JP4941405B2 - Method for removing aluminum oxide from crucible inner surface and crucible regeneration method - Google Patents

Description

  The present invention relates to a method for removing aluminum oxide solidified in a crucible and adhering to the inner surface of the crucible, and a method for regenerating a crucible.

  As a method for producing a single crystal from a raw material melt contained in a crucible, a Nacken method, a capillary method, a Czochralski method, a Kyropoulos method and the like are known. When a single crystal is grown by these methods, not all of the raw material charged into the crucible can be taken out as a single crystal, and a part of the raw material melt remains in the crucible. In order to reuse the remaining melt (residual melt), a new solid raw material may be added and crystal growth may be performed again.

  However, when a solid raw material is added to the remaining melt and crystal growth is repeated, contamination progresses due to precipitates from the crucible, impurities in the raw material, etc., and the melt in the crucible becomes unsuitable as a raw material. In such a case, it is necessary to perform an operation for removing the solid material formed by solidification of the remaining melt from the inner surface of the crucible.

  When the melt is solidified in the crucible, the solid substance firmly adheres to the inner surface of the crucible. Therefore, it is very difficult to remove the solid substance sufficiently. For example, if an electric drill is used to remove the solid material adhered to the inner surface of the crucible, depending on the solid state of the solid material, a strong impact is applied to the crucible, causing damage such as cracking, breaking, and penetration. There is a risk that.

In addition to the physical removal method as described above, a method of removing a solid substance fixed on the inner surface of the crucible by heat treatment or chemical treatment has been studied. For example, Patent Document 1 below describes a method in which an iridium crucible is heated in an upside down state to melt and flow out deposits, and then the crucible is treated with a phosphoric acid solution. Patent Documents 2 and 3 below describe a method of removing deposits by subjecting a quartz crucible to heat treatment or chemical treatment.
Japanese Patent Publication No. 5-71554 Japanese Patent Publication No. 6-53634 Japanese Patent Laid-Open No. 11-43392

  By the way, in the above-described method for growing a single crystal, a crucible made of a material having high heat resistance is generally used. For example, tungsten (melting point: 3407 ° C.), molybdenum (melting point: 2617 ° C.), platinum ( Melting point: 1772 ° C.) or iridium (melting point: 2410 ° C.) is used. Many crucibles made of these metal materials are inferior in workability or expensive in themselves. For this reason, if the crucible is damaged, the regeneration process requires a great deal of labor and cost. Therefore, there has been a demand for a method capable of sufficiently and efficiently removing the solid substance fixed to the crucible so that it can be repeatedly used as many times as possible.

  In the method of heating the crucible upside down as in the method described in Patent Document 1 above, simply melting and flowing out the solid substance, the crucible is brought to a temperature sufficiently higher than the melting point of the solid substance. It needs to be heated. By doing so, the viscosity of the melt is sufficiently lowered, and it can be expected that the residual amount of the solid substance on the bottom surface and inner surface of the crucible will be reduced. However, it is difficult to uniformly heat the entire crucible, and if the crucible is heated to an excessively high temperature, the crucible may be deteriorated. In some cases, the crucible may be locally heated and melt.

  In addition, in chemical removal methods using chemicals such as phosphoric acid solution and hydrofluoric acid solution, depending on the type and amount of the solid substance that is fixed, the treatment speed is generally slow and the removal treatment takes a lot of time. There is a problem.

  The present invention has been made in view of the above circumstances, and a method capable of sufficiently and efficiently removing aluminum oxide solidified in a crucible and adhering to the inner surface of the crucible, and a crucible regeneration method using the same The purpose is to provide.

  The present inventors have also used a tool such as an electric drill to remove solid substances such as aluminum oxide adhering to the inner surface of the crucible. However, the working efficiency is remarkably low, and when the crucible is significantly deformed as shown in FIG. 1 due to the expansion or contraction of the melt, an area where the tool does not reach is formed on the inner surface of the crucible. It could not be removed sufficiently. The crucible 20 shown in FIG. 1 is an iridium crucible (opening inner diameter 105 mm) used for melting raw materials, and FIGS. 1 (a) and 1 (b) are used for single crystal growth before use. Shown after each used.

