JPH01172300A - Annealing method for lithium tantalate single crystal - Google Patents

Abstract

PURPOSE:To remarkably shorten the time necessary for annealing and to eliminate the need for a furnace utilized for annealing by constituting the title annealing method so that lithium tantalate single crystal is grown and successively annealing of single crystal is performed in the same furnace. CONSTITUTION:Lithium tantalate single crystal 15 which has been grown by immersing seed crystal 11 in melt 7 for growing lithium tantalate single crystal in a furnace core pipe 3 provided with a heater 2 for heating to the outside is separated from the melt 7 by lowering a crucible 4 held with the melt 7 therein. Then it is slowly cooled to the annealing temp. of single crystal 15 by controlling the heater 2 and furthermore after holding it at this annealing temp. only for a prescribed time, it is slowly cooled and taken out from the furnace core pipe 3.

Description

[Detailed Description of the Invention] [Summary] Regarding the improvement of the method of growing and annealing a single crystal of lithium tantalate, the aim of the method was to reduce the required time by growing lithium tantalate in a furnace tube equipped with a heater on the outside. The single crystal of lithium tantalate grown by immersing it in the melt for single crystal growth is separated from the crucible (4) containing the melt (7) by lowering it, and then the heater The single crystal is slowly cooled down to the annealing temperature of the single crystal, held at the annealing temperature for a required period of time, and then slowly cooled and taken out from the reactor core tube.

[Industrial application field]

The present invention is directed to LiTaOi single crystals, particularly LiTa0. This article relates to improvements for increasing the efficiency of single crystal annealing.

[Conventional technology]

A single crystal of LiTaO3 is grown by immersing a seed crystal in a LiTaO3 single crystal growth melt that has been heated and melted at approximately 1700°C, and gradually pulling up the seed crystal, but the internal strain created during growth is removed. Annealing will be required.

Conventionally, a single crystal grown as a seed crystal is slowly cooled to near room temperature in a single crystal growth furnace, then taken out, and then placed in an annealing furnace where it is gradually heated to the annealing temperature and held for the required time. Afterwards, it is slowly cooled and taken out, but when taking out the single crystal from the single crystal growth furnace and annealing furnace,
After reducing the temperature in the furnace to room temperature over a long period of time (about 200 hours), it takes an even longer time (about 8 hours) for the internal temperature of the single crystal to drop sufficiently.

Figure 3 shows a time chart (A) for growing a LiTaO3 single crystal and a time chart (II) for annealing the single crystal in an example of the conventional method, where the vertical axis is temperature (°C) and the horizontal axis is the required time. time (h).

In Figure 3 (a), the single crystal growth temperature is 1700°C.
After heating to 1700°C for about 4 hours and growing a single crystal for about 10 hours, the single crystal is slowly cooled for about 20 hours, and then the inside of the single crystal is brought to room temperature. After leaving it as it is for about 8 hours to lower it to
The single crystal is taken out from the furnace tube of the single crystal growth device.

For annealing the grown single crystal, the grown single crystal is placed in an annealing furnace and raised to an annealing temperature (approximately 1400°C) over about 8 hours, as shown in Figure 3 (IT).
The annealing temperature is maintained for the required time, for example, 20 hours, then slowly cooled to room temperature over about 20 hours, and then left as it is for about 8 hours to cool the inside of the single crystal to room temperature, and then the single crystal is annealed. Remove from the furnace.

Therefore, it takes about 42 hours to grow a single crystal, about 56 hours to anneal it, and the actual time required from growing the single crystal to annealing is 98 hours.

[Problem that the invention seeks to solve]

As explained above, LiTa0. When growing and annealing a single crystal ingot, it takes 20 hours and 8 hours, respectively, to cool down the temperature in the furnace to take it out from the growth furnace and annealing furnace, and to homogenize the single crystal to the inside. The total time was 56 hours, and it took about 8 hours to further cool down to -degree room temperature and then heat up to the annealing temperature, and required both a single crystal growth device and an annealing device.

[Means for solving problems]

The present invention aims to eliminate the above-mentioned problems.
According to the figure, a lithium tantalate single crystal 15 grown by immersing it in a melt 7 for growing a lithium tantalate single crystal is grown in a furnace tube 2 equipped with a heater 3 on the outside. After the crucible 4 is lowered to separate it from the melt 7 and then lifted from the melt 7, the heater 3 is controlled to slowly cool it to the annealing temperature of the single crystal 15, and after holding the crucible 4 at the annealing temperature for a predetermined time, the crucible 4 is slowly cooled. Furthermore, by controlling the heater 3, the grown single crystal 15 pulled from the melt 7 is cooled in the furnace core tube 2 at a temperature of approximately 200° above the annealing temperature of the single crystal 15. This is a method for annealing a lithium tantalate single crystal, characterized in that the temperature is slowly cooled to a temperature lower by .degree. C., and then the temperature is increased to the annealing temperature.

