JPH10152393A - Growth of bulk crystal and seed crystal for bulk crystal growth - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for growing a bulk crystal by which a growing crystal is prevented from becoming polycrystal and thereby the yield of the single crystal is prevented from being decreased by cleaning the surface of a seed crystal, placing the seed crystal in a crystalline growing apparatus while maintaining the surface clean, and starting the crystalline growth at the solid-liquid interface between the surface of the seed crystal, and a molten or a solution. SOLUTION: A seed crystal having a melting temperature higher than that of a crystal to be grown, a component different from the crystal and a low solubility to the molten or a solution of the crystal is used. The seed crystal is placed in a liquid phase epitaxial growing apparatus and heated while flowing hydrogen gas to clean the surface of the seed crystal, and the cleaned surface is protected by epitaxially growing a material to be a capping material. The protected seed crystal is taken out and placed in a crystalline growing apparatus to grow a bulk crystal. The capping material is preferably a material, etc., having a composition, a constituting element or a dopant same as that of the crystal to be grown. A sapphire is also used as the seed crystal in a case of group II-IV compound semiconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a bulk crystal, that is, a bulk crystal. For example, a single crystal of a compound semiconductor is prepared from a melt or a solution using a large-diameter seed crystal having a component different from that of a crystal to be grown. The present invention relates to a technique that is useful to apply to manufacturing.

[0002]

2. Description of the Related Art Conventionally, as a method of growing a bulk single crystal of a compound semiconductor, a growth vessel (crucible) containing a raw material melt is gradually and vertically moved relatively to a heating furnace having a temperature gradient. A vertical Bridgman (VB) method of growing a crystal by moving it, and a vertical gradient freezing (VGF) method of growing a crystal by providing a vertical temperature gradient in a raw material melt and gradually cooling it are known. ing. In the VB method and the VGF method, as shown in FIG. 2, a crucible 1 formed into a mortar shape in which the bottom of the crucible 1 is inclined so as to descend toward its center is usually used.
Then, a seed crystal 2 having the same composition as the crystal to be grown and having a considerably smaller diameter than the crystal to be grown is placed at the center of the bottom of the crucible 1 having the above shape, and the temperature profile in the furnace is adjusted by controlling the output of the heater 3. In the quartz ampoule 4, the raw material melt 5 is solidified from the seed crystal 2 to obtain a bulk single crystal 6. Alternatively, without using a seed crystal, a bulk single crystal is obtained by solidifying the raw material melt by naturally generating a nucleus at the center of the bottom of the crucible.

In addition, as a method for growing a bulk single crystal of a compound semiconductor, a raw material melt in a crucible is covered with a sealing agent such as B ₂ O ₃ and a seed crystal is brought into contact with the surface of the raw material melt to gradually form it. There is a liquid-sealed Czochralski (LEC) method for growing a crystal by pulling it up, and it is widely practiced.
The seed crystal used at this time has the same composition as the crystal to be grown and has a much smaller diameter than the crystal to be grown, as in the case of the VB method or the VGF method.

However, II- such as CdTe and ZnTe
Since the group VI compound semiconductor has low thermal conductivity and low shear stress, the conventional VB method, VGF method and LEC method have a drawback that a high-quality single crystal cannot be obtained with high yield. In addition, the conventional VB method and VG
The F method also has a disadvantage that a new nucleus is generated during the growth of the crystal shoulder from the bottom center of the crucible to the straight body, and polycrystal is easily formed. Furthermore, in the conventional VB method, VGF method, and LEC method, since a shoulder is formed in the crystal, the length of the straight body is short, and there is a disadvantage that the number of wafers that can be cut out from the grown crystal is small. .

In order to overcome the above-mentioned drawbacks, there has been proposed a method of growing a crystal having a small shoulder portion by using a seed crystal having a larger diameter than in the prior art in the VB method, the VGF method, and the LEC method. Since the shoulder does not completely disappear, the above-described drawback of polycrystallization of the grown crystal due to nucleation during growth of the shoulder remains unresolved. Further, in the case of II-VI group compound semiconductors such as CdTe and ZnTe, it is difficult to obtain a large-diameter seed crystal such as CdTe or ZnTe, so that it is extremely difficult to apply a crystal growth method using a large-diameter seed crystal. Furthermore, since the seed crystal has the same composition as the crystal to be grown, a part of the seed crystal that comes into contact with the raw material melt at the time of seeding is melted. There is also a disadvantage that temperature control is extremely difficult.

