JP2019167282A - Crystal growth apparatus - Google Patents

Abstract

To provide a single crystal growth apparatus having an auxiliary heater, capable of preventing the auxiliary heater from being oxidized and using a material except expensive noble metal as the auxiliary heater.SOLUTION: The crystal growth apparatus comprises: a metal crucible capable of storing and holding a raw material melt; an induction coil provided in the periphery of the crucible; an auxiliary heater provided below the crucible or in the periphery thereof; and a heater sealing vessel including a seal structure capable of sealing the auxiliary heater.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a crystal growth apparatus.

  As a method for producing an oxide single crystal, a crystal growth method by the Czochralski method is widely practiced.

  The oxide single crystal growth by this Czochralski method is performed, for example, by arranging an induction coil 80 outside the crucible 10 using a crystal growth apparatus as shown in FIG. An eddy current is generated in 10, whereby the crucible 10 generates heat, the raw material in the crucible 10 is melted, and the seed crystal 150 as a seed is brought into contact with the melt 160 from above and pulled up while rotating. It has become.

  Further, as the pulling progresses, the upper part of the single crystal is cooled by heat transfer from the seed rod (pickup shaft) 70 or heat radiation from the crystal surface. Since the temperature distribution in the growing single crystal becomes large, a device for keeping the temperature of the upper part of the crucible is made. For example, in order to suppress cracks due to thermal stress due to temperature differences in the crystal, a cylindrical after-heater 40 that is a heating element other than the crucible is disposed above the crucible 10. Also, a donut-shaped reflector 30 may be arranged to keep the upper part of the crucible warm.

  By the way, in recent years, the market for oxide single crystals, particularly lithium tantalate, is expanding as a surface acoustic wave device material, and the pulling length (crystal length) of the single crystal is gradually increased in order to secure the production amount. Accompanying this increase in length, it is easy to cause crystal crystallization, polycrystallization that occurs in the straight body, cracks due to thermal strain during cooling, solidification of the crucible bottom, etc. It is a cause to reduce the rate. In particular, the solidification of the raw material in the crucible changes the interface shape of the crystal due to the phenomenon that the temperature distribution in the melt 160 changes due to the release of latent heat, and the flow of the melt 160 changes depending on the solidified region. As a result, defect aggregates called polycrystallization or lineage may occur, which are a major problem in lengthening.

  In single crystal growth by the Czochralski method, the seed crystal 150 is brought into contact with the raw material melting surface of the crucible and rotated, and the crystal is grown while being gradually pulled up. In order to grow the crystal, the melt interface temperature is kept at the melting point, and the latent heat generated along with the crystal growth is radiated to the upper part of the crystal. Therefore, as the crystal grows, the high frequency induction coil 80 that is a heating source must be lowered within an appropriate range.

  In these heating methods, a high frequency current is passed through an induction coil 80 installed in the furnace, thereby generating a high frequency magnetic field. A high frequency magnetic field induces a current in a metal crucible or a metal cylindrical after-heater, and this induced current generates Joule heat in the metal.

  When the magnetic field distribution changes depending on the position of the induction coil 80 and the conductive material and the shape of the conductive material, the amount of induced current and the amount of heat generation change accordingly. When these positions are fixed, a constant heat generation distribution is determined. Therefore, the increase and decrease in high-frequency power can be handled by changing the intensity of the heat generation distribution.

  FIG. 2 is a diagram showing the result of calculating the magnetic field around the crucible 10 of the crystal growing apparatus shown in FIG. As shown in the calculation result of the magnetic field in FIG. 2, the magnetic field concentrates on the corner of a conductor such as the crucible 10. Therefore, the induced current at the corner increases, and the heat generation at the corner of the crucible 10 increases. Compared with this, heat generation at the center of the crucible bottom and the body of the crucible 10 is small. These heat generations are transferred by heat conduction or convection to determine the melt temperature distribution in the crucible.

  At the time of crystal growth, the liquid level of the melt 160 decreases as the crystal grows, and the high-frequency output is decreased so that the solid-liquid interface between the melt 160 and the crystal maintains the melting point. Along with this, the temperature decreases at the center of the crucible bottom, and in some cases, it may solidify from the center of the bottom of the crucible. In addition, if the crystal growth is continued in this state, the solidified crystal grows upward from the bottom of the crucible, and is fused with the crystal being grown, resulting in a situation where the growth must be stopped. There is.

  Therefore, proposals have been made to improve the distribution of the melt and ambient temperature by arranging a heating element other than the crucible as an auxiliary heating element.

  For example, Patent Document 1 discloses a method in which an auxiliary heat source body having a predetermined length in the height direction of the crucible and smaller than the area of the bottom surface of the crucible is disclosed in a space in the crucible base below the crucible. Has been. The auxiliary heating element has various shapes, and there is a description that any shape can be used.

JP 54-162686 A

  By the way, the auxiliary heating element (auxiliary heater) described in Patent Document 1 has a high melting point such as tungsten, molybdenum, tantalum or the like as long as it has a heat resistance when crystal growth is performed in an oxygen-free inert gas. It is also possible to use a metal.

  However, in growing an oxide single crystal such as lithium tantalate, a gas in which argon is mixed with several percent oxygen is generally used. This is to prevent oxygen deficiency from occurring due to reduction of the LT crystal during crystal growth. For this reason, in the case of a gas mixed with oxygen for growing an oxide single crystal such as lithium tantalate, the auxiliary heater is oxidized with a high melting point metal such as tungsten, molybdenum or tantalum and cannot be used. Therefore, it is desirable to use a precious metal that is difficult to oxidize as the material of these materials, and although it is expensive, iridium that is the same material as the crucible must be used.

  In addition, iridium used in the LT single crystal is sublimated by oxygen although it is slight, causing a weight reduction. The iridium auxiliary heater also decreased in weight and a discolored layer was generated on the surface.

  Therefore, in view of the above circumstances, the present invention provides a crystal growth apparatus that prevents oxidation of the auxiliary heater and enables use of materials other than expensive noble metals as the auxiliary heater in the single crystal growth apparatus provided with the auxiliary heater. With the goal.

In order to achieve the above object, a crystal growth apparatus according to one aspect of the present invention includes a metal crucible capable of storing and holding a raw material melt,
An induction coil provided around the crucible;
An auxiliary heater provided below or around the crucible;
A heater sealed container having a seal structure capable of sealing the auxiliary heater.

  According to the present invention, the growth of an oxide single crystal such as lithium tantalate in an inert gas containing oxygen prevents oxidation of the auxiliary heater, and a material other than a noble metal can be used as a material for the auxiliary heater. A single crystal growing apparatus can be provided.

It is the schematic which showed an example of the conventional crystal growth apparatus. It is the figure which showed the magnetic force line distribution and magnetic field intensity distribution of an electromagnetic field analysis. It is the figure which showed the whole structure of an example of the crystal growth apparatus which concerns on embodiment of this invention. It is the enlarged view which showed the structure of an example of the heater airtight container of the crystal growth apparatus which concerns on 1st Embodiment. It is the figure which showed the structure of an example of the heater airtight container of the crystal growing apparatus which concerns on 2nd Embodiment. It is a figure for demonstrating the behavior of the sealing material of the heater airtight container of the crystal growth apparatus which concerns on 2nd Embodiment. It is the figure which showed the structure of an example of the heater airtight container 120b of the crystal growing apparatus which concerns on 3rd Embodiment. It is the figure which showed the structure of an example of the heater airtight container 120c of the crystal growing apparatus which concerns on 4th Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

The crystal growth apparatus using the chocsky method of the present invention is a lithium niobate LiNbO ₃ grown in the atmosphere or in an inert gas atmosphere containing oxygen (hereinafter sometimes abbreviated as “LN”), This is a crystal growth apparatus used for the production of oxide single crystals such as lithium tantalate LiTaO ₃ (hereinafter sometimes abbreviated as “LT”) and yttrium aluminum garnet Y ₃ Al ₅ O ₁₂ (hereinafter YAG). The Czochralski method is called a seed cut according to a certain crystal orientation. Usually, the tip of a single crystal of about several millimeters is infiltrated into a melt of the same composition, and is gradually pulled up while rotating. This is a method for producing a single crystal having the same orientation.

  FIG. 1 is a schematic diagram showing an example of a conventional crystal growth apparatus. The conventional crystal growth apparatus does not include an auxiliary heater, but includes a crucible 10, a crucible base 20, a reflector 30, an after heater 40, heat insulating materials 50 and 60, a seed rod 70, and an induction coil 80.

  Further, as an improvement on the conventional pulling device, as described in Patent Document 1, an auxiliary heater can be installed in a crucible base or the like.

  Conventionally, since oxide crystals are grown in an atmosphere containing oxygen, materials that oxidize at high temperatures other than noble metals such as platinum, rhodium, and iridium cannot be used as auxiliary heaters. That is, rare metals such as platinum, rhodium and iridium can be used continuously until the end of their lifetime, although they are depleted by oxidation. However, metals other than the above-mentioned noble metals need to be frequently replaced by oxidation, and the cost is high even if the metal itself is inexpensive.

  As a result of examining the method for preventing oxidation of the auxiliary heater 110, the inventors have come to the conclusion that the oxidation can be prevented by sealing the auxiliary heater 110 made of metal in a heat insulating material as shown in FIG. However, since the temperature of the auxiliary heater 110 is 2000 ° C. or higher, pressure is received from the heat insulating material 60, etc., in the structure that is simply embedded in the heat insulating material 60, the thermal expansion between the heat insulating material 60 and the metal auxiliary heater 110 is performed. It becomes easy to crack by the stress due to the difference in rate and the thermal expansion of the residual gas. Further, it is technically difficult to vacuum seal the auxiliary heater 110 in the heat insulating material 60.

  Therefore, as a result of examining the sealing method, the inventors have solved the above problem by sealing an inert gas using a high-boiling liquid sealing material. The contents will be described below.

  FIG. 3 is a diagram showing an overall configuration of an example of a crystal growth apparatus according to an embodiment of the present invention. As shown in FIG. 3, the crystal growing apparatus according to the present embodiment includes a crucible 10, a heater sealed container 120, a reflector 30, an after heater 40, heat insulating materials 50 and 60, a seed bar 70, and an induction. The coil 80, the high frequency power supply 85, the mounting table 90, the chamber 100, and the auxiliary heater 110 are included. In the crystal growth apparatus according to the present embodiment, the same reference numerals are used for the same components as those of the conventional crystal growth apparatus shown in FIG.

  The point that the crucible base 20 that supports the crucible 10 is a heater sealed container 120 is a point that is greatly different from the conventional crystal growth apparatus. The heater sealed container 120 is a container that can accommodate the auxiliary heater 110 in a sealed state. The auxiliary heater 110 is provided inside the heater sealed container 120. The heater sealed container 120 also has a function as the crucible base 20 and supports the crucible 10 from below.

  Next, individual components of the crystal growth apparatus according to this embodiment will be described.

  The crucible 10 is a container for storing and holding a crystal raw material and growing a single crystal. Since the crucible 10 functions as a heating element by high-frequency induction heating, a metal having low resistance and high conductivity is used. Since oxide crystals such as LT are grown in an oxygen-containing atmosphere, a heat resistant noble metal, simple substance such as platinum (Pt), rhodium (Rh), iridium (Ir), or an alloy thereof may be used. preferable.

  The reflector 30 is a reflector that is disposed on the upper end surface of the crucible 10 and extends horizontally inward from the upper end surface of the crucible 10. That is, the reflector 30 has a function of reflecting heat rising upward from the crucible 10 and returning it downward. As shown in FIG. 4, the reflector 30 may have a portion extending not only inside the crucible 10 but also outside. The reflector 30 also generates heat due to induction heating of the induction coil 80.

  The after heater 40 is provided so as to extend upward above the crucible 10, more specifically, above the reflector 30. It has a cylindrical shape and is arranged so as to surround the crucible 10. The after heater 40 has a slightly smaller diameter than the crucible 10, for example. The after heater 40 has a function of heating the rising single crystal from the side surface when the single crystal is pulled up. The after heater 40 also generates heat by induction heating of the induction coil 80.

  Thus, since the reflector 30 and the after heater 40 are required to have the same characteristics as the crucible material, the reflector 30 and the after heater 40 are made of a simple substance such as precious metal, platinum (Pt), rhodium (Rh), iridium (Ir), or an alloy thereof. Is preferred.

  The heat insulating material 50 is a heat shielding means for covering the crucible 10, the reflector 30, and the after heater 40 to reduce the release of these heats to the outside. The heat insulating material 50 functions as a refractory material container, and sintered refractories such as alumina, zirconia, magnesia, and calcia are used.

  The heat insulating material 60 is a heat shielding means that covers the periphery of the crucible 10 and reduces heat radiation from the crucible 10. For the heat insulating material 60 arranged around the crucible 10, it is preferable to use a sintered body such as alumina, zirconia, magnesia, and calcia that can be deformed during heating and cooling, bubbles, and powder. In addition, the heat insulating material 60 does not need to be installed as needed. The bubble means a hollow spherical raw material.

  The seed bar 70 is a means for pulling up the single crystal from the crucible 10. A seed crystal 150 is held at the lower end of the seed bar 70, and the seed crystal 150 is brought into contact with the raw material melt 160 held in the crucible 10, and the seed bar 70 is pulled up while rotating to grow a single crystal. Let

  The induction coil 80 is a magnetic field generating means for inductively heating the crucible 10, the reflector 30, the after heater 40, and the auxiliary heater 110. By supplying high-frequency power from the high-frequency power source 85 to the induction coil 80, the induction coil 80 generates a magnetic field, generating eddy currents in the crucible 10, the reflector 30, the after heater 40, and the auxiliary heater 110 made of a conductor, These are heated by induction heating.

