JPS6236097A - Production of single crystal and device therefor - Google Patents

Abstract

PURPOSE:To reduce the elution of O2 into the melt from a crucible and to obtain the titled single crystal with less variance of the resistance values in the crystal plane and capable of providing a low-O2 silicon wafer which is useful for a power transistor, etc., by pulling up a seed crystal while impressing a progressive magnetic field on the melt in the crucible. CONSTITUTION:A melt 4 of Si, etc., is charged in a crucible 3 and heated by a heater 6. A progressive magnetic field is generated by an upright cylindrical electromagnet 1 provided on the outer periphery of the outer wall 2 of a cham ber and impressed on the melt 4. A seed crystal is pulled up while exerting downward force on the melt 4 to control thermal convection of the melt and a single crystal 5 is grown.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a single crystal of a semiconductor such as St or GaAs or an inorganic compound by a pull-down process, and an apparatus therefor.

[Conventional technology]

The pulling method is also called the Czochralski method, and has the advantage of easily producing large-diameter single-crystal ingots.
It is practically used in the production of single crystals such as aAs. However, there were drawbacks such as a high concentration of oxygen impurities and the occurrence of striped defects (growth stripes) called striations.

In order to solve these drawbacks, for example,
No. 953 proposes applying a static magnetic field to molten Si in a crucible to suppress the flow of the molten Si. Si
Since the solid-liquid distribution coefficient of oxygen in the liquid is 1.25, which is larger than 1, the oxygen concentration of the Si melt in contact with the single crystal during the drawing and drawing process is equal to the concentration of the mother liquid phase, as shown in Figure 2. becomes lower. Therefore, by suppressing the flow of molten Si, the amount of oxygen trapped in the solid/liquid interface from the mother liquid phase can be reduced.

The oxygen concentration in the single crystal decreases. Furthermore, if the flow of molten Si is suppressed, molten Sf will be reduced from 5i02 used in the crucible.
The elution of oxygen into the water is also reduced. It is believed that the oxygen concentration in the single crystal ingot decreases due to the two effects described above.

On the other hand, in JP-A-59-131597, GaAs
When producing single crystals using the Czochralski method, high quality crystals free of J&long lengths are obtained by applying a static magnetic field.

Furthermore, Japanese Patent Laid-Open No. 55-10405 proposes applying a rotating magnetic field to the Si melt to rotate the Si melt.

Japanese Journal of Appli
ed Physics.

vol 19 (1980) p, p, L-33~3
According to the experimental results published in 2006, when a single crystal ingot is rotated in the same direction as the rotation of the L St melt, the oxygen concentration decreases, and roughly speaking, when the crucible is rotated in the same direction as the rotation of the Si melt. As it rotates, the oxygen concentration further decreases. When the Si melt is rotated in the same direction as the rotation direction of the single crystal ingot and the crucible, the Si melt is static relative to the single crystal ingot and the crucible, so it is necessary to apply a static magnetic field. It is thought that the same effect as the law can be obtained.

Now, in the Czochralski method, a single crystal ingot is pulled while rotating. One purpose of this is to make the doping element concentration uniform in the horizontal plane of the ingot. As shown in FIG. 2, since doping elements such as P and B have solid-liquid partition coefficients smaller than 1, the concentration at the solid/liquid interface becomes higher than the nJ liquid phase concentration, contrary to oxygen. This P
The solid/liquid interface concentration of and B is determined by the balance between the discharge rate accompanying solidification and the diffusion rate into the mother liquid phase.

If the crystal is not rotated, thermal convection 10 as shown in Figure 3 occurs, and this cleaning effect promotes diffusion, resulting in a lower concentration of P and B at the interface near the sides of the crystal than in the center. . When a single crystal ingot is rotated, as shown in Figure 4, an upward flow of Si melt (forced convection 11) is generated in the center of the crystal, which has the effect of making the concentration of P and B in the center similar to that at the edges. be. Therefore, the forced convection caused by the crystal rotation has the effect of making the doping element concentration uniform in the horizontal plane of the ingot.

When a static magnetic field is applied to a Si or GaAs melt, not only thermal convection 11 but also strong 11 convection, which has a useful function as described above, is suppressed. Furthermore, when the Si melt is rotated in the same direction as the Si melt by a rotating magnetic field, the forced convection shown in FIG. 4 is also weakened. As a result, when applying a static or rotating magnetic field,
The disadvantage is that the distribution of doping element concentration within the ingot plane increases non-uniformity.

[Problem that the invention seeks to solve]

The present invention aims to reduce the elution of oxygen from the crucible material 5i02 into the Si melt without causing adverse effects such as non-uniformity of doping elements and impurity elements within the single crystal plane. .

[Means for solving problems]

The present inventors have conducted various studies on methods of preventing only thermal convection without reducing forced convection caused by crystal rotation, and as a result, they have discovered the present invention.

The present invention prevents thermal convection within the melt by applying a traveling magnetic field to the melt within the crucible, thereby reducing elution of the crucible material.

A method for producing a single crystal from a molten material by a pulling method, characterized in that crystal growth is performed by pulling a seed crystal while applying a traveling magnetic field to the molten material in a container.

Furthermore, the apparatus of the present invention is an apparatus exclusively used for carrying out the above method, which comprises: a) a single crystal cutting container equipped with a heating device and containing a molten substance; b) a container surrounding the outer periphery of the side wall of the container; A device for producing a single crystal, comprising means for applying a downward traveling magnetic field to a molten substance in a container.

