Abstract:
The present invention relates to methods for pulling a single crystal wherein the induction of dislocation can be inhibited and a single crystal can be held safely. An apparatus for pulling a single crystal having a straightening vane in the shape of an inverted truncated cone whose upper and lower planes are removed, which is located between a crucible and a single crystal, is used. The gap between the lower end portion of the straightening vane and the surface of a melt filled into the crucible can be selected in the range of 30-200 mm. Where the gap is set large in the range of 30-200 mm, the temperature of the front portion of a seed crystal is raised till the difference in temperature between the front portion thereof and the melt (the range of 1380-1480° C.) becomes almost zero. The seed crystal is brought into contact with the melt, a neck is formed with being heated, and a main body is pulled from the melt. Alternatively, an apparatus for pulling a single crystal having a crucible with through holes formed on the upper part thereof, or an apparatus for pulling a single crystal having an auxiliary heating means which has a body surrounding a seed crystal located near above the melt surface and a transfer mechanism for pulling the body is used in order to achieve the object.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to methods and apparatus for pulling a single crystal and, more particularly, to methods for pulling a single crystal wherein a single crystal of silicon or the like is pulled by a pulling method such as the Czochralski method (hereinafter, referred to as the CZ method), and an apparatus for pulling a single crystal. 
     2. Description of the Relevant Art 
     At present, the majority of silicon single crystals (ingots) used for manufacturing a substrate for forming a circuit component of a LSI (large scale integrated circuit) and the like have been pulled by the CZ method. FIG. 1 is a sectional view of a conventional apparatus for pulling a single crystal using the CZ method, and in the figure, reference numeral  11  represents a crucible. 
     The crucible  11  comprises a bottomed cylindrical quartz crucible  11   a  and a bottomed cylindrical graphite crucible  11   b  fitted on the outer side of the quartz crucible  11   a . The crucible  11  is supported with a support shaft  18  which rotates in the direction shown by the arrow A in the figure at a prescribed speed. A heater  12  of a resistance heating type and a heat insulating mold  17 , arranged around the heater  12 , are concentrically arranged around the crucible  11 . The crucible  11  is charged with a melt  13  of a material for forming a crystal which is melted by the heater  12 . On the central axis of the crucible  11 , a pulling axis  14  made of a pulling rod or wire, which is suspended, and at the front of the pulling rod or wire, a seed crystal  15  is held by a holder  14   a . These parts are arranged within a water cooled type chamber  19  wherein pressure of the chamber can be controlled. 
     A method for pulling a single crystal  16  using the above-mentioned apparatus for pulling a single crystal is described below by reference to FIGS. 1 and 2. FIGS.  2 ( a )-( d ) are partially enlarged front views diagrammatically showing the seed crystal  15  and the steps in a conventional method for pulling a single crystal. 
     Although it is not shown in FIG. 1, an electric current is applied to the heater  12  so as to melt the material for forming a crystal. after reducing the pressure in the chamber  19 . Then, an inert gas is introduced into the chamber  19  so as to make an inert gas atmosphere at a prescribed pressure within the chamber  19 . 
     While the pulling axis  14  is rotated on the same axis in the reverse direction of the support shaft  18  at a prescribed speed, the seed crystal  15 , held by the holder  14   a , is descended and is brought into contact with the melt  13  so as to make the front portion  15   a  of the seed crystal  15  partially melt into the melt  13 . Then, the pulling of the single crystal  16  from the melt  13  is started. This is referred to as the seeding as shown in (FIG.  2 ( a ). 
     In making a crystal grow at the front portion  15   a  of the seed crystal  15 , the pulling axis  14  is pulled at a higher speed than the below-described pulling speed in the formation of a main body  16   c . The crystal is narrowed to have a prescribed diameter, leading to the formation of a neck  16   a . This is referred to as the necking step (FIG.  2 ( b )). 
     By slowing down the pulling speed of the pulling axis  14  (hereinafter, simply referred to as the pulling speed), the neck  16   a  is made to grow to have a prescribed diameter, leading to the formation of a shoulder  16   b  (FIG.  2 ( c )). 
     By pulling the pulling axis  14  at a fixed rate, the main body  16   c  having a uniform diameter and a prescribed length is formed (FIG.  2 ( d )). 
     Although it is not shown in FIG. 2, in order to prevent induction of high density dislocation to the single crystal  16  by a sudden temperature change when the separation of the single crystal  16  from the melt  13  approaches, the diameter of the single crystal  16  is gradually decreased so that the temperature of the whole single crystal  16  is gradually lowered, leading to the formation of an end-cone. Next, the single crystal  16  is separated from the melt  13 . Finally, the single crystal  16  is cooled at the end of the pulling of the single crystal  16 . 
     One of the important steps in the pulling of the single crystal  16  is the above-mentioned necking step called the Dash method (J. Appl. Phys. 30 [4] (1959) W. C. Dash. p.459-473) (FIG.  2 ( b )). 
     The object of the necking step is described below. In the above seeding step (FIG.  2 ( a )), the front portion  15   a  of the seed crystal  15  is preheated to some extent and is brought into contact with the melt  13 . Ordinarily, there is a difference of 100° C. or more between the preheating temperature (about 1300° C. and less) and the melting point of the seed crystal  15  (about 1410° C.). Therefore, in contact with the melt  13 , the front portion  15   a  of the seed crystal  15  has a steep temperature gradient, leading to the induction of dislocation caused by a thermal stress thereto. It is necessary to make the single crystal  16  grow after excluding the dislocation which propagates and inhibits single crystal growth. Since the dislocation generally tends to grow in the vertical direction to the growth interface of the single crystal  16 , the shape of the growth interface (the front plane of the neck  16   a ) is made downward convex, so as to exclude the dislocation outward. 
     In the pulling of a single crystal, the faster the pulling speed, the smaller the diameter of the single crystal, or the more downwardly convex the shape of the growth interface of the single crystal. Therefore, in the above necking step, it is desired that the pulling speed be made as fast as possible to make the diameter of the neck  16   a  smaller, or to make the shape of the growth interface more downwardly convex, so as to efficiently exclude the dislocation outward. 
     In the above conventional method for pulling a single crystal, the seed crystal  15  having a diameter of, for example about 12 mm has been generally used in order to pull the single crystal  16  having a diameter of about 6 inches and a weight of 80 kg or so. In this case, the larger the diameter of the neck  16   a  is, the more safely the single crystal  16  can be supported, while the smaller the diameter of the neck  16   a  is, the more efficiently the dislocation can be excluded. In order to meet both of the requirements, the neck  16   a  having a diameter of 3 mm or so is selected. 
     Recently, however, in order to produce a more highly integrated semiconductor device at a lower cost and more efficiently, the wafer has been required to have a larger diameter. Now, for example, the production of the single crystal  16  having a diameter of about 12 inches (300 mm) and a weight of 300 kg or so is desired. When the diameter of the single crystal  16  is made larger, the weight of the shoulder  16   b  band tail inevitably becomes heavier. It becomes necessary to lengthen the main body  16   c  which can form a product in order to obtain the profitable yield. In other words, it becomes necessary to grow a heavy single crystal. 
     When the requirement is satisfied, the neck  16   a  having a conventional diameter (usually 3 mm or so) cannot withstand the weight of the pulled single crystal  16  and breaks, resulting in the falling of the single crystal  16 . 
     In growing the above heavy single crystal  16 , the diameter of the neck  16   a  needs to be about 5 mm or more in order to prevent the occurrence of troubles such as a fall of the single crystal  16  and to pull the single crystal  16  safely, which is calculated from the silicon strength (about 16 kgf/mm 2 ). However, when the diameter of the neck  16   a  is 5 mm or more, the dislocation which is induced in contact of the seed crystal  15  with the melt  13  cannot be sufficiently excluded outward. 
