Method for manufacturing silicon single crystal

Abstract

To provide a method for manufacturing a silicon single crystal using a crucible protective sheet which is hard to be consumed even if it is used for long time crystal-pulling such as multi-pulling.SOLUTION: A method for manufacturing a silicon single crystal by a CZ method in which an energization time of a heater for heating a silicon raw material in one time pulling batch is 500 hours or more comprises pulling the silicon single crystal in a state of placing a carbon crucible protective sheet between a quartz crucible and a carbon support crucible. The carbon crucible protective sheet is characterized such that when a measurement tank having a capacity of 2,000 cc and an opening area of an air vent of 490 mm2 is prepared, and the air vent is connected to one main surface side of the crucible protective sheet in a state of decompressing the inside of the measurement tank to 200 Pa or less, and the other main surface side of the crucible protective sheet is released to the atmosphere, a pressure change amount inside the measurement tank at the lapse of 30 minutes after starting the atmospheric air release becomes 104.9 Pa or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a crucible protection sheet used for pulling silicon single crystals by the Czochralski method (CZ method), and a method for producing silicon single crystals using the same. [Background technology]

[0002] Most silicon single crystals used as substrate materials for semiconductor devices are produced by the CZ method. In the CZ method, a seed crystal is immersed in silicon melt contained in a crucible, and the seed crystal is gradually raised while the seed crystal and crucible are rotated, causing a single crystal to grow at the bottom of the seed crystal. The CZ method makes it possible to produce large-diameter silicon single crystals with a diameter of 300 mm or more with a high yield.

[0003] In the CZ method, the crucible that contains the silicon melt has a double structure with an inner quartz crucible and an outer graphite support crucible, and the quartz crucible is placed in the support crucible inside the pulling furnace. For example, Patent Document 1 describes a support crucible made of a carbon fiber reinforced carbon composite material (carbon composite).

[0004] Quartz crucibles are made of glass and are prone to cracking and chipping, so they must be handled with care when placed in a support crucible. Another problem is that SiO gases generated from the quartz crucible can react with the carbon support crucible, causing it to turn into SiC or reduce in thickness.

[0005] To address this problem, a carbon protective sheet is interposed between the quartz crucible and the support crucible (see, for example, Patent Document 1). Because the support crucible, which is a molded body made of carbon composite, is expensive, it is preferable to minimize its wear. Interposing a carbon sheet can prevent reactions between the support crucible and the quartz crucible, thereby extending the life of the support crucible. Furthermore, it can cushion impacts on the quartz crucible when it is placed inside the support crucible, and also makes it easier to remove the quartz crucible from the support crucible.

[0006] Regarding crucible protection sheets for pulling silicon single crystals, for example, Patent Document 2 describes a crucible protection sheet made of expanded graphite, having a thermal conductivity of 120 W / (m·K) in the plane direction, and a compression rate of 20% or more when compressed in the thickness direction with a pressure of 34.3 MPa. Also, Patent Document 3 describes a crucible protection sheet made of expanded graphite, having a total ash content of 100 massppm or less, and having a weight percentage of specific elements of multiple impurities of 3 massppm or less. Patent Document 4 describes a crucible protection sheet having a gas permeability of 1.0×10 -4 cm 2 / s or less, and the bulk density is 0.5 to 1.6 Mg / m 3 The document describes a crucible protection sheet made of a graphite expansion sheet. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-245155 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-19138 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-81388 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-215162 Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, with the improvement of crystal pulling technology, the so-called multi-pulling process has become more common. In multi-pulling, multiple silicon single crystals are pulled in one pulling batch, which means that the crystal pulling time is very long, and the heater current time can exceed 500 hours. When the crystal pulling time is so long, the thermal load on the furnace components becomes very large, and the crucible protection sheet is completely worn out during the crystal pulling process. This not only accelerates the wear of the supporting crucible, but also causes a sudden drop in the oxygen concentration in the silicon single crystal, resulting in the failure to meet the desired oxygen concentration specification. In recent years, there has been a tendency for the upper and lower limits of the required oxygen concentration specification (manufacturing specification) to narrow, and the upper and lower limits of the oxygen concentration specification (manufacturing specification) have become as narrow as 3 × 10 17 atoms / cm 3 Since very narrow specifications such as the following (ASTM F-121(1979)) are sometimes required, the problem of oxygen concentration not being within the specifications is significant.

