JPH05124887A - Production of single crystal and device therefor - Google Patents

Abstract

PURPOSE:To improve the yield of the single crystal and to increase a growth rate by shutting off the convection of the melt from as solid-liquid boundary so as to form the solid-liquid boundary to a shape having a convex face toward the melt direction. CONSTITUTION:The heater of an electric furnace consists of a heater 1 for controlling the solid-liquid boundary position, a heater 2 for forming the melt, and a heater 3 for preventing the rapid cooling of an ingot. These heaters are kept at 1245 to 1250 deg.C or 1150 to 1200 deg.C near the respective m.p. (m.p.=1238 deg.C). The heater 1 for controlling the solid-liquid boundary position and the heater 2 for forming the melt are parted from each other to provide a spacing 14, by which the valley TL (= about 1233 to 1237 deg.C) of temp. is formed and the temp. gradient between the valley of the temp. and the solid- liquid boundary 10 is substantially maintained at 0 deg.C/cm. As a result, the convention in the melt is shut off at above and below and the solid-liquid boundary 10 does no longer receive the influence of the convection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal manufacturing method and apparatus capable of growing a high quality single crystal by the vertical Bridgman method (VB method).

[0002]

2. Description of the Related Art As shown in FIGS. 2A and 2B, a conventional vertical Bridgman method for producing a single crystal has a melt forming section 11, a solid-liquid interface section 12 and a cooling chamber arranged vertically in a furnace. By providing the portion 13, a gentle temperature distribution 20 is formed in the direction of gravity in the furnace from a high temperature region 21 to an interface temperature region 22 near the melting point to a low temperature region 23. High temperature region 2 forming this temperature distribution 20
By lowering the crucible 4 below the melt 6, the melt 6 is moved to the low temperature region 23 through the interface temperature region 22 to grow the single crystal 5.

[0003]

As described above, in the conventional vertical Bridgman method, the temperature distribution in the high temperature region 21 above the solid-liquid interface 10 is such that the temperature gradually rises above the solid-liquid interface 10. Therefore, the convection of the melt 6 (indicated by an arrow) affects the solid-liquid interface 10 position. Therefore, as shown in FIG. 3 (B), the solid-liquid interface shape 9 tends to be concave in the melt direction (arrow a) opposite to the seed crystal 8. As a result, defects are easily taken in from the crucible wall, the single crystal yield is poor, and the growth rate must be slowed (for example, 1 to 3 mm).
/ H).

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art by providing a buffer zone for preventing the convection of the melt from affecting the solid-liquid interface, resulting in a good single crystal yield and growth. It is an object of the present invention to provide a novel method for producing a single crystal having a high speed and an apparatus thereof.

[0005]

According to the method for producing a single crystal of the present invention, in the vertical direction in the furnace, the melting point is passed from the high temperature region forming the melt to the interface temperature region near the melting point for controlling the solid-liquid interface position. A method for producing a single crystal by the vertical Bridgman method in which a columnar single crystal is grown by forming a temperature distribution reaching a lower temperature region and moving a melt in the high temperature region to a low temperature region through an interface temperature region. In, a valley of temperature distribution is formed between the high temperature region and the interface temperature region, and the temperature gradient is substantially 0 ° C./c in the crystal growth axis direction between the valley portion of this temperature and the solid-liquid interface.
It is set to m.

In this case, in order to improve the single crystal yield and increase the growth rate, the relationship between the distance L between the temperature valley and the solid-liquid interface and the crystal diameter d is expressed by the following equation: 0.5d It is desirable to satisfy ≦ L ≦ 2d.

Further, the apparatus for producing a single crystal according to the present invention comprises a high temperature heating part for forming a high temperature region for forming a melt and a crystal for controlling a solid-liquid interface position in order to form a temperature distribution in a vertical direction in the furnace. Equipped with an interface heating unit that creates an interface temperature region near the melting point and a low temperature heating unit that creates a low temperature region lower than the melting point, and move the crucible containing the crystal raw material from the high temperature heating unit to the low temperature heating unit through the interface heating unit. In the apparatus for producing a single crystal by the vertical Bridgman method in which the single crystal is grown by going down, a gap is provided between the high temperature heating part and the interface heating part, and the valley of the temperature distribution is formed by this gap.

In this case, cooling means may be provided instead of the gap or in the gap.