Therefore, the applicant of the present invention has previously disclosed a melt having a melting point higher than the growth temperature of the crystal to be grown as a seed crystal, a component different from that of the crystal to be grown, and containing a constituent element of the crystal to be grown. Alternatively, a crystal growth method using a thin single-crystal substrate having low solubility in a solution, for example, a substrate made of sapphire (aluminum oxide: Al ₂ O ₃ ) has been proposed (International Application No. PCT / JP95 / 02025). FIG. 1 schematically shows an apparatus used for carrying out the crystal growth method. The bottom of the crucible 10 is formed flat, and a thin seed crystal substrate 12 having the same diameter as the diameter of the straight body of the grown crystal can be placed on the bottom of the crucible 10. And it consists of different components from the crystal to be grown,
A seed crystal substrate 12 having the same diameter as the diameter of the straight body of the grown crystal is set on the bottom of the crucible 10, and the temperature profile in the furnace is adjusted by controlling the output of the heater 3. By solidifying the raw material melt 5 from the substrate 12, a bulk single crystal 16 having no shoulder is obtained. For example, instead of the raw material melt 5, a solution using Te and ZnTe as a solvent and a solute, respectively, and using the seed crystal substrate 1
By using a sapphire substrate as 2, a ZnTe single crystal is grown from the solution.

[0007]

However, our subsequent research has revealed that the above prior art has the following problems. That is, in the prior art, since the seed crystal substrate is made of a crystal that is stable with respect to the solution containing the precipitated crystals as a solute or the raw material melt, the surface of the seed crystal substrate is brought into contact with the solution before starting crystal growth. Alternatively, so-called meltback, which is slightly dissolved in the raw material melt, does not occur. For example, liquid phase epitaxial growth (LPE)
In the method, the surface of the substrate for epitaxial growth is cleaned by meltback before starting the epitaxial growth. However, in the crystal growth method according to the above-mentioned prior application, since the surface of the seed crystal substrate is not cleaned by meltback before the start of crystal growth, nuclei are generated from dirt on the substrate surface and crystals grow abnormally, As a result, the grown crystal becomes polycrystalline, and the yield of the single crystal is reduced.

The present invention has been made in view of the above circumstances, and when performing crystal growth using a seed crystal having a component different from that of the crystal to be grown, the surface of the seed crystal is cleaned before starting the crystal growth. In addition, an object of the present invention is to protect a surface of a cleaned substrate in a clean state, thereby preventing polycrystallization of a grown crystal and preventing a decrease in yield of a single crystal.

[0009]

Means for Solving the Problems To achieve the above object, the present inventors used a seed crystal substrate made of sapphire and prepared a vertical bridgeman (VB) from a solution containing Te and ZnTe as a solvent and a solute, respectively. ) Method by ZnTe
When the single crystal was grown, when the single crystal was obtained, the adhesion between the substrate and the grown crystal was good, and both the surface of the seed crystal substrate and the contact surface between the grown crystal and the seed crystal substrate were bright. I was On the other hand, when polycrystals were generated, the adhesion between the substrate and the grown crystal was poor, and the surface of the seed crystal substrate and the contact surface between the grown crystal and the seed crystal substrate were clouded. In growing the crystal, the surface of the seed crystal substrate is etched and cleaned in advance, and then the seed crystal substrate is set in the crucible. After the crucible is set, the temperature on the seed crystal substrate side is kept high in the crystal growing apparatus. By doing so, the raw material melt or solution is stirred by convection to clean the surface of the seed crystal substrate, and then crystal growth is started, but the yield of single crystals is about 70 to
80%, and there is still room for improving the yield of single crystals.

Based on the above results, the present inventors have found that the cause of polycrystal generation is that the surface of the seed crystal substrate is not sufficiently cleaned, and that the substrate surface is exposed to the atmosphere after etching the substrate surface. I thought that it would be polluted by touching.