     In order to solve the problem, a method for growing a heavy single crystal was proposed in Japanese Kokai No. 62-288191, wherein the diameter is once increased after growing the neck  16   a , and is reduced and is increased again, so as to form a high-strength holding portion having a large diameter. which is mechanically held. It is possible to hold the heavy single crystal by this method, but a special jig, control, and the like which are exclusive to the mechanical holding are required in order to perform the mechanical holding in the method. In addition, when the mechanical holding is conducted on the high-strength holding portion, there is a possibility that shaking or the like is given to the high-strength holding portion, so that the growing portion is caused to have dislocation by the shaking or the like. As a result, there is a probability that the yield of the product is lowered. One of the present inventors invented a method for pulling a single crystal  16 , wherein by irradiating the front portion  15   a  of a seed crystal  15  with a laserbeam or the like from a laser beam generator or the like, the temperature of the front portion  15   a  of the seed crystal  15  is gradually raised so as to be almost the same temperature as that of a melt  13 , and then, the seed crystal  15  is brought into contact with the melt  13 , and the single crystal  16  is pulled from the melt  13  without forming a neck  16   a  (Japanese Patent Application No. 08-43765). In this method, since the temperature of the front portion  15   a  is adjusted to be made close to that of the melt  13  before the seed crystal  15  is brought into contact with the melt  13 , a sudden change in temperature (thermal shock) caused by the contact with the melt  13  can be reduced and the number of induced dislocations can be decreased. Therefore, even if the neck  16   a  is not formed, the single crystal  16  can be pulled with a decreased number of the induced dislocations, and the single crystal  16  heavier than before can be pulled. 
     However, since the irradiation of the laser beam is usually conducted only from one direction, the seed crystal  15  can be heated only from one direction. so that it is difficult to uniformly heat the front portion  15   a  of the seed crystal  15 . As a result, it is difficult to perfectly exclude the thermal shock which affects the front portion  15   a  in contact of the seed crystal  15  with the melt  13 , so that it is difficult to perfectly inhibit the induction of the dislocations to the single crystal  16 . 
     SUMMARY OF THE INVENTION 
     The present invention was developed in order to solve the above problems, and it is an object of the present invention to provide methods and apparatus for pulling a single crystal, wherein the induction of dislocation can be inhibited almost perfectly and a single crystal can be held safely even when the single crystal has a large diameter, or a heavy weight. 
     FIG. 3 is a sectional view diagrammatically showing the principal part of a conventional apparatus for pulling a single crystal in which a straightening vane is arranged. Here, the same marks are affixed to the same constructions as those of a conventional apparatus for pulling a single crystal shown in FIG.  1 . and the descriptions thereof are omitted. 
     Reference numeral  10  in the figure represents a straightening vane. The straightening vane  10 , having a shape of an inverted truncated cone in which the upper and lower planes are removed, surrounds a pulled single crystal  16  and is arranged so that the lower end portion thereof is located near the surface of a melt  13  within a crucible  11 . Ordinarily, the gap G between the lower end portion of the straightening vane  10  and the melt surface  13   a  is 15-20 mm or so. 
     In a series of processes for pulling the single crystal  16 , the straightening vane  10  shown in FIG. 3 is often used in order to efficiently eliminate silicon vapor, oxygen, and the like from the system. Therefore, the gap G is controlled from the viewpoint of the oxygen concentration control and the growth rate control. 
     The present inventors brought seed crystals  15  having various diameters into contact with the melt  13  with the conditions of various gaps (for example, various values between 15 mm and 45 mm) and further formed necks  16   a  having various diameters, so as to examine the incidence of dislocations. As a result, they ascertained that as the gap G becomes larger, the dislocation-free rate is improved while the number of induced dislocations on the contact interface of the melt  13  decreases. They also ascertained that as the diameters of the seed crystal  15  and the neck  16   a  become smaller, the dislocation-free rate is improved. 
     Furthermore, the present inventors formed through holes (slits) on the upper part of a graphite crucible  11   b  (FIG.  1 ), and brought the seed crystals  15  having various diameters into contact with the melt  13  with the conditions of various slit opening ratios (ratios of the total horizontal length of the slits to the perimeter of the crucible  11 ) and various heights of the slits (including the case of no slit), so as to examine the incidence of dislocations. As a result, they found that when the graphite crucible  11   b  having the slits formed with the conditions of the opening ratios and the heights within certain ranges is used, the induction of dislocations can be inhibited even if a large seed crystal  15  having a diameter of 10 mm or so is used. 
     It appears that the reasons for the above new knowledge are as follows. 
     1. With a larger gap G (or through the slits), the radiant quantity of a heater  12  to the seed crystal  15  increases, so that the temperature of the front portion  15   a  of the seed crystal  15  is easily raised. Therefore, the difference in temperature between the front portion  15   a  and the melt  13  in contact of the seed crystal  15  with the melt  13  becomes smaller, so that a thermal shock in the contact is reduced, leading to a decrease in number of the induced dislocations in the contact. 
     2. As the diameter of the seed crystal  15  becomes smaller, the heat capacity in the front portion  15   a  of the seed crystal  15  decreases, so that the temperature of the front portion  15   a  changes smoothly based on the difference in temperature between the front portion  15   a  and the melt  13  in the contact. Therefore, the temperature distribution in the horizontal direction of the front portion  15   a  becomes difficult to be caused in the contact, so that a thermal stress which affects the front portion  15   a  becomes smaller, leading to a decrease in number of the induced dislocations in the contact. 
     3. With a larger gap G (or through the slits), the radiant quantity of the heater  12  to the neck  16   a  increases in the formation of the neck  16   a . FIG.  4 ( a ) is a diagram showing the temperature distribution in the neck  16   a  in the formation of the neck  16   a  when the radiant quantity  12   a  is increased, and FIG.  4 ( b ) is a diagram showing the temperature distribution in the neck  16   a  in the formation of the neck  16   a  by a conventional method. 
     In FIG.  4 ( b ), since the neck  16   a  is strongly cooled by the flow of Ar gas, the isothermal line L b  is upward convex. In FIG.  4 ( a ), since the radiant quantity  12   a  of the heater  12  is increased, the isothermal line L a  is close to a plane in shape. The temperature gradient of the neck  16   a  in the horizontal direction becomes small, the thermal stress which affects the neck  16   a  is reduced, and the speed of dislocation movement decreases. As a result, the speed of propagation of the dislocation becomes low, so that the dislocation elimination ability in the neck  16   a  increases. 
     The present inventors further found from the above new knowledge, the reasons thereof, and the like that it is possible to reduce the number of induced dislocations in the contact and to increase the dislocation rejection ability in the neck  16   a  by making the front portion  15   a  of the seed crystal  15  uniformly hot from the whole periphery thereof, or heating the neck  16   a , using an apparatus for pulling a single crystal having an auxiliary heating means wherein a heating body is located so as to surround the seed crystal  15  and/or the neck  16   a.    
     In the method for pulling a single crystal ( 1 ) according to the present invention, an apparatus for pulling a single crystal having a crucible to be charged with a melt, a heater located around the crucible, and a straightening vane is used. The straightening vane has a body surrounding a pulled single crystal in the shape of an inverted truncated cone or a cylinder in which the upper and lower planes are removed, which is located between the crucible and the single crystal. The gap between the lower end portion of the body and the surface of the melt filled into the crucible (hereinafter, referred to as the gap) can be selected in the range of 30-200 mm. The method for pulling a single crystal ( 1 ) is characterized by using the above apparatus, raising the temperature of the front portion of the seed crystal till the difference in temperature between the front portion and the melt (1380-1480° C.) becomes almost zero, where the above gap is set large, bringing the seed crystal into contact with the melt, and pulling the single crystal without forming a neck. 
     In the method for pulling a single crystal ( 1 ), since the temperature of the front portion of the seed crystal is made close to that of the melt until both of them can be deemed almost the same before bringing the seed crystal into contact with the melt, a thermal shock in the front portion of the seed crystal caused by the contact with the melt can be reduced, leading to an inhibition of the induction of dislocations. Therefore, even if the neck is not formed, a dislocation-free single crystal can be pulled. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. 
