JP2008290889A - DEVICE AND METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for manufacturing an SiC single crystal by a solution method capable of growing the SiC single crystal without causing cracks, peeling or dropping even when a large diameter seed crystal is used. <P>SOLUTION: In the device, the lower end surface D of a pulling shaft X has a flat part P to be adhered with a seed crystal S and recessed parts E provided in the flat part P. In the manufacturing of the SiC single crystal, the device is used in following way: (1) the flat part P is adhered to the seed crystal and each recessed part E serves as a cavity; or (2) SiC is crystallized from a melt of Si or a Si-based alloy by cooling the melt under such conditions that the seed crystal is brought into contact with the lower end surface D and the melt is arranged in the recessed parts E of the lower end surface D, and the seed crystal is adhered to the lower end surface D by using the crystallized SiC. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus and a method for producing an SiC single crystal by a solution method, and more particularly to an improvement in a method for holding an SiC seed crystal.

  Since SiC has a larger energy band gap than Si, various techniques for producing high-quality SiC single crystals suitable as semiconductor materials have been proposed. A wide variety of SiC single crystal production methods have been tried so far, but the sublimation method and the solution method are currently most common. Although the sublimation method has a high growth rate, it has a defect that defects such as micropipes and transformation of crystal polymorphism are likely to occur. On the other hand, a solution method without these defects is considered promising, although the growth rate is relatively slow. Yes.

  The manufacturing method of the SiC single crystal by the solution method maintains a temperature gradient in which the temperature decreases from the inside toward the melt surface in the Si melt in the graphite crucible. C dissolved in the Si melt from the graphite crucible in the lower high temperature part rises mainly by the convection of the melt, reaches the low temperature part near the melt surface, and becomes supersaturated. An SiC seed crystal is held at the lower end of the graphite shaft immediately below the melt surface, and supersaturated C is crystallized as an SiC single crystal by epitaxial growth on the SiC seed crystal.

  As a method for holding the seed crystal at the lower end of the graphite shaft, mechanical holding or holding by adhesion can be considered. The mechanical holding is performed by fitting the seed crystal in a groove or the like provided at the lower end of the graphite shaft and mechanically tightening and fixing it, so that the seed crystal can be reliably prevented from falling. However, the positional relationship between the graphite axis and the seed crystal is limited, and there is a problem that normal growth is hindered due to the influence of polycrystals grown on the graphite axis during single crystal growth. Therefore, generally, a method of fixing to the lower end surface of the graphite shaft with an adhesive is performed. As an example of holding with an adhesive, Patent Document 1 discloses a method of crystal growth by bringing a seed crystal into contact with a melt added with a transition metal. However, a new problem emerged when the diameter of the grown crystal was increased.

  That is, conventionally, a relatively small-diameter seed crystal having a diameter of 20 mm or less has been used. However, in order to increase the diameter of a growth crystal, if a growth crystal can be obtained with a large-diameter seed crystal, a small-diameter seed crystal is used. This makes it possible to shorten the growth process required for the diameter expansion.

  Therefore, when a large-diameter seed crystal having a diameter of 20 mm or more is uniformly bonded to the entire lower surface of the graphite shaft having an area of about 50 to 80% of the area of the seed crystal surface as in the conventional case, crystal growth starts. At the time of contact with the solution, which was the previous step for the purpose of the test, cracking of the seed crystal and peeling / dropping from the graphite shaft occurred, and it was found that it was not possible to proceed to the actual crystal growth stage.

  This is due to the internal stress due to the temperature difference in the seed crystal and the interfacial stress due to the difference in thermal expansion between the seed crystal and the graphite axis, which occurs when the seed crystal is brought into contact with a high-temperature solution of 1600 ° C. or higher. It is thought to be. Both the internal stress and the interfacial stress were not so large when the seed crystal had a relatively small diameter of 20 mm or less as in the prior art, but became large when the seed crystal had a large diameter exceeding 20 mm in diameter. Since it exceeds the strength of the crystal itself and the adhesive strength between the seed crystal and the graphite shaft, it is considered that the seed crystal is cracked or peeled off or dropped off from the graphite shaft.

