Method for the production of silicon single crystals

Abstract

A manufacturing process for single-crystal silicon according to a Czochralski process using a single-crystal growing apparatus, the apparatus comprising: a chamber; a crucible located in the chamber; a heater configured to heat the crucible and thus produce a dopant melt comprising a silicon melt and red phosphorus or arsenic in high concentrations as a dopant added to the silicon melt, the heater comprising an upper heating device configured to heat an upper side face of the crucible and a lower heating device configured to heat a lower side face of the crucible; and a growing unit configured to grow a seed crystal after the seed crystal has been brought into contact with the dopant melt.wherein the process comprises: forming a shoulder of single-crystal silicon; and forming a straight body with a target diameter of 200 mm or more, wherein the manufacturing conditions are adjusted such that the resistivity, when using arsenic as a dopant, ranges from 1.5 mΩ·cm to 3.5 mΩ·cm and when using red phosphorus as a dopant, ranges from 0.6 mΩ·cm to 1.2 mΩ·cm, and during shoulder formation, while a heating ratio calculated as the division of a quantity of heat from the lower heating device by a quantity of heat from the upper heating device is maintained at 1, the crucible is rotated at a speed maintained at 16 rpm or more and 30 rpm or less from the beginning of shoulder formation until a diameter of the shoulder being formed reaches half the target diameter of the straight body or more.and the rotational speed of the crucible is reduced at this time or thereafter.

Description

TECHNICAL AREA The present invention relates to a manufacturing process for single-crystal silicon. STATE OF THE ART Recently, there has been a demand for single-crystal silicon with low resistivity. In a known manufacturing process for such single-crystal silicon, in which a dense n-type dopant is added, single-crystal formation is sometimes difficult, and therefore studies have been carried out to avoid this problem (see, for example, patent literature 1). Patent literature 1 discloses that the addition of a large amount of the dopant significantly increases freezing point depression, thus causing compositional supercooling, and induces abnormal growth (cell growth) at a crystal growth interface, which differs from silicon growth on a silicon growth surface, when such compositional supercooling is large, making single crystal formation difficult. According to the manufacturing process described in patent literature 1, which takes into account that a temperature gradient in a silicon melt cannot be directly measured, single-crystal silicon is produced in such a way that a predetermined relationship is satisfied between a temperature gradient of the single-crystal silicon, which is referred to instead of the temperature gradient in the silicon melt, a dopant concentration in the silicon melt, a drawing rate and a coefficient corresponding to the type of dopant. BIBLIOGRAPHY PATENT LITERATURE Patent literature 1 JP 2008-297167 A DE 11 2012 005 584 T5 relates to a CZ growth process for the production of high-purity silicon single crystals using a volatile n-type dopant with a low melting point (e.g., Sb, P, As), addressing dopant volatilization and the resulting instabilities in the melt surface temperature. It is proposed, in particular, to set the neck length in a range of approximately 35–45 cm and to limit the ratio of inert gas quantity to chamber pressure to 1.5 or less during crystal growth, possibly starting from the shoulder growth stage, in order to reduce dopant volatilization and contamination, as well as to increase yield / productivity. Additionally, process parameters such as pressure range and solid / liquid interface control for defect reduction are described. DE 11 2017 003 016 T5 describes a CZ manufacturing process for single-crystal silicon with stable quality at high n-doping levels, in which abnormal growth and resulting dislocations, particularly in an early stage or at the shoulder, are reduced by targeted manipulation of the temperature gradient in the doped melt. For this purpose, during shoulder formation, the crucible is heated such that a heating ratio (volume of the heating power of the lower heater divided by that of the upper heater) is increased from a predetermined value ≥1 (preferably to ≥2) to enhance convection from below and reduce the entry of temperature-unstable melt into the solid / liquid interface; optionally, a heating ratio ≤1.5 is applied for neck formation to prevent heat shock dislocations upon contact of the seed crystal with the melt. DE 100 25 870 A1 concerns the production of dislocation-free single-crystal rods (especially silicon single-crystal rods, even with high As or Sb doping) using the CZ crucible drawing process and identifies the transition zone from the initial cone to the cylindrical rod section as a typical source of defects. To avoid crystal dislocations, it is taught to form a long, acute-angled crystal cone (initial cone) with an opening angle of 30° to 90° (preferably about 40° to 60°). This prevents a change in the curvature of the solidification front during the transition to the cylindrical section and reduces the probability of dislocations. The opening angle or cone geometry is adjusted via drawing speed, crucible / crystal rotation, and melting parameters. SUMMARY OF THE INVENTION TASK(S) TO BE SOLVED BY THE INVENTION However, dislocation sometimes occurs at an early stage of crystal growth in the process for producing single-crystal silicon, thus making single-crystal formation difficult, which has shown that the process of patent literature 1 cannot always avoid the problem. It is an object of the invention to provide a manufacturing process for single-crystal silicon that can produce single-crystal silicon with stable quality. MEANS OF SOLVING THE TASK(S) After thorough studies, the