Method for manufacturing structure

Abstract

The manufacturing method of the structure has the following steps: a step of performing a first etching on the surface of a component at least of which the surface is composed of a group III nitride; and a step of performing a second etching on the surface after the first etching, wherein in the step of performing the first etching, a flat portion newly appeared due to etching and a convex portion raised relative to the flat portion due to being difficult to etch compared with the flat portion are formed on the surface, and in the step of performing the second etching, the convex portion is etched to make it lower.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a structure. Background Art

[0002] Group III nitrides such as gallium nitride (GaN) are used as materials for manufacturing semiconductor devices such as light-emitting elements and transistors. Group III nitrides are also attracting attention as materials for microelectromechanical systems (MEMS).

[0003] As an etching technique for forming various structures of group III nitrides such as GaN, photoelectrochemical (PEC) etching has been proposed (see, for example, non-patent document 1). PEC etching is a wet etching method that causes less damage than general dry etching, and is preferred in terms of simplicity of apparatus compared to special dry etching methods such as neutral particle beam etching (see, for example, non-patent document 2) and atomic layer etching (see, for example, non-patent document 3) that causes less damage.

[0004] Prior art literature

[0005] Non-patent literature

[0006] Non-patent document 1: J.Murata et al., "Photo-electrochemical etching of free-standing GaN wafer surfaces grown by hydride vapor phase epitaxy", Electrochimica Acta 171 (2015) 89-95

[0007] Non-patent document 2: S. Samukawa, JJAP, 45 (2006) 2395.

[0008] Non-patent document 3: T. Faraz, ECS J. Solid Stat. Scie. & Technol., 4, N5023 (2015). Summary of the invention

[0009] Problem that the invention aims to solve

[0010] An object of the present invention is to provide a technique for improving the flatness of a surface formed by PEC etching of a group III nitride.

[0011] Solutions for solving problems

[0012] According to one embodiment of the present invention, there is provided a method for manufacturing a structure, which comprises the following steps:

[0013] A step of performing a first etching on the surface of the member at least the surface of which is made of group III nitride; and

[0014] a step of performing a second etching on the surface on which the first etching was performed,

[0015] In the step of performing the first etching, a flat portion newly formed by etching and a convex portion raised relative to the flat portion due to being difficult to be etched compared to the flat portion are formed on the surface.

[0016] In the step of performing the second etching, the convex portion is etched so as to be lowered.

[0017] Effects of the Invention

[0018] Provided is a technique for improving the flatness of a surface formed by PEC etching of a group III nitride. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 (a) is a schematic cross-sectional view showing an example of a wafer, Figure 1 (b) is a schematic cross-sectional view of a PEC etching apparatus illustrating a PEC etching process.

[0020] Figure 2 (a) is a schematic cross-sectional view showing an example of a wafer subjected to PEC etching. Figure 2 (b) is a schematic cross-sectional view of a planarization etching apparatus illustrating a planarization etching step.

[0021] Figure 3 (a)~ Figure 3 (c) is a schematic cross-sectional view of a wafer summarizing and illustrating the PEC etching process and the planarization etching process according to the first embodiment of the present invention.

[0022] Figure 4 (a)~ Figure 4 (c) is a schematic cross-sectional view illustrating the shape of the wafer (structure) after processing.

[0023] Figure 5 is an AFM image of the epitaxial layer surface in the experimental example.

[0024] Figure 6 (a) is an AFM image of the unplanarized bottom in the experimental example. Figure 6 (b) is an AFM image of the flattened bottom in the experimental example.

[0025] Figure 7 (a)~ Figure 7(e) is a schematic cross-sectional view of a wafer summarizing and illustrating the PEC etching process and the planarization etching process described in the second embodiment.

[0026] Figure 8 1 is a schematic cross-sectional view illustrating a PEC object having a cathode pad.

[0027] Fig. 9 It is a schematic cross-sectional view of a planarization etching device according to another embodiment. DETAILED DESCRIPTION

[0028] <First Embodiment>

[0029] The method for manufacturing the structure 150 according to the first embodiment of the present invention is described. The method for manufacturing the structure 150 according to this embodiment includes the following steps: performing a first etching step on the surface 20 of the etching object 10; and performing a second etching step on the surface 20 subjected to the first etching.

[0030] The structure 150 is a member including the etching object 10 (hereinafter also referred to as the processed wafer 10) on which the first etching and the second etching are performed. It can be a member (semiconductor device, micro-electromechanical system (MEMS) etc.) on which other members such as electrodes are provided as needed, or it can be the processed wafer 10 itself (see Figure 4 (a)~ Figure 4 (c)).

[0031] First, the step of performing the first etching will be described. Figure 1 (a) is a schematic cross-sectional view illustrating an etching target object 10 (hereinafter also referred to as a wafer 10). The wafer 10 is a member in which at least a surface 20 to be subjected to the first etching is composed of a group III nitride.

[0032] Wafer 10 may be, for example, a III-nitride substrate such as a gallium nitride (GaN) substrate, or an epitaxial substrate obtained by epitaxially growing a III-nitride layer on a growth substrate. The growth substrate of the epitaxial substrate may be, for example, a sapphire substrate, a silicon carbide (SiC) substrate, a silicon (Si) substrate, or a homogeneous substrate such as a GaN substrate. The growth substrate of the epitaxial substrate may be, for example, semi-insulating, or, for example, conductive. Here, "semi-insulating" means, for example, a resistivity of 10 5 In contrast, for example, when the resistivity is less than 10 5 The state of Ωcm is called "conductivity".

