JP3787452B2 - Method for producing silicon single crystal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of pulling and manufacturing a silicon single crystal rod.
[0002]
[Prior art]
Conventionally, as a silicon single crystal manufacturing apparatus, as shown in FIG. 6, a quartz crucible 4 in which a silicon melt 2 is stored is housed in a chamber 3, and the outer peripheral surface of the silicon single crystal rod 1 and the quartz crucible 4 A pulling device (Japanese Patent Publication No. 57-40119) in which a heat shielding member 7 is inserted so as to surround the silicon single crystal rod 1 between the peripheral surface and the peripheral surface is disclosed. In this apparatus, the cone portion 7a whose diameter decreases as the heat shielding member 7 faces downward, and the outer peripheral edge is connected to the lower end of the cone portion 7a and extends horizontally, and the inner peripheral edge is near the outer peripheral surface of the silicon single crystal rod 1. The ring portion 7b reaches, and the inner peripheral edge is connected to the upper end of the cone portion 7a and extends horizontally, and the outer peripheral edge reaches the upper surface of the heat insulating cylinder 8 and has a flange portion 7c. The heat shielding member 7 is fixed by placing the flange portion 7 c on the upper surface of the heat insulating cylinder 8. Reference numeral 6 in FIG. 6 is a susceptor that covers the outer surface of the quartz crucible 4, and reference numeral 9 is a heater that surrounds the outer peripheral surface of the quartz crucible 4 at a predetermined interval from the quartz crucible.
[0003]
In the pulling device configured as described above, when the silicon single crystal rod 1 is pulled up from the silicon melt 2, the liquid surface of the silicon melt 2 gradually decreases to expose the inner peripheral wall of the quartz crucible 4. Radiant heat from the inner peripheral wall of the quartz crucible 4 is directed to the outer peripheral surface of the silicon single crystal rod 1, but this radiant heat is blocked by the heat shielding member 7 and does not reach the outer peripheral surface of the silicon single crystal rod 1. As a result, solidification of the silicon single crystal rod 1 being pulled is not delayed, and the silicon single crystal rod 1 is cooled quickly.
[0004]
[Problems to be solved by the invention]
In the conventional pulling apparatus disclosed in Japanese Patent Publication No. 57-40119, the susceptor and the heater are made of carbon, and the heat shielding member is made of tungsten, niobium, tantalum, carbon or the like. When the heat shielding member is made of carbon, the susceptor, the heater, and the heat shielding member may contain other metal impurities such as Fe in the manufacturing process. In this case, when the silicon single crystal rod is pulled, the metal Since impurities and carbon jump out from the surface of the heat shielding member and the like and adhere to the outer peripheral surface of the silicon single crystal rod, there is a problem that it is difficult to achieve high purity of the silicon single crystal rod.
Further, in the pulling apparatus disclosed in the above-mentioned Japanese Patent Publication No. 57-40119, since the quartz crucible is eluted at a very high temperature when pulling up the silicon single crystal rod, the bubbles in the quartz crucible burst and the silicon melt is melted. A minute piece of quartz crucible is mixed in. As a result, there is a problem that the crystal dislocation of the silicon single crystal rod is increased and the single crystallization rate, that is, the free rate is lowered.
[0005]
An object of the present invention is to provide a method for producing a silicon single crystal capable of increasing the purity of a silicon single crystal rod by preventing metal impurities and carbon from jumping out of a heat shielding member during pulling. It is in.
Another object of the present invention is to provide a method for producing a silicon single crystal capable of improving the single crystallization rate of a silicon single crystal rod by suppressing bursting of bubbles in a quartz crucible during pulling.
Yet another object of the present invention is to increase the flow rate of inert gas passing between the lower end of the heat shielding member and the silicon melt surface when the pressure in the chamber is high, thereby increasing the oxygen in the silicon single crystal rod. An object of the present invention is to provide a method for producing a silicon single crystal in which the concentration can be easily adjusted to a low optimum value.
