JPS6389488A - Production of single crystal - Google Patents

Abstract

PURPOSE:To produce the title single crystal in optimum thermal environment by shielding the heat radiation from the wall of a melting crucible to the single crystal at the time of producing a single crystal by a rotary pulling up method. CONSTITUTION:A heat shielding body 11, an annular body having an inverted L-shaped cross section extending toward the center, is provided at the slightly upper part of the inner wall surface of an alumina crucible 3, and the lower end is hung down between the inner wall of a Pt-Rh crucible 1a and a single crystal 6. The heat shielding body 11 consists of a ceramic heat-resistant material or a noble metal such as Pt-Rh. Such a furnace is used, and a seed crystal 8 is brought into contact with the surface of a raw material melt 5 in the crucible 1a and then pulled up while being rotated to produce a single crystal 7. Consequently, since the heat radiated from the side wall of the crucible 1a is shielded by the heat shielding body 11, the temp. gradient at the upper part of the melt 5 is not excessively eased even when a large-bore crucible is used, the heat insulating effect can be changed by changing the material and shape of the heat shielding body 11, and the temp. gradient can be optionally set in accordance with the kind of the single crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a method for producing a single crystal by a rotational pulling method.

(Prior art) Single crystals such as LiTaO3 and Li2B4O7 are suitable for SAW device substrates because they have piezoelectricity at room temperature, have a zero temperature coefficient, and have a large orientation with a coupling coefficient of 2, about 1.0%. It is widely used as

Conventionally, such LiTaO3 and Li 2 B 407
A method for producing a single crystal, such as a method for producing a single crystal, in which a seed crystal to be pulled up is brought into contact with the melt surface of a molten raw material in a melting crucible, and the seed crystal is pulled up while rotating to produce a single crystal. has been adopted.

Such a conventional method for manufacturing a single crystal will be explained with reference to FIG.

The platinum crucible 1, which serves as a melting crucible for storing raw materials, is surrounded by a bubble alumina 2, an aluminum crucible 3, etc., and a high frequency work coil 4 installed around the outer periphery of the aluminum crucible 3 is used to melt the inside of the platinum crucible 1. For example, if a Li2B4O7 single crystal is to be produced, the contained raw material for the single crystal is Li2B4O7 powder or 1. Li2CO3 and B
A raw material melt 5 is prepared by induction heating a mixture of 2O5.

The single crystal 6 is produced by bringing the seed crystal 8 attached to the lower end of the seed holder 7 provided on the central axis of the platinum crucible 1 into contact with the surface of the raw material melt 5 while controlling the temperature of the raw material melt 5.
This is done by pulling up while rotating.

In such a single crystal manufacturing method, a single crystal 6 is pulled from a high temperature raw material melt 5 to a low temperature side above the platinum crucible 1.
is gradually cooled and causes thermal distortion, which may cause cracks. Therefore, an after-heater 9, an alumina heat-insulating tube 10, etc. are installed on the top of the platinum crucible 1 to make the temperature gradient gentle. Prevents cracks from occurring due to thermal distortion.

However, if the temperature gradient becomes too gentle, another problem may occur in which the single crystal 6 becomes bent and polycrystals are more likely to form.Also, the optimal temperature gradient varies depending on the type of single crystal 6 to be manufactured. Efforts have been made to create a temperature atmosphere suitable for the type of single crystal to be produced by changing the relative position and shape of the platinum crucible 1, after-heater 9, and high-frequency work coil 4, or by changing the heat retention state by the refractory.

(Problems to be Solved by the Invention) However, in the conventional single crystal manufacturing method as described above, (a) When the diameter of the melting crucible is increased, heat dissipation from the upper part of the melting crucible and the raw material melt increases. As a result, the temperature gradient on the surface of the raw material melt becomes too gentle, making it unsuitable for producing single crystals that require a steeper temperature gradient than in the state where there is no part of the material. It becomes difficult to easily achieve intermediate temperature gradients.

(b) When the diameter of the pulled single crystal is increased to increase the productivity of single crystals and devices using single crystals, the melting crucible becomes larger due to the larger diameter, and a large weight of raw material melt is produced at a high temperature close to the melting point. must be accommodated, and the load on the melting crucible increases due to repeated solidification and melting of the original fI melt. Therefore, the deformation of the melting crucible becomes large, and the temperature distribution of the raw material melt in the melting crucible worsens, which not only causes a decrease in yield, but also shortens the life of the melting crucible and increases the cost of producing single crystals. Further, deformation of the crucible causes damage such as cracks to the refractory surrounding the crucible.

