JP7095403B2 - Heat treatment method for oxide single crystal - Google Patents

Description

In the present invention, an oxide single crystal ingot grown by a pulling method such as the Czochralski method (hereinafter abbreviated as Cz method) is housed in a ceramic container, and the ceramic container is placed in a flat hearth in a heating furnace. It is related to the method of heat-treating the oxide single crystal ingot while it is placed on a table to alleviate the "thermal strain" of the oxide single crystal ingot, and in particular, even if the oxide single crystal ingot to be treated becomes large (that is,). It relates to a heat treatment method for an oxide single crystal that avoids non-uniform heat treatment and damage to a ceramic container (even if the diameter of the ingot becomes large).

Oxide single crystals such as lithium tantalate (hereinafter abbreviated as LT) single crystal and lithium niobate (hereinafter abbreviated as LN) single crystal are generally grown by using a pulling method such as the Cz method. .. The Cz method is a method in which a seed crystal is brought into contact with a raw material melt in a crucible, and the seed crystal is pulled up while rotating to grow a single crystal in the same direction as the seed crystal. In the Cz method, crystal growth proceeds by solidifying the growth interface, so that a temperature gradient is generated between the previously solidified portion and the growth interface. Then, by creating a temperature gradient, "thermal strain" due to the temperature difference is introduced into the crystal that has been grown.

When the above "heat strain" is introduced into the grown crystal, cracks are generated in the subsequent processing step. Therefore, the oxide single crystal grown by the Cz method is subjected to annealing treatment (heat treatment) at a temperature below the melting point. This is done to alleviate the above "heat distortion". In the annealing treatment, it is preferable to keep the entire crystal at a uniform temperature, and in particular, in the single crystal growth by the Cz method, a large "thermal strain" is introduced near the boundary between the crystal shoulder portion and the crystal straight body portion where the change in diameter is large. Therefore, it is preferable to make the temperature difference between the crystal shoulder portion and the crystal straight body portion as small as possible in the annealing treatment.

Since single crystals of LT (melting point: about 1650 ° C.) and LN (melting point: about 1250 ° C.) are annealed at a temperature exceeding 1000 ° C., an electric furnace equipped with a resistance heating type heater is generally selected. To. As the heating element of the electric furnace, molybdenum disilicate or silicon carbide is selected according to the annealing temperature, but the heating element is not limited to these.

In the annealing treatment, the entire crystal is kept at a uniform temperature for a long time, and the temperature is slowly cooled so that the temperature difference does not occur again, and the temperature is returned to room temperature to alleviate "heat distortion" and prevent cracks in the subsequent processing process. Therefore, it is necessary to keep the temperature uniform under high temperature.

By the way, in the annealing treatment (heat treatment) of the oxide single crystal ingot having a crystal shoulder portion and a crystal straight body portion, the heat treatment is performed by accommodating the ingot in a ceramic container and covering the entire ingot with the container. However, cracks may occur in the ingot at the portion where the oxide single crystal ingot and the ceramic container are in contact with each other. It is considered that this cause is caused by the thermal non-uniformity of the contact portion in the oxide single crystal ingot and the stress non-uniformity due to the own weight of the oxide single crystal ingot.

Therefore, in Patent Document 1, as shown in FIG. 5, a cylinder having an inner bottom surface in which the upper portion is open and five groups of small lumps having a lump diameter of 2 mm or more and less than 10 mm, which are made of the same material as the oxide single crystal ingot, are spread. The lower member 9 has an inner wall surface and a top wall surface that cover the entire oxide single crystal ingot 1 housed in the lower member 9 of the shape and the inner bottom surface of the lower member 9 via a group of small lumps. A ceramic container is formed by the tubular upper member 8 to be fitted, and the ceramic container containing the oxide single crystal ingot is placed directly on the flat hearth 6 of the electric furnace (not shown). A method has been proposed in which heat treatment is performed in this state to alleviate the "thermal strain" of the oxide single crystal ingot, and as shown in FIG. 6, a mass having an open upper portion and made of the same material as the oxide single crystal ingot. A cylindrical lower member 12 having an inner bottom surface in which five groups of small lumps having a diameter of 2 mm or more and less than 10 mm are spread, and the middle member 11 and the upper member 10 are fitted to form a ceramic container. Similarly, a method for alleviating the "thermal strain" of the oxide single crystal ingot has been proposed.

