JP2011108721A - Method of manufacturing silicon carbide substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a large-diameter silicon carbide substrate having superior crystallinity. <P>SOLUTION: The method of manufacturing a silicon carbide substrate includes a step of preparing a plurality of SiC substrates 20 consisting of single crystal silicon carbide, a step of arranging a supporting substrate 10 to touch one main surfaces 20C of the plurality of SiC substrates 20 while the plurality of SiC substrates 20 are arranged side by side in plan view, and a step of interconnecting the plurality of SiC substrates 20 by means of the supporting substrate 10. In the step of interconnecting the plurality of SiC substrates 20, a step of heating the supporting substrate 10, and a step of cooling the supporting substrate 10 are carried out repeatedly. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a silicon carbide substrate, and more particularly to a method for manufacturing a silicon carbide substrate capable of easily manufacturing a large-diameter silicon carbide substrate.

  In recent years, silicon carbide (SiC) has been increasingly adopted as a material constituting semiconductor devices in order to enable higher breakdown voltage, lower loss, and use in high-temperature environments. Silicon carbide is a wide band gap semiconductor having a larger band gap than silicon that has been widely used as a material for forming semiconductor devices. Therefore, by adopting silicon carbide as a material constituting the semiconductor device, it is possible to achieve a high breakdown voltage and a low on-resistance of the semiconductor device. In addition, a semiconductor device that employs silicon carbide as a material has an advantage that a decrease in characteristics when used in a high temperature environment is small as compared with a semiconductor device that employs silicon as a material.

  On the other hand, in order to efficiently manufacture a semiconductor device, it is effective to use a large-diameter substrate. Therefore, various studies have been made on a silicon carbide substrate made of single crystal silicon carbide having a diameter of 3 inches or 4 inches and a method for manufacturing the same, and a method for manufacturing a silicon carbide substrate using, for example, a sublimation method has been proposed (for example, a patent References 1-3).

US Patent Application Publication No. 2006/0073707 US Patent Application Publication No. 2007/020977 US Patent Application Publication No. 2006/0075958

  However, from the viewpoint of further improving the efficiency of the manufacture of the semiconductor device, a further increase in diameter (for example, 4 inches or more) is required for the silicon carbide substrate. Here, in order to fabricate a large-diameter silicon carbide substrate by the sublimation method, it is necessary to widen the region where the temperature is uniform. However, since the growth temperature of silicon carbide in the sublimation method is as high as 2000 ° C. or higher and it is difficult to control the temperature, it is not easy to widen the region where the temperature is uniform. Therefore, there is a problem that it is not easy to produce a silicon carbide substrate having a large diameter (for example, 4 inches or more) excellent in crystallinity even when a sublimation method in which a large diameter is relatively easy is used.

  Therefore, an object of the present invention is to provide a method for producing a large-diameter silicon carbide substrate having excellent crystallinity.

  A method for manufacturing a silicon carbide substrate according to the present invention includes a step of preparing a plurality of SiC substrates made of single crystal silicon carbide, and a plurality of SiC substrates in a state where a plurality of SiC substrates are arranged side by side in a plan view. The method includes a step of arranging a support substrate so as to be in contact with one main surface of the substrate, and a step of connecting a plurality of SiC substrates with the support substrate. In the step of connecting a plurality of SiC substrates, the step of heating the support substrate and the step of cooling the support substrate are repeated.

  In the method for manufacturing a silicon carbide substrate of the present invention, a plurality of SiC substrates made of single crystal silicon carbide are connected to each other by a support substrate in a state where a plurality of SiC substrates are arranged in a plan view. As described above, it is difficult to increase the diameter of a substrate made of single crystal silicon carbide while maintaining high quality. On the other hand, by arranging a plurality of SiC substrates taken from a small-diameter silicon carbide single crystal, which can be easily improved in quality, and then connecting them with a large-diameter support substrate, the crystallinity is excellent. A silicon carbide substrate that can be handled as a large-diameter silicon carbide substrate can be obtained. Furthermore, in the method for manufacturing a silicon carbide substrate of the present invention, when a plurality of SiC substrates are connected to each other by a support substrate, heating and cooling of the support substrate are repeatedly performed. By bonding the support substrate and the SiC substrate in this way, the damage to the SiC substrate is suppressed compared to the case where the support substrate and the SiC substrate are bonded by continuously heating the support substrate. Can do. Thus, according to the method for manufacturing a silicon carbide substrate of the present invention, a large-diameter silicon carbide substrate having excellent crystallinity can be manufactured.

  In the method for manufacturing a silicon carbide substrate of the present invention, the support substrate may be made of silicon carbide. Thereby, since a SiC substrate and a support substrate consist of the same kind of material, the difference of both linear expansion coefficients can be suppressed, and the curvature etc. in the silicon carbide substrate manufactured can be suppressed. Here, the silicon carbide constituting the support substrate can take any form of single crystal, polycrystal, and amorphous depending on the structure of the support substrate to be prepared, heating conditions, and the like.

  In the method for manufacturing a silicon carbide substrate of the present invention, preferably, in the step of heating the support substrate, the support substrate is heated to a temperature of 1800 ° C. or higher and 2500 ° C. or lower.

