JPH0351673B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a single crystal of a semiconductor such as Si or GaAs or an inorganic compound by a pulling method, and an apparatus therefor. [Prior Art] The pulling method is also called the Czyochralski method, and it is used in the production of single crystals such as Si and GaAs because it has advantages such as the ease of obtaining large-diameter single crystal ingots. 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 shortcomings, for example,
-50953 proposes applying a static magnetic field to molten Si in a crucible to suppress the flow of the molten Si. The solid-liquid equilibrium partition coefficient of oxygen in Si is 1.25 and 1
Therefore, the oxygen concentration of the Si melt in contact with the single crystal being pulled is lower than the concentration of the mother liquid phase, as shown in FIG. Therefore, by suppressing the flow of molten Si and reducing the amount of oxygen transported from the mother liquid phase to the solid/liquid interface, the oxygen concentration in the single crystal will be reduced. Furthermore, suppressing the flow of molten Si also reduces the elution of oxygen from SiO ₂ used in the crucible to molten Si. It is believed that the oxygen concentration in the single crystal ingot decreases due to the above two effects. On the other hand, in Japanese Patent Application Laid-Open No. 59-131597, when a GaAs single crystal is manufactured by the Czyochralski method, a high quality crystal without growth striations is obtained by applying a static magnetic field. Furthermore, Japanese Patent Laid-Open No. 10405/1983 proposes applying a rotating magnetic field to the Si melt to rotate the Si melt. Japanese Journal of Applied Physics, vol.
19 (1980) ppL-33-36, the oxygen concentration decreases when a single crystal ingot is rotated in the same direction as the rotation of the Si melt, and the crucible is also rotated in the same direction as the rotation of the Si melt. When rotating in the same direction, the oxygen concentration decreases further. If the Si melt is rotated in the same direction as the rotation direction of the single crystal ingot and the crucible, the Si melt will remain stationary relative to the single crystal ingot and the crucible. It is thought that similar effects can be obtained. Now, in the Czyochralski method, a single crystal ingot is pulled up 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 mother liquid phase concentration, contrary to oxygen. The solid/liquid interface concentration of P 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, an upward flow of Si melt (forced convection 11) is generated in the center of the crystal, as shown in Figure 4, and P is increased in the center.
This has the effect of making the concentration of B and B similar to that at the end. Therefore, forced convection caused by 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 Si or GaAs melt, thermal convection 1
1, but also suppresses forced convection, which plays a useful role as described above. Also, 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 weakened. As a result, when a static magnetic field or a rotating magnetic field is applied, there is a drawback that the distribution of doping element concentration within the ingot surface becomes non-uniform. [Problems to be Solved by the Invention] The present invention eliminates the problem of non-uniformity of doping elements and impurity elements within a single crystal plane, and also allows oxygen to be transferred from SiO ₂ of the crucible material into the Si melt. The purpose is to reduce elution. [Means for Solving the Problems] The present inventors have studied various methods for preventing only thermal convection without reducing forced convection due to crystal rotation, and as a result, have discovered the present invention. The present invention prevents thermal convection within the melt by applying a downward traveling magnetic field to the melt in the crucible,
This reduces the elution of the crucible material, and in the method of manufacturing single crystals from molten material by the pulling method, while applying a downward traveling magnetic field to the molten material near the side wall of the crucible in the storage container. It is characterized by crystal growth by pulling up a seed crystal. Furthermore, the apparatus of the present invention is an apparatus exclusively used for carrying out the above method, and includes (a) a single crystal pulling container equipped with a heating device and containing a molten substance, and (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 material container and a device for supplying it with a low frequency alternating current. [Operation] When a traveling magnetic field is applied to an electrically conductive liquid, the interaction between the induced current and the magnetic field can provide a driving force for the liquid to flow. This principle is used in electromagnetic pumps for fluid transport, etc. ing. At this time, the range in which the current is induced, that is, the penetration depth δ is expressed by the following equation. δ=(1/πfμσ) ^1/2 ...(1) where μ: 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 flow 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 is installed in an upright cylindrical shape inside the crucible.
An axially symmetrical traveling magnetic field is applied to the Si melt 4. 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, as shown in FIG. Heat convection 10 shown in FIG. 4 occurs. The present invention suppresses thermal convection 10 by applying a downward force against the buoyant force to the Si melt near the side wall of the crucible using a traveling magnetic field. [Example] Next, an example of the present invention will be described in detail. Example 1 A Si single crystal was pulled using the apparatus shown in FIG. This device stores a Si melt 4 in a crucible 3 and pulls a single crystal 5 from this melt. Crucible 3
A heater 6 is provided on the outer periphery of the chamber, and a heat shield 7 is provided on the outer periphery of the chamber, and these are covered with the chamber outer wall 2.
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 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 contains
Magnetic field strength 100 Gauss, frequency 100Hz at crucible side wall
A downward traveling magnetic field 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 rotation speeds of the crystal and crucible were 20 rpm and 10 rpm, respectively, in opposite directions. The characteristics of the example and the comparative example were compared for Si wafers manufactured by cutting out the vicinity of the head of a single crystal ingot. The results are shown in Table 1. In the example, the oxygen concentration was reduced to about 1/4 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.

〔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. In addition, 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 also be applied to pulling crystals other than Si. For example, by applying it to the pulling of GaAs, it is possible to suppress the elution of crucible materials such as silica and PBN (pyrolytic boron nitride).

[Brief explanation of drawings]

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

Claims (1)

[Claims] 1. In a method for producing a single crystal from a molten substance by a pulling method, crystal growth is achieved by pulling up a seed crystal while applying a downward traveling magnetic field to the molten substance near the side wall of a crucible in a container. A method for producing a single crystal, characterized by performing the following steps. 2. A single-crystal pulling container equipped with a heating device and containing a molten substance, an electromagnet having multiple sets of coils surrounding the outer periphery of the side wall of the container, and a device for supplying alternating current power with different phases to the coils of the electromagnet. A single-crystal manufacturing device characterized by comprising: