JPS6121195B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystal pulling apparatus suitable for use in obtaining single crystals of various materials such as semiconductors, dielectrics, and magnetic materials.

When a single crystal such as a semiconductor is grown using the Czyochralski method, vibrations and thermal convection of the melt or solution surface of the crystal material have a large influence on the quality of the grown single crystal. For example, if the vibration or thermal convection of the melt or solution surface is large, the crystals that have grown will partially re-melt, which may cause crystal defects to occur or create swirl-like defects. Generates growth stripes.

In the Czyochralski method, it has been proposed to grow the single crystal in a magnetic field, thereby reducing defects such as swirls and growth stripes. This means that the electrically conductive melt or solution
This is thought to be due to the fact that the effective viscosity is increased by applying a magnetic field, suppressing thermal convection and vibrations of the liquid surface. That is, when a fluid having electrical conductivity, ie, a conductor, moves in a magnetic field, a potential difference is generated in the fluid, and a current flows. The current flowing through this magnetic field applies a new force to the fluid that carries this current. This force is in the opposite direction of the fluid movement, so the fluid movement slows down.
This means that the apparent viscosity has increased. This is called magnetic viscosity. It is thought that due to the magnetic viscosity generated in this way, convection of the fluid, that is, the crystal material liquid, becomes difficult to occur.

Regarding growing this single crystal in a magnetic field, for example, see the Journal of Applied Physics,
Vol.37.No.5, P2021 (1966), and Journal of
It is described in Materials Science 5 (1970) P822.

On the other hand, in a normal pulling device, a seed crystal is brought into contact with the liquid surface of the crystal material on the central axis of a container containing a crystal material plate, that is, a crucible, to pull the crystal. In order to compensate for the deviation of the thermal center due to the heating means placed around the crucible, the crystal is usually pulled while rotating to obtain a single crystal with a perfect circular cross-sectional shape. . However, especially in the above-mentioned pulling method by applying a magnetic field, since the crystal material liquid is held in a stationary state and stabilized by applying a magnetic field, it is difficult to apply the above-mentioned rotational pulling method to this method. This rotation is undesirable, and as the temperature increases and decreases due to this rotation, rotational growth streaks are generated in the pulled and grown crystal. Therefore, in such a crystal pulling method, particularly in a crystal pulling method by applying a magnetic field, it is desirable to avoid rotational pulling of the crystal. However, in reality,
The heating means in this type of pulling device is such that heaters are arranged around the crucible in which the crystal material liquid is stored, for example, in a zigzag pattern along the axis of the crucible, and continuously so as to cover the entire outer periphery of the crucible. It consists of being done. That is, the heating means is integrally constructed around the entire circumference, and the thermal center is likely to shift, and since it is impossible to correct the thermal center if it shifts, it is necessary to grow a crystal with a perfect circular cross section. This rotation has become indispensable.

The present invention avoids these drawbacks and provides a crystal pulling apparatus that can grow crystals having a perfectly circular cross section without producing growth stripes due to rotation.

An example of a crystal pulling apparatus according to the present invention will be explained with reference to FIGS. 1 and 2. 1 in the figure shows the apparatus of the present invention as a whole. 2 designates a container, for example a quartz crucible, in which a melt or solution 3 of a crystalline material, in particular electrically conductive, is accommodated, for example a silicon melt. A heating means 4 is arranged around the outer periphery of this container 2 .

Outside the heating means 4, for example, a cylindrical heat shield or a jacket 6 cooled by water cooling is arranged as required, and a permanent magnet,
Alternatively, for example, a DC magnetic field generating means 7 consisting of an electromagnet
is placed. 8 is a single crystal seed, and 9 is its pulling chuck.

In the present invention, the heating means 4 is divided into equal angular intervals in the circumferential direction around the axis of the container 2 and therefore the pulling axis of the seeds 8, and heating elements 51 are each independently controlled. , 52, 53...... In the illustrated example, eight heating elements or heaters 5 are arranged at equal pitches.
1, 52...58 constitute the heating means 4, and each heating element 51, 52...5
8 may be arranged, for example, in a zigzag pattern along the circumferential surface of the container 2 in a direction along its axis.

On the other hand, inside the container 2, each heating element 5 of the heating means 4
Elements for detecting temperature, such as thermocouples 11, 12, 13, correspond to 1, 52, 53...58, respectively.
...... 18 on the same circumference with respect to the axis of the container 2, the arrangement angle of each heating element 51, 52, 53... 58, facing each heating element 51, 52, 53... 58 Arrange with angular spacing equal to spacing.