(c) If you want to pull up all the raw material melt or charge a powdered raw material with a low density, you will have to pull the single crystal from a low melt surface level, so from the crucible wall above the raw material melt surface. The heat dissipation becomes large and the temperature gradient becomes too gentle, making it difficult to pull the single crystal.

(d) When alumina cement is used to join an alumina tube seed holder and a seed crystal, if the joint becomes too hot, the seed crystal and alumina react and deteriorate, causing the seed crystal to fall.

There are problems such as (a), (c), and (d) in the above problems.
Problem (b) is due to the increase in heat dissipation from the crucible wall and raw material melt surface due to the larger diameter of the melting crucible, and the lowering of the raw material melt surface further promotes a too gentle temperature gradient. Both problems were caused by a lack of freedom in setting the temperature inside the melting crucible due to increased weight and thermal expansion due to the increased capacity of the melting crucible.

The present invention solves the above-mentioned problems, and provides a method for manufacturing single crystals that can manufacture single crystals in an optimal thermal environment by mainly shielding a part of the radiant heat from the melting crucible wall to the single crystal. The purpose is to provide.

[Configuration of the Invention (Means for Solving Problems)] The method for producing a single crystal of the present invention involves bringing a seed crystal into contact with the surface of the raw material melt in a melting crucible, and pulling up the seed crystal while rotating to produce a single crystal. A single crystal manufacturing method for manufacturing a crystal is characterized in that the manufacturing of the single crystal is performed while at least part of thermal radiation from the crucible wall to the single crystal is shielded.

(Function) The thermal environment inside the melting crucible can be freely set by blocking part of the thermal radiation to the pulled single crystal.

(Example) An example of the method of the present invention will be described below with reference to the drawings. Note that the same parts as in FIG. 2 are given the same reference numerals, and the explanation of the overlapping parts will be omitted.

Embodiment 1 Figure 1 is a schematic cross-sectional view showing a single crystal production furnace used in the method of the present invention, in which a slightly upper part of the inner wall surface of an aluminum crucible 3 has an inverted cross section extending toward the center. A heat shield 11, which is an annular body, is provided so that its lower end is suspended from the inner wall of the Pt-Rh crucible 1a and the single crystal 6rif1.

This heat shield 11 is made of a ceramic heat-resistant material or a noble metal such as P.
It consists of t-Rh etc.

In such a furnace, the heat shield 11 insulates heat from the side wall of the platinum crucible, so even when a large-diameter crucible is used, it is possible to prevent the temperature gradient above the raw material melt 5 from becoming too gradual. Further, by changing the material, shape, thickness, etc. of the heat shield 11, the heat insulating effect changes, and the temperature gradient can be arbitrarily set depending on the type of single crystal. Therefore, in order to pull up the entire amount of charged raw material, about 5 sides of the raw material melt are
The temperature gradient can be maintained at an appropriate level even when the charge amount is reduced to approximately half the volume of the Pt-Rh crucible 1a.

A Li Ta O3 single crystal was actually produced using the above-mentioned furnace. During production, the amount of raw material charged to the Pt-Rh crucible 1a was set at about 172, and the entire amount was withdrawn. Moreover, Pt-Rh was used as the member of the heat shield 11.

Even if the charge amount of the raw material is reduced to 172 compared to the conventional one and the raw material melt is lowered by about 5 sides, Pt-R can be maintained by using the heat shield 11.
Since the heat from the wall of the crucible 1a is blocked, the temperature gradient does not become too gentle. In addition, since Pt-Rh material is used, the insulation effect is smaller than that of alumina material, and the temperature gradient is slightly gentler because it is heated with high frequency, but the heat shield 11
Since the diameter of the Pt-Rh crucible 1a is smaller than the diameter of the Pt-Rh crucible 1a, and it is located inside the PT-Rh crucible 1a, the radiant heat from the inner wall of the Pt-Rh crucible 1a is shielded, resulting in less heat generation and an appropriate temperature gradient. ing.

