JP2018188338A - Production method of silicon single crystal, and silicon single crystal - Google Patents

Abstract

[Problem] In a method for producing silicon single crystals using the HMCZ method, a decrease in oxygen concentration at the outer periphery of a silicon single crystal is suppressed, thereby improving the uniformity of the in-plane distribution of oxygen concentration. [Solution] In a method for producing silicon single crystals using the Czochralski method, a silicon melt 2 in a quartz crucible 11 is heated using a heater 15 arranged around the periphery of the quartz crucible 11, and a silicon single crystal 3 is pulled from the silicon melt 2 while a transverse magnetic field is applied to the silicon melt 2, and the silicon single crystal is pulled under crystal pulling conditions in which the maximum point of the temperature on the inner wall surface of the quartz crucible 11 in contact with the silicon melt 2 is 1438°C or higher, and the position of said maximum point is within the projected region of the silicon single crystal in a cross section passing through the crystal central axis and perpendicular to the direction of application of the transverse magnetic field. [Selected Figure] Figure 1

Description

  The present invention relates to a method for producing a silicon single crystal by the Czochralski method (hereinafter referred to as “CZ method”), and in particular, MCZ (Magnetic field applied CZ) for pulling up a single crystal while applying a magnetic field to a silicon melt. It is about the law. The present invention also relates to a silicon single crystal manufactured by such a manufacturing method.

  The MCZ method is known as a method for producing a silicon single crystal by the CZ method (see, for example, Patent Documents 1 and 2). In the MCZ method, the melt convection is suppressed by applying a magnetic field to the silicon melt in the quartz crucible, and the elution of oxygen from the quartz crucible is suppressed. There are various methods of applying a magnetic field, but the HMCZ (Horizontal MCZ) method in which a single crystal is pulled up while applying a horizontal magnetic field (transverse magnetic field) is in practical use.

  Regarding the MCZ method, for example, Patent Document 1 describes a method of reducing the decrease in the oxygen concentration in the outer periphery of the crystal by setting the magnetic field center position to 0 to 80 mm above the liquid surface. Further, in Patent Document 2, after pulling up a silicon single crystal having a diameter of 458 mm + α, the outer periphery is ground to 450 mm, so that there is no low oxygen region at the wafer peripheral part and the in-plane distribution of oxygen concentration is 450 mm. A method of manufacturing a silicon wafer is described.

  In Patent Document 3, in order to make the in-plane distribution of the temperature gradient in the crystal pulling direction near the solid-liquid interface uniform, heat is intensively supplied to the center of the crystal growth front, thereby A method is described in which an upward flow (see FIG. 5 of Patent Document 3) is made centering on the flow. In Patent Document 3, a cusp magnetic field is applied, a bottom heater is disposed below the crucible, and the bottom heater heats the center of the crucible bottom more strongly than the periphery of the crucible bottom. The temperature is increased intensively.

  Regarding heating control of the silicon melt, for example, Patent Document 4 describes a method of keeping the oxygen concentration in the crystal low by controlling the output ratio of the lower heater to the upper heater of the two-split heater to 4 or more. . Further, in Patent Document 5, a side heater and a bottom heater are provided in the MCZ method in which a cusp magnetic field is applied, and the ratio of the heating amount q of the bottom heater to the total heating amount Q of the side heater and the bottom heater (q / A method is described in which, by increasing Q), a decrease in the oxygen concentration accompanying a decrease in the remaining amount of silicon melt is avoided, and the oxygen concentration distribution in the crystal pulling direction is made uniform.

Japanese Patent Laid-Open No. 2007-204312 JP 2009-274903 A JP 2004-292309 A JP 2011-51806 A JP-A-10-273392

  In the conventional HMCZ method, a method of heating a melt using a single heater surrounding a quartz crucible is common, but when a silicon single crystal is pulled up while heating the melt with such a heater, There is a problem that the oxygen concentration in the outer peripheral portion of the crystal becomes low and it is difficult to make the in-plane distribution of the oxygen concentration uniform.

  Even if it is a silicon single crystal with a low oxygen concentration at the outer periphery, after pulling it up to a diameter sufficiently larger than the target diameter of the silicon wafer, the oxygen concentration of the silicon wafer is removed by removing the low oxygen concentration by peripheral grinding. It is possible to make the in-plane distribution uniform. However, in this case, there is a problem that the manufacturing cost increases because it is necessary to further increase the diameter of the ingot.

  In Patent Document 3, the melt convection rising at the center of the crucible is generated along with two inner vortices out of four large vortices, and this melt convection does not pass through the vicinity of the gas-liquid interface. Supplied to the solid-liquid interface. On the other hand, the two outer vortex flows rise along the inner wall surface of the crucible, and then generate melt convection toward the crucible center (solid-liquid interface). When the loop size of the two outer vortex flows is large, the melt convection having a reduced oxygen concentration is supplied to the solid-liquid interface through the vicinity of the gas-liquid interface. There is a problem that the oxygen concentration of the water is lowered. In particular, in the cusp magnetic field type MCZ method, fluctuations in the melt convection in the radial direction tend to occur, and the loop size of the two outer vortices fluctuates and temporarily increases, so that the oxygen concentration in the outer peripheral portion decreases. There is a fear.

  Accordingly, an object of the present invention is to provide a method for producing a silicon single crystal by the HMCZ method capable of suppressing a decrease in oxygen concentration at the outer peripheral portion of the silicon single crystal and thereby improving the uniformity of the in-plane distribution of oxygen concentration. There is to do. Another object of the present invention is to provide a silicon single crystal capable of easily manufacturing a silicon wafer with improved uniformity of in-plane distribution of oxygen concentration.

