JP2005067989A - Apparatus for growing single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for growing a single crystal, with which the temperature gradient of a crystal growth part can be controlled to be constant over late stage from initial stage, the crystal growth speed can be preferably controlled, and a large size and long single crystal can be manufactured stably. <P>SOLUTION: This apparatus for growing the single crystal is equipped with a crucible 5 for accommodating a raw material, an induction coil 6 arranged at the outside of the crucible 5, a pulling rod 8 to whose tip end a seed crystal is arranged and which is capable of being moved in the up-and-down direction in such a state that it can rotate in the crucible 5, a furnace wall 1 which is arranged so as to surround the crucible 5 and the pulling rod 8, and an auxiliary heating element 11 disposed on the outside face of the crucible 5. It is possible to unify the temperature gradient of the crucible 5 from initial stage to final stage of the crystal growth by using the auxiliary heating element 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a single crystal growth apparatus for manufacturing a single crystal such as lithium niobate or lithium tantalate by a rotary pulling method, and more particularly to a single crystal growth apparatus that can stably increase the length and diameter of a single crystal. About.

  As a conventional single crystal growth method for oxide single crystals such as lithium niobate and lithium tantalate, a rotation pulling method (Czochralski method: CZ method) is generally known. In this conventional method, a crucible, a heater, and a single crystal pulling rod are installed inside the heat insulation wall, and the raw material stored in the crucible is melted by the heater, and a seed crystal installed at the tip of the pulling rod Is soaked in the melt of the raw material, and the single crystal is pulled up and grown from the seed crystal while rotating.

  As a configuration of the heater, a heater heating method is known in which a heater made of a metal resistor or the like is installed around a crucible and the raw material in the crucible is indirectly melted by heating the heater. In this configuration, since the heat resistance between the heater and the crucible is large, the heat generated by the heater cannot be efficiently transmitted to the crucible, and in order to melt the raw material powder, the heater power is increased and the heater itself is increased. It is necessary to increase the temperature of

  However, if the temperature of the heater itself is made higher, furnace materials such as the furnace wall around the heater are thermally deteriorated. As a result, it is difficult to grow a single crystal having a high melting point such as lithium niobate or lithium tantalate. There was a problem that.

  As a method for solving the problem, an induction heating method is known. This conventional induction heating type single crystal growth apparatus will be described with reference to FIG. FIG. 3 is a cross-sectional view of a conventional single crystal growth apparatus. In FIG. 3, a hollow cylindrical box 33 is constituted by a furnace wall 31 made of a heat-resistant material such as alumina ceramics, and a lid portion 32 placed on the furnace wall 31. The part is provided with a hole 37 penetrating therethrough.

  A pulling bar 38 that can be rotated and moved up and down is disposed through the hole 37, and a seed crystal 39 is fixed to a lower end thereof. A crucible 35 made of a high melting point metal such as iridium filled with a raw material is installed inside a container 34 made of a heat insulating material such as bubble alumina ceramics in the center of the box 33.

  A substantially cylindrical after-heater 40 made of iridium or the like is installed on the upper part of the crucible 35, and has a function of gradually cooling the pulled single crystal after growth. In this single crystal growing apparatus, by applying an AC voltage to the induction coil 36, an eddy current in the direction opposite to the current flowing through the induction coil 36 is generated on the surface of the crucible 35 by electromagnetic induction, and the Joule heat causes the crucible 35 Is directly heated, and the raw material powder filled in the crucible 35 becomes a melt. After that, the pulling bar 38 is lowered while rotating, the seed crystal 39 attached to the pulling bar 38 is brought into contact with the surface of the melt, and then the single crystal is grown by pulling up at a very slow speed. Can do.

  In this method, an induction coil 36 is installed outside the crucible 35 made of a high melting point metal such as platinum or iridium, and an eddy current is generated on the surface of the crucible 35 by applying an AC voltage to the induction coil 36. The crucible 35 is directly heated by the Joule heat so that efficient heating can be performed, and the raw material powder can be sufficiently heated and melted without damaging the furnace wall 31 and the like around the crucible 35. A single crystal can be grown.

