JP2021075425A - Method for manufacturing silicon single crystal - Google Patents

Abstract

To provide a method for manufacturing a silicon single crystal, capable of manufacturing the silicon single crystal having more uniform oxygen concentration distribution in the silicon crystal length direction.SOLUTION: The method for manufacturing a silicon single crystal includes pulling the silicon single crystal from a silicon melt stored in a quartz glass crucible 3 by the Czochralski method. Within 20% is a variation in oxygen concentration in the crystal growth axis direction of the silicon single crystal pulled using the quartz glass crucible having the ratio t/T of the thickness t of the transparent inner layer to the thickness T of the side wall of the quartz glass crucible controlled from the upper part of the side wall of the quartz glass crucible to the lower portion thereof.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method for producing a silicon single crystal by the Czochralski method (CZ method), and relates to a method for producing a silicon single crystal capable of producing a silicon single crystal having a more uniform oxygen concentration in the crystal length direction.

In the growth of a silicon single crystal by the CZ method, polysilicon as a raw material is filled in a quartz glass crucible 51 installed in a chamber 50 as shown in FIG. 8, and a heater 52 provided around the quartz glass crucible 51 is used for poly. After heating and melting silicon to form a silicon melt M, the seed crystal (seed) P attached to the seed chuck is immersed in the silicon melt M, and the seed chuck and the quartz glass crucible 51 are placed in the same direction or in the opposite direction. This is done by pulling up the seed chuck while rotating it to.

Generally, when the temperature of the silicon melt M stabilizes prior to the start of pulling, the seed crystal P is brought into contact with the silicon melt M to melt the tip of the seed crystal P, and then necking is performed. Necking is an indispensable step for removing dislocations generated in a silicon single crystal due to a thermal shock generated by contact between the seed crystal P and the silicon melt M.
The neck portion P1 is formed by this necking. Further, the neck portion P1 is required to have a diameter of about 5 mm and a length of 30 to 40 mm or more in the case of a crystal having a diameter of 300 mm, for example.

The steps after the start of pulling include a step of forming a shoulder portion C1 that spreads the crystal to the diameter of the straight body portion after the end of necking, a step of forming a straight body portion C2 that grows a single crystal to be a product, and a process of forming the straight body portion. A step of forming a tail portion (not shown) is performed in which the diameter of the single crystal after the step is gradually reduced.

By the way, since the inner surface of the quartz glass crucible 51 comes into contact with the silicon melt M and dissolves, oxygen contained in the quartz glass crucible 51 dissolves in the silicon melt M and reacts with the silicon melt M to form SiOx. Become. Most of this SiOx evaporates from the free surface of the melt and is discharged together with the inert gas (Ar or the like) introduced into the single crystal pulling device.

Here, some SiOx is incorporated into the growing single crystal, and the oxygen incorporated into the silicon single crystal has an effect of suppressing heavy metal gettering and slip dislocations due to oxygen precipitates in the semiconductor device manufacturing process. ..
However, if the oxygen precipitate is present in the active layer in the process of manufacturing a semiconductor device, there is a risk that the electrical characteristics will be adversely affected. Therefore, it is required to manufacture a wafer having an appropriate oxygen concentration according to the type of semiconductor device.

In addition, the upper part of the straight body that grew in the early stage of pulling has a large amount of silicon melted in the quartz glass crucible, and the contact area between the inner wall surface of the crucible and the silicon melt is large, so the amount of oxygen eluted from the quartz glass crucible. It is pulled up in a state where there are many. As the single crystal is pulled up, the amount of silicon melt in the crucible decreases, so the contact area between the inner wall surface of the crucible and the silicon melt becomes smaller, and oxygen from the quartz glass crucible to the silicon melt becomes smaller. The amount of elution decreases.

Therefore, the oxygen concentration in the silicon melt tends to be unstable, and the oxygen concentration distribution in the growth direction of the single crystal tends to be non-uniform (for example, the oxygen concentration is higher in the upper part and lower in the lower part). In this single crystal growing step, in order to improve the yield, it has been desired to control the oxygen concentration in the crystal growing axis direction to be uniform.

