FIG. 2A shows a cross section of the substrate 1. A plurality of BPDs 20 are present on the substrate 1, but one BPD 20 is shown as a representative in FIG. The BPD 20 appears as a single line on the cross section of the substrate 1, and the tip 21 of the line appears on the crystal growth surface 5 (surface on which epitaxial growth is performed) of the substrate 1.

  Next, the substrate 1 is subjected to heat treatment. The heat treatment according to the present invention refers to heating the substrate 1 at a temperature of 1700 ° C. to 2200 ° C. for a predetermined time in an inert gas or in a vacuum.

  Although the heat treatment is not particularly shown, for example, a crucible capable of accommodating the substrate 1, a processing chamber formed of quartz, graphite surrounding the crucible disposed in the processing chamber, and a coil disposed outside the processing chamber And using a device equipped with. The substrate 1 is accommodated in the crucible and covered, the crucible is placed in the processing chamber, and graphite is placed around the crucible. Then, an inert gas is supplied into the processing chamber, or the processing chamber is evacuated, and a high-frequency current is supplied to the coil. Thereby, the board | substrate 1 in a crucible is heated.

  The heating temperature is the temperature of the atmosphere in which the substrate 1 is heated. A specific heating temperature is 1700 ° C to 2200 ° C, preferably 1700 ° C to 2000 ° C. The current flowing through the coil and the structure of the crucible and the processing chamber is adjusted so that the temperature is reached. In addition, when it exceeds 2200 degreeC, the silicon carbide of the board | substrate 1 will sublime. Moreover, although there is no limitation in particular in heating time, for example, 1-120 minutes are preferable (details are mentioned later).

As the inert gas, argon (Ar) gas, nitrogen (N ₂ ) gas, or helium (He) gas can be used. In the case where the heat treatment is performed in a vacuum, it is preferable that the atmospheric pressure in the treatment chamber be 100 Pa or less.

  As shown in FIG. 2B, by performing a heat treatment on the substrate 1, the leading end of the BPD 20 is converted into a TED 30 in the substrate 1. The principle that the BPD 20 is converted to the TED 30 will be described later.

  Then, as shown in FIG. 2C, the epitaxial film 2 is grown on the crystal growth surface 5 of the substrate 1 by performing epitaxial growth of silicon carbide on the crystal growth surface 5 of the substrate 1. The crystal growth method of the epitaxial film 2 is not particularly limited, but is preferably performed by, for example, a CVD method.

  During crystal growth of the epitaxial film 2, the TED 30 converted from the BPD 20 propagates from the substrate 1 to the epitaxial film 2 as it is. Although not particularly illustrated, BPD that has not been converted into TED 30 by the heat treatment in substrate 1 is propagated as it is to BPD in epitaxial film 2, or part is converted to TED at the interface between substrate 1 and epitaxial film 2. The

  In this way, the wafer 10 composed of the substrate 1 and the epitaxial film 2 is produced.

  In conventional techniques such as Non-Patent Document 1 and Non-Patent Document 7, the conversion from BPD 20 to TED 30 is performed at the interface between substrate 1 and epitaxial film 2.

  On the other hand, also in the method for manufacturing a silicon carbide wafer according to the present embodiment, conversion from BPD 20 to TED 30 can occur at the interface between substrate 1 and epitaxial film 2. In addition to that, the BPD 20 is converted into the TED 30 in the region R in the substrate 1. Therefore, according to this manufacturing method, it is possible to manufacture the wafer 10 in which the BPD 20 is further reduced.

  Thus, this manufacturing method can manufacture the wafer 10 suitable as a material of the semiconductor element for which high withstand voltage property and high reliability are calculated | required by reducing BPD20.

  Further, in the prior art, in order to convert BPD into TED, an etching process such as molten KOH or RIE is performed on the substrate. In general, when an etching process is performed, a process for polishing and flattening the surface is required when a semiconductor element is manufactured. However, since this manufacturing method does not require such an etching process, the surface of the substrate 1 can be kept flat. Further, the etching process and the accompanying planarization process are not necessary, and the manufacturing process can be simplified.

  Furthermore, this manufacturing method can be applied without the need to limit the off-angle and crystal plane (Si plane, C plane) of the substrate 1, and there are no restrictions on the conditions for growing the epitaxial film 2.

  As shown in FIG. 3, a plurality of epitaxial films 2 may be formed by further epitaxially growing silicon carbide on epitaxial film 2 of wafer 10 described above. The thickness of the epitaxial film 2 and the number of times of epitaxial growth are not particularly limited. What is necessary is just to set suitably according to the film thickness and element structure of the wafer 10 to desire.

  Since the TED 30 converted from the BPD 20 by the substrate 1 propagates as it is to the plurality of epitaxial films 2, the wafer 10 having a desired film thickness with the BPD 20 reduced can be manufactured.

