JP2009149452A - Method for growing semiconductor crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing a semiconductor crystal by which a high quality semiconductor crystal can be obtained with good reproducibility, and to provide a semiconductor crystal in which the dislocation density is uniform. <P>SOLUTION: In a furnace 1 for growing the semiconductor crystal by a VGF (vertical gradient freeze) method, a melt 34 accommodated in a crucible 20 is heated from the side face side and the opening part side of the crucible in a state where the melt 34 is brought into contact with a seed crystal 30 provided at one end of the crucible 20, whereby at least during crystal growth, the heating temperature on the opening part side is held to be higher than the heating temperature on the side face side, so that the temperature at one end of the crucible 20 on the seed crystal 30 side is held lower than the temperature at the other end of the crucible 20 (the opening part side of the crucible 20). Under such conditions, a single crystal of a compound semiconductor crystal is grown by gradually solidifying the melt 34 from the seed crystal 30 side toward the other end of the crucible 20 by lowering the temperature of the melt 34. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor crystal growth method. In particular, the present invention relates to a semiconductor crystal growth method for growing a semiconductor crystal from a semiconductor melt.

  Conventionally, as a method for growing a III-V compound semiconductor crystal or the like, vertical slow cooling, which is a vertical growth method in which a single crystal is grown by gradually solidifying a semiconductor melt from below to above in a crucible. A (Vertical Gradient Freeze: VGF) method and a Vertical Bridgman (VB) method are known.

For example, Patent Document 1 includes a container for storing a raw material melt, a temperature gradient furnace disposed around the container, and means for moving the temperature gradient furnace relative to the container, and one end of the container Describes a single crystal production apparatus using a BN container in which B ₂ O ₃ is contained in the wall of the container.

According to the single crystal manufacturing apparatus described in Patent Document 1, since B ₂ O ₃ oozes out gradually from the wall surface of the BN container during use and the wall surface of the crucible is covered with the B ₂ O ₃ film, It is possible to prevent generation of crystal nuclei caused by contact with the irregular wall surface of the crucible surface.
Japanese Patent No. 2558515

  However, in the conventional compound semiconductor crystal manufacturing apparatus described in Patent Document 1, twins and polycrystals may be generated during crystal growth. In some cases, the density of dislocation defects generated inside the crystal varies greatly along the crystal growth direction inside the crystal. The present inventor has found that the density of transition defects generated inside the crystal changes along the crystal growth direction inside the crystal because of a temperature gradient in the radial direction of the growing crystal. It came to the knowledge of. Furthermore, the density of defects may vary with each crystal growth, and it has been difficult to obtain a single crystal with few defects with good reproducibility.

  Accordingly, an object of the present invention is to provide a semiconductor crystal growth method capable of obtaining a high-quality semiconductor crystal with good reproducibility, and further to provide a semiconductor crystal having a uniform dislocation density.

  In order to achieve the above-mentioned object, the present invention heats a crucible containing a semiconductor seed crystal and a semiconductor raw material to use the raw material as a melt, a raw material melting step, a crucible side surface, and a crucible opening side. And a crystal growth step for growing a single crystal of the semiconductor while maintaining the temperature heated from the opening side higher than the temperature heated from the side surface at least during crystal growth. Is done.

  In the semiconductor crystal growth method, the crystal growth step may grow the single crystal by solidifying the melt by lowering the crucible in the region heated from the side surface and the opening side. In the crystal growth step, the single crystal may be grown by solidifying the melt by gradually lowering the temperature heated from the side surface side and the temperature heated from the opening side. Further, in the crystal growth step, at least during the progress of crystal growth, the single crystal may be grown without having an inflection point in the temperature distribution in the vertical direction (crystal growth direction) in the melt.

  Further, in the semiconductor crystal growth method, the crystal growth step is performed at least during the progress of the crystal growth, in which the temperature distribution in the vertical direction (crystal growth direction) in the solidified single crystal has no inflection point. You may grow. In the crystal growth step, the single crystal may be grown with the moving speed of the crystal growth interface being substantially constant. Further, the semiconductor may be a III-V group compound semiconductor, and the semiconductor may be GaAs.

  According to the semiconductor crystal growth method of the present invention, a high-quality semiconductor crystal can be obtained with good reproducibility, and furthermore, a semiconductor crystal with a uniform dislocation density can be obtained.

[First Embodiment]
FIG. 1 shows an outline of a cross section of a crystal growth furnace according to a first embodiment of the present invention.

(Structure of crystal growth furnace 1)
The crystal growth furnace 1 according to the first embodiment accommodates a crucible 20 as a container for accommodating a raw material of a growing compound semiconductor crystal, a susceptor 50 as a crucible accommodating container for accommodating the crucible 20, and a susceptor 50. A susceptor support member 55 that holds the crucible 20 from above, and an upper heater 10 as an upper heating unit that heats the crucible 20 from above, and an outer peripheral heater 12 as a plurality of outer peripheral heating units that heat the crucible 20 from the side.

  Further, the crystal growth furnace 1 includes a plurality of heat insulating materials 60 that prevent heat generated by the upper heater 10 and the plurality of outer peripheral heaters 12 from being transmitted to the outside of the crystal growth furnace 1, and one outer peripheral heater 12 ( For example, a heat insulating material 62 provided between the outer peripheral heater 12b) and another outer peripheral heater 12 (for example, the outer peripheral heater 12c), a chamber 70 that covers the plurality of heat insulating materials 60, the heat insulating materials 62, and the like from the outside. Is provided.