In response to the above problem, in Patent Document 1 (Japanese Patent Laid-Open No. 6-56571), an inverted truncated cone-shaped or cylindrical heat-shielding jig is arranged above the silicon melt, and the silicon melt surface and the heat-shielding cure are provided. A method of controlling the oxygen concentration of a single crystal by adjusting the gap with the lower end of the jig is disclosed.
According to the method disclosed in Patent Document 1, the melt surface is cooled by the inert gas supplied from above the heat shield jig to the melt surface, and the heat radiated from the ruts to the melt surface is shielded. The degree can be accurately controlled, and as a result, the diffusion evaporation of oxygen in the melt can be controlled, and the amount of oxygen supplied to the single crystal can be controlled.

Further, Patent Document 2 (Republished WO2001 / 063027) discloses that the oxygen concentration is controlled by changing the flow rate and pressure of the inert gas flowing into the furnace according to the amount of pulling up.
According to the method disclosed in Patent Document 2, the amount of oxygen evaporating as an oxide from the surface of the melt near the crystal growth interface can be easily adjusted by changing the flow rate or pressure of the inert gas in the furnace. The amount of oxygen contained in the silicon melt can be easily controlled.

Japanese Patent Application Laid-Open No. 6-56571 Republished WO 2001/063027

However, all of the methods disclosed in Patent Documents 1 and 2 can make the crystal oxygen concentration in the crystal growth axis direction uniform, but have the following problems.
Specifically, in the method disclosed in Patent Document 1, the temperature of the silicon melt surface changes due to the gap between the silicon melt surface and the heat shielding jig, and the temperature distribution in the crystal height direction changes. Since it changes, it affects the formation of crystal defects such as void-like defects (COP) and oxygen precipitates (BMD), and there is a problem that the distribution of crystal defects becomes non-uniform.

Further, in the method disclosed in Patent Document 2, the amount of SiO gas evaporated from the melt is adjusted by the flow rate and pressure of the inert gas, and when the flow rate of the inert gas is large, the gas is exhausted. There is a problem that a vacuum pump having high exhaust performance is required for the pump, which increases the cost. On the other hand, when the flow rate of the inert gas is small, there is a problem that the dirt in the furnace is not exhausted and the single crystallization rate is lowered.

The present inventor does not use a heat shield jig as in the method disclosed in Patent Document 1, but uses the flow rate and pressure of the inert gas from the melt as in the method disclosed in Patent Document 2. The amount of evaporation of SiO gas in the above was not adjusted, and a new method was examined.
As a result, the crystal growth of the silicon single crystal to be pulled up by adjusting the ratio t / T of the thickness t of the transparent inner layer to the wall thickness T of the quartz glass crucible along the height direction of the quartz glass crucible. It has been found that the oxygen concentration in the axial direction can be controlled, and the present invention has been completed.

The present invention has been made under the above-mentioned circumstances, and by adjusting the ratio t / T of the thickness t of the transparent inner layer to the wall thickness T of the quartz glass rut, the silicon crystal length direction. An object of the present invention is to provide a method for producing a silicon single crystal capable of producing a silicon single crystal having a more uniform oxygen concentration distribution.

The method for producing a silicon single crystal according to the present invention, which has been made to solve the above problems, uses a quartz glass turret having an opaque outer layer and a transparent inner layer from a silicon melt contained in the quartz glass rug. A method for producing a silicon single crystal in which a silicon single crystal is pulled up by the Czochralski method, wherein the ratio t / T of the thickness t of the transparent inner layer to the thickness T of the side wall of the quartz glass rutsubo is the side wall of the quartz glass rutsubo. It is characterized in that the variation of the oxygen concentration in the crystal growth axis direction of the silicon single crystal to be pulled up is within 20% by using the quartz glass rutsubo adjusted from the upper part to the lower part.
Here, the quartz glass crucible is divided into a plurality of regions from the upper part to the lower part of the side wall of the quartz glass crucible, and the ratio t / T of the thickness t of the transparent inner layer to the thickness T of the side wall of the quartz glass crucible. However, it is desirable that the adjustment is made for each of the plurality of regions.
Further, it is desirable that the ratio t / T of the thickness t of the transparent inner layer to the thickness T of the side wall of the quartz glass crucible is in the range of more than 0.05 and less than 0.8.