  When the support substrate is made of silicon carbide, if the heating temperature of the support substrate is less than 1800 ° C., it takes a long time to join the SiC substrate and the support substrate. On the other hand, if the heating temperature of the support substrate exceeds 2500 ° C., the manufactured silicon carbide substrate may be damaged. Therefore, the heating temperature of the support substrate is preferably set to 1800 ° C. or higher and 2500 ° C. or lower.

  In the method for manufacturing a silicon carbide substrate of the present invention, in the step of heating the support substrate, the support substrate is heated from the main surface side opposite to the SiC substrate, so that the temperature of the SiC substrate is lower than that of the support substrate. May be maintained.

  Thus, by heating so that a support substrate may become high temperature rather than a SiC substrate, the silicon carbide which comprises a support substrate sublimates, reaches | attains a SiC substrate, and solidifies. The SiC substrate and the support substrate are easily joined by the progress of such a phenomenon.

  In the method for manufacturing a silicon carbide substrate of the present invention, the support substrate may be made of a refractory metal having a melting point of 1800 ° C. or higher.

  Thus, when the melting point of the support substrate is 1800 ° C. or higher, a silicon carbide substrate that can be used for manufacturing a semiconductor device including a process heated to a high temperature such as activation annealing can be manufactured. Moreover, when the silicon carbide substrate is used for manufacturing a vertical semiconductor device in which a current flows in the thickness direction of the silicon carbide substrate, for example, by forming the support substrate from a metal that is a conductor, the semiconductor device to be manufactured The resistance of the substrate can be reduced. As the refractory metal, for example, molybdenum, tantalum, tungsten, niobium, iridium, ruthenium, zirconium, titanium, nickel and the like can be employed.

  In the method for manufacturing a silicon carbide substrate of the present invention, in the step of heating the support substrate, the support substrate may be heated to a temperature range equal to or higher than the melting point of the refractory metal.

  Thereby, a support substrate and a SiC substrate can be joined easily. Here, when the heating temperature of the support substrate greatly exceeds the melting point of the refractory metal, the support substrate may not be able to maintain a desired shape. Therefore, it is preferable that the support substrate is substantially heated to the melting point. Specifically, the support substrate is preferably heated to a temperature range not lower than the melting point and not higher than 100 ° C. higher than the melting point. Moreover, in order to maintain a support substrate in a desired shape, it is preferable that the time for which a support substrate is heated more than melting | fusing point in the process of heating a support substrate is 5 minutes or less per time of heating.

  In the method for manufacturing a silicon carbide substrate of the present invention, in the step of heating the support substrate, the support substrate may be heated by at least one of heating by laser irradiation and lamp heating.

  Both heating by laser irradiation and lamp heating are heating methods suitable for the step of connecting the plurality of SiC substrates that repeat heating and cooling. Note that heating by laser irradiation and lamp heating may be performed in combination, or only one may be performed.

  In the method for manufacturing a silicon carbide substrate of the present invention, preferably, the thickness of the support substrate is not less than 1 μm and not more than 1 mm.

  When the thickness of the support substrate is less than 1 μm, it may be difficult to connect the SiC substrates with sufficient strength. On the other hand, if the thickness of the support substrate exceeds 1 mm, the thickness of the manufactured silicon carbide substrate increases. For example, when a silicon carbide substrate is used for manufacturing a vertical semiconductor device, the thickness of the substrate in the manufactured semiconductor device is increased. Resistance increases. Therefore, the thickness of the support substrate is preferably 1 μm or more and 1 mm or less.

  In the method for manufacturing a silicon carbide substrate of the present invention, in the step of connecting the plurality of SiC substrates, the main surface opposite to the support substrate of the plurality of SiC substrates has an off angle of 50 with respect to the {0001} plane. A plurality of SiC substrates may be connected so as to be at least 65 ° and at most 65 °.

  By growing hexagonal single crystal silicon carbide in the <0001> direction, a high-quality single crystal can be efficiently produced. And from the silicon carbide single crystal grown in the <0001> direction, a silicon carbide substrate having a {0001} plane as a main surface can be efficiently collected. On the other hand, there may be a case where a high-performance semiconductor device can be manufactured by using a silicon carbide substrate having a main surface with an off angle of 50 ° or more and 65 ° or less with respect to the plane orientation {0001}.

  Specifically, for example, a silicon carbide substrate used for manufacturing a MOSFET generally has a main surface with an off angle of about 8 ° with respect to the plane orientation {0001}. An epitaxial growth layer is formed on the main surface, and an oxide film, an electrode, and the like are formed on the epitaxial growth layer, thereby obtaining a MOSFET. In this MOSFET, a channel region is formed in a region including the interface between the epitaxial growth layer and the oxide film. However, in the MOSFET having such a structure, the off-angle of the main surface of the substrate with respect to the {0001} plane is about 8 °, so that the interface between the epitaxial growth layer and the oxide film in which the channel region is formed Many interface states are formed in the vicinity, hindering carrier travel, and channel mobility is lowered.

