JP2006151745A - Method for producing single crystal and oxide single crystal obtained by using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a single crystal, which is based on a Czochralski method and by which an oxide single crystal having uniform characteristics and an arbitrary length can be grown in high reproductibility. <P>SOLUTION: In the method for producing the single crystal, comprising immersing a seed crystal 13 attached to a pulling shaft into a raw material melt 14 heated and melted in a crucible 11, and growing the oxide single crystal by pulling the seed crystal 13, the ratio (d/D) of the diameter of a grown crystal 15 to the inner diameter of the crucible 11 is set to be within a range of 0.45-0.65, and the ratio (H/D) of the height at the inner diameter side of the crucible 11 to the inner diameter of the crucible 11 is set to be within a range of 0.4-1.5. Further, as the material of the crucible 11, a material containing at least one kind of iridium, molybdenum, tungsten and rhenium is used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a single crystal by the Czochralski method and sapphire.

  FIG. 2 shows a cross-sectional view of a conventional single crystal manufacturing apparatus using the Czochralski method.

  The crucible 11 for producing a single crystal is induction-heated by the high-frequency heating coil 15, and the raw material in the crucible 11 is heated to the melting point or higher to form the melt 14. On the crucible 11 and the raw material melt 14, a rotary pulling shaft 12 to which a seed crystal 13 is attached is provided. The single crystal 15 is pulled up and grown after contacting the seed crystal 13 with the surface of the melt 14. In order to grow the single crystal 15 having a diameter of a certain size, in general, the weight or weight change of the actual grown crystal is detected with respect to the crystal weight or weight change when it is assumed to have the target diameter. By comparing the detected weight and weight change with the calculated weight and weight change, the temperature of the melt can be changed by means of high frequency and resistance heating, and the weight and weight change of the crystal to be grown can be increased or decreased. A technique for controlling the diameter is used.

  At this time, the melt inside the crucible needs to have a temperature distribution in the radial direction and the pulling direction. If there is no temperature gradient in the crucible wall direction, the temperature of the melt is changed to control the diameter. Further, the crystal is separated from the melt, or the crystal grows from the melt surface or the crucible wall, which makes it difficult to control the diameter and makes the crystal growth itself difficult. Therefore, it is necessary to make appropriate the relationship between the diameter of the crucible to be heated and the crystal diameter to be grown, which is a factor affecting the temperature distribution in the radial direction and the pulling direction of the melt inside the crucible.

  In Patent Document 1, as a method for producing a compound semiconductor single crystal with high reproducibility and high yield by the LEC method, the ratio of the crystal to be grown and the diameter of the crucible {(crucible diameter) / (crystal diameter)} is 2.2. A method for producing a single crystal in the range of ~ 3.2 has been reported.

  This is because, when the ratio of the diameter of the crystal to be grown and the crucible is less than 2.2, the solid-liquid interface is not stable, and a concave portion is likely to be formed on the melt side. It is supposed to lead to the formation of grain boundaries. If the ratio of the diameter of the crystal to be grown and the crucible is 3.2 or more, the weight of the crystal grown per unit time is measured, this is arithmetically processed to calculate the crystal diameter, and the heating means In general, the output of the heater is controlled, and if the ratio of the diameter of the crystal to be grown and the diameter of the crucible becomes too large, the response to the diameter with respect to the control of the output of the heater becomes slow. Furthermore, it is supposed that the fluctuation of the diameter of the crystal to be grown becomes large. If the crystal diameter fluctuates drastically, the solid-liquid interface is not stabilized, and a concave portion is likely to be formed on the melt side. Dislocations are concentrated and lead to the formation of lineage and subgrain boundaries.

  Furthermore, in Patent Document 2, when a gallium phosphide single crystal having a diameter of 63.5 mm or more is grown as a liquid sealing pull-up method (LEC method) using boron oxide (B 2 O 3), the crystal diameter / crucible inner diameter is 0. A method for producing a gallium phosphide single crystal that is .7 or less has been reported.

  By using the above method, the temperature difference between the melt surface and the liquid sealant surface can be reduced, and bubbles near the solid-liquid interface are prevented from being taken into the crystal, and voids are generated on the crystal top side. This can be suppressed and generation of voids in the wafer can be suppressed.

