JP2006278402A - Manufacturing method of nitride semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a nitride semiconductor capable of manufacturing superior single crystal of nitride semiconductor having high quality. <P>SOLUTION: The manufacturing method of a nitride semiconductor includes a first step of forming an amorphous GaN layer, a second step of forming a micro three-dimensional crystal nucleus, by subjecting the GaN layer formed in the first step to temperature rising annealing for partial crystallization, a third step of forming a periodic lamination structure in which an Al<SB>x</SB>Ga<SB>1-x</SB>N (0≤x<1) layer and an AlN layer are laminated alternately by a plurality of layers on the micro three-dimensional crystal nucleus formed in the second step, and a fourth step of forming a single-crystal layer of the nitride semiconductor on the periodic lamination structure formed in the third step. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a nitride semiconductor, and more particularly to a method for manufacturing a nitride semiconductor capable of producing a high-quality nitride semiconductor.

  In recent years, nitride semiconductors have attracted a great deal of attention as materials for devices that generate light in the deep ultraviolet wavelength region (wavelength 200 to 350 nm).

  Typical examples of the nitride semiconductor used as a material for a device that generates light in the deep ultraviolet wavelength region (wavelength 200 to 350 nm) include GaN, AlGaN, and AlN.

  Conventionally, such single crystals such as GaN, AlN, or AlGaN have been manufactured by a manufacturing method as described below.

  For the production of single crystals such as GaN, AlN or AlGaN, conventionally known methods such as metal organic vapor phase epitaxy (MOVPE), hydride vapor phase epitaxy (HVPE), and molecular beam epitaxy (MBE) are known. A crystal growth apparatus is used.

  FIG. 1 is a schematic configuration explanatory diagram of a metal organic vapor phase epitaxy (MOVPE) apparatus which is a crystal growth apparatus used in the present invention among such known crystal growth apparatuses. A crystal growth reactor 12 having an inlet 12a for introducing a raw material gas into the interior and an exhaust port 12b for exhausting a gas existing inside, and a surface disposed inside the crystal growth reactor 12 A susceptor 16 for placing a substrate 14 on which a single crystal such as GaN, AlN or AlGaN is deposited, and an induction heating coil 18 wound around the outer periphery of the crystal growth reactor 12 to inductively heat the susceptor 16; It is comprised.

  A method for manufacturing a single crystal of GaN, AlGaN or AlN described below is manufactured by growing a single crystal using the crystal growth apparatus 10 described above.

I. First, a method for producing a GaN single crystal will be described.

  Manufacture of the single crystal of GaN is performed by processing in the order of the process of the following stages (1-1)-(1-6). In specifying GaN manufactured in the steps (1-1) to (1-6), it is referred to as “(1-x) system”.

  In the following description, a graph showing a change in reflectance accompanying a change in the growth time of (1-x) GaN produced by stages (1-1) to (1-6) shown in FIG. FIG. 3A is a Nomarski optical microscope photograph taken at the end of the stage (1-2) shown in FIG. 3A, FIG. 4B is a conceptual cross-sectional view of the substrate 14 at the end of the stage (1-2) shown in FIG. Nomarski optical microscope photograph taken at the end of the stage (1-3) shown in (a), conceptual cross-sectional view of the substrate 14 at the end of the stage (1-3) shown in FIG. 4 (b), FIG. A Nomarski optical micrograph photographed at the end of the stage (1-4) shown in FIG. 5 and a conceptual sectional view of the substrate 14 at the end of the stage (1-4) shown in FIG.

Stage (1-1): (. Specifically, a sapphire substrate) The substrate 14 for growing a single crystal of GaN low temperature and then furnace pressure and the substrate temperature 550 ° C. as 200 mbar, the TMG and NH ₃ The amorphous GaN layer is formed to a thickness of 20 nm by flowing into the crystal growth reactor 12. At this time, when the surface of the formed amorphous GaN layer is observed, a flat film is formed.

Stage (1-2): After stage (1-1), the substrate temperature of the substrate 14 is raised to 1050 ° C., which is the growth temperature of GaN, in 6 minutes under the flow of H ₂ and NH ₃ . At this time, the amorphous GaN layer is partially crystallized. That is, from the Nomarski optical microscope photograph taken at the end of the stage (1-2) shown in FIG. 3A, the crystallized portion of the GaN layer on the surface of the substrate 14 can be observed as a minute three-dimensional crystal nucleus. . FIG. 3B shows a conceptual cross-sectional view of the substrate 14 at the end of the stage (1-2).

  Stage (1-3): After the substrate temperature of the substrate 14 reaches 1050 ° C., when the TMG flow is restarted, the growth of GaN will start. Three-dimensional growth based on the formed small three-dimensional crystal nucleus occurs, and the initial nucleus develops three-dimensionally. That is, from the Nomarski optical microscope photograph taken at the end of the stage (1-3) shown in FIG. 4A, a three-dimensional facet structure in which minute three-dimensional crystal nuclei are three-dimensionally grown on the surface of the substrate 14 can be observed. FIG. 4B shows a conceptual cross-sectional view of the substrate 14 at the end of the stage (1-3).

  Stage (1-4): As the growth progresses and the film thickness becomes about 100 to 150 nm, the three-dimensional facet structures in which minute three-dimensional crystal nuclei are three-dimensionally grown come to associate with each other. At that time, the substrate temperature of the substrate 14 is raised to 1080 ° C. in order to increase the growth temperature. FIG. 5A shows a Nomarski optical microscope photograph taken at the end of the stage (1-4), and FIG. 5B shows a sectional concept of the substrate 14 at the end of the stage (1-3). The figure is shown.

  Stage (1-5): After the stage (1-4), when the growth is continued, a substantially flat surface appears with a film thickness of about 250 to 500 nm.

Stage (1-6): Finally, a GaN layer having a thickness of about 1 to 2 μm is formed. According to the X-ray evaluation, GaN single crystals of (002) rocking curve half width of 250 to 350 arcsec and (100) rocking curve half width of 400 to arcsec were obtained. The threading dislocation density is 3 × 10 ^{8 to} cm ⁻² .

The GaN layer manufactured in the steps (1-1) to (1-6) described above has sufficient quality as a base layer of a blue LED element using InGaN as an active layer.

II. Next, a method for producing an AlN single crystal will be described.

  In the following, as a method for producing a single crystal of AlN, a production method according to the steps (2-1) to (2-4) and a production method according to the steps (3-1) to (3-6) Will be described.

  AlN is manufactured by processing in the order of steps (2-1) to (2-4) or stages (3-1) to (3-6). In specifying the AlN manufactured in the steps (2-1) to (2-4), it is referred to as “(2-x) system”, and the stages (3-1) to (3-6) are used. In identifying the AlN produced in the process of), it is referred to as “(3-x) system”.

II-1. (2-x) Production Method of AlN Stage (2-1): The temperature of the substrate 14 (specifically, a sapphire substrate) on which an AlN single crystal is grown is set to a low temperature of 620 ° C. TMA and NH ₃ are flowed into the crystal growth reactor 12 at a pressure of 100 mbar, and an amorphous AlN layer is formed to a thickness of 40 nm. At this time, when the surface of the formed amorphous AlN layer is observed, a flat film is formed.

Stage (2-2): After stage (2-1), the substrate temperature of the substrate 14 is raised to 1130 ° C., which is the growth temperature of AlN, in 4 minutes under the flow of H ₂ and NH ₃ . At this time, the amorphous AlN layer is partially crystallized, but unlike the amorphous GaN layer, a clear three-dimensional structure is not formed and remains flat at the microscope level. .

  Stage (2-3): When the substrate temperature of the substrate 14 reaches 1130 ° C. and the furnace pressure is 50 mbar and the TMA flow is resumed, the growth of AlN will be started, but the stage (2-2) Since the surface formed in step (1) is flat, unlike the stage (1-2), the flat surface is secured from the initial stage of growth and the growth proceeds.

Stage (2-4): Finally, an AlN layer having a thickness of about 1 to 2 μm is formed. According to the X-ray evaluation, AlN single crystals having (002) rocking curve half width of 1000 to arcsec and (100) rocking curve half width of 3000 to arcsec were obtained. The threading dislocation density is 3 × 10 ^{10 to} cm ⁻² .

That is, in the AlN manufacturing method using the stages (2-1) to (2-4), the initial stage of the GaN manufacturing method using the stages (1-1) to (1-6) described above is the initial stage. It is considered that the crystal quality is not improved because there is no nucleation and association process.

II-2. (3-x) Production Method of AlN The (3-x) production method of AlN is an improvement of the production method of AlN by stages (2-1) to (2-4).

Stage (3-1): The substrate temperature of the substrate 14 (specifically, a sapphire substrate) on which an AlN single crystal is grown is set to a low temperature of 620 ° C., the furnace pressure is set to 100 mbar, and TMA and NH ₃ are mixed. The film is flowed into the crystal growth reactor 12 to form an amorphous AlN film having a thickness of less than 40 nm. Thus, when the film thickness of amorphous AlN grown at a low temperature is reduced from 40 nm, the state of adhesion of amorphous AlN grown at a low temperature is locally uneven on sapphire, unlike when it is as thick as 40 nm. Will occur. The unevenness becomes more prominent as the formed AlN film becomes thinner.

Stage (3-2): After stage (3-1), the substrate temperature of substrate 14 is raised to 1130 ° C., which is the growth temperature of AlN, in 4 minutes under the flow of H ₂ and NH ₃ . At this time, the local unevenness formed in the stage (3-1) remains preserved.

  Stage (3-3): After the substrate temperature of the substrate 14 reaches 1130 ° C., the furnace pressure is set to 50 mbar, and when the TMA flow is resumed, the growth of AlN is started. Growth proceeds using the local unevenness formed in 3-1) as a seed.

  Stage (3-4): The surface obtained by subsequent AlN film growth becomes rougher as the local unevenness becomes more conspicuous, that is, as the film thickness of amorphous AlN grown at low temperature becomes thinner.

  Stage (3-5): In order not to cause surface roughness in stage (3-4), if an alternate supply method suitable for securing a flat surface is applied to AlN growth, surface roughness is suppressed and flat AlN A membrane can be obtained.

