JPS5825078B2 - Single crystal manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing a single crystal.

The present invention is a method for producing a single crystal in which the temperature of the crucible must be lowered in order to maintain a constant diameter of the grown single crystal. The present invention provides an advantageous manufacturing method that can be applied to the production of large single crystals such as i T a03 ) and lithium niobate (LiNb03).

When producing large single crystals, the surface position of the melt decreases as the crystal is pulled up.

In particular, in the case of X-axis pulled LiT a 03 single crystal for surface wave applications where cracks will appear unless the temperature gradient is made gentler, if approximately 50% of the melt is pulled, crystals will crystallize from the bottom of the crucible, resulting in more than 50% It is difficult to raise it.

This is a major obstacle when considering crystal manufacturing costs.

■ The crystal length that can be created in one time is approximately 50% of that of the melt.
Therefore, in order to create long crystals corresponding to approximately 100% of the melt, crystal creation must be performed twice, resulting in extremely high costs.

■ Since the remaining melt that was not pulled into the crucible is as large as about 50%, the crucible is greatly deformed and the number of times the crucible can be used is reduced.

■ In order to create large elongated crystals, a larger crucible is required, which is very inefficient and costly.

The present invention has been made in view of the above points, and is a method for producing a single crystal that can grow most of the melt in the crucible (approximately 80% or more) as a high-quality single crystal when growing a single crystal using a heating furnace. It provides:

That is, the effective heating position of the heating device, for example, a high frequency heating furnace, is moved downward relative to the lowering of the liquid level of the self-molten material in the crucible.

Next, an embodiment of the method of the present invention will be described with reference to the drawings.

A sintered body 20 of LiT a 03 is placed in a platinum rhodium crucible 1 having a size of 9 omml, a height of 80 mm, and a thickness of 2 mm.
oOg is put therein and melted by high frequency heating using a work coil 2 in a heating device such as a furnace as shown in FIG.

In this case, the middle part of the effective heating position of the work coil 2, for example, center position A, is brought to a preset position in the depth direction of the crucible, for example, depth direction center position B (both represent the height positional relationship in the vertical direction). Adjust as follows.

After melting, a single crystal having a crystal diameter of, for example, 50 Da is pulled and grown using the seed crystal 5 having the X-axis (=a-axis) orientation.

Since this grown crystal is easily broken, a reflector plate 3 is used as shown in FIG. 1 to adjust the temperature gradient in the furnace to be gentle.

The crystal was produced at a pulling speed of 3 m, rn: 1 hour (h), 2 revolutions: 3 orpm"r, and the output of the oscillator was gradually lowered, that is, the temperature inside the crucible was gradually lowered.

Since the melt level falls as the crystal is pulled up, the growth rate is, for example, about 5 mm/h.

When the length has decreased by about 601n1ft, crystals begin to crystallize from the bottom of the crucible and collide with the produced crystal, making it impossible to increase the length of the crystal any further.

This is because the melt surface lowers as the crystal is pulled up, and therefore the center position of the melt is relatively lower from the center position AA of the work coil 2 in this experiment than the center position at the start of crystal creation (see Figure 1). b), the temperature gradient in the crucible, the convection in the melt, etc. changed, and the temperature at the bottom of the crucible 1 became lower than the solid-liquid interface of the pulled crystal, and the crystals began to crystallize from the bottom of the crucible. be.

Therefore, as the melt level descends, the crucible 1 is moved so that the center position of the melt in the crucible 1 comes to the center position at the start of crystal creation.
If the work coil 2 is raised or the work coil 2 is lowered, the temperature gradient inside the crucible 1 and the convection within the melt hardly change, and crystals can be stably formed.

That is, if the descending speed of the crucible 1 or work coil 2 is set to 14 times the descending speed of the melt surface, the crystal can be pulled stably.

Conventionally, as published in Japanese Patent Publication No. 15604/1983, as a method of preventing deterioration of crystal quality due to a change in temperature gradient at the solid-liquid interface due to a drop in the liquid level due to crystal pulling, there is The downward movement of the target is carried out at the same time, and the top of the heating section is always at the same level as the top surface of the melt (the descending speed of the crucible or heating section is the same as the descending speed of the melt surface)
A method has been reported that is characterized in that the

The difference between this method and the method of the present invention will be explained using FIG. 2.

In FIG. 2 1a, the depth center B of the melt in the crucible 1 is the center position A of the work coil.

The positional relationship in the case of the conventional method when the crystal is pulled and the amount of the melt becomes half of the amount in the crucible is shown in FIG.

In FIG. 2, A and B' almost match.

