JPH08310890A - Production of crystal - Google Patents

Abstract

PURPOSE: To obtain a method useful for production of a large-sized crystal of semiconductor oxide, etc., by subjecting an object to be heated to high-frequency induction heating at a frequency to maximize electromagnetic force. CONSTITUTION: The object to be heated is subjected to the high-frequency induction heating by the frequency at which the magnitude of the skin depth P(m) expressed by the equation [δis the dielectric constant (Ωm)<-1> , μ is the relative magnetic permeability of the object to be heated, (f) is the frequency (Hz)] attains 0.3 to 2 of the radius of the object to be heated in this process for production of the crystal by the high-frequency induction heating simultaneously using the plural different frequencies. More specifically, this process is a process for production by a floating zone meting method of the high-frequency induction heating. Namely, the frequency is specified according to the dielectric constant and magnetic permeability of the object to be heated independently from the frequency for heating and melting, by which the ratio of the electromagnetic force acting on the object to be heated is increased with respect to the electric power for heating consumed in the object. The electromagnetic force is so acted as to support the melt from below in the floating zone melt method of the high-frequency induction heating, by which the growth of the large-diameter crystal is made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal manufacturing method by high frequency induction heating. For more information,
The present invention relates to a method for producing crystals by high frequency induction heating, which is useful for producing crystals of semiconductors, oxides, etc. by the high frequency induction heating floating zone melting method, the high frequency induction heating levitation melting method and the like.

[0002]

2. Description of the Related Art Conventionally, there have been remarkable technological developments in electronic devices such as semiconductors and optical functional equipments, and the demands for high-quality crystal materials have increased with the developments. As such a high-quality crystal material, for example, a high-purity silicon crystal with a large diameter,
There are oxide crystals, high-purity metals, and the like, and many methods have been devised in the methods for producing these crystals.

Among several crystal growth methods, high frequency induction heating floating zone melting method (F
Z method) is a particularly important means. The high-frequency induction heating floating zone melting method (FZ method) is characterized in that a single crystal can be grown without contact between a raw material crystal and a container such as a crucible, and a high-purity and low-defect crystal can be obtained. Have The FZ method is widely used industrially for the silicon crystal as well as the pulling method, but the vapor pressure control FZ method is the optimum crystal growth method for obtaining a high quality crystal also in the compound semiconductor.

In high frequency induction heating, a high frequency current is passed through a heating coil to induce an induction current in the object to be heated, and heating is performed by Joule heat of this induction current. The induced current flows in a limited area from the surface of the object to be heated, and an amount called the skin depth is used as a standard for this area. Skin depth p (m)
Is defined by the following equation.

[0005]

[Equation 2]

[0006] The depth of heating determines the depth of heating. The temperature distribution in the object to be heated is greatly affected by the heating depth. Further, in the high frequency induction heating method, not only Joule heat caused by the induction current but also an electromagnetic force is generated in the object to be heated by the interaction between the induction current and the magnetic field created by the high frequency current flowing in the heating coil. This electromagnetic force generally acts in the direction of tightening the ligament and has a great influence on the shape of the ligament and the holding property of the ligament.

In the conventional high frequency induction heating method, since high frequency induction heating is performed using a single frequency, the heating depth of the object to be heated and the electromagnetic force acting on the object to be heated from the heating coil are It has been fixed at a single frequency value. For example, in the high frequency induction heating floating zone melting method which is one of the high frequency induction heating methods, the single frequency is often used from 450 kHz to 5 MHz, but it is mainly determined from the temperature distribution in the object to be heated. This is because the temperature distribution inside the object to be heated has a great influence on the quality of the grown crystal.

However, in the conventional high-frequency induction heating floating zone melting method in which a single frequency is selected, GaA having a large diameter is used.
It is difficult to grow a single crystal of a compound semiconductor such as s. When growing a single crystal of a compound semiconductor such as GaAs by the high frequency induction heating floating zone method, it is necessary to apply the optimum (arsenic) vapor pressure in the sealed tube to strictly grow the stoichiometric composition of the crystal. Is. For this reason, the heating coil is installed outside the sealed tube, the distance between the crystal and the heating coil becomes large, and the width of the melt zone is wide, and it easily drops, and it is usually difficult to grow large-diameter crystals.

On the other hand, in recent years, various studies have been conducted on the high frequency induction heating levitation melting method, which is one of the high frequency induction heating methods, in order to explore the possibility of producing large-diameter crystals. This high-frequency induction heating levitation melting method uses a high-frequency induction heating coil (generally called a cold crucible) consisting of a concentrator with a slit and a primary coil arranged around the concentrator to levitate the object to be heated. , And then is characterized by growing a crystal.

