JP6593401B2 - Method for producing silicon single crystal - Google Patents

Description

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

Cs in the silicon single crystal becomes Ci in the device process and combines with Oi to form a CiOi defect. The CiOi defect causes a device failure.
Here, the carbon concentration in the crystal is controlled by controlling the contamination rate of CO mixed into the raw material melt from the high-temperature carbon member such as a heater in the furnace and the graphite crucible, and the evaporation rate of CO from the raw material melt. It is known to reduce. Note that CO (gas) from the high-temperature carbon member is generated based on the following reaction formula.
SiO (gas) + 2C (solid) → CO (gas) + SiC (solid)

  Therefore, in Patent Document 1, the upper end position of the graphite crucible from the time of melting the raw material to the start of pulling of the silicon single crystal is controlled so as to be 5 mm or more and 95 mm or less upward from the upper end of the heater, and silicon From the time of melting the single crystal material to the end of pulling, the exhaust cross-sectional area of the exhaust flow path in the gap between the lower end of the radiation shield and the melt surface is less than the cross-sectional area of the exhaust flow path formed by the inner cylinder and the outer cylinder. A technique for controlling the above is disclosed.

JP-A-2006-56026

  However, in the technique described in Patent Document 1, the relative positions of the graphite crucible and the heater are unique to the hot zone, and the optimum range differs for each hot zone. For this reason, there exists a subject that the optimal range which reduces the carbon concentration in a crystal cannot be determined uniquely.

  The objective of this invention is providing the manufacturing method of the silicon single crystal which can reduce the carbon concentration in a silicon single crystal reliably.

  The inventors set a plurality of control factors that may affect the carbon concentration in the silicon single crystal, and conducted a factor analysis on these based on the experimental design method. As a result, the present inventors have found that the carbon concentration in the silicon single crystal can be reliably reduced by controlling the distance between the silicon melt surface and the shielding plate disposed on the silicon melt surface. .

The method for producing a silicon single crystal according to the present invention includes a quartz crucible into which a silicon raw material is charged, a heater for melting the silicon single crystal in the quartz crucible, and a heat shield disposed above the quartz crucible. A silicon single crystal manufacturing method for manufacturing a silicon single crystal by the Czochralski method using the pulled-up device, wherein the silicon raw material in the quartz crucible is melted and the heat shielding is performed when the silicon raw material is melted. The silicon raw material is melted in a state where the distance from the lower end of the body is maintained at 86 mm or more and 132 mm or less .
In the present invention, it is preferable to maintain the distance between the surface of the silicon melt in the quartz crucible and the lower end of the thermal shield at 100 mm or more and 125 mm or less.

  According to this invention, in the melting process of the silicon raw material, the distance between the surface of the silicon melt and the heat shield is maintained in the above range. As a result, CO (gas) existing on the melt surface can be efficiently eliminated, so that the carbon concentration of the pulled silicon single crystal can be reliably reduced.

In the present invention, the distance between the liquid level of the silicon melt in the quartz crucible and the lower end of the thermal shield is the distance between the crucible height of the quartz crucible, the upper end of the quartz crucible and the upper end position of the heater. And the distance between the liquid surface of the silicon melt in the quartz crucible and the lower end of the heat shield and the flow rate of the argon gas supplied into the quartz crucible are determined by an experimental design method. Is preferred.
According to the present invention, the most effective control factor can be found with a small number of experiments from among a plurality of control factors that can reduce the mixing of CO (gas) into the silicon melt. The control factor that should be controlled efficiently can be acquired.

In the present invention, the melting of the silicon raw material is performed by putting the silicon raw material into the quartz crucible and melting it, and then sequentially suspending the suspended rod-shaped silicon raw material on the silicon melt surface. preferable.
According to the present invention, a small amount of silicon raw material that can be charged is melted while maintaining the distance between the liquid surface of the silicon melt and the lower end of the heat shield, and then the rod-shaped silicon raw material is suspended. In the wet state, let it melt and melt. Therefore, during the melting of the silicon raw material, the rod-shaped silicon raw material can be charged while maintaining the distance between the surface of the silicon melt and the lower end of the heat shield.