[0009] Specifications (manufacturing specifications) are specifications related to the quality of silicon single crystals that are set in advance based on customer specifications before the silicon single crystals are manufactured, and refer to the range of allowable quality for silicon single crystals when manufacturing them. Oxygen concentration specifications are the allowable range for the oxygen concentration of silicon single crystals. Generally, oxygen concentration specifications have upper and lower limits, and silicon single crystals are manufactured so that their oxygen concentration falls within that range. Single crystals with oxygen concentrations within that range are considered acceptable products, and if they meet other quality requirements, they are subsequently processed into wafer products and shipped. However, single crystals with oxygen concentrations outside that range are rejected and do not become wafer products.

[0010] The above-mentioned problem of oxygen concentration being out of specification never occurred in the first and second pieces of multi-pulling, but only occurred when the third piece was pulled. This is a new issue that became apparent when the heater energization time was extremely long, at over 500 hours. Furthermore, the above problem occurred when the upper and lower limits of the oxygen concentration spec (manufacturing specification) were 3 x 1017 atoms / cm 3 This is a problem that occurs when producing the following silicon single crystals, and is a problem that has become more pronounced due to the requirement for narrow oxygen concentration specifications.

[0011] Therefore, an object of the present invention is to provide a crucible protective sheet that is resistant to wear even when used for long-term crystal pulling such as multi-pulling, etc. Another object of the present invention is to provide a method for producing a silicon single crystal using such a crucible protective sheet. [Means for solving the problem]

[0012] As a result of extensive research to solve the above problems, the inventors of the present application discovered that since wear of the crucible protective sheet occurs due to a chemical reaction with silicon monoxide gas generated during the crystal pulling process, the more difficult it is for gas to penetrate into the sheet, the more wear can be prevented, thereby extending the life of the crucible protective sheet.

[0013] The present invention is based on such technical findings, and the crucible protection sheet of the present invention is used in pulling silicon single crystals by the CZ method, in which the heater for heating the silicon raw material is energized for 500 hours or more in one pulling batch, and is a carbon crucible protection sheet to be laid between a quartz crucible and a carbon support crucible, and has a volume of 2000 cc and an opening area of ​​a vent hole of 490 mm 2 a measuring tank having a pressure reduced to 200 Pa or less, the vent hole is connected to one main surface of the crucible protection sheet, and the other main surface of the crucible protection sheet is opened to the atmosphere; the amount of pressure change in the measuring tank is 104.9 Pa or less 30 minutes after the opening to the atmosphere begins.

[0014] According to the present invention, it is possible to provide a crucible protection sheet that is resistant to complete consumption even when used in a long-term crystal pulling process such as multi-pulling, in which the heater is energized for 500 hours or more.

[0015] In the present invention, the term "pulling batch" refers to a series of steps for producing silicon single crystals using the CZ method, starting with the step of placing a quartz crucible containing silicon raw material in a pulling apparatus, followed by the intermediate steps of melting the raw material and pulling the crystal, and ending with the cooling step of cooling the inside of the pulling apparatus so that it can be opened to the atmosphere after the single crystal is produced. In the case of multi-pulling, the intermediate steps of melting the raw material and pulling the crystal are performed multiple times.

[0016] In the present invention, the pressure change amount is preferably not more than 53.5 Pa. This makes it possible to avoid the oxygen concentration in the silicon single crystal from falling outside the specification.

[0017] In the present invention, the thickness of the crucible protection sheet is preferably 0.3 to 0.8 mm, and particularly preferably 0.4 to 0.6 mm, because if the crucible protection sheet is thinner than 0.3 mm, there is a very high probability that the sheet will disappear during crystal pulling and the supporting crucible will deteriorate, and if it exceeds 0.8 mm, the flexibility will decrease and it will be difficult to lay it inside the supporting crucible.

