JP2004196569A - Silicon single crystal pulling method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for pulling a silicon single crystal by applying horizontal magnetic field which realizes low-oxygen concentration in the silicon single crystal. <P>SOLUTION: A method wherein the silicon single crystal is pulled while applying horizontal magnetic field to a silicon melt prepared by melting polysilicon filled in a quartz crucible by a heater, is improved. A relative flow rate, defined as a value obtained by dividing an inert gas flow rate (unit [L/min]) by a furnace pressure (unit [Torr]), is controlled to ≤1.0. The center of the horizontal magnetic field is moved along with the change in the liquid level of the silicon melt. A rate of change in crystal length is adjusted while keeping a relative flow rate range of ≤1.0 according to the distribution of oxygen concentration in the growth axis direction of the silicon single crystal being pulled. In the depth direction of the silicon melt, the center of the horizontal magnetic field is adjusted to a position with the lowest oxygen concentration between the center of the melt to the vicinity of the liquid level. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention, transverse magnetic field applied pulling (H orizontal M agnetic Field Applied Cz ochralski hereinafter referred to as HMCZ) low oxygen concentration in the growth axis direction relates pulling method of a silicon single crystal by the apparatus for, particularly HMCZ silicon single crystal The present invention relates to a method for pulling a silicon single crystal that can be realized.
[0002]
[Prior art]
FIG. 1 schematically shows a conventional HMCZ apparatus.
[0003]
In FIG. 1, a horizontal magnetic field applying device 1 is arranged on the outer periphery of a furnace body 2. A graphite crucible 3 is provided in the furnace body 2 and a quartz crucible 4 is held therein. The graphite heater 5 melts the polysilicon filled in the quartz crucible 4 to form a silicon melt 6. While applying a horizontal magnetic field to the silicon melt 6, the silicon single crystal 7 is pulled up. At this time, a radiation shield 8 is provided above the silicon melt 6. The radiation shield 8 is held by the radiation shield support cylinder 9. A graphite internal heat retaining cylinder 10 is disposed so as to surround the graphite heater 5 serving as a heat source, and a high heat insulating thermal retaining cylinder 11 is disposed outside the graphite internal heat retaining cylinder 10. Further, an upper heat insulating plate 12 is arranged on the upper surface of the high heat insulating heat insulating cylinder 11. Below the graphite crucible 3, a graphite shaft 13 for holding the graphite crucible 3 and a graphite crucible tray 14 are arranged, and a lower tray 15 is arranged at the lowest part.
[0004]
As shown in FIG. 2, in the magnetic field distribution generated in the left and right coils 1, a region of relatively strong magnetic flux density (similar to the magnetic flux density of the coil central axis) near the coil central axis is indicated by hatching in FIG. Where it is formed.
[0005]
In pulling an HMCZ silicon single crystal by such an HMCZ apparatus, a horizontal magnetic field is applied to the silicon melt, and thermal convection of the melt is suppressed, which is effective in reducing the oxygen concentration of the HMCZ silicon single crystal. Furthermore, the greater the magnetic flux density of the horizontal magnetic field applied from the outside of the furnace body 2, the greater the effect of suppressing the heat convection of the melt, so the oxygen concentration is further reduced.
[0006]
On the other hand, when a CZ silicon single crystal is pulled by a non-magnetic field pulling device (CZ device) that does not apply a magnetic field to the silicon melt, the oxygen concentration of the CZ silicon single crystal is adjusted by increasing or decreasing the inert gas flow rate and the furnace pressure. Can be controlled. When the value obtained by dividing the inert gas flow rate (unit [liter / mm]) by the furnace pressure (unit [Torr]) is defined as the specific flow rate, if the specific flow rate is large, the oxygen concentration becomes low and the specific flow rate is small. And the oxygen concentration increases.
[0007]
By the way, the HMCZ silicon single crystal pulled by the HMCZ apparatus is used as a raw material for impurity doping by neutron irradiation. After neutron irradiation, heat treatment is performed to recover damage to the crystal lattice arrangement due to irradiation, and it is known that this time causes a reduction in lifetime.
[0008]
In Japanese Patent No. 2635450, the oxygen concentration is limited in a HMCZ silicon single crystal that has been subjected to neutron irradiation in order to prevent a decrease in the lifetime after the damage recovery heat treatment. For example, in the case of irradiation with a heavy water reactor, it is determined to be 0.90 × 10 ¹⁸ [atoms / cm ³ ] (JEIDA) (1.44 × 10 ¹⁸ [atoms / cm ³ ] (old ASTM)) or less. In the case of light water reactor irradiation, it is specified to be 0.50 × 10 ¹⁸ [atoms / cm ³ ] (JEIDA) (0.80 × 10 ¹⁸ [atoms / cm ³ ] (old ASTM)) or less.
