Method for estimating oxygen concentration in silicon single crystal, method for producing silicon single crystal, and silicon single crystal production apparatus

Abstract

[Problem] To provide: a method for estimating the oxygen concentration in a silicon single crystal, said method being capable of producing silicon single crystals having the same quality by preventing bipolarization of the oxygen concentration in the silicon single crystals; a method for producing a silicon single crystal; and an apparatus for producing a silicon single crystal. [Solution] In a method for estimating the oxygen concentration in a silicon single crystal according to the present invention, when a silicon single crystal is pulled up, while applying a horizontal magnetic field to a silicon melt in a quartz crucible, the height (gap) of the melt surface is measured (S21) and the oxygen concentration in the silicon single crystal is estimated from microscopic fluctuations of the height (gap) of the melt surface (S22 to S26).

Description

[Technical field]

[0001] The present invention relates to a method for estimating an oxygen concentration in a silicon single crystal produced by the Czochralski method (CZ method), and also to a method and apparatus for producing a silicon single crystal using such an oxygen concentration estimation method, and in particular to the MCZ method (Magnetic field applied Czochralski method) in which a single crystal is pulled up while a magnetic field is applied to a melt. [Background technology]

[0002] The MCZ method is known as a method for producing silicon single crystals using the CZ method. The MCZ method suppresses melt convection by pulling up a single crystal while applying a magnetic field to the silicon melt in a quartz crucible. By suppressing melt convection, it is possible to suppress the reaction between the quartz crucible and the melt, and to suppress the amount of oxygen dissolved in the silicon melt, thereby keeping the oxygen concentration of the silicon single crystal low.

[0003] There are several known methods for applying a magnetic field, but the Horizontal MCZ method, which applies a horizontal magnetic field, is becoming more and more popular. In the HMCZ method, a magnetic field perpendicular to the side wall of the quartz crucible is applied, which effectively suppresses melt convection near the side wall of the crucible and reduces the amount of oxygen dissolved from the crucible. On the other hand, the effect of suppressing convection at the melt surface is small, and the evaporation of oxygen (silicon oxide) from the melt surface is not suppressed, so the oxygen concentration in the melt can be reduced. Therefore, single crystals with a low oxygen concentration can be grown.

[0004] Regarding the HMCZ method, for example, Patent Document 1 describes a method of measuring the surface temperature of the silicon melt at a position where the hot zone has a plane-asymmetric structure in at least one of a neck process and a shoulder formation process of a silicon single crystal, and estimating the oxygen concentration in the silicon single crystal from the surface temperature.

[0005] Patent Document 2 also describes that the inert gas flowing between the lower end of the thermal shield and the surface of the silicon melt forms a flow distribution that is asymmetric with respect to a plane including the crystal pulling axis and the application direction of the horizontal magnetic field, and is asymmetrical with respect to the crystal pulling axis, and that the asymmetrical and asymmetrical flow distribution of the inert gas is maintained in the absence of a magnetic field until all of the silicon raw material in the quartz crucible is melted. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-151499 A [Patent Document 2] JP 2019-151503 A Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, it has become known that when pulling silicon single crystals using the Czochralski method in which a horizontal magnetic field is applied, even if the silicon single crystals are pulled using the same pulling apparatus and under the same pulling conditions, the quality of the pulled silicon single crystals is not the same, and in particular, the oxygen concentration in the silicon single crystal becomes polarized.

[0008] The techniques described in Patent Documents 1 and 2 are intended to solve these problems, but it is desirable to be able to solve the problems in other ways as well.

[0009] Therefore, an object of the present invention is to provide a method for estimating the oxygen concentration of a silicon single crystal, a method for manufacturing a silicon single crystal, and a silicon single crystal manufacturing apparatus that are capable of preventing polarization of the oxygen concentration in a silicon single crystal and producing silicon single crystals of the same quality. [Means for solving the problem]

[0010] In order to solve the above problem, the method for estimating the oxygen concentration of a silicon single crystal according to the present invention is characterized in that when a silicon single crystal is pulled up while a transverse magnetic field is applied to a silicon melt in a quartz crucible, the height of the melt surface of the silicon melt is measured, and the oxygen concentration of the silicon single crystal is estimated from minute fluctuations in the height of the melt surface.

[0011] According to the present invention, it is possible to estimate whether the oxygen concentration of the silicon single crystal will be relatively high or relatively low, i.e., the direction of polarization of the oxygen concentration of the silicon single crystal. Therefore, by controlling the crystal growth conditions based on the estimated oxygen concentration, it is possible to suppress the fluctuation of the oxygen concentration of the silicon single crystal in the crystal growth direction.

[0012] In the method for estimating oxygen concentration in silicon single crystal according to the present invention, the height of the melt surface is preferably measured periodically at a sampling period of 50 seconds or less, and more preferably the sampling period is 10 seconds or less. This makes it possible to capture minute fluctuations in the melt surface due to differences in the convection mode of the silicon melt, and to estimate the direction of polarization of the oxygen concentration from the minute fluctuations in the melt surface. The shorter the sampling period, the clearer the minute fluctuations in the melt surface can be captured, but since the amount of data becomes enormous, it is preferable to set the sampling period to 1 second or more.

