JP2007335650A - Method of heating silicon carbide semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of heating a silicon carbide semiconductor substrate etc. which can suppress sublimation of silicon atoms or carbon atoms without executing processes having complexity or difficulty and without damaging a device forming surface of the silicon carbide semiconductor substrate. <P>SOLUTION: In this method of heating a silicon carbide semiconductor substrate, silicon carbide particles 3 are placed on a recessed region of a recess portion formed on a susceptor 13. Further, the silicon carbide semiconductor substrate 1 is placed on the susceptor 13 so that the device forming surface 5 may be directed to the susceptor 13 side and an upper part of the recess portion may be closed. After that, the silicon carbide semiconductor substrate 1 is heated by heating the susceptor 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for heating a silicon carbide semiconductor substrate.

  In order to activate the impurity region formed in the surface of the silicon carbide semiconductor substrate, the silicon carbide semiconductor substrate needs to be subjected to high-temperature heat treatment. As the heat treatment of the silicon carbide semiconductor substrate, there are the following conventional techniques.

  In the first conventional technique, a carbon susceptor on which a silicon carbide semiconductor substrate is placed is inserted into a quartz tube. Here, the quartz tube after the insertion of the susceptor is in a vacuum or is filled with argon gas or the like. And after the said susceptor insertion, the temperature of the said susceptor is heated to 1600-1800 degreeC by high frequency induction heating. By receiving heat from the susceptor, heating of the silicon carbide semiconductor substrate is realized.

  The second prior art (see Patent Document 1) is an applied technique to the first prior art, and the specific contents are as follows. In the second prior art, a silicon carbide semiconductor substrate is placed on a susceptor, and a carbon heating element is brought into surface contact with the upper surface of the silicon carbide semiconductor substrate. Then, the susceptor and the heating element are heated by high frequency induction heating in a state where the heating element is brought into surface contact to cover the surface of the silicon carbide semiconductor substrate as described above. The silicon carbide semiconductor substrate is heated by receiving heat from the susceptor and the heating element.

JP 2005-197464 A

  By the way, the wavelength of infrared rays radiated at a temperature of 1600 to 1800 ° C. is distributed in a wavelength region of 1 to 10 microns (having a peak at about 2 microns) (non-patent document: heat transfer engineering data (revision 4)). Edition), published by Maruzen, pp 156). However, silicon carbide hardly absorbs infrared rays in the wavelength range (Non-patent document: Properties of Advanced Semiconductor Materials, John Wiley & Sons, Inc., pp 127).

  Therefore, in a vacuum, in the heating method according to the first prior art, the silicon carbide semiconductor substrate is heated by solid-solid heat conduction only from the point of contact with the susceptor that generates heat. It will be.

  The contact surfaces of the silicon carbide semiconductor substrate and the susceptor usually have a warp rather than a perfect plane. Therefore, the entire contact surface between the silicon carbide semiconductor substrate and the susceptor is not in contact, and the contact is about several points (theoretically, three points). For this reason, the heating state of the silicon carbide semiconductor substrate from the susceptor changes depending on the number of contact points and the contact location between the silicon carbide semiconductor substrate and the susceptor. In addition, since the number of contact points is small, heat is transmitted only from that point, so it is necessary to transfer heat through the substrate, and heating takes time.

  Further, in the gas atmosphere, in addition to the solid-solid heat conduction between the silicon carbide semiconductor substrate and the susceptor, there is also the solid-gas-solid heat conduction through the gas between the susceptor and the silicon carbide semiconductor substrate. . In this case, the distance between the substrate and the susceptor at each point of the substrate and the susceptor varies depending on the flatness of the silicon carbide semiconductor substrate and the susceptor. For this reason, effective thermal conductivity and a heating state will change.

  In summary, in the case of the first prior art, the silicon carbide semiconductor substrate cannot be heated uniformly, and since it is heated only from the contact portion, the heat supply from the susceptor to the silicon carbide semiconductor substrate is long. The problem of taking time arises. In addition, there is a problem that thermal stress is generated due to uneven heating and the substrate is broken.

  In addition, when the silicon carbide semiconductor substrate reaches a high temperature, silicon atoms and carbon atoms constituting the silicon carbide semiconductor substrate are sublimated at their respective sublimation rates. Each of the sublimated atoms jumps out in a vacuum or an argon gas atmosphere, and as a result, the composition ratio of silicon atoms and carbon atoms on the surface of the silicon carbide semiconductor substrate is changed. That is, in the case of the first prior art, there is also a problem that the surface roughness of the silicon carbide semiconductor substrate is caused by sublimation. In the heating method according to the second prior art, it is described that sublimation of silicon atoms and the like is suppressed because the surface of the silicon carbide semiconductor substrate is covered with a heating element.

  By the way, in order to exert the above sublimation suppressing effect, it is premised that the heating element and the silicon carbide semiconductor substrate, and the susceptor and the silicon carbide semiconductor substrate are in a surface contact state. In order to enable the surface contact state, in order to improve the flatness, eliminate surface irregularities, make the surface roughness very good, and correct the warped silicon carbide semiconductor substrate to a flat surface In addition, it is necessary to correct the substrate by applying an external force.

  However, it is very difficult to improve the flatness of each member until the surface is brought into a complete surface contact state. Further, by pressing the silicon carbide semiconductor substrate by applying an external force, there is a possibility of damaging the device forming surface which is important for device operation, and the device yield is reduced.

  As described above, in the second prior art, in order to suppress sublimation of silicon atoms or the like, it is necessary to perform a process having a difficulty of completely contacting the surface, or damage to the device formation surface. There is a problem that it must be given.