According to the heat treatment method for the oxide single crystal proposed in Patent Document 1, the group 5 of the small lumps has a significantly larger lump diameter than the conventional powder composed of the oxide single crystal, and therefore, under high temperature conditions. Since the lithium (Li) component (components constituting LT and LN single crystals) is unlikely to volatilize and the surface area of the small lump 5 is small, even if the ceramic container and the small lump 5 come into direct contact with each other, the container and the small lump 5 are in direct contact with each other. Since the reaction between the 5 is unlikely to occur and the diameter of the small lump 5 is less than 10 mm, the oxide single crystal ingot housed in the ceramic container does not collapse during the heat treatment. Therefore, the oxide single crystal ingot can be stably housed in an inexpensive ceramic container, and the entire oxide single crystal ingot is covered with the ceramic container, which causes uneven heating of the ingot and deterioration of the ceramic container. It was a method of alleviating the "thermal strain" of the oxide single crystal ingot without causing it.

By the way, with the spread of smart phones and the like in recent years, the market for surface elastic wave filters (hereinafter abbreviated as SAW filters) for mobile communication devices continues to expand, and the above-mentioned LTs and LNs, which are materials for SAW filters, etc. Demand for single crystal substrates is also growing. In order to reduce the cost of the SAW filter manufacturing process, the size of oxide single crystal substrates such as LT and LN has been increased from the conventional φ3 inch to φ4 inch and φ6 inch, and the oxides grown. The single crystal ingot is getting larger (that is, the diameter of the ingot is getting bigger). The conventional oxide single crystal size did not cause a problem, but as the size of the grown oxide single crystal ingot increased, the heat treatment for the ingot was non-uniform and the ceramic container was damaged (crack on the bottom of the container). Etc. have occurred.

Japanese Unexamined Patent Publication No. 2017-193453

In the annealing treatment (heat treatment) of the oxide single crystal, there is a problem that cracks occur on the bottom surface of the container when the grown oxide single crystal becomes large (that is, the diameter of the single crystal becomes large). It is considered that the ceramic container became larger in accordance with the converted oxide single crystal, so that a temperature difference occurred between the central portion and the outer peripheral portion on the bottom surface of the ceramic container.

When a temperature difference begins to occur between the central portion and the outer peripheral portion of the bottom surface of the container, the heat treatment for the oxide single crystal becomes non-uniform, so that cracks are likely to occur in the oxide single crystal and cracks also occur in the bottom surface of the container. This makes it difficult to retain the oxide single crystal.

The present invention has been made by paying attention to such a problem, and the problem thereof is that even if the oxide single crystal (oxide single crystal ingot) to be treated becomes large, the heat treatment is non-uniform and the ceramic container is made. It is an object of the present invention to provide a heat treatment method for an oxide single crystal in which damage and the like are avoided.

As a result of diligent research by the present inventor in order to solve the above problems, the fitting method of the ceramic container adopted in Patent Document 1 has been changed, and the flat hearth base in the heating furnace is made of ceramic. After changing to a method in which the container is not placed directly, it was discovered that even if the oxide single crystal (oxide single crystal ingot) to be treated becomes large, non-uniform heat treatment and damage to the ceramic container can be avoided. .. The present invention has been completed based on such technical discoveries.

That is, the first invention according to the present invention is
The oxide single crystal ingot grown by the pulling method is housed in a ceramic container, and the above container is placed on a flat hearth pedestal installed in a heating furnace to heat the oxide single crystal ingot in the container. In the heat treatment method for oxide single crystals
An inner container composed of the same material as the oxide single crystal ingot and having a mass diameter of 2 mm or more and less than 10 mm spread on the inner bottom surface and accommodating the oxide single crystal ingot via the small mass group, and the inner container. The ceramic container is composed of an outer cylinder having an inner diameter larger than the outer diameter of the inner container and arranged so as to surround the outer peripheral surface of the oxide single crystal ingot housed in the inner container.
A plate-shaped spacer is interposed between the flat hearth pedestal and the inner container and the outer cylinder placed on the hearth pedestal, and the plate-shaped spacer is placed in the heating furnace to the center of the outer bottom surface of the inner container. By forming a vent to supply and discharge the heated air, the heated air in the heating furnace is supplied to the exposed outer bottom surface of the inner container, and the heated air is sent from the gap between the inner container and the outer cylinder. It is characterized in that the oxide single crystal ingot is heat-treated by supplying it into the outer cylinder.

Further, the second invention according to the present invention is
In the heat treatment method for an oxide single crystal according to the first invention,
The plate-shaped spacer is made of the same ceramic material as the above container.
The third invention is
In the method for heat-treating an oxide single crystal according to the first invention or the second invention.
The area of the outer bottom surface of the inner container in contact with the plate-shaped spacer is 10% or more and 50% or less of the total area of the outer bottom surface.