Stage (3-6): As described above, the film thickness of amorphous AlN grown at a low temperature is reduced, and finally the thickness of about 1 to 2 μm is obtained while ensuring flatness by the alternate supply method. An AlN layer is formed. In the X-ray evaluation, AlN single crystals having (002) rocking curve half-width of ~ 100 arcsec and (100) rocking curve half-width of ~ 2000 arcsec were obtained. The threading dislocation density is 10 ¹⁰ cm ⁻² .

III. Next, a method for producing an AlGaN single crystal that is substantially useful for realizing a deep ultraviolet light-emitting device will be described.

  In the following, as a method for producing a single crystal of AlGaN, production by the process of stage (4-1) in which an AlGaN layer is formed on the GaN layer formed in stages (1-1) to (1-6). The method and the low-temperature growth amorphous AlN layer formed in the stage (2-1) are once formed on the GaN layer formed in the stages (1-1) to (1-6), and then the AlGaN layer is formed. And the stage (6) in which an AlGaN layer is formed on the AlN layer formed in stages (2-1) to (2-4). -1), a manufacturing method according to the stage (7-1) process of forming an AlGaN layer on the AlN layer formed at the stages (3-1) to (3-6), Stage (2-1) to (2 2) or the manufacturing method according to the stage (8-1) process of forming an AlGaN layer on the low-temperature-grown amorphous AlN layer formed in the stages (3-1) to (3-2). To do.

  AlGaN is manufactured by processing the processes of each stage described above in order. In specifying the AlGaN manufactured in the process of the stage (4-1), it is referred to as “(4-1) system” and manufactured in the processes of the stages (5-1) to (5-3). In specifying AlGaN, it is referred to as “(5-x) system”, and in specifying AlGaN manufactured in the stage (6-1), it is referred to as “(6-1) system”. In specifying the AlGaN manufactured in the process of the stage (7-1), it is referred to as “(7-1) system”, and in specifying the AlGaN manufactured in the process of the stage (8-1). It will be referred to as “(8-1) system”.

III-1. (4-1) Production method of AlGaN (formation of AlGaN layer on thick GaN layer)
Stage (4-1): AlGaN is formed on GaN having a thickness of about 2 μm formed by stages (1-1) to (1-6) at 1120 ° C. and a furnace pressure of 50 mbar. As the Al composition ratio increases, the AlGaN layer cracks with a thin film thickness as a critical value (although depending on the crystal growth conditions, cracks occur with a film thickness of about 300 nm in Al _0.2 Ga _0.8 N. In the case of Al _0.35 Ga _0.65 N, cracks occur with a film thickness of about 100 nm.) Within the critical film thickness where cracks do not occur, it is possible to form crystalline AlGaN that is relatively inherited from the high quality of the underlying GaN layer. However, the light-emitting element must have a sufficiently thick electrode layer. With this method, it is not possible to ensure a film thickness that allows the electrode layer to be formed while avoiding cracks.

III-2. (5-x) Manufacturing Method of AlGaN (Formation of AlGaN Layer on Thick GaN Layer)
Stage (5-1): An amorphous AlN layer grown at a low temperature of 620 ° C. as in (2-1) on GaN having a thickness of about 2 μm formed by stages (1-1) to (1-6). A thickness of about 40 nm is formed at a furnace pressure of 100 mbar.

Stage (5-2): After stage (5-1), under the flow of H ₂ and NH ₃ as in (2-2), the substrate temperature of the substrate 14 is increased to 1120 ° C., which is the growth temperature of AlGaN, for 4 minutes. Raise the temperature.

Stage (5-3): When the substrate temperature of the substrate 14 reaches 1120 ° C., the furnace pressure is set to 50 mbar, and when the TMG and TMA flows are started, AlGaN is grown. According to this method, the occurrence of cracks can be avoided, but the half width of the X-ray (002) rocking curve does not change significantly from that of the underlying GaN layer. The price range increases significantly. As a result, the threading dislocation density is 10 ^{10 to} cm ⁻² .

III-3. (6-1) Manufacturing method of AlGaN (formation of AlGaN layer on thick AlN layer)
Stage (6-1): AlGaN is formed on AlN having a thickness of about 1 μm formed by stages (2-1) to (2-4) at 1120 ° C. and a furnace pressure of 50 mbar. According to this technique, cracks do not occur, but inherit the threading dislocation density of the underlying AlN layer, and although the AlGaN layer has a flat surface, the crystal quality does not improve, and the threading dislocation density is 10 ^{10 to} cm ^−2. It will be something like that.

III-4. (7-1) Manufacturing method of AlGaN system (formation of AlGaN layer on thick AlN layer)
Stage (7-1): AlGaN is formed on AlN having a thickness of about 1 μm formed by stages (3-1) to (3-6) at 1120 ° C. and a furnace pressure of 50 mbar. According to this method, cracks do not occur, but the tendency to hardly obtain a flat surface by inheriting the surface state of the underlying AlN layer becomes significant. Further, depending on the situation, a film in which the AlGaN composition fluctuates locally is formed. The crystal quality is the same as or worse than that of the underlying AlN, and the threading dislocation density is still 10 ^{10 to} cm ⁻² . In the case of forming AlGaN on the stages (3-1) to (3-6) used for improving the quality of AlN obtained in the stages (2-1) to (2-4) Rather, only the disadvantages stand out.

III-5. (8-1) Manufacturing method of AlGaN (formation of AlGaN layer on low-temperature grown amorphous AlN layer)
Stage (8-1): AlGaN 1120 is deposited on the amorphous AlN layer grown at a low temperature formed in stages (2-1) to (2-2) or stages (3-1) to (3-2). It is formed at a temperature of 50 ° C. and a furnace pressure of 50 mbar. Even with this method, the situation is similar to (6-1) AlGaN and (7-1) AlGaN, and the crystal quality is not improved.

That is, according to the conventional method described above, there is a problem that it is very difficult to obtain an AlGaN layer having the same quality as that of a GaN layer that has succeeded in an InGaN-based blue light-emitting LED.

  However, considering the phenomenon caused by the conventional method described above in detail, the following consideration can be obtained.

  (A) In order to improve the crystal quality, particularly to reduce the threading dislocation density, it is necessary to form three-dimensional nuclei that can be clearly observed at the microscope level in the initial stage.

  (B) It is necessary to associate the three-dimensional nuclei by lateral growth.

  (C) Finally, it should be prevented from cracking.

Here, an effective technique for realizing the above (a) is to use low-temperature grown amorphous GaN. That is, in order to realize the above (a), the processes of stages (1-1) to (1-2) are used as shown in the manufacturing method according to the processes of stages (9-1) to (9-4). Then, an AlGaN layer may be formed thereafter. According to the manufacturing method according to the steps (9-1) to (9-4), since the film thickness of the GaN layer corresponding to the base is at most 20 nm, it is different from the system using GaN having a film thickness of 2 μm. The critical film thickness at which cracks occur was greatly increased. In the applicant's experiment, the Al _0.2 Ga _0.8 N layer is crack-free up to a film thickness of about 3 μm, and the Al _0.35 Ga _0.65 N layer is up to a film thickness of about 1 μm. Was confirmed.

  Below, the manufacturing method by the process of stages (9-1)-(9-4) is demonstrated as a manufacturing method of the single crystal of AlGaN. AlGaN is manufactured by processing in the order of the steps (9-1) to (9-4). In addition, when specifying AlGaN manufactured in the steps (9-1) to (9-4), it is referred to as “(9-x) system”.

  Stage (9-1): The same processing as in stage (1-1) is performed.

  Stage (9-2): The same processing as in stage (1-2) is performed.

Stage (9-3): After the substrate temperature of the substrate 14 reaches 1050 ° C., the furnace pressure is immediately set to 50 mbar, and the growth of AlGaN is started by the TMG, TMA, and NH ₃ flows. In the middle, the substrate temperature is raised to 1120 ° C. Then, unlike the stage (1-3), the growth proceeds in such a manner that the minute three-dimensional nucleus formed in the stage (1-2) is immediately filled.

Stage (9-4): Finally, an Al _0.35 Ga _0.65 N layer having a thickness of about 1 μm is formed. In the X-ray evaluation, AlGaN having a quality of (002) rocking curve half width of about 600 arcsec and (100) rocking curve half width of about 1800 arcsec was obtained. The threading dislocation density is about 1 × 10 ¹⁰ cm ⁻² .

According to the manufacturing method by the processes of the stages (9-1) to (9-4), it is possible to obtain AlGaN of high quality to some extent, but excellent nitrides having higher quality including AlGaN. There was a strong demand for the development of semiconductor single crystals.

Note that the prior art that the applicant of the present application knows at the time of filing a patent application is not an invention related to a known literature invention, so there is no prior art document information to be described.

  The present invention has been made in view of the above-described demand for the prior art, and an object of the present invention is to provide a nitride capable of producing a high-quality nitride semiconductor single crystal. An object of the present invention is to provide a method for manufacturing a semiconductor.

In order to achieve the above object, according to the first aspect of the present invention, in the method for manufacturing a nitride semiconductor, the first step of forming an amorphous GaN layer and the first step are formed. The second step of partially crystallizing the GaN layer by annealing to form a micro three-dimensional crystal nucleus, and the Al _x on the micro three-dimensional crystal nucleus formed in the second step. A third step of forming a periodic laminated structure in which a plurality of Ga _1-x N (0 ≦ x <1) layers and AlN layers are alternately laminated; and the periodic laminated structure formed in the third step. And a fourth step of forming a single crystal layer of the nitride semiconductor.

The invention according to claim 2 of the present invention is the invention according to claim 1 of the present invention, wherein the nitride semiconductor forming the single crystal layer in the fourth step is Al _y Ga _{1−. y} N (0 ≦ y ≦ 1).

According to a third aspect of the present invention, in the nitride semiconductor manufacturing method, the first step of forming the amorphous GaN layer and the GaN layer formed in the first step are elevated. A second step of partially crystallizing by thermal annealing to form a micro three-dimensional crystal nucleus, and a micro three-dimensional by growing GaN on the micro three-dimensional crystal nucleus formed in the second step. A third step of forming a three-dimensional facet structure in which crystal nuclei are developed, and an Al _x Ga _1-x N (0 ≦ x <1) layer on the three-dimensional facet structure formed in the third step A fourth step of forming a periodic stacked structure in which a plurality of AlN layers and AlN layers are alternately stacked, and a fifth step of forming a single crystal layer of a nitride semiconductor on the periodic stacked structure formed in the fourth step The It has a tep.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the nitride semiconductor forming the single crystal layer in the fifth step is Al _y Ga _{1−. y} N (0 ≦ y ≦ 1).

According to a fifth aspect of the present invention, in the nitride semiconductor manufacturing method, the first step of forming the amorphous GaN layer and the GaN layer formed in the first step are elevated. A second step of partially crystallizing by thermal annealing to form a micro three-dimensional crystal nucleus, and a micro three-dimensional by growing GaN on the micro three-dimensional crystal nucleus formed in the second step. A third step of forming a three-dimensional facet structure in which crystal nuclei are developed; a fourth step of interrupting the GaN growth of the three-dimensional facet structure formed in the third step and annealing at elevated temperature; After performing the temperature increase annealing in the fourth step, a fifth step of forming a periodic stacked structure in which a plurality of Al _x Ga _1-x N (0 ≦ x <1) layers and AlN layers are alternately stacked. And a sixth step of forming a single crystal layer of a nitride semiconductor on the periodic laminated structure formed in the fifth step.

According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the nitride semiconductor forming the single crystal layer in the sixth step is Al _y Ga _{1−. y} N (0 ≦ y ≦ 1).

  According to the present invention, it is possible to produce an excellent nitride semiconductor single crystal having significantly higher quality than conventional ones.

  Hereinafter, an example of an embodiment of a nitride semiconductor manufacturing method according to the present invention will be described in detail with reference to the accompanying drawings.

  In the nitride semiconductor manufacturing method according to the present invention, a known crystal growth apparatus such as the crystal growth apparatus 10 described above is used as the crystal growth apparatus.

First, a manufacturing method for manufacturing a single crystal of AlGaN as a nitride semiconductor according to a first embodiment of a manufacturing method of a nitride semiconductor according to the present invention will be described.

  The production of the AlGaN single crystal according to the first embodiment of the method for producing a nitride semiconductor according to the present invention is performed by processing in the order of the steps (10-1) to (10-4) shown below. Is called. In specifying the AlGaN manufactured in the steps (10-1) to (10-4), it is referred to as “(10-x) system”.

  Stage (10-1): The same processing as in stage (1-1) is performed.

  Stage (10-2): The same processing as in stage (1-2) is performed.

Stage (10-3): Immediately after the substrate temperature of the substrate 14 reaches 1050 ° C., the furnace pressure is set to 50 mbar, an AlGaN layer having a thickness of about 20 to 40 nm by TMG, TMA, NH ₃ flow, and TMA, NH A periodic laminated structure is formed by alternately laminating about 10 to 20 periods of AlN layers having a film thickness of about 5 nm by _three flows. In the middle, the substrate temperature is raised to 1120 ° C. Then, unlike the stage (1-3), the growth proceeds in such a manner that the minute three-dimensional nucleus formed in the stage (1-2) is immediately filled.

  Stage (10-4): After completing the production of the periodic laminated structure in stage (10-3), the process shifts to AlGaN growth.

According to the manufacturing method according to the stages (10-1) to (10-4), the crack generation critical film thickness is 1 μm at most in the manufacturing method according to the above-described stages (9-1) to (9-3). It was also confirmed that the Al _0.35 Ga _0.65 N layer, which was about, was crack-free up to a film thickness of about 3 μm. In the X-ray evaluation, it was found that the manufacturing method according to the steps (9-1) to (9-3) was equivalent to or slightly better than the manufacturing method. The threading dislocation density is also equivalent to the manufacturing method according to the steps (9-1) to (9-3).

Next, a manufacturing method for manufacturing a single crystal of AlGaN as a nitride semiconductor according to a second embodiment of the manufacturing method of a nitride semiconductor according to the present invention will be described.

  The second embodiment of the nitride semiconductor manufacturing method according to the present invention has been made in view of the above-mentioned “(b) It is necessary to associate the three-dimensional nuclei by lateral growth”. And includes processing for associating three-dimensional nuclei by lateral growth. Specifically, the processes from the stages (1-1) to (1-3) are performed, and then the process proceeds to fabrication of a periodic stacked structure and AlGaN growth.

  That is, the production of the single crystal of AlGaN according to the second embodiment of the method for producing a nitride semiconductor according to the present invention is performed in the order of the steps (11-1) to (11-5) shown below. Is done. In specifying the AlGaN manufactured in the steps (11-1) to (11-5), it is referred to as “(11-x) system”.

  In the following description, a Nomarski optical micrograph taken at the end of the stage (11-2) shown in FIG. 7A, and the substrate 14 at the end of the stage (11-2) shown in FIG. 7B. , A Nomarski optical micrograph taken at the end of the stage (11-3) shown in FIG. 8 (a), and a cross-sectional concept of the substrate 14 at the end of the stage (11-3) shown in FIG. 8 (b). The Nomarski optical micrograph photographed at the end of the stage (11-4) shown in FIG. 9 is also referred to.

  Stage (11-1): The same processing as in stage (1-1) is performed.

  Stage (11-2): The same processing as in stage (1-2) is performed (see FIGS. 7A and 7B).

  Stage (11-3): The same process as in stage (1-3) is performed (see FIGS. 8A and 8B).

Stage (11-4): Immediately thereafter, the furnace pressure was set to 50 mbar, an AlGaN layer having a thickness of about 20 to 40 nm by TMG, TMA, and NH ₃ flows, and an AlN layer having a thickness of about 5 nm by TMA and NH ₃ flows Are periodically stacked for about 10 to 20 periods. In the middle, the substrate temperature is raised to 1120 ° C. Then, unlike the stage (1-4), the stage (11-3), that is, the growth does not proceed in a form in which the minute three-dimensional crystal nucleus formed in the stage (1-3) is immediately filled. . That is, as shown in the Nomarski optical micrograph of FIG. 9, the growth progresses in such a manner that the flatness is gradually recovered or the three-dimensional nuclear structure is preserved.

  Stage (11-5): After the fabrication of the periodic laminated structure in stage (11-4), when shifting to AlGaN growth, the growth shifts to fill the three-dimensional structure, and a flat surface is obtained with growth of about 500 nm. It is done.

  The (11-x) AlGaN layer produced in the steps (11-1) to (11-5) was produced in the steps (10-1) to (10-4) (10 -X) Although the critical film thickness at which cracks occur is thinner than the AlGaN layer of the x system, the X-ray evaluation is about 400 arcsec at (002) and about 1400 arcsec at 100), which is a better value than the (10-x) system. Indicates.

Next, a manufacturing method for manufacturing an AlGaN single crystal as a nitride semiconductor according to a third embodiment of the manufacturing method of a nitride semiconductor according to the present invention will be described.

  The third embodiment of the method for manufacturing a nitride semiconductor according to the present invention has been made in view of the above-mentioned “(b) It is necessary to associate the three-dimensional nuclei by lateral growth”. And includes processing for associating three-dimensional nuclei by lateral growth. Specifically, the processes from stage (1-1) to (1-3) are performed, and then the process shifts to a process peculiar to the third embodiment of the nitride semiconductor manufacturing method according to the present invention. It is a thing.

  That is, the production of the single crystal of AlGaN according to the third embodiment of the method for producing a nitride semiconductor according to the present invention is performed in the order of the steps (12-1) to (12-8) shown below. Is done. In specifying the AlGaN manufactured in the steps (12-1) to (12-8), it is referred to as “(12-x) system”.

  In the following description, a graph showing a change in reflectance accompanying a change in the growth time of (12-x) AlGaN produced by stages (12-1) to (12-8) shown in FIG. FIG. 7A is a Nomarski optical microscope photograph taken at the end of the stage (12-2) shown in FIG. 7A, and FIG. 8 is a conceptual cross-sectional view of the substrate 14 at the end of the stage (12-2) shown in FIG. Nomarski optical microscope photograph taken at the end of the stage (12-3) shown in (a), conceptual cross-sectional view of the substrate 14 at the end of the stage (12-3) shown in FIG. 8 (b), FIG. Nomarski optical micrograph taken at the end of the stage (12-6) (at the end of (12-5)) shown in FIG. 10, at the end of the stage (12-6) ((12-5) shown in FIG. 10B) ) Conceptual sectional view of the substrate 14 in FIG. And references together Nomarski optical microscope photograph taken at the end of stage (12-7) shown in Figure 11.

  Stage (12-1): The same processing as in stage (1-1) is performed.

  Stage (12-2): The same processing as stage (1-2) is performed (see FIGS. 7A and 7B).

  Stage (12-3): The same processing as in stage (1-3) is performed (see FIGS. 8A and 8B).

Stage (12-4): Growth progresses and three-dimensional nuclei meet from a thickness of about 100 to 150 nm (a phenomenon that occurs in stage (1-4)), but in stage (12-4) Stops the TMG flow and interrupts GaN growth just before the meeting begins. At that time, the NH ₃ flow is not stopped.

Stage (12-5): From the stage (12-4) state, the substrate temperature is increased to 1120 ° C., and the NH ₃ flow rate is increased to about 1.5 times the flow rate during GaN growth (specifically, , Rose from 2L to 3L during GaN growth.) The rising time is 1 minute 30 seconds, and the waiting time at 1120 ° C. is 1 minute 30 seconds.

  Stage (12-6): Although the growth was interrupted as a result of the processing of stage (12-5), it was generated in stage (12-2) and developed in stage (12-3) 3 The dimensional nucleus structure moves to a flat one (see FIGS. 10A and 10B). This stage (12-6) is a stage for ensuring flatness equivalent to the stage (1-4), but the stage (1-4) is flattened by crystal growth while the stage ( 12-4) to (12-6) are flattened by temperature rising annealing during interruption of growth after stopping the TMG flow.

Stage (12-7): After the processing of stage (12-6), the same processing as the processing of stages (11-4) to (11-5) is performed. That is, after that, the furnace pressure is quickly set to 50 mbar, and an AlGaN layer having a thickness of about 20 to 40 nm by TMG, TMA, and NH ₃ flows and an AlN layer having a thickness of about 5 nm by TMA and NH ₃ flows are alternately alternated. A periodic laminated structure is formed by laminating about 10 to 20 periods. Since the substrate temperature has already been raised to 1120 ° C. in the stage (12-5), the temperature is not raised in the stage (12-7). In the stage (12-7), the growth proceeds in the form of preserving the flat surface obtained in the stage (12-6) or further improving the flatness (see FIG. 11).

  Stage (12-8): After the production of the periodic laminated structure in stage (12-7), the process shifts to AlGaN growth. The critical film thickness at which cracking occurs is equal to or slightly larger than the (11-x) AlGaN produced by the stages (11-1) to (11-5). In other words, the critical film thickness for crack generation is smaller than that of the AlGaN film obtained by the (10-x) system produced by the stages (10-1) to (10-4). In the X-ray evaluation, (002) is about 400 arcsec, which is equivalent to the (11-x) system, but (100) shows ~ 1200 arcsec and a better value than the (11-x) system.

Here, regarding the X-ray evaluation of the (12-x) system, as shown in Table 1, (002) is equivalent to the (11-x) system, but the value of (100) is good. The reason is as follows.

  That is, the X-ray (002) half width value indicates the degree of C-axis orientation shift of the crystal and indirectly suggests the screw dislocation density during threading dislocations. The screw dislocation is a dislocation incidental to spiral growth originating from a three-dimensional structure generated by the initial nucleus and subsequent three-dimensional structure formation.

  In the (10-x) type, (11-x) type and (12-x) type production methods, stages (10-1) to (10-) are used for low-temperature amorphous GaN growth for initial nucleation, respectively. 2), stages (11-1) to (11-2) and stages (12-1) to (12-2), all of which are common processes, and stage (1 -1) to (1-2).

  Here, the difference between the (10-x) type manufacturing method and the (11-x) type and (12-x) type manufacturing method is the stage (specifically) in which the initial nucleus is developed three-dimensionally thereafter. (In other words, it is stage (1-3)). In the manufacturing methods of the (11-x) system and the (12-x) system, since the stages so far are common, the values of the X-ray (002) are almost equal.

  On the other hand, the value of the X-ray (100) half width indicates the degree to which the crystal is deviated from rotation about the C axis, and is closely related to the edge dislocation density during threading dislocation. The superiority of the (12-x) -based AlGaN formation method can be seen.

The embodiment described above can be modified as shown in the following (1) to (3).

(1) In each of the above-described embodiments, an Al _x Ga _1-x N (0 ≦ x <1) layer having a thickness of about 20 to 40 nm by TMG, TMA, and NH ₃ flows, and TMA and NH ₃ flows. A periodic laminated structure was formed by alternately laminating AlN layers having a thickness of about 5 nm for about 10 to 20 periods. Here, x, which is the composition of the Al _x Ga _1-x N (0 ≦ x <1) layer, is basically Al _y Ga _1-y N (0 ≦ y) subsequently formed on the periodic laminated structure. ≦ 1) It is selected so as to be “x = y” with respect to the composition y of the layer, but is not limited to this, and further, Al _x Ga _1-x Of course, the film thickness of the N (0 ≦ x <1) layer and the AlN layer is not limited to the above, and the number of periods of the periodic laminated structure is not limited to the above. .

(2) In the above-described embodiment, the case where a single crystal layer of AlGaN is manufactured as a nitride semiconductor has been described. However, the present invention is not limited to this, and the manufacture of the nitride semiconductor of the present invention is not limited to this. According to the method, a single crystal layer of GaN or AlN can be manufactured as a nitride semiconductor. That is, in the above-described embodiment, the case where the single crystals of Al _0.2 Ga _0.8 N and Al _0.35 Ga _0.65 N are manufactured as the nitride semiconductor has been described. This is not apparent from the details of the nitride semiconductor manufacturing method according to the present invention. That is, in the method for producing a nitride semiconductor according to the present invention, the stage for improving the crystal quality is the formation of micro three-dimensional crystal nuclei (stages (10-1) to (10-2), stage (11- 1) to (11-2), stages (12-1) to (12-2)), and further three-dimensional facet structure formation (stage (11-3), stage (12) following three-dimensional crystal nucleation depending on circumstances. -3)), and further up to replanarization (stages (12-4) to (12-6)) by temperature rising annealing subsequent to the formation of the three-dimensional facet structure depending on the situation, and the GaN layer for improving the crystal quality. _Al x _{Ga 1-x} N after forming stage (0 ≦ x <1) / AlN multilayer structure formed stage (stage (10-3), the stage (11-4), the stage (12-7)) Can separate functions as a stage for crack suppression. Therefore, manufacture of a nitride semiconductor according to the present invention in which a nitride semiconductor is formed after going through a GaN layer forming stage for improving crystal quality and an Al _x Ga _1-x N (0 ≦ x <1) / AlN multilayer structure forming stage According to the method, it is possible to manufacture a single crystal layer having a general composition of Al _y Ga _1-y N (0 ≦ y ≦ 1) including GaN and AlN as a nitride semiconductor.

  (3) You may make it combine the above-mentioned embodiment and the modification shown in above-mentioned (1) thru | or (2) suitably.

  The present invention can be used as a material for a device that generates light in the deep ultraviolet wavelength region.

FIG. 1 is an explanatory diagram of a schematic configuration of a crystal growth apparatus. FIG. 2 is a graph showing a change in reflectance accompanying a change in growth time of (1-x) GaN produced by stages (1-1) to (1-6). FIG. 3A is a Nomarski optical microscope photograph taken at the end of the stage (1-2), and FIG. 3B is a conceptual cross-sectional view of the substrate at the end of the stage (1-2). 4A is a Nomarski optical microscope photograph taken at the end of the stage (1-3), and FIG. 4B is a conceptual cross-sectional view of the substrate at the end of the stage (1-3). FIG. 5A is a Nomarski optical microscope photograph taken at the end of the stage (1-4), and FIG. 5B is a conceptual cross-sectional view of the substrate at the end of the stage (1-4). FIG. 6 is a graph showing a change in reflectance accompanying a change in growth time of (12-x) AlGaN produced by stages (12-1) to (12-8). FIG. 7A is a Nomarski optical micrograph taken at the end of the stage (12-2) (common at the end of the stage (11-2), the same as at the end of the stage (1-2)). FIG. 7B is a conceptual cross-sectional view of the substrate at the end of the stage (12-2) (same as the end of the stage (11-2) and the same as the end of the stage (1-2)). FIG. 8A is a Nomarski optical micrograph taken at the end of the stage (12-3) (same as the end of the stage (11-3), the same as the end of the stage (1-3)). FIG. 8B is a conceptual cross-sectional view of the substrate at the end of the stage (12-3) (same as the end of the stage (11-3), the same as the end of the stage (1-3)). . FIG. 9 is a Nomarski optical micrograph taken at the end of the stage (11-4). FIG. 10A is a Nomarski optical micrograph taken on stage (12-6) (at the end of stage (12-5)), and FIG. 10B shows stage (12-6) (stage ( 12-5) is a conceptual cross-sectional view of a substrate at the time of completion of 12-5). FIG. 11 is a Nomarski optical micrograph taken at the end of the stage (12-7).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Crystal growth apparatus 12 Crystal growth reactor 12a Inlet 12b Exhaust port 14 Crystal growth reactor 16 Susceptor 18 Induction heating coil

Claims (6)

In the method for manufacturing a nitride semiconductor,
A first step of forming an amorphous GaN layer;
A second step in which the GaN layer formed in the first step is partially crystallized by annealing at a high temperature to form a micro three-dimensional crystal nucleus;
A periodic stacked structure in which a plurality of Al _x Ga _1-x N (0 ≦ x <1) layers and AlN layers are alternately stacked is formed on the micro three-dimensional crystal nucleus formed in the second step. The third step;
And a fourth step of forming a single crystal layer of the nitride semiconductor on the periodic stacked structure formed in the third step. In the manufacturing method of the nitride semiconductor according to claim 1,
The nitride semiconductor forming the single crystal layer in the fourth step is Al _y Ga _1-y N (0 ≦ y ≦ 1). In the method for manufacturing a nitride semiconductor,
A first step of forming an amorphous GaN layer;
A second step in which the GaN layer formed in the first step is partially crystallized by annealing at a high temperature to form a micro three-dimensional crystal nucleus;
A third step of forming a three-dimensional facet structure in which a minute three-dimensional crystal nucleus is developed by growing GaN on the minute three-dimensional crystal nucleus formed in the second step;
A periodic stacked structure in which a plurality of Al _x Ga _1-x N (0 ≦ x <1) layers and AlN layers are alternately stacked is formed on the three-dimensional facet structure formed in the third step. 4 steps,
And a fifth step of forming a single crystal layer of the nitride semiconductor on the periodic laminated structure formed in the fourth step. In the manufacturing method of the nitride semiconductor according to claim 3,
The nitride semiconductor forming the single crystal layer in the fifth step is Al _y Ga _1-y N (0 ≦ y ≦ 1). In the method for manufacturing a nitride semiconductor,
A first step of forming an amorphous GaN layer;
A second step in which the GaN layer formed in the first step is partially crystallized by annealing at a high temperature to form a micro three-dimensional crystal nucleus;
A third step of forming a three-dimensional facet structure in which a minute three-dimensional crystal nucleus is developed by growing GaN on the minute three-dimensional crystal nucleus formed in the second step;
A fourth step in which the GaN growth of the three-dimensional facet structure formed in the third step is interrupted to perform temperature rising annealing;
A fifth step of forming a periodic laminated structure in which a plurality of Al _x Ga _1-x N (0 ≦ x <1) layers and AlN layers are alternately laminated after performing the temperature increase annealing in the fourth step; ,
And a sixth step of forming a single crystal layer of the nitride semiconductor on the periodic laminated structure formed in the fifth step. In the manufacturing method of the nitride semiconductor according to claim 5,
The nitride semiconductor forming a single crystal layer in the sixth step is Al _y Ga _1-y N (0 ≦ y ≦ 1).