  Therefore, an object of the present invention is to provide a method for heating a silicon carbide semiconductor substrate that can heat the silicon carbide semiconductor substrate in a short time and uniformly using heat generated by a susceptor. Also, a silicon carbide semiconductor substrate heating method capable of suppressing sublimation of silicon atoms and carbon atoms without damaging the device formation surface of the silicon carbide semiconductor substrate without taking into account complicated and difficult processes. The purpose is to provide.

  In order to achieve the above object, a silicon carbide semiconductor substrate heating method according to claim 1 according to the present invention includes: (A) placing silicon carbide particles in a recessed region of a recess formed in a susceptor. And (B) placing a silicon carbide semiconductor substrate on the susceptor so as to close an upper portion of the recess so that a device forming surface faces the susceptor, and (C) the step (A), (B), and the step of heating the silicon carbide semiconductor substrate by heating the susceptor.

  The method for heating a silicon carbide semiconductor substrate according to claim 1 of the present invention includes (A) a step of placing silicon carbide particles in a recessed region of a recess formed in a susceptor, and (B) a device formation surface. A step of placing a silicon carbide semiconductor substrate on the susceptor so that the upper portion of the recess is closed so that the surface faces the susceptor, and (C) after the steps (A) and (B), Heating the silicon carbide semiconductor substrate by heating the susceptor.

  During the heat treatment of the silicon carbide semiconductor substrate, silicon atoms and carbon atoms are sublimated from the device formation surface and the silicon carbide particles in the semi-enclosed space formed by the silicon carbide semiconductor substrate and the recess. Therefore, as the silicon carbide particles are introduced, the semi-enclosed space can be sublimated and saturated earlier. Therefore, sublimation of silicon atoms and the like from the device formation surface can be suppressed earlier. In other words, the sublimation suppressing function can be exhibited without damaging the device forming surface of the silicon carbide semiconductor substrate or the like without taking into account complicated or difficult processes and without applying external force or the like. In addition, if the said sublimation is suppressed, it can suppress that the surface state of a device formation surface changes.

  Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.

<Embodiment 1>
A method for heating a silicon carbide semiconductor substrate according to the present embodiment will be described with reference to FIG. Here, FIG. 1 is a cross-sectional view showing a state in which the silicon carbide semiconductor substrate is heated. First, the configuration of an apparatus in which the method for heating a silicon carbide semiconductor substrate according to the present embodiment is performed will be described. As shown in FIG. 1, there is a cylindrical quartz tube 11, and a high frequency induction heating coil 12 is wound around the outer peripheral surface of the quartz tube 11. In addition, a heating element 10 made of carbon, for example, is disposed on the quartz tube 11. Further, the carbon susceptor 13 is formed with a two-stage digging that can be grasped as a recess as a whole. The diameter of the upper digging serving as the first recess is slightly larger than the diameter of the silicon carbide semiconductor substrate 1. Further, the diameter of the lower digging which becomes the second recess is slightly smaller than the diameter of the silicon carbide semiconductor substrate 1. That is, the two-stage digging is formed by an upper digging and a lower digging connected to the bottom of the upper digging and having a smaller opening width than the upper digging. Yes.

  Next, the procedure of the method for heating the silicon carbide semiconductor substrate according to this embodiment will be described. First, silicon carbide semiconductor substrate 1 is placed on the bottom of the first recess formed on susceptor 13. Thereby, the upper part of the lower digging is closed, and a semi-sealed space is formed. Silicon carbide semiconductor substrate 1 is placed so that device formation surface 5 of the silicon carbide semiconductor substrate faces susceptor 13 side. Further, the outer periphery of silicon carbide semiconductor substrate 1 is in contact with the bottom of the upper digging. Usually, no device is formed in most of the outer peripheral portion of the silicon carbide semiconductor substrate 1. Moreover, you may form uneven | corrugated shape in the bottom part (namely, support part of the silicon carbide semiconductor substrate 1) of the upper digging. Thereby, since the contact area of silicon carbide semiconductor substrate 1 and the bottom of the upper digging can be reduced, it is possible to suppress heat from being transmitted to silicon carbide semiconductor substrate 1 from the contact portion.

  Next, a large number of carbon particles 2 are placed on the entire surface (including almost the entire surface) of the silicon carbide semiconductor substrate 1 placed on the susceptor 13. Here, the particle diameter of the carbon particles 2 to be placed can be selected to have an arbitrary size, but it is desirable to use particles having a particle diameter as small as possible in order to increase the number of contact points. More specifically, as shown in FIG. 1, carbon particles 2 are introduced into a recessed portion formed by the upper surface of silicon carbide semiconductor substrate 1 and the side surface of the upper digging. The device forming surface 5 faces the susceptor 13 side. Therefore, carbon particles 2 are placed and introduced on the main surface of silicon carbide semiconductor substrate 1 that faces device formation surface 5.

  Here, carbon particles 2 are placed / introduced on the silicon carbide semiconductor substrate 1 by one layer. For example, by adopting the following method, the carbon particles 2 can be placed and introduced by one layer. First, the upper dig is formed so that the depth of the upper dig matches the sum of the thickness of the silicon carbide semiconductor substrate 1 and the particle diameter of the carbon particles 2. Next, with the silicon carbide semiconductor substrate 1 placed on the bottom of the upper dig, carbon particles 2 are placed on the silicon carbide semiconductor substrate 1 so as to fill the upper dig. Thereafter, only the carbon particles 2 protruding above the susceptor 13 are removed. By this process, the carbon particles 2 can be placed / introduced on the silicon carbide semiconductor substrate 1 by one layer.

  The susceptor 13 that has been subjected to this process is inserted into the cavity of the quartz tube 11 (see FIG. 1). Then, the silicon carbide semiconductor substrate 1 is heated by heating the susceptor 13 and the carbon heating element 10 with the carbon particles 2 placed and introduced on the silicon carbide semiconductor substrate 1. The procedure for heating silicon carbide semiconductor substrate 1 is as follows. First, a current is passed through the high frequency induction heating coil 12. Then, a magnetic field is generated in the quartz tube 11. Then, an induced current flows in the carbonized susceptor 13 and the carbonized heating element 10 by the magnetic field. The susceptor 13 and the heating element 10 generate heat when the induced current flows. In the above, the susceptor 13 and the heating element 10 generate heat, and the temperature of the susceptor 13 and the heating element 10 becomes about 1600 to 1800 ° C. Then, infrared rays having a predetermined wavelength are radiated from the susceptor 13 and the heating element 10.

  Here, as described in “Problems to be Solved by the Invention”, the silicon carbide semiconductor substrate 1 hardly absorbs infrared rays generated in the temperature range (Non-patent Document: Properties of Advanced Semiconductor Materials, John Wiley & Sons, Inc., pp 127). Therefore, most of the generated infrared light passes through silicon carbide semiconductor substrate 1. However, the carbon particles 2 can absorb infrared rays generated in the temperature range. Therefore, the carbon particles 2 absorb the infrared rays radiated from the susceptor 13 and the heating element 10, and as a result, the carbon particles 2 are heated. Here, a large number of carbon particles 2 are placed on silicon carbide semiconductor substrate 1. Therefore, the carbon particles 2 and the silicon carbide semiconductor substrate 1 are in point contact at a number of locations (see FIG. 1). As described above, the carbon particles 2 having an arbitrary particle size can be selected. If the size of the silicon carbide semiconductor substrate 1 is 50 mm and the size of the spherical carbon particles 2 is 100 μm, the number of contact points between the silicon carbide semiconductor substrate 1 and the carbon particles 2 is about 200,000. When the size of the spherical carbon particles 2 is 10 μm, the number of contact points between the silicon carbide semiconductor substrate 1 and the carbon particles 2 is about 20 million.

  As can be seen from this, the number of contact points between the silicon carbide semiconductor substrate 1 and the carbon particles 2 increases as the carbon particles 2 having a smaller particle diameter are selected (adopted). If the number of contact points is increased not only in a vacuum but also in a gas atmosphere such as argon which has solid-gas-solid heat conduction, the heat conduction between the solid and the solid becomes dominant. Moreover, if the carbon particle 2 with a small particle diameter is selected (adopted), its volume will also decrease. When the volume of the carbon particle 2 decreases, the heat capacity decreases accordingly. Therefore, the temperature increase rate of the carbon particles 2 becomes faster. For this reason, the heat transfer efficiency from the carbon particles 2 to the silicon carbide semiconductor substrate 1 is improved, and the heat treatment of the silicon carbide semiconductor substrate 1 can be completed in a short time.

  Further, as shown in FIG. 1, fine voids are formed between the adjacent carbon particles 2 and the silicon carbide semiconductor substrate 1. In a gas atmosphere such as argon gas, heat is transferred from the heated carbon particles 2 to the silicon carbide semiconductor substrate 1 by two heat conduction mechanisms of solid-solid and solid-gas-solid. As the particle diameter of the void also becomes smaller, the gap becomes smaller, the heat transfer performance in the gas improves, and it helps to finish the heat treatment earlier.

  The reason why the two carbon particle layers are made one is as follows. That is, when there are a plurality of carbon particles 2, it is considered that the infrared rays emitted from the susceptor 13 and the heating element 10 are received by the carbon particles 2 of different layers and the efficiency is lowered. This is because the infrared rays radiated from the susceptor 13 and passed through the silicon carbide semiconductor substrate 1 are received by the carbon particles 2 in contact with the silicon carbide semiconductor substrate 1, but the infrared rays emitted from the heating element 10 are at the top. Since the carbon particles 2 receive light, the heat of the heated carbon particles 2 transfers heat to the underlying carbon particles 2 by heat conduction or radiation, and the carbon particles in contact with the silicon carbide semiconductor substrate 1. Since 2 cannot be heated directly, it is thought that efficiency falls.

  After the heat treatment of the silicon carbide semiconductor substrate 1 is completed for a predetermined time, the susceptor 13 on which the silicon carbide semiconductor substrate 1 and the carbon particles 2 are placed is taken out from the quartz tube 11 and cooled to room temperature. By performing the heat treatment, the impurity region formed in silicon carbide semiconductor substrate 1 is activated.

  As described above, in the method for heating a silicon carbide semiconductor substrate according to the present embodiment, a large number of carbon particles 2 are placed on silicon carbide semiconductor substrate 1. And in the said state, the heat processing of the silicon carbide semiconductor substrate 1 using heat_generation | fever of susceptor 13 grade | etc., Are implemented. Therefore, the infrared rays radiated from the susceptor 13 and the heating element 10 are once absorbed by the carbon particles 2. Here, as described above, the carbon particles 2 are in point contact with the silicon carbide semiconductor substrate 1 at a number of points (even if the silicon carbide semiconductor substrate 1 has a warp, the flatness of the silicon carbide substrate 1 is also reduced). Even when the value is low, the point contact is realized at many points). Therefore, silicon carbide semiconductor substrate 1 can be heated through carbon particles 2 in a short time and uniformly.

  In the present embodiment, a recess (more specifically, two levels of digging) is formed in the susceptor 13. Then, silicon carbide semiconductor substrate 1 is placed on the bottom of the recess (more specifically, the bottom of the upper digging), and in a recess formed by the top surface of silicon carbide semiconductor substrate 1 and the side surface of the recess. A large number of carbon particles 2 are introduced. Therefore, silicon carbide semiconductor substrate 1 can be stably placed on susceptor 13 and a plurality of carbon particles 2 can be stably placed on silicon carbide semiconductor substrate 1 (that is, during the heat treatment). Even if some vibration occurs, the carbon particles 2 can be prevented from spilling from the silicon carbide semiconductor substrate 1).

