METHOD FOR MEASURING DISTANCE BETWEEN LOWER END SURFACE OF HEAT INSULATION MEMBER AND SURFACE OF MATERIAL MELT, METHOD FOR CONTROLLING DISTANCE BETWEEN LOWER END SURFACE OF HEAT INSULATION MEMBER AND SURFACE OF MATERIAL MELT, AND METHOD FOR MANUFACTURING SILICON SINGLE CRYSTAL

Abstract

The present invention is a method for installing a heat shield member positioned above a raw material melt surface, and measuring the distance between the heat shield member lower end surface and the raw material melt surface, when pulling a silicon single crystal while applying a magnetic field to a raw material melt within a crucible by the Czochralski method, wherein the method for measuring the distance between the heat shield member lower end surface and the raw material melt surface is characterized by involving forming a through-hole in the heat shield member lower end surface, actually measuring the distance between the heat shield member lower end surface and the raw material melt surface, observing the position of a mirror image of the through-hole reflected on the raw material melt surface by using a fixed-point observation machine, subsequently measuring the distance by which the mirror image moves while the silicon single crystal is pulled, and calculating the distance between the heat shield member lower end surface and the raw material melt surface from the actually measured value and the distance by which the mirror image moves. There is thereby provided a measurement method with which it is possible to accurately measure the distance between the heat shield member lower end surface and the raw material melt surface.

Description

[Technical field]

[0001] The present invention relates to a method for measuring the distance between the lower end face of a heat insulating member arranged above the raw material melt surface and the raw material melt surface when a silicon single crystal is pulled up from the raw material melt in a crucible by the Czochralski method, a method for controlling said distance, and a method for producing a silicon single crystal. [Background technology]

[0002] As a method for producing silicon single crystals used in the manufacture of semiconductor devices, the Czochralski method (CZ method), in which a silicon single crystal is grown and pulled from a raw material melt in a quartz crucible, is widely used. In the CZ method, a seed crystal is immersed in the raw material melt (silicon melt) in a quartz crucible in an inert gas atmosphere, and the quartz crucible and the seed crystal are pulled up while rotating to grow a silicon single crystal of a desired diameter.

[0003] In recent years, crystal defects (grown-in defects) in silicon wafers have become a problem due to the high integration of semiconductor elements and the accompanying progress in miniaturization. Crystal defects are a factor that deteriorates the characteristics of semiconductor elements, and their impact is becoming even greater with the progress in miniaturization of elements. Known examples of such crystal defects include octahedral void-like defects that are aggregates of vacancies in silicon single crystals produced by the CZ method (Non-Patent Document 1) and dislocation clusters that form as aggregates of interstitial silicon (Non-Patent Document 2).

[0004] It has been shown that the amount of these crystal defects introduced is determined by the temperature gradient of the crystal at the growth interface and the growth rate of the silicon single crystal (Non-Patent Document 3). Regarding a method for producing a low-defect silicon single crystal utilizing this, for example, Patent Document 1 discloses slowing down the growth rate of the silicon single crystal, and Patent Document 2 discloses pulling up the silicon single crystal at a speed not exceeding the maximum pulling rate that is approximately proportional to the temperature gradient in the boundary region between the solid phase and liquid phase of the silicon single crystal. Furthermore, an improved CZ method (Non-Patent Document 4) focusing on the temperature gradient (G) and growth rate (V) during crystal growth has been reported, and it is necessary to control the crystal temperature gradient with high precision.

[0005] In these methods, in order to control the crystal temperature gradient, a cylindrical or inverted cone-shaped structure (heat shield) that blocks radiant heat is provided around the silicon single crystal grown above the melt surface. This has the advantage that the crystal temperature gradient at high temperatures can be increased, allowing defect-free crystals to be obtained quickly. However, in order to accurately control the crystal temperature gradient, it is necessary to control with great precision the distance between the raw material melt surface and the lower end face of the heat shield located above the raw material melt surface (hereinafter sometimes referred to as DPM) to a specified distance.

[0006] Moreover, as the crystal diameter increases, the melt surface position changes significantly due to the weight of the quartz crucible (variation in wall thickness), deformation during operation, expansion, etc., resulting in the problem that the melt surface position changes for each crystal growth batch. For this reason, it is becoming increasingly difficult to precisely control the distance between the melt surface and the heat insulating member to a specified distance.

[0007] To improve these problems, for example, Patent Document 3 proposes placing a reference reflector (reference mark) in a CZ furnace and measuring the relative distance between the real image of the reference reflector and the mirror image of the reference reflector reflected on the melt surface, thereby measuring the distance between the reference reflector and the melt surface. Based on the measurement results, the distance between the melt surface and the heat insulating member is precisely controlled to a predetermined distance.

[0008] Furthermore, Patent Document 4 shows a method of considering the inclination of the raw material melt due to the rotation of the crucible in order to obtain a stable mirror image of the reference reflector. Patent Document 5 shows a method of improving position detection errors by applying a magnetic field to make the reflected image clearer, and Patent Document 6 shows a method of improving position detection errors by providing a reference reflector inside a recess provided on the lower end surface of a heat insulating member and making the reflected image clearer by the difference in brightness between the reflector and other positions.

[0009] In these methods, a real image of a reference reflector and a mirror image of the reference reflector are captured by a detection means such as an optical camera, and the brightness of the captured real image and mirror image of the reference reflector are quantized (binarized) into two levels by determining a certain threshold (binarized level threshold). In other words, they are distinguished into areas that are brighter or darker than the binary level threshold. Then, the position of the reference reflector is measured, and the measured value is converted to measure the distance of the real image or mirror image.

[0010] However, as time passes during the crystal growth process, the brightness of the mirror image of the reference reflector reflected on the melt surface changes, causing the detection value of the optical camera before binarization to fluctuate, or noise different from the mirror image of the reference reflector, such as molten metal splashes adhering to structural components inside the CZ furnace, may be detected, making it difficult to stably and accurately measure the distance between the reference reflector and the melt surface.

[0011] In order to improve this problem, Patent Document 6 provides a reference reflector inside a recess that is recessed below the bottom end of the heat shield, thereby clarifying the shadow of the mirror image of the reference reflector and suppressing false detections in fixed-point observations using binarization, thereby improving detection accuracy. However, even with this structure and detection method, the radiated light from the high-temperature silicon melt is strong, so the recess at the bottom end of the heat shield alone may not provide sufficient contrast, resulting in false detections. In particular, with a narrow DPM, the amount of light increases even further, making it difficult to detect the reference reflector.

[0012] On the other hand, when a raw material melt is placed in a quartz crucible with a diameter of 800 mm or more and a silicon single crystal with a diameter of 300 mm or more is produced without applying a magnetic field, the melt surface vibrates, and the exact position of the melt surface cannot be detected stably. In this case, the relative distance between the reference reflector and the melt surface cannot be measured stably and accurately.

[0013] If the measurement result of the relative distance between the reference reflector and the melt surface is inaccurate, the distance between the raw material melt surface and the heat insulating member cannot be controlled to a predetermined distance with high precision, and as a result, silicon single crystals of desired quality cannot be produced with high productivity. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Publication No. 6-56588 [Patent Document 2] Japanese Patent Application Publication No. 7-257991 [Patent Document 3] Japanese Patent Application Publication No. 6-116083 [Patent Document 4] JP 2001-342095 A [Patent Document 5] JP 2008-195545 A [Patent Document 6] JP 2012-1387 A [Non-patent literature]

[0015] [Non-Patent Document 1] "Analysis of side-wall structure of grown-in twin-type octahedral defects in Czochralski silicon", Jpn. J.Appl. Phys. Vol. 37(1998), pp.1667-1670 [Non-Patent Document 2] "Evaluation of microdefects in as-grown silicon crystals", Mat. Res. Soc. Symp. Proc. Vol. 262(1992), p-p51-56 [Non-Patent Document 3] "The mechanism of swirl defects formation in silicon, Journal of Crystal growth", Vol. 59, Issue 3 (1982), p-p625-643 [Non-Patent Document 4] Journal of the Japanese Society for Crystal Growth, vol.25 No.5, (1998), p-p207-213 Summary of the Invention [Problem to be solved by the invention]

[0016] The present invention has been made to solve the above problems, and aims to provide a measurement method that can accurately measure the distance between the lower end surface of a heat insulating member and the raw material melt surface, a control method that can accurately control the distance between the lower end surface of a heat insulating member and the raw material melt surface, and a silicon single crystal production method that can produce a silicon single crystal while accurately controlling the distance between the lower end surface of a heat insulating member and the raw material melt surface. [Means for solving the problem]

[0017] In order to solve the above problems, the present invention provides a method for pulling a silicon single crystal while applying a magnetic field to a raw material melt in a crucible by the Czochralski method, comprising the steps of: installing a heat insulating member located above a raw material melt surface; and measuring a distance between a lower end surface of the heat insulating member and the raw material melt surface, A through hole is formed in the lower end surface of the heat insulating member, The distance between the lower end surface of the heat insulating member and the raw material melt surface is actually measured, and the position of the mirror image of the through hole reflected on the raw material melt surface is observed by a fixed point observation device, and then The present invention provides a method for measuring the distance between the lower end surface of the heat insulating member and the raw material melt surface, characterized in that the movement distance of the mirror image is measured by the fixed-point observation device during pulling of the silicon single crystal, and the distance between the lower end surface of the heat insulating member and the raw material melt surface is calculated from the actual measurement value and the movement distance of the mirror image.

[0018] According to this measurement method, even when there is strong radiant light from the high-temperature raw material melt or when the amount of light increases further in a narrow DPM, the light-dark contrast between the through hole and other parts in the mirror image can be maintained, making it possible to measure the molten material level position with high accuracy, and ultimately to measure the distance between the lower end surface of the heat shield and the raw material melt level with high accuracy.

[0019] More specifically, in a heat shield having a through hole on its lower end surface, even if there is strong radiant light from the high-temperature raw material melt, the radiant light passes through the through hole, so the amount of reflected light is extremely small, and a strong contrast between the light and dark areas can be formed between the through hole and the reflective part of the lower end part of the heat shield other than the through hole. By detecting such a strong contrast between the light and dark areas, the through hole can be detected with high accuracy even under the influence of strong radiant light from the high-temperature raw material melt or in a state where the amount of light increases further in a narrow DPM, and based on this, the distance between the lower end surface of the heat shield and the raw material melt surface can be measured with high accuracy.

[0020] In addition, when white quartz or transparent quartz, which has a lower emissivity than the graphite parts used for the heat shield, is used for the reference reflector, even if the light and dark of the heat shield is removed, the difference in emissivity between the reference reflector and the hot water splash portion of the raw material molten liquid attached to the lower end of the heat shield is small, and the hot water splash portion may be erroneously detected. On the other hand, in the dark portion detection by the through hole in the measurement method of the present invention, not only the lower end of the heat shield other than the through hole but also the hot water splash portion becomes a bright portion, which is also effective in preventing erroneous detection due to hot water splash.

[0021] Furthermore, when white quartz or transparent quartz is used as the reference reflector, problems such as breakage due to thermal load over long-term use, contamination due to falling during operation, and changes in detection values ​​due to deformation can occur, but such problems do not arise with the measurement method of the present invention, which uses a heat-shielding member with a through hole.

[0022] In addition, if only a recess is formed at the bottom end of the heat shield, the radiant light does not pass through, and the radiant light from multiple directions is reflected inside the recess, so although there will be some brightness and darkness compared to the other bottom ends of the heat shield, the reflected light will not result in a clearly dark area. Only by allowing the radiant light to pass through the through holes as in the present invention can it be possible to form strong brightness and darkness areas and greatly improve detection accuracy.

[0023] For example, in observing the position of the mirror image of the through hole, the through hole can be detected as a dark area and the area other than the through hole as a bright area in the mirror image of the lower end of the heat shield projected onto the raw material melt surface.

[0024] According to the measurement method of the present invention, even when there is strong radiant light from the high-temperature raw material melt or when the amount of light increases further in a narrow DPM, the light-dark contrast of the mirror image of the lower end of the heat shield can be sufficiently maintained, so that the DPM can be stably and accurately measured by detecting the through hole as a dark area in the mirror image of the lower end of the heat shield.

[0025] Furthermore, when actually measuring the distance between the lower end surface of the heat insulation member and the raw material melt surface, a reference position detector arranged above the raw material melt detects the lower end of a seed crystal for growing the silicon single crystal and sets it as a reference position, and then the lower end of the seed crystal is lowered to between the lower end surface of the heat insulation member and the raw material melt surface, and the crucible is raised to bring the lower end of the seed crystal into contact with the raw material melt surface, and the distance between the lower end surface of the heat insulation member and the raw material melt surface can be actually measured based on the distance from the contact position to the reference position and the distance from the lower end surface of the heat insulation member to the reference position.

[0026] In this way, the reference position detector arranged above the raw material melt detects the lower end of the seed crystal for growing the silicon single crystal and sets it as the seed crystal reference position, and then the lower end of the seed crystal is lowered between the lower end surface of the heat insulating member and the raw material melt surface, and the crucible is raised to bring the lower end of the seed crystal into contact with the raw material melt surface, and the distance between the lower end surface of the heat insulating member and the raw material melt surface is measured based on the distance from the contact position to the reference position and the distance from the lower end surface of the heat insulating member to the reference position, thereby making it possible to measure the distance between the lower end surface of the heat insulating member and the raw material melt surface with a simple operation. In addition, since the distance between the lower end surface of the heat insulating member and the raw material melt surface is measured by the seed crystal, there is little risk of the raw material melt being contaminated by impurities, and a high-quality silicon single crystal can be grown. Furthermore, by lowering the lower end of the seed crystal between the lower end of the heat insulating member and the raw material melt surface, there is no risk of the raw material melt adhering to the heat insulating member when the crucible is raised and the seed crystal comes into contact with the raw material melt surface.

[0027] In this case, for example, the central magnetic field strength of the applied magnetic field can be 10G to 5000G, which is a horizontal magnetic field.

[0028] Alternatively, the applied magnetic field may be a cusp magnetic field.

[0029] By using a heat shield with a through hole, there are no other dark areas other than the through hole at the bottom end of the heat shield, making it very easy to detect, and DPM measurement and control are possible even under weak magnetic field strength conditions where it was previously difficult to detect a reflector, and the present invention can be applied to horizontal magnetic fields with a central magnetic field strength of several tens of G and cusp magnetic fields with a central magnetic field strength of approximately 0 G. Thus, the present invention can stably perform DPM measurement in horizontal magnetic fields with a central magnetic field strength ranging from a weak magnetic field strength of several tens of G to a strong magnetic field strength of 5000 G, or can be applied to a cusp magnetic field with a central magnetic field strength of approximately 0 G.

[0030] For example, the horizontal cross-sectional shape of the through hole may be circular or polygonal, and the diameter or the diameter of the circumscribed circle may be 4 mm or more and 20 mm or less.

[0031] It is more preferable that the diameter of the through hole or the diameter of the circumscribing circle is 8 mm or more and 15 mm or less.

[0032] In the present invention, the through holes are used to form dark spaces by allowing radiant light to pass through, so there are no particular restrictions on the shape or size of the through holes. However, the horizontal cross-sectional shape may be circular or polygonal, with the diameter or circumscribing circle having a diameter of 4 mm or more and 20 mm or less, more preferably 8 mm or more and 15 mm or less.

[0033] The present invention also provides a method for controlling the distance between the lower end surface of a heat insulating member and the raw material melt surface, characterized in that the distance between the lower end surface of a heat insulating member and the raw material melt surface, measured by the method for measuring the distance between the lower end surface of a heat insulating member and the raw material melt surface of the present invention, is fed back during pulling of the silicon single crystal, and the crucible or the heat insulating member is moved so that the distance between the lower end surface of the heat insulating member and the raw material melt surface becomes a set value.

[0034] In this way, in the control method of the present invention, a heat insulating member having a through hole that enables highly accurate detection when detecting the position of the mirror image of the lower end surface of the heat insulating member reflected on the raw material melt surface with a fixed-point observation device during pulling of a silicon single crystal is used, and the mirror image of the through hole reflected on the raw material melt surface is detected as a dark area. This makes it possible to maintain the light-dark contrast in the mirror image of the lower end surface of the heat insulating member even when there is strong radiant light from the high-temperature raw material melt or when the amount of light increases further in a narrow DPM, and makes it possible to stably and accurately measure and control the distance between the lower end surface of the heat insulating member and the raw material melt surface.

[0035] Furthermore, compared to using white quartz or transparent quartz as the reference reflector, which has a lower emissivity than the graphite parts used in the heat shield, in the present invention, dark area detection using the through hole not only detects the lower end surface of the heat shield other than the through hole, but also the molten metal splash area as bright areas, making it possible to avoid erroneous detection of noise that is different from the mirror image of the reference reflector, such as molten metal splashes attached to structural parts inside the CZ furnace.

[0036] Furthermore, compared to using white quartz or transparent quartz as the reference reflector, the present invention, which uses a through hole as the reference reflector, does not cause problems such as breakage during long-term use due to thermal load, contamination due to falling during operation, or changes in detection values ​​due to deformation.

[0037] In this regard, the "reference reflector" in the present invention is a reference reflector that is located on the lower end surface of the heat insulating member and reflects a mirror image onto the raw material melt surface. By observing this mirror image, the distance between the lower end surface of the heat insulating member and the raw material melt surface can be calculated, and the position of the raw material melt surface can be controlled.

[0038] The present invention also provides a method for producing a silicon single crystal, characterized in that the method for controlling the distance between the lower end surface of a heat insulating member and the surface of the raw material melt of the present invention is used to control the distance between the lower end surface of the heat insulating member and the surface of the raw material melt, thereby producing a silicon single crystal.

[0039] In this way, by producing silicon single crystals using the silicon single crystal manufacturing method of the present invention, the distance between the lower end surface of the heat shield and the raw material melt surface can be measured and controlled with high precision, allowing the crystal axis temperature gradient in the crystal growth axis direction to be controlled extremely precisely, and high-quality silicon single crystals can be produced efficiently and with high productivity. Effect of the Invention

[0040] As described above, according to the method of measuring the distance between the lower end surface of the heat insulating member and the raw material melt surface of the present invention, the distance between the lower end surface of the heat insulating member and the raw material melt surface can be measured more stably and accurately.

[0041] According to the method for controlling the distance between the lower end surface of the heat insulating member and the raw material melt surface of the present invention, the distance between the lower end surface of the heat insulating member and the raw material melt surface can be controlled with high precision by controlling the distance between the lower end surface of the heat insulating member and the raw material melt surface based on the measurement results of the measurement method of the present invention. This makes it possible to control the crystal axis temperature gradient in the crystal growth axis direction with extreme precision, and high-quality silicon single crystals can be produced efficiently and with high productivity. In addition, by controlling the distance between the lower end surface of the heat insulating member and the raw material melt surface so that it does not become equal to or smaller than a lower limit, contact between the lower end surface of the heat insulating member and the raw material melt surface can be prevented, and silicon single crystals can be grown safely.

[0042] Furthermore, according to the method for producing a silicon single crystal of the present invention, the distance between the lower end surface of the heat insulating member and the surface of the raw material melt can be controlled with high precision by the control method of the present invention, making it possible to control the crystal axis temperature gradient in the crystal growth axis direction with extreme precision, and thus enabling high-quality silicon single crystals to be produced efficiently and with high productivity. [Brief description of the drawings]

[0043] [Figure 1] 1 is a schematic diagram of a silicon single crystal pulling apparatus that can be used in the present invention. [Diagram 2] 4 is a schematic diagram illustrating an example of a method for measuring the distance between the lower end surface of a heat insulating member and the surface of a raw material melt according to the present invention. FIG. [Diagram 3] 3 is a schematic diagram of an example of a mirror image of a lower end surface of a heat shield obtained by a fixed-point observation device in the arrangement of FIG. 2. [Figure 4] 3 is a schematic diagram showing an example of a change in position of a mirror image of a lower end surface of a heat shield obtained by a fixed-point observation device in the arrangement of FIG. 2. [Diagram 5] 1 is a diagram illustrating an example of a method for actually measuring the distance between the lower end surface of a heat insulating member and the surface of a raw material melt using a seed crystal. FIG. [Figure 6] 2 is an enlarged schematic cross-sectional view of a portion of the silicon single crystal pulling apparatus shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The present invention will now be described in more detail. As described above, conventionally, a reference reflector is placed in a CZ furnace, and the distance between the reference reflector and the melt surface is measured by measuring the relative distance between the real image of the reference reflector and the mirror image of the reference reflector reflected on the melt surface. This measurement is performed by capturing the real image of the reference reflector and the mirror image of the reference reflector with a detection means such as an optical camera, and quantizing the brightness of the captured real image and mirror image of the reference reflector into two output values ​​by determining a certain threshold value (binary level threshold value) (binary processing).

[0045] However, when there is strong radiant light from the high-temperature silicon melt, or when the amount of light increases further in a narrow DPM, the detection value of the optical camera before binarization fluctuates, or noise that is different from the mirror image of the reference reflector, such as molten metal splashes adhering to structural components inside the CZ furnace, becomes more likely to be detected, making it difficult to stably and accurately measure the distance between the reference reflector and the melt surface.

