JP2010052978A - Method for producing group iii nitride single crystal - Google Patents

Abstract

Provided is a method for manufacturing a nitride body that can continuously grow a single crystal in a high quality state without easily cracking even when a group III nitride single crystal grows thick. To do.
A method of manufacturing a group III nitride single crystal in which a group III nitride single crystal 3b is continuously grown on a seed substrate 3a by vapor phase growth to produce a single crystal 3b in bulk. Thus, the control temperature applied from the outside for crystal growth is increased in accordance with the increase in the thickness of the single crystal 3b to be grown. The vapor phase growth method is a hydride vapor phase growth method.
[Selection] Figure 1

Description

  The present invention relates to a group III nitride single crystal in which a bulk body of a group III nitride single crystal (group III nitride single crystal) such as GaN, AlN, or AlGaN is grown on a surface of a substrate by a vapor phase growth method. It relates to a manufacturing method.

  Nitride objects such as GaN and AlGaN are used in electronic elements such as light emitting elements such as light emitting diodes (LEDs) and semiconductor lasers (LDs), power devices such as transistors and power FETs (Field Effect Transistors). , Expansion of use is expected.

However, Group 3 nitride single crystals such as GaN and AlGaN have a high melting point and a high equilibrium vapor pressure of N (nitrogen), which makes it difficult to produce bulk single crystals from the liquid phase. is there. Therefore, a thin film made of a group III nitride object is vapor-phase grown on a heterogeneous substrate (a substrate made of a material different from the growing nitride object) such as sapphire (Al ₂ O ₃ ), silicon carbide (SiC), and the like Thin films have been used for various devices.

Furthermore, in recent years, a self-standing GaN single crystal substrate has been put into practical use by a vapor phase growth method such as a hydride vapor phase growth method (HVPE method; Hydride Vapor Phase Epitaxy method) (see, for example, Patent Document 1). Research is also being conducted on a method for producing an AlN single crystal by the HVPE method (for example, see Patent Document 2).
Japanese Patent Laid-Open No. 2000-12900 JP 2006-16294 A

  Conventionally, a substrate made of a group III nitride single crystal produced by the HVPE method is grown on a thick film using a sapphire or GaAs substrate as a seed substrate, and then the seed substrate is peeled off to form a group III nitride single crystal substrate. It has gained. However, a dissimilar substrate such as sapphire has a large lattice constant difference from a growth film made of a group III nitride single crystal such as GaN or AlGaN to be grown. For example, since the lattice mismatch between sapphire and GaN is 13.7%, dislocations are likely to occur when an epitaxial film of GaN is grown on sapphire. Since LEDs require higher brightness and electronic devices require higher power, it is necessary to reduce such dislocations from the substrate.

  Furthermore, in order to use these light-emitting elements and electronic elements for general purposes, it is indispensable to reduce the cost of the substrate. However, the upper limit of the thickness of the thick film growth is about several millimeters. If the thickness is larger than that, the substrate is easily cracked and the quality of the film itself is easily deteriorated, which is an obstacle to the cost reduction of the substrate.

  The present invention has been completed in view of the above-mentioned conventional problems, and an object of the present invention is to provide a method for producing a group III nitride single crystal that solves these problems.

  The method for producing a group III nitride single crystal of the present invention is a group III nitride in which a group III nitride single crystal is continuously grown on a seed substrate by vapor phase growth to produce a single crystal in bulk. In the method for producing a single crystal, a control temperature applied from the outside for crystal growth is increased in accordance with an increase in the thickness of the single crystal to be grown.

  At this time, the vapor phase growth method is preferably a hydride vapor phase growth method.

  The group III nitride single crystal is preferably composed of a GaN single crystal, an AlN single crystal, or a mixed crystal thereof.

  Furthermore, it is desirable that the seed substrate is composed of a GaN single crystal, an AlN single crystal, or a mixed crystal thereof.

  In the method for producing a group 3 nitride single crystal of the present invention, the control temperature applied from the outside for crystal growth is increased in accordance with the increase in the thickness of the single crystal to be grown. Thereby, even if the group 3 nitride single crystal grows and becomes thick, the single crystal can be continuously grown in a high quality state without easily cracking.

