JP2706210B2 - Liquid crystal growth method and liquid crystal growth apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

This invention relates to liquid crystal growth.
Solution crystal growth that can lower the growth temperature is expected as a bulk crystal growth technique for compound semiconductors having a high vapor pressure, particularly II-VI group compound semiconductors.

[0002]

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

The use of solution growth makes it possible to lower the crystal growth temperature of II-VI compound semiconductors,
Good quality crystals may be obtained. II as solvent
A group II element or V which is a constituent element of a group VI compound semiconductor;
A method using a group I element has been proposed.

[0004] Referring to FIG. 3, a 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 a graph of the temperature distribution set in the crystal growth apparatus.

A crystal growth vessel 1 is formed by connecting two kinds 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 at a lower portion in the crystal growth vessel 1.

The heat sink 6 has a recess on its upper surface for mounting the seed crystal 5, and is fixed to the crystal growth vessel 1. Seed crystal 5 in dent on top of heat sink 6
Is mounted thereon, and a cylindrical seed stopper 4 having an appropriate length is inserted from above, and is fixed to the crystal growth vessel 1. Note that, before the raw material is filled, for example, the upper part of the crystal growth vessel 1 is open.

[0007] Se-Te is used as a solvent 3 in a crystal growth vessel 1.
(Se and Te at a predetermined mixing ratio) As a source crystal 2, a sufficient amount of ZnSe polycrystal is inserted into a desired amount of grown crystal so that supply of the source is not stopped halfway. In addition,
If only Se is used as a solvent for ZnSe crystal growth, Zn
Low solubility of Se. The reason for using Se-Te is to add Te to increase the solubility. After the source crystal 2 and the solvent 3 are charged, the inside of the crystal growth vessel 1 is evacuated to vacuum, and the opening is sealed.

The thus prepared crystal growth ampoule is
It is placed in an externally heated electric furnace with a temperature gradient 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 furnace tube 7, and a vertical space for accommodating the crystal growth vessel 1 is formed inside the furnace tube 7.

As shown on the right side of the figure, a vertical temperature distribution is set in the furnace tube 7 that is higher at the upper portion and lower at the lower portion. The temperature at the position where the source crystal 2 is arranged is represented by 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 vessel 1 is arranged in such a temperature distribution, the source crystal 2 in the high-temperature part dissolves in the solvent 3 until the saturation solubility in the high-temperature part. The saturation solubility in the high temperature part is higher than the saturation solubility in the low temperature part. The source crystal component dissolved in the solvent 3 moves to the low-temperature part by diffusion, and makes the solution in the low-temperature part supersaturated.

When the seed crystal 5 is arranged in the low temperature part and comes into contact with the supersaturated solution, crystal growth occurs on the seed crystal 5. Thus, a bulk single crystal is grown on the seed crystal 5.

This growth is performed at a constant temperature until the source crystal is exhausted, and a constant growth rate is obtained.

[0013]

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

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

[0016]

According to the liquid crystal growth method of the present invention, a temperature difference is formed above and below a solvent, a source crystal is arranged at a high temperature part of the solvent, and a crystal is grown at a low temperature part of the solvent. In the phase crystal growth method, a step of supplying a solute from a source crystal and growing the crystal at a substantially constant growth rate, stopping the supply of the solute from the source crystal , and heat-treating the grown crystal in a saturated solution at a crystal growth temperature . And a process.

[0017]

The crystal is grown by the liquid 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 with the central portion rising from the peripheral portion. It was recognized that the upper surface of the columnar grown crystal having the upper surface became substantially planar.

When the solute is supplied from the source crystal and the solution is in a supersaturated state, the deposition rate is more dominant than the dissolution rate, and the crystal growth rate at the center is higher than that at the periphery. Since the growth rate is higher 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 the solute is stopped, the redistribution of the solute molecules on the surface becomes dominant, the central portion of the grown crystal is redissolved, and the peripheral portion is re-precipitated, so that the crystal grows substantially according to the temperature distribution. It is thought that a surface will be obtained.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, ZnSe of II-VI compound semiconductor will be described.
Will be described by taking as an example the case of growing using a Se—Te solvent. ZnSe is a material expected as a blue light emitting semiconductor device.

FIG. 3 shows a crystal growth apparatus used in the embodiment of the present invention. A cross-sectional view of the crystal growth apparatus is shown on the left side of the figure, and a temperature distribution set in the furnace is shown on the right side of the figure. A crystal growth vessel 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 surface of the grown crystal container 1 is cleaned by etching with hydrofluoric acid. Crystal growth vessel 1 with clean surface
A heat sink 6 made of a material having a good thermal conductivity such as carbon is accommodated in the bottom of the substrate, and subjected to vacuum baking. The heat sink 6 is partially cut in advance, 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 (111) plane orientation is prepared. Note that (111)
It is also possible to use a ZnSe single crystal other than a plane. After the seed crystal 5 is mirror-polished, it is washed and mirror-etched. The seed crystal 5 prepared as described above is placed in a recess formed on the upper surface of the heat sink 6, and a 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 vessel 1. After disposing the seed stopper 4, the seed stopper 4 is fixed by recessing the crystal growth vessel 1.

