JP2009173503A - Single crystal pulling device and method for manufacturing single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for reducing carbon concentration in a single crystal and preventing occurrence of dislocation even when a single crystal to be grown has a large diameter. <P>SOLUTION: A single crystal pulling device is disclosed, which has a radiation shield 6 disposed above a crucible 3 and shielding a single crystal C against radiation heat, gas supply means 13, 14, 17 supplying an inert gas G from above the radiation shield 6 into the crucible 3, and discharge means 18, 19 discharging the inert gas G passing through the crucible 3 to the outside of a furnace 2. The radiation shield 6 is placed in such a manner that a gap area between the outer circumference of the shield 6 and the inner circumference of the crucible 3 at the nearest portion ranges from 10% to less than 35% of the liquid surface area of a melt M and that a gap dimension between the lower end of the radiation shield 6 and the melt liquid surface is smaller than the width dimension in a radial direction of the lower end face of the radiation shield 6. The inert gas G supplied to the crucible 3 by the gas supply means 13, 14, 17 is discharged by the discharge means 18, 19 via the gap formed by the placement of the radiation shield 6. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a single crystal pulling apparatus and a single crystal manufacturing method for pulling up while growing a single crystal by the Czochralski method (hereinafter referred to as “CZ method”).

  The CZ method is widely used for the growth of silicon single crystals. In this method, the seed crystal is brought into contact with the surface of the silicon melt contained in the crucible, the crucible is rotated, and the seed crystal is pulled upward while rotating in the opposite direction. In this way, a single crystal is formed.

  As shown in FIG. 8, in the pulling method using the conventional CZ method, first, raw silicon is loaded into a quartz glass crucible 51 and heated by a carbon heater 52 to obtain a silicon melt M. Thereafter, the seed crystal P attached to the pulling wire 50 is brought into contact with the silicon melt M to pull up the silicon crystal C.

  In general, prior to the start of pulling, after the temperature of the silicon melt M is stabilized, as shown in FIG. 9, necking is performed in which the seed crystal P is brought into contact with the silicon melt M to dissolve the tip of the seed crystal P. Necking is an indispensable process for removing dislocations generated in a silicon single crystal due to thermal shock generated by contact between the seed crystal P and the silicon melt M. The neck portion P1 is formed by this necking. The neck portion P1 is generally required to have a diameter of 3 to 4 mm and a length of 30 to 40 mm or more.

In addition, as a process after the start of pulling, after necking is completed, a crown process for expanding the crystal to the diameter of the straight body part, a straight body process for growing a single crystal as a product, and a single crystal diameter after the straight body process are gradually reduced. The tail process is performed.
In the furnace, in order to exhaust SiO gas generated from the melt M, an inert gas G (for example, Ar gas) is supplied into the crucible from above the crucible 51 and passes over the melt surface. The air is exhausted from the lower exhaust port 54.

By the way, in recent years, the hot zone structure such as the crucible 51 has been enlarged with the increase in the charge amount due to the large diameter of the single crystal. For this reason, the operation under the furnace pressure of about 100 to 300 mbar (about 75 to about 225 torr) has been the mainstream from the conventional operation under the furnace pressure of about 10 mbar (about 7.5 torr). .
However, when the furnace pressure increases, the CO gas generated from the carbon heater 52 and the like during melting tends to be mixed into the melt M and taken into the crystal, and the carbon concentration in the crystal increases.

In order to solve such a problem, Patent Document 1 discloses that the furnace pressure during melting is controlled to be as low as 5 to 60 mbar (about 3.75 to about 40 torr) to prevent CO gas from being mixed into the melt M. A method for reducing the carbon concentration in a silicon single crystal is disclosed.
In the example of Patent Document 1, it is described that the defect rate due to the carbon concentration can be reduced in pulling up a silicon single crystal having a diameter of 6 inches (152.4 mm).

  In addition, the miniaturization of elements has progressed due to the recent high integration in semiconductor devices, and accordingly, the problem of grow-in defects introduced during crystal growth of single crystals has become important. This grow-in defect is an FPD (Flow Pattern) that is caused by voids in which vacancy-type point defects are gathered when a crystal pulling speed V (mm / min) is relatively high when a silicon single crystal is grown. Defect), COP (Crystal Originated Particle), etc., which are present in high density throughout the crystal diameter direction.

In order to reduce the grown-in defect and grow a high-quality silicon single crystal having a desired defect region or a desired defect-free region, Patent Document 2 discloses that the pulling rate is V (mm / min), and the vicinity of the solid-liquid interface. Single crystal production that controls the value of V / G (mm ² / ° C./min) within a predetermined range, where G (° C./mm) is the crystal temperature gradient in the pulling axis direction between the melting point of silicon and 1400 ° C. A method is disclosed.

In recent years, the control of the V / G value is generally performed. However, since the crystal temperature gradient G is uniquely determined by the structure of the hot zone, the V / G value is controlled by the pulling speed. This has been done by adjusting V.
However, since the crystal temperature gradient G decreases as the growth of the single crystal proceeds, in order to keep the V / G value within the predetermined range, the pulling speed V must be decreased. There was a problem that the time required for straight body part growth became longer and productivity was lowered.
In response to such a technical problem, Patent Document 3 discloses that the change in the crystal temperature gradient G is reduced by largely controlling the distance between the radiation shield and the melt surface, and the pulling speed V is not lowered. A method for efficiently producing crystals in a short time is disclosed.
Japanese Patent No. 2635456 JP-A-11-147786 JP 2005-15312 A

As described above, according to the method disclosed in Patent Document 1, the carbon concentration can be reduced for single crystal growth having a diameter of about 6 inches (152.4 mm) as described in the examples.
However, in the method disclosed in Patent Document 1, when growing a single crystal having a larger diameter, in order to melt a large amount of raw material silicon in a state where the furnace pressure is low, the heating power by the carbon heater 52 is increased. As a result, there is a problem that a large amount of CO gas is generated from the carbon member such as the carbon heater 52 in the furnace body, which affects the carbon concentration of the single crystal.

Further, if the single crystal to be grown has a large diameter, the operation time from the melting of the raw material silicon to the pulling of the single crystal becomes long. Therefore, the melt M is exposed to CO gas for a long time, and even if the furnace pressure is controlled to be low, the CO gas is mixed into the melt, resulting in a high carbon concentration in the grown single crystal. There was a problem of becoming.
In particular, in the formation of a gas flow path in the crucible, conventionally, as shown in FIG. 8, turbulent flow of the inert gas G is likely to occur, and the CO gas generated in the furnace is caught in the turbulent flow and melted surface. There was a technical problem that the CO gas was apt to be mixed in by the molten liquid.

Further, as described above, in the large-diameter and high-quality single crystal growth, it is important to control the V / G value. However, as in the manufacturing method described in Patent Document 3, the radiation shield 55, the melt surface, If the interval of is large, the change in the temperature gradient G can be kept small, but the flow rate of the inert gas G in the crucible cannot be sufficiently secured.
That is, since the flow rate of the inert gas G in the crucible is slow, the CO gas cannot be efficiently discharged out of the crucible, and the dissociation from the inner surface of the crucible reaches the growing single crystal and is transformed. There is a problem that is likely to occur.

  The present invention has been made under the circumstances as described above, and in a single crystal pulling apparatus that pulls a silicon single crystal from a crucible by the Czochralski method, even if the single crystal to be grown has a large diameter, An object of the present invention is to provide a single crystal pulling apparatus and a single crystal manufacturing method capable of reducing the carbon concentration in the single crystal and preventing transition.

