JP4336600B2 - Seed crystal for pulling silicon single crystal and method for producing silicon single crystal using the same - Google Patents

Description

  The present invention relates to a seed crystal for pulling a silicon single crystal by the Czochralski method and a method for producing a silicon single crystal using this seeding.

  When a silicon single crystal is produced by the Czochralski method (CZ method), slip dislocations that occur at high density in the silicon seed crystal due to thermal shock when the silicon seed crystal is brought into contact with the silicon melt can reach the silicon single crystal ingot. Propagated. In order to eliminate this slip dislocation, the crystal is grown to a dislocation-free crystal having a diameter of about 3 mm (hereinafter referred to as “neck portion”), and then the shoulder is formed by expanding the crystal to a predetermined diameter. A so-called dash neck method for growing a single crystal having a constant diameter is employed.

  Recently, however, there has been a demand for pulling up a large-diameter silicon single crystal (12 inches) and lengthening the pulling single crystal, and it has been pointed out that the seed crystal by the conventional dash neck method has insufficient strength at the neck. Various countermeasures have been studied.

As a prior art corresponding to such a problem, there has been proposed a silicon single crystal growth method corresponding to an increase in the diameter and length of a single crystal by sharpening the tip of the seed crystal without using the dash neck method. This method sharpens the tip of the seed crystal to reduce the contact area with the melt and makes it difficult to form a thermal shock or a rapid temperature gradient of the seed crystal (Patent Document 1). In another prior art, the tip surface of the seed crystal in contact with the melt is processed so that the heat emissivity is 0.6 to 0.9, or is oxidized and a SiO ₂ film is formed on the tip. (Patent Document 2). In addition, as a seed crystal that eliminates slip dislocation without necking, there is a seed crystal in which the oxygen concentration in the seed crystal is 15 ppma or less and the tip is sharp or the sharp tip is cut off (Patent Document) 3). Furthermore, a seed crystal doped with nitrogen is known as a seed crystal that eliminates slip dislocation without performing necking (Patent Document 4). There is also known a prior art that reduces the occurrence of slip dislocation by doping a seed crystal with a high concentration of B (boron) (Patent Document 5).
Japanese Patent Laid-Open No. 10-203898 (Claims) JP-A-8-290994 (Claims) JP-A-11-292687 (Claims) JP 2000-128691 A (Claims) JP-A-4-139092 (Claims)

  Each of the above prior arts has the following problems. That is, in Patent Document 1, since the tip of the seed crystal is sharpened, the contact area with the melt is reduced, and the heat capacity of the tip is also reduced, so that the thermal shock or rapid temperature gradient of the seed crystal is less likely to be formed. There was a limit to the dislocation elimination. That is, even if the contact portion of the seed crystal with the melt is made small, the large temperature difference between the seed crystal and the melt has not yet been eliminated. The thermal stress generated upon contact exceeded the dislocation generation stress, and eventually dislocations were generated in the seed crystal.

  Further, the method of machining the surface of the seed crystal of Patent Document 2 to increase the heat emissivity of the surface cannot completely remove the surface distortion introduced by the processing, but rather dislocation due to thermal shock. It was easy to increase and it was difficult to obtain dislocation-free crystals. Neither the oxygen concentration range in the seed crystal of Patent Document 3 nor the nitrogen crystal doped in the seed crystal of Patent Document 4 can completely suppress the occurrence of dislocation due to thermal shock. When a seed crystal doped with a high concentration of boron is used, impurities such as boron that lower the resistivity of the single crystal to be grown are used, so it cannot be used for crystal growth other than low resistivity. There were such difficulties.

  Accordingly, the present invention provides a silicon single crystal without reducing the dislocation-free success rate by diffusing impurities such as boron or phosphorus or coating a carbon film on the tip of the silicon single crystal pulling seed crystal. An object of the present invention is to provide a large-diameter, high-weight seed crystal for pulling a silicon single crystal that can improve the productivity.

The present invention relates to a seed crystal used for pulling a silicon single crystal by the Czochralski method, wherein an impurity diffusion layer in which impurities are diffused is formed on the surface of the tip portion on the side in contact with the melt, and the impurity diffusion Ri inner layer extrinsic diffusion layer der layer, wherein the thickness of the impurity diffusion layer has a 5μm or more and the impurity concentration of the impurity diffusion layer is 1 × 10 ²⁰ atoms / cm ³ or more for pulling a silicon single crystal seed crystal to (claim wherein 1) said impurity for pulling a silicon single crystal seed crystal of claim 1 which is phosphorus or boron (claim 2) and claim 1 or 2 A method for producing a silicon single crystal, wherein the silicon single crystal is pulled using the seed crystal for pulling up a silicon single crystal described in ( 3 ).

