JP2023042297A - Crucible protection sheet and manufacturing method of silicon single crystal using the same - Google Patents

Abstract

To provide a crucible protection sheet hard to be worn in using for lifting a crystal for a long time such as a multiple lifting.SOLUTION: A crucible protection sheet 21 according to the invention is used for lifting a silicon single crystal by CZ method, in which an energization time of a heater for heating a silicon raw material in a single lifting batch is 500 hours or more, and is a carbon sheet that is laid between a silica crucible and a support crucible made of carbon. When a measurement tank 30 with a volume of 2000 cc and a vent hole 31 with an opening area of 490 mm2 are prepared, and the vent hole 31 is connected to one main surface side of the crucible protection sheet 21 and the other main surface side of the crucible protection sheet 21 is opened to the atmosphere while an inside of the measurement tank 30 is evacuated to 200 Pa or less, a pressure change inside the measurement tank 30 in 30 minutes after starting opening to the atmosphere is 104.9 Pa or less.SELECTED DRAWING: Figure 3

Description

TECHNICAL FIELD The present invention relates to a crucible protection sheet used for pulling a silicon single crystal by the Czochralski method (CZ method) and a method for producing a silicon single crystal using the crucible protection sheet.

Most of the silicon single crystals used as substrate materials for semiconductor devices are manufactured by the CZ method. In the CZ method, a seed crystal is immersed in a silicon melt contained in a crucible, and the seed crystal and the crucible are rotated while the seed crystal is gradually raised to grow a single crystal at the lower end of the seed crystal. According to the CZ method, large-diameter silicon single crystals with a diameter of 300 mm or more can be produced with a high yield.

In the CZ method, the crucible containing the silicon melt has a double structure with a quartz crucible on the inside and a supporting crucible made of graphite on the outside. be. For example, Patent Literature 1 describes a supporting crucible made of a carbon fiber reinforced carbon composite material (carbon composite).

Since the quartz crucible is made of glass and is easily cracked or chipped, sufficient care must be taken when handling it in the supporting crucible. Moreover, there is also a problem that SiO gas or the like generated from the quartz crucible reacts with the supporting crucible made of carbon, causing the supporting crucible to become SiC or thin.

In order to deal with such problems, a protective sheet made of carbon is interposed between the quartz crucible and the supporting crucible (see, for example, Patent Document 1). Since the support crucible, which is a molded body made of carbon composite, is expensive, it is preferable to suppress its consumption as much as possible, and when a carbon sheet is interposed, the reaction between the support crucible and the quartz crucible is suppressed to extend the life of the support crucible. be able to. In addition, it is possible to absorb the impact on the quartz crucible when the quartz crucible is set in the supporting crucible, and it is also possible to easily take out the quartz crucible from the supporting crucible.

Regarding a crucible protective sheet for pulling a silicon single crystal, for example, in Patent Document 2, it is made of expanded graphite, has a thermal conductivity of 120 W / (m K) in the plane direction, and is applied with a pressure of 34.3 MPa from the thickness direction. A crucible protective sheet having a compressibility of 20% or more when pressurized and compressed is described. Further, Patent Document 3 describes a crucible protective sheet made of expanded graphite, having a total ash content of 100 mass ppm or less, and having a specific element weight ratio of 3 mass ppm or less among a plurality of mixed impurities. Patent Document 4 describes a crucible protection sheet made of an expanded graphite sheet having a gas permeability of 1.0×10 ⁻⁴ cm ² /s or less and a bulk density of 0.5 to 1.6 Mg/m ³ . ing.

JP 2013-245155 A Japanese Unexamined Patent Application Publication No. 2008-19138 JP 2008-81388 A JP 2009-215162 A

In recent years, due to improvements in crystal pulling technology, there have been many opportunities to implement a so-called multi-pulling process. In the multi-pulling, since a plurality of silicon single crystals are pulled in one pulling batch, the crystal pulling time is very long, and the heater power-on time sometimes exceeds 500 hours. If the crystal pulling time is very long, the heat load on the parts in the furnace becomes very large, and the crucible protection sheet is completely worn out during crystal pulling, which not only accelerates the wear of the supporting crucible, but also , there is a problem that the oxygen concentration in the silicon single crystal drops rapidly and the desired oxygen concentration specification cannot be satisfied. In recent years, there is a tendency for the upper and lower limits of the required oxygen concentration specifications (manufacturing specifications) to become narrower, and the width of the upper and lower limits of the oxygen concentration specifications (manufacturing specifications) is 3×10 ¹⁷ atoms/cm ³ or less (ASTM F -121 (1979)), a very narrow specification is sometimes required, so the problem of oxygen concentration being out of specification is remarkable.