  However, in the conventional single crystal growth apparatus shown in FIG. 3, the magnetic field generated by the induction coil 36 is concentrated on the upper and lower ends of the crucible 35, and eddy currents are formed on the outer periphery of the bottom surface of the crucible 35 and the outermost periphery of the crucible 35. There is a problem that local heat generation increases in these portions. The crystallinity of a single crystal depends on the crystal growth rate, and the crystal growth rate depends on the temperature gradient. Therefore, in order to stably grow a good single crystal, it is necessary to maintain a constant temperature gradient at the solid-liquid interface in the crystal growth part. However, in this conventional single crystal growth apparatus, the inside of the crucible 35 is entirely hot, while the upper part of the crucible 35 is cold, so that a stable single crystal with an appropriate temperature gradient is provided at the initial stage of crystal growth. However, in the latter stage of crystal growth, the liquid level drops and the crystal growth part falls into the crucible 35, so that a sufficient temperature gradient cannot be obtained and a single crystal cannot be obtained stably. There is a fatal problem that large single crystals cannot be obtained.

  As a countermeasure for this problem, in the single crystal growth apparatus using the induction heating type CZ method, the crucible and the induction coil are moved as the liquid level is lowered, and the relative positional relationship between the melt and the liquid level is determined. It has been proposed to keep (see, for example, Patent Document 1).

However, in this method, although the height of magnetic flux can be changed by changing the positional relationship between the coil and the crucible, the magnetic flux is concentrated at the upper and lower ends of the crucible. Therefore, the temperature distribution in the crucible cannot be changed greatly, and as a result, a stable single crystal can be obtained with an appropriate temperature gradient in the early stage of crystal growth. However, there was a problem that a stable single crystal could not be obtained.
Japanese Patent Publication No.58-25078 Japanese Patent Publication No.57-50757

  The present invention has been made in view of the problems in the conventional technology as described above, and the object thereof is to control the temperature gradient of the crystal growth part from the initial stage to the late stage of the crystal growth. An object of the present invention is to provide a single crystal growth apparatus capable of controlling a growth rate well and stably producing a large and long single crystal.

  The apparatus for growing a single crystal according to the present invention includes a crucible containing a raw material, an induction coil for performing induction heating of the crucible disposed outside the crucible, and a seed crystal disposed at a tip, and the inside of the crucible can be rotated. And a heat-insulating wall disposed so as to surround the crucible and the pull-up bar, and an auxiliary heating element disposed on the outer surface of the crucible. It is characterized by.

  Moreover, the single crystal growing apparatus of the present invention is characterized in that, in the above-mentioned configuration, the outer surface of the crucible has a circular cross section, and the auxiliary heating element has a ring shape.

  Moreover, the single crystal growing apparatus of the present invention is characterized in that, in the above configuration, the auxiliary heating element is movable in the vertical direction on the outer surface of the crucible.

  According to the single crystal growing apparatus of the present invention, a crucible containing a raw material, an induction coil disposed outside the crucible and performing induction heating of the crucible by applying an alternating voltage, and a seed crystal at the tip And a heat-up bar that moves up and down while rotating inside the crucible, and a heat insulating wall disposed so as to surround the crucible and the pull-up bar, and disposed on the outer surface of the crucible. Since the auxiliary heating element is provided, by controlling the position of the auxiliary heating element, the heat generation density distribution on the surface of the crucible can be controlled optimally for crystal growth, so from the initial stage to the final stage of crystal growth. The temperature gradient in the crystal growth part can be kept optimal, and as a result, a large single crystal having a large diameter can be stably grown.

  In addition, according to the single crystal growth apparatus of the present invention, it can be configured by disposing an auxiliary heating element on the outer surface of the crucible with respect to the conventional single crystal growth apparatus, without significant change of the apparatus, A single crystal growing apparatus capable of manufacturing a large single crystal can be provided.