[0033] The surface 20 is preferably composed of a c-plane of a group III nitride crystal. Here, "composed of a c-plane" means that the low-index crystal plane closest to the surface 20 is the c-plane of the group III nitride crystal constituting the surface 20. The group III nitride constituting the surface 20 has dislocations (threading dislocations), and the dislocations are distributed in the surface 20 at a predetermined density.

[0034] Photoelectrochemical (PEC) etching is performed as the first etching. PEC etching is performed on the etched area 21 which is at least a part of the surface 20. The object 100 to be processed by PEC etching (hereinafter also referred to as PEC object 100) has a wafer 10 and, if necessary, a mask 50 etc. provided on the wafer 10.

[0035] The mask 50 defines an etched region 21 on the surface 20. The mask 50 may be formed of a conductive material such as titanium (Ti), or may be formed of a non-conductive material such as a resist or silicon oxide. The PEC object 100 may be the wafer 10 itself without the mask 50, and the etched region 21 may be the entire surface 20 of the wafer 10.

[0036] Figure 1 (b) is a schematic cross-sectional view of a PEC etching apparatus 200 for performing a first etching step (hereinafter also referred to as a PEC etching step). The PEC etching apparatus 200 includes a container 210 for storing an etching solution 201 and a light source 220 for emitting ultraviolet (UV) light 221 .

[0037] In the PEC etching process, while the PEC object 100 is immersed in the etching solution 201, the UV light 221 is irradiated to the etched area 21 through the etching solution 201. As a result, the surface 20 subjected to PEC etching, that is, the surface 120 (hereinafter also referred to as the PEC rear surface 120) is formed. It should be noted that the PEC rear surface 120 can be regarded as the bottom 120 (refer to FIG. 1 ) of the region 110 (hereinafter also referred to as the removal region 110) in the wafer 10 where the group III nitride is removed by PEC etching. Figure 2 After etching to a predetermined depth, the PEC etching process is completed.

[0038] The mechanism of PEC etching is described in more detail. GaN is described as an example of a group III nitride to be etched.

[0039] As the etching solution 201 for PEC etching, an alkaline or acidic etching solution 201 containing oxygen for generating an oxide of a group III element contained in the group III nitride constituting the etched region 21 and an oxidizing agent that accepts electrons can be used.

[0040] As the oxidizing agent, there can be exemplified peroxydisulfate ions (S2O8 2- ). The following is an example of supplying S2O8 from potassium persulfate (K2S2O8). 2- But S2O8 2- It can be supplied by other substances, such as sodium peroxodisulfate (Na2S2O8), ammonium peroxodisulfate (ammonium persulfate, (NH4)2S2O8), etc.

[0041] As a first example of the etching solution 201, there can be cited an etching solution obtained by mixing a potassium hydroxide (KOH) aqueous solution with a potassium persulfate (K2S2O8) aqueous solution, which is alkaline at the start of PEC etching. This etching solution 201 is prepared, for example, by mixing a 0.01M KOH aqueous solution with a 0.05M K2S2O8 aqueous solution in a ratio of 1:1. The concentration of the KOH aqueous solution, the concentration of the K2S2O8 aqueous solution, and the mixing ratio of these aqueous solutions can be appropriately adjusted as needed. It should be noted that the etching solution 201 obtained by mixing the KOH aqueous solution and the K2S2O8 aqueous solution can also be made acidic at the start of PEC etching, for example, by reducing the concentration of the KOH aqueous solution.

[0042] The PEC etching mechanism when the etching solution 201 of the first example is used is described. By irradiating the etched area 21 with UV light 221 having a wavelength of less than 365 nm, holes and electrons are generated in pairs in the GaN constituting the etched area 21. The generated holes decompose GaN into Ga 3+ and N2 (chemical formula 1), and further, Ga 3+ The hydroxide ion (OH - ) is oxidized, thereby generating gallium oxide (Ga2O3) (chemical formula 2). And the generated Ga2O3 dissolves in alkali (or acid). In this way, PEC etching of GaN is performed. It should be noted that the generated holes react with water, and the water is decomposed, thereby generating oxygen (chemical formula 3).

[0043] [Chemical formula 1]

[0044]

[0045] [Chemical formula 2]

[0046]

[0047] [Chemical formula 3]

[0048]

[0049] In addition, K2S2O8 dissolves in water to generate persulfate ions (S2O8 2-)(chemical formula 4), by S2O8 2- UV light 221 is irradiated to generate sulfate ion radicals (SO4 -* Free radicals) (chemical formula 5). The electrons that are paired with holes are the same as SO4 -* The free radicals react with water, and the water is decomposed, thereby generating hydrogen (chemical formula 6). As described above, in the PEC etching of this embodiment, SO4 -* Free radicals can consume electrons that are paired with holes in GaN, so PEC etching can be performed. It should be noted that as PEC etching proceeds, sulfate ions (SO4 2- ) will increase, and therefore, the acidity of the etching solution 201 gradually becomes stronger (the pH gradually decreases).