  Regarding techniques related to seed crystal retention in the solution method, Patent Document 2 discloses an SiC single crystal adhesive and bonding method, Patent Document 3 discloses a seed crystal fixing device and fixing method, and Patent Document 4 discloses a seed crystal fixing method. However, no consideration is given to the above-mentioned specific problems associated with the increase in the diameter of the seed crystal.

JP 2000-264790 A JP 2005-263540 A JP 2006-347867 A JP 2005-263539 A

  An object of the present invention is to provide an apparatus and a method for producing an SiC single crystal by a solution method that enables crystal growth without causing cracking, peeling, or dropping even with a large-diameter seed crystal.

In order to achieve the above object, the SiC single crystal manufacturing apparatus according to the present invention maintains a temperature gradient in the Si melt in the graphite crucible that decreases in temperature from the inside toward the melt surface. In the apparatus for growing the SiC single crystal starting from the lower surface, the lower surface of the SiC seed crystal bonded to the lower end surface is brought into contact with the melt.
The lower end surface of the pulling shaft has a flat part bonded to the seed crystal and a recess in the flat part.

  Moreover, the manufacturing method of the SiC single crystal of this invention is characterized by the following (1) or (2).

  (1) A method for producing a SiC single crystal using the apparatus of the present invention, wherein the flat portion is bonded to the seed crystal, and the depression is used as a cavity.

  (2) A method for producing a SiC single crystal using the apparatus of the present invention, wherein the seed crystal is in contact with the lower end surface, and a Si or Si-based alloy melt is disposed in the recess of the lower end surface. By cooling in a state, SiC is crystallized from the melt, and the lower end surface and the seed crystal are bonded by the crystallized SiC.

  The SiC single crystal manufacturing apparatus according to the present invention has a configuration in which the lower end surface of the pulling shaft has a flat portion bonded to the seed crystal and a recess in the flat portion, thereby manufacturing the SiC single crystal according to the present invention. The following effects can be obtained through the method.

  (1) In the method in which the flat portion of the lower end surface of the pulling shaft is bonded to the seed crystal and the dent is used as a cavity, the seed crystal is not constrained in the dent portion, so internal stress generated upon contact with the solution Further, since the interfacial stress is relaxed, cracking, peeling and dropping are prevented even with a large-diameter seed crystal.

  That is, in this method, the internal stress and interfacial stress are reduced to a level that does not reach the seed crystal strength and adhesive strength due to the “stress relaxation effect” in the recessed portion where the seed crystal and the lower end surface of the pulling shaft are not in contact. This prevents the seed crystal from cracking, peeling and dropping.

  (2) The seed crystal is in contact with the lower end surface of the pulling shaft, and Si or Si-based alloy melt is placed in the recess on the lower end surface, and cooling is performed to crystallize SiC from the melt. In the method in which the lower end surface and the seed crystal are bonded with SiC, the bonding between the seed crystal and the lower end surface of the pulling shaft is performed much more strongly than with the adhesive, so that the deformation of the seed crystal is constrained. Therefore (= because the seed crystal is reinforced by the lower end of the pulling shaft), it can overcome internal stress and interface stress generated when contacting with the solution. Is prevented.

  That is, in the case of this method, the “strengthening effect” due to deformation restraint increases the effective crystal strength and adhesive strength over the internal stress and interface stress generated when contacting with the solution, and the seed crystal cracks, peels Dropping is prevented.

  In the SiC single crystal manufacturing apparatus of the present invention, the lower end surface of the pulling shaft is composed of a flat portion bonded to the seed crystal and a recess in the flat portion.

  In one desirable embodiment, the lower end surface of the pulling shaft that holds the seed crystal has a flat portion divided into a plurality of groove-shaped depressions.

  In the examples shown in FIGS. 1A, 1B, 1B, 1C, and 1C, the three-direction grooves E intersecting the flat circular lower end surface D at an inclination angle of 60 °. Are digged in four in each direction and divided into a large number of flat surfaces P. Further, in the example shown in FIG. 2 (A) photograph, (B) sketch (plan view), and (C) cross-sectional view, two directions of grooves E perpendicular to each other are formed in the flat circular lower end surface D in each direction. Four pieces are dug up and divided into a large number of flat surfaces P.

  The following usage patterns are possible on the lower end surface.