inventors discovered the following. Growth striations form within single-crystal silicon. These striations are not planar but curved, corresponding to the shape of a solid-liquid interface obtained during the single-crystal silicon production process (e.g., a curved shape indented upwards in the center). If the surface temperature of the silicon melt in the vicinity of the single-crystal silicon is stable, the growth striations retain essentially the same shape. The surface of the silicon melt is subject not only to convection of the silicon melt itself, but also to factors that make the temperature unstable, such as heat extraction by a purge gas and the heat of vaporization resulting from the evaporation of the dopant. If, as a consequence of an unstable surface temperature of the silicon melt, a high-temperature silicon melt enters the solid-liquid interface, the single-crystal silicon is melted (remelted) and re-solidifies, thus creating curved growth lines that are, for example, indented downwards in the center. As shown in Fig.As shown in Figure 1, it was subsequently found that a remelt growth area (A) forms between the lowest growth stripe (P1) of upwardly indented growth stripes extending radially over a shoulder and the uppermost growth stripe (P2) of downwardly indented growth stripes below growth stripe P1 and in a circumferential region of the shoulder of a single-crystal silicon (SM). Furthermore, investigations into the relationship between the generation of Zone A remelting growth and the occurrence of dislocation revealed that Zone A remelting growth with a maximum height (H) (hereinafter referred to simply as "height") of 200 µm or more is associated with the occurrence of dislocation in the shoulder and, consequently, dislocation in the straight body. In contrast, it was found that no dislocation in the shoulder or straight body occurs when Zone A remelting growth with a height (H) of 200 µm or more is not generated. The invention is based on the above finding. The problem mentioned above is solved by the subject matter of the independent claims. Examples and technical descriptions of devices, products and / or methods in the description and / or drawings that are not covered by the claims are not presented as embodiments of the invention, but rather as prior art or as examples to aid in understanding the invention.According to one aspect of an example, a manufacturing process for single-crystal silicon according to a Czochralski process, using a single-crystal growing apparatus comprising a chamber; a crucible located in the chamber; a heater configured to heat the crucible and thus produce a dopant melt comprising a silicon melt and a dopant added to the silicon melt; and a growing unit configured to grow a seed crystal after the seed crystal has been brought into contact with the dopant melt, includes: the formation of a shoulder of the single-crystal silicon, and the formation of a straight body of the single-crystal silicon.In shoulder formation, the shoulder is formed in such a way that a portion of growth lines extending radially across the shoulder has an outer end that is interrupted by another portion of growth lines in such a way that it does not reach a circumferential area of ​​the shoulder, and that no zone of remelting growth with a height of 200 µm or more in any growth direction is created. In the above aspect, no dislocation occurs in the shoulder and the straight body, so that single-crystal silicon of stable quality can be produced. According to the invention, a manufacturing process for single-crystal silicon according to a Czochralski process, using a single-crystal growing apparatus comprising a chamber; a crucible located in the chamber; a heater configured to heat the crucible and thus generate a dopant melt comprising a silicon melt and red phosphorus or arsenic as a dopant added to the silicon melt; and a growing unit configured to grow a single crystal after the seed crystal has been brought into contact with the dopant melt, includes: forming a shoulder of the single-crystal silicon; and forming a straight body with a target diameter of 200 mm or more. During shoulder formation, the crucible is rotated at 16 rpm or more and 30 rpm or less. Although a typical crucible rotation speed for the straight body formation step ranges from 2 rpm to 12 rpm, in the above scenario, the crucible is rotated at a relatively high speed, as described above. This reduces convection of the silicon melt and consequently decreases temperature fluctuations at the silicon melt surface. Such a simple adjustment of the crucible speed can reduce remelting resulting from temperature destabilization and, consequently, the formation of Zone A of remelt growth. In this way, no dislocation occurs in the shoulder and the straight body, allowing for the production of single-crystal silicon of stable quality. In the above aspect, during shoulder formation, the crucible is rotated at 16 rpm or more until a point at which the diameter of the forming shoulder reaches half the target diameter of the straight body or more, and the rotational speed of the crucible is reduced at that point or thereafter. Similarly, in the straight body formation step, rotating the crucible at 16 rpm or more sometimes causes an uneven distribution within the plane, for example, of the oxygen concentration and the specific resistance of the straight body, so that the rotational speed of the crucible must be reduced for this step. However, if the reduction in the crucible's rotational speed begins before the shoulder diameter reaches half the target diameter of the straight body, dislocation cannot be effectively reduced, even if the crucible is rotated at 16 rpm or more. In the above aspect, the rotational speed of the crucible is controlled under the above conditions, which reduces not only the dislocation in the straight body, but also the uneven distribution of, for example, the oxygen concentration and the specific resistance. According to another aspect of the disclosure, a manufacturing process for single-crystal silicon according to a Czochralski process using a single-crystal growing apparatus includes a chamber; a crucible located in the chamber; a heater configured to produce a dopant melt comprising a silicon melt and red phosphorus or arsenic as a dopant added to the silicon melt, the heater comprising an upper heater configured to heat a surface at the top of the crucible and a lower heater configured to heat a surface at the bottom of the crucible;and a pull-up unit configured to pull up a seed crystal after the seed crystal has been brought into contact with the melt containing added dopant, including: formation of a shoulder of the single-crystal silicon; and formation of a straight body with a target diameter of 200 mm or more. During shoulder formation, the crucible is rotated at 14 rpm or more until a diameter of the forming shoulder reaches half the target diameter of the straight body or more, while the crucible is heated such that a heating ratio, calculated by dividing a volume of heat from the lower heater by a volume of heat from the upper heater, is increased from a predetermined value of 1 or more; and a rotational speed of the crucible is reduced at or thereafter while maintaining the heating ratio constant. As described above, the surface of the melt with added dopant is exposed to a large heat extraction by purge gas and / or heat of vaporization resulting from the vaporization of the dopant, so that the temperature of the liquid at the surface of the melt with added dopant becomes unstable. In the above scenario, the heating ratio is set greater than 1 (i.e., the volume of heat from the lower heater is set greater than that from the upper heater to increase the convection rising from the bottom of the crucible and flowing towards the outside of the crucible after reaching the solid-liquid interface). This convection flows in the opposite direction to the convection with an unstable liquid temperature flowing from the surface of the melt with added dopant towards the crystal, thus preventing the melt with an unstable liquid temperature from entering the solid-liquid interface, while allowing the melt with a relatively stable liquid temperature to rise from the bottom and flow into the solid-liquid interface.This reduces remelting due to temperature destabilization and consequently the formation of Zone A of remelting growth. Therefore, no dislocation occurs in the shoulder and the straight body, allowing the production of single-crystal silicon with stable quality. BRIEF DESCRIPTION OF THE DRAWING(S) Fig. 1 schematically shows a zone of remelt growth. Fig. 2 schematically shows a setup of a device for growing a single crystal according to an exemplary embodiment of the invention. Fig. 3 shows manufacturing conditions according to the exemplary embodiment. Fig. 4A shows manufacturing conditions according to an illustrative example, in particular a relationship between the length of the single-crystal silicon and the rotational speed of the crucible. Fig. 4B shows manufacturing conditions according to the illustrative example, in particular a relationship between the length of the single-crystal silicon and a heating ratio. Fig. 5 shows manufacturing conditions for Experiment 1 in the examples according to the invention. Fig. 6 is a graph related to Experiment 2 in the examples, showing a relationship between the height and the number of the zone(s) of remelt growth.Figure 7A is a graph related to Experiment 3 in the Examples, showing a temperature fluctuation of the melt surface at a crucible rotation speed of 10 rpm. Figure 7B is a graph related to Experiment 3 in the Examples, showing a temperature fluctuation of the melt surface at a crucible rotation speed of 12 rpm. Figure 7C is a graph related to Experiment 3 in the Examples, showing a temperature fluctuation of the melt surface at a crucible rotation speed of 14 rpm. Figure 8A is a graph related to Experiment 3 in the Examples, showing a temperature fluctuation of the melt surface at a crucible rotation speed of 16 rpm. Fig. 8B is a graph related to Experiment 3 in the Examples, showing a temperature fluctuation of the melt surface at a crucible rotation speed of 18 rpm.Figure 8C is a graph related to Experiment 3 in the Examples, showing a temperature fluctuation of the melt surface at a crucible rotation speed of 20 rpm. Figure 9 shows the production conditions for Experiment 4 in the Examples. Figure 10A shows the production conditions for Experiment 5 in the Examples, in particular a relationship between the length of the single-crystal silicon and the crucible rotation speed. Figure 10B shows the production conditions for Experiment 5 in the Examples, in particular a relationship between the length of the single-crystal silicon and the heating ratio. Figure 11 is a graph related to Experiment 6 in the Examples, showing a relationship between the resistivity and the crucible rotation speed that does not cause dislocation. DESCRIPTION OF THE FORM(S) Exemplary embodiment(s) An exemplary embodiment of the invention is described below with reference to the accompanying drawings. Construction of a device for growing a single crystal As shown in Fig. 2, a device (1) for growing a single crystal, which is a device usable for the CZ (Czochralski) process, includes a body (2) of the growing device and a control unit (3). The body (2) of the lifting device includes a chamber (21), a crucible (22) arranged in the center of the chamber (21), a heater (23) designed to heat the crucible (22), a heat-insulating cylinder (24), a lifting cable (25) (lifting unit) and a heat shield (26). A gas inlet (21A), through which an inert gas (e.g., argon gas) is introduced into the chamber (21), is provided at an upper part of the chamber (21). A gas outlet (21B), through which the gas in the chamber (21) is discharged