JP6922870B2 - Method for manufacturing silicon single crystal - Google Patents

Description

The present invention relates to a method for producing a silicon single crystal.

Cs in the silicon single crystal becomes Ci in the device process and combines with Oi to form a CiOi defect. CiOi defects cause device failure.
Here, the carbon concentration in the silicon single crystal controls the contamination rate of CO mixed in the silicon melt from the high-temperature carbon member such as the heater in the furnace and the graphite crucible, and the evaporation rate of CO from the silicon melt. It is known to reduce this. CO (gas) from the high temperature carbon member is mainly generated based on the following reaction formula.
SiO (gas) + 2C (solid) → CO (gas) + SiC (solid)
or,
SiC (solid) + SiO (gas) → CO (gas) + 2Si (solid)

Therefore, in Patent Document 1, the position of the upper end of the graphite crucible from the time of melting the raw material to the start of pulling up the silicon single crystal is controlled to be 5 mm or more and 95 mm or less upward from the upper end of the heater, and silicon is used. From the time when the raw material of the single crystal is melted to the time when the pulling is completed, the exhaust cross-sectional area of the exhaust flow path in the gap between the lower end of the radiation shield and the surface of the melt is less than the cross-sectional area of the exhaust flow path formed by the inner cylinder and the outer cylinder. The technology for controlling the crucible is disclosed.

Japanese Unexamined Patent Publication No. 2016-56026

However, with the technique described in Patent Document 1, there is a possibility that the carbon concentration in the second and subsequent silicon single crystals cannot be sufficiently reduced.

An object of the present invention is to provide a method for producing a silicon single crystal capable of reducing the carbon concentration in the second and subsequent silicon single crystals in the production of the silicon single crystal.

The method for producing a silicon single crystal of the present invention is arranged above the crucible so as to surround the crucible containing the silicon raw material, the heater for melting the silicon raw material in the crucible, and the growing silicon single crystal, and at least. One that constitutes the crucible by the chokralski method using a pulling device including a heat shield having a surface made of a carbon material and a crucible, a heater, and a chamber accommodating the heat shield. This is a method for producing a silicon single crystal in which a plurality of silicon single crystals are continuously produced with a quartz crucible. By introducing an inert gas into the chamber and pulling up the seed crystal landed on the silicon melt. It includes a growing step of growing a silicon single crystal, a separating step of separating the silicon single crystal from the silicon melt, and a cooling step of cooling while pulling up the silicon single crystal.
The gap adjusting step further includes a gap adjusting step for adjusting the gap between the lower end of the heat shield and the liquid level of the silicon melt in the cooling step performed on the silicon single crystal excluding the silicon single crystal to be finally grown. Is the cooling step without changing the carbon concentration of the silicon melt when the cooling step is performed while performing the gap adjusting step from the state when the silicon single crystal is separated in the separating step. The gap is adjusted so as to be smaller than the carbon concentration in the case of the above.

In the present invention, the carbon material means a material in which CO (gas) is generated by the above-mentioned chemical reaction, and examples thereof include a graphite material and a carbon fiber reinforced carbon material. Further, examples thereof include materials subjected to surface treatment such as SiC surface treatment and pyrolytic carbon coating.
According to the present invention, since the gap during the cooling step performed on the silicon single crystal other than the silicon single crystal to be grown last is adjusted, the carbon concentration in the second and subsequent silicon single crystals can be reduced.
Even if the gap adjusting step is performed after the last silicon single crystal is grown, it does not contribute to the reduction of the carbon concentration because there is no silicon single crystal to be grown next. However, in the present invention, the gap adjusting step is performed after the last silicon single crystal is grown. Therefore, it is possible to prevent the time required for the silicon single crystal manufacturing process from becoming long.

In the method for producing a silicon single crystal of the present invention, the growing step grows the silicon single crystal so that the diameter of the straight body portion after cylindrical grinding is 200 mm, and the gap adjusting step raises the gap to 75 mm or more. It is preferable to adjust it to 140 mm or less.

In the method for producing a silicon single crystal of the present invention, the growing step grows the silicon single crystal so that the diameter of the straight body portion after cylindrical grinding is 300 mm, and the gap adjusting step raises the gap to 80 mm or more. It is preferable to adjust it to 285 mm or less.

The schematic diagram of the pulling device which concerns on the related technique of this invention and one Embodiment. The flowchart of the manufacturing method of a silicon single crystal in the said related art. The schematic diagram which shows the state in the vicinity of the silicon melt in the pulling device. The graph which shows the result of the experiment 1 performed for deriving the present invention, and shows the relationship between the gap and the carbon concentration of a silicon melt. The graph which shows the result of the experiment 2 performed for deriving the present invention, and shows the relationship between the gap and the carbon concentration of a silicon melt. The flowchart of the manufacturing method of the silicon single crystal in one said embodiment.