[0046] In addition, for example, when producing silicon single crystals with a diameter of 300 mm or more, if the raw material melt surface vibrates, the reference reflector becomes unclear and the accurate position of the melt surface cannot be detected stably. If the measurement result of the relative distance between the reference reflector and the melt surface is inaccurate, the distance between the melt surface and the heat insulating member cannot be controlled to a predetermined distance with high precision. As a result, silicon single crystals of the desired quality cannot be produced with good productivity.

[0047] The present inventors have conducted extensive research and studies to solve these problems, and have come up with the idea that, in order to measure the distance between the lower end surface of the heat insulating member and the surface of the raw material melt more stably and accurately, the lower end of the heat insulating member located above the surface of the raw material melt may be provided with a through hole to form a dark area where reflection of radiant light is suppressed, and the lower end portion of the heat insulating member located above the surface of the raw material melt may be made a bright area, so that strong light and dark may be provided in the mirror image of the through hole reflected on the surface of the raw material melt, thereby completing the present invention.

[0048] That is, the present invention is a method for measuring a distance between a lower end surface of a heat insulating member and a surface of a raw material melt when a silicon single crystal is pulled up while a magnetic field is applied to the raw material melt in a crucible by the Czochralski method, the method comprising the steps of: A through hole is formed in the lower end surface of the heat insulating member, The distance between the lower end surface of the heat insulating member and the raw material melt surface is actually measured, and the position of the mirror image of the through hole reflected on the raw material melt surface is observed by a fixed point observation device, and then This method for measuring the distance between the lower end surface of the heat insulating member and the raw material melt surface is characterized in that the movement distance of the mirror image is measured by the fixed-point observation device during pulling of the silicon single crystal, and the distance between the lower end surface of the heat insulating member and the raw material melt surface is calculated from the actual measurement value and the movement distance of the mirror image.

[0049] The present invention also relates to a method for controlling the distance between the lower end surface of a heat insulating member and the raw material melt surface, characterized in that the distance between the lower end surface of a heat insulating member and the raw material melt surface, measured by the method for measuring the distance between the lower end surface of a heat insulating member and the raw material melt surface of the present invention, is fed back during pulling of the silicon single crystal, and the crucible or the heat insulating member is moved so that the distance between the lower end surface of the heat insulating member and the raw material melt surface becomes a set value.

[0050] Furthermore, the present invention provides a method for producing a silicon single crystal, characterized in that the method for controlling the distance between the lower end surface of a heat insulating member and the surface of the raw material melt of the present invention is used to control the distance between the lower end surface of the heat insulating member and the surface of the raw material melt, thereby producing a silicon single crystal.

[0051] The present invention will be described in detail below with reference to the drawings, but the present invention is not limited thereto.

[0052] [Silicon single crystal pulling equipment] First, an example of a silicon single crystal pulling apparatus that can be used in the method of measuring the distance between the lower end surface of a heat insulating member and the surface of a raw material melt, the method of controlling said distance, and the method of producing a silicon single crystal according to the present invention will be described with reference to Fig. 1. However, the apparatus in which the present invention can be practiced is not limited to that shown in Fig. 1, and the present invention can also be practiced in other apparatuses.

[0053] The silicon single crystal pulling apparatus (manufacturing apparatus) 100 shown in FIG. 1 comprises a main chamber 9a for accommodating components such as a quartz crucible 1a, a pulling chamber 9b connected above the main chamber 9a, a heat insulating member 11 for controlling the crystal temperature gradient, a gas straightening cylinder 10 connected above the heat insulating member 11, a heater 2 for heating and melting the polycrystalline silicon raw material loaded into the quartz crucible 1a, a graphite crucible 1b for supporting the quartz crucible 1a, insulation materials (insulation cylinder 8a and insulation plate 8b) for preventing heat from the heater 2 from being directly radiated to the main chamber 9a, a wire 5 for pulling the silicon single crystal, a crucible shaft 6 for supporting the quartz crucible 1a and the graphite crucible 1b, and a control device 16 configured to control the positions of the quartz crucible 1a and the graphite crucible 1b via the crucible shaft 6.

[0054] The polycrystalline silicon raw material in the quartz crucible 1a is melted by the heat from the heater 2 to become the raw material melt 3 shown in Fig. 1. The silicon single crystal manufacturing apparatus 100 further includes a magnetic field generating device 12 configured to apply a magnetic field to the raw material melt 3.

[0055] A seed crystal 7 for growing a silicon single crystal 4 is attached to the lower end of the wire 5 .

[0056] In addition, the silicon single crystal manufacturing apparatus 100 further includes a fixed point observation device 14 configured to detect a mirror image of the lower end surface 11a of the heat shield 11 projected onto the liquid surface 3a of the raw material melt 3, and a measurement and calculation device 15 electrically connected to the fixed point observation device 14 and the control device 16.

[0057] The heat shield 11 shown in FIG. 1 will be described in detail later.

[0058] The fixed-point observation device 14 is not particularly limited, but may be, for example, a commonly used optical camera (such as a CCD camera).

[0059] [Method for measuring the distance between the lower end surface of the heat shield and the surface of the raw material melt] The method for measuring the distance between the lower end surface of a heat insulating member and the surface of a raw material melt of the present invention is a method for measuring the distance between the lower end surface of the heat insulating member and the surface of a raw material melt when a silicon single crystal is pulled up while a magnetic field is applied to the raw material melt in a crucible by the Czochralski method, the method comprising the steps of: A through hole is formed in the lower end surface of the heat insulating member, The distance between the lower end surface of the heat insulating member and the raw material melt surface is actually measured, and the position of the mirror image of the through hole reflected on the raw material melt surface is observed by a fixed point observation device, and then The method is characterized in that the moving distance of the mirror image is measured by the fixed-point observation device during pulling of the silicon single crystal, and the distance between the lower end surface of the heat insulating member and the surface of the raw material melt is calculated from the actual measurement value and the moving distance of the mirror image.

[0060] Hereinafter, an example of a method of measuring the distance between the lower end face of the heat insulating member and the raw material melt surface according to the present invention will be described with reference to FIG. 1 again and also to FIGS.

[0061] Fig. 2 is a schematic diagram for explaining an example of a method for measuring the distance between the lower end surface of a heat insulating member and the raw material melt surface of the present invention, and is a diagram showing the movement of the raw material melt surface and the positional relationship of each member. Fig. 3 is a schematic diagram of an example of a mirror image of the lower end surface of a heat insulating member obtained by a fixed point observation device in the arrangement of Fig. 2. Fig. 4 is a schematic diagram of an example of a position change of the mirror image of the lower end surface of a heat insulating member obtained by a fixed point observation device in the arrangement of Fig. 2.

[0062] In the single crystal pulling apparatus 100 shown in Figure 1, a through hole 13 serving as a reference reflector is provided in the lower end surface 11a (hereinafter, heat shield lower end surface 11a) of a heat shield 11 located above the liquid surface 3a of the raw material melt 3 (hereinafter, raw material melt surface 3a), as shown diagrammatically in Figure 2.