Next, the fourth invention according to the present invention is
In the heat treatment method for an oxide single crystal according to any one of the first invention to the third invention.
It is characterized in that the plate-shaped spacer is composed of a plurality of plate materials so that two or more vents for supplying and discharging heated air are symmetrically formed in the central portion of the outer bottom surface of the exposed inner container.
The fifth invention is
In the heat treatment method for an oxide single crystal according to any one of the first to fourth inventions.
The plate-shaped spacer is characterized in that the thickness is set to 10 mm or more.
Moreover, the sixth invention is
In the heat treatment method for an oxide single crystal according to any one of the first invention to the fifth invention.
The oxide single crystal is characterized by being composed of a lithium tantalate single crystal or a lithium niobate single crystal.

The present invention relates to the present invention in which an oxide single crystal ingot grown by a pulling method is housed in a ceramic container, and the ceramic container is placed on a flat hearth in a heating furnace to heat the oxide single crystal ingot. The heat treatment method is
An inner container composed of the same material as the oxide single crystal ingot and having a mass diameter of 2 mm or more and less than 10 mm spread on the inner bottom surface and accommodating the oxide single crystal ingot via the small mass group, and the inner side thereof. The ceramic container is composed of an outer cylinder having an inner diameter larger than the outer diameter of the container and arranged so as to surround the outer peripheral surface of the oxide single crystal ingot housed in the inner container, and the flat shape. A plate-shaped spacer is interposed between the hearth and the inner container and the outer cylinder placed on the hearth, and the plate -shaped spacer is heated to the center of the outer bottom surface of the inner container. The heated air in the heating furnace is supplied to the exposed outer bottom surface of the inner container by forming a vent for supplying and discharging the air, and the heated air is supplied from the gap between the inner container and the outer cylinder inside the outer cylinder. It is characterized in that the oxide single crystal ingot is heat-treated by supplying it to the container.

According to the heat treatment method according to the present invention, the heated air in the heating furnace is supplied to the exposed inner bottom surface of the inner container, so that the central portion and the peripheral portion of the outer bottom surface of the inner container can be heated evenly. Moreover, since the heated air in the heating furnace is supplied into the outer cylinder through the gap between the inner container and the outer cylinder, the oxidation housed in the ceramic container composed of the inner container and the outer cylinder. It is possible to uniformly heat a single crystal ingot.

Explanatory drawing which shows the heat treatment method of the oxide single crystal which concerns on Example 1 of this invention. Explanatory drawing which shows the heat treatment method of the oxide single crystal which concerns on Example 2 of this invention. Ceramic according to Example 1 composed of a plate-shaped spacer composed of four arc-shaped plate materials, an inner container placed on a flat hearth stand with the plate-shaped spacer interposed therebetween, and an outer cylinder. Bottom view of the container. It is composed of a plate-shaped spacer made of one ceramic plate material having a flat C-shaped shape, an inner container and an outer cylinder placed on a flat hearth stand with the plate-shaped spacer interposed therebetween. The bottom view of the ceramic container which concerns on Example 5. It is explanatory drawing which shows the heat treatment method of the oxide single crystal using the ceramic container composed of the lower member and the upper member of Patent Document 1. It is explanatory drawing which shows the heat treatment method of the oxide single crystal using the ceramic container composed of the lower member, the middle member and the upper member of Patent Document 1.

Hereinafter, embodiments of the present invention will be described in detail.

(1) Heat Treatment Method for Oxide Single Crystal According to the Present Invention In the heat treatment method for the oxide single crystal according to the present invention, the oxide single crystal ingot grown by the pulling method is housed in a ceramic container as described above. , The same material as the oxide single crystal ingot in the method of heat treatment of the oxide single crystal in which the container is placed on a flat furnace bed installed in the heating furnace and the oxide single crystal ingot in the container is heat-treated. An inner container composed of 2 mm or more and less than 10 mm in diameter is spread on the inner bottom surface and an oxide single crystal ingot is housed through the small mass group, and an inner diameter larger than the outer diameter of the inner container. The ceramic container is composed of an outer cylinder having and arranged so as to surround the outer peripheral surface of the oxide single crystal ingot housed in the inner container, and the flat hearth stand and the furnace are used. A plate-shaped spacer is interposed between the inner container and the outer cylinder placed on the floor, and the plate-shaped spacer is provided with a vent for supplying and discharging the heated air in the heating furnace to the center of the outer bottom surface of the inner container. The heated air in the heating furnace is supplied to the outer bottom surface of the inner container that is formed and exposed, and the heated air is supplied from the gap between the inner container and the outer cylinder into the outer cylinder to supply a simple oxide. It is characterized by heat-treating a crystalline ingot.

(2) Ceramic container The material of the ceramic container composed of the inner container and the outer cylinder is not particularly limited, and can be arbitrarily selected according to the annealing temperature and the shape. For example, one or more materials selected from alumina (aluminum oxide), zirconia (zirconium oxide), magnesia, mullite, silicon carbide and the like can be used.