And each of these temperature detection elements 11, 12, 1
3. Based on the temperature detected by 18, the corresponding heating elements 51, 52, 53...58, respectively.
These heating elements 51, 5
2, 53, . . . 58 so that the thermal center of the heating means 4 always lies on the central axis of the container 2 during single crystal pulling and growth.

Electricity is supplied to the energizing heater 5 of the heating means 4 using a substantially direct current with a ripple component suppressed to 4% or less, or an alternating current or pulsating current of 1 kHz or more. It has been confirmed that when such a current is applied, unnecessary vibrations caused by the interaction of the heating means 4 with the magnetic field can be avoided.

In the apparatus of the present invention described above, in order to pull and grow a crystal, a magnetic field of, for example, 4000 G (Gauss) is applied to the crystal material liquid 3 by the magnetic field generating means 7,
In this state, the seed 8 is brought into contact with the surface of the crystal material liquid 3 in the container 2 on the axis of the container 2, that is, on the thermal center axis of the heating means 4, and the crystal material is grown without being rotated. Perform upbringing and training. The crystal grown by the apparatus of the present invention has a perfect circular cross section even though the crystal is pulled without rotation. This combined effect of increasing the viscosity of the crystal material liquid 3 and effectively suppressing the occurrence of convection and vibrations allows for high-quality crystal growth with fewer crystal defects such as temperature fluctuations, mechanical vibrations, and crystal stripes caused by impurity contamination. I was able to do that. That is, in the present invention, the heating means 4 includes heating elements 51, 52, 53, .
By structuring the crystal so that its thermal center is in a predetermined position, and by pulling the crystal without rotating it, it is possible to avoid macroscopic temperature fluctuations. By applying a magnetic field, so to speak, microscopic temperature fluctuations can be avoided.

Figure 3 shows the results assuming temperature fluctuations when a magnetic field is applied and when a magnetic field is not applied at a certain point of the crystal material 3 in the container 2. In the figure, time domains A and D indicate when the magnetic field is applied. state of not doing,
In time domains B and C, magnetic fields of 4100 G and 1800 G are applied, respectively, and as is clear from this, when a magnetic field is applied, the temperature fluctuation is drastically reduced compared to when no magnetic field is applied.

In addition, crystals grown by applying a magnetic field are
The decrease in purity due to contamination of the constituent components of the container 2 and the occurrence of crystal defects due to this can be reduced, and this is believed to be due to the following reasons. That is, for example, when the container 2 is a quartz crucible,
Oxygen, which is a component of this, dissolves in the solution 3, which causes a decrease in the purity of the grown crystal, but the contamination of this impurity has a large effect on the movement of the crystal material solution 3 in the container 2, especially the movement due to convection. I found out that it depends. More specifically, when the crystal material solution is stored in the container 2, the constituent components of the container 2 dissolve into the crystal material solution in contact with the container 2, but in this case, the thermal convection within the container 2 is relatively intense. When this happens, the container components dissolved in the part that comes into contact with the container are quickly carried away to other parts by thermal convection, and as a result, the dissolved concentration of the container components in the crystal material liquid quickly decreases. As a result, the dissolved concentration of the container components at the contact area of the crystal material liquid with the container is reduced.
Container components are more likely to dissolve into the crystal material liquid,
Its dissolution increases to or near saturation solubility. In this way, when the convection of the solution 3 is relatively strong, the components of the container are significantly dissolved into the liquid that is in contact with this container, and the speed at which these components move to other parts of the liquid becomes large. Therefore, impurities due to the container components in the crystal grown from this increase. However, in the method of the present invention, as described above, a magnetic field is applied to the crystal material liquid, thereby suppressing the convection of the crystal material liquid, thereby reducing the mixing of container components into the solution 1 described above. This makes it possible to increase the purity of the grown crystal.

[Brief explanation of the drawing]

1 and 2 are a top view and a sectional view, respectively, of an example of a crystal pulling apparatus according to the present invention, and FIG. 3 is a measurement curve diagram of temperature fluctuations of a crystal material liquid. 1 is a crystal pulling device according to the present invention, 3 is a melt or solution of a crystal material, 2 is a container thereof, 4 is a heating means,
51, 52...58 are heating elements thereof, and 7 is a magnetic field generating means.

Claims (1)

[Claims] 1. A container in which a melt or solution of a crystalline material is stored, and a container on the outer peripheral side of the container that is divided from each other along the vertical direction of the container and independently controlled to control the horizontal temperature distribution of the melt or solution. A crystal pulling device comprising a heating element for uniformity and means for applying a magnetic field.