The present invention has been made based on the above considerations, and has a melting point higher than the growth temperature of the crystal to be grown, a component different from that of the crystal to be grown, and a component containing a constituent element of the crystal to be grown as a component. When a seed crystal having a property of low solubility in a liquid or solution is brought into contact with the melt or the solution to grow a bulk crystal from the melt or the solution, a solid crystal of the melt or the solution and the seed crystal is formed. Before starting crystal growth from the liquid interface,
A cleaning step of cleaning a surface of the seed crystal that comes into contact with the melt or the solution or a surface that can come into contact with the melt or the solution, and protecting the surface of the seed crystal that has been cleaned by the cleaning step A cleaning process including a protection step for bringing the device into a possible state is performed. Therefore, the surface of the seed crystal that is in contact with the melt or solution or the surface that can be in contact with the melt or solution is cleaned, and the seed crystal is crystallized while keeping the cleaned surface clean. It can be placed in a growth apparatus and brought into contact with the melt or solution.

In the above invention, when performing the cleaning step, the atmosphere in which the seed crystal is placed is a reducing atmosphere or a vacuum atmosphere, and the seed crystal is heat-treated in the reducing atmosphere or the vacuum atmosphere. You may. In that case, the seed crystal is heated to a predetermined temperature by a heater in a reducing atmosphere or a vacuum atmosphere to perform heat treatment. Then, the surface of the seed crystal can be cleaned without being exposed to the atmosphere.

In the above invention, when the protection step is performed, the surface of the seed crystal, which has been cleaned in the cleaning step, is made of a material having the same composition as the crystal to be grown and constituent elements of the crystal to be grown. A material that can be a solution containing the constituent elements of the crystal to be grown, a material that can be a solvent for the solution, a material that can be a dopant mixed as impurities into the crystal to be grown, and a material that includes a component that can be the dopant. It may be covered with a cap material made of one or more selected materials and made of a material that can be melted or dissolved at a crystal growth temperature. In this case, following the cleaning step, the surface of the seed crystal is covered and protected with a cap material made of the above-mentioned various materials. Then, the cleaned surface of the seed crystal can be kept in a clean state. In addition, when the cap material is made of a material that can be a dopant or a material containing a component that can be a dopant, it is possible to save the trouble of charging the crucible with impurities that are the dopant.

In the above invention, the seed crystal is placed in a crucible, and a material for growing a crystal, a material capable of forming a solution capable of precipitating the crystal, or a material capable of forming a solvent for the solution is provided in the crucible. The crucible is heated by a heater to make the raw material or the material in the crucible liquid, and the liquid is mechanically stirred to clean the surface of the seed crystal that comes into contact with the liquid. The liquid or a solid obtained by cooling the liquid may be kept in contact with the surface of the seed crystal. In this case, the surface of the seed crystal is cleaned by stirring the liquid in the crucible, and the liquid is solidified together with the seed crystal to be used as a cap material, thereby protecting the surface of the seed crystal.
Then, the cleaned surface of the seed crystal can be kept in a clean state.

More specifically, the crystal to be grown is CdTe, and the cap material is made of one or more materials selected from the group consisting of Cd, Te and CdTe. In this case, since the cap material has the same composition as the crystal to be grown or a constituent element of the crystal to be grown, unnecessary impurities do not need to be mixed into the grown crystal.

The crystal to be grown is ZnTe,
The cap material is made of Zn, Te, ZnTe, Al, G
a, In, ZnCl ₂ , ZnBr _2, and ZnI _2, and one or more materials selected from the group consisting of ZnI ₂ . In this case, since the cap material has the same composition as the crystal to be grown or a constituent element of the crystal to be grown, or an impurity serving as a dopant or a compound containing the impurity,
Unnecessary impurities do not enter the grown crystal.

The crystal to be grown is ZnSe,
The cap material is Zn, Se, ZnSe, Al, G
a, In, ZnCl ₂ , ZnBr _2, and ZnI _2, and one or more materials selected from the group consisting of ZnI ₂ . In this case, since the cap material has the same composition as the crystal to be grown or a constituent element of the crystal to be grown, or an impurity serving as a dopant or a compound containing the impurity,
Unnecessary impurities do not enter the grown crystal.

