JPH0160000B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a crystal growth method for obtaining single crystals, for example semiconductor crystals.

Background technology and its problems For example, the Czyochralski method (CZ method) is widely used to grow semiconductor single crystals. In this method, a single crystal is grown by dipping a seed crystal into a semiconductor melt dissolved in a quartz crucible and pulling it up.In this case, oxygen is removed by the reaction between the semiconductor melt and the quartz crucible. There is a lot of contamination, and the oxygen concentration in the pulled crystal is on the order of 10 ¹⁸ /cm ³ .
This excess oxygen in the crystal causes various defects, such as stacking faults, oxygen precipitates, and dislocation loops, to occur during heat treatment processes such as integrated circuit manufacturing processes, causing deterioration of the characteristics of semiconductor devices. In addition to such crystal defects, single-crystal semiconductors also suffer from non-uniform microscopic impurity distribution in the crystal called growth striations. The cause of this growth streak is thermal convection in the melt. The effects are known to be important. On the other hand, thermal convection in a liquid having electrical conductivity is suppressed by a magnetic field. That is, when an electrically conductive object moves in a magnetic field, a potential difference is generated within the object and a current flows. on the other hand,
A force acts on a current carrier moving in a magnetic field, so an object receives a new force. Taking the example of the CZ method now,
If thermal convection is occurring, and a magnetic field is applied in a direction across it, the electrically conductive fluid will cross the lines of magnetic force, and as a result, a current will flow in the direction perpendicular to the direction of fluid motion and the magnetic field. . Therefore, a force is generated in the direction perpendicular to the current and magnetic field. This force is in the opposite direction to thermal convection, suppressing convection, and apparently increasing the viscosity of the fluid.

Figure 1 shows a single crystal growth apparatus that grows a single crystal in such a magnetic field, where 1 is a chamber in which the single crystal is grown, and 2 is a quartz chamber containing an electrically conductive liquid 3. In a container such as a crucible, 4
5 is a heating means for the liquid body 3 made of, for example, a graphite heating element, and 5 is a magnetic field generating device so that a magnetic field generated by the device is applied to the liquid body 3.
A seed crystal 7 grows a single crystal 8 by being immersed in the liquid 3 and pulled up from it.

In such a device, the magnetic field generating means 5 may have a structure (hereinafter referred to as pole piece type) in which a chamber 1 is held between the chamber 1 and coils are wound around pole pieces on both sides of the chamber 1 as shown in the figure (hereinafter referred to as pole piece type). The almost horizontal magnetic flux generated is the liquid material 3.
Alternatively, by arranging a coil body wound around the outer periphery of the chamber 1 (hereinafter referred to as a solenoid type), by energizing this coil body, the coil is moved in the axial direction (vertical direction), that is, by energizing the coil body. A magnetic field in the direction of gravity is applied to the liquid material 3. However, both the pole piece type magnetic field device and the solenoid type magnetic field device in which a coil is wound have advantages and disadvantages. In other words, when using a pole piece type, the weight and size are large, whereas when using a solenoid type, although it can be smaller in weight and overall size compared to the pole piece type, When using a solenoid type configuration such as this, a large leakage magnetic field is generated at the upper and lower ends of the coil, which has a negative effect on other electric motors and instruments. Requires. Furthermore, it has the disadvantage of high power consumption. In addition, as mentioned above, in order to efficiently suppress thermal convection using a magnetic field, it is desirable to apply a magnetic field perpendicular to the convection flow, but the above-mentioned pole piece type or solenoid type Each of these methods mainly operates only in either the horizontal direction or the vertical direction, and has a problem in its efficiency.

Purpose of the Invention In the present invention, the above-mentioned crystal growth apparatus has a solenoid type configuration as its magnetic field generator, and is further improved so that the magnetic field effectively acts on crystal growth, and the overall size is small. It is an object of the present invention to provide a crystal growth apparatus that is lightweight, can drastically reduce the adverse effects of leakage magnetic fields on others, and can also reduce power consumption.

Summary of the Invention The present invention comprises a container containing an electrically conductive liquid such as a silicon melt, a means for heating the liquid, and a coil body disposed to surround the container. In particular, this coil body is provided with two or more regions with different winding directions (current directions), and the winding directions of adjacent regions are opposite to each other. A magnetic field is applied to the liquid in the container by energizing the container.

Embodiment An example of a crystal growth apparatus according to the present invention will be described with reference to FIG. 2. In FIG. 2, parts corresponding to those in FIG.

In the present invention, a container 2 containing an electrically conductive liquid 3, for example, a silicon semiconductor melt, is used.
A coil body 10, that is, a solenoid type magnetic field generator is placed around the outer periphery of the heating element 4 in the figure, and its winding axis direction is the center of the crystal pulling direction along the vertical direction in the example of FIG. 2
Arrange the windings so that they match the center of the and,
In particular, in the present invention, the coil body 10 is arranged in three areas 10A, 10B, 1 in the axial direction, for example, the central part in the axial direction and the upper and lower ends thereof.
0C, and the adjacent regions 10A and 10B, 10A and 10C are wound in opposite directions. That is, in FIG. 2, this coil body 10 is indicated by a circle mark and a ● mark. For example, when the circle mark indicates the current direction from the top to the bottom of the page in FIG. Conversely, the direction of flow is from the bottom to the top of the page.

