JPH08208367A - Liquid crystal growth method and liquid crystal growth apparatus - Google Patents

Abstract

(57) [Summary] [Object] With regard to liquid crystal growth, an object thereof is to provide a crystal growth technique capable of obtaining a columnar grown crystal having a substantially planar upper surface. [Structure] In a liquid phase crystal growth method in which a temperature difference is formed above and below a solvent, a source crystal is placed in a high temperature part of the solvent, and crystal growth is performed in a low temperature part of the solvent, a solute is supplied from the source crystal to obtain a substantially constant temperature. The method is characterized by including a step of performing crystal growth at a growth rate and a step of stopping the supply of the solvent from the source crystal and heat treating the grown crystal in a saturated solution.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to liquid phase crystal growth.
Solution crystal growth, which can lower the growth temperature, is expected as a bulk crystal growth technique for compound semiconductors with high vapor pressure, particularly II-VI group compound semiconductors.

[0002]

2. Description of the Related Art II-VI compound semiconductors have a high melting point and the vapor pressures of the constituent elements are high. Therefore, not only high pressure resistance is required for the crystal growth container in melt growth, but also high density crystal defects are likely to occur in the grown crystal.

Utilizing solution growth makes it possible to lower the crystal growth temperature of II-VI group compound semiconductors.
There is a possibility of obtaining good quality crystals. II as a solvent
-Group II element or V which is a constituent element of group VI compound semiconductor
Methods using Group I elements have been proposed.

Referring to FIG. 3, the conventional II-
A crystal growth method by solution growth of a Group VI compound semiconductor will be described. The left side of the figure shows the crystal growth apparatus in cross section, and the right side shows the temperature distribution set in the crystal growth apparatus in the form of a graph.

A crystal growth container 1 is formed by connecting two types of quartz tubes having appropriate diameters. At the beginning, the upper end is left open. A heat sink 6 made of a material having a high thermal conductivity such as carbon is arranged in the lower part of the crystal growth container 1.

The heat sink 6 has a recess for mounting the seed crystal 5 on its upper surface, and is fixed to the crystal growth container 1. Seed crystal 5 in the depression on the top of heat sink 6
Is placed, and a cylindrical seed stopper 4 having an appropriate length is inserted from above and fixed to the crystal growth container 1. In addition, in the state before the raw material is filled, for example, the upper portion of the crystal growth container 1 is opened.

Se-Te is used as the solvent 3 in the crystal growth container 1.
(Se and Te at a predetermined mixing ratio), and a sufficient amount of grown crystal as the source crystal 2 is inserted with a sufficient amount of ZnSe polycrystal so that the supply of the source does not stop halfway. In addition,
When only Se is used as a solvent for ZnSe crystal growth, Zn
The solubility of Se is low. Se-Te is used because Te is added to increase the solubility. After the source crystal 2 and the solvent 3 are charged, the inside of the crystal growth container 1 is evacuated and the open portion is sealed.

The crystal growth ampoule thus prepared is
It is placed in an externally heated electric furnace in which a temperature gradient is set as shown on the right side of FIG. The external heating type electric furnace is configured by winding a heater wire 8 around a core tube 7, and a vertical space for accommodating the crystal growth container 1 is formed inside the core tube 7.

Inside the core tube 7, as shown on the right side of the drawing, a temperature distribution in the vertical direction is set, which is high in the upper part and low in the lower part. The temperature at the position where the source crystal 2 is arranged is T
s, the temperature at the position on the surface of the seed crystal 5 where crystal growth occurs is indicated by Tg. Ts> Tg.

When the crystal growth container 1 is placed in such a temperature distribution, the source crystal 2 in the high temperature portion is dissolved in the solvent 3 up to the saturation solubility in the high temperature portion. The saturated solubility in the high temperature part is higher than the saturated solubility in the low temperature part. The source crystal component dissolved in the solvent 3 also moves to the low temperature part by diffusion, so that the solution in the low temperature part is supersaturated.