[0063] As shown in Fig. 1, the through hole 13 is different from the opening through which the pulled silicon single crystal 4 passes. As shown in Fig. 1, the through hole 13 penetrates the heat shield 11 in a direction substantially parallel to the pulling direction of the silicon single crystal 4, i.e., the crystal growth axis direction. One end of the through hole 13 opens to the lower end surface 11a of the heat shield 11 (lower end face 11a of the heat shield).

[0064] Next, the distance 21 (shown in FIG. 2) between the lower end surface 11a of the heat insulating member and the raw material melt surface 3a is measured, and the position of the mirror image R1 reflected on the raw material melt surface 3a of the through hole 13 serving as the reference reflector is observed by the fixed point observation device 14 as shown in FIG. 2. FIG. 3 shows the mirror image R of the lower end surface 11a of the heat insulating member observed by the fixed point observation device 14 in the arrangement of FIG. 2, and the mirror image R1 of the through hole 13 included therein. Then, during pulling of the silicon single crystal 4, the moving distance B of the mirror image of the through hole 13 is measured by the fixed point observation device 14, and the distance 21 between the lower end surface 11a of the heat insulating member and the raw material melt surface 3a (hereinafter, also referred to as DPM 21) is calculated from the actual measurement value A and the moving distance B of the mirror image. A specific example of the calculation means will be described later. FIG. 4 shows a schematic diagram of the movement of the mirror image of the through hole 13 from position R1 to position R2 in the mirror image R observed by the fixed point observation device 14.

[0065] In this way, by using the through hole 13 formed in the lower end surface 11a of the heat shield as the reference reflector, the radiant light from the raw material melt 3 passes through the through hole 13, resulting in an extremely small amount of reflected light, and a strong light-dark contrast can be formed between the reflective parts of the lower end surface 11a of the heat shield and other parts than the through hole 13. This suppresses fluctuations in the detection value due to binary value processing, and allows for stable and accurate measurement of the distance between the lower end surface 11a of the heat shield and the raw material melt surface 3a.

[0066] Moreover, the through-hole 13 is not particularly limited in shape or size as long as it can pass radiant light and form a dark portion. For example, the horizontal cross-sectional shape may be circular or polygonal, and the diameter or circumscribing circle of the through-hole 13 may be 4 mm or more and 20 mm or less (more preferably 8 mm or more and 15 mm or less), and the area of ​​the through-hole 13 at the upper end and the lower end may be different, and may not necessarily be the same. There is no need to particularly limit the installation position of the through-hole 13 as long as the reflected image (mirror image) of the lower end surface 11a of the heat insulating member including the through-hole 13 can be observed by the fixed-point observation device 14. As mentioned above, the through-hole 13 is different from the opening of the heat insulating member 11 through which the silicon single crystal 4 to be pulled passes. The direction in which the through-hole 13 extends is not particularly limited, but it is preferable that the through-hole 13 extends in a direction substantially parallel to the crystal growth axis direction (vertical direction).

[0067] In addition, since the radiant light from the raw material melt 3 passes through the through hole 13, even if the raw material melt 3 or the entire inside of the furnace (main chamber 9a) becomes hotter and the radiant light increases, or even if the DPM (the distance between the lower end 11a of the heat shield and the raw material melt surface 3a) is narrow and the amount of light increases due to multiple radiation from the raw material melt surface 3a and the lower end surface 11a of the heat shield, there is a stronger contrast between light and dark between the mirror image of the through hole 13 through which the radiant light passes and the mirror image of other parts of the lower end surface 11a of the heat shield which become brighter due to reflection. Therefore, the distance between the lower end surface 11a of the heat shield and the raw material melt surface 3a can be measured accurately even under the influence of strong radiant light from the high-temperature raw material melt 3 or in a state where the amount of light increases further due to a narrow DPM.

[0068] Furthermore, compared to the case where white quartz or transparent quartz, which has a lower emissivity than the graphite parts used in the heat shield, is used as the reference reflector, the through hole 13, which forms a dark area, forms a light-dark contrast with respect to the splash portion of the silicon melt adhering to the lower end of the heat shield, which may cause erroneous detection when white quartz or transparent quartz, which has a lower emissivity, is used, and is therefore effective in preventing erroneous detection of the splash portion.

[0069] Furthermore, when white quartz or transparent quartz is used as the reference reflector, problems such as breakage due to thermal load during long-term use, contamination due to falling during operation, and changes in detection values ​​due to deformation occur, but the through-hole 13 provided as the reference reflector is a hollow with no substance that could lead to breakage, so such problems do not occur.

[0070] In addition, if the heat shield 11 has a through hole 13 provided as a reference reflector, there are no other dark areas other than the through hole 13 on the lower end surface 11a of the heat shield, making it very easy to detect. This makes it possible to perform DPM measurement and control even under weak magnetic field strength conditions where it was previously difficult to detect a reflector, and it can also be applied to horizontal magnetic fields with a central magnetic field strength of several tens of G and cusp magnetic fields with a central magnetic field strength of almost 0 G.

[0071] An example of measuring the distance 21 between the heat insulating member lower end surface 11a and the raw material melt surface 3a is shown in Fig. 5. Fig. 5 is a diagram for explaining an example of a method for measuring the distance between the heat insulating member lower end surface and the raw material melt surface.

[0072] A case will be described in which a seed crystal 7 is used as shown in FIG. 5 to actually measure the distance 21 between the lower end surface 11a of the heat insulating member and the raw material melt surface 3a.

[0073] First, the reference position detector 18 disposed above the raw material melt surface 3a detects the lower end 7T of the seed crystal 7 for growing the silicon single crystal 4 shown in Fig. 1, and the position is set as the seed crystal reference position 7a. In Fig. 5, the seed crystal 7 is held by a seed crystal holder 19 connected to the lower end of the wire 5.

[0074] Meanwhile, a distance 22 from the lower end surface 11a of the heat insulating member to the seed crystal reference position 7a is obtained in advance.

[0075] Thereafter, the lower end 7T of the seed crystal 7 is lowered between the raw material melt level 3a and the lower end surface 11a of the heat insulating member 11 having the through hole 13 serving as a reference reflector. At this time, the lower end 7T of the seed crystal 7 is stopped at a predetermined reference position 7b where the position of the raw material melt level 3a becomes the desired DPM 21 when the crucibles 1a and 1b are later raised and brought into contact with the liquid level 3a of the raw material melt 3.

[0076] Then, the crucibles 1a and 1b are raised using the crucible shaft 6, and the lower end 7T of the seed crystal 7 is brought into contact with the liquid surface 3a of the raw material melt 3 at the above-mentioned predetermined reference position 7b. The position 7b of this contact becomes the reference position when the seed crystal raw material melt reaches the liquid, and the distance 23 between this position 7b and the seed crystal reference position 7a can be measured. The distance 21 between the heat insulating member lower end surface 11a and the raw material melt surface 3a can be actually measured and the actual measurement value A can be obtained using the measured value of this distance 23 and the distance 22 from the heat insulating member lower end surface 11a to the seed crystal reference position 7a, which is known in advance.

