JPH0952790A - Single crystal growth apparatus and single crystal growth process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a single crystal growing apparatus and a single crystal growing process able to manufacture a longer single crystal. SOLUTION: The single crystal growing apparatus 100 equips a shielding body 11 intercepting radiant heat which propagate from a crucible 4 to a single crystal 10. The shielding body 11 is consisted of a cylindrical part 11a and a collar part 11b provided facing toward outside on an upper end of the cylindrical part 11a and an outer edge of the collar part 11b is fixed on the upper end of heat insulating mold 9. Air holes 11c for letting off high temperature gas within space A devided by the shielding body 11 is provided in the collar part 11b. High temperature of the shielding body 11 is avoided by the air holes 11c and also high temperature gas doesn't flow into the crucible 4 and temperature gradient within the growing single crystal 10 can be enlarged. A length L of the cylindrical part 11a is so set up as a suitable length that distance (h) between a lower end of the cylindrical part 11a and a surface of sealing agent 3 be from >=0 to <=100mm. The distance (h) is always controlled so as to be kept within the prescribed range during crystal growth. Thereby, it is prevented that the temperature gradient within crystal becomes smaller, and the longer single crystal can be grown.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for growing a single crystal, and more particularly to a technology for growing a single crystal of a compound semiconductor such as GaAs by a liquid sealed Czochralski (LEC) method.

[0002]

2. Description of the Related Art Conventionally, as a main method for producing a single crystal of a compound semiconductor such as GaAs, a raw material and a sealant are melted in a crucible, and a seed crystal is brought into contact with the surface of the raw material melt and rotated. The LEC method is known in which a single crystal is grown by gradually pulling it up. In the Czochralski method including the LEC method, the solid-liquid interface between the raw material melt and the grown crystal is downwardly convex, that is, the lower end of the grown crystal bulges into the raw material melt from its edge to the center. It is important to keep the shape. For that purpose, the amount of heat received by the growing crystal may be reduced and the amount of heat transferred upward in the crystal may be increased.

Conventionally, in order to satisfy the above-mentioned thermal environment, it has been proposed to provide a heat shield plate in the crucible (Japanese Patent Laid-Open No. 62-2169).
No. 95 publication. ), Or providing a cooling fin in the range from near the solid-liquid interface to near the side surface of the crystal (disclosed in JP-A-4-130084).
And so on.

[0004]

However, according to the study conducted by the present inventors, it is possible to grow the GaAs single crystal to a certain extent only by providing the heat shield plate and the cooling fin having the above-described conventional structure. (100 mm) GaAs
Although a single crystal can be obtained, it has been found that it is extremely difficult to obtain a longer single crystal (about 150 to 200 mm or longer).

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a crystal growth apparatus suitable for producing a longer single crystal.

Another object of the present invention is to provide a method for growing a longer single crystal by a pulling method.

[0007]

In order to achieve the above object, the inventors of the present invention have conducted further studies, and a heat shield is provided on the inner surface of the crucible in order to prevent the grown crystal from being heated by receiving radiant heat from the crucible wall. And the side surface of the growing crystal, and to prevent hot gas from accumulating in the space partitioned by the heat shield and trapping heat, vent holes are provided in the heat shield so that the hot gas escapes. It was found to be effective to do. This is because, in the above-described configuration in which the heat shield plate and cooling fins are provided, high temperature gas accumulates in the space partitioned by the heat shield plate and cooling fins to become a heat source, and the accumulated high temperature gas flows into the crucible. It is based on the clarification by the present inventors that there is a drawback that the crystal is heated and the temperature gradient in the crystal becomes small due to the heating.

The present invention was made on the basis of the above findings. The raw material placed in the crucible is heated by a heater to be melted, and a seed crystal is brought into contact with the upper surface of the raw material melt to gradually pull it up. In the single crystal growing apparatus for growing a single crystal by, between the inner surface of the crucible and the side surface of the growing crystal, the growing crystal is substantially surrounded to prevent the growing crystal from being heated by radiant heat from the crucible. The shield is
It is provided so as to be upwardly separated from the surface of the melt in the crucible by a predetermined height, and the high temperature gas in the space partitioned by the shield is provided above the shield above the shield. It is characterized in that a ventilation hole is provided to allow it to escape into the space. As a result, during the crystal growth, it is possible to prevent the growing crystal from receiving radiant heat from the crucible, and at the same time, the hot gas in the space partitioned by the shield escapes upward through the vent holes. be able to.

