JPH11209197A - Production of silicon single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a silicon single crystal by which dislocation in a later contraction process easily disappears by reducing introducing density of slip dislocation at the time of dipping a seed crystal in a silicon molten liquid in MCZ method, the slip dislocation is made to disappear in high probability and a single crystal bar is made to grow to improve nondislocation success rate thereof even at a larger contraction diameter than heretofore and productivity of the single crystal bar having large diameter and high weight is improved. SOLUTION: In the manufacturing method of the silicon single crystal by MCZ method (magnetic field applying Czockralsky method) in which top end of the seed crystal is brought into contact with the silicon molten liquid and then is subjected to necking to grow the single crystal bar, seeding is executed while the magnetic field is not applied to a part or whole of a single crystal cone part or magnetic field with intensity lower than that applied thereto during pulling-up a single crystal straight cylindrical part is applied at least from seeding to necking or after starting of pulling-up operation after the lapse of operation at least from the seeding to the necking at least during the seeding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a Czochralski method for applying a magnetic field (Magnetic-field-applied Czochrals method).
The present invention relates to a method for manufacturing a silicon single crystal in which necking is performed by using a seed crystal according to a ki method (MCZ method) to eliminate dislocations and then grow a silicon single crystal rod.

[0002]

2. Description of the Related Art Conventionally, in the production of a silicon single crystal by the MCZ method, single crystal silicon is used as a seed crystal.
This is brought into contact with a silicon melt to which a magnetic field has been applied, and then slowly pulled up while rotating to grow a single crystal rod. At this time, when a magnetic field is applied to the silicon melt, the convection of the silicon melt is suppressed, and the vibration and temperature fluctuation of the growth interface due to the convection are reduced, and the growth stripes in the grown silicon single crystal are significantly reduced. Defect introduction into a crystal such as a defect is suppressed.

[0003] In the seeding in which the seed crystal is first brought into contact with the silicon melt, when the seed crystal is brought into contact with the silicon melt, slip dislocations that propagate from the slip dislocations generated at high density in the seed crystal by thermal shock are generated. In order to extinguish the crystal, a so-called seed drawing (necking), in which the diameter is once reduced to about 3 mm to form a drawn portion, is performed, and then the crystal is thickened to a desired diameter, and a dislocation-free silicon single crystal is pulled up. I have. Such a method of producing a seed aperture is widely known as a Dash Necking method,
This is an important step when pulling a silicon single crystal rod by the CZ method or the MCZ method.

[0004] The shape of a seed crystal that has been conventionally used is, for example, a cylindrical or prismatic silicon single crystal having a diameter or a side of about 8 to 20 mm provided with a cutout for setting in a seed holder. The shape of the tip below the seed crystal that comes into contact with the silicon melt is flat. And
In order to withstand the weight of a heavy single crystal rod and safely pull it up, it is difficult to make the thickness of the seed crystal smaller than the above given the strength of the material.

[0005] In the seed crystal having such a shape, since the heat capacity of the tip in contact with the silicon melt is large, a sudden temperature difference occurs in the seed crystal at the moment when the seed crystal comes into contact with the silicon melt, causing slip dislocation. At a high density. Therefore, necking is required to eliminate the slip dislocation and grow a silicon 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 the minimum diameter to about 3 to 5 mm. It is desirable that the minimum diameter be 4 mm or less, and with the recent increase in silicon single crystal diameter, the strength is insufficient to support a heavier single crystal rod. During this time, there was a fear that a serious accident such as a breakage of the narrow drawing portion and a drop of the single crystal rod would occur.

In particular, in the MCZ method, since the viscosity of the melt is increased by applying a magnetic field, it is difficult to perform necking by narrowing down, and thus the silicon melt temperature is set to be higher than that of the normal CZ method, so that necking is easy. Like that.
However, when the temperature of the silicon melt is increased, slip dislocation generated when the seed crystal comes into contact with the silicon melt at the time of seeding is likely to occur, and there is a problem that the slip dislocation density is higher than that of the normal CZ method.

Further, if a large-diameter silicon single crystal having a diameter of 12 inches or more is to be pulled up from a large-diameter crucible in the future, a large amount of silicon melt becomes difficult to control convection, so that a magnetic field must be applied. It is necessary to further suppress convection and prevent temperature fluctuation.In the case of pulling a large-diameter silicon single crystal to which a magnetic field is applied in the future, slip dislocation is caused in the drawing process as the temperature of the silicon melt becomes higher. Is difficult to remove.

[0009]

One of the reasons why the slip dislocation is difficult to be removed is considered to be a large slip dislocation density generated when the seed crystal comes into contact with the silicon melt. In other words, the higher the density of the generated slip dislocations, the more it is necessary to reduce the diameter in order to eliminate all the slip dislocations. In the case of a drawing with a diameter of about 5 mm, the force for moving the slip dislocations to the side is weak. In addition, whether or not the dislocations are finally eliminated is a matter of probability depending on the density of the slip dislocations. This means that the density of slip dislocations introduced by seeding affects the ease of dislocation-free.

Accordingly, the present invention has been made in view of such a conventional problem. In the MCZ method, the density of slip dislocations introduced when a seed crystal is immersed in a silicon melt is reduced to reduce the subsequent drawing. In the process, slip dislocations are easily eliminated, and even at larger drawing diameters, slip dislocations can be eliminated with a high probability, dislocations can be eliminated and single crystal rods can be grown, and the success rate of dislocation removal can be improved, and large diameters can be improved. Another object of the present invention is to provide a method for producing a silicon single crystal which improves productivity of a single crystal rod having a high weight.

[0011]

According to a first aspect of the present invention, there is provided a method for solving the above-mentioned problems, comprising the steps of contacting the tip of a seed crystal with a silicon melt by a Czochralski method of applying a magnetic field. In a method for producing a silicon single crystal in which necking is performed and a single crystal rod is grown, at least at the time of seeding, no magnetic field is applied, or a magnetic field weaker than the applied magnetic field strength during pulling up the single crystal straight body is applied. A method for producing a silicon single crystal, characterized by performing seeding.

As described above, in the method for producing a silicon single crystal in which necking is performed and single crystal growth is performed by the MCZ method in which a magnetic field is applied, no magnetic field is applied at least at the time of seeding, or the single crystal straight body is removed. If seeding is performed by applying a magnetic field weaker than the applied magnetic field strength during pulling,
Compared with the normal MCZ method in which the entire process from seeding to pulling of the single crystal straight body part under a magnetic field environment, it is possible to lower the temperature of the silicon melt at the time of seeding and suppress the density of slip dislocations. it can. Therefore, the slip dislocation can be eliminated even with a relatively large aperture diameter, and the success rate of dislocation-free can be improved.

Therefore, when pulling a large-diameter, heavy-weight single crystal from a large-diameter crucible that is difficult to grow without applying a magnetic field, the conventional drawing technique is utilized, and the dislocation-free success rate is almost 100%. Is achieved, the reproducibility is good, and long-term stabilization can be achieved. 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.

In this case, as described in claim 2, the magnetic field is applied without a magnetic field at least from seeding to necking, or a magnetic field weaker than the applied magnetic field strength during pulling up the single crystal straight body. Is desirably applied to perform necking. If such a magnetic field environment is continued at least from seeding to the drawing process, an interface shape in which slip dislocations are more likely to escape from the periphery of the drawing due to the size of the meniscus angle when entering the drawing after seeding, and slip dislocations remain in the crystal The probability decreases, which contributes to a further improvement in the dislocation-free success rate.

According to a third aspect of the present invention, there is provided a silicon single crystal in which the tip of a seed crystal is brought into contact with a silicon melt by the Czochralski method of applying a magnetic field, and necking is performed to grow a single crystal rod. In the crystal manufacturing method, at least after starting seeding and necking and then starting pulling operation, a part of the single crystal cone part or up to the whole cone part is grown without a magnetic field, or application during pulling the single crystal straight body part A method for producing a silicon single crystal, characterized in that a cone portion is grown by applying a magnetic field weaker than the magnetic field intensity.

If such a magnetic field environment is seeded and continued through the seed aperture and in the middle of the single crystal cone portion or to the entire cone portion, slip dislocation is less likely to occur even during cone growth, so that stable cone growth can be performed. Then, the single crystal body can be continuously pulled up without dislocation, and a high dislocation-free success rate can be obtained.

As described in claim 4, if the shape of the tip of the seed crystal is a sharp shape,
The above-described magnetic field environment of the present invention is also effective when seeding using a seed crystal having a sharp tip. That is, since the cross-sectional area of the seed crystal tip is small, the thermal shock at the time of seeding is small, and the slip dislocation generated at the time of seeding can be further suppressed, and the success rate of dislocation-free can be improved.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. The present inventors have found that in the seeding method in which necking is performed during the growth of a silicon single crystal by the MCZ method, the dislocation-free success rate may not reach a satisfactory level, and the cause has been investigated and investigated. The present inventors have found that the strength of the magnetic field during seeding is closely related to the occurrence of slip dislocation, and have completed the present invention under detailed conditions.