  In contrast, in the step of connecting the plurality of SiC substrates to each other, the main surface of the SiC substrate opposite to the support substrate has an off angle with respect to the {0001} plane of 50 ° or more and 65 ° or less. Since the off angle of the main surface of the silicon carbide substrate to the {0001} plane is not less than 50 ° and not more than 65 °, formation of the interface state is reduced, and a MOSFET with reduced on-resistance can be manufactured. .

  In the method for manufacturing a silicon carbide substrate of the present invention, in the step of connecting a plurality of SiC substrates, an angle formed between the off orientation of the main surface opposite to the support substrate of the SiC substrate and the <1-100> direction A plurality of SiC substrates may be connected so that the angle is 5 ° or less.

  The <1-100> direction is a typical off orientation in the silicon carbide substrate. Then, by setting the variation in off orientation due to the variation in slicing in the substrate manufacturing process to 5 ° or less, the formation of an epitaxially grown layer on the silicon carbide substrate can be facilitated.

  In the method for manufacturing a silicon carbide substrate of the present invention, in the step of connecting a plurality of SiC substrates, {03-38} in the <1-100> direction on the main surface of the SiC substrate opposite to the support substrate. A plurality of SiC substrates may be connected so that the off angle with respect to the surface is -3 ° or more and 5 ° or less.

  Thereby, the channel mobility when a MOSFET is fabricated using a silicon carbide substrate can be further improved. Here, the reason why the off angle with respect to the plane orientation {03-38} is set to −3 ° to + 5 ° is that, as a result of investigating the relationship between the channel mobility and the off angle, the channel mobility is particularly high within this range. Is based on the obtained.

  The “off angle with respect to the {03-38} plane in the <1-100> direction” is an orthogonal projection of the normal of the principal surface to the plane extending in the <1-100> direction and the <0001> direction. It is an angle formed with the normal of the {03-38} plane, and its sign is positive when the orthographic projection approaches parallel to the <1-100> direction, and the orthographic projection is in the <0001> direction. The case of approaching parallel to is negative.

  In addition, it is more preferable that the surface orientation of the main surface is substantially {03-38}, and it is further preferable that the surface orientation of the main surface is {03-38}. Here, the surface orientation of the main surface is substantially {03-38}, taking into account the processing accuracy of the substrate, etc., the substrate is within the range of the off angle where the surface orientation can be substantially regarded as {03-38}. In this case, the off-angle range is, for example, a range where the off-angle is ± 2 ° with respect to {03-38}. As a result, the above-described channel mobility can be further improved.

  In the method for manufacturing a silicon carbide substrate of the present invention, in the step of connecting a plurality of SiC substrates, an angle formed between the off orientation of the main surface opposite to the support substrate of the SiC substrate and the <11-20> direction. A plurality of SiC substrates may be connected so that the angle is 5 ° or less.

  The <11-20> direction is a typical off orientation in the silicon carbide substrate, similarly to the <1-100> direction. Then, by setting the variation in the off orientation due to the variation in the slice processing in the substrate manufacturing process to ± 5 °, it is possible to facilitate the formation of the epitaxial growth layer on the SiC substrate.

  In the method for manufacturing a silicon carbide substrate, in the step of arranging the support substrate so as to contact one main surface of the plurality of SiC substrates, a support substrate made of silicon carbide having a higher impurity density than the SiC substrate is arranged. May be.

Thereby, the resistivity of the support substrate can be reduced, and a silicon carbide substrate suitable for manufacturing a vertical semiconductor device (a semiconductor device in which current flows in the thickness direction of the substrate) can be manufactured. Here, from the viewpoint of reducing the resistivity of the support substrate, in the step of disposing the support substrate, a support substrate having an impurity density exceeding 2 × 10 ¹⁹ cm ⁻³ may be disposed.

  As is clear from the above description, according to the method for manufacturing a silicon carbide substrate of the present invention, a large-diameter silicon carbide substrate having excellent crystallinity can be manufactured.

3 is a flowchart showing an outline of a method for manufacturing a silicon carbide substrate in the first embodiment. 3 is a schematic cross sectional view for illustrating the method for manufacturing the silicon carbide substrate in the first embodiment. FIG. 5 is a schematic plan view for illustrating the method for manufacturing the silicon carbide substrate in the first embodiment. FIG. 1 is a schematic cross sectional view showing a structure of a silicon carbide substrate in a first embodiment. 5 is a flowchart showing an outline of a method for manufacturing a silicon carbide substrate in a second embodiment. FIG. 11 is a schematic cross sectional view for illustrating the method for manufacturing the silicon carbide substrate in the second embodiment. FIG. 6 is a schematic cross sectional view showing a structure of a silicon carbide substrate in a second embodiment. It is a schematic sectional drawing which shows the structure of vertical MOSFET. It is a flowchart which shows the outline of the manufacturing method of vertical MOSFET. It is a schematic sectional drawing for demonstrating the manufacturing method of vertical MOSFET. It is a schematic sectional drawing for demonstrating the manufacturing method of vertical MOSFET. It is a schematic sectional drawing for demonstrating the manufacturing method of vertical MOSFET. It is a schematic sectional drawing for demonstrating the manufacturing method of vertical MOSFET.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

(Embodiment 1)
First, Embodiment 1 which is one embodiment of the present invention will be described with reference to FIGS. 2 corresponds to a cross-sectional view taken along line II-II in FIG. Referring to FIG. 1, in the method for manufacturing a silicon carbide substrate in the present embodiment, a substrate preparation step is first performed as a step (S10). In this step (S10), referring to FIG. 2, for example, support substrate 10 made of single crystal silicon carbide and a plurality of SiC substrates 20 made of single crystal silicon carbide are prepared.