  As shown in FIG. 4A, after the wafer 10 is obtained, the substrate 1 on which the BPD 20 exists at a high density may be removed. The substrate 1 may be removed by an appropriate method such as mechanical polishing, chemical treatment, or ion etching. As a result, a wafer 11 made of the single epitaxial film 2 having a low BPD density as shown in FIG. 4B is obtained.

  Further, as shown in FIG. 4C, after obtaining the wafer 11 described above, epitaxial growth of silicon carbide is further performed once or a plurality of times on the surface on which the substrate 1 was present, and non-heating is performed. The epitaxial film 3 may be formed. The film thickness of the non-heated epitaxial film 3 and the number of times of epitaxial growth are not particularly limited. What is necessary is just to set suitably according to the whole film thickness and element structure of a desired wafer. Thereby, a wafer 12 having a low BPD density and having the non-heated epitaxial film 3 on the side where the substrate 1 was present can be obtained.

  Here, the principle that BPD is converted to TED by the above-described heat treatment will be described. FIG. 5A is a cross-sectional view as seen from the direction in which BPD grows, and FIGS. 5B and 5C are cross-sectional views along the direction in which BPD grows.

  As shown in FIG. 5A, an attractive force (mirror force) is generated between the BPD 20 and the mirror image dislocation 22. The mirror image force f acts in a direction in which the BPD 20 is attracted to the surface (crystal growth surface 5) side of the substrate 1. The magnitude | f | of the mirror image force f is expressed by the following equation.

  As shown in FIG. 5B, the BPD 20 propagates from the back surface of the substrate 1 (the surface opposite to the crystal growth surface 5) toward the crystal growth surface 5, and the tip portion 21 of the BPD 20 reaches the crystal growth surface 5. Appears. As described above, the distance between the BPD 20 and the crystal growth surface 5 becomes shorter as the distance from the tip portion 21 becomes closer. Therefore, according to the equation (1), the magnitude of the mirror image force f increases as the BPD 20 is closer to the tip portion 21.

  Then, as shown in FIG. 5C, when sufficient thermal energy is applied to the substrate 1, the BPD 20 can move, and the tip 21 of the BPD 20 receives the image force f and is bent toward the crystal growth surface 5. , Converted to TED30.

  At this time, the closer to the tip 21 side, the larger the image force f is applied, so that the tip 21 of the BPD 20 is gradually converted to the TED 30. If heating time is lengthened, the length L of BPD20 converted into TED30 can be lengthened. Therefore, the heating time in the heat treatment of the manufacturing method described above is not particularly limited, and may be appropriately adjusted such that heating is performed until the depth D of the TED 30 reaches a desired depth. Thus, by optimizing the heating temperature and heating time, the BPD 20 of the substrate 1 can be reduced to the limit.

<Embodiment 2>
In the first embodiment, the BPD in the substrate 1 is converted to TED by heating the substrate 1 in an inert gas or in a vacuum at a predetermined temperature for a predetermined time. Such a heat treatment is not limited to the target for the substrate 1 but may be an epitaxial film provided on the substrate. Thereby, BPD in the epitaxial film is converted to TED in the same manner as described above.

  FIG. 6 is a cross-sectional view of the SiC wafer according to the present embodiment. In addition, the same code | symbol is attached | subjected to the same thing as Embodiment 1, and the overlapping description is abbreviate | omitted.

  As shown in FIG. 6A, the wafer 10 includes a substrate 1, an epitaxial film 2 provided on the substrate 1, and an unheated epitaxial film 3 provided on the epitaxial film 2. The non-heated epitaxial film 3 is a thin film made of silicon carbide produced by a CVD method or the like, and is not subjected to heat treatment in an inert gas or vacuum. The epitaxial film 2 corresponds to the first epitaxial film of claim 16, and the non-heated epitaxial film 3 corresponds to the second epitaxial film of claim 16.

  A plurality of BPDs 20 are present on the substrate 1. In the figure, four BPDs 20 are illustrated.

  In the epitaxial film 2, four BPDs 20 are propagated as they are from the substrate 1, and three of them are converted into TEDs 30. As will be described in detail later, the conversion from the BPD 20 to the TED 30 is performed by heating the epitaxial film 2 in an inert gas or in a vacuum at a predetermined temperature for a predetermined time.

  In the non-heated epitaxial film 3, three TEDs 30 converted by the epitaxial film 2 propagate as they are, and one BPD 20 that has not been converted by the epitaxial film 2 propagates as it is.

  In the epitaxial film 2, 20% or more of the BPD propagated from the substrate 1 is converted to TED. In the illustrated example, three BPDs 20 of the four BPDs 20 in the epitaxial film 2 are converted to the TED 30, so that 75% of all the BPDs 20 in the epitaxial film 2 are converted to the TED 30.

