JP2007099580A - Method of and apparatus for producing oxide single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To grow a high quality crystal with good yield by topically controlling the temperature distribution of a raw material solution. <P>SOLUTION: In a crystal production apparatus, a seed crystal is disposed in a crucible 1 held in a furnace 10, and a raw material filled in the crucible 1 is heated to be melted. Crystal growth is carried out by slowly cooling the melted raw material from the lower portion of the crucible 1 toward its upper portion. In this case, the apparatus is provided with an exothermic body 6 for adjusting the temperature in the furnace 10 to that suitable for crystal growth, a cooling plate 7 disposed in contact with the bottom of the crucible 1, and a cooling tube 8 which is thermally bonded to the cooling plate 7 and cools it by making a heat transfer medium to flow. Thus, the temperature gradient of the melted raw material in the crucible 1 is controlled by controlling the flow of the heat transfer medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an oxide single crystal and a crystal manufacturing apparatus. More specifically, in the vertical Bridgman method and the vertical temperature gradient solidification method, the temperature distribution of a raw material solution is locally controlled to thereby achieve high quality. The present invention relates to an oxide single crystal manufacturing method and a crystal manufacturing apparatus for growing a crystal with high yield.

  Conventionally, the oxide crystal material is produced by a horizontal Bridgman method in which the melt in the growth vessel is gradually solidified from the seed crystal, and the growth vessel is placed vertically to give a temperature gradient and moved to the lower temperature side. A vertical Bridgman method for solidifying crystals and a vertical temperature gradient solidification method for solidifying crystals by changing the temperature gradient by fixing the growth vessel vertically are known (for example, see Patent Document 1).

  With reference to FIG. 1, a method for producing a crystal material by a conventional vertical Bridgman method will be described. A seed crystal 4 and a raw material 2 are placed in a crucible 1. The raw material 2 is heated and dissolved by the heating element 6 to obtain the raw material solution 2. The heating amount of the heating element 6 is adjusted to keep the inside of the crystal production furnace at a constant temperature gradient curve 5. When the raw material solution 2 is cooled by moving the crucible 1 to the low temperature side at a constant speed, the crystal 3 that has reached the crystal growth temperature grows into a crystal having the same crystal orientation as the seed crystal 4, and the enlarged portion The grown crystal 3 is obtained through the growth process and the constant diameter portion growth process.

  At this time, since the growth crystal 3 grows sequentially with the seed crystal 4 as a nucleus, it can inherit the crystal orientation of the seed crystal 4 and grow as the growth crystal 3 having the same crystal orientation as the crystal orientation of the seed crystal 4. . The quality of the grown crystal 3 is greatly influenced by the crystal quality at the initial stage of growth, and the initial quality depends on the state of the solid-liquid interface between the seed crystal 4 and the raw material solution 2 in the seeding process. In the conventional method, the temperature gradient in the seeding process is determined by the temperature control of the heating element 4 for melting the raw material and the position control of the crucible 1. In particular, local control of the temperature distribution near the solid-liquid interface between the raw material solution and the grown crystal has not been performed.

JP 59-107996 A JP 61-101486 A JP 2000-63193 A JP 2000-72586 A JP 53-28085 A

  However, in the conventional method for producing a crystal material, a steep temperature gradient in the furnace is necessary for controlling the growth rate in the seeding process, the diameter-increasing part growth process, and the constant-diameter part growth process. In order to obtain a steep temperature gradient, a large furnace body structure that accommodates a plurality of heating elements and a heat insulating material is necessary. In addition, in order to advance crystal growth, a mechanism for moving the crucible up and down or a mechanism for moving the heating element up and down is necessary, and the structure of the crystal manufacturing apparatus is complicated and large, and the apparatus price is high. There was a problem. Furthermore, only one crucible crystal can be grown from a single crystal manufacturing process, and the price of the grown crystal is naturally high.

  In the pulling method different from the vertical Bridgman method and the vertical temperature gradient solidification method, it is known that the refrigerant is supplied to the bottom of the crucible and the temperature of a part of the crucible is controlled by a single pipe. For example, in the method for producing a single crystal of Patent Document 2, heating control is selectively performed by a cylindrical heater provided at the lower part of a crucible. However, this method is intended to control the convection of the raw material melt and does not contribute to the generation and growth of crystal nuclei at the bottom of the crucible. The pulling method of Patent Document 3 is intended to form a temperature gradient in the radial direction of the raw material melt, and does not contribute to the generation and growth of crystal nuclei at the bottom of the crucible.