The means for applying a traveling magnetic field consists of an electromagnet surrounding the side wall of the molten substance container and a device for supplying low frequency evening radio waves to the electromagnet.

[Effect]

When a traveling magnetic field is applied to a dominant liquid, the interaction between the induced current and the magnetic field can provide a driving force for the liquid to flow, and this principle is used in electromagnetic pumps for fluid transport and the like. At this time, the range in which the current is induced, that is, the penetration depth δ, is determined by the following formula:% δ=(1,/πfruσ)I72
1) Here, final: magnetic permeability σ: electrical conductivity.

As the frequency f of the traveling magnetic field increases, the penetration depth δ
decreases.

Therefore, by selecting an appropriate frequency according to the purpose, the penetration depth δ, in other words, the range of the driving force of the driving force can be changed.

FIG. 1 shows the configuration of the apparatus of the present invention, in which an electromagnet 1 for generating a traveling magnetic field is installed outside the chamber outer wall 2 so as to surround the side wall of the crucible 3. This electromagnet 1 has an upright cylindrical shape and applies an axially symmetrical traveling magnetic field to the Si melt 4 in the crucible.

Since the Si melt in the crucible 3 is heated by the heater 6 via the crucible 3, the temperature of the Si melt near the side wall of the crucible becomes higher than that inside the crucible, and due to the buoyancy caused by this temperature difference, Heat convection 10 shown in FIG. 4 occurs. The present invention uses a traveling magnetic field to apply -h to the Si melt near the side wall of the crucible.
Thermal convection 10 is suppressed by reducing the downward force that resists the buoyant force.

〔Example〕

Next, embodiments of the present invention will be described in detail.

Example 1 A Sim crystal was pulled using the apparatus shown in FIG. This device stores a Si melt 4 in a crucible 3, and pulls a width bonded product 5 from the melt.

A heater 6 is provided on the outer periphery of the crucible 3, and a heat shield 7 is provided on the outer periphery of the crucible 3, and these are covered by the outer wall 2 of the chamber. An electromagnet 1 is provided on the outer periphery of the chamber outer wall 2 so as to surround the side wall of the crucible 3. The electromagnet 1 is supplied with an upstream alternating current that generates a traveling magnetic field from a low frequency oscillator (not shown).

In the embodiment of the present invention, the melt in the crucible.

Magnetic field strength 100 Gauss, frequency 100H at crucible side wall
A downward traveling magnetic field of z was applied. Furthermore, in a comparative example, the same device was used to perform pulling without applying a magnetic field. In both Examples and Comparative Examples, the rotational speeds of the crystal and crucible were 20 rpm and 1Orpm, respectively, in opposite directions.

S manufactured by cutting from near the head of a single crystal ingot
For i-wafers, characteristics of Examples and Comparative Examples were compared.

The results are shown in Table 1.

In the example, the oxygen concentration was slightly reduced compared to the comparative example. This is thought to be due to the effect that the elution of oxygen from the silica of the crucible material was reduced due to the suppression of thermal convection. On the other hand, the resistance value variation within the wafer surface is the same between the example and the comparative example.

As described above, according to the present invention, the oxygen concentration can be significantly reduced without increasing the non-uniformity of the doping element distribution within the wafer surface, in other words, the resistance value distribution.

Example 2 Next, the effect of changing the strength of the magnetic field will be described in accordance with an example of the present invention. Using the same apparatus as in Example 1, a Si single crystal was pulled by changing the applied magnetic field. The rotation speed of the crystal and crucible was 2 in both Examples and Comparative Examples.
0 rpm and 10 rpm were set in opposite directions. Thereafter, the oxygen concentration was measured for the St sea urchin/\ which was produced by cutting out the vicinity of the head of the single crystal ingot, as shown in Figure 5. As shown in the figure, as the strength of the magnetic field increases, the oxygen concentration decreases. Therefore, according to the present invention, the oxygen concentration can be controlled within a desired range by adjusting the strength of the magnetic field.

〔Effect of the invention〕

According to the present invention, silicon wafers with low oxygen concentrations necessary for power transistors and the like can be manufactured using pulled crystals. Furthermore, the pulled Si crystal produced by the method of the present invention has little variation in resistance value within the crystal plane, and can be used for manufacturing wafers for highly integrated circuits with controlled oxygen concentration.

The present invention can be applied to crystals other than Si. For example, by applying it to GaAs crystals, the elution of silica and PBN (pyrolytic boron nitride), which are crucible materials, can be suppressed. That is removable.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the structure of the present invention, and FIG.
Figure 3 is a schematic diagram showing the impurity element concentration distribution near the liquid interface. Figure 3 is a schematic diagram showing the melt flow when the crystal is not rotated.
The figure is a schematic diagram showing the melt flow when rotating the crystal.
The figure is a graph showing the relationship between magnetic field strength and oxygen concentration. l...Electromagnet 2...Chamber outer wall 3...
- Crucible 4... Melt 5... Pulled single crystal 6... Heater 7... Heat shield 10...
・Heat convection 11...forced convection

Claims (1)

[Claims] 1. A method for producing a single crystal from a molten substance by a pulling method, characterized in that crystal growth is performed by pulling up a seed crystal while applying a traveling magnetic field to the molten substance in a container. A method for producing single crystals. 2. A single-crystal pulling container equipped with a heating device and containing a molten substance, and a means provided around the outer periphery of the side wall of the container for applying a downward traveling magnetic field to the molten substance within the container. Equipment for producing single crystals.