  The crystal growth furnace 1 according to the present embodiment grows a single crystal of a compound semiconductor crystal by a VGF method. That is, in the crystal growth furnace 1, one end of the crucible 20 on the seed crystal 30 side is placed in the crucible 20 with the melt 34 accommodated in the crucible 20 in contact with the seed crystal 30 installed at one end of the crucible 20. The melt 34 is gradually solidified from the seed crystal 30 side toward the other end of the crucible 20 by lowering the temperature of the melt 34 while maintaining a lower temperature than the other end (opening side of the crucible 20). Thus, a single crystal of the compound semiconductor crystal is grown. The compound semiconductor crystal grown in the crystal growth furnace 1 is, for example, a single crystal of GaAs that is a III-V group compound semiconductor.

  The crucible 20 has a narrow diameter portion 25 as a seed crystal arrangement portion that accommodates the seed crystal 30 of the compound semiconductor crystal, an inclined portion 26 that is provided continuously to the narrow diameter portion 25 at a predetermined angle, and a continuous to the inclined portion 26. And a straight body portion 27 having a circular cross section including a portion substantially parallel to the longitudinal direction of the small-diameter portion 25. The straight body portion 27 of the crucible 20 has a substantially circular shape in a top view, and is formed in a substantially cylindrical shape having a diameter of 160 mm and a length of 300 mm as an example. The crucible 20 is made of pyrolytic boron nitride (pBN). The crucible 20 can also be formed from quartz.

That is, the crucible 20 has a narrow diameter portion 25 at the bottom and a crucible opening 22 that exposes the inside of the crucible 20 at the end of the substantially cylindrical straight barrel portion 27. The crucible 20 accommodates the seed crystal 30 in the small diameter portion 25 and also accommodates a predetermined amount of the compound semiconductor crystal material introduced from the crucible opening 22 and a predetermined dopant for p-type or n-type. The crucible 20 further accommodates a liquid sealing material 40 such as B ₂ O ₃ . The raw material of the compound semiconductor crystal is a growing compound semiconductor polycrystal.

  In the crucible 20, the compound semiconductor raw material melt 34 melted at a predetermined temperature comes into contact with the seed crystal 30 of the small diameter portion 25 to form a single crystal. The generated single crystal gradually grows as a growth crystal 32 in the crucible 20 from the seed crystal 30 side to the upper side of the crystal growth furnace 1.

  The susceptor 50 is made of graphite and holds and accommodates the crucible 20. The susceptor support member 55 is provided so that it can be moved up and down and rotated freely in the crystal growth furnace 1. The susceptor 50 is mounted and held on the susceptor support member 55. In this case, the susceptor lower part 52 below the susceptor 50 comes into contact with the susceptor support member 55, and the susceptor 50 is mounted on the susceptor support member 55. Thereby, the crucible 20 can be rotated during crystal growth for the purpose of keeping the temperature distribution in the crucible 20 gentle and constant.

  Each of the plurality of outer peripheral heaters 12 is disposed along a direction from the upper part to the lower part of the crystal growth furnace 1. In this case, the plurality of outer peripheral heaters 12 are respectively arranged at predetermined height positions inside the crystal growth furnace 1 so as to surround the periphery of the susceptor 50. Specifically, the outer peripheral heater 12a, the outer peripheral heater 12b disposed under the outer peripheral heater 12a, the outer peripheral heater 12c disposed under the outer peripheral heater 12b, and the outer heater 12c. The outer peripheral heater 12d is arranged along the direction from the upper part to the lower part of the crystal growth furnace 1.

  The set temperatures of the plurality of outer peripheral heaters 12 are set so as to decrease sequentially along the direction from the top to the bottom of the crystal growth furnace 1. That is, the set temperatures of the plurality of outer heaters 12 are set so that the set temperature of the outer heater 12a> the set temperature of the outer heater 12b> the set temperature of the outer heater 12c> the set temperature of the outer heater 12d. The

  The upper heater 10 is disposed above the crucible opening 22. That is, the upper heater 10 is disposed closer to the crucible opening 22 than the small diameter portion 25 in which the seed crystal 30 is accommodated. The upper heater 10 heats the melt 34 in the crucible 20 from the susceptor upper portion 51 and the crucible opening 22 side. That is, the upper heater 10 heats the end face without heating the side face of the crucible 20. The upper heater 10 has a heat generating surface, and the heat generating surface is disposed substantially perpendicular to the longitudinal direction of the crucible 20. In other words, the heat generating surface is arranged substantially horizontally with the liquid surface of the melt 34 accommodated in the crucible 20.

  The upper heater 10 supplies heat for heating the melt 34 from above the melt 34 so that the heat flow flows in one direction from above to below the crucible 20. That is, the upper heater 10 melts a predetermined amount of heat into the melt so that the heat flow passing through the melt 34 in the crucible 20 becomes a substantially straight line from the crucible opening 22 side toward the seed crystal 30 side. 34 is supplied from above.

  The set temperature of the upper heater 10 is set higher than any set temperature of the plurality of outer peripheral heaters 12. In addition, as long as the upper heater 10 is arrange | positioned above the crucible opening part 22, the shape and magnitude | size and the position with respect to the outer periphery heater 12 are not ask | required. The crystal growth furnace 1 can also be formed by further including a lower heater for heating the crucible 20 from the susceptor lower part 52 side. The lower heater is disposed in the chamber 70 so that the heating surface thereof is substantially parallel to the liquid surface of the melt 34 in the crucible 20.

  Each of the upper heater 10, the lower heater, and the plurality of outer peripheral heaters 12 is configured as a resistance heater formed of a material such as silicon carbide (SiC), for example. The upper heater 10, the lower heater, and the plurality of outer heaters 12 can each be constituted by a carbon heater, an infrared heater, a heater that uses a heating element heated by an RF coil as a secondary heater, or the like.

