JPH09249495A - Seed crystal for pulling-up single crystal and pulling-up of single crystal using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heavyweight single crystal by using a silicon seed crystal with the oxygen concentration controlled within a specified range to effectively exclude introduction of dislocations in the beginning of single crystal formation and also exclude neck formation so as to prevent the single crystal being pulled-up from falling. SOLUTION: This seed crystal for pulling up a single crystal consists of silicon with an oxygen concentration of 12 to 18×10<17> /cm. In the pulling-up of signals crystal, the diameter (l) of the seed crystal 15 is set at >=6mm; after preheating its tip 15a, the seed crystal is dipped into a silicon melt 33, melted, and a shoulder 16b is formed without necking; subsequently, the main body is formed, and the resultant single crystal is pulled-up. In the above process, the length L of the tip 15a to be dipped into the melt 33 and to be melted is at least the diameter (l) of the seed crystal 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seed crystal for pulling a single crystal and a method for pulling a single crystal using the seed crystal. More specifically, it is used for growing a silicon single crystal used as a semiconductor material. The present invention relates to a seed crystal for pulling a single crystal and a single crystal pulling method using the seed crystal.

[0002]

2. Description of the Related Art There are various methods for growing a single crystal, one of which is a pulling method represented by the Czochralski method (hereinafter referred to as the CZ method). FIG. 5 shows a conventional C
It is sectional drawing which showed typically the principal part of the single crystal pulling apparatus used for Z method, and 31 in the figure shows the crucible.

The crucible 31 comprises a bottomed cylindrical quartz crucible 31a and a bottomed cylindrical graphite crucible 31b fitted to the outside of the quartz crucible 31a. 31 is supported by a support shaft 39 that rotates at a predetermined speed in the direction of the arrow in the figure. This crucible 3
On the outside of 1, a resistance heating type heater 32 and a heater 3
On the outside of 2, there is a heat insulating cylinder 4 for promoting heat transfer to the crucible 31.
2 are arranged concentrically, and the crucible 31 is filled with a melt 33 of the raw material for a single crystal, which is melted by the heater 32.

A pulling shaft 34 made of a pulling rod or a wire is hung on the central axis of the crucible 31, and a seed chuck 34 is provided at the tip of the pulling shaft 34.
The seed crystal 35 is attached via a.

In order to pull up the single crystal 36 by the above-mentioned single crystal pulling apparatus, first, the seed crystal 35 is immersed in the melt 33, and the seed crystal 35 is made to adapt to the melt 33,
Start pulling up (hereinafter referred to as a seeding step). After that, the seed crystal 35 is thinly drawn at a predetermined pulling speed until it has a predetermined diameter, and a neck 36a of the single crystal 36 is formed (hereinafter, referred to as a necking step). Thereafter, the pulling rate is reduced to grow the single crystal 36 to a predetermined diameter,
A shoulder 36b of the single crystal 36 is formed (hereinafter referred to as a shoulder forming step). After that, a single crystal 36 having a constant diameter and a predetermined length is grown at a constant pulling rate, and the single crystal 3
6 main body (constant diameter part) 36c is formed (hereinafter,
It is referred to as a body forming process).

Regarding the purpose of performing the above-mentioned necking step,
This will be described below. In performing the seeding step, the seed crystal bottom portion 35a is usually preheated to some extent and then applied to the melt 33, but the preheating temperature (about 1300 ° C. or lower) and the melting point of the seed crystal 35 (about 1410 ° C.) A difference of 100 ° C. or more occurs between them. Therefore, the melt 33
Upon landing on the seed crystal, dislocations due to thermal stress are introduced into the seed crystal bottom portion 35a. Since the dislocation inhibits the subsequent single crystallization, it is necessary to grow the single crystal 36 after eliminating the dislocation. Generally, the dislocations are single crystal 36
In the necking step, the growth interface is formed in a downward convex shape to eliminate the dislocations.

Generally, in the necking step,
The narrower the diameter of the neck 36a, the more downwardly convex the shape of the growth interface, and the more efficiently the dislocations can be eliminated.