The specifications (manufacturing specifications) refer to the specifications related to the quality of the single crystal, which are set in advance based on the customer's specifications before manufacturing the silicon single crystal. It refers to the acceptable range of quality. The oxygen concentration specification is the allowable range for the oxygen concentration of the silicon single crystal. Generally, the oxygen concentration specification has upper and lower limits, and the silicon single crystal is adjusted so that the oxygen concentration falls within that range. manufactured. Single crystals with an oxygen concentration within that range are accepted products, and if other quality conditions are met, wafer products are shipped after subsequent processing, but single crystals with an oxygen concentration outside that range are rejected products. and does not constitute a wafer product.

The above-mentioned problem of the oxygen concentration being out of specification does not occur in the first and second multi-pulling operations, but occurs only when the third pull-up occurs. This is a new problem that has become apparent over time. In addition, the above problem is a problem that occurs when manufacturing a silicon single crystal having an oxygen concentration specification (manufacturing specification) with an upper and lower limit of 3×10 ¹⁷ atoms/cm ³ or less, and a narrow oxygen concentration specification is required. This is a problem that has become conspicuous.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a crucible protective sheet that is less likely to be worn out even when used for long-term crystal pulling such as multi-pulling. Another object of the present invention is to provide a method for producing a silicon single crystal using such a crucible protective sheet.

The inventors of the present application have made intensive studies to solve the above problems, and found that the consumption of the crucible protective sheet is caused by a chemical reaction with silicon monoxide gas generated during the crystal pulling process, so that the gas penetrates into the sheet. It has been found that consumption can be prevented to the extent that it is difficult to remove the crucible, thereby prolonging the life of the crucible protective sheet.

The present invention is based on such technical knowledge, and the crucible protection sheet according to the present invention is a silicon single crystal produced by the CZ method, in which a heater for heating the silicon raw material is energized for 500 hours or more in one pulling batch. A measurement tank is prepared, which is a carbon crucible protection sheet used for pulling up and laid between the quartz crucible and the carbon support crucible, and has a volume of 2000 cc and a vent opening area of 490 mm ² . , when the pressure in the measurement tank is reduced to 200 Pa or less, the ventilation port is connected to one main surface side of the crucible protection sheet, and the other main surface side of the crucible protection sheet is exposed to the atmosphere; The amount of pressure change in the measurement tank is 104.9 Pa or less 30 minutes after the start of the measurement.

According to the present invention, it is possible to provide a crucible protective sheet that is completely resistant to wear even when used in a long-time crystal pulling process such as multi-pulling, in which the heater energization time is 500 hours or longer.

In the present invention, the "pulling batch" collectively expresses a series of manufacturing steps of a silicon single crystal by the CZ method, starting with the step of setting a quartz crucible containing a silicon raw material in a pulling device, It means a series of steps from the raw material melting step and the crystal pulling step, which are intermediate steps, to the cooling step of cooling the inside of the pulling device so that the inside of the pulling device can be opened to the atmosphere after the production of the single crystal. In the case of multi-pulling, the raw material melting step and the crystal pulling step, which are intermediate steps, are performed multiple times.

In the present invention, the pressure change amount is preferably 53.5 Pa or less. This makes it possible to prevent the oxygen concentration in the silicon single crystal from being out of specification.

In the present invention, the thickness of the crucible protection sheet is preferably 0.3 to 0.8 mm, particularly preferably 0.4 to 0.6 mm. This is because if the thickness of the crucible protection sheet is thinner than 0.3 mm, the sheet will disappear during crystal pulling, resulting in deterioration of the supporting crucible. This is because it becomes difficult to lay the cable inside.

In the present invention, it is preferable that the residual ratio of the crucible protective sheet after the completion of the pulling batch is 80% or more. Here, it is defined as residual rate (%)=(seat weight after use/seat weight before use)×100. If the residual ratio of the crucible protective sheet is 80% or more, it is possible to greatly reduce the probability that the oxygen concentration of the silicon single crystal will be out of specification.