  The heat insulating material 60 is provided so as to surround the outer sides of the plurality of outer peripheral heaters 12 and the upper heater 10. By providing the heat insulating material 60, the heat generated by the plurality of outer peripheral heaters 12 and the upper heater 10 can be efficiently transferred to the crucible 20. On the other hand, the heat insulating material 62 is provided between one outer peripheral heater 12 and another outer heater 12 in order to ensure a predetermined temperature difference between the outer peripheral heater 12 and the other outer heater 12. Placed in.

  The chamber 70 includes a crucible 20, a susceptor 50 that accommodates the crucible 20, a susceptor support member 55 that holds the susceptor 50, an upper heater 10, a plurality of outer peripheral heaters 12, a heat insulating material 60, and a heat insulating material 62. Seal. The crystal growth furnace 1 has a function for setting the atmosphere in the chamber 70 to a predetermined gas atmosphere (for example, an inert atmosphere such as nitrogen) and a gas pressure control function for maintaining the pressure in the chamber 70 at a constant value. Have.

  In the crystal growth furnace 1 according to the present embodiment, not only a GaAs single crystal but also other III-V group compound semiconductor crystals can be grown. For example, a single crystal of a compound semiconductor such as InP, InAs, GaSb, or InSb can be grown using the crystal growth furnace 1. In addition, a ternary mixed crystal of a III-V compound semiconductor crystal such as AlGaAs, InGaAs, or InGaP or a quaternary mixed crystal of a III-V compound semiconductor crystal such as AlGaInP is used by using the crystal growth furnace 1. It can also grow.

  In addition, the crystal growth furnace 1 can be used to grow II-VI group compound semiconductor crystals such as ZnSe and CdTe or IV group semiconductor crystals such as Si and Ge. Further, the crystal growth furnace 1 can be used to grow a metal crystal, an oxide crystal, or a fluoride crystal, which is a crystal of a material that is not a compound semiconductor crystal or a semiconductor crystal.

  In the present embodiment, when the compound semiconductor melt 34 grown in the crucible 20 has a dissociation pressure equal to or higher than atmospheric pressure, the chamber 70 may be used as a pressure vessel. By using the chamber 70 as a pressure vessel, even if the compound semiconductor melt 34 has a dissociation pressure equal to or higher than the atmospheric pressure, by setting the inside of the chamber 70 to a pressure equal to or higher than the dissociation pressure, A single crystal of a compound semiconductor can be grown while preventing evaporation and the like.

  Further, the entire crucible 20 can be enclosed in an ampoule made of quartz or the like. Then, an ampoule in which the crucible 20 is sealed can be placed at a predetermined position in the crystal growth furnace 1 to grow a compound semiconductor single crystal.

  In the crystal growth furnace 1 according to the present embodiment, the growth crystal 32 as a single crystal is grown from the melt 34 in the crucible 20 by gradually lowering the susceptor support member 55. The method is not limited to this. For example, without lowering the susceptor support member 55, the set temperature of the upper heater 10 and the plurality of outer peripheral heaters 12 is gradually decreased at a predetermined speed, and the temperature inside the crucible 20 is decreased to grow the grown crystal 32. It may be grown.

  Further, in the crystal growth furnace 1 according to the present embodiment, the compound semiconductor melt 34 accommodated in the crucible 20 is brought into contact with the seed crystal 30 and from above the seed crystal 30 to above the crucible 20. Although a VB method or a VGF method, which is a method for gradually growing a single crystal toward the target, is used, a semiconductor crystal growth method similar to this method can be applied to the crystal growth furnace 1.

  For example, a horizontal boat method in which solidification of the melt proceeds in a horizontal direction in a state where a container for storing a semiconductor melt is horizontally installed in the crystal growth furnace 1 and a seed crystal is disposed at one end of the container is applied. can do. In addition, the crystal growth furnace 1 is applied with the Kyropulos method in which the solidification of the melt proceeds from the top to the bottom while the container for containing the semiconductor melt is installed vertically and the seed crystal is disposed at the upper end of the container. can do.

  Further, a furnace body moving method (Traveling Furnace method: TF method) in which a furnace body having a heater is moved with respect to the crucible 20 to perform crystal growth can be applied to the crystal growth furnace 1.

  Further, in the crystal growth furnace 1 according to the present embodiment, the plurality of outer peripheral heaters 12 are not essential if the upper heater 10 is provided, but when the melt 34 to be heated in the crucible 20 is larger than a predetermined amount, When the temperature gradient in the vertical direction in the crucible 20 becomes larger than a predetermined temperature gradient, it is preferable to configure the crystal growth furnace 1 by combining the upper heater 10 and the plurality of outer peripheral heaters 12.

  FIG. 2 shows an outline of a cross section of a crystal growth furnace according to a comparative example.

  The crystal growth furnace 2 according to the comparative example has substantially the same configuration as the crystal growth furnace 1 except that the upper heater 10 is removed from the crystal growth furnace 1 according to the first embodiment of the present invention. Detailed description is omitted.

  FIG. 3 shows a schematic temperature distribution in the crystal growth furnace according to the comparative example.

  In the crystal growth furnace 2 according to the comparative example, only a plurality of outer peripheral heaters 12 are installed as means for heating the crucible 20. Therefore, the crucible 20 is heated only from the crucible side face 24 side. Therefore, in the crucible 20, the temperature decreases from the side close to the outer peripheral heater 12 toward the center line of the crystal growth furnace 2 indicated by the AA line.

