JP2010030891A - Compound semiconductor crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a large, high-quality semiconductor crystal that can be prepared at a low cost. <P>SOLUTION: The semiconductor crystal 50 comprising a compound has a diameter of ≥6 in and an average dislocation density of ≤1×10<SP>4</SP>cm<SP>-2</SP>. The semiconductor crystal 50 is a single crystal of GaAs or of one selected from the group consisting of CdTe, InAs and GaSb and has a boron concentration of ≤3×10<SP>16</SP>cm<SP>-3</SP>. The ingot has a carbon concentration of from 0.5×10<SP>15</SP>cm<SP>-3</SP>to 1.5×10<SP>15</SP>cm<SP>-3</SP>throughout its region having a solidification ratio of 0.1-0.8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor crystal, and more particularly to a compound semiconductor crystal for manufacturing a GaAs substrate or the like used for an optical device, an electronic device, or the like.

  Among semiconductor crystals, for example, a GaAs crystal is industrially manufactured by a pulling method (LEC method), a horizontal boat method (HB method, HGF method), and a vertical boat method (VB method, VGF method). In particular, the pulling method and the vertical boat method are simple because the yield is improved because the cross section of the obtained crystal is the same circle as the substrate, and the large diameter is easy due to the symmetry of the produced crystal. As a method for producing crystals, there are many advantages over the horizontal boat method.

  Moreover, as an example of a semiconductor crystal manufacturing apparatus, there is an apparatus in which a carbon heater and a crucible for containing a raw material melt are installed in a high-pressure vessel made of stainless steel. Such an apparatus is used for the LEC method, the VB method, the VGF method, or the like.

  FIG. 5 is a cross-sectional view showing a schematic configuration of an example of an apparatus for manufacturing a semiconductor crystal used in the pulling method as an example of an apparatus using such a stainless steel high-pressure vessel.

  Referring to FIG. 5, this apparatus includes a crucible 2 supported by a lower shaft 4 and a carbon heater 3 in a stainless steel high-pressure vessel 11. A heat insulating material 5 is interposed between the carbon heater 3 and the stainless steel high-pressure vessel 11 in order to prevent damage to the stainless steel high-pressure vessel 11 due to heating of the carbon heater 3.

  When crystal growth is performed using such an apparatus, first, a GaAs raw material is filled in the crucible 2 and heated by the carbon heater 3 to produce a raw material melt 60. In order to prevent evaporation of As from the raw material melt 60, the surface of the raw material melt 60 is sealed with a liquid sealing material 70, and the pulling shaft 14 with a seed crystal 55 attached to the tip is pulled in the direction of the arrow, Crystal growth is performed in a high-pressure atmosphere. In this way, a GaAs single crystal 50 is obtained.

  FIG. 6 is a cross-sectional view showing a schematic configuration of an example of a semiconductor crystal manufacturing apparatus used in a vertical boat method such as a VB method or a VGF method, which is another example of an apparatus using a stainless steel high-pressure vessel. .

  Referring to FIG. 6, in this apparatus, a seed crystal 55 is installed in the lower part of crucible 2, and the seed crystal 55 is moved by moving the lower shaft 4 downward as indicated by an arrow or moving the temperature distribution. The raw material melt 60 is solidified in order from 55 to crystal growth. Other configurations are the same as those of the apparatus shown in FIG.

  As another example of the crystal growth apparatus, there is a quartz ampoule in which a crucible or boat containing a raw material melt is enclosed and heated from the outside of the ampoule. This apparatus is used for horizontal boat methods such as HB method and HGF method and vertical boat methods such as VB method and VGF method.

FIG. 7 is a sectional view showing a schematic configuration of an example of an apparatus using such a quartz ampule.
Referring to FIG. 7, in this apparatus, a crucible 2 is enclosed in a quartz ampule 21, and a heater 3 such as Kanthal is provided outside the ampule 21. The quartz ampule 21 is supported by the lower shaft 4, and crystal growth is performed by moving the lower shaft 4 downward as indicated by an arrow or moving the temperature distribution.

  On the other hand, as a method for synthesizing a GaAs raw material for growing a crystal, a method of reacting Ga contained in a crucible with As vapor generated by controlling the temperature of an As source outside the crucible (hereinafter referred to as “As injection method”). And Ga and As are charged in the crucible at the same time and heated to react at once. Both methods are performed in a high-pressure vessel under liquid sealing. In particular, the latter method requires a high pressure of several tens of atmospheres because the vapor pressure of As becomes very high.

  GaAs polycrystal is produced by cooling the raw material synthesized as described above. On the other hand, a single crystal is manufactured by charging a crucible as a raw material using a once-prepared polycrystal and a method of growing a single crystal subsequent to the raw material synthesis.

  In addition, Patent Document 1 describes an example in which silicon carbide is used in a semiconductor heat treatment furnace. However, there is no disclosure about the effect of using such an apparatus for single crystal growth.

  Patent Document 2 describes an apparatus in which the entire apparatus is placed in a stainless steel vessel and a semiconductor single crystal such as GaAs is grown by a pulling method. This apparatus is characterized in that a solid gasket is used as a heat-resistant sealing material because a silicon carbide container is exposed to a high temperature. However, the heat-resistant sealing material has poor airtightness and cannot provide a sufficient pressure difference between inside and outside.