Crystal growth occurs on the seed crystal 5 when the seed crystal 5 is arranged at a low temperature portion and comes into contact with the supersaturated solution. In this way, a bulk single crystal is grown on the seed crystal 5.

This growth is carried out at a constant temperature until the source crystals are exhausted, and a constant growth rate is obtained.

[0013]

The shape of the grown crystal produced by the conventional technique is a convex shape in which the central portion is higher than the peripheral portion.

Since the diameter of the crystal in the convex portion in the horizontal plane is small, it is not possible to cut out a wafer having a uniform diameter. Therefore, it is necessary to cut off or scrape the convex portion,
The wafer cannot be cut out efficiently by using 0%.

An object of the present invention is to provide a crystal growth technique capable of obtaining a columnar grown crystal having a substantially flat upper surface.

[0016]

A liquid crystal growth method of the present invention is a liquid in which a temperature difference is formed above and below a solvent, a source crystal is arranged in a high temperature portion of the solvent, and crystal growth is performed in a low temperature portion of the solvent. The phase crystal growth method includes a step of supplying a solute from a source crystal and growing the crystal at a substantially constant growth rate, and a step of stopping the solute supply from the source crystal and heat treating the grown crystal in a saturated solution. It is characterized by

[0017]

[Function] The crystal is grown by the liquid phase crystal growth method, the supply of the solute from the source crystal is stopped, and the grown crystal is heat-treated in a saturated solution to form a convex shape in which the central portion is higher than the peripheral portion. It was confirmed that the top surface of the grown crystal, which had a cylindrical shape with the top surface, became substantially flat.

When the solute is supplied from the source crystal and the solution is in a supersaturated state, the precipitation rate is more dominant than the dissolution rate, and the crystal growth rate at the central portion is higher than that at the peripheral portion. Since it is faster than the crystal growth rate, it is considered that a columnar single crystal having a convex upper surface with a raised central portion grows.

However, when the supply of solute is stopped, the redistribution of solute molecules on the surface becomes dominant, the central part of the grown crystal is redissolved, and reprecipitation occurs in the peripheral part, and the growth follows the temperature distribution. It is thought that the face will be obtained.

[0020]

EXAMPLES Hereinafter, ZnSe of II-VI group compound semiconductors will be described.
Will be described by taking as an example the case of growing with a Se-Te solvent. ZnSe is a material expected as a blue light emitting semiconductor element.

FIG. 3 shows a crystal growth apparatus used in the embodiment of the present invention. The left side of the figure shows a cross-sectional view of the crystal growth apparatus, and the right side of the figure shows the temperature distribution set in the furnace. A crystal growth container 1 is prepared by connecting a small diameter quartz tube 1a having an appropriate diameter and a large diameter quartz tube 1b. At this stage, the upper part of the large-diameter quartz tube 1b is open.

The growth crystal container 1 is etched with hydrofluoric acid to clean the surface. Crystal growth container 1 with clean surface
A heat sink 6 made of a material having a high thermal conductivity such as carbon is housed in the bottom of the substrate and vacuum baked. A part of the heat sink 6 is preliminarily carved, and the heat sink 6 is fixed by deforming the growth container 1 accordingly.

As the seed crystal 5, a ZnSe single crystal having a plane orientation (111) plane is prepared. Note that (111)
It is also possible to use a ZnSe single crystal other than the plane. After the seed crystal 5 is mirror-polished, it is washed and mirror-etched. The seed crystal 5 thus prepared is placed in the recess formed on the upper surface of the heat sink 6, and the cylindrical seed stopper 4 made of a material such as quartz is inserted thereon.

The upper surface of the seed crystal 5 is substantially flush with the upper surface of the heat sink 6. The upper end of the seed stopper 4 is arranged slightly below the small-diameter upper end of the crystal growth container 1. After disposing the seed stopper 4, the seed stopper 4 is fixed by recessing the crystal growth container 1.

After that, Se-T having a predetermined composition is used as the solvent 3.
The e-mixture and the source crystal 2 are charged into the crystal growth container 1 with ZnSe polycrystals in an amount necessary for the desired amount of grown crystals in consideration of the amount of solvent and the solubility. Source crystal 2 is
The seed stopper 4 is a lump having a size larger than the inner diameter of the seed stopper 4 and is held by utilizing the step of the crystal growth container 1.