In this single crystal growing apparatus, the distance between the lower end of the shield and the surface of the melt in the crucible is longer than 0 mm and 100 mm or less, preferably about 30 mm or less. The reason is that, according to the experiments conducted by the present inventors, a single crystal was obtained when the lower end of the shield was immersed in a melt in a crucible (a liquid sealant in the LEC method for growing a compound semiconductor such as GaAs). If the distance between the lower end of the shield and the surface of the melt in the crucible is 100 mm, it will average 15
This is because a single crystal having a length of 5 mm can be obtained, and the effect of shielding the radiant heat from the crucible having a distance of more than 100 mm becomes small, and the effect of the shield cannot be expected. If the distance between the lower end of the shield and the surface of the melt in the crucible is about 30 mm or less, a single crystal with a length of 200 mm can be obtained.

Further, according to the present invention, when a raw material placed in a crucible is heated by a heater to be melted, a seed crystal is brought into contact with the upper surface of the raw material melt and gradually pulled up to grow a single crystal. While gradually raising the crucible and maintaining the distance between the lower end of the shield provided between the inner surface of the crucible and the side surface of the grown crystal and the surface of the melt in the crucible within a predetermined range, The radiant heat from the crucible is shielded to prevent the growth crystal from being heated by the radiant heat, and the high-temperature gas in the space partitioned by the shield by the ventilation hole provided on the upper part of the shield is higher than that of the shield. It is characterized in that the crystal is grown so as to escape into the upper space. This can prevent the crystal from being heated by the radiant heat from the crucible and the high-temperature gas accumulated in the space partitioned by the shield, and the temperature gradient in the crystal can be maintained at an appropriate level.

In the present invention, it is advisable to grow crystals while maintaining the distance between the lower end of the shield and the surface of the melt in the crucible to be longer than 0 mm and 100 mm or less, preferably about 30 mm or less. . The reason is that, as described above, according to the experiments conducted by the present inventors, the lower end of the shield is immersed in the melt in the crucible (the liquid sealant in the LEC method) or the lower end of the shield. This is because a long single crystal cannot be obtained if the distance from the surface of the melt in the crucible exceeds 100 mm.

Further, while covering the raw material melt with a liquid sealing material which is heated and melted by the heater,
If a single crystal of a compound semiconductor such as s is grown, it is 150 to 2
A long single crystal such as GaAs having a length of about 00 mm can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example in which the crystal growth apparatus according to the present invention is applied to a pulling furnace by the LEC method. As shown in FIG.
Is a high-pressure container 1 whose inside is pressurized to about 20 atm by an inert gas or nitrogen gas, a crucible 4 for containing a raw material 2 and a sealant 3, and a crucible shaft for rotatably and vertically moving the crucible 4. 5, a pulling shaft 7 for holding the seed crystal 6 rotatably and vertically movable at the lower end, a heater 8 for heating and melting the raw material 2 and the sealant 3, and surrounding the heater 8 to raise the temperature of the container 1 to a high temperature. A heat-insulating cylinder 9 for protecting the crystal 10 from the crucible 4, and a shield 11 for shielding radiant heat from the crucible 4 to the crystal 10 interposed between the inner surface of the crucible 4 and the side surface of the grown crystal 10 so as to surround the crystal 10. It has been configured.

The shield 11 is formed, for example, in a top hat shape by a tubular portion 11a surrounding the grown crystal 10 and a flange portion 11b provided on the upper end of the tubular portion 11a so as to face outward. , PBN (pyrolytic boron nitride), alumina, molybdenum, or tungsten, which are heat resistant and do not contaminate the crystal 10. The outer edge of the collar portion 11b is fixed to the upper end of the heat insulating cylinder 9. The collar portion 11b is provided with ventilation holes 11c penetrating through the front and back (up and down).

Through the ventilation hole 11c, the shield 11,
Since the high temperature gas in the space A partitioned by the heat insulation cylinder 9 and the heater 8 escapes to the upper space B in the container 1, the shielding plate 11
Does not reach a high temperature and hot gas does not flow into the crucible 4. Therefore, the temperature gradient in the grown crystal 10 can be increased. Since the shield 11 is fixed to the heat insulating cylinder 9, the upper space B becomes a space having a large volume, which is effective for increasing the temperature gradient in the grown crystal 10.

