JPS63215587A - Production of single crystal - Google Patents

Abstract

PURPOSE:To effectively suppress convection in the horizontal direction without strengthening magnetic field, by immersing a cylindrical heat convection suppressing column in a raw material melt for single crystal at a concentric position and producing single crystal by pulling method. CONSTITUTION:A crucible 5 is supported on a lower shaft 7 in a pressure container 10 and raw material melt 6 is packed in a crucible 5. A heat 3 to heat the raw material melt 6 is set on the periphery of the crucible 5. When an upper shaft 8 is raised while being rotated, single crystal 1 is pulled up from the raw material melt 6. A magnetic field applying device 4 generates magnetic field advancing from one pole to the other in the horizontal direction in space wherein the raw material melt 6 and the heater 3 exist. A cylindrical heat convection suppressing column 2 is immersed in the raw material melt 6 concentrically with the crucible 5. The raw material melt 6 is halved into inner melt and outer melt by the heat convection suppressing column 2. Since there are slits 11, the heights of the liquid level of the inner and outer melt are equal. When the single crystal 1 is pulled up, the inner melt and the outer melt are reduced while maintaining the same height.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field The present invention relates to an improvement in a method for producing a single crystal by a pulling method.

Here, single crystals include Si, GaAs, G
aP.

Semiconductor single crystals such as InP, LNO, BSO, BC,0
Broadly refers to single crystals, such as dielectric single crystals.

There are many ways to grow single crystals, but they can be broadly categorized as follows:
The boat method and the towing method are used. The boat method, such as the horizontal Bridgman method or the gradient freeze method, involves placing a raw material melt in a quartz boat inside a quartz tube and cooling it from one end to grow a single crystal.

In the pulling method, a raw material melt is placed in a crucible, a seed crystal is immersed in the raw material melt, seeded, and a single crystal is pulled by pulling the seed crystal.

The most common pulling method is the Czochralski method (CZ
, Czochralski method). The raw material in the crucible is heated to form a melt, and a single crystal is pulled up using a seed crystal. It can be used to pull Si single crystals.

In the case of pulling GaAs, GaP, etc., it is difficult to obtain a stoichiometric l-IJ lac single crystal because the dissociation pressure of As and P at the melting point of the compound is high. Therefore, the raw material melt is covered with a layer of B2O3, and high pressure is applied using an inert gas. This results in As.

Volatization of P, etc. can be prevented.

Such a method is called the liquid capsule method.
apsulated Czochralski L E
C).

(a) Conventional technology Both the CZ method and the LEC method pull up a single crystal perpendicularly from the surface of the raw material melt. There is no way to forcibly specify the diameter of a single crystal.

Therefore, diameter control must be performed. This is done by increasing or decreasing the power of the heater heating the crucible.

In order to be able to control the diameter, stability of the diameter must be a prerequisite. In order to keep the diameter constant, the crucible and the seed crystal are often rotated in opposite directions.

Due to opposing rotations, the temperature distribution in the rotation direction is made uniform,
The diameter can be made uniform all around.

However, the occurrence of temperature distribution in the vertical direction and the radial direction cannot be suppressed by these rotations.

The heater is provided so as to surround the crucible. It is a cylindrical heater. Since the heater and crucible do not frequently move relative to each other in the vertical direction, there is a temperature difference in the vertical direction.

The heater directly ignites the crucible wall. The heat from the wall heats the raw material melt.

Heat is transferred from the crucible wall to the raw material melt by convection, conduction,
By radiation. Since it is a liquid, convection is the most dominant of these.

Convection is macroscopic fluid movement. The direction of convection depends on the dimensions of the heater, the dimensions of the crucible, and their relative positions. In many cases, the flow is upward at the outer periphery and downward at the inner center. At the surface, the flow becomes centripetal.

Furthermore, the raw material melt is rotating. Coriolis occurs, so the surface convection becomes a vortex.

When the vortices gather at the center, vortex threads are created in the fluid near the center. The generation of vortices and eddy currents causes unsteady disturbance in the melt.

The greater the power of the heater, the greater the force of convection.

The interface between the bottom of the growing crystal and the raw material melt is called the solid-liquid interface.

The solid-liquid interface is one type of isothermal blood.

If convection is active, a complex vortex will occur at the center of the surface of the raw material melt. Therefore, severe temperature fluctuations occur near the solid-liquid interface.

Fluctuations in the temperature of the melt can cause crystal defects or make the impurity concentration non-uniform.

