JP6885286B2 - Method for manufacturing silicon single crystal - Google Patents

Description

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

Conventionally, the quartz crucible described in Patent Document 1 is known as a quartz crucible having an excellent single crystallization rate and a good partial heating effect in a method for producing a silicon single crystal.
The quartz crucible described in Patent Document 1 has a transparent glass layer whose inner surface of the wall body substantially does not contain air bubbles, and has an infrared transmittance of 30% to any portion including a curved portion and a bottom portion from the side wall portion of the crucible. It is 80%, and the difference in infrared transmittance at any plurality of locations in each portion is 30% or less.

Japanese Unexamined Patent Publication No. 9-157082

However, even if the infrared transmittance of the quartz crucible is set within a certain range as in Patent Document 1 and the difference is set within a certain range, the infrared transmittance of each quartz crucible cannot be made constant.
In particular, in a silicon single crystal, it is formed at a crystal growth rate between the crystal growth rate dominated by the OSF region and the crystal growth rate dominated by the L / DL region, and is formed in a pore-dominant region (Pv region) and a lattice. The margin of the crystal growth rate in the defect-free region in which the inter-silicon dominant region (Pi region) is mixed is easily affected by the infrared transmittance of the quartz alcove.
The difference in the infrared transmittance of the quartz crucible due to the individual difference of the quartz crucible greatly affects the margin of the crystal growth rate in the defect-free region of the silicon single crystal, and the difference in the infrared transmittance of the quartz crucible causes the increase in the defect-free region. There is a problem that the speed margin is not stable and the acquisition rate of a single crystal in the defect-free region is reduced.

An object of the present invention is to provide a method for producing a silicon single crystal in which the margin of the crystal growth rate in the defect-free region does not fluctuate significantly even if there are individual differences in the infrared transmittance of the quartz crucible.

In the method for producing a silicon single crystal of the present invention, a quartz pot into which a silicon raw material is charged, a heater for melting the silicon raw material in the quartz pot, and an upper portion of the quartz pot are arranged to shield infrared rays from the heater. A method for producing a silicon single crystal by the Chokralsky method, in which a seed crystal is pulled above the quartz single crystal by using a pulling device provided with a heat shield to produce the quartz single crystal. The first step of acquiring the infrared transmittance and the second step of adjusting the distance between the liquid level of the silicon melt in the quartz pot and the lower end of the heat shield based on the acquired infrared transmittance. The third step of pulling up the silicon single crystal is carried out.

According to the present invention, it is possible to obtain variations in the infrared transmittance of the quartz crucible used for pulling up the silicon single crystal by the first step. Then, in the second step, the shielding rate of infrared rays from the heater can be adjusted according to the individual difference in the infrared transmittance of the quartz crucible, and in the third step, the silicon single crystal can be pulled up. Therefore, even when the infrared transmittances of the quartz crucibles are different, the silicon single crystal can be pulled up without a large fluctuation in the margin of the crystal growth rate in the defect-free region.

In the present invention, in the third step, the silicon in the quartz crucible is based on the distance between the liquid level of the silicon melt in the quartz crucible adjusted by the second step and the lower end of the heat shield. It is preferable to maintain or increase or decrease the distance between the liquid level of the melt and the lower end of the heat shield.
According to the present invention, when the thermal environment surrounding the silicon single crystal does not change with the progress of pulling up the silicon single crystal in the third step, the liquid level of the silicon melt in the quartz crucible and the heat shield The single crystal can be pulled up while maintaining the distance from the lower end.
On the other hand, if the distance between the liquid level of the silicon melt in the quartz crucible and the lower end of the heat shield is maintained and the thermal environment changes significantly, increase or decrease this to offset the change in the thermal environment. Can be done. Therefore, even if the pulling of the silicon single crystal progresses, the temperature gradient in the pulling axial direction of the silicon single crystal can be stabilized, and the margin of the crystal velocity in the defect-free region can be secured stably in the longitudinal direction of the silicon single crystal. it can.

In the present invention, in the first step, it is preferable to estimate the infrared transmittance based on the thickness of the bubble layer of the quartz crucible.
According to the present invention, since the infrared transmittance is estimated based on the thickness of the bubble layer of the quartz crucible, it is easy to obtain the infrared transmittance.

In the present invention, the second step is 96% or more with respect to the reference distance between the liquid level of the silicon melt in the quartz crucible and the heat shield plate in the infrared transmission rate of the quartz crucible as a reference. It is preferable to adjust the distance between the liquid level of the silicon melt in the quartz crucible and the lower end of the heat shield in the range of 103% or less.
According to the present invention, by setting the range to be adjusted in the second step to this range, it is possible to stably pull the silicon single crystal without significantly changing the hot zone in the silicon single crystal pulling device. it can.

The schematic diagram which shows the defect region generated by the change of the crystal growth rate for demonstrating the process leading to this invention. The schematic diagram which shows the structure of the silicon single crystal pulling apparatus which concerns on embodiment of this invention. The cross-sectional view which shows the structure of the quartz crucible in the said Embodiment. The schematic diagram which shows the structure of the apparatus which measures the infrared transmittance of a quartz crucible in the said embodiment. The graph which shows the relationship between the thickness of the bubble layer of the quartz crucible and the infrared transmittance in the said embodiment. The schematic diagram for demonstrating the distance between the liquid surface of the silicon melt and the lower end of a heat shield in the said embodiment. The graph which shows the relationship between the change amount of the liquid level Gap in the said embodiment, and the crystal growth rate margin in a defect-free region. The graph which shows the relationship between the change rate of the liquid level Gap and the infrared transmittance in the said embodiment. The schematic diagram which shows the measuring method of the thickness of a quartz crucible in the said Embodiment. The schematic diagram which shows the method of measuring the thickness of the transparent layer of a quartz crucible in the said Embodiment. The flowchart which shows the manufacturing method of the silicon single crystal in the said Embodiment. The graph which compared the Example and the comparative example of this invention.

[1] Background to the present invention FIG. 1 shows a position in the crystal plane and a defect region caused by a change in the crystal growth rate. The left side of FIG. 1 is the case where there is no infrared transmission, and the right side of FIG. 1 is the case where there is infrared transmission. When the crystal growth rate is increased, the OSF (Oxidation Induced Stacking Fault) region and further, the COP (Crystal Originated Pattern Defect) region increases.
On the other hand, when the crystal growth rate is slowed down, the L / DL (Large Dislocation Loop) region increases.

The defect-free region is formed at a crystal growth rate between the crystal growth rate dominated by the OSF region and the crystal growth rate dominated by the L / DL region, and is dominated by the pore-dominant region (Pv region) and the interstitial silicon. It is an area in which an area (Pi area) is mixed. It can be said that the defect-free crystal pulled up at the crystal growth rate in the defect-free region is a high-quality silicon single crystal having no or very few Grown-in defects such as COP and dislocation clusters. Therefore, it is important to control the pulling up of the silicon single crystal by the crystal growth rate in the defect-free region in order to ensure the quality of the silicon single crystal.

As can be seen from FIG. 1, the margin of the crystal growth rate in the defect-free region (the margin in which the entire surface becomes the defect-free region when made into a wafer) is affected by the infrared transmittance of the quartz rut 3A, and there is no infrared transmittance. It was confirmed that the margin of the crystal growth rate in the defect-free region is large and the margin of the crystal growth rate in the defect-free region is small when there is infrared transmittance.
The present invention has been devised based on such findings. Embodiments of the present invention will be described in detail below.

[2] Structure of Silicon Single Crystal Pulling Device 1 FIG. 2 is a schematic view showing an example of the structure of a silicon single crystal pulling device 1 to which the method for producing a silicon single crystal 10 according to the embodiment of the present invention can be applied. It is shown. The pulling device 1 is a device for pulling the silicon single crystal 10 by the Czochralski method, and includes a chamber 2 forming an outer shell and a crucible 3 arranged in the center of the chamber 2.
The crucible 3 has a double structure composed of an inner quartz crucible 3A and an outer graphite crucible 3B, and is fixed to the upper end of a support shaft 4 capable of rotating and raising and lowering.

A resistance heating type heater 5 surrounding the crucible 3 is provided on the outside of the crucible 3, and a heat insulating material 6 is provided on the outside of the resistance heating type heater 5 along the inner surface of the chamber 2.
Above the crucible 3, a pull-up shaft 7 such as a wire that rotates coaxially with the support shaft 4 in the opposite direction or the same direction at a predetermined speed is provided. A seed crystal 8 is attached to the lower end of the pulling shaft 7.

