JP7047752B2 - Manufacturing method of single crystal silicon - Google Patents

Description

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

Silicon wafers used as substrates for semiconductor devices are often manufactured by subjecting single crystal silicon ingots manufactured by the Czochralski method (CZ method) to wafer processing.

FIG. 1 shows an example of a general single crystal pulling device for growing a single crystal silicon ingot by the CZ method. The single crystal pulling device 100 shown in this figure is provided with a crucible 52 for accommodating silicon raw materials such as polycrystalline silicon in the chamber 51. The crucible 52 is composed of a quartz crucible 52a and a carbon crucible 52b, and the quartz crucible 52a is housed in the carbon crucible 52b. Further, at the lower part of the crucible 52, a crucible rotation elevating shaft 53 that rotates the carbon crucible 52b in the circumferential direction and raises and lowers the carbon crucible 52b in the vertical direction is attached. Further, a heater 54 is arranged around the carbon crucible 52b, and the silicon raw material housed in the quartz crucible 52a is heated to form a silicon melt M.

A pull-up shaft 55 for pulling up the single crystal silicon ingot I is provided in the upper part of the chamber 51, and the seed crystal S is held by the seed crystal cage 56 fixed to the tip of the pull-up shaft 55. Further, a gas introduction port 57 and a gas discharge port 58 are provided in the upper part and the lower part of the chamber 51, respectively, and during the growth of the single crystal silicon ingot I, argon (Ar) is formed in the chamber 51 from the gas introduction port 57. It is configured to supply an inert gas such as gas, pass it along the outer peripheral surface of the ingot I, and discharge it from the gas discharge port 58.

Further, in the chamber 51, a cylindrical heat shielding member 60 surrounding the outer peripheral surface of the ingot I being grown is provided. The heat shielding member 60 shields the radiant heat from the side wall of the heater 54, the silicon melt M, and the carbon pot 52b to promote the cooling of the single crystal silicon ingot I to be pulled up, while keeping the outer peripheral surface of the ingot I warm. It suppresses a large difference in temperature gradient in the crystal axis direction between the central portion and the outer peripheral portion of the single crystal silicon ingot I.

Using the above device 100, the single crystal silicon ingot I is grown as follows. First, the quartz crucible 52a is filled with a silicon raw material, and the silicon raw material filled in the quartz crucible 52a is heated by the heater 54 while the inside of the chamber 51 is maintained in an inert gas atmosphere such as Ar gas under reduced pressure. And melted to obtain a silicon melt M. Next, the height position of the carbon crucible 52b is adjusted by the crucible rotation elevating shaft 53, and the height position of the liquid level of the silicon melt M is set to the height position set with respect to the height position of the upper end of the heater 54. adjust. Then, the seed crystal S is immersed in the silicon melt M under the manufacturing conditions adjusted so that the single crystal silicon having the desired specifications can be obtained, and the crucible 52 and the pulling shaft 55 are rotated in the set directions. However, the seed crystal S is pulled up by the pulling shaft 55. In this way, the single crystal silicon ingot I can be manufactured.

Oxygen concentration is one of the specifications of the single crystal silicon. Single crystal silicon with low oxygen concentration and high oxygen concentration is manufactured based on the specifications, but in recent years, it has been required to strictly control the oxygen concentration of single crystal silicon, and from the specifications of the allowable oxygen concentration. The deviation is getting smaller and smaller.

Against this background, for example, Patent Document 1 proposes a method of irradiating the liquid surface of the silicon melt M with two projected lights to calculate the liquid level position when manufacturing a single crystal silicon by the CZ method. Has been done. According to the method described in Patent Document 1, it is possible to operate the silicon melt M while keeping the liquid level position constant with high accuracy at all times, and it is possible to reduce the variation in oxygen concentration in the pulled-up single crystal ingot. ing.

Japanese Unexamined Patent Publication No. 2002-13966

Generally, as described in Patent Document 1, carbon is used according to the amount of growth of the single crystal silicon so that the liquid level position of the silicon melt M is always constant during the growth of the single crystal silicon. An operation of raising the crucible 52b is performed. However, when the present inventor repeatedly produced single crystal silicon without changing other production conditions while keeping the liquid level position of the silicon melt M constant, the oxygen concentration of the obtained silicon single crystal grew. It was found that the desired oxygen concentration gradually deviated as the number of times increased.

Therefore, an object of the present invention is to provide a method for producing single crystal silicon capable of suppressing the oxygen concentration of the produced single crystal silicon from deviating from a desired value.

The present invention that solves the above problems is as follows.
[1] A silicon raw material is filled in a quartz crucible housed in a carbon crucible arranged in a single crystal pulling device, and the silicon raw material is melted by a heater arranged around the carbon crucible. The first step of making a silicon melt and
After the first step, the height position of the liquid surface of the silicon melt is adjusted to the height position set with respect to the height position of the upper end of the heater by adjusting the height position of the carbon crucible. The second step to do and
Under the production conditions adjusted so as to obtain a single crystal silicon having a desired oxygen concentration, the seed crystal is immersed in the silicon melt and pulled up, and the single crystal silicon is grown at the lower end of the seed crystal. With a process,
A method for producing single crystal silicon by the Czochralski method, in which a plurality of single crystal silicons are produced by repeating the operation of producing the single crystal silicon by performing the first step to the third step.
The relationship between the difference between the height position of the upper end of the heater and the height position of the upper end of the carbon crucible and the actual value of the oxygen concentration of the manufactured single crystal silicon is obtained in advance for the manufacturing conditions. ,
A method for producing single crystal silicon, which comprises modifying the production conditions based on the obtained relationship in the third step.

[2] After the third step, the oxygen concentration of the produced single crystal silicon was measured.
In the next batch
After the second step, the difference between the height of the upper end of the heater and the height of the upper end of the carbon crucible was obtained, and from the obtained difference and the relationship, the oxygen concentration of the single crystal silicon produced in the third step was described. The method for producing single crystal silicon according to the above [1], wherein the deviation from the set oxygen concentration is predicted, and the third step is performed by modifying the production conditions so as to cancel the predicted deviation. ..

[3] In each batch
After the second step, the difference between the height of the upper end of the heater and the height of the upper end of the carbon crucible was obtained, and from the obtained difference and the relationship, the oxygen concentration of the single crystal silicon produced in the third step was determined. The production of the single crystal silicon according to the above [1], wherein the deviation from the set oxygen concentration is predicted, and the third step is performed by modifying the production conditions so as to cancel the predicted deviation. Method.

[4] The production conditions are at least one of the rotation speed of the crucible, the rotation speed of the seed crystal, the output of the heater, the flow rate of the inert gas introduced into the single crystal pulling device, and the pressure in the chamber. The method for producing a single crystal silicon according to any one of the above [1] to [3].

According to the present invention, it is possible to prevent the oxygen concentration of the produced single crystal silicon from deviating from a desired value.

It is a figure which shows an example of the general single crystal pulling apparatus which grows a single crystal silicon ingot by the CZ method. It is a figure explaining the cause which the difference between the height of the upper end of a heater and the height of the liquid level of a silicon melt fluctuates for each batch. It is a figure which shows the oxygen concentration in the pulling direction of the single crystal silicon produced in each batch of the conventional example. It is a figure which shows the oxygen concentration in the pulling direction of the single crystal silicon produced in each batch of Invention Example 1. FIG. It is a figure which shows the oxygen concentration in the pulling direction of the single crystal silicon produced in each batch of Invention Example 2. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present inventor has diligently investigated the cause of the oxygen concentration of the produced single crystal silicon deviating from the desired oxygen concentration when the single crystal silicon is repeatedly produced by the CZ method. Since the source of oxygen in the single crystal silicon is the quartz crucible 52a, it is considered that the deviation in the oxygen concentration is due to the change in the state of the quartz crucible 52a.