By using the seed crystal of the present invention in which high concentration impurities are diffused on the surface, the diameter of the neck portion can be in the range of 5 to 10 mm even when pulling up a large silicon single crystal having a large diameter. Since the neck portion having a diameter that is significantly thicker than the diameter of the seed restricting portion of 3 mm can be formed, it is possible to prevent a drop to the melt due to breakage or the like. Further, according to this, it is possible to apply to crystal pulling of high resistance having a resistance of 1 Ω · cm or more . In other words, since the temperature difference with the silicon melt can be reduced, the thermal stress generated when contacting with the melt is easily smaller than the dislocation generation stress, and the dislocation density at the beginning of the neck is reduced to zero. can do.

The present invention is a silicon seed crystal used for pulling a silicon single crystal by the Czochralski method, and its characteristic configuration is to diffuse impurities such as boron and phosphorus in the tip of the silicon seed crystal . When the impurity diffusion layer is formed at the tip, boron is used for manufacturing the P-type semiconductor substrate, and phosphorus is used for manufacturing the N-type semiconductor substrate. As the seed crystal itself, a conventional silicon seed crystal is used as it is in any case.

In the case where impurities are diffused at the tip, boron or phosphorus with a high concentration of 1 × 10 ²⁰ atoms / cm ³ or more is diffused near the portion of the seed crystal in contact with the melt (measured by SIMS). . If the diffusion concentration of boron or phosphorus is less than 1 × 10 ²⁰ atoms / cm ³ , the thermal shock when the seed crystal comes into contact with the melt cannot be sufficiently relaxed, and it is sufficient that dislocation occurs in the seed crystal. Cannot be avoided. In the crystal growth using the seed crystal, misfit dislocations may occur when the crystal is grown from an impurity diffusion layer in which a high concentration of impurities is diffused. After the contact, the crystal growth is started after the impurity diffusion layer is completely dissolved, so that the occurrence of misfit dislocations can also be suppressed.

Although the impurity diffusion layer diffused a high concentration of impurities, the volume is expanded and softened as compared with the conventional non-diffusion layer. Therefore, when the tip is brought into contact with the melt, the impurity diffuses. It is considered that the surface portion that is easily affinized with the melt relaxes the thermal shock of the seed crystal, thereby avoiding the occurrence of dislocations in the seed crystal. As described above, the formation of such a surface layer is achieved by diffusing a high concentration impurity of 1 × 10 ²⁰ atoms / cm ³ or more into the tip surface portion of the seed crystal. As a method of diffusing impurities such as boron and phosphorus in the tip portion of the silicon seed crystal, a normal diffusion method is used as it is. That is, as shown in FIG. 2, for example, P ₂ O ₅ 31 is applied to the tip surface of a conventional silicon seed crystal 30 in the case of N-type semiconductor manufacture, and B ₂ O ₃ 32 is applied in the case of P-type semiconductor manufacture. Then, this is treated with an Ar gas at a temperature of 1300 ° C. for 20 hours to diffuse boron or phosphorus into the tip of the seed crystal. The thickness of the impurity diffusion layer obtained thereby is preferably at least 5 μm. If the thickness of the impurity diffusion layer is less than 5 μm, the thermal shock at the time of contact with the melt cannot be sufficiently mitigated. More preferably, it is 5 μm or more and 10 μm or less.

As described above, according to the present invention, since the impurity is diffused at the tip of the seed crystal and the impurity is formed as a diffusion layer, it is possible to suppress the occurrence of dislocation of the seed crystal when the silicon single crystal is pulled. There is no need to form a small seed drawing part having a diameter of 3 mm, and a silicon single crystal having a high success rate of dislocation can be grown even in a thick neck part having a diameter of 5 mm or more. Note that the shape of the seed crystal is generally a cylindrical shape or a square shape, and the present invention can be applied to this. Furthermore, as shown in FIG. 1, by making the tip of the seed crystal sharp, dislocations generated by thermal shock can be suppressed, and the success rate of dislocation-free crystals can be further improved.

  Examples (1-3) and comparative examples (1, 2) of the silicon single crystal pulling seed crystal in which impurities are diffused at the tip of the seed crystal will be described below. In these examples and comparative examples, the shape of the seed crystal used at the time of pulling, the state of the tip, the seed crystal diameter, the minimum diameter of the neck part at the time of neck formation, the target diameter of the pulled single crystal, the crystal straight body part And the dislocation-free rate of the straight body part are shown. Note that the dislocation-free rate here means that the straight body of the single crystal ingot pulled up under the above conditions is sliced with a wire saw and then etched with an acidic mixed chemical solution to completely remove crushed waste generated by the wire saw. This is the dislocation-free rate when evaluated by X-ray topography after removal.