In other words, the generation of voids takes place in order to compensate for the rapid growth of the crystal at the solid-liquid interface or the decrease in the temperature of the melt by being rapidly cooled when the crystal head comes out of the liquid sealant. It is said that bubbles near the solid-liquid interface are taken into the crystal because the melt is supersaturated due to rapid heating and bubbles are generated. Therefore, the crystal diameter / crucible inner diameter is set to 0.7 or less for the purpose of reducing the temperature difference between the melt surface and the liquid sealant surface.
JP 2001-80989 A JP 2003-192498 A

  However, in sapphire crystal growth, the thermal conductivity of the melt or crystal is high and the crystal is transparent to infrared rays, so the crystal or melt is difficult to absorb the radiant heat from the inner wall of the crucible and the inner diameter of the crucible. When the diameter of the crystal to be grown is small, it is difficult to control the diameter of the crystal because the temperature gradient on the surface of the melt near the crucible center cannot be sufficiently obtained with respect to the temperature gradient near the crucible wall.

  In addition, when the crystal diameter is large, the area where the grown crystal comes into contact with the melt increases, and heat radiation due to the radiant heat from the melt below the crystal increases through the crystal, so the temperature of the melt decreases and the crystal in the melt direction decreases. Growth is likely to occur, and the bottom of the crystal becomes excessively convex to lower the quality of the crystal, and it may be difficult to grow the crystal by contacting the bottom of the crucible.

  Accordingly, the present invention provides a method for producing a single crystal by the Czochralski method, wherein the ratio of the diameter of the grown crystal to the inner diameter of the crucible (crystal diameter d / crucible inner diameter D) is in the range of 0.45 to 0.65. It is characterized by being set to.

  Moreover, in the manufacturing method of the single crystal by the Czochralski method, the ratio of the inner diameter side height of the crucible to the inner diameter of the crucible (crucible inner diameter side height H / crucible inner diameter D) is in the range of 0.5 to 1.5. It is characterized by being set to.

  Furthermore, in the method for producing a single crystal by the Czochralski method, the crucible contains at least one of iridium, molybdenum, tungsten, and rhenium.

  In addition, an oxide single crystal is manufactured using the method for manufacturing a single crystal of the present invention, and the impurity content of the oxide single crystal is 1% or less.

  According to the method for producing a single crystal according to the present invention, the ratio of the diameter of the grown crystal to the inner diameter of the crucible (crystal diameter d / crucible inner diameter D) is set in the range of 0.45 to 0.65, Therefore, it becomes easy to control the diameter of the crystal, and the bottom of the crystal is not greatly lowered. Thereby, the crystal obtained by the method for producing a single crystal of the present invention has a high quality without crystal defects such as grain boundaries and lineage. Furthermore, by setting the ratio of the inner diameter side height of the crucible to the inner diameter of the crucible (crucible inner diameter side height H / crucible inner diameter D) in the range of 0.5 to 1.5, solid liquefaction can be achieved by convection of the melt. High quality crystals with few crystal defects can be grown by diffusing bubbles and impurities accumulated at the interface.

  Furthermore, according to the present invention, since the crucible contains at least one of iridium, molybdenum, tungsten, or rhenium, there is no reaction with the melt, and the crystal can be grown in an atmosphere containing oxygen or an inert atmosphere. It becomes possible.

In addition, in the method for producing an oxide single crystal, by using the method for producing a single crystal of the present invention, it is possible to stably grow a crystal with high productivity, and to grow a high-quality crystal with few crystal defects. Can do. Furthermore, crystal growth under oxygen and inert atmosphere becomes possible.

  Further, the single crystal manufacturing method of the present invention can grow a crystal with few crystal defects, and the sapphire substrate formed from the crystal has few defects and is suitable for epitaxial growth on the substrate. Therefore, it is guaranteed to be particularly suitable for crystal growth for manufacturing a sapphire substrate.

  An embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view showing an embodiment of a single crystal manufacturing apparatus according to the method of the present invention.

  The crucible 11 for producing a single crystal is disposed in a concave portion of a heat insulating material 17 disposed in a bottomed cylindrical crucible holding container 16, and a raw material melt 14 is disposed in the crucible 11. Has been.

