JP3536085B2 - Convection suppression device in melt - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for handling liquid metal in a broad sense, and particularly in a semiconductor single crystal growing apparatus, convection in a melt by a high frequency electromagnetic field for suppressing convection in the melt. The present invention relates to a suppression device.

[0002]

2. Description of the Related Art The quality of a semiconductor single crystal is greatly affected by convection in a melt. Therefore, in the current single crystal growth apparatus, a device for applying a DC magnetic field or a rotating magnetic field is attached, and a DC magnetic field or a rotating magnetic field is applied to the melt to grow a single crystal while suppressing convection.

To explain this point in more detail, conventionally, when growing a single crystal of a semiconductor such as silicon from a melt, it is known that convection in the melt has a great influence on the quality of the grown single crystal. Therefore, it is known that a high quality single crystal can be obtained by suppressing this convection. A semiconductor melt such as silicon has a high free electron density as the temperature rises and can be regarded as a conductor. If a magnetic field is applied to the conductor, the movement of the conductor can be stopped by the Lorentz force. In order to suppress convection using such a principle, in 1966, researchers in the United Kingdom developed a device for growing a single crystal by suppressing convection by attaching a DC electromagnet or a DC superconducting electromagnet to the single crystal growth device. , Nature
Published in.

After that, the electromagnets were arranged so as to generate a vertical magnetic field (1982: Chikawa et al., Japan) and those arranged so as to generate a horizontal magnetic field (198).
0 years: Hoshi et al., Japan), those arranged so as to generate a cusp magnetic field (1989: Hirauchi et al., Japan), etc. were devised. Currently, actual silicon single crystals are grown using electromagnets arranged in these forms, and in order to pursue the relationship between the melt behavior and the quality of the grown single crystals deeper,
Researches related to these are also actively conducted.

Further, recently, a German research group arranged a number of electromagnets horizontally around the melt and controlled the electromagnets to which a current was applied by a relay so that a rotating magnetic field was generated in the melt. Therefore, it has been found that the magnetic field strength smaller than the above DC magnetic field is effective in suppressing convection.

On the other hand, under radiant heating or resistance heating, such convection in the melt mainly occurs on the ground due to the influence of gravity (buoyancy). In outer space, buoyancy does not occur because of zero gravity, and it is considered that single crystals grow under the condition of no convection. However, in the usual single crystal growth method, the melt has a free surface, and if there is a temperature distribution or a concentration distribution on the free surface, the surface tension becomes uneven, and convection is driven by the difference in surface tension. (Marangoni convection) occurs. Therefore, it is recognized that it is difficult to grow a single crystal under the condition of no convection even in the universe, and the development of an effective convection suppression method in the space experiment is desired.

[0007]

[Problems to be Solved by the Invention] The above direct current (superconductivity)
In the method of suppressing convection using an electromagnet, particularly when growing a large single crystal, a strong magnetic field is required to be 1000 gauss or more, and thus a large electromagnet and a power source are required. Further, even in the method of suppressing convection by using a rotating magnetic field, the required magnetic field strength is as weak as about 200 Gauss, but in growing a large single crystal, a large electromagnet is still required and energy consumption is increased. . Also,
It is not realistic to launch such a large electromagnet into outer space in order to perform space experiments efficiently. Therefore, it is desired to develop a device that can easily and reliably suppress convection in the melt.

Therefore, an object of the present invention is to provide an apparatus capable of simply and reliably suppressing convection in a melt caused by a difference in surface tension with a small apparatus.

[0009]

In order to solve the above-mentioned problems, the present invention according to claim 1 provides a heating and melting means by radiant heating or resistance heating, and a space between a heating melt free surface generated by the heating. And a coil disposed opposite to each other, and high-frequency applying means for applying a high-frequency current to the coil,
The high-frequency applying means is an in-melt convection suppressing device characterized by controlling a supply frequency or a supply current so as to cancel the convection generated in the heated melt.