[0018] In the present invention, the remaining rate of the crucible protective sheet after the completion of a pulling batch is preferably 80% or more. Here, the remaining rate (%) is defined as (sheet weight after use / sheet weight before use) × 100. If the remaining rate of the crucible protective sheet is 80% or more, the probability that the oxygen concentration of the silicon single crystal will be out of specification can be significantly reduced.

[0019] The crucible protective sheet according to the present invention is preferably used in multi-pulling, in which three or more silicon single crystals are pulled in one pulling batch, and the ratio of the length of the portion of the straight body portion (constant diameter portion) of the third silicon single crystal where the oxygen concentration of a silicon wafer cut from a portion after 60% of the crystal length is outside the specification to the total length of the straight body portion (constant diameter portion) of the third silicon single crystal (Oi deviation rate) is preferably 10% or less. According to the present invention, it is possible to prevent the oxygen concentration of the silicon single crystal from being outside the specification due to the crucible protective sheet.

[0020] In the present invention, the upper and lower limits of the oxygen concentration specification (manufacturing specification) of the silicon single crystal are 3×10 17 atoms / cm 3 (ASTM F-121 (1979)) or less. In recent years, the upper and lower limits of the oxygen concentration specifications required for silicon single crystals have tended to narrow. The crucible protective sheet according to the present invention is suitable for producing silicon single crystals that satisfy such oxygen concentration specifications.

[0021] In the present invention, the diameter of the silicon single crystal is preferably 300 mm or more. When the diameter of the silicon single crystal is 300 mm or more, a single pulling batch generally takes a long time, and the time for which the heater for heating the silicon raw material is energized also takes a long time, so the crucible protective sheet of the present invention is effective.

[0022] Furthermore, the present invention relates to a method for producing a silicon single crystal by the CZ method, in which the power supply time of a heater for heating a silicon raw material in one pulling batch is 500 hours or more, and the silicon single crystal is pulled in a state in which a carbon crucible protection sheet is placed between a quartz crucible and a carbon support crucible, and the crucible protection sheet has a volume of 2000 cc and an opening area of ​​a vent hole of 490 mm 2 a measuring tank having a pressure reduced to 200 Pa or less, the vent hole is connected to one main surface of the crucible protection sheet, and the other main surface of the crucible protection sheet is opened to the atmosphere; the amount of pressure change in the measuring tank is 104.9 Pa or less 30 minutes after the opening to the atmosphere begins.

[0023] In the present invention, the pressure change amount is preferably not more than 53.5 Pa. This makes it possible to avoid the oxygen concentration in the silicon single crystal from falling outside the specification.

[0024] In the present invention, it is preferable to pull three or more silicon single crystals in one pulling batch. According to the present invention, the crucible protection sheet is unlikely to be completely worn out even when used in such a long crystal pulling process, so that not only can deterioration of the supporting crucible be prevented, but also deviations from the oxygen concentration specification in the silicon single crystal can be prevented.

[0025] In the present invention, the upper and lower limits of the oxygen concentration specification (manufacturing specification) of the silicon single crystal are 3×10 17 atoms / cm 3 (ASTM F-121 (1979)) or less. In recent years, the upper and lower limits of the oxygen concentration specifications required for silicon single crystals have tended to narrow. The crucible protective sheet according to the present invention is suitable for producing silicon single crystals that satisfy such oxygen concentration specifications. [Effects of the Invention]

[0026] According to the present invention, it is possible to provide a crucible protective sheet that is resistant to wear even when used for long-term crystal pulling such as multi-pulling, etc. Furthermore, according to the present invention, it is possible to provide a method for producing a silicon single crystal using such a crucible protective sheet. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram for explaining a method for producing a silicon single crystal according to an embodiment of the present invention, and is a schematic side cross-sectional view showing the configuration of a single crystal production apparatus. [Figure 2] FIG. 2 is a schematic exploded view of a double-structure crucible, illustrating the crucible protection sheet. [Figure 3] FIG. 3 is a schematic diagram showing a method for measuring the amount of pressure change in the crucible protective sheet. [Figure 4] FIG. 4 is a schematic diagram showing a measurement system for the amount of pressure change in the crucible protection sheet. [Figure 5] FIG. 5 is a graph showing the relationship between the pressure change amount and the survival rate of the crucible protective sheet. [Figure 6]FIG. 6 is a graph showing the relationship between the position in the longitudinal direction of the silicon single crystal (crystal length) and the oxygen concentration in the silicon single crystal. [Figure 7] FIG. 7 is a graph showing the Oi deviation rates at 60% and beyond of the crystal length of silicon single crystals grown using sheet samples #1, #5, and #6. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0029] FIG. 1 is a diagram for explaining a method for producing a silicon single crystal according to an embodiment of the present invention, and is a schematic side cross-sectional view showing the configuration of a single crystal production apparatus.