  Further, the pulling method of Patent Document 4 is intended to suppress the temperature fluctuation of the melt, and the pulling method of Patent Document 5 is intended to precipitate foreign substances mixed in the raw material melt, and each has a crystal nucleus at the bottom of the crucible. Does not contribute to the generation and growth of

  The present invention has been made in view of such problems. The object of the present invention is to locally control the temperature distribution of the raw material solution so as to grow a high-quality crystal with a high yield. The object is to provide a crystal manufacturing method and a crystal manufacturing apparatus.

  In order to achieve such an object, the invention according to claim 1 is characterized in that seed crystals are placed in a crucible held in a furnace, and the raw material charged in the crucible is heated and dissolved. A first step of adjusting the temperature in the furnace to a temperature suitable for crystal growth in a method for producing an oxide single crystal in which a raw material solution is gradually cooled upward from below the crucible; And a second step of controlling the temperature gradient in the vicinity of the solid-liquid interface between the raw material solution and the grown crystal by cooling the bottom surface of the crucible.

  According to a second aspect of the present invention, in the second step of the first aspect, the heat medium is caused to flow through a cooling pipe thermally coupled to a cooling plate disposed in contact with the bottom of the crucible. The cooling plate is cooled, the flow rate of the heat medium is controlled, and the temperature gradient is controlled.

  The method according to claim 3 is characterized in that the main component of the crystal according to claim 1 or 2 is composed of periodic group Ia group and Va group, wherein group Ia is potassium, group Va is niobium, It contains at least one of tantalum.

  According to a fourth aspect of the present invention, the main component of the crystal according to the first, second, or third aspect is composed of a periodic table Ia group and Va group, the Ia group is potassium, and the Va group is It contains at least one of niobium and tantalum, and includes one or a plurality of kinds of periodic table Ia and IIa as added impurities.

  In the invention according to claim 5, the seed crystal is arranged in a crucible held in a furnace, the raw material filled in the crucible is heated and dissolved, and the raw material solution is moved upward from below the crucible. In the crystal manufacturing apparatus for crystal growth by slow cooling, a heating element for adjusting the temperature in the furnace to a temperature suitable for crystal growth, a cooling plate disposed in contact with the bottom of the crucible, and the cooling plate A cooling pipe that is thermally coupled and cools the cooling plate by flowing a heating medium; and a means for controlling a temperature gradient of the raw material solution in the crucible by controlling a flow rate of the heating medium. It is characterized by that.

  The invention according to claim 6 is the crystal manufacturing apparatus according to claim 5, further comprising a heat sink disposed in contact with the bottom surface of the crucible and thermally coupled to the cooling plate. .

  The invention according to claim 7 is the crystal manufacturing apparatus according to claim 5 or 6, which is installed on a side wall of the bottom of the crucible, and locally heats a part of the crucible, thereby A heater for controlling the temperature gradient is further provided.

  As described above, according to the present invention, the cooling plate disposed in contact with the bottom of the crucible and the cooling pipe that is thermally coupled to the cooling plate and cools the cooling plate by flowing a heat medium are provided. By controlling the flow rate of the heat medium and controlling the temperature gradient of the raw material solution in the crucible, it is possible to grow high quality crystals with high yield.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 2 shows a cooling setter of a crystal manufacturing apparatus according to an embodiment of the present invention. The cooling setter 7 is a plate-like cooling plate and uses a material having both heat resistance, high thermal conductivity, and mechanical strength such as zirconia. The crucible 1 is placed on the upper surface of the cooling setter 7 via the crucible holding ring 9. A cooling pipe 8 is provided on the lower surface of the cooling setter 7 at an appropriate interval. By controlling the flow rate of the heat medium such as water, gas, refrigerant material, etc. flowing through the cooling pipe 8, the raw material solution in the crucible 1 is controlled to a temperature gradient suitable for crystal growth.

  When the temperature gradient of the raw material solution is larger than the appropriate temperature gradient, the flow rate of the heat medium is increased to reduce the temperature gradient. Further, when the temperature gradient of the raw material solution is smaller than the appropriate temperature gradient, the flow rate of the heat medium is decreased to increase the temperature gradient. The temperature of the heat medium is basically room temperature, but the temperature can be controlled via a temperature control device such as a cooler if necessary. The total flow rate of the heat medium can also be reduced by the temperature control device. When a further temperature gradient is required, the cooling pipe can be densely arranged and the temperature gradient control can be performed in combination with the flow rate control and temperature control of the heat medium.

