JP2021031356A - Method for manufacturing silicon single crystal - Google Patents

Abstract

To provide a method for manufacturing a silicon single crystal, capable of reducing oxygen concentration in a crystal growth axial direction, achieving a uniformity of the oxygen concentration and achieving the uniformity of oxygen concentration on a substrate surface vertical to the crystal growth axis.SOLUTION: In the method for manufacturing a silicon single crystal, capable of growing the silicon single crystal while applying a magnetic field in a horizontal direction when pulling the silicon single crystal from a silicon melt in a quartz glass crucible, a center of the magnetic field in the horizontal direction is positioned in the silicon melt under a free surface in the central part of the silicon single crystal; an intensity of the magnetic field is at least 2000 gauss while pulling the silicon single crystal; a flow of the silicon melt flowing to the quartz crucible side wall from the silicon single crystal side exists on the surface of the silicon melt; and a flow rate of the silicon melt flowing to the quartz glass crucible side wall from the silicon single crystal side is 0.16 m/s or less.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a silicon single crystal, in particular, reducing the oxygen concentration, improving the uniformity of the oxygen concentration in the direction of the crystal growth axis, and further improving the uniformity of the oxygen concentration in the substrate plane perpendicular to the crystal growth axis. The present invention relates to a method for producing a silicon single crystal capable of achieving the above.

The oxygen concentration of the silicon substrate by the conventional CZ method has been relatively high (≧ 1.0 × 10 ¹⁸ atoms / cm ³ ) for the purpose of gettering effect, but in recent years CMOS (Complementary Metal) has been the mainstream. Oxide Semiconductor) Image sensors and the like are required to have a ^{low oxygen substrate (<1.0 × 10 18} atoms / cm ^{3) in order to reduce white scratches.}
The silicon substrate is manufactured from a silicon single crystal, and the method for manufacturing this silicon single crystal is the Czochralski method (CZ) in which the silicon single crystal is pulled up while growing the single crystal from the silicon melt in the quartz glass crucible. Law) is widely used.

In this method for producing a silicon single crystal, as a method for adjusting the oxygen concentration of the silicon single crystal, a magnetic field application method for controlling convection as shown in Patent Documents 1, 2 and 3 and an inert method as shown in Patent Document 4 are used. There are known methods for controlling the flow rate of gas and the pressure inside the furnace, controlling the rotation of a quartz glass crucible, and controlling the rotation of a silicon single crystal as shown in Patent Document 5.

Special Publication No. 58-50953 Japanese Unexamined Patent Publication No. 2000-264784 Japanese Unexamined Patent Publication No. 4-31386 Japanese Unexamined Patent Publication No. 9-142990 Japanese Unexamined Patent Publication No. 2005-145724

By the way, even if the method of adjusting the oxygen concentration of the silicon single crystal is used, the oxygen concentration becomes high in the latter half of the straight body portion (the latter half of the pulling portion) of the silicon single crystal, and the oxygen concentration in the crystal growth axis direction becomes uniform. There was a problem that it was not possible to measure sex.

Specifically, the oxygen concentration of the silicon single crystal is such that the silicon melt reacts with the quartz component of the quartz glass crucible, dissolves the side wall of the quartz glass crucible, and oxygen is taken into the silicon melt. Therefore, if the silicon melt is incorporated into the silicon single crystal before the oxygen incorporated in the silicon melt is diffused or released, the oxygen concentration of the silicon single crystal increases.
Therefore, it is necessary to control the flow (convection) in the silicon melt so that the oxygen incorporated in the silicon melt is diffused or released before being incorporated into the silicon single crystal.

The flow in the silicon melt is controlled by using the method for adjusting the oxygen concentration of the silicon single crystal described above when the amount of the silicon melt in the quartz glass crucible is large (convection). Can be controlled.
However, when the amount of silicon melt in the quartz glass pot is small (the latter half of the straight body of the silicon single crystal (the latter half of pulling up)), the flow in the silicon melt cannot be controlled, and the straight body of the silicon single crystal. There is a problem that the oxygen concentration becomes high in the latter half portion (the latter half portion of pulling up), and it is not possible to achieve uniformity of the oxygen concentration in the crystal growth axis direction of the silicon single crystal.

In order to solve this problem, in Patent Document 3, the magnetic field strength is increased from 3000 gauss to 2000 gauss, 1000 gauss, and 500 gauss as it is pulled up (as the amount of silicon melt contained in the quartz glass decreases). It has been proposed to reduce it.
However, when the magnetic field strength is reduced to 3000 gauss, 2000 gauss, 1000 gauss, and 500 gauss and the magnetic field is lowered, the variation in the oxygen concentration in the substrate surface perpendicular to the crystal growth axis becomes large, and the oxygen in the substrate surface becomes large. There was a technical problem that the uniformity of concentration was hindered.

In order to solve this problem, the present inventors aim to reduce the oxygen concentration, make the oxygen concentration in the substrate plane perpendicular to the crystal growth axis uniform, and make the oxygen concentration in the crystal growth axis direction uniform. Diligently studied.
In this study, the present inventors focused on the flow of the surface of the silicon melt, and when the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall side of the quartz glass crucible was equal to or less than a specific flow velocity, the oxygen concentration was increased. It was found that the reduction can be achieved and the uniformity of the oxygen concentration in the crystal growth axis direction can be achieved, and the present invention has been completed.

The present invention provides a method for producing a silicon single crystal, which can reduce the oxygen concentration, achieve the uniformity of the oxygen concentration in the crystal growth axis direction, and achieve the uniformity of the oxygen concentration in the substrate plane perpendicular to the crystal growth axis. The purpose is to provide.