  Therefore, the present inventors have made extensive studies on a method for efficiently removing aluminum oxide adhering to the inner surface of the crucible. As a result, it was found that altering aluminum oxide by introducing calcium oxide into the crucible and melting aluminum oxide and calcium oxide is extremely effective for the removal treatment, and the following invention was completed. It was.

  That is, the present invention is a method for removing aluminum oxide that has solidified in a crucible and adhered to the inner surface of the crucible, the supplying step of supplying calcium oxide into the crucible, and heating the crucible into the crucible. After the aluminum oxide and calcium oxide are melted, the mixed solid in the crucible is cooled by a heat treatment step to obtain a mixed solid in the crucible and a mechanical treatment or a chemical treatment, or both treatments. A removal step is provided.

  According to the above method of the present invention, calcium oxide is supplied into the crucible, and the temperature is raised in a state where the aluminum oxide and the calcium oxide are in contact with each other, so that the reaction proceeds from the portion where both are in contact, and the aluminum oxide Melts at a temperature lower than the melting point of. Compared to heating a crucible containing only aluminum oxide without supplying calcium oxide, the melting point is lowered as described above, so the difference between the melting temperature of the crucible and the set temperature of the heat treatment should be increased. Can do. As a result, it can fully suppress that a crucible is overheated and damaged.

  According to the test conducted by the inventors, the mixed solid containing aluminum oxide and calcium oxide has a significantly lower mechanical strength than that containing no calcium oxide. Can be easily removed. Moreover, since the mixed solid has an etching rate of about 10 to 100 times faster by chemical treatment than that containing no calcium oxide, it can be efficiently removed by chemical treatment. Furthermore, by using a combination of mechanical treatment and chemical treatment, the mixed solid in the crucible can be more sufficiently and efficiently removed.

  The present invention is also a crucible recycling method for recycling used crucibles, the step of removing the aluminum oxide solidified in the crucible and adhering to the inner surface of the crucible by the above removal method according to the present invention. A crucible reproduction method is provided.

  Since the said crucible reproduction | regeneration method has the process of performing the said removal method based on this invention, the removal process of aluminum oxide can be performed efficiently. Further, since the aluminum oxide can be sufficiently removed, the crucible can be regenerated to a reusable state.

  ADVANTAGE OF THE INVENTION According to this invention, the method which can fully and efficiently remove the aluminum oxide which solidified in the crucible and adhered to the inner surface of the said crucible, and a crucible reproduction | regeneration method using the same are provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail. Here, a case where the crucible after the single crystal growth by the Czochralski method is subjected to the regeneration process using the heating furnace of the single crystal manufacturing apparatus is illustrated.

  FIG. 2 is a schematic cross-sectional view showing an example of a basic configuration of an apparatus used for single crystal growth based on the Czochralski method. This figure shows a state in which the single crystal 1 is pulled up by the rod 12 to form a straight body portion of the ingot.

(Single crystal manufacturing equipment)
A single crystal manufacturing apparatus 10 shown in FIG. 2 has a high-frequency induction heating furnace 14. The high frequency induction heating furnace 14 is a bottomed container having a cylindrical side wall having fire resistance. A high frequency induction coil 15 is wound around the side surface of the bottom of the high frequency induction heating furnace 14. A crucible 20 (for example, an iridium crucible) is disposed on the bottom surface inside the high-frequency induction heating furnace 14. The crucible 20 also serves as a high frequency induction heater. Then, when aluminum oxide as a raw material of the sapphire single crystal 1 is put into the crucible 20 and high frequency induction is applied to the high frequency induction coil 15, the crucible 20 is heated and an aluminum oxide melt 18 is obtained.

  In the center of the bottom of the high frequency induction heating furnace 14, an opening (not shown) penetrating from the inside of the high frequency induction heating furnace 14 to the outside is provided. The crucible support bar 16 is inserted from the outside of the high frequency induction heating furnace 14 through the opening, and the tip of the crucible support bar 16 is connected to the bottom of the crucible 20. By rotating the crucible support rod 16, the crucible 20 can be rotated in the high frequency induction heating furnace 14. A space between the opening and the crucible support rod 16 is sealed with packing or the like.

(Method of removing aluminum oxide solidified in the crucible)
When the production of the sapphire single crystal is completed and the crucible 20 is taken out from the high-frequency induction heating furnace 14, the solid material S (hereinafter “removal” in some cases) is formed on the inner surface of the crucible 20 by solidifying the remaining aluminum oxide melt 18. The target substance S ”is fixed. Depending on the growing conditions and the like, the crucible 20 may be significantly deformed as shown in FIG.

