Method for producing substrate for crystal growth

Abstract

To provide a method for producing a substrate for crystal growth that can grow a high-quality semiconductor crystal stably.SOLUTION: A method for producing a substrate S for crystal growth includes a graphene layer lamination step of laminating a graphene layer 11 on a surface of a sapphire substrate 10. The graphene layer lamination step finishes the execution while a plurality of through-holes 11A from which a surface of the sapphire substrate 10 is exposed is formed in the graphene layer 11.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a substrate for crystal growth. [Background technology]

[0002] Patent Document 1 discloses a technique in which a mask layer with groove-shaped openings is laminated on a graphene layer laminated on a GaN layer, and GaN crystals with reduced dislocations are grown using a CVD method. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-175694 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when using the method of Patent Document 1, the quality of the obtained GaN crystal tends to vary, such as there being many dislocations in the region corresponding to the upper part of the opening, and there has been a demand for a technology for growing stable, high-quality GaN crystals.

[0005] The present invention has been made in consideration of the above-mentioned conventional situation, and an object of the present invention is to provide a method for producing a crystal growth substrate that allows stable crystal growth of high-quality semiconductor crystals. [Means for solving the problem]

[0006] The method for producing a crystal growth substrate of the first invention comprises the steps of: a graphene layer lamination step of laminating a graphene layer on a surface of a substrate, The graphene layer stacking step is completed when a plurality of through-holes exposing the surface of the substrate are formed in the graphene layer.

[0007] The method for producing a crystal growth substrate of the second invention comprises: a graphene layer lamination step of laminating a graphene layer on a surface of the substrate; a through-hole forming step of forming a plurality of through-holes in the graphene layer so that the surface of the substrate is exposed after the graphene layer laminating step is performed; Equipped with.

[0008] The method for producing a crystal growth substrate of the third invention comprises: a graphene layer lamination step of laminating a graphene layer on a surface of a substrate, In the graphene layer stacking step, a plurality of defects having a size equal to or larger than a seven-membered ring are formed in the graphene layer.

[0009] According to the methods for producing a crystal growth substrate of the first, second and third inventions, it is possible to produce a substrate from which high-quality semiconductor crystals can be stably produced. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing a method for producing a crystal growth substrate in Example 1. FIG. [Figure 2] (A) is an atomic force microscope image of the prepared crystal growth substrate viewed from the surface side, and (B) is a graph showing the results of Raman scattering spectroscopy observation of a graphene layer stacked on a sapphire substrate. [Figure 3] FIG. 1 is a schematic diagram illustrating the mechanism by which hydrogen atoms held on a crystal growth substrate are released. [Figure 4] These are the results of XPS measurements of the hydrogen termination state at the graphene-sapphire interface. [Figure 5] FIG. 2 is a schematic diagram showing a process of growing a GaN layer using the prepared crystal growth substrate. [Figure 6] These are SEM images of the front surface of each crystal growth substrate on which a GaN layer was grown by varying the execution time of the crystal growth process. [Figure 7] This is an SEM image of the surface of a GaN layer that has been crystal-grown to cover the entire surface of the graphene layer and has been subjected to etch-pit etching (phosphoric acid, 180°C for 3 minutes). [Figure 8] FIG. 10 is a schematic diagram of a graphene layer of a crystal growth substrate according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] A preferred embodiment of the present invention will now be described.

[0012] In the method for producing a crystal growth substrate according to the first and second aspects of the present invention, in the graphene layer lamination step, hydrogen atoms are held between the substrate and the graphene layer, and when the substrate is heated after the graphene layer lamination step, the hydrogen atoms can be desorbed through the through-holes. In this case, the desorption of hydrogen atoms reduces the distance between the surface of the graphene layer and the surface of the substrate, which makes it easier for crystalline information of the substrate to be appropriately transmitted to the semiconductor crystal to be laminated on the graphene layer, facilitating the production of high-quality semiconductor crystals.