  Further, according to the single crystal growth apparatus of the present invention, when the cross-sectional shape of the outer surface of the crucible is circular and the auxiliary heating element is ring-shaped, the magnetic flux generated by the induction coil is effectively concentrated on the auxiliary heating element. The current generated thereby can be efficiently used as a closed flow eddy current to generate heat and the crucible can be heated evenly, so that the effect of soaking the raw material by the auxiliary heating element can be effectively demonstrated. Thus, a large single crystal having a large diameter can be manufactured more stably.

  Further, according to the single crystal growth apparatus of the present invention, when the auxiliary heating element is movable in the vertical direction on the outer surface of the crucible, the position of the auxiliary heating element is moved in accordance with the crystal growth, and the crystal growth section is constantly Since the upper part of the crystal growth part can be set to a low temperature and the lower part can be set to a high temperature, a stable crystal can be obtained with an appropriate temperature gradient in the early stage of crystal growth. From the initial stage of crystal growth to the end of crystal growth where the crystal grows large and the liquid level of the raw material melt is reduced, since the temperature gradient in the growth part is insufficient and stable crystals cannot be obtained. The temperature gradient of the crystal growth part can be stably controlled and kept optimal, and as a result, a large single crystal having a large diameter can be manufactured more stably.

  In the single crystal growth apparatus of the present invention, a crucible containing a raw material, an induction coil that is arranged outside the crucible and performs induction heating of the crucible by applying an AC voltage, and a seed crystal is arranged at the tip, Auxiliary heat generation provided on the outer surface of the crucible, including a lifting rod capable of rotating up and down in the crucible and a heat insulating wall disposed so as to surround the crucible and the lifting rod. It has a body. As this auxiliary heating element, for example, by forming a ring-shaped projection made of a conductor so as to surround the outer surface of the crucible, a magnetic field generated by the induction coil concentrates on the projection and a large eddy current is generated in the projection. And can function as an auxiliary heating element. As a result, the amount of heat generated by the protrusion is larger than that of the surrounding area, so that the temperature of the outer surface of the crucible provided with the protrusion as an auxiliary heating element is increased compared to the surrounding area. And the position of this auxiliary heating element is moved corresponding to the liquid surface of the raw material melt in accordance with the crystal growth, and continuously placed at the lower part of the crystal growth part, so that the upper part of the crystal growth part has a low temperature, Since the lower part can be heated, the temperature gradient of the crystal growth part can be controlled stably from the beginning of crystal growth to the end of crystal growth when the crystal grows large and the melt level of the raw material decreases. Can do. As a result, a single crystal growing apparatus capable of stably producing a large single crystal having a large diameter is obtained.

  Hereinafter, the single crystal growing apparatus of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of an embodiment of a single crystal growth apparatus of the present invention. In FIG. 1, 1 is a furnace wall made of a heat-resistant material, 5 is a crucible, 6 is an induction coil, 8 is a lifting rod, and 11 is an auxiliary heating element disposed on the outer surface of the crucible 5.

  In the single crystal growth apparatus of the present invention shown in FIG. 1, a hollow cylindrical box 3 is formed by a furnace wall 1 as a heat insulating wall made of a heat-resistant material made of alumina ceramics and a lid portion 2 placed on the furnace wall 1. The lid portion 2 is provided with a hole portion 7 penetrating through the central portion thereof. A pulling rod 8 that can be rotated and moved up and down is disposed through the hole 7, and a seed crystal 9 is fixedly disposed at the tip thereof.

  An after heater 10 is installed on the upper part of the crucible 5 and has a function of gradually cooling the pulled single crystal after crystal growth. A substantially cylindrical crucible 15 made of a high melting point metal such as platinum or iridium is installed in the center inside the box 3 through a container 4 made of a heat insulating material such as bubble alumina ceramics. ing.

  In addition, an induction coil 6 that performs induction heating of the crucible 5 is disposed outside the crucible 5, around the box 3 in which the container 4 is installed in this example.

  In the single crystal growth apparatus of the present invention, for example, a ring-shaped auxiliary heating element 11 is disposed on the outer surface of the crucible 5 so as to surround it. Further, the auxiliary heating element 11 can move the outer surface of the crucible 5 in the vertical direction by a mechanism (not shown).