  As a result of intensive studies on the mechanism by which the oxygen concentration in the outer peripheral portion of the silicon single crystal decreases, the inventors of the present application have found that the oxygen concentration in the outer peripheral portion of the silicon single crystal is reduced by passing through the gas-liquid interface. It has been found that the melt convection with reduced is supplied to the solid-liquid interface, and the decrease in oxygen concentration can be suppressed by suppressing the occurrence of such melt convection. For this purpose, the amount of heat applied to the lower portion of the silicon melt is made larger than the amount of heat applied to the upper portion of the silicon melt, and in particular, the maximum point of the temperature of the inner wall surface of the quartz crucible in contact with the silicon melt is 1438 ° C. It is necessary to control the crystal pulling condition so that the maximum point exists in the projected region of the silicon single crystal on the inner wall surface of the quartz crucible (hereinafter referred to as a projected region, see FIG. 4B). is there. When heating is performed so that the maximum temperature of the inner wall surface of the quartz crucible in contact with the silicon melt is 1438 ° C. or more, two large eddy currents can be generated with an upward flow that rises near the center of the quartz crucible. . Conversely, if two large vortices are generated, it can be said that the maximum point of the temperature of the inner wall surface of the quartz crucible in contact with the silicon melt is 1438 ° C. or higher. In this case, the melt in which the oxygen from the quartz crucible is dissolved at a high concentration has a flow distribution in which the melt flows directly from the quartz crucible to the solid-liquid interface without going through the gas-liquid interface, so the oxygen concentration at the outer periphery of the single crystal is reduced Can be suppressed.

  The present invention is based on such technical knowledge, and the method for producing a silicon single crystal according to the present invention heats the silicon melt in the quartz crucible using a heater arranged around the quartz crucible, A method for producing a silicon single crystal by the Czochralski method of pulling up a silicon single crystal from the silicon melt while applying a transverse magnetic field to the silicon melt, wherein the application of the transverse magnetic field passes through the crystal central axis. In the cross section perpendicular to the direction, the maximum temperature of the inner wall surface of the quartz crucible in contact with the silicon melt is within the projected region of the silicon single crystal, and the silicon under crystal pulling conditions is 1438 ° C. or higher. It is characterized by pulling up a single crystal.

  In the method for producing a silicon single crystal according to the present invention, the crystal pulling condition is determined based on a calculation result of heat transfer analysis of the quartz crucible and the silicon melt by a three-dimensional simulation (hereinafter referred to as 3D simulation). Is preferred. As a result, it was possible to accurately predict the crystal pulling conditions in which two large eddy currents accompanied by a central upward flow are generated in the silicon melt, and the uniformity of the in-plane distribution of oxygen concentration was improved in the actual crystal pulling. The production yield of silicon single crystals can be increased.

  In the present invention, the heater is a multi-stage heater divided in the vertical direction, and the output ratio of the lowermost heater to the uppermost heater is preferably larger than 1. In this case, the heater includes an upper heater and a lower heater which are divided into two in the vertical direction, and the output ratio of the lower heater to the upper heater is preferably 2 or more and 5 or less. As a result, the maximum temperature point of the inner wall surface of the quartz crucible in contact with the silicon melt is 1438 ° C. or higher, and the silicon melt heating condition is performed such that the maximum point exists in the projected region of the silicon single crystal. be able to.

  In the present invention, the maximum strength of the transverse magnetic field in the silicon melt on the crystal central axis is preferably 0.15 T or more and 0.6 T or less, which is a general magnetic field strength range of HMCZ. The rotational speed of the silicon single crystal is preferably 5 rpm or more and 30 rpm or less. Furthermore, the rotation speed of the quartz crucible is preferably 0.1 rpm or more and 4 rpm or less. According to these crystal pulling conditions, the maximum point of the temperature of the inner wall surface of the quartz crucible in contact with the silicon melt can be set to 1438 ° C. or more, and this maximum point can be generated in the projected region of the silicon single crystal. . In this case, the silicon melt descends along the inner wall surface of the quartz crucible, and then rises near the center of the quartz crucible to form thermal convection that flows directly into the solid-liquid interface. It is possible to prevent the liquid from being supplied to the outer peripheral portion of the solid-liquid interface.

  In the present invention, the maximum diameter of the silicon single crystal is preferably 300 mm or more. This is because such a large-diameter silicon single crystal tends to have a low oxygen concentration at the outer periphery, and the effects of the present invention are remarkable. In this case, the diameter of the quartz crucible used for pulling up the silicon single crystal is preferably 800 mm or more.

  The silicon single crystal according to the present invention is a bulk silicon single crystal manufactured by the HMCZ method, and has a plurality of measured values of oxygen concentration in a region near the outer periphery up to 15 mm radially inward from the outermost periphery of the straight body portion. The maximum value, the minimum value, and the average value of the oxygen concentration are obtained from the above, and the amount of decrease in the oxygen concentration consisting of a value obtained by dividing the difference between the maximum value and the minimum value by the average value is 0.01 or less. And According to this, a silicon wafer with improved uniformity of in-plane distribution of oxygen concentration can be easily manufactured. The bulk silicon single crystal means a silicon single crystal in a state after being taken out from the single crystal pulling apparatus and before the outer peripheral portion of the single crystal is removed by outer peripheral grinding.

  According to the present invention, in the HMCZ method of pulling up a silicon single crystal while applying a transverse magnetic field, it is possible to suppress a decrease in oxygen concentration at the outer peripheral portion of the silicon single crystal. Accordingly, it is possible to easily manufacture a silicon wafer with improved uniformity of in-plane distribution of oxygen concentration.

FIG. 1 is a side sectional view schematically showing a configuration of a single crystal manufacturing apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining a method of manufacturing a silicon single crystal according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing the shape of a silicon single crystal ingot. FIG. 4 is a diagram for explaining the flow distribution of the silicon melt in a cross section passing through the crystal central axis and perpendicular to the magnetic field application direction in the HMCZ method. In particular, FIG. 4 (a) is a general view using a single heater. In the case of the heating method, (b) shows the case of the heating method in which the output ratio of the upper and lower heaters of the split heater is 1: 2. FIG. 5 is a graph showing calculated values of the oxygen concentration distribution in the radial direction in the straight body portion of the silicon single crystal under conditions 1 to 7. FIG. 6 is a bar graph showing the magnitude of the decrease in oxygen concentration in the vicinity of the outer periphery under conditions 1-7. FIG. 7 is a flow distribution diagram of the silicon melts under conditions 2 and 7, in particular, the upper diagram shows the flow distribution of the cross section passing through the crystal central axis and perpendicular to the direction of application of the transverse magnetic field, and the lower diagram is The flow distributions of the cross sections passing through the crystal central axis and parallel to the direction in which the transverse magnetic field is applied are shown. FIG. 8 is a bar graph showing the maximum temperature (relative value) in the projection region of the single crystal at the bottom of the crucible under conditions 1-7. FIG. 9 is a graph showing the oxygen concentration distribution in the radial direction of the silicon wafer, with the horizontal axis representing the radial position and the vertical axis representing the oxygen concentration. FIG. 10 is a graph showing the oxygen concentration distribution in the radial direction of the silicon wafer, with the horizontal axis representing the radial position and the vertical axis representing the oxygen concentration.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a side sectional view schematically showing a configuration of a single crystal manufacturing apparatus according to an embodiment of the present invention.