The crystal growth container 1 thus filled with the source crystal 2 and the solvent 3 is connected to a vacuum evacuation device, the interior thereof is evacuated to a vacuum degree higher than 2 × 10 ^-6 Torr, and the open end is sealed. Stop.

The crystal growth container 1 thus prepared is placed in an electric furnace having a predetermined temperature distribution as shown on the right side of FIG. The electric furnace has a structure in which a heater wire 8 is wound around a furnace core tube 7 that forms a vertical space in which the crystal growth container 1 can be housed.

In the electric furnace, the temperature of the position where the source crystal 2 is arranged is represented by Ts, and the temperature of the portion of the surface of the seed crystal 5 where crystal growth occurs is represented by Tg. Source crystal 2
Dissolves in the solvent 3 to the saturation solubility at the source temperature Ts. The source crystal component diffuses in the solvent and moves to a low temperature part. Since the saturated solubility is low in the low temperature part, the solution becomes a supersaturated solution. By contacting the seed crystal 5 with a supersaturated solution having an appropriate degree of supersaturation, the seed crystal 5
Crystal growth occurs on top.

The states inside the crystal growth container 1 before the start of crystal growth and immediately after the end of crystal growth are shown in FIGS. 1 (A) and 1 (B), respectively. Immediately after completion of crystal growth, as shown in FIG.
The source crystal 2 is completely dissolved in the solvent 3, and the upper surface of the grown crystal 9 has a convex shape in which the central portion is higher than the peripheral portion.

After the source crystal 2 is completely dissolved, heat treatment is carried out as it is in a saturated solution for a predetermined time. The state of the inside of the crystal growth container after sufficient heat treatment is shown in FIG. Since the upper surface of the grown crystal 9 is heat-treated,
It is flat.

For example, under the growth condition that the temperature (growth temperature) Tg of the surface of the seed crystal 5 is 950 ° C. and the temperature gradient is 15 ° C./cm, the amount of the source crystal 2 is such that the source crystal disappears after 550 hours of growth. When charged, a columnar grown crystal having a convex upper surface at a growth time of 510 hours, a central portion height of about 10 mm, and a peripheral portion height of about 7 mm was obtained.

Under the same condition, the crystal growth is started and the heat treatment is continued under the same temperature condition after the source crystal disappears.
When taken out after 0 hours, both the center and the periphery are about 1
A columnar grown crystal of 0.5 mm was obtained.

When crystal growth is carried out for 600 hours under the condition that the source crystal does not disappear, it has a convex upper surface, the center height is about 12 mm, and the peripheral height is about 12 mm. Only 8 mm columnar grown crystals were obtained.

A wafer having a uniform diameter can be cut out from this grown crystal only at 2/3 of the height of the central portion, and the remaining portion needs to be cut off or scraped off. As described above, the length of the portion where the diameter of the horizontal plane of the columnar grown crystal is uniform is 60 after the crystal growth by heat treatment without the source crystal.
It was shorter than the length of the columnar grown crystal obtained by taking out after 0 hour.

As described above, according to the present embodiment, the length of the crystal capable of cutting a uniform wafer is longer than that of the crystal prepared by the conventional method, and the grown crystal is used almost 100%. Then, the wafer can be cut out.

Next, an embodiment in which a side chamber for separating the source crystal remaining after the crystal growing step from the solution is provided on the side surface of the upper part of the crystal growth container 1 will be described. Figure 2
Figure 3 shows the crystal growth according to the example of the present invention. FIG. 2 (A)
Is before the start of growth, and FIG. 2 (B) is after the end of crystal growth.
(C) shows the state in the crystal growth container after the heat treatment step.

As shown in FIG. 2A, the crystal growth container 1
A side chamber portion 11 for separating the source crystal remaining after the crystal growth step from the solution is provided on the upper side surface of 0. The bottom cutoff 11a of the side chamber 11 is preferably higher than the upper surface of the solvent.