The method for producing a silicon single crystal to achieve the above object is to grow a silicon single crystal while applying a horizontal magnetic field when pulling the silicon single crystal from a silicon melt in a quartz glass crucible. In the crystal manufacturing method, there is a flow of the silicon melt flowing from the silicon single crystal side to the silica crucible side wall on the surface of the silicon melt, and the flow velocity of the silicon melt flowing from the silicon single crystal side to the quartz glass crucible side wall is high. It is characterized by being 0.16 m / s or less.

In the present invention, the oxygen concentration of the silicon single crystal is reduced by setting the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the quartz glass rut to 0.16 m / s or less during the pulling up of the silicon single crystal. Therefore, the uniformity of the oxygen concentration in the direction of the crystal growth axis and the uniformity of the oxygen concentration in the substrate plane perpendicular to the crystal growth axis can be achieved.

As a flow of the silicon melt on the surface of the silicon melt, for example, it flows from the silicon single crystal side to the side wall side of the quartz glass crucible, then flows downward in contact with (along) the side wall of the quartz glass crucible, and rises from the bottom surface of the quartz glass crucible. There is a flow to do.

When this silicon melt flows in contact with the side wall of the quartz glass rut, silicon at the melting point is chemically active, so the silicon melt reacts with the quartz component of the quartz glass to dissolve the side wall of the quartz glass rut, and O Take in (oxygen).
Then, if oxygen is incorporated into the silicon single crystal before the oxygen is released and diffused from the silicon melt, the oxygen concentration of the silicon single crystal increases.
That is, when the flow from the silicon single crystal side to the side wall side of the quartz glass crucible becomes faster, the flow rising from the bottom surface of the quartz glass crucible also becomes faster, and oxygen is taken into the silicon single crystal before being released and diffused from the silicon melt. The degree increases.

In particular, when the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall side of the quartz glass rutsubo exceeds 0.16 m / s, the flow of the silicon melt rising from the bottom surface of the quartz glass rutsubo becomes faster, and silicon Before oxygen is released and diffused from the melt, it may be incorporated into the silicon single crystal, which is not preferable.

Here, it is desirable that the center of the magnetic field in the horizontal direction is located in the silicon melt within a range of 60 mm below the surface of the melt, and the magnetic field strength is at least 2000 gauss during the pulling of the silicon single crystal.

If the magnetic field strength is less than 2000 gauss, it becomes difficult to control the flow of the silicon melt. In particular, when the magnetic field is set to a low magnetic field, the variation in oxygen concentration in the substrate surface perpendicular to the crystal growth axis becomes large, and the oxygen concentration in the substrate surface cannot be made uniform, which is not preferable.
When the magnetic field strength exceeds 4000 gauss, the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the quartz glass crucible becomes 0.16 m / s or more, and the melt having a high oxygen concentration reaches the crystal. It is not preferable because it ends up. Therefore, the magnetic field strength is preferably 2000 gauss to 4000 gauss.
The position of the center of the magnetic field is preferably within a range of 60 mm downward from the surface of the melt, and more preferably within a range of 20 mm downward from the surface of the melt.

Further, the center of the magnetic field in the horizontal direction is located below the center of the silicon single crystal, and the magnetic field strength is at least 3000 gauss while pulling up the straight body portion of the silicon single crystal having a solidification rate of 0.4 or less. It is desirable to gradually reduce the magnetic field strength from the solidification rate of 0.4 to a solidification rate of 0.6, and to set the magnetic field strength to 2000 gauss after the solidification rate of 0.6.

Since the magnetic field strength is at least 3000 gauss during pulling up the straight body of the silicon single crystal with a solidification rate of 0.4 or less, the flow in the silicon melt can be controlled, the oxygen concentration is reduced, and the silicon single crystal crystal growth. The uniformity of the oxygen concentration in the axial direction can be achieved, the variation in the oxygen concentration in the substrate surface perpendicular to the crystal growth axis can be suppressed, and the uniformity of the oxygen concentration in the substrate surface can be achieved.

The magnetic field strength is gradually reduced from the solidification rate of 0.4 to a solidification rate of 0.6, and in particular, the magnetic field strength is set to 2000 gauss after the solidification rate of 0.6.
Therefore, the oxygen concentration can be reduced, the oxygen concentration in the crystal growth axis direction of the silicon single crystal can be made uniform, and the variation in the oxygen concentration in the substrate plane perpendicular to the crystal growth axis can be suppressed, and the oxygen concentration in the substrate plane can be suppressed. The uniformity of oxygen concentration can be further improved.

In addition, the radius of the silicon single crystal [mm] ÷ radius of the rut [mm] × the rotation speed of the silicon single crystal [rpm] × the magnetic field strength [Gauss] ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) [mm] It is desirable that the value calculated from is 190 or less.
If the value calculated from the radius of the silicon single crystal ÷ crucible radius × silicon single crystal rotation speed × magnetic field strength ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) is 190 or less, from the silicon single crystal side. The flow velocity of the silicon melt flowing on the side wall of the crucible can be 0.16 m / s or less.
As a result, as described above, the oxygen concentration of the silicon single crystal can be reduced, and the oxygen concentration in the crystal growth axis direction and the oxygen concentration in the substrate plane perpendicular to the crystal growth axis can be achieved. Can be done.

