JPH11349398A - Production of silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the proliferation of dislocation and improve the success ratio of the production of dislocation free crystal and to improve the productivity and yield of a single crystal rod having large diameter and heavy weight by adjusting the interstitial oxygen concentration taken into the crystal during necking operation at or above a specific level. SOLUTION: The proliferation of dislocation can be controlled and a success ratio of the production of dislocation free crystal can be maintained to >=95% by keeping the oxygen concentration to >=1 ppma (JEIDA) during the necking procedure. The effect is especially remarkable at the construction diameter of >=5 mm. The oxygen concentration is higher the better and a dislocation free crystal can be produced even in the case of forming a thick constricted part having a diameter of >=5 mm when the oxygen concentration is >=5 ppma. The increase in the interstitial oxygen concentration in the constricting part and a constricted part during the necking operation can be achieved e.g. by inserting a rod, plate, block, etc., of an oxygen-source substance (e.g. quartz) in molten silicon near the center of the crucible during the seed constriction process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon single crystal in which necking is performed using a seed crystal by a Czochralski method (CZ method) to grow a silicon single crystal rod.

[0002]

2. Description of the Related Art Conventionally, in the production of a silicon single crystal by the CZ method, a single crystal silicon is used as a seed crystal, which is brought into contact with a silicon melt and then slowly pulled up while being rotated to thereby obtain a single crystal rod. Growing. At this time, after contacting the seed crystal with the silicon melt, in order to eliminate dislocations caused by propagation from slip dislocations generated at high density in the seed crystal due to thermal shock, a tapered narrowing portion for narrowing the seed crystal and Next, a so-called seed drawing (necking) for forming a drawn portion (neck) whose diameter is once reduced to about 3 mm is performed, and then the crystal is thickened to a desired diameter to pull up a dislocation-free silicon single crystal. . Such seed squeezing is performed by Dash Necking.
It is widely known as a method, and is a common sense when pulling a silicon single crystal rod by the CZ method.

That is, the shape of a seed crystal that has been conventionally used is, for example, a cylindrical or prismatic single crystal having a diameter or a side of about 8 to 20 mm provided with a cutout for setting the seed crystal in a seed holder. The shape of the lower end that first contacts the silicon melt is a flat surface. And in order to withstand the weight of a heavy single crystal rod and safely raise it,
It is difficult to make the thickness of the seed crystal smaller than the above due to the strength of the material.

[0004] In the seed crystal having such a shape, since the heat capacity of the tip in contact with the melt is large, a sudden temperature difference occurs in the crystal at the moment when the seed crystal comes into contact with the melt, and slip dislocations are generated at a high density. To be generated. Therefore, necking is required to eliminate the dislocation and grow a single crystal.

However, in such a state, even if various necking conditions are selected, in order to eliminate dislocations, it is necessary to narrow down at least the minimum diameter to about 3 to 5 mm. With the increase in diameter, the strength is not enough to support the heavier single-crystal rod, and during pulling of the single-crystal rod, this narrow narrowed part breaks and the single-crystal rod falls. An accident could occur.

In order to solve such a problem, the present applicant has previously disclosed Japanese Patent Application Laid-Open No. 5-139880 and Japanese Patent Application No. 8-871.
No. 87 was proposed. In these inventions, the tip of the seed crystal has a wedge shape or a shape having a hollow portion, and the slip dislocation entering when the seed crystal comes into contact with the silicon melt is reduced as much as possible, so that the diameter of the drawn portion is relatively large. Even so, dislocations can be eliminated, thereby improving the strength of the constricted portion.

According to this method, the thickness of the constricted portion can be increased, so that the strength of the constricted portion can be improved to some extent. However, there is no change in forming a constricted portion with necking. In recent years, the strength of pulling a single crystal rod having a larger diameter and a longer length, for example, 150 kg or more may be insufficient, and a fundamental solution has not been reached.

What is problematic in the necking seeding method using a seed having a special shape at the tip is the success rate of dislocation-free. That is, in these methods, once the dislocation-free crystal has failed, the process cannot be performed again without exchanging the seed crystal. Therefore, it is particularly important to improve the success rate. It is not possible to eliminate dislocation even if the thickness of necking is simply increased. In the conventional necking, when the diameter is 6 to 7 mm or more, the probability of dislocation removal becomes extremely low. Here, the dislocation-free success rate is a value expressed as a percentage of the number of silicon single crystals in which no dislocation has occurred with respect to the number of pulled silicon single crystals.