Example 1
Seed crystal shape: Sharp pointed shape (cylindrical shape)
Tip: 1 × 10 ²¹ atoms / cm ³ diffusion (SIMS; secondary ion) on the surface of boron
Mass spectrometry) Impurity diffusion layer 10μm formation (SR method)
Seed crystal diameter: 20 mm diameter
Minimum neck diameter: 5 mm
Target diameter: 12 inches Crystal straight body length: 1.0m
No dislocation rate: 95%
(Example 2)
Seed crystal shape: Sharp pointed shape (cylindrical shape)
Tip: 1 × 10 ²¹ atoms / cm ³ diffusion (SIMS; secondary ion) on the surface of boron
Mass spectrometry) Impurity diffusion layer 10μm formation (SR method)
Seed crystal diameter: 20 mm diameter
Minimum neck diameter: 10 mm
Target diameter: 12 inches Crystal straight body length: 1.0m
No dislocation rate: 90%
(Example 3)
Seed crystal shape: Flat tip (cylindrical shape)
Tip: 1 × 10 ²¹ atoms / cm ³ diffusion (SIMS; secondary ion) on the surface of boron
Mass spectrometry) Impurity diffusion layer 10μm formation (SR method)
Seed crystal diameter: 20 mm diameter
Minimum neck diameter: 10 mm
Target diameter: 12 inches Crystal straight body length: 1.0m
Non-dislocation rate: 80%
(Comparative Example 1)
Seed crystal shape: Sharp pointed shape (cylindrical shape)
Tip: Seed crystal without impurity diffusion layer Seed crystal diameter: 20 mm diameter
Minimum neck diameter: 5 mm
Target diameter: 12 inches Crystal straight body length: 1.0m
Dislocation-free rate: 55%
(Comparative Example 2)
Seed crystal shape: Flat tip (cylindrical shape)
Tip: Seed crystal without impurity diffusion layer Seed crystal diameter: 20 mm diameter
Minimum neck diameter: 5 mm
Target diameter: 12 inches Crystal straight body length: 1.0m
Dislocation-free rate: 25%
The following is confirmed from the examples and comparative examples. When an impurity diffusion layer is not formed at the tip using a seed crystal with a flat tip (Comparative Example 2), the dislocation-free rate is as low as 25% when the minimum diameter of the neck is 5 mm. Even with a sharp shape (Comparative Example 1), the dislocation-free rate is improved only to 55%. However, even when a seed crystal having a flat tip is used, when high-concentration impurities are diffused in the tip (Example 3), the dislocation-free rate is obtained even when the minimum diameter of the neck is expanded to 10 mm. Improves to 80%. Further, when the tip portion has a sharp shape (Examples 1 and 2), a silicon single crystal having a high dislocation-free rate of 90% or more can be obtained even if the minimum diameter of the neck portion is 10 mm. As a result, it is possible to form a neck portion that can sufficiently maintain the utility even when the diameter is increased to 12 inches and the length is increased , and the dislocation-free rate is also improved.

BRIEF DESCRIPTION OF THE DRAWINGS It is explanatory drawing which showed a part of seed crystal of one Example of this invention typically, (A) showed the whole tip part of a seed crystal, (B) is boron of the tip part. Explanatory drawing which shows only spreading | diffusion . Explanatory drawing explaining the manufacturing method of the seed crystal which becomes one Example of this invention .

10, 30 ... silicon single crystal, 11, 12 ... diffusion layer, 31 ...... _P 2 _{O 5} coating, 32 ...... _B 2 _{O 3} coating.

Claims (3)

A seed crystal used for pulling a silicon single crystal by the Czochralski method, wherein an impurity diffusion layer in which impurities are diffused is formed on the surface of the tip portion on the side in contact with the melt, and the inner layer of the impurity diffusion layer is impurity Ri non-diffusing layer der, the thickness of the impurity diffusion layer is not less 5μm or more and the impurity concentration of the impurity diffusion layer, a silicon single, characterized in that it is 1 × 10 ²⁰ atoms / cm ³ or more Seed crystal for crystal pulling. The silicon single crystal pulling seed crystal according to claim 1, wherein the impurity is phosphorus or boron. A method for producing a silicon single crystal, wherein the silicon single crystal is pulled using the seed crystal for pulling a silicon single crystal according to claim 1 or 2 .

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