In order to solve the above-described problems, a single crystal pulling apparatus according to the present invention generates a raw silicon melt with a crucible in a furnace and pulls the single crystal from the crucible by the Czochralski method. In the upper apparatus, a radiation shield provided above the crucible, surrounding the periphery of the single crystal and having an upper portion and a lower portion formed to shield radiation heat to the single crystal, and from above the radiation shield to the inside of the crucible Gas supply means for supplying an inert gas to the crucible, and exhaust means for exhausting the inert gas that has passed through the crucible out of the furnace body, wherein the radiation shield includes an outer peripheral surface of the radiation shield and a crucible of the crucible. The gap area at the closest part to the inner peripheral surface is 10% or more and less than 35% of the liquid surface area of the melt, and the gap dimension between the lower end of the radiation shield and the melt surface is the radiation. The inert gas, which is arranged so as to be shorter than the radial width dimension of the lower end surface of the mold, is supplied into the crucible by the gas supply means via the gap formed by the arrangement of the radiation shield. The exhaust means is characterized by being exhausted.
In the single crystal pulling step, the gas supply means and the exhaust means cause the average flow rate of the inert gas in the gap between the lower end of the radiation shield and the melt surface to be between the radiation shield and the single crystal. It is desirable to control the state so as to be lower than the average flow rate of the inert gas in the gap at the closest part.

Thus, by setting the clearance dimension between the outer peripheral surface of the radiation shield and the inner peripheral surface of the crucible, the gas flow passing through the crucible is rectified, and the generation of turbulent flow in the crucible is suppressed. The CO gas that has entered can be exhausted from the crucible without stagnation.
Furthermore, since the gap distance to the melt surface is controlled to be shorter than the radial width dimension of the lower end surface of the radiation shield, the flow rate of the inert gas in the outer diameter direction is increased, and the crucible is separated. It is possible to form a situation where it is difficult to reach a single crystal and to prevent transition.
Therefore, the risk of transition is remarkably reduced, and a high-quality silicon single crystal with a low carbon concentration can be stably obtained even with a large diameter.

In addition, it is desirable that the lower end surface of the radiation shield is formed in a tapered shape that is reduced in diameter toward the lower side so as to have an inclination angle of 9 degrees at the maximum with respect to the melt surface.
By doing in this way, the radiant heat from a heater can be shielded more and a better thermal history can be given to the silicon single crystal under growth.

In order to solve the above-described problem, a method for producing a single crystal according to the present invention is a method for producing a single crystal by using the single crystal pulling apparatus and pulling the single crystal from the crucible, wherein the furnace pressure is reduced. A step of introducing an inert gas at a flow rate of 10 L / min to 200 L / min by setting the pressure in the furnace to 10 to 80 torr, melting the raw silicon, setting the pressure in the furnace to 30 to 190 torr, and It is characterized in that an inert gas is introduced at a flow rate of 50 L / min or more and 150 L / min or less and a step of pulling up the single crystal is performed.
By controlling the pressure in the furnace and the inert gas, a high quality effect by the single crystal pulling apparatus can be stably obtained.

  According to the present invention, in a single crystal pulling apparatus that pulls a silicon single crystal from a crucible by the Czochralski method, even if the single crystal to be grown has a large diameter, the carbon concentration in the single crystal is reduced, A single crystal pulling apparatus and a method for manufacturing a single crystal can be obtained.

Embodiments of a single crystal pulling apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of a single crystal pulling apparatus 1 according to the present invention.
This single crystal pulling apparatus 1 includes a furnace body 2 formed by superposing a pull chamber 2b on a cylindrical main chamber 2a, a crucible 3 provided in the furnace body 2, and a semiconductor loaded in the crucible 3. And a carbon heater 4 for melting a raw material (raw material silicon) M. The crucible 3 has a double structure, and the inner side is constituted by a quartz glass crucible 3a and the outer side is constituted by a graphite crucible 3b.
Further, in the furnace body 2, a heat insulating member 7 is provided around the heater 4.

  Further, a pulling mechanism 5 for pulling up the single crystal C is provided above the furnace body 2. The pulling mechanism 5 includes a winding mechanism 5a driven by a motor and a pulling wire 5b wound on the winding mechanism 5a. It consists of. A seed crystal P is attached to the tip of the wire 5b and pulled up while growing the single crystal C.