  Patent Document 3 describes an example in which silicon carbide is used as a crucible. However, there is no disclosure about using silicon carbide as a reaction tube.

  As the degree of integration of semiconductor elements increases, there is an increasing demand for large GaAs semiconductor single crystals of 6 inches or more. On the other hand, a low-cost and high-quality semiconductor crystal is required.

JP-A-7-2221038 JP-A-2-233578 Japanese Patent Laid-Open No. 2-120292

  As the degree of integration of semiconductor elements increases, it is necessary to increase the size of semiconductor crystals. In the case of a compound semiconductor crystal, a GaAs crystal having a diameter of 4 inches is currently in practical use. Furthermore, the necessity of increasing the size of such compound semiconductor crystals is increasing, and various research and development have been conducted for that purpose. However, mass production of large-sized compound semiconductor crystals has many limitations, and production of large-sized compound semiconductor crystals exceeding 4 inches has not been put into practical use.

  For example, when the stainless steel high-pressure vessel shown in FIG. 5 or FIG. 6 as described above is used, a heat insulating layer must be inserted between the heater and the stainless steel vessel, and the size of the equipment is necessarily increased. There is a problem that the equipment cost increases due to the increase in size.

  Furthermore, in the method shown in FIG. 5 or FIG. 6, carbon is used as the heater. Since the melting point of GaAs is 1238 ° C., it is necessary to heat to a high temperature of about 1300 ° C. when preparing the raw material melt. Here, the vapor pressure of carbon is small even at a high temperature of about 1300 ° C. Therefore, carbon is a material suitable for use as a heater. However, carbon is an electrically active element in the production of GaAs semiconductor single crystals. Therefore, it is necessary to control the carbon concentration in order to obtain a high-quality single crystal. Here, in the case of the method using the stainless steel high-pressure vessel shown in FIG. 5 or FIG. 6 as described above, since GaAs to be synthesized and carbon are in the same space, the content is controlled. Various ideas are required. As a result, there is a problem that the equipment cost is high.

  On the other hand, when the quartz ampule shown in FIG. 7 as described above is used, the ampule may be deformed or cracked, so that it is difficult to charge a large amount of raw material to produce a large crystal. There was a problem. In addition, since the ampoule is sealed, there is a problem that the raw material cannot be formed in that case and cannot be applied to the As injection method. Furthermore, there is a problem that the atmosphere gas cannot be controlled after the ampoule is sealed.

  An object of the present invention is to provide a compound semiconductor crystal such as GaAs that can solve the above-described conventional problems and satisfy two requirements of high quality and large size, and a compound semiconductor crystal substrate using the compound semiconductor crystal.

The compound semiconductor crystal according to the present invention is a semiconductor crystal made of a compound and has a diameter of 6 inches or more and an average dislocation density of 1 × 10 ⁴ cm ⁻² or less.

  The compound semiconductor crystal according to the present invention widely includes compound semiconductors such as GaAs, CdTe, InAs, and GaSb. The compound semiconductor crystal includes single crystals and polycrystals.

The compound semiconductor crystal substrate according to the present invention is a semiconductor crystal substrate made of a compound and having a diameter of 6 inches or more and an average dislocation density of 1 × 10 ⁴ cm ⁻² or less.

  In the present specification, “average dislocation density” refers to an in-plane average value of dislocation density when a substrate cut out from a crystal is etched and evaluated as an etch pit density.

In the present invention, “the average dislocation density is 1 × 10 ⁴ cm ⁻² or less” means that the average dislocation density of a substrate having a diameter of 6 inches or more cut out from any position of the crystal is 1 × 10 6. ^It means ⁴ cm ^-2 or less.

The compound semiconductor crystal according to the present invention has a diameter of 6 inches or more, an average dislocation density of 1 × 10 ⁴ cm ⁻² or less, and an extremely low defect density.

It is sectional drawing which shows schematic structure of the manufacturing apparatus which can be used when manufacturing the compound semiconductor crystal concerning this Embodiment. It is a fragmentary sectional view which expands and shows the connection part of the reaction tube and stainless steel flange in FIG. It is sectional drawing which shows schematic structure of the other manufacturing apparatus which can be used when manufacturing the compound semiconductor crystal concerning this Embodiment. It is sectional drawing which shows schematic structure of the manufacturing apparatus used when manufacturing the compound semiconductor crystal as a comparative form of this invention. It is sectional drawing which shows schematic structure of an example of the manufacturing apparatus of the semiconductor crystal using the conventional high pressure vessel made from stainless steel. It is sectional drawing which shows schematic structure of the other example of the manufacturing apparatus of the semiconductor crystal using the conventional high pressure vessel made from stainless steel. It is sectional drawing which shows schematic structure of an example of the manufacturing apparatus of the semiconductor crystal using the conventional quartz ampule.