  In the present embodiment, a plurality of carbon particles 2 are placed on the main surface of silicon carbide semiconductor substrate 1 that faces device formation surface 5. Therefore, the device forming surface 5 can be prevented from being contaminated by the carbon particles 2.

  In the present embodiment, the susceptor 13 is formed with two digs as described above. Then, silicon carbide semiconductor substrate 1 is placed on the bottom of the upper digging so as to close the upper part of the lower digging. Therefore, the silicon carbide semiconductor substrate 1 serves as a lower embedded lid, and the lower embedded region and the substrate 1 form a semi-sealed space. Thereby, silicon atoms and carbon atoms sublimated from the device formation surface 5 can be confined in the quasi-enclosed space. That is, sublimation of silicon atoms or the like can be saturated in the quasi-enclosed space. Thus, when sublimation is saturated, sublimation from the device formation surface 5 does not occur. As described above, the silicon carbide semiconductor substrate 1 serves as a lower embedded lid, so that sublimation from the device forming surface 5 can be suppressed. That is, the sublimation suppressing function can be exhibited without damaging the device forming surface 5 of the silicon carbide semiconductor substrate 1 without taking into account the steps having complexity and difficulty, and without applying an external force or the like. In addition, when the said sublimation is suppressed, it can suppress that the surface state of the device formation surface 5 changes. Here, if the volume of the semi-enclosed space is reduced, the sublimation is saturated at an earlier stage, so that the effect of suppressing sublimation is further exhibited.

  The device formation surface 5 faces the susceptor 13 side. Therefore, the device forming surface 5 can be prevented from being contaminated by foreign matters such as dust in the quartz tube 11.

  Further, the outer peripheral portion of the silicon carbide semiconductor substrate 1 is usually a frame portion and is a region where no device is formed. Further, as can be seen from the above aspect, the silicon carbide semiconductor substrate 1 and the susceptor 13 (more specifically, the upper embedded bottom) are in contact with only a part of the outer peripheral portion of the substrate 1. is there. That is, all or most of the region of the device formation surface 5 is not in contact with the susceptor 13 (more specifically, the bottom of the upper burying). Therefore, contamination of the device forming surface 5 caused by contact with the susceptor 13 can also be prevented.

  In the present embodiment, carbon particles 2 are placed or introduced for one layer on silicon carbide semiconductor substrate 1. Therefore, the layer thickness of the carbon particles 2 can be minimized. Thus, when the total volume of the carbon particle 2 decreases, the heat capacity of the entire layer of the carbon particle 2 decreases accordingly. Therefore, the temperature increase rate of the layer of carbon particles 2 becomes faster. For this reason, the heat transfer efficiency from the carbon particles 2 to the silicon carbide semiconductor substrate 1 is improved, and the heat treatment of the silicon carbide semiconductor substrate 1 can be completed in a short time.

  In the present embodiment, the heating element 10 is disposed above the carbon particles 2. The silicon carbide semiconductor substrate 1 is heated by heating the heating element 10 and the susceptor 13. Therefore, the heat treatment of silicon carbide semiconductor substrate 1 can be completed in a shorter time.

  As shown in FIG. 1, the heating element 10 may be arranged at a predetermined distance from the susceptor 13. Although not shown, the heating element 10 is arranged so that the lower surface of the heating element 10 (the lower surface is a flat plate as in FIG. 1) and the upper surface of the susceptor 13 are in contact (that is, the carbonized heating element). 10 and covers the carbonized susceptor 13 and / or the silicon carbide semiconductor substrate 1), and in this state, the heat treatment of the silicon carbide semiconductor substrate 1 using the heat generation of the heating element 10 and the susceptor 13 may be performed. . By performing a heat treatment in a state where the lower surface of the heating element 10 and the upper surface of the susceptor 13 are in contact with each other, the heat generated by the heating element 10 is more efficiently transferred to the silicon carbide semiconductor substrate 1 through the carbon particles 2. can do.

  Further, the heating element 10 and the susceptor 13 are arranged in a predetermined region in the cavity of the quartz tube 11 (that is, as shown in FIG. 1, the arrangement position of the heating element 10 and the arrangement position of the susceptor 13). And are not distributed). Therefore, it is not necessary to wind the high-frequency induction heating coil 12 around the entire outer peripheral surface of the quartz tube 11, and a certain limited surface (that is, the heating element 10 and the susceptor 13 are firmly arranged on the outer peripheral surface of the quartz tube 11. It is only necessary to wrap around the surface corresponding to the area.

  As shown in FIG. 2, a recess is formed on the side of the heating element 10 facing the silicon carbide semiconductor substrate, and the lower surface of the heating element 10 and the upper surface of the susceptor 13 are in contact with each other. Silicon carbide semiconductor substrate 1 may be heated while the upper surface of substrate 1 is covered. By doing so, even when the lower surface of the heating element 10 and the upper surface of the susceptor 13 are brought into contact with each other during the heat treatment of the silicon carbide semiconductor substrate 1, due to the presence of the recesses, the silicon carbide semiconductor substrate 1 is subjected to the contact. It is possible to prevent an external force resulting from contact from being applied via the carbon particles 2.

