JPH06305880A - Production of silicon single crystal and apparatus for its production - Google Patents

Abstract

PURPOSE:To obtain a high-quality silicon single crystal having a small point defect density. CONSTITUTION:This method for producing a silicon single crystal is to pull up the silicon single crystal from a melt in a crucible. In the method, the control is carried out so that a solidification interface 15 may bulge from a melt interface 6 to the side of a grown single crystal ingot 10 and the extent of the maximum protrusion (h) from the melt interface 6 thereof may exceed 15mm. Thereby, the single crystal is grown.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for manufacturing a silicon single crystal. More specifically, the present invention relates to a manufacturing method and a manufacturing apparatus capable of obtaining a high quality silicon single crystal having a small point defect density.

[0002]

As a method for producing a single crystal, the Czochralski method (CZ method) for pulling a crystal from a melt in a crucible while growing the crystal is widely used.

In order to obtain a silicon single crystal by the CZ method, for example, a single crystal manufacturing apparatus having a structure schematically shown in FIG. 6 is used. Single crystal manufacturing apparatus 61
Has a chamber 2 including a heating chamber portion 2a and a pulling chamber portion 2b as shown in FIG. Inside the heating chamber portion 2a, a quartz crucible 4 supported by a rotary shaft 3 extending through a chamber bottom portion by a driving device (not shown) located outside the chamber 2 is arranged. A cylindrical heater 5 that surrounds the crucible 4 at a predetermined interval is provided, and a heat insulating material 6 is arranged outside the heater 5. In this example, the outer periphery of the quartz crucible 4 is protected by a graphite crucible 7, and the graphite crucible 7 is supported by the rotating shaft 4 via a graphite tray 8.

On the other hand, the pulling chamber portion 2b is extended above the heating chamber portion 2a along the pulling axis of the silicon single crystal ingot 10 pulled from the silicon melt 9 formed in the quartz crucible 4. Further, it is a portion having an inner diameter smaller than that of the heating chamber portion 2a.

Further, a pulling wire 14 having a chuck 13 for holding the seed crystal 12 is arranged in the chamber 2 through the upper wall surface of the chamber and hanging down from above, and the pulling wire 14 is provided. The wire pulling device 11 provided on the upper portion of the pulling chamber portion 2b enables the lifting and lowering while rotating.

In the manufacturing apparatus 61 having such a structure, in order to grow a single crystal, first, the quartz crucible 4 is charged with a predetermined amount of raw materials such as polycrystalline silicon and a dopant added as required. The raw material is melted by heating with the heater 5 to form the melt 9. Then, the seed crystal 1 attached to the melt 9 at the tip of the pulling wire 14
2 is soaked, the quartz crucible 4 and the seed crystal 12 are pulled up while being rotated, and the single crystal ingot 1 is attached to the lower end of the seed crystal 12.
It grows 0.

In such a single crystal pulling method, the flow of the inert gas in the single crystal pulling apparatus is rectified,
In order to increase the cooling rate of the growing single crystal, a cylindrical body is provided that hangs from the upper wall surface of the heating chamber and surrounds the growing silicon single crystal as an axis (for example, JP-A-47-26388). No. publication) is known.

Further, it is possible to prevent the SiO gas generated from the melt from condensing on the wall surface of the chamber 2 and dropping to reach the growth interface of the single crystal to cause dislocation of the crystal. For the purpose of blocking the radiant heat from the crucible wall and increasing the pulling rate, the upper flat annular rim projecting from the edge of the crucible and the lower end attached to this annular rim are centered around the silicon single crystal being pulled. Providing a cover composed of a silicon single crystal and an inverted conical connecting portion close to the melt (see, for example, Japanese Examined Patent Publication No. 57-4
No. 0119) is also known.

[0009]

By the way, a large amount of impurities are mixed in the silicon single crystal grown by the above-mentioned single crystal pulling method by the melting of the quartz crucible 4, and the oxygen impurities are precipitated by the subsequent heat treatment. The formation of oxygen-induced stacking faults (OSF) has become a problem.
The degree of occurrence of such OSF depends on whether a single crystal manufacturing apparatus provided with a cylindrical body or an inverted conical cover as described above is used, or a single crystal manufacturing apparatus not provided with these is used. Compared with the above, it will be almost the same or rather more.