  (1) In the first usage pattern, the flat upper surface S1 of the seed crystal S is bonded and fixed to the divided flat surface P of the lower end surface D of the pulling shaft X with an adhesive. The groove E having a V-shaped cross section exists as a cavity with the opening being closed by the flat upper surface S1 of the seed crystal S.

  When the seed crystal S held in this state is brought into contact with the Si solution surface, the seed crystal S is rapidly heated by a high-temperature Si solution at 1600 ° C. or higher. The seed crystal S is preheated to about 1800 ° C., but due to a temperature difference with the Si solution, internal stress is generated in the seed crystal S and interfacial stress is generated at the bonded portion with the lower end surface D. At that time, the internal stress and the interface stress are relieved in the groove E that is not in contact with the seed crystal S, that is, in the hollow portion. Decrease to a level not exceeding.

  (2) In the second usage pattern, the flat upper surface S1 of the seed crystal S is in contact with the lower end surface D of the pulling shaft X, and a Si or Si-based alloy melt is disposed in the groove E of the lower end surface D. By cooling in a state, SiC is crystallized from the melt, and the lower end face D and the seed crystal S are bonded together by the crystallized SiC.

  This usage pattern is further divided into the following two modes according to a specific method of arranging a melt of Si or a Si-based alloy in the groove E.

  (2-1) In the first aspect, Si or Si base alloy is arranged in the groove E of the lower end face D, the flat upper surface S1 of the seed crystal S is brought into contact with the lower end face D, and Si or Si base Heat above the melting point of the alloy.

  (2-2) In the second mode, the groove E is in a form communicating to the outer periphery of the lower end surface D as in the examples of FIGS. 1 and 2, and the seed crystal S is temporarily bonded to the lower end surface D, and Si or Immerse in the melt of Si-based alloy.

  In any embodiment, the seed crystal S is extremely strongly bonded to the lower end surface D of the pulling shaft X by SiC crystallized from the melt by cooling after the melt is disposed.

  When the seed crystal S held in this state is brought into contact with the Si solution surface, the seed crystal S is rapidly heated by a high-temperature Si solution at 1600 ° C. or higher. The seed crystal S is preheated to about 1800 ° C., but due to a temperature difference with the Si solution, internal stress is generated in the seed crystal S and interfacial stress is generated at the bonded portion with the lower end surface D. The seed crystal S is reinforced by being firmly bonded to the lower end surface D of the pulling shaft X and restraining deformation, and can withstand the internal stress and the interface stress.

  The recess provided in the lower end surface D of the pulling shaft X is not necessarily limited to the groove E communicated to the outer periphery of the lower end surface D as shown in FIGS. Good. Some examples are shown in FIG. The recess may be located not only in the flat part P but also outside the flat part P.

  FIG. 3A is an example in which grooves E in three directions intersecting each other at approximately 60 ° are provided as in the example of FIG. 1, but, unlike the example of FIG. Absent. The lower end surface D is divided into a number of flat surfaces P by grooves E.

  FIG. 3B shows an example in which grooves E in two directions substantially orthogonal to each other are provided as in FIG. 2, but does not reach the outer periphery of the lower end surface D unlike the example of FIG. 2. The lower end surface D is divided into a number of flat surfaces P by grooves E.

  FIG. 3C shows an example in which a number of grooves E are provided concentrically. The lower end surface D is divided into a number of flat surfaces P by grooves E.

  FIG. 3D shows an example in which one groove E on a meander is provided. The lower end surface D is not divided by the groove E and is a single flat surface.

  FIG. 3 (E) is an example in which a number of short grooves E are arranged in a skewered manner with one long groove E, and this is provided for three skewers. In this case as well, the lower end surface D is not divided by the grooves E. One flat surface.

  FIG. 3F is an example in which one spiral groove E is provided. In this case, the lower end surface D is not divided by the groove E and is a single flat surface.

  FIG. 3G shows an example in which a large number of dimples E are provided. In this case as well, the lower end surface D is not divided by the groove E and is a single flat surface.

[Example 1]
According to the first usage pattern of the lower end surface D of the pulling shaft according to the present invention, the groove E having the configuration shown in FIGS. 1 and 2 is provided as a recess, and the SiC seed crystal is adhered and held on a large number of flat surfaces P with an adhesive. Then, an experiment for growing a SiC single crystal was conducted. The seed crystal sizes were φ25 mm and φ50 mm.