<Embodiment 2>
A method for heating a silicon carbide semiconductor substrate according to the present embodiment will be described with reference to FIG. Here, FIG. 3 is a cross-sectional view showing a state in which the silicon carbide semiconductor substrate is heated. First, the configuration of an apparatus in which the method for heating a silicon carbide semiconductor substrate according to the present embodiment is performed will be described. As shown in FIG. 3, there is a cylindrical quartz tube 11, and a high frequency induction heating coil 12 is wound around the outer peripheral surface of the quartz tube 11. In addition, a heating element 10 made of carbon, for example, is disposed on the quartz tube 11. The carbon susceptor 13 is formed with two levels of digging (which can be grasped as a recess as a whole). The diameter (opening width) of the upper digging (which can be grasped as the first recess) is slightly larger than the diameter of the silicon carbide semiconductor substrate 1. Further, the diameter (opening width) of the lower digging (which can be grasped as the second recess) is slightly smaller than the diameter of the silicon carbide semiconductor substrate 1. That is, the two-stage digging is formed by an upper digging and a lower digging connected to the bottom of the upper digging and having a smaller opening width than the upper digging. .

  Next, the procedure of the method for heating the silicon carbide semiconductor substrate according to this embodiment will be described. First, a plurality (a large number) of silicon carbide particles 3 are introduced into a recessed region of a two-stage digging (which can be grasped as a recess) formed in the susceptor 13. More specifically, a plurality (a large number) of silicon carbide particles 3 are introduced into a recessed region of a lower digging (which can be grasped as a second recess). The depth of the lower digging is larger than the particle diameter of the silicon carbide particles 3. Here, the particle diameter of the silicon carbide particles 3 to be introduced can be selected as an arbitrary size. In FIG. 3, only one silicon carbide particle 3 is introduced, but the silicon carbide particle 3 may be introduced over multiple layers. However, it is desirable that the device formation surface 5 of the silicon carbide semiconductor substrate 1 described later and the silicon carbide particles 3 do not contact each other.

  Next, silicon carbide semiconductor substrate 1 is placed on susceptor 13. Here, unlike FIG. 3, a one-stage digging (which can be grasped as a recess) is created, a plurality (a large number) of silicon carbide particles 3 are introduced into the digging, and then the digging is closed. As described above, the silicon carbide semiconductor substrate 1 may be placed on the susceptor 13. However, in the present embodiment, as shown in FIG. 3, the susceptor 13 is formed with two levels of excavation. Then, as described above, after introducing the silicon carbide particles 3 into the lower digging (which can be grasped as the second recess), the upper digging is performed so as to close the upper portion of the lower digging ( Silicon carbide semiconductor substrate 1 is placed on the bottom of the first concave portion. Silicon carbide semiconductor substrate 1 is placed such that device formation surface 5 of silicon carbide semiconductor substrate 1 faces the susceptor 13 side.

  Further, the outer periphery of silicon carbide semiconductor substrate 1 is in contact with the bottom of the upper digging. The outer peripheral portion of the silicon carbide semiconductor substrate 1 has many portions where devices are not formed. Moreover, you may form uneven | corrugated shape in the bottom part (namely, support part of the silicon carbide semiconductor substrate 1) of the upper digging. Thereby, the contact area between silicon carbide semiconductor substrate 1 and the bottom of the upper digging can be reduced, and heat can be prevented from being transmitted to silicon carbide semiconductor substrate 1 from the contact portion. By placing the silicon carbide semiconductor substrate 1, a semi-sealed space is formed in the lower digging.

  The susceptor 13 that has been subjected to this process is inserted into the cavity of the quartz tube 11 (see FIG. 3). Then, the silicon carbide semiconductor substrate 1 is heated by heating the susceptor 13. In the present embodiment, carbonized heating element 10 is provided above silicon carbide semiconductor substrate 1, and silicon carbide semiconductor substrate 1 is heated by heating heating element 10 and susceptor 13.

  The procedure for heating silicon carbide semiconductor substrate 1 is as follows. First, a current is passed through the high frequency induction heating coil 12. Then, a magnetic field is generated in the quartz tube 11. Then, an induced current flows in the carbonized susceptor 13 and the carbonized heating element 10 by the magnetic field. The susceptor 13 and the heating element 10 generate heat when the induced current flows. Then, the silicon carbide semiconductor substrate 1 is heated by receiving heat from the susceptor 13 or receiving heat from the heating element 10. After the heat treatment is performed for a predetermined time (that is, after the heat treatment of the silicon carbide semiconductor substrate 1 is completed), the susceptor 13 is taken out from the quartz tube 11. By performing the heat treatment, the impurity region formed in silicon carbide semiconductor substrate 1 is activated.

  Here, when the silicon carbide semiconductor substrate 1 is heat-treated, if sublimation of silicon atoms or carbon atoms can be saturated in the semi-enclosed space, sublimation of silicon atoms or the like is eliminated after the saturation state. Therefore, if the saturation state of sublimation can be achieved earlier in the semi-enclosed space, sublimation of silicon atoms or the like can be eliminated earlier.

  As described above, in the method for heating silicon carbide semiconductor substrate 1 according to the present embodiment, the susceptor 13 is dug (recessed). Then, silicon carbide particles 3 are introduced into the digging. Furthermore, the device formation surface 5 of the silicon carbide semiconductor substrate 1 faces the susceptor 13 side, and the digging is closed by the silicon carbide semiconductor substrate 1.

  Therefore, silicon carbide semiconductor substrate 1 serves as a lower-stage embedding lid, and the lower-stage embedding and silicon carbide semiconductor substrate 1 form a semi-enclosed space. Here, during the heat treatment of the silicon carbide semiconductor substrate 1, silicon atoms and carbon atoms are sublimated from the device formation surface 5 and the silicon carbide particles 3, but the silicon carbide particles 3 are introduced, The subsealed space can be saturated with sublimation earlier. Therefore, by applying the heating method according to the present embodiment, sublimation of silicon atoms and the like from the device formation surface 5 can be suppressed earlier. That is, the sublimation suppressing function can be exhibited without damaging the device forming surface 5 of the silicon carbide semiconductor substrate 1 without taking into account the steps having complexity and difficulty, and without applying an external force or the like. In addition, when the said sublimation is suppressed, it can suppress that the surface state of the device formation surface 5 changes.