     Since an apparatus having only an alteration of the gap G between the lower end portion of the body of the straightening vane and the surface of the melt filled into the crucible is used, a new special jig or the like is not required, so that an increase in cost of the pulling of a single crystal is not caused, compared with a conventional method. Since the neck need not be formed, the size of the whole seed crystal can be smaller than that in a usual pulling method. Therefore, since a cheaper seed crystal can be used, the cost of the pulling of a single crystal can be reduced. 
     The method for pulling a single crystal ( 2 ) according to the present invention is characterized by using an apparatus for pulling a single crystal having a crucible to be charged with a melt, a heater located around the crucible, and the like, wherein through holes and/or slits are formed on the upper part of the crucible, bringing a seed crystal into contact with the melt after raising the temperature of the front portion of the seed crystal until the difference in temperature between the front portion and the melt becomes almost zero, and pulling a single crystal without forming a neck. 
     The shapes of the through holes are not limited in any way, which are allowed to be a circle, an ellipse, or the like, besides a rectangle. 
     The slits described here, which are not included in the through holes, are in the form of a cut or the like, having an open upper part unlike the through holes, and the shapes thereof are not limited in any way, similarly to those of the through holes. 
     In the method for pulling a single crystal ( 2 ), since the temperature of the front portion of the seed crystal is made close to that of the melt until both of them can be deemed almost the same before bringing the seed crystal into contact with the melt, a thermal shock in the front portion of the seed crystal caused by the contact with the melt can be reduced, leading to an inhibition of the induction of dislocations. Therefore, even if the neck is not formed, a dislocation-free single crystal can be pulled. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. 
     Since an apparatus having only a difference that the through holes and/or slits are formed on the crucible is used, a new special jig or the like is not required, so that almost no increase in cost of the pulling of a single crystal is caused, compared with a conventional method. Since the neck need not be formed, the size of the whole seed crystal can be smaller than that in a usual pulling method. Therefore, since a cheaper seed crystal can be used, the cost of the pulling of a single crystal can be reduced. 
     The method for pulling a single crystal ( 3 ) according to the present invention is characterized by using an apparatus for pulling a single crystal having a crucible to be charged with a melt, a heater located around the crucible, and an auxiliary heating means which has a body surrounding a seed crystal located near above the melt surface and a transfer mechanism for pulling the body, bringing the seed crystal into contact with the melt after raising the temperature of the front portion of the seed crystal using the auxiliary heating means until the difference in temperature between the front portion and the melt becomes almost zero, and pulling a single crystal without forming a neck. 
     In the method for pulling a single crystal ( 3 ), since the temperature of the front portion of the seed crystal is made close to that of the melt until both of them can be deemed almost the same before bringing the seed crystal into contact with the melt, a thermal shock in the front portion of the seed crystal caused by the contact with the melt can be reduced, leading to an inhibition of the induction of dislocations. Therefore, even if the neck is not formed, a dislocation-free single crystal can be pulled. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. 
     Since the neck need not be formed, the size of the whole seed crystal can be smaller than that in a usual pulling method. Therefore, since a cheaper seed crystal can be used, the cost of the pulling of a single crystal can be reduced. In the formation of a main body and the like, the body of the auxiliary heating means can be pulled upward by the transfer mechanism so that the body thereof is out of the way of the pulling of a single crystal. 
     The method for pulling a single crystal ( 4 ) according to the present invention is characterized by using an apparatus for pulling a single crystal wherein through holes and/or slits are formed on the upper part of a crucible in the method for pulling a single crystal ( 1 ). 
     In the method for pulling a single crystal ( 4 ), the gap G between the lower end portion of the body of the straightening vane and the surface of the melt filled into the crucible is set to be large, and in addition, the crucible having the through holes and/or slits formed on the upper part thereof is used. Therefore, the temperature of the front portion of the seed crystal can be made close to that of the melt more easily. 
     The method for pulling a single crystal ( 5 ) according to the present invention is characterized by using an apparatus for pulling a single crystal having the crucible on which through holes and/or slits having a ratio of the total horizontal length of 10% or more to the perimeter of the crucible are formed in the method for pulling a single crystal ( 2 ) or ( 4 ). 
     In the method for pulling a single crystal ( 5 ), since the crucible which has the through holes and/or slits having a ratio of the total horizontal length of 10% or more to the perimeter of the crucible is used, the front portion of the seed crystal can be rapidly heated efficiently. 
     The method for pulling a single crystal ( 6 ) according to the present invention is characterized by using an apparatus having an auxiliary heating means which has a body surrounding a seed crystal located near above the melt surface and a transfer mechanism for pulling the body in the method for pulling a single crystal ( 1 ), ( 2 ), ( 4 ), or ( 5 ). 
     In the method for pulling a single crystal ( 6 ), by using the apparatus having the auxiliary heating means wherein the body can be positioned so as to surround the seed crystal, the temperature of the front portion of the seed crystal can be made close to that of the melt easily and uniformly. In the formation of a main body and the like, the body of the auxiliary heating means can be pulled upward by the transfer mechanism so that the body thereof is out of the way of the pulling of a single crystal. 
     In the method for pulling a single crystal ( 7 ) according to the present invention, an apparatus for pulling a single crystal having a crucible to be charged with a melt, a heater located around the crucible, and a straightening vane is used. The straightening vane has a body surrounding a pulled single crystal in the shape of an inverted truncated cone or a cylinder in which the upper and lower planes are removed, which is located between the crucible and the single crystal. The gap between the lower end portion of the body and the surface of the melt filled into the crucible (hereinafter, referred to as the gap) can be selected in the range of 30-200 mm. The method for pulling a single crystal ( 7 ) is characterized by using the above apparatus, bringing a seed crystal into contact with the melt where the gap is set to be large, and forming a neck with heating in a method for pulling a single crystal wherein the seed crystal is brought into contact with the melt filled in the crucible, the neck is formed by pulling the seed crystal, and a main body is pulled. 
     In the method for pulling a single crystal ( 7 ), by forming the neck with heating, the heat distribution in the neck is made planer and a thermal stress which affects the neck is reduced, so that the dislocation elimination ability in the neck can be increased. Therefore, since the dislocation can be eliminated even if the neck has a larger diameter, the single crystal can be pulled without propagating the dislocation even if a conventional neck having a small diameter is not formed. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. Since an apparatus having only an alteration of the gap G, compared with a conventional method, is used, a new special jig or the like is not required, so that an increase in cost is not caused. 
     The method for pulling a single crystal ( 8 ) according to the present invention is characterized by using an apparatus for pulling a single crystal having a heater located around a crucible and the crucible which has through holes and/or slits formed on the upper part thereof, forming a neck with heating in a method for pulling a single crystal wherein a seed crystal is brought into contact with a melt filled in the crucible, the neck is formed by pulling the seed crystal, and a main body is pulled. 
     In the method for pulling a single crystal ( 8 ), by heating the neck, the heat distribution in the neck is made planer and a thermal stress which affects the neck is reduced, so that the dislocation elimination ability in the neck can be increased. Therefore, since the dislocation can be eliminated even if the neck has a larger diameter, the single crystal can be pulled without propagating the dislocation even if a conventional neck having a small diameter is not formed. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. Since an apparatus having only a difference that the through holes and/or slits are formed on the crucible, compared with a conventional method, is used, a new special jig or the like is not required, so that a large increase in cost is not caused. 