  A portion having a thickness of 2 μm in the thickness direction in the epitaxial film 2 is defined as a region R. More than 60% of the conversion from BPD to TED performed in the epitaxial film 2 is performed in the region R. In the illustrated example, three BPDs 20 in the epitaxial film 2 are converted to TED 30, and two BPDs 20 in the region R are converted to TED 30. That is, 67% (2/3 = 0.666...) Of the conversion from BPD 20 to TED 30 performed in the epitaxial film 2 is performed in the region R.

  The reason why the BPD 20 is intensively converted into the TED 30 in the region R within the thickness of 2 μm is that the epitaxial film 2 is subjected to a heat treatment as described later. That is, as described in the principle of the first embodiment, the depth of the TED 30 can be adjusted by appropriately adjusting the temperature and time for heating the epitaxial film 2. It is considered that the TED converted outside the region R is naturally converted from BPD as the epitaxial film 2 grows.

  The position of the region R is located at a predetermined depth D from the interface between the epitaxial film 2 and the non-heated epitaxial film 3. The depth D is not particularly limited, but is, for example, 0.1 μm to 10 μm from the interface. This depth D can be controlled by the temperature and time of the heat treatment.

  Further, as the wafer 10 in which the BPD 20 is converted into the TED 30 in the epitaxial film 2, there is an embodiment shown in FIG.

  As shown in the drawing, a wafer 10 formed by forming a non-heated epitaxial film 3 on a substrate 1, forming an epitaxial film 2, subjecting the epitaxial film 2 to heat treatment, and further forming a non-heated epitaxial film 3. It may be.

  In this case, the claimed first epitaxial film is the epitaxial film 2, and the claimed second epitaxial film is the uppermost non-heated epitaxial film 3. That is, another epitaxial film may be interposed between the first epitaxial film and the substrate.

  Even in such a case, 20% or more of the BPD propagated to the epitaxial film 2 (first epitaxial film) is converted to TED, and 60% or more of the conversion from BPD to TED is performed in the region R. ing.

  The BPD 20 existing in the epitaxial film 2 and the non-heated epitaxial film 3 on the wafer 10 has the following relationship.

  For example, in the epitaxial film 2 shown in FIG. 6A, the BPD 20 propagated from the substrate 1 is converted into the TED 30 by the heat treatment. In the non-heated epitaxial film 3, the TED 30 converted by the epitaxial film 2 and the BPD 20 that has not been converted into the TED 30 in the epitaxial film 2 are propagated.

  The density of the BPD 20 included in the non-heated epitaxial film 3 is 80% or less of the density of the BPD 20 included in the epitaxial film 2. The density of the BPD 20 of the epitaxial film 2 is the number per unit area of BPD contained in the epitaxial film 2. The same applies to the density of the BPD 20 of the non-heated epitaxial film 3.

  In the example shown in FIG. 6A, the epitaxial film 2 includes four BPDs 20 (three of which are converted to TED 30), and the non-heated epitaxial film 3 includes one BPD 20. Therefore, the density (1 piece / unit area) of the BPD 20 of the non-heated epitaxial film 3 is 80% or less of the density (4 pieces / unit area) of the BPD 20 of the epitaxial film 2.

  As described above, in the wafer 10, the BPD 20 is converted into the TED 30 in the epitaxial film 2.

  In the prior art, a very small part of the BPD 20 is converted into the TED 30 in the epitaxial film 2 as it grows. Such conversion from the BPD 20 to the TED 30 occurs at an unspecified place in the depth direction of the epitaxial film.

  On the other hand, in the wafer 10 according to the present embodiment, a part of the BPD 20 is converted into TED by the epitaxial film 2 as in the conventional technique. In addition, in the wafer 10, 20% or more of the BPD 20 is converted to TED 30 in the epitaxial film 2. Therefore, the wafer 10 according to the present embodiment has a further reduced BPD 20. In the wafer 10, the BPD 20 is converted into the TED 30 at a predetermined depth of the epitaxial film 2.

  Thus, since the BPD 20 is reduced, the wafer 10 according to the present embodiment is suitable as a material for a semiconductor element that requires high voltage resistance and a semiconductor element that requires high reliability. The wafer 10 is not limited to the off-angle of the substrate 1 or the crystal plane (Si plane, C plane). Therefore, a wafer 10 having an off angle and a crystal plane suitable for manufacturing a semiconductor element is provided.

  FIG. 7 is a cross-sectional view showing the method for manufacturing the silicon carbide wafer according to the second embodiment.

  FIG. 7A shows a cross section of the substrate 1 on which the epitaxial film 2 is formed. A plurality of BPDs 20 are present in the substrate 1, but one BPD 20 is shown as a representative in the figure. The BPD 20 on the substrate 1 propagates as it is to the epitaxial film 2.

  Next, heat treatment is performed on the epitaxial film 2 of the substrate 1 in an inert gas or in a vacuum. The heat treatment is performed on the entire substrate 1, and the heating method, atmosphere, temperature, and time are the same as those in the first embodiment.