  As can be seen from the above consideration, the smaller the volume of the semi-enclosed space, or the larger the volume and surface area of the silicon carbide particles 3, the earlier the sublimation of silicon atoms and the like from the device formation surface 5 can be suppressed. it can. From this point of view, it is desirable to introduce the silicon carbide particles 3 into the lower digging over multiple layers. It is also desirable to make the depth of the lower dig as shallow as possible. Further, it is desirable that the particle size of the silicon carbide particles 3 is smaller (because when the plurality of silicon carbide particles 3 are introduced into the lower digging of the same depth and the same bottom area, the smaller the particle size, the more This is because the silicon carbide particles 3 can be introduced, and the total surface area of the silicon carbide particles 3 is increased).

  In addition, from the viewpoint of preventing contamination of the device forming surface 5 by the silicon carbide particles 3, it is desirable that the silicon carbide particles 3 and the device forming surface 5 do not contact each other. Further, as can be seen from the above, in order to obtain the sublimation suppression effect, the silicon carbide semiconductor substrate 1 is not subjected to a special process (that is, a process having difficulty), and the device forming surface 5 is damaged. There is no.

  The device formation surface 5 faces the susceptor 13 side. Therefore, the device forming surface 5 can be prevented from being contaminated by foreign matters such as dust in the quartz tube 11. In general, the outer peripheral portion of silicon carbide semiconductor substrate 1 is a region where no device is formed. As can be seen from the above aspect, the silicon carbide semiconductor substrate 1 and the susceptor 13 (more specifically, the upper embedded bottom) are in contact with only a part of the outer peripheral portion of the substrate 1. If the contact portion is selected, a state where all the devices formed on the device forming surface are not in contact with the susceptor 13 (more specifically, the bottom of the upper embedded portion) can be created. Therefore, contamination of the device forming surface 5 caused by contact with the susceptor 13 can also be prevented.

  In the present embodiment, heating element 10 is arranged above silicon carbide semiconductor substrate 1. The silicon carbide semiconductor substrate 1 is heated by heating the heating element 10 and the susceptor 13. Therefore, the heat treatment of silicon carbide semiconductor substrate 1 can be completed in a short time.

  As shown in FIG. 3, the heating element 10 may be arranged at a predetermined distance from the susceptor 13. Although not shown, the heating element 10 is arranged so that the lower surface of the heating element 10 (the lower surface is a flat plate as in FIG. 3) and the upper surface of the susceptor 13 are in contact (that is, the carbonized heating element). 10 may cover the susceptor 13 made of carbonized), and in this state, the heat treatment of the silicon carbide semiconductor substrate 1 may be performed using the heat generated by the heating element 10 and the susceptor 13 described above.

  By performing heat treatment while the lower surface of the heating element 10 and the upper surface of the susceptor 13 are in contact with each other, the heat can be transmitted to the silicon carbide semiconductor substrate 1 more efficiently. Further, the heating element 10 and the susceptor 13 are arranged in a predetermined region in the cavity of the quartz tube 11 (that is, as shown in FIG. 3, the arrangement position of the heating element 10 and the arrangement position of the susceptor 13 are arranged. And are not distributed). Therefore, it is not necessary to wind the high-frequency induction heating coil 12 around the entire outer peripheral surface of the quartz tube 11, and a certain limited surface (that is, the heating element 10 and the susceptor 13 are firmly arranged on the outer peripheral surface of the quartz tube 11. It is only necessary to wrap around the surface corresponding to the area.

  As shown in FIG. 4, a recess is formed on the side of the heating element 10 facing the silicon carbide semiconductor substrate, and the lower surface of the heating element 10 and the upper surface of the susceptor 13 are in contact with each other, and the silicon carbide semiconductor substrate is formed by the recess. The silicon carbide semiconductor substrate 1 may be heated in a state where the upper surface of 1 is covered. By doing so, even when the lower surface of the heating element 10 and the upper surface of the susceptor 13 are brought into contact with each other during the heat treatment of the silicon carbide semiconductor substrate 1, due to the presence of the recesses, the silicon carbide semiconductor substrate 1 is subjected to the contact. It is possible to prevent an external force resulting from contact from being applied via the carbon particles 2.

<Embodiment 3>
A method for heating a silicon carbide semiconductor substrate according to the present embodiment will be described with reference to FIG. Here, FIG. 5 is a cross-sectional view showing a state in which the silicon carbide semiconductor substrate is heated. As can be seen from a comparison between FIG. 3 and FIG. 5 (that is, a comparison between the second embodiment and the present embodiment), in the present embodiment, the first embodiment will be described on the silicon carbide semiconductor substrate 1. As described above, a plurality (large number) of carbon particles 2 are placed. In other words, in the method for heating a silicon carbide semiconductor substrate according to the present embodiment, the following steps are added in addition to the steps described in the second embodiment. In other words, in the present embodiment, after the silicon carbide semiconductor substrate 1 is placed on the susceptor 13 (see the second embodiment), a plurality (more specifically, many) of silicon carbide semiconductor substrate 1 are formed on the silicon carbide semiconductor substrate 1. A step of placing the carbon particles 2 is added (see FIG. 5).