[0009]

When the space between the interface heating part and the high temperature heating part is widened to provide a gap or a cooling means for forming a valley of the temperature distribution between them, convection in the melt is blocked up and down, and By setting the temperature gradient to 0 ° C./cm, the solid-liquid interface shape becomes convex in the melt direction, and the single crystal yield is improved. This means that the growth rate is substantially increased because the growth rate is conventionally suppressed to be convex.

The distance L between the valley of the temperature distribution and the solid-liquid interface is L
The reason for setting ≧ 0.5d is that, in the case of L <0.5d, even if the valley portion of the temperature distribution is provided, the convection of the melt reaches the solid-liquid interface and is not effective. Further, L ≦ 2d means that in the case of L> 2d, since the height of the melt is too high, it is difficult to maintain the temperature gradient in the axial direction of the melt at 0 ° C./cm, There is a probability that a new convection will be formed in the middle of the temperature valley and the solid-liquid interface, or the temperature of the temperature valley will be too low and the melt will solidify in that area. Because it will be higher. It is preferable that L, which is practically stable, be about d. As a single crystal, there is a III-V group compound semiconductor crystal such as GaAs.

[0011]

EXAMPLES Example 1 An explanation will be given with reference to FIG. 1 showing an apparatus for producing a single crystal by the VB method according to this example and its temperature distribution diagram. The furnace is composed of a vertical electric furnace and has a predetermined temperature distribution 18 (see FIG. 1).
A cylindrical heater forming (B)) is provided. This heater is divided into three parts in the vertical direction, and a solid-liquid interface position control heater 1 forming an interface heating part in the central part, a melt forming heater 2 forming a high temperature heating part in the upper part, and a low temperature heating part in the lower part. It comprises a heater 3 for preventing the rapid cooling of the ingot.
Each heater has an interface temperature range near the melting point (mp = 1238 ° C.) 16, a high temperature range 1524 to 1250 ° C. 15,
It is kept in the low temperature region 17 of 1150 to 1200 ° C. Between the solid-liquid interface position control heater 1 and the melt forming heater 2, there is provided a gap 14 having a dimension l = about 20 mm, and a valley T _{L of} temperature distribution (= about 1233-1237 ° C.) is formed. is doing. The distance L between the valley T _{L of the} temperature distribution and the solid-liquid interface 10 was set to about 50 mm. From the crucible size described below, the crystal diameter d
And L is about d.

A crucible 4 which is vertically movable is inserted into the cylindrical heater. The crucible 4 has an inner diameter of φ50, a straight body depth of 250 mm, and is made of PBN. A seed crystal 8 is set at the lower end of the crucible 4, and 1500 g of GaAs polycrystal and 100 g of B ₂ O ₃ are further put therein and set in a furnace. After replacing the atmosphere in the furnace with N ₂ gas, the electric furnace is heated to melt the GaAs polycrystal and B ₂ O ₃ to form a GaAs melt 6 sealed with the liquid B ₂ O ₃ 7. .. The PBN crucible 4 was slightly raised to seed the seed crystal 8 and then lowered at a speed of 5 mm / h for crystal growth. After solidifying the entire melt, it was cooled to room temperature at a rate of 50 ° C./h and taken out of the furnace. Wafers were cut from the seed and tail portions of the obtained crystal at the (100) plane, respectively, and melted KOH was etched at 350 ° C. for 15 minutes, and the dislocation density was measured.
It was less than 00 cm ^-2 . The shape 9 of the solid-liquid interface is shown in FIG.
As in (A), a convex shape was shown in the melt direction a.

Example 2 The distance L between the T _L portion and the solid-liquid interface is about 25 mm, that is, L =
Growth was performed under the same conditions as in the example except that the thickness was set to about d / 2. As a result, polycrystals were generated from the shoulder. When the solid-liquid interface shape was observed, it was slightly concave as shown in FIG. However, the growth rate from 5 mm / h to 3
A single crystal was obtained when the growth was slowed down to mm / h.
The dislocation density of this crystal was also about 5000 cm ^-2 . In any case, it was found that under the condition of L = about d / 2, the influence of the convection of the melt on the solid-liquid interface still remained.