  As shown in FIG. 1, a single crystal manufacturing apparatus 1 includes a chamber 10 (CZ furnace), a quartz crucible 11 that holds the silicon melt 2 in the chamber 10, and a graphite susceptor 12 that holds the quartz crucible 11. A rotating shaft 13 that supports the susceptor 12, a shaft drive mechanism 14 that drives the rotating shaft 13 to rotate and move up and down, a heater 15 that is disposed around the susceptor 12, an outer surface of the heater 15, and an inner surface of the chamber 10. A heat insulating material 16 disposed along the quartz crucible 11, a heat shield 17 disposed above the quartz crucible 11, and a single crystal pulling wire 18 disposed above the quartz crucible 11 and coaxially with the rotary shaft 13. And a wire take-up mechanism 19 disposed above the chamber 10.

  In addition, the single crystal manufacturing apparatus 1 includes a magnetic field generator 21 disposed outside the chamber 10, a CCD camera 22 that captures the inside of the chamber 10, an image processing unit 23 that processes an image captured by the CCD camera 22, A control unit 24 that controls the shaft driving mechanism 14, the heater 15, and the wire winding mechanism 19 based on the output of the image processing unit 23 is provided.

  The chamber 10 is composed of a main chamber 10a and an elongated cylindrical pull chamber 10b connected to the upper opening of the main chamber 10a. The quartz crucible 11, the susceptor 12, the heater 15, and the heat shield 17 are composed of the main chamber. 10a. The pull chamber 10b is provided with a gas inlet 10c for introducing an inert gas (purge gas) such as argon gas into the chamber 10, and a gas for discharging the inert gas at the lower part of the main chamber 10a. A discharge port 10d is provided. Further, a viewing window 10e is provided on the upper part of the main chamber 10a, and the growth state (solid-liquid interface) of the silicon single crystal 3 can be observed from the viewing window 10e.

  The quartz crucible 11 is a quartz glass container having a cylindrical side wall and a curved bottom. In order to maintain the shape of the quartz crucible 11 softened by heating, the susceptor 12 is held in close contact with the outer surface of the quartz crucible 11 so as to wrap the quartz crucible 11. The quartz crucible 11 and the susceptor 12 constitute a double structure crucible that supports the silicon melt in the chamber 10.

  The susceptor 12 is fixed to the upper end portion of the rotary shaft 13 extending in the vertical direction. The lower end portion of the rotating shaft 13 passes through the center of the bottom portion of the chamber 10 and is connected to a shaft drive mechanism 14 provided outside the chamber 10. The susceptor 12, the rotating shaft 13 and the shaft driving mechanism 14 constitute a rotating mechanism and a lifting mechanism for the quartz crucible 11.

  The heater 15 is used to melt the silicon raw material filled in the quartz crucible 11 and maintain the molten state. The heater 15 is a carbon resistance heating heater, and is a substantially cylindrical member provided so as to surround the entire circumference of the quartz crucible 11 in the susceptor 12. Furthermore, the outside of the heater 15 is surrounded by a heat insulating material 16, thereby improving the heat retaining property in the chamber 10.

  The heater 15 according to the present embodiment is a divided heater that is divided into two in the vertical direction, and includes an upper heater 15a and a lower heater 15b. Both the upper heater 15 a and the lower heater 15 b constitute a so-called side heater disposed so as to face the side wall portion of the quartz crucible 11. The upper heater 15a and the lower heater 15b can be controlled independently, and the power of the upper heater 15a can be made larger or smaller than that of the lower heater 15b. Although details will be described later, during the crystal pulling, the output ratio of the lower heater 15b to the upper heater 15a is set to 2-5.

  The heat shield 17 suppresses temperature fluctuations of the silicon melt 2 to form an appropriate hot zone near the solid-liquid interface, and prevents the silicon single crystal 3 from being heated by radiant heat from the heater 15 and the quartz crucible 11. It is provided for. The heat shield 17 is a graphite cylindrical member that covers a region above the silicon melt 2 excluding the pulling path of the silicon single crystal 3.

  A circular opening larger than the diameter of the silicon single crystal 3 is formed in the center of the lower end of the heat shield 17, and a pulling path for the silicon single crystal 3 is secured. As shown in the figure, the silicon single crystal 3 is pulled upward through the opening 17a. Since the diameter of the opening of the heat shield 17 is smaller than the diameter of the quartz crucible 11 and the lower end of the heat shield 17 is located inside the quartz crucible 11, the upper end of the rim of the quartz crucible 11 is lower than the lower end of the heat shield 17. However, the heat shield 17 does not interfere with the quartz crucible 11 even if it is raised upward.

  Although the amount of melt in the quartz crucible 11 decreases as the silicon single crystal 3 grows, the quartz crucible 11 is raised so that the distance (gap) between the melt surface and the heat shield 17 is constant, thereby increasing the silicon. It is possible to control the evaporation amount of the dopant from the silicon melt 2 while suppressing the temperature fluctuation of the melt 2 and making the flow rate of the gas flowing near the melt surface (purge gas guide path) constant. Therefore, the stability of the crystal defect distribution, oxygen concentration distribution, resistivity distribution, etc. in the pulling axis direction of the single crystal can be improved.

  Above the quartz crucible 11, a wire 18 that is a pulling shaft of the silicon single crystal 3 and a wire winding mechanism 19 that winds the wire 18 are provided. The wire winding mechanism 19 has a function of rotating the single crystal together with the wire 18. The wire winding mechanism 19 is disposed above the pull chamber 10b, the wire 18 extends downward from the wire winding mechanism 19 through the pull chamber 10b, and the tip of the wire 18 is located inside the main chamber 10a. The space has been reached. FIG. 1 shows a state in which the silicon single crystal 3 being grown is suspended from the wire 18. When pulling up the single crystal, the seed crystal is immersed in the silicon melt 2 and the single crystal is grown by gradually pulling up the wire 18 while rotating the quartz crucible 11 and the seed crystal, respectively.

