JPH0497989A - Production of single crystal and pulling up device for single crystal - Google Patents

Abstract

PURPOSE:To prevent a crack from being generated in NdGaO3 single crystal being left to stand by specifying the temp. gradient in the direction of a pulling-up axis of NdGaO3 single crystal. CONSTITUTION:The inside face of a heat insulating mold 5 is formed into a tapered face 5b nearly equal to an after-heater 2. The heat insulating molds 5, 6 are provided to a supporting base 8 fixed to the upper part of a crucible 1. The after-heater 2 is formed of a hollow body having a taper in the pulling-up direction and provided in the interval of 25-80mm from the liquid level of melt 7 introduced inside of this heater 2. Nd2O3 and Ga2O3 are introduced into the crucible 1 and heated by a high-frequency coil 4, and melted to form melt 7. Moreover the temp. gradient in the direction of a pulling-up axis is set at <=40 deg.C/cm in the interval (a) of 20-60mm from the liquid level of melt 7. Then seed crystal fitted to the tip of the pulling-up axis is brought into contact with melt 7 and pulled up. Grown NdGaO3 single crystal is annealed at >=1000 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing a single crystal, and more specifically, to a method for producing a single crystal, and more specifically, to a method for producing a single crystal, NdGa0. The present invention relates to a method for manufacturing a single crystal and a bow raising device.

(Prior Art) Conventionally, a pulling method has been used as the most common single crystal manufacturing method for silicon crystals and the like.

Application of the pulling method has also been attempted as a method for producing N d Ga Os single crystals.

Figure 3 shows a drawing of a conventional pulling device used for boat fishing. In Figure 0, 1 is an iridium crucible, 2 is an iridium afterheater, the point subtracted by 3 is a zirconia bubble, and 4 is high-frequency heating. The coil, 5.6 is a heat insulating cylinder, and 7 is a melt.

A sintered body of N d Ga O* is melted by a high-frequency heating coil 4, a seed crystal is attached to the melt, and the seed crystal is pulled up while rotating to grow an N d Ga Os single crystal. The crystal is heated by the tapered after-heater 2, and the cooling rate is slowed down to reduce cooling distortion. After heater 2 is installed immediately after lifting (AI degree 1650)
It is configured to slow down the cooling of the area up to about 7 cm from the

(Problems to be Solved by the Invention) When a NdGa 0° single crystal was grown by the method described with reference to FIG. 3, cracks appeared in the single crystal during the growth, making it impossible to obtain a high-quality crystal. Further, even if the crystal has few cracks, cracks may appear in the crystal while it is left standing after being taken out from the furnace. For this reason, it has been impossible to obtain a single crystal substrate with a large diameter from crystals grown using conventional methods. Furthermore, even with small diameter single crystal substrates, the yield was extremely low.

Furthermore, when N d Ga Os single crystals are grown using the conventional single crystal pulling apparatus shown in FIG. It has been found that no slope is formed and the racking problem described above occurs.

Therefore, it is an object of the present invention to provide a new single crystal manufacturing method and a pulling device that do not cause cracks during growth or when left standing after growth in a technique for growing NdGaOs single crystals using the bow raising method. purpose.

Furthermore, the present invention provides N d produced by the conventional pulling method.
An object of the present invention is to provide a method for preventing cracks from forming in a GaOs single crystal during storage.

(Means for Solving the Problems) The method according to the present invention provides a method for solving the problems of NdGa0. When growing a single crystal by the bow-raising method, the temperature gradient in the direction of the pulling axis of the N'd GaOs single crystal is set in an area of 20 mm to 60 mm from the liquid surface of the N'd Ga Os melt (hereinafter referred to as a "specific area"). This is a method for producing a single crystal, characterized in that the temperature is 40° C./cm or less at a temperature of 40° C./cm or less.

Also, a single crystal pulling device according to the present invention! is N d G
a Os single crystal pulling device, comprising: NdGa0. a crucible for accommodating a melt, a heating means for heating the melt in the crucible, and a hollow after-heater that surrounds a side surface of a single crystal pulled from an opening of the crucible and has a taper in the pulling direction; In a single crystal pulling apparatus comprising: a heat-retaining cylinder surrounding the outside of an after-heater;

The after-heater exists in a section 25 mm or more from the liquid level of the N d Ga Os melt, and the inner surface of the heat-insulating cylinder has a taper that is almost the same as the taper of the heater at a portion facing the after-heater. It is characterized by a face.