In this case, the cause of the decrease in the dislocation-free success rate has been investigated and investigated. Only the factors which have conventionally been controlled, such as the shape of the seed crystal, the heat retention time in the vicinity of the molten metal surface, and the melting speed, have been investigated. It was not always sufficient, the success rate was not always high, and sufficient reproducibility was not obtained.

[0010]

Accordingly, the present invention has been made in view of such a conventional problem, and in the case of a seeding method for necking, the growth of dislocations is suppressed, and the success rate of dislocation-free is reduced. It is a main object of the present invention to provide a method for producing a silicon single crystal capable of improving the productivity and yield of a single crystal rod having a large diameter and a high weight while improving the productivity.

[0011]

In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention is based on a seeding method in which a seed crystal is brought into contact with a melt by a Czochralski method and then necking is performed. A method for producing a silicon single crystal for growing a single crystal rod, wherein the concentration of interstitial oxygen taken in during necking is 1 ppma (JEIDA) or more.

When the concentration of oxygen taken in during necking is increased in this manner, the movement speed of dislocations in the narrowed portion of the seed crystal and the narrowed portion is reduced by oxygen atoms, and the growth of dislocations can be reliably suppressed. As a result, the dislocation-free success rate is improved, and productivity and yield can be significantly improved.

In this case, it is desirable to insert quartz into the silicon melt during necking in order to increase the interstitial oxygen concentration during necking. Thus, for example, when a quartz rod or plate is inserted near the center of the silicon melt during necking, quartz becomes a supply source of oxygen, so the oxygen concentration around the narrowed portion of the seed crystal and the narrowed portion increases. In addition, oxygen can be easily taken into the narrowing portion or the narrowing portion.

In the invention according to claim 3 of the present invention, in order to increase the interstitial oxygen concentration during the necking, it is desirable that the crucible rotate at a high speed during the necking. When the rotation of the crucible is increased in this manner, the amount of oxygen dissolved into the silicon melt from the inner wall of the quartz crucible increases, and the oxygen concentration in the melt increases. As a result, oxygen is easily taken in the narrowed portion or the narrowed portion.

Further, in the Czochralski method in which a magnetic field is applied, a method in which a magnetic field is not applied to the silicon melt during necking in order to increase the interstitial oxygen concentration during necking. Is preferred. By doing so, the convection of the silicon melt that was forcibly suppressed by applying a magnetic field is released,
Due to convection, the oxygen concentration around the narrowed part and the narrowed part of the seed crystal rises, and oxygen is easily taken in the narrowed part and the narrowed part. Suppressed, the dislocation-free success rate of the grown single crystal is improved, and productivity and yield can be significantly improved.

In the invention described in claim 5 of the present invention, it is preferable that the diameter of the drawn portion during the necking is 5 mm or more. According to the present invention, dislocation multiplication can be reliably suppressed by increasing the oxygen concentration during necking, and thus a dislocation-free single crystal can be easily produced. Therefore, its application range is particularly effective in the case of a large drawing having a drawing portion diameter of 5 mm or more, and the reproducibility of dislocation-free is extremely high, and the productivity and yield of silicon single crystal can be increased in response to the increase in diameter and weight. It greatly contributes to the improvement of

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, a configuration example of a single crystal pulling apparatus used in the present invention will be described with reference to FIG. As shown in FIG.
Is a crucible 7 and a heater 9 arranged around the crucible 7.
A crucible rotating shaft 8 for rotating the crucible 7 and a rotating mechanism thereof (not shown); a seed chuck 4 for holding the silicon seed crystal 1; a wire 5 for pulling up the seed chuck 4; It is provided with a winding mechanism (not shown) for winding. The crucible 7 is provided with a quartz crucible on the side where the silicon melt (hot water) 6 is accommodated, and a graphite crucible on the outside thereof.

Next, the method of necking and growing a single crystal of the present invention using the single crystal pulling apparatus 20 will be described. First, a high-purity polycrystalline silicon raw material is heated in a crucible 7 to a melting point (about 1420 ° C.) or higher to be melted. Next, the quartz rod 10 is immersed in the silicon melt 6 in the vicinity of the single crystal pulling position. Next, by unwinding the wire 5, the tip of the seed crystal 1 is brought into contact with or immersed substantially in the center of the surface of the melt 6. Thereafter, the crucible rotating shaft 8 is rotated in an appropriate direction, the wire 5 is wound while being rotated, the seed crystal 1 is pulled up, the necking operation is started, and the narrowed portion 2 is formed until a predetermined diameter is obtained. After growing the drawing portion 3 to a desired length while maintaining the diameter, a cone portion is formed, and the growth of a single crystal having a desired diameter is started.
Thereafter, by appropriately adjusting the pulling speed and the temperature, a substantially cylindrical single crystal rod (not shown) can be obtained.
When the necking operation is completed, it is desirable that the quartz rod 10 be pulled up from the silicon melt 6 and returned to the normal single crystal growth condition.

Another method of dipping quartz in a silicon melt during seeding for necking is to float a quartz disk on the surface of the melt. This method uses the seed holder 30 shown in FIG.
Use The seed holder 30 is composed of a seed chuck 4 that holds the silicon seed crystal 1 and has a flange-shaped slide plate 32, and an annular quartz disk 31 having a support rod 33 set up on the outer periphery. The seed chuck 4 is vertically movable by a slide plate 32 along the support rod 33, and the upper limit is stopped by a stopper 34 at the upper end of the support rod 33. The seed chuck 4 and the wire 5 for pulling up the quartz disk 31 are connected to a winding mechanism (not shown) for rotating or winding the wire 5.

The necking and single crystal growing method of the present invention using the seed holder 30 will be described in the order of FIGS. 2 (a), 2 (b) and 2 (c). First, a high-purity polycrystalline silicon material is heated and melted in a crucible (not shown) above the melting point (about 1420 ° C.). Next, the seed holder 30 is lowered in a state where the slide plate 32 of the seed chuck 4 is stopped by the upper stopper 34, and the quartz disk 31 is melted.
Contact and float on the surface. Further, the wire 5 is drawn out, the slide plate 32 is slid, the seed chuck 4 is lowered, and the tip of the seed crystal 1 is brought into contact with or immersed substantially in the center of the surface of the melt 6 (see FIG. 2A). Thereafter, the crucible is rotated in an appropriate direction, and the wire 5 is wound while being rotated, the seed crystal 1 is pulled up, the necking operation is started, the narrowed portion 2 is formed to a predetermined diameter, and the predetermined diameter is maintained. Then, the narrowed portion 3 is grown to a desired length [see FIG. 2B]. During this time, the quartz disk 31 is always in contact with the silicon melt 6. After that, the slide plate 32 of the seed chuck 4 is
At this time, the quartz disk 31 is pulled up together with the seed chuck 4 and automatically cut off from the surface of the melt 6, thus ending its role as an oxygen supply for the melt 6 during necking. Then a cone is formed,
The growth of the silicon single crystal 35 having a desired diameter starts (see FIG. 2C). Thereafter, by appropriately adjusting the pulling speed and the temperature, a substantially columnar single crystal rod can be obtained.

As described above, the present inventors have found that, in the seeding method for necking in the growth of a silicon single crystal rod, particularly when a large drawing having a diameter of 5 mm or more is formed, the dislocation-free success rate does not reach a satisfactory level. In some cases, the cause was investigated and investigated. As a result, it was found that the oxygen concentration during necking was deeply involved as a cause of this dislocation, and various conditions were closely examined to complete the present invention.

Conventionally, no consideration has been given to the oxygen concentration during necking. In ordinary necking, the concentration of oxygen incorporated in the neck is very low and is said to be less than 1 ppma. Even if necking is performed under the same conditions as growing a straight body of a single crystal rod, the oxygen in the neck is very low. This is presumably because the neck was small in volume at the time of growth, and was grown at a position where the influence of oxygen evaporation on the surface of the silicon melt was large.

On the other hand, with respect to the motion speed of dislocations in a silicon crystal, at high temperatures and under low stress, oxygen atoms have an important effect on the motion characteristics of dislocations. There is a finding that dislocation motion under low stress is not observed in CZ silicon (dislocation fixation by oxygen) (K. Sumin).
o, Japan. J. Appl. Phys. , 19,
p. L49. (1980)).

Therefore, by introducing a certain amount of oxygen into the neck, the dislocation movement speed in the neck is reduced,
We thought that the growth of dislocations could be suppressed, and when necking was performed under conditions that increased the oxygen concentration during necking, it was found that the dislocation-free success rate was improved.