In addition, the method for producing a silicon single crystal made to achieve the above object is to grow the silicon single crystal while applying a horizontal magnetic field when pulling the silicon single crystal from the silicon melt in the quartz glass rubbing pot. In the method for producing a silicon single crystal, during the pulling process of the silicon single crystal, the radius of the silicon single crystal [mm] ÷ radius of the rut [mm] × the number of rotations of the silicon single crystal [rpm] × the magnetic field strength [Gauss] ÷ (silicon melt) Distance from the surface of the shield plate to the lower end of the shielding plate) [mm] so that the value calculated from [mm] is 190 or less, the radius of the silicon single crystal, the radius of the rut, the number of rotations of the silicon single crystal, the magnetic field strength, and the surface of the silicon melt. The feature is that the distance from the to the lower end of the shielding plate is adjusted and the silicon single crystal is pulled up.

Calculated from the radius of the silicon single crystal [mm] ÷ radius of the rut [mm] x the number of rotations of the silicon single crystal [rpm] x magnetic field strength [Gauss] ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) [mm] By setting the value to 190 or less, the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the quartz glass rut can be set to 0.16 m / s or less while the silicon single crystal is being pulled up. The oxygen concentration of a single crystal can be reduced, and the uniformity of the oxygen concentration in the direction of the crystal growth axis and the uniformity of the oxygen concentration in the substrate plane perpendicular to the crystal growth axis can be achieved.

In addition, it was calculated from the radius of the silicon single crystal ÷ radius of the crucible × the number of rotations of the silicon single crystal × the magnetic field strength ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) without measuring the flow velocity of the silicon melt. From the value, it can be determined whether the flow velocity of the silicon melt flowing from the silicon single crystal side to the crucible side wall is 0.16 m / s or less.

According to the present invention, it is possible to reduce the oxygen concentration, achieve the uniformity of the oxygen concentration in the crystal growth axis direction, and achieve the uniformity of the oxygen concentration in the substrate plane perpendicular to the crystal growth axis. A manufacturing method can be obtained.

FIG. 1 is a schematic view showing the flow of the silicon melt. FIG. 2 is a schematic view showing the flow of the silicon melt in the state where the silicon melt in the quartz glass crucible is reduced from the state of FIG. FIG. 3 is a schematic view showing another flow of the silicon melt. It is the schematic which showed the flow of the silicon melt when the magnetic field strength was 1000 gauss, (a) plan view, (b) is a sectional view. It is the schematic which showed the flow of the silicon melt when the magnetic field strength was 2000 gauss, (a) plan view, (b) is a sectional view. It is the schematic which showed the flow of the silicon melt when the magnetic field strength was 3000 gauss, (a) plan view, (b) is a sectional view. It is a schematic block diagram of a silicon single crystal pulling apparatus. It is a figure which shows the change of the magnetic field strength in Experiments 1 to 4. It is a figure which shows the flow direction and the flow velocity of the surface of a silicon melt, (a) is a figure which shows the solidification rate 0.25 (magnetic field strength 3000 gauss) time point of Experiment 1, and (b) is solidification of Experiment 1. The figure which shows the time point of rate 0.6 (magnetic field strength 3000 gauss), (c) is the figure which shows the time point of solidification rate 0.6 (magnetic field strength 2000 gauss) of Experiment 2. It is a figure which shows the relationship between the solidification rate and oxygen concentration in Experiments 1 to 4. It is a figure which shows the relationship between the solidification rate in Experiments 1 to 4 and the variation of the oxygen concentration in the crystal growth axis direction of a silicon single crystal. It is a figure which shows the relationship between the magnetic field strength and the variation of the oxygen concentration in the substrate plane perpendicular to the crystal growth axis in Experiment 2, (a) is the figure which shows the measurement point, (b) is the figure at each measurement point. It is a figure which shows the variation of the oxygen concentration in the substrate surface. It is a figure which shows the change of the magnetic field strength in Experiments 5 and 6. It is a figure which shows the relationship between the solidification rate in Experiments 5 and 6 and the variation of the resistivity in the crystal growth axis direction of a silicon single crystal. It is a figure which shows the relationship between the position of the center of a magnetic field, and the oxygen concentration in Experiments 1, 16-20.

The method for producing a silicon single crystal according to the present invention is a method for producing a silicon single crystal in which a silicon single crystal is grown while applying a horizontal magnetic field when the silicon single crystal is pulled up from a silicon melt in a quartz glass crucible. On the surface of the silicon melt, there is a flow of the silicon melt flowing from the silicon single crystal side to the side wall of the quartz crucible, and the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the quartz glass crucible is 0.16 m / s. It is as follows.
In particular, it is characterized in that the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the crucible during pulling up of the silicon single crystal is 0.16 m / s or less.

The silicon melt in the quartz glass crucible is affected by the magnetic field strength, the magnetic field center position, the flow rate and furnace pressure of the inert gas, the rotation of the quartz glass crucible, the rotation of the silicon single crystal, etc., and the silicon melt in the quartz glass crucible. Changes occur in the flow of liquid (convection).

FIG. 1 is a diagram showing an example of the flow of the silicon melt M in the quartz glass crucible, and based on this figure, the flow velocity of the silicon melt M flowing from the silicon single crystal side to the side wall of the crucible is 0.16 m /. The reason for setting the value to s or less will be described.
FIG. 1 shows the result of a simulation of the flow of the silicon melt under the condition that the solidification rate was increased by 0.25 in Experiment 1 described later. When 3000 gauss was applied in the horizontal direction, the center of the magnetic field in the horizontal direction was silicon. It shows the flow of the silicon melt located in the silicon melt 20 mm below the free surface in the center of the single crystal. Further, in the figure, B indicates that the direction of the magnetic flux is from the back side of the paper surface to the front side of the paper surface.

The silicon melt M in the quartz glass crucible 1 has various flows.
For example, as shown by the arrow X1 in FIG. 1, the silicon melt has a flow that flows from above (along) in contact with the side wall 1a of the quartz glass crucible.
When this silicon melt flows in contact with (along) the side wall 1a of the quartz glass rulu pot, silicon at the melting point is chemically active, so that the silicon melt M reacts with the quartz component of the quartz glass rulu pot 1 to form quartz. The side wall 1a of the glass rut pot 1 is melted and O (oxygen) is taken in.

The oxygen-containing silicon melt M rises from the bottom surface of the crucible (bottom surface of the center of the crucible) below the silicon single crystal C, as shown by the arrow X2.
After that, as shown by the arrow X3, it flowed (serpentically) outward in the radial direction of the crucible, then returned to the lower side of the silicon single crystal C as shown by the arrow X4, and returned to the lower side of the silicon single crystal C as shown by the arrow X5. Flows from the side wall of the crucible.

In this way, the silicon melt M in which the side wall 1a of the quartz glass crucible 1 is melted and O (oxygen) is taken in, that is, the silicon melt M containing a large amount of oxygen is from the bottom surface of the crucible 1 below the silicon single crystal C. When ascending, it meanders outward in the radial direction and then reaches the free surface.
As a result, O taken into the silicon melt M diffuses, the oxygen concentration of the silicon melt M is reduced, the oxygen uptake of the silicon single crystal C is suppressed, and the oxygen concentration of the silicon single crystal C is reduced. Is planned.

Next, the flow of the silicon melt M in the quartz glass crucible 1 in a state where the silicon single crystal C is pulled up from the state of FIG. 1 and the silicon melt M in the quartz glass crucible 2 is reduced is shown in FIG. Shown. Note that FIG. 2 shows the results of a simulation of the flow of the silicon melt under the condition of raising the solidification rate of 0.6 in Experiment 1 described later.

As shown in FIG. 2, when the pulling of the silicon single crystal C progresses and the silicon melt in the quartz glass crucible 1 decreases, the generation of a large meandering flow outward in the radial direction as shown in FIG. 1 is suppressed. The flow X2 rising from the bottom surface of the crucible below the silicon single crystal C (bottom surface of the center of the crucible) becomes stronger (the flow velocity becomes faster).

In this way, when the silicon melt rises from the bottom surface of the crucible toward the lower end of the silicon single crystal C without meandering, the silicon single crystal before oxygen is diffused or released from the silicon melt that has taken in oxygen. It is taken into C.
That is, the silicon melt rising from the bottom surface of the crucible below the silicon single crystal contains a large amount of O, and if this is incorporated into the silicon single crystal, the oxygen concentration cannot be reduced and the crystal growth axis direction. The uniformity of oxygen concentration in silicon is impaired.

Here, when the flow velocity of the flow X2 rising from the bottom surface of the crucible below the silicon single crystal is small, the flow velocity of the silicon melt flowing from the silicon single crystal C side to the crucible side wall 1a is also small.
In other words, when the flow velocity of the silicon melt flow X5 flowing from the silicon single crystal side to the crucible side wall 1a is small, the flow velocity of the flow X2 rising from the crucible bottom surface 1b below the silicon single crystal C is also small.

When the flow X2 rising from the crucible bottom surface 1b below the silicon single crystal C is small, the time from the crucible side wall 1a to reach the silicon single crystal C via the crucible bottom surface 1a as shown in FIG. Or rises from the bottom of the crucible, then meanders outward in the radial direction of the crucible, passes just below the liquid surface, and is taken into the silicon crystal, so O diffuses from the silicon melt and the oxygen concentration is reduced. , The uniformity of the oxygen concentration in the direction of the crystal growth axis and the uniformity of the oxygen concentration in the substrate plane perpendicular to the crystal growth axis can be achieved.
In particular, when the flow velocity of the silicon melt flow X5 flowing from the silicon single crystal C side to the crucible side wall 1b is 0.16 m / s or less, the oxygen concentration can be further reduced, and the oxygen concentration in the crystal growth axis direction can be reduced. Variation can be suppressed.

Further, as shown in FIG. 3, as a flow of the silicon melt in the quartz glass crucible 1, for example, there is a flow Y1 that flows from the lower side to the upper side in contact with (along) the side wall 1a of the quartz glass crucible.
Also in this case, the silicon melt reacts with the quartz component of the quartz glass crucible, dissolves the side wall 1b of the quartz glass crucible, and takes in O (oxygen).

This silicon melt flows along the side wall of the quartz glass crucible 1 and reaches the free surface. After that, a flow Y2 flowing from the side wall of the quartz glass crucible 1 to the silicon single crystal side is formed.
In this flow Y2 of the silicon melt, the degree of diffusion and evaporation of O taken into the silicon melt is high, the silicon melt having a low oxygen concentration flows to the silicon single crystal side, and only the outer peripheral portion of the silicon single crystal is low. It is not preferable because it becomes a concentration and leads to deterioration of the in-plane distribution.

Also in the case shown in FIG. 3, a flow X2 rising from the bottom surface 1b of the crucible below the silicon single crystal C is formed.
That is, the silicon melt flowing from the side wall of the quartz glass crucible to the silicon single crystal side has a low oxygen concentration, and O diffuses and dissipates in the silicon melt rising from the bottom surface of the crucible below the silicon single crystal C. It does not have a high oxygen concentration.
As a result, the oxygen concentration in the central part of the silicon single crystal becomes high, while the oxygen concentration in the outer peripheral part of the silicon single crystal becomes low, so that the in-plane distribution deteriorates and the oxygen in the substrate plane perpendicular to the crystal growth axis becomes high. Concentration uniformity is impaired.
Therefore, it is desirable that the flow Y2 from the crucible side wall to the silicon single crystal side in the surface flow of the silicon melt M does not reach the silicon single crystal.