[0030] As shown in Figure 1, the single crystal manufacturing apparatus 1 includes a water-cooled chamber 10, a quartz crucible 11 that holds a silicon melt 2 within the chamber 10, a support crucible 12 that supports the quartz crucible 11, a rotating shaft 13 that supports the support crucible 12, a shaft drive mechanism 14 that drives the rotating shaft 13 to rotate and raise and lower, a heater 15 arranged around the support 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 silicon melt 2, a pulling wire 18 arranged above the quartz crucible 11 and coaxially with the rotating shaft 13, and a wire winding mechanism 19 arranged above the chamber 10.

[0031] The chamber 10 is composed of a main chamber 10a and a long, cylindrical pull chamber 10b connected to the upper opening of the main chamber 10a, and the quartz crucible 11, support crucible 12, heater 15, and heat shield 17 are provided inside the main chamber 10a. The pull chamber 10b is provided with a gas inlet 10c for introducing an inert gas (purge gas) such as argon gas and a dopant gas into the chamber 10, and the bottom of the main chamber 10a is provided with a gas outlet 10d for exhausting the atmospheric gas inside the chamber 10. In addition, a sight glass 10e is provided at the top of the main chamber 10a, and the growth status of the silicon single crystal 3 can be observed through the sight glass 10e.

[0032] The quartz crucible 11 is a cylindrical container made of silica glass and has a bottom. The support crucible 12 is a cylindrical container made of carbon composite and has a bottom, and supports the quartz crucible 11 so that the shape of the quartz crucible 11 softened by heating is maintained. The quartz crucible 11 and the support crucible 12 constitute a double-structure crucible 20 that supports the silicon melt within the chamber 10. Furthermore, a crucible protection sheet 21 is provided between the quartz crucible 11 and the support crucible 12.

[0033] The support 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 support crucible 12, the rotating shaft 13, and the shaft driving mechanism 14 constitute a rotation mechanism and an elevation mechanism for the quartz crucible 11.

[0034] 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 heat the silicon melt 2 to maintain its molten state. The heater 15 may be composed of a single member, or may be a combination of multiple members whose outputs can be controlled independently. The heater 15 is, for example, a resistance heater, and is provided so as to surround the quartz crucible 11 inside the support crucible 12. Furthermore, a heat insulating material 16 is provided outside the heater 15 so as to surround the heater 15, thereby improving the heat retention inside the chamber 10.

[0035] 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 the silicon single crystal 3 from being heated by radiant heat from the heater 15 and the quartz crucible 11. The thermal shield 17 is a substantially cylindrical graphite member, and is provided to cover the area above the silicon melt 2 excluding the pulling path for the silicon single crystal 3.

[0036] Crucible protection sheet 21 is used in the production of silicon single crystals by the CZ method, and is used in a state in which it is laid between quartz crucible 11 and carbon support crucible 12. For this reason, crucible protection sheet 21 must be made of a material with a melting point of 1500°C or higher, and a material with a low melting point, such as resin, cannot be used for crucible protection sheet 21.

[0037] FIG. 2 is a schematic exploded view of the double-structure crucible 20, and is an explanatory diagram of the crucible protection sheet 21.

[0038] 2, crucible 20 is a combination of quartz crucible 11 and support crucible 12, with crucible protection sheet 21 provided between quartz crucible 11 and support crucible 12. Quartz crucible 11 has a substantially cylindrical side wall 11a, a gently curved bottom 11b, and corners 11c provided between side wall 11a and bottom 11b. Support crucible 12 also has a substantially cylindrical side wall 12a, a gently curved bottom 12b, and corners 12c provided between side wall 12a and bottom 12b.

[0039] The crucible protection sheet 21 functions as a buffer material to prevent cracking or chipping of the quartz crucible 11 and to improve adhesion to the inner surface of the support crucible 12. The crucible protection sheet 21 also functions as a protective sheet to reduce wear on the support crucible 12. The crucible protection sheet 21 in FIG. 2 is in a state where it has been deformed to fit the shape of the inner surface of the support crucible 12.

[0040] If the quartz crucible 11 is in direct contact with the inner surface of the support crucible 12, the support crucible 12 reacts with the quartz crucible 11 and gradually thins, shortening the life of the support crucible 12, but if a crucible protection sheet 21 is interposed between them, the crucible protection sheet 21 reacts with the quartz crucible 11 instead of the support crucible 12, so that wear of the support crucible 12 can be suppressed and its life can be extended.

[0041] In this way, the crucible protection sheet 21 is also a component of the crucible 20, and together with the support crucible 12, constitutes the quartz crucible support vessel 23 that supports the quartz crucible 11. While the support crucible 12 is used repeatedly, the crucible protection sheet 21 is replaced with each pulling batch along with the quartz crucible 11, and a new one is used. By interposing the crucible protection sheet 21 of an appropriate thickness between the quartz crucible 11 and the support crucible 12, the adhesion between the quartz crucible 11 and the support crucible 12 via the crucible protection sheet 21 can be improved.

[0042] Crucible protection sheet 21 is a flexible carbon sheet, preferably an expanded graphite sheet. The thickness of the sheet is preferably 0.3 to 0.8 mm, and particularly preferably 0.4 to 0.6 mm. If the sheet is thinner than 0.3 mm, there is a high probability that the sheet will disappear during the crystal pulling process, causing deterioration of support crucible 12. If the sheet is thicker than 0.8 mm, its flexibility will decrease, making it difficult to install it inside support crucible 12.

[0043] The gas permeability of the crucible protection sheet 21 according to this embodiment is very low, with a pressure change of 104.9 Pa or less 30 minutes after starting evacuation from one main surface of the sheet. Here, the pressure change is an index showing how difficult it is for gas to pass through the crucible protection sheet. If the pressure change is large, gas will penetrate into the sheet and the reaction will progress easily. Conversely, if the pressure change is small, gas will not penetrate into the sheet easily, suppressing chemical reactions in the sheet and increasing its durability.

[0044] FIG. 3 is a schematic diagram showing a method for measuring the amount of pressure change in the crucible protective sheet 21. As shown in FIG.

[0045] 3, in measuring the amount of pressure change of the crucible protective sheet 21, the vent 31 of the measurement tank 30, which has been depressurized to about several hundred Pa, is sealed with the crucible protective sheet 21, and the vent 31 is opened to the atmosphere, and the amount of pressure change inside the measurement tank 30 after 30 minutes has elapsed is measured. When the pressure inside the measurement tank 30 at the start of the measurement is P1 and the pressure inside the measurement tank 30 30 minutes after the start of the measurement is P2, the amount of pressure change ΔP is calculated as ΔP = P2 - P1. It is preferable that the degree of vacuum inside the depressurized measurement tank 30 immediately before starting the pressure change measurement test (immediately before opening to the atmosphere) is 200 Pa or less (i.e., P1 ≦ 200 Pa).

[0046] The crucible protection sheet 21 is gradually consumed by a chemical reaction with the quartz crucible 11. During the single crystal pulling process, the crucible protection sheet 21 undergoes a primary reaction at the contact surface with the quartz crucible 11, generating silicon monoxide and carbon monoxide (C + SiO2 = SiO(g) + CO(g)). When this silicon monoxide gas penetrates the inside of the crucible protection sheet 21, the crucible protection sheet 21 undergoes a secondary reaction with the silicon monoxide gas, generating silicon carbide and carbon monoxide (SiO + 2C = SiC + CO). When silicon carbide is generated inside the crucible protection sheet 21, it reacts with the quartz crucible 11, further accelerating consumption of the crucible protection sheet 21 (SiC + 2SiO2 (quartz crucible) = 3SiO(g) + CO(g)).

[0047] Therefore, if gas easily penetrates into the interior of the crucible protective sheet 21, the crucible protective sheet 21 is easily worn out and cannot withstand long-term use. However, if gas does not easily penetrate into the interior of the crucible protective sheet 21, the above-mentioned secondary reaction can be suppressed, and the durability of the crucible protective sheet 21 can be improved.

[0048] The crucible protective sheet 21 according to this embodiment is preferably used for pulling large-diameter silicon single crystals with a diameter of 300 mm or more. This is because the thermal load on the crucible 20 is very large when pulling such large-diameter silicon single crystals, and the effect of the crucible protective sheet 21 according to this embodiment is remarkable. Furthermore, the crucible protective sheet 21 according to this embodiment is preferably used for multiple pulling. This is because the crystal pulling time is very long in the case of multiple pulling, requiring, for example, 300 hours or more for two-pull pulling and 450 hours or more for three-pull pulling, and the effect of the crucible protective sheet 21 according to this embodiment is remarkable.

[0049] When used for multi-pulling, it is preferable that the remaining rate of the crucible protection sheet 21 after three silicon single crystals are pulled without stretching (after the end of the pulling batch) is 80% or more. To achieve this, the pressure change amount of the crucible protection sheet 21 needs to be 104.9 Pa or less. This allows the oxygen concentration of the silicon wafer cut from the latter half of the silicon single crystal (especially after 60% of the crystal length) to be within a predetermined specification (for example, the upper and lower limits of the oxygen concentration are within 3×10 17 atoms / cm 3 The ratio of the portion that deviates from the standard (ASTM F-121(1979)) to the total length of the straight body portion (constant diameter portion) (Oi deviation rate) can be kept to 10% or less.

[0050] The pressure change amount of the crucible protective sheet 21 is preferably 104.9 Pa or less, and more preferably 53.5 Pa or less. If the pressure change amount of the crucible protective sheet 21 is 104.9 Pa or less, the Oi removal rate can be 10% or less. Furthermore, if the pressure change amount of the crucible protective sheet 21 is 53.5 Pa or less, the Oi removal rate can be 10% or less.

[0051] For example, even when a conventional crucible protection sheet was used in a three-piece multi-pulling operation, the first and second silicon single crystals met the desired oxygen concentration specifications, but the third silicon single crystal did not. When the crucible protection sheet was used for a relatively short time, as in the first or second pull, the oxygen concentration in the silicon single crystal did not change significantly. However, when the crucible protection sheet was used for a long time, such as 500 hours or more, as in the third pull, the crucible protection sheet deteriorated significantly in the latter half of the silicon single crystal pulling operation, causing a rapid drop in the oxygen concentration in the silicon single crystal and increasing the probability of it deviating from the desired oxygen concentration specifications.

[0052] However, when the crucible protective sheet 21 according to this embodiment is used, the oxygen concentration in the third silicon single crystal can be kept within the desired oxygen concentration specification, and the yield of silicon single crystals can be increased.

[0053] As described above, the crucible protective sheet 21 according to this embodiment has a pressure change of 104.9 Pa or less, and therefore can withstand a long crystal pulling process such as multi-pulling in which the crystal pulling time (heater energization time) is 500 hours or more. Therefore, the oxygen concentration in the silicon single crystal can be stabilized.

[0054] The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention, and it goes without saying that these modifications are also included in the scope of the present invention. [Example]

[0055] A plurality of crucible protection sheet samples #1 to #6 with different physical properties were prepared, and the thickness and pressure change amount of each sheet sample were measured.

[0056] 4 is a schematic diagram showing a measurement system for the amount of pressure change in a crucible protective sheet. As shown in the figure, the measurement system for the amount of pressure change in a sheet sample includes a measurement tank 30 attached to the sheet sample TP, a vacuum pump 33 that reduces the pressure inside the measurement tank 30, and a manometer 34 (pressure gauge) that measures the pressure inside the measurement tank 30. An air flow path is formed in the thickness direction within a certain range of the sheet sample TP, and the other area is sealed. A vent 31 of the measurement tank 30 is connected to one main surface of the sheet sample TP, and the other main surface is open to the atmosphere. Furthermore, the vacuum pump 33 and manometer 34 are connected in parallel to the vent 31 of the measurement tank 30.