The crucible protection sheet according to the present invention is preferably used for multi-pulling in which three or more silicon single crystals are pulled in one pulling batch. It is preferable that the ratio of the length of the portion where the oxygen concentration of the silicon wafer cut out from the portion having a crystal length of 60% or more is out of specification (Oi deviation rate) is 10% or less. According to the present invention, it is possible to prevent the oxygen concentration of the silicon single crystal from falling out of specification due to the crucible protection sheet.

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

In the present invention, the silicon single crystal preferably has a diameter of 300 mm or more. When the diameter of the silicon single crystal is 300 mm or more, the crucible protection sheet according to the present invention is effective because one pulling batch generally takes a long time and the energization time of the heater for heating the silicon raw material also takes a long time. be.

Furthermore, the present invention provides a method for producing a silicon single crystal by the CZ method in which a heater for heating a silicon raw material is energized for 500 hours or more in one pulling batch, comprising a quartz crucible and a support crucible made of carbon. A silicon single crystal is pulled up with a crucible protective sheet made of carbon laid between the crucible protective sheets ^. When the pressure in the tank is reduced to 200 Pa or less, the ventilation port 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 opening to the atmosphere is started. The amount of pressure change in the measurement tank after 30 minutes have passed since the measurement is 104.9 Pa or less.

In the present invention, the pressure change amount is preferably 53.5 Pa or less. This makes it possible to prevent the oxygen concentration in the silicon single crystal from being out of specification.

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 not completely worn out even when used in such a long-time crystal pulling process, so that not only can deterioration of the supporting crucible be prevented, but also the oxygen concentration specification in the silicon single crystal can be achieved. It is possible to prevent detachment.

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

According to the present invention, it is possible to provide a crucible protective sheet that is less likely to be worn out even when used for long-term crystal pulling such as multi-pulling. Moreover, according to the present invention, it is possible to provide a method for producing a silicon single crystal using such a crucible protection sheet.

FIG. 1 is a diagram for explaining a method for manufacturing 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 manufacturing apparatus. FIG. 2 is a schematic exploded view of a crucible having a double structure, and is an explanatory view of a crucible protection sheet. FIG. 3 is a schematic diagram showing a method of measuring the pressure change amount of the crucible protection sheet. FIG. 4 is a schematic diagram showing a measurement system for the amount of pressure change of the crucible protection sheet. FIG. 5 is a graph showing the relationship between the amount of pressure change and the survival rate of the crucible protection sheet. FIG. 6 is a graph showing the relationship between the longitudinal position (crystal length) of the silicon single crystal and the oxygen concentration in the silicon single crystal. FIG. 7 is a graph showing the Oi deviation rate of silicon single crystals grown using sheet samples #1, #5, and #6 after a crystal length of 60%.

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram for explaining a method for manufacturing 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 manufacturing apparatus.

As shown in FIG. 1, a single crystal manufacturing apparatus 1 includes a water-cooled chamber 10, a quartz crucible 11 holding a silicon melt 2 in the chamber 10, a supporting crucible 12 supporting the quartz crucible 11, and a supporting crucible 12, a shaft driving mechanism 14 for rotating and vertically driving the rotating shaft 13, a heater 15 arranged around the supporting crucible 12, and outside the heater 15 and along the inner surface of the chamber 10. a heat shield 17 placed above the silicon melt 2; a pull-up wire 18 placed above the quartz crucible 11 and coaxial with the rotating shaft 13; and a wire winding mechanism 19 arranged above.

The chamber 10 is composed of a main chamber 10a and an elongated cylindrical pull chamber 10b connected to an upper opening of the main chamber 10a. It is provided in the chamber 10a. The pull chamber 10b is provided with a gas introduction port 10c for introducing an inert gas (purge gas) such as argon gas or a dopant gas into the chamber 10. At the bottom of the main chamber 10a, the atmospheric gas in the chamber 10 is provided. A gas exhaust port 10d for exhausting is provided. A viewing window 10e is provided in the upper part of the main chamber 10a, and the growth status of the silicon single crystal 3 can be observed through the viewing window 10e.

The quartz crucible 11 is a bottomed cylindrical container made of silica glass. The support crucible 12 is a bottomed cylindrical container made of carbon composite, 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-structured crucible 20 that supports the silicon melt in the chamber 10 . Furthermore, a crucible protection sheet 21 is provided between the quartz crucible 11 and the support crucible 12 .