At this time, main surface 20A of SiC substrate 20 is the main surface of the silicon carbide substrate obtained by this manufacturing method (see FIG. 4 to be described later), so that SiC substrate 20 is aligned with the surface orientation of the desired main surface. The plane orientation of the main surface 20A is selected. Here, for example, SiC substrate 20 whose main surface is a {03-38} plane is prepared. Further, as the support substrate 10, for example, a substrate having an impurity density higher than 2 × 10 ¹⁹ cm ⁻³ may be employed. As SiC substrate 20, for example, a substrate having an impurity density larger than 5 × 10 ¹⁸ cm ^{−3 and} smaller than 2 × 10 ¹⁹ cm ⁻³ is employed. The support substrate 10 is not limited to a single crystal and may be prepared from a polycrystal or an amorphous material.

  Next, a substrate flattening step is performed as a step (S20). In this step (S20), referring to FIG. 2, the main surface 10B of support substrate 10 and the main surface 20C (joint surface) of SiC substrate 20 to be in contact with each other in step (S30) described later are flattened by polishing, for example. It becomes. In addition, although this process (S20) is not an indispensable process, since the space | interval of the support substrate 10 and SiC substrate 20 which opposes mutually becomes uniform by implementing this, in process (S40) mentioned later. The uniformity of reaction (bonding) within the bonding surface is improved. As a result, support substrate 10 and SiC substrate 20 can be more reliably bonded.

  Next, a lamination process is implemented as process (S30). In this step (S30), referring to FIG. 2, SiC substrate 20 is placed so as to be in contact with main surface 10B of support substrate 10, and multilayer substrate 2 is manufactured. At this time, the SiC substrates 20 adjacent to each other may be arranged at an interval, but as shown in FIG. 2, they are laid out in a matrix as viewed in plan so that the end surfaces 20B are in contact with each other. Preferably they are arranged.

  Next, a laser irradiation process is implemented as process (S40). In this step (S40), the support substrate 10 is irradiated with laser, whereby the support substrate 10 is repeatedly heated and cooled. Specifically, the support substrate 10 is irradiated with a laser while being scanned a plurality of times. Thereby, in each part of the support substrate 10, heating and cooling are repeatedly performed. Alternatively, the support substrate 10 may be irradiated with a pulsed laser. In this case, heating and cooling can be repeatedly performed for each part of the support substrate 10 in a short time even by a single scan. That is, in the present embodiment, in the step of connecting a plurality of SiC substrates 20, the step of heating support substrate 10 and the step of cooling support substrate 10 are repeatedly performed.

  At this time, as shown in FIG. 2, the support substrate 10 is heated by being irradiated with laser from the main surface 10 </ b> A side opposite to the SiC substrate 20 as indicated by the arrow α, It is preferable to maintain the temperature lower than that of the support substrate 10. Thus, by heating so that the support substrate 10 becomes higher temperature than the SiC substrate 20, the silicon carbide which comprises the support substrate 10 sublimes, reaches | attains the SiC substrate 20, and solidifies. And by progress of such a phenomenon, SiC substrate 20 and support substrate 10 can be joined easily and firmly. As a result, as shown in FIG. 4, the plurality of SiC substrates 20 are connected to each other by the support substrate 10. Through the above process, silicon carbide substrate 1 of the present invention is manufactured.

In addition, it is preferable that the wavelength of the laser used in the said process (S40) is 450 nm or more so that a laser may reach the inside of the support substrate 10 which consists of silicon carbide. Examples of usable lasers include pulse oscillation or continuous oscillation CO ₂ laser (wavelength 10.60 μm), pulse oscillation or continuous oscillation Nd: YAG laser (wavelength 1064 nm), and continuous oscillation Ar ⁺ laser (wavelength 488). .5 nm or 514.5 nm), pulse oscillation or continuous oscillation semiconductor laser (wavelength 650 to 1700 nm), and the like. Further, when the output of the employed laser is too small, it becomes difficult to sufficiently heat, while when it is too large, there is a problem that the region to be heated is too wide. For this reason, the laser output is preferably in the range of 0.1 to 100 kW in the case of continuous oscillation, and is preferably in the range of 0.1 to 10 kW in the case of pulse oscillation.