  FIG. 3A shows an example in which one embodiment of the present invention is applied to a box-type muffle furnace. A box-type muffle furnace 10 and a cooling setter 7 having a uniform temperature distribution are combined. FIG. 3B shows the furnace temperature distribution in the center longitudinal direction of the box-type muffle furnace 10. A in FIG. 3B is a temperature distribution when there is no cooling setter, that is, a state in which the temperature inside the furnace is adjusted to a temperature suitable for crystal growth by the heating element 6.

  B in FIG. 3B is a temperature distribution when temperature control is performed by installing a cooling setter. A large temperature gradient is formed at the bottom of the crucible 1 by adjusting the flow rate of the heat medium flowing through the cooling pipe 8 by control means (not shown). Referring to B, it can be seen that the temperature gradient near the solid-liquid interface between the raw material solution and the grown crystal can be controlled. According to such a structure, as long as the size of the box-type muffle furnace 10 is within the limit, there are no restrictions on the shape of the crucible and the number of crucibles, and crystal production is simultaneously performed using a large crucible or a plurality of crucibles. be able to.

  FIG. 4 shows a cooling setter in which cooling pipes of a plurality of systems are uniformly provided. The cooling pipe 18 may be provided with not only one system but a plurality of systems. By independently controlling the flow rate of the heat medium flowing through the cooling pipes 18a and 18b, temperature gradient control suitable for the target crystal growth can be performed. When a plurality of crucibles 11a and 11b are used, different temperature gradients can be realized for the crucibles 11a and 11b, and different types of crystals can be grown simultaneously.

  Moreover, as shown in FIG. 5, the cooling pipes 18c, 18d, and 18e of a plurality of systems can be non-uniformly piped. It is also possible to change the piping method for the necessary portions of the cooling setter 7 according to the target temperature gradient control.

  FIG. 6 shows a crystal manufacturing apparatus in which a cooling setter and a heat sink are combined. Instead of the crucible holding ring, a heat sink 29 adapted to the shape of the bottom of the crucible is used. The heat sink 29 improves the adhesion between the crucible 21 and the cooling setter 27 and can improve the temperature responsiveness. Further, when a plurality of crucibles are placed on one cooling setter 27, temperature control becomes easy when controlling the temperature gradient of each crucible.

  When the bottom of the crucible 21 is cooled via the cooling setter 27, the side wall of the crucible 21 is also cooled at the same time, and unnecessary temperature distribution may occur in the crucible radial direction of the raw material solution 22. In order to suppress such a temperature distribution, an additional heater 26 is installed on the lower side wall of the crucible 21. FIG. 7 shows a crystal manufacturing apparatus in which an additional heater is combined. By heating the outer wall of the crucible 21 with the additional heater 26, the temperature distribution in the crucible radial direction can be made suitable for crystal growth.

  Examples of the present invention will be specifically described below. In addition, this Example is an illustration, Comprising: It cannot be overemphasized that various changes or improvement can be performed in the range which does not deviate from the mind of this invention.

FIG. 8 shows a crystal manufacturing apparatus according to the first embodiment. In this embodiment, a vertical temperature gradient solidification method is applied to produce a KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) crystal material. A <100> -oriented KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) seed crystal 34 is disposed in each of two 2-inch diameter crucibles 31a and 31b. K ₂ CO ₃ , Ta ₂ O _5, and Nb ₂ O ₅ , which are raw materials of KTa _x Nb _1-x O ₃ , are weighed so as to have a desired composition ratio, and 1 kg each is filled in the crucibles 31 a and 31 b. . However, when the composition of the KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) seed crystal 34 is KTa _{x ′} Nb _{1-x ′} O ₃ , the composition x ′ is KTa _x Nb _x1-x to be grown. A composition that is large with respect to the composition x of O ₃ and has a high dissolution temperature is selected. The composition _x of KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) of the crucible 31a is made 5% larger than the composition x of the crucible 31b.

  The 2-inch diameter crucibles 31a and 31b are installed at equal intervals on a 220 × 220 × 7 mm zirconia cooling setter 37 installed in a muffle furnace 40 having a furnace size of 300 × 300 × 300 mm. The cooling pipe 38 is made of platinum, and two systems are provided in each of the crucibles 31a and 31b. The piping density of the cooling pipe 38a is about twice as large as the piping density of the cooling pipe 38b so that the cooling effect of the crucible 31a is greater than that of the crucible 31b. This is because the raw material solution of the crucible 31a has a Ta excess composition and the solidification temperature is about 22 ° C. higher than the raw material solution of the crucible 31b. The refrigerant in the cooling pipe 38 is made to flow at a flow rate of 3 liters / minute using air and is released into the atmosphere.