[Related Techniques of the Present Invention]
First, the related technology of the present invention will be described with reference to the drawings.
[Structure of pulling device]
As shown in FIG. 1, the pulling device 1 is a device used in the MCZ (Magnetic field applied Czochralski) method, and includes a device main body 2, a memory 3, and a control unit 4.
The apparatus main body 2 includes a chamber 21, a crucible 22 arranged in the chamber 21, a heater 23 for heating the crucible 22, a pulling portion 24, a heat shield 25, a heat insulating material 26, and a crucible driving unit. 27 and a pair of electromagnetic coils 28 are provided.

The chamber 21 includes a main chamber 211 and a pull chamber 213 connected to the upper portion of the main chamber 211 via a gate valve 212. The pull chamber 213 is provided with a gas introduction port 21A for introducing an inert gas such as Ar gas into the main chamber 211. A gas exhaust port 21B for discharging the gas in the main chamber 211 is provided below the main chamber 211.

The crucible 22 melts a silicon raw material into a silicon melt M. The crucible 22 includes a quartz crucible 221 and a support crucible 222 accommodating the quartz crucible 221.
The quartz crucible 221 is replaced each time one or more silicon single crystal SMs are grown.
On the other hand, the support crucible 222 is made of graphite or carbon fiber reinforced carbon, and is not replaced every time one silicon single crystal SM is manufactured, and when it is considered that the quartz crucible 221 cannot be properly supported. Will be exchanged. Examples of the support crucible 222 include materials having at least a surface surface such as a graphite material or a carbon fiber reinforced carbon material. Further, examples thereof include materials subjected to surface treatment such as SiC surface treatment and pyrolytic carbon coating.

The heater 23 is arranged around the crucible 22 and melts the silicon in the crucible 22.
The pull-up unit 24 includes a cable 241 to which the seed crystal SC is attached to one end, and a pull-up drive unit 242 that raises and lowers and rotates the cable 241.
At least the surface of the heat shield 25 is made of carbon material. The heat shield 25 is provided so as to surround the silicon single crystal SM when growing the silicon single crystal SM, and blocks radiant heat from the heater 23 to the silicon single crystal SM.
The crucible drive unit 27 includes a support shaft 271 that supports the support crucible 222 from below, and rotates and raises and lowers the crucible 22 at a predetermined speed.
The pair of electromagnetic coils 28 are arranged so as to sandwich the crucible 22 on the outside of the chamber 21.

The memory 3 stores various information necessary for manufacturing the silicon single crystal SM, such as the gas flow rate in the chamber 21, the furnace pressure, the power input to the heater 23, the rotation speed of the crucible 22 and the silicon single crystal SM, and the position of the crucible 22. I remember.
The control unit 4 manufactures the silicon single crystal SM based on various information stored in the memory 3 and the operation of the operator.

[Manufacturing method of silicon single crystal]
Next, a method for producing the silicon single crystal SM by the multi-pulling method will be described. The multi-pulling method is a method of continuously producing a plurality of silicon single crystal SMs with one quartz crucible 221 without opening the chamber 21.
First, as shown in FIG. 2, the control unit 4 controls the electromagnetic coil 28 to apply a magnetic field to the silicon melt M, and then deposits the seed crystal SC on the silicon melt M contained in the crucible 22. , The seed crystal SC is pulled up while rotating the crucible 22 to grow the silicon single crystal SM (step S1: growing step). During this growing step, the control unit 4 adjusts the position of the crucible 22 (adjusts the gap GP) so that the gap GP between the lower end of the heat shield 25 and the liquid level of the silicon melt M becomes substantially constant. ).

After the growing process is completed or during the growing process, the control unit 4 determines whether or not to grow the next silicon single crystal SM (step S2). In step S2, when the control unit 4 determines that the growth of the preset number of silicon single crystal SMs has not been completed and the next growth is to be performed, the tail portion of the silicon single crystal SM is silicon-melted. A step of separating from the liquid M (step S3: separation step) is performed. After that, the control unit 4 stops the application of the magnetic field and cools the silicon single crystal SM separated from the silicon melt M while pulling it up (step S4: cooling step), and the cooled silicon single crystal SM After being housed in the pull chamber 213, the gate valve 212 is closed, and a step (step S5: take-out step) of taking out the silicon single crystal SM from the pull chamber 213 is performed. Generally, the gap GP after the cutting step is maintained as it is at the time of the growing step.
The control unit 4 adds a silicon raw material to the crucible 22, melts the silicon raw material while applying a magnetic field to the silicon melt M (step S6: recharge step), then returns to the growing step, and returns to the next silicon single crystal. Started manufacturing SM.