As described above, according to the method for producing a silicon single crystal according to the present invention, the ratio t of the thickness t of the transparent inner layer to the wall thickness T of the quartz glass crucible along the height direction of the quartz glass crucible. By adjusting / T and controlling the oxygen concentration in the crystal growth axis direction of the silicon single crystal to be pulled up, the variation in the oxygen concentration in the crystal growth axis direction of the silicon single crystal to be pulled up is suppressed, and the oxygen concentration is made more uniform. Can be done.

According to the present invention, by adjusting the ratio t / T of the thickness t of the transparent inner layer to the wall thickness T of the quartz glass rut, silicon single silicon having a more uniform oxygen concentration distribution in the silicon crystal length direction. A method for producing a silicon single crystal capable of producing a crystal can be obtained.

FIG. 1 is a cross-sectional view of a single crystal pulling device in which the method for producing a silicon single crystal according to the present invention is carried out. FIG. 2 is a cross-sectional view of a quartz glass crucible included in the single crystal pulling device of FIG. FIG. 3 is a partially enlarged cross-sectional view of the quartz glass crucible of FIG. FIG. 4 is a flow showing a flow of a method for producing a silicon single crystal according to the present invention. 5 (a), (b), and (c) are cross-sectional views showing the relationship between the amount of silicon melt and the crucible, which changes with crystal pulling. FIG. 6 is a graph showing the results of Example (Experiment 1). FIG. 7 is a graph showing the results of Example (Experiment 2). FIG. 8 is a cross-sectional view for explaining a process of pulling up a silicon single crystal by the Czochralski method.

Hereinafter, a method for producing a silicon single crystal according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a single crystal pulling device in which the method for producing a silicon single crystal according to the present invention is carried out. FIG. 2 is a cross-sectional view of a quartz glass crucible included in the single crystal pulling device of FIG.
The single crystal pulling device 1 includes a furnace body 10 formed by superimposing a pull chamber 10b on a cylindrical main chamber 10a, and is provided in the furnace body 10 so as to be rotatable and elevating around a vertical axis. It includes a carbon susceptor (or graphite susceptor) 2 and a quartz glass crucible 3 (hereinafter, simply referred to as a crucible 3) held by the carbon susceptor 2. The crucible 3 can rotate around a vertical axis as the carbon susceptor 2 rotates.

Here, the configuration of the crucible 3 will be described in detail with reference to FIGS. 2 and 3.
The crucible 3 is formed, for example, with a bottom portion 31 having a diameter of 800 mm and having a predetermined curvature, a corner portion 32 formed around the bottom portion 31 and having a predetermined curvature, and a straight body portion extending upward from the corner portion 32. It has 33 and. A crucible opening (upper end opening) is formed at the upper end of the straight body portion 33.
As shown in FIG. 2, the crucible 3 has a two-layer structure consisting of an opaque outer layer 3A (opaque layer) and a transparent inner layer 3B (transparent layer).

Of these, the opaque outer layer 3A is made of natural raw material quartz glass, and the transparent inner layer 3B is made of, for example, high-purity synthetic raw material quartz glass.
Here, opaque means a state in which a large number of bubbles (pores) are contained in the quartz glass and the quartz glass is apparently cloudy. Further, the natural raw material quartz glass means silica glass produced by melting a natural material such as crystal, and the synthetic raw material quartz glass means, for example, a synthetic raw material synthesized by hydrolysis of silicon alkoxide is melted. It means the silica glass to be manufactured.

Then, in this manufacturing method, a quartz glass crucible in which the ratio t / T of the thickness t of the transparent inner layer to the wall thickness T of the quartz glass crucible is adjusted (set) in the crucible height direction is used.
As described above, in the process of pulling up the single crystal, the oxygen concentration in the silicon melt is not stable, and the oxygen concentration distribution in the growth direction of the single crystal tends to be non-uniform. In addition to changes in the oxygen concentration in the melt, how it becomes non-uniform depends on the magnetic field strength, magnetic field center position, inert gas flow rate and furnace pressure, quartz glass crucible 3, rotation, single crystal rotation, etc. It is influenced by the parameters.

Therefore, in the present invention, in a certain single crystal pulling device, the tendency of the oxygen concentration distribution in which the pulled single crystal becomes non-uniform (for example, the distribution in which the oxygen concentration in the upper part of the crystal is higher than that in the lower part) is grasped in advance. Then, the ratio t / T is adjusted based on the ratio.
In the present embodiment, the case where the tendency of the oxygen concentration distribution is such that the oxygen concentration in the upper part of the crystal is higher than that in the lower part will be described as an example.

As shown enlarged in FIG. 3, along the height direction of the straight body portion 33 of the crucible 3, for example, the crucible upper portion 33A, the crucible middle portion 33B, and the crucible lower portion 33C have a crucible wall thickness (opaque outer layer 3A and opaque). The ratio t / T of the thickness t of the transparent inner layer 3B to T) T, which is the total thickness of the inner layer 3B, is set to be greater than 0.05 and less than 0.8.
For example, the ratio t / T is set from a small value to a large value from the upper 33A to the lower 33C. Specifically, for example, in the upper portion 33A, the ratio t / T of the thickness t of the transparent inner layer 3B to the crucible wall thickness T is set to 0.10, and the ratio t / T of the intermediate portion 33B is set to 0.3. The ratio t / T of the lower 33C is set to 0.6.

When the ratio t / T is 0.05 or less (when the thickness of the transparent inner layer 3B is too thin), all the transparent inner layer 3B is melted during crystal growth, and the opaque outer layer 3A containing bubbles is a silicon melt. It is exposed on the M side, and there is a risk that minute quartz particles will come off. In that case, there is a risk that the particles will reach the surface of the melt and the dislocation rate will increase, or that air bubbles will be taken into the crystal and air pockets will be formed.
On the other hand, when the ratio t / T is 0.8 or more (when the thickness of the transparent inner layer 3B is too thick), the uniform diffusion of heat by the opaque outer layer 3A becomes insufficient, making temperature control difficult, or the product. There are drawbacks such as high price.

The ratio t / T is defined as described above because the heat transfer coefficients of the opaque outer layer 3A and the transparent inner layer 3B are different. Since the opaque outer layer 3A contains a large amount of bubbles, heat is uniformly diffused and a uniform temperature distribution is obtained. On the other hand, the transparent inner layer 3B has a high thermal conductivity and it is difficult to control the temperature.

Therefore, when the ratio t / T of the transparent inner layer 3B to the wall thickness T of the crucible 3 is small, the opaque outer layer 3A that uniformly diffuses heat becomes thick, and it is not necessary to heat the crucible 3 more than necessary. Since the inner surface temperature can be lowered, the amount of quartz dissolved in the silicon melt M can be reduced.
On the other hand, when the ratio t / T of the transparent inner layer 3B to the wall thickness T of the crucible 3 is large, the heat conduction is large, so that the inner surface temperature of the crucible becomes high, the amount of quartz dissolved increases, and the silicon melt M The amount of quartz dissolved in the material can be increased.

Since the amount of the silicon melt decreases as the crystal growth progresses, the influence of the oxygen concentration on the single crystal to be grown shifts from the upper part 33A of the crucible where the silicon melt surface M1 is located to the middle part 33B and the lower part 33C.
Further, as described above, since the amount of oxygen in the silicon melt is large in the initial stage of pulling up when the amount of silicon melt in the quartz glass crucible is large, the oxygen concentration tends to be higher in the upper part of the single crystal.
Therefore, in the embodiment of the present invention, the ratio t / T of the upper part 33A, the middle part 33B, and the lower part 33C of the crucible in which the silicon melt surface M1 that most affects the crystal oxygen concentration moves in order is, as an example, quartz glass. By setting the crucible so that it increases from the upper part to the lower part, the oxygen concentration in the crystal growth axis direction is controlled to be more uniform.

Next, returning to the description of FIG. 1, below the carbon susceptor 2, a rotary drive unit 14 such as a rotary motor that rotates the carbon susceptor 2 around a vertical axis, and an elevating drive unit 15 that moves the carbon susceptor 2 up and down. Is provided.
The rotation drive control unit 14a is connected to the rotation drive unit 14, and the lift drive control unit 15a is connected to the lift drive unit 15.

Further, the single crystal pulling device 1 includes a side heater 4 by resistance heating that melts the semiconductor raw material (raw polysilicon) loaded in the crucible 3 into a silicon melt M (hereinafter, simply referred to as melt M). It is provided with a pulling mechanism 9 that winds up the wire 6 and pulls up the single crystal C to be grown. A seed crystal P is attached to the tip of the wire 6 of the pulling mechanism 9.