  The mounting table 90 is a mounting table for supporting the heat insulating material 50 including the crucible 10 and the like. The mounting table 90 is also made of a sintered refractory such as alumina, zirconia, magnesia, calcia, etc., like the heat insulating material 509.

  The chamber 100 is a means for covering the entire crystal growth apparatus including the heat insulating material 50, the mounting table 90, and the induction coil 80, and is provided to prevent heat dissipation.

  Next, the auxiliary heater 110 and the heater sealed container 120 will be described in more detail.

  First, an electromagnetic field analysis was performed when a high-frequency current was passed through the induction coil 80 of the conventional crystal growth apparatus having the configuration shown in FIG. FIG. 2 shows the magnetic field line distribution and the magnetic field strength distribution in the electromagnetic field analysis. As shown in FIG. 2, in a region surrounded by a conductor such as the crucible 10 or the after heater 40, a magnetic field line cannot enter the lower side of the bottom of the crucible 10, a magnetic field line is sparse and the magnetic field line density is small. You can see that the energy is small.

  If there is a conductive material near the high-frequency magnetic field lines, an eddy current is generated in the conductive material. Since the conductive material has electrical resistance, Joule heat proportional to the square of the current is generated, and the conductive material self-heats. Since the eddy current increases as the magnetic field strength increases, as shown in FIG. 2, heat generation at the outer peripheral portion of the bottom surface of the crucible 10 and the outer periphery of the reflector 30 increases.

  Since the magnetic field lines cannot penetrate into the conductor, if there is a conductive material that blocks the magnetic field lines, the magnetic field energy around it will be reduced.

  Therefore, an auxiliary heater 110 is provided with a conductor placed at a position other than the crucible, and heat generation by induction heating of the auxiliary heater 110 was examined. From FIG. 2, the auxiliary heater 110 can be disposed on the lower side of the crucible 10 or on the outer side of the diameter of the crucible bottom. In particular, it is preferable to dispose outside the diameter of the crucible bottom. As described above, the lower side of the crucible is a region where the magnetic property cannot enter and the magnetic field lines are sparse, and the heat generation efficiency is small. On the other hand, the outside of the bottom of the crucible is close to the high-frequency magnetic field lines and has high heat generation efficiency. Therefore, in the following description, an example in which the position of the auxiliary heater 110 is at the lower part of the crucible and outside the diameter of the crucible bottom will be described. Note that the position, shape, and size of the auxiliary heater 110 can be variously changed according to the application and are arbitrary.

  FIG. 4 is an enlarged view showing an example of the configuration of the heater sealed container 120 of the crystal growing apparatus according to the first embodiment. As described above, the heater sealed container 120 is provided below the crucible 10 to support the crucible 10 from below, and accommodates and seals the auxiliary heater 110.

  As shown in FIG. 4, the heater sealed container 120 that seals the auxiliary heater 110 is provided with a lid 121 made of a dense heat insulating material, a convex portion 1221 having a smaller maximum diameter than the lid 121 and on which the lid 121 is placed, and the auxiliary heater 110. A support base 122 having a possible shoulder 1222, a tray 123 having an inner diameter larger than the diameter of the lid 121, and a sealing material 124 that melts at a high temperature between the lid and the tray. In addition, a thermocouple storage tube 125 may be provided on the center bottom surface of the support base 122 as necessary. Here, the dense heat insulating material means a heat insulating material that can be sealed and does not have air permeability, and does not mean that the material is specially processed to be denser than usual. When vacuum evacuation or the like is performed, the inside and the outside can be shielded, and the internal pressure can be reduced.

  Note that the sealing material 124 is solid at room temperature, and is preferably powder or granular. By making the sealing material 124 solid at room temperature, the inside of the growth furnace is replaced with an inert gas containing a rare gas such as nitrogen gas or argon before the temperature rises, so that the sealing material 124 is also provided at a place where the auxiliary heater 110 is located. Since it is solid, there is a gap between the powders or particles of the sealing material 124, and the space inside the sealing material 124 can be replaced with an inert gas. Note that the pressure may be reduced using an evacuation unit such as a vacuum pump at the time of replacement, and then argon gas may be introduced into the growth furnace. The inside of the growth furnace can be easily replaced with a rare gas, and a space without oxygen can be formed. When the temperature rises, the sealing material 124 melts, and the outside air is blocked by being present as a liquid in the gap between the tray 123, the support base 122, and the lid 121. That is, the gap structure between the lid 121, the support base 122, and the tray 123 can be sealed with the sealing material 124, and the space inside the sealing material 124 can be sealed. Since the auxiliary heater 110 is installed inside the sealing material 124, the auxiliary heater 110 can be sealed in an environment that does not come into contact with oxygen.