In the present specification, the same reference numerals in the drawings indicate the same or corresponding parts.
≪Compound semiconductor crystal≫
The compound semiconductor single crystal grown by the VB method has the most remarkable effect of the present invention. According to the present invention, a compound semiconductor crystal having a diameter of 6 inches or more and an average dislocation density of 1 × 10 ⁴ cm ⁻² or less can be easily obtained. Further, by controlling the cooling method and the like, a compound semiconductor crystal having an average dislocation density of about 1 to 5 × 10 ³ cm ⁻² can be provided. With such a low dislocation density, the electrical characteristics can be made uniform.

Further, according to the present invention, boron (B) concentration of 3 × 10 ¹⁶ cm ^-3 or less, preferably also provide 1 × 10 ¹⁶ cm ^-3 or less of the compound semiconductor crystal. Boron (B) is said to reduce the activation rate after ion implantation. Therefore, the device characteristics can be improved by reducing the concentration of boron (B).

In addition, since the compound semiconductor crystal according to the present invention has few dislocations, the residual strain is small. Therefore, even when the size is increased, it has sufficient strength to withstand practical use with a thickness of 500 to 700 μm. The average residual strain of the substrate measured by the photoelastic method is 1 × 10 ⁻⁵ or less.

In addition, the compound semiconductor crystal according to the present invention has a feature that the slope of the carbon concentration distribution in the length direction is extremely small when viewed as an ingot. That is, by controlling the CO gas concentration in the reaction tube, the carbon (C) concentration distribution can be made uniform over the length direction. According to the present invention, the diameter is 6 inches or more, the average dislocation density is 1 × 10 ⁴ cm ⁻² or less, and the carbon concentration with respect to the target value is in a range of a solidification rate of 0.1 to 0.8. Thus, a compound semiconductor single crystal ingot controlled within ± 50% can be obtained. That is, for example, when the carbon concentration is set to 1 × 10 ¹⁵ cm ⁻³ , the carbon concentration of the actually obtained crystal is controlled to be within ± 50% of the set value over the entire length. Therefore, the yield is improved when the substrate is cut out from the ingot.

  The reason why the variation in the carbon concentration can be reduced by the present invention is that the CO gas concentration in the reaction tube can be precisely controlled throughout the growth. This effect becomes more effective by making the reaction tube material not containing carbon or using a material coated with a material not containing carbon. Furthermore, as will be described later, according to the present invention, a carbon heater is not used as in the case of crystal growth by a conventional high-pressure chamber. Therefore, since the crystal can be grown in a carbon-free state in the reaction tube, the carbon concentration distribution can be made uniform.

  In Examples 1 and 2 to be described later, an example of manufacturing a compound semiconductor crystal having a diameter of 6 inches is shown. However, the present invention can also be applied to manufacturing a compound semiconductor crystal of a larger size such as 8 inches. .

<< Compound Semiconductor Crystal Manufacturing Apparatus and Manufacturing Method Using the Manufacturing Apparatus >>
A manufacturing apparatus that can be used when manufacturing a compound semiconductor crystal according to the present invention has at least one open end and is selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, and aluminum oxide. A reaction tube made of one material, or any one material selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, boron nitride, aluminum oxide, magnesium oxide, mullite, and carbon as a base material and having an acid-resistant surface. A reaction tube made of a composite material forming a gasifying or airtight film, a heating means disposed around the reaction tube in an atmospheric pressure atmosphere, and an open end so as to seal the reaction tube A flange to be attached and a crucible installed in the reaction tube for containing the raw material of the compound semiconductor crystal are provided.

  In the present specification, “mullite” refers to a mixture of aluminum oxide and silicon oxide.

  Examples of the “oxidation resistant or airtight film” include a thin film made of silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, or silicon oxide. These films are formed on a substrate. It can be formed by coating.

  The “reaction tube made of a composite material” includes, for example, a surface of a base material made of carbon such as graphite formed by coating the above-mentioned oxidation resistant or airtight film, or a base made of silicon carbide. Examples thereof include those obtained by oxidizing the surface of the material, or those obtained by improving the oxidation resistance by forming a thin film made of silicon oxide on the surface by coating.

  More preferably, the manufacturing apparatus for manufacturing a compound semiconductor crystal according to the present invention has an open end at least at one end, and is any one selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, and aluminum oxide. Oxidation resistance on the surface of a reaction tube made of material or any one material selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, boron nitride, aluminum oxide, magnesium oxide, mullite and carbon Or it is attached to the open end so that the reaction tube made of a composite material forming an airtight film, the heating means disposed around the reaction tube in an atmospheric pressure atmosphere, and the reaction tube are sealed. A flange, a crucible installed in the reaction tube for containing the raw material of the compound semiconductor crystal, and a connecting portion between the flange and the open end of the reaction tube A sealing member for sealing, and a sealing maintaining means for maintaining the temperature of the connecting portion between the flange and the open end of the reaction tube so that the sealing function by the sealing member can be maintained. Yes.

  In the above manufacturing apparatus, the sealing maintaining means includes providing a heat insulating material between the heating portion by the heating means of the reaction tube and the connection portion between the flange and the open end of the reaction tube.

  In the manufacturing apparatus, the sealing maintaining means includes circulating cooling water in a jacket attached to the flange.