<Adhesion method>
Two types of adhesives of compositions A and B shown in Table 1 were used.

  The adhesion procedure was as follows.

  1) The surface temperature of the lower end surface of the graphite lifting shaft is heated to 80 to 100 ° C., and the A or B adhesive in Table 1 is uniformly applied to the flat portion of the lower end surface.

  2) A seed crystal is affixed to the lower end surface to which the adhesive is applied, a load of about 0.05 to 0.5 kgf is applied to the adhesive surface, and the heat is removed to room temperature.

  3) Using a heated atmosphere furnace (a degreasing furnace and a firing furnace), the adhesive was thermoset under the following conditions.

      After heating and holding at 200 ° C. × 1 hr + 700 ° C. × 2 hr, the furnace is cooled to room temperature.

  Using the seed crystal bonded as described above, an SiC single crystal was grown using the apparatus shown in FIG.

  An SiC single crystal growth apparatus 100 shown in FIG. 4 covers a graphite crucible 10 with a heat insulating material 12, heats it with a high-frequency coil 14, forms an Si solution 16 therein, and places SiC at the lower end of a graphite shaft 18 inserted from above. The seed crystal 20 is held. The temperature of the SiC seed crystal 20 is monitored by a W-Re thermocouple 22, and the liquid surface temperature of the Si solution 16 is monitored by a radiation thermometer (pyrometer) 24. The radiation thermometer 24 is installed in an observation window 26 above the solution surface where the solution surface can be directly observed, and can measure the solution temperature before and after contacting the seed crystal 20 with the solution. Moreover, the W-Re thermocouple 22 was installed inside the graphite axis (position of 2 mm from the seed crystal) to which the seed crystal 20 is bonded, and the temperature immediately after the contact between the solution 16 and the seed crystal 20 was measured.

  The growth conditions were as follows.

Seed crystal preheating temperature: 1835 ° C
Si solution surface temperature: 1917 ° C
Furnace atmosphere: Ar (101 ° C)
Growth time: 10 hours [Example 2]
According to the second usage pattern of the lower end surface D of the pulling shaft according to the present invention, a groove E having the configuration shown in FIGS. 1 and 2 is provided as a depression, and a SiC seed crystal is temporarily bonded to many flat surfaces P with an adhesive. An experiment was conducted in which Si was grown by depositing Si in the groove E and bonding the seed crystal with SiC crystallized by melting and cooling.

  The temporary bonding method was the same as the bonding method of Example 1, and was performed using the same adhesives A and B and the same bonding procedure.

  Next, Si melt was arranged in the groove by the following procedure.

  1) The graphite shaft lower end to which the seed crystal is temporarily bonded is immersed in a Si solution heated and held at 1600 ° C.

  2) Immerse for 5 minutes and allow the Si solution to enter the groove E from the outer periphery of the lower end surface D of the graphite shaft.

      The Si solution that has entered the groove dissolves carbon from the graphite while in contact with the back surface of the graphite and the seed crystal.

  3) The lower end of the graphite shaft is pulled up from the Si solution and slowly cooled. As a result, an infinite number of SiC fine crystals crystallize on the graphite and the seed crystal back surface of the groove inner wall from the Si solution that has entered the groove and dissolved carbon, and the graphite axis lower end surface and the seed crystal back surface Glue firmly.

  Moreover, the following method was also performed as a method of arranging the Si melt in the groove.

  1) Disperse granular and powdery Si in the groove.

  2) The seed crystal is temporarily bonded with an adhesive.

  3) Heat treatment at 1600 ° C. or higher is performed in a firing furnace to melt Si in the groove and then cool.

  As in the above method, an infinite number of SiC fine crystals crystallize on the graphite on the inner wall of the groove and on the back surface of the seed crystal from the Si solution in which carbon is melted by melting in the groove. The end face and the seed crystal back face are firmly bonded. FIG. 5 shows a cross-sectional photograph of an example in which SiC is crystallized to bond the graphite shaft and the seed crystal.

[Conventional example]
For comparison, a SiC single crystal growth experiment was performed under the same growth conditions as above for the conventional example in which a seed crystal was pasted on the front surface with the graphite shaft lower end surface D kept flat as in the past. .

  Table 2 summarizes the results of experiments according to Example 1, Example 2, and the conventional example.