when a vacuum pump (not shown) is operated, is provided at a lower part of the chamber (21). The inert gas is introduced into the chamber (21) at a predetermined gas flow rate through the gas inlet (21A) at the upper part of the chamber (21) under control by the control unit (3). The introduced gas is then discharged through the gas outlet (21B) at the lower part of the chamber (21) after flowing from the top to the bottom inside the chamber (21). The pressure (oven pressure) inside the chamber (21) is to be controlled by the control unit (3). The crucible (22) is designed to melt polycrystalline silicon (i.e., a material from a silicon wafer) and thus provide a silicon melt (M). The crucible (22) is supported by a support shaft (27) that is rotatable at a predetermined speed and movable vertically. The crucible (22) encloses a cylindrical quartz crucible (221) with a closed bottom and a support crucible (222) made of a carbon material that accommodates the quartz crucible (221). The heater (23) is located near the crucible (22) to melt the silicon inside the crucible (22). The heater (23) includes an upper heater (231), which is designed to heat a surface on the top of the crucible (22), and a lower heater (232), which is located below the upper heater (231) and is designed to heat a surface on the bottom of the crucible (22). The heat-insulating cylinder (24) is arranged around the crucible (22) and the heater (23). The pull-up cable 25 has a first end connected to a pull-up drive (not shown) located above the crucible (22), and a second end connected to a seed crystal SC. The pull-up cable is vertically movable at a predetermined speed and rotatable about an axis of the pull-up cable (25) when the pull-up drive is controlled by the control unit (3). The heat shield (26) is designed to block radiant heat emitted upwards by the heater (23). The control unit (3) is designed to control, for example, the gas flow rate and furnace pressure in the chamber (21), the temperature of the heat exerted by the heater (23) on the crucible (22) and the respective rotational speeds of the crucible (22) and the single-crystal silicon (SM), for example, on the basis of information stored in a memory (31) and / or input by a person operating the device, in order to produce the single-crystal silicon (SM). Manufacturing process for single-crystal silicon Next, a description of a manufacturing process for single-crystal silicon (silicon single crystal) (SM) is given. It should be noted that, for example, a straight body of the single-crystal silicon (SM) to be produced has a target diameter (R) of 200 mm in the exemplary embodiment, but that the single-crystal silicon (SM) can be produced with a different target diameter, such as 300 mm and 450 mm. First, the control unit (3) of the device (1) for growing the single crystal sets the production conditions for the single-crystal silicon (SM), such as the resistivity, oxygen concentration, argon flux rate, furnace pressure, the respective rotational speeds of the crucible (22) and the single-crystal silicon (SM), and a heating ratio between the upper heater (231) and the lower heater (232). The production conditions can be entered by a person operating the device or calculated by the control unit (3), for example, based on a target oxygen concentration entered by a person operating the device. The specific resistance preferably ranges from 1.5 mΩ·cm to 3.5 mΩ·cm when using arsenic as a dopant and preferably from 0.6 mΩ·cm to 1.2 mΩ·cm when using red phosphorus as a dopant. Furthermore, in the exemplary embodiment, the heating ratio is set to 1 (i.e., the heating volume for the upper part of the crucible (22) is the same as the heating volume for the lower part), but it can be set to any value in the range of 1 to 4. If the heating ratio is less than 1 (i.e., the heating volume for the lower part is smaller than the heating volume for the upper part), convection from the bottom of the crucible (22) towards or below a solid-liquid interface may not be strong enough to weaken convection with an unstable liquid temperature from a surface of a melt (MD) with added dopant towards a crystal, and thus dislocation due to a destabilized temperature may not be reduced.However, if the heating ratio is greater than 4, a large heat load on the lower part of the crucible (22) can cause deformation of the crucible (22) and / or flaking of quartz. Next, the control unit (3) controls the upper heater (231) and the lower heater (232) based on the preset heating ratio, thus heating the crucible (22) so that the polycrystalline silicon material (silicon material) and the dopant in the crucible (22) melt, producing a melt (MD) with added dopant. The control unit (3) then controls the single-crystal puller (1) to introduce an argon gas at a preset flow rate through the gas inlet (21A) into the chamber (21) and to reduce the pressure in the chamber (21), maintaining an inert atmosphere at reduced pressure in the chamber (21). The control unit (3) then performs a step of neck formation, a step of shoulder formation, a step of straight body formation, and a step of tail formation. During the neck formation step, the control unit (3) moves the pull-up cable (25) downwards to immerse the seed crystal (SC) in the melt (MD) containing the added dopant, and pulls the pull-up cable (25) upwards while the crucible (22) and the pull-up cable (25) rotate in a predetermined direction, thus forming a neck (SM1). It should be noted that the rotational speed of the crucible (22) for the neck formation step is preferably the same as the rotational speed at the beginning of the shoulder formation step. In the shoulder formation step, a shoulder (SM2) is formed in such a way that a zone (A) of remelt growth with a height (H) of 200 µm or more is not generated in the shoulder (SM2), as shown in Fig. 1. Specifically, as shown in Fig. 3, the control unit (3) pulls up the pull-up cable (25) while the crucible (22) is rotated at a rotational speed (Sr1) (Sr1 ≥ 16 rpm). Sr1 can be set to any value equal to or greater than 16 rpm, but is preferably 30 rpm or less. This is because a rotational speed (Sr1) above 30 rpm destabilizes the operation of the single-crystal pull-up device (1) and thus causes deformation of the shoulder (SM2). It should be noted that the abscissa axis in each of Figs. 3 to 5, 9 and 10 represents a length of single-crystal silicon (silicon single crystal) (SM), excluding the neck (SM1). Subsequently, the rotational speed, maintained at Sr1, is gradually reduced at a predetermined point in time when the diameter of the drawn single-crystal silicon (SM) (shoulder (SM2)) reaches (1 / 2)R (half the target diameter of the straight body) or more (i.e., when the length of the single-crystal silicon (SM) reaches L1). Specifically, the rotational speed is linearly reduced until it reaches the value Sr2 suitable for forming the straight body when the diameter of the single-crystal silicon (SM) becomes R (i.e., when the formation of the shoulder (SM2) is complete). The heating ratio is maintained at 1 during the shoulder formation step. It should be noted that Sr2 preferably ranges from 4 rpm to 12 rpm.A rotational speed (Sr2) of less than 4 rpm destabilizes the melt (MD) with added dopant and causes dislocation, and Sr2 above 12 rpm increases the unevenness of the distribution of oxygen concentration within the plane and of the specific resistance in the single-crystal silicon (SM) and thus destabilizes the crystal quality. Subsequently, the step of forming the straight body and the step of forming the tail are carried out, thus completing the production of single-crystal silicon (SM). Advantage(s) of exemplary embodiment(s) In the exemplary embodiment, the shoulder formation step is carried out in such a way that the remelting growth zone (A) with a height (H) of 200 µm or more is not generated in the shoulder (SM2), thus reducing the occurrence of dislocation in the shoulder (SM2) and consequently the occurrence of dislocation in the straight body. Single-crystal silicon (SM) of stable quality can be produced in this way. Furthermore, single-crystal silicon with less dislocation can be easily produced by rotating the crucible (22) during the shoulder formation step at a rotational speed of 16 rpm or more and 30 rpm or less. Furthermore, the rotational speed at Sr1 is maintained until the diameter of the shoulder (SM2) reaches (1 / 2)R and is gradually reduced at a predetermined time when the diameter reaches (1 / 2)R or more, thereby not only reducing the dislocation in the straight body, but also the unevenness of, for example, the distribution of oxygen concentration and the distribution of specific resistance. Modification(s) It is understood that the scope of the invention is not limited by the exemplary embodiment above, but that various improvements and modifications compatible with the invention are possible, and furthermore specific processes, setups and the like can be changed in practice of the invention, as long as the objective of the invention can be achieved. In some illustrative examples, the step of shoulder formation is carried out, as shown, for example, in Fig. 4A and Fig. 4B. In this case, the control unit (3) sets the heating ratio to a predetermined value equal to or greater than 1 (“1” in Fig. 4B) and begins heating the crucible (22). Simultaneously, the pull-up cable (25) is pulled up while the crucible (22) is rotated with Sr3 (Sr3 ≥ 14 rpm). Sr3 can be set to any value equal to or greater than 14 rpm, but preferably 30 rpm or less. This is because an Sr3 value above 30 rpm destabilizes the operation of the device (1) for pulling up a single crystal and causes deformation of the single-crystal silicon (SM). Subsequently, while maintaining the rotational speed at Sr3, the heating ratio is gradually increased. When the diameter of the single-crystal silicon (SM) reaches (1 / 2)R or more (i.e., the length of the single-crystal silicon (SM) reaches L2) and the heating ratio T is reached, the rotational speed is gradually decreased while the heating ratio is kept constant. Specifically, the rotational speed is decreased linearly such that Sr2 is reached upon completion of shoulder formation. It should be noted that T preferably ranges from 1.5 to 4. Furthermore, Sr2 preferably ranges from 4 rpm to 12 rpm, as described in the exemplary embodiment above. Subsequently, the step of forming the straight body and the step of forming the tail are carried out, thus completing the production of single-crystal silicon (SM). In such a process, T is controlled as described above, thereby increasing convection from the bottom of the crucible (22) towards or below the solid-liquid interface, and reducing convection with an unstable liquid temperature from the surface of the melt (MD) with added dopant towards the crystal. Consequently, the shoulder formation step can be carried out in such a way that a zone (A) of remelt growth with a height (H) of 200 µm or more is not formed in the shoulder, and thus single-crystal silicon of stable quality is produced. In the manufacturing process shown in Fig. 3 and in the illustrative example shown in Fig. 4 and Fig. 4B, the rotational speed for the shoulder formation step can be maintained at Sr1 and Sr3, respectively. In the exemplary embodiment above, the rotational speed of the crucible (22) is linearly reduced at or after the predetermined time, and the heating ratio is linearly and gradually increased from a predetermined value equal to or greater than 1. However, such linear reductions and increases are merely examples. For instance, the reduction and increase could be non-linear or stepwise. Example(s) The invention is described in more detail below with reference to examples. It should be noted, however, that the scope of the invention is in no way limited by these examples. Experiment 1: Relationship between crucible rotation