The temperature is raised to 1400 ° C. at which the raw material is sufficiently dissolved, and is maintained for 5 hours to realize the K (Ta, Nb) O ₃ raw material solution 32. Thereafter, the heating value of the heating element 36 is adjusted to around 1350 ° C. suitable for crystal growth. While measuring the temperature with a thermocouple 35 installed at the bottom of the crucible so that the crucible 31a is about 20 ° C. lower than the crucible 31b, the exhaust air temperature of the refrigerant in the cooling pipe 38 is measured to determine the air flow rate. Finely adjust the seeding process. Crystal growth is performed by gradually lowering the temperature of the heating element 36 at about 0.5 ° C./hour so that the crystal growth interface moves at a rate of 1 mm / day.

The raw material solution 32 of KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) gradually crystallizes from the lower temperature crucible starting from the KTa _{x ′} Nb _{1-x ′} O ₃ seed crystal 34, A grown crystal 33 of KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) grows. After the crystal growth is completed, the heating element 36 is gradually cooled to room temperature over 12 hours by adjusting the heating value of the heating element 36.

When the grown crystal 33 of K (Ta, Nb) O ₃ produced from the crucibles 31a and 31b is taken out, a single crystal with a <100> orientation in which a {100} facet plane that is four-fold symmetric appears in both grown crystals. Obtainable. The facet plane does not shrink and disappear until it is exposed in the vicinity of the starting point of the constant diameter portion until all the crystals grow and reach the bottom of the grown crystal that becomes only the solvent. Both grown crystals are free from cracks and defects, and high quality crystals can be grown with good yield.

FIG. 9 shows a crystal manufacturing apparatus according to the second embodiment. This embodiment is applied to the vertical temperature gradient solidification method to produce a KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) crystal material. A <100> orientation KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) seed crystal 44 is disposed in each of the 3 inch crucible 41 and the 2 inch crucible 51. K ₂ CO ₃ , Ta ₂ O ₅ and Nb ₂ O ₅ which are raw materials of KTa _x Nb _1-x O ₃ are weighed so as to have a composition ratio of x = 0.8, and a 2-inch diameter crucible 51 1 kg is charged, and 3 kg crucible 41 is filled with 1.7 kg. However, when the composition of the seed crystal of KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) is KTa _{x ′} Nb _{1-x ′} O ₃ , the composition x ′ is KTa _x Nb _1-x O ₃ to be grown. A composition having a high melting temperature and a high melting temperature is selected.

  The 3-inch diameter crucible 41 and the 2-inch diameter crucible 51 are installed at equal intervals on a 220 × 220 × 7 mm zirconia cooling setter 47 installed in a muffle furnace 50 having an in-furnace size of 300 × 300 × 300 mm. To do. The cooling pipe 48 is made of platinum and piped so as to cover the entire bottom surface of the crucibles 41 and 51. The coolant in the cooling pipe 48 is made to flow at a flow rate of 2 liters / minute using cooling water mixed with an additive that raises the boiling point, and is circulated through the cooling device.

The temperature is raised to 1400 ° C. at which the raw material is sufficiently dissolved and held for 5 hours to realize the K (Ta, Nb) O ₃ raw material solution 42. Thereafter, the heating value of the heating element 46 is adjusted to around 1370 ° C. suitable for crystal growth. While measuring the temperature with the thermocouple 45 installed at the bottom of the crucible, the outlet temperature of the cooling water of the cooling pipe 48 is measured, the flow rate is finely adjusted, and the seeding step is performed. Crystal growth is performed by gradually lowering the temperature of the heating element 46 at about 0.5 ° C./hour so that the crystal growth interface moves at a rate of 1 mm / day.

The raw material solution 42 of KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) is gradually crystallized from the lower temperature crucible starting from the KTa _{x ′} Nb _{1-x ′} O ₃ seed crystal 44, A growth crystal 43 of KTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) grows. After the crystal growth is completed, the heating element 46 is gradually cooled to room temperature over 12 hours by adjusting the heating value of the heating element 46.