     The method for pulling a single crystal ( 9 ) according to the present invention is characterized by using an apparatus for pulling a single crystal which has a heater located around a crucible and an auxiliary heating means having a body surrounding a seed crystal located near above a melt and a transfer mechanism for pulling the body, forming a neck with heating in a method for pulling a single crystal wherein the seed crystal is brought into contact with the melt filled in the crucible, the neck is formed by pulling the seed crystal, and a main body is pulled. 
     In the method for pulling a single crystal ( 9 ), by heating the neck, the heat distribution in the neck is made planer and a thermal stress which affects the neck is reduced, so that the dislocation elimination ability in the neck can be increased. Therefore, since the dislocation can be eliminated even if the neck has a larger diameter, the single crystal can be pulled without propagating the dislocation even if a conventional neck having a small diameter is not formed. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. In the formation of a main body and the like, the body of the auxiliary heating means can be pulled upward by the transfer mechanism so that the body thereof is out of the way of the pulling of a single crystal. 
     The method for pulling a single crystal ( 10 ) according to the present invention is characterized by using an apparatus for pulling a single crystal wherein through holes and/or slits are formed on the upper part of a crucible in the method for pulling a single crystal ( 7 ). 
     In the method for pulling a single crystal ( 10 ), by using the crucible having the through holes and/or slits formed on the upper part thereof, the neck can be heated more easily. As a result, the dislocation elimination ability in the neck can be further increased. 
     The method for pulling a single crystal ( 11 ) according to the present invention is characterized by using an apparatus for pulling a single crystal having the crucible on which through holes and/or slits having a ratio of the total horizontal length of 10% or more to the perimeter of the crucible are formed in the method for pulling a single crystal ( 8 ) or ( 10 ). 
     In the method for pulling a single crystal ( 11 ), by using the crucible on which the through holes and/or slits having a ratio of the total horizontal length of 10% or more to the perimeter of the crucible are formed, the neck can be sufficiently heated. 
     The method for pulling a single crystal ( 12 ) according to the present invention is characterized by using an apparatus having an auxiliary heating means which has a body surrounding a seed crystal located near above the melt surface and a transfer mechanism for pulling the body in the method for pulling a single crystal ( 7 ), ( 8 ), ( 10 ), or ( 11 ). 
     In the method for pulling a single crystal ( 12 ), by using the apparatus having the auxiliary heating means wherein the body is positioned so as to surround the neck and the like, the neck can be heated easily and uniformly. As a result, the dislocation elimination ability in the neck can be further increased. In the formation of a main body and the like, the body of the auxiliary heating means can be pulled upward by the transfer mechanism so that the body thereof is out of the way of the pulling of a single crystal. 
     The method for pulling a single crystal ( 13 ) according to the present invention is characterized by forming a neck having a diameter of 5-15 mm in one of the methods for pulling a single crystal ( 7 )-( 12 ). 
     In the method for pulling a single crystal ( 13 ), since the diameter of the neck is 5 mm or more, even a single crystal whose main body has a diameter of about 12 inches, having a heavy weight of 300 kg or so can be sufficiently supported in the pulling thereof. Since the diameter of the neck is 15 mm and less, the heat distribution in the neck becomes planer, so that the high dislocation elimination ability can be obtained in the neck. 
     The method for pulling a single crystal ( 14 ) according to the present invention is characterized by bringing the seed crystal into contact with the melt after raising the temperature of the front portion of the seed crystal until the difference in temperature between the front portion and the melt (1380-1480° C.) becomes almost zero in one of the methods for pulling a single crystal ( 7 )-( 13 ). 
     In the method for pulling a single crystal ( 14 ), since the temperature of the front portion of the seed crystal is made close to that of the melt (1380-1480° C. until both of them can be deemed almost the same before bringing the seed crystal into contact with the melt, a thermal shock in the front portion of the seed crystal caused by the contact with the melt can be reduced, leading to an inhibition of the induction of dislocations. Furthermore, by forming the neck with heating, the heat distribution in the neck is made planer and the thermal stress which affects the neck is reduced, so that the dislocation elimination ability in the neck can be increased. Therefore, even if a seed crystal having a large diameter is used, the number of induced dislocations can be eliminated, and even if the neck has a larger diameter, the dislocations can be rejected. Even if a seed crystal having a large diameter is used and the neck has a larger diameter, a single crystal can be pulled without propagating the dislocations. Even when a heavier dislocation-free single crystal than before is pulled, the single crystal can be sufficiently supported. 
     The method for pulling a single crystal ( 15 ) according to the present invention is characterized by bringing a seed crystal into contact with a melt after raising the temperature of the front portion of the seed crystal to 1380-1480° C. in one of the methods for pulling a single crystal ( 1 )-( 6 ), or ( 14 ). 
     In the method for pulling a single crystal ( 15 ), the seed crystal can be brought into contact with the melt with almost no dislocation induced. 
     The method for pulling a single crystal ( 16 ) according to the present invention is characterized by using a seed crystal having a diameter of 5-15 mm in one of the methods for pulling a single crystal ( 1 )-( 15 ). 
     In the method for pulling a single crystal ( 16 ), since the diameter of the seed crystal is 5 mm or more, even a single crystal whose main body has a diameter of about 12 inches, having a heavy weight of 300 kg or so can be sufficiently supported in the pulling thereof. Since the diameter of the seed crystal is 15 mm and less, the front portion of the seed crystal can be heated sufficiently before the contact with the melt, so that a thermal shock in contact with the melt can be inhibited. 
     The apparatus for pulling a single crystal ( 1 ) according to the present invention has a crucible to be charged with a melt, a heater located around the crucible, and a straightening vane having a body surrounding a pulled single crystal in the shape of an inverted truncated cone or a cylinder in which the upper and lower planes are removed. The body is located between the crucible and the single crystal, and the lower end portion thereof can be positioned near above the surface of the melt filled in the crucible. The apparatus for pulling a single crystal ( 1 ) is characterized by the gap between the melt surface and the lower end portion of the body (hereinafter, referred to as the gap) selected in the range of 30-200 mm. 
     In the apparatus for pulling a single crystal ( 1 ), since the range of the gap G is 30-200 mm. which is wide, the temperature of the front portion of the seed crystal can be raised close to that of the melt before bringing the seed crystal into contact with the melt, and a neck can be formed with heating. Accordingly, the induction of dislocations caused by a thermal shock in bringing the seed crystal into contact with the melt can be reduced, and the dislocation elimination ability in the neck can be increased. Therefore, even if a seed crystal having a large diameter is used, the number of induced dislocations can be reduced, and even if the neck has a larger diameter, the dislocations can be eliminated. As a result, a single crystal can be pulled without propagating the dislocations. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. Since the apparatus has only a difference of a larger gap G. compared with a conventional apparatus, a new special jig or the like is not required, so that an increase in cost is not caused. 
     The apparatus for pulling a single crystal ( 2 ) according to the present invention is characterized by through holes and/or slits formed on the upper part of a crucible in an apparatus for pulling a single crystal having the crucible to be ch arged with a melt, and a heater located around the crucible. 