  In this single crystal growing apparatus, an eddy current is generated on the surface of the crucible 5 by applying an AC voltage to the induction coil 6, and the crucible 5 is directly heated by the Joule heat and filled in the crucible 5. The raw material becomes a melt. Thereafter, the pulling rod 8 is lowered while being rotated, and the crystal growth can be started by bringing the seed crystal 9 disposed at the tip of the pulling rod 8 into contact with the surface of the raw material melt and then pulling it up. .

  At this time, heat generation in the crucible 5 mainly occurs in the corner portion of the crucible 5 and the auxiliary heating element 11, so that the temperature distribution in the crucible 5 becomes lower than the auxiliary heating element 11, and from the auxiliary heating element 11. It gets cold at the top. Accordingly, the auxiliary heating element 11 is moved vertically along the outer surface of the crucible 5 along with the crystal growth so that the auxiliary heating element 11 is located below the solid-liquid interface which is the crystal growth portion. Without relying on it, an appropriate temperature gradient can be obtained constantly in the crystal growth part, and a sufficient long temperature gradient cannot be obtained at the later stage of crystal growth as in the conventional single crystal growth apparatus, so that a stable and long single crystal can be obtained. This is a single crystal growth apparatus that can stably produce a large single crystal having a large diameter without the problem of being impossible.

  Next, the operation based on the configuration of the single crystal growth apparatus of the present invention will be schematically described with reference to the drawings. FIGS. 2A and 2B are schematic diagrams showing the state of the magnetic field and eddy current around the crucible by the induction coil in the conventional single crystal growth apparatus and the single crystal growth apparatus of the present invention, respectively. In FIG. 2, the same parts as those in FIGS. 1 and 3 are denoted by the same reference numerals.

  First, in the conventional single crystal growing apparatus, as shown in FIG. 2A, a magnetic field is generated around the induction coil 36 by applying an AC voltage to the induction coil 36. On the other hand, the magnetic field is substantially parallel on the outer surface of the crucible 35 made of a conductor, and the upper end (A part) of the crucible 35 and the lower end (B part) of the crucible 35 are characterized by their geometrical shape. The magnetic field will be concentrated. And since the eddy current is generated in the conductor of the crucible 35 in the direction to cancel the temporal change of the magnetic field, the eddy current is concentrated in the A part and the B part. Concentrating on B part, the inside of the crucible 35 becomes high temperature as a whole. At the initial stage of crystal growth, the solid-liquid interface is located above the inside of the crucible 35, and the top of the crucible 35 is at a low temperature, so that an appropriate temperature gradient can be formed and a good crystal can be grown. In the later stage of growth, the solid-liquid interface is lowered deep inside the crucible 35 and an appropriate temperature gradient cannot be obtained, so that it is difficult to stably grow a good crystal.

  On the other hand, according to the single crystal growth apparatus of the present invention, as shown in FIG. 2B, a magnetic field is generated around the induction coil 6 by applying an AC voltage to the induction coil 6. The magnetic field generated by the induction coil 6 is concentrated at the upper end (A part) of the crucible 5 and the lower end (B part) of the crucible 5 as in the conventional single crystal growth apparatus. The auxiliary heating element 11 is provided so as to form a protrusion (C part) on the outer surface of the crucible 5, and the magnetic field is concentrated on the auxiliary heating element 11 (C part). For this reason, the temperature at the auxiliary heating element 11 (C section) rises compared to the surroundings. Then, the position of the auxiliary heating element 11 is moved vertically along the outer surface of the crucible 5 in accordance with the crystal growth, and is continuously disposed at the lower part of the crystal growth part, so that the temperature is always kept at the upper part of the crystal growth part. The temperature at the lower part of the crystal growth part can be controlled stably from the beginning of crystal growth to the end of crystal growth when the crystal grows large and the melt level of the raw material decreases. As a result, a long single crystal having a large diameter can be stably manufactured.