  As described above, the heater sealed container 120 of the crystal growing apparatus according to the first embodiment covers the lower end portion of the lid 121 and the side surface near the lower end portion with the receiving plate 123 and the support table 122, and the lid 121, the receiving plate 123 and the support table. A sealing structure in which a gap between the sealing member 124 and the sealing material 124 is filled is provided.

  Note that the shoulder 1222 on which the auxiliary heater 110 is placed may be a part of the support base 122. Hereinafter, an example in which the auxiliary heater 110 is arranged on the support base 122 will be described.

  FIG. 5 is a view showing a configuration of an example of the heater sealed container 120a of the crystal growing apparatus according to the second embodiment.

  In FIG. 5, the lid 121a is different from the heater sealed container 120 of the crystal growth apparatus according to the first embodiment in that the lid 121a has a thin portion 1211 at the lower part of the side surface. As described above, the structure may be such that the volume of the internal space surrounded by the sealing material 124 is increased.

  Next, the behavior of the sealing material 124 in the heater sealed container 120a of the crystal growing apparatus according to the second embodiment will be described.

  FIG. 6 is a view for explaining the behavior of the sealing material 124 of the heater hermetic container 120a of the crystal growing apparatus according to the second embodiment. 6A is a diagram showing an example of the state of the sealing material 124 immediately after melting, and FIG. 6B is a diagram showing an example of the state of the sealing material 124 in a high temperature state.

  As shown in FIG. 6A, immediately after melting, the sealing material 124 is in a state of covering the lower end portion of the lid 121a and the side surface portion above it. Even in the normal temperature state before melting, except that the sealing material 124 is in the form of powder or particles, it is the same state as FIG.

  At normal temperature, the sealing material 124 is in the form of powder or particles, and the inner space 130 provided with the auxiliary heater 110 surrounded by the inner peripheral surface of the lid 121a, the outer surface of the support base 122, and the sealing material 124, the lid Aeration is possible in the outer space 131 outside the outer surface of 121a. Therefore, after the inside of the growth furnace is evacuated, a rare gas such as argon or an inert gas such as nitrogen is supplied into the growth furnace, so that the rare gas or the inert gas is contained in the growth furnace including the internal space 130. It is possible to fill. Thereby, not only the external space 131 but also the internal space 130 can be made an atmosphere of a rare gas or an inert gas. That is, a space without oxygen can be obtained.

  Thereafter, when the temperature rises, the sealing material 124 melts. Immediately after melting, the height of the sealing material 124 is the same in the internal space 130 and the external space 131 of the lid 121a as shown in FIG. State.

  As shown in FIG. 6B, when the temperature rises higher than the melting temperature of the sealing material 124, the gas in the internal space 130 with the auxiliary heater 110 thermally expands, and as shown in FIG. The sealing material 124 is pushed outward. The liquid level of the sealing material 124 is at a position where the internal pressure balances the sum of the weight difference between the inside and outside of the sealing material 124 and the external pressure. Assuming that the heater temperature rises to 2000 ° C. (2273 K) and the temperature of the internal gas is equal to that, and using the ideal gas equation of state PV = nRT, a gas with a melting point of 400 ° C. (673 K) is about 3 at 2000 ° C. The volume expands 4 times. Therefore, there is a possibility that the sealing material 124 is pushed out and the gap between the lower end portion of the lid 121a and the tray 123 cannot be sealed. Therefore, as shown in FIGS. 5 and 6, in the heater sealed container 120a of the crystal growth apparatus according to the second embodiment, a thin portion 1211 is provided at a position where the sealing material 124 on the side surface of the lid 121a is filled, The melt pool 1300 of the sealing material 124 is enlarged from the middle, and when the temperature increases and the pressure increases and the liquid level decreases, the volume increases and the pressure decreases. In addition, if a structure in which the sealing material 124 is expanded so that a space more than 2.5 times the inner space is formed in the inner and outer sealing material holding portions, the sealing material 124 flows out to the outside due to volume expansion. There is no.

  In addition, after the sealing material is melted, a predetermined amount of the crystal material in the crucible 10 is dissolved in a state where a gas obtained by mixing a few volume% oxygen gas with an inert gas such as argon or an inert gas such as nitrogen is supplied. The temperature is raised to grow the crystal.

  FIG. 7 is a view showing a configuration of an example of the heater sealed container 120b of the crystal growing apparatus according to the third embodiment. The heater sealed container 120b of the crystal growth apparatus according to the third embodiment is the second embodiment in that a seal lid 140 is provided in a space 131 between the outer surface of the lid 121a and the inner surface of the tray 123. This is different from the heater sealed container 120a of the crystal growing apparatus according to FIG.