[0008]

In the conventional method for pulling a single crystal described above, the diameter is about 6 inches and the weight is 80 inches.
12m in diameter to pull up the single crystal 36 of about kg
It was general to use a seed crystal 35 of about m. The diameter of the neck 36a at that time was usually set to about 2 to 3 mm so that the single crystal 36 can be pulled up safely and the dislocations can be efficiently eliminated. However, high integration of semiconductor devices in recent years,
In order to meet the demands for cost reduction and high productivity, it has been required to increase the diameter of the wafer. Recently, for example, it is desired to manufacture a single crystal 36 having a diameter of about 12 inches and a weight of about 300 kg. . In this case, with the conventional neck 36a diameter (usually about 3 mm), the neck 36a is not able to bear the weight of the pulled single crystal 36 and is damaged, and the single crystal 36 falls.

In growing the above-mentioned heavy single crystal 36, in order to prevent accidents such as dropping of the single crystal 36 and to safely pull up the single crystal 36, the silicon strength (about 16 kg) is required.
It is necessary to increase the diameter of the neck 36a to about 6 mm, calculated from f / mm ² ). However, the neck 36
When the a-diameter is reduced to this extent, the dislocation introduced at the time of landing the seed crystal 35 on the melt 33 cannot be sufficiently eliminated, and there is a problem that the yield is remarkably reduced.

The present invention has been made in view of the above problems, and a seed crystal for pulling a single crystal capable of efficiently eliminating dislocations even when pulling a heavy single crystal, and a necking. It is an object of the present invention to provide a method for pulling a single crystal using the seed crystal, which does not require a step, and can pull a large-weight single crystal safely and at low cost with good yield.

[0011]

In order to achieve the above object, the seed crystal (1) for pulling a single crystal according to the present invention has an oxygen concentration in the range of 13 to 18 × 10 ¹⁷ / cm ³ . It is characterized by being.

According to the seed crystal for pulling a single crystal (1), the oxygen concentration is in the range of 13 to 18 × 10 ¹⁷ / cm ³ , which is higher than the general oxygen concentration (11 × 10 ¹⁷ / cm ³ ). In addition, the stress level required for the dislocation introduced at the time of landing to propagate in the upper direction of the seed crystal can be made higher than usual. That is, since the dislocations do not propagate unless a stress higher than usual works, the dislocations can be propagated without propagating the dislocations by melting the portion where the dislocations are introduced at the time of landing in the melt at an appropriate speed. The introduced portion can be removed, and a single crystal based on a seed crystal without dislocation can be pulled up. Therefore, the dislocation-free rate of the pulled single crystal can be increased.

The seed crystal (2) for pulling a single crystal according to the present invention is characterized in that the seed crystal (1) for pulling a single crystal has a seed crystal diameter of 6 mm or more.

According to the seed crystal for pulling a single crystal (2), the same effect as that of the seed crystal for pulling a single crystal (1) can be obtained, and the seed crystal diameter is 6 mm or more. Even when pulling a large weight single crystal as described above, the seed crystal has a silicon strength (about 1%).
It has a sufficient strength calculated from 6 kgf / mm ² ), and there is no fear of accident such as dropping of the single crystal due to breakage of the seed crystal, and the single crystal can be pulled up safely.

In the method (1) for pulling a single crystal according to the present invention, either the seed crystal (1) or (2) is used, and the tip end portion of the seed crystal is immersed in a melt and melted. After that, the single crystal is pulled up without forming a neck.

According to the above single crystal pulling method (1),
When the tip of the seed crystal having dislocations introduced at the time of landing is once melted, the upward propagation of dislocations can be suppressed by oxygen. Therefore, based on seed crystals without dislocations,
The single crystal can be pulled up. As a result, since the dislocations hardly propagate to the pulled single crystal, the dislocation-free single crystal can be efficiently pulled up even if the necking step is omitted. Also,
Since the necking step can be omitted, there is no need to support the single crystal with a thin neck, and the seed crystal diameter is the smallest diameter for supporting the single crystal, and if the strength of the seed crystal is sufficiently considered, it will be large. Even a heavy single crystal can be safely pulled without fear of an accident such as dropping. Further, since it is not necessary to form the neck, the seed crystal can be thinned from about 12 mm in the past to about 6 mm, the raw material cost required for the seed crystal can be reduced, and the pulling process can be simplified. You can

Further, since any one of the seed crystals (1) and (2), that is, a seed crystal in which dislocations are not introduced, is used, dislocations are hardly introduced in the pulled single crystal,
The dislocation-free rate in a single crystal can also be improved. Therefore, the yield of the pulled single crystal can be improved.