[0077] In this way, the distance 21 between the heat insulating member lower end surface 11a and the raw material melt surface 3a is measured using the seed crystal 7 to obtain the measured value A, and thus the distance 21 between the heat insulating member lower end surface 11a and the raw material melt surface 3a can be measured with a simple operation. Furthermore, since the distance 21 between the heat insulating member lower end surface 11a and the raw material melt surface 3a is measured using the seed crystal 7, there is little risk of the raw material melt 3 being contaminated by impurities, and a high-quality silicon single crystal can be grown. Furthermore, by lowering the lower end 7T of the seed crystal 7 between the heat insulating member lower end surface 11a and the raw material melt surface 3a, there is no risk of the raw material melt 3 adhering to the heat insulating member 11 when the crucibles 1a and 1b are raised and the seed crystal 7 comes into contact with the raw material melt surface 3a.

[0078] To detect the contact between the seed crystal 7 and the raw material melt 3, the wire 5 suspending the seed crystal 7 and the crucible shaft 6 supporting the crucibles 1a and 1b filled with the raw material melt 3 are electrically connected by a measuring device 17 as shown in Fig. 5. Then, when the crucibles 1a and 1b are raised and the raw material melt 3 comes into contact with the seed crystal 7, the measuring device 17 electrically detects this. The crucible position at this time is recorded, and the distance 21 between the lower end surface 11a of the heat insulating member and the raw material melt surface 3a at this crucible position, i.e., the position of the raw material melt surface 3a, can be measured.

[0079] Then, using the method described above, an actual measurement value A of the distance 21 between the lower end surface 11a of the heat insulating member and the raw material melt surface 3a is obtained, and at the same time, the position of the mirror image R1 projected and reflected on the raw material melt surface 3a of the through hole 13, which serves as a reference reflector, is observed by a fixed-point observation device 14.

[0080] Next, the silicon single crystal 4 is pulled up using a silicon single crystal pulling apparatus 100 shown in FIG.

[0081] Such a pulling apparatus 100 can pull up a silicon single crystal 4 as follows. Before measuring the distance 21 between the heat insulating member lower end surface 11a and the raw material melt surface 3a, a high-purity polycrystalline silicon raw material is placed in the quartz crucible 1a and heated to the melting point of silicon (about 1420°C) or higher by the heater 2 arranged around the graphite crucible 1b to melt the raw material melt 3, thereby preparing the raw material melt 3. Then, the distance 21 between the heat insulating member lower end surface 11a and the raw material melt surface 3a is measured as described above, and the position of the mirror image R1 reflected by the raw material melt surface 3a of the through hole 13, which is the reference reflector, is observed by the fixed-point observation device 14.

[0082] Next, a method for measuring the distance 21 between the lower end surface 11a of the heat insulating member and the raw material melt surface 3a while the silicon single crystal 4 is being pulled will be described.

[0083] When pulling up a silicon single crystal from the raw material melt 3 housed in the quartz crucible 1a, the liquid level 3a of the raw material melt 3 drops. For example, as shown in FIG. 2, when the liquid level 3a of the raw material melt 3 drops to a new position of the liquid level 3a', the position of the mirror image of the through hole 13 serving as the reference reflector projected onto the liquid level 3a of the raw material melt 3 moves from the position R1 captured by the fixed-point observation machine 14 as described above before the silicon single crystal 4 is pulled up to the position R2 shown in FIG. 2 corresponding to the liquid level 3a'.

[0084] At this time, the moving distance B of the mirror image from the position R1 to the position R2 as shown in FIG. 4 is converted by the measurement arithmetic unit 15 connected to the fixed-point observation machine 14 into the moving distance C of the liquid level of the raw material melt from the position 3a to the position 3a'. This conversion can be geometrically calculated as follows from the positions and angles of the fixed-point observation machine 14 and the like. Let C be the moving distance of the raw material melt 3, B be the moving distance of the mirror image, and θ be the reflection angle of the mirror image. Then, B = 2Csinθ is obtained. From this equation, the moving distance C of the liquid level 3a of the raw material melt 3 can be obtained from the moving distance B of the mirror image obtained by the fixed-point observation machine 14. And the DPM 21 when the mirror image of the through hole 13 is at the position R2 can be obtained by adding the moving distance C of the liquid level 3a of the raw material melt 3 to the actually measured value A obtained previously.

[0085] At this time, if θ > 30°, then C < B, so the minute movement of the liquid level 3a of the raw material melt 3 can be greatly enlarged by the movement of the mirror image of the through hole 13, and the change amount (moving distance) C from the actually measured value A of the DPM 21 can be measured.

[0086] However, in order to calculate the DPM 21 more accurately, before pulling up the silicon single crystal 4, for example, based on the moving distance B of the mirror image of the through hole 13 observed when the crucible position, that is, the liquid level 3a of the raw material melt 3, is further lowered by 20 mm from the reference position, a conversion coefficient may be obtained in advance.

[0087] By doing this, simply by capturing the movement distance B of the mirror image of through hole 13 with fixed-point observation device 14 while silicon single crystal 4 is being pulled, it is possible to accurately calculate DPM 21 between lower end surface 11a of heat insulating member 11 and liquid level 3a of raw material melt 3 from actual measurement value A of DPM before pulling silicon single crystal 4 and movement distance C of liquid level 3a of raw material melt 3 calculated from movement distance B of the mirror image of through hole 13. Calculation of DPM 21 before pulling silicon single crystal 4 can be made by crucible position control device 16 based on actual measurement value A.

[0088] In this way, according to the method of measuring the distance between the lower end surface of the heat insulating member and the raw material melt surface of the present invention, the distance between the lower end surface of the heat insulating member and the raw material melt surface can be measured stably and accurately even during pulling of a silicon single crystal.

[0089] [Method of controlling the distance between the lower end surface of the heat shield and the surface of the raw material melt] The method for controlling the distance between the lower end surface of the heat insulating member and the raw material melt surface of the present invention is characterized in that the distance between the lower end surface of the heat insulating member and the raw material melt surface, measured by the method for measuring the distance between the lower end surface of the heat insulating member and the raw material melt surface of the present invention, is fed back during pulling of the silicon single crystal, and the crucible or the heat insulating member is moved so that the distance between the lower end surface of the heat insulating member and the raw material melt surface becomes a set value.

[0090] In the method of the present invention for controlling the distance between the lower end surface of the heat insulating member and the raw material melt surface, in order to control the distance between the lower end surface of the heat insulating member and the raw material melt surface, the movement distance of the mirror image is observed at fixed points during pulling of the silicon single crystal, and the distance between the lower end surface of the heat insulating member and the raw material melt surface, measured by the method of the present invention for measuring the distance between the lower end surface of the heat insulating member and the raw material melt surface described above, is fed back at any time.

[0091] 1 is used, the crucibles 1a and 1b or the heat insulating member 11 are moved so that the distance 21 between the heat insulating member lower end surface 11a and the raw material melt surface 3a becomes a set value. The crucible can be moved by vertically moving the crucible axis 6, and the heat insulating member 11 can be moved by, for example, vertically moving the straightening cylinder 10 connected to the heat insulating member 11 using a straightening cylinder moving mechanism (not shown).

[0092] In this way, by feeding back the DPM measurement value during pulling of the silicon single crystal and moving the crucible or the heat insulating member so that the distance between the lower end surface of the heat insulating member and the raw material melt surface becomes a set value, the distance between the lower end surface of the heat insulating member and the raw material melt surface can be controlled with high precision.