  For example, the isothermal line 90c closest to the outer peripheral heater 12a of the crystal growth furnace 2 moves from the isothermal line 90b closer to the crucible 20 than the isothermal line 90c and the isothermal line 90a closer to the crucible 20 than the isothermal line 90b. As the temperature decreases. Thereby, a temperature gradient is generated in the radial direction of the crucible 20 in the melt 34 of the compound semiconductor in the crucible 20. This temperature gradient is a gradient in which the temperature decreases from the outer periphery of the crucible 20 toward the center of the crucible 20.

  Here, the growth of the single crystal of the compound semiconductor starts from the upper end portion of the seed crystal 30. Then, the compound semiconductor melt 34 gradually solidifies from the lower side to the upper side of the crucible 20, and a single crystal having the same orientation as the seed crystal 30 grows. In this case, since it is necessary to provide a predetermined temperature difference in the vertical direction of the crystal growth furnace 2, the plurality of outer peripheral heaters 12 of the crystal growth furnace 2 are set to different temperatures, and the crystal growth furnace 2 is moved downward from above. Is provided in multiple stages.

  In the crystal growth furnace 2 according to the comparative example, the set temperatures of the plurality of outer peripheral heaters 12 are the set temperature of the outer peripheral heater 12a> the set temperature of the outer peripheral heater 12b> the set temperature of the outer peripheral heater 12c> the outer peripheral heater. The temperature is set to 12d. Unlike the crystal growth furnace 1 according to the first embodiment, the crystal growth furnace 2 does not include the upper heater 10. Therefore, a region where the crucible 20 is not heated is formed between the one outer peripheral heater 12 and another outer heater 12 provided adjacent to the one outer heater 12.

  For this reason, in a region not heated between one outer peripheral heater 12 and another outer peripheral heater 12 adjacent to the one outer heater 12, for example, in a region located between the isothermal line 90g and the isothermal line 90h. The temperature in the corresponding crucible 20 is lower than that of the portion of the crucible 20 heated by the outer peripheral heater 12. Thereby, the temperature gradient generated in the radial direction of the crucible 20 is not constant in the vertical direction of the crystal growth furnace 2.

  Therefore, in the crystal growth furnace 2, the temperature gradient in the radial direction in the crucible 20 changes in a complicated manner in the vertical direction of the crucible 20 depending on the relationship between the position of the outer peripheral heater 12 and the position where the crucible 20 is disposed. That is, the temperature gradient in the direction from the center of the crucible 20 toward the crucible side surface 24 is greatly different at each position in the vertical direction of the crucible 20. Furthermore, in the crystal growth furnace 2, heat is transferred from the crucible side surface 24 into the crucible 20, so that the heat flow flowing from the melt 34 in the crucible 20 to the growth crystal 32 gradually proceeds from the crucible side surface 24 toward the center of the crucible 20. It proceeds while bending the direction of travel to the bottom of the crucible 20.

  When crystal growth of a compound semiconductor is performed using such a crystal growth furnace 2, a portion in the crucible 20 in which the temperature gradient in the radial direction of the crucible 20 is larger than the predetermined temperature gradient is a portion smaller than the predetermined temperature gradient. A crystal having a crystal dislocation density larger than that of the crystal grown in step 1 grows. Further, since the temperature distribution in the crystal growing in the crucible 20 changes depending on the growth position of the crystal, the density of dislocations generated in the grown crystal varies along the longitudinal direction of the grown crystal 32.

  Therefore, there are variations in the crystal characteristics other than the dislocations generated in the crystal, for example, the distribution of the electrical characteristics of the crystal and the distribution of the optical characteristics of the crystal determined according to the dislocations existing in the crystal. Furthermore, since the temperature gradient in the vicinity of the crystal growth interface changes with the progress of crystal growth, it is difficult to keep the rate of crystal growth uniform, and the progress of crystal growth becomes unstable. As a result, when a compound semiconductor is grown in the crystal growth furnace 2, the probability that twins or polycrystals are generated increases.

  In addition, the shape of the several isotherm 90 shown in FIG. 3 is shown with the typical shape for the simplification of description. That is, the heat conduction inherent to the materials forming each of the plurality of outer peripheral heaters 12, the plurality of heat insulating materials 60 and 62, the compound semiconductor melt 34, the grown crystal, the crucible 20, the susceptor 50, the atmospheric gas, and the like. It is shown as a schematic isotherm 90 that does not consider the influence of rate, transmission rate, radiation rate, and the like.

  FIG. 4 shows a schematic temperature distribution in the crystal growth furnace according to the first embodiment of the present invention.

  In the crystal growth furnace 1 according to the first embodiment, the upper heater 10 is provided above the crucible 20. In particular, by keeping the temperature of the upper heater 10 higher than the temperature of the outer heater 12, the influence of the heat of the outer heater 12 transferred from the crucible side surface 24 is relatively reduced, and the crystal according to the comparative example Compared with the growth furnace 2, the radial temperature gradient in the crucible 20 can be made gentler. For example, as in the isotherm 90i and the isotherm 90j shown in FIG. 4, the temperature gradient in the direction along the radial direction of the crucible 20 changes more rapidly than in the case of the crystal growth furnace 2 according to the comparative example. The part can be eliminated.

  That is, in the crystal growth furnace 1 according to the first embodiment, by providing the upper heater 10 above the crucible 20, the radial temperature gradient in the crucible 20 can be maintained at a predetermined value or less. . The crystal growth furnace 1 can advance the crystal growth in the crucible 20 while maintaining the temperature gradient in the radial direction in the crucible 20 at a predetermined value or less. Thereby, the isothermal surfaces in the melt 34 and the growth crystal 32 are maintained substantially flat. Further, by providing the upper heater 10, it is possible to control the isothermal surfaces in the melt 34 and the growth crystal 32 so as to be substantially parallel to the solid-liquid interface shape between the growth crystal 32 and the melt 34. That is, in the melt 34 and the growth crystal 32, there is no inflection point in the temperature distribution in the direction along the crystal growth direction during the progress of crystal growth.

