JP2019202915A - Heat treatment method for oxide single crystal - Google Patents

Abstract

To provide a method of heat-treating an oxide single crystal in which a ceramic-made container houses an oxide single crystal ingot 1 raised in a lifting method, and is placed on a flat furnace bottom 6 of a heating furnace.SOLUTION: A ceramic-made container consists of an inside container 3 which has a group of pellets 5, made of the same material with an oxide single crystal, spread over an inner bottom face, and houses an ingot 1 across the group of pellets 5 interposed, and an outside cylinder body 2 which has an inner diameter larger than the external diameter of the inside container and is arranged surrounding an outer peripheral surface of the ingot. While a plate-like spacer 4 is interposed between the flat furnace bottom 6 and the inside container and outside cylinder body mounted on the flat furnace bottom, heating air in a heating furnace is supplied to an exposed inside container outer bottom face, and heating air is supplied from the gap between the inside container and outside cylinder body into the outside cylinder body so as to perform a heat treatment for reducing thermal strain of the ingot.SELECTED DRAWING: Figure 1

Description

  The present invention accommodates an oxide single crystal ingot grown by a pulling method such as the Czochralski method (hereinafter abbreviated as Cz method) in a ceramic vessel, and the ceramic vessel is a flat hearth in a heating furnace. The present invention relates to a method for reducing the “thermal strain” of an oxide single crystal ingot by heat-treating the oxide single crystal ingot in a state where it is placed on a table, and in particular, even if the oxide single crystal ingot to be processed is enlarged (that is, The present invention relates to a method for heat treatment of an oxide single crystal that can prevent uneven heat treatment and breakage of a ceramic container even if the diameter of the ingot is increased.

  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 using a pulling method such as the Cz method. . The Cz method is a method for growing a single crystal having the same orientation as the seed crystal by bringing the seed crystal into contact with the raw material melt in the crucible and pulling the seed crystal while rotating it. In the Cz method, crystal growth proceeds by solidifying the growth interface, and therefore a temperature gradient is generated between the previously solidified portion and the growth interface. Then, by generating a temperature gradient, “thermal strain” due to the temperature difference is introduced into the crystal after the growth is completed.

  When the above-mentioned “thermal strain” is introduced into the grown crystal, cracks are generated in the subsequent processing steps. Therefore, the oxide single crystal grown by the Cz method is subjected to annealing treatment (heat treatment) at a temperature below the melting point. The above-mentioned “thermal distortion” is alleviated. The annealing treatment is preferably performed at a uniform temperature throughout the crystal. In particular, in the case of single crystal growth by the Cz method, large “thermal strain” is introduced near the boundary between the crystal shoulder and the crystal straight body where the change in diameter is large. Therefore, it is preferable to reduce the temperature difference between the crystal shoulder and the crystal straight body as much 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 temperatures exceeding 1000 ° C., an electric furnace equipped with a resistance heating type heater is generally selected. The The heating element of the electric furnace is selected from molybdenum disilicide and silicon carbide depending on the annealing temperature, but is not limited to these heating elements.

  In the annealing treatment, the entire crystal is kept at a uniform temperature for a long time, and is gradually cooled back to room temperature so as not to cause a temperature difference, thereby relieving "thermal distortion" and preventing cracks in subsequent processing steps. Therefore, it is necessary to keep the temperature uniform at high temperatures.