The shape of the ceramic container composed of the inner container and the outer cylinder is circular or polygonal so that the diameter or inscribed circle is 1.2D to 2.0D with respect to the diameter D of the oxide single crystal ingot. By making it rectangular, it is possible to prevent the ceramic container and the oxide single crystal ingot from coming into direct contact with each other without impairing the filling rate of the electric furnace. Further, by setting the height of the outer cylinder to 1.1H to 1.5H with respect to the total length H of the oxide single crystal ingot, the outer peripheral surface of the oxide single crystal ingot housed in the inner container is the outer cylinder. Since it is surrounded by, it is possible to prevent uneven heating of the oxide single crystal ingot.

During the annealing treatment (heat treatment), the outer periphery of the oxide single crystal ingot housed in the inner container is prevented from directly irradiating the oxide single crystal ingot with the heat rays from the heating element of the heat treatment heating furnace. It is necessary to make the surface surrounded by the outer cylinder.

Further, it is required that the inner diameter of the outer cylinder is larger than the outer diameter of the inner container. This is because the heated air in the heat treatment heating furnace is supplied from the gap between the inner container and the outer cylinder into the outer cylinder to heat-treat the oxide single crystal ingot.

(3) Plate-shaped spacer The material of the plate-shaped spacer interposed between the flat hearth pedestal in the heating furnace for heat treatment and the inner container and the outer cylinder placed on the hearth pedestal is particularly limited. It can be arbitrarily selected according to the annealing temperature and shape. For example, one or more materials selected from alumina (aluminum oxide), zirconia (zirconium oxide), magnesia, mulite, silicon carbide and the like can be used, but the same material as the ceramic container is more preferable.

Further, the shape of the plate material constituting the plate-shaped spacer is not particularly limited, and the shape can be appropriately selected according to the usage situation. For example, the shape can be selected from a square, a rectangle, a round shape, a fan shape, and the like.

When the area of the outer bottom surface of the inner container in contact with the plate-shaped spacer is large, the area of the outer bottom surface of the inner container exposed is small, so that the heating effect of the outer bottom surface of the inner container by the heated air is reduced. Therefore, the area of the outer bottom surface of the inner container in contact with the plate-shaped spacer is preferably 10% or more and 50% or less of the total area of the outer bottom surface.

In addition, regarding the number of vents (voids) for supplying and discharging the heated air in the heating furnace to the central part of the outer bottom surface of the inner container that is exposed, there are two or more places so that the heated air can be efficiently supplied and discharged. It is preferable that two or more vents are formed symmetrically in the vertical and horizontal directions.

The thickness of the plate-shaped spacer is preferably 10 mm or more so as to have sufficient resistance to the load of the inner container containing the oxide single crystal ingot, and the plate-shaped spacer is a plurality of plate materials. It is desirable that the thickness of each plate material is the same when it is composed of.

(4) Small lumps spread on the inner bottom surface of the inner container The small lumps made of the same material as the oxide single crystal ingot are lumps produced by crushing single crystals of LT (LiTaO ₃ ) or LN (LiNbO ₃ ). It means a mass of oxide single crystals having a diameter of 2 mm or more and less than 10 mm.

Small lumps of oxide single crystals having a lump diameter of 2 mm or more and less than 10 mm have a significantly larger lump diameter than conventional powders composed of oxide single crystals, and therefore have a lithium (Li) component (LT) under high temperature conditions. Since volatilization of (components constituting LN single crystals) is unlikely to occur and the surface area of the small lumps is small, even if the ceramic container and the small lumps come into direct contact with each other, the reaction between the container and the small lumps is unlikely to occur (that is, ceramic). (Since it has poor reactivity with the container, the chemical deterioration of the container is suppressed), and since the mass diameter of the small mass is less than 10 mm, the oxide single crystal ingot contained in the inner container collapses during the heat treatment. There is no such thing.

If the lump diameter is less than 2 mm, the surface area of the lump increases and the reactivity with the inner container increases. Further, when the lump diameter of the small lump is 10 mm or more, the placement of the oxide single crystal ingot becomes unstable, and the oxide single crystal ingot collapses during the heat treatment, which causes a crack defect.

(5) Oxide single crystal An oxide single crystal premised on a heat treatment method for an oxide single crystal, and examples thereof include lithium tantalate (LT: LiTaO ₃ ) and lithium niobate (LN: LiNbO ₃ ).

Hereinafter, examples of the present invention will be specifically described with reference to comparative examples, but the technical configuration according to the present invention is not limited to the configurations of these examples.