On the other hand, in step S2, when the control unit 4 has completed the growth of the preset number of silicon single crystal SMs and determines that the next growth is not performed, the control unit 4 may perform steps S3 to S5. The same disconnection step (step S7), cooling step (step S8), and extraction step (step S9) are performed, and the process is completed.
By the above processing, a plurality of silicon single crystal SMs are continuously produced.

[Background to lead to the present invention]
As a result of intensive research, the present inventor has obtained the following findings.
Generally, in the growing process, at the stage of growing the tail portion SM4 as shown in FIG. 3, the crucible 22 is heated as compared with the time of growing the straight body portion SM3 in order to make the diameter smaller than that of the straight body portion SM3. The temperature is high. Since the amount of the silicon melt M remaining in the crucible 22 is small after the disconnection step and before the recharge step, if the heating temperature is lowered, the silicon melt M may solidify. Therefore, even after the disconnection step, the heating temperature is set to the same temperature as or higher than that at the time of growing the tail portion SM4.

One of the causes of carbon mixing in the silicon single crystal SM is that SiO (gas) evaporated from the silicon melt M reacts with C (solid) of the heat shield 25 to generate CO (gas). It is conceivable that CO (gas) is mixed in the silicon melt M.
As the heating temperature of the crucible 22 increases, the amount of SiO (gas) evaporated from the silicon melt M increases. As a result, it is considered that the amount of CO (gas) caused by the SiO (gas) and the heat shield 25 also increases, and the carbon concentration of the silicon single crystal SM to be grown next increases.

As described above, from the viewpoint of suppressing the solidification of the silicon melt M, it is difficult to lower the heating temperature of the crucible 22 after the separation step, and in order to reduce the carbon concentration of the silicon single crystal SM, it is necessary to reduce the carbon concentration of the silicon single crystal SM. A measure to reduce CO (gas) mixed in the silicon melt M can be considered.
Therefore, we focused on the gap GP as a factor that may contribute to the reduction of CO (gas), and conducted the following experiments.

[Experiment 1]
Using the heat flow analysis program, the gap GP after the cutting step after growing the silicon single crystal SM under the following conditions is set to various values, and the carbon concentration in the silicon melt M at the end of the cooling step is simulated. Was done. The results are shown in Table 1 and FIG. The gap GP at the end of the growing process was set to 50 mm, the flow rate and heating temperature of the inert gas GS were the same as those at the end of the growing process, and the carbon concentration was evaluated by setting the carbon concentration to 1 when the gap GP was 50 mm. The time ratio was used.
Inner diameter of quartz crucible 221: 24 inches Diameter of silicon single crystal SM: 210 mm (size that the straight body after cylindrical grinding becomes 200 mm)

As shown in Table 1 and FIG. 4, it was confirmed that when the gap GP increased, the carbon concentration decreased once, but increased again. Specifically, it was confirmed that when the gap GP is 75 mm or more and 140 mm or less, the carbon concentration becomes an allowable value of 0.2 or less. In particular, when the gap GP was 100 mm or more and 125 mm or less, it was confirmed that the carbon concentration was as small as 0.121 or less.

[Experiment 2]
The inner diameter of the quartz crucible 221 and the diameter of the silicon single crystal SM were set to the following conditions, the device main body 2 and each member housed therein were increased due to the size change of the silicon single crystal SM, and the flow rate of the inert gas. Was increased due to the size change of the apparatus main body 2, and the same simulation as in Experiment 1 was performed.
The results are shown in Tables 2 and 3 and FIG. The carbon concentration was evaluated in the same manner as in Experiment 1.
Inner diameter of quartz crucible 221: 32 inches Diameter of silicon single crystal SM: 315 mm (size that the straight body after cylindrical grinding becomes 300 mm)

As shown in Tables 2 and 3 and FIG. 5, it was confirmed that when the gap GP increased, the carbon concentration decreased once but increased again, as in Experiment 1. Specifically, it was confirmed that when the gap GP is 80 mm or more and 285 mm or less, the carbon concentration becomes an allowable value of 0.2 or less. In particular, it was confirmed that when the gap GP is 100 mm or more and 250 mm or less, the carbon concentration becomes a small value of 0.107 or less, and when the gap GP is 125 mm or more and 200 mm or less, the carbon concentration becomes a smaller value of 0.029 or less. ..