[0057] The sheet sample TP was sealed by covering both sides with acrylic plates 35, sealing the outer periphery of the sheet sample TP with silicon bond 36, and clamping and holding this laminate between two metal plates 38. A rubber packing 37 (O-ring) was provided between the laminate and the metal plates 38. The amount of pressure change was measured using a tank with a volume of 2000 cc and an opening diameter of the tank vent 31 of Φ25 mm (opening area 490 mm 2 ) measurement tank 30 was used.

[0058] Next, to actually measure the amount of pressure change in the sheet sample TP, the inside of the measurement tank 30 was depressurized to below 200 Pa using the vacuum pump 33, and then the valve on the vacuum pump 33 side was closed and the valve on the vent 31 side was opened to start measuring the pressure inside the measurement tank 30. The manometer 34 measured the pressure P1 in the measurement tank 30 at the start of the measurement and the pressure P2 in the measurement tank 30 30 minutes after the start of the measurement, and the amount of pressure change ΔP = P2 - P1 was calculated. The results are shown in Table 1.

[0059] [Table 1]

[0060] A small pressure change ΔP indicates that gas does not easily pass through the sheet. As mentioned above, the reaction between the carbon sheet and the quartz crucible generates SiO gas and CO gas, and then the SiO gas reacts with the carbon sheet again to generate SiC gas. The first reaction between the carbon sheet and the quartz crucible cannot be prevented, but the second reaction between the SiO gas and the carbon sheet can be prevented by preventing gas from entering the carbon sheet.

[0061] If the gas permeability of the sheet sample TP is high, the air on the other main surface side that is open to the atmosphere passes through the sheet sample TP and heads toward the inside of the measurement tank 30, so the pressure inside the measurement tank 30 increases and the amount of pressure change becomes large. On the other hand, if the gas permeability of the sheet sample TP is low, the air on the other main surface side that is open to the atmosphere cannot pass through the sheet sample, so the pressure inside the measurement tank 30 does not increase and the amount of pressure change becomes small.

[0062] Next, sheet samples #1 to #5 were used to perform multiple pulling of silicon single crystals for 300 mm wafers, and the remaining rate of the crucible protection sheet was evaluated after the pulling process was completed. The remaining rate is the weight ratio of the crucible protection sheet expressed as a percentage, and is calculated as (sheet weight after multiple pulling of three sheets) / (initial sheet weight) × 100.

[0063] Figure 5 is a graph showing the relationship between pressure change and survival rate for crucible protection sheet samples #2, #5, and #6. As shown in the figure, the survival rate for sheet sample #2 was 5%, the survival rate for sheet sample #6 was 80%, and the survival rate for sheet sample #5 was 105%. The reason why the survival rate for sheet sample #5 exceeded 100% is thought to be because a portion of sheet sample #5 reacted with silicon monoxide gas and turned into silicon carbide.

[0064] Next, multiple silicon single crystals were pulled using crucible protection sheet samples #1, #5, and #6, and the oxygen concentration of the third silicon single crystal obtained in each multiple pulling process was evaluated. In particular, wafers were cut from the portion after 60% of the crystal length, and the oxygen concentration (ASTM F-121 (1979)) of each wafer was measured to evaluate whether the wafer met the specified oxygen concentration specifications. The crystal length was a relative value, expressed as a percentage, with the start position of the crystal's straight body portion being 0% and the end position of the straight body portion being 100%.

[0065] 6 is a graph showing the relationship between the longitudinal position (crystal length) of silicon single crystals grown using sheet samples #1, #5, and #6 and the oxygen concentration in the silicon single crystals. As shown in the figure, when sheet sample #1 according to the comparative example was used, the oxygen concentration was 10×10 after 60% of the crystal length. 17 atoms / cm 3 However, when the sheet samples #5 and #6 according to the embodiment were used, no such decrease in oxygen concentration was observed.

