JP5823889B2 - Seed crystal and manufacturing method thereof, crystal growth apparatus and crystal growth method - Google Patents

Description

  The present invention relates to a seed crystal for growing a silicon carbide crystal by a solution method, a manufacturing method thereof, a crystal growth apparatus, and a crystal growth method.

  Silicon carbide (Silicon Carbide: hereinafter referred to as “SiC”), which is a compound of carbon and silicon, has a wider band gap than silicon, a large electric field strength leading to dielectric breakdown, and excellent withstand voltage characteristics. Furthermore, it has excellent thermal conductivity, heat resistance, chemical resistance, radiation resistance, and the like. SiC crystals having such various advantages are attracting attention in a wide range of fields such as heavy electric fields including nuclear power, transportation fields including automobiles and aviation, household electrical appliance fields, and space fields.

  As a method for growing a SiC single crystal, a solution method is known (see, for example, Patent Document 1). In the solution method, the upper surface of a seed crystal made of SiC is held by a holding member, and the lower surface thereof is brought into contact with a silicon-containing silicon melt, and then the seed crystal is pulled up to bring the lower surface of the seed crystal from the melt. This is a method for growing a SiC single crystal. Such solution methods are expected to increase the size and length of SiC single crystals.

  However, since the lower surface of the seed crystal used in the conventional solution method as described in Patent Document 1 is exposed, the lower surface tends to be contaminated before being brought into contact with the melt. In addition, dislocations, micropipes and the like are easily generated in the growing SiC crystal, and it has been difficult to grow a high-quality SiC crystal.

JP 2000-264790 A

  An object of the present invention is to provide a seed crystal capable of growing a high-quality silicon carbide crystal by a solution method, a manufacturing method thereof, a crystal growth apparatus, and a crystal growth method.

  The seed crystal of the present invention grows a silicon carbide crystal by a solution method, and has an upper surface held by a holding member and a lower surface on which the crystal located on the side opposite to the upper surface is grown. A seed crystal main body, and a film made of silicon provided on the lower surface.

  The method for producing a seed crystal of the present invention comprises a step of preparing a seed crystal body made of silicon carbide having an upper surface held by a holding member and a lower surface on which a crystal located on the opposite side of the upper surface is grown, and the seed crystal Providing a film made of silicon on the lower surface of the main body.

  The crystal growth apparatus according to the present invention includes a crucible for storing a silicon melt containing carbon, a holding member that can be taken into and out of the crucible opening, and the upper surface of the seed crystal body held by the holding member. The seed crystal according to claim 1.

  The crystal growth method of the present invention includes a step of holding the upper surface of the seed crystal body in the seed crystal according to the present invention described above by a holding member, and immersing the coating of the seed crystal in a silicon-containing melt. A step of dissolving the coating in the melt and bringing a lower surface of the seed crystal body into contact with the melt; and pulling up the seed crystal body to form silicon carbide from the melt on the lower surface of the seed crystal body. And growing a crystal.

  According to the present invention, since the seed crystal has a film made of silicon provided on the lower surface of the seed crystal body, the lower surface of the seed crystal body is protected by the film until immersed in a silicon melt containing carbon. Therefore, contamination of the lower surface of the seed crystal body can be suppressed. Further, since the film is made of silicon, it dissolves when immersed in the melt, and the dissolved film can be made less likely to be an impurity with respect to the melt. Furthermore, since a SiC crystal is grown on the lower surface of the seed crystal body exposed by dissolution of the film, it is possible to grow a high-quality SiC crystal in which the occurrence of dislocations, micropipes, and the like is suppressed.

It is a schematic explanatory drawing which shows the crystal growth apparatus which concerns on one Embodiment of this invention. It is the elements on larger scale which show the seed crystal vicinity in the crystal growth apparatus of FIG. It is an expanded sectional view which expands a part of seed crystal main part and film | membrane of FIG. 2 is a graph schematically showing the relationship between the film thickness and the porosity of the film in FIG.