  A gas inlet 10c for introducing an inert gas into the chamber 10 is provided at the top of the pull chamber 10b, and a gas exhaust for exhausting the inert gas in the chamber 10 is provided at the bottom of the main chamber 10a. An outlet 10d is provided. The inert gas is introduced into the chamber 10 from the gas inlet 10c, and the introduction amount is controlled by a valve. Further, since the inert gas in the sealed chamber 10 is exhausted from the gas outlet 10d to the outside of the chamber 10, the SiO gas and CO gas generated in the chamber 10 are collected to keep the inside of the chamber 10 clean. Is possible. Although not shown, a vacuum pump is connected to the gas discharge port 10d through a pipe, and the flow rate is controlled by a valve while sucking an inert gas in the chamber 10 by the vacuum pump. Is kept at a constant reduced pressure.

  The magnetic field generator 21 applies a transverse magnetic field (horizontal magnetic field) to the silicon melt 2. The maximum intensity of the transverse magnetic field in the silicon melt 2 on the crystal central axis (on the extension line of the crystal pulling axis) is 0.15 to 0.6 (T), which is a general magnetic field strength range of HMCZ. preferable. By applying a magnetic field to the silicon melt 2, melt convection in a direction perpendicular to the magnetic field lines can be suppressed. Therefore, elution of oxygen from the quartz crucible 11 can be suppressed, and the oxygen concentration in the silicon single crystal can be reduced.

  A viewing window 10e for observing the inside is provided in the upper part of the main chamber 10a, and the CCD camera 22 is installed outside the viewing window 10e. During the single crystal pulling process, the CCD camera 22 takes an image of the boundary portion between the silicon single crystal 3 and the silicon melt 2 that can be seen through the opening 17a of the heat shield 17 from the viewing window 10e. The CCD camera 22 is connected to the image processing unit 23, the captured image is processed by the image processing unit 23, and the processing result is used by the control unit 24 to control crystal pulling conditions.

  FIG. 2 is a flowchart for explaining a method of manufacturing a silicon single crystal according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing the shape of a silicon single crystal ingot.

  As shown in FIGS. 2 and 3, in the manufacture of the silicon single crystal 3, the silicon raw material in the quartz crucible 11 is heated to generate the silicon melt 2 (step S11). Thereafter, the seed crystal attached to the tip end portion of the wire 18 is lowered and deposited on the silicon melt 2 (step S12).

  Next, a single crystal pulling step is performed in which the single crystal is grown by gradually pulling the seed crystal while maintaining the contact state with the silicon melt 2. In the single crystal pulling step, a necking step (step S13) for forming a neck portion 3a with a narrowed crystal diameter for dislocation elimination, and a shoulder portion in which the crystal diameter gradually increases to obtain a specified diameter. The shoulder portion growing step (step S14) for forming 3b, the body portion growing step (step S15) for forming the body portion 3c (straight body portion) in which the crystal diameter is kept constant, and the crystal diameter gradually decreased. The tail portion growing step (step S16) for forming the tail portion 3d is sequentially performed, and the tail portion growing step is ended by finally separating the single crystal from the melt surface. As described above, the silicon single crystal ingot 3 having the neck portion 3a, the shoulder portion 3b, the body portion 3c, and the tail portion 3d in order from the upper end (top) to the lower end (bottom) of the single crystal is completed.

  During the pulling process of the single crystal, the CCD camera 22 takes an image of the boundary between the silicon single crystal 3 and the silicon melt 2 in order to control the diameter of the silicon single crystal 3 and the liquid surface position of the silicon melt 2. The diameter of the single crystal at the solid-liquid interface and the distance (gap) between the melt surface and the heat shield 17 are calculated from the photographed image. The control unit 24 controls the pulling conditions such as the pulling speed of the wire 18 and the power of the heater 15 so that the diameter of the silicon single crystal 3 becomes the target diameter. The control unit 24 controls the height position of the quartz crucible 11 so that the distance between the melt surface and the heat shield 17 is constant.

  The silicon single crystal manufacturing method according to the present embodiment uses a two-part heater as the heater 15 in the transverse magnetic field type MCZ method, and the output ratio between the upper heater 15a and the lower heater 15b during crystal pulling is 1: 2 to 1: Set within the range of 5. The rotation speed of the silicon single crystal 3 is preferably 5 to 30 rpm, and the rotation speed of the quartz crucible 11 is preferably 0.1 to 4 rpm. This is because when the crystal rotation speed is less than 5 rpm, the flow distribution of the melt does not become the central upward flow, and the decrease in the oxygen concentration in the outer peripheral portion cannot be suppressed. This is because the crystal becomes stable and the crystal shake increases and the crystal quality deteriorates.

  When pulling up a silicon single crystal under the above-described crystal pulling conditions, the maximum point of the temperature of the inner wall surface of the quartz crucible 11 in contact with the silicon melt is 1438 ° C. or higher. The maximum point of the temperature of the inner wall surface of the quartz crucible 11 is preferably generated at the center of the bottom of the crucible, but may deviate from the center due to the deviation of melt convection. Even in such a case, if the maximum point is generated in the projected region of the silicon single crystal, the flow distribution rises near the center of the quartz crucible 11 and flows directly into the solid-liquid interface without passing through the gas-liquid interface. Therefore, it is possible to suppress a decrease in the oxygen concentration at the outer peripheral portion of the single crystal, and to realize a uniform in-plane distribution of the oxygen concentration.

  The flow distribution of the silicon melt 2 during crystal pulling and the temperature of the inner wall surface of the quartz crucible 11 can be predicted from 3D simulation of comprehensive heat transfer analysis. During crystal pulling, the silicon melt descends along the inner wall surface of the quartz crucible 11, rises at the center of the quartz crucible 11, and has a flow distribution that flows directly to the solid-liquid interface without passing through the gas-liquid interface. Control crystal pulling conditions. Such crystal pulling conditions can be determined based on the calculation results of the temperature distribution of the quartz crucible 11 and the silicon melt by 3D simulation. That is, the magnetic field strength, the crystal rotation speed, the crucible rotation speed, the output ratio of the lower heater to the upper heater, the crystal pulling speed, the argon flow rate, the furnace pressure, and the melt amount are variable parameters, and various calculations with these parameters changed are performed. And determining whether the position of the maximum point of the temperature of the inner wall surface of the quartz crucible 11 in contact with the silicon melt is within the projection region, and whether the temperature is 1438 ° C. or higher, the optimum crystal pulling condition is determined. Can be selected.

  Further, the actual temperature of the inner wall surface of the bottom portion of the quartz crucible 11 during crystal pulling can be obtained from the measured temperature of a thermocouple attached to the outer surface of the susceptor 12. By measuring the temperature at the center of the bottom of the susceptor 12 with a thermocouple and applying this temperature to the conditions of the heat transfer analysis 3D simulation, the temperature of the inner wall surface of the bottom of the quartz crucible 11 can be calculated.

  Furthermore, the temperature of the inner wall surface at the bottom of the quartz crucible 11 can be estimated by measuring the in-plane distribution of the oxygen concentration of the wafer. That is, if the in-plane oxygen concentration distribution of the wafer is uniform, it can be concluded that the maximum point of the temperature of the inner wall surface of the quartz crucible 11 in contact with the silicon melt is 1438 ° C. or higher.

  Next, a mechanism for suppressing a decrease in oxygen concentration in the outer peripheral portion of the single crystal will be described.

  First, an oxygen introduction path to the silicon single crystal 3 being pulled will be described. Oxygen is introduced into the silicon melt 2 by melting the quartz crucible 11 that holds the silicon melt 2, and is transported by diffusion and convection of the silicon melt 2. Most of the molten oxygen evaporates as silicon monoxide (SiO) at the gas-liquid interface and is discharged out of the melt, but a part is transported to the growth interface and taken into the silicon single crystal. Therefore, the oxygen concentration in the single crystal greatly depends on the convection behavior of the silicon melt.

  Next, the flow distribution of the silicon melt in the HMCZ method will be described. In the HMCZ method, the silicon melt forms a circulation flow in a plane perpendicular to the direction of the applied magnetic field, and the circulation flow is a roll-like flow that extends in the magnetic field application direction while maintaining the shape. In order to grasp these flows, the flow state of a cross section passing through the crystal central axis and perpendicular to the magnetic field application direction may be observed.

  FIG. 4 is a diagram for explaining the flow distribution of the silicon melt in a cross section passing through the crystal central axis and perpendicular to the magnetic field application direction in the HMCZ method. In particular, FIG. 4 (a) is a general view using a single heater. In the case of the heating method, (b) is a heating method in which the output ratio of the upper heater and the lower heater of the divided heater is 1: 2, and the maximum temperature of the inner wall surface of the quartz crucible in the projection region is 1438 ° C. or higher. Each case is shown.

  As shown in FIG. 4 (a), in the silicon melt, there is a circulating flow that rises at the side wall of the crucible and descends under the crystal, and a growth interface under the crystal from the center toward the outer periphery. There are two types of circulating flow. The former is a flow caused by the temperature of the side of the crucible raised by the cylindrical heater 15 arranged opposite to the side of the crucible and the resulting heat convection, and the latter is the discharge flow accompanying the crystal rotation.

  In FIG. 4A, oxygen in the silicon melt introduced from the quartz crucible 11 is transported vertically upward on the side surface of the crucible by a circulating flow caused by thermal convection, and passes through the gas-liquid interface before rotating the crystal. It is transported to the crystal growth interface by the circulating flow associated with. At this time, since dissolved oxygen evaporates at the gas-liquid interface, the concentration of dissolved oxygen in the silicon melt after passing through the gas-liquid interface is significantly reduced. Since the silicon melt having the reduced oxygen concentration is transported from the outside of the crystal growth interface, the oxygen concentration at the crystal growth interface becomes extremely low at the outer periphery. Therefore, the oxygen concentration in the crystal is generally low at the outer periphery.

  On the other hand, as shown in FIG. 4B, when the crystal rotation speed is 5.0 rpm or more and the output ratio of the upper heater 15a and the lower heater 15b of the heater 15 is 1: 2, the crystal growth interface is A flow distribution in which the silicon melt flows directly from the crucible to the solid-liquid interface without passing through can be obtained. This is because the flow toward the crystal growth interface under the crystal is relatively increased by increasing the crystal rotation speed, and the amount of heat flowing from the side surface of the silicon melt by relatively increasing the output of the lower heater 15b. The amount of heat flowing from the lower part is larger than that, and buoyancy is generated near the lower part.

  According to the above mechanism, the maximum temperature point of the inner wall surface of the quartz crucible in contact with the silicon melt is 1438 ° C. or higher under the condition that a flow distribution in which an upward flow exists near the center of the quartz crucible 11 is obtained. In addition, the position of the maximum point is within the range from the crucible center to the crystal radius in a cross section passing through the crystal central axis and perpendicular to the application direction of the transverse magnetic field. The maximum point of the temperature of the inner wall surface of the quartz crucible in contact with the silicon melt is preferably 1537 ° C. or lower. If it is 1537 degrees C or less, a single crystal can be manufactured safely, without a quartz crucible softening and deform | transforming large.

  As described above, in the conventional HMCZ method, the flow path of the silicon melt goes to the solid-liquid interface via the gas-liquid interface, so that a region having an extremely low oxygen concentration is formed in the outer peripheral portion of the crystal. However, in the HMCZ method according to the present invention, it is possible to form a flow path through which the silicon melt flows to the crystal interface without going through the gas-liquid interface, so that the oxygen concentration in the outer periphery of the crystal is prevented from becoming extremely low. Thus, the in-plane distribution of the oxygen concentration can be made uniform.

  Since the silicon single crystal ingot according to the present embodiment shown in FIG. 3 is manufactured as described above, the uniformity of the in-plane distribution of the oxygen concentration is good. In an as-grown bulk single crystal that has not been peripherally ground, the oxygen concentration in the vicinity of the outer periphery from the outermost periphery to 15 mm radially inward is measured at regular intervals in the radial direction, and the oxygen concentration is determined from a plurality of measured values. When the maximum value, the minimum value, and the average value are calculated, and the value obtained by dividing the difference between the maximum value and the minimum value by the average value is determined as the “decrease amount of oxygen concentration”, the value of the decrease amount of oxygen concentration is 0. .01 or less.

  As described above, the silicon single crystal manufacturing method according to the present embodiment uses the two-part heater for heating the silicon melt in the HMCZ method in which a transverse magnetic field is applied, and the lower heater 15b with respect to the upper heater 15a during crystal pulling. By setting the output ratio to 2 or more, the maximum temperature of the inner wall surface of the quartz crucible 11 in contact with the silicon melt 2 is set to 1438 ° C. or more, and the position of the maximum point passes through the crystal central axis and extends laterally. It can be generated within a range from the crucible center to the crystal radius in a cross section perpendicular to the direction of application of the magnetic field. As a result, two large vortex flows accompanied by a center upward flow can be generated in the silicon melt, and a flow path through which the silicon melt flows to the crystal interface without passing through the gas-liquid interface can be formed. Therefore, it is possible to suppress a decrease in the oxygen concentration at the outer peripheral portion of the silicon single crystal, and to achieve a uniform in-plane distribution of the oxygen concentration.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in the above embodiment, a two-split heater composed of the upper heater 15a and the lower heater 15b is used. However, the number of vertical divisions of the heater 15 is not particularly limited, and may be three or more. When such a multistage heater is used, the maximum point of the temperature of the inner wall surface of the quartz crucible in contact with the silicon melt is set to 1438 ° C. or higher by increasing the output ratio of the lowermost heater to the uppermost heater to be greater than 1. It becomes possible.

  Moreover, in the said embodiment, although the manufacturing method of the silicon single crystal ingot whose crystal diameter used for manufacture of a 300 mm wafer is 300 mm or more (diameter 300-340 mm) was mentioned as an example, the manufacturing method (diameter of a 450 mm wafer) 450 to 490 mm), or a method for producing a silicon single crystal as a raw material for a silicon wafer having a diameter of 200 mm or less. However, in the case of a silicon single crystal having a large crystal diameter, the oxygen concentration in the outer peripheral portion of the crystal is significantly reduced. Therefore, the present invention can be preferably used for manufacturing a silicon single crystal having a maximum diameter of 300 mm or more.

  A comprehensive heat transfer analysis was performed by 3D simulation simulating the inside of the CZ furnace, and the in-plane distribution of the oxygen concentration of the silicon single crystal and the convection of the silicon melt when various parameters were changed were predicted. In the 3D simulation, a two-part heater is used as the cylindrical heater 15 arranged on the side surface of the silicon melt, and various control factors such as crystal rotation and crucible rotation are used in addition to the output ratio of the lower heater to the upper heater. The flow distribution of the silicon melt was calculated by setting.

  In the 3D simulation, the entire three-dimensional shape inside the CZ furnace was modeled, the silicon melt and the argon atmosphere were handled as fluids, and the other members were handled as solids. At this time, at least the modeling of the silicon melt shape needs to be expressed by a three-dimensional mesh structure in order to grasp a complicated three-dimensional flow state. The temperature was calculated from the equation considering the heat conduction, heat transfer and radiation, and the fluid flow was calculated from the Navier-Stokes equation. In addition, a transverse magnetic field was applied, and thereby induced current and Lorentz force generated in the silicon melt were calculated. The calculated Lorentz force was coupled to the external force term in the Navier-Stokes equation.

  It was assumed that oxygen was introduced into the silicon melt by the melting of the quartz crucible, and oxygen was dissolved until a saturated concentration was reached at the interface between the two. It was assumed that oxygen in the silicon melt chemically changed until the equilibrium concentration of silicon monoxide was reached at the gas-liquid interface between the silicon melt and the argon atmosphere. The reaction rate of the quantity reaction was assumed to be infinitely fast. It was assumed that oxygen in the silicon melt was taken into the silicon single crystal with a segregation coefficient of 1 at the solid-liquid interface between the silicon melt and the silicon single crystal.

  The target was a CZ furnace corresponding to 300 mm crystal pulling, the crystal diameter was 310 mm, the diameter of the quartz crucible was 800 mm (32 inches), the silicon melt was 200 kg, and the crystal pulling speed was fixed at 1.0 mm / min. The maximum intensity of the transverse magnetic field in the melt in the crucible on the crystal central axis was set to an appropriate value within the range of 0.2T to 0.4T in accordance with other conditions. On the other hand, the crystal rotation speed, the crucible rotation speed, the argon flow rate, the furnace pressure, and the output ratio of the lower heater to the upper heater are set as variable parameters, and each is set as shown in Table 1, and the calculation of conditions 1 to 7 is performed. did.

FIG. 5 is a graph showing calculated values of the oxygen concentration distribution in the radial direction in the straight body portion of the silicon single crystal under conditions 1 to 7. The area from the center of the crystal to the outermost periphery is divided into regions with an interval of 5 mm in the radial direction, and the average value of the oxygen concentration in that region is shown. This value corresponds to the value measured at the center position of the region when measuring the oxygen concentration. The horizontal axis indicates the radial position (m) from the crystal center, and the vertical axis indicates the oxygen concentration (atoms / cm ³ ).

  As is clear from FIG. 5, in conditions 1 to 6, it was found that the oxygen concentration in the vicinity of the outer periphery having a radius of 140 mm to 155 mm from the crystal center decreased, which deteriorated the uniformity of the in-plane distribution of oxygen concentration. . On the other hand, under condition 7, the oxygen concentration in the vicinity of the outer periphery did not decrease, and it was found that the uniformity of the in-plane distribution of oxygen concentration was very good.

  Next, the magnitude of the decrease in oxygen concentration in the vicinity of the outer periphery was evaluated.

  FIG. 6 is a bar graph showing the magnitude of the oxygen concentration drop (drop amount) in the vicinity of the outer periphery under conditions 1-7. The magnitude of the decrease in oxygen concentration was determined by (maximum value−minimum value) / average value. The smaller this index is, the smaller the decrease in oxygen concentration in the vicinity of the outer periphery having a radius of 140 mm to 155 mm from the crystal center.

  The magnitude of the decrease in oxygen concentration in condition 7 is 0.002735, and as is clear from FIG. 6, as compared with other conditions 1 to 6, condition 7 is the oxygen concentration near the outer periphery of the single crystal. It became clear that the decrease was extremely small.

  Next, in order to clarify the phenomenon of the decrease in oxygen concentration in the vicinity of the outer periphery of the single crystal, the flow distributions under conditions 2 where the decrease in oxygen concentration is large and conditions 7 where the decrease in oxygen concentration is small are compared. did.

  FIG. 7 is a flow distribution diagram of the silicon melts under conditions 2 and 7, in particular, the upper diagram shows the flow distribution of the cross section passing through the crystal central axis and perpendicular to the direction of application of the transverse magnetic field, and the lower diagram is The flow distributions of the cross sections passing through the crystal central axis and parallel to the direction in which the transverse magnetic field is applied are shown.

  As shown in the upper part of FIG. 7, in both conditions 2 and 7, vortices were formed on a plane perpendicular to the direction of magnetic field application, and the flow distribution extended in the direction of magnetic field application while maintaining the shape. In particular, in condition 2, there was one large vortex, but in condition 7, there were two large vortices, and an upward flow of melt was generated near the center of the quartz crucible. Note that the flow distribution under all conditions (conditions 1 to 6) except condition 7 had one vortex as in condition 2.

  When considering the oxygen transport route, under condition 2, oxygen introduced from the quartz crucible into the melt is transported by one vortex and is transported to the solid-liquid interface via the gas-liquid interface on one side. When passing through the gas-liquid interface, oxygen evaporates as silicon monoxide into the argon atmosphere, and the silicon melt with reduced oxygen concentration is carried directly to the solid-liquid interface, so the oxygen concentration decreases near the periphery of the crystal. Is considered to occur.

  On the other hand, when two vortex flows with an upward flow exist near the center of the quartz crucible as in condition 7, oxygen introduced from the quartz crucible into the melt directly enters the solid-liquid interface without passing through the gas-liquid interface. Since it is transported, it is considered that a decrease in oxygen concentration in the vicinity of the crystal periphery does not occur. Therefore, it is considered that a decrease in oxygen concentration in the vicinity of the outer periphery can be avoided by generating such a center upward flow within the range from the crystal central axis to the crystal radius.

  As described above, the cause of the two eddy currents accompanying the upward flow in the vicinity of the center of the quartz crucible in the condition 7 is different from the other conditions in that the output ratio of the two-part heater is 1: 2 at the top: down, and the quartz This is because the amount of heating from below the crucible is increased. As a result, the temperature at the bottom of the crucible rises, and the silicon melt is strongly heated from below, and it is considered that an upward flow is formed by thermal convection at the center of the crucible.

  From this consideration, it is considered that heat convection should be promoted at the center of the melt in the crucible in order to form two vortex flows with a center upward flow. The magnitude of thermal convection is stronger as the temperature difference between the upper and lower parts of the fluid is larger. In the CZ method, the upper part of the fluid is a solid-liquid interface, and the temperature of the solid-liquid interface is fixed at the melting point (1412 ° C.). Therefore, it is considered that the generation of the center upward flow can be promoted by increasing the temperature of the crucible bottom.

  FIG. 8 is a bar graph showing the maximum temperature in the projection region of the single crystal at the bottom of the crucible under conditions 1-7.

  As shown in FIG. 8, the maximum temperature in the region within the crystal diameter at the bottom of the crucible is 1438 ° C. under the largest condition 7. In other conditions, the condition 5 is the highest and is 1437 ° C., but in the condition 5, no center upward flow is formed. Therefore, if the maximum temperature in the region within the crystal diameter at the bottom of the crucible is 1438 ° C. or higher, a center upward flow can be formed, thereby preventing a decrease in oxygen concentration in the vicinity of the outer periphery, and an in-plane distribution of oxygen concentration. It was found that a silicon single crystal with good uniformity can be obtained.

  Next, an actual pulling process of the silicon single crystal was performed based on the simulation result. At that time, the output ratio of the upper and lower stages of the two-split heater arranged around the silicon melt was variously changed. The output ratio of the upper and lower heaters is 1: 1 (level A), 1: 1.5 (level B), 1: 2 (level C), 1: 3 (level D), 1: 4 (level) E), 1: 5 (level F). All other crystal pulling conditions were the same, the crystal rotation speed was 5 rpm, the strength of the transverse magnetic field was 0.3 T, and the crystal diameter of the straight body portion was 320 mm.

  Next, the wafer was cut out from a position of 500 mm downward from the upper end of the straight body portion of each silicon single crystal, and the oxygen concentration distribution in the radial direction of the wafer was measured. FTIR was used to measure the oxygen concentration, and the area from the wafer center to 150 mm in the radial direction was measured at 10 mm intervals, and the average value was obtained. In addition, all the measured values of the oxygen concentration in the crystal described in this specification are measured values in accordance with the standard of ASTM F-121 (1979). Table 2 shows the measurement results of the oxygen concentration.

  As is clear from Table 2, the silicon single crystal could be pulled from level A to level E. However, at level F, the crystal was dislocated in the straight body portion, and a single crystal could not be obtained.

  Next, the oxygen concentration in the region of 140 mm to 157 mm in the radial direction from the wafer center was measured at 1 mm intervals, and the oxygen concentration distribution near the outer periphery was measured in detail. The outermost peripheral region of 158 mm to 160 mm in the radial direction from the wafer center was excluded because the measurement value was affected by the wafer side surface shape. The result is shown in FIG.

  As shown in FIG. 9, paying attention to the decrease in the oxygen concentration at the outer peripheral portion of the wafer, the decrease in the oxygen concentration was observed at the level A and level B after the radius of 152 mm. In level C, the region where the oxygen concentration was reduced was narrower than in levels A and B, and only one point at a position of 157 mm in the radial direction from the wafer center. The results for Level D and Level E were similar to Level C.

  Next, a region deviating from ± 5% of the average oxygen concentration shown in Table 2 was defined as a low oxygen region, and the width of the low oxygen region was determined. The results are summarized in Table 3. Here, the oxygen concentration in the region outside the radial direction 157 mm from the wafer center was extrapolated from the oxygen concentration at a position of 155 to 157 mm to determine whether the region was a low oxygen region.