When the grown crystal 43 of K (Ta, Nb) O ₃ produced from the 3 inch diameter crucible 41 and the 2 inch diameter crucible 51 was taken out, a four-fold symmetric {100} facet surface was revealed for both grown crystals. A <100> -oriented single crystal can be obtained. The facet plane does not shrink and disappear until it is exposed in the vicinity of the starting point of the constant diameter portion until all the crystals grow and reach the bottom of the grown crystal that becomes only the solvent. Both grown crystals are free from cracks and defects, and high quality crystals can be grown with good yield.

  Although the vertical Bridgman method has been described in the present embodiment, the present invention can be applied not only to the vertical temperature gradient solidification method but also to the horizontal Bridgman method and the horizontal temperature gradient solidification method.

  The main component of the crystal is composed of a periodic table Ia group and a Va group, the Ia group is potassium, the Va group contains at least one of niobium and tantalum, and the periodic table Ia, One or more of Group IIa can also be included.

It is a figure for demonstrating the preparation methods of the crystal material by the conventional vertical Bridgman method It is a figure which shows the cooling setter of the crystal manufacturing apparatus concerning one Embodiment of this invention. It is a figure which shows the example which applied one Embodiment of this invention to the box-type muffle furnace. It is a figure which shows the cooling setter which wired the cooling pipe of several systems uniformly. It is a figure which shows the cooling setter which piped the cooling pipe of several systems unevenly. It is a figure which shows the crystal manufacturing apparatus which combined the cooling setter and the heat sink. It is a figure which shows the crystal manufacturing apparatus which combined the cooling setter, the heat sink, and the additional heater. 1 is a diagram showing a crystal manufacturing apparatus according to Example 1. FIG. 6 is a diagram showing a crystal manufacturing apparatus according to Example 2. FIG.

Explanation of symbols

1,11,21,31,41,51 Crucible 2,22,32,42 Raw material solution 3,23,33,43 Growing crystal 4,24,34,44 Seed crystal 5 Furnace temperature distribution 6,36,46 Heat generation Body 7, 27, 37, 47 Cooling setter 8, 18, 28, 38, 48 Cooling pipe 9, 19 Crucible retaining ring 10, 40, 50 Muffle furnace 26 Additional heater 29, 39, 49 Heat sink 30 Heat insulating material 35, 45 Thermoelectric versus

Claims (7)

Oxidation in which seed crystals are placed in a crucible held in a furnace, the raw material filled in the crucible is heated and dissolved, and the raw material solution is gradually cooled upward from below the crucible to grow crystals. In a method for producing a single crystal,
A first step of adjusting the temperature in the furnace to a temperature suitable for crystal growth;
And a second step of controlling a temperature gradient in the vicinity of the solid-liquid interface between the raw material solution and the grown crystal by cooling the bottom surface of the crucible.   In the second step, the cooling plate is cooled by flowing a heating medium through a cooling pipe thermally coupled to the cooling plate disposed in contact with the bottom of the crucible, and the flow rate of the heating medium is controlled. The method for producing an oxide single crystal according to claim 1, wherein the temperature gradient is controlled.   The main component of the crystal is composed of groups Ia and Va in the periodic table, wherein group Ia is potassium, and group Va includes at least one of niobium and tantalum. The manufacturing method of the oxide single crystal of description.   The main component of the crystal is composed of a periodic table Ia group and a Va group, the Ia group is potassium, the Va group contains at least one of niobium and tantalum, and the periodic table Ia, IIa is added as an additive impurity. 4. The method for producing an oxide single crystal according to claim 1, wherein the oxide single crystal includes one or more kinds of groups. A crystal in which a seed crystal is arranged in a crucible held in a furnace, a raw material filled in the crucible is heated and melted, and a raw material solution is gradually cooled upward from below the crucible to grow crystals. In manufacturing equipment,
A heating element for adjusting the temperature in the furnace to a temperature suitable for crystal growth;
A cooling plate disposed in contact with the bottom of the crucible;
A cooling pipe that is thermally coupled to the cooling plate and cools the cooling plate by flowing a heat medium;
And a means for controlling the temperature gradient of the raw material solution in the crucible by controlling the flow rate of the heat medium.   The crystal manufacturing apparatus according to claim 5, further comprising a heat sink disposed in contact with a bottom surface of the crucible and thermally coupled to the cooling plate. The heater according to claim 5 or 6, further comprising a heater that is installed on a side wall of the bottom of the crucible and controls a temperature gradient of the raw material solution by locally heating a part of the crucible. Crystal manufacturing equipment.

Images