The support crucible 12 is fixed to the upper end of the rotating shaft 13 , and the lower end of the rotating shaft 13 penetrates the bottom of the chamber 10 and is connected to a shaft driving mechanism 14 provided outside the chamber 10 . The supporting crucible 12 , rotating shaft 13 and shaft driving mechanism 14 constitute a rotating mechanism and an elevating mechanism for the quartz crucible 11 .

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 a plurality of members whose output 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 . Further, a heat insulating material 16 is provided outside the heater 15 so as to surround the heater 15, thereby increasing heat retention in the chamber 10. As shown in FIG.

The heat shield 17 suppresses temperature fluctuations in the silicon melt 2 to form an appropriate hot zone near the crystal growth interface, and prevents heating of the silicon single crystal 3 by radiant heat from the heater 15 and the quartz crucible 11. is established for The heat shield 17 is a substantially cylindrical member made of graphite, and is provided so as to cover the area above the silicon melt 2 excluding the pulling path of the silicon single crystal 3 .

The crucible protection sheet 21 is used for manufacturing silicon single crystals by the CZ method, and is used in a state of being laid between the quartz crucible 11 and the support crucible 12 made of carbon. Therefore, the crucible protection sheet 21 must be made of a material having a melting point of 1500° C. or higher, and a low melting point material such as resin cannot be used for the crucible protection sheet 21 .

FIG. 2 is a schematic exploded view of the double-structured crucible 20 and is an explanatory view of the crucible protection sheet 21. As shown in FIG.

As shown in FIG. 2 , the crucible 20 is a combination of a quartz crucible 11 and a support crucible 12 , and a crucible protection sheet 21 is provided between the quartz crucible 11 and the support crucible 12 . The quartz crucible 11 has a substantially cylindrical side wall portion 11a, a gently curved bottom portion 11b, and a corner portion 11c provided between the side wall portion 11a and the bottom portion 11b. The support crucible 12 also has a generally cylindrical sidewall 12a, a gently curved bottom 12b, and a corner 12c provided between the sidewall 12a and the bottom 12b.

The crucible protection sheet 21 prevents the quartz crucible 11 from cracking or chipping and functions as a cushioning material for increasing the adhesion to the inner surface of the support crucible 12 . The crucible protection sheet 21 also functions as a protection sheet for suppressing wear of the support crucible 12 . The crucible protection sheet 21 in FIG. 2 is in a state of being deformed according to the shape of the inner surface of the support crucible 12 .

If the quartz crucible 11 is in direct contact with the inner surface of the supporting crucible 12, the supporting crucible 12 reacts with the quartz crucible 11 and gradually loses its thickness, shortening the life of the supporting crucible 12. When the crucible protection sheet 21 is interposed, 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.

As described above, the crucible protection sheet 21 is also a component of the crucible 20 , and constitutes the quartz crucible support container 23 that supports the quartz crucible 11 together with the support crucible 12 . While the support crucible 12 is used repeatedly, the crucible protection sheet 21 is replaced together with the quartz crucible 11 for each pulling batch, and a new one is used. By interposing the crucible protection sheet 21 having 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 enhanced.

The crucible protection sheet 21 is a flexible carbon sheet, preferably an expanded graphite sheet. Moreover, the thickness of the sheet is preferably 0.3 to 0.8 mm, particularly preferably 0.4 to 0.6 mm. This is because if the sheet is thinner than 0.3 mm, the sheet disappears during the crystal pulling process and the supporting crucible 12 is likely to deteriorate. This is because, as a result, laying in the support crucible 12 becomes difficult.

The crucible protection sheet 21 according to the present embodiment has a very low gas permeability, and the pressure change is 104.9 Pa or less 30 minutes after the start of evacuation from one main surface of the sheet. Here, the amount of pressure change is an index indicating the difficulty of gas passage to the crucible protection sheet. If the amount of pressure change is large, the gas permeates into the sheet and the reaction proceeds easily. Conversely, if the amount of pressure change is small, it is difficult for the gas to penetrate into the sheet, so the chemical reaction of the sheet can be suppressed and the durability can be enhanced.

FIG. 3 is a schematic diagram showing a method of measuring the amount of pressure change of the crucible protection sheet 21. As shown in FIG.