[0093] Here, the reason why the distance between the lower end surface of the heat insulating member and the surface of the raw material melt can be controlled with high precision will be described in more detail.

[0094] 6 is an enlarged schematic cross-sectional view of a part of the silicon single crystal pulling apparatus shown in FIG. 1. For example, as shown in FIG. 6, incident light 31 is incident on the raw material melt surface 3a, and at least a part of it becomes reflected light 32 at the raw material melt surface 3a and enters the lower end surface 11a of the heat insulating member. This reflected light 32 passes through the through hole 13 opened in the lower end surface 11a of the heat insulating member as light 33, so that reflection is suppressed at the through hole 13 portion. In addition, radiant light 34 from the raw material melt 3 also passes through the through hole 13, so that reflection is suppressed at the through hole 13 portion. On the other hand, the portion of the lower end surface 11a of the heat insulating member other than the through hole 13 reflects at least a part of the reflected light 32 and radiant light 34 from the raw material melt 3, and the reflected light reaches the raw material melt 3. As a result, in a mirror image R of the lower end surface 11a of the heat insulating member projected onto the raw material melt surface 3a and observed by a fixed point observation device 14, the through hole 13 appears as a dark area R1 and other areas appear as bright areas, as shown in FIG.

[0095] In this way, by using the through hole 13 opened in the heat shield lower end surface 11a as the reference reflector, light such as radiant light from the raw material melt 3 passes through the through hole 13, so that the amount of reflected light is extremely small, and in the mirror image R, a strong light-dark contrast can be formed between the portion R1 of the through hole 13 and the reflective portion of the heat shield lower end surface 11a other than the through hole 13. Since the mirror image R obtained in this way has suppressed fluctuations in the detection value due to binary value processing, it can exhibit high reliability as a mirror image in a state where the distance (DPM) 21 between the heat shield lower end surface 11a and the raw material melt surface 3a is set to a set value.

[0096] As explained above, the method for measuring the distance between the lower end face of the heat insulating member and the surface of the raw material melt of the present invention makes it possible to measure the distance (DPM) between the lower end face of the heat insulating member and the surface of the raw material melt more stably and accurately even during pulling of a silicon single crystal. In the control method of the present invention, the measurement result is fed back, and the crucible or the heat insulating member is moved so that the DPM becomes the set value, thereby making it possible to correct the deviation of the DPM from the set value at any time.

[0097] Therefore, according to the method of controlling the distance between the lower end surface of the heat insulating member and the raw material melt surface of the present invention, the distance between the lower end surface of the heat insulating member and the raw material melt surface can be controlled with high precision even while the silicon single crystal is being pulled up.

[0098] [Silicon single crystal manufacturing method] The silicon single crystal production method of the present invention is characterized in that the distance between the lower end surface of a heat insulating member and the raw material melt surface is controlled by the method of controlling the distance between the lower end surface of a heat insulating member and the raw material melt surface of the present invention, thereby producing a silicon single crystal.

[0099] When growing high-quality silicon single crystals such as defect-free crystals, the distance (DPM) between the raw material melt and the heat shield placed above it is very important. This is because the margin for producing defect-free crystals is very narrow, and this must be achieved in all directions in the crystal plane. The temperature gradient around the crystal changes significantly by changing the DPM, so the DPM can be used as a control factor to equalize the temperature gradient between the center and the periphery. Furthermore, since the in-plane temperature gradient changes along the crystal length, in order to create a defect-free crystal in the entire length direction, the DPM must be changed according to the crystal length.

[0100] Therefore, by controlling the distance between the lower end surface of the heat insulating member and the raw material melt surface using the above-mentioned method of the present invention, and producing a silicon single crystal, the distance between the lower end surface of the heat insulating member and the raw material melt surface can be controlled with high precision, so that the crystal axis temperature gradient in the crystal growth axis direction can be controlled extremely precisely, and high-quality silicon single crystals can be produced efficiently and with high productivity.

[0101] Furthermore, by making the silicon single crystal produced by the above-mentioned method for producing a silicon single crystal defect-free all over in the radial direction, the yield in the production of the silicon single crystal with defect-free regions is further improved.

[0102] In this way, by producing silicon single crystals using the silicon single crystal production method of the present invention, the distance between the lower end surface of the heat shield and the raw material melt surface can be measured and controlled with high precision, thereby enabling extremely precise control of the crystal axis temperature gradient in the crystal growth axis direction, and making it possible to efficiently produce high-quality silicon single crystals. EXAMPLES

[0103] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0104] (Example) In the examples, silicon single crystals were pulled in the following manner.

[0105] As a silicon single crystal pulling apparatus, a silicon single crystal pulling apparatus 100 having the same configuration as that shown in Fig. 1 was prepared. The heat shield 11 used was a long-life molten metal splash attached to its lower end surface 11a, with a circular through hole 13 with a diameter of 10 mm provided as a reference reflector at a position where its mirror image could be measured by a fixed-point observation device 14.

[0106] In the prepared silicon single crystal pulling apparatus 100, 360 kg of silicon polycrystalline raw material was filled into a quartz crucible 1a with an aperture of 800 mm (for pulling silicon single crystals with a diameter of 300 mm). The silicon polycrystalline raw material was melted by a heater 2 to form a raw material melt 3, and then a horizontal magnetic field with a central magnetic field strength of 4000 G was applied to this raw material melt by a magnet 12.

[0107] Then, the seed crystal 7 was used to measure the distance (DPM) 21 between the lower end surface 11a of the heat insulating member 11 and the liquid level 3a of the raw material melt 3. The measurement method was as follows. First, as shown in FIG. 5, the lower end 7T of the seed crystal 7 was detected by the reference position detector 18, and the position was set as the seed crystal reference position 7a. The distance 22 from the lower end surface 11a of the heat insulating member to the seed crystal reference position 7a was obtained from the dimensions of the gas straightening tube and the heat insulating member 11. Then, the seed crystal 7 was lowered, and the crucibles 1a and 1b were raised to bring the liquid level 3a of the raw material melt 3 into contact with the lower end 7T of the seed crystal 7, and the lower end 7T of the seed crystal 7 was stopped at a position where the liquid level 3a of the raw material melt 3 was at a desired position. Next, the crucibles 1a and 1b were raised to bring the lower end 7T of the seed crystal 7 into contact with the liquid level 3a of the raw material melt 3. Then, the distance 23 from this contact position (reference position when the seed crystal raw material melt reaches the liquid) 7b to the seed crystal reference position 7a was obtained. The difference between this distance 23 and the previously obtained distance 22 from the lower end surface 11a of the heat insulating member to this seed crystal reference position 7a was actually measured as the distance (DPM) 21 between the lower end surface 11a of the heat insulating member 11 and the liquid level 3a of the raw material melt 3. The contact between the liquid level 3a of the raw material melt 3 and the seed crystal 7 was detected by the actual measurement device 17 sensing that electricity flowed from the seed crystal 7 to the crucible axis 6. The value of the distance 21 at the moment of detection was set as the set value A. At this time, the position R1 of the mirror image of the through hole 13 projected on the raw material melt level 3a was detected by the fixed point observation device (camera) 14. At this time, the conversion coefficient was also determined at the same time. That is, the movement distance B of the mirror image R1 of the through hole 13 was measured when the crucibles 1a and 1b were lowered by 20 mm (the movement distance C of the raw material melt surface shown in Figure 2), and the movement distance C of the liquid surface 3a of the raw material melt 3 was calculated from the movement distance B of the mirror image of the through hole 13 during pulling up of the silicon single crystal 4.