  Here, the particle diameter of the carbon particles 2 to be mounted can be selected to have an arbitrary size (for example, about 10 μm to 100 μm). Further, the silicon carbide semiconductor substrate 1 is placed on the bottom of the upper digging in the two digging (see FIG. 5). Further, as described in the second embodiment, silicon carbide semiconductor substrate 1 is placed on susceptor 13 so as to close the upper part of the lower digging (see FIG. 5). Furthermore, as can be understood from the description of the second embodiment, the carbon particles 2 are placed and introduced on the main surface of the silicon carbide semiconductor substrate 1 facing the device formation surface.

  More specifically, the steps added to the present embodiment are as follows. As shown in FIG. 5, carbon particles 2 are introduced into a recessed portion formed by the upper surface of silicon carbide semiconductor substrate 1 and the side surface of the upper digging. The device forming surface 5 faces the susceptor 13 side. Therefore, carbon particles 2 are placed and introduced on the main surface of silicon carbide semiconductor substrate 1 that faces device formation surface 5. Here, carbon particles 2 are placed and introduced on one layer of silicon carbide semiconductor substrate 1. For example, by adopting the following method, the carbon particles 2 can be placed and introduced by one layer.

  First, the upper dig is formed so that the depth of the upper dig matches the sum of the thickness of the silicon carbide semiconductor substrate 1 and the particle diameter of the carbon particles 2. Next, with the silicon carbide semiconductor substrate 1 placed on the bottom of the upper dig, carbon particles 2 are placed on the susceptor 13 so as to fill the upper dig. Thereafter, only the carbon particles 2 on the susceptor 13 are removed. By this process, the carbon particles 2 can be placed / introduced on the silicon carbide semiconductor substrate 1 by one layer.

  The susceptor 13 on which the carbon particles 2 are placed is inserted into the cavity of the quartz tube 11 as described in the second embodiment (see FIG. 5). Then, the silicon carbide semiconductor substrate 1 is heated by heating the susceptor 13. In the present embodiment, carbonized heating element 10 is provided above silicon carbide semiconductor substrate 1, and silicon carbide semiconductor substrate 1 is heated by heating heating element 10 and susceptor 13.

  As described above, in the present embodiment, a step of placing carbon particles 2 is added after the step of placing silicon carbide semiconductor substrate 1 and before inserting susceptor 13 into quartz tube 11. . Except for the added process, the process is the same as that described in the second embodiment, and a detailed description thereof will be omitted.

  In the method for heating a silicon carbide semiconductor substrate according to the present embodiment, the silicon carbide semiconductor substrate 1 is subjected to the heat treatment with the carbon particles 2 placed on the silicon carbide semiconductor substrate 1. Therefore, the carbon particles 2 exhibit the following effects during the heat treatment in the quartz tube 11. In the above, when the susceptor 13 and the heating element 10 are heated and their temperature reaches about 1600 to 1800 ° C., infrared rays of a predetermined wavelength are radiated from the susceptor 13 and the heating element 10. Here, as described in the first embodiment, the silicon carbide semiconductor substrate 1 hardly absorbs infrared rays generated in the temperature range (Non-patent Document: Properties of Advanced Semiconductor Materials, John Wiley & Sons, Inc., pp 127). . Therefore, most of the generated infrared light passes through silicon carbide semiconductor substrate 1.

  However, the carbon particles 2 can absorb infrared rays generated in the temperature range. Therefore, the carbon particles 2 absorb the infrared rays radiated from the susceptor 13 and the heating element 10, and as a result, the carbon particles 2 are heated. Here, a large number of carbon particles 2 are placed on silicon carbide semiconductor substrate 1. Therefore, the carbon particles 2 and the silicon carbide semiconductor substrate 1 are in point contact at a number of locations (see FIG. 5). Further, as shown in FIG. 5, fine voids are formed between the adjacent carbon particles 2 and the silicon carbide semiconductor substrate 1. Therefore, heat is transferred from the heated carbon particles 2 to the silicon carbide semiconductor substrate 1 by two heat conduction mechanisms of solid-solid and solid-gas-solid (it can be grasped as an effect of the carbon particles 2).

  As described above, the carbon particles 2 having an arbitrary particle size can be selected. Here, as described in the first embodiment, the number of contact points between the silicon carbide semiconductor substrate 1 and the carbon particles 2 increases as the carbon particles 2 having a smaller particle diameter are selected (adopted). Thus, if the number of contact points is increased, the heat conduction between the solids becomes dominant.

  Moreover, if the carbon particle 2 having a small particle diameter is selected (adopted), the volume of the carbon particle 2 is naturally reduced. When the volume of the carbon particles 2 decreases, the heat capacity of the carbon particles 2 decreases accordingly. Therefore, the temperature increase rate of the carbon particles 2 becomes faster. For this reason, the heat transfer efficiency from the carbon particles 2 to the silicon carbide semiconductor substrate 1 is improved, and the heat treatment of the silicon carbide semiconductor substrate 1 can be completed in a short time.

  In the method for heating a silicon carbide semiconductor substrate according to the present embodiment, the silicon carbide semiconductor substrate 1 is subjected to heat treatment in a state where a plurality (large number) of carbon particles 2 are placed on the silicon carbide semiconductor substrate 1. . Therefore, the infrared rays radiated from the susceptor 13 and the heating element 10 are once absorbed by the carbon particles 2. Here, as described above, the carbon particles 2 are in point contact with the silicon carbide semiconductor substrate 1 at a number of points (even if the silicon carbide semiconductor substrate 1 has a warp, the flatness of the silicon carbide substrate 1 is also reduced). Even when the value is low, the point contact is realized at many points). Therefore, silicon carbide semiconductor substrate 1 can be heated through carbon particles 2 in a short time and uniformly.