In the chamber 2, a cylindrical water-cooled body 11 surrounding the silicon single crystal 10 being grown above the silicon melt 9 in the crucible 3 is arranged.
The water-cooled body 11 is made of, for example, a metal having good thermal conductivity such as copper, and the silicon single crystal 10 is forcibly cooled by the cooling water circulated inside. The water-cooled body 11 promotes cooling of the silicon single crystal 10 during growth, and plays a role of controlling the temperature gradient in the pulling shaft 7 direction of the central portion of the single crystal and the outer peripheral portion of the single crystal.

Further, a tubular heat shield 12 is arranged so as to surround the outer peripheral surface and the lower end surface of the water-cooled body 11.
The heat shield 12 blocks the high-temperature radiant heat from the silicon melt 9 in the crucible 3, the heater 5, and the side wall of the crucible 3 with respect to the growing silicon single crystal 10, and the solid liquid as the crystal growth interface. In the vicinity of the interface, it suppresses the diffusion of heat to the outside and plays a role of controlling the temperature gradient in the pulling axial direction of the central portion of the single crystal and the outer peripheral portion of the single crystal.
Further, the heat shield 12 also has a function as a rectifying cylinder that exhausts the evaporation from the silicon melt 9 to the outside of the furnace by the inert gas introduced from above the furnace.

A gas introduction port 13 for introducing an inert gas such as argon gas (hereinafter referred to as Ar gas) into the chamber 2 is provided in the upper part of the chamber 2. An exhaust port 14 is provided in the lower part of the chamber 2 to suck and discharge the gas in the chamber 2 by driving a vacuum pump (not shown).
The inert gas introduced into the chamber 2 from the gas introduction port 13 descends between the growing silicon single crystal 10 and the heat shield 12, and the lower end of the heat shield 12 and the liquid level of the silicon melt 9. After passing through the gap between the two, the gas flows toward the outside of the heat shield 12 and further toward the outside of the crucible 3, then descends the outside of the crucible 3 and is discharged from the exhaust port 14.

When the silicon single crystal 10 is produced using such a pulling device 1, the heater 5 uses a solid raw material such as polycrystalline silicon filled in the crucible 3 while maintaining the inside of the chamber 2 in an inert gas atmosphere under reduced pressure. Is melted by heating to form a silicon melt 9.
When the silicon melt 9 is formed in the crucible 3, the pulling shaft 7 is lowered to immerse the seed crystal 8 in the silicon melt 9, and the crucible 3 and the pulling shaft 7 are rotated in a predetermined direction while the pulling shaft is rotated. 7 is gradually pulled up, thereby growing a silicon single crystal 10 connected to the seed crystal 8.

[3] Infrared Transmittance of Quartz Crucible 3A As shown in FIG. 3, the quartz crucible 3A constituting the pulling device 1 of the silicon single crystal 10 and into which the silicon raw material is charged has two layers, a transparent layer 31 and a bubble layer 32. It is a structure. The quartz crucible 3A includes not only a two-layer structure but also a three-layer structure in which a transparent layer is provided on the outside of the bubble layer 32.
The transparent layer 31 is formed on the inner surface of the quartz crucible 3A. The transparent layer 31 is composed of a vitreous layer containing almost no bubbles, and transmits infrared rays radiated from the heater 5 more than the bubble layer 32.
The bubble layer 32 is formed on the outer surface of the quartz crucible 3A. The bubble layer 32 is composed of a layer containing a multi-layered bubble inside, and infrared rays radiated from the heater 5 are reflected and scattered by the bubbles inside.

The infrared transmittance changes depending on the thickness of the bubble layer 32. If the bubble layer 32 is thick, the infrared transmittance decreases, and if the bubble layer 32 is thin, the infrared transmittance increases.
Specifically, the relationship between the infrared transmittance and the thickness of the bubble layer 32 can be obtained by measuring using the infrared transmittance measuring device 20 shown in FIG.
The infrared transmittance measuring device 20 includes a power supply 21, a halogen heater 22, and a laser power meter 23. A sample obtained by crushing the quartz crucible 3A is placed on the detection element of the laser power meter 23, the power supply 21 is turned on, the halogen heater 22 is turned on, and the laser intensity detected by the laser power meter 23 is measured. The distance between the detection element of the laser power meter 23 and the halogen heater 22 is set to, for example, 43 mm.

