JP2006290641A - Production method of compound single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a compound single crystal through an LEC (liquid encapsulated Czochralski) method, whereby a solid-liquid interface can be controlled to be convexly curved toward a melt, even when growing a large-diameter single crystal. <P>SOLUTION: A ring-shaped under-crucible heater 10 is placed below the peripheral side of a bottom wall of a crucible 7, and its heater surface is slanted off the horizontal plane so that it faces the bottom side of a crucible sidewall 7a. The crucible side wall is heated by the under-crucible heater 10 via the crucible bottom wall to form a large natural convection S of a GaAs melt 6 that rises near the crucible wall and flows toward a growing GaAs single crystal 3. The natural convection S overcomes a forced convection formed near the solid-liquid interface by a relative rotation of the GaAs single crystal 3 and the crucible 7 and becomes the dominant convection in the GaAs melt 6, which enables the solid-liquid interface to be convexly curved toward the GaAs melt 6. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a compound single crystal by a liquid sealing pulling method (LEC method), and more particularly to a method for producing a compound single crystal in which convection in a melt is improved by a heating means.

  Compound semiconductors have been widely used in high-speed integrated circuits, opto-electronic integrated circuits, and other electronic devices due to the high quality of single crystals. Among these, gallium arsenide (GaAs), a group III-V compound semiconductor, has a feature that the electron mobility is faster than that of silicon, and a wafer having a specific resistance of 10 7 Ω · cm or more is easy to manufacture. At present, GaAs single crystals are mainly manufactured by the liquid sealing pulling method (LEC method).

A method for producing a GaAs single crystal by the LEC method will be described with reference to FIG.
The GaAs single crystal manufacturing apparatus (pulling furnace) by the LEC method shown in FIG. 5 is a chamber 9 which is a pressure vessel, a pulling shaft 1 for pulling up the crystal, and a PBN (Pyrolytic) which is a container for containing a compound semiconductor material. A crucible 7 made of Boron Nitride), a crucible shaft 8 that supports the crucible 7, and a carbon heater 5 as a heating means installed around the crucible 7.

In manufacturing the crystal, first, Ga, As, and B ₂ O ₃ (boron trioxide) as a sealing agent are put in the crucible 7, and the crucible 7 is set in the chamber 9. A seed crystal 2 having a target orientation is attached to the tip of the pulling shaft 1. Next, the chamber 9 is evacuated and filled with an inert gas, and then the heater 5 is energized, the temperature in the chamber 9 is increased, and Ga and As are synthesized to produce a GaAs polycrystal. Thereafter, the temperature is further raised to melt the GaAs, and the surface of the GaAs melt 6 is covered with the B ₂ O ₃ melt 4.

  Subsequently, the pull-up shaft 1 and the crucible shaft 8 are relatively rotated. In this state, the pulling shaft 1 is lowered until the seed crystal 2 attached to the tip of the pulling shaft 1 comes into contact with the GaAs melt 6. Thereafter, the seed crystal 2 is slowly pulled up while rotating to grow a GaAs single crystal 3.

  Incidentally, in the production of a compound single crystal by the LEC method, there is a problem that the solid-liquid interface tends to be concave on the melt side and polycrystallizes from that portion. In particular, in a large-diameter crystal having a crystal diameter of 100 mm or more to be grown, the importance of the solid-liquid interface is more important than that of a small-diameter crystal, and it is necessary to have a convex surface stably on the melt side.

Therefore, in order to make the shape of the solid-liquid interface convex toward the melt side, attempts have been made to control the amount of heat generated by the heater and improve the shape of the heater and hot zone. For example, paying attention to the relationship between the depth of the initial raw material melt in the crucible, the length of the overlapping portion of the upper and lower slits of the heater, and the temperature at the bottom of the crucible, these are grown under certain conditions. (Refer to Patent Document 1).
Japanese Patent Publication No. 6-88873

However, in the conventional technique described above, when growing a large-diameter single crystal, it is difficult to stably control the solid-liquid interface shape to be convex toward the melt side.
More specifically, the solid-liquid interface shape that affects the generation of crystal defects is closely related to the convection in the melt of the raw material melt (GaAs melt). This convection in the melt consists of natural convection that rises from the vicinity of the crucible wall due to the temperature difference in the melt and moves toward the growing crystal, and forced convection that swirls near the solid-liquid interface due to the relative rotation of the crystal and crucible. is there. As the crystal diameter increases, forced convection near the solid-liquid interface due to rotation becomes dominant. For this reason, the solid-liquid interface shape tends to be concave on the melt side. Since dislocations propagate perpendicularly to the solid-liquid interface, if the solid-liquid interface is concave on the melt side, the dislocations will collect and polycrystallize, resulting in poor crystal quality. It is.