First, as a seed crystal, the surface of a prismatic 15 mm square silicon single crystal (tip at a flat surface) as shown in FIG. A magnetic field was applied to the entire process from the seeding process to the single crystal straight body portion pulling process to grow a single crystal rod having a diameter of 150 mm, and the dislocation-free success rate was investigated (Test No. 1 to No. 1).
4).

After the raw polycrystalline silicon was melted using the seed crystal, a horizontal magnetic field of 4000 gauss was applied.
Here, the magnetic field intensity indicates the intensity at the central position of the melt.
Then, while maintaining the magnetic field strength as it is, seeding-drawing (necking) -single crystal cone-single crystal diameter 150 mm
The straight body was pulled up by 10 cm to form a round, then cooled and taken out of the furnace. The removed crystal was subjected to a Secco etching treatment to examine the disappearance of slip dislocations, and the dislocation-free success rate was obtained. The results are shown in Table 1.

Here, the Secco etching means that the strained layer on the surface is first removed by etching with a mixed solution of hydrofluoric acid and nitric acid and then mixed with K ₂ Cr ₂ O ₇ , hydrofluoric acid and water. It is etched with a liquid, and is used to check for the occurrence of slip dislocation on the crystal surface. The dislocation-free success rate (%) [also referred to as the DF conversion rate] is a value expressed as a percentage of the number of pulled silicon single crystals in which no slip dislocation occurred to the number of pulled silicon single crystals.

[0022]

[Table 1]

As is clear from Table 1, when seeding is performed in a state where a magnetic field is applied, the pit density on the side surface of the welded portion is 7 to 8 ×
10 ⁴ (/ cm ²⁾ and a high aperture diameter capable of maintaining a 100% DF rate is about 4mm is limited, it begins fallen diameter becomes thick to about 5mm and dislocation-free successful ratio, more a diaphragm diameter in the crystal It can be seen that slip dislocations occur and the DF conversion rate sharply decreases.

Next, in order to investigate the influence of the magnetic field, the seeding-drawing-single-crystal cone-single-crystal straight body portion was pulled without applying a magnetic field after melting the raw material polycrystal. The conditions other than the magnetic field are the same as above (Test Nos. 5 to 8). The results are shown in Table 2.

[0025]

[Table 2]

As is clear from Table 2, when seeding without any magnetic field in all processes, the pit density on the side surface of the welded portion is 2-3 × 10 ^4.
(/ Cm ² ), but the drawing diameter at which the DF conversion ratio can be maintained at 100% is limited to about 5 mm, and it can be seen that slip dislocation occurs in the crystal and the DF conversion ratio is reduced when the drawing diameter is larger than that. However, the tendency of the DF conversion rate to decrease is much slower than when the entire process magnetic field is applied.

Next, the effect of varying the magnetic field strength was investigated (Test Nos. 9 to 12). As a seed crystal, 15
The surface of a silicon single crystal of mm square (the tip is a flat surface) is etched about 400 μm with a mixed acid, and has a diameter of 1 mm.
A 50 mm single crystal rod was grown to investigate the dislocation-free success rate.

After the raw material polycrystalline silicon was melted using the above seed crystal, seeding was performed without applying a magnetic field, and the horizontal magnetic field intensity was gradually increased from 0 to 4000 gauss between the aperture and the single crystal cone. And 4000gauss
After reaching a single crystal diameter 150mm straight body 10cm
After growing until rounded. Thereafter, the crystal was cooled and taken out of the furnace, and the taken-out crystal was subjected to a Secco etching treatment to investigate the disappearance of slip dislocations. The results are shown in Table 3 as dislocation-free success rates.

[0029]

[Table 3]

Referring to Table 3, when seeding, no magnetic field was applied.
When the magnetic field strength is gradually increased from the aperture to the cone, the pit density on the side surface of the welded portion is 2-3 × 10 ⁴ (/ cm 2).
² ) and the entire process were as low as in the case of no magnetic field, and a large aperture of up to 6 mm in aperture diameter was possible. It can be seen that slip dislocation occurs in the crystal when the drawing is larger than that, and the DF conversion ratio is reduced. The tendency to decrease the DF conversion rate is also gentler than when the magnetic field is applied in all the processes, as in the case where the magnetic field is not applied in all the processes.