The single crystal pulling method (2) according to the present invention is the same as the single crystal pulling method (1).
The feature is that the length of the seed crystal to be melted is 6 mm or more.

According to the single crystal pulling method (2), since the length of the seed crystal to be melted is 6 mm or more, most of the dislocation portion where dislocation is introduced by heat shock (the portion where the dislocation exists) is melted. And the rest can be a seed crystal consisting only of dislocation-free portions. Therefore, the yield of the pulled single crystal can be further improved.

On the other hand, when the length of the seed crystal to be melted is shorter than 6 mm, the dislocations may remain, which hinders the subsequent single crystallization.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a seed crystal for pulling a single crystal and a method for pulling a single crystal using the seed crystal according to the present invention will be described below with reference to the drawings. In addition, the same reference numerals are given to the components having the same functions as the conventional ones.

<Embodiment> FIGS. 1A to 1D are schematic views showing a seed crystal for pulling a single crystal and a single crystal pulling method using the seed crystal according to the embodiment in the order of steps. FIG. 2 is a partial side view, and FIG. 2 is a schematic cross-sectional view showing a state in which a single crystal is pulled by the single crystal pulling method according to the embodiment.

First, the seed crystal 15 having a diameter (l) of 6 mm or more is lowered to just above the melt 33 to form the seed crystal 1.
5 is preheated (FIG. 1 (a)). The oxygen concentration of the seed crystal 15 is set in the range of 13 to 18 × 10 ¹⁷ / cm ³ . Then, the seed crystal 15 is allowed to land on the surface of the melt 33 (FIG. 1 (b)). At this time, the tip portion 15a of the seed crystal 15
From above, dislocations (not shown) are introduced toward the upper part of the seed crystal 15 by the thermal stress acting at the time of landing. Thereafter, the seed crystal 15 is lowered at a predetermined speed, and the tip portion 15a (the portion where dislocations are introduced) of the seed crystal 15 is melted into the melt 33.
Immerse in and melt. The melting length (L) is 6
mm or more (FIG. 1 (c)). Thus, seed crystal 1
By melting the tip portion 15a of No. 5 into the seed crystal 15
The remaining portion of the can be a dislocation-free portion only.
After that, the necking process which has been performed conventionally is omitted and the process proceeds to the shoulder forming process, where the single crystal 16 is grown to a predetermined diameter by pulling at a predetermined pulling rate to form a shoulder 16b (FIG. 1 (d)). ). After that, the process moves to the body forming step to form the main body 16c (FIG. 2).

Generally, the relationship shown in FIG. 3 is established between the stress acting on the seed crystal 15 and the speed at which the dislocation introduced into the seed crystal 15 propagates due to the stress.

In FIG. 3, the vertical axis represents the dislocation propagation velocity (v), and the horizontal axis represents the stress (σ) acting on the seed crystal.

The seed crystal has a general oxygen concentration (11 × 10 ¹⁷
/ Cm ³ ), the graph A shows that when the oxygen concentration in the seed crystal 15 is 13 × 10 ¹⁷ / cm ³ , the graph B shows that the oxygen concentration is 18 × 10 ¹⁷ / cm ^3.
If, then graph C is obtained.

That is, when the seed crystal has a general oxygen concentration (graph A), dislocation propagates when a stress of σ ₁ or more acts (the propagation speed of dislocation becomes 0 or more). On the other hand, in the case of having an oxygen concentration of 13 × 10 ¹⁷ / cm ³ (graph B), the dislocations do not propagate and 18 × 10 ¹⁷ / cm 3 unless the stress of σ ₂ acts. ³
When it has the oxygen concentration of (graph C),
The dislocations do not propagate unless the stress of σ ₃ works. Here, the magnitude of stress is σ ₁ <σ ₂ <σ ₃ . Thus, the higher the oxygen concentration, the more the propagation of the dislocation can be suppressed.

