JP7249913B2 - Manufacturing method of silicon single crystal - Google Patents

Description

The present invention relates to a method for producing a silicon single crystal, and in particular, reduces the oxygen concentration, improves the uniformity of the oxygen concentration in the direction of the crystal growth axis, and further improves the uniformity of the oxygen concentration within the substrate surface perpendicular to the crystal growth axis. It is related with the manufacturing method of the silicon single crystal which can aim at.

In the conventional CZ method, the oxygen concentration in silicon substrates has been relatively high (≧1.0×10 ¹⁸ atoms/cm ³ ) in order to achieve a gettering effect. Oxide Semiconductor) image sensors, etc. require low-oxygen substrates (<1.0×10 ¹⁸ atoms/cm ³ ) to reduce white defects.
Silicon substrates are manufactured from silicon single crystals. As a method for manufacturing this silicon single crystal, the Czochralski method (CZ Law) is widely used.

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

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

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) 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 sexuality.

Specifically, the silicon melt reacts with the quartz component of the silica glass crucible to dissolve the side walls of the silica glass crucible, and oxygen is incorporated into the silicon melt. Therefore, if the silicon melt is taken into the silicon single crystal before the oxygen taken into 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 taken into the silicon melt diffuses or is released before being taken into the silicon single crystal.

When the amount of silicon melt in the quartz glass crucible is large, the flow (convection) in the silicon melt is controlled by using the above-described method of adjusting the oxygen concentration of the silicon single crystal. can be controlled.
However, when the amount of silicon melt in the quartz glass crucible is small (the latter half of the straight body portion of the silicon single crystal (the latter half of pulling)), the flow in the silicon melt cannot be controlled, and the straight body of the silicon single crystal cannot be controlled. There is a problem that the oxygen concentration is high in the latter half of the portion (the latter half of the pulling), and the uniformity of the oxygen concentration in the crystal growth axis direction of the silicon single crystal cannot be achieved.

In order to solve this problem, Patent Document 3 discloses that the magnetic field strength is increased from 3000 gauss, 2000 gauss, 1000 gauss and 500 gauss as the pulling (as the amount of silicon melt contained in the quartz glass decreases). is proposed to be lowered.
However, when the magnetic field strength is decreased to 3000 gauss, 2000 gauss, 1000 gauss, and 500 gauss, and the magnetic field is reduced to a low magnetic field, the variation in the oxygen concentration in the substrate plane perpendicular to the crystal growth axis increases, and the oxygen concentration in the substrate plane increases. There is a technical problem that the uniformity of concentration is disturbed.

In order to solve these problems, the present inventors have attempted to reduce the oxygen concentration, improve the uniformity of the oxygen concentration in the substrate plane perpendicular to the crystal growth axis, and the uniformity of the oxygen concentration in the direction of the crystal growth axis. studied diligently.
In this research, the present inventors focused on the flow on the surface of the silicon melt, and found that when the flow velocity of the silicon melt flowing from the silicon single crystal side to the silica glass crucible side wall side is below a specific flow velocity, the oxygen concentration The inventors have found that it is possible to reduce the oxygen content and to achieve uniformity of the oxygen concentration in the direction of the crystal growth axis, and have completed the present invention.

The present invention provides a method for producing a silicon single crystal that can reduce the oxygen concentration, achieve uniformity in the oxygen concentration along the crystal growth axis, and achieve uniformity in the oxygen concentration within the substrate surface perpendicular to the crystal growth axis. intended to provide

A method for producing a silicon single crystal, which has been devised to achieve the above object, is a silicon single crystal that grows while applying a horizontal magnetic field when pulling a silicon single crystal from a silicon melt in a quartz glass crucible. In the crystal manufacturing method, a flow of the silicon melt flows from the silicon single crystal side to the silica crucible side wall on the silicon melt surface, and the flow velocity of the silicon melt flowing from the silicon single crystal side to the silica glass crucible side wall is 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 crucible to 0.16 m/s or less during the pulling of the silicon single crystal. Therefore, uniformity of oxygen concentration in the crystal growth axis direction and uniformity of oxygen concentration in the substrate plane perpendicular to the crystal growth axis can be achieved.