  By the way, annealing treatment (heat treatment) of the oxide single crystal ingot having a crystal shoulder and a crystal straight body portion is carried out by accommodating the ingot in a ceramic container and covering the entire ingot with the container. However, cracks may occur in the ingot where the oxide single crystal ingot and the ceramic container are in contact with each other. This is believed to be due to thermal nonuniformity at the contact site in the oxide single crystal ingot and nonuniform stress due to the 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 an upper part is opened and a group of small lumps having a diameter of 2 mm or more and less than 10 mm and made of the same material as an oxide single crystal ingot is spread. A lower member 9 having a shape, and an inner wall surface and a ceiling wall surface on which the entire oxide single crystal ingot 1 accommodated on the inner bottom surface of the lower member 9 via a small group 5 is covered. A ceramic container is constituted by the cylindrical upper member 8 to be fitted, and the ceramic container containing the oxide single crystal ingot is directly placed on the flat hearth base 6 of an electric furnace (not shown). In this state, a method of reducing the “thermal strain” of the oxide single crystal ingot by heat treatment is proposed, and as shown in FIG. 6, a lump is formed of the same material as that of the oxide single crystal ingot with the top opened. 5 groups of small bobs with a diameter of 2 mm or more and less than 10 mm A cylindrical lower member 12 having a spread inner bottom surface, a middle member 11 and an upper member 10 are fitted together to form a ceramic container. Similar to FIG. 5, the “thermal strain of an oxide single crystal ingot is formed. ”Has been proposed.

  And according to the heat processing method of the oxide single crystal proposed by patent document 1, since the said lump 5 group has a remarkably large lump diameter compared with the conventional powder comprised with an oxide single crystal, on high temperature conditions Since the volatilization of the lithium (Li) component (the component constituting the LT or LN single crystal) does not easily occur and the surface area of the nodule 5 is small, the container and the nodule even when the ceramic vessel and the nodule 5 are in direct contact with each other The reaction between 5 is difficult to occur, and since the lump 5 has a lump diameter of less than 10 mm, the oxide single crystal ingot accommodated in the ceramic container does not fall during the heat treatment. For this reason, the oxide single crystal ingot can be stably accommodated in an inexpensive ceramic container, and the entire oxide single crystal ingot is covered with the ceramic container, resulting in uneven heating of the ingot and deterioration of the ceramic container. This is a method in which the “thermal distortion” of the oxide single crystal ingot is alleviated without the use of an oxide.

  By the way, with the recent spread of smart phones and the like, the market for surface acoustic wave filters (hereinafter abbreviated as SAW filters) for mobile communication devices continues to expand, and the above-mentioned LT, LN, etc., which are materials for SAW filters The demand for single crystal substrates is growing. In order to reduce the cost of the SAW filter manufacturing process, the oxide single crystal substrate size of LT, LN, etc. has been increased from the conventional φ3 inch to φ4 inch, φ6 inch, and the grown oxide. Single crystal ingots have become larger (that is, the ingot diameter has increased). The conventional oxide single crystal size was not a problem, but with the increase in the size of the grown oxide single crystal ingot, the heat treatment on the ingot was uneven and the ceramic container was damaged (crack on the bottom of the container). Etc. are occurring.

JP 2017-193453 A

  In the annealing treatment (heat treatment) of the oxide single crystal, when the grown oxide single crystal is enlarged (that is, the diameter of the single crystal is increased), there is a problem that a crack is generated on the bottom of the container. This is probably because the ceramic container has become larger in accordance with the oxide single crystal thus formed, and therefore a temperature difference occurs between the center and the outer periphery of the bottom surface of the ceramic container.

  And if a temperature difference begins to occur between the center and the outer periphery of the bottom surface of the container, the heat treatment to the oxide single crystal becomes non-uniform and cracks are likely to occur in the oxide single crystal, and cracks also occur in the bottom surface of the container. Therefore, it becomes difficult to hold the oxide single crystal.

  The present invention has been made paying attention to such problems, and the problem is that even if the oxide single crystal (oxide single crystal ingot) to be processed is enlarged, the heat treatment is not uniform and the ceramic container is made. It is an object of the present invention to provide a method for heat treatment of an oxide single crystal in which damage of the oxide is avoided.

  As a result of continual research by the inventor in order to solve the above problems, the method for fitting the ceramic container adopted in Patent Document 1 is changed, and the flat hearth in the heating furnace is made of ceramic. When the method was changed so that the container was not placed directly, it was discovered that even if the oxide single crystal to be processed (oxide single crystal ingot) was enlarged, non-uniform heat treatment and damage to the ceramic container could be avoided. . The present invention has been completed based on such technical findings.