According to the seed crystal 15 for pulling a single crystal as described above, the oxygen concentration is in the range of 13 to 18 × 10 ¹⁷ / cm ³ , which is higher than the general oxygen concentration (11 × 10 ¹⁷ / cm ³ ). Therefore, the dislocation introduced at the time of landing is caused by the seed crystal 1
The stress level required to propagate in the upper direction of 5 can be increased more than usual. That is, seed crystal 1
The dislocations will not propagate unless a higher level of stress is applied to No. 5. Therefore, by dissolving the portion (the tip portion 15a) into which the dislocation is introduced at the time of landing in the melt at a predetermined speed, the dislocation is not propagated,
The dislocation-introduced portion (tip portion 15a) can be removed, and the single crystal can be pulled up based on the seed crystal having no dislocation. Therefore, the dislocation-free rate of the pulled single crystal can be increased.

Since the seed crystal diameter (l) is 6 mm or more, the seed crystal 15 is calculated from the silicon strength (about 16 kgf / mm ² ) even when pulling a large weight single crystal 16 of about 300 kg, for example. Therefore, the single crystal 16 can be pulled up safely without fear of accident such as dropping of the single crystal 16 due to breakage of the seed crystal 15.

Further, according to the single crystal pulling method using the seed crystal 15 described above, since the single crystal 16 can be pulled up based on the seed crystal 15 consisting of only dislocation-free portions, the single crystal to be pulled up No dislocations are introduced into 16 and the necking step can be omitted. Further, since the necking step is unnecessary, it is not necessary to support the single crystal 16 by the thin neck 36a (FIG. 5), and the seed crystal diameter (l) is the single crystal 16.
The diameter of the single crystal 16 is the smallest for supporting, and even if the single crystal 16 has a large weight, it can be safely pulled up without fear of an accident such as dropping. Further, since it is not necessary to form the neck 36a, the seed crystal 15 has a conventional diameter of 12 mm.
It can be reduced from about 6 mm to about 6 mm, and the raw material cost required for the seed crystal can be reduced.

Further, by setting the length (L) of the seed crystal 15 to be melted to 6 mm or more, the portion where dislocations are introduced can be almost melted and the rest is the seed crystal 15 which is composed of only dislocation-free portions. can do. The yield of the single crystal 16 can be improved by pulling the single crystal 16 using the seed crystal 15 consisting of only the dislocation-free portion.

[0032]

[Examples and Comparative Examples] The single crystals are pulled by the seed crystals for pulling single crystals according to the examples and comparative examples and the single crystal pulling method using the seed crystals, and DF (Dis
The results of examining the location free rate will be described. In each of the examples and comparative examples, a single crystal having a diameter of about 12 inches and a length of about 1000 mm and a total weight of about 300 kg was pulled 10 times. The DF ratio was shown by the ratio of the number of single crystals in which dislocations did not occur at all out of 10 single crystals pulled under the same conditions. The presence or absence of the dislocation can be determined by external observation, but this time, it was determined by observing the sliced single crystal with an X-ray topography.

FIGS. 4 (a) and 4 (b) are schematic enlarged left side views showing the single crystal pulling methods according to Examples 1 to 5 and Comparative Examples 1 to 4. The growth conditions common to the pulling of each single crystal are shown in Table 1 below.

[0034]

[Table 1]

<Example 1> In Example 1, the single crystal 16 was pulled in the following manner by the method shown in FIGS. 1, 2 and 4 (a) and the conditions shown in Table 1. The oxygen concentration of the seed crystal 15 is 13 × 10 ¹⁷ / cm ³ .