The length L of the tubular portion 11a is such that the distance h between the lower end of the tubular portion 11a and the surface of the sealant 3 is greater than 0 mm and 1
It is suitable that the length is 100 mm or less. The reason is that it becomes difficult to obtain a single crystal when the lower end of the tubular portion 11a is immersed in the sealant 3 (in this case, the distance h is 0 mm), and when the distance h exceeds 100 mm. The effect of blocking the radiant heat from the crucible 4 is reduced and the crystal 10
This is because it is heated by the radiant heat from the crucible 4 and the temperature gradient in the crystal 10 becomes small. Here, during the crystal growth, the crucible shaft 5 is gradually raised so that the distance h between the lower end of the tubular portion 11a and the surface of the sealant 3 is always kept constant.

The shield 11 is not limited to the one having the cross-sectional shape shown in FIG. 1 and may have a tapered shape by inclining the tubular portion 11a. In this way, the shape of the shield 11 and particularly the tubular portion 1
The shape and the length L of 1a and the opening ratio of the ventilation hole 11c (ratio of the opening area of the ventilation hole 11c to the entire area of the collar portion 11b including the opening area of the ventilation hole 11c) were grown appropriately. The temperature gradient in the crystal 10 may be controlled to an appropriate size.

The high-pressure vessel 1 has a water-cooled high-pressure jacket structure made of metal such as stainless steel, and is cooled by cooling water (not shown) flowing around it. Further, the inside of the container 1 is made into a predetermined atmosphere by a gas supply device and a gas discharge device (not shown) connected to the container 1. At that time, the pressure in the container 1 is controlled to be a predetermined pressure based on the detection value of a pressure sensor (not shown).

The crucible 4 is made of pBN or the like.

The heat insulation cylinder 9 is made of graphite or graphite felt.

A displacement sensor for detecting the amount of displacement of the pulling shaft and a weight sensor (load cell etc.) for controlling the diameter of the crystal are attached to the pulling shaft 7.

A displacement sensor for measuring the amount of displacement of the crucible shaft 5 is attached to the crucible shaft 5. During crystal growth,
A displacement amount of the liquid surface of the raw material melt 2 is calculated by a computer (not shown) connected to the displacement sensor and the weight sensor of the pulling shaft 7 based on the detected values of the sensors, and the calculated value and the crucible shaft connected to the computer. The ascending amount of the crucible 4 is controlled based on the detection value of the displacement sensor 5.

The crystal growth apparatus 100 having the above-mentioned structure is
It can also be used when growing crystals by the Czochralski method other than the LEC method.

[0024]

EXAMPLES The features of the present invention will be clarified below with reference to Examples and Comparative Examples. Needless to say, the present invention is not limited to the following examples.

Example 1 A GaAs single crystal was grown by the LEC method using the crystal growing apparatus 100 having the structure shown in FIG. The shield 11 of the growing apparatus 100 is made of graphite. The cylindrical portion 11 of the shield 11
The sectional shape of a was circular with an inner diameter of 200 mm. Then, the length L of the tubular portion 11a is set to an appropriate length and the tubular portion 11a
The distance h between the lower end of the sealant and the surface of the sealant 3 was set to 30 mm. Further, ventilation holes 11c were provided in the collar portion 11b of the shield 11 so that the area ratio (opening ratio) was 90%. The inner diameter of the heat insulating cylinder 9 was 350 mm.

Into a crucible 4 made of pBN (pyrolytic boron nitride) having an inner diameter of 300 mm, 15 kg of high-purity GaAs raw material 2 and 2.5 kg of B ₂ O ₃ as a sealing agent ₃ were put, and the crucible shaft in the high-pressure vessel 1 was put into the crucible shaft. 5 was installed. After evacuating the inside of the high-pressure container 1 with a vacuum pump (not shown), Ar gas was introduced to make the inside of the container 1 an Ar gas atmosphere of 20 atm. After that, the raw material 2 and the sealant 3 in the crucible 4 are melted by supplying power to the heater 8, and the seed crystal 6 is fed to the raw material melt 2 while controlling the electric power supplied to the heater 8 so as to obtain a predetermined temperature environment. Contacted the surface. The predetermined temperature environment is an environment in which the temperature distribution in the furnace is such that the solid-liquid interface shape between the crystal (seed crystal 6 or grown crystal 10) and the raw material melt 2 is convex downward.

While the pulling shaft 7 is rotated clockwise at 6 rpm and the crucible shaft 5 is rotated counterclockwise at 20 rpm, the crystal shaft 7 is raised at a pulling speed of 6 to 10 mm / hour to obtain a diameter of 110 mm (4 20 inches in length
A 0 mm GaAs crystal (growth direction <100>) was grown. The number of breeding was 4 times. During the crystal growth, the distance h between the lower end of the cylindrical portion 11a of the shield 11 and the surface of the sealant 3 is h.
The crucible 4 was gradually moved upward by the crucible shaft 5 so that the temperature was kept constant (30 mm).