  In the manufacturing apparatus, the sealing maintaining means includes air-cooling a connection portion between the flange and the open end of the reaction tube.

The manufacturing apparatus further includes a shaft member connected to the crucible via a flange.
In the manufacturing apparatus, the reaction tube is used by being arranged in the vertical direction, and the shaft member can move up and down a crucible installed inside the reaction tube.

  The manufacturing apparatus further includes at least one temperature measuring means in the vicinity of the crucible via the flange.

The compound semiconductor crystal manufactured in the manufacturing apparatus is preferably a GaAs crystal.
In the manufacturing apparatus, the pressure inside the reaction tube is maintained to be higher than atmospheric pressure, and the pressure outside the reaction tube is atmospheric pressure.

  The manufacturing apparatus may further include a reservoir for storing the second raw material of the compound semiconductor crystal in the reaction tube, and the reservoir may have a pipe for introducing the gas of the second raw material into the crucible. . For example, when manufacturing a GaAs crystal in such an apparatus, the raw material stored in the crucible is Ga, and the second raw material stored in the reservoir is As.

  A manufacturing method for manufacturing a compound semiconductor crystal according to the present invention can use the above manufacturing apparatus, has an open end at least at one end, and is selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, and aluminum oxide. Or a reaction tube made of any one material selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, boron nitride, aluminum oxide, magnesium oxide, mullite, and carbon. A step of installing a crucible containing a compound semiconductor crystal raw material in a reaction tube made of a composite material having an oxidation resistant or airtight film formed on the surface, and a step of sealing the reaction tube by attaching a flange to the open end A step of keeping the inside of the reaction tube in an inert gas atmosphere, and the surrounding of the reaction tube in an atmospheric pressure atmosphere. The heating means, forming a material melt by solidifying the raw material melt, and a, a step of growing a compound semiconductor crystal.

  In the above manufacturing method, when the manufacturing apparatus further includes a reservoir and a pipe, the step of installing the crucible containing the compound semiconductor crystal raw material in the reaction tube includes the step of filling the crucible with Ga, A step of filling the reservoir with As and a step of forming a crucible filled with Ga and a reservoir filled with As in the reaction tube, and forming the raw material melt filled in the crucible A step of heating Ga to a temperature equal to or higher than the melting point of GaAs by heating means, a step of heating and vaporizing As filled in the reservoir by the heating means to form As vapor, and the formed As vapor through a pipe And introducing into Ga and forming a GaAs melt in the crucible.

  In the manufacturing method, the step of growing the compound semiconductor crystal uses the VB method, but may use the VGF method.

  As described above, the manufacturing apparatus for manufacturing a compound semiconductor crystal according to the present invention is a reaction tube made of any one material selected from the group consisting of silicon carbide, silicon nitride, aluminum nitride, and aluminum oxide, or carbonized. A composite in which any one material selected from the group consisting of silicon, silicon nitride, aluminum nitride, boron nitride, aluminum oxide, magnesium oxide, mullite and carbon is used as a base material and an oxidation resistant or airtight film is formed on the surface thereof A reaction tube made of material is provided. Therefore, unlike the case where a conventional quartz ampoule is used, there is no possibility of deformation or cracking of the reaction tube, and a large amount of raw material can be charged to produce a large crystal.

  In addition, when a reaction tube made of silicon carbide is used, it is less expensive than a conventional stainless steel high-pressure vessel. Thus, according to such a manufacturing apparatus, the equipment cost for manufacturing a compound semiconductor crystal is greatly reduced. It becomes possible to do.

  In the manufacturing apparatus, a reaction tube made of silicon nitride, a reaction tube made of aluminum nitride, a reaction tube made of aluminum oxide, or carbon such as silicon nitride, aluminum nitride, boron nitride, aluminum oxide, magnesium oxide, mullite, etc. In the case of using a reaction tube made of a base material not containing carbon, it is possible to prevent carbon from being mixed into the semiconductor material. As a result, high purity of the semiconductor material can be achieved.

  Further, in the above manufacturing apparatus, even when a base material made of a carbon material such as graphite having no oxidation resistance or a material such as porous aluminum oxide or mullite having no airtightness is used, the surface is made resistant to oxidation. By coating with an airtight material, it is possible to effectively prevent the reaction tube from being deformed or cracked. Since these base materials are very inexpensive, a compound semiconductor crystal can be obtained at low cost according to such a manufacturing apparatus.

  Even when a substrate containing carbon such as silicon carbide or graphite is used, it is possible to prevent carbon from being mixed into the semiconductor material by coating the surface with a material not containing carbon. Even when a low-purity base material such as mullite is used, high purity of the compound semiconductor crystal can be achieved by coating the surface with a high-purity material.

  In the production apparatus, the reaction tube has an open end at least at one end, and a flange is attached to the open end. Therefore, unlike the case of using a conventional quartz ampule, the reaction tube can be used repeatedly. As a result, the manufacturing cost can be reduced.

  In the manufacturing apparatus, since the temperature measuring means is provided in the vicinity of the crucible, crystal growth with high reproducibility can be performed.

  Further, unlike the case where the ampoule is sealed in the above manufacturing apparatus, the raw material can be formed in that case, and can also be applied to the As injection method. In addition, unlike the case of sealing an ampule, the in-situ control of the atmospheric gas partial pressure in the reaction tube is possible, and the impurity concentration can be easily adjusted.

  Moreover, according to the said manufacturing apparatus, the compound semiconductor single crystal with the extremely small inclination of the carbon concentration distribution in a length direction is obtained. Hereinafter, an example of a specific method for producing a compound semiconductor single crystal among the compound semiconductor crystals according to the present invention will be described with reference to FIG.

  FIG. 1 is a cross-sectional view showing a schematic configuration of a manufacturing apparatus that can be used when manufacturing a compound semiconductor crystal according to the present embodiment.

  Referring to FIG. 1, this apparatus has an inner diameter of 170 mm, a thickness of 3 mm, a silicon carbide reaction tube 1 having open ends at both ends, and an atmospheric pressure atmosphere around the silicon carbide reaction tube 1. A cantal heater 3 having five zones is provided.

  The feature of this manufacturing apparatus is that the outside of the heater is not sealed as shown in FIG. In the conventional LEC method, as described in Patent Document 2 described above, since crystal growth in a high-pressure chamber is necessary, a carbon heater having low reactivity has been used. On the other hand, in this manufacturing apparatus, since a heater is provided in the atmosphere outside the reaction tube, a low-cost iron-based heater can be used. Since this type of heater can be easily made into multistage zones, a temperature distribution with very good temperature controllability can be formed. Further, when the carbon heater is not used, the crystal growth can be performed with the inside of the silicon carbide reaction tube in a carbon-free state, so that the variation in the carbon concentration in the crystal can be reduced.

Stainless steel flanges 9 are attached to both open ends of the silicon carbide reaction tube 1.
FIG. 2 is an enlarged partial cross-sectional view showing a connection portion between the silicon carbide reaction tube 1 and the stainless steel flange 9.

  Referring to FIG. 2, the connection portion between silicon carbide reaction tube 1 and stainless steel flange 9 has a Wilson seal structure, and packing 12 is interposed to ensure airtightness. As the packing 12, an elastic body such as an O-ring is used, and specifically, a fluororesin or the like can be used in addition to rubber. As shown in FIG. 2, the selectivity of the material that can be used as the packing 12 is wide because, in the Wilson seal structure, the packing 12 exists outside the reaction tube 1 made of silicon carbide, and therefore the material of the packing 12 is silicon carbide. This is because there is no possibility of being mixed as an impurity in the compound semiconductor crystal grown in the reaction tube 1.

  Moreover, in this example, the seal part of the connection part of the silicon carbide reaction tube 1 and the stainless steel flange 9 is provided in the low temperature part. Therefore, since a material such as rubber and fluororesin having excellent airtightness can be used as the sealing material, the pressure difference between the inside and outside of the silicon carbide reaction tube 1 can be made sufficiently large.

  A jacket is attached to the flange 9, and cooling water is circulated in the jacket to cool the connection portion between the silicon carbide reaction tube 1 and the flange 9. It is configured to maintain the sex.

  In order to maintain the airtightness of the connection portion between the silicon carbide reaction tube 1 and the flange 9, in addition to using such a jacket, for example, the connection portion is forcibly cooled by air, or the distance between the reaction tube and the connection portion is reduced. It can be separated and air-cooled in the atmosphere.

  An exhaust pipe insertion port 16 and a gas introduction pipe insertion port 17 are formed on the flange 9 attached to the upper part of the silicon carbide reaction tube 1. An exhaust pipe 18 for exhausting the inside of the silicon carbide reaction tube 1 to a vacuum is inserted in the exhaust pipe insertion port 16, and a gas is introduced into the silicon carbide reaction tube 1 in the gas introduction pipe insertion port 17. A gas introduction pipe 19 for introducing the gas is inserted.

  On the other hand, in the center of the flange 9 attached to the lower part of the reaction tube 1 made of silicon carbide, a lower shaft 4 that can move up and down is installed, and a raw material of the compound semiconductor crystal is placed at the tip of the lower shaft 4. A crucible 2 for housing is placed. A thermocouple insertion port 15 is formed in the flange 9 attached to the lower part of the silicon carbide reaction tube 1. A thermocouple 13 for measuring the temperature near the side surface of the crucible 2 is inserted into the thermocouple insertion port 15. It is also possible to provide a thermocouple port on the upper flange and insert the thermocouple into the crucible from above. The thermocouple may measure the temperature at the bottom of the crucible by passing inside the lower shaft. In addition to the thermocouple, a radiation thermometer can be used as the temperature measuring means.

  Using the manufacturing apparatus configured as described above, a 6-inch diameter GaAs single crystal can be manufactured by the VB method as follows.

First, a seed crystal made of a GaAs single crystal is put into a cap portion at the lower end of a 6-inch diameter crucible 2 placed at the tip of the lower shaft 4. Next, 20 kg of GaAs polycrystalline raw material and 300 g of B ₂ O ₃ 70 for sealing the surface of the raw material melt 60 are charged in the crucible 2.