First, the seed crystal 15 having a diameter of about 10 mm is lowered to just above the melt 33 to preheat the seed crystal 15,
After that, the seed crystal 15 is allowed to land on the surface of the melt 33,
The seed crystal 15 is made to adapt to the melt 33. After this, 0.2
The seed crystal 15 is lowered at a speed of mm / min, and the seed crystal 1
The tip portion 15a of No. 5 is immersed in the melt 33 to form the seed crystal 15
About 20 mm is melted from the tip portion 15a of the. After this, the seed crystal 15 was pulled at a pulling rate of about 0.3 mm / min.
By pulling up and adjusting the temperature of the heater 32, the single crystal 1 is moved within 100 mm below the seed crystal bottom surface 15a.
6 shoulders 16b were formed and grown to a diameter of 12 inches. Then, at a pulling speed of about 0.5 mm / min, the main body 16c with a diameter of 12 inches is
It was grown to a length of about 1000 mm.

The DF ratio of the single crystal 16 produced by the method according to Example 1 was 7/10. That is, no dislocation was observed in 7 of the 10 pulled up. Moreover, the number of drops of the single crystal 16 is 0/1.
It was 0, and the single crystal 16 did not drop.

<Example 2> In Example 2, the oxygen concentration was 1
The seed crystal 15 of 6 × 10 ¹⁷ / cm ³ was used, and other conditions and methods were the same as in the case of Example 1.

The DF ratio of the single crystal 16 produced by the method according to Example 2 was 8/10. That is, generation of dislocations was not confirmed at all in 8 of the 10 pulled up. Moreover, the number of drops of the single crystal 16 is 0/1.
It was 0, and the single crystal 16 did not drop.

<Third Embodiment> In the third embodiment, the oxygen concentration is 1
The seed crystal 15 of 8 × 10 ¹⁷ / cm ³ was used, and other conditions and methods were the same as in the case of Example 1.

The DF ratio of the single crystal 16 produced by the method according to Example 3 was 9/10. That is, no dislocation was observed in 9 out of 10 pulled up. Moreover, the number of drops of the single crystal 16 is 0/1.
It was 0, and the single crystal 16 did not drop.

<Example 4> In Example 4, the diameter is about 6 mm.
Seed crystal 15 of Example 1 was used, and other conditions and methods were the same as in the case of Example 1. The oxygen concentration of the seed crystal 15 is 13 × 10 ¹⁷ / cm ³ as in the case of Example 1.

The DF ratio of the single crystal 16 produced by the method according to Example 4 was 7/10. That is, no dislocation was observed in 7 of the 10 pulled up. Moreover, the number of drops of the single crystal 16 is 0/1.
It was 0, and the single crystal 16 did not drop.

<Embodiment 5> In Embodiment 5, the diameter is about 6 mm.
Seed crystal 15 of Example 1 was used, and other conditions and methods were the same as in the case of Example 1. The oxygen concentration of the seed crystal 15 is 16 × 10 ¹⁷ / cm ³ as in the case of Example 2.

The DF ratio of the single crystal 16 produced by the method according to Example 5 was 8/10. That is, generation of dislocations was not confirmed at all in 8 of the 10 pulled up. Moreover, the number of drops of the single crystal 16 is 0/1.
It was 0, and the single crystal 16 did not drop.

Comparative Example 1 In Comparative Example 1, the single crystal 26 was pulled by the method shown in FIGS. 1, 2 and 4 (a) and the conditions shown in Table 1. The method of pulling the single crystal 26 is the same as that of the first embodiment except the oxygen concentration of the seed crystal 25, and the description thereof is omitted here. The oxygen concentration of the seed crystal 25 is 11 × 10 ¹⁷ / c.
It was m ^3.

The DF ratio of the single crystal 26 produced by the method according to Comparative Example 1 was 6/10. That is, generation of dislocations was not confirmed at all in 6 out of 10 pulled up. In addition, the number of drops of the single crystal 26 is 0/1
It was 0, and the single crystal 26 did not drop.

Comparative Example 2 In Comparative Example 2, the single crystal 46 was pulled up after the neck 46a having a diameter of 10 mm was formed by the method shown in FIGS. 4B and 5 and the conditions shown in Table 1. . The oxygen concentration of the seed crystal 45 was set to 16 × 10 ¹⁷ / cm ³ as in the case of Example 2. Further, the oxygen concentration of the pulled single crystal 46 is 11 × 10 as usual.
^{It was set to 17} / cm ³ .