A heater drive control unit 4a for controlling the amount of power supplied is connected to the side heater 4, and a rotation drive control unit 9a for controlling the rotation drive thereof is connected to the pulling mechanism 9.
Further, in the single crystal pulling device 1, for example, an electromagnetic coil 8 for applying a magnetic field is installed outside the furnace body 2. When a predetermined current is applied to the magnetic field application electromagnetic coil 8, a horizontal magnetic field having a predetermined strength is applied to the silicon melt M in the crucible 3. An electromagnetic coil control unit 8a that controls the operation of the electromagnetic coil 8 for applying a magnetic field is connected to the electromagnetic coil 8.

That is, in the present embodiment, the MCZ method (Magnetic field applied CZ method) in which a magnetic field is applied into the melt M to grow a single crystal is carried out, thereby controlling the convection of the silicon melt M and causing the single crystal. It is designed to stabilize the crystallization.

Further, above the melt M formed in the crucible 3, a radiation shield 7 surrounding the circumference of the single crystal C is arranged. The radiant shield 7 has openings formed at the upper and lower portions, shields excess radiant heat from the side heater 4 and the melt M, etc. with respect to the growing single crystal C, and rectifies the gas flow in the furnace. ..
The gap between the lower end of the radiation shield 7 and the surface of the molten liquid is controlled so as to maintain a constant distance according to the desired characteristics of the single crystal to be grown.

Further, the single crystal pulling device 1 includes a computer 11 having a storage device 11a and an arithmetic control device 11b, and includes a rotation drive control unit 14a, an elevating drive control unit 15a, an electromagnetic coil control unit 8a, and a rotation drive control unit 9a. Are connected to the arithmetic control device 11b, respectively.

In the single crystal pulling device 1 configured in this way, for example, when growing a single crystal C having a diameter of 300 mm, pulling is performed as follows. That is, first, the raw material polysilicon (for example, 350 kg) is loaded into the crucible 3, and the crystal growth step is started based on the program stored in the storage device 11a of the computer 11.

First, the raw material loaded in the crucible 3 with the inside of the furnace body 10 having a predetermined atmosphere (mainly an inert gas such as argon gas) and the crucible 3 being rotated at a predetermined rotation speed (rpm). The polysilicon is melted by heating by the side heater 4 to form a melt M (step S1 in FIG. 4).

Next, a predetermined current is passed through the magnetic field application electromagnetic coil 8, and a horizontal magnetic field is started to be applied into the melt M at a magnetic flux density (for example, 2500 Gauss) set in the range of 1000 to 4000 Gauss (step of FIG. 4). S2).
Further, the wire 6 is lowered, the seed crystal P is brought into contact with the melt M, the tip portion of the seed crystal P is melted, and then necking is performed and the neck portion P1 is started to be formed (step S3 in FIG. 4). ..
When the neck portion P1 is formed, the pulling conditions are adjusted with the power supplied to the side heater 4, the pulling speed, the magnetic field application strength, and the like as parameters, and the seeds are seeded at a predetermined rotation speed in the direction opposite to the rotation direction of the rutsubo 3. The crystal P starts rotating.

Then, the crystal diameter is gradually increased to form the shoulder portion C1 (step S4 in FIG. 4), and the process proceeds to the step of forming the straight body portion C2 to be the product portion (step S5 in FIG. 4).
Here, the oxygen concentration in the single crystal grown from the silicon melt M into which the oxygen eluted from the crucible 3 is introduced is, for example, the magnetic field strength, the magnetic field center position, the flow rate of the inert gas, the furnace pressure, and the quartz glass crucible. Parameters such as rotation of 3 and rotation of a single crystal have an effect.

The oxygen concentration distribution in the crystal growth axis direction is affected by the above parameters, but conventionally, it is difficult to make the oxygen concentration in the crystal growth axis direction uniform only by controlling the above parameters.
Therefore, in the embodiment of the present invention, in addition to the above parameter conditions, the crystal growth axis is adjusted by adjusting the ratio t / T of the thickness t of the transparent inner layer 3B to the crucible wall thickness T in the height direction of the crucible 3. Control the crystal oxygen concentration in the direction.

