Method and apparatus for surface treatment of substrate

Abstract

To process the surfaces of group III semiconductors into desired shapes by performing industrial etching using various solvents.SOLUTION: The surface of the group III semiconductor substrate is processed by a selection step of selecting at least one surface treatment solution from a plurality of surface treatment solutions containing a tetramethylammonium hydroxide aqueous solution and alcohol, and an immersion step of immersing the group III semiconductor substrate in the selected surface treatment solution. For example, by applying the above-described process to a LED100 in which n-type GaN layer 102, light-emitting layer 103, and p-type GaN layer 104 are stacked on GaN substrate 101, the front face (N-polar face) of p-type GaN layer 104 can be roughened into a desired shape. Further, by using the above-described steps for the β - gallium oxide substrate, steps having a desired shape can be formed on the substrate surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surface treatment method and a surface treatment apparatus for a semiconductor substrate. [Background technology]

[0002] In recent years, Group III semiconductors such as gallium nitride (GaN) and gallium oxide (Ga2O3) have been expected to be the next generation of semiconductor devices due to their large band gap and excellent optical and electrical properties.

[0003] For example, β-type gallium oxide (β-Ga2O3) has a larger breakdown field than silicon (Si), a conventional semiconductor material, and is expected to be a material for power devices from the perspective of miniaturization and low loss. When applying this β-type gallium oxide to Schottky barrier diodes (SBDs), it is important to achieve step-flow growth of the homoepitaxial layer and to control the substrate surface morphology before growth.

[0004] Gallium nitride is also a promising material for optical devices such as LEDs, and LEDs using GaN substrates in particular are expected to be high-brightness LED materials because they can handle large currents. To maximize the light-emitting performance of these LEDs, it is important to roughen the substrate surface to improve light extraction efficiency (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-149462 Summary of the Invention [Problem to be solved by the invention]

[0006] To take advantage of the excellent properties of group III semiconductors, processing technology is required to process the surface of the semiconductor substrate into the desired shape, and it is desirable that this processing can be carried out under room temperature conditions.

[0007] The present invention provides a surface treatment method that can process the surface of a group III semiconductor into a desired shape under room temperature conditions by performing wet etching using different types of etching solutions. [Means for solving the problem]

[0008] The surface treatment method of the present invention is a surface treatment method for processing the surface of a Group III semiconductor substrate by wet etching, and includes a selection step of selecting at least one surface treatment solution from a plurality of surface treatment solutions each containing an aqueous tetramethylammonium hydroxide solution and an alcohol, and an immersion step of immersing the Group III semiconductor substrate in the surface treatment solution selected in the selection step.

[0009] The surface treatment device of the present invention processes the surface of a Group III semiconductor substrate by wet etching, and includes a container into which a surface treatment solution is poured, and an immersion table on which a Group III semiconductor substrate is loaded and which immerses the Group III semiconductor substrate in the surface treatment solution, and at least one surface treatment solution selected from a plurality of surface treatment solutions containing an aqueous solution of tetramethylammonium hydroxide and an alcohol is poured into the container. [Effects of the Invention]

[0010] According to the present invention, the surface of a group III semiconductor substrate can be processed into a desired shape by wet etching using different types of etching liquid. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram schematically illustrating a vertical cross section of an LED according to a first embodiment. [Figure 2] Diagram explaining the state of light inside an LED [Figure 3]Schematic diagram showing the polarity of GaN [Figure 4] Schematic diagram of surface treatment equipment [Figure 5] Schematic diagram of a surface treatment device that uses multiple surface treatment solutions [Figure 6] Flowchart showing the flow of wet etching processing [Figure 7] Schematic diagram of epitaxial layer growth [Figure 8] Figure showing the results of immersing an n-GaN freestanding substrate for 0.5 hours [Figure 9] Figure showing the results of immersing an n-GaN freestanding substrate for one hour [Figure 10] Figure showing the results of immersing an n-GaN freestanding substrate for 1.5 hours [Figure 11] Figure showing the results of immersing an n-GaN freestanding substrate for 2 hours [Figure 12] Figure showing the results of immersing an n-GaN freestanding substrate for 2.5 hours [Figure 13] Figure showing the results of immersing an n-GaN freestanding substrate for 3 hours [Figure 14] Figure showing the results of wet etching a β-type gallium oxide substrate [Figure 15] A graph showing the relationship between hydroxide ion concentration and conductivity when the concentration of the surface treatment solution is changed. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0013] (First embodiment) In this embodiment, the surface processing of an optical device (LED) using gallium nitride (GaN) as an example of a group III semiconductor will be described.

