JPS6033291A - Preparation of single crystal silicon - Google Patents

Abstract

PURPOSE:To obtain single crystal silicon having uniform concn. of impurity and oxygen in the growth direction and radial direction by changing continuously the strength of magnetic field impressed to the molten silicon in a quartz crucible in accordance with the pulled amt. of single crystal silicon. CONSTITUTION:A seed crystal suspended freely rotatable from the top of a chamber is dipped in molten silicon in a quartz crucible while impressing a magnetic field to the molten silicon, and the seed crystal is pulled up while changing the strength of the magnetic field continuously in accordance with the pulled amt. of the single crystal silicon. For example, pulling of a single crystal is performed by setting preliminarily a program for changing continuously the strength of magnetic strength from 3,000 gauss at the initial stage of pulling to ca. 1,500 gauss at the end stage of pulling to a computor control in order to make uniform the concn. of oxygen in the growth direction of the single crystal silicon. As the result, the difference between the max. value and the min. value of the oxygen concn. in the growth direction of single crystal silicon becomes 2.0X 10<17>/cm<2>. Therefore, the uniformity is improved.

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing high quality single crystal silicon.

Conventionally, single crystal silicon used in the manufacture of semiconductor devices has been mainly manufactured by the Czochralski method (CZ method). In this method, a silicon raw material is placed in a quartz ridge rotatably supported in a chamber, melted, a seed crystal suspended rotatably from the top of the chamber is immersed in the molten silicon, and the seed crystal is pulled up. It is used to manufacture single-crystal silicon.

However, due to the convection of molten silicon, the impurity concentration decreases in both the growth direction and radial direction of single crystal silicon.
Poor uniformity in oxygen concentration was a cause of deterioration in the quality of single crystal silicon.

Therefore, a method (hereinafter abbreviated as MCZ method) is known in which the convection is suppressed by applying a magnetic field to the molten silicon in the C2 method, thereby attempting to improve the quality of single crystal silicon.

However, it has been found that even the above MCZ method cannot significantly improve the uniformity of impurity concentration and oxygen concentration in single crystal silicon.

For example, in Figures 1 and 2, the strength of the magnetic field is O(
The relationship between the solidification rate of silicon, the oxygen concentration, and the specific resistance value is shown when holding constant values of 1000, 1500, 2000, and 3000 Gauss (Conventional) C2 method).

It can be seen from Figure 1 that the oxygen concentration decreases as the assimilation rate (pulling rate) increases, and also decreases in proportion to the strength of the magnetic field. The difference between the maximum and minimum oxygen concentration is approximately 7.5 x 1017 cnr3 for 0 Gauss, while it is approximately 3. OX 10”
With 'G11-', the uniformity is only slightly improved.

Furthermore, from FIG. 2, it can be seen that the resistivity value also decreases as the solidification rate (pulling rate) increases, and increases slightly in proportion to the strength of the magnetic field, but that it has little dependence on the strength of the magnetic field. The difference between the specific resistance value of Sametaisen and the J\ value is θ Gauss,
Approximately 11Ω-Nishiki, while in the case of 3000 Gauss,
The force is about 0750-α, and the uniformity is slightly improved.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a method for manufacturing single-crystal silicon that can make the impurity concentration and oxygen concentration uniform in both the growth direction and the warp direction of the single-crystal silicon. is.

The present invention, Nagisa et al., conducted various studies on the reason why the uniformity of impurity concentration and oxygen concentration in single crystal silicon is not significantly improved by the conventional MCZ method. As a result, although the strength of convection in molten silicon is affected by the amount of melt, in the conventional MCZ method, the strength of the magnetic field is kept constant, so convection can be suppressed according to changes in the amount of melt. However, they found that it is possible to achieve a value of 1 by uniformizing the physical property values in single crystal silicon, and have accomplished the present invention.

That is, the method for manufacturing single crystal silicon of the present invention is characterized in that the strength of the magnetic field applied to molten silicon is continuously changed in accordance with the amount of pulling of single crystal silicon.

By continuously changing the strength of the magnetic field in this way, it is possible to effectively suppress convection in response to changes in the strength of convection due to changes in the amount of melt, thereby increasing the quality of single-crystal silicon. I can do something.

Embodiments of the present invention will be described below with reference to FIGS. 3 to 6.

In order to equalize the oxygen concentration in the growth direction of single-crystal silicon, the strength of the magnetic plate is raised in advance by computer control as shown in Figure 3. From the initial level of 3000 Gauss, the strength of the magnetic plate is continuously increased until the final stage. A program was given to vary the temperature up to about 1,500 Gauss, and the pulling of single crystal silicon was omitted.

As a result, as shown in FIG. 4, the difference between the maximum and minimum oxygen concentrations in the growth direction of single crystal silicon is approximately 2. Ox10
cm, the uniformity could be improved.

Furthermore, as mentioned above, the resistivity value has little dependence on the strength of the magnetic field, so as shown in FIG. 5, there is almost no change in /l compared to the conventional method.

In addition, when the oxygen concentration in the radial direction at the head of single crystal silicon was measured, as shown in Figure 6, the difference between the maximum value and the minimum value was determined by the conventional CZ method (when no magnetic field was applied, the curve in the figure In I), it was about 4.5 x 1017 cm-3, whereas in the method of the present invention (curve ■ in the figure), it was about 1.8 x 10
It was found that uniformity was improved in the radial direction as well. Although not shown, it was also found that the uniformity of the radial specific resistance values was also improved.

In the above example, the main purpose was to improve the uniformity of the oxygen concentration in single crystal silicon, but it is also possible to improve the uniformity of the specific resistance value by changing the method of changing the strength of the magnetic field. You can also do it.

In addition, the computer determines not only the strength of the magnetic field, but also
By simultaneously controlling driving conditions such as the crystal rotation speed and the crystal rotation speed, as well as the temperature of the melt surface, it is possible to further improve the quality of single-crystal silicon.

Furthermore, the method of the present invention can be applied to other conductive materials other than silicon, and can be applied to any pulling device.

As described above in detail, the present invention can provide an M-arycrystalline method for single-crystal silicon that can make the impurity concentration and oxygen concentration uniform both in the growth direction and in the radial direction of single-crystal silicon.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between the solidification rate of single crystal silicon and oxygen concentration by the conventional method, and Figure 2 is a diagram showing the relationship between the solidification rate of single crystal silicon and the specific resistance value by the conventional method!
Figure 3 is a diagram showing changes in magnetic field strength in an embodiment of the method of the present invention, and Figure 4 shows the relationship between the assimilation rate of single crystal silicon and the degree of oxygen in an embodiment of the method of the present invention. Fig. 5 shows the relationship between the solidification rate and specific resistance value of single crystal silicon in an embodiment of the method of the present invention, and Fig. 6 shows the diameter in the conventional method and an embodiment of the method of the present invention. FIG. 2 is a diagram showing directional oxygen concentration distribution.

Claims (1)

[Claims] While applying a magnetic field to molten silicon in a quartz crucible that is rotatably supported in the chamber, a seed crystal that is rotatably suspended from the top of the chamber is immersed, and the seed crystal is pulled up to form a single crystal. A method for manufacturing single crystal silicon, characterized in that the strength of the magnetic field is continuously changed according to the amount of pulling of single crystal silicon.