  Also in the crystal growth furnace 1 according to the first embodiment, similarly to the crystal growth furnace 2 according to the comparative example, the set temperature of the peripheral heater 12a> the set temperature of the peripheral heater 12b> the set of the peripheral heater 12c. Set temperature> set temperature of outer peripheral heater 12d. However, unlike the crystal growth furnace 2 according to the comparative example, the crystal growth furnace 1 includes an upper heater 10.

  In the crystal growth furnace 1, the inside of the crucible 20 can be heated from the upper part of the crucible 20 by providing the upper heater 10. Thereby, the region where the crucible 20 between the one outer peripheral heater 12 and the other outer heater 12 provided adjacent to the one outer heater 12 is not heated is heated by the heat from the upper heater 10. The Rukoto. Therefore, the variation in the temperature gradient in the radial direction of the crucible 20 at each position in the vertical direction of the crucible 20 can be reduced as compared with the case where the upper heater 10 is not provided.

  In each of the crucibles 20, each of the plurality of isotherms 90 is substantially parallel at any position in the vertical direction of the crucible 20. For example, the isotherm 90i, the isotherm 90j below the isotherm 90i, the isotherm 90k below the isotherm 90j, and the isotherm 90l below the isotherm 90k are substantially parallel to each other. . The crystal growth is performed with the moving speed of the interface between the growth crystal 32 and the melt 34 being substantially constant.

  When crystal growth of a compound semiconductor is carried out using such a crystal growth furnace 1, the temperature gradient in the radial direction of the crucible 20 becomes smaller than that of the crystal growth furnace 2 according to the comparative example, and thus occurs in the growing crystal. Dislocations are reduced compared to crystals grown in the crystal growth furnace 2. In addition, since the temperature gradient during crystal growth in the crucible 20 is stabilized regardless of the crystal growth position, variation in the density of dislocations generated in the grown crystal is reduced.

  Therefore, variations in crystal characteristics other than the dislocations generated in the crystal, for example, the distribution of the electrical characteristics of the crystal and the distribution of the optical characteristics of the crystal determined according to the dislocations existing in the crystal are reduced. In addition, the variation in the dislocation density existing in the crystal reduces the variation in the mechanical characteristics of the grown crystal. Furthermore, since the temperature gradient in the vicinity of the crystal growth interface can be kept substantially constant during the progress of crystal growth, the progress of crystal growth is stabilized. As a result, when a compound semiconductor is grown in the crystal growth furnace 1, the generation of twins or polycrystals can be suppressed.

(Effects of the first embodiment)
According to the crystal growth furnace 1 according to the first embodiment of the present invention, since the temperature gradient in the radial direction in the crucible 20 during crystal growth can be moderated, defects such as dislocations in the grown crystal 32 can be obtained. The generation density of can be reduced. Since the generation density of defects in the grown crystal 32 can be reduced, in the semiconductor crystal grown using the crystal growth furnace 1, the electrical characteristics in the semiconductor substrate formed from the grown semiconductor crystal, In-plane uniformity is improved with respect to optical characteristics and mechanical characteristics.

  Further, according to the crystal growth furnace 1 according to the first embodiment, the heat flow from the upper side to the lower side of the crucible 20 can be realized, and the temperature gradient in the radial direction of the crucible 20 can be moderated. The thermal history received by the growth crystal 32 during growth can be made substantially constant regardless of the portion of the growth crystal 32. This reduces variations in defect density, electrical characteristics, optical characteristics, mechanical characteristics, and the like among a plurality of semiconductor substrates formed by slicing the grown crystal 32.

  Further, according to the crystal growth furnace 1 according to the first embodiment, since the temperature gradient in the vicinity of the growth interface during crystal growth can be kept substantially constant, a rapid temperature change in the melt 34 can be caused. The crystal growth process is stabilized. Therefore, the probability that twins and polycrystals are generated in the grown crystal 32 can be reduced.

  Further, according to the crystal growth furnace 1 according to the first embodiment, the heat flow from the upper side to the lower side of the crucible 20 can be realized, so that the change in the temperature environment accompanying the crystal growth can be reduced in the longitudinal direction of the growing crystal. The thermal stress applied to the inside of the grown crystal 32 generated by the crystal growth is reduced. Thereby, even when long crystal growth is performed, the occurrence of defects such as dislocations occurring in the grown crystal 32 is suppressed, so that the electrical in the semiconductor substrate formed from the grown semiconductor crystal is suppressed. In-plane uniformity is improved with respect to characteristics, optical characteristics, mechanical characteristics, and the like.

  Further, according to the crystal growth furnace 1 according to the first embodiment, the radial temperature gradient in the crucible 20 during crystal growth can be made gentle, so that the diameter of the crucible 20 is larger. In-plane uniformity is improved with respect to electrical characteristics, optical characteristics, mechanical characteristics, and the like in a semiconductor substrate formed from a semiconductor crystal grown more significantly.

[Second Embodiment]
FIG. 5 shows an outline of a cross section of a crystal growth furnace according to the second embodiment of the present invention.

  The crystal growth furnace 3 according to the second embodiment is different from the crystal growth furnace 1 according to the first embodiment except that there is a heat conduction member 15 disposed between the upper heaters 11. Since the configuration is substantially the same, detailed description is omitted except for differences.