Subsequently, the absolute value of the magnetic field intensity was changed, and the application process was changed to investigate (test Nos. 13 to 16). As a seed crystal, a single crystal rod having a diameter of 150 mm was grown by using a silicon single crystal of 15 mm square (the tip of which is flat at the surface) etched with a mixed acid to about 400 μm, and the dislocation-free success rate was investigated. Using the seed crystal, after melting the raw material polycrystalline silicon, apply a magnetic field of 1000 gauss and perform a seeding-drawing step, and after the drawing is completed, gradually increase the horizontal magnetic field strength from 1000 to 4000 gauss between the single crystal cones. Was. Then, after reaching 4000 gauss, a straight body portion having a single crystal diameter of 150 mm was grown to 10 cm and rounded. Thereafter, the crystal was cooled and taken out of the furnace, and the taken-out crystal was subjected to a Secco etching treatment to investigate the disappearance of slip dislocations. The results are shown in Table 4 as dislocation-free success rates.

[0032]

[Table 4]

As is clear from Table 4, when the seeding-drawing step is performed with a weak magnetic field strength and is gradually increased from the drawing to the single crystal cone step to a predetermined magnetic field strength, the pit density on the side surface of the welded portion is reduced. 3 to 3.5 × 10 ⁴ (/ cm ² ), which is slightly higher than in the case of no magnetic field in all steps, but the aperture diameter is D
When the F conversion rate was allowed up to 70%, a 6 mm thick drawing became possible. It can be seen that slip dislocation occurs in the crystal when the drawing is larger than that, and the DF conversion ratio is reduced. The tendency to decrease the DF conversion rate is also gentler than when the magnetic field is applied in all the processes, as in the case where the magnetic field is not applied in all the processes.

As described above, in the dislocation-free seeding method for necking by the MCZ method according to the present invention, as described in Tables 3 and 4, seeding-drawing-single-crystal cone is used as a factor for improving the dislocation-free success rate. It became clear that the method of applying the magnetic field in the process was closely related.

That is, the feature of the present invention is that (1) seeding is performed by applying no magnetic field at least at the time of seeding or by applying a magnetic field weaker than the applied magnetic field strength during pulling up the single crystal straight body. A method for manufacturing a silicon single crystal.
And (2) applying no magnetic field at least from seeding to necking or applying a magnetic field weaker than the applied magnetic field strength during pulling up the single crystal straight body portion to perform necking;
A method for manufacturing a silicon single crystal. Further, (3) at least after starting seeding and necking and then starting a pulling operation, a magnetic field is not applied to a part of the single crystal cone portion or up to the entire cone portion, or an applied magnetic field intensity during pulling the single crystal straight body portion Necking by applying a weaker magnetic field,
A method for manufacturing a silicon single crystal.

According to the method for producing a silicon single crystal by applying the above three types of magnetic fields, in the necking of the MCZ method, it is possible to achieve a large drawing having a diameter of about 5 to 6 mm, which is almost twice as large as that of the conventional method. Achievement rate of 100% can be achieved, and it is not impossible to make a 7mm-diameter thick drawing. The MCZ method can fully cope with future increase in diameter and weight. This can improve the performance, yield, and cost reduction.

The reason why the above-described method of applying a magnetic field is effective in eliminating dislocations will be described with reference to the drawings. 1 shows (a) seeding, (b) emptying, and (c) meniscus in the absence of a magnetic field, and FIG. 2 (a) in a 4000gauss horizontal magnetic field.
Seeding, (b) emptying, (c) meniscus, FIG.
The meniscus during seeding-idling in a horizontal field of 4000gauss is shown.

Generally, when the seed crystal 1 is brought into contact with the surface of the silicon melt 2 to perform seeding (FIG. 1A), a fusion ring 5 is generated around the seed crystal 1. It is necessary to adjust the temperature of the silicon melt 2 to an appropriate temperature just before starting the necking. At this time,
For example, when the seed crystal 1 is a square rod, the seed crystal 1 is pulled up with a constant length and a small diameter in order to form a corner, and this is called idle drawing (FIG. 1B). And at this time, CZ with no magnetic field
In the method, the tip of the seed crystal 1
It has been empirically known that if seeding is performed at such a temperature that does not cause (remelting), the emptying operation proceeds smoothly.

On the other hand, when a magnetic field is applied, the seed crystal 1
It has been empirically found that the temperature of the silicon melt 2 needs to be set higher so that the melt back 3 at the tip of the silicon melt 2 becomes larger than that in the case of the CZ method (FIG. 2A). The reason is that the viscosity of the silicon melt 2 is increased by the application of a magnetic field, so if the silicon melt 2 is evacuated from the same temperature as in the case of the CZ method, the meniscus angle 4 becomes small, and the fused portion between the seed crystal and the silicon melt suddenly expands. (Fig. 3). In other words, it can be said that the increase in viscosity due to the magnetic field is corrected by increasing the temperature of the silicon melt 2. However, since the temperature at the time of seeding is high, the degree of thermal shock is higher than that of the CZ method, and the generated slip dislocation density is higher. Therefore, in the present invention, seeding is performed by not applying a magnetic field at least at the time of seeding, or applying a magnetic field weaker than the applied magnetic field strength during pulling up the single crystal straight body.