[0066] 7 is a graph showing the Oi deviation rates at 60% or more of the crystal length for silicon single crystals grown using sheet samples #1, #5, and #6. As shown in the figure, sheet sample #1 (comparative example) with a pressure change of 143.8 Pa had a high Oi deviation rate of approximately 30%, whereas sheet sample #6 (example) with a pressure change of 104.9 Pa had an Oi deviation rate of approximately 7.5%, a good result below 10%. Furthermore, sheet sample #5 (example) with a pressure change of 53.5 Pa had an Oi deviation rate of 0%, an ideal result. [Explanation of symbols]

[0067] 1. Single crystal manufacturing equipment 2. Silicon melt 3. Silicon single crystal 10 chambers 10a Main Chamber 10b Pull chamber 10c Gas inlet 10d Gas exhaust port 10e Sight glass 11 Quartz crucible 11a Side wall part 11b Bottom 11c Corner 12 Support crucible 12a Side wall part 12b bottom 12c Corner 12 Quartz crucible 13 Rotating shaft 14 Shaft drive mechanism 15 Heater 16. Insulation 17 Heat shield 18 wires 19 Wire winding mechanism 20 Crucible 21 Crucible protection sheet 23 Quartz crucible support container 30 Measuring Tank 31 Ventilation hole 33 Vacuum Pump 34 Manometer 35 Acrylic Plate 36 Silicon Bond 37 Rubber packing (O-ring) 38 Metal plate TP sheet sample

Claims

1. A method for producing a silicon single crystal by a CZ method in which the energization time of a heater for heating a silicon raw material in one pulling batch is 500 hours or more, A silicon single crystal is pulled with a carbon crucible protection sheet placed between the quartz crucible and the carbon support crucible. The crucible protection sheet has a volume of 2000 cc and an opening area of ​​the ventilation hole of 490 mm ２ a measuring tank having a pressure of 200 Pa or less, connecting the vent port to one main surface of the crucible protective sheet while reducing the pressure inside the measuring tank to 200 Pa or less, and opening the other main surface of the crucible protective sheet to the atmosphere, wherein the amount of pressure change inside the measuring tank is 104.9 Pa or less 30 minutes after the start of opening to the atmosphere.

2. The method for producing a silicon single crystal according to claim 1 , wherein the pressure change amount is 53.5 Pa or less.

3. The method for producing a silicon single crystal according to claim 1 or 2, wherein three or more silicon single crystals are pulled in one pulling batch.

4. The upper and lower limits of the oxygen concentration specification of the silicon single crystal are 3×10 １７ atoms / cm ３ 3. The method for producing a silicon single crystal according to claim 1, wherein the hardness is equal to or less than ASTM F-121(1979).

5. The method for producing a silicon single crystal according to claim 1 or 2, wherein the silicon single crystal has a diameter of 300 mm or more.

6. preparing a carbon crucible protection sheet; The volume is 200cc and the opening area of ​​the vent is 490mm ２ a measuring tank having a pressure of 200 Pa or less, connecting the vent port to one main surface of the crucible protection sheet, and opening the other main surface of the crucible protection sheet to the atmosphere, and measuring a pressure change amount in the measuring tank 30 minutes after opening to the atmosphere; When the pressure change amount of the crucible protection sheet is 104.9 Pa or less, the crucible protection sheet is placed between the quartz crucible and a supporting crucible made of carbon; and performing a single batch of pulling of silicon single crystals by a CZ method using the quartz crucible accommodated in the support crucible via the crucible protection sheet, The method for producing a silicon single crystal is characterized in that the heater for heating the silicon raw material is energized for 500 hours or more in one pulling batch.

7. 7. The method for producing a silicon single crystal according to claim 6, wherein the step of placing the crucible protection sheet between the quartz crucible and the carbon support crucible is performed when the pressure change amount of the crucible protection sheet is 53.5 Pa or less.

8. The method for producing a silicon single crystal according to claim 6 or 7, wherein three or more silicon single crystals are pulled in one pulling batch.

9. The upper and lower limits of the oxygen concentration specification of the silicon single crystal are 3×10 １７ atoms / cm ３ 8. The method for producing a silicon single crystal according to claim 6, wherein the hardness is equal to or less than ASTM F-121(1979).

10. The method for producing a silicon single crystal according to claim 6 or 7, wherein the silicon single crystal has a diameter of 300 mm or more.

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