However, in such a high-frequency induction heating levitation melting method, although various melting conditions have been studied, a very large force is required to levitate a large-scale object to be heated at a practical level. Yes, even today
It has been unsuccessful to levitate a large-capacity object to be heated at a practical level, and it must be said that many problems still remain in the production of large crystals.

Recently, in the high-frequency induction heating levitation melting method, it has been studied to use two different frequencies, but it has not been sufficiently examined what kind of frequency should be selected. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a new crystal production method by high-frequency induction heating, which solves the drawbacks of the prior art and enables the provision of large-diameter crystals. I am trying.

[0012]

In order to solve the above-mentioned problems, the present invention is a method for producing a crystal by high-frequency induction heating which uses a plurality of different frequencies at the same time. Provided is a crystal production method characterized by high-frequency induction heating at a frequency that is maximized.

The present invention is also a method for producing a crystal by high-frequency induction heating which uses a plurality of different frequencies at the same time.

[0014]

(Equation 3)

The size of the skin depth P (m) represented by
Also provided is a crystal manufacturing method characterized by performing high-frequency induction heating at a frequency of 0.3 to 2 with respect to the radius of an object to be heated, and more specifically, a high-frequency induction heating floating zone melting method as described above. Provide a manufacturing method.

[0016]

That is, the present invention specifies the frequency independently of the frequency for heating and melting according to the conductivity and magnetic permeability of the object to be heated, and the heating power consumed in the object to be heated. On the other hand, the ratio of the electromagnetic force acting on the object to be heated is increased. As a result, for example, in the high-frequency induction heating floating zone melting method, by placing the heating coil of the relevant frequency below the zone forming position, the electromagnetic force can support the zone from below. Therefore, large-diameter crystal growth becomes possible. Further, in the high frequency induction heating levitation melting method, it becomes possible to efficiently levitate a large amount of object to be heated by its electromagnetic force. Such dependence of electromagnetic force on the frequency is not considered at all in the conventional high-frequency heating induction method, and in that sense, the present invention seems to be very novel.

In the present invention, the relationship between "skin depth / radius of object to be heated" and "electromagnetic force (N) / heating power (W)" is as shown in FIG. 1, and the frequency is sufficiently low. That is, when “skin depth / radius of object to be heated” is large, the ratio of electromagnetic force to heating power is almost constant. When the frequency is high, the skin thickness is small, and the “skin depth / radius of the object to be heated” is small, the ratio of the electromagnetic force to the heating power decreases at around 0.59. Further, the efficiency of the electromagnetic force and heating power acting on the object to be heated decreases as the frequency decreases, so that there is an optimum frequency range for effectively utilizing the electromagnetic force.

Furthermore, as can be seen from FIG. 1,
It can be seen that even if the frequency is lowered so that “skin depth / radius of heated object” becomes larger than 0.59, the effect of obtaining a large electromagnetic force becomes small. Therefore, in the present invention, the skin depth P (m) is generally in the range of 0.3 to 2 with respect to the radius of the object to be heated. The frequency is set so that this skin depth is reached, and the electromagnetic force is maximized. More preferably, the skin depth is about 0.34 to 0.84. By selecting "skin depth / radius of heated object" in this range, it becomes possible to efficiently obtain the electromagnetic force acting on the heated object.

The present invention will be described in more detail below with reference to examples.

[0020]

Example 1 The power consumed by the object to be heated and the electromagnetic force acting on the object to be heated from the heating coil were calculated by the finite element method. The calculation was used in a three-dimensional model, and its rz plane is shown in FIG. Here, A is a heating coil and B is an object to be heated.

As shown in FIG. 2, the heating coil (A) has an inner diameter of 17 mm, an outer diameter of 25 mm and a thickness of 2 mm.
It was a turn coil, and the size of the object to be heated (B) was 8.5 mm in radius and 10 mm in length, and the distance between the lower surface of the object to be heated and the lower surface of the coil was 10 mm. Using this model, the conductivity of 1e7, 1e6, and 1.
Considering three types of objects to be heated of 32e5 (Ωm) ⁻¹ , the relationship between frequency and “electromagnetic force (N) / heating power (W)” is shown in FIG. In FIG. 3, the horizontal axis represents frequency, and the vertical axis represents “electromagnetic force (N) / heating power (W)”. The heating power is the power consumed by the entire object to be heated (unit W), the electromagnetic force. Is indicated by the component (unit N) of the electromagnetic force acting upward.