As shown in FIG. 3, in the measurement of the amount of pressure change in the crucible protection sheet 21, the vent 31 of the measurement tank 30, which is decompressed to about several hundred Pa, is sealed with the crucible protection sheet 21, and the vent 31 is exposed to the atmosphere. It is opened and the amount of pressure change in the measurement tank 30 is measured after 30 minutes have passed. When the pressure in the measurement tank 30 at the start of measurement is P ₁ and the pressure in the measurement tank 30 at 30 minutes after the start of measurement is P ₂ , the pressure change amount ΔP=P ₂ -P ₁ is obtained. It is preferable that the degree of vacuum in the decompressed measurement tank 30 be 200 Pa or less (that is, P ₁ ≤ 200 Pa) immediately before starting the pressure change measurement test (immediately before opening to the atmosphere).

The crucible protection sheet 21 is gradually consumed by chemical reaction with the quartz crucible 11 . During the single crystal pulling process, the crucible protection sheet 21 undergoes a primary reaction on the contact surface with the quartz crucible 11 to generate silicon monoxide and carbon monoxide (C+SiO ₂ =SiO(g)+CO(g)). When this silicon monoxide gas penetrates into the crucible protection sheet 21, the crucible protection sheet 21 undergoes a secondary reaction with the silicon monoxide gas to generate 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 eroding the crucible protection sheet 21 (SiC+2SiO ₂ (quartz crucible)=3SiO(g)+CO(g)). .

Therefore, when the gas easily penetrates into the crucible protection sheet 21, the crucible protection sheet 21 is easily worn out and cannot withstand long-term use. However, when the gas does not easily permeate the inside of the crucible protection sheet 21, the secondary reaction described above can be suppressed and the durability of the crucible protection sheet 21 can be improved.

The crucible protection sheet 21 according to this embodiment is preferably used for pulling a large-diameter silicon single crystal having a diameter of 300 mm or more. This is because the heat load applied to the crucible 20 is very large when pulling such a large-diameter silicon single crystal, and the effect of the crucible protection sheet 21 according to the present embodiment is remarkable. Furthermore, the crucible protection sheet 21 according to this embodiment is preferably used for multi-pulling. In the case of multi-pulling, the crystal pulling time is very long. For example, it takes 300 hours or more in the case of two-pulling, and 450 hours or more in the case of three-pulling. because it is prominent.

When used for multi-pulling, it is preferable that the residual ratio of the crucible protective sheet 21 after pulling three silicon single crystals without stretching (after completion of batch pulling) is 80% or more. For this purpose, it is necessary that the pressure change amount of the crucible protection sheet 21 is 104.9 Pa or less. As a result, the oxygen concentration of the silicon wafer cut from the latter half of the silicon single crystal (particularly after the crystal length is 60% or later) meets the predetermined specifications (for example, the upper and lower limits of the oxygen concentration are 3×10 ¹⁷ atoms/cm ³ (ASTM F-121 (1979) and below) can be suppressed to 10% or less of the ratio (Oi deviation rate) to the total length of the straight body portion (constant diameter portion).

The pressure change amount of the crucible protection sheet 21 is preferably 104.9 Pa or less, more preferably 53.5 Pa or less. If the pressure change amount of the crucible protection sheet 21 is 104.9 Pa or less, the Oi removal rate can be made 10% or less. Further, if the pressure change amount of the crucible protection sheet 21 is 53.5 Pa or less, the Oi removal rate can be made 10% or less.

For example, even when a conventional crucible protection sheet is used for three multi-pulling, the first and second silicon single crystals satisfy the desired oxygen concentration specifications, and only the third silicon single crystal satisfies the desired oxygen concentration specifications. was not satisfied. When the crucible protection sheet is used for a relatively short period of time as in the first or second case, the oxygen concentration in the silicon single crystal does not change significantly. In the case of the above long time, the crucible protective sheet deteriorates significantly in the latter half of the pulling of the silicon single crystal, and as a result, the oxygen concentration in the silicon single crystal drops rapidly and there is a probability that the oxygen concentration will deviate from the desired oxygen concentration specification. get higher

However, when the crucible protection sheet 21 according to the present 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.

As described above, the crucible protection sheet 21 according to the present embodiment has a pressure change amount of 104.9 Pa or less. It can withstand the pulling process. Therefore, the oxygen concentration in the silicon single crystal can be stabilized.

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention, which are also included in the scope of the present invention. Needless to say.

A plurality of crucible protective sheet samples #1 to #6 having different physical properties were prepared, and the thickness and pressure variation of each sheet sample were measured.

FIG. 4 is a schematic diagram showing a measurement system for the amount of pressure change of the crucible protection sheet. As shown, the system for measuring the amount of pressure change in the sheet sample includes a measurement tank 30 attached to the sheet sample TP, a vacuum pump 33 for reducing the pressure in the measurement tank 30, and a manometer 34 for measuring the pressure in the measurement tank 30. (pressure gauge). 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. The main surface side of is open to the atmosphere. Furthermore, a vacuum pump 33 and a manometer 34 are connected in parallel to the vent 31 of the measuring tank 30 .

The sealed state of the sheet sample TP is obtained by covering both sides with an acrylic plate 35, further sealing the outer peripheral surface of the sheet sample TP with a silicon bond 36, and holding the laminate under pressure between two metal plates 38. It was realized. A rubber packing 37 (O-ring) was provided between the laminate and the metal plate 38 . A measurement tank 30 having a volume of 2000 cc and an opening diameter of Φ25 mm (opening area of 490 mm ² ) of the tank vent 31 was used to measure the amount of pressure change.

Next, in order to actually measure the amount of pressure change in the sheet sample TP, after reducing the pressure in the measurement tank 30 to 200 Pa or less by the vacuum pump 33, the valve on the side of the vacuum pump 33 is closed and the pressure on the side of the vent 31 is reduced. A valve was opened to start measuring the pressure in the measuring tank 30 . The manometer 34 measured the pressure P1 of the measurement tank 30 at the start of measurement and the pressure P2 of the measurement tank 30 30 minutes after the start of measurement, respectively, to obtain the pressure change amount ΔP=P2−P1. Table 1 shows the results.

The fact that the pressure change amount ΔP is small indicates that it is difficult for the gas to pass through the sheet. As described above, the reaction between the carbon sheet and the quartz crucible generates SiO gas and CO gas, and the SiO gas and the carbon sheet react again to generate SiC gas. Although the initial reaction between the carbon sheet and the quartz crucible cannot be prevented, re-reaction between the SiO gas and the carbon sheet can be prevented by preventing the gas from entering the carbon sheet.

When the gas permeability of the sheet sample TP is high, the atmosphere on the other main surface side that is open to the atmosphere passes through the sheet sample TP and goes into the measurement tank 30, so the pressure in the measurement tank 30 rises, and the pressure change amount becomes larger. On the other hand, when the gas permeability of the sheet sample TP is low, the atmosphere on the other main surface side that is open to the atmosphere cannot pass through the sheet sample, so the pressure in the measurement tank 30 does not rise and the pressure change amount becomes small.

Next, using sheet samples #1 to #5, multi-pulling of silicon single crystals for 300 mm wafers was carried out, and the survival rate of the crucible protective sheet was evaluated after the pulling process was completed. The residual rate is the weight ratio of the crucible protective sheet expressed as a percentage, which is (sheet weight after completion of pulling up three multi-pieces)/(initial sheet weight)×100.

FIG. 5 is a graph showing the relationship between the amount of change in pressure and the survival rate of crucible protection sheet samples #2, #5 and #6. As shown, sheet sample #2 had a residual rate of 5%, sheet sample #6 had a residual rate of 80%, and sheet sample #5 had a residual rate of 105%. The reason why the residual rate of sheet sample #5 exceeded 100% is considered to be that part of sheet sample #5 reacted with silicon monoxide gas and turned into silicon carbide.

Next, multi-pulling of silicon single crystals was performed using crucible protection sheet samples #1, #5 and #6, and the oxygen concentration of the third silicon single crystal obtained in each multi-pulling process was evaluated. In particular, wafers were cut from a portion having a crystal length of 60% or more, and the oxygen concentration (ASTM F-121 (1979)) of each wafer was determined to evaluate whether or not the wafer satisfies predetermined oxygen concentration specifications. The crystal length is a relative value, and is expressed as a percentage, with the start position of the straight body portion of the crystal being 0% and the end position of the straight body portion being 100%.

FIG. 6 is a graph showing the relationship between the longitudinal position (crystal length) of the silicon single crystal grown using the sheet samples #1, #5, and #6 and the oxygen concentration in the silicon single crystal. As shown in the figure, when the sheet sample #1 according to the comparative example was used, many wafers with crystal lengths of 60% or more and oxygen concentrations of 10×10 ¹⁷ atoms/cm ³ or less were obtained. However, when sheet samples #5 and #6 according to the examples were used, such a decrease in oxygen concentration was not observed.