[0050] [Chemical formula 4]

[0051]

[0052] [Chemical formula 5]

[0053]

[0054] [Chemical formula 6]

[0055]

[0056] As a second example of the etching solution 201, an etching solution that is obtained by mixing a phosphoric acid (H3PO4) aqueous solution with a potassium persulfate (K2S2O8) aqueous solution and is acidic at the beginning of PEC etching can be cited. This etching solution 201 is prepared, for example, by mixing a 0.01M H3PO4 aqueous solution with a 0.05M K2S2O8 aqueous solution in a ratio of 1:1. The concentration of the H3PO4 aqueous solution, the concentration of the K2S2O8 aqueous solution, and the mixing ratio of these aqueous solutions can be appropriately adjusted as needed. Both the H3PO4 aqueous solution and the K2S2O8 aqueous solution are acidic, so the etching solution 201 formed by mixing the H3PO4 aqueous solution and the K2S2O8 aqueous solution is acidic at any mixing ratio. It should be noted that since the K2S2O8 aqueous solution itself is acidic, as the etching solution 201 that is acidic at the beginning of etching, only the K2S2O8 aqueous solution can be used. At this time, the concentration of the K2S2O8 aqueous solution can be set to 0.025M, for example.

[0057] From the viewpoint of making it easy to use the resist as the mask 50, it is preferred that the etching solution 201 is acidic from the moment the PEC etching starts. This is because if the etching solution 201 is alkaline, the resist mask is easily peeled off. It should be noted that when Ti or silicon oxide is used as the mask 50, there is no particular problem whether the etching solution 201 is acidic or alkaline.

[0058] It can be inferred that the PEC etching mechanism when the etching solution 201 of the second example is to replace (chemical formula 1) to (chemical formula 3) described for the etching solution 201 of the first example with (chemical formula 7). In other words, GaN, holes generated by irradiation with UV light 221 and water react to generate Ga2O3 and hydrogen ions (H + ) and N2 (chemical formula 7). And the generated Ga2O3 is dissolved in acid. In this way, PEC etching of GaN is performed. It should be noted that the electrons generated in pairs with holes as shown in (chemical formula 4) to (chemical formula 6) are oxidized by S2O8 2- The mechanism of consumption is the same as that in the case of using the etching solution 201 of the first example.

[0059] [Chemical formula 7]

[0060]

[0061] As shown in (chemical formula 5), ​​as S2O8 2- Generate SO4 -* The free radical method may use at least one of irradiation with UV light 221 and heating. When irradiation with UV light 221 is used, in order to increase the S2O8 2- The light absorption can efficiently generate SO4 -* The wavelength of the UV light 221 is preferably 200 nm or more and less than 310 nm. In other words, holes are efficiently generated in the group III nitride in the wafer 10 by irradiation with the UV light 221 and S2O8 is efficiently generated in the etching solution 201. 2- Generate SO4 -* From the perspective of free radicals, it is preferred that the wavelength of UV light 221 be greater than 200 nm and less than 310 nm. 2- Generate SO4 -* In the case of free radicals, the wavelength of the UV light 221 can be set to (365 nm or less and) 310 nm or more.

[0062] By irradiation of UV light 221, S2O8 2- Generate SO4 -* When the free radical is generated, the distance L (wafer configuration depth) from the surface 20 of the wafer 10 to the upper surface of the etching solution 201 (refer to Figure 1 (b)) is preferably set to be greater than 1 mm and less than 100 mm. If the distance L is too short, for example, less than 1 mm, the SO4 generated in the etching solution 201 above the wafer 10 -*The amount of free radicals may become unstable due to the change of the distance L. It should be noted that if the distance L is short, it is difficult to control the height of the liquid level. Therefore, the distance L is preferably 1 mm or more, more preferably 3 mm or more, and further preferably 5 mm or more. In addition, if the distance L is too long, for example, exceeding 100 mm, an excessive amount of SO4 that does not participate in PEC etching is generated in the etching solution 201 above the wafer 10. -* The free radicals are generated, and therefore, the utilization efficiency of the etching solution 201 is reduced.

[0063] PEC etching can also be performed on group III nitrides other than GaN as exemplified. The group III element contained in the group III nitride can be at least one of aluminum (Al), gallium (Ga) and indium (In). The concept of PEC etching of the Al component or the In component in the group III nitride is the same as the concept described for the Ga component with reference to (chemical formula 1) and (chemical formula 2) or (chemical formula 7). In other words, holes are generated by irradiation with UV light 221, thereby generating Al oxides or In oxides, and these oxides are dissolved in alkali or acid, so that PEC etching can be performed. The wavelength of UV light 221 can be appropriately changed according to the composition of the group III nitride to be etched. Taking the PEC etching of GaN as a benchmark, when Al is contained, shorter wavelength light can be used, and when In is contained, longer wavelength light can also be used. In other words, light of a wavelength at which the group III nitride can be PEC-etched can be appropriately selected and used according to the composition of the group III nitride to be processed.

[0064] In addition, when an epitaxial substrate having a semi-insulating substrate is used as the wafer 10 and a mask 50 formed of a non-conductive material is used, a cathode pad 30 as described below may be used to promote PEC etching. Figure 8 1 is a schematic cross-sectional view showing a PEC object 100 having a cathode pad 30. The cathode pad 30 is a conductive member formed of a conductive material, and is provided in a manner in contact with at least a portion of the surface of a conductive region of the wafer 10, the conductive region of the wafer 10 being electrically connected to the etched region 21. The cathode pad 30 is provided in a manner in which at least a portion of the cathode pad 30, for example, the upper surface, contacts the etching solution 201 during PEC etching.

[0065] According to (chemical formula 1) and (chemical formula) or (chemical formula 7), it can be understood that the etched area 21 where PEC etching occurs functions as an anode that consumes holes. In addition, according to (chemical formula 6), it can be understood that the surface of the cathode pad 30, which is a conductive member electrically connected to the etched area 21 and in contact with the etching solution 201, functions as a cathode that consumes (releases) electrons. In this way, by using the cathode pad 30, PEC etching can also be promoted.

[0066] It should be noted that, in the above description, PEC etching is exemplified by causing the etching solution 201 to contain an oxidant that accepts electrons to consume electrons, but PEC etching may also be performed in other ways. Specifically, PEC etching may also be performed in the following manner: instead of causing the etching solution 201 to contain an oxidant, the cathode electrode is immersed in the etching solution 201 and the etched area 21 to be the anode electrode is electrically connected to the cathode electrode via an external circuit, thereby consuming electrons.

[0067] Next, the step of performing the second etching will be described. By performing the step of performing the first etching (PEC etching step), the surface 20 on which the PEC etching is performed, that is, the surface 120 (PEC rear surface 120) is formed. Figure 2 (a) is a schematic cross-sectional view illustrating a wafer 10 subjected to PEC etching.

[0068] As described above, dislocations are distributed at a predetermined density on the surface 20 of the wafer 10. In dislocations, the lifetime of holes is short, so PEC etching is difficult to occur. Therefore, at the position corresponding to the dislocation on the PEC rear surface 120, a convex portion 122 is easily formed as a dissolved residual portion of PEC etching. In other words, in the PEC etching process, a flat portion 121 (a portion without dislocations and PEC etching) newly appeared due to PEC etching and a convex portion 122 that is raised relative to the flat portion 121 and is generated because it is difficult to be PEC-etched compared to the flat portion 121 are formed on the PEC rear surface 120. The convex portion 122 is a dissolved residual portion of PEC etching, and therefore, its maximum height is also less than the depth (thickness) of the removal area 110.

[0069] In the second etching step (hereinafter also referred to as the planarization etching step), the second etching (hereinafter also referred to as the planarization etching) is performed on the PEC rear surface 120. The wafer 10 formed with the PEC rear surface 120 becomes the object 140 (hereinafter also referred to as the planarization object 140) to be planarized in the planarization etching step.

[0070] In the planarization etching process, more specifically, the convex portion 122 is etched (selectively relative to the flat portion 121) to lower the convex portion 122. "Planarization" means that by lowering the convex portion 122, the flatness of the PEC rear surface 120 is improved compared to before the planarization etching.

[0071] As the planarization etching, for example, wet etching using an acidic or alkaline etching solution (non-PEC etching) can be used. As the etching solution for the planarization etching, for example, a hydrochloric acid (HCl) aqueous solution, a mixed aqueous solution of hydrochloric acid (HCl) and hydrogen peroxide (H2O2) (hydrochloric acid perhydrate), a mixed aqueous solution of sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) (piranha solution), a tetramethylammonium hydroxide (TMAH) aqueous solution, a hydrogen fluoride aqueous solution (hydrofluoric acid), a potassium hydroxide (KOH) aqueous solution, etc. can be used.

[0072] Figure 2 (b) is a schematic cross-sectional view of a flattening etching apparatus 300 showing a flattening etching process. The flattening etching apparatus 300 has a container 310 for storing an etching liquid 301. In the flattening process, the convex portion 122 is etched by immersing the flattening object 140 in the etching liquid 301. Thus, the PEC rear surface 120 is flattened. After the convex portion 122 is etched to a predetermined depth, the flattening etching process is terminated.

[0073] Planarization etching is not PEC etching. Therefore, in the planarization etching process, UV light is not irradiated to the surface 20 of the wafer 10. Here, "no UV light is irradiated" means that (strong) UV light that would cause useless PEC etching is not irradiated.

[0074] It is known that it is difficult to etch the c-plane of group III nitrides such as GaN, but PEC etching can etch group III nitrides regardless of the crystal orientation, so even the c-plane can be etched. PEC etching is performed while irradiating UV light 221 from above the surface 20 of the wafer 10, which is the c-plane, so that the group III nitride constituting the surface 20 is etched from a direction perpendicular to the surface 20 (in other words, along the thickness direction of the wafer 10).

[0075] In contrast, the planarization etching is performed in the form of a conventional wet etching, for example, a non-PEC etching using an etching solution such as hydrochloric acid permeate. In conventional wet etching, the c-plane of the group III nitride is difficult to etch, and therefore, the flat portion 121 composed of the c-plane in the PEC rear surface 120 is not etched. However, the convex portion 122 is composed of crystal planes other than the c-plane, and therefore, can be etched using conventional etching. Therefore, by the planarization etching, the convex portion 122 can be selectively etched relative to the flat portion 121. The planarization etching etches the crystal planes other than the c-plane, in other words, the crystal planes intersecting the c-plane, and etches the convex portion 122 from a direction that is non-perpendicular to the c-plane (in other words, along a direction intersecting the thickness direction of the wafer 10 (lateral direction)).

[0076] By etching the convex portion 122 by planarization etching, the convex portion 122 can be lowered and the PEC rear surface 120 can be made close to flatness, in other words, the convex portion 122 can be made close to the c-plane constituting the flat portion 121. When the convex portion 122 is etched and close to the c-plane, etching is difficult to proceed. Therefore, in the planarization etching process of this embodiment, it is possible to suppress the convex portion 122 from being over-etched, and it is easy to end the planarization etching with the PEC rear surface 120 being substantially flat.

[0077] Figure 3 (a)~ Figure 3 (c) is a schematic cross-sectional view of the wafer 10 which summarizes and illustrates the PEC etching process and the planarization etching process described in the first embodiment. Figure 3 (a) shows the wafer 10 before the start of PEC etching.

[0078] Figure 3 (b) shows the wafer 10 after the PEC etching is completed (and before the planarization etching is started). In the wafer 10 after the PEC etching is completed (and before the planarization etching is started), a surface 20 subjected to PEC etching, i.e., a PEC rear surface 120 is formed, and a flat portion 121 and a convex portion 122 are formed in the PEC rear surface 120.

[0079] Figure 3 (c) shows the wafer 10 after the planarization etching is completed. In the wafer 10 after the planarization etching is completed, the PEC rear surface 120 in which the protrusions 122 are lowered (removed), that is, the surface 130 (hereinafter also referred to as the planarized rear surface 130) is formed.

[0080] After the planarization etching step is completed, in other words, after the wafer 10 (processed wafer 10) subjected to PEC etching and planarization etching is obtained, other steps (electrode formation step, etc.) are performed according to the structure of the desired structure 150. In this way, the structure 150 is manufactured.

[0081] Figure 4 (a)~ Figure 4 (c) is a schematic cross-sectional view illustrating the shape of the processed wafer 10. The planarized surface 130 is indicated by a bold line. The shape of the processed wafer 10 is not particularly limited and can be appropriately selected according to the structure of the structure 150 to be manufactured. Figure 4 (a) shows an example of a shape in which a concave portion is formed in the processed wafer 10 (a shape in which a portion of the concave portion is removed by PEC etching). Figure 4 (b) shows an example of a shape in which a convex portion is formed in the processed wafer 10 (a shape in which the outer portion of the convex portion is removed by PEC etching). Figure 4 (c) shows an example in which the processed wafer 10 has a flat plate shape (a shape in which the entire surface 20 of the wafer 10 is removed by PEC etching).

[0082] As described above, according to the planarization etching of the present embodiment, the flatness of the surface formed by performing PEC etching on the wafer 10 can be improved.

[0083] Next, an experimental example of PEC etching and planarization etching is described. In this experimental example, an epitaxial substrate having a growth substrate and a group III nitride layer as follows is used. The growth substrate is a semi-insulating SiC substrate. The group III nitride layer (hereinafter also referred to as the epitaxial layer) is a stacked structure of a nucleation layer composed of AlN, a channel layer composed of GaN and having a thickness of 0.75 μm, a barrier layer composed of AlGaN (Al composition is 0.22) and having a thickness of 24 nm, and a cap layer composed of GaN and having a thickness of 5 nm.

[0084] The PEC etching was performed as follows: a 0.025 M aqueous solution of K2S2O8 was used as an etching solution while the etching was performed at 3.8 mW / cm 2 The wafer was irradiated with UV light of wavelength 260 nm at an intensity of 100 nm for 120 minutes. The wafer configuration depth L was set to 5 mm. The mask was formed of silicon oxide. It should be noted that the cathode pad was formed of titanium. A recessed portion with a depth of 23.2 nm was formed. Since the thickness of the cover layer was 5 nm and the thickness of the barrier layer was 24 nm, the thickness of the barrier layer remaining under the recessed portion was 5.8 nm.

[0085] After the PEC etching, the bottom of the recess is flattened by planarization etching. The planarization etching is performed for 10 minutes using hydrochloric acid water (for example, a solution obtained by mixing 30% HCl and 30% H2O2 in a ratio of 1:1) as an etching solution.

[0086] An atomic force microscope (AFM) was used to observe a 1000 nm square area for the surface of the epitaxial layer before PEC etching (hereinafter referred to as the epitaxial layer surface), the bottom of the recessed portion formed by PEC etching but not subjected to planarization etching (hereinafter referred to as the unplanarized bottom), and the bottom of the recessed portion subjected to planarization etching after PEC etching (hereinafter referred to as the planarized bottom).

[0087] Figure 5 This is an AFM image of the epitaxial layer surface. The arithmetic mean roughness (Ra) of the epitaxial layer surface measured by AFM was 0.14 nm.

[0088] Figure 6 (a) is an AFM image of an unplanarized bottom. In the unplanarized bottom, convex portions are observed at positions corresponding to dislocations. It can be observed that the heights of the multiple convex portions distributed in the unplanarized bottom tend to be non-constant. The height of the largest convex portion exceeds 10 nm.

[0089] The Ra of the unplanarized bottom measured by AFM is 0.22nm. The Ra of the epitaxial layer surface is, for example, 0.14nm, while the Ra of the unplanarized bottom is, for example, 0.22nm. Although the unplanarized bottom has a convex portion, its Ra is, for example, less than 2 times the Ra of the epitaxial layer surface, and is not increased that much. The reason can be said to be that the PEC etching is performed in a manner that makes the flat portion occupying most of the area of ​​the unplanarized bottom have high flatness, in other words, in a manner that the high flatness of the epitaxial layer surface is almost not damaged in the flat portion.

[0090] Figure 6 (b) is an AFM image of the flattened bottom. It can be seen that the convex part observed in the unflattened bottom is not clearly observed in the flattened bottom, and the bottom of the concave part has been flattened. In the flattened bottom, the position where the convex part is presumed to have been formed, that is, the position corresponding to the dislocation, is observed in the form of a bright area, which is distinguished from the flat part.

[0091] The Ra of the flattened bottom measured by AFM is 0.24nm. The Ra of the unflattened bottom is, for example, 0.22nm. In contrast, the Ra of the flattened bottom is, for example, 0.24nm, which is slightly larger. This difference can be considered to be an error caused by the difference between the measurement area of ​​the unflattened bottom and the measurement area of ​​the flattened bottom. It can be considered that the Ra of the unflattened bottom is the same as the Ra of the flattened bottom. It can be said that it is difficult to clearly distinguish the unflattened bottom from the flattened bottom only by Ra. From the AFM image of the flattened bottom, it can be seen that by flattening etching, the convex portion can be selectively etched relative to the flat portion.

[0092] It should be noted that, in the surface (PEC post-surface) 120 subjected to PEC etching, the damage to the group III nitride crystal caused by etching is small (for example, compared with dry etching).

[0093] In addition, in the surface (PEC rear surface) 120 subjected to PEC etching, less halogen elements remain as compared to the surface of the wafer 10 processed by dry etching. When the wafer 10 is to be processed by dry etching, an etching gas containing halogen elements is caused to impact the surface 20, or a reaction is used to halogenate the surface 20, so that halogen elements remain on the processed surface (within the surface portion of the specified thickness). Compared with such dry etching, the PEC etching and planarization etching in the present embodiment can be performed in the form of wet etching so that no halogen elements remain on the PEC rear surface 120 and the planarization rear surface 130 (within the surface portion of the specified thickness). The concentration of halogen elements (e.g., chlorine (Cl)) in the PEC rear surface 120 and the planarization rear surface 130 is preferably less than 1×10 15 / cm 3 , more preferably less than 5×10 14 / cm 3 , and more preferably less than 2×10 14 / cm 3 .

[0094] <Second Embodiment>

[0095] Next, the second embodiment will be described. In the first embodiment, a method of performing planarization etching after the PEC etching is completed is exemplified. In other words, a method of performing planarization etching once after etching to a final depth by one PEC etching is exemplified.

[0096] In the second embodiment, the following method is illustrated: before performing PEC etching to the final depth, in the stage of performing PEC etching to the intermediate depth, flattening etching is performed, and then PEC etching is performed again. In other words, in this embodiment, a method of alternately and repeatedly performing PEC etching and flattening etching is illustrated. Flattening etching can also be performed multiple times as needed. As in the first embodiment, flattening etching can also be performed after the PEC etching is completed (performed to the final depth).

[0097] The second embodiment can also be referred to as a method in which a portion of the entire depth to be PEC-etched is etched in each PEC-etching, and planarization etching is performed after each PEC-etching.

[0098] Figure 7 (a)~ Figure 7(e) is a schematic cross-sectional view of the wafer 10 which summarizes and illustrates the PEC etching process and the planarization etching process described in the second embodiment. Figure 7 (a) shows the wafer 10 before the start of PEC etching.

[0099] Figure 7 (b) shows the wafer 10 at a stage after the first PEC etching is performed to etch a certain depth. Figure 7 (c) indicates Figure 7 The wafer 10 shown in (b) is a wafer 10 at a stage after planarization etching has been performed. Figure 7 (d) means in Figure 7 The wafer 10 in (c) is at a stage after the second PEC etching is performed to etch a certain depth after the planarization etching. Figure 7 (e) indicates Figure 7 The wafer 10 shown in (d) is a wafer 10 at a stage after the planarization etching is performed.

[0100] In the second embodiment, the depth of etching in each PEC etching is shallower than that in the first embodiment. Figure 7 (b) and Figure 7 (d)) of the first embodiment (refer to Figure 3 Compared with (b)), the formed convex portion 122 is lower as a whole, and the height difference between the convex portions 122 is small.

[0101] Therefore, in the flattening etching (per one time) of the present embodiment, it is easy to etch the protrusion 122, and it is easy to make the height of the protrusion 122 after etching uniform. In addition, by repeating the flattening etching multiple times, it is possible to more reliably etch the protrusion 122. Therefore, in the present embodiment, the flatness of the finally obtained flattened surface 130 can be further improved.

[0102] <Other Implementation Methods>

[0103] The embodiments of the present invention have been specifically described above. However, the present invention is not limited to the above-described embodiments, and various changes, improvements, combinations, etc. can be made without departing from the spirit and scope of the present invention.

[0104] For example, as the planarization etching, a method other than the above method may be used. In the above embodiment, as the planarization etching, a method of wet etching (non-PEC etching) using an acidic or alkaline etching solution is exemplified, in other words, a method of chemically etching the protrusion 122. As long as the planarization etching is to etch the protrusion 122 in a manner that flattens the PEC rear surface 120, its mechanism is not particularly limited. Therefore, the planarization etching can be performed by etching based on other mechanisms other than chemical etching. By combining etching based on multiple mechanisms, the planarization etching can be performed more effectively.

[0105] The planarization etching can be performed, for example, by mechanically removing the protrusion 122. As a mechanical planarization etching, for example, bubbling cleaning can be used, and in addition, for example, brushing can be used. As an etching solution (cleaning solution) for bubbling cleaning, for example, hydrochloric acid water as illustrated in the above embodiment can be listed. When the protrusion 122 is etched using hydrochloric acid water, bubbles are violently generated. Therefore, the protrusion 122 can be destroyed and removed by the impact generated by the bubbles. It can be said that hydrochloric acid water is an etching solution for chemically etching and mechanically etching the protrusion 122.

[0106] In addition, for example, the following apparatus can be used as the planarization etching apparatus 300 . Fig. 9 Schematic cross-sectional view of a planarization etching apparatus 300 according to another embodiment. The planarization etching apparatus 300 according to another embodiment has a structure in which a liquid flow generating mechanism 320 and a vibration generating mechanism 330 are added to the planarization etching apparatus 300 according to the above embodiment. The liquid flow generating mechanism 320 generates a liquid flow (flow) in the etching liquid 301. The vibration generating mechanism 330 is, for example, an ultrasonic generator, and applies vibration to the etching liquid 301. By performing at least one of generating a liquid flow (flow) in the etching liquid 301 and applying vibration to the etching liquid 301, the effect of mechanically etching the protrusion 122 can be enhanced.

[0107] <Preferred Mode of the Invention>

[0108] Hereinafter, preferred embodiments of the present invention will be described.

[0109] (Note 1)

[0110] A method for manufacturing a structure, comprising the following steps:

[0111] A step of performing a first etching on the surface of the member at least the surface of which is made of group III nitride; and

[0112] a step of performing a second etching on the surface on which the first etching was performed,

[0113] In the step of performing the first etching, a flat portion newly formed by etching and a convex portion raised relative to the flat portion due to being harder to be etched than the flat portion are formed on the surface.

[0114] In the step of performing the second etching, the convex portion is made lower by etching the convex portion (selectively with respect to the flat portion).

[0115] (Note 2)

[0116] The method for manufacturing a structure according to Supplementary Note 1, wherein the protrusion is formed at a position corresponding to a dislocation of the group III nitride constituting the member.

[0117] (Note 3)

[0118] The method for producing a structure according to Appendix 1 or 2, wherein the surface is composed of a c-plane of a group III nitride,

[0119] The first etching etches the group III nitride in a direction perpendicular to the surface.

[0120] The second etching is performed by etching the protrusion from a direction that is non-perpendicular to the c-plane.

[0121] (Note 4)

[0122] The method for manufacturing a structure according to Supplementary Note 3, wherein the first etching is photoelectrochemical etching.

[0123] (Note 5)

[0124] The method for manufacturing a structure according to Supplement 3 or 4, wherein the second etching is wet etching using an acidic or alkaline etching solution (not photoelectrochemical etching).

[0125] (Note 6)

[0126] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 5, wherein the first etching etches the group III nitride in a direction perpendicular to the surface,

[0127] The second etching mechanically removes the protrusion.

[0128] (Note 7)

[0129] The method for manufacturing a structure according to Supplementary Note 6, wherein the first etching is photoelectrochemical etching.

[0130] (Note 8)

[0131] The method for manufacturing a structure according to Supplementary Note 6 or 7, wherein the second etching is bubble cleaning.

[0132] (Note 9)

[0133] The method for manufacturing a structure according to any one of Supplementary Notes 6 to 8, wherein the second etching is brush cleaning.

[0134] (Note 10)

[0135] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 9, wherein the first etching is photoelectrochemical etching, and the group III nitride is etched in a direction perpendicular to the surface by irradiating the surface with ultraviolet light from above.

[0136] (Note 11)

[0137] The method for producing a structure according to any one of Supplementary Notes 1 to 10, wherein in the second etching, ultraviolet light (such as that which causes photoelectrochemical etching) is not irradiated on the surface.

[0138] (Note 12)

[0139] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 11, wherein in the second etching, the convex portion is selectively etched with respect to the flat portion.

[0140] (Note 13)

[0141] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 12, wherein the first etching is photoelectrochemical etching,

[0142] The etching solution for the photoelectrochemical etching is an alkaline or acidic etching solution containing an electron-accepting oxidant.

[0143] (Note 14)

[0144] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 13, wherein the first etching is photoelectrochemical etching,

[0145] In the first etching, the distance from the surface to the upper surface of the etching solution in the photoelectrochemical etching is preferably 1 mm to 100 mm, more preferably 3 mm to 100 mm, and even more preferably 5 mm to 100 mm.

[0146] (Note 15)

[0147] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 14, wherein the first etching is photoelectrochemical etching,

[0148] In the first etching, the photoelectrochemical etching is performed with a mask disposed on the surface.