  This crucible is installed in the reaction tube 1 made of silicon carbide, and a flange 9 is attached and sealed. Subsequently, the exhaust pipe 18 is used to evacuate the silicon carbide reaction tube 1 to a vacuum, and then the temperature is raised by the cantal heater 3. During the temperature increase, nitrogen gas is introduced into the silicon carbide reaction tube 1 using the gas introduction pipe 19 and adjusted so that the pressure in the silicon carbide reaction tube 1 is about 2 atm when the temperature increase is completed. .

  The raw material melt 60 is formed by melting the GaAs polycrystalline raw material by heating with the cantal heater 3. After adjusting the temperature of the seed crystal to be around 1238 ° C., which is the melting point of GaAs, and to adjust the temperature of the side surface of the crucible 2 to be about 1250 ° C. To move downward.

  Thus, the GaAs single crystal 50 is grown by solidifying the raw material melt 60 sequentially from the seed crystal placed in the lower end of the crucible 2.

  In the above embodiment, an example of an apparatus provided with an aluminum oxide reaction tube having open ends at both ends has been shown, but the open end of the aluminum oxide reaction tube is formed at least at one end. Good.

  Further, in the above embodiment, only the production of GaAs crystal has been described. However, in addition to the GaAs crystal, the production apparatus and the production method described above include a compound semiconductor crystal such as CdTe crystal, InAs crystal, and GaSb crystal, and a silicon semiconductor crystal. It can also be applied to germanium semiconductor crystals.

  In the above embodiment, the reaction tube made of aluminum oxide has been described as an example. However, the reaction tube is not only made of aluminum oxide alone, but also made of silicon nitride, aluminum nitride or silicon carbide alone, or silicon carbide. It is also possible to use a composite material made of silicon nitride, aluminum nitride, boron nitride, aluminum oxide, magnesium oxide, mullite or carbon and having an oxidation resistant or airtight film formed on the surface thereof.

  Next, an example of a method for producing a compound semiconductor polycrystal among the compound semiconductor crystals according to the present invention will be described with reference to FIG.

  FIG. 3 is a cross-sectional view showing a schematic configuration of another manufacturing apparatus that can be used when manufacturing the compound semiconductor crystal according to the present embodiment. The reaction tube is made of aluminum nitride.

  Referring to FIG. 3, in this apparatus, the thermal insulator 8 is interposed, so that the Kanthal heater 3 having five zones is divided into one zone above the thermal insulator 8 and four zones below it. Has been. Moreover, the heat insulating material 8 is installed also in the aluminum nitride reaction tube 1 at the same height as the heat insulating material 8 interposed between the heaters.

  A crucible 2 is installed below the heat insulating material 8 in the reaction tube 1 made of aluminum nitride. On the other hand, a reservoir 6 is installed above the heat insulating material 8 in the reaction tube 1 made of aluminum nitride. A pipe 7 is connected to the reservoir 6, and the pipe 7 is configured to reach the raw material melt 60 charged in the crucible 2.

  Since the other configuration is exactly the same as that of the manufacturing apparatus shown in FIG.

  Using the manufacturing apparatus configured as described above, a 6-inch diameter GaAs polycrystal can be manufactured by the VB method as follows.

First, 14.5 kg of high-purity liquid Ga and 300 g of B ₂ O for sealing the surface of the raw material melt 60 in a 6-inch diameter pBN crucible 2 placed at the tip of the lower shaft 4. ₃ Charge 70. In addition, 15.5 kg of high-purity As80 is charged in the reservoir 6 installed on the heat insulating material 8. The positions of the reservoir 6 and the crucible 2 are adjusted so that the tip of the pipe 7 connected to the reservoir 6 reaches the liquid Ga 60 through the hole provided in the heat insulating material 8. This is installed in the reaction tube 1 made of aluminum nitride, and a flange 9 is attached and sealed.

  Subsequently, the inside of the reaction tube 1 made of aluminum nitride is evacuated to vacuum using the exhaust pipe 18, and then the temperature is raised by the cantal heater 3. At this time, the temperature of the thermocouple 13 installed on the side surface of the crucible 2 is adjusted to about 1250 ° C. On the other hand, the temperature in the reservoir 6 is adjusted to be maintained at 500 ° C. or lower. Further, during the temperature rise, nitrogen gas is introduced into the aluminum nitride reaction tube 1 using the gas introduction pipe 19 so that the pressure in the aluminum nitride reaction tube 1 becomes about 2 atm when the temperature rise is completed. adjust.

  Thereafter, the temperature in the reservoir 6 is raised to about 650 ° C. to generate As vapor, and the As vapor is injected into the liquid Ga through the pipe 7 to cause a reaction, thereby producing the GaAs melt 60 in the crucible 2.

  After completion of the synthesis reaction of the GaAs melt, the temperature at the bottom of the crucible 2 is adjusted to be around 1238 ° C., which is the melting point of GaAs, and then the lower shaft is moved downward as indicated by an arrow at a speed of 10 mm / hour.

  Thus, the GaAs polycrystal 50 is grown by solidifying the raw material melt 60 in order from the bottom of the crucible.