(Embodiment 2) The length L of the tubular portion 11a of the shield 11 is 100 mm, and the lower end of the tubular portion 11a and the sealant 3 are used.
A GaAs crystal was grown with the distance h from the surface of the substrate being 100 mm. The number of breeding was 4 times. During crystal growth,
The crucible 4 was gradually raised so that the distance h between the lower end of the tubular portion 11a of the shield 11 and the surface of the sealant 3 was always kept constant (100 mm). The other conditions were the same as in Example 1 above.

(Comparative Example) GaAs without the shield 11
Was grown three times. The other conditions were the same as in Example 1 above.

(Results) Table 1 shows the lengths of the single crystal portions of the GaAs crystals (length 200 mm) obtained in Examples 1 and 2 and Comparative Example.

[0031]

[Table 1]

From Table 1, as in Examples 1 and 2, the shield 1
It can be seen that when 1 is provided, the length of the single crystal portion becomes longer than when the shield 11 is not provided (comparative example). Also,
By comparing Example 1 and Example 2, the shielding plate 11
The smaller the distance h between the lower end of the cylindrical portion 11a and the surface of the sealant 3, the longer the length of the single crystal portion. Particularly, when the distance h is 30 mm as in Example 1, the obtained crystal is obtained. It can be seen that the whole of (200 mm) becomes a single crystal.

Therefore, the shield 11 is provided, and the cylindrical portion 11 thereof is provided.
By making the lower end of a close to the surface of the encapsulant 3, a GaAs crystal with a high single crystallization rate (the length of the single crystal portion is 150 mm to 200 mm) can be obtained.

[0034]

According to the present invention, it is possible to prevent the growing crystal from receiving radiant heat from the crucible during the crystal growth, and to prevent the high temperature gas in the space partitioned by the shield. Since it can escape upward through the ventilation holes, it is possible to prevent the temperature gradient in the crystal from becoming small due to the radiant heat or the heating of the crystal by the high temperature gas, and it is possible to grow a longer single crystal.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example in which a crystal growth apparatus according to the present invention is applied to a pulling furnace by the LEC method.

[Explanation of symbols]

A Space partitioned by shield B Space above shield h h Distance between bottom of shield and surface of sealant (melt in crucible) 2 Raw material melt 3 Sealant 4 Crucible 6 Seed crystal 8 Heater 10 Growth Crystal 11 Shield 11c Vent 100 Crystal Growth Device

Claims (6)

[Claims] 1. A single crystal growing apparatus for growing a single crystal by heating a raw material placed in a crucible with a heater to melt it, bringing a seed crystal into contact with the upper surface of the raw material melt, and gradually pulling it up. , Between the inner surface of the crucible and the side surface of the growing crystal, a shield that substantially surrounds the growing crystal and prevents the growing crystal from being heated by radiant heat from the crucible, from the surface of the melt in the crucible. It is provided so as to be separated upward by a predetermined height, and a ventilation hole is provided in the upper part of the shield to let hot gas in the space partitioned by the shield escape to a space above the shield. A single crystal growth apparatus characterized by being provided. 2. The distance between the lower end of the shield and the surface of the melt in the crucible is longer than 0 mm and 100 mm or less, preferably about 30 mm or less. Single crystal growth equipment. 3. A single crystal is grown by heating a raw material placed in a crucible with a heater to melt it, bringing a seed crystal into contact with the upper surface of the raw material melt, and gradually pulling it up to grow the single crystal. While keeping the distance between the lower end of the shield provided between the inner surface of the crucible and the side surface of the grown crystal gradually rising and the surface of the melt in the crucible within a predetermined range, from the crucible by the shield. The radiant heat is shielded to prevent the growth crystal from being heated by the radiant heat, and the high temperature gas in the space partitioned by the shield by the ventilation hole provided above the shield is transferred to a space above the shield. A method for growing a single crystal, characterized in that the crystal is grown so as to escape. 4. The crystal is grown while keeping the distance between the lower end of the shield and the surface of the melt in the crucible longer than 0 mm and 100 mm or less, preferably about 30 mm or less. Item 3. The single crystal growth method according to Item 3. 5. A single crystal of a compound semiconductor according to claim 3, wherein a single crystal of a compound semiconductor is grown while the raw material melt is covered with a liquid sealing material which is heated and melted by the heater. Training method. 6. The method for growing a single crystal according to claim 5, wherein the compound semiconductor is GaAs.