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

When this silicon melt flows in contact with the side wall of the silica glass crucible, since silicon at its melting point is chemically active, the silicon melt reacts with the quartz component of the silica glass, dissolves the side wall of the silica glass crucible, and O Take in (oxygen).
If oxygen is taken into the silicon single crystal before being 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 silica glass crucible side wall side becomes faster, the flow rising from the silica glass crucible bottom surface also becomes faster, and oxygen is taken into the silicon single crystal before it is released and diffused from the silicon melt. 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 silica glass crucible exceeds 0.16 m/s, the flow of the silicon melt rising from the bottom surface of the silica glass crucible also increases, Before oxygen is released and diffused from the melt, it may be taken into the silicon single crystal, which is not preferable.

Here, it is desirable that the center of the horizontal magnetic field is located in the silicon melt within a range of 60 mm below the melt surface, 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, if the magnetic field is low, the variation in the oxygen concentration in the substrate plane perpendicular to the crystal growth axis becomes large, making it impossible to achieve uniformity in the oxygen concentration in the substrate plane, which is not preferable.
When the magnetic field intensity 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 with a high oxygen concentration reaches the crystal. I don't like it because I can't put it away. Therefore, the magnetic field strength is preferably 2000 Gauss to 4000 Gauss.
The position of the magnetic field center is preferably within a range of 60 mm below the melt surface, more preferably within a range of 20 mm below the melt surface.

Further, the center of the horizontal magnetic field is located below the central portion of the silicon single crystal, and the magnetic field strength is at least 3000 gauss during pulling of the straight body portion of the silicon single crystal with a solidification rate of 0.4 or less, It is desirable that the magnetic field intensity is gradually decreased from a solidification rate of 0.4 to a solidification rate of 0.6, and the magnetic field strength is set to 2000 Gauss after the solidification rate of 0.6.

Since the magnetic field strength is at least 3000 gauss during the pulling of the straight body portion 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 crystal growth of the silicon single crystal is achieved. The uniformity of the oxygen concentration in the axial direction can be achieved, and the variation in the oxygen concentration within the substrate surface perpendicular to the crystal growth axis can be suppressed, so that the uniformity of the oxygen concentration within the substrate surface can be achieved.

The magnetic field strength is gradually decreased from the solidification rate of 0.4 to the solidification rate of 0.6, and in particular, after the solidification rate of 0.6, the magnetic field strength is set to 2000 gauss.
Therefore, it is possible to reduce the oxygen concentration and make the oxygen concentration uniform in the crystal growth axis direction of the silicon single crystal. The uniformity of oxygen concentration can be improved.

Radius of silicon single crystal [mm] / crucible radius [mm] × number of revolutions of silicon single crystal [rpm] × magnetic field strength [Gauss] / (distance from the surface of the silicon melt to the lower end of the shielding plate) [mm] is preferably 190 or less.
If the value calculated from this silicon single crystal radius/crucible radius×silicon single crystal rotational speed×magnetic field intensity/(distance from the surface of the silicon melt to the lower end of the shielding plate) is 190 or less, 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 in the silicon 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 within the substrate surface perpendicular to the crystal growth axis can be achieved. can be done.

Further, a method for producing a silicon single crystal, which has been devised to achieve the above object, includes growing a silicon single crystal while applying a horizontal magnetic field when pulling a silicon single crystal from a silicon melt in a quartz glass crucible. In the method for producing a silicon single crystal, during the step of pulling the silicon single crystal, the following conditions are obtained: radius of silicon single crystal [mm]/crucible radius [mm] x number of rotations of silicon single crystal [rpm] x magnetic field strength [Gauss]/(silicon melt The radius of the silicon single crystal, the crucible radius, the number of revolutions of the silicon single crystal, the magnetic field strength, the surface of the silicon melt, and the to the lower end of the shielding plate is adjusted, and the silicon single crystal is pulled up.