Further, the seed crystal may be made of sapphire. Further, the seed crystal of the present invention comprises: a cleaning step of cleaning a surface that comes into contact with the melt or the solution or a surface that can come into contact with the melt or the solution; and the surface of the seed crystal that has been cleaned by the cleaning step. A seed crystal for bulk crystal growth, which has been subjected to a cleaning process including a protection step of bringing the surface of the seed crystal into a protectable state.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a bulk crystal growth method according to the present invention will be described. As a seed crystal,
It is made of a material having a melting point higher than the growth temperature of the crystal to be grown, a component different from that of the crystal to be grown, and having a low solubility in a melt or a solution containing a constituent element of the crystal to be grown as a component. Use a single crystal. A seed crystal having such characteristics is first placed in a liquid phase epitaxy (LPE) apparatus, and hydrogen gas is flowed into the apparatus. Then, in a state where the surface of the seed crystal is exposed to a hydrogen stream, heat treatment is performed by heating with a heater to clean the surface of the seed crystal. When the cleaning of the seed crystal surface is completed, the material serving as a cap material is epitaxially grown on the cleaned surface of the seed crystal without removing the seed crystal from the LPE apparatus, and the surface of the seed crystal is cleaned. Protect. After protecting the surface of the seed crystal with a cap material, the seed crystal is taken out from the LPE apparatus, and the taken out seed crystal is set in a known crystal growth apparatus to grow a bulk crystal.

The cap material is made of a material having the same composition as the crystal to be grown, a material composed of the constituent elements of the crystal to be grown, a material that can be a solution containing the constituent element of the crystal to be grown, a material that can be a solvent of the solution, and a crystal that can be grown. Selected from the group consisting of a material that can be a dopant mixed as an impurity into the material and a material containing a component that can be the dopant.
Or it consists of two or more materials. The seed crystal surface is coated with a cap material by, for example, chemical vapor deposition (CV).
It can be performed by a known film forming method such as D) method, molecular beam epitaxy (MBE) method, vapor phase epitaxy (VPE) method, high frequency method or magnetron type sputtering method, vacuum evaporation method or dip coating method. When the cap material is formed by any of the above-described various film forming methods, the seed crystal is subjected to a heat treatment in a reducing atmosphere or a vacuum atmosphere in an apparatus used in the film forming method before starting the film forming. Then, the surface of the seed crystal may be cleaned. The cap material, when the seed crystal coated with the cap material is brought into contact with a raw material melt or a solution to grow a crystal,
At the crystal growth temperature, it is easily dissolved in the raw material melt or solution.

Here, when growing a single crystal of a II-VI compound semiconductor such as CdTe or ZnTe, for example, a single crystal of sapphire can be used as a seed crystal.
In that case, the surface of the seed crystal is cleaned at a heat treatment temperature of 900C to 1100C. If the heat treatment temperature is lower than 900 ° C., there is a disadvantage that the surface cannot be sufficiently cleaned, and if it exceeds 1100 ° C., there is a problem that cleaning and capping cannot be performed with a simple apparatus using a quartz tube or the like.

When growing a CdTe single crystal, for example, one or more materials selected from the group consisting of Cd, Te and CdTe can be used as the cap material. When growing a ZnTe single crystal, for example, Zn, Te, ZnTe, Al, G
One or more materials selected from the group consisting of a, In, ZnCl ₂ , ZnBr _2, and ZnI ₂ can be used. When growing a ZnSe single crystal, for example, Zn, Se , ZnSe, Al, G
One, two or more materials selected from the group consisting of a, In, ZnCl ₂ , ZnBr ₂ and ZnI ₂ can be used. Here, Al, Ga, In, Cl (chlorine), B
r (bromine) and I (iodine) are both ZnTe or Zn
It is an element that becomes a dopant in Se or the like. The material used as the cap material may be single crystal or polycrystal. Further, it is desirable that the thickness of the cap material is 100 Å or more. Cap material thickness is 1
If the thickness is smaller than 00 Å, an oxide film which is hardly dissolved in the raw material melt or solution is formed over the entire cap material.

As a crystal growth method, a vertical gradient freezing (VGF) method, a liquid sealing Czochralski (LEC) method, a Czochralski (CZ) method, a vertical Bridgman (VB) method, or the like is applied. be able to.