[0013] In the present invention, the resolution of the measurement value of the height of the melt surface is preferably 0.1 mm or less. This allows accurate capture of minute fluctuations in the melt surface due to differences in the convection modes of the silicon melt, and allows estimation of the direction of polarization of the oxygen concentration from the minute fluctuations in the melt surface. The minute fluctuations in the melt surface due to differences in the convection modes of the silicon melt fluctuate up and down in a short period of 50 seconds or less, and the amount of fluctuation is small, with a standard deviation value of 1 mm or less. In addition, by determining a measurement range on the melt surface and measuring the height position of the melt surface, the minute fluctuations in the melt surface can be grasped. In other words, the minute fluctuations refer to vertical fluctuations with a standard deviation of the melt surface height of 1 mm or less when the melt surface height is measured at a sampling period of 50 seconds or less.

[0014] The method for estimating the oxygen concentration in a silicon single crystal according to the present invention preferably identifies a correlation between minute fluctuations in the melt surface height and the direction of polarization of the oxygen concentration from data on the past performance of pulling silicon single crystals, and estimates the oxygen concentration in the silicon single crystal based on the correlation, thereby improving the accuracy of estimating the direction of polarization of the oxygen concentration in the silicon single crystal.

[0015] The method for estimating the oxygen concentration in a silicon single crystal according to the present invention preferably identifies a crystal portion where the oxygen concentration is polarized from data on the past performance of pulling silicon single crystals, and sets the period during which the crystal portion is grown as the sampling period for measuring the height of the melt surface, thereby improving the accuracy of estimating the direction of the oxygen concentration polarization in the silicon single crystal.

[0016] The method for estimating the oxygen concentration in a silicon single crystal according to the present invention preferably estimates the oxygen concentration in the silicon single crystal from minute fluctuations in the height of the melt surface measured within a certain range downward from the upper end of the body portion of the silicon single crystal, thereby making it possible to estimate the direction of oxygen concentration polarization at an early stage and suppress fluctuations in the oxygen concentration in the silicon single crystal, thereby producing a single crystal with a uniform oxygen concentration distribution in the crystal axis direction.

[0017] In grasping the minute fluctuations in the melt level, it is preferable to measure the height position of the melt level based on the lower end of a thermal shield arranged above the silicon melt. That is, it is preferable to grasp the minute fluctuations in the height of the melt level by measuring the gap (hereinafter sometimes referred to as GAP) between the thermal shield arranged above the silicon melt and the melt level. The minute fluctuations in the melt level can be accurately measured from the fluctuations in the measured gap value. Therefore, it is possible to improve the accuracy of estimating the oxygen concentration of the silicon single crystal.

[0018] In addition, a method for producing a silicon single crystal according to the present invention includes a silicon single crystal production process in which a silicon single crystal is pulled up while applying a transverse magnetic field to a silicon melt in a quartz crucible, and the silicon single crystal production process is characterized in that the oxygen concentration of the silicon single crystal is estimated by the above-mentioned method for estimating oxygen concentration in a silicon single crystal according to the present invention, and crystal growth conditions are adjusted so that the estimated value of the oxygen concentration of the silicon single crystal approaches a target value.

[0019] Furthermore, the silicon single crystal manufacturing apparatus according to the present invention comprises a crystal pulling furnace, a quartz crucible supporting a silicon melt in the crystal pulling furnace, a crucible rotation mechanism for rotating and raising and lowering the quartz crucible, a magnetic field generating device for applying a transverse magnetic field to the silicon melt, a crystal pulling mechanism for pulling a silicon single crystal from the silicon melt, a melt level measuring means for periodically measuring the height of the melt level of the silicon melt, and a control unit for controlling crystal growth conditions, wherein the control unit estimates the oxygen concentration of the silicon single crystal from the behavior of minute fluctuations in the height of the melt level, and adjusts the crystal growth conditions so that the estimated value of the oxygen concentration of the silicon single crystal approaches a target value.

[0020] According to the present invention, it is possible to estimate whether the oxygen concentration of the silicon single crystal will be relatively high or relatively low from minute fluctuations in the melt surface, and therefore it is possible to suppress fluctuations in the oxygen concentration of the silicon single crystal in the crystal growth direction by controlling the crystal growth conditions based on the estimated oxygen concentration.