Radius of silicon single crystal [mm] / crucible radius [mm] × rotation speed of silicon single crystal [rpm] × 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 be 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 crucible can be 0.16 m/s or less during the pulling of the silicon single crystal. The oxygen concentration of the 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 within the substrate surface perpendicular to the crystal growth axis can be achieved.

In addition, without measuring the flow velocity of the silicon melt, it was calculated from the following: radius of silicon single crystal / crucible radius × number of revolutions of silicon single crystal × magnetic field strength / (distance from the surface of the silicon melt to the lower end of the shielding plate) Depending on the value, it can be determined whether the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the crucible 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 direction of the crystal growth axis, and achieve the uniformity of the oxygen concentration within the substrate surface perpendicular to the crystal growth axis. A manufacturing method can be obtained.

FIG. 1 is a schematic diagram showing the flow of silicon melt. FIG. 2 is a schematic diagram showing the flow of the silicon melt in a state in which the silicon melt in the silica glass crucible has decreased from the state of FIG. FIG. 3 is a schematic diagram showing another flow of silicon melt. It is the schematic which showed the flow of the silicon melt when the magnetic field intensity was made into 1000 Gauss, (a) is a top view, (b) is sectional drawing. It is the schematic which showed the flow of the silicon melt when the magnetic field intensity was made into 2000 Gauss, (a) is a top view, (b) is sectional drawing. It is the schematic which showed the flow of the silicon melt when the magnetic field intensity was made into 3000 Gauss, (a) is a top view, (b) is sectional drawing. 1 is a schematic configuration diagram of a silicon single crystal pulling apparatus; FIG. FIG. 4 is a diagram showing changes in magnetic field intensity in Experiments 1 to 4; FIG. 10 is a diagram showing the flow direction and flow velocity on the surface of the silicon melt, where (a) is a diagram showing the solidification rate of Experiment 1 at 0.25 (magnetic field strength 3000 gauss), and (b) is the solidification of Experiment 1. FIG. 10C is a diagram showing the time point at a solidification rate of 0.6 (magnetic field strength of 3000 gauss), and (c) is a diagram showing the time point of Experiment 2 at a solidification rate of 0.6 (magnetic field strength of 2000 gauss). FIG. 4 is a diagram showing the relationship between solidification rate and oxygen concentration in Experiments 1 to 4; FIG. 4 is a diagram showing the relationship between the solidification rate in Experiments 1 to 4 and the variation in oxygen concentration in the crystal growth axis direction of a silicon single crystal. FIG. 4 is a diagram showing the relationship between the magnetic field intensity and the variation in the oxygen concentration in the substrate plane perpendicular to the crystal growth axis in Experiment 2, where (a) is a diagram showing the measurement points, and (b) is at each measurement point. It is a figure which shows the dispersion|variation in oxygen concentration in a substrate surface. FIG. 10 is a diagram showing changes in magnetic field intensity in Experiments 5 and 6; FIG. 10 is a diagram showing the relationship between the solidification rate in Experiments 5 and 6 and the variation in resistivity in the crystal growth axis direction of the silicon single crystal. FIG. 10 is a diagram showing the relationship between the position of the center of the magnetic field and the oxygen concentration in Experiments 1 and 16 to 20;

In the method for producing a silicon single crystal according to the present invention, when pulling a silicon single crystal from a silicon melt in a quartz glass crucible, the silicon single crystal is grown while applying a horizontal magnetic field. , the flow of the silicon melt flowing from the silicon single crystal side to the silica crucible side wall exists on the silicon melt surface, and the flow velocity of the silicon melt flowing from the silicon single crystal side to the silica glass crucible side wall 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 of the silicon single crystal is 0.16 m/s or less.