According to the first embodiment, the seed crystal is subjected to a high-temperature heat treatment in a stream of hydrogen to clean its surface, and the surface of the cleaned seed crystal is covered with a cap material to protect it. Since the seed crystal can be placed in a crystal growth apparatus and crystal growth can be started while the surface of the seed crystal is kept clean, polycrystallization of the grown crystal can be prevented. The yield of crystals can be prevented from lowering.

Instead of cleaning the surface of the seed crystal in a hydrogen stream, the surface of the seed crystal may be cleaned by heat-treating the seed crystal in a vacuum atmosphere.

The second method of growing a bulk crystal according to the present invention
An embodiment will be described. A seed crystal made of a single crystal made of a material having the same characteristics as in the first embodiment is used, and the seed crystal is attached to the bottom of a crucible having the shape shown in FIG. Then, a raw material of a crystal to be grown, a material capable of forming a solution capable of precipitating the crystal, or a material capable of forming a solvent of the solution are placed in the crucible, and are placed in a furnace tube of a heating furnace. Here, as the heating furnace, a furnace (hereinafter, referred to as a stirring furnace) capable of mechanically swinging a furnace tube up and down to thereby stir the liquid in the crucible is used. . Then, nitrogen gas is introduced into the furnace tube to make the furnace tube a nitrogen atmosphere, and then heated by a heater to melt the material in the crucible. Thereafter, the liquid in the crucible shaking the furnace tube is sufficiently stirred to clean the surface of the seed crystal. When the cleaning of the seed crystal surface is completed, the liquid in the crucible being cooled is solidified. At that time, if the liquid in the crucible cools and solidifies, the solidified object will cover the cleaned surface of the seed crystal, so that the solidified object has a function as a cap material. become.

When the liquid in the crucible is solidified, the crucible is taken out of the furnace tube of the stirring furnace, and the crucible is set in a known crystal growing apparatus to grow bulk crystals. that time,
In the crucible, the composition of the solidified material that also serves as the cap material is
If the composition is not suitable for conducting crystal growth,
Replenish the missing components to achieve the desired composition.
The solidified material that also serves as the replenished substance and cap material is
It is easily melted at the crystal growth temperature to form a raw material melt or solution having a desired composition.

Also in the second embodiment, when growing a single crystal of a II-VI group compound semiconductor such as ZnTe or ZnSe, for example, a single crystal of sapphire can be used as a seed crystal.

When growing a ZnTe single crystal, the material to be put into the crucible when cleaning the surface of the seed crystal in a stirring furnace is a ZnTe polycrystalline raw material.
And Te, Te as a solvent, or ZnTe as a Te solvent and a solute. Further, when growing a ZnSe single crystal, the material to be put into the crucible when cleaning the surface of the seed crystal in a stirring furnace is a ZnSe polycrystalline raw material, Zn and Se when directly synthesized, Se as a solvent, Alternatively, it is ZnSe which is a Se solvent and a solute.

As a crystal growth method, a vertical gradient freezing (VGF) method, a liquid-sealed Czochralski (LEC) method, a Czochralski (CZ) method, a vertical Bridgman (VB) method, or the like is applied. be able to.

According to the second embodiment, a seed crystal is placed in a crucible, and a material of a crystal to be grown in the crucible, a material capable of forming a solution capable of depositing the crystal, or a material capable of forming a solvent of the solution The crucible is heated to make the material liquid, and the surface of the seed crystal is cleaned by mechanically agitating the liquid, and then cooled to solidify the liquid in the crucible to be cleaned. In order to cover and protect the surface of the seed crystal, the seed crystal can be placed in a crystal growth apparatus and crystal growth can be started while keeping the surface of the seed crystal clean, so that the grown crystal Can be prevented, and the yield of single crystals can be prevented from lowering.

[0032]

EXAMPLES Specific examples of single crystal growth to which the present invention is applied are shown below, but the present invention is not limited by the following specific examples. Example 1 A single crystal of CdTe was grown by a VGF method using a sapphire substrate as a seed crystal. First, a sapphire substrate having a plane orientation of (0001) (a disk shape having a diameter of 2 inches) is set in a film forming chamber of a vapor phase growth apparatus, and a hydrogen gas is flowed into the film forming chamber. The substrate surface was cleaned by heat treatment for 20 minutes. Thereafter, while the sapphire substrate was mounted in the vapor phase growth apparatus, the substrate temperature was raised to 400 ° C., and a cap material made of a 1 μm-thick CdTe thin film was continuously vapor-phase grown on the sapphire substrate surface.