  In the method for manufacturing a silicon carbide substrate in the present embodiment, a plurality of SiC substrates 20 made of single crystal silicon carbide are connected by support substrate 10 in a state where a plurality of SiC substrates 20 are arranged in a plan view. For this reason, by arranging a plurality of SiC substrates 20 taken from a small-diameter silicon carbide single crystal that can be easily improved in quality in a plane, and connecting them with a support substrate 10 having a large-diameter, the crystallinity is excellent. Silicon carbide substrate 1 that can be handled as a large-diameter silicon carbide substrate can be obtained. Furthermore, since the heating and cooling of the support substrate 10 are repeated in the step (S40) and the support substrate 10 and the SiC substrate 20 are joined, the damage to the SiC substrate 20 compared to the case of continuous heating is caused. Can be suppressed. As a result, according to the method for manufacturing a silicon carbide substrate in the present embodiment, a large-diameter silicon carbide substrate having excellent crystallinity can be manufactured.

  Here, in the step (S40), the support substrate 10 is preferably heated to a temperature of 1800 ° C. or higher and 2500 ° C. or lower. Thereby, SiC substrate 20 and support substrate 10 can be joined in a short time while suppressing damage caused by heating on silicon carbide substrate 1 to be manufactured.

  The thickness of the support substrate 10 is preferably 1 μm or more and 1 mm or less. Thereby, SiC substrates 20 can be bonded with sufficient strength, and resistance in the thickness direction of silicon carbide substrate 1 can be suppressed.

  Further, main surface 20A of SiC substrate 20 may have an off angle of 50 ° to 65 ° with respect to the {0001} plane. Thereby, when a MOSFET is manufactured using manufactured silicon carbide substrate 1, formation of an interface state in the channel region is reduced, and a MOSFET with reduced on-resistance can be obtained. On the other hand, in consideration of ease of manufacture, main surface 20A of SiC substrate 20 may be a {0001} plane.

  Further, the angle formed between the off orientation of main surface 20A of SiC substrate 20 and the <1-100> direction may be 5 ° or less. The <1-100> direction is a typical off orientation in the silicon carbide substrate. Further, by setting the variation in the off orientation due to the variation in the slice processing in the manufacturing process of the substrate to 5 ° or less, the formation of the epitaxial growth layer on the silicon carbide substrate 1 can be facilitated.

  Further, in silicon carbide substrate 1, the off angle of main surface 20 </ b> A of SiC substrate 20 with respect to the {03-38} plane in the <1-100> direction is preferably −3 ° to 5 °. Thereby, the channel mobility in the case where a MOSFET is manufactured using silicon carbide substrate 1 to be manufactured can be further improved.

  On the other hand, the angle formed between the off orientation of main surface 20A of SiC substrate 20 and the <11-20> direction may be 5 ° or less.

  <11-20> is also a typical off orientation in a silicon carbide substrate. Then, by setting the variation in the off orientation due to the variation in the slice processing in the substrate manufacturing process to ± 5 °, the silicon carbide substrate 1 manufactured by the method for manufacturing the silicon carbide substrate according to the present embodiment is applied. The formation of an epitaxial growth layer can be facilitated.

(Embodiment 2)
Next, with reference to FIGS. 5 to 7, a second embodiment which is another embodiment of the present invention will be described. The method for manufacturing the silicon carbide substrate in the second embodiment is performed basically in the same manner as in the first embodiment. However, the second embodiment is different from the first embodiment in that a metal substrate is employed as the support substrate and lamp heating is employed instead of heating by laser irradiation. .

  Referring to FIG. 5, in the method for manufacturing a silicon carbide substrate in the present embodiment, first, in the substrate preparation step performed as step (S <b> 10), the same as in Embodiment 1 with reference to FIG. 6. A plurality of SiC substrates 20 are prepared, and a support substrate 10 made of a refractory metal having a melting point of 1800 ° C. or higher is prepared. As the refractory metal constituting the support substrate 10, for example, molybdenum, tantalum, tungsten, niobium, iridium, ruthenium, zirconium, titanium, nickel and the like can be employed.

  Next, after the steps (S20) and (S30) are performed and the multilayer substrate 2 is manufactured in the same manner as in the first embodiment, the lamp heating step performed as the step (S41), and the step (S42) And the cooling process carried out as is repeated alternately. Specifically, referring to FIG. 6, in step (S41), support substrate 10 is heated by lamp heating. As the lamp, an infrared lamp, a halogen lamp, or the like can be employed. On the other hand, in the step (S42), the lamp heating is interrupted and the support substrate 10 is cooled. By repeatedly performing such steps (S41) and (S42) alternately, heating and cooling are repeatedly performed on the entire support substrate 10. Thereby, support substrate 10 and SiC substrate 20 are joined. As a result, the plurality of SiC substrates 20 are connected by the support substrate 10. Through the above process, silicon carbide substrate 1 in the second embodiment shown in FIG. 7 is completed.

  Here, in the step (S41), the support substrate 10 is preferably heated to a temperature range equal to or higher than the melting point of the refractory metal constituting the support substrate 10. Thereby, support substrate 10 and SiC substrate 20 can be easily joined.

  In the above embodiment, heating by laser irradiation is employed when the support substrate 10 is made of silicon carbide, and lamp heating is employed when the support substrate is made of a refractory metal. However, the support substrate 10 is made of silicon carbide. In some cases, lamp heating may be employed, or when the support substrate 10 is made of a refractory metal, heating by laser irradiation may be employed. Moreover, you may implement combining the heating by laser irradiation, and lamp heating.