  The present invention solves the above-described problems and provides a method for producing a compound single crystal that allows the solid-liquid interface shape to be controlled to a convex surface on the melt side even when growing a large-diameter single crystal.

  According to a first aspect of the present invention, a raw material and a sealing agent are housed in a crucible, the inside of the crucible is heated by a heating means provided around the crucible to melt the raw material and the sealing agent, and a seed is added to the molten raw material melt. In the method for producing a compound single crystal using a liquid-sealed pulling method for growing a compound single crystal by bringing the seed crystal into contact with the crystal and pulling the seed crystal while rotating relative to the crucible, the bottom of the crucible A bottom heating means is provided below the wall outer peripheral side. The bottom heating means heats the crucible side wall through the crucible bottom wall, and rises from the vicinity of the crucible wall toward the growing compound single crystal. A method for producing a compound single crystal characterized by forming natural convection of a raw material melt.

  In this manner, the crucible side wall is heated through the bottom wall of the crucible by the bottom heating means, and the natural convection of the large raw material melt rising from the vicinity of the crucible wall toward the growing compound single crystal is formed. Therefore, overcoming the forced convection near the solid-liquid interface caused by the relative rotation of the single crystal and the crucible, natural convection is dominant in the convection in the raw material melt, and the solid-liquid interface shape is It becomes controllable to the convex side.

  According to a second invention, in the first invention, the bottom heating means is a ring-shaped heater along the outer peripheral portion of the crucible bottom wall, and the heater surface has a horizontal surface whose inner peripheral side is higher than the outer peripheral side. The diameter of the compound single crystal that is formed so as to be inclined with respect to the heater and alternately has slits cut in the radial direction from the inner peripheral edge and the outer peripheral edge of the heater and grows the length B of the slit. The value α (α = B / A) divided by A satisfies 0.1 ≦ α ≦ 0.45, and the inclination angle θ of the heater surface with respect to the horizontal plane satisfies 30 ° ≦ θ ≦ 40 °. It is a manufacturing method of the compound single crystal characterized.

  According to the present invention, natural convection of a large raw material melt rising from the vicinity of the crucible wall toward the growing compound single crystal is formed, so that the melt is ideal for growing a single crystal. It is possible to form a solid-liquid interface shape that is convex on the side. Therefore, a high-quality compound single crystal can be produced with a high yield.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an apparatus for producing a compound single crystal used in this embodiment. This single crystal manufacturing apparatus is made of PBN crucible 7 containing raw materials Ga and As and B ₂ O ₃ which is a sealing agent for preventing volatilization of As, and this crucible 7 is installed and filled with an inert gas. A chamber (pressure vessel) 9 which is a furnace body to be operated, a seed crystal 2 is attached to the lower end thereof, a pulling shaft 1 provided in the chamber 9 so as to be able to rotate and move up and down, and a crucible 7 in the chamber 9 A crucible shaft 8 that can be rotated and moved up and down, a main heater 15 as a heating means provided so as to surround the outer periphery of the crucible side wall 7a, and a bottom portion provided below the outer peripheral side of the crucible bottom wall 7b. It has a crucible lower heater 10 as a heating means, and a heat retaining member 16 disposed around the heaters 15 and 10.

  The main heater 15 is a cylindrical carbon heater, which is divided into three parts, an upper part, a middle part, and a lower part, so that the temperature can be controlled for each part. However, as a whole, the main heater 15 is longer in the vertical direction than the crucible 7. The length is long and is provided so as to surround the outer periphery of the crucible 7.

  The crucible lower heater 10 is a ring-shaped or annular heater along the outer peripheral portion of the crucible bottom wall 7 b, and is a carbon heater similar to the main heater 15. The heater surface facing the crucible bottom wall 7b of the lower crucible heater 10 has a conical surface shape that gradually increases from the outer peripheral side to the inner peripheral side, and the heater surface faces the bottom side of the crucible side wall 7a. Inclined by a tilt angle (the base angle of the cone) θ with respect to the horizontal plane.

  In addition, the lower crucible heater 10 has inner slits 11 and outer slits 12 alternately in the radial direction (width direction) from the inner peripheral edge portion 10a and the outer peripheral edge portion 10b of the heater 10, as shown in FIG. A belt-like heater in which the heater wire meanders is arranged in an annular shape. The inner slit 11 and the outer slit 12 have the same length B, and the slits 11 and 12 are formed at equal intervals along the circumferential direction of the annular crucible lower heater 10. The cylindrical main heater 15 is also provided with slits alternately as shown in FIG. 2 in the vertical direction from the upper end of the heater and the lower end of the heater.