[Effect]

According to the above means, by annealing the single crystal subsequent to growth of the single crystal, there is no need to cool the single crystal immediately after growth to room temperature, and the time required for annealing is shortened accordingly.

[Example] The method of the present invention will be described below with reference to a schematic diagram of an apparatus related to the method of the present invention.

FIG. 1 is a sectional side view showing the main structure and operation of an apparatus according to an embodiment of the method of the present invention, and FIG. 2 is an example of a time chart for growing and annealing a single crystal using the apparatus.

In Fig. 1, (a) is a diagram showing the apparatus in a state of growing a single crystal, and (rl) is a diagram showing the apparatus in an annealing state of the grown single crystal. An apparatus 1 for annealing crystals includes a furnace tube 2 with a high-frequency induction heating coil 3 disposed outside, and an iridium (
It houses a crucible 4 made of Ir). An alumina crucible 6 is mounted on a vertically movable shaft 5, and a heat insulating material (zirconia bubble) 8 is filled between the Ir crucible 4 containing a melt 7 for single crystal growth and the alumina crucible 6.

The tube 9 made of platinum <pt>-rhodium (Rh) is for equalizing the single crystal growth temperature and annealing temperature in the furnace, and is provided outside the alumina crucible 6 and is a hollow tube that can move up and down. The shaft 12 that supports the zero seed crystal 11 supported by the shaft 10 and is pulled up as the single crystal grows passes through the lid 13 of the reactor core tube 2 and the heat reflecting plate 14 lined in the lid 13. It can be moved up and down. Note that a hollow shaft 16 through which the shaft 5 passes is movable up and down and supports the cylinder 9.

In FIGS. 1(A) and 2, a predetermined high-frequency current is passed through the heater 3 to heat it to 1700° C., which is the single crystal growth temperature, for about 4 hours, and maintain the temperature within the furnace tube 2.
A single crystal is grown in the seed crystal 11, and when the growth of a predetermined single crystal 15 is completed after about 10 hours, the crucible 4 is lowered as shown in FIG. 15 is slowly cooled to about 1200°C. Then, the internal strain of the single crystal 15 is removed (annealed) by heating to the annealing temperature of 1400°C over about 3 hours and maintaining this temperature for about 20 hours. It took about 20 hours to complete the furnace core tube 2.
After slowly cooling the inside to room temperature and leaving it for about 8 hours,
The single crystal 15 is taken out from the furnace tube 2, and the growth and annealing of the single crystal 15 is completed.

Therefore, the single crystal that conventionally required 98 hours to grow and anneal according to the time chart of FIG. 2 can be grown and annealed in 71 hours according to the method of the present invention.

〔Effect of the invention〕

As explained above, according to the method of the present invention, the time from the time when the growth of the LiTaO3 single crystal is completed to the time when annealing is started can be significantly shortened, and a furnace for annealing is not required.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing the main structure and operating method of an apparatus according to an embodiment of the method of the present invention, and FIG. 2 is a time chart for growing and annealing a single crystal using the apparatus shown in FIG. As an example, FIG. 3 is a time chart of single crystal growth and annealing using a conventional method. In the figure, 1 is LiTa0. Single crystal growth, annealing equipment and equipment, 2 is a furnace tube, 3 is a heater, 4 is a crucible, 7 is a melt for single crystal growth, 15 is a single crystal of LiTaO3. ro (i) (Q
)fu 1 illusion

Claims (2)

[Claims] (1) Furnace tube (2) with heater (3) installed on the outside
Inside, melt for single crystal growth of lithium tantalate (7)
Lithium tantalate single crystal (15
) is separated from the melt (7) by lowering the crucible (4) containing the melt (7), and then the heater (3)
is slowly cooled to the annealing temperature of the single crystal (15), held at the annealing temperature for a predetermined time, and then slowly cooled,
A method for annealing a lithium tantalate single crystal, the method comprising removing the lithium tantalate single crystal from the furnace core tube (2). (2) Controlling the heater (3) to melt the melt (7)
The grown single crystal (15) pulled from the furnace tube (2) is slowly cooled to a temperature approximately 200°C lower than the annealing temperature of the single crystal (15), and then raised to the annealing temperature. The method of annealing a lithium tantalate single crystal according to claim 1, characterized in that the annealing is performed.