  In the present embodiment, a recess (more specifically, two levels of digging) is formed in the susceptor 13. Then, silicon carbide semiconductor substrate 1 is placed on the bottom of the recess (more specifically, the bottom of the upper digging), and in a recess formed by the top surface of silicon carbide semiconductor substrate 1 and the side surface of the recess. A large number of carbon particles 2 are introduced. Therefore, silicon carbide semiconductor substrate 1 can be stably placed on susceptor 13 and a plurality of carbon particles 2 can be stably placed on silicon carbide semiconductor substrate 1 (that is, during the heat treatment). Even if some vibration occurs, the carbon particles 2 can be prevented from spilling from the silicon carbide semiconductor substrate 1). Carbon particles 2 are placed and introduced on the main surface of silicon carbide semiconductor substrate 1 that is not the device formation surface (that is, on the main surface opposite to the device formation surface). Therefore, the device forming surface 5 can be prevented from being contaminated by the carbon particles 2.

  Further, the carbon particles 2 are placed or introduced for one layer on the silicon carbide semiconductor substrate 1. Therefore, the layer thickness of the carbon particles 2 can be minimized. Thus, when the total volume of the carbon particle 2 decreases, the heat capacity of the entire layer of the carbon particle 2 decreases accordingly. Therefore, the temperature increase rate of the layer of carbon particles 2 becomes faster. For this reason, the heat transfer efficiency from the carbon particles 2 to the silicon carbide semiconductor substrate 1 is improved, and the heat treatment of the silicon carbide semiconductor substrate 1 can be completed in a short time.

  Moreover, in this Embodiment, as shown in FIG. 5, the heat generating body 10 is arrange | positioned only the predetermined distance above the carbon particle 2. As shown in FIG. The silicon carbide semiconductor substrate 1 is heated by heating the heating element 10 and the susceptor 13. However, although not shown, the heating element 10 is arranged so that the lower surface of the heating element 10 (the lower surface is a flat plate as in FIG. 5) and the upper surface of the susceptor 13 are in contact (that is, the carbonized heating element). 10 may cover the susceptor 13 made of carbonized), and in this state, the heat treatment of the silicon carbide semiconductor substrate 1 may be performed using the heat generated by the heating element 10 and the susceptor 13 described above. The effect obtained by performing the heat treatment in a contact state between the lower surface of the heating element 10 and the upper surface of the susceptor 13 is the same as in the first and second embodiments.

  As shown in FIG. 6, a recess is formed on the side of the heating element 10 facing the silicon carbide semiconductor substrate, and the lower surface of the heating element 10 and the upper surface of the susceptor 13 are in contact with each other. Silicon carbide semiconductor substrate 1 may be heated while the upper surface of substrate 1 is covered. By doing so, even when the lower surface of the heating element 10 and the upper surface of the susceptor 13 are brought into contact with each other during the heat treatment of the silicon carbide semiconductor substrate 1, due to the presence of the recesses, the silicon carbide semiconductor substrate 1 is subjected to the contact. It is possible to prevent an external force resulting from contact from being applied via the carbon particles 2.

3 is a diagram for illustrating a method for heating a silicon carbide semiconductor substrate according to the first embodiment. 6 is a view showing another embodiment of a method for heating a silicon carbide semiconductor substrate according to the first embodiment. 6 is a diagram for illustrating a method for heating a silicon carbide semiconductor substrate according to the second embodiment. 10 is a view showing another embodiment of a method for heating a silicon carbide semiconductor substrate according to the second embodiment. 10 is a diagram for illustrating a method for heating a silicon carbide semiconductor substrate according to the third embodiment. 10 is a view showing another embodiment of a method for heating a silicon carbide semiconductor substrate according to the third embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon carbide semiconductor substrate, 2 Carbon particle, 3 Silicon carbide particle, 5 Device formation surface, 10 Heating element, 11 Quartz tube, 12 High frequency induction heating coil, 13 Susceptor.

Claims (6)

(A) placing silicon carbide particles in a recessed region of the recess formed in the susceptor;
(B) placing a silicon carbide semiconductor substrate on the susceptor so as to close the upper portion of the recess so that the device formation surface faces the susceptor;
(C) After the steps (A) and (B), the step of heating the silicon carbide semiconductor substrate by heating the susceptor is provided.
A method for heating a silicon carbide semiconductor substrate. The recess is formed of a first recess and a second recess that is connected to the bottom of the first recess and has a smaller opening width than the first recess.
The step (A)
A step of introducing the silicon carbide particles into the recessed region of the second recess,
The step (B)
Placing the silicon carbide semiconductor substrate on the bottom of the first recess so as to close the top of the second recess,
(D) The method further includes a step of placing carbon particles on a recessed portion formed by the upper surface of the silicon carbide semiconductor substrate and the side surface of the first recess.
The method for heating a silicon carbide semiconductor substrate according to claim 1. The step (D)
A step of placing the carbon particles on the silicon carbide semiconductor substrate by one layer;
The method for heating a silicon carbide semiconductor substrate according to claim 2. A heating element is disposed above the silicon carbide semiconductor substrate or above the carbon particles,
The step (C)
Heating the silicon carbide semiconductor substrate by heating the heating element and the susceptor;
The method for heating a silicon carbide semiconductor substrate according to claim 1 or 2. The step (C)
Heating the silicon carbide semiconductor substrate in a state where the lower surface of the heating element and the upper surface of the susceptor are in contact with each other;
The method for heating a silicon carbide semiconductor substrate according to claim 4. The heating element has a recess formed on the side facing the silicon carbide semiconductor substrate,
The step (C)
Heating the silicon carbide semiconductor substrate in a state where the lower surface of the heating element is in contact with the upper surface of the susceptor and the upper surface of the silicon carbide semiconductor substrate is covered by the recess.
The method for heating a silicon carbide semiconductor substrate according to claim 5.

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