  The crystal growth furnace 3 according to the second embodiment includes an upper heater 11 above the outer periphery of the crucible 20. As an example, the crystal growth furnace 3 includes the upper heater 11 so that at least the crucible opening 22 is covered when viewed from above. The crystal growth furnace 3 is located between the upper heaters 11 and above the crucible opening 22 and receives heat generated by the upper heater 11 from the upper heater 11 and radiates the heat to the outside. A member 15 is provided. As an example, the heat conducting member 15 can be formed of aluminum nitride (AlN).

(Effect of the second embodiment)
According to the crystal growth furnace 3 according to the second embodiment, even when it is difficult to place the upper heater 11 directly above the crucible 20, the heat conducting member 15 is used as the upper heater 11. Since it functions as a so-called secondary heater that dissipates heat from the crucible opening 22 side, the melt 34 in the crucible 20 can be indirectly heated from above. Thereby, the same effect as the crystal growth furnace 1 according to the first embodiment can be obtained.

(Modification)
The crystal growth furnace 1 and the crystal growth furnace 3 according to the first embodiment and the second embodiment of the present invention prevent volatilization and evaporation of the melt 34 of the raw material of the compound semiconductor in the crucible 20. For the purpose, a lid for closing the crucible opening 22 may be further provided. For the purpose of efficiently transferring heat from the upper heater 10 to the melt 34 in the crucible 20, it is preferable to form a lid that closes the crucible opening 22 from a material having high thermal conductivity. As an example, the lid can be made of AlN.

  Further, the crystal growth furnace according to the present invention is provided as long as the upper heater 10 is provided to heat the melt 34 in the crucible 20 from above the crucible opening 22 and the temperature of the upper heater is higher than that of the outer heater. May have another heater at any position. As an example, a crystal growth furnace may be configured in which a heater is provided below the crucible 20 so that the temperature gradient in the vertical direction of the crucible 20 can be controlled.

  Further, for the purpose of stabilizing the growth conditions of the crystal of the compound semiconductor in the crucible 20 and improving the reproducibility of the growth of the single crystal, the crystal growth is combined with the cooling means on the small diameter portion 25 side of the crucible 20. A furnace can also be constructed.

  Note that the temperature gradient in the object to be heated, which is an object to be heated, becomes gentler as the size of the object to be heated is smaller. Therefore, if the size of the compound semiconductor crystal grown in the crucible 20 is small, even if the crystal growth furnace 1 or the crystal growth furnace 3 does not include the upper heater 10, the temperature gradient in the object to be heated is It is moderate. As an example, when growing a GaAs crystal having a diameter of 2 inches to 3 inches and a length of the straight body portion of about 100 mm to 150 mm, variation of dislocations generated in the growing crystal becomes a problem. The temperature gradient may not occur in the radial direction in the crucible 20.

  On the other hand, when growing a crystal such as GaAs having a diameter of 4 to 6 inches and a length of the straight body portion of 200 mm or more, the crystal growth furnace 1 or the crystal growth furnace 3 includes the upper heater 10. Otherwise, a temperature gradient in which variation of dislocations generated in the growing crystal becomes a problem may occur in the radial direction in the crucible 20.

  Therefore, the crystal growth furnace 1 and the crystal growth furnace 3 according to the first and second embodiments are, for example, long crystals having a large diameter of 4 inches or more and a straight body portion of 200 mm or more. It is effective to apply to the growth of III-V compound semiconductor crystals, especially GaAs or InP, for which growth is required.

  FIG. 6 shows a flow of a crystal growth process according to the embodiment of the present invention.

First, a seed crystal of GaAs was accommodated in the narrow diameter portion 25 of the pBN crucible 20 having a diameter of the straight body portion 27 of 160 mm and a length of the straight body portion 27 of 300 mm (S100). Subsequently, 24,000 g of pre-synthesized massive GaAs polycrystal was filled in the crucible 20 (S105). Next, 7.2 g of Si as a dopant and 400 g of B ₂ O ₃ as a liquid sealing material 40 were added into the crucible 20 (S110).

  Next, the crucible 20 was accommodated in a graphite susceptor 50 (S115). Further, the susceptor 50 is mounted on a susceptor support member 55 that can be moved up and down in the crystal growth furnace 1 and can rotate (S120). Next, the crystal growth furnace 1 was sealed, and the inside of the crystal growth furnace 1 was replaced with nitrogen gas as an inert gas (S125). Thereby, the gas atmosphere in the crystal growth furnace 1 became a nitrogen gas atmosphere.

  Subsequently, rotation of the crucible 20 was started (S130). Here, the rotational speed of the crucible 20 was set to 1 rpm. The crucible 20 was rotated by rotating the susceptor support member 55, and the rotation of the crucible 20 was continued until crystal growth was completed. Then, the upper heater 10 and the plurality of outer peripheral heaters 12 were energized to start heating the crucible 20 (S135). By continuing to heat the crucible 20 for a predetermined time after the start of the heating of the crucible 20, the GaAs polycrystal in the crucible 20 was completely melted to obtain a melt 34 (S140).

  Note that the volume of the atmospheric gas in the chamber 70 expands in the process of heating the crucible 20. Therefore, the pressure in the chamber 70 was controlled so that the pressure in the chamber 70 did not exceed 0.5 MPa. That is, in this embodiment, the gas pressure in the chamber 70 was controlled automatically and continuously so that the pressure in the chamber 70 was always maintained at 0.5 MPa even during crystal growth.