The schematic diagram which shows the structure of the pulling apparatus of the silicon single crystal which concerns on embodiment of this invention. The schematic diagram for demonstrating the control factor of the experiment design method in the said embodiment. The graph which shows the change of the carbon concentration in the control factor and silicon single crystal in the said embodiment. The graph which shows the relationship between the liquid level of the silicon melt in the said embodiment, the distance of the lower end of a heat shield, and the carbon concentration in a silicon melt. The schematic diagram showing the state of the gas flow in case the distance of the liquid level of the silicon melt in the said embodiment and the lower end of a heat shield is large. The schematic diagram showing the state of the gas flow in case the distance of the liquid level of the silicon melt in the said embodiment and the lower end of a heat shield is small. The schematic diagram showing the state of the gas flow in case the distance of the liquid level of the silicon melt in the said embodiment and the lower end of a heat shield is appropriate. The side view which shows the structure of the hanging jig | tool of the rod-shaped silicon raw material in the said embodiment. The schematic diagram for demonstrating making a silicon melt melt in the state which suspended the rod-shaped silicon raw material in the said embodiment.

[1] Structure of Silicon Single Crystal Pulling Device 1 FIG. 1 is a schematic diagram showing an example of the structure of a silicon single crystal pulling device 1 to which the silicon single crystal manufacturing method according to the embodiment of the present invention can be applied. Has been. The pulling device 1 is a device that pulls up the silicon single crystal 10 by the Czochralski method, and includes a chamber 2 that constitutes an outline and a crucible 3 that is disposed at 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 that can rotate and move up and down.

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

A cylindrical heat shield 12 is disposed in the chamber 2.
The heat shield 12 shields high temperature radiant heat from the silicon melt 9 in the crucible 3, the heater 5, and the side wall of the crucible 3 from the growing silicon single crystal 10, and at the same time, a solid liquid that is a crystal growth interface. For the vicinity of the interface, it plays the role of suppressing the diffusion of heat to the outside and controlling the temperature gradient in the pulling axis direction of the single crystal central part and the single crystal outer peripheral part.
The heat shield 12 also has a function as a rectifying cylinder that exhausts the evaporation portion from the silicon melt 9 to the outside of the furnace with an inert gas introduced from above the furnace.

A gas inlet 13 for introducing an inert gas such as argon gas (hereinafter referred to as Ar gas) into the chamber 2 is provided at the top of the chamber 2. In the lower part of the chamber 2, there is provided an exhaust port 14 through which a gas in the chamber 2 is sucked and discharged by driving a vacuum pump (not shown).
The inert gas introduced into the chamber 2 from the gas inlet 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 surface of the silicon melt 9. After passing through the gap, the air flows toward the outside of the heat shield 12 and further toward the outside of the crucible 3, and then descends outside the crucible 3 and is discharged from the exhaust port 14.

  When the silicon single crystal 10 is manufactured using such a pulling apparatus 1, a solid material such as polycrystalline silicon filled in the crucible 3 is heated to the heater 5 while the chamber 2 is maintained in an inert gas atmosphere under reduced pressure. The silicon melt 9 is formed by melting by heating. 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 7 is gradually pulled up to grow the silicon single crystal 10 connected to the seed crystal 8.

[2] Identification of the distance Gap between the liquid surface of the silicon melt 9 and the lower end of the heat shield 12 [2-1] Identification of the control factor by the experimental design method First, the present inventors are shown in FIG. , (B), the crucible height which is the height of the upper end position of the quartz crucible 3A relative to the upper end position of the graphite crucible 3B, the distance CP between the upper end positions of the graphite crucible 3B and the heater 5, and the quartz crucible 3A As a control factor, the flow rate of Ar gas, and the distance Gap between the surface of the silicon melt 9 in the quartz crucible 3A and the lower end of the heat shield 12, which control factor determines which silicon is being melted by the silicon raw material It was examined whether the carbon concentration in the melt 9 was affected. Table 1 shows each control factor and the level of each control factor. The depth of the silicon melt 9 can be set freely, and CP and Gap were changed independently. The furnace pressure was constant at 4000 Pa (value converted to 30 Torr).