It is known that the generation of such OSF is also affected by the cooling rate of the single crystal during pulling, and in a certain type of silicon single crystal, cooling of each part of the single crystal during pulling is performed. 5 ℃ / mi in the temperature range below 800 ℃
If the speed is faster than n, the generation of OSF becomes remarkable,
There is also known a structure in which the lower end of the inverted conical cover is made of an opaque body such as graphite or ceramics and the other portion is made of a transparent body such as quartz (Japanese Patent Laid-Open No. 3-88794). ing.

However, when the single crystal manufacturing apparatus having the structure disclosed in Japanese Patent Laid-Open No. 3-88794 is used, it is possible to suppress generation of OSF of a silicon single crystal of a specific kind to some extent, but it is possible to cool it. It was too slow to be practical.

Therefore, it is an object of the present invention to provide an improved method and apparatus for manufacturing a silicon single crystal. More specifically, it is an object of the present invention to provide a manufacturing method and a manufacturing apparatus capable of obtaining a high quality silicon single crystal having a small point defect density.

[0013]

SUMMARY OF THE INVENTION The present inventors have
In order to solve the above problems, attention was paid to the diffusion of point defects at the solidification interface when pulling a silicon single crystal. If the point defects taken in the single crystal can be diffused to the solidification interface with good controllability, the density of the point defects can be efficiently reduced. The general idea is that the solidification interface when pulling a single crystal is preferably as flat as possible in order to improve the crystallinity of the single crystal (Japanese Patent Laid-Open No. 47-26388).
However, the inventors of the present invention, as a result of diligent study, in obtaining a single crystal having a small point defect density by diffusing the point defects taken in the single crystal to the solidification interface, the solidification interface is on the grown single crystal ingot side. It is preferable that the bulge is a bulge, and if the bulge is controlled to a certain amount or more to pull the single crystal, it is found that a single crystal having an extremely small point defect density can be obtained. It has been reached.

That is, the present invention for solving the above-mentioned various objects is to provide a method for producing a silicon single crystal in which a silicon single crystal is pulled from a melt in a crucible. The method for producing a silicon single crystal is characterized in that the single crystal is grown by controlling the maximum protrusion amount from the melt interface to exceed 15 mm.

The present invention also provides a silicon single crystal manufacturing apparatus for pulling a silicon single crystal from a melt in a crucible,
From a cylindrical portion that surrounds the growing single crystal and whose lower end is close to the interface of the melt, and an annular portion that has an inner peripheral edge that is continuous from the upper end of this cylindrical portion and whose outer peripheral edge is connected to the inner surface of the chamber. A structured radiation screen is provided,
The lower end portion of the cylindrical portion of the radiation screen has a thermal emissivity of 0.7 or more, and the other portions have a thermal emissivity of 0.5 or less.

[0016]

The point defects taken into the crystal during solidification diffuse toward the interface in proportion to the gradient of supersaturation. The larger the temperature gradient near the solidification interface, the larger the gradient of supersaturation.
If the point defect stays in the region having a large gradient of supersaturation for a long time, the point defect is sufficiently diffused to the interface. As shown in FIG. 1, by forming a greatly swollen solidification interface 15 on the side of the grown single crystal ingot 10, the solidification interface 1
In the vicinity of 5, in the region B in the outer peripheral portion of the single crystal ingot, the isotherm is greatly inclined with respect to the pulling direction of the single crystal, so that the diffusion time is long, and in the region A in the central portion of the single crystal ingot, the temperature gradient is large. Since the diffusion rate is high, the point defects taken into the single crystal in any region are sufficiently diffused to the interface, and it becomes possible to manufacture a high quality crystal with a small point defect density.