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

FIG. 1 is a diagram showing an example of the flow of the silicon melt M in the quartz glass crucible. The reason why s is set to s or less will be explained.
FIG. 1 shows the results of a simulation of the flow of silicon melt under conditions where the solidification rate was increased by 0.25 in Experiment 1, which will be described later. It shows the flow of the silicon melt in the state of being located in the silicon melt 20 mm below the free surface at the center of the single crystal. Further, in the figure, B indicates that the direction of the magnetic flux is directed 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 indicated by an arrow X1 in FIG. 1, the silicon melt has a flow that flows from above to below while being in contact with (along) the side wall 1a of the silica glass crucible.
Then, when this silicon melt flows in contact with (along) the silica glass crucible side wall 1a, since silicon at the melting point is chemically active, the silicon melt M reacts with the quartz component of the silica glass crucible 1 to produce quartz. The sidewall 1a of the glass crucible 1 is melted and O (oxygen) is introduced.

This oxygen-containing silicon melt M rises from the bottom surface of the crucible below the silicon single crystal C (bottom surface at the center of the crucible), as indicated by an arrow X2.
Then, after flowing (meandering) radially outward of the crucible as indicated by an arrow X3, it returns below the silicon single crystal C as indicated by an arrow X4, and returns to the silicon single crystal side as indicated by an arrow X5. to 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 released from the bottom surface of the crucible 1 below the silicon single crystal C. When ascending, it reaches the free surface after a large meandering radially outward.
As a result, O taken into the silicon melt M diffuses, the oxygen concentration of the silicon melt M is reduced, the take-up of oxygen into the silicon single crystal C is suppressed, and the oxygen concentration of the silicon single crystal C is reduced. is planned.

Next, FIG. 2 shows 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. show. FIG. 2 shows the result of a simulation of the flow of silicon melt under the condition of pulling with a solidification rate of 0.6 in Experiment 1, which will be described later.

As shown in FIG. 2, as the pulling of the silicon single crystal C progresses and the amount of the silicon melt in the silica glass crucible 1 decreases, the generation of a flow that largely meanders radially outward as shown in FIG. The flow X2 rising from the crucible bottom surface (crucible center bottom surface) below the silicon single crystal C becomes stronger (the flow speed becomes faster).

Thus, when the silicon melt rises from the bottom of the crucible toward the lower end of the silicon single crystal C without meandering, the silicon single crystal rises before oxygen is diffused or released from the silicon melt containing oxygen. Incorporated 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. oxygen concentration uniformity is disturbed.

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 flow X5 flowing from the silicon single crystal C side to the crucible side wall 1a also becomes 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 low, the flow velocity of the flow X2 rising from the crucible bottom surface 1b below the silicon single crystal C is also low.

When the flow X2 rising from the crucible bottom surface 1b below the silicon single crystal C is small, as shown in FIG. Or it rises from the crucible bottom surface, then meanders outward in the crucible radial direction, passes directly under the liquid surface, and is taken into the silicon crystal, so that 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 the flow of the silicon melt in the quartz glass crucible 1, for example, there is also a flow Y1 that flows upward from below 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 walls of the quartz glass crucible 1 and reaches the free surface. Thereafter, a flow Y2 is formed that flows from the side wall of the silica glass crucible 1 to the silicon single crystal side.
This silicon melt flow Y2 has a high degree of diffusion and transpiration of O taken into the silicon melt, and the low-oxygen-concentration silicon melt flows toward the silicon single crystal, and only the outer peripheral portion of the silicon single crystal is low. This is not preferable because it increases the density 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 into the silicon melt rising from the bottom surface of the crucible below the silicon single crystal C. and the oxygen concentration is high.
As a result, the oxygen concentration in the central portion of the silicon single crystal becomes high, while the oxygen concentration in the outer peripheral portion of the silicon single crystal becomes low. Density uniformity is disturbed.
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.

Also, the flow of the silicon melt inside the quartz glass crucible is affected by the strength of the magnetic field. In particular, as the pulling of the silicon single crystal progresses and the silicon melt in the silica 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 furnace internal pressure, the rotation speed of the silica glass crucible, and the rotation speed of the silicon single crystal are the same, the flow of the silicon melt in the silica glass crucible changes depending on the strength of the magnetic field. .

For example, FIG. 4 shows the flow of silicon melt when 1000 Gauss is applied in the horizontal direction.
This FIG. 4 shows the result of a simulation of the flow of silicon melt under the condition of pulling with a solidification rate of 0.6 in Experiment 1, which will be described later. It shows the flow of the silicon melt in the state of being positioned in the silicon melt 20 mm below the free surface at the center of the silicon single crystal.
In the figure, the symbol ◯ of B indicates that the direction of the magnetic flux is directed 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. FIG. 4B is the same diagram as FIG.

As shown in FIGS. 4(a) and 4(b), in the case of 1000 gauss, a silicon melt flow Y2 flows from the side wall of the crucible to the silicon single crystal side, which is not preferable.
In addition, since the flow X2 rising from the bottom surface of the crucible below the silicon single crystal C becomes stronger, the silicon melt containing oxygen flows to the lower end of the silicon single crystal, and a large amount of oxygen is taken into the silicon single crystal, which is preferable. do not have.

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

Similarly, FIGS. 6A and 6B show the case where the magnetic field intensity is changed from 1000 gauss to 3000 gauss in the state shown in FIG.
As shown in FIG. 6, the oxygen-containing silicon melt largely meanders radially outward (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 on the surface of the silicon melt is controlled so as to flow from the silicon single crystal side to the side wall of the crucible. is preferred.
Further, when there is a flow toward the silicon single crystal side from the side wall of the crucible as a flow on the surface of the silicon melt, the flow from the side wall of the crucible toward the silicon single crystal side is controlled so as not to reach the silicon single crystal. is preferred.

In particular, the magnetic field strength is preferably at least 3000 Gauss during the pulling of the straight body of the silicon single crystal with a solidification rate of 0.4 or less, in which sufficient silicon melt exists in the quartz glass crucible.
Since a sufficient amount of silicon melt exists in the quartz glass crucible, a flow that greatly meanders radially outward as shown in FIG. 1 is generated. As a result, the oxygen in the silicon melt is diffused and diffused, so that the oxygen concentration in the silicon single crystal can be reduced.

Moreover, it is desirable to gradually decrease 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 the amount of silicon melt in the quartz glass crucible decreases, the magnetic field strength is gradually lowered to 2000 gauss after the solidification rate is 0.6. , the silicon melt containing oxygen largely meanders radially outward 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. Since the environments in FIG. 1 and FIG. 5B are the same, the oxygen concentration in the crystal axis direction becomes uniform.

In addition, 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 based on the magnetic field strength, It is affected by inert gas flow rate, furnace pressure control, quartz glass crucible rotation control, silicon single crystal rotation control, and the like.
The flow velocity of the silicon melt can be measured using a tracer or the like, but the crystal being pulled cannot be used as a product during measurement, and the work is time-consuming. Therefore, the flow velocity of the silicon melt is estimated by simulation, but the calculation time becomes enormous under conditions such as the horizontal magnetic field that require three-dimensional convection analysis.

Therefore, the present inventors studied a relational expression for easily finding the conditions for making the flow velocity of the silicon melt flowing from the silicon single crystal side to the crucible side wall to be 0.16 m/s or less.
Specifically, when the value calculated from (radius of silicon single crystal/crucible radius×rotation speed of silicon single crystal×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 for setting the radius of silicon single crystal÷crucible radius×rotational speed of silicon single crystal×magnetic field intensity÷(distance from surface of silicon melt to lower end of shielding plate) is as follows.
The driving force of the flow from the silicon crystal to the crucible wall side depends on the silicon single crystal and crucible radius, the silicon single crystal rotational 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 acts to decrease, so the crucible radius is divided (divided).

Normally, only the driving force should be considered, but the distance from the surface of the silicon melt to the bottom edge of the shielding plate affects how easily the melt oxygen concentration can be controlled, so this distance should also be considered. There is a need to. For example, if this distance is too narrow, the effect of the furnace atmosphere (Ar gas flow rate and furnace pressure) is large, making it difficult to control the magnetic field strength. Force control is enabled.
Since the number of rotations of the crucible is considered to have little effect on the flow velocity, it is not included in the above relational expression. However, the lower the rotation speed of the crucible, the more low-oxygen crystals can be obtained, so the rotation speed of the crucible is preferably 1.0 rpm or less.

(Experiments 1-4)
Using a general pulling apparatus as shown in FIG. 7, the silicon single crystal was pulled under the conditions shown in Table 1 and FIG. , the oxygen concentration in the direction of the crystal growth axis of the silicon single crystal, the variation in the oxygen concentration, and the variation in the oxygen concentration in the substrate plane perpendicular to the crystal growth axis.

First, the pulling apparatus shown in FIG. 7 will be described. This apparatus 10 has a cylindrical chamber (chamber) 11, a crucible 12 provided in the chamber 11, and raw material silicon charged in the crucible 12 is melted. and 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. A heat insulating tube 14 is provided around the carbon heater 13 in the chamber 11 . The heat insulating cylinder 14 is formed in a cylindrical shape, and a heat insulating plate 15 extending inwardly is provided at the upper end portion thereof. Further, a radiation shield (shielding plate) 16 is provided to prevent unnecessary radiation heat from the carbon heater 13 or the like to the silicon single crystal C being grown (during pulling).

Above and near the crucible 12, the radiation shield (shielding plate) 16 is formed with openings 16a and 16b at the top and bottom so as to surround the periphery of the silicon single crystal C. A tapered surface 16c is formed so that the area of the opening gradually decreases. With the radiation shield 16 provided, the purge 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 outside and is finally discharged outside the chamber 11 (outside the chamber).
A gap between the lower end of the radiation shield 16 and the surface of the silicon melt M is called a gap.

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

Although not shown, a pulling mechanism for pulling the silicon single crystal C is provided above the chamber 11 . The hoisting mechanism comprises a motor-driven winding mechanism and a hoisting wire 18 wound on the winding mechanism. A seed crystal P is attached to the tip of the wire 18, and the silicon single crystal C is pulled up while being grown.

Further, 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. The crucible 12 is rotated and the height of the crucible 12 is raised to grow the silicon single crystal C. As shown in FIG.

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

Here, Gap in Table 1 is the dimension of the gap between the radiation shield 16 and the surface of the silicon melt M, SR is the rotation speed of the crystal, CR is the rotation speed of the crucible, and the purge inert gas (Ar gas) and the pressure in the furnace are 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 at 20 mm below the surface of the silicon melt M.
That is, in Experiment 1, a silicon single crystal was pulled with a magnetic field strength of 3000 gauss.
In Experiment 2, the magnetic field strength was set to 3000 gauss, and the silicon single crystal was pulled until the solidification rate was 0.4. did
In Experiment 3, the magnetic field strength was set to 3000 gauss, the silicon single crystal was pulled until the solidification rate was 0.4, the magnetic field strength was gradually decreased to the solidification rate of 0.6, and then the magnetic field strength was set to 2000 gauss to pull the silicon single crystal. did
In experiment 4, the magnetic field strength was set to 3000 gauss, and the magnetic field strength was gradually lowered until the solidification rate was 0.2, and then the magnetic field strength was set to 2000 gauss to pull the silicon single crystal.

FIG. 9 shows the flow direction and flow velocity of the silicon melt during pulling in Experiments 1 to 4 above.
FIG. 9(a) shows the flow direction and flow velocity of the silicon melt when the solidification rate is increased by 0.25 (3000 Gauss: see FIG. 8) in Experiment 1. FIG.
FIG. 9(b) shows the flow direction and flow velocity of the silicon melt when the solidification rate is increased by 0.6 (3000 Gauss: see FIG. 8) in Experiment 1. FIG.
FIG. 9(c) shows the flow direction and flow velocity of the silicon melt when the solidification rate is increased by 0.6 (2000 Gauss: see FIG. 8) in Experiment 3. FIG.

As shown in FIG. 9(a), the maximum value of the flow velocity when the solidification rate is increased by 0.25 (3000 gauss) is within the range of 0.20 to 0.24 m/s.
Further, as shown in FIG. 9(b), the maximum value of the flow velocity when the solidification rate is increased 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. 9(c), the maximum value of the flow velocity when the solidification rate is raised to 0.6 (2000 gauss) is within the range of 0.12 to 0.16 m/s.
Therefore, when the pulling of the silicon single crystal progresses and the amount of the silicon melt in the silica glass crucible decreases, the maximum flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the silica crucible is reduced by reducing the magnetic field strength. can be 0.16 m/s or less.

Also, the oxygen concentration of the pulled silicon single crystal was measured. Measurements were made using Fourier transform infrared spectroscopy (FT-IR). The results are shown in FIG.
In Experiment 1, the oxygen concentration increased after the solidification rate of 0.6, whereas in Experiments 2, 3, and 4, no increase in the oxygen concentration was observed after the solidification rate of 0.6, 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, the flow velocity on the surface of the silicon melt is fast as can be seen from FIG. 9(b).
Therefore, the flow that meanders greatly radially outward as shown in FIG. 1 does not occur, but rises from the bottom surface of the crucible below the silicon single crystal and is taken into the silicon single crystal. As a result, it is believed that the oxygen concentration increased after the solidification rate was 0.6.

In addition, variation ΔOi of oxygen concentration in the crystal length direction of the pulled silicon single crystal was measured. Fourier transform infrared spectroscopy (FT-IR) was used for the measurement under the condition of a radial pitch of 5 mm. The results are shown in FIG.
The oxygen concentration variation ΔOi is
ΔOi = (maximum value at measurement point - minimum value)/minimum value x 100 [%].

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

Further, FIG. 12(b) shows the variation in the oxygen concentration within the substrate plane at the measured magnetic field intensity of FIG. 12(a) in Experiment 2. As shown in FIG.
That is, substrates cut out from 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 In-plane oxygen concentration variation was measured. Fourier transform infrared spectroscopy (FT-IR) was used for the measurement under the condition of a radial pitch of 5 mm. The results are 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, a silicon single crystal was pulled by changing the magnetic field intensity as shown in FIG. The raising conditions are as follows.
In Experiment 5, the magnetic field strength was set to 3000 gauss, and the magnetic field strength was gradually decreased 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, and the magnetic field strength was gradually increased until the solidification rate was 0.2. and Other conditions were the same as in Experiment 1.

Then, the in-plane resistivity variation of the substrate cut out from the pulled silicon single crystal was measured. The measurement was carried out at a pitch of 5 mm in the radial direction of the silicon substrate using a four-probe method. The results are 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 a condition under which there is a flow of 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 In addition, the flow velocity in Table 2 is a value obtained from a simulation.
That is, using the conditions shown in Table 2, when the value calculated from the following equation: radius of silicon single crystal/crucible radius×rotation speed of silicon single crystal×magnetic field strength/distance to lower end of shield plate is 190 or less, silicon It was confirmed that there is a flow of silicon melt flowing from the single crystal side to the crucible side wall, and that the flow velocity of the silicon melt flowing from the silicon single crystal side to the crucible side wall can be set to 0.16 m/s or less.
In addition, when the magnetic field strength is 1000 gauss or 1500 gauss, the flow velocity may be set to 0.16 m/s or less, but it is not preferable because good in-plane uniformity of oxygen concentration cannot be obtained.

In this way, when the value calculated from the following equation: radius of silicon single crystal/crucible radius×silicon single crystal rotation speed×magnetic field strength/(distance from surface of silicon melt to lower end of 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 becomes 0.16 m/s or less.
Therefore, without measuring the flow velocity of the silicon melt, it was calculated from the following formula: radius of silicon single crystal / crucible radius × rotation speed of silicon single crystal × magnetic field strength / (distance from the surface of the silicon melt to the lower end of the shielding plate) Depending on the value, it can be determined whether the flow velocity of the silicon melt flowing from the silicon single crystal side to the side wall of the crucible 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 melt surface), a silicon single crystal was pulled and the oxygen concentration was measured at a solidification rate of 0.25. Measurements were made using Fourier transform infrared spectroscopy (FT-IR). The results are shown in FIG.
With respect to Experiment 1, a silicon single crystal was pulled under the same conditions as in Experiment 1, except that the position of the center of the magnetic field was changed, as shown in Table 3, and the oxygen concentration was measured at a solidification rate of 0.25 (Experiment 16 ~ Experiment 20). The results are 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 melt surface (experiments 17 and 18), the oxygen concentration is 1.0×10 ¹⁸ atoms/cm. It turned out to be as low as less than ³ .

1 Silica glass crucible 1a Silica glass crucible side wall C Silicon single crystal M Silicon melt X1 Flow of silicon melt flowing downward from above while being in contact with the side wall of the silica glass crucible X2 Rising from the bottom of the crucible below the silicon single crystal C , Silicon melt flow X3 Flowing radially outward of the crucible, Silicon melt flow X4 Flowing radially inward of the crucible, returning below 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 side wall of the crucible

Claims (5)

In a method for producing a silicon single crystal, the silicon single crystal is grown while applying a horizontal magnetic field when pulling the silicon single crystal from the silicon melt in the quartz glass crucible,
A flow of the silicon melt flowing from the silicon single crystal side to the silica crucible side wall exists on the silicon melt surface, and the flow velocity of the silicon melt flowing from the silicon single crystal side to the silica glass crucible side wall is 0.16 m/s or less. A method for producing a silicon single crystal, characterized by: 2. The center of the horizontal magnetic field is located in the silicon melt within 60 mm below the melt surface, and the magnetic field strength is at least 2000 Gauss during the pulling of the silicon single crystal. A method for producing a silicon single crystal as described. the center of the horizontal magnetic field is positioned below the central portion of the silicon single crystal;
The magnetic field strength is at least 3000 gauss during the pulling of the straight body of the silicon single crystal with a solidification rate of 0.4 or less,
Gradually lowering the magnetic field intensity beyond a solidification rate of 0.4 to a solidification rate of 0.6,
3. The method for producing a silicon single crystal according to claim 1, wherein the magnetic field strength is set to 2000 Gauss after the solidification rate is 0.6 or higher. Radius of silicon single crystal [mm] / crucible radius [mm] × rotation speed of silicon single crystal [rpm] × magnetic field strength [Gauss] / (distance from the surface of the silicon melt to the lower end of the shielding plate) [mm] 4. The method for producing a silicon single crystal according to any one of claims 1 to 3, wherein the obtained value is 190 or less. In a method for producing a silicon single crystal, the silicon single crystal is grown while applying a horizontal magnetic field when pulling the silicon single crystal from the silicon melt in the quartz glass crucible,
During the process of pulling the silicon single crystal,
Radius of silicon single crystal [mm] / crucible radius [mm] × rotation speed of silicon single crystal [rpm] × 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 obtained is 190 or less,
The radius of the silicon single crystal, the crucible radius, the rotation speed 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 shield plate are adjusted,
A method for producing a silicon single crystal, comprising pulling a silicon single crystal.

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