[Estimation of carbon concentration reduction mechanism]
The present inventor speculated the mechanism by which the results of Experiments 1 and 2 were obtained as follows. In the following, among the gap GPs in which the carbon concentration is an allowable value, the maximum value is expressed as a gap upper limit value and the minimum value is expressed as a gap lower limit value. Further, the flow path between the lower end of the heat shield 25 and the liquid surface of the silicon melt M is the first gas flow path R1, and the flow path located outside the heat shield 25 is the second gas flow path R2. It is expressed as.

When the gap GP is smaller than the lower limit of the gap, the flow velocity of the inert gas GS flowing through the first gas flow path R1 becomes faster than that of the lower limit of the gap or more. However, since the distance between the lower end of the heat shield 25 and the liquid surface of the silicon melt M is short, the amount of CO (gas) diffused on the surface of the silicon melt M and mixed into the silicon melt M is the first. The amount of CO (gas) discharged from the second gas flow path R2 by the inert gas GS flowing through the gas flow path R1 of the above is larger than the amount of CO (gas) discharged from the second gas flow path R2. As a result, it was estimated that the carbon concentration of the silicon melt M was higher than the permissible value.

On the other hand, when the gap GP is larger than the gap upper limit value, the flow velocity of the inert gas GS flowing through the first gas flow path R1 becomes slower than in the case where the gap GP is larger than the gap upper limit value. Therefore, the discharge of CO (gas) from the second gas flow path R2 is not promoted, and the amount of CO (gas) diffused on the surface of the silicon melt M and mixed into the silicon melt M increases. As a result, it was estimated that the carbon concentration of the silicon melt M was higher than the permissible value.

On the other hand, when the gap GP is equal to or higher than the lower limit of the gap and lower than the upper limit of the gap, the discharge of CO (gas) from the second gas flow path R2 is promoted, and the CO (gas) mixed in the silicon melt M is promoted. It was estimated that the amount of the gas was reduced and the carbon concentration of the silicon melt M became an allowable value.

From the above, in order to reduce the carbon concentration of the second and subsequent silicon single crystal SMs, the present inventor has a gap in the cooling step performed on the silicon single crystal SM excluding the silicon single crystal SM to be grown last. When adjusting the GP, the carbon concentration of the silicon melt M when the cooling process is performed while performing the adjustment does not change from the state when the silicon single crystal was separated in the gap GP disconnection step, and the cooling process is performed. It was confirmed that the gap GP should be adjusted so as to be smaller than the carbon concentration after the above.

[Embodiment]
Next, a method for producing a silicon single crystal SM by the multi-pulling method according to the embodiment of the present invention will be described. The description of the same configuration as the related technology will be omitted or simplified.

First, a pulling device 1 as shown in FIG. 1 that satisfies the conditions shown in Table 4 is prepared.

As shown in FIG. 6, the control unit 4 performs the growing step while adjusting the position of the crucible 22 so that the gap GP becomes substantially constant (step S1).
Next, when the control unit 4 determines in step S2 that the next training is to be performed, the control unit 4 performs a disconnection step (step S3). After that, the control unit 4 moves the crucible 22 up or down from the state when the silicon single crystal SM is separated from the silicon melt M while pulling up the silicon single crystal SM by performing the cooling step (step S4). This adjusts the gap GP (step S10: gap adjustment step). Further, in order to control the convection of the silicon melt M, the control unit 4 applies a magnetic field during the growth (pulling) of the silicon single crystal SM, and stops the application of the magnetic field in the cooling step after the growth.

In the gap adjusting step, when manufacturing a silicon single crystal SM having a diameter of 200 mm after cylindrical grinding, the control unit 4 preferably adjusts the gap GP to 75 mm or more and 140 mm or less, and adjusts it to 100 mm or more and 125 mm or less. It is more preferable to do so. On the other hand, when manufacturing a silicon single crystal SM having a diameter of 300 mm after cylindrical grinding, the control unit 4 preferably adjusts the gap GP to 80 mm or more and 285 mm or less, and more preferably 100 mm or more and 250 mm or less. It is more preferable to adjust the thickness to 125 mm or more and 200 mm or less. When the gap GP when the silicon single crystal SM is separated from the silicon melt M is smaller than the lower limit value in the above range, the control unit 4 increases the gap GP and is larger than the upper limit value in the above range. Reduce the gap GP.