If the magnetic field environment as described above is continued at least until the drawing step, an interface shape in which slip dislocations can easily escape from the periphery of the drawing due to the magnitude of the meniscus angle is more preferable. Further, if this magnetic field environment is continued in the middle of the single crystal cone portion or up to the entire cone portion, slip dislocation is less likely to occur even during cone growth, so that stable cone growth can be performed.

This magnetic field environment also works effectively when using a seed crystal having a sharp tip as shown in FIGS. 4 (C) and 4 (D). That is, the characteristic that the slip dislocation is easily generated is affected by the difference in meniscus angle due to the viscosity, even when seeding without dislocation using a seed crystal having a sharp tip is the same. Therefore, the present invention is also effective when using such a seed crystal having a sharp tip, whereby the occurrence of slip dislocation is almost eliminated, and the success rate of dislocation-free can be further improved.

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) can be sufficiently coped with. In the present invention, a single crystal rod of any diameter, length, and weight can be pulled in principle without using a crystal holding device or the like.

In the embodiment of the present invention, of the MCZ method for applying a magnetic field when pulling a silicon single crystal, the HMCZ method (Horizontal Magnetic field a) for applying a horizontal magnetic field is used.
pplied Czochralski crystal growth method), Cusp-MC applying a cusp magnetic field
Needless to say, the present invention can be similarly applied to the Z method, the VMCZ method applying a vertical magnetic field, and the like.

[0045]

As described above, according to the present invention,
When pulling a silicon single crystal rod by the MCZ method, in the seeding method of necking, it is possible to lower the temperature of the melt at the time of seeding, and it is possible to suppress the density of slip dislocations generated at the time of contact. However, a high slip dislocation annihilation probability can be obtained. Therefore, even when pulling a large-diameter, heavy-weight single crystal from a large-diameter crucible that is difficult to grow without applying a magnetic field, the conventional drawing technique is utilized, and the dislocation-free success rate has reached almost 100%. , Its reproducibility is good, and it can be stabilized for a long time. 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 an explanatory diagram showing seeding, emptying, and meniscus without a magnetic field. a) a perspective view at the time of seeding, b) a perspective view at the time of emptying, c) a longitudinal sectional view showing a meniscus.

FIG. 2 is an explanatory diagram showing seeding, emptying, and meniscus in a 4000 Gauss horizontal magnetic field. a) a perspective view at the time of seeding, b) a perspective view at the time of emptying, c) a longitudinal sectional view showing a meniscus.

FIG. 3 is a longitudinal sectional view showing a meniscus during seeding to emptying in a 4000 Gauss horizontal magnetic field (when the temperature of the silicon melt is set to the same value as when no magnetic field is applied).

FIG. 4 is a perspective view showing a shape of a seed crystal used in the present invention. (A) cylindrical seed crystal (tip is flat surface), (B) prismatic seed crystal (tip is flat surface), (C) conical seed crystal,
(D) Pyramidal seed crystal.

[Explanation of symbols]

 1 ... Seed crystal, 2 ... Silicon melt, 3 ... Melt back, 4 ... Meniscus angle, 5 ... Fusion ring.

Claims (4)

[Claims] In a method of manufacturing a silicon single crystal, a tip of a seed crystal is brought into contact with a silicon melt by a Czochralski method of applying a magnetic field, and then necking is performed to grow a single crystal rod. Is a method for producing a silicon single crystal, wherein seeding is performed by applying no magnetic field or applying a magnetic field weaker than the applied magnetic field strength during pulling up the single crystal straight body. 2. The method according to claim 1, wherein the magnetic field is applied without a magnetic field at least from seeding to necking, or necking is performed by applying a magnetic field weaker than the applied magnetic field strength during pulling up the single crystal straight body. The method for producing a silicon single crystal according to claim 1. 3. A method for producing a silicon single crystal in which a tip of a seed crystal is brought into contact with a silicon melt by a Czochralski method applying a magnetic field, and then necking is performed to grow a single crystal rod. After starting the pulling operation through, the part of the single crystal cone part or up to the whole cone part is grown without a magnetic field, or by applying a magnetic field weaker than the applied magnetic field strength during pulling the single crystal straight body part A method for producing a silicon single crystal, comprising growing a cone. 4. The method for producing a silicon single crystal according to claim 1, wherein the tip of the seed crystal has a pointed shape.