[0009]
[Problems to be solved by the invention]
In order to lower the oxygen concentration of the HMCZ silicon single crystal for neutron irradiation using an HMCZ device, the magnetic flux density was adjusted to the maximum value of the horizontal magnetic field application device, and the specific flow rate was further increased. No concentration could be obtained.
[0010]
For example, in the horizontal magnetic field applying device described in U.S. Pat. No. 4,565,671 shown in FIG. 3, a configuration is shown in which the center of the magnetic field and the liquid level of the melt coincide with each other, as shown in FIG. The present inventors have found that in this configuration, only the lower half of the strong magnetic field region (region of the same order as the coil center axis magnetic flux density) formed near the center of the magnetic field is effectively used.
[0011]
Further, in the horizontal magnetic field applying apparatus described in Japanese Patent Application Laid-Open No. 9-188590 shown in FIG. 4, the center of the magnetic field is adjusted near the lowermost portion of the silicon melt as shown in FIG. Also in this configuration, the present inventors have found that only the upper half of the high magnetic field region is utilized, which is extremely disadvantageous for reducing the oxygen concentration of the MHCZ silicon single crystal.
[0012]
An object of the present invention is to provide a silicon single crystal pulling method capable of realizing a low oxygen concentration of an HMCZ silicon single crystal.
[0013]
[Means for Solving the Problems]
The invention according to claim 1 of the present application is directed to a method of pulling a silicon single crystal while melting a polysilicon filled in a quartz crucible with a heater to form a silicon melt and applying a horizontal magnetic field to the silicon melt. The value obtained by dividing the flow rate of the inert gas by the pressure in the furnace is defined as a specific flow rate. This specific flow rate is controlled to 1.0 or less, and the center of the horizontal magnetic field is adjusted in accordance with the fluctuation of the liquid level of the silicon melt. It is a method for pulling a silicon single crystal, wherein the center of the horizontal magnetic field is always controlled to a predetermined position between the center of the silicon melt and the liquid surface, as viewed in the depth direction of the silicon melt by moving the silicon single crystal. .
[0014]
If the center of the horizontal magnetic field is moved (downward) in accordance with the movement (for example, down) of the liquid surface of the silicon melt, the oxygen concentration can be more accurately reduced.
[0015]
When the specific flow rate is reduced to 1 or less, the oxygen concentration of the HMCZ silicon single crystal can be reduced. On the other hand, in the case of pulling a CZ silicon single crystal in a non-magnetic field pulling apparatus (CZ apparatus) in which no magnetic field is applied to the silicon melt, the oxygen concentration decreases as the specific flow rate increases. The relationship between the specific flow rate and the oxygen concentration according to the present invention has the opposite result to the relationship in the non-magnetic field pulling apparatus in which no magnetic field is applied to the silicon melt.
[0016]
The invention according to claim 2 of the present application is directed to a silicon single crystal that adjusts a crystal length change rate within a range of a specific flow rate of 1.0 or less according to an oxygen concentration distribution in a growth axis direction of a silicon single crystal being pulled. It is a lifting method.
[0017]
With respect to the oxygen concentration distribution in the growth axis direction of the HMCZ silicon single crystal, when the specific flow rate is set to a range of 1.0 or less and the crystal length change rate is adjusted, the desired low oxygen concentration is obtained in all the pulled HMCZ silicon single crystals. The concentration can be realized more reliably.
[0018]
The invention according to claim 3 of the present application is directed to a silicon single crystal in which the center of the horizontal magnetic field is adjusted to the position where the oxygen concentration is lowest between the center of the melt and the liquid surface when viewed in the depth direction of the silicon melt. It is a lifting method.
[0019]
When the center of the magnetic field (coil center axis) is adjusted to the optimum position in the upper half section from the center of the melt when viewed in the depth direction (vertical direction) of the silicon melt, the magnetic field center is located in the lower half section from the melt center. The present inventors have found as a new finding that the low oxygen concentration effect of the MHCZ silicon single crystal is significantly improved as compared with the case of adjusting the temperature. According to this method, the entire strong magnetic field region formed near the center of the magnetic field can be effectively used. As a result, thermal convection of the melt is effectively suppressed.
[0020]
The center of the silicon melt is, as a rule, a position at a depth of half the distance from the surface of the silicon melt melted in the quartz crucible to the bottom of the melt in the quartz crucible in the depth direction. Show.
[0021]
【Example】
FIG. 5 shows an embodiment of the present invention.
[0022]
In FIG. 5, the horizontal magnetic field applying device 1 is arranged on the outer periphery of the furnace body 2 so as to be vertically movable, and a driving means and a control means therefor are not shown.