(Embodiment 3)
Next, an example of a semiconductor device manufactured using the silicon carbide substrate of the present invention manufactured by the method of manufacturing a silicon carbide substrate of the present invention will be described as a third embodiment. Referring to FIG. 8, a semiconductor device 101 according to the present invention is a vertical DiMOSFET (Double Implanted MOSFET), and includes a substrate 102, a buffer layer 121, a breakdown voltage holding layer 122, a p region 123, an n ⁺ region 124, and p ^+. A region 125, an oxide film 126, a source electrode 111 and an upper source electrode 127, a gate electrode 110, and a drain electrode 112 formed on the back side of the substrate 102 are provided. Specifically, buffer layer 121 made of silicon carbide is formed on the surface of substrate 102 made of silicon carbide of n-type conductivity. As substrate 102, the silicon carbide substrate of the present invention including silicon carbide substrate 1 described in the first and second embodiments is employed. When silicon carbide substrate 1 in the first and second embodiments is employed, buffer layer 121 is formed on SiC substrate 20 of silicon carbide substrate 1. Buffer layer 121 has n-type conductivity, and its thickness is, for example, 0.5 μm. Further, the density of the n-type conductive impurity in the buffer layer 121 can be set to, for example, 5 × 10 ¹⁷ cm ⁻³ . A breakdown voltage holding layer 122 is formed on the buffer layer 121. The breakdown voltage holding layer 122 is made of silicon carbide of n-type conductivity, and has a thickness of 10 μm, for example. Further, as the density of the n-type conductive impurity in the breakdown voltage holding layer 122, for example, a value of 5 × 10 ¹⁵ cm ⁻³ can be used.

On the surface of the breakdown voltage holding layer 122, p regions 123 having a p-type conductivity are formed at intervals. Inside the p region 123, an n ⁺ region 124 is formed in the surface layer of the p region 123. A p ⁺ region 125 is formed at a position adjacent to the n ⁺ region 124. From the n ⁺ region 124 in one p region 123 to the p region 123, the breakdown voltage holding layer 122 exposed between the two p regions 123, the other p region 123, and the n ⁺ region 124 in the other p region 123. An oxide film 126 is formed so as to extend to. A gate electrode 110 is formed on the oxide film 126. A source electrode 111 is formed on the n ⁺ region 124 and the p ⁺ region 125. An upper source electrode 127 is formed on the source electrode 111. A drain electrode 112 is formed on the back surface of the substrate 102 which is the surface opposite to the surface on which the buffer layer 121 is formed.

  In semiconductor device 101 in the present embodiment, silicon carbide substrate of the present invention such as silicon carbide substrate 1 described in the first and second embodiments is employed as substrate 102. Here, as described above, the silicon carbide substrate of the present invention is manufactured by a manufacturing method capable of manufacturing a large-diameter silicon carbide substrate excellent in crystallinity. Therefore, the semiconductor device 101 is a semiconductor device having excellent characteristics while reducing manufacturing costs.

  Next, a method for manufacturing the semiconductor device 101 shown in FIG. 8 will be described with reference to FIGS. Referring to FIG. 9, first, a substrate preparation step (S110) is performed. Here, for example, a substrate 102 (see FIG. 10) made of silicon carbide having a (03-38) plane as a main surface is prepared. As this substrate 102, the silicon carbide substrate of the present invention including silicon carbide substrate 1 manufactured by the manufacturing method described in the first or second embodiment is prepared.

  Further, as this substrate 102 (see FIG. 10), for example, a substrate having an n-type conductivity and a substrate resistance of 0.02 Ωcm may be used.

Next, as shown in FIG. 9, an epitaxial layer forming step (S120) is performed. Specifically, the buffer layer 121 is formed on the surface of the substrate 102. Buffer layer 121 is formed on SiC substrate 20 of silicon carbide substrate 1 employed as substrate 102 (see FIGS. 4 and 7). Buffer layer 121 is formed of an n-type silicon carbide, and an epitaxial layer having a thickness of 0.5 μm, for example, is formed. For example, a value of 5 × 10 ¹⁷ cm ⁻³ can be used as the density of the conductive impurities in the buffer layer 121. Then, a breakdown voltage holding layer 122 is formed on the buffer layer 121 as shown in FIG. As breakdown voltage holding layer 122, a layer made of silicon carbide of n-type conductivity is formed by an epitaxial growth method. As the thickness of the breakdown voltage holding layer 122, for example, a value of 10 μm can be used. Further, as the density of the n-type conductive impurity in the breakdown voltage holding layer 122, for example, a value of 5 × 10 ¹⁵ cm ⁻³ can be used.

Next, an injection step (S130) is performed as shown in FIG. Specifically, by using an oxide film formed by photolithography and etching as a mask, an impurity having a conductivity type of p type is implanted into the breakdown voltage holding layer 122, thereby forming the p region 123 as shown in FIG. Form. Further, after removing the used oxide film, an oxide film having a new pattern is formed again by photolithography and etching. Then, by using the oxide film as a mask, an n-type conductive impurity is implanted into a predetermined region, thereby forming an n ⁺ region 124. Further, the p ⁺ region 125 is formed by injecting a p-type conductive impurity in the same manner. As a result, a structure as shown in FIG. 11 is obtained.