[0006]
[Means for Solving the Problems]
In the invention according to claim 1, as shown in FIG. 1, the silicon melt 12 melted by the heater 19 is stored in the quartz crucible 14 in the chamber 13, and the silicon single crystal rod 11 pulled up from the silicon melt 12 is obtained. The outer peripheral surface is surrounded by the heat shielding member 27 to shield the radiant heat from the heater 19, and an inert gas is caused to flow down to the outer peripheral surface of the silicon single crystal rod 11 to be pulled up, so that the lower end of the heat shielding member 27 and the surface of the silicon melt 12 are covered. This is an improvement of a method for producing a silicon single crystal configured to pass through.
The characteristic configuration is that the pressure in the chamber 13 is set to 25 to 60 Torr while the single crystal rod 11 is pulled up, and the inert gas passes between the lower end of the heat shielding member 27 and the surface of the silicon melt 12. Is set to 0.5 to 3.5 m / sec, and when the oxygen concentration in the pulled single crystal rod 11 decreases with the pulling, the pressure in the chamber 13 is gradually reduced within the above range. the flow rate of Ru when both inert gas raised lowered within the above range, when oxygen concentration in the single crystal rod 11 are the pulling rises along with the pulling, gradually the pressure in the chamber 13 in the above range the flow rate of Ru when both inert gas is lowered there is to raise within the above range.
[0007]
In the method for producing a silicon single crystal described in claim 1, the pressure in the chamber 13 is set to a relatively high value of 25 to 60 Torr during the pulling of the silicon single crystal rod 11, so that the heater 19 and the heat shielding member Almost no metal impurities or carbon jumps out of the surface such as 27. In addition, it has been found that the concentration of metal impurities or carbon in the crystal varies depending on the flow path and flow rate of the inert gas.
Further, the quartz crucible 14 is heated by the heater 19 and the extremely high temperature silicon melt 12 is stored, so that the quartz crucible 14 is softened. However, since the pressure in the chamber 13 is set high as described above, the surface of the quartz crucible 14 is set. Can be reduced. On the other hand, if the pressure in the chamber 13 is set high as described above, oxygen in the silicon melt 12 is saturated and the quartz crucible 14 is difficult to elute into the silicon melt 12.
Further, when the pressure in the chamber 13 is set to a relatively high value of 25 to 60 Torr , the flow rate of the inert gas is set to 0.5 to 3.5 m / sec as described above, thereby the silicon single crystal rod 11 The oxygen concentration inside can be easily adjusted to an optimum value.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the silicon single crystal rod 11 is pulled up from the silicon melt 12 by a pulling device 10. A quartz crucible 14 for storing the silicon melt 12 is provided in the chamber 13 of the pulling device 12, and the outer surface of the quartz crucible 14 is covered with a susceptor 16 made of carbon. The lower surface of the quartz crucible 14 is fixed to the upper end of the support shaft 17 via the susceptor 16, and the lower portion of the support shaft 17 is connected to the crucible driving means 18. Although not shown, the crucible driving means 18 has a crucible rotating motor for rotating the quartz crucible 14 and a crucible lifting motor for moving the quartz crucible 14 up and down, and the quartz crucible 14 can be rotated in a predetermined direction by these motors. At the same time, it is movable in the vertical direction. The outer peripheral surface of the quartz crucible 14 is surrounded by a carbon heater 19 at a predetermined interval from the quartz crucible 14, and the heater 19 is surrounded by a heat retaining cylinder 21. The heater 19 heats and melts the high-purity silicon polycrystal charged in the quartz crucible 14 to form the silicon melt 12.
[0010]
A cylindrical casing 22 is connected to the upper end of the chamber 13. The casing 22 is provided with a single crystal rod pulling means 23. The pulling means 23 is a pulling head (not shown) provided at the upper end of the casing 22 so as to be rotatable in a horizontal state, a head rotating motor (not shown) for rotating the head, and a quartz crucible 14 from the head. A wire cable 24 that hangs down toward the center of rotation, a single crystal rod pulling motor (not shown) that winds or feeds the wire cable 24 provided in the head, and is suspended from the lower end of the wire cable 24 Seed crystal 26. The seed crystal 26 is immersed in the silicon melt 12 and pulled up by the wire cable 24 so that the silicon single crystal rod 11 is pulled up.