As shown in FIG. 3, the results of the factor analysis by the experimental design method showed no significant changes in the crucible height, CP, and Ar gas flow rate even if the level was changed, and the carbon inside the silicon melt 9 was not changed. It was confirmed that there was no significant effect on the concentration.
On the other hand, regarding the distance Gap between the liquid surface of the silicon melt 9 in the quartz crucible 3A and the lower end of the heat shield 12, the carbon concentration inside the silicon melt 9 is greatly reduced in the range of Gap = 100 mm to 120 mm. It was confirmed.
That is, it was confirmed that the carbon concentration inside the silicon melt 9 is affected by the distance Gap between the liquid surface of the silicon melt 9 in the quartz crucible 3A and the lower end of the heat shield 12.

[2-2] Identification of optimal range by simulation Next, the present inventors use the thermal flow analysis program CGSim of STR, and the level of the silicon melt 9 in the quartz crucible 3A and the thermal shield 12 The distance Gap at the lower end was changed, and the chemical reaction model and the gas flow at that time were simulated. The results are shown in Table 2 and FIG.

  As can be seen from Table 2 and FIG. 4, the distance Gap between the liquid surface of the silicon melt 9 in the quartz crucible 3A and the lower end of the heat shield 12 is in the range of 86 mm or more and 132 mm or less. It was confirmed that the carbon concentration was significantly reduced. In particular, in the range of 100 mm or more and 125 mm or less, the effect of reducing the carbon concentration is remarkable.

When the gas flow at the distance Gap = 187 mm was confirmed, the gas flow as shown in FIG. 5 was exhibited. When the liquid surface of the silicon melt 9 and the lower end of the heat shield 12 are separated from each other, the flow rate of Ar gas on the silicon melt 9 is reduced, and it is difficult for the CO gas on the silicon melt 9 to be discharged. The carbon concentration in the melt 9 will increase. In FIGS. 5 to 7, circles connected by lines schematically represent the gas flow.
When the distance Gap is increased, the exhaust effect is weakened and a vortex is generated above the silicon melt 9. When this vortex stays, the CO gas in the vortex becomes high in concentration, and the amount of CO gas mixed into the silicon melt 9 increases due to diffusion.
When the gas flow at the distance Gap = 67 mm was confirmed, the gas flow as shown in FIG. 6 was exhibited. When the liquid level of the silicon melt 9 and the lower end of the heat shield 12 are close to each other, the carbon concentration in the silicon melt 9 is increased by the CO gas generated from the lower end of the heat shield 12.
When the distance Gap is reduced, the amount of CO gas mixed from the heat shield 12 into the silicon melt 9 increases.

  When the gas flow at the distance Gap = 122 mm was confirmed, the gas flow as shown in FIG. 7 was exhibited. Since the distance between the liquid level of the silicon melt 9 and the lower end of the heat shield 12 is set appropriately, the flow rate of Ar gas on the silicon melt 9 does not decrease, and the CO on the silicon melt 9 decreases. The gas can be appropriately discharged, and the CO gas generated from the lower end of the heat shield 12 hardly penetrates into the silicon melt 9.

[3] Silicon raw material melting method From the above simulation results, it was found that the distance Gap between the surface of the silicon melt 9 and the heat shield 12 is preferably 86 mm or more and 132 mm or less when the silicon raw material is melted. .
However, in general, the silicon raw material is introduced into the quartz crucible 3A by introducing silicon chunks into the quartz crucible 3A. At this time, since the heat shield 12 needs to be raised, the distance Gap between the liquid surface of the silicon melt 9 and the heat shield 12 cannot be maintained in the above range.

Therefore, in this embodiment, first, in the silicon raw material melting step, an amount of silicon raw material that can be charged in a state where the distance Gap between the liquid surface of the silicon melt 9 and the heat shield 12 is maintained in the above range is charged. Then, the amount of the silicon melt 9 is increased by causing the suspended rod-shaped silicon raw material to adhere to the surface of the silicon melt 9.
As shown in FIG. 8, the hanging jig 20 includes a box hardware 21, a threaded round bar 22, a hanging plate 23, a nut 24, a pair of hooks 25, and a width adjusting plate 26.

The box metal 21 is composed of a bottomed box-like body, and a hole 21A is formed at the center of the bottom. A threaded round bar 22 is inserted through the hole 21A.
The threaded round bar 22 is composed of a rod-like body having a male thread groove formed on the outer periphery, and a nut 22A is screwed into a portion inserted through the hole 21A, and hangs downward from the lower surface of the box metal 21.
A hanging plate 23 is inserted into the lower end of the threaded round bar 22, and a nut 24 is screwed into the lower part thereof.
A plurality of holes 23 </ b> A are formed at the end portions of the hanging plate 23, and the base end portions of the hooks 25 are inserted into the respective holes 23 </ b> A.