  As shown in FIG. 7B, the BPD 20 is converted to TED 30 inside the epitaxial film 2 by the heat treatment.

  Then, as shown in FIG. 7C, silicon carbide is epitaxially grown on the epitaxial film 2 including the TED 30 converted from the BPD 20.

  By performing epitaxial growth, an epitaxial film made of silicon carbide grows on the epitaxial film 2. Since this epitaxial film is not subjected to the above heat treatment, it is referred to as an unheated epitaxial film 3.

  During the crystal growth of the non-heated epitaxial film 3, the TED 30 propagates to the non-heated epitaxial film 3 as it is. Although not particularly shown, BPD that has not been converted to TED 30 by the heat treatment in the epitaxial film 2 propagates as it is to the non-heated epitaxial film 3 as BPD. Furthermore, in the non-heated epitaxial film 3, a very small part of the BPD 20 is naturally converted into the TED 30 during the growth.

  In this way, the wafer 10 as shown in FIG. 6A is manufactured.

  As shown in FIG. 7D, one or more unheated epitaxial films 3 may be formed on the unheated epitaxial film 3 by further performing epitaxial growth once or a plurality of times. Thereby, the wafer 10 including the newly formed non-heated epitaxial film 3 can be manufactured.

  Further, by forming one or a plurality of layers of the non-heated epitaxial film 3 on the substrate 1, and then forming the epitaxial film 2, performing heat treatment, and further forming the non-heated epitaxial film 3, FIG. The wafer 10 illustrated in (b) may be formed.

  As described above, the wafer 10 in which the BPD 20 is converted into the TED 30 in the epitaxial film 2 is manufactured.

  In the prior art, a very small part of the BPD 20 is converted into the TED 30 in the epitaxial film 2 as it grows. Such conversion from BPD to TED occurs at an unspecified place in the depth direction of the epitaxial film.

  On the other hand, in the method for manufacturing a silicon carbide wafer according to the present embodiment, the conversion position from BPD to TED is determined by the temperature and time of the heat treatment (see the principle of conversion from BPD to TED in Embodiment 1). . That is, the conversion position from BPD to TED is limited to a predetermined depth from the surface of epitaxial film 2.

  Therefore, in this manufacturing method, the wafer 10 in which the BPD 20 is converted into the TED 30 can be manufactured at a predetermined depth of the epitaxial film 2 by appropriately setting the temperature and time of the heat treatment.

  As in the first embodiment, the present manufacturing method converts the BPD 20 into the TED 30 in the epitaxial film 2 to manufacture a wafer 10 suitable as a material for a semiconductor element that requires high voltage resistance and high reliability. can do. In addition, since this manufacturing method does not require an etching process as in the prior art, the surface of the substrate 1 can be kept flat, and the etching process and the accompanying flattening process can be omitted. Furthermore, this manufacturing method can be applied without the need to limit the off-angle or crystal plane (Si plane, C plane) of the substrate 1, and there are no restrictions on the conditions for growing the epitaxial film 2.

  After obtaining the wafer 10 described above, the substrate 1 on which the BPD 20 exists at a high density, or both the substrate 1 and the epitaxial film 2 may be removed.

  A wafer 13 shown in FIG. 8B is obtained by completely removing the substrate 1 and the epitaxial film 2 from the wafer 10 shown in FIG.

  A wafer 14 shown in FIG. 8C is obtained by removing a part of the substrate 1 and the epitaxial film 2 from the wafer 10 shown in FIG. In the epitaxial film 2, the BPD 20 is converted into the TED 30, but a part of the epitaxial film 2 is removed to such an extent that the BPD 20 is removed.

  A wafer 15 shown in FIG. 8D is obtained by completely removing the substrate 1 from the wafer 10 shown in FIG.

  The substrate 1 and the epitaxial film 2 may be removed by an appropriate method such as mechanical polishing, chemical treatment, or ion etching. Thereby, the wafer 13 made of only the epitaxial film 2 having a low BPD density can be obtained.

  The wafers 16 to 18 shown in FIGS. 9A to 9C are obtained by forming the non-heated epitaxial film 3 on the wafers 13 to 15 shown in FIGS. 8B to 8D, respectively. Thus, after obtaining the wafer 13 to the wafer 15 described above, epitaxial growth of silicon carbide is further performed once or plural times on the surface on the side where the substrate 1 was present, thereby forming the non-heated epitaxial film 3. May be.

  The manufacturing method using the epitaxial film as the target of the heat treatment is not limited to the above-described mode, and the following modes can be exemplified.

  FIG. 10 is a cross-sectional view illustrating the method for manufacturing the silicon carbide wafer according to the second embodiment. FIG. 10A shows the substrate 1 on which the epitaxial film 2a is formed. Within the substrate 1, there are a plurality of BPDs 20 (represented in the figure as three representatives, 20 a, 20 b, and 20 c, respectively). In the epitaxial film 2a, three BPDs 20a to 20c are propagated along with the epitaxial growth.