When a single crystal is cut lengthwise and etched with a special etchant, many stripes appear on the cut surface. These concentric stripes appear in the cross section of a single crystal. It's called striation. It is a type of crystal defect. This is a stripe that appears due to temperature fluctuations and impurity concentration fluctuations.

In order to suppress such convection of the raw material melt, it has become common practice to apply a strong magnetic field to the raw material melt.

There are charged particles such as ions and free electrons in the raw material melt. When a magnetic field is present, Lorentz forces act on charged particles. Due to the roller motion, charged particles move in a cyclotron around magnetic lines of force. In other words, it is captured by magnetic field lines.

Since free movement is blocked, the movement of charged particles becomes slower. Then, the movement of the raw material melt is suppressed.

Convection is suppressed by a magnetic field. Expressions such as effectively increasing the viscosity of the melt are also used.

When convection is suppressed, the temperature distribution in the raw material melt becomes wider. However, the temperature near the solid-liquid interface becomes stable. For this reason, it is said that high-quality single crystals can be obtained.

There are still problems to be overcome in the magnetic field applied single crystal growth method.

The magnetic field that is effective in suppressing convection of the raw material melt is extremely large. A magnetic flux density of several thousand glass is required.

If you try to obtain this using an electromagnet, you will need a large electromagnet. Electricity costs also increase.

Electromagnets are placed outside the crystal growth reactor facing each other, and a strong magnetic field is generated in the wide space between them, resulting in large magnets. The equipment will be large-scale.

If the electromagnet is a superconducting magnet, the burden on electricity costs can be reduced. However, it is difficult to adjust the strength of the magnetic field.

Also, it is easier to make the electromagnets face each other, but in this case the direction of the magnetic field will be horizontal.

A horizontal magnetic field can effectively suppress vertical convection. However, horizontal convection cannot be effectively suppressed.

This is because the Lorentz force occurs in a direction perpendicular to the direction of the magnetic field and perpendicular to the velocity of the charged particle.

By providing an air-core coil around the crystal growth furnace, a vertical magnetic field can be generated. However, the coil has a diameter larger than the outer circumference of the crystal growth furnace, making it large-scale. Also, since it is not possible to insert magnetic materials, the magnetic flux density that can be created is small even if a large current is passed through the coil.

It has almost no effect.

(E) Problems to be Solved by the Invention The Czochralski method using a magnetic field is a method invented for pulling Si semiconductor single crystals. Even now, mainly
Development is progressing with the aim of pulling Si single crystals.

Actually, when a single crystal is cut and etched,
It can be seen that the stripe spacing of IJ Anyon is wider.

However, maintaining a high magnetic field over a wide range is extremely difficult.

A huge electric current must continue to flow through a huge electromagnet. Since the heater and other conductors are inside the growth furnace, the Lorentz force causes the heater to vibrate. Even if these incidental problems are solved, it is still difficult to obtain a sufficiently strong magnetic field.

However, in reality, temperature fluctuations near the solid-liquid interface are a problem. It is sufficient if convection near the solid-liquid interface can be suppressed.

Since it is strongly required to grow single crystals economically,
Single crystals tend to have larger diameters. If a 5-inch single crystal is to be pulled, the inner diameter of the crucible must be 10 inches.

Even for compound semiconductors such as GaAs, a diameter of 3 inches is common. Then, the inner diameter of the crucible will be about 6 inches.

In this way, the convection of the entire raw material melt in a wide crucible is
Suppression through the action of a magnetic field is a wasteful method.

The magnitude of the driving force that promotes thermal convection is proportional to the Grashof number.

The Grashof number is given by the following equation.

Here, 1 is the gravitational acceleration, ΔT is the horizontal temperature difference, and R
is the radius of the container and ν is the kinematic viscosity coefficient.

Adding a magnetic field is considered to effectively increase ν. When ν is increased and the container (crucible) is large, convection increases in proportion to the third power.

When the diameter of the crucible is increased, the horizontal temperature difference ΔT also increases.

After all, the larger the crucible, the greater the magnetic flux density required to suppress convection.

It is not only necessary to simply expand the space in which the magnetic field exists, but also to increase the magnetic flux density.

In that case, a larger magnet would have to be installed. Not only does the renoid section consisting of the magnetic core and coil become larger, but the cooling device (superconducting magnet) also becomes larger.

The power supply will also be larger. Since direct current needs to flow, power costs also increase.

Furthermore, when applying a horizontal magnetic field, there is little effect in suppressing horizontal convection.

There were many problems like this.

00 Purpose It is the first object of the present invention to provide a method that can effectively suppress horizontal convection without strengthening the magnetic field in a crystal pulling method by applying a magnetic field.

A second object of the present invention is to provide a crystal growth method in which the magnetic field application device can be downsized by adding a mechanism that can suppress convection of the raw material melt.

(4) Structure In the present invention, a cylindrical heat convection suppressing tube is immersed in the raw material melt. The inner diameter U of the heat convection suppressing cylinder is larger than the outer diameter S of the single crystal to be pulled. The outer diameter ■ of the heat convection suppressing tube is smaller than the inner diameter W of the crucible.

In other words, the inequality % expression % (2) holds true. A slit is bored in the wall surface of the heat convection suppressing cylinder. This is to circulate the raw material melt.

This will be explained below with reference to the drawings.

FIG. 1 is an overall schematic diagram of a manufacturing apparatus used in the single crystal manufacturing method of the present invention.

Inside the pressure vessel 10 is a crucible 5 supported by a lower shaft 7. A raw material melt 6 is contained in the crucible 5 . There is a heater 3 around the crucible 5. The heater 3 is for heating the raw material melt 6.

An upper shaft 8 is suspended from above the pressure vessel 10. A seed crystal 9 is attached to the lower end of the upper shaft 8. When the upper shaft 8 is rotated and pulled up, the single crystal 1 is pulled up from the raw material melt 6.

A magnetic field applying device 4 is installed on the outside of the pressure vessel 10 so as to be diametrically opposed to the raw material melt 6 so as to be at the same height.

The magnetic field application device 4 generates a horizontal magnetic field from one pole toward the other pole in the space where the raw material melt 6 and the heater 3 are present.

The magnetic field application device 4 includes an electromagnet, a power source, a power control device, and the like. It may be a normal conducting magnet or a superconducting magnet.

” The applied magnetic flux density is 1000 to 10000 Gauss.

A characteristic feature of the present invention is that a cylindrical heat convection suppressing cylinder 2 is immersed in the raw material melt 6 concentrically with the crucible 5.

FIG. 2 shows a perspective view of the heat convection suppressing cylinder.

It has a cylindrical shape and has a vertical slit 11 cut therein.

The slit 11 is vertical in this example. This is because the raw material melt flows, but the dimensions must be such that convection is not transmitted inside or outside.

The slit 11 is not limited to a vertical shape. It can be long horizontally or diagonally.

The raw material melt 6 is separated from the inner melt I by the heat convection suppressing cylinder 2,
It is divided into two parts: outer melt 0 and outer melt 0. Because there is slit 11,
The height of the liquid level inside and outside is equal. As the single crystal 1 is pulled up, the inner melt I and the outer melt 0 decrease while maintaining the same height.

The heat convection suppressing cylinder 2 is made of carbon, Mo, etc. as a base,
PBN, BN, AI! It is coated with N, SiN, etc. This must not contaminate the raw material melt.

(g) Effect The raw material melt 6 is heated by the heater 3. A magnetic field is applied to suppress convection of the raw material melt. The seed crystal 9 is immersed in the raw material melt and is seeded while being rotated. Both the lower shaft 7 and the upper shaft 8 are rotated. Slowly pull up the upper shaft 8.

In this way, the single crystal 1 is pulled up following the seed crystal 9.

Due to the thermal convection suppressing cylinder 2, convection occurs independently in the inner melt I and the outer magnetic liquid O. Since the convection in the internal melt I is a convection in a narrow space, it naturally becomes weak.

The inner diameter U of the heat convection suppressing cylinder 2 enters R in equation (1), and ΔT
' is smaller than ΔT in the entire crucible. Then,
The ratio r of graphhos numbers is then. It is considered that ΔT//T is approximately U/W. Then, the ratio r of graphophos numbers is (U/W)
This means that it is about the fourth power of .

For example, if U/W=0.6 to 0.8, r representing the ratio of convection strength will be 0.13 to 0.41.

In other words, the strength of convection is significantly reduced.

Because of the slit 11, it cannot actually be said to decrease in this way. This is because the convection of the inner melt I and the outer magnetic liquid O interact through the slit 11.

However, by reducing the area of the slits 11 or shifting the distribution of the slits 11 downward, the interaction between internal and external convection can be reduced.