  As shown in Table 3, the width of the low oxygen region at levels A and B was 8 mm, whereas the width of the low oxygen region at levels C, D, and E was 4 mm. From this result, it was found that it is effective to set the output ratio of the lower heater to the upper heater of the two-split heater to 2 to 5 in order to suppress the decrease in oxygen concentration at the outer periphery of the wafer. By changing the output ratio of the lower heater to the upper heater to 2-5, the flow distribution of the silicon melt changes, and the flow distribution flows directly from the quartz crucible to the solid-liquid interface without going through the gas-liquid interface as described above. This is probably because of the change.

  Next, the upper / lower output ratio of the two-divided heater was fixed at 1: 2, the crystal rotation speed was changed variously, and the silicon single crystal was pulled up. The crystal rotation speed was 2.5 rpm (level G), 7.5 rpm (level H), and 10.0 rpm (level I). The crystal diameter was 320 mm, and all other process conditions were the same. Thereafter, the oxygen concentration in the region from the wafer center to 150 mm was measured at 10 mm intervals, and the average value was obtained. Table 4 shows the measurement results of the oxygen concentration together with the level C in Table 2.

As shown in Table 4, each of the levels G, H, and I was able to pull up the silicon single crystal in the same manner as the level C. However, at level G, the average value of oxygen concentration was as low as 7.79 atoms / cm ³ .

Next, a region from a radius of 140 mm to 157 mm was measured at 1 mm intervals, and the oxygen concentration distribution near the outer periphery was measured in detail. The result is shown in FIG.
Show.

  As shown in FIG. 10, at level G, the oxygen concentration showed a gradual decreasing trend from the wafer center toward the outer periphery. On the other hand, the region where the oxygen concentration tends to decrease at levels C, H, and I was only one point at a position of 157 mm in the radial direction from the wafer center.

  Next, a region deviating from ± 5% of the average oxygen concentration shown in Table 4 was defined as a low oxygen region, and the width of the low oxygen region was determined. The results are summarized in Table 5.

  As shown in Table 5, the width of the low oxygen region of level G was 11, whereas the width of the low oxygen region of levels C, H, and I was 4 mm. Thus, when the crystal rotation speed is 2.5 rpm, the width of the low oxygen region becomes very wide, and the in-plane distribution of the oxygen concentration deteriorates. In contrast, at levels C, H, and I where the crystal rotation speed was 5.0 rpm or higher, the width of the low oxygen region was narrowed, and the in-plane distribution of the oxygen concentration was good. This is considered that the flow distribution greatly changes when the crystal rotation speed is 5.0 rpm or more.

  In order to verify the measurement results, simulation was performed under nine conditions from levels A to I, and the maximum temperature in the single crystal projection region on the bottom of the quartz crucible was extracted. As a result, the levels C, D, E, H, and I in which the width of the low oxygen region in the outer peripheral portion was small were all 1438 ° C. or higher, and a flow distribution in which an upward flow was present near the crucible center.

  From the above results, in the HMCZ method, when the output ratio of the lower heater to the upper heater of the two-split heater is 2 to 5 and the crystal rotation speed is 5.0 or more, the oxygen concentration in the outer peripheral portion of the silicon single crystal It was found that the decrease in the amount can be greatly suppressed.

DESCRIPTION OF SYMBOLS 1 Single crystal manufacturing apparatus 2 Silicon melt 3 Silicon single crystal (ingot)
3a neck part 3b shoulder part 3c body part (straight trunk part)
3d Tail portion 10 Chamber 10a Main chamber 10b Pull chamber 10c Gas inlet 10d Gas outlet 10e Viewing window 11 Quartz crucible 12 Susceptor 13 Rotating shaft 14 Shaft drive mechanism 15 Heater 15a Upper heater 15b Lower heater 16 Heat insulating material 17 Heat shield 18 Wire 19 Wire winding mechanism 21 Magnetic field generator 22 Camera 23 Image processing unit 24 Control unit

Claims (8)

Czochral that heats the silicon melt in the quartz crucible using a heater disposed around the quartz crucible and pulls up the silicon single crystal from the silicon melt while applying a transverse magnetic field to the silicon melt. A method for producing a silicon single crystal by a ski method,
The maximum point of the temperature of the inner wall surface of the quartz crucible in contact with the silicon melt is 1438 ° C. or higher, and the position of the maximum point passes through the crystal central axis and is perpendicular to the application direction of the transverse magnetic field. A method for producing a silicon single crystal, comprising: pulling up the silicon single crystal under a crystal pulling condition that exists in a projected region of the silicon single crystal.   The method for producing a silicon single crystal according to claim 1, wherein the crystal pulling condition is determined based on a heat transfer analysis result of the quartz crucible and the silicon melt by 3D simulation.   3. The method for producing a silicon single crystal according to claim 1, wherein the heater is a multistage heater divided into two or more in the vertical direction, and an output ratio of the lowermost heater to the uppermost heater is larger than 1. 4. The heater is composed of an upper heater and a lower heater divided into two in the vertical direction.
The method for producing a silicon single crystal according to claim 3, wherein an output ratio of the lower heater to the upper heater is 2 or more and 5 or less.   5. The method for producing a silicon single crystal according to claim 1, wherein the strength of the transverse magnetic field in the silicon melt on the crystal central axis is not less than 0.15 T and not more than 0.6 T. 6.   The method for producing a silicon single crystal according to any one of claims 1 to 5, wherein a rotation speed of the silicon single crystal is 5 rpm or more and 30 rpm or less.   The method for producing a silicon single crystal according to claim 1, wherein a maximum diameter of the silicon single crystal is 300 mm or more.   A bulk silicon single crystal manufactured by the HMCZ method, wherein a maximum value, a minimum value, and a minimum value of oxygen concentration are determined from a plurality of measured values of oxygen concentration in a region near the outer periphery from the outermost periphery of the straight body portion to 15 mm radially inward. A silicon single crystal characterized in that an average value is obtained, and a drop amount of oxygen concentration consisting of a value obtained by dividing a difference between the maximum value and the minimum value by the average value is 0.01 or less.

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