The invention according to claim 2 provides the convection suppressor in a melt according to claim 1, wherein the melt is a semiconductor melt and is used in a semiconductor single crystal growing apparatus. is there.

The invention according to claim 3 is the melt convection suppressing device according to claim 1 or claim 2, characterized in that the device is used under zero gravity.

[0012]

[0013]

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION First, the background of the present invention will be briefly described. As a semiconductor single crystal growth device,
There are Czochralski method (CZ method), floating zone method (FZ method), Bridgman method, and the like. In this, F
Since the Z method does not use a crucible, it is considered that contamination of impurities from the crucible can be avoided and a high quality single crystal can be grown. Since high frequency heating is generally used in the FZ method, it is important to investigate the melt behavior under high frequency heating in order to grow a high quality single crystal. From such a viewpoint, the present inventor experimentally and analytically investigated the convection behavior in the high frequency heating FZ method silicon melt. As a result, in the high frequency heating FZ method silicon melt, the electromagnetic force convection induced by the high frequency heating becomes dominant, and the convection induced by the radiation heating or the resistance heating (Marangoni convection).
I found that the flow was in the opposite direction.

Under high-frequency heating, a high-frequency electromagnetic field is necessary to heat the melt and hold it in the molten state, so that it is necessary to apply a relatively large current, and it is difficult to adjust the applied current. is there. That is, if the applied electromagnetic field is weakened to the extent that convection is suppressed, the amount of heat applied to the melt is reduced and the melt becomes solid, making it impossible to grow a single crystal. On the other hand, in the system of radiant heating or resistance heating,
Since the high-frequency electromagnetic field does not have to contribute to heating, it is possible to adjust the strength of the applied electromagnetic field, and a force that is equivalent to the force that drives Marangoni convection and that is in the opposite direction to Marangoni convection is applied to the melt. It is possible to stop Marangoni convection completely. The present invention has been made based on such findings.

Hereinafter, the drawings showing one embodiment of the details of the present invention will be described. FIG. 1 shows an example of an FZ method single crystal growing apparatus using a radiation heating furnace (bi-elliptical mirror furnace) 1. A radiation source (light source) 2 is installed at one focus position of the FZ method single crystal growing apparatus 1, and a silicon raw material 3 is installed at the other focus position. When a current is applied to the radiation source 2, the generated heat is reflected inside the furnace and the silicon raw material 3 at the other focal position
And reaches the point where the silicon raw material 3 is melted to become a silicon melt 4. The seed crystal 5 is brought into contact with one end of the silicon melt 4, and the silicon raw material 3 and the seed crystal 5 are moved downward in synchronization with each other from the focal position, so that the silicon single crystal 6 is grown. At this time, the coil 7 is spaced on the free surface of the silicon melt 4.
Are arranged to face each other, and a high frequency current is applied to the coil 7 by a high frequency power source 8
Apply by. In this way, the convection suppression device 9 in the melt is
The device is composed of a coil 7 and a high frequency power supply 8.

In the above apparatus, convection generated by surface tension at least on the free surface of the melt, that is, Marangoni convection, is generated in the heated melt, and coils are arranged facing each other with a space on the free surface. By applying a high frequency current to this coil, a force that generates convection in the opposite direction to the Marangoni convection is generated, and the Marangoni convection can be canceled by adjusting the supplied high frequency current.

The electromagnetic force acting on the melt varies depending on the shape of the induction coil and the frequency and current applied to the induction coil.
At a high frequency of a high frequency applied current supplied of several hundreds of kHz or more, this acts on an extremely thin layer on the surface called the skin thickness, and it behaves as if it were a surface force. Therefore, by controlling this high-frequency magnetic field, Marangoni convection can be suppressed with a small current. In particular, the Marangoni convection becomes dominant in a weightless space, but the use of this device can suppress the convection, which is particularly effective when growing a semiconductor single crystal under weightlessness.