[0011]
Between the outer peripheral surface of the silicon single crystal rod 11 and the inner peripheral surface of the quartz crucible 14, a heat shielding member 27 is provided that surrounds the silicon single crystal rod 11 and shields radiant heat from the heater 19. The heat shielding member 27 is made of carbon and has a straight cylindrical portion 27a surrounding the outer peripheral surface of the silicon single crystal rod 11 to be pulled up, and a conical shape continuously connected to the lower end of the straight cylindrical portion 27a and having a diameter that decreases downward. The cone portion 27b is formed, and a flange portion 27c that is connected to the upper end of the straight tube portion 27a and projects outward in a substantially horizontal direction. The lower end of the cone portion 27b is positioned above the surface of the silicon melt 12 with a gap. The inclination angle of the cone part 27b is set in the range of 30 to 60 degrees, preferably 45 degrees with respect to the horizontal plane.
[0012]
On the other hand, a gas supply / exhaust means 34 is connected to the chamber 13 for supplying an inert gas to the silicon single crystal rod 11 side of the chamber 13 and discharging the inert gas from the crucible inner peripheral surface side of the chamber 13. The gas supply / discharge means 34 has one end connected to the peripheral wall of the casing 22 and the other end connected to a tank (not shown) for storing the inert gas, and one end connected to the lower wall of the chamber 13. The other end has a discharge pipe 34b connected to a vacuum pump (not shown). The supply pipe 34a and the discharge pipe 34b are respectively provided with first and second flow rate adjusting valves 34c and 34d for adjusting the flow rate of the inert gas flowing through these pipes 34a and 34b. As the inert gas, argon gas, helium gas, krypton gas, or the like is used, and this gas flows down to the outer peripheral surface of the silicon single crystal rod 11 to be pulled up, and between the lower end of the heat shielding member 27 and the surface of the silicon melt 12. Configured to pass through.
[0013]
The characteristic configuration of the present invention is that the pressure in the chamber 13 is set to 25 to 60 Torr, preferably 40 to 60 Torr while the silicon single crystal rod 11 is pulled up, and the lower end of the heat shielding member 27 and the surface of the silicon melt 12 The flow rate of the inert gas passing between the two is set to 0.5 to 3.5 m / sec. The reason why the pressure in the chamber 13 is limited to 25 to 60 Torr is that when it is less than 25 Torr, metal impurities such as Fe and carbon contained in the susceptor 16, the heater 19, the heat shielding member 27, etc. jump out and the outer peripheral surface of the silicon single crystal rod 11. There is a problem that the impurity concentration in the silicon single crystal rod 11 is increased due to adhering to the surface, and when the temperature exceeds 60 Torr, the temperature of the atmosphere in the chamber 13 rises, and O intervened in the chamber dividing portion (flange portion). This is because the ring has problems such as thermal damage. Further, the flow rate of the inert gas passing between the lower end of the heat shielding member 27 and the surface of the silicon melt 12 is limited to 0.5 to 3.5 m / sec. This is because there is a problem that the oxygen concentration in No. 11 becomes high, and when it exceeds 3.5 m / sec, there is a problem that the single crystallization rate decreases.
[0014]
The pressure in the chamber 13 and the flow rate of the inert gas are normally kept constant while the silicon single crystal rod 11 is pulled up, but within a range of 25-60 Torr or 0.5-3.5 m / Within the range of seconds, there may be a change during pulling of the single crystal rod 11 in order to change the oxygen concentration. Also depending on the pulling conditions of the single crystal ingot 11, when the oxygen concentration decreases with pulling, even if the oxygen concentration constant gradually decreasing the flow rate of both the inert gas when when set to a higher pressure is there. If the oxygen concentration increases with the pulling, the reverse is performed.
[0015]
A first rotary encoder (not shown) is provided on the output shaft (not shown) of the single crystal rod pulling motor, and a second rotary encoder (not shown) is provided on the output shaft (not shown) of the drum rotation motor. Not shown). The crucible driving means 18 is provided with a weight sensor (not shown) for detecting the weight of the silicon melt 12 in the quartz crucible 14 and a linear encoder (not shown) for detecting the raising / lowering position of the support shaft 17. The detection outputs of the first and second rotary encoders, the weight sensor, and the linear encoder are connected to the control input of a controller (not shown), and the control output of the controller is a crucible pulling motor, a drum rotating motor, and a crucible lifting / lowering motor. Connected to each. The controller is also provided with a memory (not shown). In this memory, the winding length of the seed crystal wire cable 24 for each detection output of the first and second rotary encoders, that is, the pulling of the silicon single crystal rod 11 is raised. Each length is stored as a first map, and the level of the silicon melt 12 in the quartz crucible 14 with respect to the detection output of the weight sensor is stored as a second map. The controller is configured to control the crucible lifting / lowering motor so as to always keep the liquid level of the silicon melt 12 in the quartz crucible 14 at a constant level based on the detection output of the weight sensor.
[0016]
In the silicon single crystal manufacturing method configured as described above, the susceptor 16, the heater 19, the heat shielding member 27, and the like are formed of carbon, but the pressure in the chamber 13 is set to a relatively high value of 25 to 60 Torr. Therefore, the metal impurities such as Fe and carbon hardly jump out from the surface of the susceptor 16 and the like. This is considered to be because when the impurities inside the susceptor 16 and the like are desorbed as gas molecules, the desorption is more difficult as the pressure is higher. As a result, since the metal impurities and carbon are hardly mixed in the inert gas in the chamber 13, the silicon single crystal rod 11 can be highly purified.
[0017]
The quartz crucible 14 is heated by the heater 19 and softens because the extremely high temperature silicon melt 12 is stored. However, since the pressure in the chamber 13 is set to a relatively high value of 25 to 60 Torr, the quartz crucible 14 Bubbles generated on the surface can be reduced. On the other hand, when the pressure in the chamber 13 is set to a relatively high value of 25 to 60 Torr, the oxygen in the silicon melt 12 is saturated (the partial pressure of oxygen is saturated), and the quartz crucible 14 becomes the silicon melt 12. Elution is difficult. As a result, the bubbles burst and the silicon melt 12 hardly contains fine fragments of the quartz crucible, and the silicon single crystal rod 11 pulled up from the silicon melt 12 hardly contains the fine fragments. The substance causing the dislocation of the crystal of the crystal rod 11 is reduced, and the single crystallization rate of the silicon single crystal rod 11, that is, the free rate can be improved.
[0018]
Furthermore, when the pressure in the chamber 13 is set to a relatively high value of 25 to 60 Torr, the flow rate of the inert gas passing between the lower end of the heat shielding member 27 and the surface of the silicon melt 12 is set to 0.5 to 3.5 m / By setting the second range, the oxygen concentration in the silicon single crystal rod 11 can be easily adjusted to an optimum value.
[0019]
【Example】
Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
A silicon single crystal rod 11 having an outer diameter of 205 mm was pulled using a silicon single crystal pulling apparatus 10 as shown in FIG. The dimensions of the heat shielding member 27 of the apparatus 10 are as follows. The diameter and length of the straight tube portion 27a were 460 mm and 380 mm, respectively. Moreover, the diameter of the upper end and lower end of the cone part 27b was 460 mm and 270 mm, and the height was 50 mm. That is, the inclination angle of the cone part 27b was 45 degrees with respect to the horizontal plane . Furthermore, the space | interval of the lower end of the cone part 27b and the silicon melt 12 was 30 mm. The heat shielding member 27, the susceptor 16 that covers the outer surface of the quartz crucible 14, and the heater 19 that surrounds the outer peripheral surface of the quartz crucible 14 with a predetermined distance from the quartz crucible 14 are formed of carbon. The pressure of the argon gas in the chamber 13 was set to 30 Torr, and the flow rate of the inert gas passing between the lower end of the heat shielding member 27 and the surface of the silicon melt 12 was set to 1.3 m / sec.
[0020]
<Example 2>
The configuration was the same as that of Example 1 except that the pressure of the argon gas in the chamber was set to 50 Torr.
<Example 3>
The configuration was the same as that of Example 1 except that the pressure of the argon gas in the chamber was set to 40 Torr.
<Example 4>
Example 1 except that the pressure of the argon gas in the chamber was set to 25 Torr, and the flow rate of the inert gas passing between the lower end of the heat shielding member and the silicon melt surface was set to 1.1 m / sec. The same configuration.
[0021]
<Examples 5 and 6>
Example 1 except that the pressure of argon gas in the chamber was set to 20 Torr, and the flow rate of the inert gas passing between the lower end of the heat shielding member and the silicon melt surface was set to 1.25 m / sec. The same configuration.
<Example 7>
Example 1 except that the pressure of the argon gas in the chamber was set to 20 Torr, and the flow rate of the inert gas passing between the lower end of the heat shielding member and the silicon melt surface was set to 1.4 m / sec. The same configuration.
<Example 8>
Example 1 except that the pressure of the argon gas in the chamber was set to 25 Torr, and the flow rate of the inert gas passing between the lower end of the heat shielding member and the silicon melt surface was set to 1.7 m / sec. The same configuration.
[0022]
<Example 9>
Example 1 except that the pressure of the argon gas in the chamber was set to 30 Torr, and the flow rate of the inert gas passing between the lower end of the heat shielding member and the silicon melt surface was set to 2.0 m / sec. The same configuration.
<Example 10>
Example 1 except that the pressure of the argon gas in the chamber was set to 30 Torr and the flow rate of the inert gas passing between the lower end of the heat shielding member and the silicon melt surface was set to 3.0 m / sec. The same configuration.
[0023]
<Comparative Example 1>
Example 1 except that the pressure of the argon gas in the chamber was set to 10 Torr and the flow rate of the inert gas passing between the lower end of the heat shielding member and the surface of the silicon melt was set to 1.3 m / sec. The same configuration.
<Comparative example 2>
Example 1 except that the pressure of argon gas in the chamber was set to 15 Torr, and the flow rate of the inert gas passing between the lower end of the heat shielding member and the silicon melt surface was set to 1.3 m / sec. The same configuration.
<Comparative Examples 3 and 4>
Example 1 except that the pressure of argon gas in the chamber was set to 15 Torr, and the flow rate of the inert gas passing between the lower end of the heat shielding member and the silicon melt surface was set to 0.8 m / sec. The same configuration.
[0024]
<Comparative test 1 and evaluation>
The silicon single crystal rods were manufactured by the pulling apparatuses of Example 1, Example 2 and Comparative Example 1, respectively, and these silicon single crystal rods were sliced to produce 10 silicon wafers. The concentration of Fe contained was measured. The Fe concentration was measured by SPV (Surface Photo Voltage) method. That is, the crystal of the silicon wafer was irradiated with light, the diffusion length was measured before and after the irradiation, and the concentration of Fe mixed as an impurity in the crystal was determined from the difference in the diffusion length before and after the irradiation. The result is shown in FIG.
As is clear from FIG. 2, the average Fe concentration in Comparative Example 1 was 6 × 10 ¹¹ atoms / cm ³ , whereas in Examples 1 and 2, the average value was 1.00 × 10 ¹⁰ atoms. / Cm ³ and 0.7 × 10 ¹⁰ atoms / cm ³ .
[0025]
<Comparative test 2 and evaluation>
The bubble contents of the opaque layer (the outer portion of the quartz crucible) of the quartz crucible used in the pulling apparatus of Example 3 and Comparative Example 2 were measured. The bubbles in the transparent layer were obtained by measuring the specific gravity of the silicon single crystal rod by the Archimedes method and then calculating from the difference between this measured value and the specific gravity of quartz (2.21 g / cm ³ ). The result is shown in FIG.
As is clear from FIG. 3, the bubble content of the opaque layer in Comparative Example 2 was 17% on average, whereas in Example 3, it was reduced to 11.5% on average.
[0026]
<Comparative test 3 and evaluation>
The single crystallization rate of the silicon single crystal rod manufactured by the pulling apparatus of Example 1 and Comparative Example 1 was measured. This single crystallization rate is determined by first measuring the weight of a silicon wafer (raw material) obtained by slicing a silicon single crystal rod, and then measuring the weight of the dislocation-free portion of this wafer. It was determined by substituting for (1).
(Single crystallization rate) = {(Weight of dislocation-free part) / (Weight of raw material)} × 100 (%)… ▲ 1 ▼
The result is shown in FIG. The single crystallization rate was expressed based on Comparative Example 1.
As is clear from FIG. 4, when Comparative Example 1 is set to 1, Example 1 is 1.25, which is 25% higher than Comparative Example 1.
[0027]
<Comparative test 4 and evaluation>
The oxygen concentration contained in the silicon single crystal rods produced by the pulling apparatuses of Examples 4 to 10 and Comparative Examples 3 and 4 was measured. Specifically, the oxygen concentration at the center of a silicon wafer obtained by slicing a silicon single crystal rod was measured by the FTIR method. This FTIR method is a method in which infrared light and reference infrared light irradiated on a wafer are respectively Fourier transformed to obtain an infrared light absorption spectrum from the difference between the two, and the oxygen concentration in the wafer can be quantitatively obtained. . The result is shown in FIG.
As is clear from FIG. 5, in Comparative Examples 3 and 4, the oxygen concentrations were 1.30 × 10 ¹⁸ atoms / cm ³ and 1.28 × 10 ¹⁸ atoms / cm ³ , whereas Examples 4 to 10 Then, it was reduced to 1.12 × 10 ¹⁸ atoms / cm ^{3 to} 1.26 × 10 ¹⁸ atoms / cm ³ .
[0028]
【The invention's effect】
As described above, according to the present invention, the pressure in the chamber during the pulling of the silicon single crystal rod is set to 25 to 60 Torr, so that metal impurities such as Fe and carbon from the surface of the heater, the heat shielding member, etc. Hardly jumps out. As a result, since the metal impurities and carbon are hardly mixed in the inert gas in the chamber, the silicon single crystal rod can be highly purified.
The quartz crucible is heated by a heater and softens because extremely high temperature silicon melt is stored, but the pressure in the chamber is set high as described above, so that bubbles generated on the surface of the quartz crucible are reduced. it can. On the other hand, when the pressure in the chamber is set high as described above, oxygen in the silicon melt is saturated and the quartz crucible is difficult to elute into the silicon melt. As a result, the bubbles burst, so that the silicon crucible is hardly mixed with the fine pieces of the quartz crucible, and the silicon single crystal rod pulled up from the silicon melt is hardly mixed with the fine pieces. cause of the dislocation of the crystalline material is reduced, single crystallization rate of the silicon single crystal rod, that is Ru can improve the free rate.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram showing a silicon single crystal pulling apparatus according to an embodiment of the present invention.
FIG. 2 is a view showing Fe concentration when the pressure in the chamber is 10 Torr, 30 Torr, and 50 Torr.
FIG. 3 is a diagram showing the bubble content of an opaque layer of a quartz crucible when the pressure in the chamber is 15 Torr and 40 Torr.
FIG. 4 is a diagram showing a single crystallization rate when the pressure in the chamber is 10 Torr and 30 Torr.
FIG. 5 is a diagram showing a change in oxygen concentration in a silicon single crystal rod when the flow rate of argon gas in the chamber is changed.
FIG. 6 is a cross-sectional configuration diagram corresponding to FIG. 1 showing a conventional silicon single crystal pulling apparatus.
[Explanation of symbols]
11 Silicon single crystal rod 12 Silicon melt 13 Chamber 14 Quartz crucible 19 Heater 27 Heat shielding member

Claims (1)

The silicon crucible (14) in the chamber (13) stores the silicon melt (12) melted by the heater (19), and the outer peripheral surface of the silicon single crystal rod (11) pulled up from the silicon melt (12). Is surrounded by a heat shielding member (27) to shield radiant heat from the heater (19), and an inert gas is allowed to flow down on the outer peripheral surface of the pulled silicon single crystal rod (11) to thereby heat the shielding member (27). In the method for producing a silicon single crystal configured to pass between the lower end of the silicon melt and the surface of the silicon melt (12),
The pressure in the chamber (13) while pulling up the single crystal rod (11) is set to 25 to 60 Torr, and between the lower end of the heat shielding member (27) and the surface of the silicon melt (12). Set the flow rate of the inert gas passing through to 0.5 to 3.5 m / second,
If the oxygen concentration in the pulled by which single crystal rod (11) decreases with pulling together the flow rate of the inert gas when Raise gradually within the range of pressure in the chamber (13) Within the range,
If the oxygen concentration in the single crystal rod (11) in which is the pulling rises along with the pulling together the flow rate of the inert gas is gradually Ru reducing the pressure within the above range in the chamber (13) A method for producing a silicon single crystal, characterized by being raised within the above range.

Images