  As shown in Table 2, when the seed crystals were held according to Example 1 and Example 2, SiC was not caused by cracking of the seed crystals, and no defects due to peeling / dropping in any of the seed crystal sizes of φ25 mm and φ50 mm. A single crystal could be grown.

  FIG. 6 shows a state in which the SiC single crystal has grown from the seed crystal at the lower end of the graphite shaft, with photographs taken from (A) the side and (B) the bottom. As shown in the figure, a regular hexagonal single crystal is grown from a circular seed crystal.

  On the other hand, when the seed crystal was held by the conventional example, the seed crystal was cracked, peeled off, and dropped off, and normal crystal growth was not performed.

  FIG. 7 shows an example of the photograph from the bottom. The seed crystal is deficient in the lower 2/3 while leaving the upper 1/3 in the photograph. The linear defect interface is considered to correspond to the cleavage plane of the SiC seed crystal. In this case, since the growth was continued without noticing the defect of the seed crystal, the crystal growth was performed only on the seed crystal remaining on the upper part.

  According to the present invention, there is provided an apparatus and a method for producing an SiC single crystal by a solution method that enables crystal growth without causing cracks, peeling or dropping even with a large-diameter seed crystal exceeding φ20 mm. .

FIG. 1 shows an embodiment in which a flat circular lower end surface D is divided into a plurality of flat surfaces P by digging four grooves in each direction, four in each direction, at an inclination angle of 60 °. It is (A) photograph which shows a form, (B) sketch (plan view), (C) sectional drawing. FIG. 2 shows an embodiment in which two perpendicular grooves E are dug into each flat circular lower end surface D and divided into a large number of flat surfaces P according to the present invention (A). ) A photograph, (B) a sketch (plan view), and (C) a sectional view. FIG. 3 is a plan view schematically showing various forms of recesses provided in the lower end surface of the pulling shaft according to the present invention. FIG. 4 is a cross-sectional view schematically showing an apparatus used for growing a SiC single crystal according to Examples 1 and 2 and the conventional example. FIG. 5 is a photograph showing SiC crystallized by cooling the Si solution in which C was dissolved in Example 2. FIG. 6 is a photograph from (A) the side surface and (B) the bottom surface showing a state in which the SiC single crystal has grown normally using the seed crystal holding method of the present invention in the examples. FIG. 7 is a photograph from the bottom showing a state in which the seed crystal was broken and normal crystal growth was not performed due to peeling and dropping in the conventional example.

Explanation of symbols

X Lifting shaft D Lower end surface of lifting shaft E Groove (dent) dug in the lower end surface
P Many flat surfaces divided by grooves S seed crystals

Claims (6)

The lower surface of the SiC seed crystal adhered to the lower end surface of the pulling shaft is brought into contact with the melt while maintaining a temperature gradient in the Si melt in the graphite crucible that decreases in temperature from the inside toward the melt surface. In an apparatus for growing a SiC single crystal starting from
The SiC single crystal manufacturing apparatus, wherein a lower end surface of the pulling shaft has a flat portion bonded to the seed crystal and a recess in the flat portion.   The SiC single crystal manufacturing apparatus according to claim 1, wherein the flat portion is divided into a plurality of grooves by the recesses. A method for producing a SiC single crystal using the apparatus according to claim 1,
A method for producing a SiC single crystal, wherein the flat portion is bonded to the seed crystal, and the depression is used as a cavity. A method for producing a SiC single crystal using the apparatus according to claim 1,
The seed crystal is in contact with the lower end surface, and Si or Si-based alloy melt is arranged in the recess of the lower end surface, and then cooled to crystallize SiC from the melt and crystallize. A method for producing a SiC single crystal, comprising bonding the lower end surface and the seed crystal with SiC. The method of claim 4, wherein
In order to place the melt in the recess,
The SiC single crystal is characterized in that the Si or Si-based alloy is disposed in the recess of the lower end surface, the seed crystal is brought into contact with the lower end surface, and heated to the melting point or higher of the Si or Si-based alloy. Production method. The method of claim 4, wherein
In order to place the melt in the recess,
A method for producing a SiC single crystal, characterized in that the recess is communicated to the outer periphery of the lower end surface, the seed crystal is temporarily bonded to the lower end surface, and immersed in a melt of the Si or Si-based alloy. .