  In order to remove the removal target substance S adhered to the inner surface of the crucible 20, in this embodiment, calcium oxide that forms a liquid phase at a temperature lower than the melting point of the removal target substance S is used together with the removal target substance S ( (See phase diagram shown in FIG. 3). The reason for using calcium oxide is that, as described above, calcium oxide has the action of lowering the melting point of aluminum oxide, and by adding calcium oxide to aluminum oxide, compared with the solidified product of aluminum oxide alone, This is because a mixed solid having low mechanical strength and chemical resistance can be obtained.

  The removal process of the removal target substance S containing aluminum oxide as a main component includes a supply process of supplying calcium oxide into the crucible 20 and melting the removal target substance S and calcium oxide in the crucible 20 by heating the crucible 20. After that, the heat treatment step of cooling to obtain these mixed solids in the crucible 20 and the removing step of removing the mixed solids in the crucible 20 by mechanical treatment and / or chemical treatment are performed. .

  The supplying step is a step of supplying calcium oxide into the crucible 20 so that the removal target substance S and calcium oxide are in contact with each other. From the viewpoint of lowering the temperature conditions in the heat treatment step, in the supply step, a predetermined amount of calcium oxide is supplied so that the molar ratio of aluminum oxide and calcium oxide in the crucible 20 is the molar ratio at these eutectic points. Is preferred.

  Since the removal target substance S and calcium oxide react and melt at the contact points between them, the calcium oxide is preferably in the form of a powder having a large contact area or a liquid melted in advance. In addition, since calcium oxide has a water absorption property and is a relatively unstable substance, it is preferable to employ calcium carbonate as a substance that is actually put into the crucible 20. When calcium carbonate is heated to about 900 ° C., it decomposes into calcium oxide and carbon dioxide.

  The heat treatment step is a step of obtaining a mixed solid containing aluminum oxide and calcium oxide in the crucible 20. In this heat treatment step, the output of the heating furnace 14 is adjusted so as to be equal to or higher than the melting point of the mixture of the substance S to be removed and calcium oxide. The heating temperature is preferably not higher than the melting point of the removal target substance S. If the heating temperature exceeds the melting point of the substance S to be removed, the crucible 20 may be locally heated to a temperature near or above the melting point of iridium, and even if such a situation does not occur, the crucible 20 There is a tendency to deteriorate under the influence of heat. Heating in the heat treatment step is desirably performed in an inert gas atmosphere in order to prevent the metal crucible from being deteriorated by oxidation, and the oxygen concentration in the atmosphere is preferably 5% by volume or less, preferably 1 volume. % Or less is more preferable.

  The removing step is a step of removing the mixed solid in the crucible 20. In this embodiment, the mixed solid in the crucible 20 is removed by subjecting the cooled crucible 20 to mechanical treatment and / or chemical treatment after the heat treatment step. Depending on the mechanical strength and chemical resistance of the mixed solid, first, the mixed solid is generally removed by mechanical treatment using a tool such as an electric drill, and then the remaining mixed solid is further removed by chemical treatment. preferable.

  Specific examples of the chemical treatment method include a method of immersing the crucible 20 in phosphoric acid at 150 to 350 ° C. or hydrofluoric acid at 20 ° C. or less for about 10 to 100 minutes. The mixed solid containing calcium oxide is easily removed by chemical treatment because the etching rate is about 10 to 100 times faster than the case of the removal target substance S alone.

  According to the method for removing aluminum oxide according to the present embodiment, the mechanical strength and chemical resistance of aluminum oxide can be reduced by the action of calcium oxide, and the aluminum oxide adhering to the crucible 20 is efficiently removed. be able to. Moreover, since the heat processing temperature in the said removal method can be implemented at temperature lower than melting | fusing point of aluminum oxide, deterioration by the heat of the crucible 20 can fully be suppressed. The crucible 20 that has been subjected to the removal process is finally regenerated after being subjected to a process of correcting deformation as required.

  The preferred embodiment of the present invention has been described in detail above, but the present invention is not limited to the above embodiment. For example, in the above embodiment, the Czochralski method is exemplified as the crystal growth, but the removal method and the regeneration method according to the present invention are applied to other crystal growth methods and crucibles used for manufacturing ceramics other than single crystals. You may apply to.