As shown in FIG. 1, a gas supply port 13 for supplying Ar gas G, which is an inert gas, into the furnace body 2 is provided in the upper portion of the pull chamber 2b.
An Ar gas supply source 17 is connected to the gas supply port 13 via a valve 14. When the valve 14 is opened, Ar gas G is supplied from the upper part of the pull chamber 2 b into the crucible 3. . In other words, the gas supply port 13, the valve 14, and the Ar gas source 17 constitute a gas supply means.

A plurality of exhaust ports 18 are provided on the bottom surface of the main chamber 2a, and an exhaust pump 19 serving as an exhaust unit is connected to the exhaust ports 18. In other words, the exhaust port 18 and the exhaust pump 19 constitute exhaust means.
In this configuration, when the exhaust pump 19 is driven and the valve 14 is opened, Ar gas G is supplied into the furnace body 2 from the gas supply port 13, forms a gas flow, and is exhausted from the exhaust port 18. It is made like that.
The gas flow rate from the gas supply port 13 is adjusted by controlling the degree of opening and closing of the valve 14 and the suction strength of the exhaust pump 19.

In the main chamber 2a, an upper portion and a lower portion are formed so as to surround the periphery of the single crystal C above and in the vicinity of the crucible 3, and extra radiant heat from the carbon heater 4 and the like is formed on the growing single crystal C. A radiation shield 6 is provided so as not to give the noise.
By providing this radiation shield 6, Ar gas G supplied into the crucible 3a from above passes along the flow path indicated by the arrow in FIG. 2 (that is, through the gap formed by the arrangement of the radiation shield 6). E) The air is exhausted outside the crucible. In addition, since the flow of Ar gas G is formed in this way, the CO gas generated from the carbon heater 4 is prevented from flowing into the crucible 3.

As shown in FIG. 3, the radiation shield 6 includes an engaging portion 6a that engages with the upper end portion of the surrounding heat insulating member 7, a cylindrical portion 6b that extends vertically downward from the engaging portion 6a, and a cylindrical portion. 6b has a taper portion 6c that tapers downward from the lower end, and a lower end portion 6d that extends from the lower end of the taper portion 6c in the inner diameter direction (substantially parallel to the melt surface).
The lower end portion 6d is formed in a tapered shape whose diameter is reduced downward so that the lower end surface preferably has an inclination angle 閘 of a maximum of +9 degrees with respect to the melt surface as shown in FIG. Thereby, the radiant heat from the heater 4 can be shielded more, and a better thermal history can be given to the silicon single crystal C.
The gap dimension D2 between the lower end of the radiation shield 6 and the melt surface is controlled to be 15 mm or more.

  Further, the lower limit of the inclination angle 閘 with respect to the melt surface of the lower end surface in the lower end portion 6d is a negative value with respect to the melt surface if the distance dimension between the lower end of the radiation shield 6 and the melt surface can be secured at least 15 mm. (For example, −10 degrees). That is, in this case, the lower end surface of the lower end portion 6d has a tapered shape with a diameter decreasing upward as shown in FIG. 5 (in FIG. 5, the gap D4 between the lower end of the radiation shield 6 and the melt surface is 15 mm or more). ).

  In addition, the narrower the gap between the lower end of the radiation shield 6 and the melt surface, the faster the flow rate of the Ar gas G in the outer diameter direction, and it is possible to prevent the deviation of the crucible 3 from reaching the single crystal C. The reason why the clearance between the lower end of the radiation shield 6 and the melt surface is at least 15 mm is that contact between the radiation shield 6 and the melt surface may occur if the clearance is smaller than 15 mm.

  As shown in FIG. 1, the single crystal pulling apparatus 1 includes a heater control unit 9 that controls the amount of power supplied to the heater 4 that controls the temperature of the silicon melt M, and a motor 10 that rotates the quartz glass crucible 3. And a motor control unit 10a for controlling the rotational speed of the motor 10. Furthermore, a lifting device 11 for controlling the height of the quartz glass crucible 3, a lifting device control unit 11a for controlling the lifting device 11, a wire reel rotating device control unit 12 for controlling the pulling speed and the number of rotations of the grown crystal, It has. These control units 9, 10a, 11a, 12 and the valve 14 and the exhaust pump 19 are connected to an arithmetic control device 8b of the computer 8.

Then, the manufacturing method of the single crystal C (for example, diameter 300mm) using such a single crystal pulling apparatus 1 is demonstrated.
In the raw material silicon melting step, first, raw material silicon (for example, 350 kg) is loaded into the crucible 3, and the valve 14 is opened by the command of the arithmetic control device 8b, and the exhaust pump 16 is driven. In addition, a flow path of Ar gas G is formed.

Here, the pressure in the furnace when the raw material silicon is melted is set to 10 to 80 torr, and the flow rate of Ar gas introduced into the furnace is set to 100 L / min or more and 200 L / min or less.
The lower the furnace pressure during melting, the lower the concentration of carbon in the single crystal because the mixing of the CO gas into the melt M is suppressed. However, if the furnace pressure is too low, the inner surface of the quartz glass crucible 3a becomes very rough. Thus, the single crystal is easily converted into dislocations. On the other hand, when the furnace pressure is too high, the carbon concentration in the silicon single crystal increases. For this reason, a furnace pressure of 10 to 80 torr is appropriate for suppressing an increase in carbon concentration during silicon melting and maintaining no dislocation.
In addition, as the flow rate of Ar gas during melting increases, the rectification improves and the carbon concentration decreases, but there is a problem that the cost increases. For this reason, the flow rate of Ar gas during silicon melting is suitably 100 L / min or more and 200 L / min or less.

  Next, based on the program stored in the storage device 8a of the computer 8, first, the heater control unit 9 is operated by the command of the arithmetic control device 8b to heat the heater 4, and the melting operation of the raw silicon of the crucible 3 is started. The

When the silicon melt M is generated, the single crystal pulling operation is started. Here, the furnace pressure is set to 30 to 190 torr, and the flow rate of Ar gas introduced into the furnace is set to 50 to 150 L / min.
The reason why the furnace pressure during silicon single crystal growth is 30 to 190 torr is that it is in a range suitable for controlling the oxygen concentration in the single crystal. The reason why the Ar gas flow rate during single crystal growth is 50 L / min or more and 150 L / min or less is that an effect can be expected to lower the carbon concentration while suppressing an increase in cost.

  When the furnace pressure and the Ar gas G flow path are formed as described above, the motor control unit 10a, the lifting device control unit 11a, and the wire reel rotation device control unit 12 are activated by a command from the arithmetic control device 8b. As the quartz glass crucible 3 rotates, the winding mechanism 5a operates to lower the wire 5b. Then, the seed crystal P attached to the wire 5b is brought into contact with the silicon melt M, and necking for melting the tip of the seed crystal P is performed to form the neck portion P1.

  Thereafter, the pulling conditions are adjusted by parameters of the power supplied to the heater 4 and the single crystal pulling speed (usually a speed of several millimeters per minute) according to the command of the arithmetic control device 8b, and the crown process, the straight body process, the tail part A single crystal pulling step such as a step is sequentially performed.

  Here, the flow path of the Ar gas G in the single crystal pulling step is formed as shown in FIG. That is, the Ar gas G introduced from the gas supply port 13 is introduced into the crucible 3 from above the radiation shield 6 together with the CO gas generated in the furnace, and on the liquid surface of the silicon melt M (with the lower end of the radiation shield 6). Then, the SiO gas generated from the melt M is introduced to the outside of the crucible 3 through the gap formed between the outer peripheral surface of the radiation shield 6 and the inner peripheral surface of the crucible 3. A gas such as Ar gas G led out of the crucible 3 is exhausted from an exhaust port 18 provided at the bottom of the crucible 3.

  Further, in this single crystal pulling step, the dimension of the gap area (gap area determined by the gap dimension D1) at the closest portion between the quartz crucible 3 and the radiation shield 6 during the growth of the silicon single crystal is the liquid of the melt M. It is set to be 10% to 35% of the surface area. The gas flow passing through the crucible 3 is rectified by the gap D1, so that the generation of turbulent flow in the crucible 3 is suppressed, and the CO gas entering the crucible from above the crucible 3 is exhausted from the crucible 3 without stagnation. To be made.

  Further, the average flow velocity of Ar gas G passing through the gap D2 between the lower end (lower end) of the radiation shield 6 and the melt surface is Ar passing through the gap D3 at the closest portion between the radiation shield 6 and the single crystal C. The gas G is controlled to be slower than the average flow velocity. Specifically, the average flow velocity of Ar gas G passing through the gap D2 between the lower end of the radiation shield 6 and the melt surface is controlled to be 1.0 m / sec or more and 5.0 m / sec or less.

Further, the quartz glass crucible is set so that the gap D2 between the lower end of the radiation shield 6 and the molten liquid surface is shorter than the radial width dimension L1 (parallel to the molten liquid surface) at the lower end surface of the shield lower end portion 6b. 3 is controlled by the operation of the lifting device 11.
As a result, the flow rate of the Ar gas G in the outer diameter direction is increased, a situation in which the dissociation of the crucible 3 is difficult to reach the single crystal C is formed, and the transition is suppressed with a high probability, and the carbon concentration is low and high. Quality silicon single crystals are produced.

As described above, according to the embodiment of the present invention, the arrangement of the radiation crucible 3 with respect to the quartz crucible 3 and the melt surface in the pulling process of the silicon single crystal is controlled.
As a result, the gas flow passing through the crucible 3 is rectified, the generation of turbulent flow in the crucible 3 is suppressed, and the CO gas that has entered the crucible from above the crucible 3 can be exhausted from the crucible 3 without stagnation.
Further, the lower end surface of the shield lower end portion 6b is formed substantially parallel to the melt surface, and the relationship between the radial width dimension L1 and the gap dimension D2 with respect to the melt surface is controlled, so that the outer diameter direction is increased. The flow rate of the Ar gas G is increased, and the dissociation of the crucible 3 can hardly reach the single crystal C, thereby preventing transition.
Therefore, according to the single crystal pulling apparatus and the method for producing a single crystal of the present invention, the risk of transition is remarkably reduced, and even with a large diameter, a high-quality silicon single crystal is stabilized with a low carbon concentration. Can be obtained.

Subsequently, the single crystal pulling apparatus and the single crystal manufacturing method according to the present invention will be further described based on examples. In this example, the effect was verified by actually performing an experiment using the single crystal pulling apparatus having the configuration described in the above embodiment.
[Example 1]
In Example 1, 350 kg of raw silicon was filled in a quartz glass crucible having a diameter of 32 inches, a single crystal having a diameter of 300 mm was pulled, and the carbon concentration in the crystal at a solidification rate of 90% was measured.
As shown in FIG. 4, the lower end surface of the radiation shield is formed so that the outer circumference is tapered downward, and the outer circumferential surface is provided with an inclination of 9 degrees with respect to the melt surface. .

Further, the gap area (gap area determined by the gap dimension D1) between the quartz crucible and the radiation shield during the growth of the silicon single crystal shown in FIG. Each condition of 30%, 50% and 70% was set.
Further, the gap D2 between the radiation shield and the melt surface is 120 mm, 40 mm, and 60 mm when the gap area (gap area determined by the gap dimension D1) between the quartz crucible and the radiation shield is 30%. The gap D3 between the lower tip of the radiation shield and the silicon single crystal C was 20 mm. Furthermore, the conditions of the radial width L1 parallel to the melt surface of the lower end surface of the radiation shield lower end were 20 mm, 40 mm, and 80 mm.

Further, the furnace pressure during melting of the raw material silicon was controlled to 10 to 80 torr, and the flow rate of Ar gas introduced into the furnace was controlled to 100 L / min to 200 L / min.
On the other hand, when pulling the single crystal, the furnace pressure was controlled to 30 to 190 torr, and the flow rate of Ar gas introduced into the furnace was controlled to 50 L / min to 150 L / min.

As a result of Example 1, the graph of FIG. 6 shows the single crystal growth result, and the graph of FIG. 7 shows the carbon concentration in the single crystal at a solidification rate of 90%.
In the graph of FIG. 6, the horizontal axis is the gap D2 (mm) between the lower end of the radiation shield and the melt surface, and the vertical axis is the radial width dimension L1 (mm) parallel to the melt surface of the lower end surface of the radiation shield. ). Further, in the figure, ◯ indicates a case where the single crystal growth is successful, Δ indicates a case where dislocation has occurred but single crystal growth has succeeded after remelting, and x indicates a case where single crystal growth has failed.

In the graph of FIG. 7, the horizontal axis represents the ratio (%) of the gap area (gap area determined by the gap dimension D1) of the closest part between the quartz crucible and the radiation shield to the liquid surface area of the melt M. The vertical axis represents the carbon concentration (10 ¹⁶ atoms / cm ³ ) at a solidification rate of 90%.

As a result of this experiment, as shown in the graph of FIG. 6, when the gap D2 between the lower end surface of the radiation shield and the melt surface is shorter than the radial width dimension L1 of the lower end surface of the radiation shield, the success rate of single crystal growth is The result was higher.
Further, as shown in the graph of FIG. 7, the carbon concentration at the solidification rate of 90% is 0.2 × 10 ¹⁶ when the ratio of the gap area determined by the gap dimension D1 is 10% or 30% of the melt surface area. Atoms / cm ³ , which is a low value. It was also found that the carbon concentration was suppressed to a sufficiently low value of 0.25 × 10 ¹⁶ atoms / cm ³ even at 35%.
On the other hand, when the ratio of the gap area determined by the gap dimension D1 is 50%, it becomes 0.4 × 10 ¹⁶ atoms / cm ³ , and when it is 70%, it becomes 0.7 × 10 ¹⁶ atoms / cm ³ , which is a high carbon concentration. It became.

Further, in terms of operation, in the case of 10% and 30% of the melt surface area of the gap area determined by the gap dimension D1, dislocation of the silicon single crystal did not occur, which was good. When the ratio of the gap area was 50% and 70%, one dislocation occurred during the growth of the silicon single crystal, but after that, the crystal was returned to the melt and remelted without being dislocated. I was able to raise it.
[Comparative Example 1]
In Comparative Example 1, a silica glass crucible was filled with 250 to 350 kg of raw silicon, a single crystal having a straight body diameter of 300 mm was pulled up, and the carbon concentration in the crystal at a solidification rate of 90% was measured.
A conventional mortar type was used as the radiation shield. The clearance dimension of the closest part between this radiation shield and the inner peripheral surface of the crucible was 50 to 70% of the melt surface area.

Further, the width dimension in the radial direction of the lower end surface of the lower end portion of the radiation shield was about 20 mm, and the gap dimension between the front end of the radiation shield and the silicon single crystal was about 20 mm.
Further, the gap between the lower end of the radiation shield and the melt surface was pulled several times under the respective conditions of 20 mm and 40 mm.
Further, the furnace pressure was set to 10 to 60 torr when the raw material silicon was melted, and the furnace pressure was set to 75 torr or more when the single crystal was pulled.

As a result of Comparative Example 1, the carbon concentration in the crystal at a solidification rate of 90% was 0.7 to 2.0 × 10 ¹⁶ atoms / cm ³ , which was a high carbon concentration.
When the gap between the lower end of the radiation shield and the melt surface was 20 mm, the single crystal growth rate was high, but many grown-in defects were observed.
On the other hand, when the gap between the lower end of the radiation shield and the molten liquid surface was 40 mm, the defect rate of the grown single crystal was low, but there were many cases of transition.

