JP2005139041A - Method for growing single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a single crystal whereby the large-diameter single crystal can be easily and stably provided. <P>SOLUTION: In the method for growing the single crystal through an FZ method, a part of a material rod 6 is subjected to induction heating by an induction heating coil 4 to form a melting zone 7 and, while the melting zone 7 is being moved, it is serially melted and solidified at its lower and upper ends, respectively, to grow the single crystal 8. The material rod 6 has protruding parts 6a, each continuing in the longitudinal direction, on its surface. This enables melting of the upper end of the material rod 6 from its center, stabilization of the melting zone 7 by shaping the upper end of the material rod 6 into a so-called bowl-shape and shortening of the melting zone 7, thereby enabling growth of the large-diameter single crystal 8. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a single crystal that can stably obtain a large-diameter and high-quality single crystal by using the FZ method (floating zone method; floating zone melting method).

  Conventionally, there is no suitable crucible made of a material that does not react with the crystal melt when high purity is required when growing a single crystal of metal or semiconductor, or because the single crystal to be grown has a high melting point. In some cases, the FZ method using an induction heating coil is used.

  In the FZ method, first, a polycrystalline cylindrical raw material rod made of a material for obtaining a single crystal is fixed to the lower shaft, and the seed crystal is fixed to the upper shaft. Then, the upper end of the raw material rod is heated and melted by the induction heating coil, and then the upper and lower shafts are moved to join the molten upper end of the raw material rod to the seed crystal. After being formed, the upper and lower shafts are moved upward while rotating in opposite directions. Accordingly, the melting zone is moved from the upper end portion of the raw material rod toward the lower end, and a single crystal is grown as the melting zone moves.

In the FZ method in which conductive crystal material is pulled up by high-frequency heating, the levitation force due to electromagnetic induction works to push the raw material melt to the center of the induction heating coil in the melting zone, so the maintenance of the melting zone depends only on the surface tension. The crystal diameter can be made relatively larger than the case where it is.
JP 2002-249393 A

  However, in induction heating with an induction heating coil, in many cases, the depth at which the induction magnetic field penetrates the raw material rod, melting zone and single crystal, that is, the skin thickness is extremely thin compared to the respective diameters. Only the melting zone and the vicinity of the surface of the single crystal are heated, and the raw material rod and the single crystal are dissolved from the surface. Therefore, as shown in a longitudinal sectional view of the state in the vicinity of the melting zone in the conventional single crystal growth method in FIG. 5, the interface 46 between the raw material rod 36 and the melting zone 37 and the interface 45 between the single crystal 38 and the melting zone 37 are shown. This shape is a convex shape that is convex toward the melting zone 37 at the center with respect to the melting zone 37.

  Therefore, in order to prevent the tip of the single crystal 38 (the lower end of the single crystal 38) and the tip of the raw material rod 36 (the upper end of the raw material rod 36) from coming into contact with each other in the melting zone 37, both of them have a convex shape. Therefore, it is necessary to make the melting zone 37 longer, which increases the hydrostatic pressure below in the melting zone 37, and eventually the melting zone 37 hangs down from the raw material rod 36. There is a fatal problem that a large single crystal cannot be grown.

  The present invention has been devised in order to solve the problems of the conventional techniques as described above, and an object of the present invention is to provide a method for growing a single crystal that can provide a large-diameter single crystal easily and stably. It is to provide.

  In the method for growing a single crystal according to the present invention, a raw material rod is induction-heated with an induction heating coil to form a melting zone, and melting and solidification are sequentially performed at the upper and lower ends of the melting zone while moving the melting zone. In the method for growing a single crystal by the FZ method for growing a single crystal, the raw material rod has a plurality of protrusions continuous in the length direction on the surface thereof.