Example 3 Growth was performed under the same conditions as in Example 1 except that L = about 2d. As a result, unless the temperature of TL was set to around 1237 ° C., the melt in the vicinity was likely to solidify, and it was often difficult to continue the growth. Therefore, T _L is 1238-
When the temperature was raised to 1239 ° C. and the growth was performed, it was found that the convection of the melt became large and the growth conditions became unstable. However, when T _L = about 1237 ° C. and the melt did not solidify, a single crystal was obtained. In this case, the dislocation density is about 5
It was 000 cm ^-2 .

Modification As a method for providing a valley of the temperature distribution between the solid-liquid interface position control heater 1 and the melt forming heater 2, the gap between the heaters was adjusted in the above-mentioned embodiment. The present invention is not limited to this. For example, a method of passing a water cooling pipe between the heaters is also effective. In short, it suffices to cool the space between the heaters. Furthermore, the present invention can be applied to the VGF method (vertical temperature gradient solidification method), and if the application to the VGF method is considered, for example, a water cooling pipe is installed above the solid-liquid interface,
A method of moving the water-cooled pipe along with the movement of the interface position is also possible. In short, on the melt side slightly away from the solid-liquid interface,
It is an important point to provide a low temperature region where the melt temperature does not solidify.

[0016]

The present invention has the following effects.

(1) By adopting a relatively simple method of providing a temperature valley in a part of the temperature distribution, a long single crystal can be obtained with good yield and speed.

(2) Distance L between temperature valley and solid-liquid interface
And the crystal diameter d are set so that d / 2 ≦ L ≦ 2d, a long single crystal can be obtained with higher yield and more speedily.

(3) Since it is only necessary to provide a gap in the existing equipment, the structure can be simplified.

(4) Since the temperature of the valley can be set to a desired temperature by providing a cooling means capable of positively cooling, the reliability of the apparatus is high.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of an apparatus for producing a single crystal by a VB method for carrying out the method of the present invention, and its temperature distribution chart.

FIG. 2 is a schematic view showing an example of a conventional single crystal manufacturing apparatus by the VB method and its temperature distribution diagram.

FIG. 3 is a crystal cross-sectional view showing a solid-liquid interface shape of a single crystal in this example and a solid-liquid interface shape of a single crystal obtained by a conventional method.

[Explanation of symbols]

1 Solid-liquid interface position control heater (interface heating part) 2 Melt forming heater (high temperature heating part) 3 Crystal ingot quenching prevention heater (low temperature heating part) 4 PBN crucible 5 GaAs single crystal 7 Liquid B ₂ O ₃ 6 GaAs melt 8 seed crystal 10 solid-liquid interface 14 gap 15 high temperature region 16 interface temperature region 17 low temperature region 18 temperature distribution d crystal diameter _TL temperature valley L _TL distance between solid-liquid interface m. p. GaAs melting point (about 1238 ℃)

Claims (4)

[Claims] 1. A temperature distribution is formed in a vertical direction in a furnace from a high temperature region forming a melt to a low temperature region lower than the melting point through an interface temperature region near a crystal melting point for controlling a solid-liquid interface position, In the method for producing a single crystal by the vertical Bridgman method of growing a columnar single crystal by moving the melt in the zone to the low temperature zone through the interface temperature zone, between the high temperature zone and the interface temperature zone A method for producing a single crystal, characterized in that a valley of temperature distribution is formed and a temperature gradient between the valley portion of this temperature and the solid-liquid interface in the interface temperature region is substantially 0 ° C./cm. .. 2. The distance L between the temperature valley and the solid-liquid interface,
The method for producing a single crystal according to claim 1, wherein the relationship with the crystal diameter d satisfies the following expression: d / 2 ≦ L ≦ 2d. 3. In order to form a temperature distribution in the furnace in the vertical direction,
A high-temperature heating unit that creates a high-temperature region that forms a melt, an interface heating unit that creates an interface temperature region near the crystal melting point that controls the solid-liquid interface position, and a low-temperature heating unit that creates a low-temperature region lower than the melting point are provided.
In the apparatus for producing a single crystal by the vertical Bridgman method of growing a single crystal by moving the crucible containing the crystal raw material from the high temperature heating section to the low temperature heating section through the interface heating section, the high temperature heating section and the interface An apparatus for producing a single crystal, wherein a gap is provided between the heating unit and a valley of temperature distribution is formed by the gap. 4. The apparatus for producing a single crystal according to claim 3, wherein cooling means is provided in place of or in the gap.