In Figure 2C, A is much lower than B'.

That is, the work coil is located below the crucible.

Although the method disclosed in Japanese Patent Publication No. 45-15604 does not crystallize crystals from the bottom of the crucible, the temperature at the bottom of the crucible becomes high and the temperature distribution and convection inside the crucible change greatly, making it difficult to obtain high-quality crystals. It becomes difficult.

In contrast, the method of the present invention not only eliminates the crystallization from the bottom of the crucible, but also hardly changes the temperature distribution and convection within the crucible, resulting in high quality crystals.

An example of the method of the invention under the same conditions as above is as follows.

Example 1 A single crystal of 50 mrr/z was pulled at a pulling speed of 3 mm/h and a rotational speed of 3 rpm, and the work coil was lowered at a speed of 1 mm/h after the shoulder of the crystal was formed.

As a result, a single crystal of 50 ynm91 x 110 mtnil was obtained, and about 80% of the melt in the crucible was also able to be made into a single crystal.

Example 2 Under exactly the same conditions as above, the lowering of the work coil was started not immediately after the creation of the crystal shoulder, but after the creation of 50g91 x 30mm1, that is, after about 30% of the melt in the crucible was created.

As in the above example, a single crystal of 50 mw91 x 100 H1 could be produced.

Example 3 Size: 70mdp Height: 707n'llt Thickness: 1m11L
215.2 g of a raw material, such as lithium carbonate, placed in a platinum crucible with a reflective plate made of platinum placed on top of the crucible.
819 g of niobium pentoxide was melted by high frequency heating.

Crystal diameter 4 at a pulling speed of 4 mm/h and a rotation speed of 25 rpm.
A single crystal of 0y was pulled.

The work coil has a diameter of about 2tnrrt/with crystal shoulders.
As a result of making the crystal while lowering the crucible, a single crystal of 40 md x 115 mail, which is about 80% of the melt in the crucible, could be made.

When the same experiment as above was carried out without lowering the work coil, the length was 70 mm1, which corresponds to about 50% of the melt! in,
It collided with the crystals that had crystallized from the bottom of the crucible, so it could not be made longer.

As explained above, according to the method of the present invention, the following effects can be obtained.

■ Most of the melt in the crucible (approximately 80% or more) was able to become a single crystal, and it was now possible to pull the melt for about twice as long as in the conventional method.

■ Comparing large and long crystals to conventional methods, crucible melting has made it possible to produce smaller crucibles smaller than the conventional method.

- The amount of remaining melt that was not pulled into the crucible was reduced to about 1/2 that of the conventional crucible, so the crucible deformed less and the number of times the crucible could be used increased by about 30%.

In the above embodiment, the relative position between the work coil position and the crucible was adjusted by lowering the position of the work coil, but in short, it is sufficient to set the relative position of the work coil and the melt. The same effect can be obtained by raising it in the same way as the coil.

It is important that the center position of the heating device in the depth direction of the crucible and the center position of the melt in the crucible in the depth direction are respectively preset intermediate positions with respect to the center in the depth direction. say something.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining an embodiment of the method of the present invention, and FIG. 2 is a comparative diagram of the conventional method and the method of the present invention. 1... Crucible, 2... Work coil,
3... Seed crystal, 4... Seed crystal holder, 6... Crucible self-melting material, 7...
Creation crystal, 8... Aluminum crucible, 9...
...Bubble alumina, A...Height of the center of the work coil, B...Height of the center of the melt in the crucible, B'...Height of the center of the melt in the crucible position (when a crystal is created and the melt surface height is lowered).

Claims (1)

[Claims] 1. A step of heating and melting the raw material in the crucible using a heating device provided around the crucible, and increasing the liquid level of the melt by placing a seed crystal in the melt and growing a single crystal. and a step of maintaining a preset position of the heating device at a depthwise intermediate portion of the heating device relative to a preset position of the depthwise intermediate portion of the melt in response to a decrease in the temperature. A method for producing a single crystal characterized by the following. 2. The manufacturing method according to claim 1, wherein the heating device is a high frequency heating device. 3. The method for producing a single crystal according to claim 1, wherein the preset position is a center position in the depth direction of the crucible for both the heating device and the melt. 4. The single crystal according to claim 1, wherein the step of maintaining the relative positional relationship is started after about 30% or more of the melt has been pulled up after the start of crystal creation. Production method. 5. The method for producing a single crystal according to claim 1, wherein the single crystal is a L I N b Os single crystal. 6. The method for producing a single crystal according to claim 1, wherein the single crystal is a LiTaO3 single crystal.