That is, in the seeding method in which necking is performed, the oxygen concentration in the narrowed portion and the narrowed portion during necking was repeatedly examined and experiments. As a result, if the oxygen concentration during necking was 1 ppma (JEIDA) or more, the growth of dislocations was increased. The dislocation-free success rate is 95
% Has been found to be possible. If the oxygen concentration is less than 1 ppma, the effect is too low to suppress the growth of dislocations.

The effect of suppressing the growth of dislocations of oxygen atoms during necking is particularly effective when the diameter of the constricted portion is 5 mm or more.
By growing the single crystal corresponding to the increase in weight, the success rate of dislocation-free operation can be increased, and the productivity, yield, and manufacturing cost can be significantly improved.

The oxygen concentration is preferably as high as possible,
pma or more, more preferably 5 ppma or more,
Even when a thick drawn portion having a diameter of 5 mm or more is formed, dislocation-free can be more reliably achieved. This tendency was particularly observed when the aperture portion was formed without applying a magnetic field.

The means for increasing the concentration of interstitial oxygen in the constricted portion and the constricted portion during necking are not particularly limited, but specific examples thereof include (1) silicon melting near the center of the crucible where the constriction is performed. A substance which becomes a supply source of oxygen in the liquid, for example, a rod or plate of quartz (SiO ₂ );
There is a method of inserting a block or the like. FIG. 1 shows a state in which an L-shaped quartz rod is immersed in a melt near the narrowed portion during pulling of the narrowed portion during the necking operation. Also,
FIG. 2 shows a state in which the quartz disk is floating near the center of the silicon melt during necking. In this case, a quartz cylinder may be immersed in the melt. The lower surface of the quartz disk is preferably inclined from one end of the disk to the other end in the radial direction or from the circumference to the center in order to suppress the influence of the surface tension of the silicon melt. With such an inclination, the influence of the surface tension that occurs when the quartz disk is separated from the silicon melt can be reduced, so that the influence of the wave of the melt that occurs when the disk is separated from the melt,
The amount of the melt adhering to the quartz disk can be suppressed. Thus, for example, when a quartz rod is inserted in the vicinity of the center of the silicon melt during necking, the oxygen concentration in this region increases, and oxygen can be easily taken into the narrowed portion or the narrowed portion.

In the method of floating a quartz disk, if the quartz disk is rotated in the melt, the amount of quartz dissolved increases,
More oxygen can be supplied. Further, since the surface of the molten metal is covered with the quartz disk, the evaporation of oxygen can be suppressed, and the effect of increasing the oxygen concentration in the melt increases. Further, by appropriately selecting the number of rotations of the seed crystal and the area of the quartz disk, the amount of oxygen supplied from the quartz disk can be adjusted.

Alternatively, (2) during the necking, the rotation of the crucible is accelerated to give forced convection to the silicon melt, and oxygen generated from quartz as the crucible material is sent to the surface near the center of the crucible. When the crucible rotates at a high speed like this,
The amount of oxygen that dissolves into the silicon melt from the inner wall of the quartz crucible increases, and the oxygen concentration in the melt rises. As a result, the oxygen concentration around the narrowed portion of the seed crystal and around the narrowed portion increases, and the oxygen is narrowed and narrowed down. It becomes easy to be taken into. Specifically, the rotation of the crucible during necking may be made faster than the rotation of the crucible during pulling up the straight body of the single crystal rod. For example, when a crucible having a diameter of 18 inches is used, the rotation of the crucible is 15 rpm or more. For example, the speed may be set. However, it is not limited to such a case.

(3) In the Czochralski method in which a magnetic field is applied, a method in which no magnetic field is applied to the silicon melt during necking is used. In this way, the convection of the silicon melt, which was forcibly suppressed by applying a magnetic field, is released, and the convection increases the oxygen concentration around the narrowed portion of the seed crystal and around the narrowed portion, thereby narrowing the oxygen. In addition to the increased oxygen content, the movement speed of dislocations is reduced and the growth of dislocations is significantly suppressed, so the success rate of dislocation-free growth of the grown single crystal is improved, and productivity and yield are improved. Can be significantly improved.
(4) Other means for increasing the oxygen concentration during necking include changing the temperature distribution in the silicon melt and increasing the gas atmosphere pressure to make it difficult for oxygen to evaporate.
And the like.