[0021] The crystal growth conditions are preferably at least one of the rotation speed of the quartz crucible, the flow rate of the inert gas supplied into the crystal pulling furnace, and the pressure inside the crystal pulling furnace, thereby making it possible to suppress fluctuations in the oxygen concentration of the silicon single crystal. Effect of the Invention

[0022] According to the present invention, it is possible to provide a method for estimating the oxygen concentration of a silicon single crystal, a method for manufacturing a silicon single crystal, and a silicon single crystal manufacturing apparatus, which are capable of preventing polarization of the oxygen concentration in the silicon single crystal and manufacturing silicon single crystals of the same quality. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic cross-sectional side view showing the configuration of a silicon single crystal manufacturing apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a flowchart showing the steps of manufacturing a silicon single crystal according to an embodiment of the present invention. [Diagram 3] FIG. 3 is a schematic cross-sectional view showing the shape of a silicon single crystal ingot. [Figure 4] FIG. 4 is a graph showing the oxygen concentration distribution of a plurality of silicon single crystals grown under the same conditions using the same silicon single crystal manufacturing apparatus. [Diagram 5] Figures 5(a) and (b) are diagrams for explaining convection of silicon melt in a crucible to which a horizontal magnetic field is applied, with Figure 5(a) showing a right-handed (clockwise) roll flow and Figure 5(b) showing a left-handed (counterclockwise) roll flow. [Figure 6] FIG. 6 is a graph showing the relationship between the oxygen concentration and the gap variation (GAP variation) of a silicon single crystal. [Figure 7] 7(a) and (b) are graphs showing the relationship between gap variation (GAP variation) and oxygen concentration, where (a) shows the case where the oxygen concentration of the silicon single crystal is high, and (b) shows the case where the oxygen concentration of the silicon single crystal is low. [Figure 8] FIG. 8 is a flowchart illustrating a method for estimating the oxygen concentration in a silicon single crystal. [Figure 9] FIG. 9 is a graph showing the oxygen concentration distribution in the silicon single crystal according to the first embodiment together with the gap variation. [Figure 10] FIG. 10 is a graph showing the oxygen concentration distribution in the silicon single crystal according to the second embodiment together with the gap variation. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0025] FIG. 1 is a schematic cross-sectional side view showing the configuration of a silicon single crystal manufacturing apparatus according to an embodiment of the present invention.

[0026] As shown in FIG. 1, the silicon single crystal manufacturing apparatus 1 includes a chamber 10 constituting a crystal pulling furnace, a quartz crucible 11 for holding a silicon melt 2 within the chamber 10, a graphite crucible 12 for holding the quartz crucible 11, a rotating shaft 13 supporting the graphite crucible 12, a shaft drive mechanism 14 for driving the rotating shaft 13 to rotate and raise and lower, a heater 15 arranged around the graphite crucible 12, an insulating material 16 arranged outside the heater 15 and along the inner surface of the chamber 10, a thermal shield 17 arranged above the quartz crucible 11, a pulling wire 18 arranged coaxially with the rotating shaft 13 above the quartz crucible 11, and a wire winding mechanism 19 arranged above the chamber 10.

[0027] The chamber 10 is composed of a main chamber 10a and a long and thin cylindrical pull chamber 10b connected to the upper opening of the main chamber 10a, and the quartz crucible 11, the graphite crucible 12, the heater 15, and the heat shield 17 are provided in the main chamber 10a. The pull chamber 10b is provided with a gas inlet 10c for introducing an inert gas (purge gas) such as Ar gas or a dopant gas into the chamber 10, and a gas outlet 10d for discharging the atmospheric gas in the chamber 10 is provided at the bottom of the main chamber 10a.

[0028] The quartz crucible 11 is a container made of quartz glass having a cylindrical side wall and a curved bottom. The graphite crucible 12 is in close contact with the outer surface of the quartz crucible 11 to encase it and hold it in order to maintain the shape of the quartz crucible 11 softened by heating. The quartz crucible 11 and the graphite crucible 12 constitute a double-structure crucible that supports the silicon melt in the chamber 10.

[0029] The graphite crucible 12 is fixed to the upper end of a rotating shaft 13, and the lower end of the rotating shaft 13 passes through the bottom of the chamber 10 and is connected to a shaft driving mechanism 14 provided outside the chamber 10. The rotating shaft 13 and the shaft driving mechanism 14 constitute a crucible rotation mechanism that drives the rotation and elevation of the quartz crucible 11 and the graphite crucible 12.

[0030] The heater 15 is used to melt the silicon raw material filled in the quartz crucible 11 to generate the silicon melt 2, and to maintain the molten state of the silicon melt 2. The heater 15 is a resistance heating heater made of carbon, and is provided so as to surround the quartz crucible 11 in the graphite crucible 12. Furthermore, a heat insulating material 16 is provided on the outside of the heater 15 so as to surround the heater 15, thereby improving the heat retention inside the chamber 10.

[0031] The thermal shield 17 is provided to suppress temperature fluctuations in the silicon melt 2 to form an appropriate hot zone near the crystal growth interface, and to prevent heating of the silicon single crystal 3 due to radiant heat from the heater 15 and the quartz crucible 11. The thermal shield 17 is a graphite member that covers the region above the silicon melt 2 excluding the pulling path of the silicon single crystal 3, and has, for example, an inverted truncated cone shape with an opening size that increases from the bottom end to the top end.

[0032] The diameter of the opening 17a at the lower end of the thermal shield 17 is larger than the diameter of the silicon single crystal 3, thereby ensuring a pulling path for the silicon single crystal 3. The diameter of the opening 17a of the thermal shield 17 is smaller than the aperture of the quartz crucible 11, and the lower end of the thermal shield 17 is located inside the quartz crucible 11. Therefore, even if the upper end of the rim of the quartz crucible 11 is raised above the lower end of the thermal shield 17, the thermal shield 17 will not interfere with the quartz crucible 11.