  Thus, in order to suppress the evaporation of the sealing material 124, as shown in FIG. 7, a seal lid 140 may be provided in a portion facing the outside air. Thereby, it can prevent reliably that the sealing material 124 overflows the outer side of the receiving tray 123. FIG.

  Further, when the heat insulating material 60 is a bubble or powder, the seal lid 140 can also prevent the powder of the heat insulating material 60 from being mixed into the sealing material 124.

  Note that the seal lid 140 does not completely seal the sealing material, and the auxiliary heater portion may have a gap to such an extent that a rare gas such as vacuum exhaust or argon or an inert gas such as nitrogen can be replaced.

  FIG. 8 is a view showing a configuration of an example of the heater sealed container 120c of the crystal growing apparatus according to the fourth embodiment. In the heater sealed container 120b of the crystal growth apparatus according to the fourth embodiment, the crucible base 21 that supports the crucible 10 is provided separately from the heater sealed container 120c, and the heater sealed container 120c has an annular shape around the crucible base 21. This is different from the heater sealed containers 120, 120a, 120b of the crystal growth apparatus according to the first to third embodiments in that the planar shape is provided.

  When growing a large-diameter crystal, the force applied to the portions of the lids 121 and 121a that support the crucible 10 is increased, and the lids 121 and 121a are easily broken. In order to prevent this, as shown in FIG. 8, the crucible base 21 and the heater sealed container 120c are separated from each other, the force from the crucible 10 is received by the crucible base 21, and no force is applied to the upper part of the heater sealed container 120c. It is said. Thereby, it is possible to grow a large-diameter crystal while maintaining the structure and durability in which the auxiliary heater 110 is not exposed to oxygen.

  Further, in the heater sealed container 120c shown in FIG. 8, the support base 122a does not have a shoulder, the auxiliary heater 110 is placed on the upper surface of the support base 122a, and the lid 121b is supported via the auxiliary heater 110. It has become. Since the lid 121b is significantly lighter than the crucible 10, there is no problem with such a structure in which the auxiliary heater 110 and the lid 121b are overlapped and supported.

  With the difference in these structures, the shapes of the internal space 130a, the external space 131a, and the seal lid 140a are also the heater sealed container 120b and the first and second implementations of the crystal growing apparatus according to the third embodiment of FIG. This is different from the heater sealed containers 120 and 120a of the crystal growing apparatus according to the embodiment.

  Further, as shown on the left side of FIG. 8, a passage 132 that allows the sealant 124 to flow between the inside and the outside of the lid 121b may be formed on the bottom surface of the tray 123a. Thus, since the sealing material 124 is configured to enter the inside of the lid 121b, the passages 132 may be formed at several locations in order to prevent the sealing material 124 from overflowing inside.

  In any of the first to fourth embodiments, the support base 122 or the crucible base 21 is provided with a thermocouple hole and a pipe 125 for measuring the temperature of the crucible bottom. Thereby, the temperature of the crucible bottom can be measured.

  The auxiliary heater 110 may be made of heat-resistant and oxidation-resistant platinum, rhodium, iridium and alloys thereof, or other high melting point metals such as tungsten, molybdenum, tantalum, or graphite. It may be produced. As described above, it is preferable that the auxiliary heater 110 is made of tungsten, molybdenum, tantalum, graphite, or the like from the viewpoint of cost reduction.

  The auxiliary heater 110 preferably has an annular shape, and the thickness thereof is preferably in the range of 0.5 mm to 3 mm, and more preferably in the range of 1 mm to 2 mm.

  The sealing material 124 is solid at room temperature (25 ° C.) and is preferably a high-boiling material, and metals such as aluminum, indium, and tin, low-melting glass, and boron oxide can be used. Care must be taken when using metal, as it can erode and reduce insulation. Low melting glass is difficult to process after solidification. Boron oxide has a high boiling point and is fixed at room temperature. Boron oxide can be dissolved in water, ethyl alcohol, acid, or alkali, and the boron oxide solidified in the heater sealed containers 120 and 120a to 120c can be easily removed after crystal growth. In the growth of compound semiconductors such as GaAs and GaP, it is used as a cap material for the LEC pulling method (liquid sealing pulling method) and is easily available. For such reasons, it is preferable to use boron oxide as the sealing material.

  In addition, as long as the lids 121, 121a, 121b cover and cover the support bases 122, 122a in a plane, and the trays 123, 123a have a size relationship including the lids 121, 121a, 121b in a plane, the lid 121 , 121a, 121b, the support bases 122, 122a, and the trays 123, 123a are not limited to a circular shape or an annular shape, and can be configured in various shapes.