Thereafter, the solvent 3 having a predetermined composition of Se-T
(e) As the source crystal 2, an amount of ZnSe polycrystal necessary for a desired amount of crystal to be grown in consideration of the amount and solubility of the solvent is charged into the crystal growth vessel 1. Source crystal 2 is
At least a lump larger than the inner diameter of the seed stopper 4 is used, and is held using the step of the crystal growth vessel 1.

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

The crystal growth vessel 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 configuration in which a heater wire 8 is wound around a furnace tube 7 forming a vertical space in which the crystal growth vessel 1 can be accommodated.

In the electric furnace, the temperature at the position where the source crystal 2 is disposed is represented by Ts, and the temperature at a portion where crystal growth occurs on the surface of the seed crystal 5 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 saturation 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.

FIGS. 1A and 1B show the state inside the crystal growth vessel 1 before the start of crystal growth and immediately after the end of crystal growth, respectively. Immediately after the 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 performed for a predetermined time in a saturated solution as it is. FIG. 1C shows a state inside the crystal growth vessel after performing a sufficient heat treatment. The upper surface of the growing crystal 9 is subjected to a heat treatment,
It is planar.

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

Under the same conditions, the crystal growth is started and the heat treatment is continued under the same temperature condition even after the source crystal disappears.
If it is taken out after 0 hours, both the center and the periphery are about 1
A 0.5 mm cylindrical growth crystal was obtained.

When the crystal growth is performed for 600 hours under the condition that the source crystal does not disappear, the upper surface has a convexly raised upper surface, the height of the center is about 12 mm, and the height of the periphery is about 12 mm. Only columnar growth crystals of 8 mm were obtained.

A wafer having a uniform diameter can be cut out from the grown crystal only at 2/3 of the height at the center, and the remaining portion needs to be cut off or cut off. As described above, the length of the portion where the diameter of the horizontal growth plane of the columnar growth crystal is uniform can be increased by 60% by heat treatment in the absence of the source crystal after crystal growth.
It was shorter than the length of the columnar crystal obtained after 0 hour.

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

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

As shown in FIG. 2A, the crystal growth vessel 1
A side chamber 11 for separating the source crystal remaining after the crystal growth step from the solution is provided on the upper side surface of the substrate. It is desirable that the bottom gap 11a of the side chamber 11 be 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 arranged in the crystal growth vessel 10 by using the same method as in the above embodiment, and sealed after evacuation. By arranging the crystal growth container 10 in an electric furnace, crystal growth occurs on the seed crystal 5.

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

As shown in FIG. 2 (C), the crystal growth vessel 10 is again turned upright, and the growth crystal 9 is subjected to a heat treatment in the saturated solution 3a, whereby the upper surface of the growth crystal 9 becomes flat. The heat treatment time at this time depends on the thickness of the grown crystal and the like, but is preferably about 10 to 100 hours.

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

In the above, the case where ZnSe is grown using a Se—Te solvent has been described as an example. In the above-described liquid crystal growth, the supply of the solute from the source crystal is stopped, and then the grown crystal is turned into a saturated solution. It is characterized in that it is heat-treated in a medium, and is applicable not only to the solution crystal growth of ZnSe using a Se—Te solvent but also to a wide range of 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,
By a simple process of keeping the grown crystal in a saturated solution even after the growth, a columnar grown crystal having a flat upper surface can be obtained. Since the upper surface is flat, the length of the crystal from which a wafer having a uniform diameter can be cut out becomes longer, and the efficiency of using the crystal can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating solution crystal growth according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating 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]

 DESCRIPTION OF SYMBOLS 1 Crystal growth container 2 Source crystal 3 Solvent 4 Seed stopper 5 Seed crystal 6 Heat sink 7 Furnace tube 8 Heater wire 9 Growth crystal 10 Crystal growth container 11 Side chamber

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasuo Okuno 2-302 Fujigaoka, Midori-ku, Yokohama-shi, Kanagawa Prefecture A302 Examiner Hideo Tokunaga

Claims (3)

(57) [Claims] 1. A liquid crystal growth method 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, wherein a solute is supplied from the source crystal. A liquid phase crystal growth method, comprising: a step of growing a crystal at a substantially constant growth rate; and a step of stopping supply of a solute from a source crystal and heat-treating the grown crystal at a crystal growth temperature in a saturated solution. . 2. The method of growing a liquid crystal 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 grown crystal. 3. A liquid phase crystal growth apparatus for forming a temperature difference above and below a solvent, disposing a source crystal in a high temperature part of the solvent, and performing crystal growth in a low temperature part of the solvent, comprising: A liquid crystal growth apparatus having a crystal growth container that accommodates and has a side chamber for separating a remaining source crystal from a solution in contact with a grown crystal after a crystal growth step on an upper side surface.