  The crucible lower heater 10 has a value α = B / A obtained by dividing the length B of the slits 11 and 12 by the crystal diameter (diameter of the GaAs single crystal 3) A to be grown, that is, the length of the slit with respect to the crystal diameter A to be grown. The ratio α of the thickness B is set so as to satisfy 0.1 ≦ α ≦ 0.45. For example, when the diameter of the grown crystal is 4 inches (101.6 mm), the slit length B (mm) is in the range of 101.6 × 0.45≈45.7 ≧ B ≧ 101.6 × 0.1≈10.2. Further, the inclination angle θ of the heater surface of the lower crucible heater 10 described above with respect to the horizontal plane is set in a range satisfying 30 ° ≦ θ ≦ 40 °.

The method for producing a GaAs single crystal using the production apparatus is basically the same as the method for producing a GaAs single crystal of the LEC method described in the prior art. That is, in FIG. 1, the crucible 7 filled with Ga, As, and B ₂ O ₃ is placed on the crucible shaft 8 in the chamber 9, and the inside of the chamber 9 is evacuated and then replaced with an inert gas. The inside is a pressurized inert gas atmosphere. Next, the inside of the crucible 7 is heated to the melting point temperature or higher by the main heater 15 and the lower crucible heater 10 to form a GaAs melt 6 whose surface is covered with the B ₂ O ₃ melt 4. Further, the crucible 7 is moved in the vertical direction by the crucible shaft 8 so that the position of the uppermost surface of the GaAs melt 6 is substantially coincident with the position of the center of the heat generating portion of the main heater 5. Thereafter, the pulling-up shaft 1 is lowered to bring the seed crystal 2 into contact with the GaAs melt 6, and the seed crystal 2 is put into the crucible 7 while gradually decreasing the temperature in the chamber 9 mainly by adjusting the output of the main heater 5. The GaAs single crystal 3 is grown by raising the pull-up shaft 1 at a constant speed while rotating relative to the.

  The present embodiment is characterized by not only the main heater 15 but also the main heater 15 in order to improve the convection in the GaAs melt 6 to a flow suitable for single crystal growth in the manufacture of a GaAs single crystal using the LEC method. Further, the lower crucible heater 10 is provided below the outer peripheral side of the crucible bottom wall 7b, and the crucible side wall 7a is heated by the lower crucible heater 10 through the crucible bottom wall 7b.

  That is, in order to heat the bottom side of the crucible side wall 7a mainly through the outer peripheral part of the crucible bottom wall 7b, the lower crucible heater 10 is placed below the outer peripheral part side of the crucible bottom wall 7b and along the outer peripheral part of the crucible bottom wall 7b. The diameter of the GaAs single crystal 3 that is formed in a ring shape and grows the length B of the inner and outer slits 11 and 12 of the lower crucible heater 10 (corresponding to the effective heat generating portion length in the width direction of the lower crucible heater 10). A value α (= B / A) divided by A is set to 0.1 to 0.45. Further, the heater surface of the lower crucible heater 10 is inclined by an inclination angle θ (30 ° to 40 °) with respect to the horizontal plane in order to face the bottom side of the crucible side wall 7a.

  By setting the lower crucible heater 10 in this way, the heat rays R radiated from the lower crucible heater 10 mainly pass through the outer peripheral portion of the crucible bottom wall 7b as shown in FIG. 1, and the bottom side of the crucible side wall 7a. Is applied to heat the outer periphery of the crucible bottom wall 7b and the bottom side of the crucible side wall 7a. (Because the heater surface of the lower crucible heater 10 is inclined with respect to the horizontal plane by the inclination angle θ, the heat ray R is inclined by the angle θ from the vertical upward direction when θ = 0 to the radially outward direction of the crucible 7. The convection in the GaAs melt 6 rises from the vicinity of the crucible 7 wall as shown in FIG. 1, and grows as a result of this heating. The flow toward the surface (natural convection S) becomes larger, the natural convection S becomes dominant, and the solid-liquid interface shape tends to be convex on the GaAs melt 6 side. This makes it possible to form an ideal solid-liquid interface shape for growing the GaAs single crystal 3.

  On the other hand, the crucible lower shaft 8 is heated by the crucible lower heater 10 when the α value exceeds 0.45 outside the above range or when the inclination angle θ of the heater surface is 25 degrees or less. Therefore, in the convection in the GaAs melt 6, forced convection swirling in the vicinity of the solid-liquid interface is dominant due to the rotation of the GaAs single crystal 3, and the solid-liquid interface shape tends to be concave on the GaAs melt 6 side. Further, when the inclination angle θ of the heater surface of the lower crucible heater 10 is 45 degrees or more, the crucible side wall 7a is not heated and the natural convection S rising from the vicinity of the crucible wall is reduced, so that the solid-liquid interface shape is convex. Hard to become.