  Thus, according to the crystal growing apparatus according to the present embodiment, the gap structure of the heater sealed containers 120, 120a to 120c is used only when the sealing material 124 is melted by using the sealing material 124 that is solid at normal temperature and melts at high temperature. By having a sealing structure that seals the inner space 130, the internal space 130 in which the auxiliary heater 110 is provided can be filled with an inert gas, and oxidation of the auxiliary heater 110 can be reliably prevented. Thereby, even if it is a metal which may be oxidized, it can be employ | adopted as the auxiliary | assistant heater 110, and cost reduction can be aimed at.

[Example]
Examples of the present invention will be described below. For ease of understanding, the reference numerals used in the description of the embodiments are attached to the corresponding components.

[Example 1]
A 6-inch LT crystal was grown using the crystal growth apparatus according to the second embodiment using the auxiliary heater sealed container 120a having the configuration of FIG. Zirconia was used for the upper lid 121a and the crucible material, and the receiving tray 123 was made of alumina. Moreover, the heat insulating material 60 installed the sintered compact made from a zirconia. The distance from the auxiliary heater 110 to the melt reservoir 1300 of the sealing material 124 is 150 mm, and the volume of the melt reservoir 1300 is the volume of the heater portion where the auxiliary heater 110 is provided (the volume of the heater portion is larger than the melt reservoir). 10 times the upper region). Boron oxide powder manufactured by Pure Chemical was used as the sealing material 124. Boron oxide weight was calculated and added to reach the top of the melt pool. The auxiliary heater 110 made of tungsten having a thickness of 1.5 mm and a width of 20 mm was installed so that the inner diameter was a distance of 5 mm from the outer periphery of the crucible and the outer periphery was a distance of 25 mm.

  Growth was performed using the crystal growth apparatus described above. In addition, the inside of the furnace was replaced with argon gas before the temperature was raised (the inside of the furnace was reduced to 0.1 atm or less by an oil rotary pump). At this time, boron oxide serving as the sealing material 124 was powder, and a portion where the auxiliary heater 110 was provided was also replaced with argon gas. In this state, the temperature was raised to 600 ° C. At this time, the sealing material 124 was melted, and the auxiliary heater 110 was sealed in the heater hermetic container 120a in a replacement atmosphere. Thereafter, the temperature was raised to a predetermined temperature so that the crystal material in the crucible 10 was dissolved while supplying a gas in which 2% by volume of oxygen gas was mixed in an argon atmosphere. After melting the crystal material in the crucible, the pulling was started and the crystal was grown.

  During growth, in order to monitor solidification from the bottom of the crucible, a thermocouple was installed in the vicinity of the bottom of the crucible, and the temperature change when solidified at the bottom of the crucible was confirmed to confirm the occurrence of solidification. Further, when solidification was confirmed at the bottom of the crucible, the crystal growth was completed.

  Further, the crystallization rate was calculated from the crystal weight of LT by the following formula (1).

Crystallization rate = crystal weight / raw material weight (1)
When solidification occurred at the bottom of the crucible, the crystal weight at that time was calculated to terminate the growth when the solidification occurred. When solidification did not occur, it was grown to a predetermined crystal length and calculated as the crystal weight.

  In addition, after the completion of the growth, the status of the auxiliary heater was confirmed. The results are listed in Table 1.

In Example 1, no solidification signal was generated during growth, and a crystal with a crystallization ratio of 47% could be grown. There was no change in the weight of the auxiliary heater 110.

[Example 2]
A pulling-up test was performed in the same manner as in Example 1 except that the molybdenum auxiliary heater 110 was installed. There was no solidification during growth, and crystals with a crystallization ratio of 46% could be grown. There was no change in the weight of the auxiliary heater 110.

[Example 3]
A pulling-up test was performed in the same manner as in Example 1 except that the graphite auxiliary heater 110 was installed. There was no solidification during the growth, and crystals with a crystallization ratio of 47% could be grown. There was no change in the weight of the auxiliary heater 110.

[Example 4]
A pull-up test was performed in the same manner as in Example 1 except that the crystal growth apparatus according to the third embodiment using the heater sealed container 120b having the configuration shown in FIG. It was. There was no solidification during growth, and crystals with a crystallization rate of 45% could be grown.

[Example 5]
The crystal growth apparatus according to the third embodiment using the heater sealed container 120b having the configuration shown in FIG. . There was no solidification during growth, and crystals with a crystallization ratio of 46% could be grown.

[Example 6]
Using the crystal growth apparatus according to the third embodiment using the heater sealed container 120b having the configuration shown in FIG. . There was no solidification during the growth, and crystals with a crystallization ratio of 47% could be grown.