  As mentioned above, although the manufacturing method using a different manufacturing apparatus was each demonstrated about the manufacturing method of a compound semiconductor single crystal and the manufacturing method of a compound semiconductor polycrystal, these manufacturing methods and manufacturing apparatuses can be used in combination with each other. . For example, a pulverized GaAs polycrystal obtained by using the manufacturing apparatus of FIG. 3 can be used as a raw material in the manufacturing apparatus of FIG. In addition, although the seed crystal is used in the manufacturing apparatus of FIG. 1, the seed crystal is not used in the manufacturing apparatus of FIG.

  In the above embodiment, only the example of the manufacturing apparatus and manufacturing method used for VB method was shown.

Example 1
1 using the manufacturing apparatus of FIG. 1 and the same method as the manufacturing method of the compound semiconductor single crystal by the manufacturing apparatus of FIG. 1 described above, using a silicon carbide reaction tube, the GaAs actually having a diameter of 6 inches by the VB method. Crystals were produced. As a result, a single crystal having a length of 25 cm was obtained. The crystals obtained had a low dislocation density and the CO gas concentration in the growing reaction tube was controlled, so that the variation in carbon concentration was small and high quality.

  Furthermore, according to the present example, the average yield when similar crystal growth was performed six times was 50%. From this, considering the price difference between the conventional apparatus equipped with a stainless steel high-pressure vessel and the apparatus equipped with the silicon carbide reaction tube of this embodiment, the production cost of the GaAs single crystal is reduced by this embodiment. It was found that it can be reduced by about 20% compared to the case of using a stainless steel high pressure vessel.

(Example 2)
Using the manufacturing apparatus of FIG. 3, a GaAs crystal having a diameter of 6 inches is actually manufactured using an aluminum nitride reaction tube by the same method as the manufacturing method of the compound semiconductor polycrystal by the manufacturing apparatus of FIG. did. As a result, about 30 kg of GaAs polycrystal was obtained. When the purity analysis of the obtained polycrystal was performed, it was below the detection limit except a matrix element and carbon and boron, and it was very high quality.

  In addition, there was no particular difference compared to the quality of crystals grown using a conventional apparatus equipped with a stainless steel high-pressure vessel as shown in FIG. Considering the price difference between the conventional apparatus having a high pressure vessel made of stainless steel and the apparatus having the reaction tube made of aluminum nitride of the present embodiment, this embodiment can reduce the manufacturing cost of GaAs polycrystal by about 30%. I understood.

(Comparative Example 1)
In the production apparatus of FIG. 4, a GaAs crystal having a diameter of 6 inches was actually produced by the LEC method using an aluminum oxide reaction tube.

  Here, FIG. 4 is a cross-sectional view showing a schematic configuration of a manufacturing apparatus used when manufacturing a compound semiconductor crystal as a comparative embodiment of the present invention. The reaction tube is made of aluminum oxide.

  Referring to FIG. 4, this apparatus is mainly used in a pulling method, and includes an aluminum oxide reaction tube 1 having open ends at both ends, and a heater disposed around aluminum reaction tube 1. 3 is provided. Flange 9 is attached to both open ends of the reaction tube 1 made of aluminum oxide.

  At the center of the flange 9 attached to the lower part of the reaction tube 1 made of aluminum oxide, the lower shaft 4 is installed so as to penetrate, and the crucible 2 is placed at the tip of the lower shaft 4. On the other hand, at the center of the flange 9 attached to the upper part of the reaction tube 1 made of aluminum oxide, a pulling shaft 14 that can be moved up and down is installed, and the pulling shaft 14 is pulled up in the direction of the arrow while crystallizing. Growing up.

  In the LEC method using such a manufacturing apparatus, it is necessary to increase the temperature gradient in order to prevent As from being lost during crystal growth. As a result, the average dislocation density and residual strain of the obtained crystal were larger than those of the crystal obtained in Example 1.

  Moreover, in this comparative example 1, since the number of zones of the heater can be easily increased due to the structure, the temperature distribution is excellent in controllability. As a result, the generation of polycrystals in the latter half of the crystal growth can be prevented, and the single crystal length is longer than that of Comparative Example 2 described later.

(Comparative Example 2)
A GaAs crystal having a diameter of 6 inches was manufactured by the conventional LEC method shown in FIG.

  As in Comparative Example 1, as a result of the need to increase the temperature gradient in order to prevent the loss of As during crystal growth, the average dislocation density and residual strain values of the obtained crystal were obtained in Example 1. It became larger than the crystal.

  Further, in the conventional LEC method, the number of heater zones cannot be increased so much due to the structure, so that there is a limit to the controllability of the temperature distribution. As a result, the generation of polycrystals in the latter half of the crystal growth could not be prevented, and the single crystal length was shortened as compared with Comparative Example 1.

(Comparative Example 3)
A GaAs crystal having a diameter of 6 inches was manufactured by the conventional liquid sealing VB method shown in FIG.

  As in Comparative Example 2, the number of heater zones cannot be increased because of the structure, and as a result, there is a limit to the controllability of the temperature distribution. Compared with Example 1, the single crystal length was shortened.