Specifically, the growth axis direction of the single crystal C raised by the above parameters such as the magnetic field strength, the magnetic field center position, the flow rate of the inert gas and the pressure inside the furnace, the rotation of the base quartz glass crucible 3, and the rotation of the single crystal. The tendency of the oxygen concentration is recorded in the storage device 11a as data in advance, the ratio t / T in the quartz glass crucible 3 is determined accordingly, and the crucible based on the ratio t / T is manufactured and used.

At the initial stage of growing the straight body portion C2, the silicon melt surface M1 is located at the upper portion 33A of the crucible as shown in FIG. 5 (a). The amount of oxygen taken into the single crystal C is most affected by the oxygen concentration in the melt M near the silicon melt surface M1.
Here, in the initial stage of growing the straight body portion C2, the amount of silicon melt is large and the contact area with the inner surface of the crucible is large, so that the oxygen concentration in the melt is high as a whole. The ratio t / T of the thickness t of the transparent inner layer 3B to the wall thickness T is set as small as 0.08, for example. That is, since the transparent inner layer 3B is formed to be thin, the opaque outer layer 3A is thick, whereby heat is diffused and made uniform. As a result, the temperature of the inner surface of the crucible is lowered, and the amount of quartz dissolved in the silicon melt M from the crucible 3 is suppressed.

As the growth of the straight body portion progresses and the silicon melt surface M1 decreases to the position of the crucible central portion 33B as shown in FIG. 5 (b), in this crucible central portion 33B, the transparent inner layer 3B with respect to the crucible wall thickness T The ratio t / T of the thickness t is set to, for example, 0.3.
Here, since the amount of the silicon melt in the crucible is decreasing, the oxygen concentration in the silicon melt tends to decrease, but the middle part 33B of the crucible where the silicon melt surface M1 is located is more transparent than the upper part 33A of the crucible. Since the inner layer 3B is thick, the amount of quartz dissolved in the crucible 3 into the silicon melt M increases.

Further growth of the straight body portion progresses, and when the silicon melt surface M1 reaches the position of the crucible lower portion 33C as shown in FIG. 5C, the thickness of the transparent inner layer 3B with respect to the crucible wall thickness T in this crucible lower portion 33C. The ratio t / T of t is set as high as 0.6, for example.
Here, since the amount of the silicon melt in the crucible is further reduced to a small amount, the oxygen concentration in the silicon melt is low, but the transparent inner layer 3B is formed thicker in the lower part 33C of the crucible. , The thermal conductivity is high. As a result, the temperature of the inner surface of the crucible rises, and the amount of quartz dissolved in the silicon melt from the crucible 3 increases.

By growing the straight body portion C2 in this way, the oxygen concentration is corrected to be uniform in the growth axis direction of the straight body portion C2.
Then, when the straight body portion C2 is formed to a predetermined length, the process proceeds to the final tail portion step (step S6 in FIG. 2). In this tail portion step, the contact area between the lower end of the crystal and the melt M is gradually reduced, the single crystal C and the melt M are separated, and a silicon single crystal is produced.

As described above, according to the present embodiment, the ratio t / T of the thickness t of the transparent inner layer to the wall thickness T of the quartz glass crucible is adjusted along the height direction of the quartz glass crucible. By controlling the oxygen concentration in the crystal growth axis direction of the silicon single crystal to be pulled up, the oxygen concentration in the crystal growth axis direction can be brought close to a desired value and made uniform.
Further, since it is only necessary to adjust the thickness t of the transparent inner layer 3B with respect to the wall thickness T of the crucible 3, the cost can be suppressed as compared with the configuration of the conventional general single crystal pulling device.
Further, since the temperature of the silicon melt surface can be controlled to be kept constant, it is possible to prevent the distribution of crystal defects from becoming non-uniform.

In the above embodiment, the ratio t / T of the thickness t of the transparent inner layer 3B to the crucible wall thickness T is set to 0.08, 0.3, 0.6, but the magnetic field is shown. The ratio t / T can be appropriately changed by changing parameters such as strength, magnetic field center position, flow rate and furnace pressure of inert gas, rotation of quartz glass crucible, and rotation of single crystal.

Further, in the above-described embodiment, the quartz glass crucible 3 is divided into three regions (33A, 33B, 33C) in the height direction, and the ratio t / T is set in each region. However, in the present invention, the ratio t / T is set. The number of the regions is not limited and can be set as appropriate.
Further, instead of setting a specific ratio t / T separately for each region, the ratio t / T may be gradually changed in the height direction of the quartz glass crucible 3.