  After such an implantation step, an activation annealing process is performed. As this activation annealing treatment, for example, argon gas is used as an atmospheric gas, and conditions such as a heating temperature of 1700 ° C. and a heating time of 30 minutes can be used.

Next, a gate insulating film forming step (S140) is performed as shown in FIG. Specifically, as illustrated in FIG. 12, an oxide film 126 is formed so as to cover the breakdown voltage holding layer 122, the p region 123, the n ⁺ region 124, and the p ⁺ region 125. As a condition for forming this oxide film 126, for example, dry oxidation (thermal oxidation) may be performed. As conditions for this dry oxidation, conditions such as a heating temperature of 1200 ° C. and a heating time of 30 minutes can be used.

Thereafter, a nitrogen annealing step (S150) is performed as shown in FIG. Specifically, the annealing process is performed using nitrogen monoxide (NO) as the atmosphere gas. As temperature conditions for the annealing treatment, for example, the heating temperature is 1100 ° C. and the heating time is 120 minutes. As a result, nitrogen atoms are introduced near the interface between the oxide film 126 and the underlying breakdown voltage holding layer 122, p region 123, n ⁺ region 124, and p ⁺ region 125. Further, after the annealing step using nitrogen monoxide as an atmospheric gas, annealing using argon (Ar) gas which is an inert gas may be performed. Specifically, argon gas may be used as the atmosphere gas, and the heating temperature may be 1100 ° C. and the heating time may be 60 minutes.

Next, an electrode formation step (S160) is performed as shown in FIG. Specifically, a resist film having a pattern is formed on the oxide film 126 by using a photolithography method. Using the resist film as a mask, portions of the oxide film located on n ⁺ region 124 and p ⁺ region 125 are removed by etching. After that, a conductor film such as a metal is formed so as to be in contact with the n ⁺ region 124 and the p ⁺ region 125 on the resist film and inside the opening formed in the oxide film 126. Thereafter, by removing the resist film, the conductor film located on the resist film is removed (lifted off). Here, for example, nickel (Ni) can be used as the conductor. As a result, as shown in FIG. 13, the source electrode 111 and the drain electrode 112 can be obtained. In addition, it is preferable to perform the heat processing for alloying here. Specifically, for example, an argon (Ar) gas that is an inert gas is used as the atmosphere gas, and a heat treatment (alloying treatment) is performed with a heating temperature of 950 ° C. and a heating time of 2 minutes.

  Thereafter, an upper source electrode 127 (see FIG. 8) is formed on the source electrode 111. Further, a drain electrode 112 (see FIG. 8) is formed on the back surface of the substrate 102. In this way, the semiconductor device 101 shown in FIG. 8 can be obtained.

  In Embodiment 3, the vertical MOSFET has been described as an example of a semiconductor device that can be manufactured using the silicon carbide substrate of the present invention. However, the semiconductor device that can be manufactured is not limited to this. For example, various semiconductor devices such as JFET (Junction Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), and Schottky barrier diode can be manufactured using the silicon carbide substrate of the present invention. It is. In the third embodiment, the case where a semiconductor device is manufactured by forming an epitaxial layer functioning as an active layer on a silicon carbide substrate having a (03-38) plane as a main surface has been described. The crystal plane that can be used as the main surface is not limited to this, and any crystal plane according to the application including the (0001) plane can be used as the main surface.

  Embodiment 1 of the present invention will be described below. An experiment was conducted to investigate a preferred heating temperature when connecting a plurality of SiC substrates using a support substrate made of silicon carbide. The experimental procedure is as follows.

  First, in the same manner as in the first embodiment, a SiC substrate is placed on a support substrate made of silicon carbide, and is heated by laser irradiation similar to the first embodiment or by lamp heating similar to the second embodiment. Heat treatment was performed. At this time, the heating temperature was set to 5 levels in the range of 1600 ° C to 3000 ° C. The heating temperature was measured using a pyrometer. And the joining state of the support substrate and SiC substrate after heat processing, and the crystallinity of a SiC substrate were investigated. Table 1 shows the experimental results.

  Referring to Table 1, when the heating temperature was 1600 ° C., the bonding state between the support substrate and the SiC substrate was insufficient regardless of the heating method. On the other hand, when the heating temperature was 3000 ° C., the crystallinity of the SiC substrate was lowered regardless of the heating method. On the other hand, when the heating temperature was 1800 ° C. to 2500 ° C., the support substrate and the SiC substrate were sufficiently bonded regardless of the heating method, and at the same time, no decrease in crystallinity of the SiC substrate was confirmed. From this, when connecting a plurality of SiC substrates using a support substrate made of silicon carbide, it can be said that the heating temperature is preferably 1800 ° C. or more and 2500 ° C. or less.

  An experiment was conducted to confirm the possibility of connection between a plurality of SiC substrates using a support substrate made of a refractory metal. Specifically, as in the case of the second embodiment, a SiC substrate is placed on a support substrate made of a refractory metal, and heating by laser irradiation as in the first embodiment or the same as in the second embodiment. The lamp was heated to the melting point of the refractory metal. As the refractory metal, molybdenum, tantalum, tungsten, niobium, iridium, ruthenium, zirconium, titanium and nickel were employed. And the joining state of the support substrate and SiC substrate after the said process was investigated.