speed and dislocation Manufacturing process for single-crystal silicon Comparative example 1 As shown in Fig. 5 and Table 1, in the shoulder formation step, the rotational speed was controlled such that the cable was pulled up while the crucible rotated at 14 rpm, and the rotational speed was gradually reduced when the diameter of the single-crystal silicon reached 100 mm (half the target straight body diameter) or more, to achieve 6 rpm at the end of shoulder formation. The heating ratio was set to a constant 1. Subsequently, the straight body formation step and the tail formation step were carried out. Table 1 shows the target straight body diameter, the dopant, and the resistivity. In the manufacturing process, the single-crystal silicon was examined to determine whether dislocation occurred. If dislocation occurred, the pull-up operation was stopped, and the single-crystal silicon was melted in a melt with added dopant (melt-back step). The above procedure was repeated until a single-crystal silicon was produced containing a straight body without dislocation. Table 1 shows the pull-up frequency (trial frequency), the dislocation frequency, and the occurrence of dislocation (dislocation rate = dislocation frequency / trial frequency). It should be noted that a single silicon single crystal with shoulder dislocation was retained as a sample for Experiment 2 (described later) without performing the remelting step. Table 1 Target diameter of the straight body: 200 mm Doping agent arsenic Specific resistance 2.0 mΩ·cm Rotation speed of the crucible (rpm) 14→6 16→6 20→6 Heating ratio 1 Trial frequency 6115 Dislocation frequency 400 Dislocation rate 67% 0% 0% Examples 1 and 2 Silicon single crystals were prepared in Examples 1 and 2 under the same conditions as in Comparative Example 1, except that the crucible was rotated at 16 rpm and 20 rpm, respectively, during the same period in Comparative Example 1 where it was rotated at 14 rpm. Table 1 shows the frequency of trials, frequency of dislocation, and rate of dislocation. Comparative examples 2 and 3, examples 3 to 6 As shown in Fig. 5 and Table 2, a silicon single crystal in Comparative Example 2 was produced under the same conditions as in Comparative Example 1, except that in the shoulder formation step the cable was pulled up while the crucible was rotated at 14 rpm, the rotation speed was started to decrease at the time when the diameter of the silicon single crystal became 165 mm (half the target diameter of the straight body) or more, and the target diameter of the straight body and the resistivity were set to the values ​​shown in Table 2. Silicon single crystals were prepared in Examples 3 and 4 under the same conditions as in Comparative Example 2, except that the crucible was rotated at 16 rpm and 20 rpm respectively during the period in which the crucible was rotated at 14 rpm in Comparative Example 2. As shown in Fig. 5, silicon single crystals in Comparative Example 3 and Examples 5 and 6 were prepared under the same conditions as in Comparative Example 2 and Examples 3 and 4, except that the dopant and the resistivity were chosen as shown in Table 3. Tables 2 and 3 show the frequency of trials, frequency of dislocation, and rate of dislocation for each of the comparison examples 2 and 3 and examples 3 to 6. Target diameter of the straight body: 330 mm Doping agent arsenic Specific resistance 2.6 mΩ·cm Rotation speed of the crucible (rpm) 14→6 16→6 20→6 Heating ratio 1 Trial frequency 323 Dislocation frequency 200 Dislocation rate 67% 0% 0% Table 3 Table 3 Target diameter of the straight body: 330 mm Doping agent red phosphorus Specific resistance 1.3 mΩ·cm Rotation speed of the crucible (rpm) 14→6 16→6 20→6 Heating ratio 1 Trial frequency 425 Dislocation frequency 300 Dislocation rate 75% 0% 0% Evaluation As shown in Tables 1 to 3, dislocation sometimes occurred in the silicon single crystals in Comparative Examples 1 to 3, whereas no dislocation occurred in any region in Examples 1 to 6. This has shown that single-crystal silicon without dislocation, enclosing a straight body with a target diameter of 200 mm or more, can be produced by setting the rotational speed of the crucible for the shoulder formation step to 16 rpm or more. Experiment 2: Relationship between dislocation and the height of the remelting growth zone The silicon single crystal from Comparative Example 1, in which dislocation occurred, was cut perpendicularly in its center in the radial direction, and the resulting cross-section of the shoulder was examined using X-rays to determine the number and height of the remelting growth zone(s). The same examination was also carried out on the silicon single crystals of Examples 1, 2, and 5, in which no dislocation occurred. The results are shown in Fig. 6. As shown in Fig. 6, the shoulder of each of Examples 1, 2, and 5 had remelt growth zones less than 200 µm high, but no remelt growth zone of 200 µm or more. In contrast, the shoulder of Comparative Example 1 had not only remelt growth zones less than 200 µm high, but also zones of 200 µm or more. Furthermore, because dislocation did not occur in the silicon single crystals of Examples 3, 4, and 6, the shoulders of Examples 3, 4, and 6 should not exhibit any remelt growth zone of 200 µm or more. Additionally, because dislocation occurred in the silicon single crystals of comparison examples 2 and 3, the shoulders of comparison examples 2 and 3 should exhibit (a) zone(s) of remelting growth with a height of 200 µm or more. In light of these findings, it has been demonstrated that single-crystal silicon can be produced without dislocation by carrying out the shoulder formation step in such a way that a zone of remelting growth with a height of 200 µm or more is not generated in the shoulder. Experiment 3: Relationship between the rotational speed of the crucible and temperature fluctuations of the melt surface A melt containing added dopant was prepared under the same conditions as for the production of typical single-crystal silicon. Argan gas was introduced into a chamber in the same manner as for the production of typical single-crystal silicon, and the pressure was set to 450 Torr (59,995 Pa). The crucible was rotated at 10 rpm, and the temperature at the center of a surface of the melt containing the added dopant was measured using an infrared radiation thermometer. Measurements were taken every second, and an average of the fluctuations was determined every 10 seconds. The results are shown in Fig. 7A. Similarly, the temperature at the center of the melt surface with added dopant was measured and evaluated for each of the rotational speeds of 12 rpm, 14 rpm, 16 rpm, 18 rpm, and 20 rpm. The results are shown in Fig. 7B, Fig. 7C, Fig. 8A, Fig. 8B, and Fig. 8C. The standard deviations of the measurement results are shown in Table 4. 104.15 123.87 142.99 162.51 182.14 202.03 As shown in the figures and Table 4, it has been demonstrated that the temperature fluctuation decreases with increasing rotational speed. This is because increasing the crucible's rotational speed reduces the convection of the melt with added dopant. Therefore, increasing the rotational speed should reduce remelting, which results from the temperature instability at the surface of the melt with added dopant, thus yielding single-crystal silicon without dislocation. Experiment 4: Relationship between the time of change in crucible rotation speed and dislocation Manufacturing process for single-crystal silicon Comparative example 4 As shown in Fig. 9 and Table 5, in the shoulder formation step, the rotational speed was controlled such that the cable was pulled up while the crucible rotated at 16 rpm. During the pull-up operation, the rotational speed was gradually reduced to 6 rpm when the diameter of the single-crystal silicon reached 100 mm or more. The rotational speed was then maintained at 6 rpm until the shoulder formation step was completed. The heating ratio was set to a constant 1. Subsequently, the straight body formation step and the tail formation step were carried out. In the manufacturing process, the remelting step was performed if the single-crystal silicon exhibited dislocation. The process was repeated in the same manner as in Experiment 1 until a single-crystal silicon was produced that enclosed a straight body without dislocation. Table 5 shows the dopant, resistivity, frequency of trials, frequency of dislocation, and dislocation rate. Target diameter of the straight body: 200 mm Doping agent arsenic Specific resistance 2.0 mΩ·cm Time of change of the crucible's rotation speed << (1 / 2) R < (1 / 2) R > (1 / 2) R Rotational speed of the crucible (rpm) 16→6 16→6 16→6 Heating ratio 111 Trial frequency 11511 Dislocation frequency 930 Dislocation rate 82% 60% 0% Comparative example 5, example 7 A silicon single crystal was produced in Comparative Example 5 under the same conditions as in Comparative Example 4, except that in the shoulder formation step the cable was pulled up while the crucible was rotated at 16 rpm, and the rotation speed was gradually reduced at the time when the diameter of the silicon single crystal was less than 100 mm, in order to reach 6 rpm at the completion of shoulder formation. A silicon single crystal was prepared in Example 7 under the same conditions as in Comparative Example 5, except that the rotational speed of the crucible was changed when the diameter of the silicon single crystal reached 100 mm or more. Table 5 shows the frequency of trials, dislocation frequency, and dislocation rate. Evaluation As shown in Table 5, dislocation occurred in the silicon single crystals of comparison examples 4 and 5, while no dislocation occurred in the silicon single crystal of example 7. This demonstrated that reducing the crucible velocity when the shoulder diameter is less than half the target diameter of the straight body is ineffective in reducing dislocation, whereas reducing the crucible velocity when the diameter reaches half or more of the target diameter of the straight body is effective in reducing dislocation. Experiment 5: Relationship between crucible rotation speed, heating ratio and dislocation In Experiment 5, comparison example 1 and example 2 were evaluated for Experiment 1 and the following examples 8 and 9. Manufacturing process for single-crystal silicon Example 8 As shown in Fig. 10A, Fig. 10B, and Table 6, a silicon single crystal was produced under the same conditions as in Comparative Example 1, except that in the shoulder formation step, the heating ratio was controlled such that the cable was pulled up while the crucible was heated at a heating ratio of 1. During the pull-up operation, the heating ratio was gradually increased to reach 2 at the point when the rotational speed began to decrease, and then the heating ratio was maintained at 2 until the shoulder formation step was completed. Table 6 shows the target straight body diameter, dopant, resistivity, trial frequency, dislocation frequency, and dislocation rate. Target diameter of the straight body: 200 mm Doping agent arsenic Specific resistance 2.0 mΩ·cm Rotation speed of the crucible (rpm) 14→6 20→6 14→6 20→6 Heating ratio 111→21→2 Trial frequency 65320 Dislocation frequency 4000 Dislocation rate 67% 0% 0% 0% Example 9 A silicon single crystal was prepared under the same conditions as in Example 8, except that the rotational speed of the crucible was controlled in the same way as in Example 2. Table 6 shows the frequency of trials, frequency of dislocations, and rate of dislocations. Evaluation As shown in Table 6, a comparison between Example 1 and Example 8, in which the crucible rotation speed was 14 rpm in both cases, demonstrated that dislocation occurs when the heating ratio is maintained at 1, whereas no dislocation occurs when the heating ratio is controlled to gradually increase from the beginning of the shoulder formation step until it