First, the seed crystal 45 having a diameter of 12 mm is lowered to just above the melt 33 to preheat the seed crystal 45, and then the seed crystal 45 is allowed to come in contact with the surface of the melt 33 to melt the seed crystal 45. Apply to liquid 33. After this, about 4 mm /
Seed crystal 45 while adjusting the temperature of heater 32 at the speed of minutes
Is pulled up to form a neck 46a having a diameter of about 10 mm and a length of about 100 mm. Next, the seed crystal 45 is pulled up at a pulling rate of 0.3 mm / min, and the temperature of the heater 32 is adjusted, so that the lower portion of the neck 46a is lowered by 10
A shoulder 46b of the single crystal 46 was formed in the range of 0 mm and grown until the diameter became 12 inches. Thereafter, at a pulling rate of 0.5 mm / min, a main body 46c having a diameter of 12 inches was grown to a length of 1000 mm.

The DF ratio of the single crystal 46 produced by the method according to Comparative Example 2 was 0/10. That is, generation of dislocations was confirmed in all the pulled single crystals 46. On the other hand, the number of drops of the single crystal 46 was 0/10, and the single crystal 46 did not drop.

Comparative Example 3 In Comparative Example 3, the single crystal 46 was pulled up after forming the neck 46a having a diameter of 6 mm.
Other conditions and methods were the same as those in Comparative Example 2.

The DF ratio of the single crystal 46 produced by the method according to Comparative Example 3 was 1/10. That is, generation of dislocations was confirmed in 9 out of 10 pulled up. Further, the number of drops of the single crystal 16 is 0/10,
The single crystal 16 did not drop.

<Comparative Example 4> In Comparative Example 4, the diameter is about 4 mm.
After forming the neck 46a, the single crystal 46 was pulled up. Other conditions and methods were the same as those in Comparative Example 2.

The DF ratio of the single crystal 46 produced by the method according to Comparative Example 4 was 9/10. That is, no dislocation was observed in 9 out of 10 pulled up. The number of single crystals 46 dropped is 8/1.
It was 0, and the single crystal 46 dropped in the middle of pulling out 8 of the 10 pulling.

As is clear from the above results, Example 1
According to the seed crystal 15 according to 3 to 3, the oxygen concentration is 1
3 × 10 ¹⁷ / cm ³ , 16 × 10 ¹⁷ / cm ³ , 18 × 1
0 ¹⁷ / cm ³ , which is higher than the general oxygen concentration (11 × 10 ¹⁷ / cm ³ ) in any case, whereby the dislocation introduced at the time of landing propagates in the upper direction of the seed crystal 15. The stress level required to do so could be higher than normal. That is, since the dislocation does not propagate unless a stress higher than usual works, the dislocation is propagated by melting the portion where the dislocation is introduced (the tip portion 15a) at the time of landing in the melt at an appropriate speed. It was possible to remove the dislocation-introduced portion (the tip portion 15a) without removing the single crystal based on the dislocation-free seed crystal. Therefore, the dislocation-free rate of the pulled single crystal could be increased.

Further, according to the method of pulling the single crystal 16 according to Examples 1 to 3, since the necking step is not necessary, it is not necessary to support the single crystal 16 by the thin neck 36a (FIG. 5). , Seed crystal diameter (10m
m) is the smallest diameter for supporting the single crystal 16, and even a large weight (300 kg) of the single crystal 16 could be safely pulled up without fear of accident such as dropping.

According to the seed crystals 15 of Examples 4 and 5, the oxygen concentrations were 13 × 10 ¹⁷ / cm ³ and 16 respectively.
Since the seed crystal diameter is 1 × 10 ¹⁷ / cm ³ and the seed crystal diameter (l) is 6 mm, the seed crystal 15 has sufficient strength even when a large weight of the single crystal 16 of about 300 kg is pulled. There was little concern about accidents such as the single crystal 16 dropping due to breakage of the crystal 15, and the single crystal 16 could be pulled up safely. Further, the seed crystal 15 has been reduced from about 12 mm in the past to about 6 mm, and thus has a volume of about 1/4.
Thus, the raw material cost required for the seed crystal 15 could be reduced.