The infrared transmittance is given as a ratio of the measured value when the sample is not arranged and the measured value when the quartz crucible 3A as a sample is arranged.
Specifically, it is given by infrared transmittance = measured value when a sample is arranged / measured value when no sample is arranged × 100 (%).
A plurality of quartz crucibles 3A having different thicknesses of the bubble layer 32 were prepared, and the infrared transmittance of each sample was measured by the infrared transmittance measuring device 20.
As shown in FIG. 5, it was confirmed that the thickness of the bubble layer 32 of the quartz crucible 3A and the infrared transmittance are in a proportional relationship. As shown in FIG. 5, the infrared transmittance of the quartz crucible 3A is in the range of 40% or more and 70% or less.

[4] Relationship between the margin of the crystal growth rate in the defect-free region and the liquid level Gap As described above, the margin of the crystal growth rate in the defect-free region changes depending on the infrared transmittance of the quartz crucible 3A. Therefore, the relationship between the position of the heat shield 12 that shields infrared rays from the heater 5 and the margin of the crystal growth rate in the defect-free region was investigated.
As shown in FIG. 6, the distance between the liquid level of the silicon melt 9 and the lower end of the heat shield 12 (hereinafter, referred to as a liquid level Gap in the specification and simply referred to as Gap in the drawings) is changed. At that time, the margin of the crystal growth rate in the defect-free region was measured.

As shown in FIG. 7, when compared at the same liquid level Gap, the margin of the crystal growth rate in the defect-free region (referred to as PvPiMargin in FIG. 7) is 0.012 mm / min in the case of no infrared transmission, and infrared transmission is performed. In the case of the present, the margin of the crystal growth rate in the defect-free region was 0.0055 mm / min. From this state, when the liquid level Gap with infrared transmission was gradually reduced, the margin of the crystal growth rate in the defect-free region gradually increased, and when the liquid level Gap was -3 mm, it was the same as without infrared transmission. It was possible to obtain a margin of crystal growth rate in the defect-free region.
From the above results, by changing the liquid level Gap, the infrared transmission amount of the quartz crucible 3A reaching the silicon single crystal 10 can be changed, and the change in the infrared transmittance due to the change in the infrared transmittance of the quartz crucible 3A can be offset.

Based on the measured values obtained in FIG. 7, the relationship between the optimum liquid level Gap that maximizes the crystal growth rate margin in the defect-free region and the infrared transmittance of the quartz crucible 3A was simulated, and a proportional relationship was obtained. It was confirmed that it could be done.
There are individual differences and variations in the infrared transmittance of the quartz crucible 3A, but even if there are variations, the optimum liquid level Gap can be easily obtained by referring to FIG.
For example, in the case of the point P3 in FIG. 8, since the infrared transmittance of the quartz crucible 3A is about 80%, the liquid level Gap is set to 96% of the optimum liquid level Gap (reference distance) at the reference point P1. , Optimal liquid level Gap can be obtained. On the other hand, in the case of the point P2, since the infrared transmittance of the quartz crucible 3A is about 40%, the optimum liquid level Gap can be obtained by setting the liquid level Gap to 103% of the optimum liquid level Gap at the reference point P1. can get.

[5] Method for measuring the thickness of the bubble layer 32 of the quartz crucible 3A by non-destruction As described above, the thickness of the bubble layer 32 of the quartz crucible 3A and the infrared transmittance are in a proportional relationship, and further, the infrared transmittance and the infrared transmittance. Since the optimum liquid level Gap is in a proportional relationship, if the thickness of the bubble layer 32 of the quartz crucible 3A can be measured non-destructively, it is possible to grasp how much the liquid level Gap should be set to obtain the optimum liquid level Gap. Therefore, the crystal growth rate margin in the defect-free region can be easily maximized.

