JP3127500B2 - Construction method of ampoule for growing single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for constructing an ampoule for accommodating a raw material, a seed crystal, a solvent material and the like, which is used when growing a single crystal by using a zone melting method.

[0002]

2. Description of the Related Art The zone melting method has been used for growing semiconductors and oxide single crystals for a long time. This method is called a zone melt method, a traveling zone (TZ) method, or a THM (traveling heater method), and specifically, one example of the compound semiconductor HgCdTe is “SPIE vol. 659, Materi.
als Technologies for IR D
ecttrs (1986) / 131-136 ".

FIG. 2 shows the principle. First, seed crystal 2, solvent material (solvent) in ampoule 1 in order from the bottom
3. The crystal raw material 4 is stacked, and finally the stopper 5 is inserted and the inside of the ampule 1 is vacuum-sealed.

Next, an ampoule 1 is placed at the center of the annular heater 6.
And the position is adjusted so that the heater 6 and the solvent material 3 are at the same height. Then, the heater 6 is energized and heated to melt the solvent material 3. When the solvent 3 has melted, the ampoule 1 is slowly lowered.

[0005] By this movement, the lower part of the raw material 4 begins to dissolve into the solvent material 3, while a single crystal is crystallized from the solvent material 3 on the seed crystal 2, and the thickness gradually increases. When 3 reaches the upper end of the ampoule 1, all the raw materials are single crystallized.

[0006] The growth of a crystal is, in the end, how to release heat at the solid-liquid interface, that is, how ideally heat is transferred from a molten raw material to a solid seed crystal or a solidified single crystal. It's all about getting away.

[0007] Here, the ideal means that the amount of heat flowing is appropriate and at the same time the heat moves at a constant rate (speed) throughout.

[0008]

Focusing on these points, a conventional method for forming an ampoule will be considered using HgCdTe as an example. The configuration method of the ampoule is a method of storing a group of materials to be stored in the ampule. According to the method of constructing the ampoule, it can be seen that there is a difference in heat transfer between the crystal growth start stage and the stage where the growth has progressed to some extent.

That is, FIG. 3A shows a crystal growth start stage, in which heat flows from the solvent material 3 as a melt to the seed crystal 2 as a solid as indicated by an arrow, and further, the ampoule 1 is heated. Escapes into the atmosphere through the bottom surface 1 'of the (B)
In the stage where the growth has progressed to some extent, the heat diffuses from the solvent material 3 through the grown crystal 7.

At this time, CdTe constituting the seed crystal 2
And HgCdTe constituting the single crystal 7 have a difference in thermal conductivity, and CdTe is larger. On the other hand, the interface between the solvent material and the grown single crystal is called the solid-liquid interface,
In order to grow a single crystal having good crystallinity, this solid-liquid interface is desirably flat or slightly convex when viewed from the single crystal side.

The shape of the solid-liquid interface is determined by the heat from the heater and the thickness of the solvent, and these conditions are adjusted in accordance with the case where crystal growth has progressed to some extent and the heat flow has become steady. is there.

Therefore, at the initial growth start stage, the degree of protrusion of the solid-liquid interface becomes large because heat escapes from CdTe which is a seed crystal. The curve indicating the shape of the solid-liquid interface is an isothermal curve, which is an iso-composition curve from the viewpoint of the crystal composition.

In order to make a crystal into a device, it must be sliced, but on the cross section of the slice, the iso-composition curve becomes many concentric circles. This indicates that the crystal composition changes from the center to the circumference in the cross section.

In order to manufacture a device having good characteristics (for example, an infrared sensor), it is necessary that the change in the composition be small.

For example, in order to obtain an infrared sensor in the 10 μm band with good characteristics, the value of Cd of HgCdTe must fall within a range of 22.0% ± 0.5% for a length of 1 cm. If a temperature condition for obtaining this value is given at the stage where the crystal growth has progressed, the error range is expanded to 22% ± 1.5% at the initial stage of the growth.