  First, the substrate 1 on which the epitaxial film 2a is formed is subjected to heat treatment in an inert gas or in a vacuum to convert BPD into TED. The heating method, atmosphere, temperature, and time are the same as those in the first embodiment.

  At this time, as shown in FIG. 10B, it is assumed that the BPD 20a is converted to the TED 30a by the epitaxial film 2a and the BPDs 20b and 20c are not converted.

  Next, as shown in FIG. 10C, epitaxial growth is performed on the epitaxial film 2a to form the epitaxial film 2b. With this epitaxial growth, the TED 30a converted from the BPD 20a propagates to the epitaxial film 2b, and the BPDs 20b and 20c propagate.

  Next, as shown in FIG. 10D, the substrate 1 on which the epitaxial film 2b is formed is subjected to heat treatment to convert the BPD into TED. At this time, it is assumed that the BPD 20b is converted to the TED 30b by the epitaxial film 2b and the BPD 20c is not converted.

  Next, the same applies to the epitaxial film 2c. That is, epitaxial growth is performed on the epitaxial film 2b to form the epitaxial film 2c, and heat treatment is performed. Thereby, as shown in FIG. 10E, the BPD 20c propagated to the epitaxial film 2c is converted into a TED 30c.

  Thus, the wafer 10 in which the three layers of epitaxial films 2a to 2c are formed on the substrate 1 is manufactured.

  According to the manufacturing method of the aspect described above, by performing heat treatment on each of the plurality of epitaxial films 2a to 2c, conversion from BPD to TED is performed on each of the epitaxial films 2a to 2c. Therefore, BPD can be more reliably converted to TED than when BPD20 is converted to TED30 with a single epitaxial film.

  As described above, the wafer 10 with the BPD reduced to the limit can be manufactured by repeating the production of the epitaxial films 2a to 2c a plurality of times and the heat treatment for each of these films.

  Although not particularly illustrated, the non-heated epitaxial film 3 may be formed by further epitaxial growth on the heat-treated epitaxial film 2c.

  FIG. 10E illustrates the three-layer epitaxial film 2, but the number is not limited to this and may be any number. Further, the non-heated epitaxial film 3 may be formed on the epitaxial film 2 that has been subjected to the heat treatment, and then the epitaxial film 2 may be formed to perform the heat treatment. In any case, since the heat treatment is performed on each of the plurality of epitaxial films 2, the wafer 10 in which the BPD is further reduced can be manufactured.

<Embodiment 3>
In the first embodiment, the heat treatment is performed on the substrate 1, and in the second embodiment, the heat treatment is performed on the epitaxial film 2. However, the heat treatment may be performed on both the substrate 1 and the epitaxial film 2.

  The manufacturing method of the SiC wafer according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 11A, the substrate 1 is subjected to heat treatment in the same manner as in the first embodiment. Thereby, in the board | substrate 1, BPD20 is converted into TED30. A part of the BPD 20 exists as it is.

  Next, as shown in FIG. 11B, epitaxial growth of silicon carbide is performed on the substrate 1 to form an epitaxial film 2. The TED 30 and the BPD 20 are propagated from the substrate 1 to the epitaxial film 2.

  Next, as shown in FIG. 11C, the epitaxial film 2 is subjected to heat treatment in the same manner as in the second embodiment. Thereby, in the epitaxial film 2, BPD20 is converted into TED30.

  Then, as shown in FIG. 11 (d), the wafer 10 is manufactured by further performing epitaxial growth on the epitaxial film 2 to form the non-heated epitaxial film 3.

  The epitaxial film 2 is not limited to a single layer and may be a plurality of layers. Further, the non-heated epitaxial film 3 is not limited to one layer, and may be a plurality of layers. Moreover, when forming the non-heated epitaxial film 3 of multiple layers, it is not necessary to carry out continuously, and the non-heated epitaxial film 3 may be sandwiched therebetween.

  According to the manufacturing method of this embodiment, since the BPD is converted into TED by the heat treatment between the substrate 1 and the epitaxial film 2, the wafer 10 with the BPD reduced to the limit can be manufactured.

<Embodiment 4>
A dopant may be introduced into the epitaxial film 2 (first epitaxial film) and the non-heated epitaxial film 3 (second epitaxial film) of the wafer 10 described in the second embodiment.

  FIG. 12 is a cross-sectional view of the wafer according to the present embodiment. As shown in the drawing, the wafer 10 is provided with an epitaxial film 2 on a substrate 1 and an unheated epitaxial film 3 thereon.

For example, a p-type dopant is introduced into the epitaxial film 2 and the non-heated epitaxial film 3. The dopant concentration of the epitaxial film 2 is relatively high (p ⁺ ), and the dopant concentration of the non-heated epitaxial film 3 is relatively low (p ⁻ ). Of course, the dopant may be n-type, the dopant concentration of the epitaxial film 2 is relatively high (N ⁺ ), and the dopant concentration of the non-heated epitaxial film 3 is relatively low (N ⁻ ). Also good. Examples of the p-type dopant include Al and Br, and examples of the n-type dopant include N.

  Such a wafer 10 can be manufactured as follows. That is, when epitaxial growth is performed on the substrate 1, a gas containing a p-type or n-type dopant is used. Thereby, the p-type or n-type epitaxial film 2 is formed. And after heat-processing to the epitaxial film 2, the non-heating epitaxial film 3 is formed.

  From the wafer 10 thus manufactured, a p-type or n-type silicon carbide semiconductor device containing a desired concentration of dopant can be manufactured. As described above, since the BPD 20 is reduced, it is suitable as a material for a silicon carbide semiconductor element that requires high voltage resistance and a silicon carbide semiconductor element that requires high reliability. In addition, since the conversion from BPD 20 to TED 30 is not performed at the interface between the epitaxial film 2 and the non-heated epitaxial film 3 as in the prior art, the semiconductor element is inactive because the dopant concentration is high. Since the process is performed inside the epitaxial film 2 serving as a region, it is more suitable as a material for obtaining a highly reliable semiconductor element.

<Other embodiments>
Various silicon carbide semiconductor elements can be manufactured using wafers 10 to 18 described in the first to fourth embodiments. For example, MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), JFET (Junction Field Effect Transistor), BJT (Bipolar Junction Transistor), IGBT (Insulated Gate Bipolar Transistor), GTO (Gate Turn-Off Thyristor), GCT Thyristor ( Gate Commutated Turn-off Thyristor, thyristor, Schottky diode, JBS (Junction Barrier Schottky) diode, MPD (Merged pn diode), pn diode, and the like.

  In the wafer 10 according to the first to fourth embodiments, since the BPD 20 is reduced, a decrease in reliability and performance of these semiconductor elements is prevented, and a high-performance semiconductor element utilizing the excellent characteristics of silicon carbide is obtained. It is done.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Comparative example]
Crystal growth was performed by a CVD method on a 4H—SiC substrate having an off angle of 8 ° in the <11-20> direction to form an epitaxial film having a thickness of about 10 μm.

[Example]
About the board | substrate which concerns on a comparative example, after performing the measurement shown in the below-mentioned test example, it heat-processed. In this heat treatment, the substrate was placed in a graphite crucible, and the crucible was placed in a graphite cylinder (hot wall) where high frequency induction heating was performed. Argon gas was supplied into the crucible and heated at 1800 ° C. for 30 minutes. The heating rate was 40 ° C./min.

[Test Example 1]
For each of the substrates according to the comparative example and the example, the distribution of various dislocations in the epitaxial film was measured.

  First, the reflected light topography measurement (SPring-8 synchrotron radiation facility) was performed on the substrate according to the comparative example to obtain a topographic image. Specifically, the substrate according to the comparative example is irradiated with X-rays (wavelength 1.54Å) obtained by monochromatizing the emitted light at an incident angle of about 20 °, and the condition of diffraction vector g = 11−28 is satisfied. The reflected light was focused on the nuclear plate to obtain a topographic image.

  After the measurement of the substrate according to the comparative example was completed, the heat treatment as described above was performed to obtain the substrate according to the example. In the same manner, a topography image was obtained.

  FIG. 13 is a topographic image of a comparative example. The dark contrast on the line appearing on the substrate according to the comparative example is BPD, the relatively small fragment-like (dot-like) contrast is TED, and the relatively large circular contrast is TSD (threading screw dislocation).

  FIG. 14A is a topographic image of the comparative example, and FIG. 14B is a topographic image of the example. These topographic images show the same region of the substrate, and it was confirmed how dislocations were changed by the heat treatment.

  As indicated by the circles in FIG. 14A, it was confirmed that eight BPDs propagated from the substrate to the epitaxial film appeared on the substrate according to the comparative example.

  FIG. 14B shows that the BPDs indicated by the four circles are in the same position before and after the heat treatment. On the other hand, the broken circles indicate that what appeared on the surface of the epitaxial film as BPD in the comparative example appeared on the epitaxial film as TED after the heat treatment. This is judged from the fact that the linear contrast in the comparative example before the heat treatment changes to the contrast on the small fragment (dot shape) after the heat treatment.

  From the observation result of the topography image, a total of 8 BPDs appeared on the surface of the epitaxial film in one region of the substrate shown in the comparative example. Of these, 4 BPDs were transformed into TED by the epitaxial film by heat treatment. You can see that it has been converted.

[Test Example 2]
Regarding the comparative example and the example, the distribution of dislocations was measured in a wider region.