First, as shown in FIG. 9, the contact terminal 41 is brought into contact with the inner peripheral surface of the quartz crucible 3A, the coordinates are measured, and the outer peripheral surface of the quartz crucible 3A is imaged with a CCD camera to measure the coordinates. The wall thickness of the quartz crucible 3A is calculated by obtaining the distance between them.
Next, as shown in FIG. 10, the laser light emitted from the laser oscillator 43 is refracted by the mirror 44 and obliquely incident on the transparent layer 31 of the quartz crucible 3A.
Then, the reflected light is imaged by the CCD camera 45, and the thickness of the transparent layer 31 is calculated from the image position of the reflected light.
The thickness of the bubble layer 32 is calculated by taking the difference between the thickness of the quartz crucible 3A and the thickness of the transparent layer 31. Regarding the refractive index when the laser light enters the transparent layer 31 of the quartz rutsubo 3A and the refractive index when the laser light enters the bubble layer 32 from the transparent layer 31, the course of the laser light is observed in advance from the thick cross-sectional direction. It can be obtained by doing.

[6] Method for Producing Silicon Single Crystal 10 Next, a method for producing the silicon single crystal 10 will be described with reference to the flowchart shown in FIG.
First, the thickness of the bubble layer 32 of the quartz crucible 3A is measured by the measuring methods shown in FIGS. 9 and 10 (step S1: first step).
Next, based on the relationship of FIG. 5, the infrared transmittance is calculated according to the thickness of the bubble layer 32 of the measured quartz crucible 3A (step S2).

Based on the relationship of FIG. 8, the point P1 corresponding to the reference infrared transmittance is grasped, and the liquid level Gap is set by changing the liquid level Gap in the range from the point P2 to the point P3 (step S3: Second step).
After the setting of the liquid level Gap is completed, the crystal growth rate margin in the defect-free region is grasped, and the pulling rate of the silicon single crystal 10 is set (step S4). The target value of the pulling rate is preferably the median value of the crystal growth rate margin in the defect-free region.

When the above is completed, the silicon single crystal 10 is started to be pulled up while maintaining the liquid level Gap (step S5: third step).
In the pulling up of the silicon single crystal 10 in the third step S5, when the thermal environment surrounding the pulled up silicon single crystal 10 does not change, the liquid level Gap is maintained and the silicon single crystal 10 is pulled up.
On the other hand, if the liquid level Gap is maintained and the thermal environment changes significantly, the change in the thermal environment is offset by increasing or decreasing the liquid level Gap and pulling up the silicon single crystal 10.

[7] Effects of the Embodiment According to the present embodiment as described above, there are the following effects.
By the first step S1, it is possible to acquire the variation in the infrared transmittance of the quartz crucible 3A used for pulling up the silicon single crystal 10. Then, in the second step S3, the amount of infrared rays shielded from the heater 5 by the heat shield 12 is adjusted by adjusting the liquid level Gap according to the individual difference in the infrared transmittance of the quartz crucible 3A. The silicon single crystal 10 can be pulled up by the third step S5. Therefore, even when the infrared transmittance of the quartz crucible 3A is different, the silicon single crystal 10 can be pulled up without significantly changing the margin of the crystal growth rate in the defect-free region.

If the thermal environment surrounding the silicon single crystal 10 does not change with the progress of pulling up the silicon single crystal in the third step S5, the liquid level Gap is maintained, the silicon single crystal 10 is pulled up, and the liquid level Gap is maintained. On the contrary, when the thermal environment changes significantly, it is possible to increase or decrease this to offset the change in the thermal environment. Therefore, even if the pulling of the silicon single crystal 10 progresses, the temperature gradient in the pulling axial direction of the silicon single crystal 10 is stabilized, and the margin of the crystal growth rate in the defect-free region is stable in the longitudinal direction of the silicon single crystal 10. Can be secured.

Since the infrared transmittance is estimated based on the thickness of the bubble layer 32 of the quartz crucible 3A, it is easy to obtain the infrared transmittance.
By setting the range to be adjusted in the second step S3 to this range, the silicon single crystal 10 can be stably pulled up without significantly changing the hot zone in the silicon single crystal 10 pulling device 1.

Next, examples of the present invention will be described. The present invention is not limited to the examples described below.
First, a quartz crucible 3A having an infrared transmittance of 50% is prepared, set in a silicon single crystal pulling device 1, and heated so that the crystal growth margin in the defect-free region when the quartz crucible 3A is used is maximized. The liquid level Gap of the shield 12 was set, and the silicon single crystal 10 was pulled up (reference example).