When repeatedly producing single crystal silicon by the CZ method, there are two cases, one is to replace the quartz crucible 52a for each batch, and the other is to continue to use the same quartz crucible 52a. When the quartz crucible 52a is replaced for each batch, the quartz crucible 52a has individual differences even if they have the same specifications, and the shape and volume vary. Therefore, when the quartz crucible 52a is replaced for each batch, the oxygen concentration of the produced single crystal silicon may deviate from the desired value even when the single crystal silicon is produced under the same production conditions.

On the other hand, when the same quartz crucible 52a is reused, there should be no deviation in oxygen concentration due to individual differences in the quartz crucible 52a. However, when the present inventor repeatedly produced single crystal silicon using the same quartz crucible 52a, it was found that the oxygen concentration deviated from the desired value as the number of batches increased.

In the process of diligently investigating the above cause, the present inventor has determined that the height of the carbon crucible 52b, and by extension, the height position of the upper end of the carbon crucible 52b with respect to the height position of the upper end of the heater 54 when pulling up the single crystal silicon. I noticed that it was different for each batch. That is, as described above, the silicon raw material filled in the quartz crucible 52a is heated and melted by the heater 54 to obtain the silicon melt M, and then the height position of the carbon crucible 52b is adjusted by the crucible rotation elevating shaft 53. Then, the height position of the liquid surface of the silicon melt M is adjusted to the height position set with respect to the height of the upper end of the heater 54. This is to prevent the quality of the single crystal from changing due to the change in the thermal history between batches when the single crystal silicon is pulled up.

The height position of the liquid level of the silicon melt M adjusted as described above is the same for all batches. Therefore, when the production of single crystal silicon is repeated using the same quartz crucible 52a, the height position of the upper end of the carbon crucible 52b should not change with respect to the height position of the upper end of the heater 54.

According to the present inventor, the change in the height position of the upper end of the carbon crucible 52b is such that the quartz crucible 52a is deformed by the heat of the silicon melt M when the single crystal silicon is pulled up, and the volume of the quartz crucible 52a is increased. I guess it was because it changed.

That is, as shown in FIG. 2, in batch 1 for producing single crystal silicon using a new quartz crucible 52a, the upper surface of the heater 54 after the height position of the liquid surface of the silicon melt M is adjusted. When the difference between the height and the height of the upper surface of the carbon crucible 52b and the height of the upper surface of the carbon crucible 52b is a, the quartz crucible 52a is deformed and the thickness of the lower portion is increased in the next batch 2. It is assumed that the height of the upper end of the quartz crucible 52a is lowered and the volume is reduced.

In this case, in batch 2, even if the same amount of silicon raw material as in batch 1 is filled in the quartz crucible 52a, the height of the liquid level of the silicon melt M in the quartz crucible 52a is higher than that in batch 1. Will be higher. Therefore, in order to adjust the height position of the liquid level of the silicon melt M to a predetermined height position with respect to the upper surface of the heater 54 in the same way as in batch 1, the crucible is compared with batch 1. It is necessary to lower the height position of 52.

In this way, while the volume changes due to the deformation of the quartz crucible 52a, the height position of the silicon melt M is adjusted to the same predetermined height position, so that the crucible 52 and the heater 54 are used for each batch. It is considered that the positional relationship changed and the amount of oxygen taken into the single crystal silicon fluctuated, and the produced oxygen concentration deviated from the desired value.

Therefore, the present inventor has diligently studied a method capable of suppressing deviation from the desired oxygen concentration even when the single crystal silicon is repeatedly produced using the quartz crucible 52a that can be thermally deformed as described above. As a result, the difference between the height position of the upper end of the heater 54 and the height position of the upper end of the carbon crucible 52b with respect to the production conditions adjusted so as to produce single crystal silicon having a desired oxygen concentration. It is extremely effective to obtain the relationship with the actual value of the oxygen concentration of the manufactured single crystal silicon in advance, and to modify the manufacturing conditions based on the above-mentioned relationship to raise the single crystal silicon. He found it and completed the present invention. Hereinafter, each step will be described.