     In the apparatus for pulling a single crystal ( 2 ), since the through holes and/or slits are formed on the upper part of the crucible, the temperature of the front portion of the seed crystal can be raised close to that of the melt before bringing the seed crystal into contact with the melt, and a neck can be formed with heating. Accordingly, the induction of dislocations caused by a thermal shock in bringing the seed crystal into contact with the melt can be reduced, and the dislocation elimination ability in the neck can be increased. Therefore, even if a seed crystal having a large diameter is used, the number of induced dislocations can be reduced, and even if the neck has a larger diameter, the dislocations can be eliminated. As a result, a single crystal can be pulled without propagating the dislocations. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. Since the apparatus has only a difference of through holes and/or slits formed on the crucible in a conventional apparatus, a new special jig or the like is not required, so that a large increase in cost is not caused. 
     The apparatus for pulling a single crystal ( 3 ) according to the present invention is characterized by having an auxiliary heating means which has a body surrounding a seed crystal and/or a neck located near above the melt surface and a transfer mechanism for pulling the body in an apparatus for pulling a single crystal having a crucible to be charged with the melt and a heater located around the crucible. 
     In the apparatus for pulling a single crystal ( 3 ), since the auxiliary heating means whose body can be positioned so as to surround the seed crystal and/or the neck is included, the temperature of the front portion of the seed crystal can be raised close to that of the melt before bringing the seed crystal into contact with the melt, and the neck can be formed with heating. Accordingly, the induction of dislocations caused by a thermal shock in bringing the seed crystal into contact with the melt can be reduced, and the dislocation elimination ability in the neck can be increased. Therefore, even if a seed crystal having a large diameter is used, the number of induced dislocations can be reduced, and even if the neck has a larger diameter, the dislocations can be eliminated. As a result, a single crystal can be pulled without propagating the dislocations. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. In the formation of a main body and the like, the body of the auxiliary heating means can be pulled upward by the transfer mechanism so that the body thereof is out of the way of the pulling of a single crystal. 
     The apparatus for pulling a single crystal ( 4 ) according to the present invention is characterized by through holes and/or slits formed on the upper part of a crucible in the apparatus for pulling a single crystal ( 1 ). 
     In the apparatus for pulling a single crystal ( 4 ), since the through holes and/or slits are formed on the upper part of the crucible, the temperature of the front portion of the seed crystal can be raised close to that of the melt more easily before bringing the seed crystal into contact with the melt, and the neck can be formed with heating. 
     The apparatus for pulling a single crystal ( 5 ) according to the present invention is characterized by the ratio of the total horizontal length of through holes and/or slits of 10% or more to the perimeter of a crucible in the apparatus for pulling a single crystal ( 2 ) or ( 4 ). 
     In the apparatus for pulling a single crystal ( 5 ), since the ratio of the total horizontal length of the through holes and/or slits is 10% or more to the perimeter of the crucible, the seed crystal and the neck can be heated sufficiently rapidly. 
     The apparatus for pulling a single crystal ( 6 ) according to the present invention is characterized by having an auxiliary heating means which has a body surrounding a seed crystal and/or a neck located near above the melt surface and a transfer mechanism for pulling the body in the apparatus for pulling a single crystal ( 1 ), ( 2 ), ( 4 ), or ( 5 ). 
     In the apparatus for pulling a single crystal ( 6 ), since the auxiliary heating means whose body can be positioned so as to surround the seed crystal and/or the neck is included, the temperature of the front portion of the seed crystal can be raised close to that of the melt easily and uniformly before bringing the seed crystal into contact with the melt, and the neck can be formed with heating. Accordingly, the induction of dislocations caused by a thermal shock in bringing the seed crystal into contact with the melt can be reduced, and the dislocation elimination ability in the neck can be increased. Therefore, even if a seed crystal having a large diameter is used, the number of induced dislocations can be reduced, and even if the neck has a larger diameter, the dislocations can be eliminated. As a result, a single crystal can be pulled without propagating the dislocations. Even a heavier single crystal than before can be sufficiently supported in the pulling thereof. In the formation of a main body and the like, the body of the auxiliary heating means can be pulled upward by the transfer mechanism so that the body thereof is out of the way of the pulling of a single crystal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic sectional view showing a conventional apparatus for pulling a single crystal used for the CZ method; 
     FIGS.  2 ( a ),  2 ( b ),  2 ( c ),  2 ( d ) are partial enlarged front views diagrammatically showing a seed crystal and the steps in a conventional method for pulling a single crystal: 
     FIG. 3 is a diagrammatic sectional view showing the principal part of a conventional apparatus for pulling a single crystal in which a straightening vane is arranged: 
     FIG.  4 ( a ) is a diagram showing a temperature distribution in a neck when the radiant quantity is increased, and 
     FIG.  4 ( b ) is a diagram showing a temperature distribution in a neck in a conventional method; 
     FIG. 5 is a diagrammatic sectional view showing the principal part of an apparatus for pulling a single crystal according to Embodiment (1) of the present invention; 
     FIG. 6 is a diagrammatic sectional view showing the principal part of an apparatus for pulling a single crystal according to Embodiment (2); 
     FIGS.  7 ( a ),  7 ( b ),  7 ( c ),  7 ( d ), and  7 ( e ) are partial enlarged front views diagrammatically showing a seed crystal and the vicinity thereof in part of the steps in a method for pulling a single crystal according to the Embodiments; and 
     FIG. 8 is a diagrammatic sectional view showing the principal part of an apparatus for pulling a single crystal according to Embodiment (3). 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the methods and apparatus for pulling a single crystal according to the present invention are described below by reference to the Figures of the drawings. Here, it is premised that a single crystal having a large diameter of 12 inches (about 300 mm) or more, or having a heavy weight is pulled. 
     Since the apparatus for pulling a single crystal according to Embodiment (1) of the present invention has the same construction as a conventional apparatus for pulling a single crystal shown in FIG. 1 except that a straightening vane is arranged therein, only the part related to the straightening vane is described here. 
     FIG. 5 is a diagrammatic sectional view showing the principal part of the apparatus for pulling a single crystal according to Embodiment (1). Reference numeral  10  in the figure represents a straightening vane. The straightening vane  10 , having a shape of an inverted truncated cone in which the upper and lower planes are removed, surrounds a pulled single crystal  6 . The lower end portion thereof is located above the surface  13   a  of a melt filled in a crucible  11  so that the gap G between the melt surface  13   a  and the lower end portion of the straightening vane  10  is 30-200 mm. 
     Since the apparatus for pulling a single crystal according to Embodiment (2) has the same construction as the conventional apparatus for pulling a single crystal shown in FIG. 1 except that through holes (or slits) are formed on a graphite crucible, only the part related to the through holes is described here. 
     FIG. 6 is a diagrammatic sectional view showing the principal part of the apparatus for pulling a single crystal according to Embodiment (2). Reference numeral  11   b  in the figure represents a graphite crucible. The graphite crucible  11   b  is fitted on the outer side of a quartz crucible  11   a . Plural through holes  11   c  are formed on the upper part of the graphite crucible  11   b . The horizontal length of the through hole  11   c  is selected so that the ratio of the total horizontal length of the plural through holes  11   c  to the perimeter of the graphite crucible  11   b  is 10% or more. It is desired that the plural through holes  11   c  be spaced uniformly on the upper part of the whole periphery of the graphite crucible  11   b , for the reason that the temperature of the front portion  5   a  of a seed crystal  5  can be raised uniformly from the whole periphery thereof or the like. 
     By using the apparatus for pulling a single crystal according to the Embodiment (1) or (2), it becomes possible to easily raise the temperature of the front portion  5   a  of the seed crystal  5  close to that of a melt  13  before bringing the seed crystal  5  into contact with the melt  13 , and to heat a formed neck  6   a.    
     The method for pulling a single crystal wherein the apparatus for pulling a single crystal according to the Embodiment (1) or (2) is used, is described below. FIGS.  7 ( a )-( e ) are partial enlarged front views diagrammatically showing a seed crystal and the vicinity thereof in part of the steps in a method for pulling a single crystal according to the Embodiments. 
     The steps before the below-described steps are conducted in the same manner as described in the Relevant Art. 