<Seed crystal>
Hereinafter, a seed crystal according to an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. As shown in FIG. 1, the seed crystal 4 of the present embodiment is provided in a crystal growth apparatus 1 described later, and grows a single crystal of SiC by a solution method.

  The seed crystal 4 of the present embodiment includes a seed crystal body 41 and a film 42. As shown in FIG. 2, the seed crystal body 41 has an upper surface 41A held by a holding member 2 to be described later, and a lower surface 41B for growing crystals located on the opposite side of the upper surface 41A, and is made of SiC. . The coating 42 is provided on the lower surface 41B of the seed crystal body 41 and is made of silicon.

  According to the seed crystal having such a configuration, the lower surface 41B of the seed crystal body 41 can be protected by the coating 42 until it is immersed in a carbon-containing silicon melt 5 described later, and therefore the lower surface 41B is contaminated. Can be suppressed. Moreover, since the film | membrane 42 consists of silicon | silicone, when immersed in the melt 5, it melt | dissolves and the lower surface 41B can be exposed.

  In the coating 42, the porosity in the vicinity of the lower surface 41B side of the seed crystal body 41 may be larger than the porosity in the vicinity of the opposite surface 42A. That is, the density of the coating 42 near the lower surface 41B side may be smaller than the density near the surface 42A. The porosity from the porosity in the vicinity of the lower surface 41B to the porosity in the vicinity of the surface 42A may be constant, and as shown in FIG. 3, the porosity is higher than that of the first layer 42a and the first layer 42a. There may be two layers having the second layer 42b.

  Thereby, since the surface area of the coating 42 near the lower surface 41B side is larger than the surface area near the surface 42A, the vicinity of the lower surface 41B side can be more easily dissolved than the vicinity of the surface 42A. Further, since the porosity increases toward the surface 42A, it is difficult to enter the coating 42 from the outside. Therefore, it is possible to enhance the effect of the above-described film 42 that dissolves when exposed to the melt 5 and exposes the lower surface 41B, and makes the lower surface 41B less susceptible to contamination.

  In order to further enhance this effect, the coating 42 may have a porosity that increases from the surface 42A opposite to the lower surface 41B side of the seed crystal body 41 toward the lower surface 41B side of the seed crystal body 41. Specifically, the porosity of the coating 42 may change stepwise as shown in FIG. 4A as it goes from the surface 42A toward the lower surface 41B, or as shown in FIG. 4B. It may change gradually. 4 shows the horizontal axis as 0 on the lower surface 41B side of the coating 42, the surface 42A as the film thickness h from the lower surface 41B side, and the vertical axis as the porosity.

  The change in the porosity in the film 42 can be controlled to the above relationship by adjusting the film formation conditions of the film 42 in film formation by sputtering, for example. The porosity (%) can be calculated by, for example, the formula: (volume / mass) × 100.

  The film 42 may contain at least one metal selected from metal materials having a melting point lower than that of silicon and forming a eutectic with silicon. Thereby, since melting | fusing point of the film | membrane 42 can be lowered | hung, the effect by the above-mentioned film | membrane 42 which melt | dissolves and exposes the lower surface 41B when immersed in the melt 5 can be heightened.

  In order to further enhance this effect, the coating 42 may have a metal concentration in the vicinity of the lower surface 41B side of the seed crystal body 41 higher than that in the vicinity of the opposite surface 42A, and from the surface 42A to the lower surface 41B. The concentration of the metal may be higher toward the side.

  Examples of the metal selected from a metal material having a lower melting point than silicon that forms a eutectic with silicon include, but are not limited to, aluminum, silver, chromium, titanium, and the like. In a metal material having a melting point lower than that of silicon, the lower limit of the melting point can be set to 800 ° C. or higher and 1100 ° C. or lower.