  According to the method for growing a single crystal of the present invention, since the shape of the raw material rod is formed into a rod shape having a plurality of protrusions continuous in the length direction on the surface thereof, in the protrusion portion with a reduced thickness in the circumferential direction of the raw material, Since the eddy currents for induction heating on the surface cancel each other in opposite directions, the eddy currents hardly flow, and the protrusions arranged on the outer peripheral surface of the raw material rod do not self-heat, so the protrusions are It will not melt on its own. On the other hand, in the rod-shaped central portion (main body portion) of the raw material rod, the eddy current circulates in a circular shape as in the conventional method for growing a single crystal, and the main body portion of the raw material rod is self-generated by the Joule heat generation. To melt. In this way, first, the central portion (rod-shaped main body portion) is heated to a high temperature and melted, and the heat is conducted to the peripheral portion (a plurality of protrusions) of the raw material rod, so that the plurality of protrusions are indirectly Can be melted. As a result, the upper end of the raw material bar has a so-called bowl-like shape in which the shape of the end face part is convex downward, and the shape of the interface between the raw material bar and the melting zone is convex downward in the center. It is possible to effectively prevent the raw material dripping from the melting zone.

  In addition, since the molten raw material is held by surface tension between adjacent protrusions on the surface of the raw material rod, the shape of the interface between the raw material rod and the melting zone can be convex downward, and stably The shape can be kept. The melt zone formed in this way has a central portion of the interface with the raw material rod below the melt zone that protrudes downward, i.e., the raw material rod side. The hydrostatic pressure that works below the melting zone can be shortened and the height of the melting zone can be reduced by setting the length of the melting zone to prevent the tip and the tip of the lower raw material rod from contacting each other. Therefore, it is possible to effectively prevent the molten raw material from dripping from the melting zone.

  As a result, according to the method for growing a single crystal of the present invention, even if the size of the single crystal to be pulled up is increased and the melting zone becomes large, the molten raw material does not sag from the melting zone. The crystal can be pulled up stably.

  Hereinafter, the method for growing a single crystal of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a longitudinal sectional view showing an example of an embodiment of the method for growing a single crystal of the present invention.

  FIG. 1 shows a longitudinal sectional view of an example of a growth apparatus for carrying out the method for growing a single crystal of the present invention. According to this, the growth apparatus used for the method for growing a single crystal of the present invention can be sealed. Single crystal is grown in a pressure vessel 12. The pressure vessel 12 is designed so that a single crystal can be grown in an inert gas atmosphere of several atmospheres in the space 13 in the pressure vessel 12. Reference numeral 6 denotes a raw material rod, and an induction heating coil 4 is used for induction heating. The induction heating coil 4 of this example is configured by winding a water-cooled copper tube in a spiral shape on a horizontal plane, and the central portion of the induction heating coil 4 forms a through-hole through which the raw material rod 6 is inserted, and the pressure vessel Is located within 12.

  Above and below the induction heating coil 4, an upper shaft drive unit 1 and a lower shaft drive unit 9 which are disposed outside the pressure vessel 12 and which can be moved up and down, and extend from the respective drive units 1 and 9, the pressure vessel 12 is hermetically sealed. An upper shaft 2 and a lower shaft 10 penetrating through the upper shaft 2 and the lower shaft 10, and an upper holder 3 and a lower holder 11 fixed to the upper shaft 2 and the lower shaft 10, respectively, are arranged. In between, the edge part of the raw material stick | rod 6 which penetrates the center part of the induction heating coil 4 is gripped. The upper shaft driving unit 1 and the lower shaft driving unit 9 are controlled to be individually movable up and down.

  Regarding the operation of the melting zone 7, the lower holder 11 is made to grip the lower end side of the raw material rod 6, and the upper end (the portion already formed into the single crystal 8 in FIG. 1) is shown in the upper holder 3. After the gripped seed crystal 5 is brought into contact with the lower end and the contact portion is positioned at the center of the through hole at the center of the induction heating coil 4, high frequency power is applied to the induction heating coil 4 to induce an induction magnetic field. The upper end portion of the raw material rod 6 brought into contact with the seed crystal 5 is locally heated and melted by Joule heat generated thereby to form the melting zone 7. The raw material rods 6 are sequentially fed into the melting zone 7 formed in this way from below, and the single crystals 8 are successively grown above the melting zone 7.

  FIG. 2 is a cross sectional view showing a cross section of the raw material rod 6 in an example of the embodiment of the method for growing a single crystal of the present invention.

  As the raw material rod 6 used in the method for growing a single crystal according to the present invention, as shown in the cross section in FIG. 2, a protrusion that is continuous in the length direction on the surface of the main body portion 6a of the rod-shaped raw material located at the center. It is important to have a shape in which a plurality of 6b are formed and arranged in the circumferential direction. FIG. 3 shows a principle explanatory view showing the state of magnetic flux and eddy current in the vicinity of the raw material rod and the induction coil when such a raw material rod 6 is used.

  FIG. 3 shows a current I flowing through the induction coil 4, a magnetic flux B generated inside the induction coil 4, and a raw material rod in a cross section obtained by taking out the raw material rod 6 and the induction coil 4 in the method for growing a single crystal of the present invention. 6 is a principle explanatory view showing a state of an eddy current J flowing on the surface of the main body portion 6a of FIG. As shown in FIG. 3, by passing an alternating current I through the induction coil 4, a magnetic flux B is generated inside the induction coil 4. As shown in FIG. 3, when the alternating current I flowing through the induction coil 4 is counterclockwise, a magnetic flux B is generated from the back side to the front side of the page. If the alternating current I flowing through the induction coil 4 changes with time, the magnetic flux B inside the induction coil 4 also changes. On the other hand, since the eddy currents J and J ′ are generated in the conductive material rod 6 in the direction to cancel the change of the magnetic flux B, the phase of the eddy currents J and J ′ flowing through the material rod 6 is increased. Is opposite in phase to the alternating current I flowing through the induction coil 4. In the raw material rod 6 in the method for growing a single crystal according to the present invention, a plurality of protrusions 6b continuous in the length direction are provided on the surface of the main body portion 6a of the raw material rod 6, and the main body portion 6a in the central portion has a rod shape. Since the raw material rod 6 having the protrusion 6b at the peripheral portion is used, the protrusion 6b having a reduced thickness in the circumferential direction of the raw material cancels the eddy currents J ′ in opposite directions on the surface. As a whole, the eddy current J ′ hardly flows through 6b. As a result, self-heating due to Joule heat generation of the eddy current J 'does not occur in the protrusion 6b on the outer peripheral portion of the raw material rod 6, and the protrusion 6b does not melt by itself. On the other hand, in the main body portion 6a of the raw material rod 6, the eddy current J circulates in a circumferential manner, and the raw material rod 6 is automatically melted from the central portion by the Joule heat generation, as in the conventional method of growing a single crystal. In this way, the central portion (main body portion 6a) is first melted at a high temperature, and the heat is conducted from the main body portion 6a of the raw material rod 6 to the peripheral portion (protrusion portion 6b), thereby indirectly melting the protrusion portion 6b. Can be made.

  FIG. 4 shows a perspective view of a main part of the raw material rod 6 thus melted, showing the vicinity of the melting zone in the method for growing a single crystal of the present invention. As can be seen from FIG. 4, the raw material rod 6 has a high temperature in the rod-shaped main body 6a and starts melting from the central portion thereof, so that the shape of the interface with the melting zone 7 at the upper end of the raw material rod 6 is It becomes a so-called bowl-like shape that is convex. Therefore, the shape of the melting zone 7 is convex downward at the center of the raw material rod 6, and the molten raw material can be effectively prevented from dripping from the melting zone 7. Moreover, between the adjacent projection parts 6b of the raw material stick | rod 6, the melted raw material is hold | maintained by surface tension, and the shape can be maintained stably. In the melting zone 7 formed in this way, the central portion of the interface with the raw material rod 6 below the melting zone 7 is convex downward, that is, the raw material rod 6 side. The length of the melting zone 7 set so as to prevent the tip of the single crystal 8 and the tip of the lower raw material rod 6 from contacting each other can be shortened, and the height of the melting zone 7 can be reduced, Since the hydrostatic pressure working below the melting zone 7 can be reduced, it is possible to effectively prevent the molten raw material from dripping from the melting zone 7. As a result of these, according to the method for growing a single crystal of the present invention, even if the size of the single crystal 8 to be pulled up is increased and the melting zone 7 becomes large, the melted raw material does not sag from the melting zone 7. The large single crystal 8 can be pulled up stably.

  In order to obtain the raw material rod 6 used in the method for growing a single crystal of the present invention as described above, a small amount of camphor, for example, is added to the raw material powder as a binder, and pressed by a rubber press or the like, and a plurality of continuous materials in the length direction are obtained. A rod-shaped green compact bar having the protrusions is prepared. Preferably, the green compact bar is heated and sintered in a vacuum or in an inert gas to a few hundreds of degrees to produce a raw material bar 6 in which impurities are blended with a desired concentration distribution.

  Using the raw material bar 6 thus produced, the lower end of the raw material bar 6 is fixed to the lower shaft 10 via the lower holder 11 in the growth apparatus as shown in FIG. Is placed in contact with the seed crystal 5 set on the upper shaft 2 via the holder 3.

  Next, the upper end of the raw material rod 6 brought into contact with the seed crystal 5 is melted by induction heating of the induction heating coil 4 to form a melting zone 7, and the upper shaft 2 and the lower shaft 10 are made to grow the single crystal 8. The raw material rod 6 is slowly moved upward in accordance with the melting speed of the raw material rod 6, the raw material rod 6 is sequentially melted at the lower part of the melting zone 7, and is sequentially solidified at the upper part, and the single crystal 8 is continued above the melting zone 7. Cultivate it.

  At this time, the raw material rod 6 has a relatively high temperature in the central portion where the rod-shaped main body portion 6a through which the eddy current flows is high, and the peripheral portion where the protruding portion 6b is at a relatively low temperature because the eddy current does not flow and does not generate heat. The upper end of the glass melts from the center. As a result, the upper end of the raw material rod 6 has a so-called bowl-like shape with the central portion projecting downward, and the molten raw material can be kept stable in the melting zone 7. In addition, between the adjacent projection parts 6a, the shape can be kept stable by the surface tension of the melted raw material. In addition, at the upper end of the raw material rod 6, the central portion of the tip of the raw material rod 6 has a bowl shape that protrudes downward, and does not protrude upwardly as in the conventional growth method. 8, the dimension (length) in the height direction of the melting zone 7 can be reduced, and the melted raw material is reduced from the melting zone 7 by reducing the hydrostatic pressure at the lower portion of the melting zone 7. Since it can prevent dripping, it becomes the growth method of the single crystal which can manufacture the large sized single crystal 8 stably.

  The protrusion 6a of the raw material rod 6 in the method for growing a single crystal of the present invention is not particularly limited in its shape as long as it has an action of canceling the eddy current on the surface of the raw material rod 6. The shape of the cross section may be any of rectangular shape, fan shape, semi-elliptical shape, triangular shape, polygonal shape, and the like.

  Further, the thickness of the protrusion 6a of the raw material rod 6 in the method for growing a single crystal of the present invention is not particularly limited, but the thickness of the protrusion 6a of the raw material rod 6 is d as shown in FIG. If the frequency of the alternating current I applied to the induction coil 4 is f, the magnetic permeability of the raw material rod 6 is μ, and the conductivity of the raw material rod 6 is g, the skin thickness δ of the raw material rod 6 is approximately expressed by the following equation (1) Given in.

δ = √ (1 / πf × g × μ) (1)
On the other hand, the thickness d of the protrusion 6a is preferably in the range represented by the following formula (2).

0.5 [mm] ≦ d ≦ 1.5δ [mm] (2)
This is because when the thickness d of the protrusion 6a is larger than 1.5δ, the action of canceling the eddy current J ′ in the protrusion 6a is weakened, and the eddy current J ′ becomes a non-negligible magnitude, and the self-heating of the protrusion 6a. This is because the protrusion 6a may be melted by the above. Further, when the thickness d of the protrusion 6a is 0.5 [mm] or less, it is difficult to process and it is easy to break. Therefore, the thickness d of the protrusion 6a is preferably in the range of 0.5 [mm] ≦ d ≦ 1.5δ [mm].

  Further, the height of the protrusion 6a of the raw material rod 6 in the method for growing a single crystal of the present invention is not particularly limited. However, as shown in FIG. Then, the range shown in the following formula (3) is desirable.

1.0 [mm] ≤ l ≤ 40 [mm] (3)
This is because if the height l of the projection 6a is smaller than 1.0 [mm], the raw material rod 6 does not function as a projection and melts from the outer periphery, and if the height l is larger than 40 [mm], the projection 6a. This is because the tip of the metal may not melt. Therefore, the length l of the protrusion 6a is preferably in the range of 1.0 [mm] ≦ l ≦ 40 [mm].