  From the experimental results of the above examples, by using the single crystal pulling apparatus and the single crystal manufacturing method of the present invention, even if the single crystal to be grown has a large diameter, the carbon concentration in the single crystal is reduced, It was confirmed that metastasis could be prevented.

  The present invention relates to a single crystal pulling apparatus and a single crystal manufacturing method for pulling a single crystal by the Czochralski method, and is suitably used in the semiconductor manufacturing industry and the like.

FIG. 1 is a block diagram schematically showing the configuration of a single crystal pulling apparatus according to the present invention. FIG. 2 is a view showing a gas flow of an inert gas in the furnace of the single crystal pulling apparatus of FIG. FIG. 3 is a partially enlarged view of a radiation shield provided in the single crystal pulling apparatus of FIG. FIG. 4 is a view showing a modification of the radiation shield provided in the single crystal pulling apparatus of FIG. FIG. 5 is a view showing another modification of the radiation shield provided in the single crystal pulling apparatus of FIG. FIG. 6 is a diagram showing the results of the example. FIG. 7 is another diagram showing the results of the example. FIG. 8 is a diagram for explaining a pulling method using the conventional CZ method. FIG. 9 is a diagram for explaining formation of a neck portion in a pulling method using a conventional CZ method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single crystal pulling apparatus 2 Furnace body 2a Main chamber 2b Pull chamber 3 Crucible 4 Heater 5 Pulling mechanism 6 Radiation shield 6a Locking part 6b Cylindrical part 6c Taper part 6d Lower end part 7 Heat insulation member 8 Computer 8a Storage apparatus 8b Arithmetic storage apparatus 13 Gas supply port (gas supply means)
14 Valve (gas supply means)
17 Ar gas supply source (gas supply means)
18 Exhaust port (exhaust means)
19 Exhaust pump (exhaust means)
C single crystal G Ar gas (inert gas)
M Raw material silicon, Silicon melt P Seed crystal P1 Neck

Claims (4)

In a single crystal pulling apparatus that generates a raw material silicon melt with a crucible in the furnace and pulls the single crystal from the crucible by the Czochralski method.
A radiation shield which is provided above the crucible, surrounds the periphery of the single crystal and has an upper portion and a lower portion to shield radiation heat to the single crystal; and an inert gas in the crucible from above the radiation shield. Gas supply means for supplying the exhaust gas, and exhaust means for exhausting the inert gas that has passed through the crucible out of the furnace body,
In the radiation shield, a gap area at the closest portion between the outer peripheral surface of the radiation shield and the inner peripheral surface of the crucible is 10% or more and less than 35% of the liquid surface area of the melt,
And the gap dimension between the lower end surface of the radiation shield and the melt surface is arranged to be shorter than the width dimension in the radial direction of the lower end surface of the radiation shield,
The single crystal pulling apparatus, wherein the inert gas supplied into the crucible by the gas supply means is exhausted by the exhaust means through the gap formed by the arrangement of the radiation shield. .   In the single crystal pulling step, the gas supply means and the exhaust means cause the average flow velocity of the inert gas in the gap between the lower end of the radiation shield and the melt surface to be the closest distance between the radiation shield and the single crystal. 2. The single crystal pulling apparatus according to claim 1, wherein the single crystal pulling apparatus is controlled to be lower than an average flow rate of the inert gas in the gap in the section.   The lower end surface of the radiation shield is formed in a taper shape with a diameter decreasing downward so as to have an inclination angle of 9 degrees at the maximum with respect to the melt surface. The single crystal pulling apparatus described in 1. A method for producing a single crystal, wherein the single crystal pulling apparatus according to any one of claims 1 to 3 is used to pull the single crystal from the crucible,
A step of melting the raw material silicon by introducing an inert gas at a flow rate of 100 L / min or more and 200 L / min or less to a furnace pressure of 10 to 80 torr and a furnace pressure;
Producing a single crystal characterized by performing a step of pulling the single crystal by introducing an inert gas at a flow rate of 50 L / min to 150 L / min at a flow rate of 50 L / min to 150 L / min. Method.

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