Another embodiment of the present invention is shown in FIG.
In the apparatus of FIG. 2, a CZ method single crystal growing apparatus 10 is used, and the raw material silicon is melted in the crucible 12 by the resistance heating apparatus 11 to become the silicon melt 4. Silicon melt 4
When the seed crystal 5 is brought into contact with and moved upward, the silicon single crystal 6 is grown. At this time, the coil 7 is arranged so as to face the free surface of the silicon melt 4 with a space, and a high frequency current is applied to the coil 7 by a high frequency power source 8. The in-melt convection suppression device 9 is a device including a coil 7 and a high frequency power supply 8. Also in this apparatus, Marangoni convection occurs in the heated melt, but the convection can be suppressed by controlling the high frequency supplied to the coil.

As described above, the invention according to claim 1 of the present application comprises high- frequency applying means for applying a high-frequency current to the coil, the coils being arranged opposite to each other on the free surface of the melt for heating, and the high-frequency applying means being provided . Means are generated in the heated melt
Control the supply frequency or supply current to cancel the convection
Control , it is possible to generate a force that causes convection in the opposite direction to the convection caused by uneven surface tension due to temperature distribution or concentration distribution generated on the free surface of the melt, and suppress convection in the melt. . The high-frequency generator that suppresses the convection may be small in size, and is simple and easy to handle. In particular, the high frequency applying means
Is supplied so as to cancel the convection that is occurring in the heated melt
Generated in the heated melt because the frequency or supply current is controlled
The convection that is occurring can be surely suppressed.

In the invention according to claim 2 of the present application, since the melt is a semiconductor melt and the present invention is used for a semiconductor single crystal growing apparatus, it is particularly necessary to suppress convection in the melt. The present invention can be effectively used in a growing device.

In the invention according to claim 3 of the present application, since the apparatus is used under zero gravity, it is possible to suppress Marangoni convection, which is a convection mainly generated in the melt under zero gravity, and the semiconductor under zero gravity. It is particularly effective for a single crystal growing device.

[0023]

In the invention according to claim 4 of the present application, since the melt is obtained by radiant heating, it is not necessary to use a crucible, and it is possible to prevent impurities from being mixed into the melt.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, in which a convection suppressor in a melt is attached to a radiant heating FZ single crystal growing device.

FIG. 2 is a configuration diagram showing an example in which the convection device in a melt of the present invention is attached to a single crystal growth device by the CZ method.

[Explanation of symbols]

1 Radiant heating FZ method single crystal growth equipment 2 Radiation source 3 Silicon raw material 4 Silicon melt 5 seed crystals 6 Silicon single crystal 7 coils 8 high frequency power supply 9 Melt convection suppression device 10 CZ method single crystal growth apparatus 11 Resistance heating device 12 crucible

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 61-174190 (JP, A) JP-A 1-153591 (JP, A) JP-A 63-42163 (JP, A) JP-A 2001-172098 (JP, A) Munakata Tetsuo et al., High-frequency heating FZ method Visualization of convection in silicon melt and suppression of convection by magnetic field, The 36th Japan Heat Transfer Symposium Proceedings Vol. III, May 26, 1999, pp. 811-812 (58) Fields investigated (Int.Cl. ⁷ , DB name) C30B 1/00-35/00 JSTPlus (JOIS)

Claims (3)

(57) [Claims] 1. A heating / melting means by radiant heating or resistance heating, and a high-frequency applying means for applying a high-frequency current to the coil by disposing a coil facing each other on a free surface of a heated melt generated by the heating. An apparatus for suppressing convection in a melt, characterized in that the high-frequency applying means controls the supply frequency or the supply current so as to cancel the convection generated in the heated melt. 2. The convection device in a melt according to claim 1, wherein the melt is a semiconductor melt and is used in a semiconductor single crystal growth apparatus. 3. The melt convection suppression device according to claim 1, wherein the device is used under zero gravity.