That is, the first invention according to the present invention is:
The oxide single crystal ingot grown by the pulling method is accommodated in a ceramic vessel, and the vessel is placed on a flat hearth installed in a heating furnace to heat-treat the oxide single crystal ingot in the vessel. In the heat treatment method of the oxide single crystal to be
An inner container in which a small lump group having a lump diameter of 2 mm or more and less than 10 mm made of the same material as the oxide single crystal ingot is spread on the inner bottom surface and the oxide single crystal ingot is accommodated through the small lump group; An outer cylindrical body having an inner diameter larger than the outer diameter of the inner container and disposed so as to surround the outer peripheral surface of the oxide single crystal ingot accommodated in the inner container, and constituting the ceramic container; and
A plate-like spacer is interposed between the flat hearth base and the inner vessel and outer cylinder mounted on the hearth base, and the heated air in the heating furnace is exposed on the outer bottom surface of the inner vessel. And heating the oxide single crystal ingot by supplying air heated from the gap between the inner container and the outer cylinder 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-like spacer is composed of the same ceramic material as the container,
The third invention is
In the heat treatment method for 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-like spacer is 10% or more and 50% or less of the total area of the outer bottom surface.

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

According to the present invention, an oxide single crystal ingot grown by a pulling method is accommodated in a ceramic vessel, and the ceramic vessel is placed on a flat hearth in a heating furnace to heat-treat the oxide single crystal ingot. The heat treatment method is
An inner container in which small clusters having a diameter of 2 mm or more and less than 10 mm made of the same material as the oxide single crystal ingot are spread on the inner bottom surface and the oxide single crystal ingot is accommodated through the small clusters; The ceramic container is constituted by an outer cylindrical body having an inner diameter larger than the outer diameter of the container and disposed so as to surround the outer peripheral surface of the oxide single crystal ingot accommodated in the inner container, and the flat shape A plate-like spacer is interposed between the hearth bed and the inner vessel and outer cylinder mounted on the hearth bed to supply the heated air in the heating furnace to the exposed inner vessel outer bottom surface. At the same time, the oxide single crystal ingot is heat-treated by supplying air heated from the gap between the inner container and the outer cylinder into the outer cylinder.

  According to the heat treatment method of the present invention, since the heated air in the heating furnace is supplied to the exposed inner container outer bottom surface, it becomes possible to uniformly heat the central portion and the peripheral portion of the inner container outer bottom surface. And 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 accommodated in the ceramic container constituted by the inner container and the outer cylinder It becomes possible to heat-treat a single crystal ingot uniformly.

Explanatory drawing which shows the heat processing method of the oxide single crystal which concerns on Example 1 of this invention. Explanatory drawing which shows the heat processing method of the oxide single crystal which concerns on Example 2 of this invention. A ceramic according to the first embodiment including a plate-like spacer composed of four arc-shaped plate members, an inner container placed on a flat hearth with the plate-like spacer interposed, and an outer cylinder. The bottom view of a container made. It is composed of a plate-like spacer composed of a single ceramic plate having a planar C-shape, an inner container and an outer cylinder placed on a flat hearth with the plate-like spacer interposed. 6 is a bottom view of a ceramic container according to Embodiment 5. FIG. Explanatory drawing which shows the heat processing method of the oxide single crystal using the ceramic container comprised by the lower side member and upper side member of patent document 1. FIG. Explanatory drawing which shows the heat processing method of the oxide single crystal using the ceramic container comprised by the lower side member of patent document 1, an inner side member, and an upper side member.