Further, the flow of the silicon melt in the quartz glass crucible is affected by the magnetic field strength. In particular, when the pulling of the silicon single crystal progresses and the amount of the silicon melt in the quartz glass crucible decreases, the flow of the silicon melt flowing from the silicon single crystal side to the side wall of the crucible changes due to the strong influence of the magnetic field strength.
That is, even if the flow rate of the inert gas, the pressure in the furnace, the rotation speed of the quartz glass crucible, and the rotation speed of the silicon single crystal are the same, the flow of the silicon melt in the quartz glass crucible changes depending on the magnitude of the magnetic field strength. ..

For example, FIG. 4 shows the flow of the silicon melt when 1000 gauss is applied in the horizontal direction.
FIG. 4 shows the result of simulating the flow of the silicon melt under the condition of raising the solidification rate of 0.6 in Experiment 1 described later, and when 1000 gauss was applied in the horizontal direction, the center of the magnetic field in the horizontal direction was set. It shows the flow of the silicon melt located in the silicon melt 20 mm below the free surface in the center of the silicon single crystal.
Further, in the figure, the symbol ○ point of B indicates that the direction of the magnetic flux is from the back side of the paper surface to the front side of the paper surface. The arrow symbol B indicates the direction of the magnetic flux. Note that FIG. 4B is the same diagram as that of FIG.

As shown in FIGS. 4 (a) and 4 (b), in the case of 1000 gauss, the flow Y2 of the silicon melt flowing from the side wall of the crucible to the silicon single crystal side is generated, which is not preferable.
Further, since the flow X2 rising from the bottom surface of the crucible below the silicon single crystal C becomes strong, the silicon melt in which oxygen is incorporated flows to the lower end of the silicon single crystal, and a large amount of oxygen is incorporated into the silicon single crystal, which is preferable. Absent.

Further, in the state shown in FIG. 4, the case where the magnetic field strength is changed from 1000 gauss to 2000 gauss is shown in FIGS. 5 (a) and 5 (b).
As shown in FIG. 5, the oxygen-containing silicon melt meanders outward in the radial direction (flow X3) and rises. As a result, the oxygen in the silicon melt diffuses, and the oxygen concentration can be reduced.

Similarly, in the state shown in FIG. 4, the case where the magnetic field strength is changed from 1000 gauss to 3000 gauss is shown in FIGS. 6 (a) and 6 (b).
As shown in FIG. 6, the oxygen-containing silicon melt meanders outward in the radial direction (flow X3) and rises. As a result, the oxygen in the silicon melt diffuses, and the oxygen concentration can be reduced.

Therefore, during the pulling of the silicon single crystal, the magnetic field strength is at least 2000 gauss, and the flow of the silicon melt flowing from the silicon single crystal side to the side wall of the crucible is controlled as a flow on the surface of the silicon melt. Is preferable.
Further, when there is a flow from the crucible side wall toward the silicon single crystal side as a flow on the surface of the silicon melt, the flow from the crucible side wall toward the silicon single crystal side is controlled so as not to reach the silicon single crystal. Is preferable.

In particular, the magnetic field strength is preferably at least 3000 gauss during pulling up of the straight body portion of a silicon single crystal having a solidification rate of 0.4 or less, in which a sufficient silicon melt is present in the quartz glass crucible.
Due to the presence of sufficient silicon melt in the quartz glass crucible, a large meandering flow occurs outward in the radial direction as shown in FIG. As a result, oxygen in the silicon melt is diffused and dissipated, so that the oxygen concentration of the silicon single crystal can be reduced.

Further, it is desirable to gradually reduce the magnetic field strength from the solidification rate of 0.4 to the solidification rate of 0.6, and to set the magnetic field strength to 2000 gauss after the solidification rate of 0.6.
As shown in FIGS. 5 (a) and 5 (b), when the magnetic field strength is gradually lowered in the quartz glass crucible as the silicon melt decreases, and the magnetic field strength is set to 2000 gauss after the solidification rate of 0.6. The oxygen-containing silicon melt meanders outward in the radial direction and rises from the bottom surface of the crucible below the silicon single crystal. As a result, the oxygen in the silicon melt is diffused and the oxygen concentration can be reduced, and the environment shown in FIGS. 1 and 5 (b) is similar, so that the oxygen concentration in the crystal axis direction becomes uniform.

Further, the condition that there is a flow of the silicon melt flowing from the silicon single crystal side to the crucible side wall and the flow velocity of the silicon melt flowing from the silicon single crystal side to the crucible side wall is 0.16 m / s or less is the magnetic field strength. It is affected by the flow rate of inert gas, internal pressure control, rotation control of quartz glass crucible, rotation control of silicon single crystal, etc.
The flow velocity of the silicon melt can be measured using a tracer or the like, but when the measurement is performed, the crystal being pulled up cannot be used as a product, and the work is troublesome. Therefore, the flow velocity of the silicon melt is estimated by simulation, but the calculation time becomes enormous under the condition that three-dimensional convection analysis is required such as a transverse magnetic field.