     While a pulling axis  14  is rotated on the same axis in the reverse direction of a support shaft  18  at a prescribed speed, a seed crystal  5  held by a holder  14   a  is caused to descend close to the surface of a melt  13 . The seed crystal  5  is preheated so as to raise the temperature of the front portion  5   a  of the seed crystal  5  (FIG.  7 ( a )). 
     By using a seed crystal  5  having a small diameter, the cost of the seed crystal  5  can be reduced, and the heat capacity of the front portion  5   a  decreases, so that the temperature of the front portion  5   a  can be easily changed in contact of the seed crystal  5  with the melt  13 . A temperature distribution in the horizontal direction of the front portion  5   a  in contact of the seed crystal  5  with the melt  13  becomes difficult to be caused, so that a thermal stress which affects the front portion  5   a  becomes small, leading to a decrease in number of induced dislocations in contact with the melt  13 . 
     However, when the seed crystal  5  has a diameter of less than 5 mm, it is difficult to obtain a sufficient load capacity to a heavy single crystal. Therefore, the seed crystal  5  preferably has a diameter of 5 mm or more. 
     To the contrary, when the seed crystal  5  has a diameter of more than 15 mm, it is difficult to sufficiently heat the front portion  5   a  of the seed crystal  5  before the contact with the melt  13 . Therefore, the seed crystal  5  preferably has a diameter of 5-15 mm from that viewpoint. 
     Since the seed crystal  5  has a melting point of about 1410° C., the temperature of the front portion  5   a  of the seed crystal  5  is eventually raised to 1380-1480° C. In a conventional method wherein an apparatus, not having a large gap G between the melt surface  13   a  and the lower end portion of a straightening vane  10 , or having no through hole  11   c , is used, the temperature of the front portion  5   a  can be raised only to 1300° C. or so, even if the preheating time is 5-120 minutes or so, which is long. However, since the radiant quantity of a heater  12  to the seed crystal  5  is increased by using the above apparatus (FIGS.  5  and/or  6 ), the temperature of the front portion  5   a  can be easily raised close to that of the melt  13 . 
     When the temperature of the front portion  5   a  is less than 1380° C. in contact of the seed crystal  5  with the melt  13 , the dislocations caused by a thermal stress are induced to the seed crystal  5  in contact of the seed crystal  5  with the melt  13 . On the other hand, when the temperature of the front portion  5   a  exceeds 1480° C. the viscosity of the front melting portion of the seed crystal  5  is lowered, leading to the falling of the front melting portion from the front portion  5   a.    
     The seed crystal  5  is caused to descend and the front portion  5   a  is brought into contact with the melt surface  13   a  (FIG.  7 ( b )). Since the difference in temperature between the front portion  5   a  of the seed crystal  5  and the melt  13  is small in this contact, a thermal stress caused by the difference in temperature hardly affects the seed crystal  5 , so that the number of induced dislocations caused by the thermal stress decreases. 
     In making a single crystal grow at the front of the seed crystal  5 , the pulling axis  14  is pulled at a higher speed than the below-described speed of the formation of a main body  6   c . By making the shape of the growth interface (the front plane of a neck  6   a ) of a single crystal  6  downward convex, the neck  6   a  is formed (FIG.  7 ( c )). In a conventional method, the propagation of dislocations is inhibited by narrowing the diameter of the neck  6   a . However, by using the above apparatus (FIGS.  5  and/or  6 ) the neck  6   a  wherein the dislocations can be eliminated can be formed without narrowing the diameter of the neck  6   a . The reason is that the dislocation elimination ability in the neck  6   a  increases, since the heat distribution in the neck  6   a  is made planer by an increase in radiant quantity of the heater  12  to the neck  6   a  which is being pulled, leading to a decrease of the thermal stress which affects the neck  6   a.    
     The neck  6   a  preferably has a diameter of 5-15 mm. The reason is that, when the neck  6   a  has a diameter of less than 5 mm, it is difficult to obtain a sufficient load capacity to a heavy single crystal. When the neck  6   a  has a diameter of more than 15 mm, it is difficult to obtain a planer heat distribution in the neck  6   a  during the formation of the neck  6   a , so that a thermal stress which affects the neck  6   a  becomes large, leading to the lowered dislocation elimination ability in the neck  6   a.    
     By slowing down the pulling speed of the pulling axis  14 , the single crystal  6  is grown to have a prescribed diameter (12 inches or so) , leading to the formation of a shoulder  6   b  (FIG.  7 ( d )). Then, the single crystal  6  is pulled at a prescribed speed, leading to the formation of the main body  6   c  (FIG.  7 ( e )). 
     Then, in the same manner as described in the above mentioned Relevant Art, the single crystal  6  is pulled, is separated from the melt  13 , and is cooled, leading to the completion of the pulling of the single crystal  6 . 
     The apparatus for pulling a single crystal according to Embodiment (3) is described below. 
     Since the apparatus for pulling a single crystal according to Embodiment (3) has the same construction as the conventional apparatus for pulling a single crystal shown in FIG. 1 except that an auxiliary heating means is arranged therein, only the part related to the auxiliary heating means is described here. 
     FIG. 8 is a diagrammatic sectional view showing the principal part of the apparatus for pulling a single crystal according to Embodiment (3). Reference numeral  20  represents an auxiliary heating means. A body  20   a  of the auxiliary heating means  20  is made of carbon, and is arranged so as to surround a seed crystal  5 , a neck  6   a , and the like. In growing a main body  6   c  and the like, it is not desired that the body  20   a  be located around a single crystal  6 . Therefore, the auxiliary heating means  20  has a transfer mechanism (not shown) and/or an arm by which the body  20   a  can be pulled upward after the contact of the seed crystal  5  with the melt  13  and during the formation of the neck  6   a.    
     By using the apparatus for pulling a single crystal according to the Embodiment (3), too, the temperature of the front portion  5   a  of the seed crystal  5  can be raised close to that of the melt  13  before bringing the seed crystal  5  into contact with the melt  13 , and the neck  6   a  can be formed with heating. 
     By making up a new apparatus for pulling a single crystal using a combination of each characteristic of the apparatus for pulling a single crystal according to the Embodiments (1)-(3), it becomes possible to more easily and uniformly raise the temperature of the front portion  5   a  of the seed crystal  5  close to that of the melt  13 , and to form the neck  6   a  with heating. As a new apparatus for pulling a single crystal using a combination of the characteristics, an apparatus for pulling a single crystal which has both a crucible  11  having plural through holes  11   c  and an auxiliary heating means  20  can be exemplified. 
     In the methods for pulling a single crystal using the apparatus for pulling a single crystal according to the Embodiments (1)-(3), the case where the radiant quantities of the heater  12  to both the seed crystal  5  and the neck  6   a  are increased is described, but the present invention is not limited to the methods according to the Embodiments. A method for pulling a single crystal  6  wherein only the radiant quantity to the seed crystal  5  is increased and the neck  6   a  is not formed, or a method for pulling a single crystal  6  wherein only the radiant quantity to the neck  6   a  is increased so that the dislocation elimination ability in the neck  6   a  is increased, can be included as a matter of course. 
     EXAMPLES AND COMPARATIVE EXAMPLES 
     The methods and apparatus for pulling a single crystal according to Examples are described below. 
     Examples 1-4 
     In Examples 1-4, an apparatus for pulling a single crystal according to the Embodiment (1) was used. As a comparison, the case where a single crystal was pulled by a conventional method (Comparative Example 1) and the case where a high-strength mechanical holding portion was formed to pull a single crystal (Comparative Example 2 (Japanese Kokai No. 62-288191)), using a conventional apparatus for pulling a single crystal used for the CZ method (FIG.  1 ), are also described. The conditions are as follows. 
     [Common conditions to Examples 1-4, and Comparative Examples 1 and 2] 
     Prepared quantity of material for crystal: 300 kg 
     Atmosphere in chamber  19 : Ar atmosphere 
     Flow of Ar: 100 liter/min 
     Pressure in crucible: 400 Pa 
     Inner diameter of crucible  11 : 30 inches 
     Shape of single crystal  6  or  16  to be pulled 
     Diameter: 300 mm 
     Length: 1600 mm 
     Number of pulls: 10 times 
     The individual conditions, and the DF (Dislocation Free) rate and the number of falls of the single crystals  6  or  16  in each case are shown in Table 1. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Diameter of 
                   