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

(1) Oxide single crystal heat treatment method according to the present invention The oxide single crystal heat treatment method according to the present invention accommodates an oxide single crystal ingot grown by a pulling method as described above in a ceramic container. The same material as the oxide single crystal ingot, in the oxide single crystal heat treatment method, wherein the vessel is placed on a flat hearth installed in a heating furnace and the oxide single crystal ingot in the vessel is heat treated An inner container in which a group of small blocks having a diameter of 2 mm or more and less than 10 mm, which is composed of 2 and 10 mm, is laid down on the inner bottom surface and an oxide single crystal ingot is accommodated through the small group, and an inner diameter larger than the outer diameter of the inner container And the outer cylindrical body disposed so as to surround the outer peripheral surface of the oxide single crystal ingot accommodated in the inner container, and the ceramic container is configured, and the flat hearth base, the furnace Place on the floor A plate-like spacer is interposed between the inner container and the outer cylinder to supply heated air in the heating furnace to the exposed outer bottom surface of the inner container, and the gap between the inner container and the outer cylinder The air heated from above is supplied into the outer cylinder to heat-treat the oxide single crystal 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 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 cylindrical body is a circular shape or a large number such 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 square, it is possible to prevent the ceramic container and the oxide single crystal ingot from coming into direct contact 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 accommodated in the inner container is the outer cylinder. Therefore, uneven heating of the oxide single crystal ingot can be prevented.

  In the annealing process (heat treatment), the outer periphery of the oxide single crystal ingot accommodated in the inner container is not to be directly irradiated with the heat rays from the heating element of the heating furnace for heat treatment. It is necessary to make the surface surrounded by the outer cylinder.

  Moreover, 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 furnace is supplied into the outer cylinder through the gap between the inner container and 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 base in the heating furnace for heat treatment and the inner vessel and the outer cylindrical body placed on the hearth base 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, mullite, silicon carbide and the like can be used, but the same material as the ceramic container is more preferable.

  Moreover, the shape of the board | plate material which comprises a plate-shaped spacer is not specifically limited, A shape can be suitably selected according to a use condition. For example, the shape can be selected from a square, a rectangle, a circle, a sector, and the like.

  In addition, when the area of the inner container outer bottom face in contact with the plate-like spacer is large, the area of the exposed inner container outer bottom face is reduced, so that the heating effect of the inner container outer bottom face by the heated air is reduced. For this reason, it is preferable that the area of the inner container outer bottom surface in contact with the plate spacer is 10% or more and 50% or less of the entire outer bottom surface area.

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

  The thickness of the plate spacer is preferably 10 mm or more so that it has sufficient resistance to the load of the inner container in which the oxide single crystal ingot is accommodated, and the plate spacer has a plurality of plate materials. It is desirable that the thickness of each plate material be the same.

(4) Small lumps grouped on the 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 ) and LN (LiNbO ₃ ). It means a lump of oxide single crystal having a diameter of 2 mm or more and less than 10 mm.

  A small lump of an oxide single crystal having a lump diameter of 2 mm or more and less than 10 mm has a remarkably large lump diameter as compared with a conventional powder composed of an oxide single crystal. Therefore, a lithium (Li) component (LT) And components of LN single crystals are less likely to volatilize and the surface area of the small lump is small, so that the reaction between the container and the small lump hardly occurs even if the ceramic container and the small lump are in direct contact (that is, ceramic). The chemical degradation of the container is suppressed because of its poor reactivity with the container, and since the small lump diameter is less than 10 mm, the oxide single crystal ingot accommodated in the inner container falls during the heat treatment. There is nothing.

  When the lump diameter is less than 2 mm, the surface area of the small lump increases and the reactivity with the inner container increases. Moreover, when the lump diameter is 10 mm or more, the placement of the oxide single crystal ingot becomes unstable, and the oxide single crystal ingot falls down during the heat treatment, causing crack failure.

(5) Oxide single crystal An oxide single crystal based on a heat treatment method for an oxide single crystal, and includes 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. However, 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 the present example is an inner container 3 having an outer diameter of 260 mm, a height of 45 mm, and a container thickness of 5 mm. And an inner diameter larger than the outer diameter of the inner container 3 and arranged so as to surround the outer peripheral surface of the LT single crystal ingot (6 inch diameter) 1 accommodated on the inner bottom surface of the inner container 3 via the small clusters 5 groups. The outer cylinder 2 has an inner diameter of 280 mm, a height of 280 mm, and a cylinder thickness of 5 mm.

  The ceramic container composed of the inner container 3 and the outer cylinder 2 has a plate-like spacer 4 interposed in a flat hearth base 6 in an electric furnace (not shown) equipped with a resistance heating heater. As a result, the outer bottom surface of the inner container 3 is exposed, and the outer bottom surface is exposed to heated air in the electric furnace (hereinafter referred to as heated air).

