JPH0329752B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a magnetic field application rotational pulling device that pulls a single crystal while applying a magnetic field.

(Prior Art) In recent years, with the development of semiconductor devices, high-quality single crystals with fewer defects are required. Many methods for producing single crystals have been proposed, but the rotary pulling method (CZ method) and the liquid-filled rotary pulling method (LEC method) are often used industrially. GaAs, GaP, InP using the latter method
Single crystals such as

As an example, a method for manufacturing a GaAs single crystal by the LEC method will be explained with reference to FIG. 6. A cylindrical crucible 3 whose outer periphery is covered with a cylindrical support member 4 made of carbon is provided in a high-pressure vessel 1. , this crucible 3
is supported by a support shaft 9 so as to be able to rotate and move up and down, and a heater 2 is provided around the crucible 3.
The crucible is heated and maintained at a predetermined temperature. A pulling shaft 8 with a seed crystal 7 attached to the lower end is provided at the upper part of the opening surface of the crucible 3, and this pulling shaft is configured to rotate and move up and down.

The crucible 3 is filled with predetermined amounts of Ga and As as crystal raw materials and B ₂ O ₃ as a sealant, the inside of the high-pressure container is pressurized with inert gas, and the crucible 3 is heated to a predetermined temperature with the heater 2. By doing so, a GaAs melt 5 is formed in the lower layer and a B ₂ O ₃ melt 6 as a sealant is formed in the upper layer in the crucible.

Next, the pulling shaft 8 is lowered, the seed crystal 7 is passed through the sealant 6 and brought into contact with the GaAs melt 5, and then the seed crystal 7 is slowly pulled up while rotating the crucible and the pulling shaft to form the crystal 10. Make it grow.

At this time, one of the essential requirements for producing high-quality single crystals is to make the temperature gradients in the diameter direction and depth direction of the sealant 6 and crystal raw material melt 5 in the crucible as gentle as possible. .

(Problem to be solved by the invention) However, using a crucible with a diameter of 10 cm,
When the B ₂ O ₃ melt and the GaAs melt were formed, thermocouples were inserted into the center and near the peripheral wall of the crucible, and the temperature distribution in the depth direction of the melt was measured.
As shown in the graph of Figure 7, the temperature difference between the center part (curve a) and the peripheral wall part (curve b) is approximately 60°C.
The temperature gradient of the GaAs melt was approximately 20°C/cm, and the temperature gradient of B ₂ O ₃ was approximately 100°C/cm.

In order to make the above-mentioned temperature gradient in the pulling axis direction (depth direction) gentle, methods have been used to lengthen the heat generating portion of the heater or to lower the position of the crucible relative to the heater.
However, with these methods, the temperature difference in the diametrical direction becomes large, or a temperature inversion layer is formed in the melt, causing the crystal to solidify rapidly, making it difficult to obtain high-quality single crystals. It has been difficult to form a crystal raw material melt having an optimal temperature distribution.

A method of heating the crucible from the vertical direction has recently been proposed as a method to overcome the above-mentioned drawbacks, but this method increases the temperature gradient in the depth direction of the melt, making it difficult to form a temperature distribution that is optimal for pulling. do not.

These problems are also a problem with the CZ method that does not use a sealant, especially in the magnetic field rotational pulling method (MCZ method), which has attracted attention recently and pulls a single crystal while applying a magnetic field.
The problem of temperature gradients has arisen significantly. That is,
In the MCZ method, a magnetic field is applied to the crystal raw material melt in the crucible to suppress the convection of the melt and grow a high-quality single crystal. When the heater is turned off, the heat from the heater is carried out only by conduction of the melt, creating a large temperature difference across the diameter of the crucible. For this reason
In the MCZ method, the temperature difference in the diameter direction was large, making it difficult to grow high-quality crystals. This diametrical temperature difference becomes more pronounced as the diameter of the crystal to be pulled increases, making it difficult to obtain a high-quality single crystal.

An object of the present invention is to provide a single crystal pulling apparatus that heats the melt in a crucible to form the best temperature distribution for obtaining a high quality single crystal in the MCZ method.