First, in the first step, the quartz crucible 52a housed in the carbon crucible 52b is filled with the silicon raw material, and the silicon raw material is melted by the heater 54 arranged around the carbon crucible 52b to form the silicon melt M. do.

The crucible used in the present invention is a crucible 52 composed of a quartz crucible 52a and a carbon crucible 52b, and the quartz crucible 52a is housed in the carbon crucible 52b. As the carbon-made pot 52b, in addition to graphite, one made of a carbon fiber reinforced-carbon matrix-composite can be used. In the present invention, the production of single crystal silicon is repeated using the same crucible 52.

Further, as the silicon raw material, a known material such as polycrystalline silicon can be used. Appropriate dopants such as phosphorus and boron can be added to adjust the conductive type to P-type or N-type.

Next, after the first step, in the second step, by adjusting the height position of the carbon crucible 52b, the height position of the liquid level of the silicon melt M is set with respect to the height position of the upper end of the heater 54. Adjust to the set height position.

Then, in the third step, the seed crystal S is immersed in the silicon melt M and pulled up under the production conditions adjusted so that the single crystal silicon having a desired oxygen concentration can be obtained, and the seed crystal S is pulled up to the lower end of the seed crystal S. Grow single crystal silicon.

The oxygen concentration set above can be appropriately set according to the specifications, and is, for example, in the range of 11 × 10 ¹⁷ atoms / cm ³ to 13 × 10 ¹⁷ atoms / cm ³ .

The parameters for adjusting the oxygen concentration in the above range include the rotation speed of the carbon crucible 52b, the rotation speed of the seed crystal S, the output of the heater 54, and the inert gas introduced into the single crystal pulling device 100. The flow speed of the single crystal pulling device 100, the pressure in the chamber 51 of the single crystal pulling device 100, and the like can be mentioned. Therefore, these parameters are adjusted so that single crystal silicon having the desired oxygen concentration can be obtained. Then, the seed crystal S is immersed in the silicon melt M and pulled up under the adjusted production conditions, and single crystal silicon is grown at the lower end of the seed crystal S.

By repeating the above first to third steps, the production of single crystal silicon having a desired oxygen concentration is repeated, but the oxygen concentration produced by the shape change of the quartz crucible 52a is specified (desired). ) There is a deviation from. Therefore, in the present invention, the relationship between the difference between the height position of the upper end of the heater 54 and the height position of the upper end of the carbon crucible 52b and the actual value of the oxygen concentration of the manufactured single crystal silicon is determined by the single crystal silicon. Obtained for each manufacturing condition.

Then, by modifying the production conditions in the third step based on the obtained above-mentioned relationship, it is possible to suppress the deviation of the oxygen concentration of the produced single crystal silicon from the desired value. This is done, for example, when the oxygen concentration of the single crystal silicon produced after the third step is measured and the measured oxygen concentration deviates greatly from the desired value (exceeds the allowable value). It can be done by modifying the manufacturing conditions in the next batch.

Specifically, in the next batch, first, after the second step, the difference between the height of the upper end of the heater 54 and the height of the upper end of the carbon crucible 52b is obtained. Next, the deviation of the oxygen concentration of the single crystal silicon produced in the subsequent third step from the desired oxygen concentration is predicted from the obtained difference and the previously obtained relationship. Then, the third step is performed by modifying the manufacturing conditions so as to offset the predicted deviation. In this way, in the next batch, it is possible to suppress the deviation of the oxygen concentration of the produced single crystal silicon from the desired value.

The above method is a response to the case where the oxygen concentration of the produced single crystal silicon deviates greatly from the desired value. However, in each batch, the height of the upper end of the heater 54 and the carbon pot after the second step are used. The difference from the height of the upper end of 52b is obtained, and the deviation of the oxygen concentration of the single crystal silicon produced in the third step from the desired oxygen concentration is predicted from the obtained difference and the above relationship, and the third step is predicted. It is also possible to modify the manufacturing conditions so as to offset the deviation. This makes it possible to prevent the oxygen concentration of the produced single crystal silicon from deviating from the desired value in each batch.