  As a result, the support substrate and the SiC substrate were sufficiently bonded regardless of which of the above refractory metals was used. From this, it was confirmed that a plurality of SiC substrates can be connected to each other even when a supporting substrate made of a refractory metal is used.

(Appendix)
As described above, according to the method for manufacturing a silicon carbide substrate of the present invention, a large-diameter silicon carbide substrate having excellent crystallinity can be manufactured. That is, the silicon carbide substrate according to the present invention is manufactured by the method for manufacturing a single crystal substrate of the present invention. Further, as described in Embodiment Mode 3, a semiconductor device can be manufactured using the silicon carbide substrate of the present invention. That is, in the semiconductor device of the present invention, the epitaxial growth layer as the active layer is formed on the silicon carbide substrate manufactured by the method for manufacturing the silicon carbide substrate of the present invention. If it demonstrates from another viewpoint, the epitaxial growth layer as an active layer is formed in the semiconductor device of this invention on the silicon carbide substrate of the said invention. More specifically, the semiconductor device of the present invention includes the silicon carbide substrate of the present invention, an epitaxial growth layer formed on the silicon carbide substrate, and an electrode formed on the epitaxial growth layer.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The method for manufacturing a silicon carbide substrate of the present invention can be particularly advantageously applied to the manufacture of a silicon carbide substrate that requires a reduction in the manufacturing cost of a semiconductor device using the silicon carbide substrate.

DESCRIPTION OF SYMBOLS 1 Silicon carbide substrate, 2 Laminated substrate, 10 Support substrate, 10A, 10B main surface, 20 SiC substrate, 20A, 20C main surface, 20B End surface, 101 Semiconductor device, 102 Substrate, 110 Gate electrode, 111 Source electrode, 112 Drain electrode 121 buffer layer, 122 breakdown voltage holding layer, 123 p region, 124 n ⁺ region, 125 p ⁺ region, 126 oxide film, 127 upper source electrode.

Claims (12)

Preparing a plurality of SiC substrates made of single-crystal silicon carbide;
A step of arranging a support substrate so as to come into contact with one main surface of the plurality of SiC substrates in a state in which the plurality of SiC substrates are arranged side by side in a plan view;
Connecting the plurality of SiC substrates with the support substrate,
In the step of connecting the plurality of SiC substrates,
A method for manufacturing a silicon carbide substrate, wherein the step of heating the support substrate and the step of cooling the support substrate are repeated.   The method for manufacturing a silicon carbide substrate according to claim 1, wherein the support substrate is made of silicon carbide.   The method for manufacturing a silicon carbide substrate according to claim 2, wherein in the step of heating the support substrate, the support substrate is heated to a temperature of 1800 ° C. or higher and 2500 ° C. or lower.   3. The step of heating the support substrate, the SiC substrate is maintained at a temperature lower than the support substrate by heating the support substrate from the main surface side opposite to the SiC substrate. Or a method for producing a silicon carbide substrate according to 3.   The method for manufacturing a silicon carbide substrate according to claim 1, wherein the support substrate is made of a refractory metal having a melting point of 1800 ° C. or higher.   The method for manufacturing a silicon carbide substrate according to claim 5, wherein in the step of heating the support substrate, the support substrate is heated to a temperature range equal to or higher than a melting point of the refractory metal.   The method for manufacturing a silicon carbide substrate according to claim 1, wherein in the step of heating the support substrate, the support substrate is heated by at least one of heating by laser irradiation and lamp heating.   The method for manufacturing a silicon carbide substrate according to claim 1, wherein the support substrate has a thickness of 1 μm or more and 1 mm or less.   In the step of connecting the plurality of SiC substrates to each other, the main surface of the plurality of SiC substrates opposite to the support substrate has the plurality of the plurality of SiC substrates so that an off angle with respect to the {0001} plane is 50 ° or more and 65 ° or less. The manufacturing method of the silicon carbide substrate of any one of Claims 1-8 with which these SiC substrates are connected.   In the step of connecting the plurality of SiC substrates, the plurality of the plurality of SiC substrates so that an angle formed between an off orientation of a main surface of the SiC substrate opposite to the support substrate and a <1-100> direction is 5 ° or less. The method for manufacturing a silicon carbide substrate according to claim 9, wherein the SiC substrates are connected to each other.   In the step of connecting the plurality of SiC substrates, an off angle with respect to the {03-38} plane in the <1-100> direction of the main surface of the SiC substrate opposite to the support substrate is −3 ° or more 5 The method for manufacturing a silicon carbide substrate according to claim 10, wherein the plurality of SiC substrates are connected to each other so as to be less than or equal to ° C.   In the step of connecting the plurality of SiC substrates, the plurality of the plurality of SiC substrates so that an angle formed between an off orientation of a main surface of the SiC substrate opposite to the support substrate and a <11-20> direction is 5 ° or less. The method for manufacturing a silicon carbide substrate according to claim 9, wherein the SiC substrates are connected to each other.

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