JP3976745B2 - Method for producing gallium nitride compound semiconductor - Google Patents

Description

  The present invention relates to a method of manufacturing a gallium nitride compound semiconductor on a substrate.

Gallium nitride (GaN) -based compound semiconductors are widely applied to light emitting devices such as LEDs and others. For example, when GaN is grown on a sapphire substrate by using the ELO (Epitaxially Laterally Overgrown) method, a blue laser capable of continuous operation for 10,000 hours or more at room temperature has been reported. In the ELO method, a GaN layer of several microns is formed on a sapphire substrate, a striped mask SiO ₂ is formed along the <1100> direction of GaN, and GaN is regrown vertically from the opening of the mask SiO _2. Let

However, in this ELO method, only the dislocation density is reduced in the GaN layer in the portion where the mask SiO ₂ exists, and only a part of the GaN layer can obtain good characteristics.

  On the other hand, in view of lattice mismatch between sapphire and GaN, it has also been proposed to grow a GaN or AlN buffer layer on a sapphire substrate at a low temperature and further grow a GaN layer on the buffer layer. For example, the following document describes that a GaAlN buffer layer is grown on a sapphire substrate at a low temperature, and further a semiconductor layer such as GaN is formed.

Japanese Patent Laid-Open No. 4-297003

  However, even in this method, high-density dislocations are generated in the low-temperature buffer layer, so that high-density dislocations are also generated in the GaN or GaAlN layer formed on the low-temperature buffer layer. Not enough to get.

  Therefore, the applicant of the present application previously proposed the following manufacturing method in Japanese Patent Application No. 11-376842. That is, before forming the low-temperature buffer layer on the sapphire substrate, a buffer body having discrete or multiple holes is formed on the sapphire substrate, and the low-temperature buffer layer is formed on the buffer body. A semiconductor such as GaN is formed on the buffer layer.

  6 and 7 show the configuration of a GaN-based compound semiconductor manufactured by the manufacturing method previously proposed by the applicant of the present application. A SiN buffer body 12 is formed on a substrate 10 such as sapphire. The SiN buffer body 12 is not formed in a layer shape so as to cover the substrate 10 as shown in FIG. 7, but is formed so as to have discrete or plural holes 12a. In the portion of the hole 12a, the SiN buffer body 12 is not formed, and the substrate 10 is exposed. The SiN buffer body 12 formed on the substrate 10 may be in an amorphous state or a crystalline state, and has a function of inhibiting crystal growth of the low-temperature GaN buffer layer 14 formed thereon. A GaN buffer layer 14 is formed on the SiN buffer body 12 at a low temperature (for example, 500 degrees) at about 20 nm, and a GaN semiconductor layer 16 is formed on the GaN buffer layer 14 at a high temperature (for example, 1075 degrees) at about 2 μm. With such a configuration, the low temperature buffer layer 14 grows in the direction perpendicular to the surface from the holes 12a of the discretely formed SiN buffer body 12, and eventually extends in the in-plane direction so as to cover the buffer body 12. Growing up. Dislocations are likely to occur when growing in the vertical direction from the hole, but when grown in the in-plane direction, the generation of dislocations can be suppressed because they are not affected by the underlying layer, and eventually the dislocations of the GaN semiconductor layer 16 are suppressed. Can also be suppressed.

  However, even this method has a problem that a certain amount of dislocation occurs. That is, when the GaN semiconductor layer 16 is grown on the low temperature GaN buffer layer 14 at a high temperature, a part of the low temperature GaN buffer layer 14 evaporates as the substrate temperature rises as shown in FIG. Middle code 14a), since the growth of GaN starts from the remaining portion of the low-temperature GaN buffer layer 14, dislocations 16a are generated at the portion where the remaining portion collides as shown in FIG. Further, since the degree of evaporation depends on the temperature raising time, it is necessary to raise the temperature at a high speed in order to ensure reproducibility.

  The present invention has been made in view of the above problems, and an object thereof is to provide a manufacturing method capable of further reducing the dislocation density of a GaN-based semiconductor.

In order to achieve the above object, the present invention provides a method for producing a gallium nitride-based compound semiconductor in which a buffer layer is grown on a substrate at a low temperature, and a GaN-based compound semiconductor is further formed on the buffer layer. Prior to the formation, first buffer bodies are discretely formed on the substrate, and prior to the formation of the GaN-based compound semiconductor, the buffer layer is formed on the buffer layer along with the temperature rise during the formation of the GaN-based compound semiconductor. A second buffer body for preventing evaporation is formed discretely, and the second buffer body is made of silicon or a silicon compound, and is formed as a series of steps in the same apparatus as the formation of the buffer layer and the GaN-based compound semiconductor. characterized in that that.

In the present invention, each of the first and second buffer bodies is silicon or a silicon compound, and is formed as a series of steps in the same apparatus as the formation of the buffer layer and the GaN-based compound semiconductor . The two buffer bodies are preferably formed discretely so as to have a plurality of holes .

  In the present invention, a buffer body is discretely formed on a buffer layer formed at a low temperature, and this buffer body can prevent evaporation of the low-temperature buffer layer accompanying a temperature rise when forming a GaN-based compound semiconductor. The low-temperature buffer layer is crystallized during the temperature rising process, and the GaN-based compound semiconductor is nucleated from the portion of the crystallized buffer layer surface where the buffer body is not formed and grows on the buffer body in the in-plane direction. And it merges with the one generated from the adjacent nucleus to become one continuous layer. The distance to the adjacent nucleus depends on the degree of discreteness of the buffer body, but is, for example, 10 to 100 nm, which is much smaller than the film thickness (for example, 2 μm) of a GaN-based compound semiconductor grown at a high temperature and can suppress the occurrence of dislocations. It should be noted that dislocations that may occur in the boundary region with adjacent nuclei associate with adjacent dislocations during growth to form a loop, and therefore do not propagate further in the film thickness direction.

  According to the present invention, when a GaN-based semiconductor is formed on the buffer layer, the dislocation density of the GaN-based semiconductor can be reduced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows the configuration of a GaN-based compound semiconductor according to this embodiment. As shown in (a), SiN buffer bodies 12 are discretely formed on a substrate 10 such as sapphire, and a GaN buffer layer 14 is formed thereon at a low temperature (for example, 500 degrees) by about 20 nm. As shown in FIG. 7, the SiN buffer body 12 has a plurality of holes 12a, from which the low-temperature GaN buffer layer 14 grows in the vertical direction.

  In the method previously proposed by the applicant of the present application, the GaN semiconductor layer 16 is immediately grown on the low-temperature GaN buffer layer 14 at a high temperature (for example, 1075 degrees), but in this embodiment, the SiN buffer is formed on the low-temperature GaN buffer layer 14. A second SiN buffer body 15 similar to the body 12 is formed. The second SiN buffer body 15 is also discretely formed and has a plurality of holes.

  Then, after covering most (but not all) of the low-temperature GaN buffer layer 14 with the second SiN buffer body 15, the GaN semiconductor layer 16 is formed at a high temperature as shown in FIG. The Since most of the surface of the low-temperature GaN buffer layer 14 is covered with the SiN buffer body 15, the low-temperature GaN buffer layer 14 does not evaporate even when the substrate temperature is raised, and solid phase epitaxy occurs during the temperature rise process. Crystallize. Therefore, the GaN semiconductor layer 16 formed thereon can prevent the occurrence of dislocation by using the holes of the SiN buffer body 15 as nucleation sources.

FIG. 2 shows a flowchart of the manufacturing method according to this embodiment using the MOCVD method, and FIG. 3 shows a manufacturing apparatus used in this embodiment. First, the sapphire substrate 10 is placed on the susceptor 21 in the reaction tube 20, and the sapphire substrate 10 is heated to 1150 degrees using a heater 22 in an H ₂ atmosphere and heat-treated. After the heat treatment, the temperature is lowered to 500 ° C., a mixed gas of H ₂ and N ₂ is introduced from the gas introduction part 24 through the air-permeable microporous member 25, and silane gas (SiH ₄ ) is introduced from the gas introduction part 23. Then, ammonia gas (NH ₃ ) and H ₂ are supplied to form the SiN buffer body 12 (S101). The flow rate of SiH ₄ is 20 sccm, and the flow rate of NH ₃ is about 5 slm.

Next, the supply of SiH ₄ is stopped, and trimethyl gallium (TMG), NH ₃ , and H ₂ are supplied from the gas inlet 23 to grow the GaN buffer layer 14 while maintaining the substrate temperature at 450 degrees (S102). . The growth time of the GaN buffer layer 14 is about 75 seconds, and is grown about 20 nm.

Next, the supply of TMG is stopped, and SiH ₄ , NH ₃ , and H ₂ are supplied again from the gas introduction unit 23 to form the second SiN buffer body 15 (S103). The formation conditions of the second SiN buffer body 15 can be the same as the formation conditions of the first SiN buffer body 12.

After forming the second SiN buffer body 15, the substrate 10 is heated to 1075 degrees by the heater 22, and TMG, NH ₃ and H ₂ are supplied from the gas introduction part 23 to grow the GaN semiconductor layer 16 (S 104). .

  Thus, dislocation of the GaN semiconductor layer 16 can be effectively suppressed by preventing the GaN buffer layer 14 from evaporating with the second SiN buffer body 15.

  A GaN-based semiconductor was prepared by atmospheric pressure MOCVD under the following conditions.

(1) Conventional example Sapphire substrate / low temperature growth GaN buffer layer / high temperature growth GaN layer

(2) Applicant's proposal (comparative example)
Sapphire substrate / SiN buffer body / low temperature growth GaN buffer layer / high temperature growth GaN layer

(3) Examples 10 ppm hydrogen diluted SiH ₄ , NH ₃ and TMG were used as raw materials in any of the examples of sapphire substrate / first SiN buffer body / low temperature growth GaN buffer layer / second SiN buffer body / high temperature growth GaN layer. . In all examples, the growth conditions of the low temperature growth GaN buffer layer and the high temperature growth GaN layer are the same. The growth temperature of the low temperature growth GaN buffer layer is 500 degrees and the growth time is 75 seconds. If this growth temperature is in the range of 450 to 600 degrees, substantially the same effect can be obtained. The growth temperature of the high temperature growth GaN layer is 1075 degrees. The formation temperature of the first and second SiN buffer bodies is 500 degrees (the same as the low temperature growth GaN buffer layer), and the flow rates of hydrogen diluted SiH ₄ and NH ₃ are 20 sccm and 5 slm, respectively. Although the formation time was changed in the range of 50 sec to 150 sec, the best result was obtained at 125 sec as proposed by the applicant of the present application. In any example, after the growth of the low-temperature growth GaN buffer layer is completed, the temperature is raised to 1075 degrees, which is the growth temperature of the high-temperature growth GaN layer, in 7 minutes, and the dislocation density is measured using a planar TEM (transmission electron microscope). did. The results are shown below.

Thus, the dislocation density was in the order of conventional example> comparative example> example, and the dislocation density could be reduced by the method of the example. The measurement of 0.1 × 10 ⁸ cm ^-2 or less for observation area is small in the case of Example was difficult.

  Further, it was confirmed that when the temperature raising time was increased from 7 minutes to 10 minutes and 15 minutes, the surface gradually became rough in the conventional example. In the comparative example, a reduction in dislocation density was observed in a part of the wafer. That is, in order to ensure the reproducibility of the dislocation density reduction, it is necessary to accurately control the temperature raising time. On the other hand, in the examples, although a slight increase in dislocation density and surface roughness were observed, the influence was remarkably small as compared with the conventional example and the comparative example. Therefore, it is very easy to ensure the reproducibility of reducing the dislocation density in the examples.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various change is possible.

For example, in this embodiment, the dislocation density of the GaN semiconductor layer 16 is reduced, but there may be a case where strain remains in the GaN semiconductor layer 16. Therefore, as proposed in Japanese Patent Application No. 2000-143826 by the applicant of the present application, before the first SiN buffer body 12 is formed, crystal nucleation inhibition layers may be formed discretely on the substrate 10. it can. The crystal nucleus generation-inhibiting layer can be made of a material that does not generate or has few crystal nuclei such as SiO ₂ , SiN, and Si. For example, SiO ₂ can be discretely formed in stripes having a width of ₂ to 50 μm.

FIG. 4 shows the configuration of the GaN-based semiconductor formed in this way. The difference from FIG. 1B is that stripe-like SiO ₂ 11 is formed between the substrate 10 and the first buffer body 12. When SiO ₂ 11 is formed in this manner and the first SiN buffer body 12, the GaN buffer layer 14, the second SiN buffer body 15, and the GaN semiconductor layer 16 are formed thereon, these layers are made of SiO ₂ 11. It grows from the opening and eventually grows in the in-plane direction to cover the SiO ₂ , and associates with the layer grown from the other opening to relieve the distortion of the GaN semiconductor layer 16. Thereby, a GaN-based semiconductor having both a low dislocation density and strain can be obtained.

  In addition, after the GaN semiconductor layer 16 is formed as shown in FIG. 1B, an InGaN layer is formed on the GaN semiconductor layer 16, and an AlGaN layer is further formed to alleviate strain of the GaN semiconductor layer 16. You can also.

  FIG. 5 shows the configuration of the GaN-based semiconductor in this case. The difference from FIG. 1B is that an InGaN layer 18 and an AlGaN layer 20 are formed on the GaN semiconductor layer 16. The InGaN layer 18 can be set to 0.001 to 1 μm, for example, and the In composition can be set to 0.02 to 0.5 wt%, for example. Since the hardness of the InGaN layer 18 is smaller than that of the GaN semiconductor layer 16, the strain of the GaN semiconductor layer 16 is absorbed by the InGaN layer 18, and a device structure having no cracks can be obtained.

  Instead of the InGaN layer 18, a superlattice layer (or multilayer quantum well MQW) having a quantum well structure may be formed. The superlattice layer can be formed by alternately laminating InGaN and GaN having a thickness of 2 to 3 nm.

  Further, in the present embodiment, it is assumed that the first buffer body 12 is formed. However, the GaN buffer layer 14 is formed on the substrate without forming the first buffer body 12, and the second buffer body 14 is formed on the GaN buffer layer 14. When the buffer body 15 is formed and then the GaN semiconductor layer 16 is formed, the growth of the GaN semiconductor layer 16 is interrupted in the middle to interpose a discretely formed third buffer body, and then the growth is resumed. Thus, the GaN semiconductor layer 16 may be formed. Also in this method, the dislocation density of the GaN semiconductor layer 16 can be reduced by the third buffer body while preventing the low temperature GaN buffer layer 14 from being evaporated by the second buffer body 15. Of course, all of the first buffer body 12, the second buffer body 15, and the third buffer body can be formed.

In the present embodiment, the buffer body can use Si or SiO _{2 in} addition to SiN.

It is a block diagram of the GaN-type compound semiconductor of embodiment. It is a manufacturing process flowchart of an embodiment. It is a conceptual lineblock diagram of a manufacturing device of an embodiment. It is a block diagram of the GaN-type compound semiconductor of other embodiment. It is a block diagram of the GaN-type compound semiconductor of other embodiment. It is a block diagram of the GaN-type compound semiconductor of related technology. It is a top view of a buffer body. It is explanatory drawing (the 1) of the related technique shown by FIG. It is explanatory drawing (the 2) of the related technique shown by FIG.

Explanation of symbols

  10 substrate, 12 first buffer body, 14 GaN buffer layer, 15 second buffer body, 16 GaN semiconductor layer.

Claims (2)

In the method for producing a gallium nitride compound semiconductor, a buffer layer is grown on the substrate at a low temperature, and a GaN compound semiconductor is further formed on the buffer layer.
Prior to the formation of the buffer layer, first buffer bodies are discretely formed on the substrate, and prior to the formation of the GaN-based compound semiconductor, the temperature rises when the GaN-based compound semiconductor is formed on the buffer layer. A second buffer body for preventing evaporation of the buffer layer is formed discretely, and the second buffer body is silicon or a silicon compound, and a series of steps in the same apparatus as the formation of the buffer layer and the GaN-based compound semiconductor are provided. A method of manufacturing a gallium nitride-based compound semiconductor, characterized by being formed as a step . The method of claim 1, wherein
Each of the first and second buffer bodies is silicon or a silicon compound, and is formed as a series of steps in the same apparatus as the formation of the buffer layer and the GaN-based compound semiconductor, and the first and second buffer bodies are A method of manufacturing a gallium nitride compound semiconductor, wherein the gallium nitride compound semiconductor is discretely formed so as to have a plurality of holes .

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