Here, in the process of melting the GaAs polycrystal in the crucible 20, B ₂ O ₃ added into the crucible 20 softened earlier than the GaAs polycrystal melted. The softened B ₂ O ₃ turned into a transparent water tank and covered the surface of the melt 34. Thereby, the volatilization of As due to the decomposition of GaAs could be suppressed.

  Subsequently, the set temperature of the upper heater 10 was set to 1295 ° C. (S145). In addition, the set temperature of the plurality of outer peripheral heaters 12 is set to a temperature that decreases from the top to the bottom of the crystal growth furnace 1 (S145). Specifically, the set temperature of the outer peripheral heater 12 a disposed at the position closest to the upper heater 10 among the plurality of outer peripheral heaters 12 was set to 1260 ° C. And the setting temperature of the outer periphery heater 12b arrange | positioned under the outer periphery heater 12a was set to 1240 degreeC.

  Further, the set temperature of the outer peripheral heater 12c disposed under the outer peripheral heater 12b is set to 1100 ° C., and the set temperature of the outer peripheral heater 12d disposed under the outer peripheral heater 12c is set to 1050 ° C. (S145). ). And after setting the temperature of the top heater 10 and the some outer periphery heater 12, it hold | maintained for 4 hours until the temperature of the melt 34 became stable (S150).

  In step S150, the position of the crucible 20 relative to the positions of the upper heater 10 and the plurality of outer peripheral heaters 12 was determined based on a temperature distribution measured by inserting a thermocouple into the crystal growth furnace 1 in advance. Specifically, in order to prevent the seed crystal 30 from melting and disappearing while holding the crucible 20, a 1238 ° C. isotherm, which is the melting point of GaAs, is applied to the upper end portion of the seed crystal 30. The crucible 20 was placed in

  After the temperature in the crystal growth furnace 1 is stabilized, the susceptor support member 55 is lowered at a speed of 4 mm / h while rotating at a rotation speed of 1 rpm, and the crucible 20 is lowered below the crystal growth furnace 1 (S155). ). Then, when the crucible 20 is lowered about 240 mm over about 2.5 days, the lowering of the crucible 20 is stopped, and it takes 24 hours so that the temperature of the upper heater 10 and the plurality of outer peripheral heaters 12 becomes 950 ° C. And gradually cooled (S160).

  Thereafter, the temperature of the upper heater 10 and the plurality of outer heaters 12 was decreased at a rate of −20 ° C./h until the temperature of the upper heater 10 and the plurality of outer heaters 12 reached 400 ° C. Subsequently, energization of the upper heater 10 and the plurality of outer peripheral heaters 12 was stopped, and the crucible 20 was cooled to room temperature (S165). After the crucible 20 was cooled to room temperature, it was confirmed that the grown crystal 32 in the crucible 20 was a GaAs single crystal over the entire length.

  In addition, the crystal growth was performed 20 times continuously in the steps S100 to S165. As a result, it was possible to obtain a crystal whose entire length was a single crystal of GaAs in any crystal growth.

  One of the 20 GaAs single crystals obtained in the process shown in FIG. 6 was selected using the crystal growth furnace 1. Then, a portion corresponding to the straight body portion of one selected GaAs single crystal was sliced to cut out a plurality of substantially circular wafers having a (100) plane. Next, the cut wafer surface was etched with molten KOH. Subsequently, density measurement of pits generated corresponding to dislocations, that is, dislocation density measurement was performed.

  FIG. 7 shows the distribution in the crystal longitudinal direction of the average dislocation density in the wafer plane of a GaAs single crystal grown in the crystal growth furnace according to the embodiment of the present invention.

In the GaAs single crystal grown in the crystal growth furnace according to the example of the present invention, generation of defects such as lineage was not observed over the entire length. The average dislocation density in the cut wafer surface was 0.5 × 10 ⁴ cm ⁻² or less over the entire straight body of the GaAs single crystal. Specifically, the length of the straight body portion of the GaAs single crystal is 250 mm, and the average dislocation density is 0.3 × 10 ⁴ cm ⁻² to 0.3 mm within the range of at least 5 mm to 250 mm of the GaAs single crystal. The range was 5 × 10 ⁴ cm ⁻² . The difference between the minimum value and the maximum value of the average dislocation density was less than 0.2 × 10 ⁴ cm ⁻² .

Further, the other 19 GaAs single crystals were also cut out from the seed crystal side of the GaAs single crystal, the central portion of the straight body portion, and the tail portion of the straight body portion, and etched with molten KOH. And the dislocation density measurement similar to the above was carried out. As a result, the average dislocation density was 0.5 × 10 ⁴ cm ⁻² or less in any part of all 19 GaAs single crystals. That is, it was shown that a crystal having an average dislocation density of a predetermined value or less can be obtained with good reproducibility for any of the 19 GaAs single crystals.

(Growth A of Comparative Example)
First, using the crystal growth furnace 2 according to the comparative example, the GaAs single crystal was grown in the same process as in FIG. That is, in the crystal growth furnace 2 that does not include the upper heater 10, except for the conditions such as energization of the upper heater 10 (S 135), setting of the set temperature (S 145), and slow cooling (S 160), other conditions are set. A GaAs single crystal was grown in the same manner. The GaAs single crystal was grown twice by the crystal growth furnace 2.

  In the GaAs crystal obtained by the first growth, polycrystal was generated in a portion where the crucible 20 moved from the inclined portion 26 to the straight body portion 27, and a GaAs single crystal was not obtained. In the second growth, polycrystal was generated in the straight body portion of the obtained GaAs crystal, and a single crystal of GaAs could not be obtained over the entire length.