  In the coating 42, the surface roughness of the surface 42 </ b> A opposite to the lower surface 41 </ b> B of the seed crystal body 41 may be larger than the surface roughness of the lower surface 41 </ b> B of the seed crystal body 41. Thereby, since the surface area of the surface 42A is increased, the coating 42 can be easily dissolved from the surface 42A side with respect to the melt 5 and dissolves when exposed to the melt 5 to expose the lower surface 41B. The effect by 42 can be heightened. In order to make the surface roughness in the above relationship, for example, the surface 42A of the coating 42 may be subjected to a polishing process or the like.

  The thickness of the film 42 can be set to 0.5 μm or more and 10 μm or less. The layer structure of the coating 42 may be either a single layer structure or a multilayer structure. In the case of a multi-layer structure, for example, a plurality of layers in which the crystallinity of silicon of the coating 42 is changed may be stacked, or the melting point may be lowered toward the lower surface 41B of the seed crystal body 41 in the multi-layer structure. Good.

<Method for producing seed crystal>
Next, a method for manufacturing a seed crystal according to an embodiment of the present invention will be described taking as an example the case of manufacturing the seed crystal 4 according to the above-described embodiment.

The seed crystal manufacturing method of the present embodiment includes the following steps (i) and (ii).
(I) The process of preparing the seed crystal main body 41 which concerns on one Embodiment mentioned above.
(Ii) A step of providing a coating 42 made of silicon on the lower surface 41B of the seed crystal body 41.

  The seed crystal 4 is manufactured through the above steps. In the step (ii) of providing the coating 42, for example, a sputtering method or a vapor deposition method can be used for the coating 42. In particular, when the coating 42 is provided by the sputtering method in the step (ii) of providing the coating 42, the porosity of the coating 42 can be easily changed depending on the sputtering conditions, so that productivity can be improved.

<Crystal growth equipment>
Next, a crystal growth apparatus according to an embodiment of the present invention will be described. As shown in FIG. 1, the crystal growth apparatus 1 of the present embodiment includes a crucible 6, a crucible container 7 that accommodates the crucible 6 below, a crucible 6, and the seed crystal 4 according to the embodiment described above. A heat insulating material 8 positioned between the crucible container 7 and a heating mechanism 10 for heating the crucible 6 are provided.

  The crucible 6 has a function as a container for containing the silicon melt 5 containing carbon. The crystal growth apparatus 1 of this embodiment grows a SiC crystal by creating a state close to thermal equilibrium inside the crucible 6. Examples of the constituent material of the crucible 6 include carbon (graphite).

  The crucible container 7 has a function of holding the crucible 6 inside. The heat insulating material 8 has a function of covering the outer peripheral portion of the crucible 6 and suppressing heat dissipation from the crucible 6 to keep the crucible 6 at a constant temperature.

  The heating mechanism 10 has a function of heating the crucible 6. The heating mechanism 10 of the present embodiment employs an electromagnetic induction heating method that heats the crucible 6 with electromagnetic waves. Specifically, the heating mechanism 10 of the present embodiment includes a coil 11 and an AC power source 12.

  The coil 11 is composed of a conductor, and the lower region of the outer peripheral portion of the crucible container 7 is spirally wound. The AC power supply 12 is electrically connected to the coil 11 so that an AC current can flow through the coil 11. In addition, when the thing with a high current value of alternating current is used for the alternating current power supply 12, the time which heats the inside of the crucible 6 to preset temperature can be shortened.

  The crucible 6 is heated by the heating mechanism 10 of the present embodiment as follows. First, an alternating current is passed through the coil 11 using the alternating current power source 12 to generate an electromagnetic field in the space including the heat insulating material 8. This electromagnetic field causes an induced current to flow through the crucible 6. The induced current flowing in the crucible 6 is converted into thermal energy by various losses such as Joule heat generation due to electric resistance and heat generation due to hysteresis loss. That is, the crucible 6 is heated by the heat loss of the induced current.