                 Number of 
                   
                   
               
               
                   
                 Width of 
                 seed 
                 Diameter of 
                 falls 
                 DF 
                   
               
               
                   
                 gap 
                 crystal 
                 neck 
                 (/10) 
                 rate 
                 Remarks 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Comparative 
                 20 mm 
                 15 mm 
                 4 mm 
                 10 
                 — 
                 Conventional 
               
               
                 Example 1 
                   
                   
                   
                   
                   
                 method 
               
               
                 Comparative 
                 20 mm 
                 15 mm 
                 4 mm 
                 0 
                 50% 
                 Mechanical 
               
               
                 Example 2 
                   
                   
                   
                   
                   
                 holding 
               
               
                   
                   
                   
                   
                   
                   
                 method 
               
               
                 Example 1 
                 80 mm 
                  7 mm 
                 7 mm 
                 0 
                 100%  
               
               
                 Example 2 
                 50 mm 
                  7 mm 
                 7 mm 
                 0 
                 80% 
               
               
                 Example 3 
                 80 mm 
                 15 mm 
                 7 mm 
                 0 
                 90% 
               
               
                 Example 4 
                 80 mm 
                 11 mm 
                 11 mm  
                 0 
                 70% 
               
               
                   
               
             
          
         
       
     
     As is obvious from the results shown in Table 1, in each of the Examples 1-4, the number of dislocations induced to the seed crystals  5  decreased and in addition, the dislocation elimination ability in the necks  6   a  increased, resulting in the DF rate of the pulled single crystals  6  of 70% or more. Since the seed crystals  5  and the necks  6   a  had sufficiently large diameters to pull heavy single crystals (e.g. a diameter of at least 7 mm), the number of falls was 0 (/10). 
     On the other hand, in the Comparative Example 1, since the diameters of the necks  16   a  were narrowed to be 4 mm, it appears that the dislocations were eliminated. But the single crystals  16  could not be supported sufficiently, so that the number of falls was 10 (/10), or all of the single crystals  16  fell. In the Comparative Example 2, since the mechanical holding method was adopted, the number of falls was 0 (/10). But since it was difficult to sufficiently lessen (restrict) the shaking in the holding of the high-strength holding portion by the mechanical holding mechanism, the dislocations were induced, resulting in the DF rate of 50%. 
     From each condition and result in the Examples 1-4, the below {circle around (1)}-{circle around (3)} are derived. 
     {circle around (1)} The DF rate is improved by setting the gap G wide. 
     Example 1: Width of gap G (80 mm) DF rate (100%) 
     Example 2: Width of gap G (50 mm) DF rate (80%) 
     {circle around (2)} The DF rate is improved by using a seed crystal  5  having a small diameter. 
     Example 1: Diameter of seed crystal (7 mm) DF rate (100%) 
     Example 3: Diameter of seed crystal (15 mm) DF rate (90%) 
     {circle around (3)} The DF rate is improved by forming a neck  6   a  on a seed crystal  5  having a small diameter. 
     Example 1: Diameter of seed crystal and neck (7 mm) DF rate (100%) 
     Example 4: Diameter of seed crystal and neck (11 mm) DF rate (70%) 
     From the above {circle around (1)}-{circle around (3)}, the new knowledge by the present inventors shown in SUMMARY OF THE INVENTION was confirmed. 
     Examples 5-9 
     Examples 5-9 wherein an apparatus for pulling a single crystal according to the Embodiment (2) was used are described below. As a comparison, the cases where a single crystal was pulled by a conventional method (Comparative Examples 3 and 5) and the case where a high-strength mechanical holding portion was formed to pull a single crystal (Comparative Example 4 (Japanese Kokai No. 62-288191)), using a conventional apparatus for pulling a single crystal used for the CZ method (FIG.  1 ), are also described. The conditions are as follows. [Common conditions to Examples 5-9, and Comparative Examples 3-5] 
     Prepared quantity of material for crystal: 300 kg 
     Atmosphere in chamber  19 : Ar atmosphere 
     Flow of Ar: 100 liter/min 
     Pressure in crucible: 400 Pa 
     Inner diameter of crucible  11 : 30 inches 
     Shape of single crystal  6  or  16  to be pulled 
     Diameter: 300 mm 
     Length: 1600 mm 
     Number of pulls: 5 times 
     The individual conditions, and the DF rate and the number of falls of the single crystals  6  or  16  in each case are shown in Table 2. Here, the through hole opening ratio is a ratio of the total horizontal length of plural through holes  11   c  to the perimeter of a crucible  11 . 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 through hole 
                 Height of 
                 Diameter of 
                 Number of 
                   
                   
               
               
                   
                 opening 
                 through 
                 seed crystal 
                 falls 
                 DF 
               
               
                   
                 ratio 
                 hole 
                 and neck 
                 ( /5) 
                 rate 
                 Remarks 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Comparative 
                 0% 
                  0 mm 
                 4 mm 
                 5 
                 — 
                 Conventional 
               
               
                 Example 3 
                   
                   
                   
                   
                   
                 method 
               
               
                 Comparative 
                 0% 
                  0 mm 
                 4 mm 
                 0 
                 40% 
                 Mechanical 
               
               
                 Example 4 
                   
                   
                   
                   
                   
                 holding 
               
               
                   
                   
                   
                   
                   
                   
                 method 
               
               
                 Comparative 
                 0% 
                  0 mm 
                 8 mm 
                 0 
                 0% 
                 Conventional 
               
               
                 Example 5 
                   
                   
                   
                   
                   
                 method 
               
               
                 Example 5 
                 5% 
                 64 mm 
                 8 mm 
                 0 
                 60% 
               
               
                 Example 6 
                 40% 
                 64 mm 
                 8 mm 
                 0 
                 100% 
               
               
                 Example 7 
                 40% 
                 32 mm 
                 8 mm 
                 0 
                 80% 
               
               
                 Example 8 
                 40% 
                 128 mm  
                 8 mm 
                 0 
                 100% 
               
               
                 Example 9 
                 40% 
                 65 mm 
                 14 mm  
                 0 
                 20% 
               
               
                   
               
             
          
         