  When the BPD of the comparative example was measured in a wider area, 114 BPDs appeared on the surface of the epitaxial film. On the other hand, when the BPD of the example was measured for the same region, 23 of 114 BPDs corresponding to about 20% were converted to TED. In another sample having an epitaxial film having a thickness of about 20 μm subjected to the same heat treatment, 23 out of 49 BPDs corresponding to about 47% were converted to TED.

[Test Example 3]
A topography image was obtained in the same manner as in Test Example 1 for a sample having an epitaxial film with a thickness of about 10 μm obtained by the same method as in the comparative example. Next, this sample was subjected to the same heat treatment as in Example, and a topography image was obtained in the same manner after the heat treatment. When the topography image obtained after the heat treatment was examined, it was confirmed that a total of 67 BPDs were converted to TED in the epitaxial film. Next, when the topography image obtained before the heat treatment was examined, one of 67 BPDs converted to TED in the epitaxial film (corresponding to about 1.5%) was naturally grown during the epitaxial growth. It was confirmed that this happened. That is, it was found that about 1.5% of 67 BPDs converted to TED in the epitaxial film were converted to TED during the epitaxial growth, and the remaining 98.5% was caused by the heat treatment. . In another sample having an epitaxial film with a thickness of about 20 μm, which is processed in the same manner, about 12% of the BPD converted into TED in the epitaxial film is converted into TED during epitaxial growth, and the remaining 88% is heated. It turns out that it was caused by processing.

[Test Example 4]
FIG. 15 shows the result of examining in which depth direction the conversion from BPD to TED caused by the heat treatment was performed from the film surface in the epitaxial film. In the illustrated sample, an epitaxial film is formed on a substrate and then heat treatment is performed at 1800 ° C. The heat treatment time is 5 minutes. The film thickness of the epitaxial film is about 10 μm. In the measurement, the frequency of conversion from BPD to TED in the epitaxial film by the heat treatment was examined by comparatively examining the synchrotron radiation reflection topography acquired before and after the heat treatment. At the same time, in the synchrotron radiation topography image of what was converted from BPD to TED, the distance from the epitaxial film surface where the conversion occurred was examined by examining the length of BPD in the epitaxial film in the direction parallel to the off-tilt of the substrate Asked. As a result, the frequency with respect to the distance from the surface of the epitaxial film was clarified for the conversion from BPD to TED. As shown in FIG. 15, a region of 5.5 μm ± 1 μm from the surface of the epitaxial film (5.5 μm corresponds to D in FIG. 6A, and ± 1 μm (2 μm) corresponds to R in FIG. 6A. It was confirmed that more than 68% of the conversion from BPD to TED occurred.

[Test Example 5]
The BPD on the surface of the substrate before producing the epitaxial film was measured. In the measurement, a topographic image was formed on the substrate in the same manner as in Test Example 1, the BPD that appeared in the topographic image was counted, and the BPD per unit area was calculated. As a result, on the substrate surface, the density of BPD was about 4000 pieces / cm ² .

A topographic image was formed on a substrate according to an example in which an epitaxial film was formed on the substrate and heat treatment was performed. When BPD and TED appearing in the topography image were counted, most of the BPD was converted to TED, and the density of BPD in the epitaxial film was about 5 pieces / cm ² .

[Test Example 6]
As a result of performing the same experiment and analysis by changing the high-temperature heat treatment temperature in the range of 1500 to 2200 ° C. and the heat treatment time in the range of 5 to 240 minutes, the conversion from BPD to TED was not confirmed at 1500 to 1600 ° C. The conversion from BPD to TED was confirmed at 1700 ° C or higher. The probability of conversion from BPD to TED increased as the temperature increased. However, sublimation of the SiC surface started to accelerate in the temperature region exceeding 2000 ° C., and the heat treatment temperature was unsuitable above 2200 ° C. In addition, as the heat treatment time increased, the probability of conversion from BPD to TED increased, but it was almost saturated after 120 minutes. The position where the conversion from BPD to TED by the heat treatment occurred moved in the deep direction from the surface of the epitaxial film as the temperature or time of the high-temperature heat treatment increased, but in any case, it was ± 1 μm from a certain depth. Over 60% of the conversion from BPD to TED was performed within the range.

  The present invention can be used in an industrial field using a silicon carbide semiconductor element.