  The material of the ceramic container was alumina (aluminum oxide). Further, the plate-like spacer 4 is composed of four arc-shaped plate members as shown in FIG. 3, the material is the same as the ceramic container, and the thickness of the arc-shaped plate member is 10 mm. The small blob 5 is made of the same material as the LT single crystal, the LT single crystal is pulverized, coarse single crystals are removed with a sieve having an opening of 10 mm, and fine crystals are obtained with a sieve having an opening of 2 mm. After the powder is removed to obtain a small mass group having a mass diameter of about 2 mm to 10 mm, it is spread on the inner bottom surface of the inner container 3 so that the thickness of the small mass group layer is 30 mm. Further, in FIG. 3, a symbol d indicates a gap due to a difference between the inner diameter of the outer cylinder 2 and the outer diameter of the inner container 3.

  Then, the four arc-shaped plate members constituting the plate-like spacer 4 are shown in FIG. 3 so that both the inner vessel 3 and the outer cylinder 2 constituting the ceramic vessel can be placed on the plate-like spacer 4. An inner container 3 that is placed on a flat hearth (not shown) and in which small groups 5 are spread on the inner bottom surface is placed on four arc-shaped plate members, After accommodating the LT single crystal ingot 1 on the inner bottom surface of the inner container 3, the outer cylindrical body 2 was placed on four arc-shaped plate members 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-like spacer 4 constituted by four arc-shaped plate members is adjusted to be 10% of the total area of the outer bottom surface, By arranging the four arc-shaped plate members so as to be vertically and horizontally symmetrical with respect to the outer peripheral portion, four vent holes (air gaps) for supplying and discharging heated air to the outer bottom surface of the inner container 3 are formed vertically and horizontally symmetrically. Has been.

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

  When the appearance of the inner container 3 and the outer cylindrical body 2 after the completion of the annealing treatment (heat treatment) and the inner bottom surface of the inner container 3 were examined, no cracks or deterioration was confirmed, and the LT single crystal contained in the inner container 3 was confirmed. No cracks were observed in the ingot 1. Also, four arc-shaped plate members (ceramic plate spacers 4) interposed between the ceramic vessel constituted by the inner vessel 3 and the outer cylindrical body 2 and the flat hearth base 6 are made of LT single crystal. It was also confirmed that the ingot 1 was resistant to the load of the inner container 3 in which the ingot 1 was accommodated.

  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 good products could be obtained.

  Further, when the appearance of the inner container 3 and the outer cylindrical body 2 after 10 repetitions and the inner bottom surface of the inner container 3 were examined, no cracks or deterioration was confirmed, and the four arc-shaped plate members were also damaged. Etc. were not confirmed.

[Example 2]
The LT single crystal ingot is annealed (heat treated) in the same manner as in Example 1 except that the outer cylindrical body 7 shown in FIG. 2 whose upper end is closed is applied, and the inner container 3 after the annealing (heat treated) is completed. When the appearance of the outer cylindrical body 7 and the inner bottom surface of the inner container 3 were examined, no cracks or deterioration was confirmed, and no cracks were confirmed in the LT single crystal ingot 1 accommodated in the inner container 3. Further, four arc-shaped plate members (ceramic plate spacers 4) interposed between the ceramic vessel constituted by the inner vessel 3 and the outer cylindrical body 7 and the flat hearth base 6 are made of LT single crystal. It was also confirmed that the ingot 1 was resistant to the load of the inner container 3 in which the ingot 1 was accommodated.

  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 good products could be obtained as in Example 1.