Next, the quartz crucible 3A having an infrared transmittance of 70% was changed, and the silicon single crystal 10 was pulled up under the same conditions as in the reference example (comparative example).
Then, using the quartz crucible 3A having an infrared transmittance of 70% as it is, the liquid level Gap of the heat shield 12 was set to 96% of the initial liquid level Gap, and the silicon single crystal 10 was pulled up. (Example).
In each of the reference example, the comparative example, and the embodiment, 10 silicon single crystals 10 are pulled up.

In the reference example, the comparative example, and the example, the portion of the silicon single crystal outside the defect-free region was regarded as a defective product. The defective product was determined by cutting the silicon single crystal 10 into a plurality of ingot blocks, collecting single-wafered samples from both ends thereof, and confirming the presence or absence of OSF and L / DL.
For the ingot block of the sample determined to be defective, a single leaf sample is further collected, and a single leaf sample is collected until OSF and L / DL are exhausted. Then, the defective product length in the silicon single crystal 10 was divided by the total pull-up length of 10 silicon single crystals 10 to calculate the defective rate. The results are shown in FIG.

As can be seen from FIG. 12, the defect rate of the silicon single crystal 10 pulled up using the quartz crucible 3A having an infrared transmittance of 50% was 1%, but it was changed to the quartz crucible 3A having an infrared transmittance of 70%. In the comparative example in which the silicon single crystal 10 was pulled up, the defect rate increased to 6.8%.
On the other hand, in the example in which the liquid level Gap was changed to 96% and the heat shield 12 was brought close to the liquid level of the silicon melt 9, it was confirmed that the defect rate could be reduced to 1.0%.
Therefore, it can be said that the defect rate of defect-free crystals can be reduced by changing the liquid level Gap according to the infrared transmittance of the quartz crucible 3A.

1 ... Pulling device, 2 ... Chamber, 3 ... Crucible, 3A ... Quartz crucible, 3B ... Graphite crucible, 4 ... Support shaft, 5 ... Heater, 6 ... Insulation material, 7 ... Pulling shaft, 8 ... Seed crystal, 9 ... Silicon Melt, 10 ... Silicon single crystal, 11 ... Water cooler, 12 ... Heat shield, 13 ... Gas inlet, 14 ... Exhaust port, 20 ... Infrared transmittance measuring device, 21 ... Power supply, 22 ... Halogen heater, 23 ... Laser power meter, 31 ... transparent layer, 32 ... bubble layer, 41 ... contact terminal, 43 ... laser oscillator, 44 ... mirror, 45 ... CCD camera, S1 ... 1st step, S3 ... 2nd step, S5 ... 3rd step ..

Claims (4)

A pulling device including a quartz crucible into which a silicon raw material is charged, a heater for melting the silicon raw material in the quartz crucible, and a heat shield arranged above the quartz crucible to shield infrared rays from the heater. It is a method for producing a silicon single crystal by the Czochralski method for producing a silicon single crystal by pulling the seed crystal above the quartz crucible.
The first step of acquiring the infrared transmittance of the quartz crucible and
A second step of adjusting the distance between the liquid level of the silicon melt in the quartz crucible and the lower end of the heat shield based on the acquired infrared transmittance, and
The third step of pulling up the silicon single crystal and
A method for producing a silicon single crystal, which comprises carrying out. In the method for producing a silicon single crystal according to claim 1,
The third step is a method for producing a silicon single crystal, which comprises pulling up the silicon single crystal by maintaining or increasing or decreasing the distance based on a change in the thermal environment surrounding the pulled up silicon single crystal. In the method for producing a silicon single crystal according to claim 1 or 2.
The first step is a method for producing a silicon single crystal, which comprises estimating infrared transmittance based on the thickness of the bubble layer of the quartz crucible. In the method for producing a silicon single crystal according to any one of claims 1 to 3.
The second step is in the range of 96% or more and 103% or less with respect to the reference distance between the liquid level of the silicon melt in the quartz crucible and the lower end of the heat shield in the reference infrared transmittance. A method for producing a silicon single crystal, which comprises adjusting the distance between the liquid level of the silicon melt in the quartz crucible and the lower end of the heat shield.

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