(Means for Solving the Problems) In the present invention, a cylindrical heater is arranged along the outer surface of the crucible in a single crystal pulling apparatus in the MCZ method, and an upper part is continuously connected to the upper end of the cylindrical heater. The present invention is characterized in that a truncated conical heater is provided extending inwardly and having a diameter-reduced opening at the upper end and having a diameter through which the crucible can pass.

When the melt in the crucible is heated using a heater with the structure described above, it is heated from the outer periphery of the crucible and is heated more strongly toward the center than the surface of the melt by the radiant heat of the truncated conical heater. , the temperature gradient in the diameter direction and depth direction of the crucible becomes smaller,
A melt with an optimal temperature distribution for crystal pulling will be formed.

Next, the present invention will be explained with reference to the drawings. FIGS. 1 and 2 show an embodiment of the heater for a single crystal pulling apparatus of the present invention, in which a cylindrical shape is formed by a comb-shaped heater member 11 made of graphite. The cylindrical heater portion 13 is located along the side surface of the crucible. At the upper end of this cylindrical heater section 13, a truncated conical heater 14 is provided that extends inwardly at the upper end and has an opening 15 with a reduced diameter at the upper end. The heater members of the cylindrical heater section 13 and the heater members of the truncated conical heater section 14 are continuously integrated, and the lower ends of the adjacent heater members of the cylindrical heater section 13 are electrically connected to each other. Similarly, the upper end of the heater member next to the truncated conical heater part 14 is shifted from the cylindrical heater part by one and is electrically connected to every other heater part, so that overall, both heater parts meander. The heater member is composed of a single heater member having a shape, and both ends of the heater member are connected to heater electrodes (not shown). A heat-resistant insulating material 12 is interposed between each motor member 11 to suppress damage and shoots due to vibrations generated during operation. In this embodiment, the cylindrical heater section 13 is supported by a heat-resistant and insulating table 16 having a hole 17 in the center through which the crucible support shaft 9 passes.

The height and diameter of the cylindrical heater part of the heater configured as above, the height and inclination angle of the truncated conical heater part, and the diameter of the opening are determined by the size of the crucible, the type of crystal raw material melt, and the diameter of the crystal to be pulled. should be determined taking into consideration the crystal pulling conditions, etc., but the crystal pulling operation can be performed more easily if the diameter of the opening of the truncated conical heater is larger than the diameter of the crucible.

(Function) When a crucible filled with crystal raw materials is heated by a heater configured as described above, a truncated conical heater is present not only on the outer periphery of the crucible but also at the top, and the diameter of the opening of this truncated conical heater is is smaller than the inner diameter of the cylindrical heater, the surface of the crystal raw material melt in the crucible is heated by the radiant heat of the truncated conical heater, and is heated particularly strongly toward the center, so that The temperature distribution and the temperature distribution in the depth direction become gentler.

As an example, in the LEC single crystal manufacturing apparatus shown in Fig. 6, only the heater is configured as shown in Fig. 1, and the rest is placed in the crucible under the same conditions.
As a result of forming a GaAs melt and measuring the temperature distribution of the melt at the center and the peripheral wall using a thermocouple, we found that the temperature at the center (curve a) and the peripheral wall (curve b) was as shown in the graph of Figure 3. The distribution is almost the same, and the temperature distribution in the depth direction of the melt is approximately 20°C/cm above the interface between the GaAs melt and the B ₂ O ₃ melt, compared to when heated with a conventional heater shape. The temperature distribution becomes ~1/40 smaller in the diameter direction and about 1/5 smaller in the depth direction.

A GaAs single crystal with a diameter of 50 mm was cut out by pulling the crystal from the heated GaAs melt as described above, and the dislocation density distribution of the resulting wafer was measured. As shown in (a), the dislocation density distribution is approximately 10 ^-3 cm ² over the entire surface of the wafer excluding the periphery, compared to the dislocation density distribution (curve b) of a crystal grown using a heater with a conventional structure. It decreased by about 1/10, and the W-shaped distribution now shows a U-shaped distribution.