The extent to which the large error range extends in the length direction of the crystal was examined for several examples of grown crystals. That is, in the case of this example, it turned out that it is about 10 mm.

Since the length of the crystal is 60 mm, it is about 17 mm.
% Of the crystals would not be usable. Since the crystal growth rate is 0.15 mm / H, the total growth time is 400
It is time, 17% of which is 67 hours, which means that time, energy and materials (resources) are wasted.

An object of the present invention is to provide a single crystal so that the flow of heat from the solvent material to the crystal side is constant even at the initial stage of growing a single crystal or at a stage where growth has progressed to some extent. An object of the present invention is to provide a method of forming an ampoule for growing a crystal.

[0019]

In order to achieve the above object, in the method of constructing an ampoule for growing a single crystal according to the present invention, when forming an ampoule for growing a single crystal by a band melting method, a starting material ingot is used. The portion including the cut lower end is disposed at the bottom of the ampoule as a discarded material, and the seed crystal, the solvent material, and the raw material ingot are sequentially stacked thereon and filled in the ampoule.

[0020]

[Function] By placing the same material as the crystal to be grown under the seed crystal, the heat flow is restricted by this material, the good heat conduction of the seed crystal is hindered, and even in the initial stage of crystal growth. Thus, a heat flow at the solid-liquid interface similar to the stage where the growth has progressed to some extent is realized. The thickness of the material placed under the seed crystal may be half its diameter.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. The ingot of HgCdTe, which is a single crystal raw material,
In the same manner as in the prior art, in a round-sealed (test tube type) ampule made of high-purity quartz having an inner diameter of 20 mm, mercury, cadmium, and tellurium were synthesized to make the length 70 mm.

A solvent material was prepared in the same manner. The raw material ingot was cut into a hemisphere and a cylinder by cutting a rounded portion at the lower end at a distance of 10 mm from the bottom. The solvent material was sliced to a thickness of 10 mm.

Separately, a high-purity quartz ampoule 1 having an inner diameter of 20 mm, which is also enclosed in a circle, is prepared, and as shown in FIG. A solvent material 3 and finally a cylindrical raw material ingot 4 were stacked. Note that a thin Te layer having a thickness of 300 μm was inserted between the seed crystal 2 and the waste material 8 in order to improve thermal contact.

The entire ampoule thus constructed is evacuated to a high vacuum with a vacuum pump, sealed with a stopper 5 and then suspended in an annular heater 6, which is then grown under the same conditions as before. Was done.

When the grown HgCdTe single crystal was cut longitudinally and the solid-liquid interface was examined, the solid-liquid interface at the initial stage of crystal growth, that is, the boundary between the seed crystal and the single crystal, was changed to the solid-liquid interface at the final stage. It was found that the interface, that is, the boundary between the solvent and the single crystal that reached the uppermost part of the ampoule also showed a slightly upwardly convex shape with the same curvature. In other words, the heat flow was optimized by the effect of the waste material at the solid-liquid interface in the initial stage.

[0026]

As described above in detail, according to the present invention, since the flow of heat is invariable between the initial stage of growing a single crystal and the subsequent stages, a single crystal having a uniform composition over the whole is obtained. Has the effect that can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional method.

FIG. 3 is a view showing a stage of growing a single crystal, and FIG.
Shows the initial stage, and (b) shows the stage where the breeding has progressed to some extent.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ampoule 2 Seed crystal 3 Solvent material 4 Raw material 5 Plug 6 Heater 8 Discarded material

Claims (1)

(57) [Claims] When an ampoule for growing a single crystal is formed by a zone melting method, a portion including a lower end portion cut out from a raw material ingot is disposed at the bottom of the ampoule as a discarded material, and is sequentially placed thereon. A method for forming an ampule for growing a single crystal, comprising stacking a seed crystal, a solvent material, and a raw material ingot and filling the ampule.