DESCRIPTION OF SYMBOLS 1 Silicon carbide substrate 2, 2a-2c Epitaxial film 3 Unheated epitaxial film 4 SiC layer 5 Crystal growth surface 10 Wafer 20 Basal plane dislocation (BPD)
21 tip 22 mirror image dislocation 30 threading edge dislocation (TED)

Claims (20)

By heat-treating the silicon carbide substrate at 1700 ° C. to 2200 ° C. in an inert gas atmosphere or vacuum, the tip of the basal plane dislocation of the silicon carbide substrate is converted into a threading edge dislocation,
A method for manufacturing a silicon carbide wafer, comprising epitaxially growing silicon carbide on the silicon carbide substrate. In the manufacturing method of the silicon carbide wafer of Claim 1,
A method for producing a silicon carbide wafer, comprising performing epitaxial growth and heat treatment of silicon carbide a plurality of times. In the manufacturing method of the silicon carbide wafer of Claim 1 or Claim 2,
A method of manufacturing a silicon carbide wafer, wherein epitaxial growth of silicon carbide is further performed once or a plurality of times on the epitaxial film. In the manufacturing method of the silicon carbide wafer as described in any one of Claims 1-3,
A method of manufacturing a silicon carbide wafer, comprising removing the silicon carbide substrate after performing epitaxial growth. In the manufacturing method of the silicon carbide wafer of Claim 4,
A method of manufacturing a silicon carbide wafer, wherein epitaxial growth of silicon carbide is further performed once or a plurality of times on the surface of the epitaxial film obtained by removing the silicon carbide substrate. An epitaxial film made of silicon carbide is formed on a silicon carbide substrate,
In an inert gas atmosphere or in vacuum, the epitaxial film is heat-treated at 1700 ° C. to 2200 ° C. to convert the tip of the basal plane dislocation of the epitaxial film into a threading edge dislocation,
A method for producing a silicon carbide wafer, comprising: epitaxially growing silicon carbide on the epitaxial film to cause crystal growth of an epitaxial film with reduced basal plane dislocations. In the manufacturing method of the silicon carbide wafer of Claim 6,
A method for producing a silicon carbide wafer, comprising performing epitaxial growth and heat treatment of silicon carbide a plurality of times. In the manufacturing method of the silicon carbide wafer of Claim 6 or Claim 7,
A method of manufacturing a silicon carbide wafer, wherein epitaxial growth of silicon carbide is further performed once or a plurality of times on the epitaxial film. In the manufacturing method of the silicon carbide wafer as described in any one of Claims 1-8,
When the epitaxial growth is performed, a dopant is introduced into the epitaxial film using a gas containing the dopant. A method for manufacturing a silicon carbide wafer, comprising: In the manufacturing method of the silicon carbide wafer as described in any one of Claims 6-9,
After the epitaxial growth is performed, the silicon carbide substrate is removed, or the silicon carbide substrate and the epitaxial film subjected to the heat treatment are removed. In the method for manufacturing a silicon carbide wafer according to claim 10,
Further, epitaxial growth of silicon carbide is further performed once or a plurality of times on the surface of the epitaxial film obtained by removing the silicon carbide substrate or the silicon carbide substrate and the epitaxial film subjected to the heat treatment. A method for manufacturing a silicon carbide wafer.   A silicon carbide substrate in which 20% or more of basal plane dislocations are converted to threading edge dislocations in a region of 0.1 μm or more and 10 μm or less from the surface of the silicon carbide substrate. An epitaxial film is formed on the silicon carbide substrate,
In the silicon carbide substrate, 20% or more of the basal plane dislocations are converted into threading edge dislocations in a region of 0.1 μm or more and 10 μm or less from the interface between the silicon carbide substrate and the epitaxial film. A silicon carbide wafer. A first epitaxial film on the silicon carbide substrate and a second epitaxial film on the first epitaxial film;
In the first epitaxial film, basal plane defects are converted into threading edge dislocations,
A silicon carbide wafer, wherein the density of basal plane dislocations contained in the second epitaxial film is 80% or less of the density of basal plane defects contained in the first epitaxial film. The silicon carbide wafer according to claim 14,
The dopant concentration contained in a 2nd epitaxial film is lower than the dopant concentration contained in a 1st epitaxial film. The silicon carbide wafer characterized by the above-mentioned. A plurality of epitaxial films are formed on the silicon carbide substrate,
Two adjacent epitaxial films of the plurality of epitaxial films, a silicon carbide wafer having a first epitaxial film on the side close to the silicon carbide substrate and a second epitaxial film on the far side,
In the first epitaxial film, 20% or more of basal plane defects are converted into threading edge dislocations,
60% or more of conversion from a basal plane defect to a threading edge dislocation is performed in a region within 2 μm in the thickness direction in the first epitaxial film. The silicon carbide wafer according to claim 16,
80% or more of the conversion from basal plane defects to threading edge dislocations is performed in a region of 0.1 μm or more and 10 μm or less from the interface with the second epitaxial film in the first epitaxial film. A featured silicon carbide wafer. In the silicon carbide wafer according to any one of claims 13 to 17,
The silicon carbide wafer, wherein the silicon carbide substrate is removed. The silicon carbide wafer according to claim 18,
An epitaxial film is formed on the surface of the side from which the silicon carbide substrate has been removed.   A silicon carbide semiconductor device manufactured using the silicon carbide wafer according to any one of claims 13 to 19.