[0108] After completing the above settings, the setting value A of DPM21 was set to 100 mm, 50 mm, and 20 mm, respectively, and a magnetic field was applied under each of the following magnetic field conditions: a horizontal magnetic field with central magnetic field strengths of 5000 G, 3000 G, 1000 G, 500 G, and 10 G, and a cusp magnetic field with a crucible wall (straight body) magnetic field strength of 2000 G. While measuring and controlling the DPM21 to the setting value A, a total of 18 silicon single crystals were pulled, one at a time under each condition.

[0109] (Comparative Example) In the comparative example, a heat shield with a service life similar to that used in the example was prepared, a concave false detection suppression mechanism was provided on the surface of the lower end of the heat shield, and a reference reflector with a white quartz tip was attached inside the concave false detection suppression mechanism. A silicon single crystal was pulled in the same manner as in the example, using a silicon single crystal manufacturing apparatus with the same configuration as in Figure 1, while controlling the DPM21 to the measurement and set value A.

[0110] [result] The results of DPM21 detection during pulling of one crystal under each of the conditions in the examples and comparative examples are shown in Tables 1 and 2 below.

[0111] [Table 1]

[0112] [Table 2]

[0113] In Tables 1 and 2 above, a false detection is defined as a deviation of 0.2% or more from the average detection value of DPM21 per minute compared to the average detection value one minute earlier. The results are indicated with an ◯ if there were no false detections during pulling of the crystal body, a △ if there were false detections, albeit at a low frequency, and an × if DPM measurement and control were impossible due to a false detection.

[0114] As shown in Table 2, in the comparative example, as the set value A of DPM21, i.e., the distance 21 between the lower end surface 11a of the heat shield 11 and the liquid level 3a of the raw material melt 3, becomes smaller (the set DPM becomes narrower), the number of false detections increases. This is considered to be due to the fact that, in the comparative example, the amount of light increases due to multiple radiation between the liquid level 3a of the raw material melt 3 and the lower end surface 11a of the heat shield 11.

[0115] In contrast, in the embodiment, as is clear from Table 1, it is understood that DPM21 can be measured with high accuracy even in a state where the light amount increases with a narrow DPM.

[0116] Furthermore, in the comparative example, as is clear from Table 2, it was difficult to detect the reflector under weak magnetic field strength conditions, whereas in the embodiment, as is clear from Table 1, it was possible to measure and control the DPM21 even in a horizontal magnetic field with a central magnetic field strength of several tens of G and a cusp magnetic field with a central magnetic field strength of approximately 0 G.

[0117] That is, in the example, the distance between the raw material melt surface and the lower end surface of the heat insulating member could be measured and controlled more accurately than in the comparative example.

[0118] Thus, according to the present invention, even under conditions where false detection or detection itself was difficult in the past, the through-hole to be detected passes through the radiant light from the raw material melt, and a strong light-dark contrast can be formed between the reflective part of the lower end part of the heat shield other than the through-hole, making detection by, for example, binary value processing easy, and enabling stable and highly accurate measurement and control of DPM. And, by manufacturing silicon single crystals while controlling DPM with such stability and high accuracy, the present invention makes it possible to extremely precisely control the crystal axis temperature gradient in the silicon single crystal growth axis direction, and efficiently produce high-quality silicon single crystals.

[0119] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention.

Claims

1. A method for pulling a silicon single crystal while applying a magnetic field to a raw material melt in a crucible by the Czochralski method, comprising: disposing a heat insulating member above a raw material melt surface; and measuring a distance between a lower end surface of the heat insulating member and the raw material melt surface, A through hole is formed in the lower end surface of the heat insulating member, The distance between the lower end surface of the heat insulating member and the raw material melt surface is measured to obtain an actual measurement value, and the position of the mirror image of the through hole reflected on the raw material melt surface is observed by a fixed point observation device, a fixed-point observation device that measures the movement distance of the mirror image during pulling of the silicon single crystal, and calculates the distance between the lower end surface of the heat shield and the raw material melt surface from the actual measurement value and the movement distance of the mirror image.

2. 2. The method for measuring the distance between a lower end surface of a heat shield and a raw material melt surface according to claim 1, characterized in that, in observing the position of the mirror image of the through hole, the through hole is detected as a dark area and a part other than the through hole is detected as a bright area in the mirror image of the lower end of the heat shield projected onto the raw material melt surface.

3. 3. The method for measuring the distance between the lower end surface of the heat insulation member and the raw material melt surface according to claim 1 or 2, characterized in that, when actually measuring the distance between the lower end surface of the heat insulation member and the raw material melt surface, a reference position detector arranged above the raw material melt detects the lower end of a seed crystal for growing the silicon single crystal and sets it as a reference position, and then the lower end of the seed crystal is lowered to between the lower end surface of the heat insulation member and the raw material melt surface, and the crucible is raised to bring the lower end of the seed crystal into contact with the raw material melt surface, and the distance between the lower end surface of the heat insulation member and the raw material melt surface is measured based on the distance from the contact position to the reference position and the distance from the lower end surface of the heat insulation member to the reference position.

4. 4. The method for measuring the distance between the lower end surface of the heat insulating member and the surface of the raw material melt according to claim 1, wherein the central magnetic field strength of the applied magnetic field is a horizontal magnetic field of 10 G to 5000 G.

5. 4. The method for measuring the distance between a lower end surface of a heat insulating member and a surface of a raw material melt according to claim 1, wherein the applied magnetic field is a cusp magnetic field.

6. 6. The method for measuring the distance between the lower end surface of a heat shield and the surface of a raw material melt according to claim 1, wherein the horizontal cross-sectional shape of the through hole is circular or polygonal, and the diameter or the diameter of the circumscribed circle is 4 mm or more and 20 mm or less.

7. 7. The method for measuring the distance between the lower end face of the heat insulating member and the surface of the raw material melt according to claim 6, wherein the diameter of the through hole or the diameter of the circumscribing circle is set to 8 mm or more and 15 mm or less.

8. 8. A method for controlling the distance between the lower end surface of a heat insulating member and the raw material melt surface, comprising: feeding back the distance between the lower end surface of a heat insulating member and the raw material melt surface measured by the method for measuring the distance between the lower end surface of a heat insulating member and the raw material melt surface described in any one of claims 1 to 7 during pulling of the silicon single crystal; and moving the crucible or the heat insulating member so that the distance between the lower end surface of the heat insulating member and the raw material melt surface becomes a set value.

9. 9. A method for producing a silicon single crystal, comprising controlling a distance between a lower end surface of a heat insulating member and a surface of a raw material melt by a method for controlling a distance between the lower end surface of a heat insulating member and a surface of the raw material melt according to claim 8, thereby producing a silicon single crystal.

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