Next, the sapphire substrate protected by the cap material was taken out of the vapor phase growth apparatus, placed on the bottom of a graphite (2 inch inner diameter) crucible made of graphite, and pressed and fixed by a pressing member. Then, the crucible was filled with 550 g of CdTe polycrystalline raw material, and placed in a growth chamber for a quartz ampule. Also, after putting a sufficient amount of Cd into the reservoir of the quartz ampule to control the vapor pressure, the quartz ampule is placed in a 2 × 10 ^-6 To
Sealed in rr vacuum.

Next, the quartz ampoule was placed at a predetermined position in a crystal growing furnace, and the quartz ampule was heated at 1100 ° C. by a heater and kept in that state for 2 days.

Thereafter, the temperature profile in the crystal growing furnace is set to a desired profile by controlling the output of the heater, and the temperature profile is gradually changed while controlling the vapor pressure of Cd to grow the crystal from the sapphire substrate surface. I let it. When the obtained crystal was examined, it was a CdTe single crystal having good adhesion to the sapphire substrate. When the CdTe single crystal was mechanically peeled off from the sapphire substrate, the interface between the sapphire substrate and the grown crystal was mirror-finished. When the crystal growth was repeated in the same manner, the yield of the single crystal was about 80% to 85%.
%Met.

Example 2 Using the heating furnace shown in FIG.
Using a sapphire substrate as a seed crystal, a ZnTe single crystal was grown by a VB method from a solution obtained by dissolving ZnTe in a Te solvent. First, a sapphire substrate having a plane orientation of (0001) (a disk shape having a diameter of 2 inches) was subjected to a heat treatment at 1100 ° C. for 20 minutes in a hydrogen stream by an LPE apparatus to clean the surface of the sapphire substrate. Thereafter, while the sapphire substrate is mounted in the LPE apparatus, Te is continuously brought into contact with the surface of the sapphire substrate, and the surface of the substrate is reduced to a thickness of 0.1 mm.
It was covered with a cap material made of 1 μm of Te.

Next, the sapphire substrate protected by the cap material is taken out of the LPE device, and placed on the bottom of a graphite (2 inch inner diameter) crucible made of graphite.
It was pressed and fixed by a pressing member (not shown). In the crucible, 240 g of Te as a solvent and 550 g of a ZnTe polycrystalline raw material as a solute (crystal growth temperature 1)
The amount is enough to dissolve in 240 g of Te solvent at 100 ° C. ), And the crucible was sealed in a quartz ampoule under a vacuum of 2 × 10 ⁻⁶ Torr.

Next, the quartz ampoule was placed at a predetermined position in a crystal growing furnace, and the quartz ampule was heated at 1100 ° C. by a heater, and kept in this state for 2 days to sufficiently dissolve the solute. At that time, the quartz ampoule was placed in the soaking zone in the crystal growing furnace.

After the solute was sufficiently dissolved, the temperature distribution in the crystal growing furnace was changed by a heater so that the temperature was lowered with a temperature gradient of 10 ° C./cm toward the lower part of the furnace. During this temperature gradient, the ampoule was moved to the low temperature side at a speed of 3 cm / day to grow crystals from the sapphire substrate surface. When the obtained crystal was examined, it was a ZnTe single crystal. When the crystal growth was repeated in the same manner, the yield of the single crystal was about 80% to 85%.

Example 3 Using the heating furnace shown in FIG.
Using a sapphire substrate as a seed crystal, a ZnTe single crystal was grown by a VB method from a solution obtained by dissolving ZnTe in a Te solvent. First, a sapphire substrate having a plane orientation of (0001) (a disk shape having a diameter of 2 inches) was placed on the bottom of a graphite (2 inch inner diameter) crucible made of graphite, and pressed and fixed by a pressing member (not shown). The crucible was filled with 240 g of Te as a solvent, and the crucible was set in a furnace tube of a stirring furnace.

In this state, nitrogen gas was introduced into the furnace tube of the stirring furnace to form a nitrogen atmosphere in the furnace tube, and then 600 ° C. higher than the melting point of Te (449.5 ° C.) by a heater.
To melt the Te in the crucible. Thereafter, the furnace tube was rocked for 24 hours, and the Te solvent in the crucible was sufficiently stirred to clean the surface of the sapphire substrate. After the stirring, the crucible was cooled, and Te in the crucible was solidified to form a cap material.