The above-mentioned modifications of the manufacturing conditions include the rotation speed of the crucible 52, the rotation speed of the seed crystal S, the output of the heater 54, the flow rate of the inert gas introduced into the single crystal pulling device 100, and the chamber of the single crystal pulling device 100. This can be done by changing the pressure in 51. How much the oxygen concentration should be changed by changing these parameters depends on the specifications and manufacturing conditions of the single crystal pulling device, and therefore cannot be unconditionally determined. Therefore, it is preferable to obtain the relationship between the amount of change in the parameter and the amount of change in the oxygen concentration in advance, and modify the manufacturing conditions based on the obtained relationship.

(Conventional example)
The single crystal silicon ingot I was pulled up by using the single crystal pulling device 100 shown in FIG. 1, and the single crystal silicon was manufactured. Specifically, first, the quartz crucible 52a was filled with polysilicon as a silicon raw material, the inside of the chamber 51 was depressurized to supply Ar gas as an inert gas, and then the crucible 52 was filled with the heater 54. A silicon raw material such as polysilicon was heated and melted to obtain a silicon melt M (first step). Next, the height position of the carbon crucible 52b was adjusted by the crucible rotation elevating shaft 53, and the height position of the liquid level of the silicon melt M was adjusted to the position set with respect to the height position of the upper end of the heater 54. (Second step). Then, the rotation speed of the crucible 52, the rotation speed of the seed crystal S (pulled crystal), and the Ar gas so that the single crystal silicon having the desired oxygen concentration (12.0 × 10 ¹⁷ atoms / cm ³ ) can be obtained. The single crystal silicon ingot I was pulled up to produce the single crystal silicon by adjusting the production conditions such as the flow rate of the heater 54, the output of the heater 54, and the pressure in the chamber 51 (third step).

Three batches of single crystal silicon were produced with the first to third steps as one batch. Table 1 shows the difference in height position from the upper end of the carbon crucible 52b with respect to the height position of the upper end of the heater 54 in each batch. A negative value in Table 1 means that the heater 54 is located below the upper end in the vertical direction. Further, FIG. 3 shows the oxygen concentration (interstitial oxygen concentration O _i ) in the crystal pulling direction of the single crystal silicon produced in each batch.

(Invention Example 1)
As shown in FIG. 3, since the deviation of the oxygen concentration of the single crystal silicon produced in the conventional batch 3 from the desired value (12.0 × 10 ¹⁷ atoms / cm ³ ) was large, the additional single crystal was added. Silicon was manufactured (batch 4). At that time, from the relationship between the difference between the height position of the upper end of the heater 54 and the height position of the upper end of the carbon crucible 52b, which was obtained in advance, and the actual value of the oxygen concentration of the manufactured single crystal silicon. The flow rate of Ar gas was adjusted so as to offset the above deviation. Table 2 shows the difference in height position from the upper end of the carbon crucible 52b with respect to the height position of the upper end of the heater 54 in the batch 4. Further, the oxygen concentration (interstitial oxygen concentration O _i ) of the single crystal silicon produced in batch 4 in the crystal pulling direction is shown in FIG. 4 together with the oxygen concentration of the single crystal silicon produced in batches 1 to 3.

(Invention Example 2)
The production of single crystal silicon was carried out three times in the same manner as in the conventional example. However, in each batch, after the second step, the difference between the height of the upper end of the heater 54 and the height of the upper end of the carbon crucible 52b is obtained, and the obtained difference and the height of the upper end of the heater 54 and the carbon obtained in advance are obtained. From the relationship between the difference from the height of the upper end of the crucible 52b and the actual value of the oxygen concentration of the produced single crystal silicon, the oxygen concentration of the single crystal silicon produced in the third step is from the desired oxygen concentration. The deviation was predicted, and the third step was performed by modifying the manufacturing conditions so as to offset the predicted deviation. Other conditions are the same as in the conventional example. Table 3 shows the difference in height position from the upper end of the carbon crucible 52b with respect to the height position of the upper end of the heater 54 in each batch. Further, FIG. 5 shows the oxygen concentration (interstitial oxygen concentration O _i ) in the crystal pulling direction of the single crystal silicon produced in each batch.