  Since the auxiliary heating element 11 in the single crystal growth apparatus of the present invention is made of a conductor and protrudes from the outer surface of the crucible 5, heat generation due to the effect of concentration of the magnetic field from the induction coil 6 can be obtained. However, the shape is not particularly limited. That is, the cross-sectional shape is not limited to a triangle as in the example shown in FIGS. 1 and 2B, and may be a rectangle, a trapezoid, a circle, a semicircle, a semi-ellipse, a polygon, or the like. However, in order to concentrate the magnetic field from the induction coil 6 more efficiently, it is desirable that the tip of the portion that becomes the protrusion has a sharp shape, and the cross-sectional shape of the tip of the protrusion has a semicircular diameter or A sharper triangle or quadrangle is desirable than an oval or curved surface.

  Also, according to the single crystal growing apparatus of the present invention, when the cross-sectional shape of the outer surface of the crucible 5 is circular and the auxiliary heating element 11 disposed on the outer surface is ring-shaped, the auxiliary heating element 11 The current generated by the concentration of the magnetic flux on the projecting portion can be used as the eddy current of the closed flow efficiently and the crucible 5 can be heated evenly. As a result, a long single crystal having a large diameter can be more stably produced.

  In addition, when the auxiliary heating element 11 has a ring shape, the shape may be a rectangle, a triangle, or a polygon in addition to a circle. In these cases, the cross-sectional shape of the outer surface of the crucible 5 is also the same. It is desirable to have a combined shape. However, in order to obtain uniform heat generation with the auxiliary heating element 11, and to efficiently transmit the heat generation to the crucible 5, the auxiliary heating element 11 has a circular ring shape and the cross-sectional shape of the outer surface of the crucible 5 is also circular. A shape is preferable.

  Further, it is preferable that the inner peripheral surface of the ring-shaped auxiliary heating element 11 and the outer surface of the crucible 5 are in contact with each other in order to efficiently transfer the heat generated by the auxiliary heating element 11 to the raw material through the crucible 5. In order to facilitate the movement of the auxiliary heating element 11 in the vertical direction, a minute gap that does not greatly hinder the movement of heat may be provided between the auxiliary heating element 11 and the crucible 5.

  Further, according to the single crystal growing apparatus of the present invention, the height of the auxiliary heating element 11 from the outer surface of the crucible 5 is preferably set to 1 mm to 50 mm. Thereby, a large concentration of magnetic flux is obtained in the auxiliary heating element 11 as the protrusion, and the heat generated in the concentrated portion of the magnetic flux can be more effectively contributed to the heating of the raw material through the crucible 5, as a result. It is possible to stably produce a large single crystal having a large diameter. If the height of the auxiliary heating element 11 from the outer surface of the crucible 5 is less than 1 mm, the concentration of the magnetic field on the auxiliary heating element 11 hardly occurs and the effect of heat generation on the auxiliary heating element 11 tends to be weakened. It is in. In addition, when the height of the auxiliary heating element 11 exceeds 50 mm, a large amount of heat is generated due to a large magnetic field concentration, but the heating portion of the auxiliary heating element 11 (the tip of the auxiliary heating element 11 increases as the height increases). Part) to the root (outer surface of the crucible 5) increases, and the heat generated in the auxiliary heating element 11 tends not to be efficiently transferred to the raw material. Therefore, the height of the auxiliary heating element 11 from the outer surface of the crucible 5 is preferably 1 mm to 50 mm.

  Further, according to the single crystal growing apparatus of the present invention, when the auxiliary heating element 11 is movable in the vertical direction on the outer surface of the crucible 5, the position of the auxiliary heating element 11 is set in the vertical direction according to the crystal growth. Since the temperature is always lower at the upper part of the crystal growth part and higher at the lower part, the crystal grows greatly from the initial stage of the crystal growth. The temperature gradient of the crystal growth part can be controlled to the desired state stably until the end of the crystal growth when the melt level is lowered. As a result, a large single crystal with a large diameter can be manufactured more stably. can do.

  Next, a specific example of the single crystal growth apparatus of the present invention will be described.