Next, the crucible was taken out of the furnace tube of the stirring furnace, and 550 g of ZnTe was placed as a solute in the crucible.
Polycrystalline raw material (240 g at a crystal growth temperature of 1100 ° C)
This is an amount that is sufficiently dissolved in a Te solvent. ), And the crucible was sealed in a quartz ampoule under a vacuum of 2 × 10 ⁻⁶ Torr.

Next, the quartz ampoule was placed at a predetermined position in a crystal growing furnace, and the quartz ampule was heated at 1100 ° C. by a heater, and kept in this state for 2 days to sufficiently dissolve the solute. At that time, the quartz ampoule was placed in the soaking zone in the crystal growing furnace.

After the solute was sufficiently dissolved, the temperature distribution in the crystal growing furnace was changed by a heater so that the temperature was lowered by a temperature gradient of 10 ° C./cm toward the lower part of the furnace. During this temperature gradient, the ampoule was moved to the low temperature side at a speed of 3 cm / day to grow crystals from the sapphire substrate surface. When the obtained crystal was examined, it was a ZnTe single crystal having good adhesion to the sapphire substrate. When the ZnTe single crystal was mechanically peeled from the sapphire substrate, the interface between both the sapphire substrate and the grown crystal was in a mirror state. When the crystal growth was repeated in the same manner, the yield of the single crystal was about 80% to 8%.
5%.

(Comparative Example) Using the heating furnace shown in FIG. 1, a sapphire substrate was used as a seed crystal, and a CdTe single crystal was grown by the VGF method. First, a sapphire substrate having a (0001) plane orientation was placed on the bottom of a graphite crucible, and pressed and fixed by a pressing member (not shown). The crucible was filled with 550 g of CdTe polycrystalline raw material and placed in a growth chamber for a quartz ampoule. In addition, a sufficient amount of Cd for controlling the vapor pressure was put in the reservoir of the quartz ampule, and then the quartz ampule was sealed in a vacuum of 2 × 10 ⁻⁶ Torr.

Next, the quartz ampule was placed at a predetermined position in a crystal growing furnace, and the quartz ampule was heated at 1100 ° C. by a heater and kept in that state for 2 days.

Then, the output of the heater is controlled to set the temperature profile in the crystal growth furnace to a desired profile, and the temperature profile is gradually changed while controlling the vapor pressure of Cd to grow the crystal from the sapphire substrate surface. I let it. When the obtained crystal was examined, it was found to be polycrystalline. When the crystal growth was repeated in the same manner, the yield of the single crystal was about 10%.

In each of the above embodiments, CdTe and Z
Although an example in which a single crystal of nTe is grown has been described, the present invention is not limited to this, and the present invention is also applicable to the case of growing a bulk crystal of another II-VI compound semiconductor such as ZnSe or a III-V compound semiconductor. It is. In particular, a II-VI compound semiconductor single crystal having a melting point as high as 1100 ° C. or higher (for example, CdZnT
e) or a II-VI compound semiconductor single crystal (eg, Cd
(Te, CdZnTe, etc.) when grown in a quartz ampoule, the conventional method of cleaning a seed crystal substrate by convection with a temperature gradient cannot be performed sufficiently in a short time due to factors such as damage to the quartz container. The method is an effective and economical means. (Mp of CdTe is 1090 ° C)

[0049]

According to the method for growing a bulk crystal according to the present invention, it has a melting point higher than the growth temperature of the crystal to be grown, has a different component from the crystal to be grown, and has a constituent element of the crystal to be grown as a component. When growing a bulk crystal from the melt or the solution by contacting a seed crystal having a property of low solubility in the melt or the solution containing the melt or the solution, the melt or the solution is mixed with the seed crystal. A cleaning step of cleaning a surface of the seed crystal that comes into contact with the melt or the solution or a surface that can come into contact with the melt or the solution before starting crystal growth from the solid-liquid interface of the And a protection step of bringing the surface of the seed crystal cleaned by the step into a state where the seed crystal can be protected, so that the seed crystal is brought into contact with the melt or the solution. A seed crystal is placed in a crystal growth apparatus while the surface to be contacted or the surface that can come into contact with the melt or solution is kept clean and the cleaned surface is kept in a clean state, and the surface is brought into contact with the melt or solution. Therefore, the single crystal can be grown with high yield.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a crystal growth apparatus used for a VB method or a VGF method using a large-diameter sapphire substrate as a seed crystal.