First, comparing the conventional example and the invention example 1, as is clear from Tables 1 and 2, in both the conventional example and the invention example 1, the position of the upper end of the carbon crucible 52b as the production of the single crystal silicon is repeated. Can be seen to move downwards. As is clear from FIG. 3, the oxygen concentration of the single crystal silicon produced in the conventional batch 3 was significantly reduced from the desired value of 12.0 × 10 ¹⁷ atoms / cm ³ . However, as shown in FIG. 4, the oxygen concentration of the single crystal silicon produced in the batch 4 of Invention Example 1 was almost as specified. As for Invention Example 2, as is clear from Table 3, the position of the upper end of the carbon crucible 52b moved downward as the production of single crystal silicon was repeated, as in the conventional example and Invention Example 1. Further, as shown in FIG. 5, it was found that the oxygen concentration of the produced single crystal silicon in each batch was almost as specified.

According to the present invention, it is possible to suppress the oxygen concentration of the produced single crystal silicon from deviating from a desired value, which is useful in the semiconductor wafer manufacturing industry.

51 Chamber 52 Crucible 52a Quartz crucible 52b Carbon crucible 53 Crucible rotation elevating shaft 54 Heater 55 Pulling shaft 56 Seed crystal cage 57 Gas inlet 58 Gas outlet 60 Heat shielding member 100 Single crystal pulling device

Claims (3)

A silicon raw material is filled in a quartz crucible housed in a carbon crucible arranged in a single crystal pulling device, and the silicon raw material is melted by a heater arranged around the carbon crucible to melt a silicon melt. The first step and
After the first step, the height position of the liquid surface of the silicon melt is adjusted to the height position set with respect to the height position of the upper end of the heater by adjusting the height position of the carbon crucible. The second step to do and
Under the production conditions adjusted so as to obtain a single crystal silicon having a desired oxygen concentration, the seed crystal is immersed in the silicon melt and pulled up, and the single crystal silicon is grown at the lower end of the seed crystal. With a process,
A method for producing single crystal silicon by the Czochralski method, in which a plurality of single crystal silicons are produced by repeating the operation of producing the single crystal silicon by performing the first step to the third step.
The relationship between the difference between the height position of the upper end of the heater and the height position of the upper end of the carbon crucible and the actual value of the oxygen concentration of the manufactured single crystal silicon is obtained in advance for the manufacturing conditions. ,
In the third step, the manufacturing conditions are modified based on the obtained relationship .
The method for producing single crystal silicon , wherein the production condition is at least one of the output of the heater, the flow rate of the inert gas introduced into the single crystal pulling device, and the pressure in the chamber . After the third step, the oxygen concentration of the produced single crystal silicon was measured.
In the next batch
After the second step, the difference between the height position of the upper end of the heater and the height position of the upper end of the carbon crucible was obtained, and the single crystal silicon produced in the third step was obtained from the obtained difference and the relationship. The single crystal according to claim 1, wherein the deviation of the oxygen concentration from the desired oxygen concentration is predicted, and the third step is performed by modifying the production conditions so as to cancel the predicted deviation. How to make silicon. In each batch
After the second step, the difference between the height position of the upper end of the heater and the height position of the upper end of the carbon crucible was obtained, and the single crystal silicon produced in the third step was obtained from the obtained difference and the relationship. The single crystal according to claim 1, wherein the deviation of the oxygen concentration from the desired oxygen concentration is predicted, and the third step is performed by modifying the production conditions so as to cancel the predicted deviation. How to make silicon.

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