The present invention will be explained in detail below.

The present inventors measured the temperature gradient inside the pulling furnace as shown in FIG. 3 and found that it was extremely high in the above-mentioned specific section. This specific section is N d Ga O
Regarding the growth of s single crystals, it was found that this is the section where strain is most likely to occur, and that setting a gentle temperature gradient is effective in preventing cracks, and the method of the present invention was completed.

That is, when the temperature gradient in a specific section exceeds 40° C./cm, strain tends to occur in the specific section, leading to the occurrence of cracks. On the other hand, even if a temperature gradient of 40° C./cm or less is set outside the specific section, which is an area insensitive to cracking, it is not effective in preventing cracking. Also N d G
Since the degree of solidification is low below 20 mm from the liquid level of the aOs melt, and the l1 of the NdGaOs melt
If the distance exceeds 60 mm from the surface, the shrinkage strain due to solidification has passed the peak, so the temperature setting of the present invention has no effect.

In order to create such a temperature gradient, N in the crucible must be
When the means for heating the dG a O* melt is a high-frequency induction coil, it is necessary to make the refractory structure around the crucible dense and to adjust the position of the after-heater. Furthermore, when heating the crucible by resistance heating, an auxiliary heater is further provided and a predetermined temperature gradient can be set by heating a specific section.

Hereinafter, specific operations of the single crystal growth method will be explained.

The raw materials for the single crystal production method of the present invention are Nd, 0. and GaJi powder. These oxide powders are preferably of high purity of about 4N. Although these oxides can be mixed and immediately melted in a crucible, it is preferable to use a raw material obtained by CIP molding the mixed powder and then sintering it, in order to reduce evaporation of the raw material during melting. The sintered body was filled into an Ir crucible and heated to 1550 to 1 by high frequency heating or resistance heating.
Melts at 680°C. When the raw material is melted, a pulling rod equipped with a seed crystal is brought into contact with the melt from above, and the pulling rod is pulled up while rotating to grow an N d Ga Os single crystal. At this time, it is necessary that a specific section on the melt surface of the pulling furnace satisfies the above temperature gradient condition.

In order to prevent the occurrence of cracks in ingots grown by conventional methods during standing, the method of the present invention is also characterized by annealing at a temperature of 1000° C. or higher after pulling. This makes it possible to uniformly heat the ingot over its entire length and cross section, and to remove strain remaining in the ingot after pulling, thereby reducing cracks. However, in the conventional method, there are no cracks immediately after the growth (although cracks occur during the growth, so it is necessary to anneal as soon as possible after the pulling. Alternatively, if conditions for good soaking are obtained, continuous annealing may be performed after raising the bow in a pulling furnace.

The inventor also studied various pulling furnace structures, and as a result,
The after-heater includes at least the N d Ga
The cracks are present in an area 25 mm or more from the surface of the Os melt, and the inner surface of the heat insulating cylinder is designed to have a tapered surface that is almost the same as the taper of the heater in the part facing the heater. We have found that this can be prevented.

Conventional after-heaters are used in areas where cracks are most likely to occur (i.e., in areas 2
In the apparatus of the present invention, the position where the after-heater is to be installed was specified, since it is not provided to effectively and gradually lower the temperature in the specified section (0 mm to 60 mm). That is,
If the position where the after-heater is provided coincides with the specific section, the temperature gradient will become steeper on the tip side of the ingot, making it easier for cracks to occur. Furthermore, even if the afterheater is installed in the entire section up to 60mm from the melt surface, cracks are likely to occur as well.What is effective for cracking is to shift the afterheater 5mm above the specific section below it. It is. However, the upper side of the afterheater is placed 120 mm from the liquid level of the N d Ga Os melt.
It is preferable to provide an after-heater within the range of 25 to 120 mm, since if the temperature gradient ν is shifted by more than 20 mm, the temperature gradient ν will not become even gentler.

Furthermore, while conventional heat-insulating tubes were effective in keeping the entire device warm, they were not effective in keeping the areas where cracks were most likely to occur, so the structure of the heat-insulating tube was improved. First of all, by attaching a taper similar to that of the afterheater to the inner surface of the heat insulating cylinder, we made sure that as much of the heat from the afterheater as possible was directed toward the ingot.