  Note that an induction current may be passed through the melt 5 by this electromagnetic field to cause the melt 5 itself to generate heat. When the melt 5 itself is heated, the crucible 6 need not be heated. Moreover, although the electromagnetic induction heating system is employ | adopted for the heating mechanism 10 of this embodiment, it may replace with this and may employ | adopt another system. If a specific example is given, the heat transfer system etc. which transfer the heat which generate | occur | produced with exothermic resistors, such as carbon will be mentioned. When the heat transfer type heating mechanism 10 is employed, a heating resistor may be disposed between the crucible 6 and the heat insulating material 8.

  The crystal growth apparatus 1 further includes a carry-in / out mechanism 13 for carrying the seed crystal 4 into the melt 5 located inside the crucible 6 and carrying out the SiC single crystal grown from the melt 5. The carry-in / out mechanism 13 includes a holding member 2 that can be taken into and out of the crucible 6 through the opening 6 </ b> A of the crucible 6, and a power source 14.

  The holding member 2 has a three-dimensional shape, for example, a rod shape or a rectangular parallelepiped shape, and is positioned so as to correspond to the opening 6A. As shown in FIG. 2, the holding member 2 has a lower end surface 2A located on the crucible 6 side, and holds the seed crystal 4 on the lower end surface 2A.

  The movement of the holding member 2 is controlled by the power source 14 in the vertical direction, that is, the D1 direction and the D2 direction, so that the portion of the holding member 2 located on the lower end surface 2A side extends from the opening 6A of the crucible 6 6 is configured to be able to be taken in and out. Therefore, in the present embodiment, the SiC crystal grown on the lower surface 41B of the seed crystal 4 and the seed crystal body 41 is carried in and out by the holding member 2. The D1 direction means a downward direction on the physical space, and the D2 direction means an upward direction on the physical space.

  Examples of the constituent material of the holding member 2 include a material containing carbon as a main component, and examples of the carbon include a polycrystal of carbon and a fired body obtained by firing carbon.

  As shown in FIG. 2, the holding member 2 of the present embodiment is provided with an adhesive 3 on the lower end surface 2 </ b> A, and holds the upper surface 41 </ b> A of the seed crystal body 41 via the adhesive 3. The area of the lower end surface 2A of the holding member 2 may be larger or smaller than the area of the upper surface 41A of the seed crystal body 41. In the present embodiment, the area of the lower end surface 2A of the holding member 2 is smaller than the area of the upper surface 41A of the seed crystal body 41. When the area of the lower end surface 2A of the holding member 2 is larger than the area of the upper surface 41A of the seed crystal body 41, the entire upper surface 41A of the seed crystal body 41 can be held via the adhesive 3. The holding force by the holding member 2 can be increased.

  Examples of the shape of the lower end surface 2A of the holding member 2 include, for example, a polygonal shape such as a square shape, a circular shape, and the like in the end surface view. The end view means a state in which the holding member 2 is viewed from the lower end surface 2A side.

  Examples of the adhesive 3 include a carbon adhesive, a ceramic adhesive containing a ceramic material such as alumina or zirconium, and the like, and in order to prevent the seed crystal 4 from dropping from the holding member 2, the melting point of the melt 5. Those having a higher melting point may be used. In this case, since the seed crystal 4 can be prevented from falling off, the crystal grown on the lower surface 41B of the seed crystal body 41 can be enlarged, and the productivity can be improved.

  As shown in FIG. 1, the crystal growth apparatus 1 is connected to an AC power source 12 of the heating mechanism 10 and a power source 14 of the carry-in / out mechanism 13, and further includes a control unit 15 that controls them. . That is, in the crystal growth apparatus 1 of the present embodiment, the control unit 15 controls the heating and temperature control of the melt 5 and the carry-in / out of the seed crystal 4 in conjunction with each other. The control unit 15 includes a central processing unit and a storage device such as a memory, and includes, for example, a known computer.