[0033] Although the amount of melt in the quartz crucible 11 decreases as the silicon single crystal 3 grows, by raising the quartz crucible 11 so that the gap GA between the lower end of the thermal shield 17 and the melt surface 2s remains constant, it is possible to suppress temperature fluctuations in the silicon melt 2 and to control the amount of dopant evaporated from the silicon melt 2 by keeping constant the flow rate of the gas flowing near the melt surface 2s. This makes it possible to improve the stability of the crystal defect distribution, oxygen concentration distribution, resistivity distribution, etc. in the pulling axis direction of the silicon single crystal 3.

[0034] Above the quartz crucible 11, there is provided a pull wire 18 which is a shaft for pulling up the silicon single crystal 3, and a wire winding mechanism 19 for winding up the pull wire 18. The wire winding mechanism 19 has a function of rotating the silicon single crystal 3 together with the pull wire 18. The wire winding mechanism 19 is disposed above the pull chamber 10b, and the pull wire 18 extends downward from the wire winding mechanism 19 through the pull chamber 10b, and the tip of the pull wire 18 reaches the internal space of the main chamber 10a. FIG. 1 shows a state in which the silicon single crystal 3 is being grown and is suspended from the pull wire 18. When the silicon single crystal 3 is pulled up, the pull wire 18 is gradually pulled up while rotating the quartz crucible 11 and the silicon single crystal 3, respectively, to grow the silicon single crystal 3. In this way, the pull wire 18 and the wire winding mechanism 19 constitute a crystal pulling mechanism for pulling up the silicon single crystal 3 from the silicon melt 2.

[0035] A sight window 10e for observing the inside is provided at the top of the main chamber 10a, and the growing status of the silicon single crystal 3 can be observed through the sight window 10e. A camera 20 is installed outside the sight window 10e. During the single crystal pulling process, the camera 20 photographs the boundary between the silicon single crystal 3 and the silicon melt 2, which is seen through the sight window 10e and the opening 17a of the thermal shield 17, from diagonally above. The image captured by the camera 20 is processed by an image processor 21, and the processed results are used in a controller 22 to control the crystal growing conditions.

[0036] The silicon single crystal manufacturing apparatus 1 includes a magnetic field generator 30 that applies a transverse magnetic field (horizontal magnetic field) to the silicon melt 2 in the quartz crucible 11. The magnetic field generator 30 includes a pair of electromagnet coils 31A, 31B arranged opposite each other across the main chamber 10a. The electromagnet coils 31A, 31B operate according to instructions from the control unit 22, and the magnetic field strength is controlled. The center position (magnetic field center position) of the horizontal magnetic field generated by the magnetic field generator 30 refers to the height direction position of a horizontal line (magnetic field center line) connecting the centers of the electromagnet coils 31A, 31B arranged opposite each other. The horizontal magnetic field method can effectively suppress convection of the silicon melt 2.

[0037] In the process of pulling up the silicon single crystal 3, a seed crystal is lowered and immersed in the silicon melt 2, and then the seed crystal is slowly raised while rotating the seed crystal and the quartz crucible 11, thereby growing a substantially cylindrical silicon single crystal 3 below the seed crystal. At this time, the diameter of the silicon single crystal 3 is controlled by controlling the pulling speed and the power of the heater 15. In addition, by applying a horizontal magnetic field to the silicon melt 2, melt convection in a direction perpendicular to the magnetic field lines is suppressed.

[0038] Fig. 2 is a flow chart showing the steps of manufacturing a silicon single crystal according to an embodiment of the present invention, and Fig. 3 is a schematic cross-sectional view showing the shape of a silicon single crystal ingot.

[0039] As shown in FIG. 2, the production of a silicon single crystal according to this embodiment includes a raw material melting process S11 in which the silicon raw material in a quartz crucible 11 is heated and melted by a heater 15 to produce a silicon melt 2, a liquid contact process S12 in which a seed crystal attached to the tip of a pulling wire 18 is lowered to contact the silicon melt 2, and a crystal pulling process S13 in which the seed crystal is gradually pulled up while maintaining contact with the silicon melt 2 to grow a single crystal.

[0040] The crystal pulling step S13 includes a necking step S14 for forming a neck portion 3a in which the crystal diameter is narrowed to eliminate dislocations, a shoulder portion growing step S15 for forming a shoulder portion 3b in which the crystal diameter gradually increases, a body portion growing step S16 for forming a body portion 3c in which the crystal diameter is maintained at a specified diameter (e.g., 320 mm), and a tail portion growing step S17 for forming a tail portion 3d in which the crystal diameter gradually decreases, and at the end of the tail portion growing step S17, the silicon single crystal 3 is separated from the silicon melt 2. In this way, as shown in FIG. 3, a silicon single crystal ingot 3I having the neck portion 3a, shoulder portion 3b, body portion 3c, and tail portion 3d is completed.

[0041] A magnetic field application step S18 is carried out in parallel with the crystal pulling step S13. In the magnetic field application step S18, a transverse magnetic field (horizontal magnetic field) is applied to the silicon melt 2 in the quartz crucible 11 during the period from the start of the liquid landing step S12 to the end of the body portion growing step S16. This makes it possible to suppress convection in the silicon melt 2 and suppress dissolution of oxygen from the quartz crucible 11 into the silicon melt 2. In addition, rippling of the melt surface 2s can be suppressed to stabilize the crystal pulling step.

[0042] In the crystal pulling step S13, the height position of the melt surface 2s and the diameter of the silicon single crystal 3 are obtained from the image captured by the camera 20, and in particular the height position of the melt surface 2s is obtained as the gap GA between the lower end of the thermal shield 17 and the melt surface 2s. The crystal diameter and the gap are feedback controlled according to a profile that is predetermined in accordance with the crystal growth stage. The camera 20 and the image processing unit 21 constitute a melt surface measuring means that periodically measures the height of the melt surface 2s of the silicon melt 2.

[0043] In the body part growth process S16, the gap is precisely measured at a very short sampling period, and the oxygen concentration of the silicon single crystal is estimated from minute gap fluctuations. Then, the crystal growth conditions are adjusted based on the estimated oxygen concentration. Specifically, when the estimated oxygen concentration is higher than the target value, the crystal growth conditions are adjusted so that the oxygen concentration is lowered, and when the estimated oxygen concentration is lower than the target value, the crystal growth conditions are adjusted so that the oxygen concentration is higher. The crystal growth conditions are at least one of the rotation speed of the quartz crucible, the Ar gas flow rate, and the furnace pressure.

[0044] Next, a method for estimating the oxygen concentration in a silicon single crystal will be described in detail.

[0045] FIG. 4 is a graph showing the oxygen concentration distribution of multiple silicon single crystals grown under the same conditions using the same silicon single crystal manufacturing apparatus. The horizontal axis shows the crystal length (relative value) and the vertical axis shows the oxygen concentration (×10 17 atoms / cm 3 The crystal length (relative value) indicates the relative position in the growth direction of the silicon single crystal, with the start position of the body portion being 0% and the end position of the body portion being 100%.

[0046] As shown in FIG. 4, the oxygen concentration distribution in the crystal growth direction of the silicon single crystal is divided into high and low oxygen concentrations in the front half of the body (here, the range from the upper end (0%) of the body to 40%). The fundamental cause of the polarization of the oxygen concentration in the silicon single crystal 3 is not clear, but it is believed that the melt convection MC in the quartz crucible 11 has an effect. That is, as shown in FIGS. 5(a) and (b), it is speculated that the oxygen concentration is high and low depending on whether the melt convection MC in the quartz crucible 11 becomes a right-handed (clockwise) roll flow (see FIG. 5(a)) or a left-handed (counterclockwise) roll flow (see FIG. 5(b)) as viewed from the direction of travel of the horizontal magnetic field HZ. It is not clear whether the oxygen concentration in the silicon single crystal 3 is high or low when the melt convection MC is right-handed / left-handed.

[0047] The big problem is that even if the silicon single crystal 3 is grown under the same growth conditions using the same silicon single crystal manufacturing apparatus 1, the melt convection MC is not uniquely determined to be clockwise or counterclockwise, and the oxygen concentration is polarized due to the difference in the convection mode. This makes it impossible to keep the oxygen concentration in the silicon single crystal 3 within the standard over its entire length, and the manufacturing yield of the silicon single crystal 3 deteriorates.

[0048] FIG. 6 is a graph showing the relationship between the oxygen concentration of the silicon single crystal and the measured value of minute gap fluctuation, where the horizontal axis shows minute gap fluctuation (GAP fluctuation) and the vertical axis shows the oxygen concentration of the silicon single crystal in the bipolar region. In particular, the horizontal axis shows the standard deviation σ (mm) of the gap measurement value when the crystal length of the body part is in the range of 0 to 100 mm, and the vertical axis shows the average value (×10 17 atoms / cm 3 ) are shown, respectively.

[0049] As shown in Figure 6, the oxygen concentration in the silicon single crystal is polarized, and when the oxygen concentration is low, the minute gap fluctuation σ is large, and when the oxygen concentration is high, the minute gap fluctuation σ is small. In other words, there is a strong correlation between the minute gap fluctuation and the oxygen concentration of the silicon single crystal.

[0050] 7(a) and (b) are graphs showing the relationship between minute gap fluctuations and oxygen concentration, where the horizontal axis is the crystal length (relative value), the left vertical axis is the gap fluctuation σ (mm), and the right vertical axis is the oxygen concentration ( ×10 17 atoms / cm 3 7(a) shows the case where the oxygen concentration in the silicon single crystal is high, and FIG. 7(b) shows the case where the oxygen concentration in the silicon single crystal is low.

[0051] As shown in Fig. 7(a), when the gap fluctuation is small, the oxygen concentration tends to be high when the crystal length of the body is within 60%. On the other hand, the gap fluctuation is small and stable.

[0052] On the other hand, as shown in Fig. 7(b), when the gap fluctuation is large, the oxygen concentration tends to be low when the crystal length of the body is in the range of 40% or less. On the other hand, it can be seen that the gap fluctuation σ becomes large when the crystal length of the body is in the range of 40% or less.

[0053] As described above, there is a certain correlation between the gap variation and the oxygen concentration. Therefore, in this embodiment, the gap variation is measured during the body portion growth process, the direction of the polarization of the oxygen concentration in the silicon single crystal is estimated based on the gap variation, and the crystal growth conditions are adjusted based on the estimation result to suppress the polarization of the oxygen concentration and stabilize the crystal quality.

[0054] The phenomenon of the gap fluctuation becoming large does not necessarily occur when the oxygen concentration in the silicon single crystal becomes low, but may occur when the oxygen concentration in the silicon single crystal becomes high, and the relationship between the behavior of the gap fluctuation and the polarization of the oxygen concentration differs for each silicon single crystal manufacturing device. Also, the polarization of the oxygen concentration does not necessarily occur immediately after the start of the body part growth process, but may occur after the growth of the body part has progressed to a certain extent, and differs for each silicon single crystal manufacturing device. Therefore, the relationship between the behavior of the gap fluctuation and the direction of the polarization of the oxygen concentration (whether the oxygen concentration becomes high mode / low mode when the gap fluctuation is high) and the sampling period of the gap measurement value for estimating the oxygen concentration (oxygen concentration estimation period) need to be set for each silicon single crystal manufacturing device based on the actual data of pulling multiple silicon single crystals in the past.

[0055] FIG. 8 is a flowchart illustrating a method for estimating the oxygen concentration in a silicon single crystal.

[0056] As shown in FIG. 8, in estimating the oxygen concentration, a gap, which is the height of the melt surface based on the thermal shield, is measured at a predetermined sampling period during a preset oxygen concentration estimation period (step S21).

[0057] The oxygen concentration estimation period is a sampling period of the gap measurement value for estimating the oxygen concentration set during the body part growth process, and is obtained from past pulling records. For example, in one silicon single crystal manufacturing device, the oxygen concentration tends to become polarized immediately after the start of the body part growth, so the growth period of the crystal part of the body part with a crystal length of 0 to 100 mm is set as the sampling period of the gap measurement value. In another silicon single crystal manufacturing device, the oxygen concentration tends to become polarized when the body part has grown to a certain extent, so the growth period of the crystal part of the body part with a crystal length of 300 to 400 mm is set as the sampling period of the gap measurement value.

[0058] The sampling period of the gap measurement value is set to a very short period of 50 seconds or less. The sampling period is preferably 10 seconds or less. Usually, the gap needs to be measured for liquid level position control, which maintains the liquid level position constant by raising the crucible in accordance with the drop in the melt level due to consumption of silicon melt, but it is not necessary to measure at such a short sampling period, which is at most one to several minutes. However, when the gap measurement value is used to estimate the oxygen concentration, the gap sampling period needs to be very short, which makes it possible to capture small local fluctuations in the height of the melt level due to changes in melt convection.

[0059] The resolution of the gap measurement is 1 mm or less, and preferably 0.1 mm or less. By setting the resolution of the gap measurement to 1 mm or less, it is possible to accurately capture small local fluctuations in the melt surface height that accompany changes in melt convection.

[0060] Next, a standard deviation σ, which is an index showing the magnitude of the gap fluctuation measured during the oxygen concentration estimation period (sampling period), is calculated (step S22). The gap fluctuation is not limited to the standard deviation, and may be calculated as, for example, the deviation between the instantaneous value and the moving average value, and in this case, the number of steps of the moving average is preferably 10 or more.

[0061] Next, the gap fluctuation σ is compared with a threshold value σth (step S23), and if the gap fluctuation σ is equal to or greater than the threshold value σth (σ≧σth), it is estimated that the oxygen concentration will be relatively low (steps S24Y, S25), and if the gap fluctuation σ is less than the threshold value σth (σ<σth), it is estimated that the oxygen concentration will be relatively high (steps S24N, S26).

[0062] As described above, the relationship between the behavior of the gap fluctuation and the direction of polarization of the oxygen concentration differs for each silicon single crystal manufacturing apparatus 1. For example, in one apparatus, the oxygen concentration may become relatively low when the gap fluctuation σ is equal to or greater than the threshold σth, while in another apparatus, the oxygen concentration may become relatively high when the gap fluctuation σ is equal to or greater than the threshold σth. This tendency is almost the same for the same silicon single crystal manufacturing apparatus. Therefore, it is necessary to specify in advance the correlation between the gap fluctuation and the direction of polarization of the oxygen concentration for each silicon single crystal manufacturing apparatus, and to estimate the direction of polarization of the oxygen concentration based on this correlation.

[0063] Next, the crystal growth conditions are adjusted based on the estimated oxygen concentration (step S27). Examples of the crystal growth conditions include the rotation speed of the quartz crucible, the flow rate of the inert gas supplied into the chamber 10 (crystal pulling furnace), and the pressure inside the chamber 10. For example, the oxygen concentration can be increased by increasing the rotation speed of the quartz crucible, and conversely, the oxygen concentration can be decreased by decreasing the rotation speed.

[0064] As described above, the method for producing a silicon single crystal according to this embodiment measures the gap at a predetermined sampling period when growth of the body portion of the silicon single crystal begins, and estimates the direction of polarization of the oxygen concentration in the silicon single crystal from the magnitude of the gap fluctuation, and therefore, the crystal growth conditions can be controlled based on the estimation results, thereby reducing the variation in oxygen concentration in the crystal growth direction of the silicon single crystal.

[0065] Although a preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention.

[0066] For example, in the above embodiment, the gap between the thermal shield and the melt surface is measured with a camera, and the oxygen concentration in the silicon single crystal is estimated from the behavior of the gap fluctuation. However, the present invention is not limited to such a method, and various methods can be adopted that can monitor the melt surface and measure minute height fluctuations in local areas of the melt surface, and the oxygen concentration can be estimated from the behavior of the local height fluctuations of the melt surface. EXAMPLES

[0067] Example 1 A silicon single crystal with a diameter of approximately 310 mm was pulled by the HMCZ method. During the crystal pulling process, the range in the crystal longitudinal direction from the start position of the silicon single crystal's body part to a position 100 mm away was designated as the oxygen mode evaluation region for evaluating the direction of polarization of the oxygen concentration in the silicon single crystal, and the gap fluctuation within the oxygen mode evaluation region was monitored to obtain the standard deviation σ, which is an index of gap fluctuation. Note that although the gap between the thermal shield and the melt surface can be measured along the entire circumference of the lower end of the thermal shield, the standard deviation σ of the gap fluctuation was calculated using the measurement value of the local gap at a part of the lower end of the thermal shield, not the entire circumference of the lower end of the thermal shield.

[0068] The threshold value of the gap fluctuation is set to σth = 0.15. When the gap fluctuation is smaller than the threshold (σ<0.15), the mode is high oxygen mode, and when it is equal to or greater than the threshold (σ≧0.15), the mode is low oxygen mode. Based on the data of the past silicon single crystal pulling (POR), the oxygen concentration is set to the target value (12 × 10 17 atoms / cm 3 The crystal growth conditions (Ar flow rate and furnace pressure) were adjusted so that

[0069] Since it was not known which oxygen mode would be used at the start of crystal growth, the oxygen concentration adjustment parameters (Ar flow rate and furnace pressure) were set on the assumption that the high oxygen mode would be used. When the crystal length of the body part reached L = 100 mm, σ was < 0.15, so it was determined that the "high oxygen mode" would be used, and the oxygen concentration adjustment parameters (Ar flow rate and furnace pressure) were maintained at the same settings as at the start of crystal growth, and the body part growth process was continued.

[0070] The distribution of oxygen concentration in the crystal growth direction of the silicon single crystal ingot thus pulled according to Example 1 was evaluated. The results are shown in FIG.

[0071] FIG. 9 is a graph showing the oxygen concentration distribution in the silicon single crystal according to Example 1 together with the gap fluctuation, in which the horizontal axis is the crystal length (relative value), the left vertical axis is the gap fluctuation σ (mm), and the right vertical axis is the oxygen concentration (atoms / cm 3 ) in Fig. 9. In Fig. 9, the eight square plots indicate the oxygen concentration distribution of the silicon single crystal according to Example 1, in which the crystal growth conditions were adjusted based on the estimated oxygen mode. Meanwhile, the many diamond plots indicate the oxygen concentration distribution (bipolar distribution) of the silicon single crystal according to the comparative example (conventional) in which the oxygen concentration was not estimated and the crystal growth conditions were not adjusted. Furthermore, the very steep line graph below indicates Example 1 4 shows the change in gap variation measured during the silicon single crystal growth process by

[0072] As is clear from FIG. 9, the oxygen concentration distribution of the silicon single crystal according to Example 1 is closer to the target value (here, 12×10 17 atoms / cm 3 ) is closer to

[0073] Example 2 A silicon single crystal was pulled using the same crystal pulling apparatus and under the same crystal pulling conditions as in Example 1. Since it was not known which oxygen mode would be used at the start of crystal growth, the oxygen concentration adjustment parameters (Ar flow rate and furnace pressure) were set on the assumption that the mode would be high oxygen mode. When the crystal length L of the body part reached 100 mm, σ was ≥ 0.15, so it was determined that the mode would be "low oxygen mode," and the oxygen concentration adjustment parameters (Ar flow rate and furnace pressure) were changed to the adjustment parameters for low oxygen concentration, and the body part growth process was continued.

[0074] FIG. 10 is a graph showing the oxygen concentration distribution in the silicon single crystal according to Example 2 together with the gap fluctuation, in which the horizontal axis is the crystal length (relative value), the left vertical axis is the gap fluctuation σ (mm), and the right vertical axis is the oxygen concentration (atoms / cm 3 10, nine square plots indicate the oxygen concentration distribution of the silicon single crystal according to Example 2, in which the crystal growth conditions were adjusted based on the estimated oxygen mode. Meanwhile, many diamond plots indicate the oxygen concentration distribution (bipolar distribution) of the silicon single crystal according to the comparative example (conventional) in which the oxygen concentration was not estimated and the crystal growth conditions were not adjusted. Furthermore, the very steep line graph below indicates the change in gap fluctuation measured during the growth process of the silicon single crystal according to Example 2.