(Growth B of Comparative Example)
Next, using the crystal growth furnace 2 according to the comparative example, the setting relating to the upper heater 10 is excluded, and the descending speed of the crucible 20 in S155 of FIG. 6 is set to 2.5 mm / hr, and the crystal growth speed is set. Crystal growth was carried out at a slower rate. Other conditions are the same as in FIG. However, in the embodiment described with reference to FIG. 6, the crucible 20 was lowered for about 2.5 days. In this comparative example, four days were required. The GaAs crystal obtained in this growth was a single crystal over the entire length.

  Next, a portion corresponding to the straight body portion of the obtained GaAs single crystal was sliced to cut out a plurality of substantially circular wafers having a (100) plane. Next, the cut wafer surface was etched with molten KOH. Subsequently, dislocation density was measured.

  FIG. 8 shows the distribution in the crystal longitudinal direction of the average dislocation density in the wafer plane of the GaAs single crystal grown in the crystal growth furnace according to the comparative example.

In the GaAs single crystal grown in the crystal growth furnace according to the comparative example, the average in-wafer plane is about 0.6 × 10 ⁴ cm ⁻² even at the lowest average dislocation density in the crystal, and 10 × The dislocation density exceeded 10 ³ cm ⁻² . The difference between the minimum value and the maximum value of the average dislocation density was at least 0.4 × 10 ⁴ cm ⁻² or more. Furthermore, many lineage defects were observed in the region where the dislocation density was high in the wafer plane.

  Referring to FIG. 8, the crystal obtained by the growth B of the comparative example showed an average dislocation density which is generally higher than that of the crystal according to the example of the present invention. Further, the change in dislocation density distribution was large along the longitudinal direction of the grown crystal. This is because the heating of the crystal depends only on the outer peripheral heater 12 on the side surface 24 of the crucible, so that the change in the thermal stress applied to the grown crystal 32 in accordance with the change in the positional relationship between the crucible 20 and the outer peripheral heater 12. It was speculated that it was big.

  In addition, in the growth B of the comparative example, the growth was performed 10 times. As a result, the seven crystals became single crystals over the entire length of the crystal, but for the two crystals, polycrystals were generated in the middle of the straight body portion of the crystal. In addition, with respect to the remaining one crystal, twinning was observed in a portion where the crucible 20 transitioned from the inclined portion 26 to the straight body portion 27. This was also presumed to be due to the large change in thermal stress applied to the crystal.

  While the embodiments and examples of the present invention have been described above, the embodiments and examples described above do not limit the invention according to the claims. In addition, not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

It is a schematic diagram of the section of the crystal growth furnace concerning a 1st embodiment. It is a schematic diagram of the section of the crystal growth furnace concerning a comparative example. It is a schematic diagram of the temperature distribution in the crystal growth furnace which concerns on a comparative example. It is a schematic diagram of the temperature distribution in the crystal growth furnace which concerns on 1st Embodiment. It is a schematic diagram of the cross section of the crystal growth furnace which concerns on 2nd Embodiment. It is a flowchart of crystal growth concerning an example. FIG. 6 is a distribution diagram of an average dislocation density in a wafer plane of a GaAs single crystal grown in a crystal growth furnace according to an example in a crystal longitudinal direction. It is a distribution map of the crystal dislocation direction of the average dislocation density in the wafer surface of the GaAs single crystal grown in the crystal growth furnace concerning a comparative example.

Explanation of symbols

1, 2, 3 Crystal growth furnace 10, 11 Upper heater 12a, 12b, 12c, 12d Outer peripheral heater 15 Heat conduction member 20 Crucible 20a, 20b Crucible end 22 Crucible opening 24 Crucible side 25 Small diameter part 26 Inclined part 27 Direct barrel part 30 Seed crystal 30a Seed crystal end 32 Grown crystal 34 Melt 40 Liquid sealing material 50 Susceptor 51 Upper part of susceptor 52 Lower part of susceptor 55 Susceptor support member 60, 62 Heat insulating material 70 Chamber 90a, 90b, 90c, 90d, 90e, 90f, 90g, 90h isotherm 90i, 90j, 90k, 90l isotherm

Claims (8)

A raw material melting step in which a crucible containing a semiconductor seed crystal and the semiconductor raw material is heated to use the raw material as a melt,
The semiconductor single crystal is heated from the side surface of the crucible and the opening side of the crucible, and at least during the crystal growth, the temperature heated from the opening side is maintained higher than the temperature heated from the side surface side. A method for growing a semiconductor crystal, comprising:   2. The semiconductor crystal according to claim 1, wherein in the crystal growth step, the single crystal is grown by solidifying the melt by lowering the crucible in a region heated from the side surface side and the opening side. Growth method.   2. The semiconductor according to claim 1, wherein in the crystal growth step, the single crystal is grown by solidifying the melt by gradually lowering a temperature heated from the side surface side and a temperature heated from the opening side. Crystal growth method.   The crystal growth step grows the single crystal without causing an inflection point in the temperature distribution in the vertical direction (crystal growth direction) in the melt at least during the progress of crystal growth. The semiconductor crystal growth method according to any one of the above.   2. The crystal growth step grows the single crystal without causing an inflection point in a temperature distribution in a vertical direction (crystal growth direction) in the solidified single crystal at least during the progress of crystal growth. 4. The semiconductor crystal growth method according to any one of items 1 to 3.   4. The semiconductor crystal growth method according to claim 1, wherein in the crystal growth step, the single crystal is grown with a moving speed of a crystal growth interface being substantially constant. 5.   The semiconductor crystal growth method according to claim 1, wherein the semiconductor is a group III-V compound semiconductor.   The semiconductor crystal growth method according to claim 1, wherein the semiconductor is GaAs.

Images