FIG. 7 is a graph showing the Oi deviation rate of silicon single crystals grown using sheet samples #1, #5, and #6 after a crystal length of 60%. As shown in the figure, the sheet sample #1 (comparative example) with a pressure change of 143.8 Pa had a high Oi deviation rate of about 30%, whereas the sheet with a pressure change of 104.9 Pa Sample #6 (Example) had an Oi deviation rate of about 7.5%, which was a good result of less than 10%. Sheet sample #5 (Example) having a pressure change amount of 53.5 Pa had an Oi removal rate of 0%, which was an ideal result.

1 single crystal manufacturing apparatus 2 silicon melt 3 silicon single crystal 10 chamber 10a main chamber 10b pull chamber 10c gas introduction port 10d gas exhaust port 10e viewing window 11 quartz crucible 11a side wall portion 11b bottom portion 11c corner portion 12 supporting crucible 12a side wall portion 12b Bottom 12c Corner 12 Quartz crucible 13 Rotating shaft 14 Shaft driving mechanism 15 Heater 16 Heat insulating material 17 Heat shield 18 Wire 19 Wire winding mechanism 20 Crucible 21 Crucible protection sheet 23 Quartz crucible support container 30 Measurement tank 31 Vent 33 Vacuum pump 34 Manometer 35 Acrylic plate 36 Silicon bond 37 Rubber packing (O-ring)
38 metal plate TP sheet sample

Claims (11)

Used for pulling a silicon single crystal by the CZ method in which the heater power supply time for heating the silicon raw material is 500 hours or more in one pulling batch, and is laid between the quartz crucible and the carbon support crucible. A crucible protection sheet of
Prepare a measurement tank having a volume of 2000 cc and an opening area of a vent of 490 mm ² , and connect the vent to one main surface side of the crucible protection sheet while reducing the pressure in the measurement tank to 200 Pa or less, When the other main surface side of the crucible protection sheet is exposed to the atmosphere, the amount of pressure change in the measurement tank after 30 minutes from the start of the opening to the atmosphere is 104.9 Pa or less. crucible protection sheet. 2. The crucible protection sheet according to claim 1, wherein said pressure change amount is 53.5 Pa or less. The crucible protection sheet according to claim 1 or 2, having a thickness of 0.3 mm or more and 0.8 mm or less. The crucible protective sheet according to any one of claims 1 to 3, which has a residual rate of 80% or more after completion of the pulling batch. It is used for multi-pulling to pull three or more silicon single crystals in one pulling batch, and the oxygen concentration of the silicon wafer cut from 60% or more of the total length of the straight body part of the third silicon single crystal is specified. The crucible protection sheet according to any one of claims 1 to 4, wherein the ratio of the length of the portion that becomes detached (Oi detachment rate) is 10% or less. The crucible protection according to any one of claims 1 to 5, wherein the upper and lower limits of the oxygen concentration spec of the silicon single crystal are 3 × 10 ¹⁷ atoms/cm ³ (ASTM F-121 (1979)) or less. sheet. The crucible protection sheet according to any one of claims 1 to 6, wherein the silicon single crystal has a diameter of 300 mm or more. A method for producing a silicon single crystal by a CZ method in which a heater for heating a silicon raw material is energized for 500 hours or more in one pulling batch,
A silicon single crystal is pulled up with a carbon crucible protection sheet laid between the quartz crucible and the carbon support crucible,
For the crucible protection sheet, a measurement tank having a volume of 2000 cc and an opening area of a vent opening of 490 mm ² is prepared. When the crucible protection sheet is connected to the surface side and the other main surface side of the crucible protection sheet is exposed to the atmosphere, the amount of pressure change in the measurement tank 30 minutes after the start of the opening to the atmosphere is 104.9 Pa or less. A method for producing a silicon single crystal, characterized by: 9. The method for producing a silicon single crystal according to claim 8, wherein said pressure variation is 53.5 Pa or less. 10. The method for producing a silicon single crystal according to claim 8, wherein three or more silicon single crystals are pulled in one pulling batch. The silicon single crystal according to any one of claims 8 to 10, wherein the width of the upper and lower limits of the oxygen concentration spec of the silicon single crystal is 3 × 10 ¹⁷ atoms/cm ³ (ASTM F-121 (1979)) or less. Crystal production method.

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