  Further, when the appearance of the inner container 3 and the outer cylindrical body 7 after 10 repetitions and the inner bottom surface of the inner container 3 were examined, no cracks or deterioration was confirmed, and the four arc-shaped plate members 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-like spacer 4 composed of four arc-shaped plate members is adjusted to be 50% of the total area of the outer bottom surface. When the ingot is annealed (heat treatment), and the appearance of the inner container 3 and the outer cylinder 2 after the annealing process (heat treatment) is completed and the inner bottom surface of the inner container 3 are examined, cracks and deterioration are not confirmed. No cracks were observed in the LT single crystal ingot 1 accommodated in the inner container 3. Also, four arc-shaped plate members (ceramic plate spacers 4) interposed between the ceramic vessel constituted by the inner vessel 3 and the outer cylindrical body 2 and the flat hearth base 6 are made of LT single crystal. It was also confirmed that the ingot 1 was resistant to the load of the inner container 3 in which the ingot 1 was accommodated.

  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 good products could be obtained as in Example 1.

  Further, when the appearance of the inner container 3 and the outer cylindrical body 2 after 10 repetitions and the inner bottom surface of the inner container 3 were examined, no cracks or deterioration was confirmed, and the four arc-shaped plate members 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-like spacer 4 composed of four arc-shaped plate members is adjusted to be 60% of the total area of the outer bottom surface. When the ingot is annealed (heat treatment), and the appearance of the inner container 3 and the outer cylinder 2 after the annealing process (heat treatment) is completed and the inner bottom surface of the inner container 3 are examined, cracks and deterioration are not confirmed. No cracks were observed in the LT single crystal ingot 1 accommodated in the inner container 3. Also, four arc-shaped plate members (ceramic plate spacers 4) interposed between the ceramic vessel constituted by the inner vessel 3 and the outer cylindrical body 2 and the flat hearth base 6 are made of LT single crystal. It was also confirmed that the ingot 1 was resistant to the load of the inner container 3 in which the ingot 1 was accommodated.

  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 about two LT single crystal ingots, Cracks were confirmed. The reason why the processing effect is slightly inferior to that of the first embodiment is that the area of the outer bottom surface of the inner container 3 in contact with the plate-like spacer 4 is as large as 60% of the total area of the outer bottom surface. This is probably because the heating effect of the outer bottom surface by the heated air is reduced by the reduction in the area of the outer bottom surface of the inner container 3 exposed.

  Further, when the appearance of the inner container 3 and the outer cylindrical body 2 after repeating 10 times and the inner bottom surface of the inner container 3 were examined, some cracks were confirmed, but the arc-shaped plate material was not damaged. There wasn't.

[Example 5]
The ceramic plate-like spacer 4 interposed between the ceramic vessel constituted by the inner vessel 3 and the outer cylindrical body 2 and the flat hearth base 6 has a single vent (gap) as shown in FIG. The LT single crystal ingot is annealed (heat treatment) in the same manner as in Example 1 except that it is composed of a single ceramic plate material having a planar C-character shape forming the shape, and after the annealing treatment (heat treatment) is completed. When the appearance of the inner container 3 and the outer cylindrical body 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 accommodated in the inner container 3. It was not confirmed. In addition, the ceramic plate-like spacer 4 having a plane C character shape interposed between the ceramic vessel constituted by the inner vessel 3 and the outer cylindrical body 2 and the flat hearth base 6 is composed of the LT single crystal ingot 1. It was also confirmed that it had resistance to the load of the accommodated inner container 3.

  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, six good products could be obtained, but cracks were observed in the four LT single crystal ingots. confirmed. The reason why the processing effect is inferior to that of Example 1 is that the ceramic plate-like spacer 4 having a plane C character shape is applied, so that the ventilation hole (void) becomes a single, and the single ventilation hole (void) ), The heating effect supplied to the outer bottom surface of the inner container 3 is reduced, and the heating effect of the outer bottom surface is reduced, and the air is supplied into the outer cylindrical body 2 from the gap between the inner container 3 and the outer cylindrical body 2. This is thought to be due to a decrease in heated air.

  Further, when the appearance of the inner container 3 and the outer cylindrical body 2 after 10 repetitions and the inner bottom surface of the inner container 3 were examined, cracks and radial breakage were partially confirmed. No breakage or the like of the ceramic plate-like spacer 4 having the above was confirmed.