  Further, in the conventional LE-VB method, crystal growth is performed under a low pressure in an environment where carbon parts such as a heater and a heat insulating material are present. As a result, compared with Example 1, the C concentration (carbon concentration) and B concentration (boron concentration) of the obtained crystal were high.

(Comparative Example 4)
A GaAs crystal having a diameter of 4 inches was grown by the conventional quartz ampule-encapsulated VB method shown in FIG.

  In the conventional quartz ampule encapsulated VB method, the carbon concentration in the quartz ampule cannot be controlled during crystal growth. As a result, the uniformity of the carbon concentration was poor.

  In addition, because of the problem of the strength of the quartz ampule, it was impossible to grow a crystal having a diameter of 6 inches.

(Summary of results)
The results of Examples 1 and 2 and Comparative Examples 1 to 4 described above are shown in Table 1 below.

(Comparative Example 5)
Si-doped GaAs was grown by the VGF method under a N ₂ gas pressure of ₂ atm using a reaction tube made of hermetic high-purity silicon nitride. As a result, a single crystal having a diameter of 3 inches and a length of 20 cm was obtained.

As a result of investigating the purity of the obtained crystal, it was found that the concentration of all impurities including carbon other than Si was 5 × 10 ¹⁴ cm ⁻³ or less throughout the crystal, and the purity was very high.

(Comparative Example 6)
Undoped GaAs was grown by the VGF method at a N ₂ gas pressure of 1.2 atm using a reaction tube made of a composite material in which the surface of a graphite substrate was coated with silicon carbide at a thickness of 50 μm. The reaction tube achieved an ultimate vacuum of 1 × 10 ⁻² torr or less, and it was confirmed that the airtightness was sufficient. As a result, a single crystal having a diameter of 3 inches and a length of 30 cm was obtained.

When the purity of the obtained crystal was investigated, the carbon concentration was 1 to 2 × 10 ¹⁵ cm ⁻³ , the other impurity concentrations were 5 × 10 ¹⁴ cm ⁻³ or less, and the specific resistance was 1 to 3 × over the entire crystal. It was 10 ⁷ Ωcm, and it was found that the GaAs crystal had very good semi-insulating properties.

(Comparative Example 7)
Growth of Si-doped GaAs by VGF method at Ar gas pressure of 1.5 atm using reaction tube made of composite material with high purity aluminum oxide coated at 100μm thickness on the surface of porous low purity mullite substrate did. The reaction tube achieved an ultimate vacuum of 1 × 10 ⁻³ torr or less, and it was confirmed that the airtightness was sufficient. As a result, a single crystal having a diameter of 3 inches and a length of 15 cm was obtained.

As a result of investigating the purity of the obtained crystal, it was found that the concentration of all impurities including carbon concentration other than Si was 5 × 10 ¹⁴ cm ⁻³ or less throughout the entire crystal, and the purity was very high.

  1 reaction tube, 2 crucible, 3 heater, 4 lower shaft, 5, 8 heat insulation, 6 reservoir, 7 pipe, 9 flange, 11 high pressure vessel made of stainless steel, 12 packing, 13 thermocouple, 14 pulling shaft, 15 thermocouple insertion Port, 16 exhaust pipe insertion port, 17 gas introduction pipe insertion port, 18 exhaust pipe, 19 gas introduction pipe, 21 quartz ampule, 50 semiconductor crystal, 60 raw material melt, 70 liquid sealing material, 80 As.

Claims (12)

A compound semiconductor crystal comprising a compound and having a diameter of 6 inches or more and an average dislocation density of 1 × 10 ⁴ cm ⁻² or less. 2. The compound semiconductor crystal according to claim 1, wherein an average dislocation density is 5 × 10 ³ cm ⁻² or less.   The compound semiconductor crystal according to claim 1 or 2, wherein the diameter is 8 inches or more.   The compound semiconductor crystal according to any one of claims 1 to 3, wherein the semiconductor crystal is GaAs.   4. The compound semiconductor crystal according to claim 1, wherein the semiconductor crystal is any one compound semiconductor material selected from the group consisting of CdTe, InAs, and GaSb. 5.   The compound semiconductor crystal according to claim 1, wherein the semiconductor crystal is a single crystal. The compound semiconductor crystal according to claim 1, wherein a boron concentration is 3 × 10 ¹⁶ cm ⁻³ or less. The compound semiconductor crystal according to claim 7, wherein a boron concentration is 1 × 10 ¹⁶ cm ⁻³ or less. The carbon concentration over a region where the solidification rate of the ingot is 0.1 to 0.8 is 0.5 × 10 ¹⁵ cm ^{−3 to} 1.5 × 10 ¹⁵ cm ^−3. Item 9. A compound semiconductor crystal according to any one of Items 8 to 10.   The compound semiconductor crystal according to any one of claims 1 to 9, wherein the carbon concentration is controlled within ± 50% with respect to a target value over a region where the solidification rate of the ingot is 0.1 to 0.8. 11. The compound semiconductor crystal according to claim 1, comprising a substrate having an average residual strain of 1 × 10 ⁻⁵ or less measured by a photoelastic method.   The compound semiconductor crystal according to any one of claims 1 to 11, comprising a substrate having a thickness of 500 to 700 µm.

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