If the gap GP is not within the above-mentioned preferable range, CO (gas) is likely to be mixed in the silicon melt M, so that the gap adjustment step is completed within 120 seconds after the disconnection step (the gap GP is within the above range). (Move the crucible 22 so that it is inside) is preferable.
By performing the above gap adjusting step, the amount of CO (gas) mixed in the silicon melt M can be reduced as compared with the case where the gap adjusting step is not performed (the gap GP is not changed from the state at the end of the growing process).

After the gap adjusting step is completed, the control unit 4 continues the cooling step of pulling up the silicon single crystal SM, and when the silicon single crystal SM is housed in the pull chamber 213, performs the taking-out step (step S5).
At the time of growing the final silicon single crystal SM, it is not necessary to perform the gap adjusting step in the cooling step.
After that, the control unit 4 performs a recharge step (step S6) of adding a silicon raw material to the crucible 22 in order to manufacture the next silicon single crystal SM, and then returns to the growing step to produce the next silicon single crystal SM. Start production. Since the gap adjusting step is performed before the growing step, it is possible to produce the silicon single crystal SM having a lower carbon concentration than the case where the gap adjusting step is not performed.

After the breeding step, when the control unit 4 determines in step S2 that the next breeding is to be performed, the processes of steps S3 to S6 and S10 described above are performed, and when it is determined that the next breeding is not performed, steps S7 to S7 to The process of S9 is performed, and the process is terminated.
As described above, by performing the gap adjusting step after growing the silicon single crystal SM excluding the last silicon single crystal SM, the carbon concentration can be increased while suppressing the time required for the silicon single crystal SM manufacturing process from becoming long. Low silicon single crystal SM can be continuously produced.

[Modification example]
The present invention is not limited to the above embodiment, and various improvements and design changes can be made without departing from the gist of the present invention.

For example, the present invention may be applied to the production of a silicon single crystal SM that does not have an electromagnetic coil 28, that is, by the so-called CZ method.
The range of the preferable gap GP in the gap adjusting step is determined by actually manufacturing the silicon single crystal SM under some conditions in which the gap GP in the cooling step is changed, and determining the carbon concentration of the silicon single crystal SM. You may.
When manufacturing a silicon single crystal SM having a diameter other than 200 mm and 300 mm after cylindrical grinding, a gap adjustment step is performed based on simulations such as Experiments 1 and 2 and the carbon concentration of the actually manufactured silicon single crystal SM. The preferred gap GP range in the above may be determined, and the gap adjusting step may be performed based on this range.
The method for producing a silicon single crystal of the present invention may be applied to a method for continuously producing a plurality of silicon single crystal SMs without charging a silicon raw material.

1 ... Pulling device, 21 ... Chamber, 22 ... Crucible, 23 ... Heater, 25 ... Heat shield, GP ... Gap, GS ... Inert gas, M ... Silicon melt, SC ... Seed crystal, SM ... Silicon single crystal.

Claims (3)

A heat shield that is arranged above the crucible so as to surround the crucible that houses the silicon raw material, the heater that melts the silicon raw material in the crucible, and the growing silicon single crystal, and at least the surface of which is made of a carbon material. A plurality of silicon single crystals are continuously formed by one quartz crucible constituting the crucible by the chokralski method using a pulling device including the crucible, the heater, and a chamber accommodating the heat shield. It is a manufacturing method of a silicon single crystal to be manufactured.
A growing step of growing a silicon single crystal by pulling up a seed crystal landed on a silicon melt while introducing an inert gas into the chamber.
A separation step of separating the silicon single crystal from the silicon melt, and
It is provided with a cooling step of cooling while pulling up the silicon single crystal.
Further provided with a gap adjusting step for adjusting the gap between the lower end of the heat shield and the liquid level of the silicon melt in the cooling step performed on the silicon single crystal excluding the silicon single crystal to be grown at the end.
In the gap adjusting step, the carbon concentration of the silicon melt when the cooling step is performed while performing the gap adjusting step does not change from the state when the silicon single crystal is separated in the separating step. A method for producing a silicon single crystal, which comprises adjusting the gap so as to be smaller than the carbon concentration when the cooling step is performed. In the method for producing a silicon single crystal according to claim 1,
In the growing step, the silicon single crystal is grown so that the diameter of the straight body portion after cylindrical grinding is 200 mm.
The gap adjusting step is a method for producing a silicon single crystal, which comprises adjusting the gap to 75 mm or more and 140 mm or less. In the method for producing a silicon single crystal according to claim 1,
In the growing step, the silicon single crystal is grown so that the diameter of the straight body portion after cylindrical grinding is 300 mm.
The gap adjusting step is a method for producing a silicon single crystal, which comprises adjusting the gap to 80 mm or more and 285 mm or less.

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