[0014] [1. Overview of GaN-based LEDs] Sapphire substrates have been mainly used for GaN-based LEDs. However, it is known that the optical output density of LEDs can be improved by using GaN substrates rather than sapphire substrates. Therefore, it is desirable to use GaN substrates to realize high-performance LEDs.

[0015] In LEDs, roughening the light extraction surface improves light extraction efficiency and device performance. In LEDs using GaN substrates, the N-polar surface needs to be roughened due to its structure. However, the N-polar surface of GaN is not resistant to chemicals, and wet etching progresses quickly, making it difficult to control the etching speed and roughened surface shape.

[0016] In this embodiment, we will explain how to control the behavior of wet etching on the N-polarity surface of GaN by using multiple etching solutions (also called surface treatment solutions) appropriately, and how to roughen the semiconductor surface shape, which is important for optical devices.

[0017] FIG. 1 is a diagram showing a vertical cross section of an LED according to a first embodiment. Reference numeral 100 denotes an LED using a GaN substrate. An n-type GaN layer 102, a light-emitting layer 103, and a p-type GaN layer 104 are stacked on a GaN substrate 101. A negative electrode 105 is provided on the n-type GaN layer 102, and a positive electrode 106 is provided on the p-type GaN layer 104. When a voltage is applied between the positive electrode 106 and the negative electrode 105, electrons contained in the n-type GaN layer 102 recombine with holes contained in the p-type GaN layer 104, causing light to be emitted from the light-emitting layer 103. The upper surface of the p-type GaN layer 104 is roughened by the presence of pillars 107. The pillars are cylindrical, conical, or other protrusions. Details of the pillars 107 will be described later.

[0018] Figure 2 is a diagram illustrating the state of light inside an LED. In Figure 2(a), 200 is an LED that has not been subjected to surface treatment. The upper surface of the p-type GaN layer 104 in LED 200 is in a state close to a mirror finish. On the other hand, in Figure 2(b), 201 is an LED that has been subjected to surface roughening. The upper surface of the p-type GaN layer 104 in LED 201 has pillars 107 formed thereon and is in a roughened state.

[0019] In the LED 200, a portion of the light 202 emitted from the light-emitting layer 103 is totally reflected between the upper surface of the p-type GaN layer 104 and the lower surface of the n-type GaN layer 102. Since the totally reflected light 202 is not emitted from the upper surface of the p-type GaN layer, the light extraction efficiency of the LED 200 is low.

[0020] On the other hand, in the LED 201, light 203 emitted from the light-emitting layer 103 is reflected by pillars 107 formed on the upper surface of the p-type GaN layer 104. Because the size and height of the pillars 107 are not constant, the angle of the light reflected toward the n-type GaN layer 102 changes almost randomly. As a result, as the light is repeatedly reflected between the pillars 107 and the lower surface of the n-type GaN layer 102, it is emitted from the pillars 107 to the outside of the LED 201. In other words, by processing the upper surface of the p-type GaN layer 104 to make it rough, the light extraction efficiency is improved.

[0021] 2. GaN Polarity Figure 3 shows a schematic diagram of the polarity of GaN. GaN has a crystallographic asymmetry along the c-axis, which is called Ga-polarity and N-polarity, respectively. 300 in Figure 3(a) shows Ga-polarity GaN, and 301 in Figure 3(b) shows N-polarity GaN.

[0022] When a GaN layer is stacked on a GaN substrate, the N-polar GaN layer shown in Fig. 3(b) is stacked. Therefore, the top surface of the p-type GaN layer 104 of the LED 100 described in Fig. 1 becomes an N-polar surface. Therefore, in order to form pillars 107 on the top surface of the p-type GaN layer 104 and roughen it, the N-polar surface of the GaN must be wet-etched.

[0023] Ga-polar and N-polar surfaces have different wet etching characteristics. Ga-polar surfaces are robust, so the etching rate is slow. Therefore, pillar formation can be controlled relatively easily by controlling the immersion time. However, N-polar surfaces have low chemical resistance and etch quickly, making it difficult to form good pillars.

[0024] [3. Basic operation of wet etching] This section explains the basic operation of wet etching to form pillars of a desired shape on the N-polarity surface of GaN and roughen the surface.

[0025] 4 is a schematic diagram of a surface treatment apparatus for wet etching. The surface treatment apparatus 400 comprises a container 401 containing a surface treatment solution 402 and an immersion table 404 on which a semiconductor substrate 403 is placed. A rotor 405 is provided at the bottom of the container 401. The rotor 405 is rotated by a magnetic force from a table 406, and the surface treatment solution 402 is stirred.

[0026] The semiconductor substrate 403 is a semiconductor substrate in which a GaN layer is formed on a GaN substrate, and the surface of the GaN layer is an N-polar surface. The number of semiconductor substrates 403 loaded on the dipping table 404 may be multiple or only one.

[0027] The surface treatment solution 402 is a solution containing an aqueous solution of tetramethylammonium hydroxide (TMAH) and alcohols. In this embodiment, ethanol is used as an example of the alcohols. That is, the surface treatment solution 402 in this embodiment is a solution containing an aqueous solution of tetramethylammonium hydroxide and ethanol.

[0028] In the surface treatment apparatus 400 configured as described above, the semiconductor substrate 403 is first loaded onto the immersion table 404 and immersed in the surface treatment solution 402 under predetermined immersion conditions. The rotor 405 then rotates to agitate the surface treatment solution 402. This causes wet etching to proceed, resulting in the formation of pillars on the surface of the semiconductor substrate 403, i.e., the N-polarity surface of the GaN, resulting in a roughened surface. The predetermined immersion conditions include the immersion time and number of immersions for immersing the immersion table 404 in the surface treatment solution 402. These conditions may be preset or may be input when the immersion table 404 is immersed.

[0029] [4. Wet etching using multiple solutions] The shape of the pillars formed by wet etching varies depending on the type and concentration of the surface treatment solution 402, as well as on conditions such as the immersion time and number of immersion times. In other words, by using different types and concentrations of surface treatment solutions, the shape of the pillars formed can be controlled, and the desired surface roughening can be achieved.

[0030] 5 is a schematic diagram of a surface treatment apparatus that uses multiple surface treatment solutions. Components with the same reference numerals as those in FIG. 4 have the same functions, and therefore will not be described. Surface treatment apparatus 500 has the same configuration as surface treatment apparatus 400, and includes a container 501 containing surface treatment solution 502, a rotor 505, and a stage 506. Dipping stage 404 loaded with semiconductor substrate 403 can be immersed in either surface treatment solution 402 or surface treatment solution 502.

[0031] Both the surface treatment solution 402 and the surface treatment solution 502 are solutions containing an aqueous solution of tetramethylammonium hydroxide and alcohols. In this embodiment, the surface treatment solution 402 is a solution containing an aqueous solution of tetramethylammonium hydroxide and ethanol. The surface treatment solution 502 is a solution containing an aqueous solution of tetramethylammonium hydroxide and isopropyl alcohol.

[0032] FIG. 6 is a flowchart showing the flow of a wet etching process. The flow of a wet etching process using multiple surface treatment solutions will be described with reference to FIGS. 5 and 6. First, a semiconductor substrate 403 is loaded onto the immersion table 404 (S600). Then, a surface treatment solution to be used for etching is selected from multiple surface treatment solutions (S601). In this embodiment, either the surface treatment solution 402 or the surface treatment solution 502 is selected. Then, immersion conditions such as the number of immersions and the immersion time are set (S602), and the immersion table 404 is immersed in the surface treatment solution selected in S601 based on the set immersion conditions (S603). Once immersion based on the predetermined immersion conditions is complete, the immersion table 404 is removed from the surface treatment solution (S604). If wet etching is to be continued (S605), the process returns to the surface treatment solution selection step (S601) and etching continues. If wet etching is to be terminated (S605), the process ends.

[0033] Here, the surface treatment solution 402 containing ethanol and the surface treatment solution 502 containing isopropyl alcohol have different etching performances on semiconductor substrates. For example, the size and shape of pillars formed when etching is performed using the surface treatment solution 402 are different from those when etching is performed using the surface treatment solution 502. Therefore, by using different surface treatment solutions, the shape of pillars formed on the surface of the semiconductor substrate 403 can be controlled, and the surface can be processed to a desired roughness.

[0034] For example, under certain immersion conditions, suppose that etching using surface treatment solution 402 results in the formation of small pillars, whereas etching using surface treatment solution 502 results in the formation of large pillars. In this case, if a finely roughened surface is desired on the surface of semiconductor substrate 403, etching is performed using surface treatment solution 402. As a result, small pillars are formed on the surface of semiconductor substrate 403, i.e., the N-polarity surface of GaN, forming a finely roughened surface. On the other hand, if a coarsely roughened surface is desired on the surface of semiconductor substrate 403, etching is performed using surface treatment solution 502. As a result, large pillars are formed on the surface of semiconductor substrate 403, i.e., the N-polarity surface of GaN, forming a coarsely roughened surface.

[0035] By using a plurality of different types of surface treatment solutions in this way, it is possible to control the roughness of the substrate surface after etching.

[0036] In this embodiment, two surface treatment solutions with different alcohol compositions are used as an example of multiple different types of surface treatment solutions, but this is not limiting. Different types of solutions with different chemical compositions or concentrations may be used. For example, three or more surface treatment solutions with different alcohol compositions may be used. Furthermore, multiple surface treatment solutions with different concentrations of tetramethylammonium hydroxide aqueous solution or alcohol concentrations may be used.

[0037] Furthermore, although etching is performed by placing the surface treatment solutions 402 and 502 in different containers 401 and 501, this is not limiting. Etching may be performed using one container while exchanging the surface treatment solutions. For example, etching may be performed while exchanging the surface treatment solutions 402 and 502.

[0038] In addition, although the dipping table 404 loaded with the semiconductor substrate 403 has been described as being immersed in either the surface treatment solution 402 or the surface treatment solution 502, this is not limiting. For example, the dipping table 404 may be immersed in a plurality of surface treatment solutions, for example, the dipping table 404 may be immersed in the surface treatment solution 402 and then in the surface treatment solution 502.

[0039] (Embodiment 2) In this embodiment, an etching process for β-type gallium oxide will be described as an example of a group III semiconductor.

[0040] As mentioned above, in Schottky barrier diodes using β-type gallium oxide, it is important to achieve step-flow growth of the homoepitaxial layer and to control the surface shape of the substrate before growth. In this embodiment, a method for forming atomic steps on the surface of a β-type gallium oxide substrate by performing wet etching using different surface treatment solutions will be described. By performing a wet etching process before deposition of the epitaxial layer, deposition of the epitaxial layer using step-flow growth becomes easier.

[0041] [1. Growth of epitaxial layer] FIG. 7 is a diagram showing the growth of an epitaxial layer. On a β-type gallium oxide substrate 700, there are wide terraces 701 that are flat at the atomic level, steps 702 that are the steps between the terraces, and kinks 703 that are uneven portions on the steps. Atom 704 is an atom adsorbed on the terrace. Atoms adsorbed on the terraces bond at the kink 703, as with atom 705, to form an epitaxial layer. In this way, by forming steps on the β-type gallium oxide substrate, step-flow growth, which is advantageous for epitaxial growth, can be achieved.

[0042] [2. Wet Etching] Wet etching for forming steps on a β-type gallium oxide substrate will be described. The surface treatment device used for wet etching is the same as that shown in Figures 4 and 5, so a detailed description will be omitted. A β-type gallium oxide substrate is used as the semiconductor substrate 403.

[0043] Surface treatment solution 402 and surface treatment solution 502 are solutions containing an aqueous tetramethylammonium hydroxide solution and alcohols. In this embodiment, a solution containing an aqueous tetramethylammonium hydroxide solution and ethanol is used as surface treatment solution 402, and a solution containing an aqueous tetramethylammonium hydroxide solution and isopropyl alcohol is used as surface treatment solution 502. The process flow of wet etching using surface treatment solution 402 and surface treatment solution 502 is similar to that shown in FIG. 6, and therefore a detailed description thereof will be omitted.

[0044] The surface treatment solution 402 containing ethanol and the surface treatment solution 502 containing isopropyl alcohol have different etching performances for a β-type gallium oxide substrate. Either solution can be used to form steps on the substrate, but the shape of the steps varies depending on the solution. In other words, by using the appropriate surface treatment solution, the shape of the steps formed on the surface of the β-type gallium oxide substrate can be controlled.

[0045] Furthermore, steps of different shapes can be formed on the β-type gallium oxide substrate by adding silicon (Si) to each of the surface treatment solutions 402 and 502. By selectively using multiple surface treatment solutions with different compositions and by selectively adding or not adding silicon (Si) to each surface treatment solution, steps of different shapes can be formed on the β-type gallium oxide substrate.

[0046] In this embodiment, the surface treatment solution is selected from a plurality of surface treatment solutions, but this is not limited to this. If the shape of the steps to be formed on the β-type gallium oxide substrate is predetermined, only a surface treatment solution suitable for the shape may be used. For example, if a surface treatment solution containing a tetramethylammonium hydroxide aqueous solution, isopropyl alcohol, and silicon is preferred, wet etching may be performed using only this surface treatment solution. [Example]

[0047] The present invention will be described below based on examples. However, the present invention is not limited to these examples. In the examples, "%" means % by weight unless otherwise specified.

[0048] Example 1 As an example of a group III semiconductor substrate, a freestanding n-GaN substrate was used for wet etching.

[0049] [Solution preparation] Three types of surface treatment solutions were used: a solution obtained by adding 16 ml of water to 4 ml of a TMAH aqueous solution (concentration 5%) (hereinafter referred to as surface treatment solution A); a solution obtained by adding 15 ml of ethanol to 3 ml of a TMAH aqueous solution (concentration 5%) (hereinafter referred to as surface treatment solution B); and a solution obtained by adding 15 ml of isopropyl alcohol to 3 ml of a TMAH aqueous solution (concentration 5%) (hereinafter referred to as surface treatment solution C).

[0050] [Wet etching] The stirring speed was set to 300 rpm, and the n-GaN freestanding substrate was immersed in surface treatment solution A. The immersion time was varied in 0.5-hour increments between 0.5 and 3 hours, and etching was performed under six conditions: 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 hours. The same procedure was performed for surface treatment solution B and surface treatment solution C.

[0051] [Cleaning the substrate] After immersion, the n-GaN freestanding substrate was removed and the surface was cleaned. The cleaning process consisted of three steps: cleaning with pure water (three times for two minutes each), cleaning with acetone (three times for two minutes each), and cleaning with ethanol (three times for two minutes each).

[0052] [Photographing the board surface] After cleaning, the surface of the n-GaN substrate was photographed using a scanning electron microscope (SEM) at magnifications of 10,000 and 50,000.

[0053] [result] The results of the wet etching are shown in FIGS.

[0054] Figure 8 shows the results of immersing an n-GaN freestanding substrate for 0.5 hours. Figure 8(a) shows the result of immersion in surface treatment solution A, Figure 8(b) shows the result of immersion in surface treatment solution B, and Figure 8(c) shows the result of immersion in surface treatment solution C. The SEM magnification for all images was 10,000 times. Figures 8(d) to (f) are the results of photographs taken at a magnification of 50,000 times for Figures 8(a) to (c). Looking at these results, it can be seen that relatively large pillars were formed in surface treatment solutions A and C, while almost no pillars were formed in surface treatment solution B.

[0055] Figure 9 shows the results of immersing an n-GaN freestanding substrate for one hour. The etching and photography conditions in Figures 9(a) to (f) correspond to those in Figures 8(a) to (f), respectively. The difference from Figure 8 is that the immersion time was increased from 0.5 hours to 1 hour. Looking at these results, it can be seen that with surface treatment solutions A and C, larger pillars were formed compared to the immersion time of 0.5 hours, but small pillars were also formed. Furthermore, with surface treatment solution B, relatively small pillars were formed.

[0056] Figures 10 to 13 show the results of immersing an n-GaN freestanding substrate for 1.5 hours, 2 hours, 2.5 hours, and 3 hours, respectively. The etching conditions in each figure (a) to (f) correspond to those in Figures 7(a) to (f), with only the immersion time being varied. Looking at these results, we can see that the shape of the pillars changes depending on the type of surface treatment solution, and also on the immersion time.

[0057] In this way, by using different etchants, we can control the wet etching behavior of the N-polar surface of the GaN substrate and form the roughened surface shape that is important for optical devices.

[0058] Example 2 In this example, wet etching was performed using a β-type gallium oxide substrate as an example of a group III semiconductor substrate.

[0059] [Solution preparation] The surface treatment solutions used for wet etching were a solution obtained by adding water to a TMAH aqueous solution (concentration 10%) (hereinafter referred to as surface treatment solution D), a solution obtained by adding ethanol to a TMAH aqueous solution (concentration 10%) (hereinafter referred to as surface treatment solution E), and a solution obtained by adding isopropyl alcohol to a TMAH aqueous solution (concentration 10%) (hereinafter referred to as surface treatment solution F).

[0060] Furthermore, a solution in which silicon was added to surface treatment solution D (hereinafter referred to as surface treatment solution G), a solution in which silicon was added to surface treatment solution E (hereinafter referred to as surface treatment solution H), and a solution in which silicon was added to surface treatment solution F (hereinafter referred to as surface treatment solution I) were used. Wet etching was performed using these six surface treatment solutions (surface treatment solutions D to I).

[0061] [Wet etching] For the wet etching, a stirrer (MS-51M manufactured by Jeio Tech Co., Ltd.) was used. The β-type gallium oxide substrate was immersed in each of six types of surface treatment solutions (surface treatment solutions D to I) for 60 minutes.

[0062] [Cleaning the substrate] After immersion, the β-type gallium oxide substrate was removed and subjected to ultrasonic cleaning. The cleaning process consisted of three steps: cleaning with pure water (three times for two minutes each), cleaning with acetone (three times for two minutes each), and cleaning with ethanol (three times for two minutes each).

[0063] [Analysis and photography of the substrate surface] After cleaning, the surface shape of the β-type gallium oxide substrate was measured using an atomic force microscope (AFM) (Hitachi High-Tech AFM5100N), and the surface of the β-type gallium oxide substrate was photographed using a scanning electron microscope (SEM) (JEOL FIB / SEM hybrid system JIB4600F).

[0064] [result] Figure 14 shows the results of wet etching using six types of surface treatment solutions (surface treatment solutions D to I). Figures 14(a) to (f) show the results using surface treatment solutions D to I, respectively. In the figure, Sq / RMS is the root mean square of the distance from the average plane to the surface, and is an index of surface roughness. This value is large for surfaces with severe irregularities, and small for surfaces with relatively many flat areas.

[0065] Figures 14(a) to (c) show that atomic steps are formed on the surface of all β-type gallium oxide substrates. However, their shape differs depending on the type of surface treatment solution. In Figure 14(a), steps are formed, but the shape is uneven along the surface. In Figures 14(b) and (c), on the other hand, the step unevenness is relatively small. However, in Figures 14(b) and (c), holes have appeared in the terrace areas.

[0066] Next, when silicon was added, atomic steps were formed on the surface of all β-type gallium oxide substrates, as can be seen from Figures 14(d) to (f). Looking at the changes when silicon was added, no significant changes were observed between Figures 14(a) and (d). However, comparing Figures 14(c) and (f), no holes were formed in the terrace area in Figure 14(f).

[0067] For epitaxial layer growth, it is desirable for the terraces to be flat, because if step-flow growth is performed with holes in the terraces, the IV characteristics (current-voltage characteristics) of the completed semiconductor device may be degraded.

[0068] In this example, the best results were obtained when using surface treatment solution I containing an aqueous solution of tetraammonium hydroxide, isopropyl alcohol, and silicon.

[0069] Example 3 In this example, the changes in hydroxide ion concentration and electrical conductivity when the concentration of the surface treatment solution is changed are measured.

[0070] The surface treatment solutions used were a solution made by adding pure water to a TMAH aqueous solution, a solution made by adding isopropyl alcohol to a TMAH aqueous solution, and a solution made by adding ethanol to a TMAH aqueous solution. The hydroxide ion concentration and conductivity were measured when the concentration of each surface treatment solution was changed between 5% and 20%. For the solution made by adding pure water to a TMAH aqueous solution, measurements were also taken at concentrations of 2.38% and 25%.

[0071] Figure 15 shows the relationship between hydroxide ion concentration and conductivity when the concentration of the surface treatment solution is changed. Figure 15(a) shows the hydroxide ion concentration when the concentration of the surface treatment solution is changed. Figure 15(b) shows the conductivity when the concentration of the surface treatment solution is changed.

[0072] These results show that the hydroxide ion concentration and conductivity change depending on the type and concentration of the surface treatment solution. Differences in the hydroxide ion concentration and conductivity of the surface treatment solution also affect the wet etching characteristics. In other words, by using different types and concentrations of surface treatment solutions, it is possible to process the surface of a semiconductor substrate into the desired shape. [Explanation of symbols]

[0073] 100, 200, 201 LEDs 101 GaN substrate 102 n-type GaN layer 103 Light-emitting layer 104 p-type GaN layer 105 Negative electrode 106 positive electrode 107 Pillar 202, 203 light 300 Ga polarity GaN 301 n-polar GaN 400, 500 Surface treatment equipment 401, 501 Container 402, 502 Surface treatment solution 403 Semiconductor Substrate 404 Soaking table 405, 505 rotor 406, 506 stand 700 β-type gallium oxide substrate 701 Terrace 702 steps 703 Kink 704, 705 atoms

Claims

1. A surface treatment method for processing a surface of a group III semiconductor substrate by wet etching, comprising: a selection step of selecting at least one surface treatment solution from a plurality of surface treatment solutions including an aqueous tetramethylammonium hydroxide solution and an alcohol; an immersion step of immersing the Group III semiconductor substrate in the surface treatment solution selected in the selection step.

2. the group III semiconductor substrate is gallium nitride (GaN); The surface treatment method according to claim 1 , wherein the immersion step involves immersing the N-polar surface of the gallium nitride in the surface treatment solution to process the N-polar surface of the gallium nitride.

3. a condition setting step of setting immersion conditions for the group III semiconductor substrate, 3. The surface treatment method according to claim 2, wherein the immersion step includes immersing the group III semiconductor substrate in the surface treatment solution based on the immersion conditions.

4. The surface treatment method according to claim 3 , wherein the alcohols contained in the plurality of surface treatment solutions have different compositions.

5. 5. The surface treatment method according to claim 4, wherein the plurality of surface treatment solutions include a first surface treatment solution containing the tetramethylammonium hydroxide and ethanol, and a second surface treatment solution containing the tetramethylammonium hydroxide and isopropyl alcohol.

6. The group III semiconductor substrate is made of β-type gallium oxide (β-Ga ２ O ３ ) and The surface treatment method according to claim 1 , wherein the immersion step includes immersing the surface of the β-type gallium oxide substrate in the surface treatment solution to process the surface of the β-type gallium oxide substrate.

7. a condition setting step of setting immersion conditions for the group III semiconductor substrate, 7. The surface treatment method according to claim 6, wherein the immersion step immerses the group III semiconductor substrate in the surface treatment solution based on the immersion conditions.

8. the plurality of surface treatment solutions includes a third surface treatment solution containing tetramethylammonium hydroxide and isopropyl alcohol; The surface treatment method according to claim 7 , wherein the selection step selects the third surface treatment solution.

9. The surface treatment method according to claim 8 , wherein the third surface treatment solution further contains silicon (Si).

10. A surface treatment apparatus for processing a surface of a group III semiconductor substrate by wet etching, comprising: a container into which the surface treatment solution is poured; an immersion table on which the group III semiconductor substrate is loaded and on which the group III semiconductor substrate is immersed in the surface treatment solution; The surface treatment device, wherein at least one surface treatment solution selected from a plurality of surface treatment solutions containing an aqueous solution of tetramethylammonium hydroxide and an alcohol is poured into the container.

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