By using this method of manufacturing single crystals, in which pulling is performed while shielding the radiant heat to the single crystal, it is possible to create an appropriate temperature gradient even with a small amount of charged raw material, and it is possible to pull up the entire amount of charged raw materials. In addition, the joint between the seed crystal 8 and the seed holder 7 was not corroded by heat. In addition, by being able to raise the total amount, P t-
The deformation of the Rh crucible 1a was almost eliminated, the life of the crucible was significantly extended, and the crucible was in a state where it could be used more than three times as many times as before. Therefore, the life of the refractory around the crucible was significantly extended, and the temperature conditions were stabilized, and there was no residual raw material in the crucible with high impurity concentration, and the production yield of single crystals was improved by about 20%.

Example 2 In the furnace used in Example 1, a Li2B+07 single crystal was actually produced using alumina material as the member of the heat shield 11. By using alumina, which has a high heat insulating effect, as the heat shield 11, the temperature gradient on the surface of the raw material melt 5 can be made steep. Since Li2B 40 y has a low melting point of 917° C. and poor thermal conductivity, it seems necessary to make the temperature gradient steeper than <<Li2B,07 in order to dissipate heat compared to LiTaO3.

The L i 2 B 407 single crystal produced in this manner had a diameter of 2 inches and a length of 50 nl, had very good reproducibility, and could be pulled in its entirety.

Example 3 A Li2 B407 single crystal was actually produced using a transparent quartz glass material as the member of the heat shield 11 of Example 1.

Since a transparent quartz glass material is used, there is no need to provide a peephole in the heat shield 11 for observation of single crystals, improving heat uniformity, and has better radiant heat transmission than alumina material.The temperature gradient is gentler. Met. In addition, since the surface was cleaner than that of alumina material, there was very little contamination from impurities. Overall, the yield of Li2B*Oy single crystals in this example was about 80%, with fewer cracks and less polycrystallization than when an alumina member was used. Note that the members of the heat shield plate are not limited to those used in the above-mentioned embodiments, and may include, for example, Pt, Ir, Si3N4, Zr.
What is necessary is to select one suitable for the required thermal environment, such as O2 or MgO.

[Effects of the Invention] As explained above, according to the method for manufacturing a single crystal of the present invention, an optimal thermal environment can be created depending on the type of single crystal by blocking at least a part of the thermal radiation to the single crystal. The effect is that it can be created.

This effect makes it easy to produce single crystals, which were difficult to produce in the past, and even if the amount of charged raw materials is reduced to prevent the melting crucible from deforming, it is easy to pull up the entire amount of charged raw materials. Deformation of the expensive melting crucible is reduced, and the life of the crucible can be greatly extended. Furthermore, if the deformation of the melting crucible is reduced, the thermal conditions of the pulling furnace will be stabilized, leading to an improvement in the yield during the production of single crystal M.

By the way, in the above-mentioned examples, the method of the present invention was applied to a high frequency heating furnace, but the method of the present invention is not limited to this, and similar effects were confirmed when applied to a resistance furnace.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a furnace according to an embodiment of the present invention, and FIG. 2 is a sectional view showing the structure of a conventional furnace. 1...Platinum crucible 1a...Pt-Rh crucible 2...Bubble alumina 3...Aluminum crucible 5. ...... Raw material melt 6 ...... Pulled single crystal 8 ...... Seed crystal 9 ... Heat shield application Person Toshiba Corporation Patent Attorney Sasa Suyama - Figure 1

Claims (5)

[Claims] (1) In a method for producing a single crystal in which a seed crystal is brought into contact with the surface of a raw material melt in a melting crucible and a single crystal is produced by pulling up the seed crystal while rotating, the production of the single crystal is carried out from the wall of the crucible. A method for manufacturing a single crystal, characterized in that at least part of the heat radiation to the single crystal is shielded. (2) The method for producing a single crystal according to claim 1, wherein the heat shielding is performed by a cylindrical heat shield placed between the single crystal and the inner wall surface of the melting crucible. (3) The method for producing a single crystal according to claim 2, wherein the heat shield is divided into a plurality of parts. (4) Shielding material is Pt, Pt-Rh, Ir, SiO_2
, Si_3N_4, Al_2O_3, ZrO_2, Mg
3. The method for producing a single crystal according to claim 2, wherein the single crystal is made of a material mainly consisting of at least one selected from O. (5) Claim 1, characterized in that the pulling of the single crystal is carried out while changing the position of the heat shield so that the temperature above the surface of the raw material melt becomes a temperature suitable for pulling the single crystal. Method for manufacturing the single crystal described.