  Further, a work coil 20 is coaxially disposed around the crucible holding container 16, and a heat insulating heat retaining disc 18 is disposed in the vicinity of the central portion on the inner diameter side of the crucible holding container 16. Further, an outer heat insulating material 19 is disposed on the upper part of the crucible holding container 16, and a pulling shaft 12 for pulling the single crystal 15 together with the seed crystal 13 is passed through the central portion of the outer heat insulating material 19. Through-holes are formed.

  First, the seed crystal 13 cut in the target crystal orientation is fixed to the tip of the pulling shaft 12. The crucible 11 is induction-heated by the work coil 20, and the raw material melt 14 is formed by heating the raw material in the crucible 11 to the melting point or higher. Then, an inert gas is flowed, the pulling shaft 12 is lowered, the tip of the seed crystal 13 is brought into contact with the surface of the melt 14, the seed crystal 13 and the melt 14 are blended, and then the pulling shaft 12 is rotated. While raising, start raising.

  First, the output of the work coil 20 is lowered so that the ratio of the diameter of the grown crystal 15 to the inner diameter of the crucible 11 (crystal diameter d / crucible inner diameter D) is in the range of 0.45 to 0.65. After controlling the diameter of 15 to form the shoulder portion of the crystal 15 in a conical shape, the straight body portion is pulled up to a certain length with the above diameter. Finally, the temperature of the melt 14 is raised by increasing the output of the work coil 20, and the diameter of the bottom of the crystal 15 is reduced by the reverse operation of expanding the diameter from the seed crystal 13 to a conical shape. 14 and crystal 15 are separated. After this operation, the temperature in the furnace 10 is lowered to room temperature, the crystal 15 is taken out of the furnace, and crystal growth is completed.

  Here, the ratio of the diameter of the grown crystal 15 to the inner diameter of the crucible 11 (crystal diameter d / crucible inner diameter D) is in the range of 0.45 to 0.65, whereby the temperature gradient from the crucible wall. The crystal diameter can be easily controlled by temperature operation, and the area of the melt 14 in contact with the crystal 15 is not increased more than necessary, so that the temperature of the melt 14 is lowered by the radiant heat transmitted through the crystal 15, It is possible to avoid quality degradation and difficulty in growing due to unstable growth of the lower part of the crystal 14, and it is possible to stably grow a crystal 15 having a high quality and a stable shape.

  However, if the ratio of the diameter of the grown crystal 15 to the inner diameter of the crucible 11 (crystal diameter d / crucible inner diameter D) is less than 0.45, the distance from the crucible 11 to the crystal 15 becomes too large, and the vicinity of the crucible 11 Such a temperature gradient cannot be obtained in the vicinity of the crystal 15, so that the control of the crystal diameter becomes unstable, which is not preferable. Further, the diameter variation of the crystal 15 is increased, and accordingly, crystal defects such as grain boundaries and lineage enter from the outer periphery of the crystal, and the defects increase to the inside of the crystal. On the other hand, when the ratio of the diameter of the grown crystal 15 to the inner diameter of the crucible 11 (crystal diameter d / crucible inner diameter D) is larger than 0.65, the distance from the crucible 11 is shortened, but the melt portion in contact with the crystal 15 is large. Therefore, the temperature of the melt 14 decreases due to heat radiation by radiant heat through the crystal 15, and crystal growth becomes difficult. Further, since the bottom of the crystal becomes greatly convex toward the melt, the macroscopic defect density of the crystal 15 is increased by incorporating bubbles and impurities near the crystal growth interface into the crystal 15.

  Furthermore, in the present invention, the ratio of the inner diameter side height of the crucible 11 to the inner diameter of the crucible 11 (crucible inner diameter side height H / crucible inner diameter D) is set in the range of 0.5 to 1.5. When the ratio between the inner diameter side of the crucible 11 and the inner diameter of the crucible 11 (crucible inner diameter side height H / crucible D inner diameter) is less than 0.5, the melt near the crucible is heated, so that the surface of the melt is crucible. Natural convection flowing from the side surface to the center of the crucible concentrates in the vicinity of the side surface of the crucible, and bubbles and impurities accumulated at the solid-liquid interface with the grown crystal are difficult to diffuse into the melt and are easily taken into the crystal 15. Further, the crystal 15 is brought into contact with the bottom of the crucible 11 by the growth of the crystal 15 toward the melt 14 due to the heat radiation of the melt 14 through the crystal 15, so that the growth becomes difficult.