The leakage magnetic flux can be significantly reduced from the upper and lower ends of the coil body 10. That is, the distribution of the magnetic field generated by the coil can be expressed as follows with respect to the central axis of the coil.

Here, μ ₀ is the magnetic permeability, n is the number of turns of the coil, I is the current value, r is the coil radius, and l is the length of the coil.

FIG. 3 shows the relationship between a coil and the magnetic field distribution on its central axis. In this example, a coil 21 whose length l and diameter are equal, that is, l = 2r.
This figure shows the magnetic field distribution on the axis of a coil 22 having a short length l=(1/2)r and arranged adjacent to each other. In this case, the magnetic field distribution on the axis regarding the coil 21 is
It is given by curve a. However, in this case, the magnetic field strength at the center point x ₀ of the coil is normalized to 1. On the other hand, a similar magnetic field distribution on the central axis of only the coil 22 whose current is 1/4 of this is shown by curve b in the figure. In this case as well, the center of the coil 21 x ₀
It is normalized by the magnetic field strength of .
Now, if we apply a current to the coil 21 in the opposite direction to that of the coil 22 and generate a magnetic field in the opposite direction,
At that time, the magnetic field portion on the central axis becomes a distribution of the difference between both curves a and b, as shown by curve c in FIG. 3, that is, as shown by curve c. That is, in this case, the end on the coil axis of only the coil 21
The magnetic field strength at Ye is a ₀ , whereas the magnetic field strength when a reverse magnetic field is generated in the coil 22 is given by a point c ₀ . Therefore, in this case, the magnetic field strength c ₀ at the Ye point is about 1/4 of a ₀ . It can be seen that by providing reversely wound coils at the upper and lower ends of the coil 21 in this manner, the strength of the magnetic field outside the coil 21 can be reduced. That is, as explained in FIG. 2, the coil body 10 as a magnetic field generator
Since the direction of the current is substantially reversed in the regions 10B and 10C on both sides of A, the magnetic field strength generated from both the upper and lower sides of the coil body 10 is reduced, that is, the generation of leakage magnetic flux is drastically reduced. I know what I'm getting.

In addition, as described above, since the coil body 10 is configured with reverse direction energization, that is, a plurality of reversely wound coil regions, the direction of the magnetic field of the magnetic flux from each region is mixed, so that the conductive liquid 2 in the container 2 is The applied magnetic field is applied almost throughout the convection of the liquid in both the horizontal and vertical directions. In other words, a magnetic field in a direction perpendicular to the convection is efficiently applied over almost the entire path of the convection, thereby making it possible to suppress the convection more effectively.

In addition, in the example mentioned above, the coil body 10 is
In this case, the coil is composed of three areas, ie, the central part 10A and both sides 10B and _10C , but for example, as shown in FIG. The entire area can be divided into four areas, or it can be divided into multiple areas, not limited to three or four areas. In addition, as shown in the same figure, the central coil area is made large in diameter, and the coil areas on both sides above and below are arranged concentrically with this large diameter coil area. It is also possible to suppress the occurrence more effectively.

Further, in the above-mentioned example, the case where the present invention is applied to the pulling method was explained, but it can also be applied to the so-called horizontal boat method, that is, the horizontal Bridgeman method, etc. In this case, the coil body 10 is arranged in a horizontal direction. It is sufficient if it is taken.

The coil body 10 having the above-mentioned structure may be a coil made of, for example, a superconducting wire, and may be arranged in a container provided on the outer periphery of the chamber and containing cooling helium.

Effects of the Invention As described above, according to the present invention, the coil body 10
Since it has a solenoid type configuration in which the magnetic field generator is configured by
In addition, despite this solenoid type configuration, by arranging the coil regions in opposite directions adjacent to each other, the generation of leakage magnetic flux can be effectively reduced, and Since a magnetic field is applied to the liquid body 3, for example, the semiconductor melt, convection can be efficiently suppressed as described above, and these effects can be combined to further reduce power consumption.

Further, by reducing the generation of leakage magnetic flux, the electromagnetic shielding means for shielding this leakage magnetic flux can be simplified, so that it is possible to further promote miniaturization and weight reduction.

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram of a conventional crystal growth apparatus used to explain the present invention, FIG. 2 is a schematic block diagram of essential parts of an example of a crystal growth apparatus according to the present invention, and FIG. 3 is an explanation thereof. FIG. 4 is a schematic diagram of the main parts of another example of the present invention, showing the relationship between the coil used for the purpose and the magnetic field distribution. 1 is a chamber, 2 is a crucible containing an electrically conductive liquid 3, 4 is a heating element, 10 is a coil body, 1
0A, 10B and 10C are the respective coil regions.

Claims (1)

[Claims] 1. A container for storing a liquid material exhibiting electrical conductivity;
and a magnetic field generating device arranged to surround the container, the magnetic field generating device having at least a coil body, and the coil body having a winding direction opposite to that of the adjacent coil body. 1. A crystal growth apparatus comprising at least two regions having different values, and applying a magnetic field to the liquid material by passing an electric current through the coil body.