  The reason why the production method of the present invention is effective is presumed as follows.

  When a bulk single crystal is vapor-grown by the HPVE method or the like, the concentration of chemical species supplied from the vapor phase is extremely higher than in the case of conventional thin film formation. These high-concentration chemical species are continuously supplied to the growth surface on the substrate, where they move (migrate) at high speed to form a single crystal. This is made possible by a sufficient temperature at the growth surface.

  The temperature (heat) required for such high-speed growth is mainly supplied via a substrate from a susceptor or the like that holds the substrate. Therefore, as the single crystal grows and becomes thicker, it is supplied to the growth surface. The heat that is generated tends to be deficient gradually. For this reason, conventionally, as the single crystal body is grown thickly, it deviates from the optimum temperature condition, and it seems that the problem of deterioration of the substrate and the problem of cracking have occurred.

  On the other hand, in the present invention, the control temperature applied from the outside for crystal growth is increased in accordance with the increase in the thickness of the single crystal to be grown, so that the single crystal grows thicker. When the surface temperature supply decreases, the temperature supply is controlled to compensate. Therefore, even when the single crystal grows and becomes thicker, the growth conditions at the optimum temperature are maintained, and as a result, it is considered that the growth can be performed in a state where it is hard to break and maintains a high quality state.

  According to the above method for producing a group III nitride single crystal of the present invention, a high-quality single crystal substrate with few crystal defects can be obtained, and the quality between the substrates can be stabilized. Therefore, the group III nitride single crystal substrate manufactured from the group III nitride single crystal of the present invention includes a light emitting element such as a light emitting diode (LED) and a semiconductor laser (LD), a transistor, a power FET (Field Effect Transistor), and the like. It is suitably used for electronic elements such as power devices.

  Hereinafter, an example of the embodiment will be described with respect to the method for producing a group III nitride single crystal of the present invention.

  FIG. 1 is a schematic cross-sectional view showing an example of a vapor phase growth apparatus for producing the group III nitride single crystal of the present invention. In FIG. 1, S is a vapor phase growth apparatus, 1 is a holding body, 2 is a quartz tube, 3a is a seed crystal substrate (seed substrate) for growth, 3b is a grown single crystal, 4a and 4b are heaters, 5a 5b is a source gas, 6 is a gas flow of a counter flow, and 7 is a gallium container. Hereinafter, the method for producing a group III nitride single crystal of the present invention will be described.

(1) First, the seed substrate 3a is placed inside the quartz tube 2 of the vapor phase growth apparatus S while being held by the holding body 1.

  Although graphite is used for the support 1, since corrosive ammonia or hydrogen chloride is used as a source gas as will be described later, the surface is coated with at least one selected from the group consisting of SiC, BN and TaC. It is preferable. Examples of the coating method include a CVD method and a sputtering method. Thereby, the corrosion resistance of the holder 1 is improved. PBN is preferable among BN. PBN is pyrogenic boron nitride (pyrolytic BN (p-BN)).

  Further, it is desirable to provide a mechanism for rotating the seed substrate 3a held around the central axis of the holding body 1 so that the seed substrate 3a rotates during crystal growth. Thereby, the uniformity of the crystal growing on the seed substrate 3a can be improved. In addition, as rotation speed, it is possible to select from the range of about 2 rpm-50 rpm, for example.

  The seed substrate 3a uses a group 3 nitride single crystal. Specifically, a gallium nitride compound semiconductor such as GaN or AlGaN, AlN, or the like can be used. When the group III nitride single crystal is a GaN single crystal, examples of the seed substrate 3a include sapphire, SiC, GaN single crystal, AlN single crystal, or a mixed crystal of GaN single crystal and AlN single crystal. it can. Among them, GaN single crystals, AlN single crystals, or mixed crystals of GaN single crystals and AlN single crystals are preferably used. The thickness of the seed substrate 3a for growth is about 0.3 to 0.6 mm. The diameter of the seed substrate 3a for growth is 20 mm to 60 mm.

  The quartz tube 2 which is the main body of the vapor phase growth apparatus S is made of quartz or the like, and a cylindrical body such as a cylindrical shape or a rectangular tube shape is preferably used.

(2) Next, the heater 4b on the holding body 1 side is heated to 700 ° C. or higher, the counter flow 6 is introduced together with the source gases 5a and 5b, and the single crystal 3b is grown on the seed substrate 3a.

  As a vapor phase growth method for this purpose, it is preferable to use a hydride vapor phase growth method (HVPE method). Other vapor phase growth methods include metal organic vapor phase growth (MOVPE), sublimation, etc., but the HVPE method is used because of its high growth rate, good quality, and ease of producing nitrided bodies. preferable. Hereinafter, an example using the HVPE method will be described.

  The source gases 5a and 5b use group V ammonia and group 3 trimethylgallium or gallium chloride, and the counterflow 6 uses nitrogen, hydrogen, or a mixed gas thereof. When gallium chloride is used as a Group 3 raw material, as will be described later, gallium chloride is generated by filling metal gallium into a quartz gallium container 7 and reacting it with flowing hydrogen chloride gas at about 800 ° C.

  The heaters 4a and 4b are provided around the outer periphery of the quartz tube 2, and, for example, a resistance heating type can be used. The heater 4b on the holding body 1 side may heat the holding body 1 and the seed substrate 3a by setting the temperature to 700 to 1000 ° C. when forming a low-temperature buffer layer or the like and 1000 to 1300 ° C. when starting single crystal growth. The low-temperature buffer layer is required when a sapphire substrate is used as the growth seed substrate 3a, and is formed at a thickness of 10 to 100 nm. Note that when the low-temperature buffer layer is formed, the gas composition is the same as that for growing the single crystal 3b.

The source gas supplied into the vapor phase growth apparatus S to grow a nitride body is ammonia (NH ₃ ) gas, gallium chloride (GaCl) gas, hydrogen chloride (HCl) gas, or the like, and also nitrogen (N ₂ ) gas. , Hydrogen (H ₂ ) gas, silane (SiH ₄ ) gas, or the like may be included.

  When hydrogen chloride gas is used, hydrogen chloride is reacted as gallium metal at a temperature of about 800 ° C. in the gallium container 7 part of the gas supply pipe of the vapor phase growth apparatus S, and supplied as source gas 5b as gallium chloride (GaCl) gas. The For this purpose, the gallium container 7 may be heated by heating the raw material supply side heater 4a to a predetermined temperature. The gallium chloride gas source gas 5b thus generated is supplied with and mixed with ammonia gas from the source gas 5a and supplied to the seed substrate 3a at a predetermined temperature, whereby GaN is formed on the surface of the seed substrate 3a. The single crystal 3b can be grown at high speed. The pressure during the reaction is usually atmospheric pressure (normal pressure) in the HPVE method.

  The flow rate ratio between ammonia gas and hydrogen chloride gas is preferably such that the flow rate of ammonia gas is about 15 to 30 times the flow rate of hydrogen chloride gas. By setting this ratio, the growth rate of the GaN single crystal can be increased, and the growth of columnar crystals that increase dislocations in the GaN single crystal can be suppressed.

  The counter flow 6 makes the source gas laminar so as not to cause turbulent flow, carries reaction products that could not contribute to the growth to the outside of the apparatus, and adheres to the inside of the quartz tube 2. It is a gas flow that is introduced to prevent or prevent. As described above, nitrogen, hydrogen, or a mixed gas thereof can be used, and the flow rate is several times to several tens of times that of the source gases 5a and 5b. Specifically, the flow rate is preferably about 3 to 20 times.

(3) Further, in the present invention, the control temperature from the outside is increased in accordance with the increase in the thickness of the single crystal 3b to be grown. Conventionally, the temperature during crystal growth is a specific temperature of 1000 to 1300 ° C. at the start of growth, and crystal growth is performed while maintaining the same temperature. In such a conventional method, there is a tendency that dislocations are generated or cracked as the single crystal becomes thicker. On the other hand, in the present invention, as the thickness of the single crystal 3b to be grown increases, the control temperature from the outside (in FIG. 1, the setting of the heater 4b provided outside the holder 1 of the quartz tube 2 is set). Temperature). Thereby, even if it grows thickly, it is hard to break and high-quality crystal growth becomes possible. The reason for this has already been described above, but is assumed to be as follows. That is, in the conventional method, as the single crystal grows, the supply amount per unit time of heat supplied to the growth surface via the holding body tends to decrease, and the temperature of the growth surface deviates from the optimum value. It seems that dislocations are generated or cracked. On the other hand, according to the configuration of the present invention, the single crystal is grown because the heat (temperature) per unit time supplied to the growth surface is increased as the single crystal grows. Even if it becomes thicker, the growth conditions at the optimum temperature are maintained, and as a result, it is considered that growth is possible in a state where it is hard to break and maintains a high quality state.

  Although the degree to which the control temperature is raised varies depending on the apparatus, it is preferable to raise the control temperature in the range of 0.1 to 5.0 ° C. with respect to the growth thickness of 1 mm of the single crystal 3b from the initial growth temperature. Theoretically, while the temperature of the growth surface of the single crystal 3b should be monitored, the temperature of the heater should be controlled so as to be within a certain range, but it is actually the outermost surface region that is involved in crystal growth. Therefore, it is practically difficult to take out only this portion and measure the temperature. Therefore, it is only necessary to determine the optimum value according to the growth apparatus to be used while repeating crystal growth while changing the value within the above-described control temperature range, and evaluating cracks and quality.

In order to process the single crystal body 3b of GaN into a substrate shape, a general wafer processing process such as semiconductor silicon can be applied, and generally the following processes may be performed.
(A) A GaN single crystal grown using a diamond grindstone is ground to a predetermined outer diameter.
(B) A wire saw in which diamond abrasive grains or the like are bonded to a single crystal of GaN, or a wire saw that cuts crystals by reciprocating motion of a wire while dropping diamond or SiC abrasive grains on a brass wire with a slurry. Cut into a wafer shape with a thickness (eg, 0.6 mm).
(C) After roughly polishing both surfaces of a single crystal wafer of GaN using diamond abrasive grains or SiC abrasive grains, the surface used in the device process is mirror-polished using colloidal silica, whereby a single crystal of GaN is polished. A wafer substrate is obtained.

  As described above, a nitride object substrate made of a GaN single crystal or the like suitable for epitaxial growth of a gallium nitride compound semiconductor applied to an optical element and an electronic element can be manufactured by the process described above.

  Note that the present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention.

For example, a seed substrate 3a made of AlN single crystal is used, aluminum is used instead of gallium, high frequency induction heating coils are used as heaters 4a and 4b, and ammonia (NH ₃ ) gas and hydrogen chloride (HCl) gas are the main components. It is possible to grow an AlN single crystal by supplying the source gas. The same applies to trimethylaluminum, which is an organic metal gas, instead of using metal aluminum instead of hydrogen chloride, which is a raw material gas.

  Moreover, FIG. 1 demonstrated the case where it grew by arrange | positioning so that the growth surface of the single crystal body 3b might become downward with respect to the perpendicular direction with respect to the seed substrate 3a. In this case, it is preferable because dust and the like can be prevented from falling on the growth surface. However, the single crystal body 3b may be arranged so that the growth surface faces upward with respect to the vertical direction or laterally with respect to the vertical direction.

  Furthermore, the vapor phase growth apparatus S is not limited to the shape as shown in FIG. 1, but can be applied to an apparatus for growing a nitride body in the vapor phase, and the source gas is also limited to the materials shown in the embodiments. However, it can be applied to a source gas capable of growing a nitride body.

  Examples of the method for manufacturing a nitride object of the present invention will be described below.

  A GaN single crystal was manufactured using the vapor phase growth apparatus S shown in FIG. First, a seed substrate 3a made of a disk-shaped GaN single crystal having a diameter of 52 mm and a thickness of 0.4 mm was used. The growth surface of the seed substrate 3a faces downward on a holder 1 made of graphite, which is installed in a quartz tube 2 which is a vapor phase growth apparatus S and is coated with 0.2 mm of SiC having an outer diameter of 60 mm and a thickness of 20 mm. The outer periphery was sandwiched and fixed so that

  Next, gallium is accommodated in the gallium container 7, the inside of the quartz tube is heated by energizing the resistance heater 4a, and the temperature of gallium is controlled to about 800 ° C. by the heater 4a, while hydrogen chloride gas is supplied at 30 cc / min. The gallium chloride was supplied from 5b as a Group 3 source gas. Almost simultaneously, ammonia gas was supplied in the amount of 750 cc / min as the group V source gas 5a. Further, the heater 4b was controlled to 1100 ° C. so that the temperature of the seed substrate 3a was 1000 ° C. Thus, the growth of the single crystal 3b of GaN was started while rotating the holder 1 at 20 rpm.

  Next, the heater 4b was gradually raised from 1100 ° C. at a rate of 1.0 ° C. per 1 mm according to the growth thickness, and crystal growth was performed to a growth thickness of 25 mm.

  After the completion of crystal growth, a single crystal of GaN was taken out from the vapor phase growth apparatus S, and peripheral grinding was performed using a diamond grindstone to an outer diameter of 50.8 mm. Thereafter, a plurality of GaN single crystal bodies that were ground on the periphery were cut into a thickness of 0.6 mm by a wire saw using a wire to which diamond abrasive grains were fixed to obtain a GaN single crystal substrate.

  Next, both sides of the GaN single crystal substrate cut out with a wire saw are roughly polished using diamond abrasive grains, and further, the surface used for crystal growth is mirror-polished by mechanochemical polishing using colloidal silica. A GaN single crystal substrate wafer having a thickness of 50.8 mm and a thickness of 0.4 mm was produced.

When the wafer surface of the GaN single crystal substrate produced as described above was observed with an X-ray topographic image, the average dislocation density was 4 × 10 ⁴ cm ⁻² .

As Comparative Example 1, a GaN single crystal was produced on a GaN single crystal seed substrate in exactly the same process except that the crystal growth was performed with the heater 4b kept constant at 1100 ° C. as the temperature during growth. Cracks occurred when the growth thickness was about 5 mm. Further, when a wafer was produced from the GaN single crystal of this comparative example and the average dislocation density up to 5 mm was measured, it was 2 × 10 ⁵ cm ⁻² , and the effectiveness of the present invention was confirmed in terms of cracks and quality. It was done.

Furthermore, as a comparative example 2, when sapphire was used as a seed substrate, the grown GaN single crystal was cracked when the growth thickness exceeded 1 mm. Moreover, the average dislocation density measured by avoiding the cracked portion was about 2 × 10 ⁸ cm ⁻² , and as in Comparative Example 1, the effectiveness of the present invention in terms of generation of cracks and quality was confirmed.

It is sectional drawing of the vapor phase growth apparatus used for the manufacturing method of the group 3 nitride single crystal of this invention.

Explanation of symbols

S: Vapor growth apparatus 1: Holding body 2: Quartz tube 3a: Seed substrate 3b: (Growth) single crystal 4a, 4b: Heaters 5a, 5b: Source gas 6: Gas flow of counter flow 7: Gallium container

Claims (4)

A method for producing a group III nitride single crystal in which a group III nitride single crystal is continuously grown on a seed substrate by vapor phase epitaxy to produce a single crystal in bulk.
A method for producing a group III nitride single crystal, wherein a control temperature applied from the outside for crystal growth is increased in accordance with an increase in thickness of the single crystal to be grown.   The method for producing a group III nitride single crystal according to claim 1, wherein the vapor phase growth method is a hydride vapor phase growth method.   The method for producing a group III nitride single crystal according to claim 1 or 2, wherein the group III nitride single crystal is composed of a GaN single crystal, an AlN single crystal, or a mixed crystal thereof.   The method for producing a group III nitride single crystal according to any one of claims 1 to 3, wherein the seed substrate is composed of a GaN single crystal, an AlN single crystal, or a mixed crystal thereof.

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