Each of the pair of hooks 25 has an upper end that is enlarged in a bolt shape, and is locked to the suspension plate 23 while being inserted into the hole 23 </ b> A of the suspension plate 23. The ends of the pair of hooks 25 are bent in the horizontal direction, and the locking claws 25A formed at the ends are arranged so as to face each other.
The width adjustment plate 26 is inserted through an intermediate portion between the pair of hooks 25. The hole 26A through which the hook 25 is inserted is formed as a long hole extending in the direction in which the pair of hooks 25 face each other.

  When such a hanging jig 20 is rotated upward by rotating the nut 24, the hanging plate 23 is pulled up, and the hook 25 is also moved upward accordingly. When the hook 25 moves upward, the width adjustment plate 26 relatively moves to the lower side of the hook 25, the non-paired hooks 25 approach each other, and the interval between the respective locking claws 25A becomes narrow. Thereby, it becomes possible to suspend the rod-shaped silicon raw material Srd (see FIG. 9).

The silicon raw material at the time of melting the silicon is first charged in an amount that allows a small amount of chunk of silicon to be charged from the opening for pulling up the thermal shield 12, and the melting of the silicon raw material is started.
When the silicon raw material is melted, as shown in FIG. 9, the rod-shaped silicon raw material Srd is sandwiched by the hanging jig 20 and moved downward from the opening for pulling up the silicon single crystal 10 of the thermal shield 12 in the suspended state. The liquid is then deposited on the surface of the silicon melt 9. Then, this operation is sequentially repeated to melt the amount of the silicon melt 9 necessary for pulling up.

At this time, the distance Gap between the liquid surface of the silicon melt 9 and the lower end of the heat shield 12 is maintained at 86 mm or more and 132 mm or less. In addition, as a method of measuring the liquid level position of the silicon melt 9, for example, a method of measuring using a melt liquid level monitoring device disclosed in Japanese Patent No. 4784401 can be employed.
Thereby, since the silicon raw material can be melted in a state in which the CO gas is hardly mixed into the silicon melt 9, the carbon concentration inside the pulled silicon single crystal 10 can be reduced.

  DESCRIPTION OF SYMBOLS 1 ... Lifting device, 2 ... Chamber, 3 ... Crucible crucible, 3A ... Quartz crucible, 3B ... Graphite crucible, 4 ... Support shaft, 5 ... Heater, 6 ... Heat insulating material, 7 ... Lifting shaft, 8 ... Seed crystal, 9 ... Silicon Melt, 10 ... Silicon single crystal, 12 ... Thermal shield, 13 ... Gas inlet, 14 ... Exhaust, 20 ... Hanging jig, 21 ... Box hardware, 21A ... Hole, 22 ... Threaded round bar, 22A ... Nut, 23 ... hanging plate, 23A ... hole, 24 ... nut, 25 ... hook, 25A ... locking claw, 26 ... width adjusting plate, 26A ... hole, CP ... distance, Gap ... distance, Srd ... rod-shaped silicon raw material .

Claims (3)

Using a pulling device comprising a quartz crucible into which a silicon raw material is charged, a heater for melting a silicon single crystal in the quartz crucible, and a heat shield disposed on the quartz crucible, the Czochralski method is used. A method for producing a silicon single crystal for producing a silicon single crystal,
When the silicon raw material is melted, the silicon raw material is melted in a state where the distance between the surface of the silicon melt in the quartz crucible and the lower end of the heat shield is maintained at 86 mm or more and 132 mm or less. A method for producing a silicon single crystal. In the manufacturing method of the silicon single crystal of Claim 1 ,
A method for producing a silicon single crystal, wherein a distance between a liquid surface of a silicon melt in the quartz crucible and a lower end of the heat shield is maintained at 100 mm or more and 125 mm or less. In the manufacturing method of the silicon single crystal of Claim 1 or Claim 2,
The melting of the silicon raw material is performed by putting the silicon raw material into the quartz crucible and melting it, and then sequentially suspending the suspended rod-shaped silicon raw material on the surface of the silicon melt. A method for producing a silicon single crystal.

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