As described above, in the present invention, the solidification interface 1
5 is for pulling while maintaining a state in which it is largely expanded from the melt interface 16 to the single crystal ingot 10 side.
Such solidification interface 15 is a conventional single crystal manufacturing apparatus as shown in FIG. 6 or a cylindrical body as disclosed in Japanese Patent Laid-Open No. 48-26388 or JP-B 57.
Even if the one provided with the inverted conical cover as disclosed in Japanese Patent No. 40119 was used, it was not possible to form a solidified interface bulging toward the single crystal ingot side to a desired degree. That is, in these device configurations, the heat flux in the side surface direction is not sufficiently larger in the vicinity of the solidification interface than in the axial direction.

In the apparatus for producing a single crystal of the present invention, a cylindrical member surrounding the growing single crystal ingot from the vicinity of the melt interface is provided, and the lower end portion of the cylindrical member is formed of a material having a large thermal emissivity. To reduce the radiant heat resistance, and to increase the radiant heat resistance by forming the other parts with a material with a small thermal emissivity to tilt the heat flux near the interface to the side and increase the solidification interface to the single crystal ingot side. It is possible to swell, further connecting the outer peripheral edge of the annular portion continuous from the top of this cylindrical member to the water-cooled chamber wall surface, so that the temperature of the cylindrical portion is sufficiently lowered by heat conduction, This makes it possible to increase the temperature gradient near the solidification interface.

Hereinafter, the present invention will be described in more detail based on the embodiments. FIG. 2 is a use state diagram schematically showing a configuration of an embodiment of the silicon single crystal manufacturing apparatus of the present invention. As shown in FIG. 2, the apparatus 1 for producing a silicon single crystal according to the present invention has a radiation screen 21 provided in a heating chamber portion 2a of a chamber 2, and other configurations are the same as those of the conventional one shown in FIG. It has substantially the same configuration as the silicon single crystal manufacturing apparatus 61. In FIG. 2, the same members as those in the apparatus shown in FIG. 6 are designated by the same reference numerals.

The radiation screen 21 has a cylindrical portion 22.
And an annular portion 23 continuous from the upper end of the cylindrical portion 22 and extending in the radial direction of the cylindrical portion 22. The outer peripheral edge of the annular portion 23 is connected and held by a support portion 24 provided on the wall surface of the water-cooled heating chamber 2a, and the cylindrical portion 22 is arranged along the axis of the chamber 2.

In the present invention, the radiation screen 2
It is desirable that the cylindrical portion 22 of No. 1 has a substantially same inner diameter from the upper end to the lower end as shown in the drawing.
The diameter may be reduced or expanded in the axial direction as long as it is slightly.

The lower end of the cylindrical portion 22 has an interface 1 of the silicon melt 9 formed in the quartz crucible 4 during the pulling operation of the single crystal.
6, the inner diameter of the cylindrical portion 22 is slightly larger than the diameter of the pulled single crystal ingot 10, and surrounds the single crystal ingot 10 at a predetermined interval. In addition, the lower end position of the cylindrical portion 22,
The distance between the outer surface of the single crystal ingot 10 and the inner surface of the cylindrical portion 22 depends on pulling conditions such as the type and diameter of the single crystal ingot to be pulled, the melt temperature, the pulling speed, and the length of the ingot. However, the lower end of the cylindrical portion 22 is about 5 to 100 above the melt interface 16.
It is located at a height of about mm, and the distance between the outer surface of the single crystal ingot 10 and the inner surface of the cylindrical portion 22 is about 5 to 50 mm.

Therefore, the cylindrical portion 22 of the radiation screen 21 has a lower end portion 22a and an upper portion 22b.
Is made of another material, and the lower end portion 22a has a thermal emissivity of 0.7 or more, more preferably 0.8.
.About.1.0, while the upper part has a thermal emissivity of 0.
It is 5 or less, more preferably 0.1 to 0.3. That is, when the thermal emissivity of the upper portion 22b of the cylindrical portion 22 exceeds 0.5, the growing single crystal ingot 10 is kept in a predetermined temperature range, for example, about 700 to 900 ° C.
It becomes difficult to cool at a sufficient cooling rate in the temperature range of 1), and if the thermal emissivity of the lower end portion 22a is less than 0.7, the thermal emissivity difference with the upper portion 22b is not sufficient. This is because the heat flux cannot be tilted laterally in the vicinity of the solidification interface, and a desired solidification interface as described later cannot be formed.

Specific examples of the material forming the lower end portion 22a include graphite, a surface-oxidized nickel-chromium alloy, and a surface-oxidized molybdenum. Of these, graphite is particularly preferable. Specific examples of the material forming the upper portion 22b include metals such as molybdenum, stainless steel, tungsten, niobium, nickel, and germanium.
Of these, molybdenum is particularly preferable. Further, it is desirable that the upper portion 22b is coated with silicon or the like in order to prevent metal contamination of the silicon single crystal.

The total length of the cylindrical portion 22 and the length of the lower end portion 22a thereof cannot be unconditionally specified because it depends on the pulling condition of the silicon single crystal as described above. Is 200-400 m
m, and the length of the lower end portion 22a is 10 to 50.
It is about mm.

The material forming the annular portion 23 of the radiation screen 21 is not particularly limited, but it is desirable that the material is the same as that of the upper portion 22a of the cylindrical portion 22.

In order to pull up a silicon single crystal by using such a single crystal manufacturing apparatus 1, polycrystalline silicon and a dopant added as necessary in the quartz crucible 4 are prepared according to a conventional method. A predetermined amount of raw material is loaded and heated by the heater 5 to melt the raw material to form a melt 9.
Then, the seed crystal 12 attached to the tip of the pulling wire 14 is immersed in the melt 9 to form the quartz crucible 4 and the seed crystal 12.
The single crystal ingot 10 is grown on the lower end of the seed crystal 12 while rotating the same. As described above, in the single crystal manufacturing apparatus according to the present invention, the radiation screen 21 is provided above the quartz crucible 4. Therefore, as shown in FIG. 1, the solidification interface 15 largely swells toward the ingot 10 side, and the maximum protrusion amount h from the melt interface 16 exceeds 15 mm, more preferably about 20 to 30 mm.
Further, since the radiation screen 21 is connected to the wall surface of the chamber 2 which is water-cooled, the temperature of the cylindrical portion 22 of the radiation screen 21 is sufficiently lowered, and the temperature gradient in the vicinity of the solidification interface 15 becomes large, for example, a 6-inch diameter silicon wafer. When pulling up the ingot for use in the area A, 4-5 ° C /
mm or about 3 to 4 ° C./mm in the B region.

Therefore, in the present invention, the diffusion of the point defects taken into the single crystal ingot 10 during solidification to the interface is promoted, and the single crystal ingot 10 having a small point defect density can be obtained.

[0029]

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 As shown in FIG. 3, the radiation screen 21 according to the present invention is arranged on the upper part of the quartz crucible 4 having a diameter of about 450 mm.
N-type silicon single crystal ingot 10 with a diameter of about 160 mm
Was pulled up at a speed of about 1.5 mm / min. The distance from the melt interface 16 at the lower end of the radiant screen 21 is 20 mm, and the length of the lower end portion 22a made of graphite of the cylindrical portion 22 of the radiant screen 21 is 30.
The length of the upper portion 22b composed of mm and molybdenum was 200 mm, and the inner diameter of the cylindrical portion 22 was 210 mm.
The maximum protrusion amount h of the solidification interface 15 from the melt interface 16 during the pulling operation of the single crystal was measured by a two-crystal X-ray topography of a longitudinally cut sample. The results are shown in Table 1. Also, a silicon wafer cut out from the obtained single crystal ingot,
After thermal oxidation at 1100 ° C. for 1 hour, etching was performed and the OSF density was observed by microscopic observation. Table 1 shows the average values of the OSF densities of the wafers cut out from the respective portions of the single crystal ingot.

COMPARATIVE EXAMPLE 1 As shown in FIG. 4, an inverted conical cover 31 as disclosed in Japanese Examined Patent Publication No. 57-40119 was placed on the upper part of the quartz crucible 4, and the diameter was about the same as in Example 1. About 160 mm n-type silicon single crystal ingot 10 about 1.5 mm / min
Pulled up at the speed of. The cover 31 is made of graphite, and its lower end has a distance of 30 mm from the melt interface 16 and its lower end has an inner diameter of 210 m.
m, the angle of inclination of the conical surface is 31 °, and the length of the conical portion is 230 m
It was m. Table 1 shows the results of measuring the maximum protrusion amount h of the solidification interface 15 and the OSF density in the same manner as in Example 1.

Comparative Example 2 As shown in FIG. 5, using a single crystal production apparatus as disclosed in Japanese Patent Application Laid-Open No. 47-26388, in which a cylindrical body 32 is hung from an upper wall surface of a heating chamber. As in Example 1, an n-type silicon single crystal ingot 10 having a diameter of about 160 mm was pulled up at a speed of about 1.5 mm / min. The cylindrical body 32 is made of graphite, and the distance from the melt interface 16 at its lower end is 10
The inner diameter was 0 mm and the inner diameter was 210 mm. Table 1 shows the results of measuring the maximum protrusion amount h of the solidification interface 15 and the OSF density in the same manner as in Example 1.

Comparative Example 3 An n-type silicon single crystal ingot 10 having a diameter of about 160 mm was pulled at a speed of about 1.0 mm / min in the same manner as in Example 1 using the single crystal manufacturing apparatus as shown in FIG. Table 1 shows the results of measuring the maximum protrusion amount h of the solidification interface 15 and the OSF density in the same manner as in Example 1.

[0033]

[Table 1]

As is clear from the results shown in Table 1, in Example 1 using the radiation screen 21 according to the present invention, a greatly swollen solidification interface 15 can be formed on the single crystal ingot 10 side. As a result, a silicon wafer having a very low OSF density could be obtained.

[0035]

As described above, according to the present invention, it is possible to form a solidified interface that swells greatly toward the single crystal ingot during pulling of the single crystal. Therefore, the point defects taken into the single crystal ingot during solidification are formed. Diffusion is promoted, and a single crystal having a small point defect density can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the shape of a solidification interface and the temperature distribution in the vicinity of the solidification interface in the method for producing a silicon single crystal of the present invention,

FIG. 2 is a use state diagram schematically showing a configuration of an embodiment of a silicon single crystal production apparatus of the present invention,

FIG. 3 is a cross-sectional view showing a main part of a device configuration according to an embodiment of the present invention,

FIG. 4 is a cross-sectional view showing a main part of a device configuration in a comparative example,

FIG. 5 is a cross-sectional view showing a main part of a device configuration in another comparative example,

FIG. 6 is a use state diagram schematically showing a configuration of a conventional silicon single crystal manufacturing apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon single crystal manufacturing apparatus, 2 ... Chamber, 2a ... Heating chamber part, 2b ... Pulling chamber part, 3 ... Rotating shaft,
4 ... Quartz crucible, 5 ... Heater, 6 ... Insulating material, 7 ... Graphite crucible, 8 ... Graphite pan, 9 ... Silicon melt, 10 ...
Single crystal ingot, 11 ... Wire pulling device, 12 ... Seed crystal, 13 ... Chuck, 14 ... Pulling wire, 15 ... Solidification interface, 16 ... Melt interface, 21 ... Radiation screen, 22
... Cylindrical part, 22a ... Lower end part of cylindrical part, 22b ... Upper part of cylindrical part, 23 ... Annular part, 24 ... Support part, A ... Central part of single crystal ingot, B ... Outer part of single crystal ingot, h ... The maximum amount of protrusion of the solidification interface from the melt interface.

Claims (2)

[Claims] 1. A method for producing a silicon single crystal in which a silicon single crystal is pulled from a melt in a crucible, a solidification interface swells from a melt interface to a grown single crystal ingot side, and a maximum protrusion amount from the melt interface is obtained. The method for producing a silicon single crystal is characterized in that the single crystal is grown so as to be over 15 mm. 2. A silicon single crystal manufacturing apparatus for pulling a silicon single crystal from a melt in a crucible, a cylindrical portion surrounding the growing single crystal and a lower end of which is close to an interface of the melt, and this cylinder. There is provided a radiant screen composed of an annular portion having an inner peripheral edge continuing from the upper end of the section and an outer peripheral edge being connected to the inner surface of the chamber. The apparatus for producing a silicon single crystal, which has a thermal emissivity of 0.5 or more in other portions and is 0.5 or less.