[0032]

EXAMPLES The present invention will be described in detail below with reference to examples of the present invention and comparative examples, but the present invention is not limited to these examples. (Example) In order to increase the oxygen concentration during necking, a quartz rod was inserted into the melt during necking, a thick drawing was performed, and a single crystal was grown by the MCZ method. The quartz crucible used was 450 mm in diameter, charged with 50 kg of raw material polycrystalline silicon, heated and melted by heating to 14 mm in diameter.
The crucible is lowered by applying a horizontal magnetic field so that the magnetic field strength at the center of the crucible becomes 3000 Gauss, and the crucible is necked to reduce the diameter of the drawn portion to 6 mm. Pulled up as diameter 150
mm single crystal was grown. Immediately before the necking operation, an L-shaped quartz rod having a diameter of 20 mm was inserted into the melt to increase the oxygen concentration in the narrowed portion and the vicinity of the narrowed portion. After necking, the quartz rod was pulled out of the melt.
When the dislocation-free success rate was evaluated, it was 95%. As a result of measuring the oxygen concentration in the narrowed portion with a Fourier transform infrared spectrometer, 1.5 ppma (JEIDA) of oxygen was detected.

(Comparative Example) A pull-up test was performed under the same conditions as in the above example except that the quartz rod was not inserted during necking, and the dislocation-free success rate was 25%. Also,
At this time, the oxygen concentration detected in the throttle portion is 0.5 ppma
(JEIDA).

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, in the embodiment of the present invention, the diameter 15
Although a 0 mm (6 inch) silicon single crystal rod is grown, recent 200 mm (8 inch) to 400 mm (1 inch)
(6 inches) or more.

The present invention is not limited to the ordinary Czochralski method, but also to the MCZ method (Magnetic field applied Czochralski crm) in which a magnetic field is applied when pulling a silicon single crystal.
It is needless to say that any form of MCZ method can be similarly applied as long as the method is the same as the conventional Czochralski method. The MCZ method is also included.

[0037]

As described above, according to the present invention,
When pulling a silicon single crystal rod by the Czochralski method, the seeding method of necking achieves a dislocation-free success rate of approximately 95% or more, and its reproducibility is good.
Long-term stabilization is possible. Therefore, it is possible to sufficiently adapt to increase in diameter, length, and weight of the single crystal rod in the future, and it is possible to remarkably improve productivity, yield, and cost.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a single crystal pulling apparatus showing a state during necking in single crystal growth of the present invention.

FIG. 2 is a schematic explanatory view showing a state during another necking in single crystal growth of the present invention. (A) A diagram showing a state in which the tip of a seed crystal and a quartz disk are in contact with the melt surface, (b) a diagram showing a state in which necking has been completed and the quartz disk has detached from the melt surface, and (c) a silicon single crystal. FIG. 4 is a diagram showing a state where growth of the GaN layer has started.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... seed crystal, 2 ... narrowing down part, 3 ... narrowing down part, 4 ... seed chuck, 5 ... wire, 6 ... silicon melt, 7 ... crucible, 8 ... crucible rotating shaft, 9 ... heater, 10 ... quartz rod, 2
0: Single crystal pulling apparatus, 30: Seed holder, 31: Quartz disk, 32: Slide plate, 33: Support rod, 34: Stopper,
35 ... Silicon single crystal.

Claims (5)

[Claims] In a method for producing a silicon single crystal in which a seed crystal is brought into contact with a melt by a Czochralski method and then a single crystal rod is grown by a seeding method for necking, interstitial oxygen taken in during necking is provided. 1p concentration
pma (JEIDA) or more. 2. The method for producing a silicon single crystal according to claim 1, wherein quartz is inserted into the silicon melt during necking in order to increase the interstitial oxygen concentration during necking. 3. The method for producing a silicon single crystal according to claim 1, wherein the rotation of the crucible is increased during necking in order to increase the interstitial oxygen concentration during necking. 4. In the Czochralski method applying a magnetic field, no magnetic field is applied to the silicon melt during necking in order to increase the interstitial oxygen concentration during necking. Any one of item 3
The method for producing a silicon single crystal described in the paragraph. 5. The drawing part diameter during necking is 5 mm.
The method for producing a silicon single crystal according to claim 1, wherein: