Substrate surface treatment method, surface treatment device and surface treatment solution

Abstract

To provide a surface treatment method, a surface treatment device and a surface treatment solution for planarization of a group III semiconductor substrate.SOLUTION: A surface treatment device comprises a holding vessel 11 to hold a surface treatment solution 12, and a contact treatment device 14 that holds a semiconductor substrate 13 and brings it into contact with the surface treatment solution 12. The holding vessel 11 is placed on a platform 16, and the surface treatment solution 12 is agitated by a rotor 15. The surface treatment solution 12 contains a tetramethylammonium hydroxide solution, an alcohol, and an additive. The surface treatment solution 12 is used for surface treatment of the semiconductor substrate 13.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a substrate surface treatment method, surface treatment apparatus and surface treatment solution applicable to the manufacturing process of semiconductor substrates, particularly Group III semiconductor substrates, used in semiconductor devices such as light-emitting diodes, semiconductor lasers and power semiconductor elements. [Background technology]

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

[0003] The manufacturing of semiconductor devices that take advantage of these excellent properties requires high-precision processing technology. Because group III semiconductors are physically and chemically stable, dry etching has been the primary method used for processing them. However, dry etching can cause damage to the surface of the semiconductor substrate, which can adversely affect its electrical and optical properties. Therefore, a method has been proposed in which wet etching is performed after dry etching to remove surface damage.

[0004] Patent Document 1 discloses a surface treatment technique for nitride semiconductors using wet etching. According to the method disclosed in this document, the surface of a nitride semiconductor is planarized by performing surface treatment using a solution in which an alcohol is added to an aqueous solution of tetramethylammonium hydroxide. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-204848 Summary of the Invention [Problem to be solved by the invention]

[0006] Planarization using a solution of tetramethylammonium hydroxide and alcohols can remove protrusions and other imperfections from the surface of a semiconductor substrate. However, depending on the type of semiconductor substrate, etch pits may occur on the substrate surface. Etch pits are depressions that occur when the substrate surface is wet etched.

[0007] The present invention has been made to solve these problems, and its object is to provide a surface treatment method, a surface treatment device, and a surface treatment solution that can polish protrusions that occur on the substrate surface during the processing of a semiconductor substrate and can also control the formation of etch pits. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the surface treatment method of the present invention performs surface treatment of a Group III semiconductor substrate by bringing the surface of the substrate into contact with a surface treatment solution containing an aqueous solution of tetramethylammonium hydroxide, an alcohol, and an additive. [Effects of the Invention]

[0009] According to the present invention, a surface treatment of a semiconductor substrate is carried out using a surface treatment solution containing an aqueous solution of tetramethylammonium hydroxide, an alcohol, and an additive, which can polish away protrusions formed on the surface of the semiconductor substrate and also control the formation of etch pits. [Brief explanation of the drawings]

[0010] [Figure 1] Schematic diagram of a surface treatment device [Figure 2] 1 is a diagram showing the surface of a semiconductor substrate after dry etching; [Figure 3] A diagram showing the surface of a gallium nitride substrate after wet etching. [Figure 4] Illustrates the substrate surface after wet etching with a solution without additives. [Figure 5]Illustrates the substrate surface after wet etching with a solution containing additives. [Figure 6] FIG. 10 is a diagram schematically illustrating a surface treatment device according to a second embodiment. [Figure 7] FIG. 10 is a diagram showing a substrate surface of a semiconductor substrate according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0012] (Embodiment 1) In this embodiment, a surface treatment using a nitride semiconductor as an example of a group III semiconductor will be described. Because nitride semiconductors are physically and chemically stable, dry etching has been the primary method used for their surface treatment. However, dry etching can cause damage such as leaving protrusions on the surface of the semiconductor substrate, which can affect the performance of semiconductor devices.

[0013] The inventors have found that the surface of a semiconductor substrate can be effectively smoothed by wet etching the substrate after dry etching using a surface treatment solution containing an aqueous tetramethylammonium hydroxide solution and an alcohol. By using this surface treatment solution, protrusions on the surface of the semiconductor substrate can be polished away, thereby reducing damage caused by dry etching.

[0014] However, when wet etching is performed using this surface treatment solution, etch pits may be formed on the substrate surface depending on the wet etching conditions and the type of semiconductor substrate. The formation of etch pits on the substrate surface may affect the performance of semiconductor devices. Therefore, from the perspective of semiconductor device manufacturing, it is generally desirable to suppress the formation of etch pits.

[0015] Therefore, we conducted extensive research into surface treatment methods that would prevent the formation of etch pits. As a result, we discovered that the formation of etch pits after wet etching can be suppressed by performing surface treatment using an aqueous solution containing tetramethylammonium hydroxide and alcohols, to which additives such as silicon have been added. At the same time, we were able to successfully polish protrusions.

[0016] The surface treatment method of the present invention is a surface treatment method for a Group III semiconductor substrate, in which the surface of the Group III semiconductor substrate is treated by bringing the surface of the Group III semiconductor substrate into contact with a surface treatment solution containing an aqueous tetramethylammonium hydroxide solution, alcohols, and additives.

[0017] This makes it possible to suppress the generation of etch pits on the substrate surface, and also to polish away protrusions and the like on the semiconductor substrate, thereby achieving satisfactory planarization of the semiconductor substrate.

[0018] The surface treatment apparatus of the present invention is a surface treatment apparatus for a Group III semiconductor substrate, and includes a holding container for holding a surface treatment solution and a contactor for holding a Group III semiconductor substrate and bringing the Group III semiconductor substrate into contact with the surface treatment solution. The surface treatment solution contains an aqueous solution of tetramethylammonium hydroxide, alcohols, and additives. By performing surface treatment using this apparatus, it is possible to suppress the formation of etch pits on the substrate surface and polish protrusions and the like on the semiconductor substrate, thereby achieving good planarization of the semiconductor substrate.

[0019] The surface treatment solution of the present invention is a surface treatment solution for use in treating the surface of a Group III semiconductor substrate, and contains an aqueous solution of tetramethylammonium hydroxide, an alcohol, and an additive. By performing surface treatment using this solution, it is possible to suppress the formation of etch pits on the substrate surface and polish protrusions and the like on the semiconductor substrate, thereby achieving good planarization of the semiconductor substrate.

[0020] The additive preferably contains at least silicon.Preferred examples of the alcohol include ethanol and isopropyl alcohol.

[0021] The above content will be explained below with reference to the drawings.

[0022] 1 is a schematic diagram showing a surface treatment apparatus according to the present embodiment. The surface treatment apparatus 10 comprises a holding container 11 and a contactor 14. The holding container 11 is a container that holds a surface treatment solution 12. The contactor 14 is a member that holds a semiconductor substrate 13 and brings the semiconductor substrate 13 into contact with the surface treatment solution 12. The semiconductor substrate 13 is a substrate that has been dry-etched. The holding container 11 is placed on a stage 16. A rotor 15 provided in the holding container 11 rotates due to a magnetic force from the stage 16, and agitates the surface treatment solution 12.

[0023] The operation of the surface treatment apparatus 10 configured as described above will be described. First, the semiconductor substrate 13 is placed in the contact treatment vessel 14 without the surface treatment solution 12 inside. For example, the contact treatment vessel 14 is provided with a groove for holding the semiconductor substrate 13, and the semiconductor substrate 13 is inserted into this groove and held therein. However, the holding mode is not limited to this, and other configurations may be used as long as they can hold the semiconductor substrate 13 at a predetermined interval.

[0024] In this embodiment, the planar semiconductor substrate 13 is disposed so that the principal surface thereof is substantially perpendicular to the liquid surface of the surface treatment solution 12. However, the planar semiconductor substrate 13 may be disposed so that the principal surface thereof is substantially parallel to the liquid surface of the surface treatment solution 12. Alternatively, the semiconductor substrate 13 may be disposed in the surface treatment solution 12 at a predetermined angle. In this embodiment, the semiconductor substrate 13 has a substantially circular planar shape, but it may also have a polygonal planar shape such as a triangle or a rectangle, or may have an elliptical shape. In this embodiment, a plurality of semiconductor substrates 13 are disposed in the surface treatment solution 12 at a time. However, it goes without saying that only one semiconductor substrate 13 may be disposed at a time.

[0025] Furthermore, even when a plurality of semiconductor substrates 13 are placed in the surface treatment solution 12 at the same time, at least one of the semiconductor substrates 13 can be different in at least one of the shape and size from the other semiconductor substrates 13. Therefore, in this embodiment, semiconductor substrates 13 of various shapes and sizes can be appropriately changed in accordance with the production form, etc., thereby improving workability, etc.

[0026] Next, when the surface treatment solution 12 is poured into the holding container 11, the semiconductor substrate 13 held in the contact treatment device 14 is immersed in the surface treatment solution 12. This starts the surface treatment of the semiconductor substrate 13. The semiconductor substrate 13 used is a gallium nitride (GaN) substrate after dry etching. While the surface treatment is progressing, the rotor 15 rotates to agitate the surface treatment solution 12.

[0027] Figure 2 is a schematic diagram of the substrate surface after dry etching of a gallium nitride substrate. Figure 2(a) is a cross-sectional view of the substrate surface, with an oxide film 21 and resist 22 formed on a gallium nitride layer 20. Flat portion 23 is the area where the oxide film has been removed by dry etching. Figure 2(b) is an enlarged view of flat portion 23. Although the surface is generally flattened by dry etching, damage such as protrusions 24 occurs in some places. The height and width of protrusions 24 are approximately 1 micrometer or less. For more precise processing, they are approximately 0.5 micrometers or less.

[0028] Next, how the semiconductor substrate is wet-etched after dry etching will be described with reference to Figures 3 to 5. The wet etching was performed using a surface treatment device 10.

[0029] 3 is a diagram showing a schematic view of the surface of a gallium nitride substrate that has been subjected to wet etching after dry etching. The surface treatment solution used was a solution containing an aqueous solution of tetramethylammonium hydroxide and an alcohol.

[0030] FIG. 3(a) is a cross-sectional view of the vicinity of the surface of a semiconductor substrate, and flat portion 30 is the portion polished by wet etching. FIG. 3(b) is a schematic diagram showing an enlargement of flat portion 30. Protrusion 31 shows the state after protrusion 24 generated by dry etching has been polished by wet etching. Furthermore, depending on conditions such as the concentration of the surface treatment solution and the etching time, etch pits 32 were generated.

[0031] In this way, wet etching using a surface treatment solution consisting of a tetramethylammonium hydroxide aqueous solution and alcohols was able to polish away the protrusions 24 that had been produced by dry etching, and reduce the damage caused by dry etching. However, etch pits 32 were produced depending on the etching conditions.

[0032] Although FIG. 3(b) shows the protrusions 24 being polished from the horizontal direction, this is not limiting and they may be polished from other directions depending on the conditions.

[0033] 4 is a schematic diagram showing the surface of a substrate in the case where wet etching is performed on a substrate in which gallium nitride is grown on a sapphire substrate (GaN / Sapphire substrate), as an example of a nitride semiconductor. The surface treatment solution used was a solution containing an aqueous solution of tetramethylammonium hydroxide and alcohols.

[0034] FIG. 4(a) is a cross-sectional view of the vicinity of the surface of a semiconductor substrate. A gallium nitride layer 20 is formed on a sapphire substrate 40, and flat portion 41 is the portion polished by wet etching. FIG. 4(b) is a schematic diagram of an enlarged view of flat portion 41, and protrusions 42 show protrusions 24 formed by dry etching that have been polished by wet etching. In this way, even when a GaN / sapphire substrate was used, protrusions 24 could be polished by wet etching using a surface treatment solution consisting of a tetramethylammonium hydroxide aqueous solution and alcohols.

[0035] However, when a GaN / Sapphire substrate was used, the polishing speed was slower than when a gallium nitride substrate was used, and more protrusions 42 remained than protrusions 31. It is believed that the aluminum contained in the sapphire affected the polishing speed. As such, the polishing behavior differed depending on the type of semiconductor substrate. Furthermore, when a GaN / Sapphire substrate was used, etch pits 43 occurred on the substrate surface.

[0036] Figure 5 is a schematic diagram showing the surface of a GaN / Sapphire substrate after wet etching. The surface treatment solution used was a solution made by adding alcohols to an aqueous solution of tetramethylammonium hydroxide, and further adding silicon as an additive.

[0037] Figure 5(a) is a cross-sectional view of the vicinity of the surface of a semiconductor substrate. Figure 5(b) is an enlarged schematic diagram of a flat portion 50, in which protrusions 51 show protrusions 24 formed by dry etching that have been polished away by wet etching. By using a surface treatment solution containing silicon as an additive, the protrusions 24 were successfully polished away. Furthermore, the formation of etch pits 43 was suppressed.

[0038] It has been explained here that the generation of etch pits 43 was suppressed when a GaN / Sapphire substrate was used. In this regard, the same effect was obtained when a gallium nitride substrate was used. That is, when wet etching was performed on a gallium nitride substrate using a surface treatment solution containing an alcohol added to a tetramethylammonium hydroxide aqueous solution and silicon as an additive, the generation of etch pits 32 described in Figure 3(b) was suppressed.

[0039] As described in this embodiment, by using the surface treatment solution of the present invention, i.e., the surface treatment solution obtained by adding alcohols and additives to a tetramethylammonium hydroxide aqueous solution, in the surface treatment of a group III semiconductor substrate, protrusions could be polished well and the generation of etch pits could be suppressed.

[0040] In this embodiment, the semiconductor substrate to be wet-etched is a nitride semiconductor such as a gallium nitride substrate or a GaN / Sapphire substrate, but is not limited to this and may be a semiconductor material such as gallium oxide.

[0041] In the present embodiment, the surface treatment is performed by immersing the semiconductor substrate 13 in the surface treatment solution 12. However, the present invention is not limited to this, and any configuration may be used as long as the surface treatment solution 12 comes into contact with the semiconductor substrate 13. For example, the surface treatment solution 12 may be poured from above the contact treatment vessel 14, and the surface treatment solution 12 may come into contact with the surface of the semiconductor substrate 13 as it flows.

[0042] In addition, although the surface treatment in this embodiment is performed at room temperature, this is not limiting. For example, the stage 16 may be equipped with a heater, and the temperature of the surface treatment solution 12 may be changed depending on the ambient temperature environment, etc.

[0043] The additive is preferably silicon, but may be, for example, a surfactant, or may contain silicon and a surfactant. The surfactant has the same effect as silicon. Preferred examples of the surfactant include glycerin and ethylene glycol.

[0044] Furthermore, in this embodiment, the surface treatment of a semiconductor substrate after dry etching has been described, but the surface treatment can also be performed on the semiconductor wafer itself. This is because small damage may have occurred during the polishing process of the semiconductor wafer. In this case, the surface treatment can be performed by holding the polished semiconductor wafer in the contact treatment vessel 14. By using the surface treatment solution of the present invention, damage such as protrusions that occurred during the production process of the semiconductor wafer can be effectively planarized.

[0045] Furthermore, for example, when silicon is used as an additive, small pieces of silicon may be added to an original solution prepared by adding an alcohol to an aqueous solution of tetramethylammonium hydroxide, and the mixture is stirred for a predetermined period of time to add silicon, thereby preparing the surface treatment solution 12. In this case, the amount of silicon added can be adjusted by appropriately changing the shape, number, or size of the silicon pieces, or the silicon content of the pieces. It is preferable to confirm the optimal amount of silicon added before production by conducting experiments or other means, depending on the substrate to be treated, the treatment process, the specifications of the treatment equipment, etc.

[0046] 1, small pieces of silicon or the like may be placed in advance in the holding vessel 11 or attached to the inner wall of the holding vessel 11, and when the treatment is to be carried out, the original solution may be placed in the holding vessel 11 and stirred, thereby enabling the surface treatment and the addition of silicon to be carried out in parallel. Furthermore, the surface treatment and the addition of silicon may be carried out in parallel by attaching or incorporating a silicon component to the semiconductor substrate 13 itself, and then placing the original solution in the holding vessel 11 and stirring it.

[0047] (Embodiment 2) In this embodiment, a method for generating etch pits by wet etching and using the etch pits to detect defects in a semiconductor substrate will be described. As described above, when wet etching is performed on a group III semiconductor substrate using a surface treatment solution containing a tetramethylammonium hydroxide aqueous solution and alcohols, etch pits may be generated depending on the etching conditions and the type of semiconductor substrate. From the perspective of semiconductor device manufacturing, it is said that these etch pits may have a negative impact on device performance.

[0048] Meanwhile, close examination of the locations where the etch pits were generated revealed that they occurred at dislocations in the semiconductor substrate, i.e., at locations where crystal defects occurred on the substrate. Generally, semiconductors such as gallium nitride contain crystal defects such as threading dislocations, which can lead to reduced device performance and a shorter device lifespan. Therefore, if the locations of crystal defects such as dislocations can be identified, it will be possible to improve the quality of semiconductor devices.

[0049] As a result of further research, it was discovered that etch pits frequently occur when wet etching is performed on gallium nitride substrates that use sapphire as a base, or substrates that have aluminum gallium nitride as a semiconductor layer. What these substrates have in common is that they contain aluminum (Al), and it is presumed that this aluminum contributes to the generation of etch pits.

[0050] The semiconductor material that has been referred to as a group III semiconductor substrate so far includes not only a substrate made of a single group III semiconductor, but also a substrate in which a group III semiconductor layer is formed in the form of a thin film on a base. For example, a semiconductor material in which an aluminum gallium nitride (AlGaN) layer is formed in the form of a film on a base is also referred to as a group III semiconductor substrate. As a representative example, a member in which an aluminum gallium nitride (AlGaN) layer is formed on a base that is 100% gallium nitride or mainly composed of gallium nitride is also referred to as a group III semiconductor substrate.

[0051] Here, it has been found that etch pits are frequently generated in semiconductor substrates using sapphire as the base or aluminum gallium nitride as the group III semiconductor layer. That is, it has been found that etch pits are generated at dislocations in the semiconductor when wet etching is performed on a group III semiconductor substrate containing aluminum in at least one of the base or group III semiconductor layer using a surface treatment solution containing a tetramethylammonium hydroxide aqueous solution and alcohols. This makes it possible to estimate the positions of crystal defects on the substrate based on the positions where etch pits are generated.

[0052] In this embodiment, a surface treatment method will be described in which etch pits are generated in a group III semiconductor substrate and the positions of crystal defects on the substrate are estimated.

[0053] The surface treatment method in this embodiment is a method for treating the surface of a semiconductor material composed of a substrate and a group III semiconductor layer, in which aluminum is contained in at least one of the substrate and the group III semiconductor layer, and the surface of the semiconductor material is treated by bringing the surface of the semiconductor material into contact with a surface treatment solution containing an aqueous tetramethylammonium hydroxide solution and an alcohol.

[0054] This surface treatment method allows for the generation of etch pits in semiconductor materials at room temperature. Because etch pits occur at dislocations in the semiconductor material, the locations of crystal defects in the semiconductor material can be estimated.

[0055] The substrate used in the aforementioned semiconductor material is preferably sapphire, since sapphire contains aluminum. In this case, the semiconductor layer may be any Group III semiconductor, such as gallium nitride. Alternatively, a semiconductor material containing aluminum gallium nitride may be used for the semiconductor layer. In this case, any material may be used for the substrate, since the semiconductor layer contains aluminum. As an example of an alcohol, ethanol or isopropyl alcohol is preferred.

[0056] The surface treatment device in this embodiment is a surface treatment device for a semiconductor material comprising a substrate and a Group III semiconductor layer, and includes a holding container for holding a surface treatment solution and a contactor for holding the semiconductor material and bringing the semiconductor material into contact with the surface treatment solution. At least one of the substrate and the Group III semiconductor layer contains aluminum, and the surface treatment solution contains an aqueous tetramethylammonium hydroxide solution and an alcohol.

[0057] This surface treatment device can generate etch pits in semiconductor materials at room temperature. Because etch pits occur at dislocations in the semiconductor material, the locations of crystal defects in the semiconductor material can be estimated.

[0058] As mentioned above, the substrate used in the semiconductor material is preferably sapphire. The semiconductor layer may be any Group III semiconductor, such as gallium nitride. Alternatively, a semiconductor material containing aluminum gallium nitride may be used. Examples of alcohols include ethanol and isopropyl alcohol.

[0059] The configuration of the surface treatment apparatus according to this embodiment is shown in FIG. 6. Components with the same reference numerals as those in FIG. 1 have the same functions, and therefore detailed description thereof will be omitted. In FIG. 6, the surface treatment solution 60 is an aqueous solution containing a tetramethylammonium hydroxide aqueous solution and alcohols. The semiconductor substrate 61 used is a GaN / Sapphire substrate having a sapphire base and a gallium nitride semiconductor layer. The semiconductor substrate 61 is held in the contact treatment vessel 14, and the surface of the substrate is treated with the surface treatment solution 60.

[0060] Figure 7(a) is a schematic diagram of the substrate surface after wet etching of a GaN / Sapphire substrate. In Figure 7(a), a substrate 70 is sapphire, on which a gallium nitride layer 71 is formed. Then, as described above, an oxide film 21 and a resist 22 are formed. A flat portion 72 is a portion polished by wet etching. Figure 7(b) is a schematic diagram of an enlarged view of the flat portion 72, showing etch pits 73 formed on the substrate surface.

[0061] The etch pits 73 were generated at dislocations in the gallium nitride layer, i.e., at locations where crystal defects exist. Therefore, by examining the locations where the etch pits 73 were generated, the locations of the crystal defects can be estimated.

[0062] The alcohol contained in the surface treatment solution may be ethanol or isopropyl alcohol. The preferred concentration of the surface treatment solution depends on the etching time. A higher concentration is preferable when the etching time is short, while a relatively low concentration is acceptable when the etching time is long. For example, when the etching time is about 3 hours, the tetramethylammonium hydroxide concentration in the surface treatment solution is preferably 20% or higher.

[0063] In this embodiment, a GaN / Sapphire substrate is used as an example of a semiconductor material, but the present invention is not limited to this. For example, a semiconductor material containing aluminum, such as aluminum gallium nitride (AlGaN), may be used for the semiconductor layer.

[0064] Another possible method for adding aluminum is to prepare a surface treatment solution 60 by adding small pieces of alumina or aluminum metal to a base solution prepared by adding an alcohol to an aqueous solution of tetramethylammonium hydroxide and stirring the mixture for a predetermined period of time. In this case, the amount of aluminum added can be adjusted by appropriately changing the shape, number, or size of the alumina pieces or the alumina content of the pieces. It is preferable to confirm the optimal amount of aluminum added through experiments before manufacturing, depending on the substrate to be treated, the treatment process, and the specifications of the treatment equipment. Alternatively, small pieces of alumina, etc., can be added to or attached to the inner wall of the holding container 11 shown in FIG. 6 . Then, during treatment, the base solution can be added to the holding container 11 and stirred, allowing surface treatment and silicon addition to be performed simultaneously.

[0065] Although etch pits are said to have a negative effect on device performance, it is possible to utilize the advantages of these etch pits. In optical devices, these etch pits can be used as a means of scattering light. In other words, by controlling the number of etch pits generated, it is possible to adjust the degree of scattering. Furthermore, in some cases, in devices where the adhesion strength between the gallium nitride film and other thin films formed on the gallium nitride film is important, it is possible to generate many etch pits and increase the adhesion strength.

[0066] In this embodiment, the semiconductor substrate to be wet-etched is a nitride semiconductor such as a gallium nitride substrate or a GaN / Sapphire substrate, but is not limited to this and may be a semiconductor material such as gallium oxide.

[0067] In the present embodiment, the surface treatment is performed by immersing the semiconductor substrate 13 in the surface treatment solution 60. However, the present invention is not limited to this, and any configuration may be used as long as the surface treatment solution 60 comes into contact with the semiconductor substrate 61. For example, the surface treatment solution 60 may be poured from above the contact treatment vessel 14, and the surface treatment solution 60 may come into contact with the surface of the semiconductor substrate 61 as it flows.

[0068] In addition, although the surface treatment in this embodiment is performed at room temperature, this is not limiting. For example, the stage 16 may be equipped with a heater, and the temperature of the surface treatment solution 60 may be changed depending on the ambient temperature environment, etc.

[0069] In this embodiment, the semiconductor substrate to be wet-etched may be a semiconductor substrate after dry etching or a semiconductor wafer itself. In either case, the positions of crystal defects can be estimated from the etch pits generated by the wet etching. [Example]

[0070] The present invention will be described below based on examples. However, the present invention is not limited to these examples. In the examples and comparative examples, "%" means % by weight unless otherwise specified.

[0071] (Example 1, Comparative Example 1) An experiment was conducted to determine whether the formation of etch pits is suppressed when silicon is added to the surface treatment solution.

[0072] <Dry etching> The group III semiconductor substrates used were gallium nitride substrates (n-GaN substrates) and GaN / Sapphire substrates (GaN / SAP substrates). The dry etching equipment used was a SAMCO RiE-101iPH. The etching conditions were as follows: chlorine gas was used as the etching gas; the etching time was 10 minutes, the bias power was 10 W, the gas flow rate was 10 sccm, the ICP power was 100 W, and the process pressure was 1 Pa.

[0073] <Wet etching> Wet etching was performed using a stirrer (HS-50E manufactured by Iuchi Corporation). The surface treatment solution was prepared by adding pure water and propanol (2-Propanol manufactured by Fujifilm Wako Pure Chemical Industries) to an aqueous solution of tetramethylammonium hydroxide (TAMAPURE-AA TMAH 25% manufactured by Tama Chemical Industries Co., Ltd.). The surface treatment solution used had a tetramethylammonium hydroxide concentration of 20%. Silicon was added as an additive in Example 1, while no additive was added in Comparative Example 1. The etching time was 3 hours in both cases. In both Example 1 and Comparative Example 1, the surface treatment solution was stirred during the experiment.

[0074] <Evaluation of etch pit suppression> The results are shown in Table 1. Comparing Example 1 and Comparative Example 1, etch pits were formed in Comparative Example 1, whereas no etch pits were formed in Example 1. The difference between these two is whether or not silicon was added to the surface treatment solution. In other words, it was confirmed that the addition of silicon as an additive suppressed the formation of etch pits.

[0075] [Table 1]

[0076] (Examples 2 and 3, Comparative Examples 2 and 3) Next, an experiment was conducted to see whether or not the addition of silicon to the surface treatment solution would improve the polishing of protrusions. Dry etching was carried out under the same conditions as above.

[0077] <Wet etching> The wet etching was performed on a gallium nitride substrate (n-GaN substrate). In Example 2 and Comparative Example 2, a GaN / Sapphire substrate was also placed in the stirrer when wet etching the n-GaN substrate. This was done to verify that the presence of aluminum during wet etching affects the removal rate of protrusions, as described in the first embodiment.

[0078] The surface treatment solution used was a solution with a 10% tetramethylammonium hydroxide concentration. Silicon was added as an additive in Examples 2 and 3, while no additive was added in Comparative Examples 2 and 3. The etching time was 30 minutes in each case, and the surface treatment solution was stirred during the experiment. Other conditions were the same as those described above.

[0079] <Evaluation of protrusion polishing> The results are shown in Table 2.

[0080] [Table 2] The "large" and "small" amounts of polishing in Table 2 indicate approximate relative evaluations. A "large" amount of polishing means that more than half of the protrusions have been polished away, and a "small" amount of polishing means that less than half of the protrusions have been polished away.

[0081] First, comparing Comparative Example 2 and Comparative Example 3, the amount of protrusions polished off was smaller in Comparative Example 2. This is thought to be due to the influence of the GaN / Sapphire substrate used in Comparative Example 2. In other words, it is thought that the aluminum contained in the GaN / Sapphire substrate had an effect and inhibited the polishing of the protrusions in Comparative Example 2.

[0082] Furthermore, comparing Example 2 and Comparative Example 2, Example 2 resulted in a greater amount of protrusions being polished off. In other words, Example 2 was able to polish off the protrusions better. The difference between Example 2 and Comparative Example 2 is whether or not silicon was added as an additive to the surface treatment solution. In Comparative Example 2, polishing of the protrusions was inhibited, but in Example 2, in which silicon was added to the surface treatment solution, polishing of the protrusions was performed well. Therefore, it is presumed that the inhibiting factor caused by aluminum was removed by silicon.

[0083] There was no difference in the amount of protrusions polished off between Example 3 and Comparative Example 3. That is, even when wet etching was performed on an n-GaN substrate alone that did not contain aluminum, there was no adverse effect of silicon, and the protrusions were polished off well.

[0084] (Example 4, Comparative Example 4) Next, we conducted an experiment to determine whether etch pits would occur when using a GaN / Sapphire substrate, which has a sapphire substrate and a gallium nitride semiconductor layer. Dry etching was performed under the same conditions as above.

[0085] <Wet etching> The wet etching was performed on a GaN / Sapphire substrate. The surface treatment solutions used were tetramethylammonium hydroxide solutions with concentrations of 10% and 20%. Example 4 used a 20% solution, and Comparative Example 4 used a 10% solution. The etching time was 3 hours in each case, and the experiment was performed while stirring the surface treatment solution. Other conditions were the same as those described above.

[0086] <Evaluation of etch pit formation> The results are shown in Table 3.

[0087] [Table 3] Etch pits were formed in Example 4, but no etch pits were formed in Comparative Example 4. When the etching time was 3 hours, it was found that etch pits were formed when the concentration of tetramethylammonium hydroxide in the surface treatment solution was 20%. [Explanation of symbols]

[0088] 10 Surface treatment equipment 11 Holding container 12, 60 Surface treatment solution 13, 61 Semiconductor substrate 14 Contact processor 15 rotor 16 Stand 20, 71 Gallium nitride layer 21 Oxide film 22 Resist 23, 30, 41, 50, 72 flat part 24, 31, 42, 51 protrusions 40 Sapphire substrate 43, 73 Etch Pit 70 Base

Claims

1. A surface treatment method for a group III semiconductor substrate, comprising: A surface treatment method for treating a surface of a Group III semiconductor substrate by contacting the surface of the Group III semiconductor substrate with a surface treatment solution containing an aqueous solution of tetramethylammonium hydroxide, alcohols, and an additive containing at least silicon.

2. The surface treatment method according to claim 1 , wherein the alcohol is ethanol or isopropyl alcohol.

3. A surface treatment apparatus for a group III semiconductor substrate, a holding vessel for holding a surface treatment solution; a contact treatment vessel that holds the group III semiconductor substrate and brings the group III semiconductor substrate into contact with the surface treatment solution, The surface treatment solution contains an aqueous solution of tetramethylammonium hydroxide, alcohols, and an additive containing at least silicon.

4. The surface treatment device according to claim 3 , wherein the alcohol is ethanol or isopropyl alcohol.

5. A surface treatment solution used for surface treatment of a group III semiconductor substrate, A surface treatment solution containing an aqueous solution of tetramethylammonium hydroxide, an alcohol, and an additive containing at least silicon.

6. The surface treatment solution according to claim 5 , wherein the alcohol is ethanol or isopropyl alcohol.

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