  Next, specific examples of the present invention will be described. In this example, in order to confirm the effect of the above embodiment, a GaAs single crystal having a diameter of 6 inches (15.24 cm) was grown. Here, by changing the slit length B of the lower crucible heater 10, the α value, which is the ratio of the slit length B to the crystal diameter (diameter of the GaAs single crystal 3) A to be grown, is set to 0.01 to 0.00. The growth was carried out by changing to 50. The inclination angle θ of the lower crucible heater 10 is constant (θ = 35 degrees).

  FIG. 3 shows the relationship of the production yield (single crystal yield) of the whole area single crystal to the α value in this case. As shown in FIG. 3, the single crystal yield starts to gradually increase as the α value increases, and the single crystal yield is 80% or higher from the 0.1th position, from 0.22 to 85%, from the 0.36th position to 90%. It became the above, and it turned out that it falls rapidly around 0.45. Accordingly, the α value for maintaining a high single crystal yield is a ratio of the slit length B to the crystal diameter A of 0.1 to 0.45, preferably 0.22 to 0.45, and more preferably 0. It is preferable to use the lower crucible heater 10 in a ratio of .36 to 0.45.

  Next, growth was performed by changing the inclination angle θ of the heater surface of the lower crucible heater 10 in the range of 0 to 55 degrees. The α value, which is the ratio of the slit length B to the crystal diameter A to be grown, was constant (α = 0.40).

  FIG. 4 shows the relationship of the production yield (single crystal yield) of the entire area single crystal to the heater inclination angle θ in this case. As the heater tilt angle θ increases, the single crystal yield begins to gradually increase. As shown in FIG. 4, when the tilt angle θ is 30 degrees, the single crystal yield reaches 90% and the tilt angle θ exceeds 40 degrees. From the vicinity, the single crystal yield is reduced to less than 90%. That is, it was found that the lower crucible heater 10 exhibits a high yield value in the range of the inclination angle θ of 30 to 40 degrees. Therefore, it is preferable that the lower crucible heater 10 is tilted in the range of the tilt angle θ of 30 to 40 degrees.

  In the above-described embodiments and examples, the case where a GaAs single crystal is manufactured by the LEC method has been described. However, the present invention is not limited to a GaAs single crystal but a method for manufacturing a compound single crystal using other materials such as GaP and InP. Of course, it can also be applied.

It is a longitudinal cross-sectional view which shows schematic structure of the compound single crystal manufacturing apparatus used by one Embodiment of this invention. It is the top view which expand | deployed and showed the ring-shaped crucible lower heater of FIG. It is the figure which showed the relationship between (alpha) value and the single crystal yield in the Example of this invention. It is the figure which showed the relationship between the inclination | tilt angle (theta) of the lower heater surface of a crucible, and the single crystal yield in the Example of this invention. It is a schematic longitudinal cross-sectional view which shows the manufacturing apparatus of the conventional compound single crystal.

Explanation of symbols

1 Pulling shaft 2 Seed crystal 3 GaAs single crystal 4 B2O3 melt 5 Main heater 6 GaAs melt 7 Crucible 7a Crucible side wall 7b Crucible bottom wall 8 Crucible shaft 9 Chamber 10 Crucible bottom heater 10a Inner peripheral edge 10b Outer peripheral edge 11 Inside Slit 12 Outer slit A Diameter of GaAs single crystal B Length of slit S Natural convection θ Angle of inclination of heater surface

Claims (2)

The raw material and the sealing agent are stored in the crucible, the inside of the crucible is heated by heating means provided around the crucible, the raw material and the sealing agent are melted, the seed crystal is brought into contact with the molten raw material melt, and the above In the method for producing a compound single crystal using a liquid sealing pulling method for growing a compound single crystal by pulling the seed crystal while rotating it relative to the crucible,
A bottom heating means is provided below the outer peripheral portion of the bottom wall of the crucible. The bottom heating means heats the crucible side wall through the crucible bottom wall, and ascends from the vicinity of the crucible wall to raise the growing compound alone. A method for producing a compound single crystal characterized by forming a natural convection of a large raw material melt toward a crystal. In the manufacturing method of the compound single crystal of Claim 1,
The bottom heating means is
A ring-shaped heater along the outer peripheral portion of the bottom wall of the crucible, the heater surface being inclined with respect to a horizontal plane such that the inner peripheral side is higher than the outer peripheral side, and the inner peripheral portion of the heater and While having alternately slits cut in the radial direction from the outer peripheral edge,
A value α obtained by dividing the length B of the slit by the diameter A of the compound single crystal to be grown is
0.1 ≦ α ≦ 0.45
And the inclination angle θ of the heater surface with respect to the horizontal plane is
30 ° ≦ θ ≦ 40 °
The manufacturing method of the compound single crystal characterized by satisfy | filling.

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