<Crystal growth method>
Next, a crystal growth method according to an embodiment of the present invention will be described taking as an example the case of using the crystal growth apparatus 1 according to the above-described embodiment. The crystal growth method of this embodiment is a method of growing a SiC single crystal.

  In the present embodiment, first, a raw material of a single crystal of SiC, that is, carbon and silicon is accommodated in the crucible 6. Next, the crucible 6 is heated by the heating mechanism 10, the SiC single crystal raw material is melted inside the crucible 6, and the silicon melt 5 containing carbon is stored inside the crucible 6.

  In the melt 5, silicon, which is an element constituting a single crystal of SiC to be grown, is melted as a solvent. The solubility of the solute element (carbon) increases as the temperature of the solvent element increases. In the present embodiment, the temperature of the melt 5 is set to 1300 ° C. or higher and 2500 ° C. or lower. When the melt 5 in which many solutes are dissolved in a solvent at such a high temperature is cooled, the solutes are deposited with thermal equilibrium as a boundary. In the present embodiment, SiC crystals are grown on the lower surface 41 </ b> B of the seed crystal body 41 by utilizing precipitation due to a temperature deviation from the thermal equilibrium.

  More specifically, the upper surface 41A of the seed crystal body 41 is held by the holding member 2, and the holding member 2 is moved in the D1 direction, so that the film 42 of the seed crystal 4 is immersed in the melt 5. Thereby, the film 42 is dissolved in the melt 5, the lower surface 41 </ b> B of the seed crystal body 41 is exposed, and the exposed lower surface 41 </ b> B is in contact with the melt 5.

  In addition, since the melt | dissolved film | membrane 42 consists of silicon as above-mentioned, it can make it difficult to become an impurity with respect to the melt 5. The immersion conditions are not particularly limited as long as the coating 42 is dissolved and the exposed lower surface 41B of the seed crystal body 41 can contact the melt 5. For example, the entire seed crystal 4 is immersed in the melt 5. May be.

  When the lower surface 41B of the seed crystal body 41 comes into contact with the melt 5, the melt 5 is cooled in the vicinity of the lower surface 41B, and as described above, the solute is deposited on the lower surface 41B at the boundary of thermal equilibrium. That is, a single crystal of SiC is grown on the lower surface 41B of the seed crystal body 41 by utilizing precipitation of crystals due to a temperature shift from thermal equilibrium. At this time, since the lower surface 41B of the seed crystal body 41 is protected by the coating 42 until it is immersed in the melt 5, the exposed lower surface 41B of the seed crystal body 41 is in a state in which contamination is suppressed. In the present embodiment, since the SiC crystal is grown on the lower surface 41B of the seed crystal body 41 in which this contamination is suppressed, a high-quality SiC crystal can be grown.

  Then, after the SiC single crystal begins to grow on the lower surface 41B of the seed crystal body 41, the seed crystal body 41 is pulled up by gradually moving the holding member 2 in the D2 direction. Thereby, a SiC single crystal can be continuously grown on the lower surface 41 </ b> B of the seed crystal body 41.

  At this time, the seed crystal 4 needs to have at least the lower surface 41B of the seed crystal body 41 in contact with the melt 5. Here, in the present embodiment, the lower surface 41B of the seed crystal body 41 is a concept that includes the lowest end of the SiC single crystal grown on the lower surface 41B of the seed crystal body 41. Therefore, when pulling up the seed crystal body 41, it is necessary to bring the lowest end of the SiC single crystal growing on the lower surface 41 </ b> B of the seed crystal body 41 into contact with the melt 5. The speed at which the holding member 2 is moved in the direction D2 is not particularly limited, and may be set as appropriate according to the growth speed of the SiC single crystal grown on the lower surface 41B of the seed crystal body 41.