Therefore, the present inventors have investigated a relational expression for easily finding a condition for the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the crucible to be 0.16 m / s or less.
Specifically, when the value calculated from the radius of the silicon single crystal ÷ crucible radius × silicon single crystal rotation speed × magnetic field strength ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) is 190 or less. It was clarified by a three-dimensional simulation that the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the crucible can be set to 0.16 m / s or less.

Here, the reason why the radius of the silicon single crystal ÷ the radius of the crucible × the number of rotations of the silicon single crystal × the magnetic field strength ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) is as follows.
The driving force of the flow from the silicon crystal to the crucible wall side is due to the silicon single crystal and the crucible radius, the silicon single crystal rotation speed and the magnetic field strength.
Here, when the crucible radius is large, the driving force of the flow from the silicon crystal to the crucible wall side works in the direction of decreasing, so the crucible radius is divided (divided).

Normally, only the driving force should be considered, but since the ease of controlling the melt oxygen concentration changes depending on the distance from the surface of the silicon melt to the lower end of the shielding plate, this distance is also taken into consideration. There is a need to. For example, if this distance is too narrow, the influence of the atmosphere inside the furnace (Ar gas flow rate and pressure inside the furnace) is large, and it is difficult to control by the magnetic field strength. Force control is effective.
Since it is considered that the rotation speed of the crucible has a small effect on the flow velocity, it is not included in the above relational expression. However, the lower the rotation speed of the crucible, the lower the oxygen crystal can be obtained. Therefore, the rotation speed of the crucible is preferably 1.0 rpm or less.

(Experiments 1-4)
Using a general pulling device as shown in FIG. 7, the silicon single crystal is pulled under the conditions shown in Tables 1 and 8, and the flow velocity of the silicon melt from the silicon single crystal side to the rutsubo side wall side during the pulling. , The variation of the oxygen concentration and the oxygen concentration in the crystal growth axis direction of the silicon single crystal, and the variation of the oxygen concentration in the substrate plane perpendicular to the crystal growth axis were measured.

First, the pulling device shown in FIG. 7 will be described. This device 10 melts a cylindrical chamber (chamber) 11, a crucible 12 provided in the chamber 11, and a raw material silicon loaded in the crucible 12. It has a carbon heater 13. The crucible 12 is composed of a quartz glass crucible 12a on the inside and a graphite crucible 12b on the outside. Further, in the chamber 11, a heat insulating cylinder 14 is provided around the outer periphery of the carbon heater 13. The heat insulating cylinder 14 is formed in a cylindrical shape, and an inwardly extending heat insulating plate 15 is provided at the upper end thereof. Further, a radiant shield (shielding plate) 16 is provided on the growing (pulling) silicon single crystal C so as not to give extra radiant heat from the carbon heater 13 or the like.

The radiation shield (shielding plate) 16 has openings 16a and 16b formed in the upper part and the lower part so as to surround the periphery of the silicon single crystal C above and in the vicinity of the crucible 12, and as it goes from the upper part to the lower part, The tapered surface 16c is formed so that the area of the opening gradually decreases. By providing the radiation shield 16, the purging inert gas (Ar gas) G supplied into the crucible 12 from above passes through the gap between the radiation shield 16 and the surface of the silicon melt M, and passes through the crucible 12. It flows out and is finally discharged to the outside of the chamber 11 (outside the chamber).
The gap between the lower end of the radiation shield 16 and the surface of the silicon melt M is called a gap.

Further, on the outside of the chamber 11, a magnetic field generator 17 for applying a magnetic field in the horizontal direction is provided. The magnetic field generated by the magnetic field generator 17 is arranged so that the center of the magnetic field in the horizontal direction is located in the silicon melt below the free surface in the center of the silicon single crystal.
Further, the magnetic field generator 17 is controlled so that the magnetic field strength is generated at least 2000 gauss during the pulling of the silicon single crystal.

Although not shown, a pulling mechanism for pulling up the silicon single crystal C is provided above the chamber 11. This pulling mechanism is composed of a winding mechanism driven by a motor and a pulling wire 18 wound around the winding mechanism. Then, a seed crystal P is attached to the tip of the wire 18 so as to pull up the silicon single crystal C while growing it.

Although not shown, the silicon single crystal manufacturing apparatus 10 includes a motor for rotating the crucible 12, an elevating device for controlling the height of the crucible 12, and a control device for controlling the motor and the elevating device. It is configured to grow the silicon single crystal C while rotating the 12 and increasing the height of the crucible 12.

Further, although not shown, a gas supply port 11a is provided in the upper part of the chamber 11 so that the purging inert gas (Ar gas) is supplied into the chamber 11. Further, a plurality of exhaust ports 11b are provided on the bottom surface of the chamber 11, and an exhaust pump (not shown) as an exhaust means is connected to the exhaust ports.
Therefore, the purging inert gas (Ar gas) G supplied into the chamber 11 from the gas supply port flows out of the rutsubo through the gap between the radiation shield 16 and the surface of the silicon melt M by the exhaust pump. Finally, the gas is discharged to the outside of the chamber 11 (outside the chamber).

Here, Gap in Table 1 is the clearance dimension between the radiation shield 16 and the surface of the silicon melt M, SR is the crystal rotation speed, CR is the crucible rotation speed, and the purging inert gas (Ar) supplied into the chamber 11. The flow rate of gas) and the pressure in the furnace are the pressures in the chamber 11.
The magnetic field strength was changed under the conditions shown in FIG. 8, and the magnetic field position was set to 20 mm below the surface of the silicon melt M.
That is, in Experiment 1, the silicon single crystal was pulled up with the magnetic field strength set to 3000 gauss.
In Experiment 2, the magnetic field strength was set to 3000 gauss and the silicon single crystal was pulled up to a solidification rate of 0.4, the magnetic field strength was gradually lowered to a solidification rate of 0.7, and then the silicon single crystal was pulled up to a solidification rate of 1500 gauss. Was done.
In Experiment 3, the magnetic field strength was set to 3000 gauss and the silicon single crystal was pulled up to a solidification rate of 0.4, the magnetic field strength was gradually lowered to a solidification rate of 0.6, and then the magnetic field strength was set to 2000 gauss and the silicon single crystal was pulled up. Was done.
In Experiment 4, the magnetic field strength was set to 3000 gauss, the magnetic field strength was gradually reduced to a solidification rate of 0.2, and then the magnetic field strength was set to 2000 gauss to pull up the silicon single crystal.

FIG. 9 shows the flow direction and the flow velocity of the silicon melt during pulling in Experiments 1 to 4.
FIG. 9A shows the flow direction and the flow velocity of the silicon melt when the solidification rate is raised by 0.25 in Experiment 1 (3000 gauss: see FIG. 8).
FIG. 9B shows the flow direction and the flow velocity of the silicon melt when the solidification rate is increased by 0.6 in Experiment 1 (3000 gauss: see FIG. 8).
FIG. 9C shows the flow direction and the flow velocity of the silicon melt when the solidification rate is increased by 0.6 in Experiment 3 (2000 gauss: see FIG. 8).

As shown in FIG. 9A, the maximum value of the flow velocity when the solidification rate is raised by 0.25 (3000 gauss) is in the range of 0.25 to 0.24 m / s.
Further, as shown in FIG. 9B, the maximum value of the flow velocity when the solidification rate is raised by 0.6 (3000 gauss) is within the range of 0.20 to 0.24 m / s.
On the other hand, as shown in FIG. 9C, the maximum value of the flow velocity when the solidification rate is raised by 0.6 (2000 gauss) is in the range of 0.12 to 0.16 m / s.
Therefore, when the pulling of the silicon single crystal progresses and the silicon melt in the quartz glass crucible decreases, the maximum value of the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the quartz crucible by lowering the magnetic field strength. Can be 0.16 m / s or less.

In addition, the oxygen concentration of the pulled-up silicon single crystal was measured. The measurement was performed using Fourier transform infrared spectroscopy (FT-IR). The result is shown in FIG.
In Experiment 1, the oxygen concentration after the solidification rate of 0.6 increased, whereas in Experiments 2, 3 and 4, no increase in the oxygen concentration after the solidification rate of 0.6 was observed, or oxygen. Even if the concentration increases, it is less than ^{1.0 × 10 18} atoms / cm ^3.

That is, as a result of applying a magnetic field of 3000 gauss after the solidification rate of 0.6, as can be seen from FIG. 9B, the flow velocity on the surface of the silicon melt is high.
Therefore, a large meandering flow outward in the radial direction as shown in FIG. 1 does not occur, and the flow rises from the bottom surface of the crucible below the silicon single crystal and is incorporated into the silicon single crystal. As a result, it is considered that the oxygen concentration increased after the solidification rate of 0.6.

In addition, the variation ΔOi of the oxygen concentration in the crystal length direction of the pulled-up silicon single crystal was measured. The measurement was performed by Fourier transform infrared spectroscopy (FT-IR) under the condition of a pitch of 5 mm in the radial direction. The result is shown in FIG.
Oxygen concentration variation ΔOi
It was calculated from the formula ΔOi = (maximum value of measurement point − minimum value) / minimum value × 100 [%].

In Experiment 2, the oxygen concentration after the solidification rate of 0.7 varies, whereas in Experiments 1, 3 and 4, no large in-plane variation in oxygen concentration is observed.
It is considered that this is because the silicon melt convection became unstable and the variation in oxygen concentration became large as a result of applying a magnetic field (1500 gauss) of 2000 gauss or less after the solidification rate of 0.7.

Further, FIG. 12 (b) shows the variation in the oxygen concentration in the substrate surface at the measured magnetic field strength of FIG. 12 (a) in Experiment 2.
That is, the substrates cut out from the solidification rates of 0.52 (Sample No. 1), 0.59 (Sample No. 2), 0.67 (Sample No. 3), and 0.75 (Sample No. 4) in Experiment 2. The variation in the in-plane oxygen concentration was measured. The measurement was performed by Fourier transform infrared spectroscopy (FT-IR) under the condition of a pitch of 5 mm in the radial direction. The result is shown in FIG. 12 (b).
As can be seen from this figure, when the magnetic field strength is 2000 gauss, there is little variation in the in-plane oxygen concentration.

(Experiments 5 and 6)
In Experiments 5 and 6, the silicon single crystal was pulled up by changing the magnetic field strength as shown in FIG. The conditions for raising the price are as follows.
In Experiment 5, the magnetic field strength was set to 3000 gauss, the magnetic field strength was gradually lowered from the solidification rate of 0.4, and the magnetic field strength was set to 2000 gauss from the solidification rate of 0.6. Other conditions were the same as in Experiment 1.
In Experiment 6, the magnetic field strength was set to 2000 gauss, the magnetic field strength was gradually increased to a solidification rate of 0.2, then the magnetic field strength was gradually decreased from the solidification rate of 0.4, and the magnetic field strength was increased to 2000 gauss from the solidification rate of 0.6. And said. Other conditions were the same as in Experiment 1.

Then, the variation in the in-plane resistivity of the substrate cut out from the pulled-up silicon single crystal was measured. The measurement was performed using a four-probe method at a pitch of 5 mm in the radial direction of the silicon substrate. The result is shown in FIG.
As is clear from FIG. 14, when the magnetic field strength is 2000 gauss, the in-plane resistivity variation is small.