The heat sink 6, the seed crystal 5, the seed stopper 4, the solvent 3 and the source crystal 2 are placed in the crystal growth container 10 by the same method as in the above-mentioned embodiment, and after vacuum evacuation, sealing is performed. By arranging this crystal growth container 10 in an electric furnace, crystal growth occurs on the seed crystal 5.

The state where the desired grown crystal 9 is obtained is shown in FIG.
It shows in (B). In this state, the upper surface of the grown crystal is
The central part has a convex shape that is higher than the peripheral part. Thereafter, the crystal growth container 10 is tilted, and the remaining source crystal 2a is transferred to the side chamber 11 above the crystal growth container and separated from the solution 3a. This operation may be performed by inclining only the crystal growth container 10 or by inclining it together with the electric furnace.

As shown in FIG. 2 (C), the crystal growth container 10 is made vertical again and the grown crystal 9 is heat-treated in the saturated solution 3a, whereby the upper surface of the grown crystal 9 becomes flat. The heat treatment time at this time is preferably about 10 to 100 hours, although it depends on the thickness of the grown crystal and the like.

In this way, a crystal capable of cutting a uniform wafer is longer than that manufactured by the conventional method, and a crystal capable of cutting a wafer using almost 100% of grown crystals is manufactured. can do.

Although the case where ZnSe is crystal-grown using the Se-Te solvent has been described above as an example, in the above-mentioned liquid-phase crystal growth, the grown crystal is saturated with a saturated solution after the solute supply from the source crystal is stopped. It is characterized in that it is heat-treated in the inside, and can be widely applied not only to the solution crystal growth of ZnSe using the Se-Te solvent but also to the solution crystal growth.

The present invention is not limited to the above embodiment. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0044]

As described above, according to the present invention,
A columnar grown crystal having a flat upper surface can be obtained by a simple process of keeping the grown crystal in a saturated solution as it is after growth. Since the upper surface is flat, the length of the crystal capable of cutting out a wafer having a uniform diameter becomes longer, and the utilization efficiency of the crystal can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining solution crystal growth according to an embodiment of the present invention.

FIG. 2 is a sectional view for explaining solution crystal growth according to another embodiment of the present invention.

FIG. 3 is a sectional view and a graph for explaining solution crystal growth.

[Explanation of symbols]

 1 Crystal Growth Container 2 Source Crystal 3 Solvent 4 Seed Stop 5 Seed Crystal 6 Heat Sink 7 Core Tube 8 Heater Wire 9 Growth Crystal 10 Crystal Growth Container 11 Side Chamber

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Kato, 1743 203, Tetsumachi, Midori-ku, Yokohama-shi, Kanagawa (72) Inventor, Naotaro Tomita 2-17-8 Eta Minami 2-17-8, Midori-ku, Yokohama, Kanagawa (72) ) Inventor Yasuo Okuno 2-37-2 Fujigaoka, Midori-ku, Yokohama-shi, Kanagawa A 302

Claims (3)

[Claims] 1. A liquid phase crystal growth method in which a temperature difference is formed above and below a solvent, a source crystal is arranged in a high temperature part of the solvent, and a crystal is grown in a low temperature part of the solvent, a solute is supplied from the source crystal, A liquid phase crystal growth method comprising: a step of performing crystal growth at a substantially constant growth rate; and a step of stopping the solute supply from the source crystal and heat treating the grown crystal in a saturated solution. 2. The liquid crystal growth method according to claim 1, wherein the step of stopping the supply of the solute and performing the heat treatment includes isolating the source crystal from a solution in contact with the growing crystal. 3. A liquid-phase crystal growth apparatus in which a temperature difference is formed above and below a solvent, a source crystal is arranged in a high temperature portion of the solvent, and crystal growth is performed in a low temperature portion of the solvent. A liquid phase crystal growth apparatus having a crystal growth container provided with a side chamber portion for accommodating and separating a remaining source crystal from a solution in contact with the growth crystal after the crystal growth step on the upper side surface.