In FIG. 3, at the frequency where the magnitude of "electromagnetic force (N) / heating power (W)" starts to decrease from a constant value, the magnitude of "skin depth / radius of heated object" is 0. .5
9 Example 2 The following Example 3 was used using graphite having the same shape as the object to be heated calculated in Example 1 above, an outer diameter of 17 mm and a length of 10 mm.
The electromagnetic force and the heating temperature acting from the same heating coil with a concentrator as those described in 1. were measured. The electromagnetic force was measured by suspending graphite with an insulating thread from an electronic balance, and the heating temperature was measured by embedding a thermocouple in graphite. The measurement frequency is 3.
1 kHz, 4.8 kHz, 10.1 kHz, 413 kHz
z. 3.1 kHz, 4.8 kHz, 10.1 kHz
In the case of z, the coil current is 1041A and the coil current is 103A at 413 kHz. The result is shown in FIG.
The heating temperature is the difference (K) from room temperature. The vertical axis of FIG. 3 is electromagnetic force (N) / heating power (W), and the amount of the vertical axis is different from that of FIG. In FIG. 4, the skin depth / radius size is 0.
Maximum between 3 and 2.0. After all 0.3 to 2.
It can be seen that the heating frequency around 0 should be selected. Example 3 FIG. 5 shows an example of single crystal growth by a vapor pressure controlled high frequency induction heating floating zone melting method.

In FIG. 5, the raw material crystal (1) and the seed crystal (2) are arranged in a quartz sealed tube (4), and the melt zone is controlled in a state where the vapor pressures of component elements that are easily volatilized are controlled. (3) is formed to grow a single crystal whose stoichiometric composition is strictly controlled. In FIG. 5, i1 and i2 are independent primary coils, which are directly connected to the high frequency induction oscillator. c1 and c2 are concentrators for the heating coils of i1 and i2, respectively, each of which is provided with a slit.

A plan view of the concentrator c1 is as shown in FIG. 6, and further, a plan view of the concentrator c2 is as shown in FIG. This primary coil i1
The induced current induced from the concentrator c1 to the concentrator c1 is turned back at the slit portion and flows in the opposite direction in the inner peripheral portion. Crystals are mainly heated by the current flowing through the inner peripheral portion, and a melt zone is formed.

It is desirable to use a frequency of about 450 kHz to 5 MHz for the primary coil i1. The primary coil i2 is preferably shaped like a mortar, and an induced current similar to that of the concentrator c1 flows through the concentrator c2, and the induced current flowing in the inner peripheral portion of the concentrator c2 exerts buoyancy on the melt zone.

Further, since the electromagnetic force due to the leakage magnetic flux generated from the mortar-shaped primary coil i2 acts in the direction of lifting the ligament, the holding property of the ligament is further increased. When a single crystal having a melt conductivity of about 1e6 (Ωm) ^-1 is manufactured using the high frequency induction heating coils shown in FIGS. 5, 6 and 7, the primary coil i2 has a high frequency of 10 kHz. A single crystal with a diameter of 17 mm can be grown by passing an electric current.

Further, according to the present invention, it is not necessary to wind the primary coils i1 and i2 completely concentrically, and by using the concentrators c1 and c2, the symmetry of the electromagnetic force acting on the fusion zone is greatly improved.

[0028]

As described in detail above, according to the present invention, a large compound semiconductor crystal such as GaAs, and
It is possible to manufacture a large mixed crystal semiconductor such as AlGaAs.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between “skin depth / radius of an object to be heated” and “electromagnetic force (N) / heating power (W)” in the present invention.

FIG. 2 is a sectional view showing the arrangement of heating coils and objects to be heated in the embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between frequency and “electromagnetic force (N) / heating power (W)” in the example of the present invention.

FIG. 4 is a diagram showing a relationship between frequency and “electromagnetic force (N) / heating temperature (K)” in an example of the present invention.

FIG. 5 is a configuration diagram showing a high frequency induction heating coil in an embodiment of the present invention.

FIG. 6 is a plan view showing a concentrator c1 according to the embodiment of the present invention.

FIG. 7 is a plan view showing a concentrator c2 in the embodiment of the present invention.

[Explanation of symbols]

 A heating coil B heated object 1 raw material crystal 2 seed crystal 3 fused zone 4 quartz sealed tube i1, i2 primary coil c1, c2 concentrator

Claims (3)

[Claims] 1. A method for producing a crystal by high-frequency induction heating using a plurality of different frequencies at the same time, wherein the high-frequency induction heating is performed at a frequency that maximizes the electromagnetic force acting on the object to be heated. . 2. A method for producing a crystal by high frequency induction heating, which uses a plurality of different frequencies simultaneously, comprising: The method for producing a crystal is characterized in that high-frequency induction heating is performed at a frequency that makes the skin depth P (m) represented by the following in the range of 0.3 to 2 with respect to the radius of the object to be heated. 3. The method according to claim 1, which is a high-frequency induction heating floating zone melting method.