[0013] In the method for producing a crystal growth substrate of the third invention, in the graphene layer deposition step, hydrogen atoms are held between the substrate and the graphene layer, and when the substrate is heated after the graphene layer deposition step, the hydrogen atoms can be desorbed through defects. In this case, the desorption of hydrogen atoms reduces the distance between the surface of the graphene layer and the surface of the substrate, so that when a semiconductor crystal is deposited on the graphene layer, crystal information of the substrate is easily transmitted to the semiconductor crystal to be deposited, facilitating the production of high-quality semiconductor crystal.

[0014] Next, a first embodiment of the present invention will be described with reference to the drawings.

[0015] Example 1 [An example of the graphene layer stacking process] First, a sapphire substrate 10 is prepared as a substrate (see FIG. 1(A)). The r-plane is exposed on the surface of the sapphire substrate 10. Here, the surface is the upper surface in FIG. 1. The sapphire substrate 10 is then immersed in methanol and cleaned for several minutes using an ultrasonic cleaner. The dried sapphire substrate 10 is then immersed in acetone and cleaned for several minutes using an ultrasonic cleaner. The dried sapphire substrate 10 is then immersed in methanol again and cleaned for several minutes using an ultrasonic cleaner.

[0016] The temperature of the thermostatic bath, which maintains the temperature of the bubbler filled with 3-hexyne, a carbon raw material, at a desired temperature, is set to 15°C, and the heating temperature of the piping connected to the reaction tube through which 3-hexyne passes is set to 35°C. Hydrogen and nitrogen are used as carrier gases. Hydrogen produced in a hydrogen purifier is used.

[0017] The sapphire substrate 10 is set in a reaction tube of a low-pressure CVD apparatus (not shown). The low-pressure CVD apparatus is capable of performing a CVD method (chemical vapor deposition). The sapphire substrate 10 is held in the reaction tube so that a carrier gas (hydrogen) hits the surface.

[0018] Next, the reaction tube is evacuated using a rotary pump to reduce the pressure inside the reaction tube to less than 1.0 kPa.

[0019] After that, continue evacuation while flowing nitrogen at 1000 sccm and hydrogen at 100 sccm into the reaction tube. Adjust the needle valve on the exhaust side to maintain the pressure inside the reaction tube at 5.0 kPa. After the pressure inside the reaction tube reaches 5.0 kPa, maintain this state for 20 minutes.

[0020] Before growing the graphene layer 11 on the surface of the sapphire substrate 10, a bubbler containing 3-hexyne, a carbon raw material, is bubbled with nitrogen at 10 sccm for 5 minutes. The temperature of the sapphire substrate 10 is then raised to 1200°C over approximately 10 minutes. The temperature of the sapphire substrate 10 is then maintained at 1200°C for a predetermined time, and the surface of the sapphire substrate 10 is cleaned and modified. 30 minutes before growing the graphene layer 11, a bubbler containing 3-hexyne is bubbled with nitrogen at 1 sccm.

[0021] Next, a graphene layer lamination process is performed to laminate a graphene layer 11 on the surface of the sapphire substrate 10. Specifically, while maintaining the temperature of the sapphire substrate 10 at 1200°C, the ratio of the mixed gas introduced into the reaction tube of the low-pressure CVD apparatus is changed from 1000 sccm of nitrogen and 100 sccm of hydrogen to a mixed gas of 999 sccm of nitrogen, 100 sccm of hydrogen, and 3-hexyne (nitrogen bubbling 1 sccm), and the pressure inside the reaction tube is set to 5.0 kPa by adjusting the exhaust needle valve.

[0022] The temperature of the sapphire substrate 10 is maintained at 1200°C in a mixed atmosphere of nitrogen, hydrogen, and 3-hexyne, and a graphene layer 11 is grown for one hour. A plurality of island-shaped graphene layers 11 are formed on the surface of the sapphire substrate 10 (see FIG. 1B). As the growth time increases, the island-shaped graphene layers 11 grow to spread along the surface of the sapphire substrate 10 (see FIG. 1C). After one hour, the supply of hydrogen and 3-hexyne (nitrogen bubbling at 1 sccm) into the reaction tube is stopped. At the same time, the temperature of the sapphire substrate 10 is naturally cooled from 1250°C to 200°C over approximately 60 minutes. At this time, the flow rate of nitrogen supplied into the reaction tube is changed from 999 sccm to 1000 sccm.

[0023] When the substrate temperature drops to 200°C or below, nitrogen is supplied to the reaction tube to bring the pressure to atmospheric. After that, the hydrogen purifier is shut down, and the sapphire substrate 10 is removed from the reaction tube of the low-pressure CVD apparatus via the preparation chamber. In this way, a graphene layer 11 is grown on the surface of the sapphire substrate 10. Thus, a crystal growth substrate S to be used for growing semiconductor crystals can be obtained.

[0024] A plurality of through holes 11A are formed in the graphene layer 11 thus deposited (see FIGS. 1(C) and 2(A)). If the graphene layer deposition step is continued for one hour or more, the through holes 11A disappear, and the entire surface of the sapphire substrate 10 is covered with the graphene layer 11. In other words, the graphene layer deposition step is completed when a plurality of through holes 11A, through which the surface of the sapphire substrate 10 is exposed, are formed in the graphene layer 11. In FIG. 2(A), the dark areas are the through holes 11A. The size of these through holes 11A can be changed by adjusting the execution time of the graphene layer deposition step. The diameter of the through holes 11A is preferably about 1 nm to 5 μm, more preferably 2 nm to 50 nm.

[0025] Figure 2(B) shows the results of Raman spectroscopy of the graphene layer 11. Raman spectroscopy is commonly used to evaluate graphene. Graphene can be evaluated based on three types of Raman peaks: the D peak, the G peak, and the 2D peak. The D peak is a peak due to structural defects in graphene and the edges of graphene. The G peak is a peak due to in-plane stretching vibrations of graphene and sp2 bonds. The 2D peak is a peak related to multi-step transitions, including interband transitions in graphene. The presence of the G peak and the 2D peak in the results of graphene evaluation using Raman spectroscopy indicates the formation of graphene. Furthermore, by comparing the magnitudes of the G peak and the 2D peak, we can obtain information about the number of stacked layers of the graphene produced. Referring to Figure 2(B), the 2D peak is stronger than the G peak. This indicates that the graphene layer 11 is a single layer of graphene.

[0026] [Example of crystal growth process] Next, a crystal growth process is performed using the crystal growth substrate S. Specifically, a GaN (gallium nitride) layer 12 is crystal-grown on the surface of the graphene layer 11 using RF-MBE. The conditions for the crystal growth process are growth temperature: 740°C, Ga molecular beam intensity: 6.0×10 -7 The conditions were: nitrogen radical cell: RF power 450 W, nitrogen flow rate: 2.0 sccm. Under these conditions, the crystal growth process was carried out for three different times: 30 minutes, 60 minutes, and 90 minutes.

[0027] Here, the hydrogen used in the graphene layer stacking step is held between the sapphire substrate 10 and the graphene layer 11 in a state where it cannot be released as hydrogen atoms H, terminating on the surface of the sapphire substrate 10 (see FIG. 3(A)). Then, when performing the crystal growth step after performing the graphene layer stacking step, the temperature of the crystal growth substrate S is heated to 740°C, whereby the hydrogen atoms H are released through each of the through holes 11A, and this brings the graphene layer 11 closer to the surface of the sapphire substrate 10 (see FIG. 3(B)), making it easier for the crystal information of the sapphire substrate 10 to be transmitted to the surface side of the graphene layer 11.