Further, the quartz glass crucible 3 has a two-layer structure of an opaque outer layer 3A and a transparent inner layer 3B, but the present invention is not limited to the structure, and if the inner layer is a transparent layer, the layer can be formed. The number is not limited.

Further, when carrying out the present invention, a method using a heat shielding jig as in the method disclosed in Patent Document 1 and a melt using the flow rate and pressure of an inert gas as in the method disclosed in Patent Document 2. A method of adjusting the amount of evaporation of SiO gas from the gas may be used in combination.

The method for producing a silicon single crystal according to the present invention will be further described based on Examples.
(Experiment 1)
In Experiment 1, by changing the ratio t / T of the thickness t of the transparent inner layer to the crucible wall thickness T in the crucible height direction, how is the oxygen concentration distribution in the pulling direction of the pulled silicon single crystal? We verified whether it would affect it.

In Experiment 1, in the single crystal pulling device having the configuration shown in the above-described embodiment, 350 kg of raw material polysilicon was put into the crucible to pull up a silicon single crystal having a diameter of 300 mm. In order to suppress the natural convection of the silicon melt, the magnetic flux density of the horizontal magnetic field applied during pulling was set to 2500 Gauss.
The flow rate of the inert gas was 90 L / min, and the pressure inside the furnace was 50 torr.
Further, the rotation speed of the crucible was set to 1 rpm, and the rotation speed of the single crystal was set to 10 rpm (the rotation directions were opposite to each other).

The ratio t / T of the thickness t of the transparent inner layer 3B to the crucible wall thickness T shown in FIG. 3 was set as shown in Table 1 in Example 1, Example 2, and Comparative Example 1.
In Example 1, the ratio t / T of the quartz crucible was set under the condition of the pulling device in which the oxygen concentration in the upper part of the pulled single crystal tended to be higher than the oxygen concentration in the lower part.
In Example 2, the ratio t / T of the quartz crucible was set under the condition of the pulling device in which the oxygen concentration in the upper part of the pulled single crystal tended to be higher than the oxygen concentration in the lower part.
Further, in Comparative Example 1, the quartz crucible ratio t / T was not changed under the condition of the pulling device in which the oxygen concentration in the upper part of the pulled single crystal tended to be higher than the oxygen concentration in the lower part.
The result of Experiment 1 is shown in the graph of FIG. The vertical axis of the graph of FIG. 6 is the oxygen concentration (× 10 ¹⁸ / cm ³ ), and the horizontal axis is the solidification rate. Table 1 shows the variation in the oxygen concentration in the axial direction of the single crystal pulled up based on the conditions of Examples 1, 2 and Comparative Example 1.

(Table 1)

As shown in the graph of FIG. 6, in Example 1, the oxygen concentration at the initial stage of crystal pulling was suppressed, and a single crystal having a low oxygen concentration and a uniform oxygen concentration in the crystal growth axis direction was obtained. Further, as shown in Table 1, the variation in oxygen concentration was suppressed to 14%.
Further, in Example 2, the oxygen concentration in the late stage of crystal pulling was improved, and a single crystal having a high oxygen concentration and a uniform oxygen concentration in the crystal growth axis direction was obtained. Further, as shown in Table 1, the variation in oxygen concentration was suppressed to 13%.
Further, in Comparative Example 1, a single crystal having a higher oxygen concentration was obtained in the upper part of the crystal. Further, as shown in Table 1, the variation in oxygen concentration was as large as 30%.
From the results of this experiment 1, it was confirmed that according to the present invention, the oxygen concentration can be controlled more uniformly in the crystal growth axis direction, and the variation in oxygen concentration can be suppressed within 20%.

(Experiment 2)
In Experiment 2, the ratio of the thickness t of the transparent inner layer to the crucible wall thickness T of the quartz crucible under the condition of the pulling device in which the oxygen concentration in the upper part of the pulled single crystal tends to be lower than the oxygen concentration in the lower part. The t / T was changed in the crucible height direction, and the variation in oxygen concentration in the height direction of the single crystal to be pulled up was verified. The conditions for pulling up the single crystal are the same as in Experiment 1.
Table 2 shows the ratio t / T in the upper part, the middle part, and the lower part of the crucible in Examples 3, 4 and Comparative Example 2, and the variation in the oxygen concentration in the axial direction of the single crystal pulled up based on those conditions.
Further, the graph of FIG. 7 shows changes in the single crystal oxygen concentration in Examples 3 and 4 and Comparative Example 2. In the graph of FIG. 7, the vertical axis is the oxygen concentration (× 10 ¹⁸ / cm ³ ), and the horizontal axis is the solidification rate.