(Experiment 7 to Experiment 15)
To easily find the condition that there is a flow of the silicon melt flowing from the silicon single crystal side to the crucible side wall and the flow velocity of the silicon melt flowing from the silicon single crystal side to the crucible side wall is 0.16 m / s or less. Confirmed the relational expression of. The flow velocity in Table 2 is a value obtained from the simulation.
That is, when the value calculated from the radius of the silicon single crystal ÷ crucible radius × silicon single crystal rotation speed × magnetic field strength ÷ distance to the lower end of the shielding plate using the conditions shown in Table 2 is 190 or less, silicon. It was confirmed that there was a flow of the silicon melt flowing from the single crystal side to the crucible side wall, and the flow velocity of the silicon melt flowing from the silicon single crystal side to the crucible side wall could be 0.16 m / s or less.
Even when the magnetic field strength is 1000 gauss and 1500 gauss, the flow velocity may be 0.16 m / s or less, but this is not preferable because good in-plane uniformity of oxygen concentration cannot be obtained.

In this way, when the value calculated from the radius of the silicon single crystal ÷ crucible radius × silicon single crystal rotation speed × magnetic field strength ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) is 190 or less, silicon The flow velocity of the silicon melt flowing from the single crystal side to the side wall of the crucible is 0.16 m / s or less.
Therefore, it was calculated from the radius of the silicon single crystal ÷ radius of the crucible × the number of rotations of the silicon single crystal × the magnetic field strength ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) without measuring the flow velocity of the silicon melt. From the value, it can be determined whether the flow velocity of the silicon melt flowing from the silicon single crystal side to the crucible side wall is 0.16 m / s or less.

(Experiment 1, Experiment 16 to Experiment 20)
As shown in Table 3, in Experiment 1 (the position of the center of the magnetic field was 20 mm below the surface of the melt), the silicon single crystal was pulled up and the oxygen concentration at a solidification rate of 0.25 was measured. The measurement was performed using Fourier transform infrared spectroscopy (FT-IR). The result is shown in FIG.
With respect to Experiment 1, as shown in Table 3, the silicon single crystal was pulled up under the same conditions as in Experiment 1 except that the position of the center of the magnetic field was changed, and the oxygen concentration at a solidification rate of 0.25 was measured (Experiment 16). ~ Experiment 20). The result is shown in FIG.

As is clear from FIG. 15, when the center of the magnetic field is located in the silicon melt within a range of 60 mm below the surface of the melt (Experiments 17, 18), the oxygen concentration is 1.0 × 10 ¹⁸ atoms / cm. It turned out to be as low as less than ^3.

1 Quartz glass crucible 1a Quartz glass crucible side wall C Silicon single crystal M Silicon melt X1 Flow of silicon melt flowing from above to downward while in contact with the side wall of quartz glass crucible X2 Ascending from the bottom of the crucible below silicon single crystal C , Silicon melt flow X3 Flow of silicon melt flowing outward of the crucible X4 Flow of silicon melt flowing inward of the crucible X4 and returning to the bottom of the silicon single crystal, Silicon melt flow X5 On the surface of the silicon melt, Flow of silicon melt flowing from the silicon single crystal side to the crucible side wall side

Claims (5)

In a method for producing a silicon single crystal in which a silicon single crystal is grown while applying a horizontal magnetic field when the silicon single crystal is pulled up from a silicon melt in a quartz glass crucible.
On the surface of the silicon melt, there is a flow of the silicon melt flowing from the silicon single crystal side to the side wall of the quartz crucible, and the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the quartz glass crucible is 0.16 m / s or less. A method for producing a silicon single crystal, which is characterized by the above. Claim 1 is characterized in that the center of the horizontal magnetic field is located in the silicon melt within a range of 60 mm below the surface of the melt, and the magnetic field strength is at least 2000 gauss during the pulling of the silicon single crystal. The method for producing a silicon single crystal according to the above. The center of the horizontal magnetic field is located below the center of the silicon single crystal.
The magnetic field strength is at least 3000 gauss during pulling up of the straight body of a silicon single crystal with a solidification rate of 0.4 or less.
Gradually reduce the magnetic field strength from the solidification rate of 0.4 to the solidification rate of 0.6.
The method for producing a silicon single crystal according to claim 1 or 2, wherein the magnetic field strength is 2000 gauss after the solidification rate of 0.6. Calculated from the radius of the silicon single crystal [mm] ÷ radius of the rut [mm] x the number of rotations of the silicon single crystal [rpm] x magnetic field strength [Gauss] ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) [mm] The method for producing a silicon single crystal according to any one of claims 1 to 3, wherein the value obtained is 190 or less. In a method for producing a silicon single crystal in which a silicon single crystal is grown while applying a horizontal magnetic field when the silicon single crystal is pulled up from a silicon melt in a quartz glass crucible.
During the pulling process of the silicon single crystal,
Calculated from the radius of the silicon single crystal [mm] ÷ radius of the rut [mm] x rotation speed of the silicon single crystal [rpm] x magnetic field strength [Gauss] ÷ (distance from the surface of the silicon melt to the lower end of the shielding plate) [mm] So that the value is 190 or less
The radius of the silicon single crystal, the radius of the crucible, the number of rotations of the silicon single crystal, the magnetic field strength, and the distance from the surface of the silicon melt to the lower end of the shielding plate are adjusted.
A method for producing a silicon single crystal, which comprises pulling up a silicon single crystal.