[0028] Here, the effectiveness of the through-holes 11A in desorption of hydrogen atoms H was confirmed by heat treatment, and the results are shown in Figure 4. Specifically, a sapphire substrate 10 covered with a graphene layer 11 having through-holes 11A formed therein was evaluated by X-ray photoelectron spectroscopy (XPS). As shown in Figure 4(A), the O1s spectrum before heat treatment shows the presence of an Al-OH component (dotted line). This peak indicates that hydrogen atoms H terminate the oxygen atoms O present on the surface of the sapphire substrate 10. The presence of this peak indicates that the sapphire substrate 10 is hydrogen-terminated. As shown in Figure 4(B), in the XPS spectrum of the substrate after heat treatment (in ultrahigh vacuum, at 1150°C for 60 minutes), the Al-OH peak intensity is reduced to less than half of that before heat treatment. This indicates that the hydrogen atoms H that were previously terminated by the hydrogen atoms H are desorbed through the through-holes 11A by the heat treatment. In contrast, when a graphene layer without through-holes was used, such a decrease in the Al-OH peak intensity was not observed even after heat treatment (not shown).

[0029] The GaN layer 12 grown on the crystal growth substrate S first starts growing in each through-hole 11A (see FIG. 5(B)). As the crystal growth process continues, the GaN layer 12 in each through-hole 11A grows in an island shape along the surface of the graphene layer 11 (see FIG. 5(C)). At this time, the GaN layer 12 grows in a crystal shape along the surface of the graphene layer 11 while being influenced by the crystal information of the sapphire substrate 10 (i.e., the crystal information of the r-plane of the sapphire substrate). Finally, adjacent island-shaped GaN layers 12 are bonded to each other (see FIG. 5(D)). The GaN layer 12 thus formed has an a-plane as its surface.

[0030] Figure 6 shows SEM images of samples obtained after the crystal growth process was performed for 30, 60, and 90 minutes. In each sample, the dark-shaded area corresponds to the a-plane GaN layer 12 surface. The light-shaded area corresponds to the exposed surface of the graphene layer 11. The thickness of the GaN layer 12 in the dark-shaded area of ​​the sample grown for 30 minutes was approximately 51 nm. The thickness of the GaN layer 12 in the dark-shaded area of ​​the sample grown for 60 minutes was approximately 103 nm. The thickness of the GaN layer 12 in the dark-shaded area of ​​the sample grown for 90 minutes was approximately 119 nm. As the growth time increased, the light-shaded area decreased and the dark-shaded area increased, resulting in an increase in the thickness of the GaN layer 12.

[0031] Fig. 7 shows an SEM image of etch-pit etching performed on the surface of the GaN layer 12, which has been grown as a crystal to cover the entire surface of the graphene layer 11. As shown in Fig. 7, a plurality of recesses 12A and a plurality of streak-like recesses 12B, each slightly recessed in a streak-like shape, are formed on the surface of the GaN layer 12. Each recess 12A is formed corresponding to a through-hole 11A in the graphene layer 11. The streak-like recess 12B corresponds to a position where adjacent island-like GaN layers 12 are bonded. The dislocation density of the recess 12A is approximately 2 × 10 6 cm -1 The dislocation density in the streak-like recess 12B is approximately 3×10 6 cm -1These dislocation densities are extremely small compared to the dislocation densities of crystals obtained by conventional crystal growth techniques, indicating that the crystalline quality of the GaN layer 12 is good.

[0032] Next, the effects of the above embodiment will be described. The method for producing a crystal growth substrate S of the present invention includes a graphene layer lamination step of laminating a graphene layer 11 on the surface of a sapphire substrate 10, and the graphene layer lamination step is completed when a plurality of through-holes 11A exposing the surface of the sapphire substrate 10 are formed in the graphene layer 11. This configuration makes it easy to satisfactorily produce two-layer laminated graphene layers 11.