[0023]
A graphite crucible 3 is provided in the furnace body 2. A quartz crucible 4 is held in the graphite crucible 3. The quartz crucible 4 is heated by the graphite heater 5, and the polysilicon filled in the quartz crucible 4 is melted to form a silicon melt 6.
[0024]
While applying a horizontal magnetic field to the silicon melt 6 by the horizontal magnetic field applying device 1, the silicon single crystal 7 is pulled up. At this time, a radiation shield 8 is provided above the silicon melt 6. The radiation shield 8 is held by the radiation shield support cylinder 9.
[0025]
A graphite internal heat retaining cylinder 10 is disposed so as to surround the graphite heater 5 serving as a heat source, and a high heat insulating thermal retaining cylinder 11 is disposed outside the graphite internal heat retaining cylinder 10. Further, an upper heat insulating plate 12 is arranged on the upper surface of the high heat insulating heat insulating cylinder 11. Below the graphite crucible 3, a graphite shaft 13 for holding the graphite crucible 3 and a graphite crucible tray 14 are arranged thereon. A lower tray 15 is disposed at the lowermost position.
[0026]
In the magnetic field distribution generated in the coil 1 of the horizontal magnetic field applying device 1, a region having a relatively strong magnetic flux density (about the same as the magnetic flux density of the coil central axis) is formed near the coil central axis. When a horizontal magnetic field is applied to the silicon melt in this way, the heat convection of the melt is suppressed. As a result, the oxygen concentration is reduced.
[0027]
In the HMCZ apparatus shown in FIG. 5, a 5-inch (100) orientation HMCZ silicon single crystal was pulled, and it was confirmed whether or not a desired low oxygen concentration could be obtained.
[0028]
In each of Examples 1 to 3, the embodiment has an 18-inch hot zone, a polysilicon charge of 60 kg, a magnetic field center of 3000 Gauss, a crucible rotation of 0.1 rpm, and a seed rotation of 13 rpm.
[0029]
As shown in FIG. 5, the distance (melt depth) from the melt surface to the lowermost portion of the melt in the vertical direction (melt depth direction) is represented by D.
[0030]
The desired oxygen concentration is set to 0.6 × 10 ¹⁸ [atoms / cm ³ ] (old ASTM) or less.
[0031]
Example 1
When the liquid level of the melt fluctuates, the center of the magnetic field (coil central axis) is always adjusted to the position of D / 4 when viewed from the liquid level of the melt in the vertical direction (the depth direction of the melt). In addition, the specific flow rate from the beginning of the pulling of the HMCZ silicon single crystal to the completion of the pulling was set at 1.0. That is, the specific flow rate was (50 liters / min) / (50 torr) = 1.0. FIG. 7 shows the oxygen concentration in this case.
[0032]
In Example 1, as can be seen from FIG. 7, the result exceeded the desired oxygen concentration on the tail side of the obtained HMCZ silicon single crystal.
[0033]
Example 2
As in Example 1, the center of the magnetic field was adjusted so as to be at the position of D / 4 when viewed from the melt surface in the vertical direction (the melt depth direction). The test was carried out by arbitrarily changing from 1.0 to 0.6. For example, the specific flow rate was (50 liters / min) / (80 torr) = 0.6. FIG. 7 also shows the oxygen concentration in this case.
[0034]
In Example 2, all of the obtained HMCZ silicon single crystals had a desired oxygen concentration.
[0035]
Example 3
The center of the magnetic field was controlled in the same manner as in Examples 1 and 2, and the specific flow rate was arbitrarily changed from 1.0 to 0.375 from the beginning to the completion of the lifting. For example, the specific flow rate was (30 l / min) / (80 torr) = 0.375. FIG. 7 also shows the oxygen concentration in this case.
[0036]
In Example 3, not only all of the obtained HMCZ silicon single crystals had a desired oxygen concentration, but also a lower oxygen concentration was obtained as compared with Example 2.
[0037]
Comparative Example 1
In Comparative Example 1, the magnetic field center was controlled in the same manner as in Example 1, and the specific flow rate was set to 1.6 from the beginning to the completion of the pulling. That is, the specific flow rate was (80 liters / min) / (50 torr) = 1.6. FIG. 7 also shows the oxygen concentration in this case.
[0038]
In Comparative Example 1, the result was that the oxygen concentration on the tail side of the obtained HMCZ silicon single crystal greatly exceeded the desired oxygen concentration. According to Comparative Example 1, it was verified that when the specific flow rate exceeded 1.0, it was disadvantageous for lowering the oxygen concentration.
[0039]
Comparative Example 2
In Comparative Example 2, the specific flow rate was set to 1.0 and the center of the magnetic field was adjusted so as to coincide with the liquid level of the melt from the beginning to the completion of the lifting (FIG. 3). FIG. 7 also shows the oxygen concentration in this case.