FIG. 2. General VB method and VGF using small diameter seed crystal
FIG. 2 is a schematic view of a crystal growth apparatus used in the method.

[Explanation of symbols]

 1,10 crucible 2 seed crystal 3 heater 4 quartz ampule 5 raw material melt 6,16 bulk single crystal 12 seed crystal substrate

Claims (9)

[Claims] 1. A crystal having a melting point higher than a growth temperature of a crystal to be grown, and having a component different from that of the crystal to be grown,
In growing a bulk crystal from the melt or solution by contacting a seed crystal having a property of low solubility in a melt or a solution containing a constituent element of the crystal to be grown as a component and the melt or the solution, Before crystal growth is started from the solid-liquid interface between the melt or solution and the seed crystal, the surface of the seed crystal that is in contact with the melt or solution or the surface that can be in contact with the melt or solution is cleaned. A cleaning method comprising: performing a cleaning process comprising: a cleaning step of performing the following steps; and a protection step of bringing the surface of the seed crystal cleaned by the cleaning step into a state in which the surface can be protected. 2. The method according to claim 1, wherein the step of cleaning includes changing the atmosphere in which the seed crystal is placed to a reducing atmosphere or a vacuum atmosphere, and heat-treating the seed crystal in the reducing atmosphere or the vacuum atmosphere. 2. The method of growing a bulk crystal according to claim 1, wherein a surface of the crystal that contacts the melt or the solution or a surface that can contact the melt or the solution is cleaned. 3. When performing the protection step, the surface of the seed crystal, which has been cleaned in the cleaning step, is grown by using a material having the same composition as the crystal to be grown and a material comprising constituent elements of the crystal to be grown. One or a material selected from the group consisting of a material that can be a solution containing a constituent element of a crystal, a material that can be a solvent of the solution, a material that can be a dopant mixed as impurities into a crystal to be grown, and a material that includes a component that can be the dopant. Consisting of two or more materials,
3. The method of growing a bulk crystal according to claim 1, wherein the surface of the seed crystal is protected by coating with a cap material made of a material that can be melted or dissolved at a crystal growth temperature. 4. A method in which said seed crystal is placed in a crucible, and a raw material of a crystal to be grown, a material capable of forming a solution capable of depositing said crystal, or a material capable of forming a solvent of said solution are charged in said crucible. Is heated by a heater to turn the raw material or the material in the crucible into a liquid, and the liquid is mechanically stirred to clean the surface of the seed crystal that comes into contact with the liquid, and then the liquid or the liquid 2. The method for growing a bulk crystal according to claim 1, wherein the surface of the seed crystal is protected by keeping contact between the solid obtained by cooling the surface and the surface of the seed crystal. . 5. The bulk crystal according to claim 3, wherein the crystal to be grown is CdTe, and said cap material is made of one or more materials selected from the group consisting of Cd, Te and CdTe. Growth method. 6. The crystal to be grown is ZnTe, and the cap material is Zn, Te, ZnTe, Al, Ga, I
n, ZnCl _2, ZnBr ₂ and method of growing a bulk crystal according to claim 3, characterized in that consists of one or more materials selected from the group consisting of ZnI _2. 7. The crystal to be grown is ZnSe, and the cap material is Zn, Se, ZnSe, Al, Ga, I
n, ZnCl _2, ZnBr ₂ and method of growing a bulk crystal according to claim 3, characterized in that consists of one or more materials selected from the group consisting of ZnI _2. 8. The sapphire seed crystal according to claim 1, wherein the seed crystal is made of sapphire.
The method for growing a bulk crystal as described above. 9. A cleaning step for cleaning a surface that comes into contact with a melt or a solution or a surface that can come into contact with a melt or a solution, and the surface of the seed crystal cleaned by the cleaning step can be protected. A seed crystal for bulk crystal growth, which has been subjected to a cleaning process including a protection step of setting a state.