  Through each of the above steps, a high-quality SiC single crystal in which generation of dislocations, micropipes, and the like is suppressed is manufactured. In the step of moving the holding member 2 in the D1 direction described above, the film 42 of the seed crystal 4 and the melt 5 may be relatively close to each other. For example, the melt 5 may be close to the film 42. Similarly, in the step of moving the holding member 2 in the direction D2, it is only necessary that the lower surface 41B of the seed crystal body 41 and the melt 5 are relatively distant from each other. For example, the melt 5 is removed from the lower surface 41B of the seed crystal body 41. You may keep away.

  As mentioned above, although several embodiment which concerns on this invention was described, this invention is not limited to the above-mentioned embodiment, It cannot be overemphasized that many corrections and changes can be added within the scope of the present invention. Yes.

  For example, in the seed crystal 4 according to the above-described embodiment, the coating 42 is provided on the lower surface 41B of the seed crystal body 41. However, in the seed crystal 4, the coating 42 is provided on at least the lower surface 41B of the seed crystal body 41. For example, when the seed crystal body 41 further has a side surface, the coating 42 may be provided from the lower surface 41B to the side surface.

DESCRIPTION OF SYMBOLS 1 Crystal growth apparatus 2 Holding member 2A Lower end surface 3 Adhesive material 4 Seed crystal 41 Seed crystal main body 41A Upper surface 41B Lower surface 42 Coating 42A Surface 5 Melt 6 Crucible 6A Opening 7 Crucible container 8 Heat insulating material 10 Heating mechanism 11 Coil 12 AC power source 13 carry-in / out mechanism 14 power source 15 control unit

Claims (10)

A seed crystal for growing silicon carbide crystals by a solution method,
Having a lower surface for growing the crystal on the opposite side the upper surface and the upper surface and held by the holding member, and the seed crystal body consisting of silicon carbide, together with and a film comprising silicon provided on said lower surface ,
The film is a seed crystal in which the surface roughness of the surface opposite to the lower surface of the seed crystal body is larger than the surface roughness of the lower surface of the seed crystal body .   2. The seed crystal according to claim 1, wherein the coating has a porosity in the vicinity of the lower surface side of the seed crystal body larger than a porosity in the vicinity of the opposite surface.   The seed crystal according to claim 2, wherein the porosity of the coating increases from the surface opposite to the lower surface side of the seed crystal body toward the lower surface side of the seed crystal body.   4. The seed crystal according to claim 1, wherein the film contains at least one metal selected from metal materials having a melting point lower than that of silicon, which forms a eutectic with silicon.   5. The seed crystal according to claim 4, wherein the coating has a higher concentration of the metal in the vicinity of the lower surface side of the seed crystal body than a concentration of the metal in the vicinity of the opposite surface.   The seed crystal according to claim 5, wherein the coating has a concentration of the metal that increases from the surface opposite to the lower surface side of the seed crystal body toward the lower surface side of the seed crystal body. A method for producing a seed crystal according to any one of claims 1 to 6,
Providing a seed crystal body made of silicon carbide having an upper surface held by a holding member and a lower surface on which a crystal located on the opposite side of the upper surface is grown;
Providing a film made of silicon on the lower surface of the seed crystal body. The method for producing a seed crystal according to claim 7 , wherein in the step of providing the coating, the coating is provided by a sputtering method. A crucible containing therein a silicon melt containing carbon;
A holding member that can be inserted into and removed from the opening of the crucible;
A crystal growth apparatus comprising the seed crystal according to claim 1, wherein the upper surface of the seed crystal body is held by the holding member. A step of holding the upper surface of the seed crystal body in the seed crystal according to any one of claims 1 to 6 by a holding member;
Immersing the coating of the seed crystal in a melt of silicon containing carbon, dissolving the coating in the melt, and bringing the lower surface of the seed crystal body into contact with the melt;
A step of pulling up the seed crystal body and growing a silicon carbide crystal from the melt on the lower surface of the seed crystal body.

Images