  On the other hand, if the ratio between the inner diameter side height of the crucible 11 and the inner diameter of the crucible 11 (crucible inner diameter side height H / crucible inner diameter D) is greater than 1.5, the natural temperature due to the temperature difference between the upper and lower portions of the melt 14 in the crucible 11 When the influence of the convection increases and the lower part of the melt 14 at the bottom of the crucible 11 has a higher temperature, natural convection rises from the bottom of the crucible 11 toward the grown crystal 15, and bubbles accumulated at the solid-liquid interface with the grown crystal 15 Convection that diffuses impurities into the melt 14 is unlikely to occur. Further, when the melt at the bottom of the crucible 11 is at a lower temperature or when there is no temperature difference, convection itself hardly occurs, and the effect of diffusing bubbles and impurities accumulated at the solid-liquid interface with the grown crystal 15 into the melt 14 is achieved. Therefore, bubbles and impurities are easily taken into the grown crystal 15 and the quality of the crystal is lowered.

  The material of the crucible 11 preferably contains at least one of iridium, molybdenum, tungsten, and rhenium. This is because there is no reaction with the melt and it is possible to grow crystals in various atmospheres such as an oxygen-containing atmosphere and an inert atmosphere. Among these materials, iridium and molybdenum are made of crucibles. This is particularly preferable from the viewpoint of processability and cost.

  Furthermore, when the sapphire single crystal grown by this manufacturing method contains impurities exceeding 1%, the quality as a transparent substrate falls by the light absorption by an impurity, or the scattering by a precipitate.

Example 1
A sapphire crystal was grown by the apparatus shown in FIG. The diameter of the target crystal was 65 mm, and a crucible made of iridium having an inner diameter of 100 mm and a depth of 100 mm was used. The crucible was charged with 2200 g of an alumina raw material having a purity of 99.99%, and the whole crucible was heated and melted, and then a seed crystal of sapphire crystal was immersed in the melt and rotated up.

  A crystal growth method was used in which the conical crystal shoulder was formed so that the diameter of the crystal was 65 mm when it was pulled 30 mm from the tip of the seed crystal, and then the temperature was controlled so that the diameter became 65 mm.

  As a result, the crystal growth method according to Example 1 made it easy to control the crystal diameter. When the diameter variation of the grown sapphire crystal was examined, it was 65 mm ± 1 mm in diameter at the length of the straight body portion of 100 mm. The diameter of bubbles and inclusions mixed in the crystal was 10 μm at the maximum.

(Example 2)
A sapphire crystal was grown by the apparatus shown in FIG. The diameter of the target crystal was 68 mm, and the crucible made of molybdenum having an inner diameter of 150 mm and a depth of 150 mm was used. The crucible was filled with 8500 g of a 99.99% purity alumina raw material, and the whole crucible was heated and melted, and then the seed crystal of sapphire crystal was immersed in the melt, and then rotated up.

A crystal growth method was used in which the conical crystal shoulder was formed so that the diameter of the crystal was 68 mm when the seed crystal was lifted 40 mm from the tip, and then the temperature was controlled so that the diameter became 68 mm.

  As a result, the crystal growth method according to Example 2 made it easy to control the crystal diameter. When the diameter variation of the grown sapphire crystal was examined, it was 68 mm ± 1 mm in diameter at the portion of the straight body portion of 150 mm in length. The diameter of bubbles and inclusions mixed in the crystal was 10 μm at the maximum.

(Comparative Example 1)
A sapphire crystal was grown by the apparatus shown in FIG. The diameter of the target crystal was 60 mm, and the crucible made of iridium having an inner diameter of 150 mm and a depth of 150 mm was used. The crucible was filled with 8500 g of a 99.99% purity alumina raw material, and the whole crucible was heated and melted, and then the seed crystal of sapphire crystal was immersed in the melt, and then rotated up.

A crystal growth method was used in which the conical crystal shoulder was formed so that the diameter of the crystal was 60 mm when it was pulled 30 mm from the tip of the seed crystal, and then the temperature was controlled so that the diameter became 60 mm.

