JPH0753297A - Method for growing single crystal - Google Patents

Abstract

PURPOSE:To grow a homogeneous crystal by introducing a melt obtd. by melting a mixture composed of a raw material having a compsn. equal to the component compsn. of a desired crystal and a flux into a small-bore pipe part and pulling up or pulling down the crystal with a seed crystal. CONSTITUTION:The raw material having the compsn. equal to the component compsn. of the desired crystal and the flux of the prescribed amt. of this raw material are mixed to obtain a mixture. This mixture is charged into a crucible 1 of a resistance heating type and is melted to obtain the raw material melt 2. This melt 2 is introduced to the small-bore pipe part 5 of the crucible 1 and is brought into contact with the seed crystal 3, and thereafter, the seed crystal 3 is pulled up or pulled down to grow the single crystal 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of growing a single crystal from a so-called in-congruent raw material melt in which the composition of the crystal and the raw material melt for growing the same are different. Regarding

[0002]

2. Description of the Related Art A pulling method (Czochralski method or CZ method) is a typical example of a crystal growth method carried out from a raw material melt, in which the crystal and the raw material melt producing it have the same composition. So-called congruent (congruent melting)
This is a method applied to a different raw material melt [point c in FIG. 4].

In this method, the composition of the grown crystal is uniform because the composition of the grown crystal and the raw material in the crucible do not change during the entire process of crystal growth.

In the crystal growth from the in-congruent melt [point in FIG. 4i], however, the composition of the melt remaining in the crucible gradually changes as the crystal grows from the raw material melt, so the growth proceeds. As a result, the composition of the crystal itself changes.

In order to avoid this problem, in actual crystal growth, a method of growing a small amount of crystals from a large amount of the raw material melt in which the composition change of the raw material melt accompanying the crystal growth is negligible, or a flux is used. A so-called flux pulling method (TSSG method) is generally adopted.

As the flux in the TSSG method, a flux material having a constituent element different from that of the crystal or a so-called self-flux having the same constituent element as the crystal but having a different composition ratio is used. The raw materials of the composition are once dissolved in these fluxes, and the temperature of the melt is lowered while precipitating and crystallizing the crystal components while being crystallized.

Alternatively, as shown in FIG. 5, a certain amount of flux is embedded in a part of the raw material rod 8, the part is locally melted to form a melting zone 9, and the melting zone 9 is moved. The so-called flux melting zone transfer method (flux zone traveling method) in which crystal growth is carried out while simultaneously melting the raw material rods 8 and precipitating crystal components from the melting zone
Is also known.

[0008]

In any of the above methods, the process of separating the crystal component dissolved in the solvent and the process of the component reaching the solid-liquid interface and being taken into the crystal simultaneously proceed. While continuing the crystal growth.

The TSSG method is said to be able to easily obtain relatively good crystals, but the raw material and the flux are mixed and melted in the crucible, and the melt is constantly flowing in the crucible by thermal convection. Since the crystal growth is carried out under the temporal and temporal temperature fluctuation due to this thermal convection, the flux is easily incorporated into the crystal.

In order to prevent this, measures to extremely slow down the crystal growth rate and the temperature drop rate of the melt are taken, but it is difficult to achieve optical quality because the two conditions are intricately correlated, and productivity is increased. There were drawbacks such as not rising.

Also in the homogeneity of the crystal, as shown in FIG. 4, for example, the raw material of the composition c1 is once melted [m1 point], and the temperature is changed.
When the crystal is deposited while descending from t1 to t2, the composition of the crystal changes from s1 to s2 as it precipitates, and the composition of the raw material melt remaining in the crucible changes from c1 to c2, resulting in a uniform crystal composition. There is also the essential problem that it is impossible to obtain.

On the other hand, in the flux melting zone transfer method shown in FIG.
Since it is difficult to maintain a stable melting zone 9 and it is necessary to keep the amount of the raw material rod 8 melted therein and the amount of the crystalline component discharged by crystallization equal, the melting zone 9 and the raw material rod 8 are separated. It is necessary to move at a speed, it is difficult to grow a homogeneous crystal because it is technically difficult that the crystal diameter easily fluctuates, the growth conditions are easily affected by subtle changes in the ambient temperature, and so on. There were also challenges.

The present invention aims to grow a homogeneous crystal from an in-congruent raw material.

[0014]

To this end, in the present invention, as shown in FIG. 1, a raw material having the same composition as the target crystal and a predetermined amount of a flux for melting it are mixed and melted in the crucible 1, By introducing a part of the melt 2 into the small-diameter pipe 5 and causing crystals to grow at the tip thereof, a device was devised to prevent the melt near the crystallization point and the melt in the surrounding crucible from mixing. .

In the case of the resistance heating type crucible 1 shown in FIG. 1, a small diameter nozzle 5 is formed by opening a hole at the bottom of the crucible and inserting a small diameter nozzle into the hole. A means was adopted in which the melt flowing through was crystallized at the tip thereof while being crystallized by using the seed crystal 3.

Further, instead of the direct heating method using the resistance heating type crucible 1 in FIG. 1, the present invention can be configured by an indirect heating method using the vertically long crucible 1 as shown in FIG. As shown, a combination of the crucible 1 and the die 8 can be used to pull up.

In any of the configurations, a raw material having the same composition as the crystal and a predetermined amount of a solvent or self-flux therefor are mixed and melted, and the melt is guided to a small-diameter mouth tube portion, and its tip hole mouth In the part, crystallization is performed while pulling down or pulling up using a seed crystal.

[0018]

According to the above-mentioned means, as shown in FIG. 1, for example, the raw material melt 2 mixed with the melting agent and melted flows into the crucible 1 and the small-diameter mouth tube portion 5 at the start of growth. Although it is filled with such a composition, the seed 3 reacts at the moment when it touches the melt at the tip of the small diameter tube portion 5 and changes to a new melt composition, but the raw material melt that participates in this reaction is Since it is limited to the small diameter pipe 5 and cannot be easily mixed with the surrounding melt, the influence of the raw material melt 2 is avoided in a short time.

When the seed crystal 3 is pulled down in this state,
The crystal component is separated from the melt from the melt in the small-diameter pipe section 5 to grow crystals on the seed crystal, and the separated and left flux is accumulated in the small-diameter pipe section 5. Finally, the small-diameter pipe section 5
The flux layer 6 will be formed therein.

In a steady state, the crystal component of the melt 2 in the crucible reaches the tip of the small-diameter tube portion 5 through the flux layer 6, and the process of crystallization while separating from the flux proceeds there.

Since the crystallization point is limited to the tip of the small diameter tube portion 5, the size of the crystal and the amount of the raw material to be crystallized are constant, so that the space between the raw material melt and the flux layer and between the flux layers. The thermal conditions such as the temperature difference between the crystal and the crystal can be easily fixed, and it has become possible to grow a homogeneous crystal even from an in-congruent raw material.

[0022]

FIG. 1 shows an example for carrying out the content of the present invention,
Potassium lithium niobate (K ₃ Li ₂ NbO) is used as a typical in-congruent (mismatched) raw material.
₅ is an example in which the method of the present invention was tried by using KLN) as a target crystal.

The starting material is potassium carbonate (K ₂ CO ₃ ),
Lithium carbonate (Li ₂ CO ₃ ), niobium pentoxide (Nb
₂ O ₅ ), a predetermined amount of formula is weighed, mixed and pressed, and then firing at 950 ° C. for 12 hours is repeated twice, and then pressed again and sintered at 960 ° C. for 10 hours. A raw material having a crystal composition was obtained.

As the self-flux for this raw material, K ₂ CO ₃ : Li ₂ CO ₃ : Nb ₂ O ₅ is 33: 22: 4.
Weighed in the ratio of 5 and fired once under similar temperature conditions,
It was heated at 1050 ° C. for 3 hours to be melted, synthesized, and mixed with the raw material at a self-flux ratio of 1: 1 to 5: 1 to fill the crucible.

A typical example of the crucible used is a resistance heating type platinum crucible 1 as shown in FIG. 1, which has a hole at its bottom and is penetrated through a platinum pipe having a diameter of about 100 to 800 microns to draw a melt. This is a structure in which the small-diameter mouth tube portion 5 is formed.

A part of the raw material melt 2 is introduced into the small diameter pipe 5,
Using the seed crystal 3 at the tip, the speed is 0.1-0.7 mm / mi
Crystal growth was performed while pulling down the seed crystal without rotating the seed crystal at n, and a transparent and homogeneous tetragonal crystal was obtained.

If a heat source is sought for high frequency heating, resistance heating, infrared light heating, etc. instead of using the crucible itself as the heat source, it is possible to select a wide range of crucible capacities and shapes. An example of the indirect heating method is shown in FIG.

In this example, a vertical pencil type is adopted for the crucible 1, and a tip hole mouth of 100 to 700 μm is opened at the tip of the crucible 1 so that the crucible 1 serves as a small-diameter pipe and the crucible 1 is placed in an infrared heating furnace. A single crystal was grown in the same procedure as above while being installed and controlling the crucible temperature.

FIG. 3 shows an example of growth by the pulling method. In the structure in which a die 7 having a small diameter is erected in the crucible 1, the raw material melt 2 is guided to the upper end of the die 7 by a capillary phenomenon. Pulling was performed using the seed crystal 3 at the tip.

Since the self-flux of the same kind of element as the crystal composition is adopted for growing KLN, they are not separated due to the difference in specific gravity, and the single crystal fiber of KLN is grown by the pulling down method in the same manner as in the pulling down. did it.

[0031]

EFFECTS OF THE INVENTION According to the present invention, the use of the small-diameter pipe 5 restricts the mixing of the melt near the crystallization point and the raw material melt around the crystallization point, and stabilizes the temperature near the crystallization point. By growing the crystal while forming the flux layer 6, it is possible to grow a homogeneous single crystal even from an in-congruent raw material melt.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention by a pulling-down method using a direct heating type resistance heating type crucible.

FIG. 2 is a view showing an example of an indirect heating type lowering method using a pencil type crucible.

FIG. 3 is a diagram showing an example of the present invention by a pulling method using a die.

FIG. 4 is a congruent of raw material melt (congruent melting),
And a phase diagram for explaining in-congruent (mismatched melting), where A and B represent two elemental components, point c is congruent composition, point i is in-congruent composition, s1 , S2 and c1, c2 are the temperature t
The composition of the crystal and the composition of the residual melt at 1 and t2, m and m1 represent the molten state of the compositions c and c1, respectively.

FIG. 5: Principle explanatory diagram of flux melting zone transfer method (flux zone traveling method)

[Explanation of symbols]

 1 is a crucible 2 is a raw material melt 3 is a seed crystal 4 is a grown crystal 5 is a small diameter mouth tube 6 is a flux layer 7 is a pulling die 8 is a raw material rod 9 having the same composition as the crystal 9 is a melted melt Melting zone made of agent 10 is a heat source for melting 11 is moving melting zone 12 is moving raw material bar

Claims (1)

[Claims] 1. In-congruent (mismatched melting)
In the growth of a single crystal performed from a raw material melt, a raw material having the same component composition as the target crystal and a predetermined amount of a flux for the raw material are mixed and melted, and the melt is guided to a small-diameter mouth tube portion, A method for growing a single crystal, which is carried out while pulling down or pulling up at the tip.