(Function) The method recited in claim 1M is a method for controlling the temperature gradient in a specific area to be gentler than before. Comparing the temperature gradients of the conventional method and the method of the present invention in a specific section, it was found that in the conventional method, the temperature suddenly decreased on the low temperature side, so the temperature gradient of the entire specific section became steep. Since cracks are likely to occur with such a temperature gradient, the present invention prevents cooling on the low temperature side to achieve a gentle temperature gradient.

The annealing of the method according to claim 2 is a means for reducing the strain remaining in the ingot after pulling. This method is effective in preventing cracks that occur during storage after being removed from the furnace in the conventional method. The apparatus according to claim 3 is an apparatus for growing a single crystal by making the temperature gradient gentle in a section relatively far from the melt surface where cracks are likely to occur in the ingot.

Hereinafter, the present invention will be explained in more detail by way of examples with reference to FIG.

(Examples) Example 1 Equimolar amounts of Nd, O, and Ga*Os were mixed and sintered at 1500° C. after CIP molding. The obtained sintered body has a diameter of 10
It was placed in a 0 mm Ir crucible 1 and melted at 1600° C. in a nitrogen atmosphere by heating with a high frequency coil 4.

Above the crucible 1 of the pulling device, Ir fixed to the support stand 8 is placed.
Afterheater 2 of 25 mm to 80 mm from the surface of melt 7
It was provided with a taper angle of 70° in a section of mm. On the outside thereof, an alumina heat-insulating cylinder 5 was provided coaxially with 2. With these, the temperature gradient in the specific section a is made gentler.

A seed crystal (diameter 6 mm) attached to the tip of a pulling rod (not shown) was brought into contact with the melt 7, and the number of revolutions was 2 Orpm.
The crystal was grown at a pulling speed of 2.0 mm/hr while controlling the output of the high frequency coil 6.

The temperature distribution of the ingot obtained by the above method is shown in FIG. 2, and the temperature gradient in specific section a was 35° C./cm.

Seven ingots were produced using the above method, and no cracks occurred during crystal growth or while the ingots were left standing.

Comparative Example When an ingot was pulled using the apparatus shown in FIG. 3 in the same manner as in Example 1 except for after-heating and heat retention conditions, the temperature gradient shown in FIG. 4 was obtained. The temperature gradient in the specific section was 70°C/cm. Cracks occurred in four ingots during growth, and cracks occurred in three ingots while they were left.

Example 2 The ingot in which no cracks occurred during growth in Comparative Example 1 (slowly cooled after growth) was immediately placed in a Matsufuru furnace with excellent heat uniformity and heated at a rate of 20°C/hr to 1400°C.
When annealing was carried out by holding the sample for 10 hours and lowering the temperature at a rate of 20° C./hr, no cracks occurred during subsequent standing.

(Effects of the Invention) As explained above, according to the present invention, in the production of N d Ga Os single crystals, it is possible to prevent the occurrence of cracks both during crystal growth and during standing, resulting in an improvement in yield. and contributes to the manufacture of large substrates.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the apparatus according to claim 3 of the present invention, FIG. 2 is a graph showing the temperature gradient in Example 1, FIG. 3 is a cross-sectional view of a conventional crystal pulling apparatus, and FIG. is a graph showing the temperature gradient in the conventional method. 1- crucible, 2- after heater, 3- zirconia bubble, 4 is high frequency heating coil, 5.6- heat insulation cylinder, 7- melt, a- specific section (20-60 m from the surface of melt 7
m section) Figure 1 Figure 3

Claims (1)

[Claims] 1. When growing an NdGaO_3 single crystal by a pulling method, the temperature gradient in the direction of the pulling axis of the NdGaO_3 single crystal is set to 20 mm to 60 mm from the liquid level of the NdGaO_3 melt.
A method for producing a single crystal, characterized in that the temperature is 40° C./cm or less in a mm section. 2. NdGaO_3 single crystal grown by the pulling method,
A method for producing a single crystal, which comprises annealing at a temperature of 1000° C. or higher after pulling. 3. NdGaO_3 single crystal pulling equipment,
a crucible for accommodating a melt of GaO_3; a heating means for heating the melt in the crucible; and a hollow after-heater that surrounds a side surface of a single crystal pulled from an opening of the crucible and has a taper in the pulling direction. , a heat-insulating cylinder surrounding the outside of the after-heater, the after-heater being present in a section approximately 25 mm or more from the liquid surface of the NdGaO_3 melt, and the inner surface of the heat-insulating cylinder A single crystal pulling apparatus characterized in that a portion facing the after-heater has a tapered surface that is substantially the same as the taper of the heater.