[Example 6]
An LT single crystal ingot is annealed (heat treatment) in the same manner as in Example 1 except that the thickness of each arc-shaped plate material constituting the ceramic plate-like spacer 4 is 5 mm, and after the annealing treatment (heat treatment) is completed. When the outer appearance of the inner container 3 and the outer cylindrical body 2 and the inner bottom surface of the inner container 3 were examined, cracks and deterioration were not confirmed, and cracks were also confirmed in the LT single crystal ingot 1 accommodated in the inner container 3. Was not. However, the four arc-shaped plate members (ceramic plate spacers 4) interposed between the ceramic vessel constituted by the inner vessel 3 and the outer cylindrical body 2 and the flat hearth base 6 have a thickness of 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.

  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 good products could be obtained as in Example 1.

  Further, when the appearance of the inner container 3 and the outer cylindrical body 2 after 10 repetitions and the inner bottom surface of the inner container 3 were examined, cracks and deterioration were not confirmed, but the four arc-shaped plate members were damaged. Etc. were confirmed.

[Comparative Example 1]
As shown in FIG. 5, the ceramic container used in Comparative Example 1 has a cylindrical lower member 9 having an inner bottom surface in which the upper part is opened and the same small group 5 as in Example 1 is spread, The lower member 9 is composed of an inner wall surface covering the entire LT single crystal ingot 1 accommodated in the lower member 9 and a cylindrical upper member 8 fitted to the lower member 9 and having a ceiling wall surface. As the material for the upper member 9 and the upper member 8, the same alumina (aluminum oxide) as in the first embodiment is used. The shape of the lower member 9 is a rectangular box-shaped structure having a side of 200 mm, a height of 100 mm, and an open top, and the shape of the upper member 8 is also lower. It is the same as the side member 9.

  Then, the 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 nodule 5 group layer is 30 mm as shown in FIG. After the placement, 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 base 6 in the electric furnace (not shown) without the ceramic plate spacer. After that, annealing treatment (heat treatment) was performed at a temperature of 1400 ° C. for 40 hours, and the appearance of the lower member 9 and the inner bottom surface of the lower member 9 after completion of the annealing treatment (heat treatment) were examined. Cracks and partial breakage were confirmed at the center of the LT, and some cracks were also observed in the LT single crystal ingot 1 accommodated in the lower member 9. Further, it was confirmed that as the diameter of the LT single crystal ingot 1 to be heat-treated increases, damage to the inner bottom surface of the lower member 9 and generation of cracks in the LT single crystal ingot 1 become more prominent.

  In place of the ceramic container shown in FIG. 5, a ceramic container constituted by 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 used. The same was true when the ceramic container was placed directly on the flat hearth base 6) without a ceramic plate spacer.

[Comparative Example 2]
A ceramic container (LT single crystal ingot 1 having the same structure as that of the first embodiment) is disposed on a flat hearth base 6 in an electric furnace (not shown) provided with a resistance heating type heater without using a plate-like spacer 4. The LT single crystal ingot was annealed (heat treated) in the same manner as in Example 1 except that the substrate was directly placed.

  Then, when the appearance of the inner container 3 and the outer cylindrical body 2 after the annealing treatment (heat treatment) was completed and the inner bottom surface of the inner container 3 were examined, cracks occurred on the inner bottom surface of the inner container 3 and were damaged radially. It was confirmed that In addition, cracks were not confirmed in the LT single crystal ingot 1 accommodated in the inner container 3, but the LT single crystal ingot 1 was removed due to a part of the small mass 5 flowing out from the damaged inner bottom surface of the inner container 3. It was leaning.

  Furthermore, the LT single crystal ingot was annealed (heat treatment) three times under the same conditions as described above, but cracks occurred on the inner bottom surface of the inner vessel 3 three times. In addition, cracks were confirmed in the LT single crystal ingot twice in 3 times.

[Comparative Example 3]
A ceramic vessel (LT single crystal ingot 1 having the same structure as in Example 2) is provided on a flat hearth base 6 in an electric furnace (not shown) equipped with a resistance heating type heater without using a plate-like spacer 4. The LT single crystal ingot was annealed (heat treatment) in the same manner as in Example 2 except that the substrate was directly placed.