Further, according to the pulling method of the single crystal 16 according to Examples 1 to 5, the seed crystal 15 (15A) to be melted is used.
Since the length (L) was 6 mm or more and 20 mm, most of the portion where dislocations were introduced could be melted, and the rest could be seed crystal 15 (15A) consisting of only dislocation-free portions. Further, the yield of the single crystal 16 (16A) could be improved by pulling the single crystal 16 (16A) using the seed crystal 15 (15A) consisting of only the dislocation-free portion.

On the other hand, according to the seed crystal 25 of Comparative Example 1, the oxygen concentration was 11 × 10 ¹⁷ / cm ^3, which was about the conventional level, and therefore the product yield was lower than that of Examples 1 to 3.

Further, according to the pulling method of the single crystal 46 according to the comparative example 2, although the oxygen concentration of the seed crystal 45 is set to be the same as that of the example 2 (16 × 10 ¹⁷ / cm ³ ), Dislocations occurred in all the pulled single crystals 46. This is considered to be due to the following reasons. First, the seed crystal 45 has a high oxygen concentration (16 × 10 ¹⁷ / cm ³ ).
, The neck 46 having a normal oxygen concentration (11 × 10 ¹⁷ / cm ³ ) is directly provided from the tip 15a without the step of melting the tip 15a in which dislocations are introduced.
Since a was formed, even if the dislocation propagation to the seed crystal 45 could be prevented, the dislocation propagation to the neck 46a could not be prevented. Also, the diameter of the neck 46a is 10
Since it is as large as mm, the propagated dislocations could not be completely removed by this degree of reduction. On the other hand, since the diameter of the neck 46a was as large as 10 mm, the single crystal 46 did not drop, and safe pulling could be performed.

According to the method of pulling up the single crystal 46 according to Comparative Example 3, the diameter of the neck 46a was reduced to 6 mm, so that the DF ratio was slightly improved as compared with the case of Comparative Example 2. Had a high probability of dislocations, and the product yield was low. It is considered that this is because even if the diameter of the neck 46a was set to 6 mm, the propagated dislocations could not be completely removed by the reduction of this extent. On the other hand,
Since the diameter of the neck 46a is about 6 mm, the single crystal 46
It was possible to carry out a safe pulling up without causing a drop.

Further, according to the pulling method of the single crystal 46 according to the comparative example 4, since the diameter of the neck 46a is narrowed down to about 4 mm, the dislocation propagated can be removed, and the DF
The rate was able to be improved significantly. However, 4m
With a diameter of about m, the strength of the neck 46a was not sufficient, and the single crystal 46 dropped with a high probability.

[Brief description of drawings]

1A to 1D are schematic partial side views showing a single crystal pulling method according to an embodiment of the present invention in the order of steps.

FIG. 2 shows a method of pulling a single crystal according to an embodiment.
It is a typical sectional view showing the state where a single crystal is pulled up.

FIG. 3 is a graph showing the relationship between the stress acting on the seed crystal and the speed at which dislocations existing in the seed crystal propagate due to the stress.

4 (a) and (b) are schematic diagrams shown for explaining a seed crystal and a single crystal pulling method using the seed crystal according to Example, Comparative Example 1 and Comparative Example 2. It is a partially expanded side view.

FIG. 5 is a schematic cross-sectional view showing a main part of a single crystal pulling apparatus used in the CZ method.

[Explanation of symbols]

 15, 25, 35, 45 Seed crystal (for pulling single crystal) 15a, 25a, 35a, 45a (Seed crystal) tip portion 16, 26, 36, 46 Single crystal

Claims (4)

[Claims] 1. An oxygen concentration of 13 to 18 × 10 ¹⁷ / cm ³
A seed crystal for pulling a single crystal, characterized in that 2. The seed crystal for pulling a single crystal according to claim 1, wherein the seed crystal has a diameter of 6 mm or more. 3. The seed crystal according to claim 1 is used, and a single crystal is formed without forming a neck after the tip portion of the seed crystal is immersed in a melt and melted. A method for pulling a single crystal, which comprises pulling. 4. The method for pulling a single crystal according to claim 3, wherein the length of the seed crystal to be melted is 6 mm or more.