[0033] In the method for producing crystal growth substrate S of the present invention, in the graphene layer stacking step, hydrogen atoms H are held between sapphire substrate 10 and graphene layer 11 in a manner that terminates surface atoms of sapphire substrate 10, and when sapphire substrate 10 is heated after the graphene layer stacking step is performed, hydrogen atoms H are desorbed through through-holes 11A. According to this configuration, the desorption of hydrogen atoms H reduces the distance between the surface of graphene layer 11 and the surface of sapphire substrate 10, so that when GaN layer 12 is stacked on graphene layer 11, crystal information of sapphire substrate 10 is easily transmitted appropriately to GaN layer 12 to be stacked, and a high-quality GaN layer 12 can be easily produced.

[0034] The present invention is not limited to the first embodiment described above with reference to the drawings, and the following embodiments are also included within the technical scope of the present invention. (1) After the graphene lamination step, a through-hole forming step may be provided in which a plurality of through-holes are formed in the graphene layer so that the surface of the sapphire substrate is exposed. For example, in the through-hole forming step, the sapphire substrate on which the graphene layer is laminated is heat-treated in the atmosphere at 400°C for approximately 27 minutes, thereby forming through-holes with a diameter of approximately 10 nm in the graphene layer. The size of the through-holes can be freely adjusted by adjusting the temperature and time in the through-hole forming step. Alternatively, through-holes can be formed by performing plasma etching in the through-hole forming step. (2) As shown in Fig. 8, in the graphene layer stacking step, a plurality of defects having a size equal to or larger than a seven-membered ring, such as seven-membered rings 111A and pyridine-type bonds 111B, are formed in the graphene layer 111. After the graphene layer stacking step is performed, the crystal growth substrate may be heated to release hydrogen atoms held between the sapphire substrate and the graphene layer 111 through the defects. (3) Not only the amount of raw material gas supplied in generating the graphene layer but also the film formation method do not have to be the method disclosed in Example 1. For example, graphene grown on copper may be transferred onto a substrate by a transfer method. (4) Instead of a sapphire substrate, any crystal substrate such as Si, GaAs, InP, SiC, or Ga2O3 may be used as the substrate. (5) The crystal growth substrate of the present invention may be used to grow other crystals such as GaAs, InP, SiC, Ga2O3, etc. Of course, the growth layer may be a multi-element mixed crystal other than these binary mixed crystals, such as InGaN, AlGaN, InGaAsP, etc. (6) The film used is not limited to graphene, but may be other two-dimensional materials such as h-BN, MoS2, WSSe, WS2, or MoTe2. (7) The atomic species that penetrate and remove the two-dimensional film are not limited to hydrogen atoms. For example, when removing an oxide film on a substrate, O is the atomic species that penetrates the two-dimensional film. [Explanation of symbols]

[0035] 10...Sapphire substrate (substrate) 11,111...graphene layers 11A...Through hole 111A...7-membered ring (defect) 111B...pyridine type bond (defect) 12...GaN layer 12A...recess 12B...Striated recess S...Crystal growth substrate

Claims

1. a graphene layer lamination step of laminating a graphene layer on a surface of a substrate, the graphene layer lamination step is completed when a plurality of through-holes exposing the surface of the substrate are formed in the graphene layer.

2. a graphene layer lamination step of laminating a graphene layer on a surface of the substrate; a through-hole forming step of forming a plurality of through-holes in the graphene layer so that the surface of the substrate is exposed after the graphene layer laminating step is performed; A method for producing a crystal growth substrate, comprising:

3. a graphene layer lamination step of laminating a graphene layer on a surface of a substrate, The graphene layer stacking step is a method for producing a crystal growth substrate, in which a plurality of defects having a size equal to or larger than a seven-membered ring are formed in the graphene layer.

4. In the graphene layer stacking step, hydrogen atoms are held between the substrate and the graphene layer, 3. The method for producing a crystal growth substrate according to claim 1, wherein when the substrate is heated after the graphene layer stacking step is performed, the hydrogen atoms are desorbed through the through-holes.

5. In the graphene layer stacking step, hydrogen atoms are held between the substrate and the graphene layer, The method for producing a crystal growth substrate according to claim 3 , wherein when the substrate is heated after the graphene layer stacking step is performed, the hydrogen atoms are desorbed via the defects.

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