reaches 2 at the point where the shoulder diameter becomes half the target diameter of the straight body or more, and then is maintained at 2 until the shoulder formation step is completed. Additionally, a comparison between Example 2 and Example 9, in which the crucible rotation speed was 20 rpm in both cases, demonstrated that no dislocation occurs regardless of whether the heating ratio is maintained at 1 or changed. Furthermore, Experiment 1 demonstrated that single-crystal silicon with a target diameter of 330 mm can be produced without dislocation by using arsenic or red phosphorus as a dopant, under the same conditions that allow the production of single-crystal silicon with a target diameter of 200 mm without dislocation. Based on these findings, it is assumed that single-crystal silicon with a target diameter of 330 mm without dislocation can be produced under the same conditions as in Examples 8 and 9 when using arsenic or red phosphorus as a dopant. Furthermore, it is assumed from the results of Experiment 1 that no zone of remelting growth with a height of 200 µm or more is produced in the shoulder of each of the silicon single crystals of Examples 8 and 9 and the silicon single crystals with a target diameter of 330 mm, which were prepared using arsenic or red phosphorus as dopants under the same conditions as in Examples 8 and 9. It has thus been demonstrated that single-crystal silicon with no dislocation, enclosing a straight body with a target diameter of 200 mm or more, can be produced by rotating the crucible at 14 rpm or more during the shoulder formation step until the shoulder diameter reaches half the target diameter of the straight body or more, while heating the crucible with a heating ratio of 1, and then decreasing the crucible speed after the above point while keeping the heating ratio constant. Experiment 6: Relationship between specific resistance of the dopant, rotational speed of the crucible and dislocation. In Experiment 6, silicon single crystals with the following properties were produced and evaluated. Target diameter of the straight body: 200 mm Doping agent: see Table 7 Specific resistance: see Table 7 Table 7 Table 7 Reference example 1: Arsenic 3.0 Reference example 2: Arsenic 1.8 Reference example 3 red phosphorus 1.5 Reference example 4 red phosphorus 0.7 For reference examples 1 to 4, the silicon single crystals were prepared by maintaining the rotational speed of the crucible within a range of 6 rpm to 20 rpm in the shoulder formation step, as shown in Fig. 10A, and maintaining the heating ratio within a range of 1 to 2, as shown in Fig. 10B, and then carrying out the straight body formation step and the tail formation step. In conjunction with reference examples 1 to 4, Fig. 11 shows a relationship between the minimum crucible rotation speed that does not cause dislocation and the resistivity of single-crystal silicon. Fig. 11 shows that rotation speeds above a line representing this relationship do not cause dislocation, while rotation speeds below the line do cause dislocation. As shown in Fig. 11, it has been demonstrated that the minimum rotational speed of the crucible that does not cause dislocation increases with a decrease in the resistivity of the single-crystal silicon. EXPLANATION OF REFERENCE SYMBOLS 1...Device for growing a single crystal, 21...Chamber, 22...Crucible, 23...Heating, 231...Upper heating, 232...Lower heating, 24...Heat-insulating cylinder, 25...Growing cable (growing unit), M...Melt of silicon, MD...Melt with added dopant, SC...Seed crystal, SM...Single-crystal silicon (silicon single crystal), SM2...Shoulder.

Claims

A manufacturing process for single-crystal silicon according to a Czochralski process using a single-crystal growing apparatus, the apparatus comprising: a chamber; a crucible located in the chamber; a heater configured to heat the crucible and thus produce a dopant melt comprising a silicon melt and red phosphorus or arsenic in high concentrations as a dopant added to the silicon melt, the heater comprising an upper heating device configured to heat an upper side face of the crucible and a lower heating device configured to heat a lower side face of the crucible; and a growing unit configured to grow a seed crystal after the seed crystal has been brought into contact with the dopant melt.wherein the process comprises: forming a shoulder of single-crystal silicon; and forming a straight body with a target diameter of 200 mm or more, wherein the manufacturing conditions are adjusted such that the resistivity, when using arsenic as a dopant, ranges from 1.5 mΩ·cm to 3.5 mΩ·cm and when using red phosphorus as a dopant, ranges from 0.6 mΩ·cm to 1.2 mΩ·cm, and during shoulder formation, while a heating ratio calculated as the division of a quantity of heat from the lower heating device by a quantity of heat from the upper heating device is maintained at 1, the crucible is rotated at a speed maintained at 16 rpm or more and 30 rpm or less from the beginning of shoulder formation until a diameter of the shoulder being formed reaches half the target diameter of the straight body or more.and the rotational speed of the crucible is reduced at this time or thereafter. Manufacturing process for single-crystal silicon according to claim 1, wherein, during the formation of the shoulder, a portion of growth lines extending radially over the shoulder has an outer end which is interrupted by another portion of the growth lines in such a way that it does not reach a circumferential area of ​​the shoulder, and wherein no zone of remelting growth with a height of 200 µm or more is generated in any growth direction. Manufacturing process for single-crystal silicon according to claim 1 or 2, wherein, during the formation of the shoulder, the rotational speed of the crucible is gradually reduced at that time or thereafter such that, upon completion of the shoulder formation, it reaches 4 rpm or more and 12 rpm or less.

Images