The effect is also noticeable when the heater according to the present invention is applied to a single crystal pulling apparatus using a magnetic field application. That is, the temperature distribution in the depth direction of the center (curve a) and peripheral wall (curve b) of the GaAs melt in the crucible was heated and melted using a heater with a conventional structure and a magnetic field of 1200 Gauss was applied. As a result, as shown in the graph of Figure 5a, there is a temperature difference of about 100°C in the diametrical direction, but when the heater was formed using the structure of the present invention and the other conditions were the same.
As a result of measuring the temperature distribution in the depth direction of the central part (curve a) and the peripheral wall part (curve b) of the GaAs melt, the fifth
As shown in Figure b, the temperature difference in the diameter direction was reduced to about 1/3, and the temperature difference in the depth direction was also significantly reduced. This is because the melt is heated not only from the outer periphery but also from the top surface, particularly at the center.

(Example) Example 1 A cylindrical heater with an inner diameter of 135 mm and a height of 150 mm, which has a truncated conical heater with an inclined part height of 25 mm and an opening with a diameter of 100 mm at the upper end, is integrally formed in the upper part of the high-pressure container. A crucible with an outside diameter of 96 mm and a height of 100 mm, filled with 500 g of Ga, 550 g of As, and 200 g of B ₂ O ₃ as a sealing agent, was installed, and argon gas was pressurized into the high-pressure container to reach 50 atmospheres, and then the heater was energized. Heated. Once there were two layers of GaAs melt and B ₂ O ₃ melt in the crucible, the temperature distribution was measured with a thermocouple and found to be 15°C/cm in the depth direction of the crucible and 1°C/cm in the diameter direction of the crucible. It was cm. In this state, the crystal pulling shaft is lowered, and once the seed crystal comes into contact with the GaAs melt, the crucible and the seed crystal are rotated relative to each other at a predetermined speed, and the seed crystal is pulled up at a speed of 8 mm/hour to a diameter of approximately 50 mm. , a GaAs single crystal with a length of about 70 mm was formed.

A wafer was cut in the <100> direction from this crystal, etched using the molten KOH method, and the dislocation density distribution was measured.
Very small single crystals/cm ² and high quality were obtained.

Next, the crucible was heated in the same manner as above, and when GaAs melt and B ₂ O ₃ melt were formed in the crucible, a magnetic field of 1000 Gauss was applied from the side of the crucible and the temperature distribution was measured. 8℃/ in the depth direction of
cm, and 4°C/cm in the diameter direction of the crucible. A crystal was pulled under the same conditions as in Example 1 with a magnetic field applied, and the growth striations of the obtained crystal were observed by the photoetching method, and there were no growth striations as seen in the LEC method. Furthermore, the amount of inherent defects
When measured by the DLTS method, the crystal density was 2×10 ¹⁵ /cm ³ , which was about an order of magnitude lower than that of crystals obtained by the usual LEC method.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, the temperature gradient of the melt inside the crucible becomes smaller in both the diametrical direction and the depth direction of the crucible. By pulling, a high quality single crystal with few dislocations is formed.
By using it as a single crystal pulling device by applying a magnetic field, it is possible to produce high-quality, large-sized crystals with good reproducibility.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing an embodiment of the heater of the present invention, FIG. 2 is a partially cutaway side view, and FIG. 3 is the temperature distribution of the melt heated by the present invention. 4 is a graph showing the dislocation density distribution of the crystal formed by this invention. FIG. 5 is a graph showing the temperature distribution of the melt under the application of a magnetic field.
FIG. 6 is a schematic diagram of a liquid-sealed rotary pulling device, and FIG. 7 is a graph showing a typical example of temperature distribution of melt in a conventional device. 1... High pressure container, 2... Heater, 3... Crucible, 5... Crystal raw material melt, 6... Liquid sealant, 7
...Seed crystal, 10...Growing crystal, 11...Heater member, 13...Cylindrical heater section, 14...Truncated conical heater section, 15...Opening.

Claims (1)

[Claims] 1. In a single crystal pulling device that places a crucible inside and pulls a single crystal by heating the inside of the crucible while applying a magnetic field from the side of the crucible, a cylindrical heater is placed along the outer surface of the crucible. death,
A truncated conical heater is provided extending continuously from the upper end of the cylindrical heater and has an opening having a diameter that allows the crucible to pass through and is formed by sloping inwardly at the upper end and reducing the diameter at the upper end. A single crystal pulling device featuring: