JP2012206862A - Radiation shield of single crystal pulling-up apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiation shield of a single crystal pulling-up apparatus, which is improved in the pulling-up speed of a single crystal and can suppress the generation of crystal defects and the dislocation of the crystal.SOLUTION: The radiation shield has a cylindrical straight barrel part 6b and a lower shoulder part 6c curving inward from the lower end of the straight barrel part and forming an opening on the lower end part. If the diameter of a single crystal to be grown is taken as Φ(mm), the thickness size tof the lower end part opening of a heat-insulating member 6d of the lower shoulder part is prescribed by expression (1): t=0.1Φto 0.5 Φ. When an inclined line at 45° against a horizontal surface described below is drawn toward the lower shoulder part from an intersection point of a virtual line extending downward the outer side surface of the heat-insulating member of the straight barrel part with the horizontal surface containing the lower end part of the heat-insulating member of the straight barrel part, the thickness size tof the heat-insulating member at the intersection point against the heat-insulating member is prescribed by expression (2): t≤2t.

Description

  The present invention relates to a radiation shield provided in a single crystal pulling apparatus that pulls up a single crystal while growing it by the Czochralski method (hereinafter referred to as “CZ method”).

  The CZ method is widely used for the growth of silicon single crystals. In this method, as shown in FIG. 7, a silicon melt M is formed in the crucible 50 by the heat of the heater 52, the seed crystal P is brought into contact with the surface thereof, the crucible 50 is rotated, and the seed crystal P The single crystal C is formed at the lower end of the seed crystal P by pulling upward while rotating in the opposite direction.

In the single crystal pulling apparatus that performs this CZ method, as disclosed in Patent Document 1, a radiation shield 51 is provided above the crucible so as to surround the pulling region of the single crystal C. The radiation shield 51 effectively blocks the radiant heat to the outer peripheral surface of the single crystal C to be grown, thereby promoting the solidification of the single crystal C being pulled up and quickly cooling the single crystal C. be able to.
Moreover, in the case of the structure which has arrange | positioned the water cooling body 53 inside the radiation shield 51 so that it may show in figure, since the heat removal effect from a crystal | crystallization improves, pulling-up speed can be made quick.
Further, by providing the heat insulating material 54 on the shield inner surface, the radiant heat can be effectively shielded.

JP 2010-52982 A

By the way, in the configuration of FIG. 7, as shown in FIG. 8, a partially enlarged view of the radiation shield 51, the heat insulating material 54 inside the shield efficiently dissipates heat from the crystal outer peripheral surface. The thickness t ₁ at the shield lower end opening is formed thin.

However, in that case, since the heat shielding effect on the crystal outer peripheral surface in the vicinity of the solid-liquid interface becomes insufficient, the heat flux in the vicinity of the crystal outer periphery (the arrow shown in the melt M and the arrow shown in the single crystal C in FIG. 7). ) Is much larger than the center portion of the crystal, and there is a problem that the supercooled portion M1 is likely to occur in the melt near the periphery of the crystal.
In particular, in the configuration in which the water-cooled body 53 is arranged as shown in the drawing and a lateral magnetic field is applied from the side of the crucible, an eccentric flow (not shown) from the center to the outside is caused in the melt M. Therefore, as shown in FIG. 6, the supercooling part M <b> 1 is more easily formed around the crystal, and there is a problem that the single crystal to be grown is easily dislocated.

On the other hand, when the thickness t ₁ of the heat insulating material 54 at the shield opening is formed thick, heat from the outer peripheral surface of the crystal is difficult to be scattered, so that the crystal pulling speed cannot be increased, and the glow-in Another problem is that crystal defects such as defects are likely to occur.

  The present invention has been made under the circumstances as described above, and is a radiation shield of a single crystal pulling apparatus that pulls a silicon single crystal from a crucible by the Czochralski method, and has a single crystal pulling speed. An object of the present invention is to provide a radiation shield for a single crystal pulling apparatus that can improve the generation of crystal defects and suppress dislocations of crystals.

The radiation shield of the single crystal pulling apparatus according to the present invention, which has been made to solve the above problems, is a single crystal pulling method in which a seed crystal is brought into contact with a silicon melt in a crucible and the silicon single crystal is pulled up by the Czochralski method. In the upper device, the outer cylinder member is disposed above the crucible so as to surround the silicon single crystal to be pulled up, and has a predetermined thickness, and a heat insulating member provided inside the outer cylinder member A radiation shield comprising: a cylindrical straight body portion; a lower shoulder portion that curves inward from the lower end of the straight body portion and forms an opening at the lower end portion; and the diameter of a single crystal to be grown is Φ _{Assuming that cry} (mm), the thickness t ₁ of the lower end opening of the heat insulating member in the lower shoulder is defined by the equation (1), and the virtual surface in which the outer surface of the heat insulating member in the straight body is extended downward. Line and the lower shoulder That from the intersection of the horizontal plane including the lower end portion of the heat insulating member, when the sloping line of 45 ° to the horizontal plane drawn toward the lower shoulder, the thickness t ₂ of the heat insulating member at the intersection for the heat insulating member , Defined by the formula (2).
[Equation 1]
t ₁ = 0.1Φ _{cry to} 0.5Φ _cry Formula (1)
t ₂ ≦ 2t ₁ Formula (2)
The heat insulating member is preferably formed of a felt material made of carbon fiber.
In addition, it is desirable that the heat insulating member in the lower shoulder portion has an inner side surface formed in a parabolic cross section and an outer side surface formed in a circular arc shape.

With this configuration, there is no thickness t ₁ of the lower end opening of the heat insulating member in the lower shoulder is too thin, sufficient can heat shield to the crystal outer peripheral surface near the solid-liquid interface, The heat flux at the crystal periphery can be reduced. As a result, it is possible to suppress the occurrence of supercooling in the melt near the crystal periphery and to prevent dislocation of the crystal.
Further, since the thickness t ₂ of the insulating member under a shoulder portion is formed moderately thin, in the case of arranging the water-cooling structure in the radiation shield, it is possible to approximate the water-cooling structure to melt surface, the crystal center Can be effectively cooled.
That is, since the pulling speed of the crystal can be improved, the transit time of the defect precipitation temperature zone can be shortened, and the generation of defects can be suppressed.

  According to the present invention, a radiation shield of a single crystal pulling apparatus that pulls a silicon single crystal from a crucible by the Czochralski method, the single crystal pulling speed is improved to suppress the occurrence of crystal defects, and Thus, it is possible to obtain a radiation shield of a single crystal pulling apparatus that can suppress the dislocation of crystals.

FIG. 1 is a sectional view showing a partial configuration of a single crystal pulling apparatus in which a radiation shield according to the present invention is arranged. FIG. 2 is a partially enlarged cross-sectional view of the radiation shield provided in the single crystal pulling apparatus of FIG. FIG. 3A to FIG. 3F are partially enlarged cross-sectional views showing modifications of the radiation shield according to the present invention. 4 (a) to 4 (d) are partially enlarged cross-sectional views showing modifications of the radiation shield according to the present invention. FIG. 5 is a graph showing experimental results of Example 1 and Comparative Example 1. FIG. 6 is a schematic diagram for explaining the intersection angle θ (deg) with the magnetic field application direction. FIG. 7 is a sectional view showing a partial configuration of a single crystal pulling apparatus in which a conventional radiation shield is arranged. FIG. 8 is a partially enlarged cross-sectional view of the radiation shield provided in the single crystal pulling apparatus of FIG.

Hereinafter, embodiments of a radiation shield of a single crystal pulling apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing a partial configuration of a single crystal pulling apparatus in which a radiation shield according to the present invention is arranged.
This single crystal pulling apparatus 1 includes a crucible 2 provided in a furnace body (not shown), a heater 3 for melting a semiconductor material (raw material polysilicon) M loaded in the crucible 2, and a single unit to be grown. And a pulling mechanism 5 for pulling up the crystal C with the wire 4. The crucible 2 has a double structure, and is composed of a quartz glass crucible on the inside and a graphite crucible on the outside. A seed crystal P is attached to the tip of the wire 4.

  A radiation shield 6 according to the present invention is provided above and in the vicinity of the crucible 2. The radiation shield 6 has an upper portion and a lower portion formed so as to surround the periphery of the single crystal C, and shields extra radiant heat from the heater 3, the melt M, and the like on the growing single crystal C. Further, the radiation shield 6 is configured by an outer cylinder member 7 having a predetermined thickness being fixed to a furnace body (not shown) and a heat insulating member 8 being provided inside the outer cylinder portion 7. .

The outer cylinder member 7 is made of, for example, high-purity graphite or graphite whose surface is coated with SiC. Moreover, the said heat insulation member 8 is formed with the felt material which consists of carbon fibers, for example.
The distance dimension (gap) between the lower end of the radiation shield 6 and the melt surface is controlled so as to maintain a predetermined distance according to desired characteristics of the single crystal to be grown.

As shown in the partially enlarged sectional view of FIG. 2, the radiation shield 6 is formed at the upper end, and is fixed to a furnace body (not shown), and extends downward from the inner peripheral edge of the flange portion 6a. It consists of a cylindrical straight body 6b and a lower shoulder 6c that curves inward from the lower end of the straight body 6b and forms an opening at the lower end.
As for the heat insulation member 8 in the lower shoulder part 6c, the inner surface 6d is formed in the cross-sectional parabola shape, and the outer surface 6e is formed in the cross-section arc shape.
When the diameter of the single crystal C to be grown is Φ _cry (mm), the thickness dimension t ₁ of the heat insulating member 8 at the lower end opening of the radiation shield 6 is defined by Expression (1).

[Equation 2]
t ₁ = 0.1Φ _{cry to} 0.5Φ _cry Formula (1)
Also, from the intersection C between the imaginary line extending the outer surface of the heat insulating member 8 in the straight body portion 6b downward and the horizontal plane at the lower end of the heat insulating member 8 in the lower shoulder portion 6c, it is 45 ° to the horizontal plane. when the sloping line drawn towards the Shitakata portion 6c, the thickness t ₂ of the heat insulating member 8 at the intersection D with respect to the heat insulating member 8 is defined by equation (2). The thickness t ₂ is the length of the line perpendicular to the inner surface of the heat insulating member 8 through the intersection D.

[Equation 3]
t ₂ ≦ 2t ₁ Formula (2)
Further, the diameter Φ1 of the lower end opening of the radiation shield 6 is defined by Expression (3).
[Equation 4]
Φ _cry + 50mm ≧ Φ ₁ ≧ Φ _cry Formula (3)
Moreover, the straight body part inner diameter Φ2 of the radiation shield 6 is defined by the equation (4).
[Equation 5]
Φ ₂ = 1.5Φ _cry 〜3Φ _cry・ ・ ・ Formula (4)

  A cylindrical water-cooled body 9 is disposed inside the straight body portion 6b of the radiation shield 6 and above the lower shoulder portion 6c. The water cooling body 9 is configured to be supplied with cooling water by a cooling water supply means (not shown) and circulate to maintain a predetermined temperature.

According to the radiation shield 6 configured as described above, the thickness dimension t ₁ of the heat insulating member 8 at the lower end opening of the lower shoulder 6c is defined according to the equation (1). Thereby, the thickness t ₁ of the lower end opening is not too thin, and the heat can be sufficiently shielded from the crystal outer peripheral surface, and the heat flux at the crystal outer periphery can be reduced. As a result, it is possible to suppress the occurrence of supercooling in the melt near the crystal periphery and to prevent dislocation of the crystal.

Further, the thickness dimension t ₂ of the lower shoulder portion 6c is defined according to the formula (2), whereby the thickness dimension of the heat insulating member 8 in the lower shoulder portion 6c is formed to be appropriately thin. The crystal center can be effectively cooled.
That is, the crystal pulling speed can be improved, the transit time of the defect precipitation temperature zone can be shortened, and the generation of defects can be suppressed.

In the embodiment described above, the lower shoulder 6c (heat insulating member 8) of the radiation shield 6 has an inner side surface 6d formed in a parabolic section and an outer surface 6e formed in an arc shape in section. Showed things.
However, the radiation shield 6 according to the present invention is not limited thereto, and the above-described effects can be obtained as long as the shape satisfies the expressions (1) and (2).
For example, the shape may be any one of the modifications shown in FIGS. 3A to 3F and FIGS. 4A to 4D.

  The radiation shield of the single crystal pulling apparatus according to the present invention will be further described based on examples. In this example, single crystal pulling was performed using the radiation shield shown in the above embodiment.

Example 1
In Example 1, the temperature distribution of the melt immediately below the crystal periphery was measured. Specifically, the amount of silicon charged to the crucible is 370 kg, the diameter of the single crystal to be grown is 300 mm, the crystal length is 1700 mm, the magnetic field strength (magnetic flux density) is 3000 gauss, the magnetic field position is 0 mm, and the lower end of the crucible The gap between the melt and the melt surface was 20 mm.
The radiation shield used was a heat insulation member having a thickness t ₁ of 55 mm at the lower end opening and a heat insulation member thickness t ₂ of 60 mm at the center of the lower shoulder.

(Comparative Example 1)
In the comparative example 1, among the conditions of the example 1, the one having the thickness dimension t ₁ of 20 mm and the thickness dimension t ₂ of 100 mm was used.
FIG. 5 shows the results of Example 1 and Comparative Example 1 as a graph. In this graph, the horizontal axis represents the crossing angle θ (deg) with the magnetic field application direction, and the vertical axis represents the melt temperature (K). Note that the crossing angle θ (deg) with the magnetic field application direction is defined as an intersection line L where an arbitrary vertical section of the silicon melt M passing through the center of the crucible 2 and the silicon melt surface contact each other as shown in FIG. This is an angle formed in the counterclockwise direction with the application direction B as 0 degree.
As shown in FIG. 5, in Comparative Example 1, the result was lower than the silicon melting point (supercooling is likely to occur) regardless of the magnetic field application direction. However, in the configuration of the present invention, the melt temperature is the silicon melting point. It was confirmed that supercooling did not occur.

(Example 2)
In Example 2, the dislocation-free rate after the growth of the crystal length of 300 mm was obtained based on the number of 10 pulled up under the conditions of Example 1.
(Comparative Example 2)
In Comparative Example 2, under the conditions of Comparative Example 2, the dislocation-free rate after forming a 300 mm crystal length was determined based on the number of ten pulls.
Table 1 shows the results (dislocation-free rate) of Example 2 and Comparative Example 2.

表１に示すように、実施例２では、１０本中８本について無転位化を達成することができた。一方、比較例２では、１０本中１本のみを無転位のまま引き上げることが出来た。

As shown in Table 1, in Example 2, dislocation-free formation was achieved for 8 out of 10 pieces. On the other hand, in Comparative Example 2, only 1 out of 10 was able to be pulled up without dislocation.

(Example 3)
In Example 3, under the conditions of Example 1, the single crystal pulling speed when grown to a crystal length of 500 mm and the glow-in defect density in the crystal were measured.
(Comparative Example 3)
In Comparative Example 3, the single crystal pulling speed when grown to a crystal length of 500 mm under the conditions of Comparative Example 1 and the glow-in defect density in the crystal were measured.

  Table 2 shows the results (pulling speed, glow-in defect density) of Example 3 and Comparative Example 3. The pulling speed in the table is shown as a relative speed (ratio) with respect to the pulling speed in Comparative Example 3. The glow-in defect density indicates a ratio between the number of glow-in defects of 80 nm or more in the wafer surface in Example 3 and the number of defects in Comparative Example 3.

As shown in Table 2, in Example 3, the pulling speed could be improved by 30% compared to the conventional example. In addition, the glow-in defects could be reduced by 20% compared to the prior art.
From the results of the above examples, it was confirmed that according to the radiation shield of the present invention, the pulling speed of the single crystal can be improved, the generation of crystal defects can be suppressed, and the dislocation of the crystal can be suppressed.

DESCRIPTION OF SYMBOLS 1 Single crystal pulling apparatus 2 Crucible 3 Heater 4 Wire 5 Pulling mechanism 6 Radiation shield 6a Flange part 6b Straight trunk | drum 6c Lower shoulder part 7 Outer cylinder member 8 Heat insulation member 9 Water cooling member C Single crystal M Silicon melt P Seed crystal θ Crossing angle with magnetic field application direction

Claims (3)

In a single crystal pulling apparatus for bringing a seed crystal into contact with a silicon melt in a crucible and pulling the silicon single crystal by the Czochralski method, the seed crystal is disposed above the crucible so as to surround the silicon single crystal to be pulled, A radiation shield consisting of an outer cylinder member formed to a thickness of, and a heat insulating member provided inside the outer cylinder member,
A cylindrical straight body, and a lower shoulder that curves inward from the lower end of the straight body and forms an opening at the lower end;
When the diameter of the single crystal to be grown is Φ _cry (mm), the thickness dimension t ₁ of the lower end opening of the heat insulating member in the lower shoulder is defined by the equation (1),
An inclined line of 45 ° with respect to a horizontal plane is formed on the lower shoulder from the intersection of an imaginary line extending the outer surface of the heat insulating member in the straight body portion downward and a horizontal plane including the lower end of the heat insulating member in the lower shoulder. when drawn toward the part, the radiation shield of the thickness t ₂ of the heat insulating member at the intersection relative to the heat insulating member may be defined by equation (2) single crystal pulling apparatus.
[Equation 1]
t ₁ = 0.1Φ _{cry to} 0.5Φ _cry Formula (1)
t ₂ ≦ 2t ₁ Formula (2)   The radiation shield for a single crystal pulling apparatus according to claim 1, wherein the heat insulating member is formed of a felt material made of carbon fiber.   3. The single crystal pulling according to claim 1, wherein an inner surface of the heat insulating member in the lower shoulder portion is formed in a parabolic section and an outer surface is formed in an arc shape in cross section. Radiation shield for upper device.

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