  First, a lid 2 having a furnace wall 1 and a hole 7 was made of a heat-resistant material made of porous alumina ceramics, and a box 3 having a length of 80 cm, a width of 80 cm and a height of 100 cm was produced by combining them. Inside, a crucible 5 made of iridium was placed through a container 4 made of a heat insulating material made of bubble alumina ceramics. The size and shape of the crucible 5 was a cylindrical shape with a closed bottom having a diameter of 15 cm and a height of 20 cm. On the outer surface of the crucible 5, a ring-shaped auxiliary heating element 11 having an inner diameter of 15.1 cm, an outer diameter of 17 cm, and a base having a length of 2 cm and a triangular cross section is installed. It can move up and down.

  For comparison, a crucible having the same dimensions and having no auxiliary heating element on the side surface was also installed in the same box for comparison.

  Then, the crucible 5 is heated by applying an alternating current of 130 A and a voltage of 170 V at a frequency of 18 kHz to the spiral induction coil 6 that is installed so as to surround the outside of the crucible 5 and has nine turns. The raw material powder of lithium niobate filled in 5 was melted to obtain a raw material melt.

  Thereafter, a pulling rod 8 to which a lithium niobate seed crystal 9 is attached is inserted from the hole 7 of the lid 2, the seed crystal 9 is brought into contact with the surface of the raw material melt, and then the pulling rod 8 is rotated while the crystal is Was raised. At this time, the height of the auxiliary heating element 11 was controlled during crystal growth so that the position was always below the crystal growth part. When the crystal was pulled up, it was held in the growth furnace for a certain time for cooling, and then the single crystal was taken out. The grown single crystal had a diameter of 10.5 cm and a length of 12 cm in both crucibles.

  When the characteristics of these single crystals were evaluated, the single crystal of lithium niobate pulled up by the single crystal growth apparatus of the present invention produced a uniform single crystal over the whole, and there was no problem with the crystallinity. There wasn't. However, the single crystal pulled by the conventional single crystal growth apparatus using a crucible without an auxiliary heating element has a large variation in diameter at the lower part of the crystal, and a polycrystal is formed at the lower part of the crystal. Cracks occurred in the pulling direction.

  From this result, according to the single crystal growth apparatus of the present invention, it is possible to reduce the temperature distribution of the raw material melt, thereby reducing the temperature distribution on the surface of the raw material melt, Even when growing a large single crystal, it is confirmed that each part of the single crystal can be grown under uniform thermal conditions, resulting in a single crystal growth apparatus that can grow a single crystal with uniform characteristics over the entire crystal. did it.

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications and improvements can be made without departing from the scope of the present invention. For example, a plurality of ring-shaped auxiliary heaters may be provided on the outer surface of the crucible as auxiliary heating elements. In this case, finer temperature distribution control and temperature gradient control are possible, and large crystal growth is possible stably.

It is sectional drawing which shows an example of embodiment of the single crystal growth apparatus of this invention. (A) And (b) is a schematic diagram which shows the magnetic field around a crucible and the state of an eddy current by the induction coil in the conventional single crystal growth apparatus and the single crystal growth apparatus of this invention, respectively. It is sectional drawing which shows the conventional single crystal growth apparatus.

Explanation of symbols

1: Furnace wall (heat insulation wall)
2: Lid 3: Box 4: Container 5: Crucible 6: Induction coil 7: Hole 8: Lifting rod
9: Seed crystal
10: After heater
11: Auxiliary heating element

Claims (3)

A crucible containing the raw material, an induction coil for inductively heating the crucible disposed outside the crucible, and a pulling rod having a seed crystal disposed at the tip and moving up and down in a rotatable state in the crucible And a heat insulating wall disposed so as to surround the crucible and the pulling rod, and an auxiliary heating element disposed on the outer surface of the crucible. The single crystal growing apparatus according to claim 1, wherein a cross-sectional shape of the outer surface of the crucible is a circular shape, and the auxiliary heating element is a ring shape. The single crystal manufacturing apparatus according to claim 1, wherein the auxiliary heating element is movable in the vertical direction on the outer surface of the crucible.

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