[0040]
In Comparative Example 2, the oxygen concentration was higher than in Example 1. According to this comparative example 2, as shown in FIG. 3, if the high magnetic field region (especially the upper half) formed near the center axis of the coil is not effectively used, it is disadvantageous for lowering the oxygen concentration. Has been verified.
[0041]
Comparative Example 3
In Comparative Example 3, the specific flow rate was set to 1.0 from the beginning to the completion of the pulling, and the center of the magnetic field was adjusted so as to coincide with the lowermost part of the melt (FIG. 4). FIG. 7 also shows the oxygen concentration in this case.
[0042]
In Comparative Example 3, the oxygen concentration was extremely higher than that in Example 1. According to Comparative Example 3, as shown in FIG. 4, the strong magnetic field region (especially the lower half) formed near the center axis of the coil is not effectively utilized, and the magnetic field center is located above the melt in the depth direction. It was verified that if the regulation was not performed in half the section, it would be extremely disadvantageous for lowering the oxygen concentration.
[0043]
In pulling a silicon single crystal by the above-mentioned HMCZ apparatus, the relationship between the specific flow rate and the oxygen concentration (which was not clarified conventionally) was verified. Successfully clarified. As a result, it was possible to find manufacturing conditions that are extremely effective in reducing the oxygen concentration of the HMCZ silicon single crystal.
[0044]
First, a value obtained by dividing an inert gas flow rate (unit [liter / min]) by a furnace pressure (unit [Torr]) is defined as a specific flow rate, and controlling this specific flow rate to 1.0 or less is extremely difficult. These are effective manufacturing conditions.
[0045]
In addition to this, it is important to adjust the center of the magnetic field (coil center axis) to the optimum position in the upper half section from the center of the melt when viewed in the vertical direction (the silicon melt depth direction). This makes it more effective to keep the oxygen concentration of the HMCZ silicon single crystal low. In particular, for neutron irradiation, the effect of preventing a reduction in the lifetime after heat treatment performed to recover damage to the crystal lattice after irradiation is remarkable.
[0046]
FIG. 8 shows a modification of the present invention.
[0047]
In the HMCZ apparatus shown in FIG. 8, in addition to the HMCZ apparatus shown in FIG. ing.
[0048]
By doing so, the power consumption of the graphite heater 5 is reduced, and as a result, the reaction between the silicon melt and the quartz crucible is reduced. Therefore, the effect of lowering the oxygen concentration of the silicon melt becomes more remarkable.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a conventional HMCZ apparatus.
FIG. 2 is an explanatory diagram showing a strong magnetic field region in the HMCZ apparatus.
FIG. 3 shows an example of a conventional relationship between a strong magnetic field region and a melt.
FIG. 4 shows another example of a conventional relationship between a strong magnetic field region and a melt.
FIG. 5 is an explanatory view showing an example of an embodiment of an HMCZ apparatus according to the present invention.
FIG. 6 is an explanatory diagram showing the relationship between the center of the magnetic field and the oxygen concentration in the conventional example and the embodiment of the present invention.
FIG. 7 is a graph showing the results of oxygen concentration in Examples of the present invention and Comparative Examples.
FIG. 8 shows a modification of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Horizontal magnetic field application apparatus 2 Furnace body 3 Graphite crucible 4 Quartz crucible 5 Graphite heater 6 Silicon melt 7 Silicon single crystal 8 Radiation shield 9 Radiation shield support cylinder 10 Graphite internal thermal insulation cylinder 11 High heat insulation thermal insulation cylinder 12 Upper thermal insulation Plate 13 Graphite shaft 14 Graphite crucible pan 15 Lower pan 16 Highly heat-insulating upper insulation tube

Claims (3)

In a method of melting the polysilicon filled in a quartz crucible with a heater to form a silicon melt and pulling a silicon single crystal while applying a horizontal magnetic field to the silicon melt, the inert gas flow rate is controlled by the furnace pressure. The divided value is defined as a specific flow rate, the specific flow rate is controlled to 1.0 or less, and the center of the horizontal magnetic field is moved in accordance with the fluctuation of the liquid level of the silicon melt to obtain the depth of the silicon melt. A method for pulling a silicon single crystal, characterized in that the center of the horizontal magnetic field is always controlled to a predetermined position between the center of the silicon melt and the liquid surface when viewed in the direction. 2. The silicon single crystal according to claim 1, wherein the crystal length change rate is adjusted within a range of a specific flow rate of 1.0 or less according to an oxygen concentration distribution in a growth axis direction of the silicon single crystal being pulled. Crystal pulling method. 2. The method for pulling a silicon single crystal according to claim 1, wherein the center of the horizontal magnetic field is controlled so as to be maintained at a position where the oxygen concentration is lowest between the center of the silicon melt and the liquid surface.

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