[Example 1]
As shown in FIG. 1, the ceramic container used in this embodiment is an inner container 3 having an outer diameter of φ260 mm, a height of 45 mm, and a container thickness of 5 mm, which has an inner bottom surface in which the upper part is open and 5 groups of small lumps are spread. And is arranged so as to surround the outer peripheral surface of the LT single crystal ingot (6 inch diameter) 1 having an inner diameter larger than the outer diameter of the inner container 3 and being housed on the inner bottom surface of the inner container 3 via a group of small lumps 5. It is composed of an outer cylinder 2 having an inner diameter of 280 mm, a height of 280 mm, and a cylinder thickness of 5 mm.

Further, in the ceramic container composed of the inner container 3 and the outer cylinder 2, a plate-shaped spacer 4 is interposed in a flat furnace bed 6 in an electric furnace (not shown) equipped with a resistance heating type heater. The outer bottom surface of the inner container 3 is exposed and the outer bottom surface is exposed to the heated air (hereinafter referred to as “heated air”) in the electric furnace.

The material of the ceramic container was alumina (aluminum oxide). Further, as shown in FIG. 3, the plate-shaped spacer 4 is composed of four arc-shaped plate materials, the material of which is the same as that of the ceramic container, and the thickness of the arc-shaped plate material is 10 mm. Further, the small lump 5 is made of the same material as the LT single crystal, the LT single crystal is crushed, the coarse single crystal is removed by a sieve having a mesh opening of 10 mm, and the fine crystal is formed by a sieve having a mesh opening of 2 mm. After removing the powder to obtain a small lump group having a lump diameter of about 2 mm to 10 mm, the inner bottom surface of the inner container 3 is spread so that the thickness of the small lump group layer is 30 mm. Further, in FIG. 3, reference numeral d indicates a gap due to the difference between the inner diameter of the outer cylinder 2 and the outer diameter of the inner container 3.

Then, as shown in FIG. 3, four arc-shaped plate materials constituting the plate-shaped spacer 4 are arranged so that the inner container 3 and the outer cylinder 2 constituting the ceramic container can both be placed on the plate-shaped spacer 4. The inner container 3 placed on a flat hearth (not shown) and having 5 small lumps spread on the inner bottom surface is placed on 4 arcuate plates, and the 5 small lumps are placed through the 5 small lumps. After accommodating the LT single crystal ingot 1 in the inner bottom surface of the inner container 3, the outer tubular body 2 was placed on four arcuate plates so as to surround the outer peripheral surface of the LT single crystal ingot 1.

At this time, the area of the outer bottom surface of the inner container 3 in contact with the plate-shaped spacer 4 composed of the four arcuate plate materials is adjusted to be 10% of the total area of the outer bottom surface, and the outer bottom surface of the inner container 3 is adjusted. By arranging the four arcuate plate materials symmetrically in the vertical and horizontal directions with respect to the outer peripheral portion, four vents (voids) for supplying and discharging heated air are formed symmetrically in the vertical and horizontal directions on the outer bottom surface of the inner container 3. Has been done.

Then, an annealing treatment (heat treatment) was carried out at a temperature of 1400 ° C. for 40 hours in the electric furnace equipped with a resistance heating type heater.

When the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined after the annealing treatment (heat treatment) was completed, no cracks or deterioration were confirmed, and the LT single crystal contained in the inner container 3 was not confirmed. No cracks were found in Ingot 1. Further, the four arc-shaped plate materials (ceramic plate-shaped spacer 4) interposed between the ceramic container composed of the inner container 3 and the outer cylinder 2 and the flat hearth 6 are LT single crystals. It was also confirmed that the ingot 1 was resistant to the load of the inner container 3 in which the ingot 1 was housed.

Then, when the annealing treatment (heat treatment) of the LT single crystal ingot was repeated 10 times under the same conditions as described above, 10 non-defective products could be obtained.

Furthermore, when the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined after repeating 10 times, no cracks or deterioration were confirmed, and the four arcuate plates were also damaged. Etc. were not confirmed.

[Example 2]
The LT single crystal ingot was annealed (heat-treated) in the same manner as in Example 1 except that the outer cylinder 7 shown in FIG. 2 with the upper end side closed was applied, and the inner container 3 after the annealing treatment (heat treatment) was completed. When the appearance of the outer cylinder 7 and the inner bottom surface of the inner container 3 were examined, no cracks or deterioration were confirmed, and no cracks were confirmed in the LT single crystal ingot 1 housed in the inner container 3. Further, the four arc-shaped plate materials (ceramic plate-shaped spacer 4) interposed between the ceramic container composed of the inner container 3 and the outer cylinder 7 and the flat hearth 6 are LT single crystals. It was also confirmed that the ingot 1 was resistant to the load of the inner container 3 containing the ingot 1.

Then, when the annealing treatment (heat treatment) of the LT single crystal ingot was repeated 10 times in the same manner as in Example 1, 10 non-defective products could be obtained as in Example 1.

Further, when the appearance of the inner container 3 and the outer cylinder 7 and the inner bottom surface of the inner container 3 were examined after repeating 10 times, no crack or deterioration was confirmed, and the four arcuate plates were also damaged. Etc. were not confirmed.

[Example 3]
LT single crystal in the same manner as in Example 1 except that the area of the outer bottom surface of the inner container 3 in contact with the plate-shaped spacer 4 composed of four arcuate plate materials is adjusted to be 50% of the total area of the outer bottom surface. When the ingot was annealed (heated) and the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined after the annealing treatment (heat treatment) was completed, no cracks or deterioration were confirmed. No crack was confirmed in the LT single crystal ingot 1 housed in the inner container 3. Further, the four arc-shaped plate materials (ceramic plate-shaped spacer 4) interposed between the ceramic container composed of the inner container 3 and the outer cylinder 2 and the flat hearth 6 are LT single crystals. It was also confirmed that the ingot 1 was resistant to the load of the inner container 3 containing the ingot 1.

Then, when the annealing treatment (heat treatment) of the LT single crystal ingot was repeated 10 times in the same manner as in Example 1, 10 non-defective products could be obtained as in Example 1.

Further, when the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined after repeating 10 times, no crack or deterioration was confirmed, and the four arcuate plates were also damaged. Etc. were not confirmed.

[Example 4]
LT single crystal in the same manner as in Example 1 except that the area of the outer bottom surface of the inner container 3 in contact with the plate-shaped spacer 4 composed of four arcuate plate materials is adjusted to be 60% of the total area of the outer bottom surface. When the ingot was annealed (heated) and the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined after the annealing treatment (heat treatment) was completed, no cracks or deterioration were confirmed. No crack was confirmed in the LT single crystal ingot 1 housed in the inner container 3. Further, the four arc-shaped plate materials (ceramic plate-shaped spacer 4) interposed between the ceramic container composed of the inner container 3 and the outer cylinder 2 and the flat hearth 6 are LT single crystals. It was also confirmed that the ingot 1 was resistant to the load of the inner container 3 containing the ingot 1.

Then, when the annealing treatment (heat treatment) of the LT single crystal ingot was repeated 10 times in the same manner as in Example 1, eight good products could be obtained, but the two LT single crystal ingots were slightly slightly different. A crack was confirmed. The reason why the treatment effect is slightly inferior to that of Example 1 is that the area of the outer bottom surface of the inner container 3 in contact with the plate-shaped spacer 4 is as large as 60% of the total area of the outer bottom surface, so that it is compared with Example 1. It is probable that the heating effect of the outer bottom surface by the heated air was reduced by the amount that the area of the outer bottom surface of the inner container 3 exposed was reduced.

Further, when the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined after repeating 10 times, some cracks were confirmed, but damage to the arcuate plate material was confirmed. There wasn't.

[Example 5]
The ceramic plate-shaped spacer 4 interposed between the ceramic container composed of the inner container 3 and the outer cylinder 2 and the flat hearth 6 is a single vent (void) as shown in FIG. The LT single crystal ingot is annealed (heated) in the same manner as in Example 1 except that it is composed of one ceramic plate material having a flat surface C character shape to form the above, and after the annealing treatment (heat treatment) is completed. When the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined, some cracks and deterioration were confirmed, but cracks were found in the LT single crystal ingot 1 housed in the inner container 3. Not confirmed. Further, the LT single crystal ingot 1 is a ceramic plate-shaped spacer 4 having a flat C-shaped shape interposed between the ceramic container composed of the inner container 3 and the outer cylinder 2 and the flat hearth base 6. It was also confirmed that the inner container 3 contained was resistant to the load.

Then, when the annealing treatment (heat treatment) of the LT single crystal ingot was repeated 10 times in the same manner as in Example 1, 6 good products could be obtained, but cracks were found in the 4 LT single crystal ingots. confirmed. The reason why the treatment effect is inferior to that of Example 1 is that the ceramic plate-shaped spacer 4 having a flat C-shaped shape is applied, so that the vents (voids) become single, and a single vent (void). ) Reduces the amount of heated air supplied and discharged to the outer bottom surface of the inner container 3, the heating effect of the outer bottom surface is reduced, and the air is supplied into the outer cylinder 2 through the gap between the inner container 3 and the outer cylinder 2. It is probable that the amount of heated air decreased.

Further, when the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined after repeating 10 times, cracks and radial damage were partially confirmed, but the flat surface C character shape was found. No damage or the like was confirmed in the ceramic plate-shaped spacer 4 having the above.

[Example 6]
The LT single crystal ingot was annealed (heat-treated) in the same manner as in Example 1 except that the thickness of each arc-shaped plate constituting the ceramic plate-shaped spacer 4 was 5 mm, and after the annealing treatment (heat treatment) was completed. When the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined, no cracks or deterioration were confirmed, and cracks were also confirmed in the LT single crystal ingot 1 housed in the inner container 3. Was not done. However, the thickness of the four arc-shaped plate materials (ceramic plate-shaped spacer 4) interposed between the ceramic container composed of the inner container 3 and the outer cylinder 2 and the flat hearth base 6 is 5 mm. It was also confirmed that the resistance to the load of the inner container 3 containing the LT single crystal ingot 1 was slightly inferior due to the thinness.

Then, when the annealing treatment (heat treatment) of the LT single crystal ingot was repeated 10 times in the same manner as in Example 1, 10 non-defective products could be obtained as in Example 1.

Further, when the appearance of the inner container 3 and the outer cylinder 2 and the inner bottom surface of the inner container 3 were examined after repeating 10 times, no cracks or deterioration were confirmed, but the four arcuate plates were damaged. Etc. were confirmed.

[Comparative Example 1]
As shown in FIG. 5, the ceramic container used in Comparative Example 1 has a tubular lower member 9 having an inner bottom surface in which the upper portion is open and the same group of 5 small lumps as in Example 1 is spread. It is composed of an inner wall surface covering the entire LT single crystal ingot 1 housed in the lower member 9 and a tubular upper member 8 having a top wall surface and fitted to the lower member 9, and these lower members. As the material of 9 and the upper member 8, the same alumina (aluminum oxide) as in Example 1 is used. Further, the shape of the lower member 9 is composed of a square box-shaped structure having a side of 200 mm and a height of 100 mm and an open upper portion, and the shape of the upper member 8 is also lower. It is the same as the side member 9.

Then, an LT single crystal ingot 1 having a diameter of 160 mm is spread on the inner bottom surface of the lower member 9 so that the thickness of the small mass 5 group layer is 30 mm, and the LT single crystal ingot 1 having a diameter of 160 mm is spread on the small mass 5 group layer as shown in FIG. After mounting, the upper member 8 having the same shape as the lower member 9 was fitted to the lower member 9 so that the entire LT single crystal ingot 1 was covered with a ceramic container.

Then, as shown in FIG. 5, the ceramic container containing the LT single crystal ingot 1 is directly placed on the flat hearth 6 in the electric furnace (not shown) without using the ceramic plate spacer. After that, an annealing treatment (heat treatment) was performed at a temperature of 1400 ° C. for 40 hours, and the appearance of the lower member 9 after the completion of the annealing treatment (heat treatment) and the inner bottom surface of the lower member 9 were examined. A crack and a partial breakage were confirmed in the central portion of the above, and a slight crack was also confirmed in the LT single crystal ingot 1 housed in the lower member 9. Further, it was also confirmed that as the diameter of the LT single crystal ingot 1 to be heat-treated becomes larger, the inner bottom surface of the lower member 9 is damaged and the LT single crystal ingot 1 is cracked.

Instead of the ceramic container of FIG. 5, a ceramic container composed of the lower member 12, the middle member 11, and the upper member 10 shown in FIG. 6 is applied, and an electric furnace (not shown) is applied. The same was true when the ceramic container was directly placed on the flat hearth 6 in) without using a ceramic plate spacer.

[Comparative Example 2]
A ceramic container (LT single crystal ingot 1) having the same structure as that of Example 1 is placed in a flat hearth 6 in an electric furnace (not shown) equipped with a resistance heating type heater without using a plate-shaped spacer 4. An annealing treatment (heat treatment) of the LT single crystal ingot was carried out in the same manner as in Example 1 except that the contained) was directly placed.

Then, when the appearance of the inner container 3 and the outer cylinder 2 after the annealing treatment (heat treatment) was completed and the inner bottom surface of the inner container 3 were examined, cracks were generated in the inner bottom surface of the inner container 3 and the inner bottom surface was damaged radially. It was confirmed that Further, no crack was confirmed in the LT single crystal ingot 1 housed in the inner container 3, but a part of the small lump 5 flowed out from the damaged inner bottom surface of the inner container 3, so that the LT single crystal ingot 1 was formed. It was leaning.

Further, the annealing treatment (heat treatment) of the LT single crystal ingot was carried out three times under the same conditions as described above, but cracks were generated on the inner bottom surface of the inner container 3 in all three times. In addition, cracks were confirmed in the LT single crystal ingot twice out of three times.

[Comparative Example 3]
A ceramic container (LT single crystal ingot 1) having the same structure as that of Example 2 is placed in a flat hearth 6 in an electric furnace (not shown) equipped with a resistance heating type heater without using a plate spacer 4. An annealing treatment (heat treatment) of the LT single crystal ingot was carried out in the same manner as in Example 2 except that the contained) was directly placed.

Then, when the appearance of the inner container 3 and the outer cylinder 7 after the annealing treatment (heat treatment) was completed and the inner bottom surface of the inner container 3 were examined, cracks were generated in the inner bottom surface of the inner container 3 and the inner bottom surface was damaged radially. It was confirmed that Further, no crack was confirmed in the LT single crystal ingot 1 housed in the inner container 3, but a part of the small lump 5 flowed out from the damaged inner bottom surface of the inner container 3, so that the LT single crystal ingot 1 was formed. It was leaning.

[Comparative Example 4]
The ceramic container composed of the inner container 3 and the outer cylinder 2 and the ceramic plate-shaped spacer 4 interposed between the flat hearth base 6 are composed of a ring-shaped ceramic plate material having a gap inside the main body. An annealing treatment (heat treatment) of the LT single crystal ingot was carried out in the same manner as in Example 1 except for the above.

Then, when the appearance of the inner container 3 and the outer cylinder 2 after the annealing treatment (heat treatment) was completed and the inner bottom surface of the inner container 3 were examined, cracks were generated in the inner bottom surface of the inner container 3 and the inner bottom surface was damaged radially. It was confirmed that In addition, cracks were also confirmed in the LT single crystal ingot 1 housed in the inner container 3.

When the ring-shaped ceramic plate material is applied, since there are no vents (voids) for supplying and discharging heated air to the outer bottom surface of the inner container 3, the supply of heated air to the outer bottom surface and the inside of the outer cylinder 2 is remarkable. Since the number is reduced, it is considered that the cracks are generated in the inner bottom surface of the inner container 3 and the LT single crystal ingot.

According to the heat treatment method for the oxide single crystal according to the present invention, the central portion and the peripheral portion of the outer bottom surface of the container containing the oxide single crystal can be heated evenly, so that the lithium tantalate single crystal or the lithium niobate single crystal can be heated evenly. It has industrial applicability used in heat treatment methods that alleviate the thermal strain of ingots.

d Gap due to the difference between the inner diameter of the outer cylinder 2 and the outer diameter of the inner container 3 1 LT single crystal ingot (oxide single crystal)
2 Outer cylinder 3 Inner container 4 Plate spacer 5 Small mass 6 Flat hearth base 7 Outer cylinder with the upper end closed 8 Upper member 9 Lower member 10 Upper member 11 Middle member 12 Lower member

Claims (6)

The oxide single crystal ingot grown by the pulling method is housed in a ceramic container, and the above container is placed on a flat hearth pedestal installed in a heating furnace to heat the oxide single crystal ingot in the container. In the heat treatment method for oxide single crystals
An inner container composed of the same material as the oxide single crystal ingot and having a mass diameter of 2 mm or more and less than 10 mm spread on the inner bottom surface and accommodating the oxide single crystal ingot via the small mass group, and the inner container. The ceramic container is composed of an outer cylinder having an inner diameter larger than the outer diameter of the inner container and arranged so as to surround the outer peripheral surface of the oxide single crystal ingot housed in the inner container.
A plate-shaped spacer is interposed between the flat hearth pedestal and the inner container and the outer cylinder placed on the hearth pedestal, and the plate-shaped spacer is placed in the heating furnace to the center of the outer bottom surface of the inner container. By forming a vent to supply and discharge the heated air, the heated air in the heating furnace is supplied to the exposed outer bottom surface of the inner container, and the heated air is sent from the gap between the inner container and the outer cylinder. A method for heat-treating an oxide single crystal, which comprises supplying it into an outer cylinder and heat-treating the oxide single crystal ingot. The method for heat-treating an oxide single crystal according to claim 1, wherein the plate-shaped spacer is made of the same ceramic material as the container. The heat treatment method for an oxide single crystal according to claim 1 or 2, wherein the area of the outer bottom surface of the inner container in contact with the plate-shaped spacer is 10% or more and 50% or less of the total area of the outer bottom surface. It is characterized in that the plate-shaped spacer is formed of a plurality of plate materials so that two or more vents for supplying and discharging heated air are symmetrically formed in the central portion of the outer bottom surface of the exposed inner container. The method for heat-treating an oxide single crystal according to any one of claims 1 to 3. The method for heat-treating an oxide single crystal according to any one of claims 1 to 4, wherein the thickness of the plate-shaped spacer is set to 10 mm or more. The heat treatment method for an oxide single crystal according to any one of claims 1 to 5, wherein the oxide single crystal is composed of a lithium tantalate single crystal or a lithium niobate single crystal.

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