       
     
     As is obvious from the results shown in Table 2, in each of the Examples 6-8, the number of dislocations induced to the seed crystals  5  decreased and in addition, the dislocation elimination ability in the necks  6   a  increased, resulting in the DF rate of the pulled single crystals  6  of 80% or more. Since the seed crystals  5  and the necks  6   a  had sufficiently large diameters to pull heavy single crystals (e.g. a diameter of at least 8 mm), the number of falls was 0 (/5). 
     On the other hand, in the Comparative Example 3, since the diameters of the seed crystals  15  and the necks  16   a  were 4 mm, which were small, it appears that the dislocations were eliminated. But the single crystals  16  could not be supported sufficiently, so that the number of falls was 5 (/5), or all of the single crystals  16  fell. 
     In the Comparative Example 4, since the mechanical holding method was adopted, the number of falls was 0 (/5). though the diameters of the seed crystals  15  and the necks  16   a  were small (4 mm). But since it was difficult to sufficiently lessen (restrict) the shaking in the holding of the high-strength holding portion by the mechanical holding mechanism, the dislocations were induced, resulting in the DF rate of 40%. 
     In the Comparative Example 5, since the diameters of the seed crystals  15  and the necks  16   a  were 8 mm, which were large, the number of falls was favorably 0 (/5). But the dislocations induced to the single crystals  16  could be hardly eliminated, resulting in the DF rate of 0%. 
     From each condition and result in the Examples 5-9, the below {circle around (1)}-{circle around (3)} are derived. 
     {circle around (1)} The DF rate is improved by setting the through hole opening ratio large. 
     Example 5: Through hole opening ratio (5%) DF rate (60%) 
     Example 6: Through hole opening ratio (40%) DF rate (100%) 
     {circle around (2)} The DF rate is improved by setting the height H of through hole  11   c  high. 
     Example 6: Height H (64 mm) DF rate (100%) 
     Example 7: Height H (32 mm) DF rate (80%) 
     Example 8: Height H (128 mm) DF rate (100%) 
     {circle around (3)} The DF rate is improved by forming a neck  6   a  on a seed crystal  5  having a small diameter. 
     Example 6: Diameter of seed crystal and neck (8 mm) DF rate (100%) 
     Example 9: Diameter of seed crystal and neck (14 mm) DF rate (20%) 
     From the above {circle around (1)}-{circle around (3)}, the new knowledge by the present inventors shown in SUMMARY OF THE INVENTION was confirmed. 
     Examples 10-13 
     Examples 10—13 wherein an apparatus for pulling a single crystal according to the Embodiment (3) was used are described below. As a comparison, the cases where a single crystal was pulled by a conventional method (Comparative Examples 6 and 8) and the case where a high-strength mechanical holding portion was formed to pull a single crystal (Comparative Example 7 (Japanese Kokai No. 62-288191)), using a conventional apparatus for pulling a single crystal used for the CZ method (FIG.  1 ), are also described. The conditions are as follows. 
     [Common conditions to Examples 10-13, and Comparative Examples 6-8] 
     Prepared quantity of material for crystal: 300 kg 
     Atmosphere in chamber  19 : Ar atmosphere 
     Flow of Ar: 100 liter/min 
     Pressure in crucible: 400 Pa 
     Inner diameter of crucible  11 : 30 inches 
     Shape of single crystal  6  or  16  to be pulled 
     Diameter: 300 mm 
     Length: 1600 mm 
     Number of pulls: 5 times 
     The individual conditions, and the DF rate and the number of falls of the single crystals  6  or  16  in each case are shown in Table 3. Here, the front temperature of seed crystal is the temperature of the front portion of the seed crystal  5  or  15  before the seed crystal  5  or  15  is brought into contact with a melt  13 , and the power in neck is a heating power of an auxiliary heating means  20  during the formation of a neck  6   a.    
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Front 
                   
                 Diameter 
                   
                   
                   
               
               
                   
                 temperature 
                   
                 of seed 
                 Number of 
               
               
                   
                 of seed 
                 Power in 
                 crystal 
                 falls 
               
               
                   
                 crystal 
                 neck 
                 and neck 
                 (/5) 
                 DF rate 
                 Remarks 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Comparative 
                 ˜1300° C. 
                 — 
                 4 mm 
                 5 
                 — 
                 Conventional 
               
               
                 Example 6 
                   
                   
                   
                   
                   
                 method 
               
               
                 Comparative 
                 ˜1300° C. 
                 — 
                 4 mm 
                 0 
                 40% 
                 Mechanical 
               
               
                 Example 7 
                   
                   
                   
                   
                   
                 holding 
               
               
                   
                   
                   
                   
                   
                   
                 method 
               
               
                 Comparative 
                 ˜1380° C. 
                 — 
                 8 mm 
                 0 
                 0% 
                 Conventional 
               
               
                 Example 8 
                   
                   
                   
                   
                   
                 method 
               
               
                 Example 10 
                 1380˜1390° C. 
                 1 kW 
                 8 mm 
                 0 
                 100% 
               
               
                 Example 11 
                 1380˜1390° C. 
                 1 kW 
                 14 mm  
                 0 
                 40% 
               
               
                 Example 12 
                 1380˜1390° C. 
                 0.5 kW   
                 8 mm 
                 0 
                 80% 
               
               
                 Example 13 
                 1380˜1390° C. 
                 1 kW 
                 8 mm 
                 0 
                 100% 
               
               
                   
               
             
          
         
       
     
     As is obvious from the results shown in Table 3, in each of the Examples 10, 12, and 13, the number of dislocations induced to the seed crystals  5  decreased and in addition, the dislocation elimination ability in the necks  6   a  increased, resulting in the DF rate of the pulled single crystals  6  of 80% or more. Since the seed crystals  5  and the necks  6   a  had sufficiently large diameters to pull heavy single crystals (e.g. a diameter of at least 8 mm), the number of falls was 0 (/5). 
     On the other hand, in the Comparative Example 6, since the diameters of the seed crystals  15  and the necks  16   a  were 4 mm, which were small, it appears that the dislocations were eliminated. But the single crystals  16  could not be supported sufficiently, so that the number of falls was 5 (/5), or all of the single crystals  16  fell. 
     In the Comparative Example 7, since the mechanical holding method was adopted, the number of falls was 0 (/5), though the diameters of the seed crystals  15  and the necks  16   a  were small (4 mm). But since it was difficult to sufficiently lessen (restrict) the shaking in the holding of the high-strength holding portion by the mechanical holding mechanism, the dislocations were induced, resulting in the DF rate of 40%. 
     In the Comparative Example 8, since the diameters of the seed crystals  15  and the necks  16   a  were 8 mm, which were large, the number of falls was favorably 0 (/5). But the dislocations induced to the single crystals  16  could be hardly eliminated, resulting in the DF rate of 0%. 
     From each condition and result in the Examples 10-13, the below {circle around (1)} and {circle around (3)} are derived. 
     {circle around (1)} The DF rate is improved by increasing a heating power during the formation of a neck  6   a.    
     Example 10: Heating power (1 kW) DF rate (100%) 
     Example 12: Heating power (0.5 kW) DF rate (80%) 
     {circle around (2)} The DF rate is improved by forming a neck  6   a  on a seed crystal  5  having a small diameter. 
     Example 10: Diameter of seed crystal and neck (8 mm) DF rate (100%) 
     Example 11: Diameter of seed crystal and neck (14 mm) DF rate (40%) 
     From the above {circle around (1)} and {circle around (2)}, the new knowledge by the present inventors shown in SUMMARY OF THE INVENTION was confirmed.