(Table 2)

As shown in the graph of FIG. 7 and Table 2, in Examples 3 and 4, by setting the ratio t / T in the upper part of the crucible to be larger than that in the lower part of the crucible, the variation in the oxygen concentration distribution in the pulling axis direction of the single crystal becomes large. It was kept small (10% or less).
On the other hand, in Comparative Example 2, the ratio t / T of the thickness of the transparent inner layer was set to be substantially constant in the crucible height direction, but the oxygen concentration at the upper part of the pulled-up single crystal was lower than that at the lower part (same as the base). As a result, the variation in oxygen concentration was large (22%).

(Experiment 3)
In Experiment 3, the appropriate range of the ratio t / T of the thickness t of the transparent inner layer to the crucible wall thickness T was verified. Judgment as to whether or not it was appropriate was made based on the dislocation rate of the crystal and the magnitude of the amount of temperature fluctuation.
Table 3 shows the ratio t / T, which is the condition in Examples 5 to 7 and Comparative Examples 3 to 6, the resulting dislocation rate of the crystal, and the amount of temperature fluctuation of the melt. In Examples 5 to 7 and Comparative Examples 3 to 6 of Experiment 3, the ratio t / T was set in order to make the oxygen concentration distribution in the pulling axis direction of the pulled single crystal uniform. Other conditions are the same as in Experiment 1.

(Table 3)

As shown in Table 3, at the ratio t / T set in Examples 5 to 7, good results were obtained with the dislocation rate being 10% or less and the temperature fluctuation amount being ± 3 ° C.
On the other hand, when there is a portion where the ratio t / T is as low as 0.05 as in Comparative Examples 3 and 4, bubbles in the opaque layer are exposed, fine quartz particles are generated, and the dislocation rate increases. ..
Further, when there is a portion having a ratio t / T of 0.80 or more as in Comparative Examples 5 and 6, the uniform diffusion of heat by the opaque outer layer becomes insufficient, the temperature control becomes difficult, and the silicon melt The amount of temperature fluctuation has increased.
From this result, it was confirmed that the range of the ratio t / T of the thickness t of the transparent inner layer to the crucible wall thickness T is preferably larger than 0.05 and less than 0.80.

1 Single crystal pulling device 2 Carbon susceptor 3 Quartz glass crucible (crucible)
4 Side heater 6 Wire 7 Radiation shield 8 Electromagnetic coil for applying magnetic field 9 Pulling mechanism 10 Furnace 11 Computer 11a Storage device 11b Arithmetic control device 14 Rotation drive unit 15 Lifting drive unit C Silicon single crystal M Silicon melt C1 Shoulder C2 Straight Body

Claims (3)

A method for producing a silicon single crystal in which a silicon single crystal is pulled up from a silicon melt contained in the quartz glass crucible by a Czochralski method using a quartz glass crucible having an opaque outer layer and a transparent inner layer.
Using a quartz glass crucible in which the ratio t / T of the thickness t of the transparent inner layer to the thickness T of the side wall of the quartz glass crucible was adjusted from the upper part to the lower part of the side wall of the quartz glass crucible.
A method for producing a silicon single crystal, characterized in that the variation in oxygen concentration in the crystal growth axis direction of the silicon single crystal to be pulled up is within 20%. The quartz glass crucible
From the upper part to the lower part of the side wall of the quartz glass crucible, it is divided into a plurality of regions, and the ratio t / T of the thickness t of the transparent inner layer to the thickness T of the side wall of the quartz glass crucible is adjusted for each of the plurality of regions. The method for producing a silicon single crystal according to claim 1, wherein the silicon single crystal is produced. Claim 1 or claim, wherein the ratio t / T of the thickness t of the transparent inner layer to the thickness T of the side wall of the quartz glass crucible is greater than 0.05 and less than 0.8. 2. The method for producing a silicon single crystal according to 2.

Images