[0075] As is clear from FIG. 10, the oxygen concentration distribution of the silicon single crystal according to Example 2 is closer to the target value (here, 12×10 17 atoms / cm 3 ) is closer to

[0076] As described above, by predicting the oxygen concentration in advance from the behavior of the gap fluctuation measured within a range from the starting position of the body part to 100 mm of the crystal length and tuning the crystal growth conditions, it was possible to bring the oxygen concentration in the silicon single crystal close to the target value. In this way, by estimating the subsequent behavior of the oxygen concentration by monitoring the gap fluctuation, the oxygen concentration in the silicon single crystal can be controlled with high precision. [Explanation of symbols]

[0077] 1. Silicon single crystal manufacturing equipment 2. Silicon melt 2s melt surface 3. Silicon single crystal 3I Silicon single crystal ingot 3a Neck 3b Shoulder section 3c Body part 3d tail 10. Chamber 10a Main Chamber 10b Pull chamber 10c Gas inlet 10d Gas outlet 10e Sightseeing window 11 Quartz crucible 12 Graphite crucible 13 Rotating shaft 14 Shaft drive mechanism 15 Heater 16 Insulation 17 Heat shield 17a Opening in thermal shield 18 Wire 19 Wire winding mechanism 20 Camera 21 Image processing section 22 Control section 30 Magnetic Field Generator 31A, 31B Electromagnet coil GA Gap HZ horizontal magnetic field MC Melt Convection

Claims

1. A method for estimating oxygen concentration in a silicon single crystal, comprising: measuring the height of a melt surface of a silicon melt in a quartz crucible while pulling up a silicon single crystal while applying a transverse magnetic field to the silicon melt; and estimating the oxygen concentration of the silicon single crystal from minute fluctuations in the height of the melt surface.

2. 2. The method for estimating an oxygen concentration in a silicon single crystal according to claim 1, wherein the height of the melt surface is measured periodically at a sampling period of 50 seconds or less.

3. 3. The method for estimating an oxygen concentration in a silicon single crystal according to claim 1, wherein a resolution of the measurement value of the height of the melt surface is 0.1 mm or less.

4. 4. The method for estimating the oxygen concentration of a silicon single crystal according to claim 1, further comprising: identifying a correlation between minute fluctuations in the height of the melt surface and a direction of polarization of the oxygen concentration from data on past performance of pulling silicon single crystals; and estimating the oxygen concentration of the silicon single crystal based on the correlation.

5. 5. The method for estimating the oxygen concentration of a silicon single crystal according to claim 1, further comprising: identifying a crystal portion in which a polarization of oxygen concentration is observed from data on past silicon single crystal pulling performance; and setting a period during which the crystal portion is being grown as a sampling period for measuring the height of the melt surface.

6. 5. A method for estimating oxygen concentration in a silicon single crystal according to claim 1, further comprising estimating the oxygen concentration in the silicon single crystal from minute fluctuations in the height of the melt surface measured within a certain range downward from the upper end of the body portion of the silicon single crystal.

7. 7. The method for estimating oxygen concentration in a silicon single crystal according to claim 1, further comprising measuring a gap between a thermal shield arranged above the silicon melt and the melt surface to grasp minute fluctuations in the height of the melt surface.

8. A method for producing a silicon single crystal, comprising the steps of: applying a transverse magnetic field to a silicon melt in a quartz crucible while pulling up a silicon single crystal, Estimating an oxygen concentration in the silicon single crystal by the method for estimating an oxygen concentration in a silicon single crystal according to any one of claims 1 to 7; A method for producing a silicon single crystal, comprising adjusting crystal growth conditions so that the estimated value of the oxygen concentration in the silicon single crystal approaches a target value.

9. 9. The method for producing a silicon single crystal according to claim 8, wherein the crystal growth conditions are at least one of a rotation speed of the quartz crucible, a flow rate of an inert gas supplied into a crystal pulling furnace, and a pressure in the crystal pulling furnace.

10. A crystal pulling furnace; a quartz crucible for supporting a silicon melt in the crystal pulling furnace; A crucible rotation mechanism that rotates and raises and lowers the quartz crucible; A magnetic field generating device that applies a transverse magnetic field to the silicon melt; a crystal pulling mechanism for pulling a silicon single crystal from the silicon melt; a melt level measuring means for periodically measuring the height of the melt level of the silicon melt; A control unit for controlling crystal growth conditions; The control unit is estimating an oxygen concentration in the silicon single crystal from minute fluctuations in the height of the melt surface; A silicon single crystal manufacturing apparatus, comprising: an apparatus for adjusting the crystal growth conditions so that an estimated value of the oxygen concentration in the silicon single crystal approaches a target value.

11. 11. The silicon single crystal manufacturing apparatus according to claim 10, wherein the crystal growth conditions are at least one of a rotation speed of the quartz crucible, a flow rate of an inert gas supplied into the crystal pulling furnace, and a pressure in the crystal pulling furnace.

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