  As a result, the crystal growth method according to Comparative Example 1 could not control the crystal diameter. When the diameter variation of the grown sapphire crystal was examined, it was 60 mm ± 5 mm in diameter at the portion of the length of the straight body portion of 150 mm. The diameter of bubbles and inclusions mixed in the crystal was 10 μm at the maximum.

(Comparative Example 2)
A sapphire crystal was grown by the apparatus shown in FIG. The target crystal had a diameter of 70 mm, and a crucible made of molybdenum having an inner diameter of 100 mm and a depth of 100 mm was used. The crucible was filled with 2200 g of a 99.99% purity alumina raw material, and the entire crucible was heated and melted, and then the seed crystal of sapphire crystal was immersed in the melt and pulled up.

A crystal growth method was used in which the conical crystal shoulder was formed so that the diameter of the crystal was 70 mm when the seed crystal was pulled 40 mm from the tip, and then the temperature was controlled so that the diameter became 70 mm.

  As a result, in the crystal growth method according to Comparative Example 2, the diameter was easily controlled up to a length of 80 mm, but the melt below the crystal was solidified and could not be grown. When the diameter variation of the grown sapphire crystal was examined, the diameter was 70 mm ± 1 mm up to 80 mm. Further, the diameter of bubbles or inclusions mixed in the crystals having a length of up to 80 mm was 10 μm at the maximum, and the number thereof was larger than those in Examples 1 and 2.

Table 1 below summarizes the above results.

  In Examples 1 and 2 in which the ratio of the diameter of the grown crystal 15 and the inner diameter of the crucible 11 (crystal diameter d / crucible inner diameter D) is in the range of 0.45 to 0.65, diameter control is easy and the diameter varies. Is small. In the case of Comparative Example 1 where (crystal diameter d / crucible inner diameter D) is less than 0.45, the diameter cannot be controlled and the fluctuation in diameter becomes large. Further, in Comparative Example 2 where (crystal diameter d / crucible inner diameter D) is larger than 0.65, diameter control was easy up to a length of 80 mm and diameter fluctuation was small, but growth was impossible after a length of 80 mm. As a result, the length of the straight body portion was shortened.

(Example 3)
A sapphire crystal was grown by the apparatus shown in FIG. The diameter of the target crystal was 60 mm, and the crucible made of iridium having an inner diameter of 100 mm and a depth of 50 mm was used. The crucible was charged with 1,200 g of a 99.99% purity alumina raw material, and the entire crucible was heated and melted, and then the seed crystal of sapphire crystal was immersed in the melt and pulled up.

  A crystal growth method was used in which the conical crystal shoulder was formed so that the diameter of the crystal was 60 mm when it was pulled 30 mm from the tip of the seed crystal, and then the temperature was controlled so that the diameter became 60 mm.

  As a result, the crystal growth method according to Example 3 made it easy to control the crystal diameter. When the diameter variation of the grown sapphire crystal was examined, it was 60 mm ± 1 mm in diameter at the portion of the length of the straight body portion of 60 mm. The diameter of bubbles and inclusions mixed in the crystal was 10 μm at the maximum.

Example 4
A sapphire crystal was grown by the apparatus shown in FIG. The target crystal had a diameter of 60 mm, and a crucible made of molybdenum having an inner diameter of 100 mm and a depth of 150 mm was used. The crucible was filled with 4300 g of an alumina raw material having a purity of 99.99%, and the whole crucible was heated and melted, and then a seed crystal of sapphire crystal was immersed in the melt and rotated up.

A crystal growth method was used in which the conical crystal shoulder was formed so that the diameter of the crystal was 60 mm when it was pulled 30 mm from the tip of the seed crystal, and then the temperature was controlled so that the diameter became 60 mm.

  As a result, the crystal growth method according to Example 4 made it easy to control the crystal diameter. When the diameter variation of the grown sapphire crystal was examined, it was 60 mm ± 1 mm in diameter at the portion of the straight body portion having a length of 150 mm. The diameter of bubbles and inclusions mixed in the crystal was 10 μm at the maximum.

(Example 5)
A sapphire crystal was grown by the apparatus shown in FIG. The diameter of the target crystal was 75 mm, and the crucible made of iridium having an inner diameter of 150 mm and a depth of 60 mm was used. The crucible was filled with 2800 g of an alumina raw material having a purity of 99.99%, and the entire crucible was heated and melted, and then a seed crystal of sapphire crystal was immersed in the melt and rotated up.

A crystal growth method was used in which the conical crystal shoulder was formed so that the diameter of the crystal was 75 mm when the seed crystal was pulled 40 mm from the tip, and then the temperature was controlled so that the diameter became 75 mm.

  As a result, in the crystal growth method according to Example 5, it was easy to control the diameter of the crystal up to the length of 70 mm of the straight body portion. When the diameter variation of the grown sapphire crystal was examined, the diameter of the straight body portion was 70 mm and the diameter was 75 mm ± 1 mm. However, when the diameter exceeded 70 mm, the bottom of the crystal was in contact with the bottom of the crucible and was difficult to grow. The diameter of bubbles and inclusions mixed in the crystal was 10 μm at the maximum.

(Comparative Example 6)
A sapphire crystal was grown by the apparatus shown in FIG. The diameter of the target crystal was 60 mm, and the crucible made of iridium having an inner diameter of 100 mm and a depth of 160 mm was used. The crucible was charged with 4500 g of an alumina raw material having a purity of 99.99%, and the whole crucible was heated and melted, and then the seed crystal of the sapphire crystal was immersed in the melt and rotated up.

A crystal growth method was used in which the conical crystal shoulder was formed so that the diameter of the crystal was 60 mm when it was pulled 30 mm from the tip of the seed crystal, and then the temperature was controlled so that the diameter became 60 mm.

  As a result, the crystal growth method according to Example 6 made it easy to control the crystal diameter. When the diameter variation of the grown sapphire crystal was examined, it was 60 mm ± 1 mm in diameter at the portion of the straight body portion having a length of 150 mm. Moreover, the diameters of the bubbles and inclusions mixed in the crystal from the length of the straight body portion of 100 mm to the bottom of the crystal were 30 μm to 100 μm.

Table 2 below summarizes the above results.

  In the case of Examples 3 and 4 where the ratio of the inner diameter side height of the crucible 11 to the inner diameter of the crucible 11 (crucible inner diameter side height H / crucible inner diameter D) was in the range of 0.5 to 1.5, it mixed into the grown crystal. The bubble diameter was as small as 10 μm at the maximum, and high quality crystals were obtained.

  Further, in Example 5 where (crucible inner diameter side height H / crucible inner diameter D) was less than 0.5, the crystal bottom contacted the crucible bottom, making it difficult to continue the growth. On the other hand, in the case of Example 6 where (crucible inner diameter side height H / crucible inner diameter D) is larger than 1.5, the diameter of the bubbles mixed in the grown crystal is as large as 100 μm at the maximum, and is grown in Examples 3 and 4. A crystal with poor quality was obtained as compared with the crystal.

It is sectional drawing which shows one Example of the single-crystal manufacturing apparatus by the method of this invention. It is sectional drawing which shows the conventional single crystal manufacturing apparatus by the Czochralski method.

Explanation of symbols

10: Inside of furnace 11: Crucible 12 of the present invention: Pulling shaft 13: Seed crystal 14: Raw material melt 15: Crystal 16: Crucible holding container 17: Insulating material 18: Insulating heat insulating disc 19: Outer insulating material 20: Work coil 21: Conventional crucible

Claims (5)

In the method for producing a single crystal by the Czochralski method, the ratio of the diameter of the grown crystal to the inner diameter of the crucible for producing the single crystal (crystal diameter d / crucible inner diameter D) is set in the range of 0.45 to 0.65. A method for producing a single crystal, characterized by comprising: The ratio between the inner diameter side height and the inner diameter of the single crystal manufacturing crucible (crucible inner diameter side height H / crucible inner diameter D) is set in a range of 0.5 to 1.5. A method for producing a single crystal. The method for producing a single crystal according to claim 1, wherein the crucible for producing the single crystal contains at least one of iridium, molybdenum, tungsten, and rhenium. An oxide single crystal produced by using the method for producing a single crystal according to any one of claims 1 to 3. The oxide single crystal according to claim 4, wherein the content of impurities is 1% or less.

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