[0149] The etching solution of the aforementioned photoelectrochemical etching (from the start time of the first etching) is an acidic etching solution,

[0150] The aforementioned mask is a resist mask.

[0151] (Note 16)

[0152] The method for manufacturing a structure according to any one of Supplementary Notes 1 to 15, wherein the first etching is photoelectrochemical etching,

[0153] The photoelectrochemical etching is performed with a mask and a conductive member disposed on the surface.

[0154] The mask is made of non-conductive material.

[0155] The aforementioned conductive component is arranged in a manner that contacts at least a portion of the surface of the conductive region of the aforementioned component, the conductive region of the component is electrically connected to the region where the aforementioned photoelectrochemical etching is to be performed, and at least a portion (upper surface) of the aforementioned conductive component is arranged in a manner that contacts the etching solution of the aforementioned photoelectrochemical etching.

[0156] (Note 17)

[0157] The method for producing a structure according to any one of Supplementary Notes 1 to 16, wherein the first etching and the second etching are repeated alternately.

[0158] (Note 18)

[0159] The method for producing a structure according to any one of Supplementary Notes 1 to 17, wherein the second etching is performed while causing an etching solution used in the second etching to generate a liquid flow (flow).

[0160] (Note 19)

[0161] The method for producing a structure according to any one of Supplementary Notes 1 to 18, wherein the second etching is performed while applying vibration to an etching liquid used in the second etching.

[0162] Description of Reference Numerals

[0163] 10…wafer, 20…(wafer) surface, 21…etched area, 30…cathode pad, 50…mask, 100…PEC object, 110…removal area, 120…PEC rear surface, 121…flat portion, 122…convex portion, 130…flattened rear surface, 140…flattened object, 150…structure, 200…PEC etching device, 201…etching liquid, 210…container, 220…light source, 221…UV light, 300…flattening etching device, 301…etching liquid, 310…container, 320…liquid flow generating mechanism, 330…vibration generating mechanism.

Claims

1. A method for manufacturing a structure, comprising the following steps: A step of performing a first etching on the surface of the member at least the surface of which is composed of a group III nitride; and a step of performing a second etching on the surface on which the first etching was performed, In the step of performing the first etching, a flat portion newly formed by etching and a convex portion raised relative to the flat portion, which is generated because it is more difficult to be etched than the flat portion, are formed on the surface. In the step of performing the second etching, the convex portion is etched so as to be lowered. The first etching is photoelectrochemical etching, The second etching is not photoelectrochemical etching, and the surface is not irradiated with ultraviolet light during the second etching.

2. The method for manufacturing a structure according to claim 1, wherein: The protrusions are formed at positions corresponding to dislocations of the group III nitride constituting the member.

3. The method for manufacturing a structure according to claim 1 or 2, wherein: The surface is composed of a c-plane of a group III nitride, The first etching etches the group III nitride from a direction perpendicular to the surface, The second etching is performed by etching the protrusion in a direction that is non-perpendicular to the c-plane.

4. The method for manufacturing a structure according to claim 3, wherein: The second etching is wet etching using an acidic or alkaline etching solution.

5. The method for manufacturing a structure according to claim 1 or 2, wherein: The first etching etches the group III nitride from a direction perpendicular to the surface, The second etching mechanically removes the protrusion.

6. The method for manufacturing a structure according to claim 5, wherein: The second etching is bubble cleaning.

7. The method for manufacturing a structure according to claim 5, wherein: The second etching is brushing.

8. The method for manufacturing a structure according to claim 1 or 2, wherein: In the first etching, the surface is irradiated with ultraviolet light from above, thereby etching the group III nitride in a direction perpendicular to the surface.

9. The method for manufacturing a structure according to claim 1 or 2, wherein: In the second etching, the convex portion is selectively etched relative to the flat portion.

10. The method for manufacturing a structure according to claim 1 or 2, wherein: The etching solution for the photoelectrochemical etching is an alkaline or acidic etching solution containing an electron-accepting oxidant.

11. The method for manufacturing a structure according to claim 1 or 2, wherein: In the first etching, a distance from the surface to an upper surface of an etching solution in the photoelectrochemical etching is 1 mm or more and 100 mm or less.

12. The method for manufacturing a structure according to claim 1 or 2, wherein: In the first etching, the photoelectrochemical etching is performed with a mask disposed on the surface. The etching solution for the photoelectrochemical etching is an acidic etching solution. The mask is a resist mask.

13. The method for manufacturing a structure according to claim 1 or 2, wherein: The photoelectrochemical etching is performed in a state where a mask and a conductive member are arranged on the surface. The mask is made of a non-conductive material. The conductive component is arranged in a manner that contacts at least a portion of the surface of the conductive region of the component, the conductive region of the component is electrically connected to the region where the photoelectrochemical etching is to be performed, and at least a portion of the conductive component is arranged in a manner that contacts the etching solution of the photoelectrochemical etching.

14. The method for manufacturing a structure according to claim 1 or 2, wherein: The first etching and the second etching are repeated alternately.

15. The method for manufacturing a structure according to claim 1 or 2, wherein: The second etching is performed while the etching solution used in the second etching is caused to flow.

16. The method for manufacturing a structure according to claim 1 or 2, wherein: The second etching is performed while applying vibration to the etching liquid used in the second etching.

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