The lower end of the heat convection suppressing tube 2 shown in FIGS. 1 and 2 is in contact with the bottom of the crucible 5. It is supported by crucible 5.

However, instead of supporting it with a crucible, it may be suspended from above with a support rod. FIG. 3 shows an example of a heat convection suppressing tube provided with a support rod 12 at its upper end for this purpose.

In this case, a small slit 13 is provided at the lower end.

As shown in FIG. 1, when attaching the heat convection suppressing tube 2 to the bottom surface of the crucible 5, a slit is required. This also does not need to exist in the vertical direction. It should be near the bottom.

As shown in FIG. 3, when hanging by a support rod, the inner melt liquid (1) and the outer magnetic liquid (0) are continuous below the thermal convection suppressing cylinder 2, so there is no need to provide any slits.

Since the radius is thus narrowed, horizontal convection is effectively suppressed. Although horizontal convection cannot be suppressed by a magnetic field (horizontal), the thermal convection suppressing tube 2 can suppress horizontal convection particularly effectively.

(e) Effect Horizontal heat convection can be effectively suppressed.

Therefore, thermal fluctuations near the solid-liquid interface can be reduced. Single crystals with few crystal defects can be manufactured.

A magnetic field application device that applies a horizontal magnetic field cannot suppress horizontal convection. However, the heat convection suppression tube
Horizontal convection can be particularly suppressed.

It acts complementary to the magnetic field and can effectively suppress thermal convection.

Even when trying to pull a large-diameter single crystal using a large-diameter crucible, thermal convection can be sufficiently suppressed even with a lower magnetic field than in the past.

Since the power of the magnetic field applying device can be reduced, the magnetic field applying device may be made smaller. Equipment costs can be significantly reduced, and single crystal manufacturing costs can be reduced.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic sectional view of an apparatus for carrying out the single crystal manufacturing method of the present invention. FIG. 2 is a perspective view of only the heat convection suppressing cylinder. FIG. 3 is a front view showing another example of a heat convection suppressing cylinder. 1... Single crystal 2... Heat convection suppressing cylinder 3... Heater 4... Magnetic field application device 5... Crucible 6. ...Raw material melt 1 ...Bottom shaft 8 ...Top shaft 9 ...Seed crystal 10 ...Pressure vessel 11 ...・Slit 12...Support rod 13...Slit ■...Inner melt 0...Outer melt W...Inner diameter of crucible■ ...Outer diameter U of the heat convection suppressing section...Inner diameter S of the heat convection suppressing section...Outer diameter of the single crystal Inventor Minamikata Profit and Loss Patent Applicant Sumitomo Electric Industries, Ltd. Figure 1 Figure 2 Figure 3

Claims (7)

[Claims] (1) Inside the pressure vessel 10, the raw material melt 6 in the crucible 5 supported by the lower shaft 7 is heated by the heater 3, and a magnetic field provided outside the pressure vessel 10 is applied. Depending on the device 4, 1000 Gauss to 10000 Gauss is added to the raw material melt 6.
By applying a Gaussian horizontal magnetic field and pulling the seed crystal 9 attached to the lower end of the upper shaft 8 into the raw material melt 6 while rotating, the single crystal 1 is pulled up following the seed crystal 9. In the manufacturing method, a cylindrical heat convection suppressing cylinder 2 having an inner diameter U larger than the outer diameter S of the single crystal 9 to be pulled and an outer diameter V smaller than the inner diameter W of the crucible 5 is placed concentrically with the crucible 5. A method for producing a single crystal, characterized in that the single crystal is immersed in a raw material melt 6 so as to have the following properties. (2) The method for producing a single crystal according to claim (1), wherein the heat convection suppressing tube 2 is in contact with the bottom of the crucible. (3) The method for producing a single crystal according to claim (1), wherein the heat convection suppressing cylinder 2 is suspended from above by a support rod 12. (4) Claim (1) or (2) characterized in that the heat convection suppressing cylinder 2 has a vertical slit 11.
Method for producing a single crystal as described in Section 1. (5) The method for producing a single crystal according to claim (1) or (2), wherein the heat convection suppressing tube 2 has an oblique slit. (6) The heat convection suppressing cylinder 2 has a small diameter circular slit 1 at the lower end.
3. A method for producing a single crystal according to claim (2) or (3), characterized in that: (7) The heat convection suppressing cylinder 2 is made of carbon coated with PBN.
1) The method for producing a single crystal as described in section 1).