  Then, when the appearance of the inner container 3 and the outer cylindrical body 7 after the annealing treatment (heat treatment) was completed and the inner bottom surface of the inner container 3 were examined, cracks occurred on the inner bottom surface of the inner container 3 and were damaged radially. It was confirmed that In addition, cracks were not confirmed in the LT single crystal ingot 1 accommodated in the inner container 3, but a part of the small nodule 5 flowed out from the damaged inner bottom surface of the inner container 3, so that the LT single crystal ingot 1 It was leaning.

[Comparative Example 4]
The ceramic plate-like spacer 4 interposed between the ceramic vessel constituted by the inner vessel 3 and the outer cylindrical body 2 and the flat hearth base 6 is constituted by a ring-shaped ceramic plate material having a gap inside the main body. An LT single crystal ingot was annealed (heat treated) in the same manner as in Example 1 except for the above.

  Then, when the appearance of the inner container 3 and the outer cylindrical body 2 after the annealing treatment (heat treatment) was completed and the inner bottom surface of the inner container 3 were examined, cracks occurred on the inner bottom surface of the inner container 3 and were damaged radially. It was confirmed that Further, cracks were also confirmed in the LT single crystal ingot 1 accommodated in the inner container 3.

  When the ring-shaped ceramic plate material is applied, the supply of heated air to the outer bottom surface and the outer cylinder 2 is remarkably eliminated because there is no vent (gap) for supplying and discharging heated air to the outer bottom surface of the inner container 3. Since it decreases, it is considered that the crack is generated in the inner bottom surface of the inner container 3 and the LT single crystal ingot.

  According to the heat treatment method for an oxide single crystal according to the present invention, since the central portion and the peripheral portion of the outer bottom surface of the container in which the oxide single crystal is accommodated can be heated uniformly, a lithium tantalate single crystal or a lithium niobate single crystal It has industrial applicability for use in heat treatment methods that relieve thermal distortion of ingots.

d Gap due to difference in inner diameter of outer cylinder 2 and outer diameter of inner container 3 1 LT single crystal ingot (oxide single crystal)
DESCRIPTION OF SYMBOLS 2 Outer cylinder 3 Inner container 4 Plate spacer 5 Small lump 6 Flat hearth stand 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 accommodated in a ceramic vessel, and the vessel is placed on a flat hearth installed in a heating furnace to heat-treat the oxide single crystal ingot in the vessel. In the heat treatment method of the oxide single crystal to be
An inner container in which a small lump group having a lump diameter of 2 mm or more and less than 10 mm made of the same material as the oxide single crystal ingot is spread on the inner bottom surface and the oxide single crystal ingot is accommodated through the small lump group; An outer cylindrical body having an inner diameter larger than the outer diameter of the inner container and disposed so as to surround the outer peripheral surface of the oxide single crystal ingot accommodated in the inner container, and constituting the ceramic container; and
A plate-like spacer is interposed between the flat hearth base and the inner vessel and outer cylinder mounted on the hearth base, and the heated air in the heating furnace is exposed on the outer bottom surface of the inner vessel. And heating the oxide single crystal ingot by supplying air heated from the gap between the inner container and the outer cylindrical body into the outer cylindrical body.   2. The oxide single crystal heat treatment method according to claim 1, wherein the plate spacer is made of the same ceramic material as that of the container.   The method for heat-treating 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 spacer is 10% or more and 50% or less of the total area of the outer bottom surface.   The plate-like spacer is constituted by a plurality of plate materials so that two or more vent holes for supplying and discharging heated air are symmetrically formed in the central portion of the exposed outer bottom surface of the inner container. The heat processing method of the oxide single crystal in any one of Claims 1-3.   The oxide single crystal heat treatment method according to any one of claims 1 to 4, wherein a thickness of the plate spacer is set to 10 mm or more.   6. The oxide single crystal heat treatment method according to claim 1, wherein the oxide single crystal is composed of a lithium tantalate single crystal or a lithium niobate single crystal.