  Moreover, although the high frequency induction heating furnace 14 was illustrated as a heating means of the crucible 20, a resistance heater etc. may be employ | adopted instead of or with this.

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to an Example.

Example 1
In an iridium crucible having a diameter of 80 mm, 900 g of an aluminum oxide raw material (melting point: about 2050 ° C.) was melted to obtain an aluminum oxide melt. When a single crystal was grown using this melt, about 640 g of a single crystal ingot was obtained. On the other hand, about 260 g (aluminum oxide: about 2.5 mol) of a solid substance mainly composed of aluminum oxide remained in the crucible taken out from the heating furnace.

  About 430 g (about 4.3 mol) of calcium carbonate, which generates calcium oxide by thermal decomposition, was put in a crucible in which aluminum oxide remained, and then the crucible was put in a heating furnace and heated to about 1600 ° C. Heating was performed under a nitrogen atmosphere. After confirming that it was melted by the image of the camera installed above the heating furnace, cooling was started.

  The removal process of the solid substance (about 490 g) remaining in the crucible taken out from the heating furnace was performed as follows. That is, the removal process in the present embodiment was performed using a power drill and removing a solid substance while applying a physical impact. Since the solid material has a relatively low mechanical strength, the work time required to sufficiently remove the solid material was within 2 hours. Thereafter, the inner surface of the crucible was chemically etched with phosphoric acid at 300 ° C. for 30 minutes in order to remove the thin solid material remaining on the inner surface of the crucible. These treatments allowed the solid material to be completely removed from the inner surface of the crucible. The iridium crucible regenerated in this way was not damaged and could be used again for crystal growth.

(Comparative Example 1)
In an iridium crucible having a diameter of 50 mm, 250 g of an aluminum oxide raw material (melting point: about 2050 ° C.) was melted to obtain an aluminum oxide melt. When a single crystal was grown using this melt, about 170 g of a single crystal ingot was obtained. On the other hand, about 80 g of a solid substance mainly made of aluminum oxide remained in the crucible taken out from the heating furnace. In order to remove the solid material, the inside of the crucible was chemically etched with phosphoric acid at 300 ° C. In this comparative example, when the treatment was continued by exchanging phosphoric acid every 5 hours, a total treatment time of 80 hours was required until the solid substance was sufficiently removed.

(Comparative Example 2)
In the same manner as in Example 1, after single-crystal growth of aluminum oxide was performed, 500 g of the solid substance remaining in the iridium crucible (diameter 110 mm) was removed as follows. That is, in the removal process in this comparative example, a solid substance was removed while applying a physical impact using an electric drill. It took 20 hours to fully remove the solid material. Thereafter, the inner surface of the crucible was chemically etched with phosphoric acid at 300 ° C. for 30 minutes in order to remove the thin solid material remaining on the inner surface of the crucible. These treatments removed the solid material completely, but the iridium crucible was found to have scratches and cracks due to physical impact, and must be repaired before being used again for crystal growth. there were.

(A), (b) is sectional drawing which respectively shows the crucible made from iridium before using and after being used for single crystal growth. It is a schematic cross section which shows an example of the basic composition of the apparatus used for manufacture of a single crystal ingot. It is a binary phase diagram of calcium oxide (CaO) and aluminum oxide (Al ₂ O ₃ ).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Single crystal, 10 ... Single crystal manufacturing apparatus, 14 ... High frequency induction heating furnace, 15 ... High frequency induction coil, 16 ... Crucible support rod, 18 ... Aluminum oxide melt, 20 ... Crucible, S ... Solid substance (substance to be removed) ).

Claims (2)

A method for removing aluminum oxide solidified in a crucible and adhering to the inner surface of the crucible,
A supplying step of supplying calcium oxide into the crucible;
A heat treatment step of heating the crucible to melt the aluminum oxide and calcium oxide in the crucible and then cooling to obtain a mixed solid in the crucible;
Removing the mixed solid in the crucible by mechanical treatment or chemical treatment, or both treatments; and
A method comprising the steps of: A crucible playing method for playing used crucibles,
A method for regenerating a crucible, comprising the step of removing aluminum oxide solidified in the crucible and adhering to the inner surface of the crucible by the method according to claim 1.

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