  Further, the shape of the main body 6a of the raw material rod 6 in the method for growing a single crystal of the present invention may be any of a cylindrical shape, a quadrangular prism shape, a polygonal prism shape, a cylindrical shape, etc., and the shape is particularly limited. Rather, various applications are possible. For example, the protrusions 6a may be provided on each of the eight sides of the octagonal columnar main body 6a to form a total of eight protrusions 6a.

  In the method for growing a single crystal according to the present invention, the number of protrusions 6a of the raw material rod 6 is not particularly limited, and various numbers can be selected. For example, when the thickness d of the protrusion 6a is small, it is desirable to provide a large number of protrusions 6a. This is because if the thickness d of the protrusion 6a is reduced, the interval between the adjacent protrusions 6a is widened. Therefore, in order to prevent the molten material from falling from the melting zone 7, the number of the protrusions 6a is increased. Is advantageous. Thus, it is possible to select the optimal number of protrusions 6a according to the viscosity of the melted raw material, the thickness d of the protrusions 6a, and the like.

A raw material rod used in the method for growing a single crystal of the present invention was produced as follows. The mixed powder of ZrB ₂ and CrB ₂ is compressed, the central part is a cylinder with an outer diameter of 40 mm and a length of 800 mm, and the outer peripheral part has a height of 10 mm, a width of 2 mm, and a length of 800 mm 16 protrusions that are continuous in the direction are provided at intervals of 22.5 °, compressed into a rod-shaped powder bar having protrusions with a length of 800 mm, and sintered at 1400 ° C. A rod-shaped raw material bar having a plurality of protrusions was produced.

  Using the rod-shaped raw material rod having the protruding portion, an induction heating type FZ apparatus is used to apply a high-frequency power of 52 kW to melt the tip of the rod-shaped raw material rod having the protruding portion. The crystals were connected to form a melt zone. The melting zone was stable without dripping. Thereafter, the molten zone was moved at a speed of 20 mm / h to produce a cylindrical single crystal having a diameter of 45 mm. The molten raw material did not sag from the molten zone, and a good cylindrical single crystal until the end. I was able to train. As a result of observing the grown single crystal, there was no twin crystal or polycrystal, and the single crystal was formed over the whole.

On the other hand, as a comparative example, a mixed powder of ZrB ₂ and CrB ₂ is compressed and compressed into a cylindrical powder rod having an outer diameter of 50 mm and a length of 800 mm, and this is sintered at 1400 ° C. A column-shaped raw material rod without a gap was produced.

  Using this cylindrical raw material rod as a comparative example, similarly, the induction zone FZ apparatus was used to move the melt zone formed by applying high-frequency power of 52 kW at a speed of 20 mm / h, When an attempt was made to produce a 45 mm single crystal, the melted raw material dropped from the lower part of the melting zone, and the single crystal could not be pulled up.

  It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

It is a longitudinal cross-sectional view which shows an example of embodiment of the growth method of the single crystal of this invention. It is a cross-sectional view of the raw material stick | rod in an example of embodiment of the growth method of the single crystal of this invention. It is principle explanatory drawing which shows the mode of the magnetic flux and eddy current in the raw material stick | rod and induction coil vicinity in an example of embodiment of the growth method of the single crystal of this invention. It is a principal part perspective view which shows the mode of the fusion zone vicinity in an example of embodiment of the growth method of the single crystal of this invention. It is a longitudinal cross-sectional view which shows the mode of the fusion zone vicinity in the growth method of the conventional single crystal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Upper shaft drive part 2 ... Upper shaft 3 ... Upper holder 4 ... Induction heating coil 5 ... Seed crystal 6 ... Raw material rod 6a ... Main-body part 6b ... Protrusion Part 7: Melting zone 8 ... Single crystal 9 ... Lower shaft drive part
10 ... Lower shaft
11 ... Lower holder
12 ... pressure vessel
13: Space inside the container

Claims (1)

By an FZ method in which a raw material rod is induction-heated with an induction heating coil to form a melting zone, and a single crystal is grown by sequentially performing melting and solidification at the upper and lower ends of the melting zone while moving the melting zone. In the method for growing a single crystal, the raw material rod has a plurality of protrusions continuous in the length direction on the surface thereof.

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