[Comparative Example 1]
A pulling-up test was performed in the same manner as in Example 1 except that the sealing material 124 was not used. During the growth, the crucible bottom temperature suddenly decreased and solidification occurred at the bottom of the crucible, and the cultivation was stopped. The surface of the tungsten heater was oxidized and cracks were generated in the auxiliary heater 110.

[Comparative Example 2]
A pulling-up test was performed in the same manner as in Example 2 except that the sealing material 124 was not used. During the growth, the crucible bottom temperature suddenly decreased and solidification occurred at the bottom of the crucible, and the cultivation was stopped. The surface of the molybdenum heater was oxidized to reddish purple and partly sublimated and thinned.

[Comparative Example 3]
An auxiliary heater 110 made of tungsten having a thickness of 1.5 mm and a width of 20 mm was installed on the same surface as the crucible bottom in the ZrO ₂ powder serving as a heat insulating material without using the auxiliary heater sealed container. The auxiliary heater 110 was installed such that the inner diameter of the auxiliary heater 110 was a distance of 5 mm from the outer periphery of the crucible and the outer periphery was a distance of 25 mm. During the growth, the temperature at the bottom of the crucible suddenly dropped and solidification occurred at the bottom of the crucible, and the growth was stopped. The surface of the tungsten heater was oxidized and evaporated to become thin, and the auxiliary heater 110 was cracked.

[Comparative Example 4]
A pulling test was performed in the same manner as in Comparative Example 3 except that molybdenum was used as the auxiliary heater 110. During the growth, the temperature at the bottom of the crucible suddenly dropped and solidification occurred at the bottom of the crucible, and the growth was stopped. The molybdenum heater surface was oxidized to reddish purple, and part of the surface was sublimated and thinned and cracked.

[Comparative Example 5]
A pulling-up test was conducted in the same manner as in Comparative Example 3 except that iridium was used as the heater. There was no generation of solidification signal during growth, and crystals with a crystallization rate of 45% could be grown. The surface of the iridium heater turned gray and the weight was reduced.

[Comparative Example 6]
A pulling-up test was performed in the same manner as in Example 1 except that the auxiliary heater 110 was not used. Solidification of the bottom of the crucible occurred at a crystallization rate of 32% during growth.

  As shown in Table 1. In Examples 1-6, the crystallization rate was 45% or more in all, and good results were obtained that solidification at the bottom of the crucible was not observed.

  On the other hand, in Comparative Examples 1 to 4, an abnormality occurred in the auxiliary heater, and crystals could not be manufactured.

  Thus, from the examples, it was shown that the crystal growth apparatus according to the present embodiment can realize a high crystallization rate without causing a heater abnormality and can cope with an increase in length.

  The preferred embodiments and examples of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments and examples, and the above-described embodiments and examples can be performed without departing from the scope of the present invention. Various modifications and substitutions can be made to the embodiments.

10 crucible 20, 21 crucible base 30 reflector 40 after heater 50, 60 heat insulating material 70 seed rod 80 induction coil 85 high frequency power supply 90 mounting base 100 chamber 110 auxiliary heater 120, 120a-120c heater sealed container 121, 121a, 121b lid 122 , 122a Support stand 1221 Convex portion 1222 Shoulder 123, 123a Receptacle 124 Sealing material 130, 131 Space 132 Passage 140 Seal lid 150 Seed crystal 160 Raw material melt

Claims (7)

A metal crucible capable of storing and holding the raw material melt;
An induction coil provided around the crucible;
An auxiliary heater provided below or around the crucible;
A crystal growing apparatus comprising: a heater sealed container having a seal structure capable of sealing the auxiliary heater.   The crystal growth apparatus according to claim 1, wherein the auxiliary heater is made of tungsten, molybdenum, tantalum, or graphite. The seal structure has a gap structure capable of holding a sealing material that melts at a high temperature,
The crystal growth apparatus according to claim 1, wherein the gap structure is not sealed when the sealing material is not melted, and the gap structure is sealed when the sealing material is melted. The sealing structure includes a lid made of a heat insulating material;
A tray having a size including the lower end of the lid,
The crystal growth apparatus according to claim 3, wherein the sealing material is held so as to cover a lower end portion of the lid on the saucer and close a gap between the saucer and a lower end portion of the lid.   The crystal growing apparatus according to claim 4, wherein the heater sealed container has a size included in the lid in a plan view, and has a support base that holds the sealing material and supports a ceiling surface of the lid.   The crystal growth according to claim 5, wherein the support base includes a convex portion that supports the ceiling surface of the lid, and a shoulder that has a height lower than the convex portion and on which the seal material can be placed. apparatus.   The crystal growth apparatus according to claim 3, wherein the sealing material is boron oxide.